DEPARTMENT OF THE INTERIOR 

FRANKLIN K. LANE, Secretary 

UNITED STATES GEOLOGICAL SURVEY I 

. GEORGE OTIS SMITH, Director 

Professional Paper 94 

ECONOMIC GEOLOGY 

OF 

GILPIN COUNTY AND ADJACENT PARTS OF CLEAR CREEl\ . . 

AND BOULDER COUNTIES, COLORADO 

BY 

EDSON S. BASTIN AND JAMES M. HILL 

WASHINGTON 

GOVERNMENT PRINTING OFFICE 

1917 
ADDITIONAL COPIES 

OF THIS PUBLICATION MAY BE PROCURED FROM 

THE SUPERINTENDENT OF DOCUMENTS 

GOVERNMENT PRINTING OFFICE 

WASHINGTON, D. C. 

AT 

$1.00 PER COPY 
CONTENTS. 

Preface, by F. L. Ransome ..................... . 

Summary of results' .............................. · 

General g~ology ............................ . 

Economic geology ................... ~ ...... . 

P AR'r I. General geography and geology, by 

Edson S. Bastin .......................... · .... . 

Chapter I. Introduction .....• .' ............... . 

Location and area of the region ......... . 

Field work and acknowledgments ........ . 

Geography and geology of the province .. . 

The Southern Rockies .............. ~ 

The Front Range .................... . 

Literature ......... ~ .................... . 

Chapter II. Topography and geography of the 

Central City quadrangle ............... . 

Relief ..••...... ~ ....................... . 

Drainage ......... ~ ...................... . 

Climate ................................ . 

Vegetation ............................. . 

Inhabitants and industries .............. . 

Chapter III. Descriptive"geology ~ ........... . 

Stratigraphy ....... · ... ~ ......... .' ...... ~. 

Pre~Cambrian metamorphosed sedimentary rocks .................... . 

Idaho Springs formatipn .......... . 

Name ..........•.... ~ ...... . 

Distribution .......... ' ... · ... . 

Lithology and structure ..... . 

General features ........ . 

Quartz-biotite schist. ~ .. . 

Biotite-sillimanite schist. 

Quartz gneiss ........... . 

Hornblende: schist and 

gneiss ............... . 

Lime-silicate rocks ...... . 

Supposed metamorphosed 

conglomerates ........ . 

Injection gneiss ......... . 

Origin ...................... . 

Age ....... .' ................ . 

Pre-Cambrian igneous rocks .......... . 

Granite gneiss ................... . 

Definition ......•............ 

Distribution and general structure ...................... . 

I.ithology .................. . 

Origin ............ : ......... . 

Age .............•............ 

Quartz diorite and associated hornblendite ..................... . 

Definition ................. .. 

Distribution ................ . 

Character .................. . 

Relations to other rocks ...... . 

Origin and age .............. . 

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13 PART I. General geography and geology-Contd. 

15 Chapter III. Descriptive geology-Continued. 

15 Stratigraphy-Continued. 

16 Pre-Cambrian igneous rocks-Contd. 

Granite pegmatite ............... . 

19 Definition .................. . 

19 Distribution ................ . 

19 Character ................... . 

20 Relations to other rocks ..... . 

20 Origin and age .............. . 

20 Silver Plume granite ............ . 

22 Definition .................. . 

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Distribution ................ . 

Character .................. . 

Relations to other rocks.: ... . 

Age .......................• 

Carboniferous(?) sandstone .........• 

Tertiary(?) intrusive rocks~ ........• 

General character and relations ... 

Age ...........................•.. 

·Quartz monzonite and quartz 

monzonite porphyry .......... . 

General character ........... . 

Principal varieties .......... . 

Uniformly porphyritic 

quartz monzonites ..... 

Seriate porphyritic quartz 

monzonites .......... . 

Nonporphyritic quartz 

monzonites ... · ....... . 

Unusual varieties ...... . 

Roc~s formed ~y magmatic differentiation within monzonite 

stocks near Caribou ........... . 

General character ........... . 

Felsic (acidic) and intermediate types ................ . 

Mafic (basic) types ......... . 

Ultramafic magnetite-rich 

types .................... . 

Nature of the differentiation ...................•.. 

Dike rocks near Nederland ....... . 

Hornblende monzonite porphyry .................. ·'· 

General character ....... . 

Distribution ............ . 

Features in detail ...... . 

Age and relations ....... . 

Hornblende and biotite an-

. desite .................... . 

General character ....... . 

Distribution ............ . 

Features in detail ...... . 

Age and relations ....... . 

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PART I. General geography and geology-Contd. 

· Chapter III. Descriptive geology-Continued. 

Stratigraphy-Continued. 

Tertiary(?) intrusive rocks-Con. 

Dike rocks near Nederland-Con. 

Hornblende and biotite diorites 

General character ...... . 

Distribution ............ . 

Features in detail ...... . 

Age and relations ....... . 

Bostonite and bostoni.te porphyry. 

General character ........... . 

Distribution ................. . 

Features in detaiL ......... . 

Origin and relation to other 

rocks .................... . 

Basalt porphyry ............... . 

Granite porphyry .............. . 

General character ........... . 

Distribution ................ . 

Features in detail .......... . 

Age and relations ........... . 

Alkali syenite porphyry ......... . 

General character ........... . 

Distribution ................ . 

Features in detaiL ......... . 

Age and relations ........... . 

Biotite latite ................... . 

General character .......... . 

Distribution ................ . 

Features in detaiL ......... . 

Age and relations ........... . 

Tertiary ( ?) terrace gravels ........... . 

Quaternary deposits ................. . 

General features ................. . 

Glaciation ....................... . 

General conditions .......... . 

Earlier or pre~ Wisconsin glacial 

stage ..................... . 

Glaciers ................ . 

Till deposits ............ . 

Outwash deposits ....... . 

Later or Wisccnsin glacial 

stage ..................... · 

Glaciers ................ . 

Glacial erosion .......... . 

TilLdeposits ............. . 

Outwash depos~ts ....... . 

Age and relations of the glacial 

stages ............ : . ... : . . . 

Pleistocene"(?) terrae~ gravels ... . 

Debris sheets ..................... . 

Recent alluvium ................ . 

Talus ............. · ............. . 

Structure ................................ . 

Foliation ...................... · ..... . 

Faults and joints ..................... . 

Igneous intrusion ................... . 

Chapter IV. Geologic history .................. . 

Pre-Cambrian time ....................... . 

Paleozoic time ..... ~ .................... . 

Mesozoic time ........................... . 

Cenozoic time ........................... . 

CONTENTS. 

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PART II. Gene~al features of the economic geology, 

by Edson S. Bastin ........................... . 

Chapter V. History of mining ......... ~ ...... . 

Finding list of claims shown on map of 

Central City and vicinity ............. . 

Finding list of claims shown on rna p of 

Idaho Springs and vicinity ........... . 

Chapter VI. General features cf the ore deposits. 

Introduction ............................. . 

Geographic distribution .................. . 

Classification by structural types .......... . 

Veins .............................. . 

Distribution .................... . 

Strikes and dips ................. . 

Width .......................... . 

Complexity of fracturing ........ . 

Persistence ..................... . 

Branching ...................... . 

Influence of wall rock on .fracturing ....................... . 

Stockworks .......................... . 

Definition ...................... . 

The Patch ...................... . 

Structure ..... ' ............ ~ .. . 

Form ...................... . 

Wall rocks .................. . 

·Mineralization .............. . 

Other stockworks ................ . 

Ores formed by magmatic segregation. 

Auriferous gravels ................ · .... . 

Ore textures ............................. . 

Geographic distribution of ore of different 

classes ................................ . 

Mineral composition of ores .............. . 

Structural relations of ores and porphyries. 

Primary variations in metal content in ore 

deposits .............................. . 

Alterations of wall rock .................. . 

Influence of wall rock on mineralization ... , 

Chapter VII. Gold-silver ores ............... . 

Predominance and general character ..... . 

Classification ............................ . 

IJode ores ............................... . 

Pyritic ores .. _ ...................... . 

Definition ..... ; ................ . 

Primary minerals ............... . 

Mineral paragenesis ............. . 

Structure and texture ............ . 

Alterations of wall rock ......... . 

Metal content .......... _ ........ . 

Galena-sphalerite ores ............... . 

Definition ...................... . 

Primary minerals ............... . 

Mineral paragenesis ............. . 

Structure and texture ............ . 

Alterations of wall rock .......... . 

Metal content ................... . 

Composite ores ....................... . 

Telluride ores ................... ~ ... . 

General Jeatures ................. . 

Primary minerals and their paragenesis .... _ .. __ ... _ ......... . 

Geographic distribution of ores .. _ ... . 

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CONTENTS. 

P AUT "' II. General features of economic geology-Con. 

Chapter VII. Gold-silver ores-Continued. 

Lode ores-Continued. 

Relations of primary gold and silver to 

commoner ore minerals ........... . 

General relations ............... . 

Pyritic ores ...................... . 

Galena-sphalerite ores ........... . 

Telluride ores ................... . 

Fineness of gold and silver ........... . 

Placers ............•................... ~ 

Chapter VIII. Uranium ores ................ . 

Introduction .....•........................ 

Principal foreign occtm·ences of pitchblende ................................ . 

The Erzgebirge ...................... . 

'l'ypes of deposits ..... : .......... . 

J oachimsthal, Bohemia .......... . 

Annaberg, Saxony .............. . 

J ohanngeorgenstadt, Saxony ..... . 

Schnee berg, Saxony ............. . 

Cornwall district, England .......... . 

Pitchblende in the Central City quadrangle ............................... . 

Chapter ~X. Tungsten,··copper,. and iron ores .. 

Tungsten ores ........................... . 

Copper ores ............................ . 

General features ...•.••............. 

Geologic relations .................... . 

Petrology of the ore-bearing dikes ... . 

Relations of ore-bearing dikes to neighboring monzonite stock ............ . 

Origin of the ore ..................... . 

Later fracturing and mineralization .. . 

Titaniferous iron ores ................... . 

Chapter X. Genesis of the prilnary ores ....... . 

Purpose of the discussion ............... . 

Relation between mineralization and volcanism ..... : ........................ . 

Agent of ore deposition ................... . 

Regional variations in mineralizing solutions ................................ . 

Differences in composition of ore-forming 

~o~utions. in different parts of mineralIzmg penod .......................... . 

Temperature and pressure of ore formation. 

Composition of mineralizing solutions ..... . 

Chapter XI. Processes affecting the ores subsequent to primary mineralization ........... . 

Post mineral faulting and fracturing ..... . 

Post mineral deposition of quartz and carbonate ............................... . 

Etching of primary minerals ............. . 

Downward enrichment ................... . 

General features .................... . 

Relation to ground-water level. ..... ~ 

Classes of ores affected ............... . 

Gold enrichment .................... · 

General conditions ............. . 

Solution and redeposition of gqld. 

Evidence of gold enrichment in 

oxidized zone ................ . 

Probable unimportance of gold 

enrichment below ground-water 

level ....................... :. 

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P AR'l' II. General features of economic geology-Con. 

Chapter XI. Processes affecting the ores subsequent to primary mineralization-Continued. 

Downward enrichment-Continued. 

Silver enrichment ................... . 

Solution of sliver in oxidized zone. 

The silver minerals and the 

active solutions ........... . 

Silver balanced by the sulphate radicle ............. . 

Silver balanced by the carbonate or the bicarbonate radicle ...................... . 

Silver balanced by chlorine .. 

Reprecipitation of silver in oxi-

. dized zone ••.•................ 

Deposition of secondary silver 

minerals below th~ ground-water 

level ........................ . 

General conditions ......... . 

Dependence on primary mineral composition ........... . 

Ruby silver and chalcopyrite 

typo of enrichment ....... . 

Minerals ................ . 

Secondary minerals in 

fractures and vugs in 

primary ore .......... ~ 

Secondary minerals as replacements of primary 

ore .......•...•......• 

Depth of silver enrichment ................ . 

Geographic distribution .. 

E:ilv:er content of enriched 

ores ................. . 

Native s.ilver and chalcocite 

type of enrichment ....... . 

Relation between the two 

types of silver eru.:ichment .. 

Copper enrichme·nt .................. . 

Solution and redeposition of cop-

. per in the oxidized zone ...... . 

Redeposition of copper below 

ground-water level ... : . ...... . 

Enrichment in other metals .......... . 

Summary of enrichment ............. . 

Chapter XII. Ore treatment, labor and royal-' 

ties, freight ra-tes, by Edson S. Bastin, Charles 

W. Henderson, and James M. Hill ......... . 

Ore treatment ........................... . 

History ............................. . 

Milling of gold ores ................. . 

Milling of silver and other ores ...... . 

Smelting .......................... . 

History ......................... . 

Early smelting and milling 

charges ...................... . 

Sampling works .................... . 

Development .................. . 

Payment for ores ............... . 

Labor and royalties ...................... . 

Freight rates ............. : .............. . 

Chapter XIII. Production, by Charles W. 

Henderson ............................... . 

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6 CONTENTS~ 

PART III. The mines, by E<lson S. Bastin and · 

James M. Hill ................................. . 

Chapter XIV. Boulder County ............... . 

Cariqou, Nederland, and vicinity ......... " 

General features ................... . 

Silver veins of Bald Mountain and 

Caribou Hill ..................... . 

Up to Date mine ............... . 

Caribou mine. : ................ . 

Wigwam Ill;ine .................... . 

Comstock mine ................. . 

Sherman vein .................. . 

No Name vein ................. . 

Cross Lode tunnel .............. . 

Gold ores of Idaho Mountain ........ . 

St. Louis IQine ................. . 

Boston and Idaho tunneL ........ . 

Eagle Bird.mine ................ . 

Great Northern mine .......... _ • 

Gold-silver veins of ·Boulder County 

Hill and Sherwood Creek ......... . 

Boulder County mine ........... . 

Jack Pot tunnel ................. . 

Pine Grove mine ................ . 

Gold King mine ................. . 

Mines near Nederland .............. . 

Blue Bird mine ............... ~ .. 

Alton tunnel ................... . 

Eldora and vicinity ..................... . 

General features ........ ~ ............ · 

Enterprise mine ..................... . 

Mogul tunnel ....................... . 

Swathmore mine ................... .. 

Koh-i·noor tunneL ................ .. 

Scandia vein ........................ . 

Jasper tunneL ................... · ... 

Summit prospect .................... . 

Other prospects .................... . 

Chapter XV. Gilpin County ................. . 

South Boulder Creek, Jennie Lind Gulch, 

and Phoenix .................... · .... .. 

Blater~ick tunnel ................... . 

· Hill and Gold ~unnel ............... . 

Rooks .County mine ................. . 

Melrose tunneL ................... .. 

Early Bird tunneL .................. . 

Black Hills vein .................... . 

Buckeye mine ...... ~ ............. .. 

· Golden Sun tunnel ................. . 

Grand Union tunnel ............... . 

Johnson tunnel. .............. ~ ..... . 

Fairhaven vein .... ~ ................. . 

Melett vein ........................ . 

Lone Star vein ..................... . 

Champion vein ..................... . 

Tunnels west of Rollinsville ......... . 

Perigo,· Gilpin, Gamble Gulch, and Moon 

Gulch ............................... . 

Pioneer tunnel ........ : ............. . 

Quindaro tunnel. ................•... 

Gold Queen vein .................... . 

Smuggler vein ..................... .. 

Bonanza tunneL ............... -.... . 

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PART III. The mines-Continued. 

Chapter XV. Gilpin County-Continued. 

Perigo, Gilpin, Gamble Gulch, and Moon 

Gulch-Continued. 

Diamond Bill group ................. . 

Officer tunneL ...................... . 

Sea Bird tunnel ..................... . 

Mountain Monarch tunneL ........... . 

Swiss tunnel ....................... . 

· Penob~cot tunneL ................ ---

Gold Dirt mine ...................... . 

Colorado tunneL ................... .. 

War Eagl~ mine ................... .. 

Perigo mine ....................... .. 

Free Gold and Mareau veins ......... . 

Golden Flint vein ................... . 

Mourttain Chief mine .............. .. 

Victoria vein ....................... .. 

Gettys burgh vein ................... . 

4pex, American City, and Kingston ..... . 

Charcoal Charlie vein ................ . 

Schultz W.onder mine: ............... . 

Pioneer tunnel ...................... . 

Geiger vein ....................... .. 

Ingram vein ....................... . 

Evergreen mine ................. · .... . 

Gold Standard and Nancy Lee veins .. 

Bullion tunneL ................... .. 

Annie H. vein ......... , ............ . 

Mackey vein ...... · ................. . 

Fish vein .......................... .. 

Plateau vein ........................ . 

Hubernocker vein .................. . 

Annie tunneL~ .. ~ .................. . 

Meteor tunneL ...................... . 

Gold Reserve vein ................... . 

Montana Hill tunnel. ............. ~ .. . 

J. W. prospect. .................... .. 

London vein ......................... . 

Moose vein .......................... . 

Illinois vein ' ........ , ............... . 

Silver Creek and Stewart Gulch .......... . 

Sherman-Macon tunnel. ............. . 

Pettibone mine ..................... . 

Reform vein .......... · .............. . 

Golden Rod mine ...... , ............. . 

Snowden vein ...................... . 

Old Kentucky mine ................ · .. 

Stewart vein ........................ . 

Caledonia vein ...................... . 

Pine Cone tunnel ........ ~ ........... . 

Johnson prospect .................... . 

Nigger and Winnebago Hills ............. . 

Casto vein .......................... . 

Spur Daisy group .................... . 

Belden tunnel .....................•. 

Hont d'Oro tunnel. ................. . 

Freedom· vein ...................... . 

Silver Hill ............. · ................ . 

Maryland Mountain ...................... · 

Hayseed vein ..................... .. 

Robert Emmet mine ................. ~. 

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PART III. The mines-Continued. 

Chapter XV: Gilpin County-Continued. 

. Nevada Hill and Prosser Gulch .......... . 

Gilpin Eureka mine ................ . 

Gold Collar mine .................... . 

Concrete mine ........... , .......... . 

Gunnell-Grand Army mine ......... : .. 

Whiting vein ........................ . 

Hubert mine ........................ . 

Prize vein ...............•........... 

Creur d'Alene mine ................. . 

Newfoundland vein ................ . 

Corydon vein ......................... . 

Central, Mammoth, Gregory, Bobtail, and 

Bates Hills ............................ . 

Maine Hamlet mine ................. . 

0. K. urine ......................... . 

Mammoth vein ...................... . 

Brooklyn mine ... ~ ................. . 

Next President mine .... ~ ............ . 

Vasa vein ................. ~ ......... . 

O'Neil vein ........................ . 

Property of Fifty Gold Mines Co ..... . 

After Supper-Sleepy Hollow vein .... . 

Carr vein ........................... . 

Golden Eagle vein ................... . 

Unexpected vein ........... ·- ....... . 

Clay County vein .................. . 

Chemung-Belmont mine ............ . 

Alps and Quartz Hills .................. . 

Kansas vein ........................ . 

Burroughs vein ............ " ......... . 

Fourth of July vein .................. . 

Quartz Hill tunnel ................... . 

Columbia tunneL ................... . 

Baxter mine ........................ . 

Climax mine ....................... . 

· Hidden Treasure- California- Gardner 

lode ............................. . 

San Juan nrine, La Crosse tunnel, and 

the Patch ................. , ... · ... . 

National mine ....................... . 

Ivanhoe vein ....................... . 

Kent County vein ........ : ......... . 

Ralls County mine ................... . 

Egyptian nrine ............ ~ ........ . 

Illinois nrine ....................... . 

Gauntlet mine: .................... . 

.German and Belcher mines .......... . 

Mitchell mine ....................... . 

Scandia nrine .......... · ............. . 

Barnes mine ........................ . 

Delmonico vein .................... . 

Alps nrine. : . ....... · ............... . 

Kirk vein ....................... ; .. . 

North urine ............. ~ .......... . 

Gem mine .............. : .......... . 

Wood mine.· ....................... . 

Jefferson-Calhoun vein .............. . 

Prompt Pay mine ................... . 

Bezant or Quartz Mill mine ......... . 

Harsh vein ........................ . 

Topeka mine ..... .- ................. . 

Rockford mine ...................... . 

CONTENTS. 

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PART III. The mines-Continued. 

Chapter XV. Gilpin County-Continued .. 

Upper Russell Gulch ....... ' ............. . 

Golden Cloud mine .................. . 

Nashville mine ..................... . 

Livingston mine ..................... . 

Rocky Mountain Terror mine ..... , .. . 

Federal mine ....................... . 

Russell vein ........... : ............. . 

Old Town mine ..................... . 

Becky Sharp urine .................. . 

Iron ·urine ........................... . 

Pewabic vein ................ : ....... . 

Bangor mine . .- .......... · ............ . 

Iron Duke mine .................... ~ . 

Hall mine .......................... . 

Lotus mine ......................... . 

Hillhouse-Columbus vein ............ . 

Gettysburgh vein ... · ................ . 

Lutz vein .......................... . 

Slide vein ........................... . 

Missouri mine ....... ·'· ..... ~ ....... . 

Justice Hill and lower part of Russell Gulch 

Gladstone vein ..................... . 

Aurora mine ....................... . 

Argo vein ........................... . 

Pittsburg mine ............... · ...... . 

West Notaway mine ..... : .......... . 

East Notaway mine ............ : ..... . 

Gulch mine ................... ,. .... . 

Pearce or Morris mine ......... " ..... . 

Justice vein ........................ . 

Willis and South Willis gulches and 

Pleasant Valley ....................... . 

Two-Forty vein ..................... . 

Saratoga mine ....................... . 

Togo vein ............................ ' 

Hazeltine vein ...................... . 

. Frontenac and Aduddell mines ....... . 

Druid mine .......... · ............... . 

Kokomo mine ....................... . 

Anchor mine ....... "·: ... : .......... . 

Chase mine ......................... . 

War Dance mine ......... ~ .......... . 

Silver Dollar vein .................. . 

Hampton mine ...................... . 

Powers .vein ...... : .................. . 

Iroquois vein ....................... . 

ProspectS on ridge between Elkhorn 

Gulch and Pleasant Valley ........ . 

Hill and Bunk House veins ......... . 

Moose mine ......................... . 

Chapter XVI. Clear Creek County ... : ....... . 

Bellevue Mountain and upper part of Virginia Can yon ......................... . 

Crown Point and Virginia mine ...... . 

Clarissa mine ........................ . 

Fairmont tunnel. ................... . 

Belman vein ....................... . 

Lake and Windsor Castle veins~ ...... . 

Two Brothers tunnel and Bald Eagle 

vein .................... : ... · ...... . 

l\1ona vein ......................... . 

Specie Payment vein ............... . 

Champion-Trio' mine.: .......... ·: .. 

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254 

254 

256 

256 

256 

256 

256 

257 

258 

258 

258 

258 

259 

259 

259 

260 

261 

263 

264 

265 

266 

266 

266 

266 

267 

268 

268. 

269 

272 

274 

274 

275 

277 

278 

279 

279 

279 

279 

280 

280 

281 

281 

281 

281 

282 

283 

284 

285 

285 

286 

288 
8 

P AHT III. The mines-Continued. 

Chapter XVI. Clear Creek County-Continued. 

Seaton Mountain, Gilson Gulch, and the 

lower part of Virginia Canyon· ......... . 

East Lake tunnel and Owatonna vein. 

Sun and Moon vein ................. . 

Santa Fe vein ..................... . 

De Lesseps tunnel ................. . 

Gem-Freighter's Friend lode ......... . 

Franklin vei~ and Silver Age 'tunneL. 

Hudson-Burr tunneL ............... . 

Metropolitan tunneL ................ . 

Seaton vein ........................ . 

Tropic tunnel ..................... . 

Crystal tunnel. .................... . 

Casino vein and Foxhall tunnel ..... . 

Early Bird tunnel ................. . 

Bell vein ........................... . 

Treasure Vault mine ................ . 

Idaho tunneL ...................... . 

Golden Rod mine ..... · ............. . 

Argo tunnel and veins cut by it ..... . 

Fall River ............................. . 

Dover and .Philadelphia tunnels ..... . 

United Gold tunneL ............... . 

Dubuque mine ...................... . 

Lucania tunneL ............... · ...... . 

Berry vein .......................... . 

U. P.R. mine .................. · .... . 

Kinda vein ......................... . 

Bourbon vein ...................... . 

Mandolina vein ...................... . 

Helen tunneL ..... : .. .............. . 

Knickerbocker tunneL .............. . 

Magdalena vein .................... .. 

Millionaire vein ..... ~ ............... . 

Denbigh vein ...................... . 

Pennsylvania tunneL ............... . 

\Vashington tunneL ....... · .......... . 

'Mohawk vein ........................ . 

Lucky Group and Philips tunneL ... . 

Standard tunneL .................. .. 

Golconda mine ....................... . 

Almaden mine ..................... . 

Seven-Forty tunneL ................. . 

Polar Star tunneL .................. .. 

Ida May tunneL .................... . 

Clifford vein ...................... .. 

Thomas tunnel ..................... . 

Boss tunneL ....... · ................. . 

Mariha:ttan tunnel .................. . 

Wyomed tunneL ... ~ ............... . 

Seaman tunnel ..................... . 

Bonnie Briar mine ................. .. 

Merry Monarch tunnel .............. . 

Alice, Yankee, and yicinity ............... . 

Aura Verde vein ..................... . 

Little Blanche tunneL ......... ~ ..... · 

Meteor vein ......................... . 

Puri.tan vein ........................ . 

Gold Anchor mine .................. . 

Chesapeake tunneL .................. . 

CONTENTS. 

Page. 

· PART III. The mines-Continued. 

Chapter XVI. Clear Creek County-Continued. 

Alice, Yankee, and vicinity-Continued. 

288 Ninety-Four tunneL ................ . 

288 Lalla vein ........................... . 

289 Princess Alice vein ................. . 

290 .Alice mine ......................... . 

290 Commercial Union tunnel ........... . 

290· Gold Reserve group ................. . 

292 Lombard mine .................... .. 

294 Cumberland mine ... ~ .............. . 

294 Gold Band vein ..................... . 

294 Ohio vein ................. · ......... . 

297 Mineral Point vein .................. . 

298 Surprise vein ....................... . 

299 Faust mine .......................... . 

300 Other mines near Yankee ............ . 

300 North Star-Mann vein ................ . 

300 1 Little Elda vein .................... . 

301 Leidenger tunneL ................... . 

303 Gold Standard vein .................. . 

303 Lawson and Empire station .............. . 

306 Maud S·. vein ....................... .. 

306 Marshall & Russell tunneL .......... . 

308 Bellevue-Hudson and Anamoosa lode. 

308 Commodore tunnel and Red Elephant 

309 group of mines ..... ~ ............... . 

309 Commodore tunneL ............. . 

309 Boulder Nest-Free America vein .. 

310 Tabor vein ..................... . 

310 White vein ..................... . 

310 Little Giant vein ................... . 

311 Panama tunneL ................... .. 

311 Platts vein and Princess of India 

311. tunnel ........................... . 

311 Murray vein ......................... . 

312 Cymric tunneL ..................... .. 

312 . Millington mine .................... . 

313 American Sisters vein .. _.,_ ........... . 

313 J o Reynolds vein ................... . 

313 Turkey Gulch .......................... . 

313 Rockford tunnel. .................... . 

315 Spring Gulch .......................... .. 

316 Silver King vein .................... . 

317 Firemen and Conductors tunneL. .... . 

317 Pioneer tunneL ..................... : 

317 Almira tunneL ..................... . 

317 Gold Chest tunneL ................. . 

318 Dumont and vicinity ............... · ..... . 

318 Blue Ridge and Senator mine ........ . 

318 Ohio Creek tunnels ................. . 

318 4-C tunnel. .......................... . 

318 Silent Friend vein ................... . 

318 Earl of.Kent mine ................... . 

319 Big Dipper vein .............. : ..... . 

319 Syndicate mine ..................... . 

319 Freeland tunneL ..................... . 

319 Gilpin and Clear Creek tu.nneL ....... . 

319 Sunshine mine ...................... . 

320 Albro vein ......................... . 

321 · Dumont group of pyritic veins ....... . 

321 Carter tunneL ..................... .. 

Page. 

321 

322 

323 

323 

326 

326 

326 

327 

327 

328 

328 

328 

328 

328 

329 

329 

330 

330 

330 

330 

331 

333 

334 

334 

335 

335 

335 

336 

336 

337 

338 

338 

339 

339 

340 

341 

341 

342 

342 

343 

343 

344 

344 

344· 

344 

. 347 

347 

348 

349 

350 

350 

352 

353 

354 

354 

355 

355 
I'AR'l' III. The mines-Continued. 

Chapter XVI. Clear Creek County-Continued. 

Mill Creek ...................•.......... _.. 

Golden Hope vein ................... . 

Cincinnati vein ...................... . 

Keith tunnel. ...................... . 

Great Northern vein .... ,. ........... . 

Trail Creek and area between Idaho Springs 

and Fall River ........................ . 

Miami tunnel. ...................... . 

Big Five or Central tunnel. .......... . 

Mayflower tunnel. ......•............. 

Crocket vein ................ · ....... . 

Centennial-Two Kings vein ......... . 

U.S. tunneL ..................... : .. 

Edgar vein .............. , ............ . 

Shafter vein ....................... ~ . 

Summit tunneL ....... .: ............ . 

Bullion King mine ........... : ...... . 

Stanley mine ....................... . 

CONTENTS. 

Page. 

355 

355 

355 

355 

356 

356 

356 

357 

358 

359 

359 

359 

360 

360. 

361 

361 

361 

PART III. The mines-Continued. 

Chapter XVI. Clear Creek County-Continued. 

Trail Creek and area between Idaho Springs 

and Fall River-Continued. 

Salisbury vein ........................ . 

Cardigan vein ...................... . 

England mine ...................... . 

Gladstone vein ..................... . 

Donna Juanita vein ................. . 

Ready Cash vein .............. "· .... . 

A. Maude Munroe vein ............... . 

Lost vein ............................ . 

Little Six tunneL .......... ; ........ . 

Wyandotte tunnel .................. . 

Josephine and Barber & Elliott veins .. 

Lincoln and South Lincoln veins ..... . 

Oro-Morning Star vein ................ . 

Metropolitan tunneL ................ . 

Hoosac tunnef ............. __ ........ . 

INDEX •••••.•.•••..••••••••• : ••••••••••• · ••.•••. 

9 

Page. 

362 

362 

362 

363 

363 

363. 

364 

364 

364 

364 

365 

365 

365 

366 

366 

369 
ILLUSTRATIONS. 

Page. 

PLATE I. Geologic map of portions of Central 

City quadrangle, Colorado .... In pocket. 

·u. Topographic map of Central City 

quadrangle, Colorado, showing location of mines outside the areas of the 

special sheets, position and· classification of veins, and positions of 

larger tu~els ................ In pocket. 

III. Geologic map of Central City and 

vicinity,......... . . . . . . . . . . . . . In pocket. 

IV. Topographic map of Central City and 

vicinity showing location and c,lassification of metalliferous veins and 

locations of principal mines .... In pocket. 

.V. Claim map of Central City and 

vicinity......... . . . . . . . . . . . . . In pocket. 

VI. Geologic map of Idaho Springs and 

vicinity......... . . . . . . . . . . . . . In pocket. 

VII. Topographic map of Idaho Springs 

and vicinity showing location and 

classification of metalliferous veins 

andlocationsof principalmines.In pocket. 

VIII. Claim map ~f Idaho. Springs and 

vicinity ....................... In pocket. 

IX. A, Dissected Tertiary pen~plain of the 

Front Range, looking southwest 

from a point near Palmer. Lake, 

Colo.; B, Another view of the pene- . 

plain showing Pikes Peak rising 

above it, taken near the same locality as Plate IX, A, but in a more 

south wes1 erl y direction. . . . . . . . . . . . 20 

X. A, Exposure of crumpled schist of the 

Idaho Springs formation in Virginia 

Canyon near Seaton Gulch; B, Injection gneiss formed by intimate 

intrusion of quartz-biotite schist of 

the Idaho Springs formation by 

grarute pegmatite. . . . . . . . . . . . . . . . . . 21 

XI. ,A, Microphotograph of bostonite porphyry from a point near Idaho 

Springs, . showing characteristic 

trachytoid texture; B, Microphotograph of lean iron ore from Caribou; 

' showing magnetite and. ilmenite 

ana augite; C, Microphotograph of 

lean iron ore from Caribou, showing 

magnetite and ilmenite, augite, and 

serpentine. . . . . . . . . . . . . . . . . . . . . . . . 52 

XII. A, Outwash plain of' later glacial 

epoch in valley of Middle Bqulder 

Creek between Eldora and N ederland, looking eastward; B, Hornblende schist of Idaho Springs formation intruded by pegmatite near 

Eldora............................ 53 

10 

PLATE XIII. A, Irregular mineralization typical of• 

stockworks of the Patch type at 

Hubert mine; B, N~twork of sphalerite veinlet~ traversing sericitized 

· granite gneiss, Boulder County vein 

ne~ Cardinal; C, Ore of cqmposite 

type from Fourth of July mine, near 

Page. 

Central City ......... .' . .'. . . . . . . . . . 96 

XIV. A, Polished surface of ore from Alice 

mine, showing progressive alteration of monzonite porphyry; B, 

Ore breccia fo.rmed by postmineral 

movement along a vein in Ivanhoe 

mine, near Nevadaville; C, Banded 

ore from Topeka vein. . . . . . . . . . . . . 97 

XV. A, Microphotograph of polished section of pitchblende ore from the 

Wood mine, Quartz Hill, Gilpin 

County; B, Microphotograph of 

dike rock from Evergreen mine, 

Pine Creek valley, Gilpin County. 124 

XVI. A, Uraninite or pitchblende fractured 

and brecciated and interspaces filled 

with ore composed principally of 

chalcopyrite, with some galena, 

pyrite, and 'sphalerite; B, Uraninite or pitchblende traversed by 

sulphide veinlets................. 125 

XVII. A, Etched crystals of galena from vug 

in Hayseed vein, near CentralCity; 

B, Caribou, looking westward from 

Boulder County Hill............... 136 

XVIII. A, Mammoth Hill from the east, showing open pits marking outcrop of 

Mammoth vein; B, Dump and ore 

bins at mouth of Argo tunnel below 

Idaho Springs, Clear Creek County. 222 

XIX. Mines of Gregory Hill and .Packard 

Gulch, from Bates Hill............ 223 

XX. Plan of a part of Bobtail tunnel...... 224 

XXI. A, GeologicplanofArgotunnel; B, Geologic plan of Big Five tunnel .. In pocket. 

XXII. Lawson and the mines of Red Elephant Hill from south side of Clear 

. Creek Valley near Lawson.... . . . . . 334 

XXIII. Vie~ looking up Silver Creek near 

Lawson ................. ~........ 335 

FIGURE 1. Index map of Colorado showing position of areas covered by this report and 

by Professional Paper 63............ 19 

2. Titaniferous iron ore from Caribou...... 48 

3. Diagram illustrating the chemical relations of stock rocks near Caribou. . . . . 49 

4. Map showing approximate distribution 

of principal silver, lead, and gold 

regions in Colorado.................. 93 
ILLUSTRATIONS. 11 

Page. Page. 

F1 JURE 5. Di~crram showing·characteristic branching vein systems as exposed in the 

FIGURE 21. G~ologic plan of Alton tunnel. ..... .. 186 

192 

workings of three mines ............ . 

6. Sketch of filled breccia in· Hubert 

n1.ine ............................. . 

7. Diagrammatic section showing relation 

of mineralization to fracture planes 

and th~ir intersections at the Alice 

mine ............................. . 

8. Camera Iucida sketches of pyrite grains 

in altered monzonite porphyry bordering the Lake vein in the Big Five 

tunnel ................ · ............ . 

9. Camera Iucida drawing of polished surface of ore from Specie Payment' vein, 

showing pyrite of the early mirieralization brecciated and traversed by 

veinlets of ore of a later period of 

mineralization .................... . 

10. Camera Iucida drawing of ore from 

Specie Payment vein, showing pyrite 

of first mineralization brecciated and 

penetrated by sphalerite, quartz, and 

chalcopyrite of a later period of mineralization ....................... . 

11. Camera Iucida drawing of polished section of ore from the Wood mine, 

Quartz Hill, showing contemporaneous intergrowth of pitchblende, chalcopyrite, and pyrite ............... . 

12. Camera Iucida drawing of polished surface of pitchblende ore from the Wood 

mine, Quartz Hill, showing contemporaneous intergrowth of pitchblende, chalcopyrite, and pyrite ..... 

13. Camera Iucida drawing of polished face 

of ore from the Calhoun mine, showing pitchblende traversed by later 

veinlets of pyrite, sphalerite, and 

galena .............. , ............. . 

14. Camera Iucida drawing of polished surface of ore from the Princess of India 

tunnel, Lawson .... ~ •...... ~ ...... . 

15. Portions of specimen shown in figure 14, 

more highly magnified ............ . 

16. Camara Iucida drawing of polished surface of ore from Senator vein, near 

Lawson, showing metMomatic replacement of galena oy pearceite and 

some chalcopyrite .................. . 

17. Camera Iucida drawing of poiished section of ·ore from Maud S. mine, near 

Empire station ................... . 

18. Diagram showing average market price 

of silver in the United States for the 

years 1859 to 1915, inclusive ....... . 

19. Camera Iucida drawing of replacement 

veinlet of silver, bornite, and chalcocite in altered pyroxenite from Up to 

Date tunnel, Caribou .............. . 

20. Geologic plan of Up to Date tunnel, 

Caribou ..............•.........•.. 

96 

97. 

98 

108 

113 

113 

123 

124 

124 

144 

144 

145 

1.45 

148 

149 

178 

22. Geologic plan of Golden Sun tunneL .• 

23. Geologic plan of Mountain Monarch tunnel ............................... . 

24. Geologic plan. of Penobscot tunnel ... . 

25. Geologic .plan of upper tunnel, Perigo 

.. mine ...................... · ...... . 

26. Geologic plan of lower tunnel, Perigo 

mine .............................. . 

27. Plan of 140-foot level, Mackey mine, 

near Apex, Colo .................. . 

28. Geologic plan of Belden tunnel. .... . 

29. Sketch showing Argo tunnel level and 

1,100-foot level of Gunnell-Grand 

Army mine ....................... . 

30. Cross section showing relations of Hubert North and South veins and the 

shafts which develop them ........ . 

31. Plan of portion of workings of Hubert 

mine .............................. . 

32. Vein system on 178-foot level of Maine 

Hamlet mine ..................... . 

33. Geologic plan of Quartz Hill tunnel .. . 

34. Stope map and north-south sections 

through shafts, California- Hidden 

Treasure lode ..................... . 

35. Plans of levels of SanJuan mine, Quartz 

Hill· .............. .' ............. .-. 

36. Geologic plan showing veins and the 

Patch as exposed in the La Crosse tunriel and positions of the Patch on the 

195 

196 

198 

199 

203 

209 

216 

219 

220 

222 

231 

233 

234 

surface and in the Argo tunnel.. . . . . . 235 

37. Plan of 20Q-foot and 300-foot levels of 

Egyptian mine. . . . . . . . . . . . . . . . . . . . 239 

38. Plan of upper levels of Barnes mine.. . 243 

3~. Section showing workings along Jefferson-Calhoun vein .......... : . . . . .. . . . 246 

40. Geologic plan of portions of the seventh 

and eighth levels of the Topeka mine. 249 

41. Plan of upper levels of Old Town mine, 

showing branching vein system. . . . 252 

42. Section in plane of Old" Town vein, 

showing portions that have been 

stoped. . . . . . . . . . . . . . . . . . . . . . . . . . . . 253 · 

43. Plans of portions ofthe 400-foot and 500-

foot levels of the Iron mine, showing 

characteristic branching vein systems 254 

44. Geologic plan of the 450-foot level on the 

Lotus vein and connecting workings 

on other veins............ . . . . . . . . . . 256 

45. Geologic plans of 500-foot, 700-foot, and 

800-foot levels of Pittsburg mine.. . . 261 

46. Geologic plans of levels of West Notaway mine......................... 263 

47. Geologic plan of 555-foot level of East 

Notaway mine ...... ~............... 265 

48. Geologic plan of Frontenac mine above 

ninth level. .. . . . . . .. . . . . . . . .. . .. .. 269 

49. Geologic plan of portion8 of the Chase 

mine............................. 275 

50. Geologic plan of portions of the Clarissa 

mine............................. 282 
12 ILLUSTRATIONS. 

FIGURE 51. Geologic plan of Fairmont tunneL .... 

52. Plan of Lake tunnel and connecting 

workings on the Windsor Castle 

vein .............................. . 

53. Geologic plan of a portion of the workings on the Specie Payment and adjacent veins ....................... . 

54. Geologic plan of Silver Age tunnel. .. . 

55. Geologic plan of Foxhall tunnel and of 

Seaton and Casino mines .......... . 

56. Geologic plan of Tropic tunnel. ...... . 

57. Geologic plan of Crystal tunneL ...... . 

58. Geologic plan of Idaho tunnel. ..... ~. 

59. Geologic plan of workings on FrontenacAduddell system of veins ·on Argo 

tunnel level ...................... . 

60. Geologic plan of Dover and Philadelphia tunnels ....................... . 

61. Geologic plan of United Gold tunn~l .. 

62. Geologic plan of Standard tunnel .... . 

63. Geologic plan of Wyomed tunnel. .... . 

64. Geologic plan of Mayflower tunnel ... . 

65. Geologic plan of Ninety-Four tunnel. 

Page, 

283 FIGURE 66. Plan and section of workings of Alice 

284 

287 

292 

295 

297 

298 

302 

305 

307 

308 

314 

318 

320 

322 

mine ............................... . 

67. Geologic plan of Marshall & Russell 

tunnel ........... : ............... . 

68. Geologic plan of Bellevue-Hudson or 

Rochester tunnel ................. . 

69. Geologic plan. of portion of Commodore 

tunnel and connecting workings ... . 

70. Geologic plan of Panama tunnel. .... . 

71. Geologic plan of Princess of India tunnel, developing the Platts vein ..... . 

72. Geologic plan of Silver King tunnel, in 

Spring Gulch ...................... . 

73. Geologic plan of portions of the Blue 

Ridge and Senator mine ............ . 

74. Geologic plan of 4-C tunnel. .......... . 

75. Geologic plans of workings of Silent 

Friend mine ...................... . 

76. Ge_ologic plan of upper Western Syndicate tunnel. ...................... . 

77. Geologic plan of Freeland tunnel. ..... . 

78. Geologic plan of Miami tunnel ....... . 

79. Geologic plan of Hoosac tunneL .... _.·: 

Page. 

324 

331 

332 

334 

336 

337 

343 

345 

348 

348 

351 

352 

356 

367 
PREFACE .. 

By F. L. RANSOME. 

The more productive metalliferous districts 

of Colorado are not distributed at random, but 

lie in a northeast-southwest belt, about 250 

miles in length, that extends· from Montezun1a 

County, in the southwest corner, to Boulder 

County, in the north-central part of the State. 

The width of this belt, inclusive of the somewhat outlying deposits of Teller and Custer 

counties, is about 115 1niles. Spurr 1 in particular has called attention to this feature of ore 

distribution, and has brought out the relation 

existing between the occurrence of the ores and 

the general geologic history and structure of 

the region, especially the dependence of ore 

deposition upon the kinds and sequence of 

Tertiary igneous activity. 

Owing to their scientific interest and industrial importance, the metalliferous deposits of 

the Colorado ore belt have been the subject of 

study by the geologists of the United States 

Geological Survey from the founding of that 

organization-. In 1879, under the directo'rShip 

of Clarence King, S. F. Emmons began his 

investigation of the Leadville deposits, and the 

c01nplete results 2 appeared in 1886. The first 

Cripple Creek report 3 was published in 1896, 

and t~e reports on the geology and mines of 

Custer County 4 in the srune year. 

In 1897 appeared the report on the Telluride 

district, 5 of the San Juan region, and in 1898 

the Jnonograph on the Aspen district. 6 A 

l I Spurr, J. E.,nnd Garrey, G. H., Economic geology orthe Georgetown 

quadrnnglo, Colo.: U. S. Geol. Survey Prof. Paper 63, pp. 102-132, 1908. 

s Emmons, S. }~., Geology nn<l mining industry of Leadville, Colo.: 

U. S. Goo!. Survey Mon. 12, 1886. 

report on the· geology of the Rico district, 7 in 

1900, was followed the next year by one on the 

ore deposits of the same district. 8 The report 

on the ore deposits of the Silverton quadrangle, 9 

in the San Juan region, was also issued in 

1901. 

The second Cripple Creek report 10 appeared 

in 1906, and the publication, in 1907, of a 

bulletin on the Downtown district of Leadville 11 marked the resumption by Mr. Emmons 

of work in the field where he had previously 

won such distinction. At the time of his 

death he and Prof. Irving were at work on a 

complete revision of the Leadville monograph. 

The greater part and completion of the task 

have· fallen to Prof. Irving, and the second 

monographic report on the Leadville district is 

now nearly ready for publication. 

About 1902 Mr. Emmons, thea in 'charge of 

the Survey's work on metalliferous deposits, 

made plans to take up the study of the ore 

deposits at the northeast end of the belt, in 

Clear Creek, Gilpin, and Boulder counties. It 

was the discovery of these ~eposits that precipitated the second great ·rush of gold-seekers 

to the West, in 1859, led to the founding of 

Denver, and marked the beginning of the 

industrial development of Colorado. Cripple 

Creek has· surpassed these three counties in 

value of annual output, and at Leadville mining operations have been conducted on a larger 

scale, but in the combined interest that attaches to a long and significant historical 

record, to number and variety of deposits, and 

a Cross, Whitmnn, and Penrose, R. A. F., jr., Geology and mining 

industries of tho Cripple Creek district, Colo.: u. s. Geol. Survey Six- 7 Cross, Whitman, and Spencer, A. C., Geology of the Rico Mountains, 

teonth Ann. Rcpt., pt. 2, pp. 1-209, 1896. Colo.: U.S. Geol. Survey Twenty-first Ann. Rept., pt. 2, pp. 7-165, 1900. 

• Cross, Whitman, Geology of Silver Cliff and the Rosita Hills, Colo.: 8 Ransome, F. L., The ore deposits of the Rico Mountains, Colo.: U.S. 

U.S. Goo!. Survey Seventeenth Ann. Ropt., pt. 2, pp. 263-403, 1896. Goo!. Survey Twonty-se:)ond Ann. Rept., pt. 2, pp. 229-398, 1901. 

l~mmons, S. F., 'L'he mines of Custer Cotmty, Colo.: U. s. Geol. Sur- \ 9 Ransome, F. L., A report on the economic geology of the Silverton 

yoy Scvontoei1th Ann. Ropt., pt. 2, pp. 405-472, 1896. quadrnngle, Colo.: U.S. Geol. Survey Bull. 182, 1901. 

a Purington, C. W., Preliminary report on the mining industries of the 10 Lindgren, Waldemar, and Ransome, F. L., Geology and gold deposits 

Telluride quadrangle, Colo.: U. S. Geol. Survey Eighteenth Ann. Rept., of the Cripple Creek district, Colo.: U. S. Geol. Survey Prof. Paper 54, 

pt. 2, pp. 745-850, 1897. 1906. 

o Spurr, J. E., Geology of the Aspen mining district, Colo.: U.S. Geol. J u Emmons, S. F.,and Irving, J.D., The Downtown district of LeadSurvey Mon. 31, 1898. . · ville, Colo.: U. S. Geol. Survey Bull. 320, 1907. 

13 
14 GEOLOGY OF GILPIN, QLEAR. CREEK, AND BOULDER COUNTIES, COLO. 

to the place where so much in mining and plemented earlier publications on the ore demetallurgic technique had its beginnings, the posits of the San Juan region. 

region is without a peer among the mining The prese'nt report on the Central City region 

districts of the Rocky Mountains. In many -rounds out the Geological Survey's inv(3stigarespects it holds in this country a position tion of the principal districts in the northeastanalogous to that of Cornwall in Great ern part of the Colorado ore belt .. Creede, an 

Britain. important district in the sou.thwestern part of 

It had been Mr. Emmons's intention to take the belt, has been studied, but the results have 

up first the Central City quadrangle, but owing not yet been published in full. 

perhaps to the fact that the topographic maps In addition to the ·reports mentioned, the 

of the Georgetown quadrangle were ready be- Geological Survey has published a number of 

fore those of the Central City quadrangle, the folios descriptive of the geology .and ore deGeorgetown area was the first to be studied, posits of parts of the Colorado or'e belt. 

and the report on it, by Spurr, Garrey, and Ball/ In the present report the ore deposits of the 

was published in 1908. Central City region ·are divided into five main 

Three years later appeared the report on th~. · classes, some of which are of exceptional interBreckenridge district, 2 lying some distance est. Special attention may be called to the 

southwest of the Georgetown quadrangle: discussion of downward enrichment, especially 

This study served to link the Georgetown work in silver, a subject to which Mr. Bastin and 

with that at Leadville. In 1911 also a bulletin his colleague, Mr. Chase Palmer, have devoted 

by Irving and Bancroft~ extended and sup- special attention during the last two years, 

1 Spurr, J. E., and Garrey, G. H., Economic geology of the Georgetown 

)

. quadrangle (together with the Empire district), Colo., with general 

geology by S. H. Ball: U.S. Geol. Survey Prof. Paper 63, 1908. 

, 2'Ransome, F. L., Geology and ore deposits of the Breckenridge district, Colo.: U. S. Geol. Survey Prof. Paper 75, 1911. -r a Irvi~g, J.D., and Bancroft, Howland, Geology and ore deposits near 

Lake C1ty, ?olo.: U. S. Geol. Survey Bull. 478, 1911. 

and to which they have made important contributions. Enrichment in lead appears to 

have been slight, a result somewhat unexpected in view of the different conclusions 

reached with ·regard to the deposits ot" the 

neighboring Breckenridge district. 

' .. 
SUMMARY OF.RESULTS. 

By Ens'oN S. BAsTIN. 

Gilpin County and the adjacent portions of 

Boulder and Clear Creek counties,· Colo., lie 

nearly west of Denver in the heart of the 

Front Range of the Rockies. Central City, 

the· seat of Gilpin County, is the oldest lodemining camp in Colorado and in total production one of the most important. 

GENERAL GEOLOGY. 

the monzonite stocks near Caribou has produced ·masses of ga~bro and iron ore, and it is 

believed that many of the dike rocks other 

than monzonite have also been derived by 

processes of magmatic differentiation from the 

·monzonitic magmas. The Tert.iary ( ~) igneous 

rocks range from felsic (acidic) varieties, such as 

granite porphyry, to ma:fio (basic) varieties, 

such as basalt porphyry, and the ultramafic 

Pre-Cambrian rocks.-Most of the rocks of titaniferous iron 'ores. Most of these intrusive 

the regioi1 are pre-Cambrian in age. Some of rocks, including the monzonites, are older 

then1 have undergone severe dynamic m'etamor- than the mineral vein:s of the district, but at 

phism, during which schistose or gneissic least one, biotite latite, is younger. 

structure has been developed; others are p~ac- · Tertiary (?) terrace gravels.-Certain terrace 

tically unmetamorphosed and are massive. gravels near Idaho Springs reaching a levellSO 

\

The oldest and most extensive of the pre- feet above the creek are of uncertain age, posCambril1n formation~ is the Idaho Springs sibly late Tertiary. 

formation, whose preponderant rock type is Quaternary deposits.-The Front Rang~ was 

biotite schist. This is the only one of the p~e- s~bjected twic~ in Pleistocen~ t~e to glac~a­

\Cam~rian formations that is b~lieved .to be of twn. o~ the alp~e type,. and glaCial or glaciosedimentary origin, and through it all the -fluVIatile deposits belongmg to both stages (the 

igneous rocks of the region have been intruded. Wisconsin and pre-Wisconsin) are present in 

Next younger are granite gneisses forming ir- the· area surveyed. In Recent time sheets of 

regular stocks many of which are of large debris have been developed in the headward 

areal extent. Apparently nearly contempo- portions of unglaciated valleys, talus deposits 

raneous with the granite gneiss is quartz along the steeper valley walls, and alluvium 

di011_te grading into hornblendite, which ~ along the streams~ 

as a few large dikes. Later than these is the Structure.-The most notable structural 

Silver Plume granite. Granite pegmatite is characteristic of the region is the intricate 

extremely abundant and is not all of the same manner in which igneous rocks ranging from 

age, some being contemporaneous with the pre-Cambrian to Tertiary ( ?) in age have been 

granite gneiss and some with the Silver Plume intruded. into the sedimentary Idaho Springs 

a ·t · formation and into one another. The intrusions gr ni e. 

Tertiary (?) intrusive rocks.-Th!3 pre-Cam- range in size from mere threads between schist 

brian rocks are intruded by a great variety of folia to stocks several miles across. Dikes are 

muoh younger igneous rocks, most of them particularly abundant and a few of them are 

porphyritic . in texture-the "porphyries" of traceable continuously' more th~n 5 miles. 

the miners. Though they show some diver- Many of the intrusions are somewhat lenticular, 

sity in age, all are believed to have been ·in- with their long axis parallel to the prevailing 

truded in Tertiary time. They occur as trend of the foliation of the inclosing rocks; 

stocks and dikes and are abundant in all parts others are extremely irregular in. form. 

of the region. The predominant rock type is · Purely dynamic processes have also played 

monzonite porphyry, which forms the bulk of a part.in the structural history, thei~ principal. 

the larger stocks and is the most abundant effect being the development of foliation in the 

dike rock. Magmatic differentiation within older pre-Cambrian rocks-the Idaho Springs 

15 
16 GEOLOGY OF GILPIN, CLEAR CREEK, AND BOULDER COUNTIES, COLO. 

formation, the granite gneiss, and some of the 

quartz diorite. The younger pre-Cambrian 

rocks are not foliated. During much later 

periods faulting took place. Some of the faults 

were formed prior to or contemporaneously 

with_ the intrusion of the Tertiary ( ~) igneous 

rocks; some were formed shortly after that intrusion and became the sites of ore deposition, 

and some were formed subsequent to the 

mineralization and displace the mineral veins. 

In places faulting may still be in progress. 

Most of the faults are of small displacement. 

Joints are numerous i'n the more rigid rocks 

and commonly parallel one or more of the directions of faulting. 

were very productive in the' sixties but are r 

now negligible. The lode ores may be classed lj 

a.s __ p:f-!:i~<?- or~~'- _gale!la~sphalerite __ ores, composite ores,-and telluride ores. ~ i 1 

The pyritic ores consist predominantly of ,_\'V'":; - ·-

pyrite and gangue minerals, with subordinate J 

amounts of chalcopyrite, tennantite, and in 

places enargite and other minerals. Enargite 

and fluorite are confined to a single group of 

pyritic veins. The characteristic wall-rock 

alterations near the pyritic veins consist in the 

development of pyrite and sericite; carbonates 

and silica are locally formed. Pyritic ores are 

widely distributed in the region and £_arry·:pl"!J.Ch 

more gold than silver in value; in many places 

tliey contain copper in profitable amounts. . 

ECONOMIC GEOJ;.OGY. In the galena-sphalerite or~s the predomi- \ .~ ~~\ (1-- ~" 

General features of the ore deposits.-The nant primary sulphides are galena, sphalerite, J ,, -) .. _:.'. ,:. - ' 

region forms p_~La_br.o_ad.mineralize<Lhelt and pyrite; they contain chalcopyrite and in : · \ 

which embraces most of the economically im- places other sulphides in smaller amounts. 

portant mining camps of Colorado. The ores The common gangue n1inera1s in ores that are ' 

of the region may_ be classed, according to the fissure fillings are quartz and calcite or siderite, , (\ 

metals which give them their predominant but in some veins barite is present, and a single 

value, as (1) gold-silver ores, which constitute group of veins .contains rhodochrosite. The 

the main __ e~onomic resource of the region; (2) characteristic wall-rock alterations consist in 

uraniun(: ores, which occur in a few places the development of sericite, carbonates, and 

only but are of much interest as a source of pyrite; other sulphides occur locally. Certain 

radium; (3) tungsten ores, which form the veins of the galena-sphalerite type carry only 

basis of the tungsten industry of Boulder negligible amounts of gold, but in others the 

County, the most productive center for this gold content is considerable. The silver conmetal in the United States; (4) ores worked tent is in general greater than in the ores of 

primarily for copper, which are represented pyritic type and has in many mines been augsolely by the Evergreen mine, near Apex; and mented through downward enrichment. The 

(5) titaniferous iron ores, which occur only copper content is usually below the commercial 

near Caribou ~nd have not been utilized com- limit, but these ores contain considerable lead 

mercially. Most of th.(L_Qres_ o~c,cur as veins, and zinc. Ores of this type are much less 

as a rule s_teeply--d!pping, which are. in part widely distributed than the pyritic ores. 

fissure -fillings and in part replacements of The composite ores have bt3en formed through 

I 

various rocks along zones of fracturing. A the fracturing of ores of the pyritic type and the ' c· I' \ 

few deposits, notably the so-called Patch, filling of the fractures with ore of the galena- ' 

_ ; near Central City, are stockworks, the copper sphalerite type, which also lines vugs inpyritic ·'~' 

ores are an integral part of monzonite dikes, ore. Certain veins are of the pyritic type at " 

and the titaniferous iron ores are irregular. one end, composite at the center, and of the 

bodies within a monzonite stock. The veins galena-sphalerite type at the other end. Other 

and stockworks are, with few exceptions, later veins are composite near the surface and become 

than the Tertiary 0) intrusive ropks; the cop- pyritic with increasing depth. Ores of this 

per and iron ores are contemporaneous with type occur principally in transition zones bethe monzonites within which they occur. The tween are~s characterized by pyritic ores and 

wall rocks have influenced the distribution and others characterized by galena-sphalerite ores . 

. character_ of the ores only through their vary- ·Their metal content is intermediate to that of 

ing susceptibility to fracturing or replacement. the two simple types. 

Gold-silver ores.-The gold-silver ores include The telluride ores show more diversity in 

both lode and placer deposits. The placers mineral character than the types already men-
SUMMARY OF RESULTS. 17 

tioned, and it is not certain that all were formed 

at the same time. Telluride ores are confined 

to the region between Central City and Idaho 

Springs and to Eldora and vicinity. The tellurides commonly occur in a gangue of chertylooking quartz and in some mines are associated 

with abundant fluorite qr with the vanadiummica roscoelite. Pyrite is invariably present, 

and tennantite occurs in some veins. The commonest telluride appears to be sylvanite, but 

petzite has been reported from one mine. Free 

gold is usufllly associated with the tellurides 

and is especially abundant near the surface. 

U1·anium ores.-Uraninite or pitchblende 

occurs in a few of the gold-silver veins, mostly 

in Quartz I-Iill, near Central City. Study of 

polished sections indicates that the pitchblende 

is contemporaneously intergrown with the same 

suite of minerals that characterizes the ores of 

the pyritic type and is cut by veinlets of the 

galena-sphalerite type. The pitchblende ores 

are provisionally regarded as a phase of the 

pyritic type of mineralization. 

Tungsten ores.-The tungsten ores of theregion are confined to Nederland and vicinity. 

They were . not studied in detail, but from 

their broader geologic relations and from the 

observations of others it is thought probable 

that they are of the same general age as the 

other ores. In a few places they carry tellurides and other n1inerals characteristic of the 

gold-silver ores. . 

OozJzJer ores.-The copper minerals of tpe 

Evergreen mine, near Apex, are bornite and 

chalcopyrite, which occur as original components of. igneous dikes of general monzoni tic 

composition. Wollastonite is locally abundant 

in these dikes. The ores are believed to have 

been formed by magmatic differentiation within a body of monzonite, possibly accompanied 

by some absorption of lime and perhaps other 

substances from the wall rocks. This is the 

only ore deposit of the region that is worked 

primarily for copper. 

Titanijerous iron ores. -Several deposits of 

titaniferous iron ore occur in Caribou Hill, where 

they form irregular bodies within ·areas of 

gabbro and pyroxenite, which in turn are inclosed by monzonite. The gabbros, pyroxenites, and iron ores are believed to have been. 

formed by m,agmatic differentiation within the 

n1onzoni te magma. The iron ore commqnly 

carries from 3 to 5 per cent of oxide of titanium 

44214-17-2 

(Ti02). Even if the metallurgic difficulties in-;-

volved in the high titanium content can be 

overcome, the inaccessibility and small size of 

these deposits preclude their successful exploitation under present economic conditions. 

Genesis of primary ores.-All the ores of the 

region are believed to be genetically connected 

with the Tertiary (~)intrusive rocks. The iron 

and copper ores are obviously so connected. 

The gold-silver ores are believed to have been 

deposited by thermal solutions emanating from 

the deeper por'tions of the momonitic magnlas 

after the portions now exposed at the surface 

had solidified. Even at the same period the 

composition of these solutions was somewhat 

different in different parts of the region, as 

shown by the highly localized enargite or pitchblende bearing phases of the pyritic ores. The 

composition of the solutions also varied progressively during the ore-forming period, ores 

of the pyritic type being deposited :fust and ores 

of the galena-sphalerite type later. Physiographic and stratigraphic evidence, as well as 

the mineral composition of the gold-silver ores, 

indicates that they were deposited under conditions of moderate intensity as regards temperature and pressure. 

The solutions that deposited the gold-silver 

ores are believed to have been alkaline or neutral in character, rich in alkalies, silica, carbonic and bicarbonic acids, iron, lead, zinc, 

and arsenic and carrying lesser amounts -of 

copper, antimony, gold, and silver. Locally 

manganese, barium, the sulphate radicle, tellurium,, fluorine, tungsten, uraniun;t., radium, 

and vanadium were present. 

Enrichment.-Enrichment in the Central City 

region has been confined mainly to the class 

of gold-silver ores. In these veins enrichment 

in gold and silver is of considerable economic 

importance, enrichment in copper of minor 

importance, and enrichment in lead and zinc 

negligible. . 

Enrichment in gold appears to be confined 

almost exclusively to portions of the ore de- 1 

posits above or immediately below the ground- \' 

water level. It has affected all types of goldsilver ores and has caused a material increase 

in the value of the ore in the oxidized zone. 

Enrichment in silver is confined mainly to the 

ores of the galena-sphalerite type. It appears 

probable that the relatively low content of 

pyritic minerals in the galena-sphalerite ores 
18 GEOLOGY OF GILPIN, CLEAR CREEK, AND BOULDER COU~TIES, COLO. 

and the presence of a carbonate gangue favoring neutral or alkaline rather than acid solutions in the secondary sulphide zone have had 

an important influence in restricting silver 

enrichment to ·ores of this type. In the oxi-· 

dized zone of these ores "there seem to have been 

impoverishment in silver ·and enrichment in 

gold. Silver. enrichment is confined to the 

ground-water zone and consists in the secondary deposition of pearceite and proustite and 

mote rarely of native silver. It is greatest in 

the first 100 or 200. feet below the natural 

ground-water level and shows· a progressive 1 decrease with increasing depth. The maximum depth at which secondary silver minerals 

were noted was 700 feet below the surface (about 

650 feet below the water level). Two types of 

mineral association were noted in the rich 

! silver ores. In one secondary sulpho-com-· 

pounds of silver-were associated with secondary 

chalcopyrite; in the other abundant native 

silver was associated with chalcocite, bornite, 

and covellite. The secondary silver minerals 

are deposited in fractures in the primary ore 

and also as metasomatic replacements of the 

primary minerals. . . 

Enrichment in copper is now.o.ere conspicuous and is confined almost wholly to .the 

ground-water zone of ores of the pyritic type; 

the oxidized ores were impoverished in copper. 

The enrichment is greatest in those deposits 

whose ores are unusually rich in primary copper minerals. Chalcocite is the principal secondary copper mineral and is developed in 

part as a filling_ in fractures or a coating in 

vugs and in part by metasomatic replacement 

of chalcopyrite and pyrite. 

Enrichment in lead was noted in only a few 

localities and is nowhere important. Zinc 

enrichment was not observed. 
ECONOMIC GEOLOGY OF GILPIN COUNTY AND ADJACENT PARTS OF 

CLEAR CREEK AND BOULDER COUNTIES, COUORADO. , 

By ·EnsoN S. BASTIN and JAMES M. HrLL. 

PART i.-GENERAL GEOGRAPHY AND GEOLOGY. 

By EDSON s. BASTIN. 

CHAPTER I.-INTRODUCTION. 

LOCATION AND AREA OF .Tf!E REGION. by 13! miles east and west, and its area is apThe region whose geology is described in this proximately 236 square miles. Denver is 26.5 

report forn1s a part of the Central City quad- miles east of the southeast corner. The western 

rangle, 'which lies in the ce~t~~ of the north portion, west of the Continental Divide, is in 

FIGURE I.-Index map of Colorado showing position of areas covered by t~is report (dark shading) and by Professional Paper 63' (light shadJng). 

half of Colorado (fig. 1) between meridians Grand County. Of the area lying east of the 

105° 30' and 105° 45' west longitude and par- divide the southern part. is in Clear Creek 

allels 39° 45' and 40° north latitude. The County, the pentral part in Gilpin County, and 

quadrangle is about 17! miles north and south the northern part in Boulder County. The 

19 
20 GEOLOGY OF GILPIN, CLEAR CREEK, AND BOULDER COUNTIES, COLO. 

quadrangle is named from Central City, the 

largest town. and the county seat of Gilpin 

County. (See Pl. I, in pocket.) The quadrangle-lies immediately north of the Georgetown quadrangle, whose geology ·has been 

. described by Spurr, Garrey, and Ball.1 

As shown on Plate I, only the eastern and 

southern parts of the Central City quadrangle 

were surveyed geologically, the higher parts, 

where little minmg has been done, not being 

covered. The greatest developments in mining are within the areas covered by the Geological Survey's Central City and Idaho Springs 

special·atlas sheets, and the geology of these 

areas has been studied· in. especial detail, the 

plane table being used in the geologic mapping. 

R. Alsdorf, Mr. George E. Collins, Mr. Henry 

P. Lowe, Mr. John C. Fleschutz, Mr. Norton H. 

Brown, Mr. James Underhill, Mr. R. B. Morton, 

Mr. Philip R. Stanhope, Mr. Henry I. Seeman, 

Mr. F. ·D. Wiley, and Mr. Ralph Chase. To 

these and to others too numerous to mention, 

whose aid was no less cheerfully giyen, the 

writer extends his sincere thanks. 

GEOGRAPHY AND GEOLOGY OF THE PROVINCE. 

THE SOUTHERN ROCKIES. 

The Central Qity quadrangle lies in the , 

heart of the Front Range of the southern 

R·ocky Mountains. Structurally the southern 

Rockies, including the- Laramie, F:r:op.t, S~wtooth, Park, Wet, and Sangre de Cristo ranges, 

FiELD WORK·AND ACKNOWLEDGMENTS. may be 'regarded "as an· anticliri.al or arched 

region, in which large ·areas of pre-Cambrian 

The topographic survey of the Central City crystalline rocks are exposed between flanking 

quadrangle :was made in 1903 by Frarik beds of Paleozoic and· Mesozoic sediq1ents.2 

Tweedy,· and the map was published ·on the On the west the sedimentary beds of the Coloscale of a mile to the inch. The mapping of the rado Plateau sweep at low angles up the arch, 

cultural features of this area, such as railroads but east of the easternmost or Front Range the 

and wagon roads, was revised by Lee Morrison sedimentary strata are bent upward at steep 

in 1910, and his revisions appear on Plates I angles. Although this simple description exmid II of this report (in pocket). In 1904 presses the broader featur~s, a closer examimore detailed topographic surveys were made nation shows that the province, instead of 

of the regions about Central City and Idaho consisting of a huge simple arch, comprises a 

Springs, by PearSon Chapman and D. F. Moor, number of diverse anticlinal folds that correas a basis for the preparation of the Idaho spond in a general way to the principal nlounSprings and Central City special maps on the tain masses, all of which show broad central 

scale of 1,000 feet to the inch. areas of crystalline pre-Cambrian rocks. 

The' geologic field work that forms the basis ·Knowledge of· the character of the rocks of 

for this report beg!tn with a month of recon .. the pre-Cambrian areas is derived from a few 

naissance by. Edson S. Bastin in the fall of 1910. widely separated regions where they have 

Detailed field work was done in the summers been studied in detail, so that few generalizaof 1911 and 1912, 1\{r. Bastin being_assisted in tions can safely be made for the province as a 

191l and 1912 by James M. Hill and in 1912 whole. The rocks include extremely old sediby Charles· W. Hender8on. mentary and intrusive igneous r!Jcks that 'have 

Mr·. Henderson also prepared· the section on been· severely dynamically m~tamorphosed, 

productio¥ and collabora~ed in the preparation acquiring foliated structure, and younger in- · 

of the section. on ore tre~tment, etc. trusive igneous rocks that have not been dyIn a region. containing so, many mines it namically n1etamorphosed in any great degree. 

would manifestly .have been impossible to ·ac- In a few localities metamorphosed pre-Camcomplish the field work in a satisfactory man- brian igneous rocks of supposed effusive origin 

ner ·and ·within a reasonable time without the have also been found. a 

ready and courteous cooperation of the men The sedimentary beds that flank the preinterested in the mining industry. Their ap- Cambrian areas show great diversity not only 

preciation made delightful a task that might in lithology but in age in different parts of the .. otherwise have been arduous. The following I 

gentlemen rendered especial service: Mr. Percy s Ransome, F. L., The Tertiary orogeny of the North American Cor- · 

dillera and its problems: Problems of American geology, pp. 287~76, 

1 Spurr, J. E., Garrey, G. H., and Ball, S. H., Economic geology of the Yale University Press, 1915. 

Georgetown quadrangle (together with the Empire district); Colorado: a Darton, N. H., Blackwelder, Eliot, and Siebenthal, C. E., U. S. 

U. S. Geol. Survey Prof. Paper 63, 1908. Gaol. Survey Geol. Atlas, Laramie-Sherman folio (No. li3), p. 3, 1910. 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 94 PLATE IX 

A. DISSECTED TERTIARY PENEPLAIN OF THE FRONT RANGE, LOOKING SOUTHWEST 

FROM A POINT NEAR PALMER LAKE, COLO. 

In the d ista nce th e mounta in peaks ri se a bove th e penepl ai n. Photograph by G. B. Ri chardso n. 

B. ANOTHER VIEW OF THE PENEPLAIN SHOWING PIKES PEAK RISING ABOVE IT. 

Ta ke n near th e same locality as Pl ate I X, A, b ut in a more south westerl y di rection. 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 94 PLATE X 

A. EXPOSURE OF CRUMPLED SCHIST OF THE IDAHO SPRINGS FORMATION 

IN VIRGINIA CANYON NEAR SEATON GULCH. 

The I ighter ba nds are inj ecti ons of pegmatite. 

B. INJECTION GNEISS FORMED BY INTIMATE INTRUSION OF QUARTZ-BIOTITE SCHIST OF THE 

IDAHO SPRINGS FORMATION BY GRANITE PEGMATITE. 

Take n from d ump of Golde n Rod tunne l, Si lve r Creek. Natura l s ize. 
INTRODUCTION. 21 

province. Along the east side of the Front date from the uplifts of the Rocky Mountains, 

Range, for example,. the' oldest be~s that rest ~hich probably began in Upper Cretaceous 

upon the pre-Cambrian rocks are in some time and continued into Tertiary time. At 

places Cambrian and in other places Penn- the time of these uplifts the pre-Cambrian 

sylvanian ,or even younger, a diversity that rocks that now constitute the cores of the ranges 

has an. important bearing on the Paleozoic were probably in most parts of the -province 

and early Mesozoic history, as is more fully buried under several thousand feet of Cretaexplained in Chapter IV (pp. 63-65). ceous and probably older strata. · To these 

The geologic evidence indicates in general were added later considerable masses of 

that in early Cretaceous time much of the area volcanic rocks, the effusive equivalents of the 

that is now mountainous lay beneath the sea, monzonitic intrusives that are so numerous in 

and it is. probable that the uplifts which have this province; As the uplift began, stream 

raised the province to its· present elevated erosion immediately commenced the task of 

position took- place in late Cretaceous and eroding this great sedimentary and volcanic 

Tertiary time, so that the Rocky Mountains blanket, and by middle or late Tertiary time 

are, in geologic terms, of comparatively recent it appears to have removed from the mountain 

origin. The cause of the uplift was compres- tracts not only these beds but considerable 

sion along east-west to northeast-sou'thwest thicknesses of the underlying pre-Can1brian 

lines. Its mechanism was bodily uplift, fault- rocks as well. By these· processes large poring, and folding. The greater uplifts and most tions of ·the province were reduced to a gently 

of the folding probably took place at this time, sloping peneplain upon which ~e higher 

butlesserupliftsoccurredsubsequently,anditis mountains stood as unreduced monadnocks. 

possible that some n1ovement is still in progress. (See Pl. IX.) Remnants of this old topography 

In addition to the dynamic processes just are recognizable over wide areas in the southern 

described, volcanism played a not inconsid- Rockies. · 

erable part in the history of -the province. In The next event that had an important 

late Cretaceous or early Tertiary time 1 mon- influence on the physiographic development {jf 

zonitic and other felsic magmas and their the province was a renewal· of uplift in late 

derivatives were intruded in great variety of Tertiary· time. Its effect was to stimulate' the 

size and form as stocks, dikes, and sills through- streams to more active erosion, thus leading, 

out much of the province, and where they to the development of youthful erosion fea..; 

reached the surface effusive rocks were devel- tures on the once mature mountain uplands. 

oped as flows, breccias, and beds of tuff. The valleys were deepened, and steep-walled 

These intrusions took place subsequent to canyons like that between Golden and Idaho 

the main uplifts of the range, and in some Springs were excavated by-the larger streams; 

parts of the province subsequent to the com- The escarpments between the plains and the 

plete removal by erosion of the great thick- mountain tracts were made higher. This 

nesses of sediments that originally covered the uplift was not continuous, however; on the 

uplifted areas. At Cripple Creek, for example,. co~trary, i~ was interrupted by halts during 

·the rocks ass~ciated with the Tertiary surface whiC~. considerable areas of the softer rock~ 

volcanic rocks are pre-Cambrian. Nearly all' flan~ng t~e ranges were· reduced to _gently 

the ore deposits of the province were formed sloping plains. Remnants of these pla1ns are 

soon after these intrusions, presumably by de- preserved in _many parts of the foothills a~ . 

Po ·t· f 1 t" th t h d th d mesas, of whiCh those near Boulder afford a s1 1011 rom so u 1ons a a e same eep- t .k. 1 d h . k . .s r1 1ng examp e. . seate source as t e Igneous roc s. p· ll th 1 f li · h 

Th h · h" h" f h . ma y, as e resu t.o c matiC c anges ·at 

e p yswgrap 1c 1story o t e provmce, t d" t" t · d · Pl · · · · f · h · . wo 1s 1nc · per10 s 111 e~stocene t1me, In so ar as 1t as an Important beanng upon 1 · f th 1 · ·t f d · h. f · b · "d · g aCiers o e a pme ype were orme m 

present geograp 1c eatures, may e sa1 to f th h" h t · B . . some o . e 1g er moun am ranges. y 

1 In the Breckenridge district (see Ransome, F. L., Geology and ore their eroding action they developed steepdeposits of the Breckenridge district, Colo.: U. S. Geol. Survey Prof. 11 d h' h · h hi h 

Paper 75, p.38, 19ll)themonzonitesintrudefossiliferousshalesof Upper wa e ~mp _1t. eaters or·CIT<]!!:~near t e g er 

Cretaceous age. In the vicinity of Boulder (see Fenneman, N. M., SUmmits, and by their deposits they blocked 

Geology or the Boulder district, Colo.: U. S. Geol. Survey Bull. 265, p. d . d t d ll 

39, 1905) dikes nod sills of felsic character intrude rocks as young as the ram age COl)J'Sefj an - C.J:'.~!t . e - 1!1!~~!:2~S . ~rna 

Pierre Cletaceous. lakes. The waters from their melting laid 
• 

22 GEOLOGY OF GILPIN, CLEAR CREEK, AND. BOULDER COUNTIES, COLO. 

down extensive beds 

many of the valleys.· .. 

of sand and gravel in aridity also appear; in the plains tracts a 

_From the disappearance of the glaciers in 

late Pleistocene time to the· present day 

degradation of the mountain tracts has proceeded under the normal influence of stream 

erosion, apparently without the stimulus of further uplift. · 

THE FRONT RANGE. 

With the foregoi.Iig brief review of the salient 

typical arid-:-climate flora prevails. 

LITERATURE. 

. Some of the more important publications 

dealing with the history, geology, mineralogy, 

and mining practice. of the region are listed 

below. Footnote references to others dealing 

with milling and metallurgy will be found in 

the chapter on ore treatment. . 

features of the southern Rocky Mountain msT:>RY. 

province in mind, attention may be narrowed CusHMAN, SAMUEL, and ·wATERMAN, J.P., The gold mines 

to its eastern and most prominent element, the of Gilpin County, Colo., 1876: 

.Front Range,. within which the regions de_. FossETT, FRANK, Colorado, two editions, 1876 and 1879. 

HALL, FRANK, History of the State of Colorado, 4 vols., 

scribed in this report lie. · The Front Range, 1889 to 1895. · 

including as its northern portion: the Laramie HoLLISTER, 0. J., The mines of Colo~ado, 1867. , 

Mountains of Wyoming, extends from the val- RAYM:OND, R. W., Statistics of mines and mining in the. 

ley of North Platte River on the north to States and Territories west of the Rocky Mountains. 

A R' h h Government Printing Office, Washington, D. C. 

the valley of rkansas lVer O:Q. 't e sout ' a Annual publications 1868 to 1875, inclusive. 

distance of over 250 miles, and its width is in RrcKARD, T. A., The development of Colorado1s mining 

general from 30 to 45 miles: . The plateau por- industry: Am. Inst. Min. Eng. Trans., vol. 26, pp. 834 

tions of the range commonly show altitudes of et seq., 1897. 

8,000 tO 9,000 feet; but. above the plateaU rise GEOLOGY AND MINERALOGY. 

isol~ted summits to altitudes of over ·14,000 ALSDORF, P.R., Occurrence, geology, and economic value 

feet. The range is bounded on the east by 'of the pitchblende deposits of Gilpin County, Colo.: 

the Great Plains, which, from an altitude of Econ. Geology, vol.' 11, PP· 266-275, 1916. · · CoLLINS, A. L., Note on the occurrence of carbonic acid 

5,000 or 6,000 feet ~t the f?ot of the range, slope gas in certain veins of Gilpin County, Colo.: 'Colorado 

gently eastward at an average rate of about 10 Sci. Soc. Proc., vol. 6, pp. 120-123, 1897-1900. 

feet to the mile. On the west . the range is· ENDLICH, F. M., Preliminary report on the mining districts 

bounded by the detached areas of sedimentary 1 of .colorado: U. S. Geol. and Geog. Survey Terr. 

rocks in North Middle and South parks. /_ Third Ann. Rep.t., ~P· 280-:293, 1873. . .· . . ' ' . . ·JENNINGS, E. P., A t1tamferous Iron ore depoBlt m Boulder 

The .principal streams drammg the Front County,· Colo.: Am. Inst. Min. Eng. Trans., vol. 44, 

Range are Platte, Arkansas,. and Grand rivers pp. 14-25, 1913. 

and their tributaries. The waters of the Platte LINDGREN, WALDEMAR, Some gold and tungsten deposits 

and Arkansas find their way. to the Gulf of Boulder County, Colo.: Econ. Geology, vol. 2, 

f M · b h f h G d h pp. 453-463, 1907. o exiCo, u t t ose o t e ran enter t e p R · Th · t' f ld 'th h , . Wh · EARCE, !CHARD,· e aSSOCla lOll 0 go WI ot er 

Gulf of Califorrua. ere the larger str~ams metals in the West: Am. Inst. Min. Eng. Tram.1., 

traverse the plateau tracts between the higher vol. 18, p. 447, 1890. · 

portions of the r~ge and the plains on either --Some notes on the occurrence ·of uraninite in: 

side, they are as a rule deeply intrenched in Colorado: Colorado Sci. Soc. Proc., vol. 5, pp. 156 e~ 

canyons that are among the most picturesque seq., 

1894-1896· . . . . . . . . . RICKARD, F:>RBES, Notes on the vem formation and m1mng 

of the moun tam features. Thmr mam feeding of Gilpin County, Colo.: Am. Inst. Min. Eng) 

ground is the higher part of tlie mountains, Trans., vol. 28, pp. 108-126, 1898. (J 

where, especially on the east or leeward side of -- Pitchblende from Quartz Hill, Gilpin County, 

the crest, the precipit.ation is h_eavy; they re- Colo.: Min. and Sci. ~ress, June 7, 1913, pp. 851-8~6. 

ceive smaller though important contributions RICKARD, T. A.,. The vems of Boulder an~ Kalgoorhe:· 

from the plateau tract, and but little from the Am. Inst. Min. Eng~ Trans., vol. 33, PP· 567 et seq.,, 

'd 1 . I d · h h d' 1902

ar~ · . P.ams .. n correspon e~ce Wit t e I- RITTER, E. A., The Evergreen copper deposit, Colo.: 

~IJ?-Ish~g altitu~e and les~enmg degree of pre- Am. Inst. Min. Eng. Trans., vol. 38, pp. 751-765,1907./ 

mpitatiOn the higher portiOns of the range be- UNDERHILL, JAMEs, Areal geology of lower Clear Creek: 

low 'timber line are characterized by a typic~I Colorado Sci. Soc. Proc., vol. 8, pp.103-122, 1905-1907. 

northern .moist-climate flora; in the plateau MINING. 

tract many plants of the same types flourish CoLLINs, G. E., Lessons from Gilpin County practice: 

with less. vigor and plants adapted to semi- Min. and Sci. Press, Sept. 17,_1910, pp. 369 et seq. 
CHAPTER !I.-TOPOGRAPHY AND GEOGRAPHY OF THE CENTRAL CITY 

QUADRANGLE. 

·RELIEF. mountains but increase the difficulties of travel. 

I As pointed out in the preceding chapter and Deposits of glacial till have had a minor influ-

\ well illustrated in Plate IX (p. 20), the pre- ence on the topography. Flats or plains are of 

Cambrian area of the Front Range of the Rocky comparatively rare occurrence and are nowhere 

·Mountains consists of an elevated plateau above of great extent. They have been formed along 

which rise the higher peaks. The plateau some of_ the larger streams by the deposition of 

tract, which is the dissected remnant of a Ter- outwash gravels by streams flowing from the 

tiary peneplain, extends from ,the escarpment glaciers. Such plains are particularly wpll dewest of Golden and Boulder abou~ to the eastern veloped near Empire, near Tolland, and beborder of the Central City quadrangle, its tween Eldora and Nederland. Another type of 

western limit ~eing marked approximately by flats developed at several places in the eastern 

.the upper ends of the steep-walled canyons· part of the quadrangle on upland tracts bealong the larger stream.s. The canyon of Mid- . tween the stream valleys is exemplified by 

dle Boulder Creek begins approximately at the Kings Flat, west of _;Nevaday~lle. Such flats 

power dam 1! miles below Nederland; that of commonly show few outcrops, being covered 

North Clear Creek begins near Blackhawk, and with a mantle of angular fragments of the unthat of Clear Creek a short distance below Idaho derlying rocks. They are areas that have been 

Springs. The major part of the quadrangle long exposed to the disintegrating effects of 

lies therefore within the central and more ele- rock weathering while at the same. time provated portion . of the mountain province, al- tected by their position froin active stream 

though a few remnants of the dissected pene- erosion, so that the mantle of weathering prodplain are recognizable between Rollinsville and ucts could accumulate. Some of them may 

Nederland and in a few other places. The be remnants of the ancient Tertiary ·peneplain. 

lowest point in the quadrangle, about 7,600 The influen~e of the structure and character 

feet in altitude, is in the valley of Clear C:reek of the hard rocks upon the topography has not 

below the mouth.· of Fall River; ·the highest been very marked. With the exception of the 

point is the summit of Parry Peak,' 13,345 feet; Idaho Springs formation most of these rockstho extreme relief is therefore about 5, 700 feet. granite, gra_nite gneiss, porphyries, and pegThe mountain slopes back from the larger matite-offer nearly the same degree of resiststreams are in general only of moderate steep- ance to erosi~n, and t~e streams have sculpness except .where they have been modified by tured them With very httle reference to their· 

glaciation, but along such streams they. are boundaries. Certain facies oif the Idaho Springs . 

co1nn1only steep, though they do not form formation which are very massive or intensely 

canyons except in the plateau tract. The injected by granite or pegmatite offer about 

slopes of the highest mountains,. formerly the same resistance to erosion· as the rocks 

gentle, have been sculptured by the glaciers of named above, but other facies weather more 

Pleistocene time into cirques or glacial. amphi- readily to form gently sloping plains or hills of 

theaters with bare precipitous walls at their rounded, subdued outlines. The area west of 

heads and having U-shaped cross sections in Central City, between Bald Mountain and Chase 

contrast with the V -shaped cross sections of Gulch, including Kings Flat, is an example of 

the purely stream-cut valleys. Such cirques subQ.ued topography in an area of schists of 

are ·particularly nun1erous and well developed the Idaho Springs formation. North of N ederon the east slope of the range, where precipi- land and between Nederland and Rollinsville 

tation was grea~er than on the west slope; they small _isolated masses of granite stand up as 

enhunce the p1cturesque char1n of the high knobs above the gently rolling schist surface. 

23 
24 GEOLOGY OF GILPIN, CLEAR CREEK, AND BOULDE~ COUNTIES, COLO. 

DRAINAGE. show great variations in different parts of the 

That portion of the region east of the Conti- ·region.- Meteorologic observations; though not 

nental Divide is drained by Clear Creek and its available for points within the Central City 

affiuents, including Fall River, and by the quadrangle, are on record for near-by points 

various branches of Boulder Creek. These similarly situated within the plateau or high 

waters finally enter the Gulf of Mexico by way mountain tracts. The mean annual temperaof Platte, Missouri, ·and Mississippi rivers. ture at a point near Longs Peak, at an eleva-~ 

The portion west of the divide is drained· by tion of 8,700 feet, is 38° F., the average rangtributaries of Fraser River, whose waters enter ing from 22.5° in February to 55° in August. 

the Gulf of California by way of Grand and At Sugar Loaf, in the plateau tract just north 

Colorado rivers. Most of the streams have of the quadrangle, the mean annual temperahigh gradients, which in the portions of the ture is A3 o. 

valleys free from glacial deposits are as a rule The mean annual precipitation for the quadp.ot l~ss than 100 feet to the mile and are locally rangle as a whole, according to the best· availas great as 600 feet to the mile. Glaciation able data, appears to be about 50 inches. 

has produced no~able drainage modifications. This is about equal to the mean annual preAs a result of glacial erosion in the cirques of cipitation of the plateau portions of the South 

the high mountains the headward portions of Atlantic States from Virginia to Georgia. In 

many streams, instead of having a somewhat the Rockies, however, the rain and snow com:e · 

uniform gradient descend in steplike fashion, for the most part not in storms of long duratheir course beinginterrupted by small lakes, tion but in short showers or flurries, many of 

· some of. which lie in rock basins while others which are severe while they last. During the 

are retained behind dams of glacial till. AI~ summer, particularly in July and August, there 

though tlie glacial features of the west side of are showers almost every aftern~on, and occathe range have not been systematically studied sional ones of unusual size may produce 

it is evident from the topo-graphic map that destructive freshets, towns like Blackhawk; 

glaciation has been much less severe and situated in narrow valleys,· being especially 

probably less extensive on the west side of the susceptible to damage from this source. In 

ran:ge than on the eas•t. The influence of the lower valleys of the region the mean annual 

'glaciation on the drainage may be appreciated precipitation is very much below the aboveby comparing the eyen gradient of many o':f mentioned average, being about 20' inches. \

1

: 

the valleys·w~st of the divide with the irregu- On. the higher slopes east of the crest of the 

larities of the lake-dotted valleys just east of rang~, on the other hand, the precipitation is 

the divide. The d~position ·of glacial gravels considerably greater than 50 inches. 

to form' the outwash plains mentione.d in the Th~ growing season, even in the lower porprecedin~ section has had the effect of lowering tions of the region, is short, extending generally 

. the stream gradients somewhat in these por- from the first of June to the middle of Septem-

. tions of their courses. her.· The first snow commonly falls in SepAs a rule only those valleys which head in tember, but seldom remains on the ground 

the high mountains carry permanent streams, long, and from that time until Christmas there 

and even these are subject to great fluctua- may be little or no further snowfall; the retions in volume. The absence of permanent mainder ·of the winter is commonly rigorous. 

streams in the valleys of the plateau tract has The air is dry throughout the region, and 

been a serious handicap in mining and milling. the prevailing winds are from the west. 

A number of small artificial lakes (see Pl. II VEGETATION. 

in pocket) in the eastern part of the regio~ have been create4 by the construction of dams Most of the Central City quadrangle lies 

to serve as ice ponds or to insure a supply of within the area of the Pike and Arapaho nadrinking wa~er ~or stock. · tiona! forests. When first settled most of the 

CLIMATE. quadrangle below timber line (11,500 to 12,000 

feet) was heavily forested, but lumbering for 

In consequence of the very considerable fuel and for mine timber has resulted in a pracrange in elevation, the climatic conditions tical destruction of the forests near the larger 
TOPOGRAPHY AND GEOGRAPHY OF CENTRAL CITY QUADRANGLE. 25 

camps, and forest fires have destroyed them in 

other a.reas. Near Central City the destruction of timber hflts been so. complete that old 

stumps and roots are dynamited for firewood. 

A detailed discussion of the flora would manifestly be out of place in a report of this character, but a few of the more striking silvic 

features may be mentioned. In the lower 

portions of the quadrangle, commonly below 

9,000 feet, the yellow pine (Pinus ponderosa) is 

common, associated with patches of Douglas 

spruce (Pseudotsuga mucronata). A~ higher 

altitudes the yellow pine is replaced by the 

lodgepole pine (Pinus murrayana), which is 

adapted to moister and cooler· conditions and 

is in general most abundant between 9,000 and 

10,000 feet. The lodgepole pine is commonly 

intermixed with Engelmann spruce (Picea engelmanni), and in particularly moist localities, 

as alop.g the stream courses, on ·the margins of 

swampy parks, at the headwaters of streams, 

and just below timber line, where there is much 

seepage, the latter becomes the predominant 

forest tree. With the Engelmann spruce may 

occur alpine firs (Abies lasiocarpa) and occasionally the beautiful silver spruce (Picea ·parryana). At the timber line, on account of the 

high winds and other climatic rigors, the Engelmann spruce becomes· dwarfed to a shrub and 

is accompanied ·by herbaceous. plants of arctic 

affinities. 

Between elevations of about 8,000 and 9,500 

feet, where the coniferous trees have been destroyed either by forest fires ·or by lumbering 

operations, angiosperm forests, predominantly 

of aspen (Populus tremuloides), have developed 

and after the first frosts many of the mountain 

slopes are ablaze with t4e golden tints of their 

leaves. ·In swampy places and along streams 

alders are common, and the larger grav~l flats 

or "parks'' along certain streams are occupied 

by an association of alders, Gambel oak, and 

several species of willow, together with grasses, 

sedges, etc. 

INHABITANTS AND INDUSTRIES. 

Nearly the entire population of the region 

is dependent in one way or another upon the 

mining industry. The railroads, with the exception of the Denver & Salt Lake, were built 

prin1arily to serve that industry. The few 

small ranches in the eastern part of the region 

are devoted largely to the raising of hay and 

garden truck to supply the neighboring. mining 

towns. The sma:ll alluvial . flats along the 

streams afford. proper soil for farming, but 

only hardy crop~. t_hat mature q~ickly thrive 

in this rigorous climate, where killing frosts 

sometimes occur in the valleys as late as June 

and as e~rly as ~eptember. During the summer season a few sheep herders from the plains 

pasture their flocks near timber line. Idaho 

Springs, rolland, Nederland, and Eldora attract a few summer visitors, and the railroad 

journey from Denver. to Corona, at the crest of 

the range, is a favored trip for tourists. 

Central City, the county seat of Gilpin 

County, with_a population in 1910 of 1,782, is 

the center of the oldest and richest mining 

district of the regi_on. Idaho Springs had ~ 

population in 1910 ·of 2,154 and is a distributing point for· the mines near Ffuf River and 1 

Chicago Creek, as well as for mines in its im~ \ 

m~diate vi?inity. Its acc~ssible. loc~tion,_ 37l 

miles by rail from Denver, 1ts n~tural beauties, 

and its soda springs make it popular also as a 

summer re~ort. The other t~'Yll~ of the region 

are. small mining camps,. many of which, like 

Caribou and Apex, were fornierly much rpore 

populous than at present. . 

Both ~entral City and Id~ho.Springs a~e ~t\\\\"l)f}-l.r served by a narrow-gage branch of the Colorado & Southern Railway that from Denver 

and Golden ascends the canyon of Clear Cr~~k 

to "The Forks," from which one branch turns 

up the valley of North Clear Creek to Blackhawk and Central City (40 niiles from Denver) 

and the other branch follows Clear Creek to 

Idaho Springs and thence to. Georgetown and ' 

Mount . McClellan. Eldora, in the no~thern 

part of the region, is the terll:iinus or' the Denver, Boulder & Western Railroad, also .a 

narrow-gage line, and is 36 miles distant by 

rail from Boulder. Nederland is <?Onnected by 

stage line with Boulder. The Denver & Salt 

Lake Railroad, which. crosses the north-central 

part of the region, is a standard-gage line extending from Denver to Steamboat Springs, in 

Middle Park. It crosses the Continental Divide 

at Corona at an elevation of 11,680 feet. 

Corona js 65 miles by rail from Denver and 

Rollinsville is 42 miles. 

:ractically all the min~s are served by moun- \ t~ c, (\~ 

tam wagon roads that are on the wHole good in 

spite of the vicissitudes of washouts. None are ' 

obliged to depend oil pack-train transportation. 
CHAPTER IlL-DESCRIPTIVE GEOLOGY. 

STRATIGRAPHY. 

PRE-CAMBRIAN METAMORPHOSED SEDIMENTARY ROCKS. 

The only pre-Cambrian rocks that can with 

assurance be classed as metamorphosed sediments are those of the Idaho Springs formation. 

AU other pre-Cambrian rocks of the quadrangle are unquestionably of igneous origin. 

IDAHO SPRINGS FORMATION .. 

NAME. 

The Idaho Springs· formation was first 

defined by Ball,t who named it from the town 

of Idaho Springs, near which characteristic 

exposuras are abundant. 

DISTRIBUTI,ON. 

The formation· underlies large areas in the 

western and northeastern parts of the Georgetown quadrangle and fully one-half of the 

geologically mapped portion of the Central 

City quadrangle. ~tis known also to be widely 

distributed to the· east, in the Blackhawk 

quadrangle. As its commoner rock types are 

somewhat less resistant to erosion 'than most 

other rocks of the region, it forms few high 

peaks or rip.ges, and for this reason it is a fair 

inference that the formation is not so .wide-

. spread in the high western unmapped portion 

of the region as in the eastern portion. 

Over certain areas, as, for example, between 

N evadaville and Mount Pisgah, the formation 

is fairly free from intrusive igneous rocks, but 

in most localities igneous rocks are associated 

with it in great abundance and in an exceedingly intimate and irregular fashion. 

Some idea of this intimate association may 

be obtained from the large-scale geqlogic. maps 

(Pis. III and VI, in pocket), but even on these 

the boundary line drawn between the Idaho 

Springs formation and granite pegmatite. or 

granite gneiss indicates in many places a somewhat arbitrary separation of an area occupied 

mainly by the Idaho Springs fo'rmation from 

another area occupied mainly by igneous rock. 

On _the small-scale geologic map (Pl. I, in 

1 Ball, S. H., General geology [of the Georgetown quadrangle): U. S. 

Cleo!. Survey Prof. Paper 63, p. 37, 1908. · 

26 

pocket) no attempt is made to subdivide the 

formation int'o its different rock types, but on 

Plates III arid VI the more unusual hornblendic and lime-silicate phases are differentiated b.y separate colors from the commoner 

phases. 

LITHOLOGY AND STRUCTURE. 

General features.-The predominant rocks of 

the Idaho Springs formation are light to dark 

gray quartz-biotite schists, in places carrying 

some hornblende or muscovite. With these 

are associated lesser amounts . of biotitesillimanite schist, quartzitic gneiss, dark-green 

hornblende schist and gneiss, and lime-silicate 

rocks that represent metamorpho3ed limestones. In a few places the formation includes 

rocks that are supposed to be metamorphosed 

conglomerates. These diverse phases are interbanded, · show transitional varieties, and are 

clearly integral parts of one fo~mation." 

The less common facies occur mostly in lensshaped masses, such as the areas of limesilicate rocks near Central City (see Pl. III), 

and not in continuous bands that might serve 

as indicators of structure. Throughout· most 

of the formation bedding planes have been 

entirely obliterated by the development of 

schistose structure, the biotite and biotitesillimanite schists in particular being highly 

foliated. On the other hand, certain bands of 

quartzitic schist that in places persist with 

fairly uniform width for several hundred feet ' 

are interpreted to represent beds, originally 

more sandy than their"' neighbors, that have 

preserved their integrity because the constituents required for the development of platy 

minerals during metamorphism were scarce. 

The general strike o£ the foliation is, in some 

parts of the region, fairly uniform ·over a 

number of square miles, but in most places 

the schists have been so disturbed by numerous 

igneous intrusions that all conceivable inclinations can be observed within a single square 

mile, and 'faulting has produced added irregularities. The foliation exhibits no broad parallelism with the axis of the range. 

The character and distribution of the prin:.. 

cipal rock types will be briefly described. It 
PRE-CAMBRIAN METAMORPHOSED SEDIMENTARY ROCKS. 27 

should be understood, however, that most of This rock is a fine-grained schist which has a 

these types pass into one another by gradations. "pepper and salt" appearance as a result of its 

Quartz-biotite schist.-The commoner facies evenness of grain and the strong color conof the formation as developed in this region trast between its quartz and biotite. The 

may be included under the term quartz-biotite principal minerals, named in the order of 

schist. These rocks range from light gray to abundance, ·are brown biotite, plagioclase, 

very dark gray in color, depending on the and quartz. Orthoclase, muscovite, apatite, 

abundance of biotite, and may be either ~agnetite, and well-rounded zircons occur in 

coarse or fine grained. In the coarse phases minor amounts. 

mica plates may be 3 to 6 millimeters in diame- A somewhat UI?-Usual variety from the 

ter and quartz and feldspar may form aggre- southwest slope of Cone Mountain shows 

gates of comparable size; in the finer phases grains of magnetite surrounded by small halos 

the average size of grain is 1 millimeter or less, of quartz and feldspar unmixed with biotite. 

and the cont:r;ast between light and dark con- These halos, which are pink, contrast strongly 

stituents gives the rock a "pepper and salt" with the gray surrounding areas, which are rich 

appearance. Schistosity is commonly better in biotite and give the rock a peculiar spotted 

developed in the coarse than in the fine varie- appearance. Similar rocks were noted by Ball 

ties, and in the former crumpling such as is in the Georgetown quadrangle. 

shown in Plate X, .A (p. 21), is common. Biotite-sillimanite schist.-According to Ball 1 

The principal minerals are quartz, biotite, the greater part of the rock of the Idaho 

muscovite, and feldspar. Microcline is the Springs formation ·as exposed in_ the Georgemost common feldspar, but plagioclase (usually town quadrangle contains sillimanite, a silicate. 

oligoclase) is very abundant in some speci- of alumina. In the Central City quadrangle 

mons, and microperthite is locally present. sillimanite-bearing schists are not abundant 

The proportion between biotite and muscovite except in the vicinity of Empire. They do 

is extremely variable, but biotite usually pre- not differ greatly in ,general appearance from 

dominates, and muscovite may be entirely ab- the quartz-biotite . schists already described 

sent. Minerals usually present in subordinate and except for the presence of sillimanite have 

amounts are apatite, magnetite, and zircon. a similar mineral composition. Ball says: 

As a rule the magnetite shows irregular out- The white or ~ee~ish-white sillimanite occurs in singl~ 

lines and the zircons are somewhat rounded. rods and bundles of rods, elongated in the plane of schisIn some places, especially near pegmatite intru- . tosity, which are cut by transverse fractures whose intersions the rock contains one or more of the stices are filled by biotite flakes and magnetite or pyrite 

· ' 1 t t li h bl d grains. In places the component rods of the aggregates m1nera s garne ' ourma ne,_ orn en e, co- cross one another, forming confused meshes. 

rundum, rutile, and andalus1te. Some hornblendic facies carry a little titanite. The elongation: of the sillimanite crystals· 

,parallel to the biotite plates is an important 

element in the .development of the schistose 

structure .. 

The foliation is due mainly to the subparallel orientation of biotite o;r muscovite 

plates and is therefore inost highly developed 

in the more micaceous varieties. Quartz gneiss.-Higbly quartzose facies of 

the formation that are believed to be metaAnalysis of quartz-biotite schist obtained near Penn mill, morphosed sandstones underlie considerable 

just below Blackhawk. areas on Sugarloaf Mountain, in the George-

[George Steiger, analyst.) town quadrangle, but no large amounts of such 

Si02 ................. 64. 23, Ti02 .... ·...... .... .. • o. 80 rocks are noted in the Central City quadrangle. 

Al20a ................ 16.45 Zr02 ................. None. A small body of rock on the southwest .slope of 

Fe:.~Os ............... · 2. 40 C02. · · · · · · · · ·······None. Cone Mountain, consisting mainly of quartz 

FeO .. · · · · · · · · · · · · ·: 4

· 

31· P20 5 • • • • • • • • • •• •• • • • • •

10 with some biotite· and very little feldspar, may l\1g0........... .. . . . . 1. 68 S................... . 03 

CaO ................ : 3.1] MnO............... . 08 be a metamorphosed argillaceous sandstone or 

. ~:o~ ~: ~ ·_ ·.·.· _- ~ ~: : : : : : lt,~O- .......... ~ .. . 

H20+ ............. . 

3. 75 BaO................. . 02 an unusually quartzose phase of the granite · 2. 14 SrO ............... Trace. gneiss. . 02 

. 89 100.01 1 Ball, S. H., op. cit., p. 38. 
28 GEOLOGY OF !}ILPIN, CLEAR. CR.EEK, AND BOULDER. COUNTIES, COLO. 

Ball 1 describes the quartz gneiss of the degree of· segregation -of felsic and mafic minGeorgetown quadrangle as follows: erals into separate bands. The schistose strucThe· quartz gneiss is a well-banded rock ·formed of fine 

to broad lam.inre, varying in color from gray to brown, red, 

or black. The texture is as a rule dense_ and vitreous, 

altho1,1gh in places it is saccharoidal. Lit-par-lit pegmatitic injections are rare, as is natural in a rock with imperfect gneissic banding. Under the microscope quartz is 

shown to be the essential constituent. The accessory minerals include all the minerals present in biotite-sillimanite 

schist, with the addition of shreds of green hornblende. 

The gneissic parting is due to the elongation of intricately 

interlocking quartz lenses, to the variation in granularity 

of the quartz of adjacent bands, and to "the linear ::i.rrange:. 

ment of discontinuous sheets of biotite blades and magnetite cubes. The darker color of certain bands of the gneiss 

is due to an unusual abundance of this biotite and magnetit~. 

ture is due almost entirely to subparallel elongation of the hornblende crystals. The average size of grain ranges from less than 1 millimeter to about 3 millimeters, but individual 

hornblende crystals may reach a length of 5 

millimeters. The principal mineral constituents, named· in the order of abundance, are 

green hornblende, quartz, and plagioclase feldspar. Minor constituents usually present are 

titanite, magnetite, arid zircon; the grains of 

zircon are· commonly well rounded. Minerals 

present in some places are augite, apatite, and 

garnet. · The plagioclase in the specimens studied microscopically ranges from oligoclase to 

Hornblende schist and gneiss.-The presence andesine in composition. Varieties with abunof hornblende in small amounts in some of the dant garnet were noted along the valley of 

quartz-biotite schists has already been men- North Clear Creek about half a mile northtioned. In ·other schists and gneisses horn- northwest of the summit of Maryland Mounblende is the predominant mafic· mineral.2 tain. The garnet is in skeleton crystals inSuch rocks commonly form small bands or closing small crystals of quartz, magnetite, and 

lenses along the contact between areas of hornblende. 

quartz-biotite schist and ·areas of granite gneiss, The hornblende schists and gneisses contrast 

. granite, or granite pegmatite, or occur wholly strongly with the quartz-biotite schists with 

within the igneous rock near such contacts. which they are associated in showing little evi_. 

This characteristic association is shown on deuce of mechanical deformation subsequent 

Plates III and VI (in pocket), on which the to their crystallization. This characteristic is 

hornblendic phases of the formation are indi- in harmony with the view already expressed 

cated by a separate symbol. . . that they have been formed from the commoner 

Near Central City, as is also well shown on rock types of the Idaho Springs formation by 

Plate III, some of the lenses of hornblende contact-metamorphi,c processes. 

schist inclosed by granite gneiss lie not far Lime-silicate rocks.-Vnder the term limefrom lenses and irregular masses of lime-silicate silicate rocks are included rocks usually massive 

rocks, and both types bear similar relations to but in places gneissic, composed of quartz, epi-

.the more common phases of the Idaho Springs dote, and garnet with locally some pyroxene, formation and to the ·granitic igneous rocks. 

The trend and degree of foliation in the horn- zoisite, hornblende, titanite, magnetite, pyrite, 

blende schists is similar to that in neighboring or calcite. Some varieties are very coarse 

areas of quartz-biotite schist. The close and grained; Ball 3 mentions crystals 6 inches in 

invariable association of the hornblende schists diameter. 

and gneisses with the quartz-biotite schist of The texture is generally very irregular, rethe Idaho Springs formation on the one hand sembling that of certain pegmatites, the various 

and with the granite gneiss and granite pegma- minerals penetrating one another irregularly 

tite on the other hand is believed to indicate and having apparently crystallized simultathat they are parts of the Idaho Springs forma- neously. The general color effect of the rocks 

tion that have been metamorphosed by the ranges from brown to green or gray, depending 

granitic intrusions., on the proportions of the component minerals. 

The texture of the hornblendic rocks ranges Lime-silicate rocks are not abundant in the 

from schistose to gneissic, depending on the Central City quadrangle and are mainly con1 Ball, s. H., op. cit., p. 41. · · , fined to a few sm~ll areas just west and north2 Mafic is .a term suggested to replace the objectionable term basic as west of Central Cl ty. As shown on Pia te III 

applied to rocks. (See Cross, Whitman, Iddings, J.P., Pirsson, L. V., 

and Washington, H. S., Jour. Geology, vol. 20, p. 561, 1912.) a Ball, S. H., op. cit., p. 42. 

I 
PRE-CAMBRIAN METAMORPHOSED SEDIMEN.TARY ROCKS. 29 

(in pocket), these areas are irregularly lenslike 

in form and are inclosed by granite gneiss. 

Near them, also inclosed by the granite gneiss, 

are lenses of hornblende schist and gneiss and 

some of quartz-biotite schist. 

In texture and mineral composition these 

rocks are similar to certain rocks in other districts known to have been formed by the metamorphic action of intrusive igneous . rocks on 

limestones. Their distribution within an igneous rock near its contact with the Idaho 

Springs formation and the close proximity and 

general similarity in form of the areas of limesilicate rocks to areas of recognizable schist 

belonging to the Idaho Springs formation inclosed in the granite gneiss point also to a contact-metamorphic origin in this district. The 

lime-silicate rocks are therefore believed to 

represent calcareous sed~en ts . of the Idaho 

Springs formation that have been con1pletely 

recrystallized and changed in mineral composition through the influence of granitic rocks 

that intrude them. Near_ Central City the 

intrusive rock was granite gneiss; in other localities it was granite pegmatite. Dynamic 

metamorphisn1 may have played some small 

part in their formation, but their massive and 

locally coarse-grained character shows that it 

was not the principal process concerned·. 

Supposed metamorphosed conglomerates.-At 

a few places in the Georgetown qu·adrangle, 

notably on Chief and Pendleton mountains, 

certain of the schists of the Idaho Springs 

formation contain lenticular or ellipsoidal 

bodies from half an inch to 4 inches long that 

resen1ble pebbles flattened in the plane of the 

schistosity. These rocks have been described 

and figured by Ball 1 and are regarded by him 

as dynrun~cally metamorphosed conglomerates. 

Rocks of this character were not found in the 

Central City quadrangle. 

Injection gneiss.~As discussed at more 

length on pages 34-35, the Idaho Springs formation was invaded by granitic material during at 

least two periods in pre-Cambrian time. The 

larger bodies of these intrusive rocks are characterized by fairly uniform texture and composition and are shown on Plate I (in pocket) 

as areas of granite gneiss and granite. Most 

of the smaller granitic masses and a few of 

considerable size (which commonly inclose 

1 Ball, S. H., op. cit., pp. 41, 177; pis. 7 and 8, A. I 

many patches of schist) are of coarser and 

more irregular texture and are. classed as pegmatite. Some of the pegmatite came from the , 

same deep source as the granite gneiss and some · 

from the later granitic intrusions. 

All these granitic rocks but in particul~r the 

pegmatites in many places intrude the schists 

of .the Idaho Springs formation in a very intimate and irregular manner. Most of the 

small intrusions have the form of long, narrow 

lenses or pinching and swelling dikes lying par_ 

allel to the foliation of the. schists or cutting 

the foliation at low angles, and in many places 

the injection of granitic material is so intimate 

that the rock becomes an injection gneiss such 

as is illustrated in Plate X, B (p. 21). Such 

injection is more common and more intimate 

in the highly micaceous schists than in those 

which are highly quartzose, but there is hardly 

any area of the Idaho, Springs formation an 

acre in extent that does not contain some injection gneiss. The manifest impracticability 

of showing the smaller details of distribution of 

schist and pegmatite necessitates much generalization in the geologic mapping. Even on the 

large-scale maps the boundaries between the 

Idaho Springs formation and granite pegmatite are arbitrarily drawn where predominance 

of one gives· way to predominance of the other. 

ORIGIN. 

The Idaho Springs formation is believed ta 

have been formed by the general dynamic 

metamorphism and local igneous metamorphism of a thick series of sedimentary rocks. 

Its original sedimentary character is inferred 

from the highly aluminous composition of 

many of its rocks, the lo.cal appearance of 

structures. resembling bedding, the presence in 

minor amounts of highly quartzose facies and 

of others that appear · to be deformed conglomerates, and finally the occurrence of 

massive.lime-silicate rocks of a type characteristically formed through the metamorphism 

of limestone. Opposed to the supposition of 

an igneous origin for any part of the formation 

is the fact that no facies of the formation have 

anywhere been observed transecting other 

facies. · The single analysis made thrpws no 

light upon its origin. 

According to this interpretation the biotite 

ru1d biotite-sillimanite· schists and hornblende 

gneisses were originally shales and arkoses the i ' . 
30 GEOLOGY OF GILPIN, CLEAR CREEK, AND .BOULDER COUNTIES, COLO. 

quartzitic gneiss was originally an impure sandstone, and the lime-silicate rocks were originally 

limestones .. 

AGE. 

DISTRIBUTION AND GENERAL STRUCTURE. 

As shown on the geologic rna p (Pl. I, . in 

pocket), granite gneiss is comparatively rare 

in the northern part of the area mapped but 

underlies nearly half of the central and southThe Idaho Springs formation forms an inti- ern parts. The areas of granite gneiss, th<;mgh 

mate part of, the complex of crystalline rocks of .irregular outl~ne, are commonly elongate in 

which at certain points on the flanks of the a northeasterly direction p·arallel to the prerange is overlain unconformably by sediments dominant trend of the inclosing schists of the 

carrying Upper Cambrian fossils. 1 The un- Idaho Springs form.ation. Some of the areas 

metamorphosed character of·. the Cambrian are 4 to 5 miles long and 2 to 3 miles across, 

rocks as compar_ed with the. highly n1etamor- but most of these large masses inclose small 

phosed character of the Idaho Springs forma- areas of the Idaho Springs formation. · Ex-· 

tion indicates that the latter is very much cellent exposures of the granite gneiss are 

older; its age may therefore be placed as cer- numerous on the surface and in the mines near 

tainly pre-Cambrian. Among the. pre-Cam- Central City and along the lower course of' 

brian rocks of the quadrangle it is the oldest, Fall River. E:x;posures -in many parts of the 

being intruded by all the others, which, as region show that the granite gneiss intrudes 

already stated,. are without exception,of igneous the rocks of the Idaho Springs formation. At 

origin. It is therefore the basement formation one ·place on the road in the upper part of' 

and probably origi~ally underlaid all the region Virginia Canyon the . granite gneiss incloses. 

covered by this report. Adequate information fragments of schist of the Idaho Springs fornlais not at hand for correlating its rocks with any tion. In the valley· of Fall River about 1! 

rocks froni parts of the Front Range outside of miles above its mouth the transition from an 

the Georgetown and Centr~l City quadrangles. area of granite gneiss to an area of the Idaho 

Its highly .metal!lorphosed character indicates Springs formation takes place gradually in a. 

that it is much older tl1an the slightly meta- distance of 200 to 300 feet. In passing from 

morphosed pre-Cambrian quartzites of certain the schist toward the gneiss a gradual increase. 

parts of the r~nge, which have been provi- is first noted in the amount of pegmatite that. 

sionally classed by Van !lise 2 and others as injects the schist, then a few bands of granite 

Algonkian. ' . gneiss appear in the pegmatized schist, and . . PRE-CAMBRIAN IGNEOUS ROCKS. 

. Igneous rocks of pre-Cambrian age underlie 

nearly half of the area surveyed and include 

granite gneiss, granite, granite pegmatite, and 

hornblendite. 

GRANITE GNEISS. 

DEFINITION. 

The granite. gneisses of this district have 

acquired a gneissic structure through dynamic 

nietamorphisni. As in the massive granites, 

their essential minerals are quartz, alkali feldspar, and either muscovite or biotite. - Similar 

rocks in the Georgetown quadrangle have been 

described by Ball 8 under the nanie gneissoid 

granito. 

1 Cross, Whitman, U. S. Geol. Survey Geol. Atlas, Pikes Peak folio 

(No.7), 1891. · 

1 Van Rise, C. R., and Leith, C. K., Pre-Cambrian geology of North 

America: U.S; Geol. Survey Bull. 360, p. 827, 1909. 

a Ball, S. H., op. cit., p. 49. 

finally both schist and. pegmatite decrease in 

abundance, eventually leaving . only granite· 

gn~lSS. 

The relations of the granite gneiss to thegranite peginatlte are twofold. Pegnlatitictransition zones, such as that described in the· 

last paragraph, at the borders of areas of 

granite gneiss indicate that some of the granite· 

pegmatite is merely a phase of the granite 

gneiss intrusion. At many other localities 

the granite gneiss was observed to becmne· 

pegmatitic near schist contacts; thus on thesouth wall of the. valley of Middla Boulder· 

Creek about lt miles east of Eldora the schists. 

of the Idaho Springs forn1ation, which are 

here in part hornblendio, are intruded by 

granite gneiss. The contact between the two· 

is in most places parallel to the schist foliation, 

but in places transgresses it at a small angle. 

The granite gneiss is commonly pegmatitic 

next· to the schist and in places sends off peg-· 
PR.E-CAMBR.IAN IGNEOUS ROCKS. 31 

matitic apophyses that' cut bluntly across the their abundance, are whit~ or pink feldspar, 

schist folia. In some localities irregular bodies quartz, and biotite. Ap. unusually dark phase 

of granite pegmatite occur wholly within ~reas of mottled appearance seen about 1! miles 

of granite gneiss, the two ro'cks grading into southwest' of Dumont is about one-half biotite 

each other. In contrast to these relations, but is interbanded with the more common vawhich indicate contmnporaneity, other pegma- rieties. In some varieties muscovite is also 

tites sharply cut the granite gneiss and are abundant, and rarely it is present to ·the practherefore of later origin. Near ·the head of tical exclusion of biotite, as in the Lucania 

Virginia Canyon both the granite gneiss and . tunnel from about 4,450 to 6,200 feet from the 

tho Idaho Springs formation are sharply cut portal. Microscopic study reveals the presence 

by pegmatite dikes, son1o of which parallel tho in most specimens of magnetite in .. small irregfoliation while others transgress it. Similar ular grains and of zircon and apatite. Garnet is 

relations were noted half a mile north-north- present locally but is generally not conspicuous. 

west of the summit of Maryland Mountain. The texture is allotriomorphic granular. The 

'VVhero the granite gneiss and the Idaho Springs feldspars include orthoctase, microcline, and 

formation are adjacent tho foliation ,of the two oligoclase. Ball 1 has shown that a part of the 

is usually about parallel. miorocline replaces other feldspars and quartz 

LITHOLOGY. 

The granite gneiss shows much diversity in 

different parts of the region and even within a 

single outcrop. The color on fresh surfaces 

varies from light gray through pale pink to dark 

gray; weathered surfaces may be deeper pink 

oi· buff from oxidation of the mafic (basic) 

minerals. The average size of grain ranges 

from 1 millimeter or even less to 4 or 5 millimeters. Gneissic structure i;3 commonly well 

developed but in some places ,is lacking; massive facies are separable from the later granites 

only where actual gradation into typical granite 

gneiss can be traced. In th~ region southwest 

· and northeast of Dumont, for example, much 

of the rock mapped as granite gnei~s is a finegrained massive granite, but in a few localities 

it shows well-defined· foliation striking about 

N. 20° E. The breadth and conspicuousness 

of the folia commonly increases with the coarseness of grain. As shown later, the gneissic 

structure is due 'mainly to the segregation of 

biotite along certain discontinuous bands and 

of quartz and feldspar along others. The folia 

are nowhere crenulated. Pegmatitic facies are 

present here and there as bands parallel to the 

foliation and of fairly even width within the 

main body of the gneiss or ·in less regular relations near the contact between the granite 

gneiss and the Idaho Sprmgs formation. In 

general pegmatite is much ·less abundantly 

associated with the granite gneiss than with the 

schists of the Idaho Springs formation. 

The constituents of the granite gneiss visible 

to the unaided eye, named in the usual order of 

and was therefore formed somewhat later than 

the general recrystallization of the rock. Micrographic intergrowths of one or more of the 

feldspar varieties with quartz are ·common. 

Weathered phases show the secondary minerals 

usual in altered granitic rocks, which require 

no special mention. · 

The gneissic structure has evidently been 

developed by' complete' recrystallization under 

high pressure. During this process the mica 

plates assumed subparallel orientation at right 

angles to the direction of compression, and in 

some varieties of the gneiss were more or less 

segregated in discontinuous bands separated 

by bands wholly free from mica. Many of the 

quartz grains also became more or less elongate 

in the same direction. 

ORIGIN. 

The granite gneiss is believed to be a granitic 

intrusive rock that has received a foliated 

structure as a result of dynamic metamorphism 

subsequent to its intrusion. Its intrusive cha.racter is attested (1) by apophyses from the 

gneiss masses that penetrate the rocks of the 

Idaho Springs formation, transgressing their 

foliation, (2) by angular schist fragments inclosed in the granite gneiss, and (3) by contactmetamorphic effects produced in rocks of the 

Idaho Springs formation inclosed by or bordering on masses of granite gneiss. 

Subsequent to their intrusion, perhaps long 

afterward, the rocks were subjected to dynamic metamorphism that in some places produced partial recrystallization, with tho devol1 Ball, S. H., op. cit., p. 50. 
32 GEOLOGY OF GILPIN, CLEAR. CREEK, AND BOULDER. COUNTIES, COLO. 

opment of foliated structure. The fact that 

the mechani~m- of this change was recrystallization rather than fracturing and granulation 

indicates that the metamorphism took place 

-under high pressure, presumably while the 

rocks were deeply buried. 

Long after the recrystallization, when the 

rocks were no .longer deeply buried, the granite 

gneiss was locally fractured and granulated. 

Attention has been directed to the variable 

character of the granite gneiss, but these ·variations are qf an order common in granitic intrusive rocks and are readily attributable to 

magmatic differentiation or to varying amounts 

of recrystallization during dynamic metamorphism; they are not at all comparable with 

. the much greater variations characteristic of 

the Idaho Springs formation. 

AGE. 

The granite gneiss is a part of the pre-Cambrian axis of the Front Range. Its structural 

relations and its degree of metamorphism 

indicate that it is intermediate in age between 

the oldest and the youngest of the pre-Cambrian rocks. It is distinctly younger than the 

oldest pre-Cambrian formation, the Idaho 

Springs, which it .intrudes. Moreover, the 

Idaho· Springs formation was evid~ntly schistose prior to the intrusion of the granite gneiss 

magma, and the magma in many places followed this schistosity as the direction of 

easiest access. At least one considerable period 

of dynamic metamorphism therefore intervened between the deposition of the sediments 

of the Idaho Springs formation and the intrusion of the granite gneiss magma. On the 

other. hand, the granite gneiss is itself intruded 

by granite pegmatite and massive granite of 

later pre-Cambrian age._ 

QUARTZ DIORITE AND ASSOCIATED 

HORNBLENDITE. 

.DEFINITION.~ 

The next group to be described consists of 

massive to slightly gneissic coarse-grained 

rocks varying from quartz diorites to hornblendites in mineral compositiqn. Similar 

rocks occurring in the Ge.orgetown quadrangle 

were described by Ball,! They intrude the 

granite gneiss and the rocks of th~ Idaho 

Springs formation. · 

1 Ball, S. H., op. cit., pp. 54-5i. 

DISTRmUTION. 

These rocks 'occur principally in the central 

and southern parts of the area surveyed. The 

largest body extends from a point.ll miles east 

of Yankee northeastward to ~1on~an.a Mountain 

and Pine-Creek, and its width for most ·of this 

distance is nearly half a mile. Most ·of the 

other bodies form broad dikes whose trend is 

northeast, parallel to the prevailing trend of the 

foliation in the inclosing schists and gneisses. 

The longest of these dikes extends northeastward 

from the summit of Mount Pisgah for about 2! 

miles, with outliers on both the southwest and 

th~ northeast. In t_he northern part' of the 

area surveyed quartz diorite has been observed 

only in two small patches north of Nederland. 

(See Pl. I, in pocket.) . 

CHARACTER. 

·The commonest rock type belonging to this 

group is a true quartz diorite, a wholly:crystalline rock of medium grain (most of the mineral 

grains being 1 to 5 millimeters across)-,- mottled 

black and white on fresh surfaces and having a 

general tone effect of dark gray. The rock is 

usually massive, though locally it shows faint 

foliation. The weathered surfaces are somewhat lighter in color, and some are rusty 

through the oxidation of the iron-bearing minerals. Microscopic study of fresh specimens 

shows that the fabric is seriate homeoid,2 and 

the original minerals, named in the order of 

general abundance, are plagioclase (mostly near 

Ab45An55), brown biotite, green pleochroic 

hornblende, quartz, magnetite, apatite, and 

zircon. In some specimens from the Georgetown quadrangle Balls noted small amounts of 

original rutile, orthoclase, ilmenite, and titanite. 

Apatite and zircon form small euhedral grains, 

and some grains of hornblende and magnetite 

are subhedral, but the other constituents are 

anhedral. In a few localities pyroxene is present in addition to hornblende. In the section 

studied the pyroxene was partly altered to 

hornblende and its original character was not 

accurately determinable. Balls noted diallage 

in soPle of his specimens. 

In .mariy localities variations may be observed from ~he commoner type described 

2 The term seriate as applied to the fabric of igneous rocks signifies 

that the size of. the· grains varies gradually or in a continuous series. 

Homeoid signifies that the range in size of the grains is small. See 

Iddings, J. P., Igneous rocks, vol. 1, p. 196, 1909. 

a Ball, s. H., op. cit., pp. 54-.55. 
PRE-CA~BRIAN IGNEOUS ROCKS. 33 

above to varieties poorer in iron-bearing minerols and of light-gray color. The lighter rock 

commonly occurs as irregular lenses in the 

darker. Ball 1 describes phases from the adjacent Georgetown quadrangle that are almost 

wholly plagioclase. Still more common are 

variations toward rocks that are richer in ironbearing minerals and are termed hornblendites 

frmn. the great predominance of hornblende. 

A typical hornblendite from the valley of the 

West Fork of Clear Creek is nearly black and 

of medium grain (1 to 5 millimeters for most 

of the mineral grains) and consists of . green 

hornblende, plagioclase, quartz, magnetite, and 

apatite, named in the order of abundance. The 

apatite crystals are euhedral, but the other 

minerals are anhedral. The rock shows a faint 

foliation which appears to be the result of 

flowage while the magma was still viscous. 

Ball 2 recognized enstatite in some of the hornblendites of the Georgetown quadrangle. In 

mineral composition these hornblendites somewhat resemble the hornblende schists of the 

Idaho Springs formation, but they may usually 

oe differentiated from the schists by their more 

massive and coarser texture, by their gradation 

into quartz diorite, and by the fact that, unlike 

the hornblende schists, they are ·not characteristically associated with lime-silicate rocks or 

biotite schists of the Idaho Springs formation. 

Weathering produces the usual suite of secondary minerals, such as sericite, chlorite, 

epidote, and calcite, in more or less abundance. 

RELATIONS TO OTHER ROCKS. 

The quartz diorite and hornblendite are 

clearly intrusive into the rocks of the Idaho 

Springs formation. In the lower· part of the 

valley of Elk Creek, southwest of Apex, angular fragments of schist belonging to the Idaho 

Springs formation are inclosed in the quartz 

diorite. A number of the quartz diorite dikes 

lie parallel to the prevailing trend of the foliation of the inclosing Idaho Springs formation. 

At many localities quartz diorite· or hornblendite is intruded by granite pegmatite, and 

at a few places, as 3! miles west of Empire, 

they are intruded by the Silver Plume granite. 

The relations of the quartz diorite and 

hon1blendite to the granite gneiss are not so 

clear. Three-quarters of a mile southwest of 

Apex the quartz diorite appears to be intrusive 

1 Dnll, S. H., op. cit., pp. 54-55. , 

44214°-17-3 

in the granite gneiss. At other localities the 

relations, although somewhat obscure, suggest 

that the quartz 'diorite is intruded by granite 

which is now somewhat gneissic; in such areas, 

however, it can not be definitely shown that 

this granite is contemporaneous with the typical granite gneiss. There is a somewhat striking resemblance between some varieties of 

the quartz diorite and certain dark-colored 

rocks that are clearly differentiation products 

of the granite gneiss magma. 

ORIGIN AND AGE. 

It is clear from the relations already set 

for~h that the quartz diorite and its associated 

ligp.ter and darker colored facies are intrusive 

igneous rocks of. pre-Cambrian age. They 

were intruded subsequent to the development 

of most ·of the foliation in the Idaho Springs 

formation but before the intrusion of the Silver Plume granite and its associated pegmatite. The relation of the quartz diorite to the 

granite gneiss, though far from clear, suggests 

that the two rocks are of nearly the same age 

and possibly came from a common magmatic 

source. An alternative hypothesis suggested 

by Ball 2 assumes that the quartz diorites and 

hornblendites are derived from the same magmatic source as certain pre-Cambrian quartz 

monzonites that occupy large areas in the 

Georgetown quadrangle but are not exposed 

within the surveyed portions of the Central 

City quadrangle. 

GRANITE PEGMATITE. 

DEFINITION. 

Under the name granite pegmatite are included rocks of coarse and usually irregular 

texture containing the same minerals as are 

found in normal granites. The principal constituents are potash feldspar, quartz, biotite, 

and muscovite, but many other minerals are 

present in subordinate amounts. As explained 

later, all the granite pegmatite of this region is 

not of the same age. 

DISTRmUTION. 

Granite pegmatite in masses too small to 

map is abundant throughout most of the area 

mapped as Idaho Springs formation on Plate I 

(in pocket). Most of these small intrusions 

have the form of long, narrow lenses or pinch2 Idem, p. 56. 
34 GEOI.;OGY OF GILPIN, CLEAR CREEK, AND BOULDER COUNTIES, COLO. 

ing and swelling dikes lying parallel to the foliation of the schists or cutting ·it at small angles. 

Other masses of pegmatite are exceedingly irregular and may transect the schist foliation in 

various directions and even inclose angular 

fragments of- schist.· In many places the intrusion of pegmatite is so intimate that the 

rock becomes an injection gneiss, and locally 

the ·pegmatite magma penetrated the·schist so 

intimately that isolated ''eyes" of pegmatite 

were developed (see Pl. X, 13, p. 21), which 

show no evidence of strain and can not be re...; 

garded as pegmatite fragments isolated as a 

result of shearing. The mechanism of the development of niost of the bands and lenses. appears to have been intrusion under pressure, 

but many of the small isolated "eyes" of pegmatite may have been formed through metasomatic· replacement. Hardly any area of 

schist an acre in extent is wholly free from pegmatite. (See Pl. XII, B, p. 53.) Conversely, 

there is more or less schist in the areas that are 

largely pegmatite. 

Although some areas of pegmatite are closely 

assoeiated with areas of granite gneiss or of the 

Silver Plume granite, pegmatite is in general 

most abundant between the larger areas of 

these rocks. A peculiar and as yet unexplained 

feature of the distribution of the pegmatite is 

its rather intimate association with many of the 

masses of quartz diorite arid hornblendite. 

CHARACTER. 

The predominant constituent of the pegmatites of this region is potash feldspar'(orthoclase 

or microcline), in places. perthitically intergrown with soda feldspar (albite); next in 

abundance is g!ay qu~rtz, which con1monly 

aggregates as inuch as 6 inches across. It is 

locally the only .iron-bearing mineral present. 

Lithium and boron minerals and minerals containing the rare earths, such as are found in 

granite pegmatites in some parts of the United 

States, were not noted in the· Central City 

quadrangle. If present they are certainly in 

small amounts. 

Highly quartzose varieties of the pegmatite . 

are very rare. A lens of white· quartz 15 feet 

in maximum width lying parallel to the schist 

foliation just southwest of the summit of Pewabic Mountain may represent an extreme product 

from a pegmatite magma. It can not, how- · 

ever, be traced into pegmatite, and no minerals 

other than quartz were noted in it. There is 

certainly no genetic connection in this region 

between pegmatites and metalliferous veins, 

even the more quartzose vein types. 

The granite pegmatites of the Central City 

quadrangle are characterized by erratic variations in coarseness and by a wholly irregular 

association of their component minerals; cavities of any kind are rare, and extreme coarseness is also rare. In one of the coarsest bodies, 

about half a mile southeast of Pisgah Lake, 

there are masses of pure white quartz 4 feet 

across, single feldspar crystals 1 foot across, 

and abti.ndant graphic granite ranging from 

coarse to :fuie. 

The relations of the pegmatites to the schists 

of the Idaho Springs formation show that the 

pegmatites were intruded after most of the 

dynamic metamorphism in this region took 

place. None of them show any appreciable 

deformation that can not be explained by 

faulting and its atte~dant shearing. 

carries numerous fluid inclusions. Muscovite RELATioNs TO OTHER Rpcxs. 

or biotite, or both, are usually present, together It has· already been stated that the granite 

with minor amounts of magnetite and black pegmatites are intrusive into the rocks· of the 

tourmaline. Red g~rnet, apatite, zircon, allan- Idaho Springs formation. Some of the pegite, and beryl occur locally in srp.all crystals .. matite dearly came from the same magmatic 

Ip. ~ fe~ pegiD:atite masses magnetite is fairly. source as the granite gneiss, as is shown, for 

abundant. One such mass lies near Central instance, by exposures near the head of Missouri 

City, on the ridge between South Willis GUlch Creek, where irregular masses of pegmatite inand Pleasant Valley, and it carries magnetite eluding .much graphic granite grade into and 

crystals as rp.uch as 1 inch in diameter. Ball 1 are wholly inclosed by granite gneiss. Certain 

mentions localities in the Georgetown quad- bands forming an integral part of granite gneiss 

rangle where magnetite forms over one-third of may exhibit pegmatitic textures. Commonly 

the volume of the pegmatite and occurs in gr~nite gneiss takes on pegmatitic textures next 

single crystals as much as 4 inches across and in to schist contacts and even sends off pegmatitic 

• 1 nan, s. H., op. cit., p. ~1. dike offshoots cutting the foliation of the schist. 
PRE-CAMBRIAN IGNEOUS ROCKS. 35. 

Other masses of granite pegmatite show tran-. granite gneiss and granite that the pegmatite 

sitions to the Silver Plume granite and evi- ·of the southeastern part of the quadrangle 

dently came from the same magmatic source. came mainly from· the granite gneiss magma. 

' Numerous examples are found near Rollins- and that of the northeastern part of the quadville and Nederland. Most of the' pegmatites rangle came mainly from the Sil~er Plume 

that cut sharply twross the foliation of the granite magma. As already stated, the granite· 

granite gneiss probably belong in this group, gneiss and the Silver Plume granite, though 

though others may be late offshoots from· the probably of widely diverse ages, are both begrn.nite-gneiss magma itself. Finally, certain li,eved to be·pre-Cambrian. So far as observed· 

pegmatites sharply cut the Silver Plume the Tertiary ( ~) porphyry magmas yield~d no 

granite and are regarded as late offshoots from pegmatitic facies. · 

still molten interior portions of the granite 

mass after the exterior portions had crystallized 

and become somewhat fractured. 

ORIGIN AND AGE. 

' In practically all districts where pegmatites 

are found they are associated more or lessintimately with certain types of massive igneous 

rocks. Pegmatites of the _type here described 

are invariably associated with granites or similar rocks, and the association is so intimate and 

so invp,riable as to suggest at once that the 

n1assive and the pegmatitic rocks were derived 

from a common magmatic source. In the opinion of 1nost geologists the pegmatites crystallized frmn portions of the magma that were 

richer than the average in the elements of 

water and in some localities in other so-called 

mineralizers, such as lithium and boron. The 

abundant presence of these mineralizers permitted the n1agma to remain fluid to a lower 

temperature than that at which the normal 

granite solidified and facilit.ated the development of large crystals. Many granite pegmatites appear to have come from the interior 

fluid portions of granitic masses after the exteriOI· portiOI}S had crystallized as massive 

granite; a granite pegmatite dike cutting massive granite may therefore be only slightly 

younger than the granite itself. 

The granite pegmatites of the Central City 

quadrangle are believed to have been derived 

in part from the granite gneiss magma and in 

part froni the Silver Plume granite magma. 

As the pegmatites derived from each of these 

sources are similar in mineral character, it is 

possible to distinguish then1 only i~ the relatively few places where they caR be traced into 

granite gneiss or granite. The relative importance of the two magmas ~s sources of pegmatites can not be estimated; it seems probable, however, form the areal .distribution of 

SILVER PLUME GRANITE. 

DEFINITION. 

The name Silver Plume granite was applied 

by Ball to a medium-grained, usually porphy-· 

ritic qiotite granite that forn1s numerous stocks 

and dikes in the vicinity of Silver Plume and 

Georgetown. In the present report all th~ · 

granite of the region that is distinctiy younger · 

than the granite gneiss is cla~sed under this 

heading, although there may be some question 

whether all of it is the precise equivalent of the 

granite of the type locality near Silver Plume. 

DISTRIBUTION. 

The Silver Plume granite is widely distributed through all but the southeastern portion 

of the region, as is shown on Plate I (in pocket). 

It forms irregular stocks, commonly more or 

less elongate parallel to the prevailing trend. 

of the foliation in the inclosing schist of the· 

Idaho Springs formation or the granite gneiss .. 

The largest body, just northeast of Caribou, is. 

about 3 miles ·across. 

CHARACTER. 

The Silver Plume granite ranges in color 

from light gray or pale pink in the commoner 

varieties to dark gray in facies richer in ironbearing minerals. The texture is medium to 

coarse grained and commonly nla.ssive, although some varieties are porphyroid from the 

development of crystals of potash feldspar as 

much as 2 or 3 centimeters in length. In a few 

localities the texture is typically porphyritic1 

phenocrysts of potash feldspar as much as 3: 

or even 5 millimeters long lying in a uniformly 

even-grained groundmass. Such a porphyritic 

granite occurs 1! miles west of Phoenixville. 

The rocks in a few places show faint gneissic:. 

structure, especially near the borders of tho 

granite areas. 
36 GEOLOGY OF _GILPIN, CLEAR. CHEEK, AND BOULDER COUNTIES, COLO. 

Typical representatives of the commonest 

type are well exposed near Empire station- and 

Empire a.n:d may be described as light-gray 

to pinkish, wholly crystalline medium-grained 

massive rocks, most of the minerf:tl grains being 1 mill!meter to 5 millimeters in diameter. 

The fabric is seriate homeoid to porphyroid.1 

Microscopic examination shows that the origi-

. nal minerals, named ·in their usual order of 

abundance, are oligoclase, orthoclase and microcline, quartz, biotite, apatite, magnetite, and 

muscovite. The mineral grains· are anhedral 

with the exception of the small well-crystallized 

apatite prisms. There are in a few places 

micrographic intergrowths of quartz and oligoclase. · Slight mechanicaJ deformation since 

crystallization is evidenced by straining and 

son1e granulation of the quartz, much of the 

granulated quartz showing a coarse mosaic 

pattern. As a result of weathering sericite 

is developed from oligoclase and chlorite frorp. 

biotite;·some epidote and calcite may also form. 

Pegmatitic varieties are common in association with the normal facies of the Silver Plume 

granite, as pointed out on page 35. 

In places· rocks of dioritic appeara:Q_ce are 

associated with the common facies of the Silver 

Plume granite. Gradations ~n .some places 

between the two types indicate that both came 

from a common magmatic source. Where the 

two types do not grade into each other it is 

usually the light-colored rock that intrudes 

the darker, indicating that the dark varieties 

were differentiated early in the process of intrusion. Most of the dark-colored varieties 

differ from the commoner types mainly in the 

absence or scarcity of potash feldspar and the 

:proportionally greater abundance of iron-bear-

·ing minerals. Titanite and zircon may appear. 

The 'plagioclase, as in the commoner types, 

is oligoclase or oligoclase-andesine. In some 

of the darkest rocks hornblende ·is nearly 

as abundant as biotite. Dark-colored varieties 

are well exposed in the cliffs west of Silver 

Lake, near Alice. 

Dark-colored granite forms a lens-shaped 

mass about ~hree-fourths of a mile long just 

south of Central City, and a small mass of 

granite of identical appearance occurs in the 

valley of MissouriCreek about 1 mile north of 

Missouri Lake. In spite of the fact that most 

1 For explanation of terms see Iddings, J. P., Igneous rocks, vol. 1, 

p. 196, 1909. 

of the dark-colored facies of the Silver Plume· 

granite are of small areal extent as compared 

with the dark granite near Central City, it is 

thought probable that the latter is correctly 

classed as a 'variety of the Silver Plume granite. 

At one place near Central City a dike of biotite 

pegmatite 4 to 6 inches wide cuts the dark 

granite, and near the head of Spring Gulch 

the dark granite cuts sharply across the 

foliation of granite gneiss. Its relations to 

other rocks are therefore consistent with the 

interpretation that it is a differentiate from 

the Silver Plume granite. Moreover, there are 

local gradations into relatively small e.reas 

of light-gray to pinkish granite which closely 

resembles the normal Silver Plume granite 

except for the presence of a few small crystals 

of purple fluorite and numerous small yellowish-brown garnets. The dark-colored granite 

forming the greate:r: part of the mass south of 

Central City may be described as a massive 

dark-gray medium-g::-ained rock with seriate 

homeoid fabric. The original minerals, named 

in the order of abundance, are plagioclase 

(oligoclase-andesine), biotite, quartz, magnet~ 

ite, titanite, and apatite. The apatite crystals are euhedral, the magnetite subhedral, and 

all the other minerals anhedral. There is no 

evidence of any great amount of mashing or. 

recrystallization subsequent to solidification. 

RELATIONS TO OTHER ROCXS. 

The Silver Plume granite is intrusive into 

most of· the pre-Cambrian rocks of the quadrangle. At an elevation of 9,950 feet, on the 

crest of Red Elephant Hill, near Lawson, a 

mass of this granite (too small to map) cuts 

across the foliation of the granite gneiss and 

incloses angular fragments of the gneiss, 

whicl;l show no evidence of absorption. The 

granite of the southeast slope of Boulder Hill 

shows numerous included masses of schist of 

the Idaho Springs formation. About threequarters of a mile west of Lawson the Silver 

Plume· granite appears to intrude quartz 

diorite; near this point also the granite cuts 

not only the schist of the Idaho Springs formation, but .-also stringers of granite pegmatite 

in the schist. 

The only rocks observed to cut the Silver 

Plume granite are the porphyries of probable 

Tertiary age and a few dikes of pegmatite 

which probably came from the same magmatic 
TERTIARY ( ? ) INTRUSIVE RO.CKS. 37 

source as tho granite itself. A 2-foot dike of 

coarse peg1natite, composed wholly of quartz 

and pink feldspar, cuts the granite on the Cliffs 

just northwest of Empire station. In the 

Oro Verde tunnel, near Alice, the granite is 

intruded by coarse biotite pegmatite. 

To summarize, the Silver Plume granite 

intrudes all tho rocks that in the preceding 

pages have been referred to the pre-Cambrian 

and is itself intruded by pegmatite and by 

Tertiary 0) porphyries. 

AGE. 

Tho Silver Plume granite is believed to be 

pre-Cambrian .in age, .{tnd with the exception 

of its own pegmatitiy phases it is the youngest 

of the pre-Cambrian rq_cks of the region. The 

possibility of a Paleo~pic age for this granite 

can not be excluded ~n the basis of any evidence found within the Central City quadrangle, but whore Paleozoic rocks are exposed 

on tho flanks of the Front Range no granites 

intrusive in them have been noted. 

CARBONIFEROUS ( 1) SANDSTONE. 

Residual bowlders of silicified sandstone 

and quartzite occur at three points in the 

The well-sorted character of the sandstone indicates 

lacustrine or marine origin, while from the thorough cementation and the almost complete removal by erosion of 

what was once perhaps an extensive formation it may be 

inferred that the rock is of considerable age. It is; however, much younger than the youngest pre-Cambrian 

pegmatite, since before the deposition of the pebbles in 

the sandstone the pegmatite must have cooled beneath a 

considerable cap of overlying rock, which was removed 

by erosion prior to the depression of the land beneath the 

water in which the sand was deposited. Five . miles 

south of the quadrangle, on North Fork of the South 

Platte about 1 mile above Shawnee, a lithologically similar 

sandstone rests ·unconformably upon the Idaho Springs 

formation at an elevation of approximately 8,200 feet. 

Similar sandstone is exposed on the north bank of the 

same stream at Pine post office, 15 miles south of east of 

the southeast corner of the quadrangle. This sandstone 

belt strikes N. 60° W. and dips 70° to 80° SW. and is 

probably a block dropped by parallel faults into the 

Rosalie (pre-Cambrian) granite. The sandstone, which 

includes small pebbles of the Rosalie granite, is similar 

to that of the residuals in the Georgetown quadrangle, 

although the.red and white coloring matter is somewhat 

more· unevenly distributed. Lithologically this rock is 

very like the Fountain sandstone (Carboniferous) of the 

foothills of the Colorado Range. This portion of the range 

was at some time covered by the sea, which extended 

over the whole or a part of the Georgetown quadrangle, 

·and if the above correlation be correct the submergence 

was in late Carboniferous time, although a different age is 

quite possible. 

Georgetown quadrangle. At one of these TERTIARY ( 1) INTRUSIVE ROCKS. 

localities, Cascade Creek, the bowlders are so 

abundant that the original exposure of the GENERAL CHARACTER AND RELATIONS. 

sandstone could not have been much above In all parts of the area surveyed igneous 

tho present surface. No residual sandstone rocks intrusive in the pre-Cambrian formaor quartzite were noted in the area covered tions are of common occurrence. These inby the present report, but as these rocks pre- trusives forn1 irregular stocks and dikes whose 

sumably once covered at least part of this area form and distribution are well shown on 

Ball's description of their appearance in the Plate I (in pocket). The commonest rock 

Georgetown quadrangle 1 is inserted here. types are monzonites and related quartz 

The medium-gl'ained, well-silicified sandstone and monzonites, in large part porphyritic in texquartzite is yellowish brown, pink, red, or purple in color. ture. These rocks make up practically the 

The sem.iporous character of certain bowlders indicates whole mass of the larger stocks and many 

that some lime carbonatc,as cement may have been asso- of the dikes and quantitatively far exceed all 

ciated with silica. Well-rounded pebbles of quartz other types among the Tertiary ( ~) intrusives. 

monzonite, hornblende gneiss, and pegmatite are em- bedded here and there in the finer matrix. ·Under the The remaining types occur (1) as dikes and 

microscope the silicified sandstone proves. to be com- small stocks and lenses and (2) to a less6r 

posed of well-rounded grains of .quartz with one or more extent as irregular masses within monzonite 

grains of plagioclase and rounded rock fragments in stocks. The second mode of occurrence finds 

most of the thin sections. The quartz, which contains its principal exemplification in the titaniferous 

zircon granules, was derived partly from the gneisses and 

partly from the plutonic rocks of the pre-Cambrian fonna- iron ores and associated gabbros, peridotites, 

tiona. Quartz in optical continuity with the rounded etc., near Caribou, which are clearly differgrains, from which it is separated by a film of limonite, is' . entiation products from a monzonite magma. 

the chief cement, although a little hematite and chlorite The first mode of occurrence is represented by 

also occur. the bostonites of the southern part of the 

1 Ba'u, S. H., op. cit., pp. 6G-67. region and the andesites, diorites, and basalts 

•. 
3-8 GEOLOGY OF GILPIN, CLEAR CREEK, AND BOULDER COUNTIES, COLO. 

of the northeastern part. Although many of 

these dike rocks differ greatly in mineral 

composition from the quartz monzonites, 

it is probable that most of them came from the 

same magmatic source as the monzonites and 

are essentially contemporaneous with them. 

Their different mineral composition is attributed to magmatic differentiation at considerable depth prior to their intrusion. 

There are cogent reasons for the belief 

-express~d above that most of the rocks that 

:intrude the pre-Cambrian' rocks, the "por-

-phyries" of the miners, were derived from a 

common source or sources and are of essentially the same age. First, in spite of the 

presence of stocks of monzonite in the north-

.eastern part of the quadrangle, monzonite 

dikes are practically absent, their place being 

taken by dikes of an<Jesite, diorite, and basalt. 

In view of the abundance of monz<;mite dikes 

in other parts o~ the quadrangle their absence 

in that region is difficult to explain except on 

the assumption that more mafic (basic) dikes 

are themselves differentiation products from 

the inonzonitic magmas and so supplement the 

inonzoni te dikes of the regions of lesser magmatic differentiation. Second, the only district in which .the more mafic dikes are abundant, the area about Nederland and Caribou, 

is adjacent to the one monzonite stock which 

shows within itself a notable amount ·of differentiation into more mafic rock-that is, 

the Caribou stock, which carries the titan~­

erous iron ores. This association suggests 

that both the mafic dikes and the iron ores 

are the result of magmatic differentiation 

·within a magma of monzonitic composition, 

the iron ores. having been formed by differentiation in place or nearly so and the dikes 

by differentiation followed by intrusion. This 

view receives ·substantial confirmation from 

the apparent passage of some of the dikes at 

their west ends into the monzonite stock. 

That the bostonites and alaskites of the 

southeastern part of the Central City quadrangle are genetically connected with the 

monzonites can not be so confidently asserted. 

The bostonites and alaskites have nowhere 

been observed in contact with the monzonites. 

In certain areas, ·as near Idaho Springs, both 

bostonite and monzonite dikes are abundant, 

but in other areas, as between Central City 

~nd Yankee, all the dikes are bostonite, even 

though stocks of monzonite occur close by. 

Both bostonite and monzonite are older than 

the mineral veins. Although the evidence 

for a genetic co~ection of these other rocks 

with the monzonites is therefore not so strong 

as in the case of the dikes of the northeast 

corner. of the qu~drangle, such a connection 

is regarded as probable. From a study of 

the relations of these rocks in the Georgetown 

quadrangle Spurr and Garrey 1 reached· the 

same conclusion. These writers regarded the 

alkali syenite and the biotite latite of the 

Idaho Springs region as later than the monzonite and bostonite and later than the mineral 

veins. Tlie writer found no additional evidence bearing on this point . 

As monzonitic rocks constitute most of the 

stocks and many of the dikes, their total 

volume is many times the combined volume of 

all oth~r types. It is therefore probable that 

the parent magma from which the various 

rock types arose through differentiation had 

very nearly the average composition of the 

large monzonite ~tocks. 

As the Tertiary ( n intrusive rocks are not 

greatly different in their resistance to erosion 

from the pre-Cambrian rocks with which they 

are associated there is little correspondence 

between the topography and the form of the 

intrusive masses. The dike outcrops are usually not conspicuous, and many dikes are 

traceable only with difficulty by the presence 

of "float" material between scattered outcrops or by "float" alone. 

As clearly set forth in a summary by Ball/ 

the intrusive porphyries and related rocks of 

the Georgetown ·and Central City quadrangles 

form part of an extensive belt of intrusive porphyries that extends from the vicinity of 

Boulder southwestward to Breckenridge, Leadville, and Aspen. In sedimentary rocks they 

characteristically occur as sheets; in the preCambrian complex, as dikes and stocks. The 

predominant types throughout the belt bear 

a general resem~lance to one another and in a 

broad way are probably contemporaneous. 

In this porphyry belt are sit11ated many of the 

~ost productive mining camps in Colorado. 

1 Spurr, J. E., and Garrey, G. H., U.S. Gaol. Survey Prof. Paper 63, 

pp. 135-136, 1908. 

2 Ball, S. H., op. cit., pp. 67-70. 
TERTIARY ( ? ) INTRUSIVE ROCKS. 39 

AGE. 

The geologic relations within the Central 

City 'and Georgetown quadrangles indicate 

merely that the "porphyries" are younger 

than the pre-Cambrian rocks, which they cut, 

and are with a few exceptions older thari the 

ore deposits. The geology of neighboring 

areas, however.. gives much additional light 

on their age relations. 

At Leadville S. F. Emmons 1 found evidence 

that the porphyries were of late Cretaceous 

age. Spurr 2 assigned the same age to the 

porphyries of Aspen, and Ransome 3 believes 

that the intrusion of the porphyries of Breckenridge took place at the end of the Cretaceous period.· 

The intrusive sheets of. porphyry in the 

vicinity of Boulder were examined by Ball 4 

and R. D. George and were found to be lithologically siinilar to certain of the porphyries 

of the, Georgetown quadrangle. These sheets 

were found to cut the Niobrara and Pierre 

fonnatiqns and the "Red Beds," and they 

are therefore late Cretaceous or younger in 

age, a conclusion in accord with the views of 

Fenneman. 5 

In the sedimentary formations flanking the 

pre-Cambrian core of the Front Range west of 

Denver debris of volcanic rocks first appears, 

according to Cross,0 in the Denver formation. 

'l'his debris is andesitic and may well have 

been derived frmn flows that were the surface 

equivalents of the monzonites and related intrusive rocks. The Denver formation is of 

early Tertiary age. Beds composed largely of 

coarse andesitic Inaterial, resting unconformably on upturned Cretaceous rocks, have been 

noted also in Middle Park, on the west side of 

the Front Range. 

All the evidence available therefore indicates an early Tertiary age for the intrusive 

porphyries and related rocks of the Central 

City quadrangle and adjacent regions. 

/ t Emmons, S. F., Geology and mining industry of Leadville, Colo.: 

\ 

U.S. Geol. Survey Mon. 12, p. 29,1, 1886. 

I Spurr, J. E., Geology of the Aspen mining district, Colo.: U.S. Geol. 

Survey Mon. 31, p. 53, 1898. 

\

. a Itansome, ]~. L., Geology and ore deposits of the Breckenridge dis· 

trlct, Colo.: U.S. Goo!. Survey Prof. Paper 75, p. 182, 1911. 

4 Ball, S. H., op. cit., p. 71. 

o Fenneman, N. M., Geology of the Boulder district, Colo.: U.S. Geol, 

Survey Bull. 265, pp. 35-40, 1905. 

6 Cross, Whitman, Geology of the Denver Basin in Colorado: U. S. 

~ Geol. Survey Mon. 27, pp. 34-202, 1896. 

QUARTZ MONZONITE AND QUARTZ l\IONZONITE 

PORPHYRY. 

GENERAL CHARACTER. 

The quartz· monzonites of the Central City 

quadrangle are composed of orthoclase feldspar, calcic plagioclase feldspar, some quartz, 

and usually some iron-bearing minerals. There 

are great variations in the proportions of the 

minerals, in coarseness, and in the degree to 

which phenocrysts are developed. · In many 

localities iron-bearing minerals are not conspicuous, but in certain types they may be 

present in amounts reaching 30 or 40 ·per cent 

by volume and give to the rock a dark-gray 

color. In the porphyritic varieties the phenocrysts may be wholly feldspar or there may 

also be some of quartz or iron-bearing minerals. 

The phenocrysts may be small or large, ranging from 1 millimeter to 3 centimeters, and may 

be all of the same order of magnitude or of 

heterogeneous sizes. The groundmass appears 

structureless (aphanitic) to the unaided eye and 

in fresh specimens 1s light gray to purplish 

gray in color. In the nonporphyritic varieties 

the texture may be porphyroid .or, more 

rarely, rather evenly granular. A few dikes 

are coarsely porphyritic at the center and 

more finely porphyritic or massive at their 

borders. Many varieties are usually present 

within the same monzonite stock, and even 

along a single narrow dike there may be very 

considerable variations in character. The 

monzonites .. are usually massive; only in a 

few places do they show a slight banding 

attributable to differential movement during 

crystallization. 

Quartz monzonites and' monzonite porphyries are present in nearly all parts of the 

area surveyed. The largest masses are the 

stocks near Apex, Ute Mountain, and Caribou.· 

Dikes are particularly abundant in the vicinity 

of Idaho Springs. The details of distribution 

are fully shown on the geologic maps (Pls. I, 

III, and VI, in pocket). 

PRmCIPAL VARIETIES. 

Uniformly porphyritic quartz monzonites.-A 

variety· of quartz monzonite which is common 

in the area between Perigo, Phoenixville, Tol:-

lan~, and Apex but is not abundant elsewhere in the region shows in fresh specimens 
40 GEOLOGY OF GILPIN, CLEAR :cREEK, AND 'BOULDER CO.UNTIES, COLO. 

a ·blue-gray to purplish-gray fine-grained (apha.: 

nitic) groundmass through which are scattered a profusion of pink feldspar phenocrysts, commonly 2 to 3 millimeters in diameter. A few quartz phenocrysts are present. 

In altered specimens the groundmass may be 

lighter gray or 'pale lilac-colored and the 

feldspar phenocrysts white through the development of sericite or green through the development of chlorite. 

A particularly fresh specimen of monzonite 

of this type from a point about- 2 miles due 

north of Apex may be described as follows: 

Texture porphyritic, abundant euhedral phenocrysts of pale-pink feldspar, mostly 2 to 3 

millimeters in diameter, and a few of quartz, 

lying in a blue gray aphanitic groundmass. 

Under the microscope the feldspar phenocrysts are seen to be in part plagioclase (near 

Ab70An30) and in part orthoclase; the two 

varieties are apparently about equally abundant. Some of the few quartz phenocrysts 

are euhedral, but most of them are rounded or 

have embayments as a result of resorption. 

A few small biotite phenocrysts or biotite 

aggregates. about 0. 7 millimeter in greatest 

dimension were also noted. The groundmass 

is microgranular and appears to be mainly 

feldspar (species indeterminate) with some 

quartz and biotite and abundant minute grains 

of magnetite. A few of the grains of magnetite 

attain a diameter of 0.2 millimeter. 

In a porphyry of very similar appearance 

from the Champion mine, near Phoenixville, 

the phenocrysts are all orthoclase, but plagioclase· and quartz as well as orthoclase occur 

in the microcrystalline groundmass, which 

in h~nd specimens appears purplish gray. 

A few monzonite dikes present a peculiar 

"pepper and salt" appearance, euhedral crystals of feldspar, mostly 1 to 2 millimeters in 

diameter, being scattered in unusual profusion through a dark-gray to brownish-gray 

aphanitic groundmass. One of these dikes 

was an offshoot from the Gregory Hill stock 

of monzonite. The specimens collected proved 

to be to.o much altered for careful microscopic 

study. 

Other monzonites that are also uniformly 

porphyritic in texture differ from those just 

described principally in the larger size of the 

phenocrysts and the slightiy greater coarseness 

of the groundmass. These are dike rocks of 

the· .series of monzonite intrusions within 

the. area shown on Plate VI. The fresher 

specimens of these rocks show a blue-gray to 

pinkish-gray aphanitic groundmass, through 

which are scattered abundant phenocrysts of 

pink feldspar, mostly 3 to 5 millimeters in 

diameter. In altered specimens the groundmass is CO!fi-IDonly light gray to buff and the 

phenocrysts white or pale greenish. The 

groundmass of one of the freshest rocks is 

pinkish gray; through it are scattered salmoncolored phenocrysts of feldspar from 2 to · 5 

millimeters in diameter, and a smaller number of inconspicuous gray phenocrysts of 

feldspar. Under the microscope the pink 

phenocrysts are f<?und to .be euhedral crystals 

of orthoclase. The gray phenocrysts are 

plagioclase, variety not determinable. The 

microgranular groundmass carries quartz, orthoclase, plagioclase, and magnetite, the last in 

irregular open aggregates. 

Seriate porphyritic quartz monzonites.-In 

the rocks termed seriate porphyritic quartz 

monzonites the phenocrysts, even of the 

same mineral species, show great variations in 

size and may be numerous or scattered. In 

general these rocks are more prevalent than 

the uniformly porphyritic rocks. One of the 

freshest specimens illustrative of this type was 

obtained from the dump of the Almaden tunnel on Fall River. This rock carries phenocrysts of pink orthoclase from 2 to 10 millimeters in diameter and phenocrysts of lightgray plagioclase from 2 to 8 millimeters in 

diameter, scattered through a dark-gray aphanitic groundmass. Prisms of green hornblende 

as much as 3 millimeters in length, and of 

magnetite and titanite as long as 1 millimeter 

are also recognizable. Microscopic study shows 

that many of the plagioClase phenocrysts show 

zonal structure, the central portions being 

oligoclase (about Ab85An15) and the outer 

portions appearing to be andesine. All the 

above-mentioned minerals show euhedral 

forms. The microscope reveals the presence 

of quartz in phenocrysts as much as 0.5 millimeter in diameter, some showing rounding of 

corners and formation of embayments as the 

result of resorption and others being ragged in 
. TERTIARY ( ? ) INTRUSIVE ROCKS. 

outline. The ground:p1ass, which is finely 

microgrunular, carries quartz, orthoclase, a:nd 

possibly plagioclase and is dotted with small 

magnetite grains whose abundance gives the 

dark-gray color to the groundmass in· the 

hand specimen. 

In porphyry from the southwest slope of 

Seaton Mountain, near Idaho Springs, some 

feldspar phenocrysts reach the unusual size of 

lt centimeters, though the .majority are less 

tha~1 3 millimeters in diameter. 

In a few localities the monzonite porphyry 

carries abundant quartz phenocrysts, some of 

which may reach 5 millimeters in diameter. 

One dike of this type is cut 4,800 feet from the 

portal in the Marshall & Russell tunnel at Empire station. Another occurs a quarter of a 

1nile northeast of Dumont. The specimens 

obtained were all much altered, but microscopic study of the specimen from the Marshall 

& Russell tunnel showed that phenocrysts of 

both orthoclase and plagioclase were present 

in addition to those of quartz, which were 

more or less rounded by resorption. Quartz 

also occurs in sn1all amounts in the groundmass. 

A number of dikes in the region between 

Idaho Springs and Lawson carry small pris1ns 

of pyroxene in notable amounts and may therefore be termed pyroxenic quartz monzonite 

porphyries. These rocks have a gray groundnlass which under the microscope is found to 

be a microgranular association of quartz, orthoclase, plagioclase, and sn1all grains of magnetite. The abundant phenocrysts, originally 

pyroxene, as shown by their form, are now an 

aggregate of chlo:rite, calcite, and magnetite. 

Nonporphyritic quartz monzonites.-Many of 

the quartz monzonites nre porphyroid to massive in fabric and therefore can not be called 

porphyries in the strict sense of the term. In 

general these are stock rocks of fine to medium 

grain, ranging from light to dark gr~y in color 

according to the abundance of iron-bearing 

minerals present. The main mass of the Caribou stock of monzonite, which may be taken 

as representative of the darkest-colored varieties, is described on page 42' and an analysis 

of it is given on page 43 (analysis 1). 

A slightly lighter colored variety of the 

quartz monzonite is typified by a rock from 

the Alice mine, near· Alice. This is .a lightgray rock of porphyroid fabric, few of the mineral grams exceeding 2 n1illimeters in diameter. 

The larger euhedral or subhedral crystals that 

give the rock its porphyroid texture are orthoclase and andesine; biotite, quartz, and .magnetite in smaller anhedral grains make up the 

rest of the rock except for a few prisms of 

apatite. Monzonite of almost identical appearance occurs at the east end of Ute Mountain. 

Monzonite forming a small stock in the valley of Fall River about three-quarters of a mile 

above the mouth of York Gulch is unusual in 

carrying numerous quartz phenocrysts as much 

as 5 millimeters in diameter. Biotite is also 

abundant 'in plates 1 millimeter or less across. 

Monzonite fro~n another locality near by carries 

some quartz phenocrysts nearly 2 centimeters 

long, many of which show perfect crystal forrp.s. 

In the extreme northeast corner of the area 

covered by Plate VI occurs a medium-grained 

monzonite that has gray feldspar for its chief 

component. In general appearance it is strikingly similar to certain anorthosites, but the 

microscope shows that the predominant gray 

feldspar is orthoclase. Plagioclase (near 

Ab70An30, oligoclase-andesine) and quartz are · 

present in lesser amounts and in smaller crystals. Magnetite occurs in numerous small 

euhedral or subhedral grains, titanite in perfect crystals, apatite in small prisms, an(\ 

purple fluorite in irregular grains that appear 

to be primary. Monzonite of practically 

identical character is cut in the Phillips tunnel, 

on Fall River, ~nd monzonite from the southeast slope of Cone Mountain, 2! mijes westnorthwest of Empire, is similar but carries 

numerous prisms, odginally green pyroxene 

but now in large part altered to hornblende. 

Unusual varieties.-A specimen collected 

1 mile south-southeast of Apex, within the 

quartz monzonite stock that makes up most 

of Utah and Oregon hills, proved on microscopic examination to be massive, medium 

grained, .and composed of orthoclase, augite, 

titanite,· and magnetite, plagioclase and quartz 

being entirely absent. This rock is therefore 

an augite syenite, but it grades into the typical 

quartz monzonite that makes up most of this 

stock. 

... 
' . 

42 GEOLOGY OF GI.LPIN, CLEAR CREEK, AND BOULDER COUNTIES, COLO. 

ROCKS FORMED BY MAGMATIC DIFFERENTIATION WITHIN MONZONITE STOCKS NEAR~ CARIBOU. 

GENERAL CRARA.CTER. 

The monzonite stocks of Caribou and of Bald 

Mountain3 northwest of Caribou, are unique 

for the region covered by this report in showing in a marked degree the effects of magm·atic 

differentiation-that is, the separation of the 

molten magma into . portions ·that were 

~heroically different and that on cooling 

formed rocks of different types. The extreme 

product of this process of differentiation has 

.been the formation of several bodies of titaniferous iron ·ore, whose economic features are 

discussed elsewhere.in this report (pp. 129-130). 

It is probable also, for the reasons set forth on 

page 38, that the andesite, diorite, and basalt 

dikes between Caribou and Nederland ·were 

also formed by differentiation'from a monzonite 

magma just prior to their intrusion into their 

present position. 

It was not found practicable in the field to 

obtain a complete series of fresh samples along 

any one line extending ·fron;t the iron ore of 

Caribou out into the normalquartz monzonite, 

but samples were selected so as to be as nearly 

as possible representative of the variations 

along most of these contacts. Chemic·al analyses of six of these samples, made by ·George 

Steiger in the laboratory of the United States 

Geological Survey, are given in the table on 

page 43, together with three analyses made by 

E. P. Jennings. 1 

The greater part· of the Caribou and Bald 

Mountain stocks is composed of monzonites 

and quartz :".llonzonites of gray color and 

medium coarseness. Inclosed by these rocks 

and forming not more than 5 per cent of the 

whole volume of the stock are a number of small 

irregular bodies of dark-colored rocks which 

are rich in iron-bearing minerals and whose 

form and position are indicated on Plate I 

(in pocket). In places a complete gradation 

may be traced from the monzonites into these 

mafic rocks, and within the latter there fl,re 

transitions from gabbros to rocks composed 

mainly of magnetite and ilmenite. In other 

1 Jennings, E. P., A titaniferous iron-ore deposit inBoulder County, 

Colo.: Am. Inst. Min. Eng. Trans., vol. 44, pp. 14-25, 1913. 

places the contacts are not gradational, the 

monzonite abutting sharply against the mafic 

rocks and even inclosing angular fragillen ts of 

them. In general, however, the evidence is 

clear that the iron-rich rocks are differentiates 

from tl~e monzonite magma and that the 

differentiation ·was followed locally by intrusion of the iron-rich product into the more 

silicic types. In the iron-ore body half a 

mile south ·of Caribou the eastern contact with 

the monzonite is gradational but the western 

contact is ·sharp: The principal types in 

these gradational series are briefly described 

below, the textural terminology proposed by 

Cross, Iddings, Pirsson, and Washington 2 

being used. 

FELSIC (ACIDIC) AND INTER~EDIATE TYPES. 

A rock collected 1 mile southeast of Caribou 

will serve to illustrat.e. the commonest type ,of 

the quartz monzonite. , 

Quartz monzonite (shoshonose; analysis 1, p. 43). In 

megascopic appearance this rock is light-gray, holocrystalline, and composed of crystals nearly all of which 

are less than 1 millimeter in diameter. The microscope 

shows that most of the crystals are between 0.1 and 1 

millimeter in diameter and that the fabric is seriate 

porphyroid. The major constituents are orthoclase, 

phigiocla8e, augite, and biotite. The minor constituents 

are magnetite, apatite, and quartz. The plagioclase is 

mostly labradorite near Ab40A~ , although a few crystals 

show zonal structure· with more sodic feldspar near the 

borders. The crystals are subhedral. Orthoclase is 

nearly equal to plagioclase in abundance and forms 

anhedral (or allotriomorphic) masses between the plagioclase crystals. Augite is abundant in pale-green and 

nonpleochroic grains showing extinction angles ( c: t )I as 

great as 46°. It forms anhedral to subhedral crystals. 

Brown biotite is about as abundant as the augite· and 

forms anhedral crystals closely associated with augite and 

magnetite. The few small quartz grains present are 

intersertal in position. Apatite forms many small prisms 

that are especially abundant in or near the crystals 

of biotite and augite and in the orthoclase. They are 

only here and there inclosed by plagioclase. Magnetite 

is present in anhedral grains, as a rule partly or wholly 

inclosed by augite or ~iotite, though in places inclosed 

by feldspar. The general order of crystallization appears 

to have been (1) apatite and magnetite, (2) plagioclase, 

augite, and biotite, essentially contemporaneous, and (3) 

orthoclase and quartz. The specimen shows practically 

no alteration by weathering. 

2 Jour. Geology, vol. 14, pp. 692-707, 1906. See also Iddings, J. P., · 

Igneous rocks, vol. 1, pp. 191-204, 1909. 
... 

Analyses of stock rocks from Caribou and vicinity. 

[In the second column under each number ·are given the molecular proportions calculated from the percentage weights given in the first column.) 

1 2 3 4 5 6 7 8 9 

SiO .... : .......... ; 

~!if~~-:·:-:-:::::::: 

56. 64 0. 944 53. 95 0. 899 52. 10 0. 870 51.43 0. 857 44. 26 0. 738 36.77 0. 613 30.47 0. 508 27. 71 0. 462 9. 60 0. 160 

17. 00 . 167 18. 56 . 182 19. 35 . 189 19. 35 . 189 13. 95 . 137 10. 29 .109 9. 04 . 089 2. 92 . 028 6. 27 . 062 

3.11 .019 3.86 .024 4.63 .029 5.32 .033 7.84 .049 10.54 .066 16.37 .103 21.80 .136 44.72 .279 

5.06 .070 4.23 .058 4.16 .058 4.70 .065 8.87 . 124 12.11 .168 14.91 .207 15.70 .218 25.31 .351 

MgO ............. . CaO ............. . 2. 79 . 070 2. 35 . 059 3. 19 . 080 3. 05 . 076 6. 59 . 165 9. 34 . 234 7. 86 . 197 17. 98 . 450 5. 16 . 129 

6. 20 .111 6. 58 . 118 7.15 . 128 7. 09 . 127 10. 41 . 186 12. 26 . 219 9. 33 . 166 G. 83 .121 · 3. 75 . 067 

NazO~--- .. -.-- · · · K.,O ............ . H;o-............ . H.20+---···:······ TIO., ............. . Zro; ............. . co., .............. . 

3.16 .051 3.36 .054 3.39 .055 3.54 .057 1.81 .029 1.16 .019 .77 .012 .19 .003 .15 .002 

3. 40 . 036 3. 88 . 041 3. 77 . 040 3. 52 . 037 1. 75 . 019 1. 38 . Q15 2. 89 . 031 None. None. Trace. Trace. . 31 . . . . . . . . 30 . . . . . . . . 06 . . . . . . . . 08 . . . . . . . . . 33 . . . . . . . . . 36 . . . . . . . . . 32 . . . . . . . . . 54 ..................... . . 70 . . . . . . . . 68 ..... ·.. . 13 . . . . . . . . 35 . . . . . . . 1. 54 . . . . . . . . 1. 70 ! ••••••• , 1. 32 . . . . . . . . 3. 51 . . . . . . . . . 51 ..... . 

N~::. . .'. ~~~. No~~~ . .'. ~~~-- .. .'. ~~ .. .'. ~~~ ... .'. ~~ ... ·. ~~~. N~~!~ .. ---~~~ .... :-.~~ ... .'. ~~~ .... :·. ~: ... ---~~: .... :·. ~~ .. ·. ---~~ ... -~·.:~ .. .'. ~~~ None. . . . . . . . . 85 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 . . . . . . . . . 18 . . . . . . . . . 21 . . . . . . . . . 22 ..................... . 

~0~~~~-----~ ~ ~ ~ ~ ~ ~ ~ ~ N~n~ .. .'. ~~~. No~~? . .'. ~~~ ... .'. ~~ .. .'. ~~~ ... ~-- ~~ .. .'. ~~. No~~~ .. .'. ~~~ .... ~-- ~~ ... .'. ~~~ .... :-.~~ ... .'. ~:~ .. ~~~~~ .. ~~~~~ .... ---~~ .. --~~~~ CI ....................•...••.•••...............•..•...........•.•.....................•.................•...•...........•..•.....•.•.•.....•••.•.••..•... 

F .................. None. . . . . . . . None. . .................................. None. . .................................................................... . 

~~€_;:_:_:_::::::::: ~~~~~ ::::::: ~~~~~ ::::::::::::::::::::::::::::::::::: ~~~:3 :::::::: -N~~:~- ::::::::'·N~~:~- :::::::: -N~~:- :::::::::::::::::::::: 

CaO. . . . . . . . . . . . . . . . . . . . . . . . • • . . . . . . . . . . ... ~ . . . . . . . . . . . . . . . • . . . . . . . . . . . . . . . . . . . . . . . ..... ~. . . 03 . . . . . . . . . 03 . . . . . . . . . 05 . . . . . . . . . . . . . . . . . .... . MnO........ ...... . 20 . 003 . 17 . 002 . 10 . 001 Trace. . . . . . . . . 19 · . 003 . 23 . 003 . 39 . 006 . 22 . 003 ............. . BaO.............. .06 ....... .13 ....... ....... ....... ....... ....... .03 ........ ,04 ........ .09 ........ Trace ...................... . SrO.............. . Trace. . . . . . . . . 07 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 03 . . . . . . . . . 02 . . . . . . . . . 04 . . . . . . . . Trace. . .................... . 

Li20 .................................... ····---~~~~ ............... -·······,········ -·······,········ ................ 1 •••••••••••••••••••••• 

99. 91 100.39 ., ....... ,99. 68, ....... ,99. 88 , ....... ,100. 32 

2. 783 ....... Undet. ~ ...... Undet. . . . . . . . 3. 074 

100.63 

Specific gravity 

(powder) ....... I 2. 837 3. 288 

1. Quartz monzonite (shoshonose), 1 mile south of Caribou. Grades into No.5. Analysis by George Steiger. 

100.12 

3.374 

100.40 

3.564 

100.03 

· Undet. 

2. Monzonite (shoshonose), half a mile south of Caribou. Analysis by George Steiger. 

3. Monzonite (shoshonose), Caribou. Analysis byE. P. Jennings. Jennings(op. cit., p. 21) states, referring to rocks 3and4: "I would classify the rock as an orthoclasebiotite gabbro in preference to calling it a monzonite, on account of the predominance of the plagioclase." 

4. Monzonite (shoshonose), Caribou. Analysis by E. P. Jennings. 

5. Gabbro (delondose), lmilesouth of Caribou. A border differentiate from No.1. Analysis by George Steiger. 

6. Homblendite (caribose), dump of Up to Date tunnel, 1 mile northwest of Caribou. Analysis by George Steiger. 

7. Magnetite-rich gabbro (eldorose), dump of Caribou mine .. Analysis by George Steiger. 

8. Magnetite peridotite (cardinalose), half a mile south of Caribou. Analysis by George Steiger. 

9. Iron ore (pomerose), Caribou. Analysis by E. P. Jennings (op. cit., p. 23). 

~ 

~ 

~ 

~ 

z 

1-3 

~ rJ2 

~ tr.i 

!;0 

0 

0 

~ 

~ 

~ 

C/.:) 
44 GEOLOGY OF GILPIN·, CLEAR CREEK, AND .BOULDER COUNTIES, COLO. 

The norm as calculated by H. S. Washington is as fol- Specimens showing interesting variations 

lows: from the commoner type of monzonite were 

Quartz.·················· 7. 62 Q= 7· 62} collected from the dump of the Caribou mine. 

Orthoclase ................ 20· 

02} . Sal, 76· 60 One of these differed from the normal monzoAlbite .............. ·. . . . . 26. 72 F=68. 98 

Anorthite ... : ............. 22. 24 _ nite in being much coarser, crystals of orthoDiopside................ 4. so} P=15_ 25 · clase and aggregates of augite and biotite 

Hypersthene .............. 10. 45 } . reaching 5 millimeters in diameter, and in 

Magn~tite. · · · · · · .- · · · · · · · 4· 

41} M=5. 93 Fern, 22.19 showing a very great preponderance of orthoIlmemte. · · · · · · · · · · · · · · · · l. 52 A clase over plagioclase. Another specim.en car- Apatite................... l. 01 =1. 01 

Sal 76. 60 . Cl II d I Fern =22_ 19, · ass : osa ane. 

Q 7.62 p=6s. 98, order 5, germanare. 

K 20 1 + N ~O' =-=~ raug 3 monzona.se CaO' so' ' . · K20' 36 . N~o,=[i' subrang 3, shoshonose. 

Formula, II.5.3.3. 

Quartz monzonite from the Up to Date tunnel, typical of much of the rock of the Bald 

Mountain stock, northwest of Caribou, is identical in nearly every particular with that just 

described. 

Another monzonite, c;ollected half a mile 

south of Caribou, was also analyzed by Mr. 

Steiger (analysis 2, p. 43). Aithough it differs 

only slightly from the rock described above,_ 

mainly in .being slightly coarser ·in grain, its 

petrographic description is inserted for the sake 

of completeness. 

ries all the minerals of the normal monzonite 

' except quartz, and in addition carries a few 

crystals of olivine associated with and in places 

inclosed by the augite and biotite. The olivine, which is somewhat serpentinized, was 

plainly one of the first minerals of the rock to 

crystallize. The feldspars predominate somewhat over the ferromagnesian minerals, so that 

the rock may properly be termed an olivine 

monzonite. 

Olivine monzonite of finer grain was observed in place on the eastern border of the 

ore-bearing gabbro half a mile south of Caribou, where it appears to grade into gabbros of 

various types. · Its petrographic features are 

briefly as follow::;: 

Olivine monzonite. Greenish gray, holocrystalline, and 

medium grained. Most of the mineral grains are between 

0.3 and 3 millimeters in diameter. The major constituents 

are plagioclase, orthoclase, augite, and biotite; the minor 

constituents apatite, magnetite, and olivine. The plagiMonzonite (shoshonose; analysis 2, p. 43). In mega- oclase is andesine close to Ab60An40 in composition; it 

scopic appearance tllis rock is dark gray, holocrystalline, forms euhedral to subhedral grains. The orthoclase is 

and medium grained, most of the crystals ranging from 0.25 about equal to plagioclase in abundance. The augite is 

to 3 millimeters in diameter. The microscope shows the pale green, nonpleochroic, and in euhedral to subhedral 

fabric to be seriate homeoid. The major constituents are grains. Biotite is abundant in anhedral grains. Apatite 

o~thoclase, plagioclase, augite, and biotite, and the minor is present as small short prisms. Magnetite forms subhe- · 

constituents apatite, magnetite, and quartz. The feld- dral to anhedral grains and constitutes perhaps 5 per cent 

spars are slightly more abundant than the ferromagnesian of the volume of the rock. Olivine, ·which is altered 

constituents. The orthoclase occurs in anhedral crystals along cracks to iron oxide an:d serpentine, is present as 

and is nearly equal in abundance to plagioclase. The scattered grains of irregular outline. The general order 

plagioClase, in subhedral crystals, is andesine-labradorite,· of crystallization was (1) apatite; (2) magnetite and 

about Ab50An50 , showing very little zonal development. olivine; (3) augite, biotite, and plagioclase. Feldspars 

The augite is pale green and nonpleochroi.c and in a few and iron-bearing minerals are about equally abundant, 

places shows alteration to green pleochroic hornblende; and there is a marked tendency for the iron minerals and 

the crystals are subhedral. The biotite is brown and apatite to group themselves in irregular aggregates. 

forms anhedral crystals about equal to augite in abundance. 

The apatite forms short, small' prisms and is associated 

mostly with the ferromagnesian minerals. The magnetite 

forms anhedral grains associated with the augite and 

biotite. Quartz is present as occasional minute grains. 

The general order of ·crystallization appears to have been 

The presence of olivine in rocks so rich in 

orthoclase is noteworthy. 

:MAFIC (BASIC) TYPES. 

(1) apatite and magnetite, (2) augite, biotite, and plagio- The transition, as a result of magmatic differclase, nearly contemporaneous, and (3) orthoclase and entiation, from monzonite into darker-colored 

quartz. In. the quantitative system this rock, like that rocks, to which the name monzonite can not 

above described, falls in shoshonose (II.5.3.3). be applied, was first studied at a locality 1 

The two·rocks described by Jennings 1 (anal- mile south of Caribou. There the main body. 

yses 3 and, 4, p. 43) also fall in the subrang of the intrusive is the quartz monzonite, alshoshonose [II.q.3.3" and 11.5.3.3(4)]. · ready described (Nor. 1, p. 43). This rock 

1 Jennings, E. P., op. cit., p. 16. grades at the border of the stock into ·a darker-
TERTIARY ( ? ) INTRUSIVE ROCKS. · 45 

colored rock, whose analysis is given in column 

5 on page 43. The darker rock shows faint 

foliation parallel to its contact with the schists, 

probably the result of flowage during crystallization. Its petrographic description is as 

follows: 

Gabbro (delondose; analysis 5, p. 43). In megascopic. 

appearance the rock is dark gray and holocrystalline. 

Most of the mineral grains are between 0.25 and 3 millilneters in diameter. Microscopic study shows that the 

fabric isser.i.ate homeoid. The major original constituents 

are plagioclase, augite, and biotite; the minor original 

constituents apatite, magnetite, pyrite, titanite, and 

quartz. Secondary minerals are. hornblende, epidote, 

calcite, chlorite, and sericite. Feldspar constitutes about 

35 to 45 per cent of the rock, and iron-bearing minerals 

make up the other 55 to 65 per cent. The plagioclase, 

which occurs in euhedral to subhedral crystals, commonly 

shows zonal structure and ranges from labradorite (Ab40 

An00) in the center of the crystals to andesine-labradorite 

(Ab55An411) at tha borders. The augite 'is pale green and 

nonpleocluoic and forms anhedral to subhedral grains. 

Most of the original augite has been altered to green, 

highly pleochroic hornblende, which in turn has altered 

in a few places to epidote. Brown biotite forms anhedral 

crystals, slightly altered to chlorite in places. Magnetite 

is abundant in anhedral grains associated with the ferromagnesian minerals. Apatite forms numerous short 

prisms associated principally with augite, hornblende, 

and biotite. Titanite and pyrite form small grains with 

the ferromagnes.ian minerals. Calcite and sericite are 

present .in small amounts as alteration products of plagioclase. In general, magnetite, apatite, and titanite 

appear to have crystallized first, the other primary minerals forming a later and practically contemporaneous 

group. 

The norm of this rock as computed by H. S. Washington is as follows: 

Orthoclase ........................... 10. 56) 

Albite._. . . .. .. .. .. .. .. .. .. .. .. .. .. .. 15. 20 Sal, 50.50 

Anortlute ............................ 24. 74 

Diopsido ........................... 17. 30. 

Hypersthene......................... 9. 54 

Olivine.............................. 4. 71 Fern 47.70 

Magnetite ............ .' ............. 11. 39 ' 

Ilmenite . . . . . . . . . . . . . . . . . . . . . . . . . . . 2. 74 

Apatite............ . . . . . . . . . . . . . . . . . . 2. 02 

Sal 50.50 Fem = 47 . 70, Class III, salfemane. 

Q or L 0 d 11 ~= · 

50 50 , or er 5, ga are. 

K20' + N ~0' 48 CaO' 89, rang (3) 4, auvergnase. 

K20~ ~!Q, subrang 3 (4), delondose (new name). Na20' 29 

Formula, III.5.(3)4.3(4). 

For this rock the writer proposes the name 

delondose, from Delonde Creek, about 1 mile 

northeast of Caribou. 

In general the rock differs from the common 

type of quartz monzonite into which it grades 

(No. 1, p. 43) in being slightly coarser grained, 

in lacking orthoclase, and in containing a greater 

abundance of ferromagnesian silicates and 

magnetite and small amounts of titanite and 

pyrite. It also shows considerable alteration. 

The chemical differences are apparent from 

the table on page 43 and figure 3 (p. 49). 

Rocks in which iron-bearing minerals· were 

even more abundant than in the specimen just 

described we.re collected from the_ immediate 

vicinity of the iron-ore bodies at Caribou village and half a mile to the' south. An especially instructive locality was the eastern margin of the ore body lying half a mile south of 

Caribou. At this place there appears to be a 

gradual passage from olivine monzonite into 

even-grained gabbro, then into gabbro with 

large hornblende crystals, and then into a 

rock whose_ most conspicuous mineral is 

biotite in plates as much as 15 centimeters in 

diameter. The gabb~os are notably richer in 

magnetite than the olivine monzonite, and they 

appe~ in turn to grade into the iron ores. The 

petrographic character of the olivine monzonite, 

which forms the most silicic member of the 

series as there exposed, has already been described (p. 44). ·This monzonite appears to 

pass by gradual transition into a mottled gabbro, which differs from it in being of coarser 

grain, in lacking orthoclase and olivine~ and in 

having slightly more calcium in the plagioclase (Ab50An50 instead of Ab60An40), but in 

which magnetite is not. notably more abundant 

and, as in the olivine monzonite, feldspar and 

iron-bearing minerals are present in nearly 

equal amounts. This gabbro in turn appears 

to grade within a few feet into a hornblende 

gabbro characterized by single crystals of horD;-

blende as much as 1 centimeter across or groups 

of such crystals as much as 3 centimeters 

across, lying in a fairly even grained groundmass. The texture of this rock is coarsely 

porphyroid. The microscopic features are as 

follows: 

Hornblende gabbro. The groundroass shows as its roost 

abundant constituents augite and sericite, and as minor 

constituents magnetite and apatite. The augite is pale 

green and nonpleochroic and shows·some alteration to green 

hornblende. Sericite forms aggregates of small shreds 

covering considerable areas and is believed to he a product 

of feldspar alteration. Apatite is abundant in short prisms. 

Magnetite appears to constitute about 15 per cent of the 

rock. It is ~n places inclosed by augite hut more commonly lies between the augite grains, conforming to their 

outlines. The phenocrysts are greenish-brown, slightly 
~ .. . 

46 GEOLOGY OF GILPIN, CLEAR CREEK, AND BOULDER COUNTIES, COLO. 

pleochroic hornblende without crystal outlines and 

inclosi.ng numerous small crystals of augite, apatite, and 

magnetite and a few of plagioclase. The plagioclase is the 

only unaltered feldspar in the rock, its inclosure in large 

hornblende crystals having had a protective effect. 

Noteworthy features of this rock are the 

coarsely porphyroid texture, the presence of 

prim~ry hornblende to the complete exclusion 

of biotite, which is an ~bundant constituent 

of most of the associated rocks, and the large 

percentage of magnetite. Another rock that 

is closely associated with the porphyroid 

gabbro just described and apparently grades 

into the iron ore is nearly half brown biotite 

in plates reaching 2 centimeters in diameter. 

Fresh samples of this rock suitable for the preparation of thin sections could not be found. 

Another type of differentiate from the Bald 

Mountain monzonite mass was collected from the 

dump of the Up to Date tunnel, 1 mile northwest 

of Caribou. It is a coarse hornblendite whose 

petrographic features are as follows: 

Hornblendite (caribose; analysis 6, p. 43). Green hornblende in prismatic crystals as much as 1.5 centimeters in 

length is the principal .component. The crystals are 

oriented in all directions; The hornblende appears to b~· 

original rather than an alteration product after pyroxene, 

but there may be some doubton this point. The mineral 

is perfectly fresh in appearance. Plagioclase is present 

in small amounts ·and has the composition of labradorite 

near Ab40 An60 • The minor constituents are biotite, apatite, magnetite, and titanite. Magnetite forms anhedral 

crystals and constitutes perhaps 5 per cent of the volume 

of the rock; .adjacent to it or intergrown with it are small 

amounts of pyrite, which appears to be original. Titanite is 

present in a few scattered grains. The general order of crystallization appears to have been (1) apatite, (2) titanite and 

magnetite, and (3) hornb1encle, biotite, and plagioclase. 

The norm of this rock as calculated by H. S. Washington 

is as follows: · 

Orthoclase. . . . . . . . . . . . . 8. 34} 

Albite ....... ··........ 1. 83 F=31. 02} 

Anorthite .............. 20. 85 Sal, 35. 33 

Nephelite.............. 4. 31 L= 4. 31 

Diopsicle ............... 24. 74}P+0=40. 04 

Olivine ................ 15.30 l 

Magnetite. . .. . .. .. .. .. . 1

4

5 .. 3

7

1

1

.} M=20. 02 Fern, 63. 42. 

Ilmenite ............. . 

Apatite. . .. . .. .. .. .. .. . 3. 36 A= 3. 36 

Sal 35.33 Fern = 63 _

42 , Class (III)IV, clofemane. 

P+O 

~ 40.04 = 20_

02 , order 2(3), scotare. 

p 24.74 . (2)3 . o=15_

30, SeCtion , teXIare. 

MgO+FeO 405 9 CaO'' 144' rang ... , uvaldase. 

MgO 234 b II 'b ( . . FeO = 168, su rang 3, can ose new name). 

Formula (III)IV.2(3).(2)3.2."3. 

For this rock the name caribose is proposed, 

after the town of Caribou. 

Highly hornblendic phases like the rock 

above described grade into phases rich in biotite. The contacts between these hornblende 

and biotite rocks and th.e monzonites are in 

some places sharp and in others gradational. 

Specimens. on the dump showed sharply angular fragments of hornblendite in the monzonite. 

ULTRAMAFIC MAGNE~ITE-RICH TYPES. 

Rocks which are richer in magnetite than 

those thus far described and some of which n1ay 

properly be termed iron ores are irregularly distributed within the gabbro masses. One of 

these rocks collected on the dump of the Caribou mine is described below. 

Magnetite-rich gabbro (eldorose; analysis 7, p. 43). 

This rock is dark green to nearly black and millimetergrained.' The microscope shows the fabric to be seriate 

porphyroid, crystals of augite as much as 7 millimeters 

across, with a few of plagioclase of corresponding size 

lying in a fine-grained groundmass of other minerals. Th~. constituents are augite, plagioclase, biotite, magnetite, and 

apatite, and all are sufficiently abundant to be designated 

as. major rather than minor. The augite is in pale-green, 

non pleochroic grains which show extinction angles as great 

as 45°; it incloses some crystals of magnetite and biotite 

and a very few of apatite. The plagioclase forms euhedral 

to subhedral grains corresponding in size to those of augite . 

It ~bows pronounced zonal structure, but its exact position 

in the plagioclase series was not determinable in the section 

studied. It incloses small crystals of augite, biotite, and 

magnetite. _ The remaining constituents (biotite, magnetite, and apatite) are in smaller crystals which, except 

where they occur as inclusions, as noted above, form a 

matrix for the augite and plagioclase. The rock shows 

twice as much apatite in the norm as No. 6 in the table on 

page 43 and more than three times as much as No. 5. 

Magnetite is notably more abundant than in any of the 

other rocks thus far described. 

The norm of this rock as computed by H. S. Washington 

is as follows: 

Orthoclase .. . .. • .. . .. .. 13. 62} F=26 41} 

Anorthite .............. 12.79 · 

Leucite ............... -. 2. 83} Sal, 32.65 

Nephelite.............. 3. 41 L= 6. 24 

g:&:~~-- ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~-~ ~ ~ ~~: ~~}P+0=29. 69l . 

Magn.etite .............. 2

4

3 .. 8

90

6

} M=2S. 76 Fern, 65. 17 

Ilmenite ...... _ ......... . 

Apatite................ 6. 72 A= 6. 72. , 

Sal _32. 65 01 - "I r d f Fern - 65_17 , ass "\, o emane. 

P+O 29. 69 cl . ----y---=28_ 76 , or er 3, svengare. 

p 11.99 . ( . o=l7. 70' section 3 4), uteiare (new name). 

MgO+FeO 404 . CaO" = 130, rang 2, eldorase (new name). 

MgO 197 . FeO = 207 ' subrang 3, eldorose (new name). 

Formula, 11IV.3.3(4)·2.3. 
TERTIARY ( ? ) INTRUSIVE ROCKS. 47 

For the section to which this rock belongs 

the writer proposes the name uteiare, from 

Ute Mountain, about 3 miles south of Eldora, 

and for the rang and subrang the names 

eldorase and eldorose, respectively, from the 

town of Eldora, 2! miles south of Caribou. 

Rocks still rich~r in magnetite belong to two 

distinct types, one composed essentially of 

magnetite, olivine, and augite and the other 

of n1agnetite and augite. Both occur within 

the san1e ore body, but their relation to each 

other could not be determined in the field 

because of the close similarity in megascopic 

appearance of the two .types. 

The magnetite-olivine type is represented by 

a specimen collected half a mile south of Caribou; its petrographic description is as follows: 

Magnetite peridotite (cardinttlose; analysis 8, p. 43). 

This is a dark-gray rock, semlmetallic in appearance fro~ 

tho abundance of magnetite, which stands out prominently 

in relief on weathered faces. Tho microscope shows 

augite, olivine (mainly altered to serpentine), and magnetito as the principal constituents. .The augite, pale gr~en 

and nonpleochroic, forms euhedral to subhedral grains 

from 0. 3 to 3 millimeters in diameter. It sho"'s incipient 

alteration to hornb~ende. Olivine is about equal to 

augjte in abundance and forms subhedral grains from 

0.3 to 1.0 millimeter in diameter. It is now mainly 

altered to serp~ntine, which accounts for the high percentage of combined. water in the analysis. Some magnetite grains are inclosed by olivine or by augite, but 

most of the magnetite forms a matrix between the olivine 

and augite grains. With the exception of the ma~netite 

inclusions the order of crystallization was (1) olivine, 

(2) augite, (3) magnetite. 

'l'he norm of this rock as calculated by H. S. Washington 

is as follows: 

Albite............ . . . . . . 1. 571 F 8 52 S 1 8 52 } '= . a' . Anorthite. . . . . . . . . . . . . . 6. 95 J 

Diopside............ . . . 21. 03}P+0=50. 72} 

Olivine ................ 29. 69 . Fern 87.44 

Magnetite... . . . . . . . . . . . 3

5

1 .. 5

17

5} _M=S6. 72 ' 

Ilmenite: .............. . 

Sal 8. 52 Cl V" f l!"'em =s7. 44 , ass , per emane. 

P+O 50. 72 l 113 • ~M-= 1 1 36. 72 , ore or , 1 1oc are. 

~=;~: ~~' section 311, bouldiare (ne~ name). 

MgO+l!'eO 668 ( d' al ( ) CaO" 96 , mng 1)2, car m ase. new name . 

~:g =~~~' subrang 211, cardiualose (new name). 

Formula, 11 113.gN.(1)2.2~.~. 

For the section to which this rock belongs 

the nmne "bouldiare" is proposed, from 

Boulder County; for the rang and subrang 

tho names "cardinalase" and "cardinalose," 

respectively, are proposed, from Cardinal station, 2 miles southeast of Caribou. 

The second type of iron ore is exemplified hy 

a specimen from the body of ore half a n1ile 

south of Caribou, described below. 

Magnetite pyroxenite.-This rock is similar in megascopic 

appearance to the magnetite peridotite of analysis 8 

(p. 43). The microscope shows that ~ts principal constituent is augite (extinction angles as great as 45°) in euhedral 

to subhedral grains showing some alteration to hornblende. 

The remainder of the rock is magnetite, mainly intersertal between the augite grains, though a few small grains 

are inclosed by augite. Apatite is absent. 

Another magnetite pyroxenite from the body 

of iron ore just northwest of Caribou is identical with this one in every respect except that 

it contains a fair abtmdance of apatite. 

No analyses were made of the magnetite pyroxenite collected by the writer, but Jennings 1 

has published an analysis of ore of this typ<3 

which is given· as No.9 in the table on page 43. 

The Illinerals present he determined by microscopic study to be the following, the percentages being calculated from the analysis: 

Ilmenite . . . . . . .. . .. . . . . . . . . . . . . . . . . 8. 50 

Magnetite ........................... 67.25 

Apatite ........................... :. . 18 

Spinel. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6. 70 

Diops:ide 2 • • • • • • • • • • • • • • • • • • • • • • • • • • 16. 89 · 

From Jennings's analysis the writer has calculated the norn1 of this rock as foUows: 

Anorthite ................. 16. 65 F=16. 65}sal, 17.

25 Nephelite................. . 57 L= . 57 

Akermanite............... • 29} 0 Olivine ....... ·............. 4. 88 = 5·

17 

Magnetite ........ · ......... 64. 73} 

Ilmenite .............. '..... 8. 51 M=76. 66 Fem, 82·

17 

(Mg, Fe)O................. S. 42 

Apatite................... . 34 A= . 34 

Sal 17.25 Cl 1..., d f Fem = 82_

17, ass ~ , o emane. 

8= ::!~, order 115, cordillare (new name). 

~=~~5~ , section 1(2), cordilliare (new name). 

MgO+FeO 480 Ca011 7 , rang 1, pomerase (new name). 

MgO 129 · FeO = 351, subrang 4, pomerose (new name). 

Formula, IV."5·1(2)·1.4. 

For the order and section to which this rock 

belongs the wri tor proposes the names cordillare and cordilliare, respectively, from the 

Cordillera, or great mountain system of this 

1 Jennings, E. P ., op. cit., p. 23. 

2 Augite according to Bastin's studies. 
48 .GEOLOGY OF GILPIN, CLEAR CREEK, AND BOULDER COUNTIES, COLO. 

region. For the .rang and subrang the names 

"' pomerase" and'' pomerose" are proposed, from 

~omeroy Mountain, just north of Caribou. 

NATURE OF THE DIFFERENTIATION. 

It has been· well established, principally 

_through the researches of Vogt 1 and of Kemp, 2 

that the titaniferous iron ores are almost exclusively products of magn1atic differenti&tio~. 

It has further been shown by V ogt 1 that in 

most of the 500 or so known occurrences of 

ti taniferous iron ores the parent rock was a 

.gabbro or norite or rarely an augite or nephelite 

syenite. The amount of silica in the parent 

~ock is generally between 48 and 54 per cent, 

lmm. 

FIGURE 2.-Titaniferous iron ore from Caribou (after E. P. Jennings). 

Dark areas are magnetite and ilmenite; light areas are augite. 

more rarely between 54 and 56 per cent. 

Vogt 3 believes that in the somewhat metamorphosed deposits of the Rodsand-Erzfeldes 

in Norway he can trace the process of magmatic differentiation from a granitic parent 

magma into a gabbroid magma and finally into 

the iron ores. The Caribou deposits show a 

. somewhat analogous mode of occurrence, in 

which a parent magma of monzonitic character 

(51.43 to 56.64 per cent Si02 and 0.76 to 0.94 

per cent Ti02 ) has differentiated into gabbroid 

rocks (30'.47 to 44.66 per cent Si02 and 1.41 to 

t Beyschlag, F., Krusch, P., and Vogt, J. H. L., Die Lagerstatten der 

nutzbaren Mineralien und Gesteine, vol. 1, pp. 247-253, 1910. Also Vogt, 

J. H. L., Zeitschr. prakt. Geologie, vol. 8, pp. 233-235, 1900. 

s Kemp, J. F., A brief review of the titaniferous magnetites: Columbia 

School of Mines Quart., vol. 20, pp. 323-356; vol. 21, pp. 56-65, 1899. 

a Vogt, J. H. L., Zeitschr. prakt. Geologie, vol. 18, p. 65, 1910. 

2.56 per cent Ti02 ), and thes~ into the iron 

ores. In the majority of described occurrences 

of such ores the 'fi02 content of the parent rock 

is from 0.3 to 1.0 per cent, but that of the derived iron ore does not generally fall below 4 

or 5 per cent and in many deposits exceeds 15 

per cent. 

In the Caribou ores .evidences of origin by 

magmatic differentiation are found (1) in the 

general form and situation of the bodies of 

gabbro and· iron ore which are irregular bodies 

lying wholly within 'the monzonite stocks; 

(2) in observed transitions from iron ore to 

gabbro and from gabbro to monzonite, an evidence whose validity.· is not annulled by the 

presence in a few places of sharp contacts 

between these different rock types; (3) in the 

consistent character of the variations in chemical composition~ as shown in the diagram on the 

opposite page; (4) in the m~neralogic gradation 

traceable from one rock type to another, notable features being the marked uniformity in 

the optical characters of the augite in all the 

rocks and the presence of olivine not only .in 

certain iron ores but in certain of the gabbros 

and n1onzonites as well. 

Jennings 4 ·regarded the iron ores as differentiations at depth f1·om the monzonite magma 

(which he termed orthoclase-biotite gabbro), the 

differentiation products having later been intruded into their present. position. The writer's 

observations indicate that they are in part differentiations in place. 

A feature of especial interest in this deposit 

is the dual character of the differentiation, 

which produced within the same gabbro body 

masses of iron ore consisting solely of magnetite, iln1enite, and augite (fig. 2), and others carrying abundant olivine. This feature is showil 

in. the diagram forming figure 3. The tendency for differentiation to proceed along two 

lines,. one of which leads to rocks very rich in 

magnesia, is apparent eveii in the more felsic · 

rocks of the Caribou district, for some of· the 

monzonites are olivine-bearing; strictly, therefore, the broken lines in figure 3 should probably · 

extend farther to the left. The process 

appears to be somewhat unusual or at least 

has not hitherto been described. Vogt 5 noted 

in certain Norwegian deposits two correlative 

lines of d~fferentiation, but they led not to two 

4 Jennings, E. P., op: cit., pp. 24-25 

6 Vogt, J. H. L., Zeitschr. prakt. Geologie, vol. 8, pp. 234-235, ~000. 
TERTIARY ( ? ) 'INTRUSIVE ROCKS. 49 

types of iron ore but to spinel-bearing iron 

ores along one line and to olivine gabbros and 

peridotites very poor in iron oxides Rlong the 

other line. 

0 

01 

0 

HORNBLENDE.MONZONITE PORPHYRY. 

General character.-The distinguishing characteristic of the hornblende monzonite porMOLECULAR PROPORTIONS 

)> s;' 

•\ i 

(For Si02 one-half the molecular proportion was used. Silica line therefore has 

half ·,ts proper gradient) . 

Monzonites 

Minor chemical features 

worthy of n1ention are the 

small percentage of . sulphur, increasing slightly 

toward tho iron-ore end of 

the series, the presence of 

small an1ounts of cob.alt 

but no nickel in some of 

the rocks, and the absence 

of chr01nimn in all that 

wore tested for this metal. 

~~~~~~~~~~-~-r------------,~----~ 

~ w 

Specimens of lean iron 

ore frmn Caribou are ~ 

~~n in fu~TI,B i ~~~~---~~~~--~G=a=~=r=o---~~---~---~ and 0. Co) 0'> b 

DIKE ROOKS NEAR NEDER- ~· 

LAND. ~ 

Tho area between Cari- [ 

bou,Nederland, anclPhoe- 5' 

nix contains a profusion of i 

dikes of prevailing east- g 

orly trend, of types not [ 

found elsewhere in thoro- "' 

gion. 'rhoy include horn- ! ~ b]endo monzonite por- ~ :j "' 

phyries, hornblende and ~· ~ ~1--!¢'-<i--+---o-~---r~-jr.<r--t--==~"---'....;.:;,;.o~=....:::......--=----J 

biotite andesites, and ., 

hornblende and biotite diOI'ites, many of tho latter a 

being very dark colored. ~ 

The distribution of the dif- = 

~ feront types is shown on (') 

Plato I (inpocket). These ~ 

various dikes are not F 

wholly contemporaneous, 

for at a number of places 

diorite dikes were observed to cut those of andesite. Nevertheless, it 

somns probable that the 

ago differences are not 

very great and that the 

dikes of all the types were 

differentiated from a common parent magma of 

m.onzonitic composition, 

as explained on page 38. 

·z:>:· 

QIN 

NO 

0 

Magnetite pyroxenite 

(Iron ore 

These dikes appear to take the place in the phyry is the great abundance of green horn-

~oderland area of the monzonite dikes so blonde phenocrysts, which in places attain a 

common in other parts of the region. length of 12 millimeters, though commonly 

. 44214°-17-4 
\, 

50 GEOLOGY OF GILPIN; CLEAR CREEK, AND BOULDER COUNTIES, COLO. 

under 7 millimeters. In fre~h specimens these . tio:r1, but have much less perfect crystal outlines 

dark-green hornbl(mdes lie in a fine-grained than in most of ·the hornblende monzonite por-

(aphariitic) groundmass which is·dark-greenish phyries. The groundmass, appears gray and 

gray, so that they are not conspicuous; in aphanitic in the hand specimen but under the 

somewhat weathered specimens, on the other microscope is. seen to be coarse.r 'than in most 

hand, the groundmass w~athers lighter gray of the ,rocks of this group; it is composed of 

and. the hornblende phenocrysts, remaining laths of plagioclase having a greater index than 

dark, become very conspicuous. Feldspar balsam, orthoclase, and abundant biotite. Secphenocrysts are practically absent.. ondary carboqate is also abundant in · the 

i Distribution.-About ten dikes of hornblende groundmass. ·The rock may be termed a 

monzonite porphyry were ·observed, all in the hornblende-biotite monzonite porphyry. 

northeastern part of the region, between Eldora, Age and relations.-The ,hornblende monCaribou, Nederland, and Rollinsville. Their zonite porphJI:ies have not been observed to 

precise position is shown on Plate I. intersect any ! other rocks among the later 

i Features in detail.-One of the freshest intrusives of the region. One dike southeast 

specimens of this rock came from the slope of of Caribou has been traced continuously into 

Eldorado Mountain, about three.:.fourths of a the Caribou stock of monzonite; for this reamile east of Eldora, and may be regarded as son and from the more general considerations 

typical for most of these dikes. It ~hows outlined on page 38, these rocks ~re believed 

~greenish-gray aphanitic groundmass in which to be contemnoraneous with the neighboring 

lie abundant prisms of nearly: black horn- monzonite stocks and therefore probably of 

blonde, a few of them 12 millimeters in length. 'Tertiary age. 

N 0 feldspar phenocrysts were certainly recog- . HORNBLENDE AND BIOTITE ANDESITE. 

nized. ·Under the microscope the pheno- General character.-The hornblende and biocrysts of green pleochroic hornblende show tite andesites are medium-coarse rocks that 

Partial alteration to chlorite and calcite. The 

are dark gray when fresh and buff or nearly groundmass consists mainly of minute .feld- white on weathering. Many variations were 

spar laths, many of which are plainly lower noted, from rocks so crowded With pheno- than balsam in index of refraction and do crysts that they are ah:nost granitic in appearnot show polysynthetic twinning; they are ance through others with only scattered phenoprobably orthoclase. Other feldspars of the crysts into felsitic phases which caD. be identigroundmass are above balsam in index of re- fied as belongi~g to this rock type only because 

fraction, show polysynthetic twinning, and 

are evidently plag!oclase. Small grains of gradation h~. been traced in a few places. 

mab&netite which are very abundant in the The constituent o~iginal minerals are plagio- clase;either hornblende or biotite, or both, and groundmass probably cause its dark color. 

Secondary calcite is also abundant in the small amounts of magnetite and apatite. · Every gradation is traceable from phases in 

groundmas. s, usually in small grains but locally which hornblende is the predominant iron- in irregular masses 1 to 2 millimeters across. bearing mineral into phases in which biotite is 

A little quartz associated with ·the. calcite is predominant. 

probably also secondary. There are a few These rocks occur exclusively as dikes, the 

small apatite prisms. greater number of which are ~oo much 

A phase of the· ··hornblende monzonite weathered at their outcrops to yield good 

porphyry which differs from the common type material for microscopic study. 

in carrying fairly numerous phenocrysts of Distribution.-The andesite dikes are confined 

feldspar crops out along the small valley to the area near Nederland, Caribou, and Eldora, 

between E:icks Gulch and Coon Trail Creek. where they are much more numerous than the 

It is dark gray on fresh exposures and shows dikes of hornblende monzonite porphyry. 

abundant phenocrysts of hornblende and less Their general trend is nearly 'due east. 

abundant phenocrysts of feldspar as m:uch as Features in detail.-Most of the andesites 

5 ·millimeters across. The feldspar pheno- are typically porphyritic, the phenocrysts 

crysts are· plagioclase, apparently andesine. being feldspar and either hornblende or bioThe hornbhmde· phenocrysts show little altera- · tite or both. The feldspar phenocrysts, so 
TERTIA~.Y < ?1 · nttRusrvE IWCKS. · 51' 

far as could be determined, are a~l plagioclase :diorite; as described on page 52; but no ex~ 

and are usually under 3 millimeterS in diameter ; posures showing their relations to the later 

though locally reaching 6 millimeters. Usually !intrusive rocks of other types wer~ noted. 

their exact character is masked by alteration For· the reasons already outlined on page 38 

products, but in two slides their composition the andesites are believ.ed to have been derived. 

w~s determined as Ab65An35 (aridesine). The . by processes of magmatic differentiation from. 

hornblende phenocrysts are rarely fresh, some ·the n1onzonite magmas of this region and,. 

of them 'being altered to biotite and· others to like the monzonites, to be of Tertiary age. 

an association of epidote, calcite, and chlorite. · · 

d HORNBLENDE AND BIOTITE DIORITES. Though usually much smaller, some in a ike 

near the Jasper mine, in Hicks Gulch, ·were General chm·acter.-The hornblende and bio-· 

2 centimeters long and 5· or 6 millimeters in tite diorites, which are dark gray to nearly 

diameter. Some of the biotite phenocrysts black on fresh surfaces, have as principal conare fresh, but many are altered to a mixture stituent$ plagioclase, hornblende, biotite, magof muscovite, biotite, and iron oxide. They netite, and their a~teration products. Some 

range from 1 to 3 millimeters in diameter. ;varieties are porphyritic and others massive. 

The· groundmass is finely microgranular and In the porphyritic varieties the ·prominent 

consists of an aggregate of altered feldspar of phenocrysts may be feldspar, biotite, or rarely 

indeterminat.e species, locally with: some horn- hornblende. Orthoclase was not observed, 

blende and secondary sericite and calcite. and the plagioclase is in general more calcic 

Magnetite is abundant in small: grains and than in the andesites. The iron-bearing minapatite in small short prisms. orals are more abundant than in the andesites, 

One of the freshest specimens collected was and the rocks are correspon9-ingly darker in 

obtained from a dike about half a mile north- color. They occur exclusively as dikes. 

east of Eldora and shows both hornblende Distribution.-The diorite dikes are confined 

and biotite. Megascopically this rock is gray to the region north of Nederland and between 

in general tone and shows light-gray stubby that town and Caribou. Two dikes recognized 

prisms of .feldspar averaging 2 to 3 milli- on the surface are shown on Plate I, and a 

n1eters in length, a few phenocrysts 9f biotite number of others are cut in the Boulder 

as n1uch as 2 millimeters across, and lath- County and Alton tunnels. 

shaped phenocrysts of what appears to be Features in. detail. _.f._ A diorite porphyry 

altered hornblende reaching 4 millimeters in having conspicuous phenocrysts of feldspar 

length. The phenocrysts are so closely crowded crops out about ll miles northwest of Nederthat the groundrnass is very inconspicuous. land,. along the northern road leading to the 

The 1nicroscope shows that the feldspar pheno- Boulder County mine. Greenish-gray feldcrysts are plagioclase of the averu.ge composition spar phenocrysts from 2 to. 3 millimeters 

Ab65An35 (andesine) 1 ~hough they, show some across are scattered in moderate abundance 

zonul structure. They are partly altered, s~ri- through a nearly black aphanitic groundmass.-

cite and calcite having been developed. The Under the microscope the feldspar phenophenocrysts of biotite are practically unaltered. crysts were determined to have a composition 

Son1e aggregates of small plates o{. biotite and about Ab25An75 (bytownite). No quartz or 

grains of. calcite in the groundmass are irregu- orthoclase was recognized. The groundmass 

lar in outline, but others have the prismatic shows laths of plagioclase. (well above balsam 

form and. six-sided cross se.ction chn.racteristic in index of refraction) disposed in all direcof hornbl'ende. It is probable that they rep- :tions, very abundant biotite and magnetite, 

resent the alteration products of this mineral. ,and much secondary calcite and chlorite. 

The groundmass is a microgranular aggregate , A representative of the varieties in which 

of unstriated feldspar, probabiy orthoclase, a ·biotite is the most conspicuous mineral 'in 

little quartz, and secondary calcite ·and sericite. th~ hand specimen is exposed in the Boulder 

Grruns that wore originally magnetite are now County tunnel about 725 feet from the portal. 

largely altered .to hematite. This rock is nearly black on fresh surfaces 

Age and relations.-At several places the and shows a profusion of crystals of various 

andesites were observed to be cut by dikes of :sizes, the largest 6 millimeters. across. The 
52 GEOLOGY OF GILPIN, CLEAR CREEK, AND BOULDER COUNTIES, COLO. 

texture is porphyroid rather than porphyritic, 

~s there is every gradation from th() large 

b~otite crys.tals to those that are very minute. 

·The microscop~ shows that biotite is the most 

abundant constituent. The other l;Ilinerals 

il,r~ ·plagioclase feldspar (well above .balsain in 

incJex), magnetite in smal.l grains, and abundant secondary calcite. The rock. contains a 

little quartz, which is probably secondary. 

. The freshest specimen of the highly hornblendic type of the diorite came from a· 6-inch 

to 1-foot dike in the Boulder County tunnel. 

This dike is cut by the Boulder County vein 

about 200 feet east of the line of the tunnel. 

It is a very dar;k gray .aphanitic rock which 

under the microscope shows green hornblende 

as. its principal constituent. This mineral 

forms laths of diverse size and orientation, the 

spaces between which are occupied by plagioclase feldspar of a high index of refraction 

and by abundant grains of magnetite. Small, 

stubby phenocrysts of plagioclase occur spar-

'ingly, but they are partly sericitized and their 

exact composition can not be determined. The 

metasomatic alterations which have affected this 

rock close to the vein are described on page 111. 

Age and relations.~The highly .micaceous 

varieties of the diorites, like that last described, are shown at several points in the 

Boulder County. tunnel to he later than hornblende-biotite· andesite dikes. Where dikes· 

of these two types intersect·the andesites show 

no change in texture near-the contact, whereas 

the diorites become finer grained and nonporphyritic within one-fourth or qne-half inch 

of the "froz~n" contacts. .The diorites are, 

however, older than the Boulder County ·vein, 

.which distinctly cuts them, ill places with 

"frozen" -contacts. Like the other younger 

intrusive rocks; the diorites and diorite porphyries are ·believed' to be of Tertiary age. 

The grounds for this belief have already been 

stated (p. 38). . ·, 

BOSTONI'.I;E. AND BOSTO~ITE PORPHYRY. 

GEJiERAL CHARACTER. 

DISTRIB:l:J:TION'. 

These rocks occur mainly as dikes, which 

exceptionally expand into lens-shaped masses 

an eighth of a mile or so across. Some of the 

dikes are of extraordinary lengths, one being 

traceable continuously from the Topeka mine, 

near Russell Gulch, northwestward for 4! 

miles. The distribution of the bostonite dikes 

between the camps of Russell Gulch and 

Nevadaville is· noteworthy, for they radiate 

from a· center near the Topeka mine in much 

the fashion that nerves radiate from a ganglion. Expansions of the dikes into narrow 

stocks occur 1 mile southeast of Dumont and 

1! miles north of Lawson. 

The bostonite and bostonite porphyries 

are confined mainly to those parts of the 

surveyed area lying southeast of Mammoth 

Gulch and east of Empire. 

Ball 1 describes bostonites occurring in the 

northern part of tlie · adjacent Georgetown 

quadrangle; there also they attain greater 

lengths than the Tertiary ( ~) dikes of any other 

type. 

FEATURES IN' DETAIL. 

Though not always distinguishable from 

'certain monzonite porphyries without :rp.icroscopic study, most ·of the bostonite porphyries 

m~y be readily recognized because of their 

pinkish,. lilac-colored, or reddish-brown body 

or groundmass through which are scattered 

pearl-gray or salmon-colored ph,;mocrysts of 

feldspar, commonly under 5 millimeters in 

length, though a few are as long as 1 or even~ 

centimeters. Some varieties contain green 

prisms of' pyroxene or its alteration products 

as· much as 5 millimeters in length. Ball 

nott3d' some 2.5 millimeters long 4I dikes in 

the Georgetown quadrangle. Penetration twins 

ill. which the individuals join each other at 

angles of 60° are not uncommon. 

. The nonpyroxenic bostonite porphyries are 

not readily differentiated without the aid of 

the. microscope from certain monzonite por-

·phy. ries of the region bet we_ en Apex, Perigo, 

· · · · and Phoenix, which have a pinkish groundmass, The bostonite~ of the ~ntral City quadrangle f h · . . . but microscopic examination o t e monzonites 

are gra~ to lila~-col~red or.reddish-brown, very shows that the roundmass is granular rather 

:fine gra~ed (miCrocry~talline) ~o~ks compos~d than· trach tic,~ as in the bostonites. In 

:pre~9minantly of alkah fel?s~ar Wit~ only small I most of th: hostonite porphyries the phenoamounts of ~u~rtz. ,V an~ties havPlg pheno- cr ts are wide! scattered, and many or' them 

c.rysts of alkali 9r alkali-calcic feldspar or of py- __:ys ____ · __ Y ____________ _ 

.roxene, Or both, a,re termed bostonite porphyry • 1 Ball, S. H., op. cit., P· 78. 
U. S. GEOLOGICAL SURVEY 

A . BOSTONITE PORPHYRY FROM A POINT NEAR 

IDAHO SPRINGS, SHOWING CHARACTERISTIC 

TRACHYTOID TEXTURE. 

In certain areas of rounded outlin e quartz poikilitically 

embeds the feldspars. Enlarged. 

PROFESSIONAL PAPER 94 PLATE XI 

B. LEAN IRON ORE FROM CARIBOU, SHOWING 

MAGNETITE AND ILMENITE AND AUGITE. 

Bl ack areas are magnetite and ilmenite; gray areas 

are augite. Enlarged 16 diameters. 

0. LEAN IRON ORE FROM CARIBOU, SHOWING MAGNETITE AND ILMENITE, 

AUGITE, AND SERPENTINE. 

Black areas are magnetite and ilmenite, white areas are serpentine formed by the alteratio n 

of olivine; some unaltered olivine remains and is gray. Enlarged 29 diameters. 
U. S. GEOLOG ICAL SURVEY PROFESSIONAL PAPER 94 PLATE XII 

A. OUTWASH PLAIN OF LATER GLACIAL EPOCH IN VALLEY OF MIDDLE BOULDER CREEK 

BETWEEN ELDORA AND NEDERLAND, LOOKING EASTWARD. 

B. HORNBLENDE SCHIST OF IDAHO SPRINGS FORMATION INTRUDED BY PEGMATITE 

NEAR ELDORA. 
TERTIARY ( ? ) INTRUSIVE ROCKS. 53 

show rhombic outlines. The non porphyritic Analys1':s of bostoniie from Red Lyon lode, Idaho Springs 

bostonites when ·fresh are usually · recogni- . district, Colo. 

zable by their lilac Or reddish-brown color, [W. T. Schaller, analyst.] 

·but where altered by surface weathering or by Si02........ .. .. . . . . 67. 41 · C02:.............. o. 56 

mineralizing solutions they are·usually bleach,ed Al20a................ 16:23 P20s-............. . 05 

buff and· can not then be ·distinguished with- Fe20a .. -- ·------.... · 85 SO a .... ·----·------ None. 

out 1nicroscopic exmnination frmn fine-grained ~~~--- ~:::::::::::: 1

: ~: ~~~ ~::::::::::::: :. ~ ~~::. monzonites. CaO................ .14 MnO .. _. __ ......... .16 

Under the microscope the boston1ites and the N~O............... 3. 95 BaO ................ Trace. 

grow1dmass of the bostonite porphyries ex- K20............... 7.19 SrO ............... None. 

hibit a characteristic trachytic Of trachytoid H20-... · · · · · · · · · · · 67 Li20 ................. None. 

texture not observed in any of the' mon·zonites. H20+ .... ·........ · · 

88 99.65 Ti02... .. . . .. .. .. . .16 

(See Pl. XI, A.) This texture is ptoduced Zr02 ......... ..... • .11 

by thin tabular crystals of feldspar 0.05 . u .rb . . r. R d L · · · l .1 • 

· · · 1 h h' h · 1.vorm o, ostontte,rom e yon oue. to 0.5 1111llnneter 1n engt , w w 1n some , .. . . . · 

places are oriented in all directions but el.se-: ~ Q_uartz · · · · · · · · · · · · · · · · · · · · · 15.42 Q:l5. 42\ 

where at·e in subparallel arrangement indicativ~ · ~~con 1 ••. • • • • •• • • • · · · · · · · · · · 1

'

1

5

8

3 zc=- 1

' 5

18

3 Sal·· 94 . \JOrunc urn.......... . . . . . . . . . . , .. o:~ ., 1 of flowing tnovement during cooling. The~e Orthoclase .................. 42. 81} · · 

crystals are soda-potash feldspar (anortho- Albite ....................... 33 .. 54 F=77.18 · :· •' ,. 

clase) and between them are irregular grains of AnortJ;Ute ... · ·- · · · ...... :.-- . 83. .. · .. , ~ . 

orthoclase. Quartz is present in the ground- Ilmemte. · · · · · · · · · · · · · · · · ·-- · · 

30} M= 1. 46\ . r • 

f . d · l h ll Magnetite................... 1. 16 

mass o some specrmens an party or w o Y Hypersthene: Fem,3.18 

en1beds a number of anorthoclase crystals. Iron metasilicate........ 1. 32} P= 1 72 The feldspar phenocrysts may all be anortho- Magnesium silicate...... . 40 · 

clase, or some may be anorthoclase and some H20, C02, and P20snot included in norm ..... ·:... 2.16 

orthoclase or oligoclase. Phenocrysts of sal- 99. 65 

mon-colored feldspar from one of the fresh- ::~ ::i~, Class I, persala~e. est ·specimens were crushed and examined Q+F 92_60 

microscopically. The index of refraction de- cz = 1.71' Subclass I, persalone. 

termined by the imtnersion method lay between Q_15.42 · d 4, 1 · 

1

,-77_

18, or er , )nttanare. 

1.52 and 1.53. The angle deter:mined on 0'+N~O' 141 . cleavage plates parallel to 010 between the CaO' 3 , rang 1, hparase. 

plane of the optic axes and the cleavage 001· K 20' 77 b 

3 1

. 

l f 4o t go Th t' · N~~- ,= , su rang , tparose. rangec rom o . ese . proper 1es · post- -~ 

tively identify the feldspar as anorthoclase. Formula, I.}· 4'.1.3. 

Scattered prismatic phenocrysts, usually under oRIGIN AND RELATION To oTHER Rocxs. 

5 tnillimeters in length, are .green pyroxene or Th~ bostonites and bostonito porphyries· 

its alteration products (hornqlencle or chlorite are intrusive in all the pre-Cambrian rocks of 

with calcite and magnetit.e). . the quadrangle. For the reasons ·given on 

By sericitizatio1,1, through the influance of . page 38 it i~. thought probable that. they·came 

mineralizing solutions, bostonite becomes' from the ·same magmatic SOUrce fi:S tho mollgreenish white; through calcitization and kao- zonites and monzonite porphyries and, like 

linization it bleaches; and through hydration them, are of Tertiary ag~. 

of its ·iron-bearing minerals it takes on various Mesozoic· ·robks . which, like the bostonite 

shades of yellow and brownish red. analyzed, fall in the subrang, liparose of the 

An analysis of bostonite from the Reel Lyon quantitative system occur in the Leadville 

lode, near Idaho Springs, is given by Spurr and and Silver Cliff districts and at Nathrop and 

Garrey,t but the position of the rock in the have been described by· Cross, and similar 

American quantitative system was not 'calcu- rocks were collected by E. B. Mathews in the 

lated by them. The analysis is repeated be- Pikes Peak region .. 2 Although no genetic 

low, and from it the norm has been calculated. connection can be assumed between these 

1 U.S. Geol. .Survey Prof. Paper 14, p. 149, 1903. 2 U.s.· Geol. Survey Prof. Paper 63, p. 134, '1908. 
.:S4 GEOLOGY OF GILPIN, CLEAR CR~E~, AND BOULDER COUNTIES, COLO. 

occUITences of liparose, magmas· of liparose I . . FEATURES IN DETAIL. 

composition were .e~dentl~ not uncom~on The granite porphyries to the unaided eye 

among the Mesozoic Intrusives and effusives show a finely crystalline groundmass of granuof Colorado. lar appearance and pale-pink color Through 

BASALT ~ORPHYRY. this are sparsely scattered phenocrysts of 

A single dike of typical basalt porphyry 4 gray. and pink feldspar under 3 millimeters in 

feet in width was cut in the Freeland tunnel, diameter and phenocrysts of light-gray quartz 

near Dumont,· at a distance of about 3, 185 nearly 1 centimeter in diameter and usually 

feet from the portal.. It is unlike any dike somewhat irregular in outline. 

found elsewhere in the quadrangle. The rock The microscope shows that the groundm8$S 

is nearly black, fine grained, ·and blotched with is a granular aggregate of quartz and orthoa few round areas of calcite that give it an clase in anhedral crystals, the feldspar slightly 

am.ygdaloidal appearance., It is made up of predominating in amount. Some plagioclase, 

augite, biotite, calcic plagioclase, magnetite, apparently albite, is perthitically intergrown 

and secondary calcite and serpentine. The with the orthoclase. Much less abundant than 

·phenocrysts ·are pseudomorphs of calcite and either quartz or feldspar are very small flakes 

:serpentine after olivine, the characteristic of biotite and grains of magnetite. These 

structure and cryst~l outline of which are iron-bearing minerals are not recognizable 

preserved. The groundmass is a very finely to the unaided eye~ The rock contains also a 

crystalline aggregate composed predominantly few small prisms of apatite. 

of augite, with brown biotite, magnetite, and AGE AND RELATIONS. 

calcic plagioclase in lesser amounts and smaller 

crystals. All the minerals of the groundmass are euhedral or subhedral, and the 

, feldspar serves as a matrix for the ironbearing minerals. With the exception of the 

olivine alteration the rock is perfectly fresh. 

There are a few sniall calcite amygdules. 

GRANITE PORPHYRY. 

GENERAL CHARACTER. 

7 

Three small qikes of porphyry just north. 

of Idaho Springs (see Pl. VI, in pocket) differ. 

The granite porphyry dikes bear the· same 

intrusive relation to the pre-Cambrian rocks 

as· the neighboring monzonite and bostonite 

dikes. They were not observed in contact 

with any of the other porphyries, but it is 

considered probable that they belong to th~ 

same general period of· igneous intrusion 

and are therefore probably Tertiary. 

ALKALI SYENITE PORPHYRY. 

GENERAL CHARACTER. 

from any of the other porphyries of the region The alkali syenite porphyry, which is not 

in having a granular groundmass whose . widely' distributed, varies considerably in 

-component grains are of unusual coarseness, so appearance from place to place, but the 

that even to the unaided \)ye tho groundmass most abundant facies is a light bluish-gray, 

:appears distinctly granular. These rocks are coarsely porphyritic rock carrying phenocrysts 

pale pinkish and show sparsely scattered of pyroxene, brownish garnet, and vitreouspheiwcrysts of quartz and feldspar; the entire looking gray feldspar. 

rock consists mainly of these two minerals. 

DISTRIBUTION. 

The granite porphyry was noted only as 

three small dikes cropping out a short distance 

northwest of Virginia Butte, on the ridge forming the west wall of Virginia Canyon. It is 

not certain that this rock corresponds to the 

granite porphyry of the western part of the 

Georgetown quadrangle, described by Ball.1 

1 Ball, S. H., op. cit., pp. 75-77. 

DISTRIBUTION. 

This rock occurs as a small stock having a 

surface diameter of 0.15 mile on the south 

side of Clear Creek, east of the mouth of Soda 

Creek. The syenite intrudes the pre-Cambrian 

rocks, inclosing near its border numerous 

fragments of the Idaho Springs formation. A 

dike of somewhat similar rock 0.2 mile long 

and 8 feet wide occurs southeast of the main 

mass; it strikes northwest and dips 60° NE. 
TERTIARY ( ? ) INTRUSIVE ROCKS. 55 

FEATURES IN' DETAIL. 

An abbreviation of Ball's description of 

these 'POrphyries1 is given below. 

The most conspicuous phenocrysts are 

greenish-black crystals . of regirite-.augite as 

much as 3 millimeters in length ana generally 

fresh. Many of them show zonal structure, 

and although some are partial crystals, other8 

. are little more than rounded grains. Less 

· abundant than pyroxene are phenocrysts 

of brownish-black garnet with metallic luster, 

reaching 1 centimeter in diameter. The garnet 

appears dark brown under the microscope and 

shows faint zonal growth; it is probably nlelanite. Son1e of its larger crystals inclose phenocrysts of other minerals~ Less conspicuous, 

but n1ore abundant than either pyroxene or 

garnet, are phenocrysts of whitish-gray feldspar, mostly anorthoclase, although a few are 

orthoclase. They range from 3 ~o 15 millimeters in -length. Small crystals of titanite, 

magnetite, and apatite are accessory. In· one 

slide a few sn1all crystals of zircon and biotite 

were seen. 

The grounclmass in ·most places is subordinate in quantity to the phenocrysts. It is 

microgranitic in texture and is made up of 

irregular n1asses· of anorthoclase and some 

orthoclase, with a little quartz in some specimens. 

Analysis of alkali syenite (laurvikose) from south side oj 

Clear Creek, near Soda Creek. 

[George Steiger, analyst.) 

Si02 ••••••••••••••••• 60.30 

Al20 3 •••••••••••••••• 18.12 

Fe20 3 ••• •• ••••••••••• 2. 45 

FeO ................ 1. 25 

MgO................. .28 

CaO................. 3. 89 

N~O ................ 5. 83 

K2Q ............. :. . . 5. 01 

H20-.............. . 75 

H20+---··········· . 77 

Ti02···············.. ·.55 

Zr02 •••••••••••••••• 

C02 •••••••••••••••• 

P20a················ 

802················ 

F ................. . 

8 ................. . 

MnO ............... . 

BaO ............... . 

0.01 

None. 

. 25 

. 06 

None. 

None . 

.12 

. 26 

99.90 

Norm of alkali syenite from a.outh side of Clear Creek. 

Quartz..................... 1. 02 Q= 1. 02} 

Ort~oclase .................. _ 29. 47} Sal, 88. 08 

Alb1te ..................... 49. 25 F= 87. 06 

Anorthite................... 8. 34 

Apatite. . . . . . . .. . . . . . . . . . . . 34 A= . 341 

Ilmenite .. ~ . . . . . . . . . . . . . . . . 1. 06} 

Magne~te... . . . . . . . . . . . . . . 3. 02 M= 4. 40 Fern, 9. 96 

Hemat1te. . . . . .. . . .. .. . . . . . . . 32 

w.oll~tonite..... . . . . . .. . . . . 3. 71} P= 5_ 22 D10ps1de... . . . .. .. . . .. .. . . 1. 51 · . 

H20, Zr02, and S03 not included in norm........ 1. 59 

99.63 

Sal 88.08 

Fern= 9. 96 , Class I, persalane. 

Q+F 88.08 C+Z =-0-. , Subclass I, persalone. 

Q 1.02 F=s7. 06, order 5, canadare. 

K20'+N~O' 147 I CaO' 30 , rang 2, pulaskase. 

K201 _53. b ,

4 1· 'k N~O'-W' su rang , aurv1 ose. 

Formula, 1.1. 5.'2.'4. 

AGE AND RELATION'S. 

Fluorite is present. in irregular ramifying 

areas in the groundn1ass and In small areas 

flecking feldspar or regirite-augite. It was 

probably introduced after the solidification of 

the rock, possibly by gases, and in. part fills 

cavities between the minerals and in part re- · Concerning the age of the alkali syenite places them. Analcite occurs in sin1ilar small 

areas, which are, however, more largely con-. Spurr and Garrey 2 

say: 

fined to the groundmass. As it occurs in The rock is typically very fresh. Very near or at the 

thin sections of very fresh rocks, it is probably contact of these syenite intrusions carbonated springs . issue, some of which are hot and others cold. From the 

an original mineral, although it may be of fresh character of the rocks, their lack of connection with 

secondary origin. The sm~ll percentage ·of ore deposits, and their association with the only hot springs 

S08 in the chemical analysis indicates tho in the region, it is very likely that the alkali syenites are 

presence of haiiynite or nqsoan, alth~:mgh the youngest of the Tertiary intrusives. 

neither mineral was recognized in the thin The syenite is believed by Spurr and Garrey 

sections. to be younger than· the ore deposits, but the 

An analysis of a specimen typical of the evidence for this belief is presumptive and not 

commoner phases of the alkali syenite is given conclusive, as in the case of the biotite latite. 

below, and its position in the American quan- In brief, the alkali syenite may, on the gentit.ative system is shown also. oral grounds stated on page 38, be regarded as 

1 Ball, S. H., op. cit., pp. 82-83. s Spurr, J. E., and Garrey, G. H., op. cit., p. 135. 
56 GEOLOGY OF GILPIN, CLEAR CREEK, AND BOULDER COUNTIES, COLO. 

probably of Tertiary age and probably though I borders of dikes, and some of the phenocrysts 

not certainly slightly y~unger than most of have been fractured during the flowage. The 

the other supposed Tertiary intrusives. . accessory minerals present, named in the order 

·A number of trachytes and andesites from of abundance, are magnetite, apatite, and zirthe Rosita Hills 1 and the Pikes Peak region con. The rock constituents are remarkably 

in Colorado, described· by Cross, fall close to fresh compared with those of most of the other 

this rock in· the quantitative · classification. "porphyries." 

Most of these rocks are believed by Cross to An analysis ofbiotite latite from the valley 

be of early Tertiary age. of Chicago Creek was published in the report on 

, BIOTITE LATITE. 

GENERAL CHARACTER. 

Rocks of identical composition are termed 

"monzonite" or (( latite," according as the 

groundmass was originally.crystalline or glassy. 

The biotite latites of the Central City and 

Geo},'getown quadrangles consist of plagioclase, 

orthoclase, and biotite, in places with a little 

hornblende, embedded in a groundmass that was 

originally glassy ·or partly so. They are gray 

to light-brown rocks in which. small . phenocrysts. of fresh-appearing biotite are common. 

They have been noted only as short dikes 

from 5 to 10 feet in width. 

DISTRD3UTION. 

Within the area covered by this report biotite latite. has been seen only .in the ,Stanley 

mine workings, near Idaho Springs. In the 

adjacent Georgetown quadrangle they are con-. 

fined to the valleys of Chicago and West Chi:.. 

cago creeks. All have a general northeast trend 

and appear to lie along a single line or zone of 

intrusion. The biotite latite of the Stanley 

mine has not been observed at the surface. 

FEATURES IN DETAIL. 

the Georgetown quadrangle, 2 but the position 

of the rock in the quantitative ~ystem was not 

calculated. The analysis is repeated below, 

the position of the rock in the quantitative 

system is calculated, and the new name freelandose is proposed for it. This name is derived from Freeland, the na~e of a mining 

camp in the Georgetown quadrangle not far "from 

the places where these rocks have been found. 

Analysis of biotite latite (jreelandose) from Chicago C.reek, 

· Georgetown quadrangle. 

[W. T. Schaller, analyst.) 

Si02-.............. 66. 44 C02 ••••••••••••••• 0. 67 

Al20 3 ..... •••• ••• • • • 14. 98 P20 5 ••• •••••• ••••••• .11 

FezOa··············· 1. 57 S03 •••••••••••• · •••• None. 

FeO............... . 43 Cl. ................. Trace? 

MgO................ .18 S ......... ·. .. .. . .. . . 02 

CaO.·............... 2. 47 MnO........... .. . .16 

N~O............... 1.12 BaO................ .11 

K20... . .. . .. . .. .. . 3. 32 SrO ............... Trace? 

H20-.............. 4. 60 Li20 ................ None. 

H20+............. 4.06 

Ti02 ................ • 20 100.42 

Zr02•••••••••••••••• • 01 

Norm of biotite latitefrom Chicago Creek. 

Corundum.................. 5. 30 C- 5. 30 S 1 87. 93 

Quartz ...... : .............. 42. 06 Q:42. 061 

·Albite ... ·.................. 9. 43 F=40. 57 

Orthoclase........... . . . . . . . 19. 46} a ' 

In most of these rocks the· groundmass Anorthite .................. 11.68 

equals or. e~ceeds the. pheno.crysts in a bun- . Apati~e ........... ~. . . . . . . . . . 34 ~= . 34) 

d.anc!3. ;:Most. of the feldspar. phenocrysts are Ilmemte. · · · · · · · · · · · · · · · · · · · 46} 

f · t 5 ·n· t · d' t d th · Magnetite................... . 93 M= 2. 35 Fern, 3. 09 

rom 1 o m1 1me ers 1n 1ame er an ose Hematite........... . . . . . . . . . 96 

of biotite usually from 0.5 to 1 millimeter, Hypersthene ......... :...... . 40 P= . 40 

though a few are as large as 1 centimeter. The H20, C02, S, and Zr02 notincludedinnorm ......• 9. 36 

phenocrysts, named in the order of abundance, 

are orthoclase, biotite, and oligoclase. The Sal 87.93 

·biotite phenocrysts are very thin. Under the 'Fern= 3 .. 09' Class I, persalane. 

microscope the groundmass is found to be Q6F =8!: ~~,Subclass I, persalone. 

mainly a clear light-brown glass, in places Q 42. 06 ' 

slightly devitrified. In it ar~ lath-shaped F= 40. 57, order 3, columbare. 

microlites of plagioclase, tabu~ar orthoclase, 

. and biotite. Flow structure is present in 

some specimens, notably in those from the 

1 Cross, Whitman, Geology of Silver Cliff and the Rosita Hills, Colo:: 

U. S. Geol. Survey Seventeenth Ann. Rept., pt. 2, pp. 273, 324, 1896. 

See also U.S. Geol. Survey Prof. Paper 14, p. 201, 1903. 

K20' + N azO' 53 . . CaO' 42, rang 3, nesenase . 

K 0' 35 . N~ ,=18 , subrang 2', freelandose (new name). 

Formula, l.J.3.3.2'. 

2U. S. Geol. Survey Prof. Paper 63, p. 134, 1908. 

100.38 
QUATERNARY DEPOSITf). 57 

AGE AND RELATIONS. 

rrhe biotite latites are believed by Spurr and 

Garrey1 to have been intruded later than most 

of the other porphyries of the Georgetown 

quadrangle and later than the mineralization. 

At the junction of Chicago and West Chicago 

creeks latite incloses a few rounded fragments 

of quartz 1nonzoni te from 4 to 6 inches in 

dian1eter, and in the Stanley mine it incloses 

fragments of bostonite porphyry and of ore. 

In having a glassy groundmass the rock contrasts strongly with the holocrystalline bostonite, with which it is closely associated, and 

the inference appears justified that it was intruded under different conditions admitting of 

more rapid cooling. 

Though the biotite latite was clearly intruded 

later than the 1nonzonites and bostonites its 

exact age can not be stated. Upon the broad 

grounds outlined on page 8 it may be provisionally regarded as Tertiary. 

The close approach of this rock in the American classification toriesenose (formula I.I.3.3.3) 

from Leadville 2 and from Silver Cliff,S of supposed Tertiary age, shows that magmas of this 

composition were not uncommon among the 

late Mesozoic effusives of Colorado. 

TERTIARY ( 1) TERRACE GRAVELS. 

In ·the vicinity of Idaho Springs there are 

small amounts of cemented gravels, whose 

upper surfac~, though somewhat irregular, 

stands on the average about 180 feet above 

Clear Creek. Wit}:lin the area covered by 

Plate VI these gravels form a short, narrow 

bench just northwest of the mouth of Gilson 

Gulch and a longer bench on the south side of 

Clear Creek, opposite the western part of the 

town of Idaho Springs. They occur most 

extensively, however, just south of the area 

covered by this report and are described by 

Spurr and Garrey 4 as follows: 

In the southeast angle formed by the union of Sodp, 

Greek with Clear Creek this terrace is underlain by a bench 

of bedrock which in few places reaches the surface, being 

usually covered with a river deposit averaging 40 feet in 

thickness. The lower 20 feet of this deposit consists of 

1 U. S. Gool. Survey Prof. Papor ~~ pp. 81, 130, 344, 1908. 

2 Cross, Whitman, Petrography of the. Leadville district: U. S. Gaol. 

Stuvoy Mon. 12, pp. 330-332, 1886. See also U. S. Geol. Survey Prof. 

Papor 14, p. 138, 1903. · 

across, Whitman, and Eakins, L. G., A new occurrence of ptilolite: 

Am. Jour. Sci.,3d sor., vol. 44, p. 101, 1892. See also U.S. Geol. Survey 

Prof. Paper 14, p. 138, 1903. · 

• Spurr, J. E., and.Garrey, G. H., op. cit., p. 313. 

large rounded bowlders, gravel, and sand; the upper portion is composed of finer gravels and silts capped by aerial 

talus or silt having an average thickness of 6 feet. . 

This portion of the deposits was formerly 

extensively worked for gold with profitable 

results. 

The narrow bench near the mouth of Gilson 

Gulch 

is a horizontal or slightly sloping shelf or iedge of coarse 

conglomerate and soft sandstone or granitic arkose, similar 

in character to the placer deposits on the other side of the 

valley. This fairly well indurated conglomerate, which is 

composed chiefly of rounded masses of gneiss and granite 

but also contains some rounded p.ebbles of porphyry 

* * * is plaStered unconformably upon the rather 

steep gneiss walls of the valley at this point. Through 

this conglomerate, and to a less extent in the underlying 

gneiss, are veins (fissure fillings) of calcite. 

The largest bowlders observed .in these 

gravels are 5 feet in diameter. The degree of 

consolidation is indicated by the fact that on 

the south side of Clear Creek untimbered drifts 

excavated 40 or 50 years ago can still be traversed for considerable distances. 

The high-terrace gravels at Idaho Springs 

rise more than 150 feet above the gravels of the 

later (Wisconsin) glacial valley train. Since 

their deposition Clear· Creek has excavated, 

near Idaho Springs, a channel at least 160 feet 

deep in t.he bedrock. The altitude of the gravels 

and the depth of this canyon, much g~eater than 

any other known to have been excavated in 

this region wholly subsequent to the earlier 

(pre-Wisconsin) glaciation, make it probable 

that the gravels are older than the glacial epoch. 

They are classed as probably late Tertiary. 

QUATERNARY DEPOSITS. 

GENER~L FEATUREI:r. 

The Quaternary deposits of the Centra.lCity 

quadrangle include (1) glacial till and associated glacio-fluviatile deposits formed at two 

stages of Pleistocene ·glaciation, (2) debris 

sheets, (3) recent alluvium, and (4) talus. The 

last .three are shown under the ·same symbol 

on the geologic map (Pl. I, in pocket). 

GLACIATION. 

GENERAL CONDITIONS. 

During the Pleistocene or glacial epoch the 

entire northern half of the continent of North 

America was covered by a great ice sheet 

which moved outward from centers of accumu- · 

lation in eastern, central, and weste~n Canada. 
58 GEOLOGY OF GILPIN, CLEAR CREEK, AND BOULDER COUNTIES, COLO. 

In western-North. America this great mass of between the two glacial stages appears to have 

ice extended only a short. distance so'uth of the been small. 

present boundary between the United. States At the west border of the Central City quadand Canada, .but local glaciers of the alpine or rangle the Clear Creek glacier appears to have 

valley type were developed in most of the extended to an altitude of about 11,000 feet; 

higher mountain ranges as far south as .central· its front, 8! miles farther east, near Dumont, 

New Mexico and the San Francisco Mountains descended to an altitude of about 7,850 feet; 

of Arizona." A few glaciers exist at the present the slope of the ice surface in this· distance, 

time near some of the higher peaks of the therefore, averaged about 370 feet to the mile. 

Cordilleran mountain ranges of the western The most easterly remnants 'of the older drift 

United States, but they are insignificant in are erratic blocks of granite at an altitude of 

extent compared with their predecessors of the 8,300. feet in the first gulch northeast of the 

glacial epoch. The history of glacial time is junction of Mill and Clear creeks. Along Clear 

very complex, for there were several stages of Creek itself traces of older drift were noted 500 

ice advance alternating with interglacial stages. feet downstream from the mouth of· the Free-. 

In Colorado t~e Front Range was more or less land tunnel, where rounded bowlders extend 

generally glaciated in its higher portions, but 75 feet above the wago.n ·road. 

the details of this glaciation have been studied Till deposits.-The till of the pre-Wisconsin 

only in the Georgetown and Central City glaciers-the material transported in, on, or 

quadrangles. There, as in most of the other beneath the ice-occurs in irregular remnants 

western mountain ranges where the subject whose form and position in the valley of Clear 

has been studied in detail, the , glacial drift Creek is shown on Plate I. The typical glacial 

is referable to two or more stages of glaciation, topography which this till once exhibited has 

somewha:t widely separated in time. been largely destroyed by erosion, the surface 

EARLIER OR PRE-WISCONSIN GLACIAL STAGE. 

as a rule being well drained and free from ponds 

or bogs. The glacial origin of the material is, 

Glaciers.-Within the Georgetown quad- however, apparent from its topographic posirangle and those portions of the Central Cjty tion, its incoherence, its 'heterogeneity in size 

quadrangle that have been studied in detail and character, and the presence of typical 

glaciers of the earlier or pre-Wisconsin stage glacial strire, especially on ·porphyry bowlders. 

I headed in the Continental Divide and moved The bowlders lying on the surface are rougheastward and northeastward dowri the valleys ened by weathering and somewhat decomposed, 

of the west and south forks of Clear Creek to a. and the till is oxidized to depths varying from 

point not far east of Dumont. In these valleys 3 to 15 feet. · 

the earlier glacial deposits extend farther down The extent of stream erosion since the deposithe valley and higher up the valley walls than tion of the older till is well shown in the valley 

those of the later or Wisconsin glacial stage. of Silver Creek, south of Lawson. This creek, 

It is noteworthy that the Mount Evans region, according to Ball 1 has cut since the early glaciain the Georgetown quadrangle, which was an tiona canyon 3,000 feet long, 100 feet in average 

area of considerable accumulation for glaciers depth, and250feetwideatthetop. Atoneplace 

of the later stage, apparently did not give rise the upper 85 feet is cut in till and the lower 15 

to notable glaciers during the earlier stage. feet in the Idaho Springs formation and pegIn the northeastern part of the Central City matite. This amount of cutting is in marked 

quadrangle evidences of the earlier glaciation contrast with that exhibited by streams of 

have not been noted, although deposits made comparable size traversing the later till. (See 

by the later glaciers are abundant. · p. 59.) 

From the differences in distribution of the Outwash deposits.-No gravel deposits were 

glaciers of the two stages, it may be .inferred noted that coUld be certainly identified as outthat the conditions of accumulation were wash from the glaciers of the earlier stage. 

notably different. The nature of these differ- Such deposits, which were doubtless abundant 

ences is conjectural, but they were probably at one time in the· valley of Clear Creek between 

not topographic, because the amount of erosion 1 Ball, S. H., op. cit., p. 86. 
QUATERNARY DEPOS~TS. 59 

Dumont and Idaho Spri:D.gs, have apparently dominate, the less resistant schist of the Idaho 

been entirely removed or reworked by subse- Springs formation being comparatively rare. 

quent stream erosion. The surface bowlders of the later till are little 

LATER oR WIScoNsiN GLACIAL sTAGE. weathered or decomposed, and the body of the 

Glaciers. -Glaciers of the later stage, be- till is practically unoxidized. Postglacial erolieved to have been contemporaneous with the sion reached a maximum along the streams of 

Wisconsin stage of the continental ice sheet, large :volume, such as Clear Creek, along which 

occupied the upper valleys of Clear Creek, Mill Ballt noted a postglacial channel southwest of 

Creek,·Fall River, Silver Creek, South Boulder ?eorgetown, 1,000 feet long and 30 feet deep, 

Creek, Middle Boulder Creek, North Fork of m the pre-Cambrian rocks. In other localities 

Middle Boul:der Creek, and North Boulder the erosion has been slight; Mill Creek, for exCreek. The distribution of these till deposits is ample, breaks over the summit of the t~rminal 

shown on Plate I. The lowest altitude reached moraine in a narrow cut about 30 feet deep and 

by these glaciers was about 8,200 feet at the then cascades down over the outer slope in a 

·front of the Clear Creek glacier, which extended number· of small bowlder-filled channels which 

to Lawson. The largest of the glaciers were unite just below the moraine intq a' single 

those of Clear Creek and Middle Bo.ulder Creek. good~sized stream. 

Glacial erosion.-The geologic s~rveys that Outwash deposits.-Deposits of bowlders and 

form the basis of this report did not extend ~ravel made by streams fed by the melting 

into the upper portions of many of the glaciated Ice are present in practically all the glacial 

valleys where sculpturing by the ice was most valleys. The most extensi;ve are the narrow 

active. Some glacial erosion was noted at the valley trains that occupy portions of the valley 

headwaters of Silver Creek, near Alice, but the floors below the terminal moraines. The 

· Alice glacier w~s small and correspondingly longest of these valley trains occupies Clear 

weak. The steep rock walls near Eldora have ~reek valley .and extends, with a few interrupundoubtedly been scoured vigorously by the twns, from a point near Lawson to a point a 

glacier that occupied that valley. Elsewhere short distance below Idaho Springs. . Its altiwithin the glaciated areas the predominant tude at Lawson is about 8,140 feet and at Idaho 

process. was deposition rather than erosion. Springs about 7,540 feet, its average slope beTill deposits.-The till deposits of the later tween these two places being therefore a little 

or Wisconsin ·glacial stage, in marked contrast over 80 feet to the mile, or about the gradient 

to those of the earlier or pre-Wisconsin stage, of the present stream. At Idaho Springs the 

have been modified only to a slight extent by Wisconsin glacial gravels rise about 20 feet 

~ater erosion and exhibit in many places the above the present flood plain of Clear Creek 

UTegular and poorly drained surfaces charac- and form the terrace upon which most of .the 

teristic of glacial topography. Lakes in basins to~ is built. The materials of the valley 

formed wh<;)lly or partly by till are . common trams are commonly well rounded. 

only near Alice and south of ·Eldora; the In the valley of North Boulder Creek the 

largest is Lake Eldora, or Peterson Lake which outwash from the melting Wisconsin glacier 

lies between a wall of schist on the north and a was not confined to a narrow valley but spread 

wall of till on the south. Distinct differentia- over a considerable area, forming an outwash 

tion of the ~ill deposits into terminal and apron that s.kirts the moraine, sloping gently 

lateral moraines is generally impossible, but away. from 1t, and merges into ~he recent 

on the south side of South Boulder Creek, from· alluvium. 

a poirit a little above Baltimore nearly to Tol-: Ne~r Empire and from 1 to 2! ri:riles southland, Mr. Hill observed a well-marked lateral west of Nederland outwash plains have been 

moraine. One of the best-defined terminal formed during the retreat of the ice, back of 

moraines is that which crosses Mill Creek at an the terminal moraines. The appearance of the 

altitude of about 9,650 feet. The front of this ~ederland plains is shown in Plate :;KII,.A. In 

moraine is steep and about 300 .feet high. It are two small lakes that presumably mark the 

Among the bowlders and cobbles granite,· places where ·blocks of ice were left behind in 

pegmatite, granite gneiss, and porphyry pre- 1 Ball, S. H., op. cit., p. 86. . 
60 GEOLOGY OF GILPIN, CLEAR CREEK, AN-D BOULDER COUNTIES, COLO. 

the glacial retreat and by their subsequent dering and underlying rocks have accumulated 

melting produced depressions that are ·now in sufficient thickness to mask the hard-rock 

filled with water. A lake of similar character formatio'ns completeJy. Such deposits are 

occurs in a smaller outwash plain near Tolland. found in Elk Park (west of Apex), at Pecks 

The glacial outwash· has in some places Fla~, north of Mount Pisgah, near The Queens 

yielded gold in paying quantities; as discussed Chair (north of q~ntral City), in Pleasant 

on page 120. . Valley, and at a number of other localities. 

AGE AND RELATIONS OF THE GLACIAL STAGES. !hey a·~pear to have been formed by the disThe considerable surface oxidation of the IntegratiOn of the bedrock under the action of 

earlier or pre-Wisconsin till and the destruc- frost, temperature changes, etc., and the 

. tion by erosion of the features typical of gradu~l downhill. creep of the disint~grated 

morainal topography. present so marked a ·matenal under the influence of gravity aided 

contrast to the slight postglacial changes in by wetting and drying, freezing and thawing, 

the later or Wisconsin .till that it is a necessary and other processes. In the accumulation of 

conclusion that the interval between the two the typical debris sheets stream ero~ion has 

stages was ?f long duration, probably much played an insignificant part. There is, how-· 

longer than the time which has elapsed since ever, a gradation from typical sheet deposits 

the later or Wisconsin stage. This conclusion of debris into stream alluvium, and· both are 

is in entire harmony with the conclusions of shown on the maps (Pls. I and VI) under the 

Salisbury in regard to the relative ages of the same symbol. The thickness of the debris 

earlier and later til~ in the Bighorn Mountains sheets can be determined only wherce they have 

in Wyoming/ and with those of Atwood fo; been penetrated by mine workings. Near -The 

the San Juan Mountains of Colorado 2 and the Queens Cl~air, north of Central City, a shaft 20 

Uinta and Wasatch mountains of Utah.3 feet deep is wholly in debris. In a few places, 

Both stages of glaciation occurred during as near The Queens Chair, where the debris is 

Pleistocene time. · composed princip-ally of porphyry, it has been 

cemented apparently by silica into a coherent 

PLEISTOCENE ( ?) TERRACE GRAVELS. 

Two gravel terraces, whose upper surfaces 

stood 55 and 25 feet, respectively,· above the 

level of the present streams, were noted by 

Ball 4 along the lower 2.2 miles of Chicago 

Creek and along Clear Creek near the mouth of 

Chicago Creek, just outside the area covered 

by this report. The age of these terraces is 

'uncertain. Ball states that the 55-foot terrace may be of glacial or preglacial age. The 

25-foot terrace stands only a short distance 

above the late glacial valley train and may 

have been formed in early glacial or interglacia~ time. · 

DEBRIS SHEETS. 

In ·gently sloping portions of ·a· number of 

valleys which have not been affected by 

glaciation and· in which stream erosion has not 

been vigorous, deposits of angular, unassorted, 

and somewhat decayed fragments of the bor1_Salisbury, R .. D., U. ~· Geol. Survey Geol. Atlas, Cloud Peak-Fort 

McKinney folio (No. 142), p. 12,1906. 

2 Atwood, W. W., Physiographic studies in the San Juan district of 

Colorado: Jour. Geology, vol. 19, p. 449, 1911. · 

3 Atwood, W. W., Glaciation of the Uinta and Wasatch mountains: 

U.S. Gaol. Survey Prof. Paper 61, p. 92. 

4 Ball, s. H., op. cit., p. 84. 

rock. 

Here and there, as noted on page 120, the 

debris sheets have yielded gold in paying 

quantities. 

The debris sheets appear to .have accumulated mainly in glacial and postglacial time, 

although the lower portions of some deposits 

may be older. They are still being formed. 

RECENT ALLUVIUM. 

Deposits of bowlders, gravel, and sand laid 

down by the present streams are found in 

nearly all the valleys, and those extensive 

enough to map have been shown on Plates I, 

III, and VI. The narrow strips of alluvium 

along the principal streams are broadened at 

intervals by fanlike contributions of alluvium 

from tributary gulches,· as at the mouths of 

Georgia and Hoosac gulches, both of which contain only temporary streams. (See Pl. VI.) 

In some places, as at the mouth of Dry Gulch 

in. Idaho Springs, these fans rest upon glacial 

outwash gravels of the Wisconsin stage. 

The recent stream alluvium has in the past 

been an important source of placer gold. (See 

p. 120.) 
STRUCTURE. 61 

TALUS. 

Deposits of talus or fragmental rock material 

that has fallen at the base of steep rock slopes 

as a result of their disintegration through 

changes in temperature, the action of frost, and 

other processes, are most abundant in the 

higher portions of the region, which have not 

been surveyed geologically. Within the surveyed an~a they are abundant only in a few 

places, as at the base of the cliffs north of Alice 

and in parts of the valley of Clear Creek above 

E~~- . STRUCTURE. 

The structural features of the Central City 

quadrangle are very ·complex, and many of 

them 1·epresent the cumulated effect of processes 

acting through long periods of geologic time. 

Tho p1·ocesses that have produced the structural 

features are (1) widespread earth mo.vements of 

compression and uplift and (2) igneous intrusion. The principal structural features developed through these processes are foliation, 

faults, and joints. 

FOLIATION. 

Under the term foliation are included both 

schistosity and gneissic structure. Foliation, 

in this region, i~ confined to the pre-Cambrian 

rocks and is in general best developed in the 

oldest and least deyeloped in the youngest of 

these rocks. The physical character of the rock 

has also been a factor in cont:r;olling foliation, 

some rocks becoming more highly foliated than 

others under the influence of the S!).me stresses. 

The preponderant direction of foliation, 

especially in the southern part of the area surveyed, is northeast, ns is indicated not only by 

direct measurements but also by the northeasterly elongation of many of the bodies of 

intrusive igneous rock, pegmatite, quartz djorite, and others. (See Pl. I.) From this prevailing trend there are many variations, foremost among which is a tendency for the lines 

of foliation to wrap around large masses of 

intrusive rocks. Thi.s tendency is particularly 

marked nenr the large masses of pre-Cambrian 

quartz monzonite in the Georgetown quadrangle. · 

The most highly foliated rocks of the region 

belong to the oldest formation, the Idaho 

Springs, which is probably sedimentary and 

into which all the igneous rocks of ·the quadrangle have been intruded. The foliation developed in most of these rocks is of the finely laminated type termed schistosity ·and described 

more at length on page 27. Its perfect development in the Idaho Springs rocks is due in part 

to the readiness with which fine argillaceous sedimen~s, such as originally made up much of this 

formation, recrystallize under differential pressure, but also to the fact that they have been 

submitted to such pressures during m~.>re,~pe­

.riods than any of the other rocks. The latter 

fact is shown by the occurrence in the next 

younger rock, the granite .gneiss, of fragments 

of the Idaho Springs formation having well-. 

developed schistosity. The granite gneiss characteristically shows a well-defined gneissic 

structure, though in a few places it is massive. 

The microscope shows that in both the granite 

gneiss and the schist of the Idaho Springs for-. 

mation the foliated structure has been developed through recrystallization without. frac-. 

turing. The change took ,place, therefore, 

under high pressure and was presumably accomplished while the rocks were deeply buried. 

In contrast to the granite gneiss and the Idaho 

Springs formation, the quartz diorite, Silver 

Plume granite, and pegmatites are characteristically. massive. Where they appear foliated 

thi~ structure may be the result of close-spaced 

shearing or of flowage during crystallization. 

Some of the granite pegmatite is ~ phase of the 

granite gneiss intrusion, and t.he absence of 

foliation in such pegmatite must be interpreted 

as evidence of its superior resistance to recrystallization under pressure compared with .. the 

finer-grained phases of the intrusion. Th~\f:act 

that the Silver Plume granite locally contains 

angular fragments of granite gneiss exhibiting 

the usual degree of gneissic structure shows 

that the foliation of the gneiss was developed 

prior to the intrusion of the granite. 

The stresses that developed the schistose 

structure in the rocks of the Idaho Springs· 

formation, flexed these rocks into a series of 

compressed folds. Small folds are recognizable 

here and there within the formation, but in the 

absence of distinctive beds that mark the same 

stratigraphic horizon over large areas, the 

larger features of this folding can not be worked 

out: 
GEOLOGY OF GILPIN, CLEAR CR:EEK, AND BOULDER COUNTIES, COLO. 

FAULTS AND JOINTS. 

The great depth at which recrystallization 

with the development of foliation took place 

was incompatible with any, considerable formation of faults and joints. These structural. features were developed mainly during later 

pe:iods, when erosion had removed great 

thicknesses of covering rocks. Some faulting 

undoubtedly accompanied the intrusion of the 

younger pre-Cambrian igneous rocks, for in 

places pegmatite and granite contacts follow 

straight sharp fractures that cross the foliation 

of the schist of the Idaho Springs-formation or 

the granite gneiss,· but most of the faulting 

took place at a later time. Some of it preceded and some followed the-intrusion of the 

Tertiary ( n J?Orphiries, and faulting is. in 

progress even at the present day. 

- · The. faulting may plausibly be regarded as 

in the main an effect of the various land movements which since Cretaceous time have 

brought the region to its present elevated 

position; to a lesser · degree it has resulted 

from the intrusion of the Tertiary ( ~) igneous 

rocks. · 

Two dominant direction,s of faulting are 

recognizable-northeast and northwest. The 

· northeasterly faults are by far the most numerous and ~ost. extensive. Both .sets dip steeply. 

These d1rectwns of faulting were established 

previous to or contemporaneous with the intrusion of the . Tertiary ( ~) igneous rocks · and 

influenc.ed their distribution, as is clearly shown 

on the map (Pl. I). Later faulting along the 

same general lines displaced the porphyries and 

created channels for ore , deposition. The 

northeasterly faults · correspond in general 

trend with the foliation in the pre-Cambrian 

rocks, and in this concordance is to be found 

perhaps the reason for their overwhelming 

preponderance ove:r; the northwesterly faults. 

Except for the few faults that displace porphyry dikes in mine workings, it is impossible 

.to obtain an estimate of the amount of movement along the fault planes. It is perfectly 

,clear, however, -that in most places the movement was small, for nowhere was it sufficient 

to c~use noteworthy displacement of a geologic 

'boundary as shown on the surface. · 

· The northeasterly faults are of great ec~­ nomic importance, for along· them nearly all 

the metalliferous veins have been deposited. 

Joints are prominent chiefly in the regions 

of extensive faulting and in gene-ral are parallel to the faults. 

IGNEOUS INTRUSION. 

The most salient structural· characteristic of 

the ·region is the intricate manner in which 

igneous rocks ranging from pre-Cambrian to 

probably Tertiary in age and from irori ores 

to quartz-rich pegmatites in composition have 

been intruded into the sedimentary Idaho 

Springs formation and into one another. The 

unraveling of this intricate association formed 

the pri~cipal problem in the geologic mapping, 

and even the large-scale l"Il:aps suffice only to 

record a generalized picture of the true relations. Ball 1 illustrates this wonderful complexity in a striking manner with the statement 

that within a distance of 1 mile near ·Lawson 

six formations alternate 76 times, or at the 

rate of one alternation to 70 feet. 

1 Ball, S. H., op. cit., p. 91. 
CHAPTER IV.-GEOLOGIC HISTORY. 

PRE-CAMBRIAN TIME. 

. The geologi~ events of the CentrEd City regwn that are recorded in its ;rocks began with 

~he de~osition in pre-Cambrian time, probably 

m marme waters, of great thicknesses of clays 

and of very minor anlOUilts of sands gravels ' ' and 1narls, now represented· by the Idaho 

Springs forn1ation. The position and ·size of 

the land masses which furnished these sedi~ 

ments and the character of their rocks are unknown, but f"ron1 the character of the Idaho 

Springs rocks it Inay be inferred that the waters 

in which t~e sediments were deposited were 

not deep and that conditions favorable for 

limestone deposition rarely held sway. During long periods o~ tune these incoherent deposits became buried to a great depth beneath 

other deposits, were consolidated to shales, 

sandstones, conglon1erates, and liinestones, and 

eventually were closely folded and recrystallized under the influence ~f con1pressive stresses 

~nd converted into the biotite schists, quartzItes, conglmnerates, and crystallii1e lin1estones 

that now 1nake up the Idaho Springs formation. The stresses that produced this Inetamorphisnl operated at great depth and possibly 

during several periods. Whether this meta~ 

morphisn1 far below the surface was accompanied by n1ountain building at the surface is 

UI1la1own; certaiiliy the present mountain range 

i~ comparatively young and in no way connected with these very ancient processes. 

Subsequent to this metamorphism but still 

in pre-Crunbrian tiine came the intrusion of a 

few broad dikes of quartz diorite grading into 

hornblendite, in the main parallel to the· schis-

. tosity of the Idaho Springs formation. After 

that were intruded in the Georgetown quadrangle, large masses of monzonite and still 

later, in both the Georgetown and Central City 

quadrangles, bodies of granite, now represented by the ~tocks and injected bands and 

lenses of granite gneiss and associated pegmatite. Solutions emanating from the·granite intrusives produced some contact metamorphism 

in parts of the Idaho Springs formation adj acent to or inclosed by them, converting biotite 

schist into hornblepde schist and crystalline 

limestone into lime-silicate rocks. The intrusion of these granitic rocks took place at great 

depths and was followed by a renewal of comprehensive stresses which iinparted to them a 

foliated structure and metamorphosed still further ~he rocks of the Idaho Springs formation. 

This metamorphism was, however, much les~ 

severe than the earlier metamorphism. 

Later in pre-Cambrian time were intruded 

great batholiths of quartz monzonite not found 

within the area covered by this ~urvey but 

occupying large areas in the Georgetown quadrangle. Then followed the intrusion of the 

Rosalie granite of the Georgetown quadrangle 

and the Silver Plume granite of the Georgetown 

and Central City quadrangles, with their various dioritic and pegmatitic facies. These rocks, 

like the earlier granitic and monzonitic intrusives, produced locally some slight contact metamorphism of the rocks of the Idaho Springs 

forn1ation. 

There are reasons for believing that at the 

time of these later intrusions the section of the 

earth's crust now exposed at the surface was 

less deeply. buried than in the earlier periods 

when regional metamorphism developed foliated structure. Evidence for this belief is 

found in the fact that. the later intrusions fractured the inclosing rocks somewhat more than 

the earlier intrusions. If this belief is warranted it must be supposed that erosion was in 

progress in this region even in pre-Cambrian 

time-:-that' is, that parts of the region were 

Iand-a conclusion that receives support from 

the reported occurrence of pre-Cambrian effusive igneous rocks in certain parts of the 

Front Range. 1 

PALEOZOIC TIME. 

Whatever may be the facts in regard to erosion in pre-Cambrian tiine, it is certain that 

very extensive erosion had taken place in the 

region now occupied by the Front Range before 

the end of the Cambrian period, for metamorphosed quartzites and conglomerates of prob1 Darton, N.H., Blackwelder, Eliot, and Siebenthal, C. E., U.S. Geol. 

Survey Geol. Atlas, Laramie-Sherman folio (No. 173), p. 3, 1910. 

63 
64 GEOLOGY OF GILPIN, CLEAR CREEK, AND BOULDER COUNTIES, COLO. 

able Upper Cambrian age, containing pebbles 

of the foliated rocks, lie in .erosional unconformity upon the pre-Cambrian crystalline complex at several places along the east flank of the 

range. 1 That parts of the region were land in 

Carboniferous time is shown by the fact that 

near Golden and Boulder the Fountain formation,2 of Pennsylvanian age, rests in erosional 

unconformity upon the pre-Cambrian rocks. 

Ball 3 found what appeared to be remnants of 

the Fountain formation in the Georgetown 

quadrangle, and if his identification was correct portions of. the region now comprised in the 

Georgetown and Central City quadrangles were 

covered by the sea during part of Pennsylvanian time. 

Although the Paleozoic history of the region 

is therefore only imperfectly known, it is probable that both erosion and sedimentation were 

in progress and that the former far overbalanced the latter, the net effect bein~ to bring 

the particular pre-Cambrian rocks which are 

now txposed for geologic study much closer to 

the surf ace. 

MESOZOIC TIME. 

Of the history of the region in· early Mesozoic 

time little is known. That certain parts of the 

area now occupied by the Front Range were 

land during portions of this time is shown by 

the fact that in Middle Park, 4 on the west flank 

of the range, and apparently also at Breckinridge 5 the Dakota sandstone, of Upper Cretaceous age, lies in erosional unconformity upon 

the pre-Cambrian crystalline complex. 

The Cretaceous seems in general to have been 

a period of submergence over most of the province. It can not be positively affirmed that the 

Cretaceous seas covered the Central City and 

Georgetown quadrangles, but it is highly probable that they did, for, as pointed out by Darton, 6 the late Cretaceous sediments now exposed along the east flank of the range do not 

become coarser nearer the mountains. 

1 Cross, Whitman, U. S. Gaol. Survey Gaol. Atlas, Pikes Peak folio 

(No.7), 1894. Richardson, G. B.', U.S. Gaol. Survey Gaol. Atlas, Castle 

Rock folio (No. 198), 1916. 

2 Fenneman, N. M., Geology of the Boulder district, Colo.: U.S. Gaol. 

Survey Bull. 265, pp. 22-23, 54-56, 1905. Emmons, S. F., Cross, Whitman, and Eldridge, G. H., Geology of the Denver Ba.Sin in Colorado: 

U.S. Gaol. Survey Mon. 27, pp. 91-92, 1896. 

a Ball, S. H., op. cit., pp. 66-67. , 

4 Hayden, F. V., Geological and geographical atlas of Colorado, 2d ed., 

sheet 12, U.S. Geol. and Geog. Survey Terr., 1881. 

5 Ransome, F. L., Geology and ore deposits of the Breckenridge district, Colo.: U.S. Gaol. Survey Prof. Paper 75, pp. 30-38, 1911. 

o Darton, N. H., U. S. Geol. Survey Geol. Atlas, Laramie-Sherman 

folio (No. 173), p. 13, 1910. 

CENOZOIC TIME. 

It has been shown that land areas existed 

in the region now occupied by the Front Range, 

even in pre-Cambrian time. Although the 

geologic evidence is not sufficient to jll:stify 

the statement that these lands never assumed 

the aspect of mountains, the scarcity of coarse 

sediments in most of the Paleozoic and Mesozoic 

formations t~at flank the range seems in 

general to point to the opposite conditionthat is, only moderate relief. The ·movement~ 

that produced· the Rocky Mountain uplift 

began in or just before Tertiary time and were 

the result of compression along east-west lines. 

The growth of the .range, however, has not 

resulted from a single simple compressive movement but is the net effect of several such movements separated by periods of quiescence and 

modified by volcanism, and some movement 

may still be in progress .. The earlier movements 

appear in general to have been of greater magnitude than the later. Although some faulting 

took place in the region even in pre-Cambrian 

time it produced little deformation until the 

beginning of the mountain~building uplifts; the 

fractures formed by these uplifts were followed 

by many of the Tertiary(~) intrusions. 

Just after the early periods of mountain 

growth, in la.te Cretaceous or early Tertiary 

time, volcanism, for the first time since the 

pre-Cambrian, again assumed importance. 

Masses of igneous material were intruded as 

dikes and stocks in the pre-Cambrian formations and in places issued at the surface, as is 

shown by the flows and tuffs· intercalate_d with 

the sediments of the Denver formatio;1 in the 

Denver ·Basin 7 and with the Dawson arkose 

of the Castle Rock .region. 8 The typical dike 

form and fine grain of many of these late Cretaceous -or early Tertiary intrusions is in 

marked contrast to the lenticular form and. 

coarse grain of many of the pre-Cambrian· in- . 

trusions and indicates that they were formed 

much nearer to the surface .. 

The intrusion of the igneous rocks ·was .followed almost immediately by the :development 

throughout the region of a large· .number of 

faults of small displacement, many -of which 

subsequently became the sites of -ore~ deposi..: 

tion. The cause of this faulting is not apparent, but it was more wide;pread than any be1 Emmons, S. F., Cross, Whitman, and Eldridge, G. H., op. cit., p. 210. 

a Richardson, G. B., U.S. Gaol. Survey Geol. Atlas, Castle nock 

folio (No. 1_98), p. 9, 1916. 
GEOLOGIC HISTORY. 65 

fore or sin~e. rhe formation of the o~e depos- higher mountains stood as unreduced monadits appears to have been intimately related nocks. (See ·Pl. IX, p. 20.) Portions of the ore 

both to tl1is faulting and to the Tertiary ( ~) deposits and the intrusive "porphyries" that 

volcanisn1. Magmatic differentiation within had been buried were laid bare by erosion, and 

one of the 1nonzonite stocks during its crystal- the ore deposits were subjected to oxidation 

lization produced the titaniferous iron ores of and downward enrichment through the influCaribou, and the solutions that ascended along ence of the atmosphere and meteoric waters. 

fracture zones and deposited the gold and sil- These alterations have been going on continuver ores of this region are believed to have come ously up to the present day. · 

fr01n the deeper parts of the igneous magmas The next important event in the geologic 

after the higher parts had solidified. The few history appears to have been the renewal of 

porphyry dikes that are later than the minerali-. uplift in late Tertiary time. This uplift was 

zation n1ay be regarded as marking the last intermittent, but its general e:fject was to stimstages of volcanisn1 in this region. · ulate the streams to renewed activity, develWith the dying out of the late Cretaceous or oping gorges in the old. plateau surface and 

early Tertiary volcanism began a long. period heightening the escarpment between the plains 

of uninterrupted erosion, during which the and 1nount1

ain tracts. 

Cretaceous sedin1ents and late Cretaceous or · In Pleistocene time climatic changes at two 

early 'l''ertiary volcanic rocks that probably distinct periods led to the development of glacovered the surface in early Tertiary times ciers of the alpine type, which accum:ulated in 

were completely removed and considerable the higher parts of the range and moved for 

thicknesses of the underlying pre-Cambrian several ~es down the larger valleys. With 

rocks were also worn away. Large portions of reverse climatic changes the glaciers disapthe mountain province ·were subdued to a p~ared and the conditions which exist to-day . 

gently sloping peneplain, upon which the were initiated. 

44214°-17-5 

PART H.-GENERAL FEATURES OF THE ECONOMIC GEOLOGY. 

By EDSON s. BASTIN. 

CHAPTER V.-HISTORY OF MINING. 

In romantic interest and as a record of' site of Denver, where they established a camp 

hurnan,achievement in the face of great di:ffi- and began prospecting. According to Rickard, 

culties and privations, the story of the discov- one of these parties followed Boulder Creek 

ery and early development of the mineral up to the forks, finding small amounts of gold. 

wealth of this region can hardly be surpassed Another party proceeded across the ridges to 

by any other chapter in the history of the Fall River and Spring Gulch. They did not 

"winning of the West." If in the brief ac- descend into the valley of North Clear Creek 

count that follows the personality of these at that time but crossed Quartz Hill and found 

pioneers is lost in the story of their practical rich gravel at Russell Gulch, named after its 

achievements, it is because the pen of a novelist discoverer, W. Green Russell. As it was .too 

rather than a .geologist is requireq ·to depict near winter to begin mining, the prospectors 

the human side of the story. returned to their camp at Cherry Creek. Six of 

The .writer is indebted to publications by the party went east to obtain provisions; r~;­

Rickard,t Fossett, 2 and Hall,3 for most of the turning in the spring of 1859. . · .... ,. 

facts ·here presented. , By the fall of 1858 rumors of the gold disIn the summer of 1849 a p~rty of seven coveries had reached eastern Kan~ms. The 

Georgians were taking a herd of thoroughbred East and especially the Middle West was still 

horses across the continent to ·California. suffering from the effects of the financial panic 

Reaching the mountains too late iri the..fall to of 1857, and this fact undoubtedly accounted 

effect a safe crossing with th~ir :stock, they in a measure .for the enthusiasm with which 

established a winter camp at the junction of any plan that promised to revive fallen· forCherry Creek and Platte River, on the present tunes was received. Prospectors in large numsite of the city of Denver, and during the fall hers traveled to the new gold field, which 

occupied themselves in prospecting the gravels became generally known as the Pikes Peak 

u1ong.Cherry Creek, but they did not penetrate field. The town at the mouth of Cherry Creek, 

into the mountain canyons for fear of the In- on the present site of Denver, was named 

dians. Gold in quantities sufficient to awaken Auralia, and there in 1858 wintered a consider-

. their hopes was found at several places, par- able number of people disappointed at the 

ticularly at a point 16 miles upstream. With small findings. of gold in that vicinity and 

the arrival of spring they proceeded to Cali- ready to stampede to any field of new disfornia, where for several years they engaged covery. At the foot of the mountains, where 

in mining, but in 1857 they sold out their in- now stands the town of Golden,' three prosterests in California nnd returned to Georgia. pectors camped for the winter. One of these 

Before separating it was agreed among several men, George A. Jackson, a native of Missouri, 

of them that in the near future they would penetrated into the mountains during the 1 

form a prospecting party to go to 'the Rocky winter of 1858 and discovered the hot soda ' 

Mountains and search for gold. In May, 1858, springs near the present site of the town of 1 

the original seven and four others met in St. Idaho Springs,· and shortly afterward, on J anu-

/ !~~uis, and in August they reac}:ted the present ary 7, 1859, .he w~shed fine gold .from the 

1 Rickard, T. A., The' development or colorado's mining industry: gravels bordermg Chrcago Creek near rts mouth. 

}

. Am. lost. Min. Eng. TrBDs., vol. 26, pp. 834 et seq., 1897. A monument now marks the site of his dis-

' l~ossctt, l<'rnok, Colorado, 1879. ... Th f J k ' fi d d a Hall, :Frank, History or the State or Colorado, 4 vols., 1889-189.'>. CO Very· e news· 0 ac son S ll an the 

67 
\ 

68 GEOLOGY OF GILPIN, CLEAR CREEK, AND BOULDER COUNTIES, COLO. 

display of his gold at Auralia, where he offered 

it in payment for tools and -supplies, precipitated a rush of prospectors to the mountains 

and resulted in the spring of 1859 in the discovery of gold at many other places. Among 

those who· joined in this rush was John 

Hamilton Gregory, a native of Georgia, who 

followed up North Clear Creek. On May 6 

GregorY. made the first lode discovery in the 

Rockies, on the lode that- bears his name (on 

Gregory No. 5 ·claim), between the present 

sites of Blackhawk and Central City. Other 

prospectors coming up North Clear Creek soon 

learned of his discovery, and the news spread 

and occasioned another rush, many hastening 

·across the hills from Cherry Creek and from the 

Jackson "-diggings," on South Clear. Creek. 

Gregory sold his two claims for $21,000 in the 

summer o{ 1859 and soon afterward left the 

district. 

,_. In June, 1859, shortly after Gregory's dis-

, covery, A. D.- Gambell discovered gold in Gamble Gulch in the Perigo region, and prospectors 

from the Jackson and Gregory diggings, spreading over the country in all directions, made 

many other discoveries at Twelve-mile, Gold IIill 

(12 miles.west of Boulder),. and other places. 

Early in· June, 1859, W. Gre.en Russell, a 

member of the original party of Georgians, had 

commenced washing gold in the gulch that 

bears his name. According to Hollister/ . "A 

week's work with six men yielded 76 ounces of 

gold. Others had taken claims above and below him, and toward the end of September 

there were 891 men at work in the gulch." 

By July 1 about 100 sluices were at work in the 

viCinity of Gregory's discovery, and yields of 

$100 to $400 fo! ~ day's work were not uncommon. Certain lodes averaged $100 a day 

· for months at a time. 

Thus was initiated the first period of mining 

in Colorado. ·The subsequent history of the 

district i~ too complex to be followed here in 

detail, but attention may be drawn to a few of 

its salient events. The discovery of other valuable lodes foP,owed fast upon 'that of . the 

Gregory lode. On May 15, 1859, the Bates lode 

was uncovered, and on May 25 the Gunnell, 

Kansas, and Burroughs. The Bobtail was discovered in June. On June 8, 1859, the miners 

at the "Gregory diggings" (Blackhawk) met 

in mass meeting and framed and adopted reso1 Hollister, 0. J., The mines of Colorado, pp. 71-72, 1867. 

I 

lutions defining the boundaries of the district 

and the conditions under which claims could 

be taken and held. One of the resolutions provided that lode claims were to be 100 feet long 

and 50 feet 'wide, and "creek" or placer claims 

were to extend 100 feet up or down the gulch and 

from wall to wall. These provisions remained 

in force until the enactment of the Federal mining act of May_ 10, 1872. Subsequent meetings 

on July 9 and 16, 1859, organized a provisional 

local government. 

In splte of wa~nings issued through the eastern newspapers by Horace Greeley and other. 

eastern men who had visited the Gregory district in 1859, a second stampede to the district, 

larger than the first, took place in the sun1mer · 

of 1860. During the early part of summer 

immigrants bound for the new gold field- arrived on the present site of Denver at the rate 

of 100 a day. The diggings became overcrowded and many hardships resulted. In that 

year the existing mining laws for the Gregory 

district were codified and amplified. The integrity of ·the local laws within each mining 

district was upheld by one ol the first acts of 

the Territorial legislature of Colorado, in 1861, 

and further supported by an act of Congress, , 

approved July 26, 1866. This act contained 

the first statement of the .famous "apex law." 

On February 26, 1861, the region, which had 

up to this time formed a part of the Territory 

of Kansas, was organized by act of Congress as 

the Terri tory of Colorado and William Gilpin 

was appointed governor. 

All the veins of the region were gold bearing : . · 

in their surface-oxidized. portions, and it was 

not until mining had been extended to the , 

underlying sulphide-bearing ores ~hat some· of ' 

the veins were found to be rich in silver. The · 

first discoveries of silver ore appear to have I 

been made in 1864 by men from the Empire 

distri'ct. They uncovered the Belmont vein, 

on McClellan Mountain, which afterward 

yielded large· amounts of rich silver ore. In 

1865 and 1866 there was a rush to the Georgetown district, and a large numb~r of rich silver 

veins were discovered. In 1869 the rich silver 

ores of the Caribou or Grand Island district, 

in Boulder County, were discovered. The 

silver veins of Silve~ Hill, near Blackhawk, 

were not discovered until1877 or 1878. 

A notable stimulus was given to the development of mining by the completion of the 

· .... _ 
HISTORY OF MINING. 69 

Union Pacific Railroad to Cheyenne in 1867, For these reasons and because of financial ills 

and particularly by the completion in the· consequent upon overcapitalization of many 

smumer of 1870 of the Denver Pacific .line properties the p.eriod betwee·n 1864 and 1868 

between Denver and Cheyenne. In August was one of depression ~n the mining ind.ustry, 

of the same year the Kansas Pacific Railroad which was only slowly alleviated as progress 

reached Denver, making two rail connections was made in the treatment of the sulphide ores. 

with the East. In 1870 the narrow-gage ·The further history of mining in the region 

railroad was completed from Denver to Golden, is so intimately bound up with the progress in [ 

and in 1872 it was extended to Blackhawk, and ore concentration and smelting that the reader · 

in 1873 to Floyd Hill, on South Clear Creek. is referred to the discussion of this development 

During the early ·years, when mining was in the chapter on ore treatment (pp. 153-171). 

confined to the gravels and to the gossans of One event, ,however, of .especial importance , 

the veins and the ores obtained were soft and ·was the completion in 1887 of the Gilpin I' 

free milling, they could be cheaply n1inecl and County tramway with 24-inph gage to serve 

amalgamated with the aiel only of suchsimple the mines of Blackhawk, Central City, and 

' devices as sluices, cradles, arrastres, and crude Russell Gulch. About $100,000 of local capital 

stamp mills. As mining progressed and depths was invested in this enterprise. 

of oO to 100 feet were attained on the veins, the For the history of some of the smaller camps 

\ oxidized ore began to give way to sulphide of the region the reader is referred to the de-

) ores, which could not be treated profitably by tailed descriptions in Part III. 

1 such simple methods. With deeper develop- The claims shown on Plates V and VIII 

\ ment, too, the handling of water ili the mines (in pocket) ~e. given in the subjoined finding 

became a. more and more serious problem. lists. 

Finding list of claims shown on map of Central City and vicinity (Pl. V). 

A-I. 1. Barnacle. 

A-II. 1. Quartz Valley placer: 

A-V. 1. Silver Mug. 

2. Bill. 

3. Mesa. 

A-VI. 1. Del Monte. 

2. Zuni. 

3. Yule. 

4. Vendome. 

5. Mystic. 

6. Hawkeye. 

7. Galton. 

8. Gardner Extension. 

9. Porphyry. · 

10. No Name. 

11. Indiana E~tension. 

12. Gold Coin. 

13. Heloe. 

14. Silver Coin. · 

A-VII. 1. Torrent. 

2. Siren. 

3. Orient. 

4. Ivanhoe,. 

5. Empire. 

6. Leontine. 

7. Soden Extension. 

8. Neptune. 

9. Keystone. 

10. Vermilion. 

11. Leonidas. 

12. Jupiter. 

Arranged by coordinates. 

A-VII. 13. Gem. 

14. Wood. 

A-VIII. ·1. Ward. 

2. Howard. 

3. Gibraltar. 

4. Pure Gold. 

5. May. 

6. Quaker City. 

7. Song.· 

8. Golden Wing. 

9. Grace. 

10. Spring. 

11. Golden Dollar. 

12. West Delaware. 

13. Shamrock. 

14. Dean Richmond. 

15. Florence D. 

16. Maldar. 

17. Monte Christo. 

18. Prompt Pay. 

19. Union. 

20. Randolph Extension. 

21. Air Line. 

22. Hazard. 

A-IX~ 1. Triton. 

2. North Fairfield. 

3. Dayton. · 

4. Fairfield. 

5. South Fairfield. 

6. Isle Royal. 

7. Jupiter. 

A-IX. 8. St. Clair. 

9. Belmont. 

10. Springdale. 

11. Montana. 

12. Shamrock II. 

13. Celtic. 

14. ·Bremen. 

15. Osoeze. 

16. Ruby. 

17. Ethlyn. 

18. Alta Monte. 

19. Morning Star. 

20. Denbigh. 

21. Tarquin. 

A-X. 1. Bronco. 

5. Bryant. 

3. Westchester. 

4. McKee. 

5. Grisley. 

6. Bob Laurie. 

7. Rajah. 

8. Slavonic. 

9. Camper Down. 

10. Nagle. 

11. Thuhderbol t. 

12. John L. Emerson. 

13. Asteroid. 

14. ·white Cloud. 

15. Golden Star. 

16. President Hayes. 

17. Phoenix. 
70 GEOLOGY OF GILPIN, CLEAR CREEK, AND BOULDER COUNT!ES, . COLO. I 

Finding list of claims shown on map of Central City and vicinity-Continued. 

Arranged by coordinates-Continued. 

A-X. 18. Summit. B-VIII. 1. Boston. B-X. 22. Acra. 

19. Legal Tender. 2. French. C-I. 1. Quartz Valley placer. 

20. Sam Lee. 3. North Eclipse. 2. Janitor. 

21. Oregon. 4. Charter Oak. C-II. 1. Francis. 

B-II. 1. Belle. 5. Gem. C-III. 1. Spur Daisy. 

2. Chicago. 6. Ezra White. 2. Monitor. 

B-III. 1. Defender. 7. Capitol. 3. Cemetery. 

2. Dictator. 8. Day Spring. 4. Boodle. 

B-IV. I. Rara A vis Extension. 9. Capitol Prize. 5. Louis. 

2. Chief. 10. Jefferson (1011). 6. Garden No. 2. 

3. "S." 11. Jefferson (768) 7. Garden. 

B-V. 1. George. 12. Delaware (460 A). C-IV. 1. Bullion No. 2. 

2. "B." 13. Delaware mill site 2. Bullion No. 6. 

3. "A." (460 B). 3. Rara A vis. 

4. Herbert. 14. Randolph. 4. J. P. Whitney. 

5. Defender. 15. Eldorado. 5. Senate. 

6. Puritan. 16. Portage. 6. Independence. 

7. Vigilant. 17. Mollie Newcombe. 7. Ready Cash. 

8. Shafts. '18. ·Arlington (5875). 8. Fissure. 

9. Suffolk. 19. Conemara. C-V. 1. Essex. 

10. Kate Kearney. 20. Morrell. 2. Bertie. 

ll. Salpiro. 21. Topeka. 3. Dover. 

12. Irving. 22. Stewart. 4. Concrete. 

13. Skelton. '23. Blanche M. 5. Champion. 

14. Essex No. 2. B-IX. 1. Cooper. 6. Balen. 

15. Amberson & Warren. 2. Orion. 7. Golden Treasure. 

16. Hubert Fork. 3. Gomer. 8. Bird. 

17. Hubert Extension. 4. Pittsburg. 9. Jay Eye See. 

B-VI. 1. Oranoake. 5. Pendleton. 10. Motto. 

2. Oranoake Extension. 6. Phoenix. ll. Humboldt. 

3. Hickory. 7. Preston. 12. Parole. 

4. Geraldine. 8. Peale. 13. Hubert. 

5. Salvator. 9. Congressional. 14. Jones. 

6. Kansas. 10. Senatorial. 15. Genuine .. 

7. Northrop. 11. Russell. 16. Membrino. 

8. Big Moon. 12. Gomer No. 2. C-VI. 1. Axtell. 

9. American Flag. 13. Homestake. 2. Douglas. 

10. Indiana. 14. Free Coinage. 3. American Flag. 

11. Keystone. B-X. 1. Tonight. 4. Kansas No. 4. 

12~ Express. 2. West Pewabic. 5. Kansas mill site (91 B). 

13. Symonds. 3. Federal. 6. Kansas (91). 

14. Cooper. 4. Becky Sharp. 7. Mill site 619 B. 

15. Powell. · 5: Rubber. 8. Ute. 

16. Flack. 6. Rocky Mountain Ter- 9. Irish Flag. 

B-VII. 1. Sun. ror. 10. Monitor. 

2. Octavia Rachel. 7. Munson. 11. Burroughs. 

3.· Soden. 8. Warfield. 12. Truran. 

4. Mineral. 9. Robert Fulton. 13. Grand River. 

5. Ina. 10. Gladstone. 14. Randell Extension. 

6. Olympia. ll. Iron West. 15: Providence. 

7. Griffin. 12. Pawtucket. 16. Hidden Treasure. 

8.- Badger. 13. "84." 17. Hidden Treasure No. 2. 

9. Courtland. 14. Legal Tender. 18. California. 

10. Caledonia. 15. Livingstone. 19. Gardner. 

11. Pyrenees. 16. North. 20. Annie. 

12. Pyren~es Extension. 17. Venus. 21. Berkley. 

13. Boston. 18. "93." 22. Flack (664). 

14. French. 19. Golden Cloud. 23. E. Flack (929). 

15. Gunn. 20. Nashville. 24. Flack (65). 

16. Delmonico. 21. Columbia. 25. Mercer County. 
HISTORY OF MINING. 71 

Finding list of claims shown on map of Central City and vicinity-Continued. 

C-VI. 26. Mercer County Extension. 

27. Badger State. 

28. Rhode Island. 

29. Kent County. 

30. Maraposa. 

31. Barker. 

32. Governor Adanis. 

33. Kansas (87). 

34. Kansas (67). 

35. Camp Grove (86). 

36. Mill site 111 B. 

37. :Mill si~e 210. 

38. Mill site 350 B. 

C-VII. l. Sugar Tit. 

2. New Pikes Peak. 

3. Mitchell. 

4. Belcher. 

5. German. 

6. Last Chance. 

7. Burro. 

8. Lizzie S .. 

9. Ingomar. 

10. Dexter. 

11. Alps. 

12. Mac)ci.e. 

13. Tigress. 

14.· Shaw. 

15. Telephone. 

16. Ethan Allen. 

17. Winslow. 

18. Kirk. 

19. Polar Star. 

20. Blagden. 

21. Effie. 

22. Day Spring Extension. 

23. \Villowdale. 

24. Calhoun (837). 

25. Bouvier. 

26. Ninette. 

C-VIII. 1. Wood. 

2. Day Spring Extension. 

3. Calhoun (231). 

4. Mayflower. 

5. Calhoun (837). 

6. Fremont. 

7. Gold King. 

8. Mill site 247. 

9. Quartz Mill. 

10. Leavenworth. 

11. Bon Ton. 

12. Paola. 

13. Topeka. 

14. Gold Ring. 

15. Wyandotte. 

16. Topeka (518). 

17. Topeka (100). 

18. East Leavenworth. 

19. Harrison. 

20. Ruby. 

Arranged by coordinates''-Continued. 

C-VIII. 21. Defiance. 

22. Ohio. 

23. Bench. 

24. Rockford. 

25. Per:rin. 

26. Hogan. 

27. Hill ~ouse. 

28. West Wyandotte. 

C-IX. 1. Nelson. 

2. Russell Pride. 

3. Denver. 

4. Lutz Extension. 

5. Rist placer. 

6. Placer (858). 

7. Wautauga. 

8. Wautauga Extension. 

9. Phillips. 

10. Crresus Extension. 

11. Crresus. 

• 12. Minnesota. 

13. Incidental. 

14 .. Rosebud. 

15. Major. 

16. Pogue. 

17. Advalorem. 

18. Oldtown. 

19. Margaret. 

20. Clayton's Dream. 

21. Success. 

22. Lotus. 

23. Hot Time. 

24. Wash Kash. 

C-X. 1. Mill site 180. 

2. Becky Sharp. 

3. Federal. 

4. Pewabic (125). 

5. Pewabic (560). 

6. Richardson. 

7. Bobtail. 

8. Iron. 

9. Bangor. 

10. Cecilia. 

11. Mars. 

12. Bloomfield. 

13. Danforth. 

14. Montclair. 

15. Fannie. 

16. J. L. 

17. Victor. 

18. Hail Storm. 

19. Esmeralda. 

20. Virginia. 

21. Togo. · 

22. Grasshopper. 

23. Ida. 

D-I. 1. Norton. 

2. Harrison. 

D-II. 1. General L'ogan. 

2. West Keystone. 

3. Only Boy. 

D-II. 4. Bon Ton. 

5. A.M. 

6. Idea. 

D-III .. 1. Gold. 

2. Two Sisters. 

3. Maggie M. 

4. P~cific. 

5. Claire-Marie. 

6. Carroll. 

7. Little Chief. 

8. Hamilton. 

9. Storm King. 

10. Iowa. 

p. Lilly Rose. 

12. Alva Adams. 

13. Prospector. 

14. Lake Superior. 

D-IV. 1. Congress. 

2. Wood. 

3. Kohinoor No.2. 

4. Columbia A venue. 

· 5. Gold Bug. 

6. Arlington. . 

7. Eureka. 

8. Baby Ruth. 

9. Marine. 

10. Carrie G. 

11. Hydrant. 

12. Grand Army. 

13. Fagan. 

D-V. 1. Retriever. 

2. Wheeler. 

3. Herman. 

•4. Josephine. 

5. Kriegbaum. 

6. Silent King. 

7. North Star. 

8. Slaughter House. 

9. Prize. 

10. Iron Rock. 

11. Prize Extension. 

12. Seuderberg. J 

13. Buena Vista. 

14. Cymbra. 

15. Ashtabula. 

16. Newfoundland. 

17. Newfoundland No.2. 

18. Sunflower. 

19. Mayflower. 

20. Ashtabula-Ahay. 

21. pyke. 

22. Windsor. 

23. Jones. 

24. Post Hole. 

25. Levis mill site. 

26. Avondale. 

D-VI. 1. Mill site 88 B. 

2. Mill site 160 B. 

3. Sullivan. 

4. Kansas (610). 
72 GEOLOGY OF GILPIN, CLEAR CREEK, AND BOULDER COUNTIES, COLO. 

Finding list of claims shown on map of Central City and vicinity-Continued. 

D-VI. 5. Monroe (643). 

6. Monroe (8420). 

7. Monroe (195). 

8. Buckeye. 

9. New Chicago. 

10. Jay Gould. 

11. Welcome. 

12. Burroughs (262). 

13. Burroughs (l76). 

14: Baker. 

15. Gold Retort. 

16. Oakland. 

17. Climax. 

, 18. Little Pittsburg. 

19. Big Bone. 

20. ·Hannibal. 

21. Edinborough. 

22. Jan Joan. 

23. Gardner. 

24. Extenuate. 

25. Rhoderick Dhu. 

26. Confidence. 

27. Illinois. 

28. Mollie Gibson. 

29; Ingalls. 

30. Bell. 

31. Pratt. 

32. Egyptian. 

33. Protection. 

34. Modoc. 

35. Mill site 101 B. 

D-VII. 1. Pikes Peak Extension. 

2. Scandia. 

3. Jessie. 

4. Blythe. 

5. North. 

6. East Calhoun (11130). 

7. Calhoun. 

8. Telegraph. 

9. Mercury. 

. 10. "K." 

11. Monadnoc. 

12. EastHarshExtension. 

13. East Calhoun (7319). 

14. West Ouno. 

D-VIII. 1. Swiss Home. 

2. New Home. 

3. Home. 

4. George Deemster. 

5. Gopher. 

6. Canton. 

7. Harsh. 

8. Maud S. (6351). 

9. Overland. 

10. Michigan Boy. 

11. Holland. 

12. Columbus. 

13. Free American. 

14. Liberty. 

15. Yukon. 

16. Anglo-Saxon .. 

Arranged by coordinates-Continued. 

D-VIII. 17. Niagara. 

18. C. H. Smith placer. 

19. Yuma. 

20. Victoria mill site(5568). 

D-IX. 1. Royal. 

2. Louisiana. 

3. Bengal. 

4. Guion. 

5. Anchor. 

6. Lutz. 

7. I XL. 

8. Lucky Boy. 

9. Liliim. 

10. Waterloo. 

11. Wellington No. 5. 

12. Wellington No.4. 

13. "83." 

14. Wellington No. 3. 

15. Pewabic. 

· 16. Wellington. 

D-X. 1. Iron Duke. 

2 .. West Wellington. 

3. Compeer. 

4. Wellington No.7. 

5. Wellington No·. 8. 

6. Bonny Bell. 

7. Clifton Bell. 

8. Bert. ' 

9. Liberty BelL 

10. Blue Bell. 

11. Old Guard. 

12. Olga. 

13. Lottie. 

14. Paris. 

15. Gold Dollar. 

E-I. 1. Onandaga Chief. 

2. Carmichel. 

E-ll. 1. Gold Cup. 

2. Montezuma. 

3. Buckeye. 

4. Bullion (9607) . 

5. Bullion ( 459). 

6. East Keystone. 

7. Delight. 

8. Easton. 

9. Ravenswood. 

10. Colorado Girl. 

11. Keystone. 

E-III. 1. Tiger. 

2. Cedar. 

3. R.H. D. 

4. Polar Star. 

5. Irene.' 

6. Harkaway. 

7. Gulnare. 

8. Minnesota. 

9. Burlington. 

10. Iowa. 

11. Freiberg. 

12. Oro. 

E-IV. 1. Little Mack. 

I 

E-IV. ·2. Rumbold~. 

3. Thurman. 

4. I. X. L. 

5. Cameron. 

6. Montrose. 

7. Buckley.' 

8. Gunnell No.2. 

9. Gunnell (71). 

10. Nominee. 

11. Silent Queen. 

12. James Henry. 

13. ·Gunnell mill site 473, 

14. Gunnell (470). 

15. Mount Lincoln. 

E-V. ~· Backsheesh. 

2. Reno. 

3. High Grade. 

4. Straub. 

5. East Nevada. 

6. St. Louis Extension. 

7. Mill site 52. 

8. Stub Tail. 

9. Belcher. 

10. Lyman. 

11. DiVernon. 

12. Kansas. 

13. Alger. 

14. Isabella. 

15. Mill site 151. 

16. Olp Rice. , 

17. Vanderbilt. 

18. Lewis. 

19. New York. 

20. Columbia. 

21. Argo. 

22. Cork. 

23. Corydon. 

E-VI. 1. Fourth of July. 

2. Thomas Freeman. 

3. Columbia (657). 

4. Columbia (567). 

5: Missouri. 

6. Harlem. 

7. Videt,te. 

8. Copper Bottom. 

9. Interocean. 

10. Hecla. 

11. Barnes. 

12. Sylvania. 

13. Gauntlet. 

14. Quaker Lane. 

15. Times. 

16. Mat France. 

17. Big Thunder. 

18. Hayes & "\"\'heeler. 

19. Continental. 

20. Mill site 155B. 

21. Pocahontas. 

22. Woodbury. 

23. Aunt Jennie .. 

24. Gibson (70). 
HISTORY OF MINING. 73 

Finding list of claims shown on map of Central City and vicinity-Continued. 

Arranged by coordinates-Continued. 

E-VL 25. Mill site 70 B. E-IX. 15. Compensation. F-IV. 19. Butler-St. Louis. 

26. Walhala. ).6. Wellington Side. 20. St. LoUis. 

27. Register. 17. We~t \Velllngton. F-V. 1. Holman. 

28. Climax. 18. London. 2. Pleasant View No.2. 

29. Burroughs. 19. Two-Forty. 3: Satisfaction. 

30. Gibson (562). E-X. 1. Compeer. 4. Mountain Lion. 

31. Independence. 2. Wellington No. 6. 5. Gilpin County. 

E-VIl. 1. Hubert. 3. Wellington No. 9. 6. East Boston. 

2. Scottish Chief. 4. J,ondon. 7. Isabel. 

.) 3. J ... oina . 5. Paris. 8. Coour d'Alene. 

4. Aunt Jennie. 6. Russell Bell. 9. Wilber. 

5. Straughton. 7. Central Bell. 10. Pierce. 

6. Skelly. ·8. Daisy Bell. 11. Pierce-Galena. 

7. Great Mammoth. 9. Two-Forty. 12. Esperanza. 

8. M.ill site 59 B. 10. Junius. 13. Cora H. 

9. Harrisburg. 11. Apis. 14. Mill site 114 B. 

10. Gold Bug. 12. Panurge. 15. Quartz Hill tunnel No.3. 

11. Tropic. 13. Actreon. 16. Quartz Hill tunnel No.6. 

12. \Vhite Pine. 14. Osoeze. 17. Minnesota. 

13. Merrimac. 15. Geoffrey. 18. Ouray. 

14. Free Coinage. F-1. 1. ·Dick Wilson. 19 .. Mill site 143 B. 

15. Diedrick. 2. Ben Crenshaw No. 2. 20. Adaline. 

16. Maud S. · 3. Ben Crenshaw. F-VI. 1. Elizabethan. 

p. Blue Ridge. F-11. 1. Central. 2. Baxter and Crispin. 

18. Queen Bee. 2. Ontario. 3. Hunter Extension. 

19. Gold King. 3. Gundy. 4. Eldorado. 

20. Cuno. 4. Tucker mill site (216). 5. National. 

21. Gettysburgh. 5. Tucker Extension. 6. Durango. I 

22. C. H. 6. Starling. 7. Mammoth West. 

E-VIII. 1. Gold Run. 7. Cliff. · 8. Summit. 

2. Gold Coin. F-Ill. 1. Cliff Extension. 9. Mountain. 

3. Peele 2. Doc Beers. 10. Pride. 

4. Center. 3. Lulu Bowen. 11. Vanderbilt. 

5. Organ. 4. Castle Rock. 12. Aspen. 

6. Emma. 5. Robert G. Ingersoll. 13. Cur~an. 

7. Pine Ridge. 6. 1\fill site 440 B. 14. Grand Junction. 

8. Cataract. 7. George W. Ellery. 15. Baby B. 

9. Russell Gulch. 8. Black Quartz. 16. Texas. 

10. Autocrat. 9. Herbert Spencer. 17. Baby A. 

11. Centennial. 10. R. P. Ranney (435). 18. Times. 

12. Ipavia. 11. R. P. Ranney (94). 19. Mat France. 

13. Cissler. 12. Louis Napoleon. 20. Wright. 

14. Wbistler. 13. Arapahoe. 21. South Brooklyn. 

15. Retriever. F-IV. 1. Troublesome. 22. Mill site 41.0 B. 

16. Gaston. 2. Review. F-VII. 1. Lincoln. 

17. Defender. 3. Castro. 2. Gladstone. 

18. Little Jennie. 4. Triangle. 3 .. Firenzi. 

E-IX. 1. Niagara No. 2. 5. Winnebago. 4. Wells. 

2. Guion. , 6. Winnebago Extension. 5. British. 

3. Star of the West. 7. Huddleston. 6. Nugget. 

4. Missouri. 8. National Bank. I 7. Old Dougherty. 

5. Ridge. 9. Teller House. 8. Imperial. 

6. Japan. 10. Grand Gift. 9. ·Theodore. 

7. Sunshine. 11.. Mechanics. 10. Come. and see. 

8. Bengal. 12. Gunnell ( 449). 11. Thornton. 

9. 'Lizzie. 13. Sapphire. 12. Sunshine. 

10. Henry Paul placer. 14. John Hay: 13. Sunnyside. 

11. Homeguard. 15. Jackson. 14. Reichstag. 

12. Wellington No. 10. 16. St. Louis No. 2. 15. Prize Baby. 

i3. \Vellirigton No. 1. 17. Tremont. F-VIIL 1. Aurora. 

14. East Wellington. 18. West St. 'Louis. 2. West Alva Adams. 
74 GEOLOGY OF GILPIN, CLEAR. CREEK, AND BOULDER COUNTIES, COLO. 

Finding list of claims shown on map. of Central City and vicinity-Continued. 

Arranged by coordinates-Continue~ .. 

F-VIII. 3. Extension. G-II. ~1. Bonanza tunnel No. 10. G-V. 22. McAdams. 

4. S.C. Booth. 12. Bonanza tunnel No. 9. 23. Mosell. 

5. Pocahontas. 13 .. Sans Souci. 24. Ontonagon. 

6. Eleventh Hour. 14. Mountain and Plain. 25. Mill site 53. 

7. Independence. 15. Mountain Club. 26. Calhoun. 

8. East Centennial. G-Ill. 1. Allie. G-VI. 1. Mammoth. 

9. Beacon of the West. ~;L. Security. 2. McAdams. 

10. Marathon. 3. Black Hawk. 3. Mammoth Side. 

11. Eliminator. 4. Alonzo Fernals. 4. Chicago. 

12. North Saratoga. 5. Greenside. 5. West.Michigan. I 

13. Decatur Extension. 6. First Centennial. 6. Republic-Gregory. \ 14. L<;>rah. 7. E~st Centennial. 7. W.est Gregory. 

15. Saratoga tunnel No. 1 8. General. 8. Cashier. 

West. 9. Dewey. 9. Montana. 

16. Congress. 10. ·Center. 10. Lake View. 

17. Gaston (369). 11. Golden Gate. 11. Mountain Rose. 

18. Saratoga West. 12. Queen of the West. 12. Poole. 

19. West Saratoga. 13. ·Virginia. 13. Protection. 

20. Vindicator. 14. Huddleston. 14.' Good Luck. 

F-IX. 1. Exterminator. 15. Maryland. 15. Empress. 

2. Waltham. 16. Bonanza tunnel No. 8; 16. Sapsfield. 

3. Timbuctoo. 17. Bonanza tunnel No. 7. G-VII. 1. Hamburg. 

4. Rover .. 18. Bonanza tunnel No. 6. 2. Gold K;ing. 

5. Henry Paul placer .. 19. Virginia Extensiop. 3. Eagle. 

6. Pewabic No. 4. 20. Bonanza .tunnel No. 5. 4. Mountain. 

7. Pewabic No.3. 21. Bonanz.a tunnel No. 4. 5. Jasper. 

8. Helmer. 22. Mill site 240 B. 6. Iowa. 

9. Banner No.2. '23. Mill site 384 B. 7. ~ismarck. 

10. New House. 24 .. Robert Emmet. 8. Gladstone. 

11. Maine. 25. Tennel & Belden. 9. Augustin. 

12. Peton. G-IV. 1 .. St. Louis No. 3. 10. Notice. 

13. West.Hazeltine. 2. Road Jr. 11. Baldwin. 

14. Quandry. 3. Bueno. 12. Little Etta. 

F-X. 1. Trentina. 4. Comstock. 13. Blaine. 

2. Elizbone. 5. Clipper. 14. Mattie May. 

3. Margaret. 6. Freedom. · G-VIII.· 1. Alva Adams. 

4. Old Jordan. 7. ·Sterling. 2. Balt'imore. 

5. Church placer. 8. Rialto. 3. Decatur. 

6. Searle. 9. Dillon. 4. Saratoga tunnel No. 1 

7. Aduddell. 10. Lottie. East. 

8. Poor Luck. G-V. 1. U. S.M. (424). 5. East Saratoga. 

G-1. 1. Wheeler mill site (382). 2. Bugher. 6. Saratoga. 

2. Tunnel Lode No.1. 3. Bull <;>f the Woods. 7. West Chase: 

3. Bonanza tunnel No. 28. 4. Gregory No.2. 8. Pandora. 

4. Bonanza tunnel No. 27. 5. Maine. 9. Chase .No. 2. · 

5: Bonanza tunnel No. 26. 6. Number One. 10. Mammoth. 

6. Bonanza tunnel No. 25. 7. Hamlet. G-IX. 1. Helmer. 

7. Bonanza tunnel No. 24. 8. Kip. 2. Mill site 148 B. 

8. Bonanza tunnel No. 23. 9. Union. 3. Mill site 147 B. 

9 .. Bonanza tunnel No. 22. 10. Mountain City. 4. H~zeltine. 

10. Bonanza tunnel No. 21. 11. Tierney. 5. Henry Paul placer. 

G-Il. 1. Bomi.nza tunnel No. 20. 12. Epizo9tic .. 6. Church placer. 

2. Bonanza tunnel No. 19. 13. McCallister. 7. Paul. . 3. Bonanza tunnel No. 18. 14. Old Bullion. G-X. 1. Howard. 

4. Bonanza tunnel No. 17. 15. Homer. 2. Kokomo. , 

5. Bon,anza tunnel No.'16. 16. Brighton. 3. Klondike. · 

6. Bonanza tunn~l No. 15. 17. Brooklyn Eagle. 4. Texas. 

7. Bonanza tunnel No. 14. 18. Waterberry. 5. Lost Float. 

8. Bonanza tunnel No. 13. 19. West Michigan. 6. Bimetallic. 

9. Bonanza tunnel No. 12. 20. Rhine. H-I. 1. L. C. :Rockwell. 

10:· Bonanza tunnel N,o. 11. 21. Schiller. 2. Brittle Sliver. 
HISTORY O:E' MINING. 75 

Finding list of claims shou;n on map of Central City and ·vicinity-Continued. 

Arranged by coordinates-Continued. 

H-I. 3. Juno. H-V. 15. Branch. H-IX. 9. Ohio. 

4. Kimber Fullerton mill 16. Orion. 10. Golden Ridge. 

site. 17. Cook (97). 11. Klondike. 

5. Arrigni mill site. H-VI. 1. Treasury. 12. Texas. 

6. Mill site 185 B. 2. Allie. H-X. 1. Mystery. 

II-II. 1. Kinney tunnel. 3. King Solomon. 2. Fate. 

2. Dumas. 4. Gold Brick. 3. Golden Ridge. 

3. Howard. 5. Humboldt. 4;. Glascow. 

4. Queens County. 6. Golden Fleece. 5. Little Annie. 

5. Mary Ella. 7. Duchess. 6. McFarlane. 

6. Oliver. 8. Katie. 7. Rob Roy. 

7. Discovery of Virginia. 9. Morning Red. 8. Palo Alto. 

8, 9. Brack Hollow. 10. Double Eagle. 9. Silver Ledge. 

H-Ili. 1. :Mill site 272 A. 11. Golden Eagle. [-I. 1. St. Louis. 

2. Maryland. 12. Evening Star. 2. Nil Desperandum. 

3. Mill site 272 B. H-VII. 1. Hoff Garten. 3. Mayflower. 

4. Bonanza tunnel No. 3. 2. Seeker-Finder. 4. Susquehanna. 

5. Bonanza tunnel No. 2. 3. Lone Tree. 5. ·wheel of Fortune. 

6. 2Etna. 4. Golden Quick. 6. Little Willie. 

7. 1\fill site 241 B. 5. N otaway Belle. I-II. 1. Mill site 221 B. 

8. Alabama. 6. Sub-Treasury. 2. Elsinore. 

9. Road of Elephant. 7. Independence. 3. Cyclops. 

10. Mill site 385 B. 8. Notaway (136). 4. Mammoth Silver. 

11. Ninety-Four. 9. Homestake. 5. Brack Hollow. 

12. Enterprise. 10. Golden Wedge. 6. Dallas. 

13. South Bend. 11. Notaway (735). 7. Mountain mill site. 

14. Surprise. 12. Buffalo. 8. Peru. 

H-IV. l. Somes. 13. Meeker. 9. Julia. 

2. Billings (200). 14. Little Raven. 10. Fannie. 

3. Billings (168). 15. Eighty-Niner. 11. St. James. 

4. Prospector. 16. Cecil. 12. Paul Jones. 

5. Smith. 17. Notaway (328). 13. East Star. 

6. Wain. 18. Hidee. 14. Slice. 

7. \Vhiteside. II-VIII. 1. Argo. 15. Pocahontas. 

8. Ontonagon. 2. La Place. I-III. 1. Tippe'canoe. 

9. Gregory (879). 3. Big Wampum. 2. Powhatan. 

10. Levitt. 4. Tiger. 3. Freedom. 

11. Eliott. 5. Nebula. 4. Smitll. 

12. Union. 6. Mohonga. 5. Extension of Bates. 

13. Saxon. 7. S. P. Chase. 6. Carbonate. 

14. Vulcan. 8. Sanger. 7. Little Giant. 

15. Gettysburgh. 9. Bosen Plume. I-IV. 1. Bates mill site. 

16. Topeka. 10. Princess Louise. 2. O.M. 

17. Bates. 11. Minnehaha. 3. P.M. 

18. Kitty. 12. New Brunswick. 4. Democrat. 

19. Hope No. 2. 13. Herschel. 5. A.M. , 

20. Next President. 14. War Dance. 6. Gregory (267). 

H-V. 1'. Hartford. 15. G. A. S. No.4. 7. Gregory Extension. 

2. Dump.- 16. Partner Newcomb .. 8. Gregory (373). 

3. Mill site 212. 17. G. A. S. No.5. 9. Mill site 2378. 

4. Atlantic. 18. Golden. 10. Mill site 186 H. 

5. 0'Neil. 19. Silver Dollar. 11. Mill site 128 B. 

6; Pennsylvania. 20. Powers. 12. Sleepy Hollow. 

7. Golden Crossing: H-IX. 1. Martin. 13. Blyth. 

8. Morning Star. 2. Conjunction. 14. Sioux City. 

9: Parole. 3. White Rock. 15. Americus. 

10. Mammoth (366)! 4. Paul. 1-V. 1. Lizzie. 

11. Puzzle 5. Kokomo. 2. Ground Hog. 

12. Fisk. 6. East Hazeltine. 3. Broadway. 

· 13. Cook No.2. 7. Hammon. 4. Bobtail (489). 

14. Washington. 8. Yellow Girl. 5. Mollie Stark. 
76 GEOLOGY OF GILPIN, CLEAR CREEK, AND BOULDER COUNTIES, COLO. 

Finding list of claims shown on map of Central City and vicinity-Continued. 

I-V. 6. Manahan. 

7. New Jersey. 

8. Fisk. 

9. Cotton. 

10. Nemeha. 

11. Warwick. 

12. Denmark. 

I-VI. 1. Lizzie. 

2. Williamsville. 

3. Artie. 

4. Hunky Dory. 

5. Bedford Co. 

6. Little Harvey. 

7. Annex. 

8. Mollie Stark Extension. 

9. Luckie Duckie. 

10. Unexpected. 

11. Carr. 

12. Little Pittsburg. 

13. Notaway Extension. 

I-VII. 1. Gulch. 

"A." B-V: 3. 

Acra. B-X: 22. 

Actreon. E-X: 13. 

Adaline. F-V: 20. 

Aduddell. F-X: 7. 

Advalorem. C-IX:-17. 

1Etna. H-Ill: 6. 

Air Line. A-VIII: 21. 

Alabama. H-Ill: 8. 

Alger. E-V: 13. 

Allie. G-III: 1; H-VI: 2. 

Alonzo Fernals. G-Ill: 4. 

Alps. C-VII: 11. 

Alta.Monte. A-IX: 18. 

Alva Adams. D-III: 12; G-VIII: I. 

A.M. D-II: 5; I-IV: 5. I 

Amberson and Warren. B-V: 15. 

American Boy. I-VII: 15. 

American Flag. B-VI: 9; C-VI: 3.' 

Americus. I-IV: 15. -

Anchor. D-IX: .5. 

Anglo-Saxon. D-VIII: 16. 

Annex. I-VI: 7. 

Annie. C-VI: 20. 

Annie Mary. I-VII: 7. 

Apis. E-X: 11. 

A,rapahoe. F-Ill: 13. 

'Artie. I-VI: 3. 

Argo. E-V: 21; H-VIII: I. 

Arlington 5875. B-VIII: 18. 

Arlington 415. D-IV: 6. 

Anigni mill site. H-I: 5. 

Ashtabula. D-V: 15. 

Ashtabula-Ahay. D-V: 20. 

Aspen. F-VI: 12. 

Asteroid. A-X: 13. 

Atlantic. H-V: 4. 

Arranged by coordinates-Continued. 

I-VII. 2. Dale:1 

3. Star •Route. 

4. Black Diam~nd. 

5. Fay. 

6. Marks. 

7. Annie Mary. 

8. Elizabeth. 

9. Evelyn. • 

10. Pittsburg. 

11. Calumet & Hecla No.2. 

12. Calumet & Hecla. 

13. Sutton. 

14. Caledonia No.2. 

15. American Boy. 

16. Helen Gould. 

17. Pittsburg Extension. 

18. Morris. 

I-VIII. 1. Uncle,Sam.' 

2. Success. 

3. Star Route. 

4. Boston Boy.· 

Arranged alphabetically. 

Augustin. G-VII: 9. 

Aunt Jennie. E-VI: 23; E-VIl: 4. 

Aurpra. F-VIII: I. 

Autocrat. E-VIII: 10. 

Avondale. D-V: 26. 

Axtell. C-VI: 1. 

"B." B-V: 2. 

Baby A. F-VI: 17. 

Baby B. F-VI: 15. 

Baby Ruth. D-IV: 8. 

Backsheesh. E-V: 1. 

Badger. B-VII: 8. 

Badger State. C-VI: 27. 

Baker. D-VI: 14. 

·Baldwin. G-VII: 11. 

Balen. 0-V: 6. 

Baltimore. G-VIII: 2. 

Bangor. C-X: 9. · 

Banner. No.2. F-IX: 9. 

Barker.· C-VI: 31. 

Barnacle. A-I: I. 

Barnes. E-VI: 11. 

Bates. H-IV: 17. 

Bates mill site. I-IV: 1. 

Baxter and Crispin. F-VI: 2. 

Beacon of the West. F-VIII: 9. 

Becky Sharp. B-X: 4; C-X: 2. 

Bedford Co. I-VI: 5. 

Belcher. C-VII: 4; "E-V: 9. 

Bell. D-VI: 30. 

Belle. B-II: I. 

Belmont. A-IX: 9. 

Bench. C-VIII: 23. 

Ben Crenshaw. F-21: 3. 

Ben Crenshaw No.2. F-I: 2~ 

Bengal. D-IX: 3; E-IX: 8. 

I-VIII. . 5. G. A. S. No.3. 

6. Meeker. 

7. Rainbow. 

8. Lorillard. 

9. Star of the West. 

10. Black Bear. 

11. Hampton. · 

12. West American Boy. 

13. G. A. S. No. I. 

14. G. A. S. No.2. 

15. Iroquois. 

16. Conjunction. 

17. Bunker Hill. 

18. Washington Extension. 

19. Mayflower. 

20. War Dance Extension. 

21. Martin. 

22. Hard to Beat. 

J-VIII. 1. Bonanza. 

2. Grand View~ 

Berkley. C-VI: 21. 

Bert. D-X: 8. 

Bertie. C-V: 2. 

·Big Bone. D-VI: 19. 

Big Moon. B-VI: 8. 

Big Thunder. E-VI: 17. 

Big Wampum .. H-VIII: 3. 

Bill. A-V: 2. 

.Billings (168). H-IV: 3. 

Billings (200). H-IV: 2. 

Bimetallic. G-X: 6. 

Bird. C-V: 8. 

Bismarck. G-VII: 7: 

Black Bear.· I-VIII: 10. 

Black Diamond. I-~II: 4. 

Black Hawk. G-Ill: 3. 

Black Quartz. F-Ill: 8. 

Blagden. 0-VII: 20. 

Blaine. G-VII: 13. 

Blanche M. B-VIII: 23. 

Bloomfield. C-X: 12. 

Blue B~ll. D-X: 10. 

Blue Ridge. E-VIl: 17. 

Blyth. I-IV: 13. 

Blythe. D-VII: 4 .. 

Bob Laurie. A-X: 6. 

Bobtail. C-X: 7. 

Bobtail (489). I-V: 4. 

'Bonanza. J .... :vrn: I. 

Bonanza tunnel No.2. 

Bonanza tunnel No.3. 

Bonanza tunnel No.4. 

Bonanza tunnel No.5. I . 

Bonanza tunnel No.6. 

Bonanza'tunnel No. 7. 

Bonanza tunnel No.8. 

. Bonanza tunnel No.9. 

H-Ill: 5. 

H-Ill: 4. 

G-Ill: 21. 

G-III: 20. 

G-Ill: 18. 

G-Ill: 17. 

G-Ill: 16. 

G-Il: 12. 
) 

HISTORY OF MINING. 77 

Finding list of claims shown on map of Central City and vicinity-Continued .. 

·Bonanza tunnel No. 10. G-Il: 11. 

Bonanza tunnel No. 11. G-Il: 10. 

Bonanza tunnel No. 12. G-Il: 9. 

Bonanza tunnel No. 13. G-Il: 8. 

Bonanza tunnel No. 14. G-Il: 7. 

Bonanza tunnel No. 15. G-II: 6. 

Bonanza tunnel No. 16. G-II: 5. 

Bonanza tunnel No. 17. G-II: 4. 

Bonanza tunnel No. 18. G-II: 3. 

Bonanza tunnel No. 19. G-II: ~. 

Bonanza tunnel No. 20. G-Il: 1. 

Bonanza tunnel No. 21.. G-1: 10. 

Bonanza tunnel No. 22. G-l; 9. 

Bonanza tunnel No. 23. G-1: 8.' 

Bonanza tunnel No. 24. G-1: 7. 

Bonanza tunnel No. 25. G-1: 6. 

Bonanza tunnel No. 26. G-1: 5. 

Bonanza tunnel No. 27. G-1: 4. 

Bonanza tunnel No. 28. G-1: 3. 

Bonny Bell. D-X: 6. 

Bon Ton. 0-VIII: 11; D-11: 4. 

Boodle. C-111: 4. 

Bosen Plume. H-VIII: 9. 

Boston. B-VII: 13; B-VIII: 1.; 

Boston Boy. I-VIII: 4. 

Bouvier. 0-VII: 25. 

Brack Hollow .. H-11: 8; H-II: 9; 

1-11: 5. 

Branch. H-V: 15. 

· Bremen. A-IX: 14. 

Broadway. 1-V: 3. 

Bronco. A-X: 1. 

Brooklyn Eagle. G-V: 17. 

Brighton. G-V: 16. ' 

British. F-VII: 5. 

Brittle Silver~ H-I: 2. 

Bryant. A-X: 2. 

Buckeye. E-li: 3; D-VI: 8. 

Buckley. E-IV: 7. 

Buena Vista. D-V: 13. 

Bueno. G-IV: 3. 

Buffalo. H-VII: 12. 

Bugher. G-V: 2. 

Bullion (459). E-li: 5. 

Bullion {9607). E-li: 4. 

Bullion No.2. 0-IV: 1. 

Bullion No.6. C-IV: 2. 

Bull of the Woods. G-V: 3. 

Bunker Hill. I-VIII: 17. 

Burlington. E-III: 9. 

Burro. C-VII: 7. 

Burroughs. E-VI: 29; C-VI: 11. 

Burroughs (176). D-VI: 13. 

Burroughs'(262). D-VI: 12. 

Butler-St. Louis. F-IV: 19. 

Caledonia. B-VII: 10. 

Caledonia No.2. I-VII: H. 

Calhoun. D-VII: .7; l1-V: 26.' 

Arranged alphabetically-Continued. 

Calhoun (837). C-VII: 24; C-VIII: 5. 

Calhoun (231). C-VIII: 3. 

·California. C-VI: 18. 

Calumet & Hecla. I-VII: 12. 

Calumet & Hecla No. 2. I-VII: 11. 

Cameron. E-IV: 5. 

Camper Down. A-X: 9. 

Camp Grove (86). C-VI: 35. 

Canton. D-VIII: 6. 

Capitol. B-VIII: 7. 

Capitol Prize. B-VIII: 9. 

Carbonate. I-III: 6. 

Carmichel. E-1:. 2. 

Carr. I-VI: 11. 

Carrie G. D-IV: 10. 

Carroll. D-Ill: 6. 

Cashier. G-VI: 8. 

Castle Rock. F-Ill: 4. 

Castro. F-IV: 3. 

Cataract. E-VIII: 8. 

Cecil. H-VII: 16. 

Cecilia. C-X: 10. 

Cedar: E-III: 2. 

Celtic~ A-IX: 13. 

Cemetery. C-111: 3. 

Centennial. E-VIII: 11. 

Center. E-VIII: 4; G-Ill: 10. 

Central. F-11: 1. 

Central Bell. E-X: 7. 

C. H. E-VII: 22. 

Champion. 0-V: 5. 

Charter Oak. B-VIII: 4. 

Chase No.2. G-VIII: 9 

Chicago. B-ll: 2; G-VI: 4. 

Chief. B-IV: 2. 

C. H. Smith placer. D-Vlll: 18. 

Church placer. F-X: 5; G-IX: 6. 

Cissler. E-VIII: 13. 

Claire-Marie. D-Ill: 5. 

Clayton's Dream. 0-IX: 20. 

Cliff. F-11: 7. 

Cliff Extension. F-Ill: 1. 

Clifton Bell. D-X: 7. 

Climax. E-VI: 28; D-VI: 17. 

Clipper. G-IV: 5. 

Cceur d'Alene. F-V: 8. 

Colorado ·Girl. E-11: 10. 

Columbia. E-V: 20; B-X: 21. 

Columbia (657). E-VI: 3. 

Columbia (567). E-VI: 4. 

Columbia A venue. D-IV: 4. 

Columbus. D-VIII: 12. 

Come and see. F-VII: 10. 

Compeer. D-X: 3; E-X: 1. 

Compensation. E-IX: 15. 

Comstock. G-IV: 4. 

Concrete. C-V: 4. 

Conemara. B-VIII: 19. 

Confidence. D-VI: 26. 

Congress. D-IV: 1; F-Vlii: 16. 

Congressional. B-IX: 9. 

Conjunction. I-VIII:.l6; H-IX: 2. 

Continental. E-VI: 19. 

Cook {97). H-V: 17. 

Cook No.2. H-V: 13. 

Cooper. B-IX: 1; B-Vl: 14. 

Copper Bottom. E-VI: 8. 

Cora H. F-V: 13. 

Cork. E-V: 22. 

Corydon. E-V: 23. 

Cotton. 1-V: 9. 

Courtland, B-VII: 9. 

Crcesus. C-IX:. ·11. 

Crcesus Extension·. C-IX: 10. 

Cuno. E-VIl: •20. 

Curran. F-VI: 13. 

Cyclops. 1-11: 3. 

Cymbra. D-V: 14. 

Daisy Bell. E-X: 8. 

Dale. I-VII: 2. 

Dallas. I-II: 6. 

Danforth. C-X: 13. 

Day Spring. B-VIII: 8. 

Day Spring Extension. C-VII: 22; 

0-VIII: 2. 

Dayton. A-IX: 3. 

Decatur. G-VIII: 3. 

Decatur Extension. F-VIII: 13. 

Defender. B-Ill: 1; B-V: '5; EVIII: 17. 

Defiance.· 0-VIII: 21. 

Delaware (460 A). B-VIII: 12. 

Delaware mill .site 460 B. B-VIII: 13. 

Delight. E-11: 7. 

Delmonico. B-VII: 16. 

Del Monte. A-VI: 1. 

Democrat. I-IV: 4. 

Denbigh. A-IX: 20 .. 

Denmark. I-V: 12. 

Denver. 0-IX: 3. 

Dewey. G-Ill: 9. 

Dexter. C-VII: 10. 

Dick Wilson. F-1: 1. 

Dictator. E-III: 2. 

Diedrick. B-VII: 15. 

Dillon. G-IV: 9. 

Discovery of Virginia. H-II: 7. 

DiVernon. E-V: 11. 

Doc Beers. F-111: 2. 

Double Eagle. H-VI: 10. 

Douglas. C-VI: 2. 

Dover. C-V: 3. 

Duchess. H-VI: 7. 

Dumas. H-II: 2. 

Dump. H-V: 2. 

Durango. F-VI: 6. 

Dyke. D-V: 21. 
78 GEOLOGY OF GILPIN, CLEAR ·CREEK, AND BOULDER COUNTIES, COLO. 

Finding list of claims shown on map of Central City and vicinity-Continued. 

Eagle. G-VII: 3. 

East Boston. F-V: 6. . 

East Calhoun (73~9). D-VII: 13. 

East Calhoun (11130). D-VII: 6. 

EastOentennial. G-III: 7; F-VIII: 8. 

East Flack (929). 0-VI: 23. 

East Harsh Extension. D-VII: 12. 

East Hazeltine. H-IX: 6. 

East Keystone. E-II: 6. 

East Leavenworth. C-VIII: 18. 

East Nevada. E-V: 5. 

Easton. E-II: 8. 

East Saratoga. G-VIII: 5. 

East Star. I-II: 13. 

East Wellington. E-IX: 14. 

Edinborough. D-VI: 21. 

Effie. 0-VII: 21. 

' Egyptian. D-VI: 32. 

Eighty-Four. B-X: 13. 

Eighty-Niner. H-VII: 15. _ 

Eighty-Three. D-IX: 13. 

Eldorado. F-VI: 4; B-VIII: 15. 

Eleventh Hour. F-VIII: 6. 

Eliminator. F-VIII: 11. 

Eliott. H-IV: 11. 

Elizabeth. I-VII: 8. 

Elizabethan. F-VI: 1. 

Elizbone. F-X: 2. 

Elsinore. I-II: 2. ' 

Emma. E-VIII: 6. 

Empire. A-VII: 5. 

Empress. G-VI: 15. 

Enterprise. H-III: 12. 

Epizootic. G-V: 12. 

Esmeralda. 0-X: 19. , 

Esperanza. F-V: 12. · 

Essex. 0-V: 1. 

Essex No."2. B-V: 14. 

Ethan Allen. 0-VII: 16. 

Ethlyn. A-IX: 17. 

Eureka. D-IV: 7. 

Evelyn. I-VII: 9. 

Evening Star. H-VI: 12. 

Express. B-VI: 12. 

Extension. F-VIII: 3. 

Extension of Bates. I-III: 5. 

Extenuate. D-VI: 24. 

Exterminator. F-IX: 1. 

Ezra White. -B-VIII: 6. 

Fagan. D-IV: 13. 

Fairfield. A-IX: 4. 

Fannie. I-II: 10; 0-X: 15. 

Fate. H-X: 2. . 

Fay. I-VII: 5. 

Federal B-X: 3; C-X: ?. 

Firenzi. F-VII: 3. 

First Centennial. G-III: 6. 

Fisk. I-V: 8; H-V: 12 .. 

Fissure. C-IV: 8. 

Arranged alphabetically-Continued. 

Flack. B-VI: 16. 

Flack (65). 0-VI: 24. 

Flack (664). 0-VI: 22. 

Florence D. A-VIII: 15. 

Fourth of July. E-VI: 1. 

Francis. 0-II: 1. 

Free American. D-VIII: 13. 

Free Coinage. B-IX: 14; E-VII: 14. 

Freedom. I-III: 3; G-IV: 6. 

Freiberg. E-III: 11. 

Frem.ont. C-VIII: 6. 

French. B-VII: 14; B-VIII: 2. 

Galton. A-VI: 7. 

Garden. 0-II~: 7. 

Garden No.2. 0-III: 6. 

Gardner. C-VI: 19; D-VI: 23. 

Gardner Extension. A-VI: 8. 

G. A. S. No. 1. I-VIII: 13. 

G. A. S. No.2. I-VIII: 14. 

G. A. S. No. '3. I-VIII: 5. 

G. A. S. No.4. H-VIII: 15; 

G. A. ·s. No. 5. H-VIII.: 17. 

Ga.ston. E-VIII: 16. 

Ga.ston (369). F-VIII: 17. 

Gauntlet. E-VI: 13. 

Gem. A-VII: 13; B-VIII: 5. 

General. G-III: 8. · 

General Logan. D-II: 1. 

Genuine. 0-V: 15. 

Geoffrey. E-X: 15. 

George. B-V: 1. 

George Deemster. D-YIII: 4. 

George W. Ellery. F-III: 7. -

Geraldine. B-VI: 4. 

German. 0-VII: 5. 

Gettysburgh. E-VII: 21; H-IV: 15. 

Gibraltar. A-VIII: 3. 

Gibson (562). E-VI: 30. 

Gibson (70). E-VI: 24. 

Gilpin County. F-V: 5. 

G I ads ton e. B-X: 10; F-VII: 2; 

G-VII: 8. 

Glascow. H-X: 4. 

Gold. D-III: 1. 

Gold Brick. H-VI: 4. 

Gold Bug. E-VII: 10; D-IV: 5. 

Gold Coin. A-VI: 12; E-VIII: 2. 

Gold Cup. E-II: 1. 

Gold Dollar. D-X: 15. 

Golden. H-VIII: 18. 

Golden Cloud. B-X: 19. 

Golden Crossing. H-V: 7. 

Golden Dollar. A-VIII: 11. 

Golden Eagle. H-VI: 11. 

Golden Fleece. H-VI: 6. 

Golden Gate. G-III: 11. 

Golden Quick. H-VII: 4. 

Golden Ridge. H-IX: 10; H-X: 3. 

Golden Star. A-X: 15. 

Golden Treasure. C-V: 7. 

Golden \Vedge. H-VII: 10. 

Golden Wing. A-VIII: 8. 

Gold King. G-VII: 2; C-VIII: 7; 

E-VII: 19. 

Gold Retort. D-VI: 15. 

Gold Ring. 0-VIII: 14. 

Gold Run. E-VIII: 1: 

Gomer. B-IX: 3. 

Gomer No.2. B-IX: 12 

Good Luck. G-VI: 14. 

Gopher. D-VIII: 5. 

Governor Adams. C-VI: 32. 

Grace. A-VIII: 9. 

Grand Army. D-IV: 12. 

Grand Gift. F-IV: 10. 

.Grand Junction. F-VI: 14. 

Grand River. 0-VI: 13. 

Grand View. J-VIII: 2. 

Grasshopper. 0-X: 22. 

Great l'!ammoth. E-VIl: 7. 

Greenside. G-III: 5. 

Gregory (879). H-IV: 9. 

Gregory No. 2. G-V: 4. 

Gregory (267). I-IV: 6. 

Gregory (373). I-IV: 8. 

Gregory Extension. I-IV: 7. 

Griffin. B-VII: 7. 

Grisley. A-X: 5. 

Ground Hog. I-V: 2. 

Guion. E-IX: 2; D-IX: 4. 

Gulch. I-VII: 1. 

Gulnare. E-III: 7. 

Gundy. F-II: 3. 

Gunn. B-VII: 15. 

·Gunnell No.2 .. E-IV: 8. 

Gunnell (71). E-IV: 9. 

Gunnell (449.) F-IV: 12. 

Gunnell (470). E-IV: 14. 

Gunnell mill site 473. E-IV: 13. 

Hail Storm. 0-X: 18. 

Hamburg. G-VII: l. 

Hamilton. D-III: 8. 

Hamlet. G-V: 7. 

Hammon. H-IX: 7. 

Hampton. I-VIII: 11. 

Hannibal. D-VI: 20. 

Hard to Beat. I-VIII: 22. 

Harkaway. E-III: 6. 

Harlem. E-VI: 6. 

Harrisburg. E-Vii: 9. 

Harrison. C-VIII: 19; D-I: 2. 

Harsh. D-VIII: 7. .. 

Hartford. H-V: 1. 

Hawkeye. A-VI: 6. 

Hayes and Wheeler. E-VI: 18. 

Hazard. A-VIII: 22. 

Hazeltine. G-IX: 4. 

Hecla. E-VI: 10. 

I 

\ 
) 

HISTORY OF MINING. 79 

Finding list of claints sho'Wn on map of Central City and vicinity-Continued. 

Arranged alphabetically-Continued. 

Helen Gould. I-VII: 16. Isabella. E-V: 14. 

Helmer. F-IX: 8; G-IX: l. Isle Royal. . A-IX: 6. 

Heloe. A-VI: 13. . Ivanhoe. A-VII: 4. 

Henry Paul placer. ~IX: 10; F-IX: LX. L. D-IX: 7; E-IV: 4. 

5; G-IX: 5. 

Herbert. B-V: 4. 

Herbert Spencer. F-Ill: 9. 

Herman. D-V: 3. 

Herschel. H-VIII: 13. 

Hickory. B-VI: 3. · 

Hidden Treasure. 0-VI: 16. 

Hidden 'l'reasure No. 2. 0-VI: 17. 

Hiclee. H-VII: 18. . 

High Grade. E-V: 3. 

Hill House. C-VIII: 27. 

Hoff Garten. H-VII: 1. 

Hogan. C-VIII: 26. 

Holland. D-VIII: 11. 

Holman. F-V: 1. 

Home. D-VIII: 3. 

Homeguard. E-IX: 11. 

Homer. G-V: 15. 

Homestake. B-IX: 13; H-VII, 9. 

Hope No. 2. H-IV: 19. 

Hot Time. 0-IX: 23. 

Howard.A-VIII: 2; H-II: 3; G-X:l. 

Hubert. E-VIl: 1; 0-V: 13. 

Hubert Extension. B-V: 17. 

Hubert Fork. D-V: 16. 

Huddleston. F-IV: 7; G-Ill: 14. 

Humboldt. C-V: 11; E-IV: 2; 

H-VI: 5. 

Hunky Dory. I-VI: 4. 

Hunter Extension. F-VI: 3. 

Hydrant. D-IV: 11. 

Ida. 0-X: 23. 

Idea. D-II: 6. 

Illinois. D-VI: 27. 

Imperial. F-VII: 8. 

Ina. B-VII: 5. 

Incidental. 0-IX: 13. 

Independence. E-VI: 31; 0-IV: 6; 

F-VIII: 7; H-VII: 7. 

Indiana. B-VI: 10. 

Indiana Extension. A-VI: 11. 

Ingalls. D-VI: 29. 

Ingomar. 0-VII: 9. 

Interocean. E-VI: 9. 

Iowa. E-III: 10; D-IU: 10; G-VII: 6. 

Ipavia. E-VIII: 12. 

Irene. E-III: 5. 

Iroquois. I-VIII: 15. 

Irish Flag. 0-VI: 9. 

Iron. 0-X: 8. 

Iron Duke. D-X: 1. 

Iron Rock. D-V: 10. 

Iron West. B-x: 11. 

Irving. B-V: 12. 

Isabel. F-V: 7. 

Jackson. F-IV: 15. 

James Henry. E-IV: 12. 

Janitor. 0-I: 2. 

Jan Joan. D-VI: 22. 

Japan. ·E-IX: 6. 

Jasper. G-VII: 5. 

Jay Eye See. 0-V: 9. 

Jay Gould. D-VI: 10. 

Jefferson (768). B-VIII: 11. 

Jefferson (lOll). B-VIII: 10. 

Jessie. D-VII: 3. 

J. L. 0-X: 16. 

,John Hay. F-IV: 14. 

John L. Emerson. A-X: 12. 

Jones. D-V: 23; 0-V: i4. 

Josephine. D-V: 4. 

J.P. Whitney. C-IV:\4. 

Julia. I-II: 9. · 

Junius. E-X: 10. 

Juno. H-I: 3. 

Jupiter. A-VII: 12; A-IX: 7. 

.·~ K." - D-VII: 10. 

Kansas. B-VI: 6; E-V: 12. 

Kansas mill site (91 B). C-VI: 5. 

Kansas No.4. C-VI: 4. 

Kansas (67). C-VI: 34. 

Kansas (87). 0-VI: 33. 

Kansas (91). 0-VI: 6. 

Kansas (610). D-VI: 4. 

Kate Kearney. B-V: 10. 

Katie. H-VI: 8. 

Kent County. C-VJ: 29. 

Keystone. A-VII: 9; B-VI: 11. 

Kimber Fullerton mill site. H-~: 4. 

King Solomon. H-VI: 3. 

Kinney tunnel. H-II: 1. 

IGp. G-V: 8. 

Kirk.· C-VII: 18. 

Kitty. H-IV: 18. 

Klondike. G-X: 3; H-IX:. 11. 

;Kokomo. G-X: 2; H-)X: 5·. 

Kohinoor No.2. D-IV: 3. 

Kriegbaum. D-V: 5. 

Lake Superior. D..,.III: 14. 

Lake View. G-VI: 10. 

La Place. H-VIII: 2. 

Last Chance. 0-VII: 6. 

L. C. Rockwell. H-I: 1. 

Leavenworth. 0-VIII: 10. 

Legal Tender. A-X: 19; B-X: 14. 

Leonidas. A-VII: n·. 

Leontine. A-VII: 6. 

Levis mill site. D-V: 25. 

Levitt. H-IV: 10. 

Lewis. E-V: 18. 

Liberty. D-VIII: 14. 

Liberty BelL D-X: 9. 

Lilian. D-IX: 9. 

Lilly Rose. D-Ill: 11. 

Lincoln. F-VII: 1. 

Little Annie. H-X: 5. 

Little Chief. D-Ill: 7. 

Little Etta. G-VII: 12. 

.Little Giant. I-III: 7. 

Little Harvey. I-VI: 6. 

Little Jennie. E-VIII: 18. 

Little Mack. E-IV: 1. 

Little Pittsburg. I-VI: 12; D-VI: 

18. ' 

Little Raven. H-VII: 14. 

Little Willie. I-I: 6. 

Lizzie. I-V: 1; I-VI: 1; E-IX: 9. 

Lizzie S. C-VII: 8. 

Livingstone: B-X: 15. 

Lorna. E-VII: 3. 

London. E-IX: 18; E-X: 4. 

Lone Tree. H-VII: 3. 

Lorah. F-VIII: 14. 

Lorillard. I-VIII: 8. 

Lost Float. G-X: 5. 

Lottie. D-X: 13;'·G-IV: 10. 

Lotus. C-IX: 22. 

Louis. C-III: 5. 

Louisiana. D-IX: 2. 

Louis Napoleon. F-Ill: 12. 

Luckie Ducky. I-VI: 9. 

Lucky Boy. D-IX: 8. 

Lulu Bowen. F-111: 3. 

Lutz. D-IX: 6. 

Lutz Extension. 0-IX: 4. 

Lyman. E-V: 10. 

McAdams. G-VI: 2; G-V: 22. 

McCallister. G-V: 13. 

Mackie. 0-VII: 12. 

Maggie M. D-Ill: 3. 

Maine. F-IX: 11; G-V: 5. 

Major. C-IX: 15. 

Maldar. A-VIII: 16. 

Mammoth. G-VI: 1; G-VIII: 10. 

Mammoth (366). H-V: 10. 

Mammoth Side. G-VI: 3. 

Mammoth Sliver. I-II: 4: 

Mammoth West. F-VI: 7. 

Manahan. I-V: 6. 

Maraposa. C-VI: 30. 

Marathon. F-VIII: 10. 

Margaret. C-IX: 19; F-X: ·3. 

Marine. D-IV: .9. 

Marks. I-VII: 6. 

Mars. C-X: 11. 

Martin. H-IX: 1; I-VIII: 21. 

Mary Ella. H-II: 5. 
80 GEOLOGY OF GILPIN, CL~AR. CREE!<, AND BOULDER COUNTIES, COLO. 

Finding lis"t of claims· shown on map of Central City and vicinity-Continued. 

Maryland. G-Ill: 15; H-III: 2. 

Mat France. E-VI: 16; F-VI: 19. 

Mattie May. G-VII: 14. 

May. A-VIII: 5. 

Mayflower. C-VIII: 4; D-V: 19; 

I-I: 3; ·I-VIII: 19. 

Maud S. E-VII: 16. 

Maud S. (6351). D-VIII: 8. 

Mechanics. F-IV: 11. 

Meeker. H-VII: 13; I-VIII: 6. 

Membrino. C-V: 16. 

Mercer County. C-VI: 25. 

Mercer County Extension. C-VI: 26. 

Mercury. D-VII: 9. 

Merrimac. E-VII: 13. 

Michigan Boy. D-VIII: 10. 

Mili site 52: E-l-V: 7. 

Mill site 53. G-V: 25. 

Mill site 59 B. E-VII: 8. 

Mill site 70 B. E-VI: 25: 

Mill site 88 B. D-VI: 1. 

Mill site 101 B. D-VI: 35. 

Mill site 111 B. C-VI: 36. 

Mill site 114 B. F-V: 14. 

Mill site 128 B. I-IV: 11. 

Mill site 143 B. F-V: 19. 

Mill site 147 B. G-IX: 3. 

Mill site 148 B. G-IX: 2. 

Mill site 151. E-V: 15. 

Mill site 155 B. E-VI: 20. 

Mill site 160 B. D-VI: 2. 

Mill site 180. C-X: 1. . 

Mill site 185 B. H-I: 6. 

Mill site 186 B. I-IV: 10. 

Mill site 210. C-VI: 37. 

Mill site 212. H-V: 3. 

Mill site 221 B. I-II: 1. 

Mill site 240 B .. G-Ill: 22. 

Mill site 241 B. H-III: 7. 

Mill site 247. C-VIII: 8. 

Mill site 272 A. H-Ill: 1. 

Mill site 272 B. H-Ili: 3. 

Mill site 350 B. C-VI: 38. 

Mill site 384 B. G-Ill: 23. 

Mill site 385 B. H-III: 10. 

Mill site 410 B. F-VI: 22. 

Mill site 440 B. F-Ill: 6. 

Mill site 619 B. C-VI: 7. 

Mill site 2378. I-IV: 9. 

Mineral. B-VII: 4. 

Minnehaha. H-VIII: 11. 

Minnesota. C-IX:12; E-III:8; 

F-V: 17. 

Missouri. E-YI: 5; E-IX: 4. 

Mitchell. C-VII: 3. 

Modoc. D-VI: 34. 

Mohonga. H-VIII: 6. 

Mollie Gibson. D-VI: 28. 

Mollie Newcombe. B-VIII: 17. 

Arranged alphabetically-Continued. 

Mollie Stark. 1-V: 5. 

Mollie Stark Extension. I-VI: 8.' 

Monadnoc. D-VII: 11. 

Monitor. C-III: 2; C-VI: 10. 

Monroe (195). D-VI: 7. 

Monroe (643). D-VI: 5. 

Monroe (8420). D-VI: 6. 

Montana. A-IX: 11; G-VI: 9. 

¥ontclair. C-=X: 14. · 

Monte Christo. A-VIII: 17. 

Mo~tezuma. E-II: 2. 

Montrose. E-IV: 6. 

Mo~ning Star. A-IX: 19;. H-V: 8. 

Morning Red. H-VI: 9. 

Morrell. B-VIII: 20. 

Morris. I-VII: 18. 

Mosell. G-V: 23. 

Motto. C-V: 10. 

Mount Lincoln. E-IV: 15. 

Mountain. F-VI: 9; G-VII: 4. 

Mountain mill site. I-II: 7. 

Mountain and Plain. G-Il: 14. 

Mountain City. G-V: 10. 

Mountain Club. G-Il: 15. 

Mountain Lion. F-V: 4. 

Mountain Rose. G-VI: 11. 

Munson. B-X: 7. 

Mystery. H-X: 1. 

Mystic. A-VI: 5. 

Nagle,.' A-X: 10. 

Nashville. B-X: 20. 

National. F-VI: 5. 

National Bank. F-IV: 8. 

Nebula. H-VIII: 5. 

Nelson. C-IX: i. 

Nemeha. I-V: 10. 

Neptune. A-VII: 8. 

New Brunswick. H-VIII: 12. 

New Chicago. D-VI: 9. 

Newfoundland·. D-V: 16. 

Newfoundland No. 2. D-V: 17. 

New Hollie. D-VIII: 2. 

New House. F-IX: 10. 

New Jersey. I-V: 7. 

New Pikes Peak. C-VII: 2. 

New York. E-V: 19. 

Next President. H-IV: 20. 

Niagara. D-VIII: 17. 

Niagara No.2. E-IX: 1. 

Nil Desperandum. I-I: 2. 

Ninety-Four. H-Ili: 11. 

Ninety-Three. B-X: 18. 

Nomine~. E-IV: 10. 

No Name. A-VI: 10. 

Norton. D-1: 1. 

North. B-X: 16; D-VII: 5. 

North Eclipse. B-VIII: 3. 

North ·Fairfield .. A-IX: 2. 

Northrop. B-VI: 7. 

North Saratoga. F-VIII: 12. 

North Star. D-V: 7. 

Notaway (136). H-VII: 8. 

Notaway (328): H-VII: 17. 

Notaway (735). H-VII: 11. 

Notaway Belle. H-VII: 5. 

Notaway Extension. I-VI: 13. 

Notice. G-VII: 10. 

Nugget. F-VII: 6. 

Number One. G-V: 6. 

Oakland. D-VI: 16. 

Octavia Rachel. B-VII: 2. 

Ohio. C-VIII: 22; H-IX: 9. 

Old Bullion. G-V: 14. 

Old Dougherty. F-VII: 7. 

Old Guard. D-X: 11. 

'Old Jordan. F-X: 4. 

Old Rice. E-V: 16. 

Oldtown. C-IX: 18. 

Olga. D-X: 12. 

Oliver. H-II: 6. 

Olympia. B-VII: 6. 

Onandaga Chief. E-I: 1. 

O'NeiL H-V: 5. 

Only Boy. D-II: 3. 

Ontario. F-II: 2. 

• Ontonagon. G-V: 24; H-IV: '8. 

0. M. I-IV: 2. 

Oranoake. B-VI: 1. 

Orano~ke Extension.· B-VI: 2. 

Oregon. A-X: 21. 

Organ: E-VIII: 5. 

Orient. A-VII: 3. 

Orion. B-IX:· 2; H-V: 16. 

Oro. E-III: 12. 

Osoeze. A-IX: 15; E-X: 14. 

Ouray. F-V: 18. 

Overland. D-VIII: 9. 

Pacific~ D-Ill: 4. 

Palo Alto. H-x: 8. 

Pandora; G-VIII: 8. 

Panurge. E-X: 12. 

Paola. C-VIII: 12. 

Paris. D-X: 14; .E-X: 5. 

Parole. C-V: 12; H-V: 9. 

Partner Newcomb. H-VIII: 16. 

Paul. G-IX: 7; H...,.JX; 4. 

Paul Jones, I-II: 12. 

Pawtucket. B-X: 12. 

Peale. B-IX: 8. 

Peck. E-VIII: 3. 

·Pendleton. B-IX: 5. 

Pennsylvania. H-V: 6. 

Perrin. C-VIII: 25. 

Peru. I-II: 8. 

Peton. F-IX: 12. 

··, 

,. 

\. 
) 

HISTORY OF MINING. 81 

Finding list of claims shown on map of Central City and vicinity-Continued. 

Pewabic. D-IX: 15. 

Pewabic (125). C-X: 4. 

Pewabic (560). C-X: 5. 

Pewabic No.3. F-IX: 7. 

Pewabic No.4. F-~X: 6. 

Phillips. C-IX: 9. 

Phoenix. A-X: i7; B-IX: 6. 

Pierce. F-V: 10. 

Pierce-Galena. F-V: 11. 

Pikes Peak Extension. D-VII: 1. 

Pine Ridge. E-VIII: 7. 

Pittsburg. B-IX: 4; I-VII: 10.' 

Pittsburg Extension. I-VII: 17. 

Placer (858). C-IX: 6. 

Pleasant View No.2. F-V: 2. 

P.M. I-IV: 3. 

Pocahontas. E-VI: 21; 1!"'-..VIII: 5; 

I-II: 15. 

Pogue. C-IX: 16. 

Polar Star. C-VII: 19; E-111: 4. 

Poole. G-VI: 12. 

Poor Luck. F-X: 8. 

Porphyry. A-VI: 9. 

Post Hole. D-V: 24. 

Portage. B-VIII: 16. · , · 

Powell. B-VI: 15. 

Powers. H-VIII: 20. 

Powhatan. ' I-III: 2. 

Pratt. D-VI: 31. 

President Hayes. A-X: 16. 

Preston. B-IX: 7. 

Pride. F-VI: 10. 

Princess Louise. H-VIII: 10. 

Prize. D-V: 9. 

Pri~e Baby. F-VII: 15. 

Prize Extension. D-V: 11. 

Prompt Pay. A-VIII: 18 .. 

Prospector. D-Ill: 13; H-IV: 4. 

Protection. D-VI: 33; G-VI-13. 

Providence. C-VI: 15. 

Pure Gold. A-VIII: 4. 

Puritan. B-V: 6. 

Puzzle. H-V: 11. 

Pyrenees. B-VII: 11. 

Pyrenees Extension. B-VII: 12. 

Quaker City. A-VIII: 6. 

Quaker Lane. E-VI: 14. 

Quandry. F-IX: 14. 

Quartz Hill tunnel No. 3. F-V: 15. 

Quartz Hill tunnel No. 6. F-V: 16. 

Quartz Mill. C-VIII: 9. 

Quartz Valley placer. A.~rr: 1; 0-I: 1. 

Queen Bee. E-VIl: 18. 

Queen of the West. G-Ill: 12. 

Queens County. H-11:· 4. 

Rainbow. I-VIII: 7. 

Rajah. A-X: 7. 

44214°-17-6 

Arranged alphabetically-Continued. 

Randell Extension. C-VI: 14. 

Randolph. B-VIII: 14. 

Randolph Extension. ·A-VIII: 20. 

Rara Avis. C-IV: 3. 

Rara Avis Extension. B-IV: 1. 

Ravenswood. E-11: 9. 

Ready Cash. C-IV: 7. 

Register. E-VI: 27. 

Reichstag. F-VII: 14. 

Eeno. E-V: 2. 

Republic-Gregory. G-VI: 6. 

Retriever. D-V: 1; E-VIII: 15. 

Review. F-IV: 2. · 

~R. H. D. E~III: 3. 

Rhine. G-V: 20. 

Rhode Island. C-VI: 28. 

Rhoderick Dhu. D-VI: 25. 

Rialto. G-IV: 8. 

Richardson. C-X: 6. 

Ridge. E-IX: 5. 

Rist Placer. ·C-IX: 5. 

Road of Elephant. H-Ili: 9. 

Road Jr. G-IV: 2. 

Robert Emmet. G-Ill: 24. 

Robert Fulton. B-X: 9. 

Robert G. Ingersoll. F-Ill: 5. 

Rob Roy. H-X: 7. 

Rockford. C-VIII: 24. 

Rocky Mountain Terror. B-X: 6. 

Rosebud. C-IX: 14. 

Rover. F-IX: 4. 

Royal. D-IX: 1. 

R. P. Ranney (94). F-Ill: 11. 

R. P. Ranney (435). F-Ill: 10. 

Rubber. B-X: 5. 

Ruby. · A-IX: 16; C-VIII: 20. 

Russell. B-IX: 11. 

Russell Bell. E-X: 6. 

Russell Gulch. E-VIII: 9. 

Russell Pride. C-IX: 2. 

Schiller. G-V: 21. 

Scottish Chief. E-VII: 2. 

Searle. F-X: 6. 

Security. G-Ill: 2. 

Seeker-Finder. .H-VII: 2. 

Senate. C-IV: 5. 

Senatorial. B-IX: 10. 

Seuderberg. D-V: 12. 

Shafts. B-V: 8. 

Shamrock. A-VIII: 13. 

Shamrock II. A-IX: 12. 

Sluiw. C-VII: 14. · 

Silent King. D-V: 6. 

Silent Queen. E-IV: 11. 

Silyer Coin. A-VI: 14. 

' Silver Dollar. H-VIII: 19. 

Silver Ledge. H..:.X: 9. 

Silver Mug. A-V: _1. 

Sioux City. I-IV: 14. 

Siren. A-VII: 2. 

·Skelly. E-VII: 6. 

Skelton. B-V: 13. 

Slaughter House. D-V: 8. 

Slavonic. A-X: 8. 

Sleepy Hollow. I-IV: 12. 

Slice. 1-11: 14. 

Smith. H-IV: 5; I-III: 4. 

Soden. B-VII: 3. 

Soden Extension. A-VII: 7. 

Somes. H-IV: 1. 

Song. A-VIII: 7. 

South Bend. H-Ill: 13 .. 

South Brooklyn. F-VI: 21. 

South Fairfield .. A-IX: 5. 

S. P. Chase. H-VIII: 7. 

Spring. A-VIII: 10. 

Springdale. A-IX: 10. 

Spur Daisy. C-111: 1. 

St. Clair. A-IX: 8. 

St. James. I-II: 11. . 

St. Louis. F-IV: 20; I-I: ·1. 

St. Louis No.2. F-lV.: 16. 

St. Louis No.3. G-IV: l. 

St. Louis Extension. E-V: 6. 

Starling. F-11: 6. 

Star of the West. E-IX: 3; I-VIII: 9. 

Star Route. I-VII: 3; I-VIII: 3. 

Sterling. G-IV: 7. 

Ste,vart. B-VIII: 22. 

"S". B-IV: 3. 

Salpiro. B-V: 11. 

Salvator. B-VI: 5. 

Sam Lee. A-X: 20. 

Sanger. ·H-VIII: 8. 

Sans Souci. G-11: 13. 

Sapphire. F..:rv: .13. 

Sapsfield. G-VI: 16. 

Saratoga. G-VIII: 6. 

Saratoga' tunnel No. 1 East. GStorm King. D-Ill: 9. 

Straub. E-V: 4. · 

VIII: 4. Straughton. E-VIl: 5. 

Saratoga tunnel No. 1 West. 

VIII: 15. 

Saratoga West. F-VIII: 18. 

Satisfaction. F-V: 3. 

Saxon. H-IV: 13. 

Scandia. D-VII: 2. 

S. C. Booth. F-VIII: 4. 

F- Stub Tail. E-V: 8. 

Sub-Treasury. H'7'VII: 6. 

Success. C-n:C: 21; I-VIII: 2.-

Suffolk. B-V: 9. . 

Sugar Tit. C-VII: 1. 

Sullivan. D-VI: 3. 

Summit. A-X: 18; F-VI: s: 
82 GEOLOGY OF GILPIN, CLEAR CREEK, ANU BOULDER COUNTIES, COLO. 

Finding list of claims shown on map of Central City and vicinity-Continued. 

· Sun. B-VII: 1. · 

Sunflower. D-V: 18. 

Sunnyside. F-VII: 13. 

Sunshine. E:....rx: 7; F-VII: 12. 

Surprise. H-Ill: 14. 

Susquehanna. I-I: 4. 

Sutton. I-VII: 13. 

Swiss Home. D-VIII: 1. 

Sylvania. E-VI: 12. 

Symonds. B-VI: 13. 

. Tarquin. A-IX: 21. 

Telegraph. D-VII: 8. 

Telephone. C-VII: 15. 

Teller House. F-IV: 9. 

"'Tennel & Belden. G-III: 25. 

Texas. F-VI: 16; G-X: 4; H-IX:'r2. 

Theodore. F-VII: 9. 

Thomas Freema~. E-VI: 2. 

Thornton. F-VII: 11. 

Thunderbolt. A-X: 11. 

Thurman. E-IV: 3. 

Tierney. G-V: 11. 

Tiger. E-III: 1; H-VIII: 4. 

Tigress. C-VII: 13. 

Timbuctoo. F-IX: 3. 

Times. E-VI: 15; F-VI: 18. 

Tippecanoe. I-III: 1. 

Togo. C-X: 21. 

Tonight. B-X: 1. 

Topeka. B-VIII: 21; C-VIII: 13; 

H-IV: 16. 

Topeka (100). 0-VIII: 17. 

Topeka (518). C:-VIII: i6. 

Torrent. A-VII: 1. 

Treasury. H-VI: 1. 

Tremont. F-IV: 17. 

Trentina. F-X: 1. 

Triangle. F-IV: 4. 

Triton. A-IX: 1. 

Tropic. E-VII: 11. 

Troublesome. F-IV: 1. 

Truran. C-VI: 12. 

Tucker E~tension. F-II: 5. 

Tucker mill site (216). F-II: 4. 

Tunnel Lode No.1. G-1: 2. 

Arranged alphabetically-Continued. 

Two Sisters. D-rn: 2. 

Two-Forty. E-IX: 19; E-X: 9. 

'Uricle Sam. I-VIII: l. 

Unexpected. I-VI: 10. 

Union. A-VIII: 19; G-V: 9; H-IV: 

12. 

U.S. M. (424). G-V: 1. 

Ute. C-VI: 8. 

Vanderbilt. F-VI: 11; E-V: 17. 

Vendome. A-VI: 4. 

Venus. B-X: 17 .. 

Vermilion. A-VII: 10. 

Victor. C-X: 17. 

Victoria mill site (5568). D-VIII: 20. 

Vidette. E-VI: 7. · 

Vigilant. B-V: 7. 

Vindicator. F-VIII: 20. 

Virginia. C-X: 20; G-Ill: 13. 

Virginia Extension. G-III: 19. 

Vulcan. H-IV: 14. 

Wain. H-IV: 6. 

Walhala. E-VI: 26. 

Waltham. F-IX: 2. 

Ward. A-VIII: 1. 

War Dance. H-VIII: 14. 

War Dance Extension. I-VIII: 20. 

Warfield. B-X: 8. 

Warwick. I-V: 11. 

Washington. H-V: 14. 

Washington Extension. I-VIII: 18. 

Wash Kash. C-IX: 24. 

Water berry. G-V: 18. 

Waterloo. D-IX: 10. 

Wautauga. C-IX:' 7. 

Wautauga Extension. C-IX: 8. 

Welcome. D-VI: 11. 

Wellington. D-IX: 16. 

Wellington No. 1. E-IX: l3. 

Wellington No.3. D.:...IX: 14. 

Wellington No.4. D-IX 12. 

Wellington No. 5. D-IX: 11. 

Wellington No. 6. E-X: 2. 

Wellington No. 7. J!-X: 4. 

Wellington No.8. D-X: 5. 

Wellington No. 9. E-X: 3. 

Wellington No. 10. E-IX: 12. 

Wellington Side. E-IX: 16. 

Wells. F-VII: 4. 

West Alva Adams. F-VIII: 2. 

West American Boy. I-VIII: 12. 

West Chase. G-VIII: 7. 

Westchester. A-X: 3. 

West Cuno. n...:vn: 14. 

West Delaware. A-VIII: 12. 

West Gregory. G-VI:' 7. 

West Hazeltine. F-IX: 13 . 

West Keystone. D-II: 2. 

West Michigan. G-V: 19; G-VI: 5. 

West Pewabic. B-X: 2. 

West Saratoga. F-VIII: 19. 

West St. Louis. F-IV: 18. 

West Wellington. D-X: 2; E-IX: 17. 

West Wyandotte. C-VIII: 28. 

Wheel of Fortune. I-I: 5. 

Wheeler. D-V: 2. 

Wheeler mill site (382). G-I: 1. 

Whistler. E-VIII: 14. 

'White Cloud. A-X: 14. 

White Pine. E-VII: 12. 

'White Rock. H-IX: 3. 

Whiteside. H-IV: 7. 

Wilber. F-V: 9. 

Williamsville. I-VI: 2. 

Willowdale. C-VII: 23. 

Windsor. D-V: 22. 

Winnebago. F-IV: 5. 

Winnebago Extension. F-IV: 6. 

Winslow. C-VII:17. 

Wood. A-VII: 14; C-VIII: 1; D-IV: 

2. 

Woodbury. E-VI: 22. 

Wright. F-VI: 20. 

Wyandotte. C-VIII: 15. 

Yellow Girl. H-IX: 8. 

Yukon. D-VIII: 15. 

Yule. A-VI: 3. ' 

Yuma. D-VIII: 19. 

Zuni. A-VI: 2. 

Finding list of claims shown on map of Idaho Springs and vicinity (Pl. VIII). 

A-I. 1. Standard. 

2. Norma. 

3. Dakota. 

4. Reciprocity. 

5. C.M. S. 

6. Boston. 

7. Satisfaction. 

8. Yosemite (12040). 

A1 IL 1. Mandolina (Yosemite) 

(6591). 

2. East Mandolina. 

Arranged by coordinates. 

A-IL 3. W. W. Kirby. 

4. Parthenon. 

5. Golden Gate. 

6. Gondola. 

7. Genesta. 

8. Brunswick. 

9. ''X." 

10. Kinda Extension. 

11. John M. Osborne placer. 

12. Lilly. 

A-III. 1. Wano. 

· A-III. 2. Annie. 

3. Umbra. 

4. Etruria. 

5. Majestic. 

6. Confidence. 

7. Mugwump. 

·8. Lady Alice. 

9. Teutonic. 

10. Hilda. 

11. June. 

·12. Jake Whitter. 
) 

HISTORY OF MINING. 83 

Finding list of claims shown on map of Idaho Springs and vicinity-Continued. 

A-IV. 1. Photographer. 

2. Big Five. 

3. Big Bonanza. 

4. Free G9ld. 

5. Sept~mber. 

6. SW'prise. 

7. Empress. 

8. Gertrude. 

9. Richard III. 

10. Holly Extension. 

11. Dubuque Extension. 

12. John M. Osborn placer. 

A-V. 1. Margaret M. 

2. Iron Mask. 

3. Guy W. 

4. Klondike. 

5. Harry. 

6. Dubuque. 

7. Bennett placer. 

8. Hoosac placer. 

9. Alpine mill site. 

10. Miner mill site. 

11. Miner. 

12. East Coyote. 

13. :Milwaukee. 

14. Clear Creek Belle. 

15. Tough Nut. 

A-VI. 1. Edna L. 

2. Heine. 

3. ·willie. 

4. Black Forest. 

5. Antelope. 

6. Anoka County. 

7. Cook. 

8. Golden Lina. 

9. Little Alice. 

10. Mount Vesuvius (998). 

A-VII. 1. Mount Vesuvius (1062). 

2. Mount lEtna. 

3: Dewey. 

4. Golden Gate. 

5. Robert Emmett. 

6. Maggie May. 

7. Morning Star. 

A-VIII. 1. Copp. 

2. Squaw. 

3.· Star. 

4. Edward. 

5. Double Eagle. 

6. Jim Corbett. 

7. Jim Jeffries. 

8. Fitz. 

9. Rochester. 

10. Edwardmillsite(422B). 

B-I. 1. Gertrude. 

2. Big Lobster .. 

3. Maggie. 

4. Minnie. 

5. Mary. 

6. Qriole. 

Arranged by coordinates-Continued. 

B-I. 7. Iowa. 

8. Plymouth. 

9. Yellowstone. 

10. Sioux City." 

11. Winlock. 

B-II. 1. Saxony. 

2. St. Louis. 

3. St. Paul. 

4. Bourbon. 

5. Lucky S.tar. 

6. Leyner .. 

7. Kinda. 

8. Lucania. 

9. U.P.R. 

10. Campania: 

11. Florence. 

12. Good Hope. 

13. Ballia. 

14. Servia. 

15. Tunnel. 

B-III. 1. Wright. 

2. Amazon. 

3. Rhoderic Dhu. 

4. Lipton. 

5. Dewey. 

6. A.H.R. 

7. Colorado. 

8. Ohio. 

9. G. R.1 

10. S. S. 

11. L. P·. 

B-IV. 1. King George. 

2. U.G. W. 

3. King Ed ward. 

4. Emperor. 

5. Little Giant. 

6. Midnight. 

7. German Tunnel No. 2. 

8. July. 

9. Gold Dollar. 

10. Gold Bullion. 

11. President. 

B-V. 1. Uncle George. 

2. Lizzie S. 

3. Dover. 

4. Lawrence L. 

5. Dierdre. 

6. Dubuque. 

7. Tornado. 

8. Annie. 

. 9. Boston (Big Hit). 

10. May Queen Tunnel. 

11. May Queen Annex. 

12. May Queen Side .. 

13. May Queen. 

14. May Queen Cross. 

15. Hoosac. 

B-VI. 1. Robinson placer. 

2. Rising Sun. 

3. J. c. 

B-VI. 4. William F. placer. 

5. Oro placer. 

6. Ellis & Stevens placer. 

B-VII. 1. Annie. 

2. Lincoln (5954). 

3. South Lincoln. 

4. Kunegunde. 

5. Lincoln (655). 

6. Lincoln (338). 

7. Josephine. 

8. Elliot & Barber. 

9. Bellevue Extension. 

10. Donna Juanita. 

11. Donna Julia placer. 

B-VIII. 1. Bellevue. 

2. Idaho View. 

3. Dolphanee. 

4. Cardigan. 

5. Manhattan. 

6. York. 

7. Cregar. 

8. Stanley. 

9. Folwell. 

C-I. 1. Sam Lee. 

2. Hauch Haus. 

3. ~West Virginia. 

4. Coring. 

5. Scott. 

6. Sister Mary. 

7. Ada J. 

8. Poutycymmer. 

9. Lauttwits. 

10. Boston Run. 

11. Arizona. 

· 12. Victor. 

13. Oregon. 

14. Vida. 

C-II. 1. Pappoose. 

2. Central. 

3. Brooklyn. 

4. City of Berlin. 

5. City of Paris. 

6. Hughes. 

7. New York. 

8. Levy. 

9. Alaska. 

10. Little Belle. 

11. Telephone. 

i2. Champion. 

13. Richmond. 

14. Specie Payment Exten· 

sion. 

15. Nell Pitkin. 

0-III. 1. Apex. 

2. Welch.· 

3. Little Annie. 

4. Big Chief. 

5~ Welch Boy. 

6. Ffestinioc. 

7. Mons. 
84 GEOLOGY OF GILPIN, CLEAR. CREEK, AND BOULDER CO UNTIE~, COLO. 

Finding list of claims shown on map of Idaho Springs and vicinity-.Qontinued. 

C-III. 8. Waverly. 

9. Spear. · 

10. Congress. 

C-IV. 1. W. R. D. 

2. Congress tunnel. 

3. German tunnel No. 1. 

4. Annex. 

5. Lucky Star. 

6. Big Chief~ 

7. Young Chief. 

~- Grouse. 

9. Gloria Mundi. 

10. Box. 

C-V. 1. Coin. 

2. Hoosac Extension. 

3. Little Johnny. 

4. McKinley. 

5. Canasota. 

6. Syracuse. 

7. Maria Collins. 

C-VI. 1. New York. 

2. New Bedford. 

3. Mab. 

4. Wall~ce. 

5. Oro Extension. 

6 .. Columbia. 

7. Oro. 

8. Golden Nugget. 

9. Mastodon. 

10. 'Old Jink. 

11. Monte Cristo. 

12. Bonnie Belle. 

13. Pennsylvania. 

14. Smith placer. 

C-VII. 1. Columbia. 

2. King Cyrus. 

3. Lost. 

4. Maud Monroe. 

5. Lea placer. 

6. Bennett placer. 

7. H. & W. placer. 

8. Gladstone. 

9. H. & W. placer. 

10. Little Harry. 

11. King. 

12. Wana & Browdoin 

placer. 

13. Dumont placer. 

14. Whale (290). 

C-VIII. 1. Pride of the West. 

2. Powell. 

3. Golden Link. 

4. Battem. 

5. Sun. 

6. Qolumbine. 

7. Enterprise. 

8. Moon. 

9. Star. 

10. Bullion King No. 1. 

11. Bullion King No. 2. 

Arranged by coordinates..:....continued. 

D-1. 1. Summit. 

2. President Hayes. 

3. Oregon. 

4. Columbia. 

5. Glennalla. 

6. Knickerbocker. 

7. Golden Star. 

8. Castleton. 

9. Williams. 

10. Rio Grande. 

11. German. 

12. Equity. 

13. Howard. 

14. Crown Point & Virginia. 

15. M. K. (17265). 

D-II. 1. Hot Pot. 

2. Sunshine. 

3. Clarissa. 

4. Nonpareil. 

5. Mixsell Tunnel No. 1. 

6. Phillips. 

7. Lucas. 

8. Enterprise. 

9. Grover Cleveland. 

10. Lilly. 

11. Kohn. 

12. East Young. 

13. Beecher. 

14. Little Annie Extension. 

15. Mona Mine. 

16. Stene.ck. 

17. Specie Payment Extension East. 

18. Trio. 

D-111. 1. Bellevue. 

2. Young. 

3. Wolverine. 

4. Governor. 

5. Peralta. 

6. Mountain Chief. 

7. Specie Payment. 

8. Rambo. 

9. Cashier. 

10. Hellen. 

11. Gold Vault. 

12. Revenue. 

D-IV. 1. Emma. 

2. Etta. 

3. European. 

4. Germany. 

5. Cleopatra. 

6. Madison. 

7. Minneapolis. 

8. Sherbrook. 

9. Indianapolis. 

10. Idalia. 

11. Bald Eagle Extension. 

D-V. 1. New Discovery. 

D-V. 2. Major Conger. 

3. Little Johnny Extension. 

{.Tom Boy. 

5. Morning Star. 

6. Virginia House. 

7. Golden Treasure. 

8. Transvaal. 

9. Morning Star Extension. 

D-VI. 1. General Funston. 

2. Golden Edith. 

3. Lily. 

4. Gold Dust. 

5.· Tee Pee. 

6. Bronaber. 

7. Summit. 

8. Loeber. 

9. Ninnian. 

D-VII. 1. Atlantic. 

2. Dominion. 

3. Rannell. 

4. Little Mac. 

5. Centennial. 

6. Lulu. 

7. Crockett. 

8. Pogue. 

· 9. Hukill (615). 

10. Hukill (126). 

11. Salisbury. 

12. Eulalie. 

13. Bullion. 

14. Vivian placer. 

15. Whale (850). 

16. Mount Olive. 

17. Wana & Browdoin 

placer. 

18. Albany placer. 

19. Graeff placer. 

D-VIII. 1. Little Joker. 

2. Bullion King. 

3. Mayflower. 

4. Lafayette. 

5. Bullion King No. 3. 

6. Bullion King No.6. 

7. Belle Extension. 

8. Bullion King No. 4. 

9. Bullion King No.5. 

E-I. · 1. Twelve-Thirty. 

2. Semel. 

3. Ada. 

. 4. Marshall. 

5. Chipmunk. 

6. Fairmont (988). 

E-II. 1. Bantala. 

2. Insulator. 

3. Blue Bell. 

· 4. Clarissa. 

5. Mixsell Tunnel No .. 2. 

6. Belman. 
) 

HISTORY OF MINING • ·85 

. Finding list of clai~s shown on map of Idaho Springs and vicinity-Continued . 

E-II. 7. Seigel. 

8. Sylph. 

9. Great Center Extension. 

10. Diamond Joe. 

11. Uncle Sam. 

E-III. 1. Valverde. 

2. Mono. 

3. No Name. 

4. Grandma. 

5. Hills. 

6. Laura. 

7. Bald Eagle. 

8. Lake West. 

9. Swansea. 

10. Margaret. 

11. Surplus. 

12. Anaconda. 

13. Two Brothers. 

14. Daniels. 

E-IV. 1. Stella. 

2. Kentuck West. 

3.· Lillie. 

4. Lucy. 

5. u.s. 

6. Fanny. 

7. Big Five. 

8. Laura. 

9. N .icholas. 

10. Good-for-Nothing. 

E-V. 1. Strong. 

2. Not Forgotten. 

3. Anon. 

4. Star. 

5. Fortune. 

6. Ljttle Comstock. 

7. Fairmont (988). 

8. Shafter (2280). 

9. Jennie Lind No. 2. 

E-VI. 1. Refugee. 

2. Lillian K. 

3. Great American. 

4. Providence. 

5. East Stanley. 

6. Little Annabel. 

7. Hannalulu. 

8. East HukDl. 

9. Edgar. 

10. Union. 

11. Virginia. 

12. Fairmont (195 A). 

E-VII. 1. Fairmont mill site (195 

B). 

2. G. & l\f. 

3. Little Ella. 

4. New Century. 

5. Lucia. 

6. Le Coup. 

7. Ella. 

8. Hyland. 

9. Wedge. 

. Arranged by coordinates-Continued, ' 

E-VIL 10. Beauzy. 

11. Coupon. 

12. Cleopatra. 

13. Little Mack. 

14. Scalloway. 

15. Aurum. 

E-VIII. 1. Borealis. 

2. Essex. 

3. Collom mill site. 

4. White placer. · 

· 5. Cooper placer. 

6. Graeff placer. 

7. Black Bear. 

· 8. Intersection. 

9. Jumbo ... 

10. Tunnel.·. 

F:-I. 1. T. M. Jr. 

2. McDonald. 

3. Pittsburg. 

4. Nector. 

5. Francis. 

6. Mugosy. 

7. Mountain No. 1. 

8. Hail Storm. 

9. Olga. 

10. Lottie. 

F-II. 1. Mountain No.2. 

2. Fairmont Extension. 

3. ·Little Billie. 

4. N ewbridge. 

5. Ace of Diamonds. 

6. Mono Extension. 

7. Quincy. 

8. Lakeside. 

·9. Lake. 

F-Ill.~ 1. Ben Franklin. 

2. Little Belle. 

3. Windsor Castle. 

4. Tar~fa. 

5. Comstock Extension. 

6. ·West Dove's Nest. 

7. Rara A vis. 

8. Kentuck. 

9. Sunol. 

10. Polaris mill site (11228 

B). 

11. Nansen. 

12. Polaris. 

13. Capricorn. 

F-IV. 1. Valentine. 

2. ·Erie. 

3. Highlander. 

4. Hudson. 

5. European. 

6. Hudson mill site (113i 

B). 

7 .. c. J. 

8. Calvin. 

9. Hortense. 

10. Helen. 

F-IV. 11. Mary. 

12. Red Jacket. 

13. Patten. 

14. M. I. X. 

15. Great Center. 

F-V. 1. Perplexity. 

2. Adrie. 

3. Keystone. 

4. Jenny Lind. 

5. Ogden. 

6. Jenny Lind No. I. 

7. Shafter (2280). 

8. Big Chief. 

9. Chief. 

10._ Christmas. 

11. Golden Chief (15158). 

12. Golden Chief No. 1 

(17192). 

13. Herstoral. 

14. Crystal. 

15. Edgar Union. 

16. Carrie. 

F-VL 1. Protection. 

2. Robson. 

3. Bryan. 

4. Came. 

5. Humphrey. 

6. Fulton. 

7. Comstock. 

8. Judge. 

9. Coupon. 

10. Mount Royal. 

11. Little Chief. 

12. Edgar No. 1. 

F-VII. 1. Edith S. 

2. Gertrude. 

3. Lewis. 

4. Hyland Extension. 

5. Olive. 

6. Leonard. 

7. Harry. 

F-VIII. 1. McMickle. 

2. Queen. 

3. Darrag~ placer. 

4. Clear Creek. 

.5. Clear Creek placer. 

6. I{arwood. 

7. Venwood. 

G-1. 1. Thirty Cents. 

2. Calcutta. · 

3. Sultan. 

4. Mountain No. 10. 

5. Mo~ntain No. 9. 

6 .. Mountain No.8. 

7. Mountain No.7 

8. Mo:untain No. 6. 

9. Mountain No. 5. 

G-Il. 1. Mountain No. 4. 

2. Mountain No.3. 

3. Aduddell. 
86 GEOLOGY OF GILPIN, CLEAR CREEK, AND BOULDER COUNTIES, ·coLO • 

. Finding list of claims shown on map of Idaho Springs and vicinity-Continued. 

G-Il. 4. Fontaine. 

5. Tarik. 

6. Lake. 

7. East Lake. 

8. Owatonna. 

9: Jewell. 

10. Atlantic. 

11. Ashland. 

G.-III. 1. Post. 

2. ,V. P.R. 

3. O'Conner. 

4. Dove's Nest. 

5. Comstock. 

6. Silver Link. 

7. Safe. 

8. Peck. 

9. Emma. 

10. Lucerne Annex. 

11. Second Lucerne. 

12 .. Jenny Lind. 

13. Lucerne. 

14. Oetta. 

15. Chester. 

16. North Park. 

G-IV. 1. Park. 

2. Park Side. 

3. Republican. 

4. Martha. 

5. Dederick. 

6. Cash. 

7. Sheldon Jackson Patten 

Extension. 

8. S. P. Remington. 

9. Ohio. 

10. The Hartman. 

11. Silver Cord. 

12. Bullion. 

13. Cornucopia. 

·14. Kangaroo. 

15. Champion. 

16. B~reas. 

17. Argo. 

18. Interocean. 

19. Ethel. 

20. East Shafter. 

G-V. 1. Champion. 

2. Modoc. 

3. Dump. 

4. Little Jonnie. 

5. Crystal. 

6. New Year. 

7. Qolumbus. 

8. Beaver. 

9. Fulton Extension. 

10. Edgar Extension. 

11. Index. 

12. Edgar No.2. 

13. Western. 

14. Early Bird·. 

15. Old Proverb. 

Arranged by coordinates-Continued. 

G-V. 16. Rattler. 

G-VI. .1. Shaw. 

2. Nonpariel. 

G-VII. 1. Newton. 

2. Goodyear. 

3. Sunnyside. 

4. Quartermaster. 

G-VIII. 1. Mancarrow placer. 

2. Terril placer (Fulton 

Water Power). 

3. Old Rackensack. 

4. Ward. 

H-I. 1. Geoffrey. 

. 2. Amador. 

3. Church placer. 

4. Frontenac mill site ( 461 

B). 

5. Clifton. 

6. Fontaine. 

7. Frontenac. 

8. Formosa. 

9. Aduddell. 

10. Good Luck. 

H-II. 1. Tee Gee Aitch. 

2. St. Vrain. 

3. Swift. 

4. Carcasonne. 

5. Soudan. 

6. Phonolite. 

7. Minnie Moore. 

H-Ill. 1. Lightning Streak. 

2. Cricket. 

3. Canton. 

4. Lead Belt. 

5. Hub. 

6. James. 

7. Competition. 

8. West Santa Fe. 

9. Main Trunk. 

10. Brighton No. 2. 

11. Little Star. 

12. Summit. 

H-IV. 1. Ticknor. 

2. Crcesus. 

3. Victor. 

4. Amazon. 

5. Peru. 

6: Bride. 

7. Fourth of July. 

8. Little Emma. 

9. Kangaroo No.2. 

10. Seaton. 

11. Little Casino. 

12. No. 2 Lode in Metropolitan Tunnel. 

13. Fraction. 

14. Tunnel Lode No.3. 

15. Beauty No. 2. 

16. Tunnel Lode No. 1. 

17. Tot~l Eclipse. 

H-IV. 18. Crockett Extension. 

H-V. 1. Josephine. 

2. Joseph A. Horn. 

3. Boss. 

4. Crockett. 

5. Tigris. 

6. Luther. 

7. Crockett m i 11 site 

(993 B). 

8. Bell Tunnel. 

9. Proverb. 

10. Esmeralda. 

11. France. 

H-VI. 1. Clyde. 

H-VIII. 1. Mount Pleasant. 

I-I. 1. Searle. 

2. Aduddell. 

3. Poor Luck. 

4. B. Poe. 

5. Alice K. 

6. Ronalds. 

7. Kent. 

8. Argo· tunnel. 

9. Argo tunnel No. 2. 

10. Half and Half. · 

11. Elkhorn. 

12. Albyn. 

I-II. 1. Albatross. 

2. No. 14758. 

3. New Years Holiday. 

4. Colorado Star. 

5. Colfax. 

6. Bertha. 

7. Iowa. · 

8. Morning Star. 

9. Minnie. 

10. Arizona. 

11. Little Ella. 

12. Hope. 

13. German American. 

I-III. 1. Sun. 

2. Moon. 

3 .. Garden. 

4. Golden Wedge. 

5. Muff. 

6. C. P. Minot. 

7. Santa Fe. 

8. White Metal. 

9. Freeze Out. 

10. Out Crop. 

11. Belman. 

12. Martial. 

13. Freidar. 

14. Max. 

15. Gem Extension. 

16. Gem. 

I-IV. 1. Bmlington. 

2. Grand Trunk. 

3. Grantham. 

4. Trust. 

\, 
HISTORY OF .MINING. 87 

Finding list of claims shown on map of Idaho Springs and vicinity-Continued. 

I-IV. 5. Boadicea. 

6. Latimer. 

7. Silver Horn. 

8. Amy C. 

9. C., B. & Q. 

10. Tropic. 

11. Seaton. 

12. Queen City. 

13. Sunny Side. 

14. Ca.sino Tunnel Lode 

No.2. 

15. Danube. 

16. Silver Queen. 

17. 'l'enwall. 

18. Ottawa. 

I-V. 1. Grand View. 

2. Euphrates. 

3. No Name mill site 

(14222 B). 

4. Gleaner. 

5. France Extension. 

6. Isabelle Hedges. 

7. Northern Light. 

8. Borealis. 

I-VI. 1. Trea.sure Vault. 

2. Aurora. 

3. Gold Quartz. 

I-VII. 1. John Paul Jones. 

I-VIII. 1. Graham placer. 

2. Montague placer. 

3.· Richard placer. 

J-I. 1. Elite. 

2. Elk. 

3. Champion. 

4. Seminole. 

5. Sullton 3. 

6. Pay Rock. 

7. Hartford. 

8. Home. 

9. North American. 

10. Elk Valley. 

11. Bi-Metallic. 

J-II. 1. Half Moon. 

2. Rochester. 

3. Stump 'l'ail. 

4. Star. 

5. William Penn. 

6. North' American. 

· 7. Moosehead. 

8. Earth. 

9. Elkstail. 

10. Cortelyou. 

11. Hitchcock. 

12. New Century. 

J-III. 1. Bread Winner. 

2. Nest Egg. 

3. Exchequer. 

4. J. J. w. 

5. Rescue. 

6. Shapleigh. 

Arranged by coordinates-Continued. 

J-Ill. 7. Legal Tender. 

8. Enid. 

9. Oro Fino. 

10. J. Warner. 

J-IV. 1. Guy. 

2. Mary F. 

3. Washington. 

4. Freighter Friend. 

5. Franklin. 

6. Florence. 

7. Veto. 

8. Congress. 

9. Prince Henry. 

10. Good Enough. 

11. Dora. 

12. Terrible. 

13. Seaton Extension. 

14. Seven-Twenty. 

15. Trojan. 

16. Dorina. 

17. Silver Queen. 

. 18. No Name. 

19. ~leaner. 

20. Bert. 

21. Alpha. 

22. Ca.ss. 

23. Frank E. 

J-V. 1. Gleaner. 

2. Harvest. 

3. Orr. 

4. Gold Leaf. 

5. Golden Fleece. 

6. Motor. 

7. Harold. 

8. Edgardine. 

9. Gertrude. 

10. Maud S. , 

11. St. L~uis., 

J-VII. 1. Chicago. 

2. K. C. 

J-VIII. 1. Martin. 

2. Dunn placer. 

3. Logan placer. 

4. Doherty placer. 

5. Lewis placer. 

6. Sears placer .. 

K-I. 1. Verticle. 

2. Reade Street. 

3. Ecl-ipse. 

4. Old Fry. 

5. Hattie Myrtle. 

6. Free Coinage. 

7. Horn Silver. 

8. Elk Valley mill site 

(813 B). 

9. New York. 

10. Consolidated. 

11. Sullton No. 2. 

12. Moose. 

13. Sullton No. 1. 

K-I. 14. Syndicate. 

K-II. 1. Root. 

2. Taft. 

3. Shaw. 

4. Bonaparte. 

5. Hilltop. 

6. Governor. 

7. Daisy. 

8. Pine Tree. 

K-Ill. 1. W. M. S. 

2. Memphis. 

3. Zo~o. 

4. Sunset. 

5. Manhattan. 

6. New York. 

7. Brooklyn. 

8. Minnekato. 

9. Big Five. 

10. Reno. 

11. Galatea. 

12. Little Blanche. 

13. Wonderful. 

14. Tom Kirby. 

15. Doc Tray. 

16. De Lesseps. 

17. Gem Extension East. 

18. Gold Finch. 

19. Night Hawk Extension. 

K-IV. 1. pum Spiro Spero. 

2. Summit. 

3. Waterloo. 

4. Seaton Extension. 

5. South. 

6. Joubert. 

7. ConnectiJ?.g Link. 

8. Magnet. 

9. Bobby Burns. 

10. Queen. 

11. Queen mill site. 

12. Franklin (87). 

13. French Flag. 

14. Freeman. 

15. Potosi. 

16. John H. 

1.7. Golden Fleece. 

18. Oscar. 

19. Blind. 

K-V. l. Allen. 

2. A. B. E. 

3. Gold Leaf. 

4. Fannie R. 

K-VII. 1. Ellison placer. 

K-VIII. l. Argo. 

2. '\Velch placer. 

3. Ellison placer. 

4. Silver Age placer. 

5. Faivre placer. 

6. Argo mill site. 

L-II. l. Home Run. 

2~ Soltaire. 
88 GEOLOGY OF GILPIN, CLEAR CREEK, 'AND BOULDER COUNTIES, COLO. 

Finding list of claims shown on map of Idaho Springs and vicinity-Continued. 

L-II. 3. Homestake. 

4. ·Golden Reward. 

5. King Dodo. 

6. Ping Pong. 

7. Wasp. 

8. Black Duke. 

9. Columbine. 

10. Horse Shoe. 

L-III. 1. Summit. 

2. Pure Gold. 

3. St. Joseph. 

A. B. E. K-V: 2. 

Ace of Diamonds. F-II: 5. 

Ada. E-I: 3. 

Ada J. C-I: 7. 

Adrie. F-V: 2. 

Aduddell. G-Il: 3; H-I: 9; I-I: 2. 

A. H. R. B-Ill: 6. 

Alacoque. L-III: 4. · 

Alaska. C-II: 9. 

Albany placer. D-VII: 18. 

Albatross·. I-II: 1. 

Albyn. I-I: 12. 

Alice K. I-I: 5. 

Allen. K-V: '1. 

Alpha. J-IV: 21. 

Alpine mill site. A-V: 9. 

Amador. H-I: 2. 

Amazon. B-III: 2; H-IV: 4. 

Amy C. I-IV: 8. 

Anaconda. E-III: 12. 

Annex. C-IV: 4. 

Annie. A-III: 2; B-V: 8; B-VII: 1. 

Anoka County. A-VI: 6. 

Anon. E-V: 3. · 

Antelope. A-VI: 5. 

Apex. C-III: 1. _ 

Argo. G-IV: 17; K-VIII: 1. 

Argo mill site. K-VIII: 6. 

Argo tunnel. I-I: 8. 

Argo tunnel No.2. I-I: 9. 

4-rizona. C-I: 11; I-II: 10. 

Artillery Man. L-IV: 12. 

Ashland. G-II : 11. 

Atlantic. D-VII: 1; G-Il: 10. 

Aurora. I-VI: 2. 

Aurum. E-VIl: 15. 

Bald Eagle. E-III: 7. 

Bald Eagle Extension. D-IV: 11. 

Ballia. B-II: 13. 

Bantala. E-II: 1. 

Battem. C-VIII: 4. 

Beauty No. 2. H-IV: 15. 

Beauzy. E-VII: 10. 

Beaver. G-V: 8. 

Beecher. D-II: 13. 

Belle Extension. D-VIii: 7. 

Bellevue. B-VIII: 1; D-III: 1. 

Arranged by coordinates-Continued. 

L-IIL 4. Alacoque. 

5. Day Dawn. 

6. Night Hawk. 

7. Celestine. 

8. ·Silver Gem. 

9. Golden Wedge. 

'10. La Frank. 

L-IV. 1. First Lode Vein. 

2. Hanging. 

3. Hudson. 

4. Montana. 

Arranged alphabetically. 

Bellevue Extension. B-VII: 9. 

Bell Tunnel. H-V: 8. 

Belman. E-II: 6; I-III: 11. 

Ben Franklin. F-III: 1. 

Bennett placer. A-V: 7; C-VII: 6. 

Bert. J-IV: 20. 

Bertha. I-II: 6. 

Big Bonanza. A-IV: 3. 

Big Chief. C-III: 4; C-IV: 6; F-V: 8. 

Big Five. A-IV: 2; E-IV: 7; K-III: 9. 

Big Lobster. B-I: 2. 

Bi~Metallic. J-I: 11. 

. Black Bear. E-VIII: 7. 

Black Duke. L-II: 8. 

Black Forest. A-VI: 4. 

Blind. K-IV: 19. 

Blue Bell. E-II: 3. 

Boadicea. · I-IV: 5. 

Bobby Burns. K-IV: 9. 

Bo:r'mie Belle. C-VI: 12. 

Bonap~rte. K-II: 4. 

Borealis. E-VIII: 1; I-V: 8. 

Boreas. G-IV: 16. 

Boss. H-V: 3. 

Boston. A-I: 6. 

Boston (Big Hit). B-V: 9. 

Bost.on Run. C-1: 10. 

Bourbon·. B-II: 4. 

Box. C-IV: 10. 

B. Poe. I-I: 4. 

Bread Winner. J-Ill: 1. 

Bride. H-IV: 6 . 

. Brighton No.2. H-II~: 10. 

Bronaber. D-VI: 6 . 

. Brooklyn. C-II: 3; K-III: 7. 

Brunswick. A-II: 8: 

Bryan. F-VI: 3. . 

Bul~on. D-VII: 13; G-IV: 12 .. 

Bullion King. D-VIII: 2. 

Bullion King No.1. C-VIII: 10. 

Bullion King No.2. C-VIII: 11. 

Bullion King No. _3. D-VIII: 5. 

Bullion King No.4. D-VIII: 8. 

Bullion King No.5; D-VIII: 9. 

Bullion King No.6. D-VIII: 6. 

Burlington. I-IV: 1. 

Calcutta. G-I: 2. 

Calvin. F-IV: 8. 

r;..Iv. 5. Tunnel. 

6. Silver Age. 

7. Ship Ahoy. 

8. Silver Age Extension. 

9. King. 

10. Gold Medal. 

11. Capon. 

12. Artillery Man. 

13. Silver Gem mill site. 

L-V. 1. Mill site 6002 B. 

L-VIII. 1. Rollins placer. 

Campania. B-II: 10. 

Canasota. C-V: 5. 

Canton. H-III: 3. 

Capon. L-IV: 11. 

Capricorn. F-III: 13. 

Carcasonne. H-II: 4. 

Cardigan. B-VIII: 4. 

Carrie. F-V: 16; F-VI: 4. 

Cash. G-IV: 6 .. 

Cashier. D-III: 9. 

CasinoTunnelLodeNo.2. I-IV: 14. 

Cass. J-IV: 22. 

Castleton. D-I: 8 . 

C., B. & Q. I-IV: 9. 

Celestine. L-III: 7. 

Centennial. D-VII: 5. 

Central. C-II: 2. 

Champion. C-II: 12; ·G-IV: 15; 

G-V: 1; J-I: 3. 

Chester. G-III: 15. 

Chicago. J-VII: 1. 

Chief. F-V: 9. 

Chipmunk. E-I: 5. 

Christmas. F-V: 10. 

Church placer. H-I: 3. 

City of Berlin. C-II: 4. 

City of Paris. C-II: 5. 

C. J. F-IV: 7. 

Clarissa. D-II: 3; E-II: 4. 

Clear Creek. F-VIII: 4. 

Clear Creek Belle. A-V: 14. 

Clear Creek placer. F-VIII: 5. 

Cleopatra. D-IV: 5; E-VII: 12. 

Clifton. H-I: 5. 

Clyde. H-VI: 1. 

C. 11. S. A-I: 5. 

Coin. C-V: 1. 

Colfax. I-II: 5. 

Collom mill site. E-VIII: 3. 

Colorado. B-III: 7. 

Colorado Star. I-II: 4. 

Columbia. C-VI: 6; C-VII: 1; D-I: 4. 

Columbine. C-VIII: 6; L-II: 9. 

Columbus. G-V: 7. 

Competition. H-III: 7. 

Comstock. F-VI: 7; o:-rn: 5. 

Com.Stock Extension. F-III: 5. 

Confidence. A-III: 6. 
HISTORY OF MINING. 89 

Finding list of claims .11how"n on map of Idaho Springs and vicinity-Continued. 

Congress. C-III: 10; J-IV: 8. 

Congress Tunnel. C-IV: 2. 

' Connecting Link. K-IV: 7. 

·Consolidated. K-I: 10. 

Cook. A-VI: 7. 

Cooper placer. E-VIII: 5. 

Copp. A-VIII: 1. 

Coring. C-I: 4. 

Cortelyou. J-II: 10. 

Cornucopia. G-IV: 13. 

Coupon. E-VII: 11; F-VI: 9. 

C. P. Minot. I-III: 6. 

Cregar. B-VIII: 7. 

Croosus. H-IV: 2. 

Cricket. H-III: 2. 

Crockett. D-VII: 7; H-V: 4. 

Crockett Extension. H-IV: I8. 

Crockett mill site (993 B). H-V: 7. 

Crown Point & Virginia. D-I: 14. 

Crystal. F-V: 14; G-V: 5. 

Daisy. K-II: 7. 

Dakota. A-I: 3. 

Daniels. E-III: 14. 

Danube. I-IV: 15. 

Darragh placer. ·F-VIII: 3. 

Day Dawn. L-III: 5. 

Dederick. G-IV: 5. 

De Lesseps. K-III: 16. 

Dewey. A-VII: 3; B-III: 5. 

Diamond Joe. E-II: 10. 

Dierdre. B-V: 5. 

Doc Tray. K-III: 15. 

Doherty placer. J-VIII: 4. 

Dolphanee. B-VIII: 3. 

.Dominion. D-VII: 2. 

Donna Juanita. B-VII: IO. 

Donna Julia placer. B-VII: 11. 

Dora. J-IV: 11. 

.Dorina. J-IV: 16. 

Double Eagle. A-VIII: 5. 

' Dover. B-V: 3. 

Dove's Nest. · G-III: 4. 

Dubuque. A-V: 6; B-V: 6. 

Dubuq'ue Extension. A-IV: 11. 

Dumont placer. C-VII: 13. 

Dump. G-V: 3. 

Dum Spiro Spero. K-IV: 1.. 

Dunn placer. J-YIII: 2. 

Early Bird. G-V: 14. 

Earth. J-II: 8. 

East Coyote. A-V: 12. 

East Hukill. E-VI: 8. 

East Lake. G-II: 7. 

East Uandolina. A-II: 2 .. 

East Shafter. G-IV: 20. 

East Stanley. E-VI: 5. 

East Young. D-II: 12. 

Eclipse. K-I: 3. 

Edgar. E-VI: 9. 

Edgar No. 1. F-VI: 12. 

Arranged alphabetically-Continued. 

Edgar No.2. G-V: 12. 

Edgardine. J-V: 8. 

Edgar Extension. G-V: 10. 

Edgar Union. F-V: 15. 

Edith S. F-VII: 1. 

Edna L. A-VI: 1. 

Ed~ard. A-VIII: 4. 

Edwardmillsite(422B). A-VIII: 10. 

Elite. J-I: 1. 

Elk. J-I: 2. 

Elkhorn. I-I: 11. 

Elkstail. J-II: 9. 

Elk Val·ley. J-I: 10. 

Elk Valley mill site (813 B). K-I: 8. 

Ella. E-VII: 7. 

Elliot & Barber, B-VII: 8. 

Ellis & Stevens placer.· B-VI: 6. 

Ellison placer. K-VII: I; K-VIII: 3. 

Emma. D-IV; I; G-Ill: 9. 

Emperor. B-IV: 4. 

Empress. A-IV: 7. 

. Enid. J-III: 8. 

Enterprise. C-VIII: 7; D-I: 8. 

Equity. D-I: 12. 

Erie. F-IV: 2. 

Esmeralda. H-V: 10. 

Essex. E-VIII: 2. 

Ethel. G-IV: I9. 

Etruria. A-III: 4. 

Et'ta. D-IV: 2. 

Eulalie. D-VII: I2. 

Euphrates. I-V: 2. 

European. D-IV: 3; F:...Iv: 5. 

Exchequer. J-III: 3. · 

Fairmont (988). E-I: 6; E-V: 7. 

Fairmont (I95 A). E-VI: 12. 

Fairmontmillsite(l95B). E-VII: I. 

Fairmont Extension. F-II: 2.· 

Faivre placer. K-VIII: 5. 

Fannie R. K-V: 4. 

Fanny. E-IV: 6. 

Ffestinioc. C-III: 6. 

First Lode Vein. L-IV: 1. 

Fitz. A-VIII: 8. 

Florence. B-II: 11; J-IV: 6. 

Folwell. B-VIII: 9. 

Fontaine. G-II: '4; H-I: 6. 

Formosa. H-I: 8. 

Fortune. E-V: 5. 

Fourth of July. H-IV: 7. 

Fraction. H-IV: 13 .. 

·France. H-V: 11. 

France Extension. I-V: 5. 

Francis. F-I: 5. 

Frank E. J-IV: 23. 

Franklin. J-IV: 5. 

Franklin (87). K-IV: 12. 

Free Coinage. K-I: 6. 

Free Gold. A-IV: 4. 

Freeman. K-IV: 14. 

Freeze Out. I-III: 9. 

Freidar. I-III: I3. · 

Freighter Friend. J-IV: 4. 

French Fiag. K-IV: I3. 

Frontenac. H-I: 7. 

Frontenac mill site (46I B). H-I: 4. 

Fulton. F-VI: 6. 

Fulton Extension. G-V: 9. 

Galatea ... K-III: Il.. 

G. & M. E-VII: 2. 

Garden. I-III: 3. 

Gem. I-III: 16. 

Gem Extension. I-III: 15. 

Gem Extension East. K-III: 17. 

General Funston. D-VI: 1. 

Genesta. A-II: 7. 

Geoffrey. H-I: 1. 

German. D-I: 11. 

German American. I-II: I3. 

German tunnel No.1. C-IV: 3. 

German tunnel No.2. B-IV: 7 . 

Germany. D-IV: 4. 

Gertrude. A-IV: 8; B-I: I; F-VII: 

2; J-V: 9. 

Gladstone. C-VII: 8. 

Gleaner. I-V: 4; J-IV: 19; J-V:. 1. 

Glennalla. D-I: 5. 

G Ioria Mundi. C-IV: 9. 

Gold Bullion. 'B-IV: 10. 

Gold Dollar. B-IV: 9. 

Gold Dust. D-VI: 4. 

Golden Chief (15158). F-V: 11. • 

Golden Chief No.1 (17192). F-V: 12. 

Golden Edith. D-VI: 2 . 

Golden Fleece. J-V: 5; K-IV: 17. 

Golden.Gate. A-II: 5; A-VII: 4. 

Golden Lina. A-VI: 8. 

Golden Link. C-VIII: 3. 

Golden Nugget. C-VI: 8. 

Golde'n Reward. L-II: 4. 

Golden Star. D-I: 7. 

Golden Treasure. D-V: 7. 

Golden Wedge. L-III: 9; I-III: 4. 

Gold Finch.· K-III: 18. 

Gold Leaf. J-V: 4; K-V: 3. 

Gold Medal. L-IV: 10. 

Gold Quartz. I-VI: 3. 

Gold Vault. D-III: 11. 

Gondola. A-II: 6. 

Good Enough. J-IV: 10. 

Good-for-Nothing. E-IV: 10. 

Good Hope. B-II: 12. 

Good Luck. H-I: 10. 

Good year. G-VII: 2. 

Governor. D-IU: 4; K-II: 6. 

G. R. B-III: 9. 

Graeff placer. D-VII: 19; E-VIII: 6. 

Graham placer. I-VIII: l. 

Grandma. E-III: 4. 

Grand Trunk. I-IV: 2. 
90 GEOLOGY OF GILPIN, CLEAR CREEK, AND BOULDER COUNTIES, COLO. 

Finding list of claims shown on map of ld(Lho Springs and vicinity-.Continued. 

Grand View. 1-V: 1. 

Grantham. I-IV: 3. 

Great American. E-VI: 3. 

Great Center. F-IV: 15. 

Great Center Extension. E-11: 9. 

Grouse. C-IV: 8. 

Grover Cleveland. D-11: 9. 

Guy. J-IV: 1. 

Guy W. A~V: 3. 

Hail Storm. F-1: 8. 

Half and Half. I-I: 10. 

Half Moon. J-11: 1. 

H. & W. placer. C-VII: 7; C-VII: 9. 

Hanging. L-IV: 2. 

Hannalulu. E-VI: 7. 

Harold. J-V: 7. 

Harry. A-V: 5; F-VII: 7. 

Hartford. J-I: 7. 

Harvest. J-V: 2. 

Harwood. F-VIII: 6. 

Hattie Myrtle. K-I: 5. 

Hauch Haus. C-I: 2. 

Heine. A-VI: 2. 

Helen. F-IV: 10 .. 

Hellen. D-Ill: 10. 

Herstoral. F-V: 13. 

Hilda. A-III: 10. 

Highlander. F-IV: 3. 

Hills. E-III: 5. 

Hilltop. K-11: 5. 

Hitchcock. J-11: 11. 

Holly Extension. A-IV: 10. 

Home. J-I: 8. 

Home Run. L-11: 1. 

Homestake. L-II: 3. 

Hoosac. B-V: 15. 

Hoosac Extension. C-V: 2. 

Hoosac placer. A-V: 8. 

Hope. 1-11: 12. 

Horn Silver. K-I: 7. 

Horse Shoe. L-II: 10. 

Hortense. F-IV: 9. 

Hot Pot. D-II: 1. 

Howard. D-1: 13. 

Hub. H-Ill: 5. 

Hudson.· F-IV: 4; L-IV: 3. 

Hudson mill site (1131 B). F-IV: 6. 

Hughes. C-II: 6. 

Hukill (126). D-VII: 10. 

Hukill (615). D-:-VII: 9. 

Humphrey. F-VI: 5. 

Hyland. E-VIl: 8. 

Hyland Extension. F-VII: 4. 

Idaho View.· B-VIII: 2. 

Idalia. D-IV: 10. 

Index. G-V: 11. 

Indianapolis. · D-IV: 9. 

Insulator. E-ll: 2. 

Interocean. G-IV: 18. 

Intersection. E-VIII: 8. 

Arranged alphabetically-Continued. 

Iowa. B-1: 7;' I-II: 7. 

·Iron Mask. A-V: 2. 

. Isabel~e Hedges. I-V: 6. 

Jake Whitter. A-III: 12. 

James. H-111: 6. 

. J. C. B-VI: 3. 

Jenny Lind. F-V: 4; G-Ill: 12. 

Jenny Lind No. 1. F-V: 6 .. 

Jenny Lind No. 2. E-V: 9. 

Jewell. G-11: 9. 

Jim Corbett. A-VIII: 6. 

Jim Jeffries. A-VIII: 7. 

J. J. W. J-Ill: 4. 

John H. K-IV: 16. 

John M. Osborne placer. A-II: 11; 

A-IV: 12. 

John Paul Jones. I-VII: 1. 

Joseph A. Horn. H-V: 2. 

Josephine. B-VII: 7; H-V: 1. 

·Joubert. K-IV: 6. 

Judge. F -"VI: 8. 

.July. B-IV: 8. 

Jumbo. E-VIII: 9. 

June. A-III: 11. 

. J. Warner. J-Ill: 10. 

Kangaroo. G-IV: 14. 

·Kangaroo No. 2. H-IV: 9. 

K. C. J-VII: 2. 

Kent. 1-1: 7. 

Kentuck. F-Ill: 8. 

Kentuck West. E-IV: 2. 

Keystone. F-V: 3. 

· Kinda. B-11: 7. 

Kinda Extension. A-II: 10 . 

. IDng. C-Vll: 11; L-IV: 9. 

King Cyrus. C-VII: 2. 

King Dodo. L-11: 5. 

King Edward. B-IV: 3. 

King George. B-IV: 1. 

Klondike. A-V: 4. 

Knickerbocker. D-I: 6. 

Kohn. D-11: 11. 

Kunegunde. B-VII: 4. 

Lady Alice. A-III: 8. 

Lafayette. D-VIII: 4. 

La Frank. L-III: 10. 

Lake. G-11: 6; F-11: 9. 

Lakeside. F-11: 8. 

Lake West. E-Ill: 8. 

Latimer. I-IV: 6. · 

Laura. E-111: 6; E-IV: 8. 

Lauttwits. C-1: 9. · 

Lawrence L.' B-V: 4. 

Le~d Belt. H-Ill: 4. 

Lea placer. C-VII: 5. 

Le Coup. E-VII: 6. 

Legal Tender. J -III: 7. 

Leonard. F-VII: 6. 

Levy. C-11: 8. 

Lewis. F-VII: 3. 

Lewis placer. J-VIII: 5. 

Leyner. B-11: 6. 

Lightning Streak. H-Ill: 1. 

Lillian K. E-VI: 2. 

Lillie. E-IV: 3. 

Lilly. A-II: 12; D-11: 10. 

Lily. D-VI: 3. 

·Lincoln (338). B-VII: 6. 

Lincoln (655). B-VII: 5. 

Linc~ln (5954). B-VII: 2. 

Lipton. B-Ill: 4. 

Little Alice. ·A-VI: 9. 

Little Annabel. E-VI: 6. 

Little Annie. C-III: 3. 

Little Annie Extension. D-11: 14. 

Little Belle. C-11: 10; F-Ill: 2. 

Little Billie. F-11: 3. 

Little Blanche. K-III: 12! 

Little Casino. H-IV: 11. 

Little Chief. F-VI: 11. 

Little Comstock. E-V: 6. 

Little Ella. E-VII: 3; I-II: 11 . 

Little Emma. H-IV: 8. 

Little Fannie Extension. D-11: 14. 

Little Giant. B-IV: 5 . 

Little Harry. C-VH: 10. 

Little Joker. D-VIII: 1. 

Little Johnny. C-V: 3. 

Little Johnny Extension. D-V: 3. 

Little Jonnie. G-V: 4. 

Little Mack. D-VII: 4; E-VII: 13. 

Little Star. H-III: 11. 

Lizzie S. B~V: 2. 

Loeber. D-VI: 8. 

Logan placer. J-VIII: 3. 

Lottie. F-I: 10. 

Lost. C-VII: 3. 

L. P. B-III: 11. 

Lucania. B-II: 8. 

·Lucas. D-II: 7. 

Lucerne. G-Ill: 13. 

Lucerne Annex. G-Ill: 10. 

Lucia. E-VIl: 5. 

Lucky Star. B-II: 5; C-IV: 5. 

Lucy. E-IV: 4. 

Lulu. D-VII: 6. 

Luther. H-V: 6. 

Mab. C-VI: 3 .. 

McDonald. F-1:·2. 

McKinley. C-V:4. 

McMickle. F-VIII: 1. 

Madison. D-IV: 6. 

Maggie. B-I: 3. 

Maggie May. A-VII: 6. 

Magnet. K-IV: 8. 

Main Trunk. H-III: 9. 

Majestic. A-III: 5. 

Major Conger. D-V: 2. 

Mancarrow placer. G-VIII: 1. 

Mandolina(Yosemite) (6591). A-II:l. 

Manhattan. B-VIII: 5; K-Ill: 5. 
HISTORY OF MINING. 91 

Finding list of claims shown on map of Idaho Springs and vicinity-Continued. 

Margaret. E-III: 10. 

Margaret M. A-V: 1. 

Maria Collins. C-V: 7. 

Marshall. E-I: 4. 

Martha.. G-IV: 4. 

Martial. I-III: 12. 

Martin. J-VIII: 1. 

Mary. B-I: 5; F-IV: 11. 

Mary F. J-IV: 2. 

Mastodon. C-VI: 9. 

Maud Monroe. C-VII: 4. 

Maud S. J-V: 10. 

Max. I-III: 14. 

Mayflower. D-VIII: 3. 

May Queen. B-V: 13. 

May Queen Annex. B-V: 11. 

May Queen Cross. B-V: 14. 

May Queen Side. B-V: 12. 

May Queen Tunnel. B-V: 10. 

Memphis. K-III: 2. 

Midnight. B-IV: 6. 

:rvmrsite 6002. L-V: L 

Milwaukee. A-V: 13. 

Miner. A-V: 11. 

Miner mill site. A-V: 10. 

Minneapolis. D-IV: 7. 

Minnekato. K-III: 8. 

Minnie. I-II: 9; B-I: 4. 

Minnie Moore. H-II: 7. 

M. I. X. F-IV: 14. 

Mi..xsell 'l'unnel No. 1. D-II: 5. 

:Mixsell Tunnell No.2. E-II: 5. 

M. K. (17265). D-1: 15. 

Modoc. G-V: 2. 

Mona Mine. D-II: 15. 

Mono. E-III: 2. 

Mono Extension. F-II: 6. 

Mons. C-III: 7. 

Montague placer. I-VIII: 2. 

Montana. L-IV: 4. 

Monte Cristo. C-VI:ll. 

Moon. O:.VIII: 8; I-III: 2. 

Moose. K-I: 12. 

Moosehead. J-II: 7. 

MorningStar. A-VII: 7; D-V: 5; III: 8. 

Morning Star Extension. D-V: 9. 

Motor. J-V: 6. 

Mount lEtna. A-VII: 2. 

Mountain No.1: F-I: 7. 

Mountain No.2. F-II: 1. 

:Mountain No.3. G-II: 2. 

Mountrun No.4. G-Il: 1. 

!\fountain No.5. G-I: 9. 

Mountain No.6. G-1: 8. 

Mountain No.7. 'G-1: 7. 

Mountain No.8. G-I: 6. 

Mountain No.9. G-1: 5. 

Mountain No. 10. G-I: 4. 

Mountain Chief. D-III: 6. 

Mount Olive. D-VII: 16. 

Arranged alphabetically-Con~inued. 

Mount Pleasant. H-VIII: L 

Mount Royal. F-VI: 10. 

Mount Vesuvius (998). A-VI: 10. 

. Motmt Vesuvius (1062). A-VII: 1. 

Muff. I-III: 5. 

Mugosy. F-I: 6. 

. Mugwump. A-,lll: 7. 

. Nansen. F-III: 11. 

Nector. F-I: 4. 

Nell Pitkin. C-II: 15. 

Nest Egg. J-III: 2. 

New Bedford. C-VI: 2. 

Newbridge. F-II: 4. 

. New Century. E-VII: 4; J-II: 12. 

, New Discovery. D-V: 1. 

Newton. G-VII: 1. 

New Year. G-V: 6. 

New Years Holiday. I-II: 3. 

. New York. C-II: 7; C-VI: 1; K-I: 

I 9; K-Ill: 6. 

Nicholas. E-IV: 9. 

Night Hawk. L-III: 6. 

Night Hawk Extension. K-III: 19. 

Ninnian. D-VI: 9. 

No Name: E-III: 3; .J-IV: 18. 

No Name mill site (14222 B). I-V: 3. 

Nonpareil. D-II: 4; G-VI: 2. 

Norma. A-I: 2. 

North American. J-1: 9; J-II: 6. 

Northern Light. I-V: 7. 

North Park. G-III:16. 

Not Forgotten. E-V: 2. 

·No. 2 Lode in Metropolitan Tunnel. 

H-IV: 12. 

No. 14758. I-II: 2. 

O'Conner. G-III: 3. 

Oetta. G-III: 14. 

Ogden. F-V: 5. 

·Ohio. B-Ill: 8; G-IV: 9 . . Old Fry. K-I: 4., 

Old Jink. C-VI: 10. 

Old Proverb. G-V: 15. 

Old Rackensack. G-VIII: 3. 

Olga. F-I: 9. 

Olive. · F-VII: 5 .. 

Oregon. C-I:13; D-I: 3. 

Oro. C-VI: 7. 

Oro Extension. C-VI: 5. 

·Oro Fino. J-Ill: 9. 

Oriole. B-1: 6. 

Oro placer. ~-VI: 5. 

Orr. J-V: 3. 

Oscar. K-IV: 18. 

Ottawa. I-IV: 18. 

Outcrop. I-III: 10. 

. Owatonna. ·G-II: 8. 

Pappoose. C-II: 1. 

·Park. G-IV: 1. 

Park Side. G-IV: 2. 

Parthenon. A-II: 4. 

Patten. F-IV: 13. 

Pay Rock. J-I: 6. 

Peck. G-III: 8. 

Pennsylvania. C-VI: 13. 

Peralta. D-IU: 5. 

Perplexity. F-V: 1. 

Peru. H-IV: 5. 

Phillips. D-II: 6. 

Phonolite. H-II: 6. 

Photographer. A-IV: 1. 

Pine Tree. K-II: 8. 

pj~g Pong. L-II: 6. 

Pittsburg. F-I:3. 

Plymouth.· B-I: 8. 

Pogue. D-VII: 8. 

Polaris. F-Ill: 12. 

Polaris mill site (11228 ). F-Ill: 10. 

Poor Luck. I-I: 3. 

Post. G-Ill: 1. 

Potosi. K-JV: 15. 

Poutycymmer. C-1: 8. 

Powell. C-VIII: 2. 

President. B-IV: 11. 

President Hayes. D-I: 2. 

Pride of the vVest. C-VIII: 1. 

Prince Henry. J-IV: 9 .. 

Protection. F-VI: 1. 

Proverb. H-V: 9. 

·Providence. E-VI: 4. 

Pure Gold. L-III: 2. 

Quartermaster. G-VII: 4. 

Queen. F-VIII: 2; K-IV: 10. 

Queen City. I-IV: 12. 

Queen mill site. K-IV: 11. 

Quincy. F-II: 7. 

Rambo. D-III: 8. 

Rannell. D-VII: 3. 

Rara Avis. F-Ill: 7.' 

Rattler. G-V: 16. 

Reade Street. K-I: 2. 

Reciprocity. A-I: 4. 

Red Jacket. F-IV: 12. 

Refugee. E-VI: l. 

Reno. K-III: 10. 

Republican. G-IV: 3. 

Rescue. J-Ill: 5. 

Revenue. D-III: 12. 

Rhoderic Dim. B-III: 3. 

Richard pJacer. I-VIII: 3. 

Richard III. A-IV:. 9. 

Richmond. 0-II: 13. 

Rio Grande. D-I: 10 .. 

Rising Sun. B-VI: 2. 

Robert Emmett. A-VII: 5 . 

Robinson placer. B-VI: 1. 

Rochester .. A-VIII: 9; J-II: 2. 

Robson. F-VI: 2. 

Rollins placer. L-VIII: 1. . -· 
\ 

\ .. , 

.. 

.. 

92 . GEOLOGY OF GILPIN,. CLEAR CREEK, AND BOULDER COUNTIES, COLO. 

Finding list of claims shown on map of Idaho ~prings and vicinity-Continued. 

Ronalda. I-I: 6. 

Root. K-II: 1. 

Safe. G-III: 7. 

Salisbury. D-VII: 11. 

Sam Lee. 0-I: 1. 

Santa Fe. I-III: 7. 

Satisfaction. A-I: 7. 

Saxony. B-II: 1. 

Scalloway. E-VII: 14. 

Scott. C-I: 5. 

Searle. I-I: 1. 

Sears placer.. J-VIP: 6. 

Seaton. H-IV: 10; I-IV:. 11. 

Seaton Extension. J-IV: 13; K-IV: 4: 

Second Lucerne. a.:..nr: 11 .. 

Seigel. E-II: 7. 

Semel. E-1: 2. 

Seminole. J-1: 4. 

September. A-IV: 5. 

Servia. B-II: 14. 

Seven Twenty. J-IV: 14. 

Shaw. G-VI: 1; K-II: 3. 

. Shafter (2280). E-V: 8; ·F-V: 7. 

Shapleigh. J-III: 6. 

Sheldon Jackso_n Patten Extension. 

G-IV: 7. 

Sherbrook. D-IV: 8. 

Ship Ahoy. L-rv: 7. 

Silver Age. L-IV: 6. 

Silver Age Extension. L-IV: 8. 

Silver Age placer. K-VIII: 4. 

Silver Cord. G-IV: 11. 

Silver Gem. L-III: 8. 

Silver Gem mill site. L-IV: 13. 

Silver Horn (Silver Star). I-IV: 7. 

Silver Link. G-III: 6. 

Silver Queen. I-IV: 16; J-IV: 17. 

Sioux City. ·B-I: 10. 

Sister Mary. C-I: ~. 

Smith placer. C-VI: 14. 

Soltaire. L-II: 2. 

Soudan. H-H: 5. 

South. K-IV: .5. 

South Lincoln. B-VII: 3. 

Spear. C-III: 9. 

specie Payment. D-III: 7. 

Specie Payment Extension. C-II. 

14. 

Spec,ie Payment Extension East. 

D-II: 17. 

S. P. Remington. G-IV: 8. 

Squaw. A-VIII: 2. 

S. S. B-Ill: 10. 

Standard. A-I: ·1. 

Stanley. B-VIII: 8. 

Star. A-VIII: 3; C-VIII: 9; E-V: 4; 

J-II: 4. 

Stella. E-IV: 1. 

Steneck. D-II: 16. 

. St. Joseph. L-III: 3. 

Arranged alphabetically-Continued. 

St. Louis. J-V: 11; B-II: 2 .. 

St. Paul. B-II: 3. 

St. Vrain. H-II: 2. 

Strong. E-V: 1. 

Stump Tail. J-II: 3. 

Sultan. G-I: 3. 

Sullton No. 1. K-I: 13. 

Sullton No. 2. K-I: 11. 

Sullton No. 3. · J-I: 5. 

Summit. D-1: 1; D-VI: 7; H-III: 12; 

K-IV: 2; L-III: 1. 

Sun. C-VIII: 5; I-III: 1. 

Sunnyside. G-VII: 3; I-IV: 13. 

. Sunol. F-III: 9. 

Sunshin~. J?-II: 2. 

Sunset. K-III: 4. 

Surplus. E-III: 11. 

Surprise. A-IV: 6. 

Swansea. E-III: 9. · 

Swift. H-II: 3. . 

Sylph. E-II: 8. 

Syndicate. K-I: 14. 

Syracuse. C-V: 6. 

Taft .. K-II: 2. 

Tarifa. F-III: 4. 

Tarik. G-II: 5. 

Tee Gee Aitch. H-II: 1. 

Tee Pee. D-VI: 5. 

Telephone. 0-II: 11. 

Ten wall. I-IV: 17. 

Terril pla·cer (Fulton Water Power). 

G-VIII: 2. . 

Terrible. J-IV: 12. 

Teutonic. · A-III-9. 

The· Hartman. G-IV: 10. 

Thirty Cents. G-I: 1. 

Ticknor. H-IV: 1. · 

Tigris. H-V: 5. 

T. M., Jr. F-I: 1. 

Tom Boy. D-V: 4. . 

Tom Kirby .. K-III: 14. 

Tornado. B-V: 7. 

Total Eclipse. H-IV: 17. 

Tough Nut. A-V: 15. 

Transvaal. D-V: -8. 

Treasure Vault. I-VI: 1. 

Trio. D-II: 18. 

Trojan. J-IV: 15. 

·Tropic. I-IV: 10. 

Trust. I-IV: 4. 

Uncle Sam. E-II: 11. 

Union. E-VI: 10. 

U. P. R'. B-II: 9. 

U. S. E-IV: 5. 

Valentine. Jr-IV: 1. 

Valverde. E-III: 1. 

Venwood. F-VIII: 7. 

Verticle. K-I: 1. 

Veto. J-IV: 7. 

Victor. 0-I: 12; H-IV: 3. 

Vida. 0-I: 14. 

Virginia. E-VI: 11. 

Virginia House. D-V: 6. 

Vivian placer. D-VII: 14. 

Wallace. 0-VI: 4. 

Wana & Hrow.doin placer. C-VII:l2; 

D-VII: 17. 

Wano.. A-III: 1. 

Ward. G-VIII: 4. 

Washington. J-IV: 3. 

Wasp. L-II: 7 . 

Waterloo. K-IV: 3,. 

Waverly. 0-III: 8. 

Wedge. E-VII: 9. 

Welch. 0-III: 2. 

Welch Boy. C-III.: 5. 

Welch placer. K-VIII: 2. 

West Dove's Nest. F-III: 6. 

Western. G-V: 13. 

West Santa Fe. H-III: 8. 

West Virginia. 0-I: 3. 

Whale (290). 0-VII: 14. 

Whale (850). D-VII: 15. 

White Metal. I-III: 8. 

White placer. _E-:VIII: 4. 

William F. placer. B-VI: 4. 

William Penn. J-II: 5. 

Williams. D-I: 9. 

Willie. A-VI: 3. 

Windsor Castle. F-III: 3. 

Win1ock. B-1: 11. 

W. M. S. K-Ill: 1. 

Wonderful. K-III: 13. 

Wolverine. D-III: 3. 

W. P. R. G-III: 2. 

W. R. D. 0-IV: 1. 

Wright. B-III: 1. 

W. \V. Kirby. A-'-II: 3. 

Tunnel. B-II: 15; E-VIII: 10; "X". A-II: 9. L-IV: 5. 

Tunnel Lode No. 1. H-IV: 16. 

Tunnel Lode No.3 .. H-IV: 14. 

Twelve-Thirty. E-I: 1. 

Two Brothers. E-III: 13. 

U. G. W. B-IV: 2. 

Umbra. A-III: 3. 

Uncle George. B-V: 1. 

Yellowston~. B-I: 9. 

York. B-VIII: 6. 

Yosemite (12040). A-I: 8. · 

Young. D-Ill: 2. 

Young Chief. C-IV: 7. 

Zozo. K-III: 3. 
) 

CHAPTER VI.-GENERAL FEATURES OF THE ORE DEPOSITS. 

INTRODUCTION. ing from the La Plata and San Juan mountains 

The Central City quadrangle is primarily a on the southwest to northern Boulder County 

gold and silver mining region, but ores of ura- on the northeast~ Within this belt' lie all the 

nium, tungsten, copper, and iron also occur important metal-mining camps of Colorado, inwithin its limits. The structural ty-pes include eluding Telluride, Aspen, Leadville, Breckenveins, stockworks, and magmatic segregations. ridge, Geoi·getown, and many others. (See 

All are believed to have been formed inTer- fig. 4.) As pointed out by Spurr a~d Garrey,t 

tiary time and to be genetically related to this mineralized belt corresponds in a general 

l!~IGURE 4.-Map showing:approximate distribution of principal silver, lead, and gold regions in Colorado. (After Spurr.) 

. . 

the Tertiary ( ~) igneous rocks of -the region. 

Long subsequent to the main 1nineralization 

the upper parts of many ore bodies were much 

altered· through the oxidizing influence· of the 

air and of meteoric waters. Such alterations 

h~ve in some places greatly augmented the 

value of the ore. 

GEOGRAPIDC DISTRIBUTION. 

way with the distribution of the Tertiary ( ~) 

intrusive rocks of the State, and the significance 

of this correspondence will be discussed later. 

Mines have been developed in nearly, all parts 

of the area surveyed in the Central City quadrangle, but they are most nm;nerous in the 

region around Central City, Blackhawk, and 

Idaho Springs, which far surpasses in . metal 

production the combined output of all the rest 

The region covered by this report forms part of the quadrangle.- Camps of lesser importance 

of a broad belt of mine;ralized territory extend-, 1 Spurr, J. E., and oarrey, o. H., op. cit., pp. 67-71. 

93 
94 GEOLOGY OF GILPIN, CLEAR CREEK, AND BOULDER dou·NTIES, COLO. 

are Dumont, Lawson, Empire, Alice, Yankee, 

Apex, Perigo, Eldora, Nederland, and Caribou. In the western high mountainous part of 

the quadrangle there are almost no developed 

mines. As this country has been much prospected, the absence of mines probably signifies 

a real deficiency in mineralization and not 

1 merely lesser accessibility. This part <?f the 

I quadrangle was not surveyed geologically. 

CLASSIFICATION BY STRUCTURAL TYPES. 

The ore deposits of this region may b~ classified according to struct11;re as veins, stockworks, 

irregular bodies formed by magmatic segregation, and auriferous gravels. The veins and 

lodes comprise gold-s'llver, uranium, and tungsten ores; the stockworks comprise only goldsilver ores; the magmatic segregations comprise iron and copl?er ores. 

tions. The distribution of the different mineralogic types of veins does not, however, correspond in any way to the relative abundance 

of veins in different .localities. It ~s believed, 

therefore, that within the area studied absence 

of veins in generaJ means absence. of fissures 

suitable for ore receptacles, and conversely that 

wherever suitable fissures were present orebearing solutions were sufficiently abundant 

and potent to form mineral veins. 

Many of the veins are nearly parallel in 

trend to certain of the porphyry dikes, but 

this is due solely to the fact that the prevailing directions of fracturing at the time of the 

intrusion of the porphyry persisted into the 

vein-forming period. Aside fron1 this, the dist~ibution of veins bears no close relation to 

the surface distributiol). of the Terti~ry ( ~) 

intrusives. 

STRIKES AND DIPS. 

VEINS. The strike of by far the greater number of 

Th~ great bulk of the ores of the quadrangle the veins lies between east and N. 45° E., 

occupy zones of minor faulting and therefore ~hut a few are northwesterly, and a very few 

form true veins. · · others take still different directions. The 

DISTRIBUTION. general accordance in strike· of most of them 

is believed to indicate that the fracturing 

Veins occur in largest numbers and in great- which preceded the ore deposition was proest size in the southeastern part of the area duced by stresses acting with considerable 

surveyed, near Idaho Springs and Central City, uniformity over large areas, though their 

within the areas covered by the large-scale effects were modified by local structural 

maps, Plates III and VI. They are moder- features such as the trend of foliation in the 

ately abundant .near Clear Creek between Du- fractured rock. ' 

m<;mt and Empire, near Alice and Yankee, and Most of the· veins have steep dips, generally 

near Caribou, but. throughout the remainder more than 60° from the horizontal. Near 

of the region ~hey are of only scattered occur- Central City the dips commonly exceed 70°. 

renee. Dips ·of less than 45° are exceedingly rare; 

The abundance of veins in different localities the lowest dip noted was 2°_to 17° in the Blue 

appears to be dependent primarily on the Bird vein, 2! miles northwest of Nederland, 

amount and character of the fracturing and which traverses Silver Plume granite. The disecondarily on variations in the character or rection of dip within the area covered by the 

abundance of mineralizing solutions. As more map of Idaho Springs and vicinity (Pl. VI) is 

fully discussed in a succeeding paragraph, the prevailingly to the north and northwest; this 

degree of fracturing was to a considerable ex- is also 'the. prevailing direction of dip of the 

tent dependent on the physical character of the foliation ·in the wall rocks. Farther north, 

rocks, and the absence of veins in certain areas within the area covered by the map of Central 

is due to the fact that these areas are underlain City and vicinity (Pl. III), the dips, which 

by rocks, such as the schists of the Idaho are steeper, are somewhat evenly divided beSprings formation, which are unsuited to the tween northwest and southeast. Changes of dip 

, development of large persistent fractures. As amounting to 20° along a single vein are not 

is pointed out in a later section, the veins in uncommon. The dip as well as the strike of some 

different parts of the region show differences in veins is markedly dependent on rock structure. 

mineral composition attributable to progressive Notable examples are found around the 

changes in the nature of the ore-forming solu- ! southern flank of Pewabic Mountain, as shown 

'\ 
I J 

l 

·~ 

.· I 

GENERAL FEATURES OF THE ORE DEPOSITS. 95 

in Plate IV, where the veins change in strike 

and clip with the shifts in the schistosity of 

the Idaho Springs formati~n. 

WIDTH. 

I The width of the workable veins ranges fron1 

. nlf an inch or even less in the telluride veins, 

ike those of the East Notaway·mine, to about 

40 feet in a nrineralized zone identified as the 

John L. Emerson vein, cut in the Lucania 

tunnel. More usual vein widths are fron1l to 5 

feet. 

COMPLEXITY OF FRACTURING. 

Exceptionally veins that are fillings of a 

single s.ilnple fissuTe have been follo:wed in 

nrining for considerable distances, as, for exrunple, in the Gladstone nrine, near Central City, 

where a sharp-walled vein ranging fron1 a 

n1ere thread to 4 inches in width has been developed. }t1ost of the veins are' n1uch 1nore 

c01nplex and are the result of nrineralization 

along a nwnber of subparallel fractures con·· 

s~ituting a fracture zone. In tnany zones of 

ft·acturing the rock 'has been brecciated and 

t}1e spaces between the fragments hB;ve bec~nne filled with ore 1ninerals. · 

j PERSISTENCE. 

! Few of the veins 1n th_is region can be 

d;efinitely traced as single fracture zones either 

0~1 the smface or in the nune workings for 

lengths of over 3,000 feet. The longest one 

noted was the Mammoth, near Central City, 

shown iii Plate III, which is traceable on the 

surface .ahnost continuously for about 6,000 

feet. The Concrete, Gunnell, and Grand Army 

vein is traceable on the surface with considerable certainty for a little over 4,000 feet. 

There seems to be no reason upon theoretical 

grounds. why in such a system of fissures as 

those occupied by the veins of this region their 

vertical extent should on the average have 

been greater than . their horizontal . extent. 

Accordingly the vertical extent of the veins 

that now appear at the surface in this region 

should be of a somewhat lesser order of magnitude than their horizontal extent, their original 

upper parts having been removed by ero,sion. 

It was therefore to be expected that many of 

the smaller veins. that appear on the surface 

should pinch out at moderate depths, as has 

been shown by mining operations.. On the 

other hand, some of the tunnels have discovered veins that do not appear at the surface. 

Many of the larger veins, however, have been 

mined successfully to depths of 1,000 to 1,500 

feet. The Old Town shaft is 1,950 feet deep 

and the California shaft 2,200 feet deep along 

the vein. The.· relations between depth and 

ore value are more fully discussed on pages 

137-138. ·rhe veins comnwnly terminate horizontally by splitting into branches too small to 

be worked. 

BRANCHING. 

Although some of the veins (such as the 

Seaton, fig. 55, and the Windsor Castle, fig. 52) 

show few important branches in the distance 

tP,at they have been followed in mining, the 

greater number are elements of complicated 

vein networks composed of master veins, 

usuaJly with northeasterly ·trends, connected 

by oblique cross veins. In following. such vein 

networks many of the mine workings become 

very complex, as shown in the plan of the Bobtail tunnel (see Pl. XX, p. 224); other characteristic branching vein systems are shown below in 

figure 5. Vertical branching of veins is no less 

characteristic and is exemplified by the union 

below the surface of the Slaughter House vein 

·with the Concrete and of the W autauga with 

the Old Town, in both cases the cause of disputes under the apex law. Vertical branching 

and pronounced curving are also shown in the 

veins of the Hubert.mine (fig. 30,p. 219). Some 

lodes have a dual character, being composed 

of two nearly parallel veins. The most striking example is to be seen in the Gem· mine, 

near Idaho Springs, in which the north and 

south veins are from 20 to 30 feet apart .. 

INFLUENCE OF WALL ROCK ON FRACTURING. 

The nature of the wall rock has exerted a 

marked influence on the extent and character 

of the fracturing. Practically all the rocks of 

the region except the schists of the Idaho 

Springs formation possess a high degree of 

rigidity, and in these rocks were formed under 

regional stresses sets of fractures, branching 

and somewhat complex, but at the same time 

sufficiently persistent ~nd open to afford favorable sites for ore deposition. The weak, easily 

crushed schistose rocks of the Idaho Springs 

formation as a rule yielded to the same stresses 

by forming innumerable short fracture seams, 
96' GEOLOGY OF GILPIN,. CLEAR CREEK, AND BOULDER COUNTIES, COLO. 

along many of which clayey gouge was produced. Only small open spaces wer~ left, and 

the fractured porti'ons of this formation were 

in general not favorable sites for ore deposition. 

Exceptions are to be. noted in certain places 

where the fractures cut sharply across the schist 

foliation and where the rigidity' of the Idaho 

Springs formation has been materially increased 

by the intrusion of large amounts of granitic 

·material. Examples of this influence of the 

wall rock on fracturing are numerous. On the 

332-foot. level of the Gold Collar mine, near 

Central City, the vein in passing from granite 

IRON MINE 

breaks up into a zone 5 or 6 feet wide, throughout which there has been slipping between the 

schist folia but no mineralization. 

·The influence of the character of the wdl 

.rock on vein formation has also been recogniz~d by George and Crawford 1 in the tungsten 

veins of Boulder County. It is exemplified on 

a large scale by the absence of notable veins 

o.ver certain large areas which are occupied 

mn,inly by. schist of the Idaho Springs formation. Such an area extends westwarq from 

Nigger Hill, near Central City, to Mount Pisgah 

and southward to the upper part of York Gulch. 

FIGURE 5.'---Diagram showing characteristic branchillg vein .systemS as exposed in the workings oi three minos. 

gneiss to schist of the Idaho Springs formation 

dies out in a series of small branching fractures 

about parallel to the schistosity. In the Creur 

d'Alene mine, just west of Central City, the 

mineralization· where the walls are· granite 

gneiss takes the form of sharp-walled sulphide 

veinlets that are plainly-fissure fillings. Where 

the wall rock is schist of the Idaho Springs 

formation sulphide veinlets are usually absent 

and the fracture zone is either barren or carries 

only scattered grains of' ·sulphides. In the 

Frontenac mine, on the fourth level west, the 

so-called Flat vein· where inclosed by walls: of 

schist heavily injected with pegmatite is a very 

definite. zone. of somewhat decomposed. and 

mineralized gouge and brecciated 'wall rock 

from 6 to 18 inches wide} but where it enters 

an area of· schist. unmixed wi~h pegmatite it 

STOCKWORXS. 

DEFINITION. 

A stockwork is an ·ore deposit of irregular 

shape made up of innumerable small branching and anastomosing veinlets. The character 

and origin of those occurring in the Central City 

region may best be set forth by considering in 

some detail the largest of these ore bodies, the 

so-called· Patch, developed in the San Juan 

mine, on Quartz Hill, near N evadaville. Comparisons will then be made with a few of the 

smaller stockworks. . ' 

THE PATCH. 

Structure.-The origin of this interesting 

deposit has been the subject of much specula1 George, R. D., and Crawford, R. D., The main tungsten area of 

'Boulder County, Colo.: Colorado Geol. Survey First Rept., p. 60, 1908. 

I 

\ "· 
, 

U, S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 94 PLATE XIII 

A. IRREGULAR MINERALIZATION TYPICAL OF STOCKWORKS OF THE 

PATCH TYPE AT HUBERT MINE. 

The sulphides and quartz fill irregu lar spaces and form irregu lar rep lacements in 

fractured and seri citized granite gne iss. From 850-foot leve l. Natu ra l size. 

B. NETWORK OF SPHALERITE VEINLETS TRAVERSING SERICITIZED GRANITE 

GNEISS, BOULDER COUNTY VEIN NEAR CARDINAL. 

Natu ra l size. 

0. ORE OF COMPOSITE TYPE FROM FOURTH OF JULY MINE, NEAR CENTRAL CITY. 

Pyritic ore has been brecc iated and the fractures filled by ore of the galena-sphalerite type. Natu ra l size. 
U. S. GEOLOG ICAL SURVEY PROFESSION AL PAPER 94 PLATE XIV 

A. POLISHED SURFACE OF ORE FROM ALICE MINE, SHOWING PROGRESSIVE 

ALTERATION OF MONZONITE PORPHYRY. 

Porphyritic texture sti II preserved on right but largely obi iterated on left. Probable position 

of this specimen with respect to principal fracture lines is indicated in figure 7, page 98. 

a, Slightly altered porphyry; b, moderately altered porphyry; c, high ly altered porphyry; 

p, pyrite. Natural size. 

B. ORE BRECCIA FORMED BY POSTMINERAL 

MOVEMENT ALONG A VEIN IN IVANHOE 

MI NE, NEAR NEVADAVILLE. 

Fragments of galena and dark -colored quartz I ie in a 

matrix of crushed granite gneiss. Natural size. 

0. BANDED ORE FROM TOPEKA VEIN. 

Centra l band of nearly b lack sphalerite is bordered 

on left by a band composed of fine aggregate of 

pyr ite, dark sphalerite, and quartz; on right by a 

band of coarse "resin" sphalerite. Natura l size. 
GENERAL FEATURES 01!, THE ORE DEPOSITS. 97 

tion and some controversy among mining men 

of tho dis.trict. Structurally it is· a body of 

irregularly fractured and brecciated rock. The 

degree of fracturing is variable. In some 

places the wall rock has merely been cut by an 

irregular network of fractures without much 

displacement (see Pl. XIII, A); elsewhere it has 

been broken into fragments that have been 

moved over one another, ·many of them becoming rounded by friction and fragments of 

different kinds becoming indiscriminately mip.-

gled. In places in the Argo tunnel the Patch 

is a breccia of rock fragments of many sizes, the 

largest 4 feet in diameter, in an arkose-like 

matrix. The brecciation reached a maximum 

along several northeastward-trending zones that 

are parallel to and in some places continuous with the veins entering the Patch. The 

principal veins entering the upper portion 

of the Patch are the California-Gardner and· 

the Rhoderick Dhu, which appear to combine 

east of the Patch as the great Heela-N ationalMammoth lode. On the level of the Argo 

tunnel the principal veins of the Patch have 

been provisionally identified as belonging to 

the Kansas-Burroughs group, the Gardner vein 

at tllis depth having appa~ently passed out of 

and south of the Patch. The Patch fracturing 

therefore appears to have been produced by 

the same forces and at the same time as the 

neighboring vein fissures. It is situated where 

a number of large fracture zones approach one 

another ·closely and where the shearing mo.vements, instead of being confined as in most 

·c.ases to these · _zones, be~ame distributed 

through all the intervening rock. 

Form.-In surface outline the Patch, as 

shown in figure 36, is oval, having a diameter of 

about 750 feet from northeast to southwest and 

of about 400 feet from northwest to southeast. 

, Its boundaries are commonly indefinite, but in 

the Argo tunnel it terminates sharply on the 

south against a vertical fault plane. From the 

surface down the breccia of the Patch persists 

without diminution in size but with marked 

diminution in mineralization to the Argo tunnel, 

a distance of approximately 1,600 feet. Its 

general form is therefore that of a "pipe" or 

"chimney" dipping steeply to the north. Its 

extent below the Argo tunnel is wholly conjectural. 

Wall rocks.-The prevailing wall rock of the 

Patch is granite gneiss, but in places bostonite 

44214°-17-· .7 

porphyry is abundant; pegmatite and schist of 

the Idaho Springs formation occur only rarely. 

The fractures traverse all these rocks indis-

. criminately. 

Mineralization.-8ome parts of the Patch 

are barren; others are heavily mineralized. 

The zones of maxiinum brecciation are in general also zones of maximum mineralization, as is 

very apparent from figure 36 and the plans of 

the San Juan workings (fig. 35). As in the 

neighboring veins (see p. 234),. the mineralization is of two types-one showing pyrite, chalcopyrite, and quartz with a little tetrahedrite 

as ore minerals and the other showing galena, 

sphalerite, chalcopyrite, and subordinate pyrite. There is little mingling of the two types. 

The ore minerals fill fractures and angular 

cavities between .fragments and also replace 

the silicates of the rock, and in most of the ore 

both processes have been operative. In many 

places the' limits of profitable mining are determinable only by assay. · 

· Further details· concerning the Patch a~ exposed in the Argo tunnel and the San Juan 

workings are given on page 234. 

OTHER STOCKWORKS. 

A much smaller stockwork is developed by 

' a large stope in the Hubert mine. Most of the 

FIGURE 6.-Sketch of filled breccia in Hubert mine. Angular fragments 

of granite gneiss lie in a matrix of galena and sphalerite. One-half 

natural size. 

workings of this .mine follow veins, but_ near 

the west end of the 850-foot lever the vein · 

begins to branch ·and then passes irito a network of sulphide stringers traversing the granite gneiss in all directions; this passes locally 

into a true filled breccia, whose appearance is 

shown in figure 6, and whose fragments have 

plainly been moved from their original position. The largest fragments are 3 inches in 

diameter and they usually show shfirp, angular 

outlines. The stockwork has a known width 

of about 35 feet and a vertical extent of over 
98 GEOLOGY OF GILPIN, CLEAR CREEK, AND BOULDER. COUNTIES, COLO. 

150 feet, apparently not reaching the surface. 

It is identical in appearance with certain portions of the Patch and was probably formed by 

similar processes acting on .a much smaller 

scale. Here the movement, initiated along the 

south vein fracture and several branches leaving it at nearly the same point, apparently 

became distributed more or less through the 

intervening rock, which fractured irregularly, 

the fragments in places moving over one 

anot~er. This fractured and porous mass became a favorable site for ore depositioJ}. 

The ore body of the Alice mine, near Alice, 

has been formed by the mineralization of an 

irregularly fractured body of porphyry, but it 

differs from the Patch in that most of the fracThese stockworks are described in more detail 

on pages 323-326. 

ORES FORMED BY MAGMATIC SEGREGATION. 

Within the Caribou monzonite stock occur 

four bodies of much more mafic (basic) rocks 

of irregular but more or le.ss rounded outline. 

The greatest dimension of any of these bodies 

is a little less than a quarter of a mile. Within 

these in turn occur several small masses of iron 

ore, some of which are lens-shaped, while others 

are wholly irregular. The contact between ore 

and wall rock is in some places sharp and in 

others. gradational. 

The copper ores of the Evergreen mine, near 

Apex, occur witl?in dikes of monzonite, and the 

metallic minerals, which are irregularly· distributed within the dikes, crystallized for the 

most part 'Contemporaneously with the silicate 

minerals of the monzonite. The ores are apparently a product of magmatic differentiation 

under localized and unusual conditions discussed at length on pages 126-129. 

AURIFEROUS GRAVELS. 

The auriferous gravels of the .region, worked ) 

in the early days, have long since ceased to be 

of any economic importance. Aside from the 

fact that some of them, probably of preglacial ~ 

. age, are cemented, they present no structural· 

peculiarities. Their bulk is small. The placer 

FrGURE 7.--qiagrammatic section showing relation of mineralization to deposits are described on pages 60 ·and 120. 

iracture plapes and their intersections at the Alice min~. The white 

areas are fresh or little altered porphyry. a, Vug at intersection of ORE TEXTURES. 

fractures; b; "nest" of minerals at intersection of fr~ctures. The . 

area c inclosed by the broken line mustrates the position which the : With the exceptwn of the tungsten ores, . specimenshowninPlateXIV,A,mighthaveoccupied~heninplace~ which were not studied by the writer IDOSt of 

The specimen itself was taken from the dump. ' . ' . · f h" · · 1 • 

.. . ; the ores o t IS regwn are massive-that Is, the 

ture openings are narrow and the fragments component minerals are distributed irregularly 

have suffered little displacement relative to one though not everywhere evenly throughout the 

another. The mineralization was accomplished ore mass. Brecciated structures . are fairly 

mainly by replacement rather than by fissure corru,non both in ores due to single mineralizafilling andwasatamaximumwheretwo or more. tion, as shoWn. in Plate XIII, A, and in those 

fractures intersected, as is shown diagrammat- due to composite or dual. mineralization, as 

ically in figure 7. At -such intersections nests shown in Plate XIII, 0. · In a few places brecof sulphides as much as 3 inches across have ciated structure has been produced by vein 

developed. Less commonly cavities or vugs fracturing subsequent to mineralization, as 

1 foot or less in diameter occur at su~h inter- · illustrated in Plate XIV, B. Irregular bandsections and are lined with sulphides. ing continuous for only short distances is not 

The ore of the Commercial Union mine, uncommon and may be due to variations either 

southwest of Alice, is structurally similar to in the proportions or in the coarseness of the 

that of the Alice mine, but the wall ~ock is . component minerals, or in both. In some 

schist of the Idaho Springs formation instead places such banding is the result of dual min-

.:>f porphyry. eralization, a fissure filled with later ore liaving 
,) 

, 

' 

GENERAL FEATURES OF THE. O~.E DEPOSITS. 99 

been formed p'l.rallel to an earlier vQin along · sidered at leng.th in succeeding chapters, but 

either its border or its center. · Here and thei·c, occasion will be taken here to pr~scnt the 

as shown in Plate XIV, 0, banding even in ore mineral characters of all these types in tabular 

deposited during a single period of mineraliza- form (p. 100} and to mention certain mineraltion is well defined, but such banding is local ogic features of general significance. For reaand is nowhere sufficiently persistent through- sons set forth in Chapter VIII (pp. 121-123) the 

out ft.n ore body to itidicate a well-marked uranium ores are believed to represent merely 

genern.l sequence in the deposition of the com- a local and unusual phase of the pyritic ores, 

ponent minerals. and their minerals are therefore listed in the 

1.,extures peculiar to the pitchblende ores are column dovoted to that type. The tungsten 

illustrated in Plate XV, A, and figure 12 (p.124) ores were not studied by the writer and are not 

and are due to the well-known tendency of included in the tabulation; their characters are 

pitohblendo to crystallize in masses of grapelike briefly sun1marized from the reports of others 

or botryoidal form. · ' on page 123. The list includes not only the 

GEOGRAPHIC DISTRIBUTION OF ORE OF 

DIFFERENT CLASSES. 

Gold-silver ores occur in nearly all parts of 

the area surveyed, although they are most 

abundant in the vicinity of Central City and 

Idaho Springs. The distribution of the several 

types of gold-silver ores is described on pages 

115-116. 

Uranium ores occur principally in a small 

group of mines on Qu~rtz' Hill, near Central 

City, but they have been found in small quantities at a few other properties, such as the 

Jo H.eynolds mine, near Lawson. They are 

regarded as a local and unusual variety of the 

gold-silver ores. · 

Orcs worked primarily for their copper content are confined to the Evergreen mine, near 

Apex, where they are the product of unusual 

and highly localized conditions. 

Tungsten ores are confined to the region between Phoenix, Nederland, and Cardinal, and 

are associnted with a series of dikes of intermedin.te to mafic (basic) composition that are 

unique in tho Centrn.l City quadrangle. 

Iron ores are confined to the immediate 

vicinity of Caribou. 

MINERAL COMPOSITION OF ORES. 

Tho ores of the Central City quadrangle may 

bo cln.ssified on the basis of their most valuable metals it1to fiv~.gro"!Jps-gold-silver ores, 

uranium ores, tungsten ores, copper ores, and 

iron ores. On tho basis of mineral association, as discussed on pages 105-116, the gold:-

silver ores may be subdivided into three 

typos-pyTitic ores, galmia-sphalerite ores, and 

telluride 01~es. Tho characteristics of each of 

those classes or subclasses of ores will be conIninerals noted by the writer but also those 

authoritatively reported by earlier observers .. 

While the physical conditions under which 

the ores of the several types were deposited 

will be discussed at length later, it may be 

noted in passit1g that all three types of gold 

ores show an entire absence of minerals characteristically formed under high temperatures 

or high pressures. Another noteworthy fact 

is the great preponderance of arsenic over antimony in both the pyritic and the galenasphalerite types of gold-silver ores. In some 

of these ores the arsenic mineral enargite is 

abundant, and most of the so-called "gray 

copper'' of the district proves on testing to be\ 

tennantite rather. than tetrahediite. A little 

antimony is indeed present in some occurrences of these minerals, but it is invariably, 

so far as the writer's observations show, much 

subordinate to arsenic. Stibnite has not been 

authoritatively reported. 

It is significant also that the wri tor's · o bservations in this region have failed to reveal 

any primary occurrences of the rich sulphocompounds of silver, whereas they ·are abun-· 

dant locally as products of downward enrich-· 

mont. Important too is the fact that among: 

these secondary silver minerals the arsenio: 

compounds proustite and pearceite are mtich. 

more abundant than the corresponding antimony compounds. The pyrite of the ores, 

if well crystallized, is commonly cubical or 

pyritohedral in form; octahedral crystals of 

pyrite were observed only it1 m1e mine, the 

Rooks County, -between Apex and Tolland. 

On the octahedral pyrite crystals are implanted small crystals of a soda-potash feldspar, the only occurrence of this silicate noted 

in the ores of the region. 
100 GEOLOGY OF GILPIN, CL~AR CREEK, AND BOULDER COUNTIES, COLO. 

Ore minerals of Central City quadrangle. 

IN OTE: The list includes minerals developed metasomatically in wall rocks as well as those that are fissure fillings. P, Primary minerals; S, minerals 

of secondary sulphide zone; 0, oxidation products;*, mineral rare.) 

Minerals. 

Native elements: 

Primary ores crystallized from mag- Primary gold-silver ores deposited by ascending thermal mas. solutions under moderately intense heat and pressure. 

Caribou iron ores. Evergreen mine 

copper ores. Pyritic or.e type. Galena-sphalerite ore type. Telluride ores. 

.~N~~r:::-:::::::::::::::::::::::::::::::::::: :::::: :::::::::::: ~ :::::: :::::: . ~ ~~ 81 ~ 1 8 ~ ~~ 81 . ~~f£~{11:::::::::::::::::::::::::::::::::::: :::::: :::::: :::::: :~:::: :::::: :::::: "p,j.' :::::: .. ~ .. ··=p·· :::::: :::::: :::::: :::::: :::::: 

sw~~~;~;~;;;_;·:::_.:·~:~:.·:~--:::::~:~; :::::: ~::::~ :::::~ ::t:: :::~:: :::::: :x: :::~~: .. ~ ... i :::~~: :;~;; .T :~;;:: :;~':: 2~~~~~ft6::::::::::::::::::::::::::::::::::: :::::::::::::::::::::::: :::::::::::: :::::·: ~ ............... s*· ...................... .. Galena.......................................................................... P* ...... :::::: "p" ...... :::::: :::::: :::::: :::::: 

Viitt~~~fiL:::::::::::::::::::::::::::::: ::.:::: :::::: :::::: :::::: :::::: :::::: ~= :::::: :::::: .. ~~- ::::::·:::::: ~~~~~ :::::: :::::: 

::!~~#~;:·:····:··:: : ..•.• : •• ::·::··· : •••• : .: •• :: •••• :. ··:··· ••• :.: .::··· ··i~· ::·:·: .::: •• ··i:· .: •• : •••• :.1:~: •• :::. ~::··· ~~::;~~~~:::: ::::::::::::::::::::::::::::::: :::::: ::::::. :::::: :::::: :::::: :::::: --~-- :::::: :::::: .. :.~. ···s·· :::::: :::::: :::::: :::::: Pryu~tit~·-·································· ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ~ :::::: :::::: ::::::.:::::: 

§t~~h:~il:~::::::::::::::::::::::::::::::::: :::::: :::::: :::::: :::::: :::::: :::::: :::::: :::::: :::::: :::::: S? ....................... . Halo ids: 

~r~~r1fe. ~~:~ ~::::::: :::::::::::::::::::::::::::::: :::::: :::::: :::::: :::::: :::::: ··=p· · :::::: :::::: ··=p? · :::::: --~~- :::::: :::::::::::: 

Oxl~~;n:.:::::::::::::::::::::::::::::: ;:;:: ::::·: :·~:~ ::~:: :::::: ;:~;; ::~:: :·:.:: ::~·: ::~:: :::·:: :·~.:.::~:: ::_::: ;:~.: r;~~n!~~~:(~;~~:2:;~~~:3~::::::::::::::::::::::: ::~~~ :::::: ::~:: ~:~:~ :::::: ::~:: :::::: :::::: ::~:: :::::: :::::·: ::~:: :::::: :::::: --~* .. 

ea,Ie~~~;~_:::::::::::::::::::::::::::::: ::::::::::: ::::: ::~~: ::~~: :::::: --~-- :::::: ::::: ; ::::::::::::::::::::::::::::: 

Smithsonite ............................................................................................. :::::: "(j,j.' :::::: :::::: :::::: 

e~:~_:::::::::::::::::::::: ::::::::: :::::::::::: :::::~ :::::::::::: ::~:: :::::::::::: :.r :::::::::::: §~ :::::::::::::::::: Sllic~~~~oclase. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . P ................................................ · · · ......... · · ... . Adularia . . . ... . ... P* ...... ...... P* ........... . 

~~ft~-~~~~~: ~!~~~~~~::::::::::::::::::::::: :::::: :::::: :::::: :.~:: :::::: :::::: ~-~~: :::::: :::::: :::::: :::::: :::::: :::::: :::::: :::::: 

Plagioclase (calcic).. . . . . . .. . . . . . . . . . . . . . . . . . P . .. .. . . . .. .. P ................................................................. . 

~o1~~ioll.iia:::::::::::::::::::::::::::::::: --~-- :::::: :::::: ~ :::::: :::::: :::::: :::::: :::::: :::::: :::::: :::_::: :::::: :::::: :::::: 

Gamet . ........ . .................. '.. p ....................................................................... . 

~N6~~::::::::::::::::::::::::::::::::::::::· .. ~ .. :::::: ::':::: .. =p·· :::::: :::::::::::: :::::: :::::::::::: :::::: :::::: :::::: :::::::::::: 

Sericite ........................ : .................... · ................. · ... · . . . . . . P . · ... · · · · · · · P · · · · · · · · · · · · P?' · · · · · · · · · · · · Biotite p ......................................................................................... . 

~Yl~~~1i~~~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : .. :: · : : : : : : : : :: : : : : ~ ~ : : : : : : : : : : : : : 

tJi~~~~~~iiH\./H HEE ./::-:: ::> f: :::::· :::::: ::~~: ·:H L:. \H. :H: ;:~~: ::::::,:E/E Sulphates: · Barite........ . .. . . . .. .. .. . . .. . .. .. . .. .. .. . . . .. .. . . .. .. . .. . . .. .. .. .. .. . . .. . . . . . . .. .. . . . .. .. . . .. .. . P .. . .. . .. .. . . P* ........... . 

~~1~~~~Ps~~r:~i~r~n~~~~:. .. ~gfEg:p~sitioii · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · 0 · · ·. · · · · · · · · · 0 · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · 

not determined, found coating uraninite at 0 G~~~~e~i~~~-~~~~~!.·!.~1~~~:::::::::::::::: :::::: :::::: :::::: :::::: :::::: :::::: :::::: :::::: ...... :::::: :::::: ··o*· :::::: :::::: :::::: ., I 

1.._ 
GE'NERAL FEATURES OF THE ORE DEPOSITS. 101 ,~i;t~_. I 

STRUCTURAL RELATIONS OF ORES AND 

PORPHYRIES. 

As has been pointed out i:n Chapter III, 'the 

later intrusive rocks of the quadrangle, though 

, showing some diversity in age, are ~II believed 

to have boon intruded either in late Cretaceous 

or early Tertiary time. The iron ores of 

Caribou and tho copper ores of the Evergreen 

n1ino, being products of magmatic differentiation, are manifestly of the same age as tho 

monzonite in which they occur; the other ore 

deposits are, with a few exceptions, later than 

these igneous rocks. 

Among tho gold-silver 'ores, those of the 

pyritic typo cut monzonite porphyry in the 

Alice mine,· near Alice; in tho San Juan, East 

Notaway, and Chase mines, near Central City; 

and at several plac~~- in tho Argo tunnel. 

Ores of tho pyritic type were observed to 

cut bostonite in tho l{ockford tunnel, near 

tho mouth of Fall Ri-V,er; the Two-Forty mine, 

near Russell Gulch, and probably also in the 

Silent Friend and Earl of I(ent mines, near 

Dmnont. 

Gold-silver ores of the galena-sphalerite type 

cut monzonite in tho. Edgar mine and Idaho 

tunnel, near Idaho Springs; in tho Silver ~go 

tunnel, in Gilson Gulch; ip. the San Juan mmo~ 

near Central City; and in a number of other 

mines. Tho galena-sphal'erito ores cut bostonito in tho Senator and Blue Ridge mines, near 

Lawson; also in the Edith S. vein as exposed 

in tho Big Five tunnel, and in the Fairmont 

tunnel near the head of Virginia Canyon. 

Telluride veins cut monzonite porphyry in 

tho East Notaway mine (see p. 264), but 

nowhere else in tho region were they found in 

contact with the late intrusives. 

Uranium ores were not observed in association·with porphyry, but. as already pointed out 

they are believed to be a phase of the pyritic 

type of gold-silver ores. Like them they were 

probably formed later than the porphyry 

intrusions. 

The tungsten ores have not been observed in 

contact with the Tertiary ( ~) intrusive rocks. 

There are a few noteworthy exceptions to 

the general rule that the ores are either contemporaneous with or later than the Tertiary 

. ( ~) intrusives. Spurr observed in the Stanley 

mine 1 near Idaho Springs biotite latite in1 Spurr, J. E., and Garrey, G. H., op. cit., p. 344. 

truding not only the earlier bostonite · porphyry but the gold-silver ore as well. The dike 

in the Stanley mine is the only known occurrence of biotite latite in the Central City 

quadrangle, and these rocks have a very sparse 

distribution in the adjacent Georgetown quadrangle. At several places in the Blue Bird 

mine, near Nederland, a gray fino-grained 

mica andesite porphyry distinctly outs the 

Blue Bird vein at sharp angles and with 

"frozen" contacts. 

PRIMARY VARIATIONS IN METAL CONTENT IN 

ORE DEPOSITS. 

Variations in the metal content in different 

parts of the same ore deposit may result 

either from variations in the degree or in the 

character of the mineralization-that is, the 

variations may be quantitative or qualitative. 

Variations in the degree of mineralizatiOI;l 

occur in every ore deposit and are dependent 

primarily on the nature of the fracturing. 

The ore at one part of a vein may be a filling 

of a single wide fissure, while a little fa;rther 

on it may fill several small nearly parallel 

fissures, nec-essitating the excavation of more 

wall rock·to obtain the same quantity of valuable metals. Where two or more fracture 

zones approach each other closely, brecciation of the intervening wall rock may occur, 

and the breccia may become highly mineralized, forming ore bodies larger than the 

typical veins but usually of lower grade, 

because proportionately more wall rock must 

be mined with the sulphides. Large:-scale 

examples of typical veins passing into mineralized breccias are found in the San Juan and 

Hubert mines, and examples on a small scale 

are common in many mines. A fissure thq,t is 

strong and well mineralized in brittle rocks 

may in passing into less brittle rocks subdivide into numerous very minute fissures of 

small individual extent that are only feebly 

mineralized, or the more plastic rocks may 

crush to a mass of fragments mixed with 

a clayey gouge that is unfavorable for ore 

deposition. Variations in mineralization due 

to this cause were noted in a number of 

mines where veins· pass from granite gneiss or 

pegmatite into schist of the Idaho Springs 

formation .. Unusually heavy mineralizati'on 

is comm9n at the junctions of the larger members of a vein system; the vein fractures at 
102 GEOLOGY OF GiLPIN, CLEAR CREEK, AND BOULDER COUNTIES, COLO. 

:such localities usually join at acute angles, and 

the wedges between the. converging veins were 

-commonly much shattered and afforded particularly favorable channels for the circulation 

of mineralizing solutions. Many of the most 

productive ore shoots of the region follow 

such junctions. An ore shoot formed in this 

·way was noted in the Chase mine, at the lo-

-cality shown by the letter C in figure 49 

-(p. 275). The Elizabeth vein, though itseH 

:rarely productive, has near its intersection with 

the productive veins of the Gunnell mine produced notable enlargements of their ore bodies. 

Equally as important as the types of variations already noted are those due to changes 

in mineral composition. Gold and silver are 

nowhere equally abundant in all the ore 

minerals, and consequently variations in the 

proportions ·of the ore minerals entail variations in the value of the ore. In certain veins, 

such as the Mammoth, near Central City, the 

ore, which consists predominantly of pyrite, 

is workaple only where chalcopyrite, a much 

more auriferous mineral ~han the pyrite; is 

also present. In the telluride veins variations 

in value dependent on the quantity of telluride 

present are likely to be very abrupt,. and rich 

<>re may be followed by lean ore of almost 

identical appearance. In certain ores the 

richer minerals. formed more abundantly in 

the later stages of the mineralization; this is 

true, for example, of chalcopyrite and tennantite in the pyritic ores, and these minerals 

.are therefore likely to be most abundant· in 

the central portions of veins or near vugs. In 

general, however, these mineralogic variations 

seem to follow no definite law and to be an 

expression of minor v~ria tions in the composition of the ore-forming solutions comparable to those larger variations that are 

expressed by the different ore types. 

A special phase of mineralogic variation is 

the result of the dual mineralization discussed D?-Ore fully on pages 112-114. As there 

pointed out, many gold-silver ores of the 

pyritic type were subsequently fractured, and 

ores of the galena-sphalerite type were deposited 

along the fractures or in vugs in the pyritic ore. 

The second mineralization affected only portions of the pyritic ore bodies, so that there may 

be transitions along . a single vein from ores 

·wholly pyritic irito composite ores and even 

into ores wholly of the galena-sphalerite 

type.· The workability of certain ores is due 

to such. dual mineralization, some of the 

earlier pyritic ore being below the commercial 

grade. The distribution of the composite 

ore being dependent on the irregularities of 

fracturing, is likely to be diverse, but in very 

many veins that have been mineralized twice 

the older pyritic mineralization is more extensive ~han the younger galena-sphalerite 

mineralization, and composite veins tend to 

pass into pyritic veins laterally or downward. 

Many of the veins along the line of the Argo 

tunnel that are composite at the surface are 

pyritic at the tunnel .level, notable examples 

being the Sun and Moon and the Gunnell 

veins. Many veins that pass from areas of 

predominantly pyritic ores to areas of predominantly galena-sphalerite ores are pyritic 

at one'_ end, of the galena-sphalerite type at 

the other, and composite between; the American-Mter Supper-Sleepy Hollow vein, in the vicinity of Blackhawk, appears to be of this type. 

Variations from QOmposite ore at one end of 

a vein to ore of .one or the other simple types 

at the other end are extremely common. 

The Hidden Treasure-California-Gardner vein 

is composite in its eastern portion and of the 

galena-sphalerite type in its western portion, and the same is true of the OwatonnaFrontenac-Aduddell-Druid-Kokomo lode. 

Dual mineralization of another type ij exhibited in the East Notaway mine, where the 

pyritic ore of the~e vein is locally 

traversed by later veinlets of te~uride ore. 

ALTERATIONS OF WALL ROCK. 

The Central City quadrangle is not a favorable region for the detailed study of wall-rock 

alterations. For trustworthy chemical comparisons the element of variation in the character of the wall rock prior to alteration must be 

practically eliminat~d, and_ this can seldom be 

done in this region of frequently alternating ... 

rock varieties. The general character of the 

·alterations has been determined, however, and 

seems to throw some light oil the nature of the 

mineralizing solutions. 

Many of the zones of fracturing along which 

the veins of the quadrangle were formed contained. few large open spaces. The mineralizing so~utions entered along many small fractures, some of them of microscopic minuteness, 

and from these gradually worked outward into 
~) 

GENERAL FEATURES OF THE ORE DEPOSITS. 103 

the wall rock, replacing the rock minerals and 

converting the rock into ore for varying distances from the fractures. 

In other fracture zones open spaces of considerable size existed and became filled with ore 

minerals, but the wall rock adjacent to such 

open spaces was also invariably mineralized, 

so1ne of it to such a degree that it became workable as concentrating ore. The processes of replacement can in general be better studied in 

the walls of filled fissures than i.n the replacement veins. 

Detailed description of the wall-rock alterations will be deferred to Chapter VII, but their 

general nature may here be summarized. The 

observations refer only to the gold-silver ores 

and their subtype uraninite-bearing ores; the 

tungsten 6res are not considered. 

The dominant wall-rock alteration associated 

with the gold-silver ores of both the pyritic and 

galena-sphalerite types consists in the replacement of all the original rock minerals except 

quartz and apatite by sulphides, sericite, and 

in some places carbonates (calcite or siderite). 

Quartz entirely resists the alteration or may 

recrystallize. A1nong the rock minerals -that 

yield to these alterations are orthoclase, plagioclase, biotite, hornblende, and magnetite. It 

may be inferred, therefore, that these ores were 

not deposited at extremely high temperatu~e or 

high pressure, for under. such conditions these 

silicates and oxides are usually stable. 

In the early stages of alteration the replacenlents are selective, sericite, for example, developing at the expense of certain rock-forn1ing 

silicates and not of others and pyrite replacing 

1nagnetite before it replaces other minerals. In 

the alteration of ferromagnesian silicates, such 

as biotite and hornblende, chlorite and epidote 

n1ay form as temporary products, to give way 

to sericite, pyrite, and calcite as the alteration 

, continues. Such features indicate that in the 

early stages at least the replacement is not a 

bodily removal of one mineral in solution and the 

deposition of another in its place but involves 

chemical interchanges between the original 

minerals of the wall rock and the mineralizing 

solutions. 

~rhe association of minerals formed by 

replacement in the walls of £lied fissures is in 

general different from that deposited in the 

fissure itself, in spite of the fact that both 

mineral associations were obviously formed 

almost contemporaneously and under the same 

general conditions of pressure and temperature. 

One of the most striking exemplifications of 

these contrasts is the scarcity or entire absence 

of galena and sphalerite in the walls of many 

fissure fillings in which these minerals are very 

abundant; in such walls pyrite is the dominant 

sulphide. Carbonates may be present in a 

filled fissure but absent from its walls. Conversely, sericite, the commonest alteration 

product in the walls, is never found in the 

fissure fillings. Chalcopyrite and tennantite, 

common constituents of certain fissure fillings, 

are rarely found in the walls. 

Differences· in mineral character analogqus 

to those between a filled fissure and its wall 

rock may in a few places be noted along the 

strike of a vein. For example, a fracture 

system that passes from an area of granite 

gneiss to an area of schist of the Idaho Springs 

formation commonly changes from a zone 

having a few open fissures to one having many 

very minute tight fissures. In consequence, 

fissure filling, the predominant process in the 

granite gneiss, gives way to replacement in the 

schist. In the Creur d'Alene n1ine, where a 

change of this sort was noted,· sharp-walled 

veinlets, some of which carry galena and 

sphalerite,1 occur in the granite gneiss but are 

supplanted where the fracture zone enters 

schist by disseminated ore carrying pyrite as 

its main sulphide. In places half the volume 

of this ore is pyrite. 

Few opportunities were afforded for determining with precision the wall-rock alterations 

associated with tho deposition of the rich 

telluride ores. In the Eldora district there 

was little ·chance to observe these ores, and in 

the vicinity of Idaho Springs and Central City 

the telluride ores were everywhere associated 

with sulphide ores, so that the alterations 

connect~d with each type ,could not be entirely 

differentia ted. 

In the War Dance mine, near Central City, 

much of the ore is ·a replacement of schist by 

fluorite, pyrite, sericite, and sylvanite. Schist 

replacement by fluorite was also noted in ore 

on the dump of the neighboring Powers mine. 

The extent to which the original wall-rock 

.texture. is destroyed in the replacement process 

varies with the nature of the texture and the 

severity of the alteration. In many places it 

is wholly effaced, and the only indications that 
\ 

\ 

\ 

104 GEOLOGY OF GILPIN, CLEAR. CREEK, AND BOULDER COUNTIES, COLO. 

what is· now ore was once ro~k are found in . are most conspicuous where. veins pass from 

the presence of sericite in the ore and its areas ·of granite gneiss into areas of schist of 

complete gradation into undoubted wall rock. the Idaho Springs formation. 

In a few localities the extreme of alteration is · - What may be termed a chemical influence 

represented by a structureless mass of minute of the wall rock on mineralization, due to the 

sericite plates. Near many ore bodies, on the mineral composition of the rock, was only 

other hand, the alterations have been less doubtfully . ;recognizable in a few places. 

severe and original foliated or porphyritic . Changes in the character of the wall rocks 

textures are still preserved. seem to exert no influence on ores that are 

While the principal key to the composition fillings of open fissures. On the other hand, 

of the ore-forming solutions is the mineral ores that are replacements show some variacomposition of the fissure fillings, the abun- tions with the nature of the rocks replaced. 

dance of sericite in the walls contributes the In the Druid mine (p. 273), for example, the 

additional information that the solutions were more micaceous folia in the Idaho Springs forvery rich in potash. The nature of the mation seem to have been replaced by valuable 

mineralizing solutions is more fully considered ore minerals more readily than less micaceous 

on pages 131-135. layers. In a number of the mines :p.ear Caribou 

INFLU:ENCE OF WALL R()CK ON MINERALIZATION. 

The different .rocks of this region, under the 

regional stresses that produced the vein 

fractures, yielded in different ways dependent 

on their varying rigidity. As, a direct consequence of these differences in the nature of 

the fracturing, differences resulted not only 

in the degree but also in the kind of mineralization, as has been pointed out above. These 

influences of the wall rocks on mineralization, 

which are purely mechanical in their nature, 

where the veins pass from: areas of monzonite 

into areas of gabbro or even more mafic 

(basic) rocks the change in wall rock must 

have resulted in changes in the nature of the 

replacement ores, but opportunities were 

lacking to study this feature. In general the 

chemical influence of changes in wall rock on' 

mineralization appears to have been minor 

and local. In this connection should be noted 

the ab.sence from this region of limesto~e, 

a rock particularly likely to exert a considerable 

influence on mineralization. 
) 

CHAPTER VII.-GOLD-SILVER ORES. 

PREDOMINANCE AND GENERAL CHARAC';I'ER. less than 5 per cent by weight of. the ore, 

Most of the ore deposits of the C<;}ntral City 

region are veins or stockworks that are worked 

primarily for ~he gold and silver which they 

contain. In some deposits copper or lead or 

rarely zinc is sufficiently abundant to be of supplementary economic importance. A few ores 

contain pitchblende, and though these ores also' 

carry considerable gold and silver and are 

probably merely a phase of the gold-silver mineralization, their description will for convenience be deferred to Chapter VIII (pp.121-123). 

In most of the gold-silver ores gold greatly 

predominates over silver in value, but in a few, 

usually as a result of downward ()nrichment in 

silver, the reverse is true. In the eady days of 

the region placer gravels were of much economic importance and the gossans of many of 

the lodes were worked by placer-mining methods, but placer mining is now practically 

extinct. · 

CLASSIFICATION. 

\ 

The gold-silver ores may be classified as lode 

ores and placel'S. The lode ores may be classified under four types-pyritic ores, galena-

' sphalerite ores, composite ores (a combination 1 of the pyritic and galena-sphalerite ores), and 

· telluride ores. 

LODE ORES. 

PYRITIC O~ES. 

DEFINITION. 

The pyritic ores consist predominantly of 

pyrite. and gangue minerals, with subordinate 

amounts of chalcopyrite, tennantite, and in 

places enargite and other metallic minerals. 

In these ores gold greatly predominates in 

value over other metals. They constitute one 

·of the principal types of gold ores in the region, 

the entire output of the Saratoga, Old Town, 

Alice, and many other mines belonging to this 

type. 

PRIMARY MINERALS. 

equivalent to less than 1.5 per cent metallic 

copper. In some shipments of rich smelting 

ore the proportion of chalcopyrite rises to 

nearly 50 per cent, or the equivalent of about 

17 per cent of copper. Tennantite is commonly present but is very subordinate to chalcopyrite. Enargite is abundant in a few v~ins. 

Silver and gold, probably alloyed, occur in the 

sulphides but are rarely visible. Other metallic 

minerals present here and there in small 

amounts are galena, sphalerite, molybdenite, 

and native bismuth. In the Alice mine argentiferous 'bismuthinite occurs in places. 

Where the ore is a replacement of the wall 

rocks the gangue minerals are t.he wall-rock· 

minerals or their a~teration products, notably 

sericite. Where the ore is a filling of open 

spaces the predominant gangue is quartz. 

Siderite is a subordinate gangue in certain deposits, and fluorite is abundant in a few veins. 

In ore deposits formed by replacement as well 

as in those formed by fissure filling gangue 

minerals may be either abundant or negligible, 

and there may be great variation in this regard 

even within a single ore.body. . 

The ores containing enargite are regarded as 

a subtype of the pyritic ores. This n1ineral is · 

practically confined to a few veins within the 

areas covered by the large-scale maps (Pls. III 

and VI), on which these veins are shown by a 

special symbol. They include the FrontenacAduddell-Kokomo, Hazeltine,Anchor, Iroquois, 

Powers, Silver Dollar-Hampton, War Dance, 

Bosen Plume, Argo, Pittsburg, and Two-Forty, 

all lying within a radius of three-quarters of a 

mile of the Hazeltine mine, in South Willis 

Gulch. In a few vei.ns, such as the Silver 

Dollar, enargite is about as abundant as pyrite, 

but in most others it is very subordinate in 

amount. ·Some of the enargite-bearing veins 

are of the composite type described later, but 

in these the enargite appears almost invariably 

to belong with the pyritic phase of the mineralization. In the enargite-bearing veins tenIn the pyr~tic ores' pyrite is always the pre- nantite is rare or absent. 

dominant sulphide. The principal copper min- Fluorite, as shown on page 114, is a characterera! is chalcopyrite, which usually constitutes istic gangue mineral in cer'tain. of the rich tellu105 
.. 

\ 

\ \ \_ . \) ' " '\,_ '.: 

106 GEOLOGY OF GILPIN, CLEAR CREEK, AND BOULDER COUNTIES, COLO. 

ride ores, but it occurs also in certain of the 

pyritic ores, particularly in' those that carry 

enargite. This association is not, however, 

invariable, for in some enargite-bearing veins, 

such as the Two-Forty, fluorite has not been 

reported, and conversely in the fluorite-bearing 

Togo vein enargite has not been noted. In 

fluorite-bearing veins of the composite type the 

fluorite, like the enargite, invariably belongs 

with the· minerals of the pyritic mineralization .. 

Fluorite-bearing veins are shown by a special 

symbol on Plates III and VI. They include the 

Chase, War Dance, Silver Dollar-Hampton, 

Powers, Iroquois, Anchor, Hazeltine, Togo, and 

Hill-Bunk House. · The fluorite is green or 

purple or more rarely colorless and in the pyritic 

veins is always a subordinate vein material. 

At one place in the Chase vein a lens 3 inches 

thick was composed wholly of fluorite. 

Tellurides occur in several localities in close 

associatiQn with ores of the pyritic type, but 

in some such occurrences-for example, in the 

East N otaway mine-the tellurides were clearly 

deposited later than the pyritic ore. Tellurides we~e reported to occur in the Gregory, 

Sleepy. Hollow, Kokomo, Casino, and Gem 

mines, but no opportunities were afforded for. 

determining their precise mode of occurrence. 

Th~ question whether the tellurides crystallized 

contemporaneously with the characteristic min-

, erals of the pyritic ores must therefore remain 

unanswered for the present. As pointed out 

on page 277, it is by no means certain that the 

telluride ore of the War Dance mine is not to 

be regarded as a phase of the pyritic mineralization. 

In one mine, the Rooks County, between 

Apex and Tolland, small crystals of ·snowywhite feldspar, probably soda orthoclase, are 

implanted on octahedral pyrite in a vug. It 

is noteworthy that this is the only occurrence 

of octahedral pyriteseen by the writer in the 

region, the usual crystal forms being cubes or 

pyritohedrons. Molybdenite in aggregates of' 

very small plates is present in a few veins, commonly as a narrow band next the walls. 

MINERAL PARAGENESIS. 

Detailed studies on many ore samples show 

that most\ of the minerals mentioned above as 

characteristic of the pyritic ores were deposited 

during a single period of mineralization. There 

can be recognized .among them, nevertheless, a 

prevailing order of crystallization analogous to 

that among the minerals of a massive igneous 

rock. In the very few veins in which !p.Olybdenite occurs it appears to have been· the first 

mineral to crystallize; a half-in.ch veinlet from 

the AQchor mine shows bands of molybdenite 

one-sixteenth to one-eighth inch thick along the 

walls, but the center is largely quartz and pyrite. In most of the ores py-rite was the first 

metallic mineral to crystallize; it continued to 

form throughout the period of ore deposition 

and very commonly lines vugs. The enargi~e 

is contemporaneous with pyrite. Chalcopyrite 

began to form early in the period of mineralization, but its deposition reached a maximum in 

the later stages, as is shown by its _characteristic abundance in the medial portions of certain veins a~d in and near many vugs. The 

tennantite shows similar relations, except that 

the period of maximum deposition of this mineral seems to have been even later than that of· 

chalcopyrite. The bismuthinite in the Alice· 

mine is apparently contemporaneous wi~h chalcopyrite. In a few places galena and sphalerite 

are found apparently intergrown contemporaneously with the characteristic minerals of the 

pyritic veins, but their quantity is· always extremely small. 

Among· the gangu~ minerals quartz crystallized throughout the period of mineralization, 

and some vugs are lined wholly with quartz, indicating that the deposition of this mineral 

locally persisted after metallic minerals had 

ceased to form. Fluorite formed most abundantly during the later stages of the mineralization. In _places it is intergrown contemporaneously with pyrite or with pyrite and enargite. In the Iroquois mine quartz and fluorite 

form veinlets traversing pyritic ore and line 

vugs in it. In the few places where siderite is 

abundant it seems to have formed late in the 

period of mineralization. In the Alice mine it 

commonly lines vugs. In the one mine in 

which soda-potash . feldspar was noted it was 

distinctly of later formation than the pyrite 

crystals upon which it was implanted, and it 

may have been formed much later and under 

wholly different physical conditions. 

The chemical significance of these mineral 

relations may be summarized in the- statement that copper, arsenic, antimony, bismuth, 

and fluorine were precipitated mainly in the 

later stages of mineralization, while iron, silica, 
·; I 

.: I J 

GOLD-SILVER ORES. 107 

and sulphur were deposited throughout the 

·process. 

STRUCTURE AND TEXTURE. 

rrhe pyritic ores are as a rule irregularly 

n1assive in texture. Banding is almost nowhere developed. In stockworks such as the 

Patch the sulphides fill small irregular spaces 

'between the rock fragments or replace the rock 

.irregularly, as fully described on. page 97 and 

·figured in Plate XIV, A. (p. 97). The structure 

-of the vein deposits depends mainly on the 

.relative importance of fissure filling and re-

·placement in the vein formation. 

The appearance of a pyritic vein that is 

:mainly the result of fissure filling may be typi-

.fied by a small vein exposed in the stream bed 

just below the juncture of Illinois and Leaven-

·worth gulches. This vein is nearly vertical 

and cuts sharply across the foliation of granite 

.gneiss. It consists of a main sharp-walled 

band of nearly solid pyrite from half an inch 

to 1! inches wide which gives off a few small 

branches. Parallel to this main band are a 

:number of minor fractures, some of which 

carry pyrite, and minute pyrite grains are disseminated through the granite gneiss for 2 to 3 

feet on each side of the main pyritic band. 

'The granite gneiss in the fractured zones shows 

much silicification, some inasses of nearly pure 

·quartz 3 inches or so wide and 4 or 5 inches 

long being developed. In these quartz masses, 

·whether large or small, the long axes are usually parallel to the general plane of the vein. 

:Many of the larger ones have a central stringer 

·of pyrite. The vein is pltralleled by a number 

·of barren fractures spaced 1 to 8 inches apart. 

An example of a pyritic replacement vein·is 

the Syndicate, near Dumont. In one place in 

the western workings it is bounded next to the 

hanging wall by a slip plane showing a little 

.gouge. A zone 4 feet wide below this consists 

·of pegmatite traversed by very irregular veinlets of pyrite that }ack d,efinite boundaries and 

grade into .pegmatite only slightly impregnated 

·with pyrite. A few small vugs in the veinlets 

.are lined with crystals of quartz and pyrite. · 

In the Old Town mine both replacement and 

.fissure filling have occurred. On the fourth 

level about 800 feet west of the shaft the vein 

-consists of 4t feet of granite gneiss heavily 

. impregnated with pyrite and traversed by 

:numerous subparallel pyrite-chalcopyrite veinlets none over a quarter of an inch in width 

and by four or five postmineral gouge-filled 

slip planes. . 

Vugs are only moderately abundant in the 

pyritic veins and are usually small. One of 

extraordinary size noted in the National mine. 

was 6 by 4 inches by 2 feet. It was surrounded 

by gneiss impregnated with pyrite and was 

lined with quartz crystals, some of them half 

an inch in diameter . 

ALTERATIONS OF WALL ROCK. 

The principal minerals developed by metasomatic processes in replacement veins or in the 

walls of filled fissur·es are sericite and pyrite. 

Carbonates have been formed in a few places. 

In the early stage of alteration the changes , 

produced are markedly selective in character, 

certain of the original mirierals of the wall rock 

altering earlier than others and in a different 

manner. The alterations in this stage clearly 

involve chemical interchanges between the 

original minerals and the entering solutions and 

are. not the result of simple substitution. 

Characteristic features are the replacement of 

plagioclase phenocrysts by sericite before sericite is developed in the groundmass or in orthoclase phenoc:r;ysts, the replacement of the outer 

rims in zonal phenocrysts of plagioclase before 

the inner parts are affected, and' the replacement of original magnetite by pyrite before 

this sulphide is extensively developed by replacement of other minerals. The last-named 

process was well shown in monzonite porphyry 

bordering the Lake. vein as exposed in the Big 

Five tunnel. The pyrite is associated with a 

whitish, opaque alteration product, of indeterminate character, and the areas occupied by 

the two minerals have outlines characteristic of 

magnetite, as is shown in figure 8. The lined 

areas are pyrite and the white areas around · 

them are "leucoxene," whose composition•was 

indeterminate. The outlines of the whole 

suggest those of magnetite, probably titaniferous, which t_he pyrite and leucoxene are 

believed to replace. Minor amounts of carbonates, usually in small irregular aggregates, 

were developed in this stage in some deposits 

but not in others. The rocks have become 

somewhat bleached, but their major textural 

featur~s, such as foliation or porphyritic texture, are still preserved . 

The incipient stages of alteration were well 

shown In monzonite porphyry 80 feet south · 
108 GEOLOGY OF GILPIN, CLEAR CREEK, AND BOULDER COUNTIES, COLO. 

of the Bride vein in the Idaho tunnel. This 

monzonite is ·bleached, but the· porphyritic 

texture is still well preserved. It is traversed 

by small fractures, along which pyrite· is 

developed in small irregular masses. The 

feldspar phenocrysts are nearly all plagioclase, 

well above balsam in index, whose precise 

variety can ·not be determined. These are 

flecked with abundant shreds of sericite except 

in the center of a few crystals, which remain 

clear. In the microgranular groundmass, on 

the other hand, no sericite is present, but 

calcite and quartz (probably in part secondary) 

are abundant. In contrast to both of these, 

certain roughly oblong areas, probably representing original hornblende or pyroxene, now 

co~sist mainly of gr~en chlorite, epidote, and 

'h MM. 

FIGURE 8.-Camera Iucida sketches of pyrite grains in altered monzonite porphyry bordering the Lake vein in the Big Five tunnel. 

a fine aggregate, which appears gray in reflected light and is probably also epidote but 

very finely divided. Iron oxides, in part hematite and in part magnetite, occur in minute 

grains and aggregates in the chlorite-epidote 

areas and in the groundmass. Pyrite occurs in 

scattered grains and irregular aggregates in the 

groundinass, but both pyrite and iron oxides are 

practically absent from the phenocrysts. 

More extensive alteration in or near pyritic 

ore bodies commonly results in. the complete 

sericitizatio:r;t of all feldspar of whatever variety, 

in the sericitization of any chlorite or epidote 

that may have formed as a temporary alteration 

p·roduct in earlier stages, and in the development of pyrite as a replacement not only of 

magnetite but of quartz and· silicates. The 

.t'.;.{. 

original quartz is in some rocks apparently un-:.-:. 

affec~ed but in others has undergone recrystal- . 

lization: Carbonates may have increased in 

abundance or may still be absent. . The sericite 

·flakes have commonly increased in size. The 

original texture of the rock may be wholly 

effaced. 

Specimens showing various stages of wallrock alteration in an unusually complete manner were obtained in the Alice mine. One of 

these is figured in Plate XIV, A (p. 97), and 

shows in a width of 4 inches almost all stages 

in the conversion of quartz monzonite porphyry 

into· typical ore. The probable situation of 

this specimen with respect to the general fracture system of the mine is shown at c in. 

figure 7 ·(p! 98). In the least-altered (right- 'lJ.:'·" 

hand) portion of this specimen (at a, Pl .... 

XIV, A) the porphyritic texture is very con-. ,.,_. 

spicuous. Under the microscope the ground- .. 

mass is seen to have been wholly recrystallized .• 

to an aggregate of quartz and orthoclase feldspar, showing the. sharpness of a mosaic and 

considerable uniformity of grain; both 1ninerals 

are clear and fresh. In the hand specimen the 

recrystallized groundmass has the appearance 

of a gray opaline matrix in which the feldspar 

and biotite phenocrysts are embedded. The 

phenocrysts of plagioclase have been wholly 

replaced by an aggregate of minute plates that 

are probably sericite, though on account of 

their minuteness the aggregate shows low 

double refraction. With this are associated 

small grains and aggregates of an iron-stained 

carbonate, presumably siderite. The biotite 

phenocrysts remain practically unaltered. ·The 

original magnetite is for the most part unaltered, though in a few places partly or wholly 

replaced by pyrite, which also occurs in a few 

small grains in the groundmass. Quartz phenocrysts appear to have been recrystallized and 

some of them merge around their borders with 

the quartz of the recrystallized groundmass. 

In a more highly altered part of the rock (b, 

Pl. XIV, A, p. 97) the porphyritic texture is not 

prominent in the hand specimen, though under 

the microscope it is fairly conspicuous. The 

same types of alteration observed in the specimen just described have progressed much. 

further. The sericite, which replaces the, 

plagioclase, has aggregated into larger flakes;· 

siderite has in places ·grown into good-sized 

crystals that show rhombohedral cleavage;. 
GOLD-SILVER ORES. 109 

the biotite phenocrysts h~ve altered to muscovite and ·siderite; magnetite has enti;rely disappeared; and pyrite has increased greatly in 

abundance. The matrix still retains its fresh 

n1osaic-like appearance, and its orthoclase 

shows no alteration. 

In ·the most highly altered facies · (c, Pl. 

XIV, A) the porphyritic texture is entirely 

obliterated and the whole rock has been converted into an irregular and rather fine grained 

aggregate of quartz and sericite associated with 

irregular areas of relatively coarse quartz. In 

this rock the feldspar of the groundmass has 

finally s11:ccumbed to sericitization. Pyrite 

occurs in greater ·abundance and in larger 

crystals than in the less altered varieties. Of 

the original minerals only apatite remains 

unaltered .. 

METAL CONTENT. 

Some conception of the· metal content of 

the smelting ores of the pyritic type may be 

gained from the following table~ The figures 

were obtained by averaging a considerable number of sampling-works assays of smelting ore· 

from each mine, and they appear to represent 

for the most part · primary ore unaffected by 

enrichment. 

Metal content of typical gold-silver ores of the pyritic type. 

Quan- Gold (ounces). Silver (ounces). 

Mine. Y"lar. tity Copper 

(short Maxi- Mini- Aver- Maxi- Mini- Aver- (per cent). 

tons). mum. mum. age. mum. mum. age. 

---

Perigo .................. 1901-1909 42.5 3.16 0.44 1.23 4.70 1. 20 1. 26 

Corkdon ............... 1892-1897 51 2.62 1.08 1. 74' 15.00 2.00 5.63 Up to 8. 

0 .................... 1893-1908 185 4.28 . 30 l. 13 10.20 3.40 5.59 2 to 10.25. 

O'Neil. ................ 1897-1908 48 12.00 . 60 3. 10 11.45 3.14 7. 13 1.80 to 8.18. · 

''li'i.fty" ············ .... 1888-1909 410 26.40 . 52 2.58 21.00 1.50 5.40 Up to 13.75. 

Carr .................... 1893-i910 400 9.06 . 72 2.88' 21.20 2.00 7.62 Up to 11.70. 

San Juan.a ............. 1888-1909 117 12. 20 Trace. 2.09 34.00 2. 15 6.81 Upto9. 

Barnes ................ 1893-1907 108 2.68 0.27 1. 19 17.40 4.00 11.81 3 to 9.55. 

Rockford .............. 1910 (b) ········ ......... 1.09 . .......... .......... 4.35 

Gladstone ........ ; ...... 1893-1910 29 8. 10 . 56 1. 49 14.00 2.40 5.35 Up to 10. 

Aurora ................ 1889-1910 114 4.88 . 87 2.24 17. 15 1.30 6.32 Up to .13.65. 

Argo .................. 1889-1908 30' 5.00 . 50 2.39 12. 13 2.50 7.31 2.10 to 16. 

Pit!Bburgh ............ ·I 1894-1909 243 12. 72 . 45 2.37 18.30 1. 50 7.52 Up to 16.60. 

1910 435 25.35 . 52 5. 77 22.65 2.00 8.93 0.30 to 16.30, 

average, 6.65. 

Two-Forty .............. 1910 (b) ......... ......... . 95 ········ ········ 5.82 Average, 0.69. 

Saratoga ............... 1893-1909 1,019 8.41 .12. . 90 13.90 1.00 2.32 Nearly always · less than 1.5. 

Chase ................. 1893-1908 193 . 8. 20 . 29 .1. 98 28.40 1. 90 6.53 Usually 1 eBB 

than 1.5. 

Specie Payment a ..•... ............ 506 7.09 . 32 1. 88 37.00 . 70 5.80 Up to 7. 

Puritan ................. 1910 6 2.60 1.12 1. 56 6.00 1. 50 2.27 Up to 2. 

Princess Alice .......... 1910 (?) ········ ········ 1. 14 ........ ·-······ 4.00 

Megalona vein in Rockford tunnel. ......... 1910 2,000 ········ ......... . 427 ........ . ........ . 769 LeAs than 0.40. 

Donaldson vein in { 1910 (b) ········ . ······· . 618 -······· .......... 1. 567 0.335. 

Rockford tunnel ..... 1911 1,000 ········ .. 

a Ores mainly pyritic. 

From this table it is seen that tll.e average 

gold content of the smelting ores is usually 

between 1 and 3 O":ffiCes and the average silver 

content between 4 and 8 ounces. The copper 

content in most of the ores is below the commercial limit of 1.5 per cent and so is not recorded in the sampling-works assays. In some 

ores, on the other hand, it may form 15 to 16'per 

cent. The silica content is extremely variable, 

but in most lots is between 30 and 70 per cent. 

.. .... 1. 1096 . ......... ......... 3.20 1.189. 

b Total shipments. 

The gold content is in general highest in veins 

which, like the Pittsburgh, are comparatively 

rich in chalcopyrite. 

It' seems unwise here to attempt any generalizations in regard to the metal content of the 

concentrating ore. The grade of the ore that 

can be profitably worked, being intimately dependent upon the cheapness of the mining 

methods and on the milling practice, varies 

greatly in different mines. Such details as 
110 GEOLOGY OF GILPIN, CLEAR CREEK, AND 'BOULDER COUNTIES, COLO. 

were obtained are given in the descriptions of 

individual mines. 

The average value of the ores and concentrates from the vicinity of Central City has been 

computed by Mr. Percy Alsdorf, who has 

kindly consented to the publi~ation of his figures here. The computations cover the shipments for one recent year, but ta~e no account 

<;>f varying mineral character of the ores. 

Average content of ores and concentrates from Cen(ral .City 

and vicinity. 

........... 

~ 

~ _...:... Q) ........... ........... rn u ...., rn Q) 

'"' ~ ........... Q) u Q) ...., u ~ Q) c. ~ 

~ ;:::l -B Q) 

'"' u ;:::l 2.- Q) 

2.- '"' '"' -B '"' Q) Q) 

"i:l Q) 0... 0 -B 

0 ~ 0... Q)· w 0 c.,:, Q rn ~ 

--------

Smelting ore .......... 1. 67 4.10 3:10 47 28 

Concentrating ore ...... . 38 1. 40 . 60 69 10 

Concentrates ........... . 80 3.00 .2..: 00 11 44 

GALENA-SPHALERITE ORES. 

DEFINITION .. 

In the galena-sphalerite ores the predominant ·primary sulphides are galena, sphalerite, 

and pyrite; chalcopyrite· and in places other 

sulphides are· present in lesser amounts. The 

common gangue minerals in the ores that are 

fissure fillings are quartz and either calcite or 

siderite. Ores of this type· like those of the 

pyritic type, occur principally in. veins ·but 

locally in stockworks. rheir deposition was 

accomplished both by . fissure fillilig and by 

replacement. · · • 

PRIMARY MINERALS. 

The principal metallic minerals of these ores 

are galena and sphalerite; pyrite is next in 

abundance and then chalcopyrite. Tennanti te and bornite are present in some of the veins 

in small amounts. A little enargite is associated with the galena and sphalerite at one 

point in the Gem vein in the Argo lateral and 

also in the Clay County mine, but enargite is 

not charact·eristic of this ore type." Native bi$.-

results. In a few veins of this type, such 

as the Franklin and Seaton, rhodochrosite is 

found. In the Franklin vein it is in places 

the most abundant gangue mineral and is so 

intercrystallized with galena, sphalerite; and 

other sulphides as to show unquestionably that 

it crystallized contemporaneously with them. 

In three veins belonging to the composite type, 

the Moose, Bellman (in Gilson Gulch), and 

Gem, rhodochrosite is locally very abundant. 

In the Bellma:p. vein it is intergrown contemporaneously with barite,· galena, and sphalerite • 

In places in the Gem mine veins of coarse pyrite 

as much as l foot in width are ·cut by a network 

of rhodochrosite veinlets. These veinlets in 

places carry specks of galena.and chalcopyrite 

so that they probably were formed at the time 1 

of the galena-sphalerite mineralization. All the 

rhodochrosite-bearing veins are in the region 

near the head of Gilson Gulch. Barite is 

locally abundant in a number of veins. · 

Gold and silver, probably alloyed, are finely 

distributed within the sulphides and in a few 

veins visible gold is abundant. The most striking examples of its occurrence are in the Klon:... 

dike vein, in the Topeka mine, where it. is 

intergrown with quartz and the primary sulphides so intimately as to leave no doubt that 

it is a primary constituent contemporaneous 

with them. 

MINERAL PARAGENESIS. 

A distinct sequence in the order of crystallization of. the minerals of the galena-sphaleri~e 

ores is much less evident than in the pyritic ores. 

Galena, sphalerite, pyrite, .chalcopyrite, bornite, 

enargite, quart~; siderite, barite, free gold, and 

rhodochrosite seem in mqst of the ores to have 

crystallized co~temporaneously. Siderite and 

calcite,: while in some places early crystalli~ations, .are elsewhere the latest ... and 0ccur·-alone 

Qr with quartz as a ]jning of vugs. Tennantite 

is much less common than in the pyritic .veins; 

where it occurs it was usD:ally one· of the last 

minerals to form. · 

STRUCTURE AND TEXTURE. 

m\}th and molybdenite .occur rarely. Primary· The galena-sphalerite ores are in general 

argentite is possibly present in a few veins. similar· structurally and texturally to those of 

Quartz is the ·principal gangue mineral, but the pyritic type. One of the very few occur:-

either siderite or calcite is abundant in some' rences of banded structure is illustrated in 

veins of this type; these carbonates in several Plate XIV, 0 (p. 97). Somewhat more proveins were tested for manganese with negative nounced banding noted in a specimen from the 
GOLD-SILVER OR-ES. 111 

dun1p of the An1erican Sisters mine near Lawson is due to the alteration of narrow bands of 

siderite and sphalerite near both walls of a 

4-inch vein. The irregular distribution of 

sulphides characteristic of the stockwork deposits has been described. on page 97 and is 

illustrated in Plate XIII, A (p. 96). A vein network from the Boulder County mine is shown 

in Plate XIII, B (p. 97). . 

ALTERATIONS OF WALL ROCK; 

Near ores of the g~lena-sphalerite type, as 

near the pyritic ores, the most conspicuous 

alteration of the wall rock is the development 

of sericite and pyrite. The alterations differ 

fr01n those near pyritic ores mainly in the more 

common and more abundant development of 

calcite, and the local development of galena 

and sphalerite. As pointed out on page 103, 

the ratio of pyrite to sphalerite and galena is 

greater in the altered wall rocks than in the ore 

that fllls fissures. Certain ores of the galenasphalerite period of mineralization that formed 

mainly by replacetuent contain pyrite as their 

predominant sulphide. 

As in the wall rock of the pyritic ores, the 

early stages of replacement are selective. This 

is well illustrated by a specimen of the granite 

gneiss that bordered the Hayseed vein. In 

this rock original microcline and quartz are 

wholly unaltered, but grains that ·appear 

originally to have been plagioclase have been 

entirely converted into an aggregate of sericite 

and calcite. 

In a specimen from the walls of the Topeka 

vein the alteration of granite gneiss has proceeded further; the quartz is unaltered, but 

all the feldspar has been replaced by an aggregate of sericite, pyrite, and sphalerite. In this 

specimen very little calcite is present. Very 

situilar alterations were noted in the granite 

gneiss walls of the Princess of India vein near 

Lawson. In porphyry tllat bordered the Lombard vein the feldspar phenocrysts have been 

wholly sericitized, whereas in the groundmass 

both sericite and calcite have been abundantly 

developeQ.. 

Metas01natisn1 of an unusual type was noted 

in the walls of the Gold Collar vein, where 

chlorite (pennine) is abundantly developed in 

the granite gneiss walls~ in addition to sericite 

and a light-colored carbonate; the 'chlorite 

gives the rock a greenish tint. 

In the Up to Date mine, near Caribou, 

pyroxenite is·. in places the wall rock of the 

Dardanell No. 2 vein. The original minerals 

of the pyroxenite were biotite, pyroxene, 

apatite, and titaniferous magnetite. The biotite has been altered to muscovite and some 

calcite, through which small grains of iron 

oxide are scattered. Pyroxene has bpen replaced by a ·mixture· of calcite and sericite or 

by sericite alone. Titaniferous magnetite has 

wholly disappeared, its place being apparently 

taken by a mi-x:ture of siderite and hematite. 

Secondary quartz has formed in aggregates 

of small grains. Irregular masses of galena 

and some sphalerite appear to have replaced 

each of the original minerals except apatite, 

which remains wholly unaltered. 

The nature of the wall-rock alteration near 

the Boulder County vein, near Cardinal, is 

well shown on the tunnel level about 200 feet 

east of the line of the tunnel. Three specin1ens 

showing different stages of alteration were collected from a 6-inch to 1-foot dike of hornblende diorite, which is cut sharply and without 

displacement by the vein. The vein· at this 

place is 6 to 15 i1~ches wide and carries from 

40 to 90 per cent of quartz. The first specimen, which was aln1ost unaltered, was taken 

several feet fron1 the vein~ it is a dark-gray 

aphanitic hornblende diorite 'crowded with 

idiomorphic lath-shaped crystals of fresh green 

hornblende varying greatly in size and oriented 

in all directions. Small stubby phenocrysts of 

plagioclase, slightly .sericitized, are scattered 

sparingly through the rock. The remainder 

of the rock consists of s1nall grains of n1agnetite and feldspar, the latter showing some alteration to sericite and calcite. The second 

specimen ,of the dike was taken 2 feet fr01n the 

vein. It is bleached to a buff color and carries 

numerous small grains of pyrite disseminated 

through it. Under the microscope the outlines 

of some of the feldspar phenocrysts are ~till 

recognizable, but the hornblende has entirely 

disappeared, the rock being converted into an 

associf;l,tion·of pyrite, sericite, calcite, and quartz. 

The third specimen was taken from the exact 

c~:m tact of vein and dike. Here the dike has 

been ··completely altered to an aggregate of 

pyrite, quartz, calcite, and sericite, and the 

original porphyritic texture has been wholly 

obliterated. The quartz is clearer and more 

abundant than in the second specimen. 
112 GEOLOGY OF GILPIN, CLEAR. CR.EEK, AND BOULDER. COUNTIES, COLO. 

The extreme of ·wail-rock alteration is exemplified by the occurrence, next to· a vein in the 

Metropolitan tunnel, of 1 to 2 inches of white 

plastic material which resembles kaolin but 

which on testing proves· to be wholly sericite. 

METAl .. CONTENT. 

richness is probably represented by an 88-

pound piece of ore from the Klondike vein, in 

the Topeka mine. This piece·carried abUndant 

free gold and on smelting yielded $5,449. 

Averages that are representative of the primary ore of smelting grade can be given only 

for those veins in which the gold content .is 

In the ores· of the galena-sphalerite type the · relatively high, for only such ores are workvariations in metal content are even greater able below the limit of downward enrichment 

than in the pyritic ores. Their maximum in silver. · 

Metal content of certain gold-silver ores of the galena-sphalerite type. 

Gold (ounces). Silver (ounces). 

QuanMine. Years. tity s s s s Copper Lead Zinc 

(short ::s ::s o.i ::s ::s o.i (per cent). (per cent). (per cent). s ~ s bl) tons). s s ~ 

·~ ';:1 ·~ ";:1 J.; 

Q) Q) 

~ ·~ > ~ 

~ 

~ ;s -< ;s ::g ~ ----

Pine Grove ....... { 1906 (a) ....... ....... 0. 24 ......... ...... 35.00 . .............. .............. . . . . . . . . . . . . 1907-8 (a) ..... ...... . 28 ........ ..... 24.00 .. ............. .............. . . . . . . . . . . . . Hayseed ........ (b) ...... ..... ..... . 75 ........ ....... 12.00 . ............. 45 to 55 . ........... Concrete c ••••••.. (?) 307 1. 03. ....... 8.00 .............. 23.80 10.60 

Hubert ......... {1888-1909 131 5.80 0.74 2.39 17.60 2.00 13. 16 Up to 6. 50 Up to 37 Up to 32 

1910 72 1. 70 1. 04 1. 38 15.90 8.00 14.00 .............. Up to 30 . ................. Ivanhoe c •••••.•. 1898-1902 11 . 90 .10 . 59 21.40 7.62 13.95 ................... 10. 90 to 54. 10 8 to" 18 

Egyptian ........ e899-1909 63 5. 77 . 28 2.98 22.30 2. 70 12.33 Up to 9. 50 . .................. .............. 1910 154 5.48 . 64 2.40 23.50 2.00 17.35 Up to 4. 65 .................. .............. Windsor Castle ... . 1897-1909 30 . 68 . 08 ......... 23.00 8.40 ............. Up to 2. 80 4 to 16 5 to 16 

Owatonna ........ 1897-1910 117 . 50 .12 . 23 d58. 80 5.70 27.57 .................. Up to 36 u-8 to 25 

Santa Fe ......... 1888-1904 91 4.00 . 25 ........ 38.00 2. 70 ....... Up to 2. 30 Up to 20 p to 5 

Franklin and ~ilver Age ....... 1888-1910 1,374 1. 52 . 05 .146 d 161.00 4.00 22.74 ................... ··············· ····up:t~-24 Seaton .... : . .... 1902-1910 202 .2.35 .12 1. 13 d.I05. 00 7.50 39.66 Up to 2. 55 Up to 26.40 

Crystal. .. ~···· ... 1888-1910 35 3.00 .15 . 76 d 95.00 5.50 37.40 Up to 3. 00. 3 to 17 6 to 16 

Albro ........... { 1908. 202 2. 77 . 48 . 54 13.00 2.50 5.65 2. 40 to 17. 00 . .................... ................ 1909 160 1. 02 . 39 . 65 21.00 7.60 10.09 e 3 to 10. 20 .................. ................. 

a Total shipments. b Reported average. c Ores mainly of galena-sphalerite type. 

In contrast to some of the ores tabulated 

above, the galena-sphalerite ·ores of Lawson 

and vicinity and of Silver Hill, near Blackhawk, are characteristically poor in gold, 

which in many shipments is present only in 

traces. Ten lots of ore shipped from the 

Beflevue-Hudson mine, '·near Empire station, 

in l908 showed the following range in metal 

content: Gold, 0.03 to 0.20 ounce to the ton; 

silver, 12.60 to 54.20 ounces to the ton; lead, 

4 to 31.60 per cent; zinc, 3 to 14 per cent. 

This ore has apparently been only slightly 

affected by downward enfichment in silver. 

Although a high gold content is found in some 

of the oxidized surface portions of. the silver 

lodes near Lawson and Empire station, the 

gold content of most of the unoxidized ore 

does not exceed 0.25 ounce to the ton. 

d High silver values probably due to downward enrichment. e Average, 4.45. 

In general the primary ores of the galenasphalerite type are poorer in gold and copper 

and richer in silver than those of the pyritic 

type. It is not practicable to give a summa:ry 

statement of the metal content of the concentrating ores of this type, because of the 

variety of milling practice and because at 

,many plants both lead and zinc concentrates 

are obtained, so that it is difficult to calculate 

the composition of the ore. Some data concerning these ores are g1ven in the detailed 

mine descriptions. 

COMPOSITE ORES. 

Many of the gold-silver ores of the region are 

the result of double mineralization, first with 

minerals characteristic of the pyritic ore type 

and later with minerals characteristic of the 
GOLD-SILVER ORES. .113 

gal~na-sphalerite ore type. Veinlets ~f the 

galena-sphalerite type· sharply cutting ore of 

the pyritic type were noted in the Salisbury 

mine, west of Ida:ho Springs; in the Rocky 

Mountain Terror mine and the Fairmont tunnel, near the head of Virginia Canyon; in the 

Frontenac lateral from the Argo tunnel; in the 

Druid mine, in South. Willis ·Gulch; in the 

Fourth of July mine, near Central City; in the 

Geiger mine, south of Apex; in the Marshall & 

Russell tunnel, near Empl.re station; .and in a 

number of others. 

In the Marshall & Ru.Ssell tunnel a 2-inch 

vein of quartz, pyrite, and chalcopyrite 1,800 

FIGURE 9.-Camern Iucida drawing of polished surface of ore from Specie 

Payment vein, showing pyrite of the early mineralization brecciated 

and traversed by veinlets of ore of a later period of mineralization, 

consisting of chalcopyrite, quartz, and sphalerite t S). 

feet from the portal is cut without displacement by a \Vein a few inches in width carrying 

sphalerite, chalcopyrite, and siderite with a 

little pyrite and galena. On the west wall of 

the Argo tunnel about 8,925 feet from the 

portal a 20-inch vein of solid pyrite is crossed 

by a l-inch stringer of galena and sphalerite. 

In the Fourth of July mine ore composed of 

nearly s~lid pyrite with some chalcopyrite has 

been brecciated and the fragments have been 

cemented by quartz, galena,· sphalerite, and 

chalcopyrite, as is shown in Plate XIII, 0 

(p. 96). At places in. the Centennial and Two 

Kings vein pyritic ore is sharply separated by 

a band of comb quartz from ore of the galena-

~2140-17--8 

sphalerite type, showing that the two are not 

contemporaneous. The mode of occurrence .of 

the ores in many other mines suggests though 

it does not demonstrate a similar relation, and 

nowhere was the reverse relation, of pyritic ore 

cutting galena-sphalerite ore, observed. · 

The field evidences of dual mineralization are 

amply confirmed by the microscopic studies of 

polished specimens. Ore from the Little Annie 

workings ·on . the Specie Payment . vein (see 

p. 286) shows that an association of pyrite and 

light-gray quartz has been brecciated and the 

spaces hetween the fragments completely filled 

with sphalerite, dark-gray quartz, and sub~ 

FIGURE 10.-Camera Iucida drawing of ore from Specie Payment vein, 

sho)Ving pyrite of first mineralization brecciated and penetrated by 

sphalerite, quartz, and chalcopyrite of a later period of mineralization. 

S, sphalerite; C, chalcopyrite. 

ordinate galena and chalcopyrite. Minute 0 

veinlets of these minerals occupy cracks in the 

pyrite or wholly inclose pyrite fragments. In 

the latter case the form of adjacent fragments 

shows clearly that they once fitted together 

(See figs. 9 and 10.) Microscopic study of ore. 

from the Maud S. vein near Empirestationshows. 

that pyrite has been brecciated in a somewhat 

similar manner and the inters paces have been. 

filled with chalcopyrite_ associated with a little 

sphalerite and quartz. 0 

• 

The relations described ab9ve appear to 

demonstrate conclusively that certain ores 

are the result of dual mineralization. The 

earlier group of minerals. in these ores is 
114. GEOLOGY OF GILPIN, CLEAR CR.EEK, AND BOULDER. COUNTIES, COLO, 

identical as regards kind and prQportion of an integral part of the typical sulphide ore or 

minerals· with 'the typical pyritic ores,· ·while occurred iri. later veihlets cutting the. sulphide 

the later group is identical with· the' typic·al ore; ·as in the East Notaway mine. The Casino 

galena-sphalerite ores. · As pointed nut on vein; .. ori Seaton Mountain; has yielded rich 

page 102, there are numerous· transitions from telluride ores, but· as only roasted samples were 

the composite ores· ·to one or the other of the seen by the -writer the relations of tellurides 

pure types. There ·can be· no question,· there- to sulphides there could not· be demonstrated. 

fore, that the composite ores are the ·result of In those mines in which the occurrence of tellu..: 

successive deposition from two s·ohitions, each rides could 'be carefully ·studied they_ were no_t 

of ·which· elsewhere deposited ore of· simple a; component of typical sulphide ores· but 

types, either ·pyritic ore· or gn1ena-sphalerite occurred· under peculiar conditions, to·: 'be 

ore. The i.itterval between the ·two mineraliza- described in the succeeding p'aragraphs. The 

tions, for reasons· ·set 'forth more fUlly on page most important producers of telllii_'ide ·ores a,t 

133,· is believed to have been short, but it was the·present time are the War Darice arid East 

sufficient to permit much local brecciation . No'taway mines, near Cen'tral City, and the 

of the earlier ore before the later ore was 'Treasure Vault mine, near Idaho Springs. 

deposited. The later galena-sphalerite portions Small amounts of telluride ores are produced 

of the ore obviously can not be attributed to near Eldora, in Boulder County, and such ores 

downward sulphide enrichment acting on ·have been found in the Casino, Gem, Kokomo, 

primary pyritic ore, for the requisite lead and Sleepy Hollow, and Gregory mines. The telluzinc are n.ot present in the pyritic ore. More- ride-be~ring veins between Idaho Springs and 

over, downward sulphide enrichment in which Central City· are shown by a special symbol 

an entirely ·different. suite of minerals· was on Plates III and VI. 

: developed was noted locally in fractures in the . composite ore. · ·PRIMARY. MINERALS AND THEIR PARAGENESIS.'. 

The metal content of the 'ores of the com- The rich telluride ores of the War Dance 

posite type is in general intermediate between and Treasure Vault mines show fluorite as an 

those of the two simple types, the pyritic and : abuJ?,dant gangue mineral. In this respect, 

th~~galena-sphalerite ores. Naturally it varies though not in most others, they resemble the 

greatly with the proportion of the two types 'telluride ores of Cripple Creek. In the Treasure 

present, and a:rJ:attempt to arrive at an average 'vault mine the telluride, which is light·yellow, 

would be :rrio.~~ :or less· ~iu.tile. and misleading.. ··carries considerable silver as well as gold and 

TELLUR~DE ·O~ES. is probably sylvanite. Samples suitable for 

detailed mineralogic study were not available. The telluride occurs in a gangue of GENERAL. FEATURES. 

'The.telluride-:bearing ores of the Central City blue-gray cherty silica, with which. are also 

quadrangle show more diversity in mineral associated small amounts of fluorite, ferrucharacter than the ores already described, and gihous calcite, and fine pyrite. The pyrite 

it. is n<;>t cert~in that all were fo.rmed at the is less abundant in the veins _than in the wall 

same time. Telluride~ _of gold and .silver. ~ay -rocks. Banding of cherty silica and ferru-

~ccur 4eFe aJ?.d t~ere in o.r~s of t~~_.py;r:itic or ginous calcite was note4. loc3;lly, and .fluorite 

galena-:spp_aJerite type, "~:?ut this .b.:as not 'been and calcite line some vugs and were there the 

f~lly -~~monstrat~~:, Pearce/ ·~oted the pres- last minerals to form; in general, P,owever, no. 

ence of te~ul,'i~JJ?.. i:r:. qertain ore$ .from the very consistent sequence was obs.~rvable in. the 

GI_'e.gory mine, .·n~ar_Bl~ckhawk, .. but th~ nature order of crystallization of the pre .~nerals. 

of the tellurium 'minera.f from which it came All the telluride ore thus far found has been 

i~,u~known .. O~e-fr~~ a_ pocket ~n ~he twelfth obtai~ed withi~ 125 ·feet of the surface and 

level of the Gem mine carried sylvanite. A carries free gold in even greater apundance than 

sample of this ore ·s~en by t~~ writer ~howed tellurides. This gold is partly and perhaps 

gr~;ty quartz as the o~ly other rp.iner,al, so it is wholly the re~ult of the oXidation of sylvanite. 

still uncertain whether th~ sylvanite formed .. For. ·many years development in the War · . · ·. ' . · · ' · · · · · ' . Dance · m. ·. irie .was cq:o.fined · to a sulphide v~in ·'· Pearce, Richard, The 'association of gold wit.h other metals in the 

W~t: :\"t· ~nst. M!n. Eng. Trans., vol. 18, p. 449, 1890. of the composite tyPe; only in 1908 WaS the 
GOLD-SIL VEE: ORES. 115 

rich telluride ore a few feet. away discovered. 

Although the sulphide and telturide. ores 

occur near together, they are not intermingled 

and show marked differences in precious-metal 

content. An assay of the sulphide ore in 

one place showed 0.2 ounce of gold and 30 

ounces of silver to t.he ton, while the telluride 

ore close by ran 20. ounces in gold and 3.5 

ounces in silver. The telluride ore occurs as a 

network of small veinlets or .an irregular replacement of the wall rock near fractures. 

The ore minerals are fluorite, quartz, ,pyrite, 

and a telluride of . gold and silver that is 

probably sylvanite. The telluride occurs as 

. flakes ·or plates of pale brass-yellow color, 

mariy of. which show nun1erous striations in 

one direction; in places the telluride flakes are 

very abundant. Native ·gold occurs but is 

less abundant cmnpared with sylvanite than 

in the Treasure Vault mine. 

The. telluride veins of the East · N otaway 

mine are characteristically 1 to 3 inches wide 

and consist of dark-gray cherty silica, finegrained pyrite, some antimonjacal tennantite, 

and varying amounts of telluride. In places 

there are several $mall anaston1osing. veinlets 

insteu.d of a single veinlet. A study of polished 

surfaces. of the rich telluride ore, supplemented 

by an examination of a thin section by trans-

.mitted light, shows that all the vein minerals 

are essentially contemporaneous·, though sulphides appear relatively 1nore abundant near 

the borders of the veinlets and sylvanite n1ore 

In speaking of the telluride ores of Eldora 

and vicinity, Lindgren~· says:: .·. 

The ores contain chiefly gold, with very little.silver, and 

the pnncipal valuable mineral is a telluride ·of gold believed to be sylvanite. The tellurides u.sually occur in a 

flinty vein matter or in the greenish roscoelite distributed 

as small specks; l~ardly ever as well-crystalli'zed mineralsPyrite is present in small amounts, chiefly 3:5 small grain~ 

in the altered country rock.' Molybdenite occurs in abmidance but is usually extremely fine .grained and intergrown with barite. On the dump it/:1 presen,ce is indicated 

by deep-blue stains on the <;>re _fragme:J?.tS. This blue 

molybdenite stain, to which attention has been drawn in 

the Cripple Creek report, 3 is believed to be the rare mineral 

ilseniannite; a compound of the oxides of molybdenum 

(Mo02.4Mo03). 

Characteristic among the gangue minera.Is of the tellu:.. 

ride veins are barite, quartz, roscoelite, ancl chalcedony. 

The quartz occurs in moderate amounts, and more frequently chalcedony takes its place, form.ing jasperoid 

masses of brown or black color, locally called hornstone. 

Barite is also very abundant and often appears crystallized 

in small and thin plates. ~ 

Mr. Rickard, in the article men~ioned, has ~ailed attention to the general occurrence' of roscoelite in the Bot~lder 

County mines-an interesting fact not elsewhere recorded. 

Roscoelite is very abundant in the ores of the Mogul tunnel 

and the Enterprise mine. It fo.rms dark yellow~green 

masses inter~o\vn with quartz or irregularly distributed 

in the ore and,· as stated above; very frequently contains 

specks of gold tellurides. Sections qf this greenish n~aterial show the roscoelite as minute greenish-yellow scales 

of micaceous character, intergrown with pyrite in small 

crystals. This mixture of roscoelite and pyrite is surrounded and invaded by a later-deposited mass of fine. 

granular quartz, with some adularia in the rhombic crystals \vhich are so characteristic in the variety of this mineral 

called 'valencianite. · 

abundant near the center. Most of the GEOGRAPHIC DISTRffiUTION OF ORES. . 

sylvanite occurs in isolated bladelike or tabular The most widely distributed ores of the re-· 

crystals, but some is intergrown and appar- gion are those of the pyritic type, to which. 

Qntly contemporaneous with antimoniacal belong most of the ores between Central City 

tennantite. and Blackhawk on the north and Pewabic 

Most of the mines near Eldora that have Mountain on the ·south, moat of those along 

produced telluride ores were idle at the time Fall River below the mouth of York Gulch,. 

of the writer's visit, and admittance was de- most of those near Alice, Yankee, and Apex,. 

·nied to the only one in operation. Little those near Perigo, Moon Gulch, _and Phoenixnew information was obta~nable, therefore, in ville, some near Eldora, and. some on Idaho 

regard to the character of . these ores; for- Mountain near Caribou. These ores are c.omtunately, they had previously been studied by mouly referred to in the region as gold. ores,._ 

Lindgren and others. In the Enterprise vein, their value being mainly in that metal. . 

according to Rickard/ "The dark-gray quartz . Of the subtypes under the pyritic ores, the 

carries finely disseminated tellurides, chiefly enargite an9, fluorite bearing veins are all Jopetzite, which rend~r a width of 2 to 2! feet cated within three-quarters of a mile of the 

sufficiently rich to yield an average <;>f 2 ounces Haz~ltine mine, in South Willis Gulch. 

of gold per ton." .. 

I · / 2 Lindgren, Waldemar, Some gold and tungsten deposits of Boulder 

• Rickard, ~L'. A., The voins of Boulder and Kalgoorlie: Am. lost. Min. County, Colo.: Econ. Geology, vol. 2, pp. 453-463, 1907. 

'J~ng. 'l'rans., vol. 33, p. SC.S, 1902. a U S. Geol. Survey Prof. Paper 54, pp. 1~4, 123, 1906. 
116 . GEOLOGY OF GILPIN, CLEAR. CREEK, AND · BOU,LDER COUNTIES, COLO. 

To the galena-sphalerite type belong most of 

the ores near Lawson and Empire station, those 

of Caribou Hill, most of those of Seaton Mountain, near Idaho Springs, most of those of a 

group on Alps Hill, northwest of Russ~ll Gulch 

camp, and most of the ores of Nigger Hill, 

Maryland Mountain, and Silver Hill, near Central City and Blackhawk. 

Ores of the composite type are, as might be 

expected, most common in the border zones 

between areas occupied largely by pyritic ores 

on the one side and by galena-sphalerite ores on 

the other. They occur principally immediately east and west of Cen,tral City and betw:een 

South Willis Gulch and the summit of Seaton 

Mountain. 

The gold~silver ores of. the telluride type are 

confined to the vicinity of Eldora and to a 

narrow belt extending from Bobtail Hill, near 

Central City, southwestward nearly to Idaho 

Springs. The second area' is economically the 

more important. 

RELATIONS OF PRIMARY GOLD AND SILVER TO 

COMMONER ORE MINERALS. 

GENERAL RELATIONS. 

The distribution of the precious metals in the 

commoner minerals of the gold-silver ores has 

been ably investigated by George E. Collins, 1 

who has long been associated with the mining 

industry of this district. With regard to his 

method of investigation Collins says: 

With a view to further study of the association of gold and 

silver with various minerals, classified samples were taken 

from representative ores, the particles being picked out 

with the aid of a lens, and the resulting samples separately 

assayed. 

The results of these tests, rearranged from the 

original tables, are given on pages 117 and 118. 

Collins says: 

When more than one figure is given under the same heading, it is for the purpose of directing attention to the widely 

different results obtained from duplicate tests. 

The present writer is -responsible for the 

grouping of the veins under pyritic ores, galenasphalerite ores, and ores of uncertain character. 

Very likely many of the samples listed in the 

third gro~p belonged to one or the other of the 

simple ore types, but as the veins from which 

I they came are known to have produced, at one 

1 The relative distribution of gold and silver values in the ores of 

Gilpin County, Colo.: Inst. Min. and. Met. T.rans., vol.l2, pp. 480-499, 

1903. ' 

point or another, both types, their exact classification is uncertain. 

PYRITIC ORES. 

The assays given by Collins corroborate in a 

definite way the general experience of mining 

men in this district. The pyritic ores which 

are richest in gold and silver are in general 

those which carry the largest amounts of 

chalcopyrite or tennantite. The "Fahlerz" 

of Collins, presumably in the main tennantite, 

in places antimonial, appears to carry silver 

more abundantly than any other sulphide. 

Further, it is well known that coarse free 

gold (alloyed with silver), in the few places 

where it occurs, is more commonly intergrown 

with quartz than w~th sulphides; these assays 

show, as might be expected, that much of the 

fine gold also is associated with the quartz 

gangue. As in general chalcopyrite and tenn.antite formed more abundantly late than 

early in the pyritic mineralization, it is evident 

that gold and silver we~e also deposited most 

abundantly in the later stages. 

In ore of the pyritic tjpe from the Gardner 

lateral in the Argo tunnel workings the portions 

carrying noticeable amounts of chalcopyrite 

and "gray copper" (probably tennantite) 

contained as much as 3.~4 ounces of gold and 

9 ounces of silver to the ton, whereas those 

portions in which pyrite was the only sulphide 

carried 0.05 to 0.50 ounce of gold and 0.50 to 

3.50 ounces of silver. 

Coarsely crystalline pyrite of the pyritic ores 

is proverbially of low grade in this district. 

A sample collected by the writer from the 

eleventh level of the Gem mine assayed only 

0.07. ounce of gold and 0.33 ounce of silver to 

the ton. Coarse pyrite collected by the writer 

from the Saratoga vein, in the Argo lateral 

2,900 feet east of the tunnel, assayed 0.16 

ounce of gold, 1.84 ounces of silver, al).d 0.10 

per oeil t' of copper. . 

The ''amorphous sooty sulphides'' mentioned in Collins's table are probably, in part at 

least, pulverulent chalcocite formed by downward sulphide enrichment. As chalcocite is 

known to be a very efficient precipitant of silver 

from its sulphate solution and of gold from its 

chloride solution (see p. 141), it is ·not surprising that this material should be rich in both 

these metals. · 
Gold, in. ounces per ton, contained in _various minerals of representative Gilpin County vein.~. 

] 

!:!; 

Pyritic o~es. 

0 

;.... 

o. 

-3 

"@ 

~ 

bt 

~ ';::; 

ee 

R ,...... 

Galena-sphalerite 

1 ores. 

I :::; 

·ee 

s. ...-;.... 

oo 

d· ~I:: 

d ~ <l) 

~ a) ~ >-.E-i ~ 0 

-~ ...., 

c:d -;a ~ 0 C) '"0 :~ 0 0 .::: 

H 0 ~ ~ 

Ores of unce~n character. 

I I I I I 

I 0 

'"0 

0 :>. 

& 00 H ~ ~ I; I) ;::l ci 0 t.o >= 0 rn ' ~ ;::l ·s c:d <l) 0 0 .S § ~ ·I-< ~ >-. ;.... 

~ t3 <l) ;::l d i.;1 ~ 0 c!) li; ,.,; I ~ 

I I 

~ <l) 

~ 

'"0 

;.... 

0 te 

s 0 0 ~ ~ 

0 ~ 

~ 0 

l---l---1---·---·---·---·---·---·---·---·---·---·---·---·---

Picked from jig concentrates: 

Pvrite: 

~ Clean..... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0. 29 0. 42 0. 84 - With a little adherent 4uartz .......... · ......................... 1. 20 . 56 .1. 48 

Chalcopyrite: 

:::::'I. o_ :~ -1-o. 43 .I:~- 67-1-~--1~ __ o._1s __ o_66 L::: 

' 

0.26 

. 64 

0.52 5. 74 

Clean .................................................... 0.4.6 ....... :~~- }Lo8~------~-----·~------~- .60 ~------l-·····1 .22~------~ .45~------~---··· 

Nearly clean ................................................. : ....... g: ~: ~- 32 0. 42 . . . . . . 1. 73 . . . . . . . 72 I 2. 16 . . . . . . 1. 22 2. 10 . 65 4. 61 

"Fahlerz" (probably tennantite\: 

Clean- --------. ---. -... --: .. · ... -. -... -...... -... ---. · .. -. . . . . . . . --. -. - . -. --. -. . . . . . ... -.I .... -·I· -. -. . . -... - . 5~ 1." ..... , ...... ,. - .... ,. - .. -.. I • - - • - • ' •••••• 

Nearly clean .................. : .................. , .............. 81 {~:·~~ }5.45 ...... ·--~-- .............. 81 2.15 ............. 60 

Galecf~an . ." ... _ ...... _ ...... __ ........ _ . __ . _ . ___ . _ ............ __ ............................... I . 75 : . .......... I. . . . . . . 36 . . . . . . . . . . . . . 86 

Nearly clean ........................... .'................. . . . . . . . . . . . . . . . . . . . . . . . . . 20 . 16 . . . . . . . . . . . . . . . . . . . 83 . . . . . . . 22 . 27 . 88 

Sphalerite: ' 

~::ci)r "c-1~~~;_ ·. ~: : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : · s.- o7 · · · .· 22 · : : : : : : : : : : ~: : : : : : : : : : : : : : : : : : : : : : : :. : : : : : : : : : : : : : · · .- 2o ·1· · i." io AJ?orphoussootysulp~ides ......... : ........................ ,1.831······'······- ······1······ ······ ······ ······1······ 1. 28 1······ ······1······ ······!······ Pick~df~~Jj~~~~~:py~te ...................................... 1 

...... ---···1 .50 ........................ 2.56 ~-10 .. 23 .. 86 ........ 46 ............ . 

Dark flinty-looking quartz: 

Cleanest practicable ........................................... · ......... , . . . . 06 ............ I ............. _ ............. _ . . . . . . . . . 10 ........•... 

With specks of pyrite and copper minerals........... . . . . . . . . . . . . 1. 00 ................ : ...... _I_ . . . . . . . . . . . . 68 . . . . . . . 84 .. ·. . . . . 82 ........... . 

Lighi:t::;' P~~~~tr~_ue:.... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . os . 10 . . . . . o~ I·... . . . . . . . . i 2 . . . . . . . . . . . . . . . . . . . o6 . H 1. 42 ~l~::~N~Et~~~-~i~~pp~r-~i~~;a:l~::::::::::::::::::: :::::: --_-34· ----~~- :::::::::::: ----~~- :::::: :::::: :~~ ----~~- :::::::::::: ----~~- :::::::::::: 

4.57 

. 21 

:.~~_; 

\ 

~ 

0 

b 

I 

r:n 

H 

~ t_:r:j 

~ 

0 

~ ~ 

~ 

~ 

-:J 
Silver, in ounces per ton, contained in various minerals of representative Gilp?,n County veins. 

Pyritic ores. I Galena-sphalerite I Ores of uncertain character. ores. 

I -

--ci 

·; 

"""' !:::: a) ~ ::l . '1j >. Q) 

0 ~ 0 !:::: 

~ ~ ~§ ~ ai H .;..; '1j a) !:::: ~ I::JJ ~ !:::: Q) ci """' ..c: I::JJ ::l 0 ~ 0 ::l !:::: a) >.E:-'o 0 I::JJ r:n !:::: 0 s ~ ..d 

I 

s ~ !:::: 0 ~ Q) ~ ::l ·s 0 -;:;' ~- ~ ~ ~ s !:::: .a 0 r:n ·.o 0 ~ ~ ;a 0 <.) ~ t:: !:::: >. ~ ~ !:::: ~ ~ ~ ~ !::: 0 0 Q) 

~ 0 ::l ::l ~ 0 ~ 

~ ~ &::: .::: 

1--1 0 ~ ~ r!l ~ ~ ~ 6 ~ 6 1---~---~---~---l---l---l---1---l-. --·---·---·---·---·---·---

Picked from jig concentrates: 

Pyrite: · . . . - · - Clean. : . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. .. .. 1. 5 2. 9 4. 1 .. .. .. 2. 4 .. .. .. 2. 0 1. 0 0. 8 l. 9 __ __ __ 1. 6 I 1. 2 

Withalittleadherentquartz ............................. ______ 3.6 4.0 4.6 ...... ______ 4.4 .................. 5.0 5.9 14.4 ............ . .Chalcopyrite: · · · · · · . · : · · .. 

Clean:~~---·······----····--············--············· 7.9 ...... 6.6 9.1 4.0 --~--· ______ 4.5 ____________ 7.9 11.8 15.4 1 ...... 

1 

..... . Nearlyclean ________________________________________________________ 11.3 14.1 ............ 12.0 8.4 16.9 ______ ...... ______ 17.1 12.6 31.5 

"Fahlerz" (prqbably tennantite): . · - · · · Clean ............. _ .. = ... , . _. ... _. .. .- . , .- .· .... .- .. _. . , .... · ............. .- ... ; ... · .... _ .. · .. , .................... ·. . 19. 5 ............ 1 ...... 1 ... _ ..• 1 .... , . , ..... . 

Nearlyclean ........ : ................................... ______ 13.3 24.9 57.2 ...... ____________ ...... 13.3 10.7 21.9 

Galena: · 61. 8 44.9 

7. 1 

67. 1 

::~;;c·~~~~---. ~ ~:: ~:::::: ~ ~:: ~: ·:::: ·: ·:: ~:::::: ·::: ~: ·:::::: :::: ~: :::::: :: :·:: :::::::: · ii." 8 · . ~~-- ~ .. ~~-- ~. ·:::::: :::::: ·is." 8 · . ~~-- ~. · i9." 8 · ~~: ~ · 3o." 7l. 3i." 2 · Sphalerite:- - . · · 1 

Clean .................................................................... 9.6 ...... 5.8 .............................. 3.0 ...... 7.0 , ..... . 

Nearlyclean .............................................................. 1 9.61······ ............ ······!···-··· ······1······ ······I······ ······I 16.3 Amorphous sooty· sulphides .......... : . __ .. __ . ." .. _____ : ... __ . __ 29. 4 ______ ...... i ______ . ____ . ______ .. ____________ . . . . 21. 4 __ ...... ____ ................. . 

Picked from jig waste: 

Dark-colored flinty quartz: : ·cleanestpracticable: .................................................. 2.1 .31 7.6 1. ..... 1 ...... 1. ..... 1. .•.•. 1 ...... 1 ...... 1 ...... 1 1.5 1 •••••• 1 .•• -••• 

With specks of pyrite and copper minerals............. . . . . . . 3. 4 . . . . . . 9. 0 1. 3 

Light-colored quartzose gangue: . 

~i::sfihl:c;~ri~!~:: :~ ·. ·.·.·.·.· ~::::::::::::::::::::::::::: · · i." i .·::::: :· 1: ~ ... ·.~·I· .. ·.~ ·1: .. ·. ~ ·1::::: :1·. 6." 6 ... 5." 9 -~-- 2." 0 ·j::::: :J::::: :J ~: ~ 1.. ~-·. ~ .1--. 4."2 

'Vith specks of pyrite and copper minerals ............................ _· . .. .. . .. .. .. 8. 0 · 5. 9 ...... { ~: ~ }13. 5 ...... __ ..... __ ..... 7. 7 , ...... , ..... . 

1-i 

1-' 

00. 

0 

t:rj 

0 

t'"l 

0 

0 

~ 

0 

1-:;j 

0 

1-4 

t'"l 

1-0 

1-4 

·~z 

Q 

~ ~ 

~ 

Q 

~ t:rj 

J1 

~ 

z 

t:::l 

t:d 

0 

q 

t'"l 

t:::l 

t:rj 

~ 

Q 

0 

q 

z 

H 

1-4 

t:rj 

JfJ 

Q 

0 

t'"l 

p 
GOLD-SILVER OR.ES. 119 

I tis not pr?bable tha·t downward enriclm~.ep.t 

has influenceCI the gold and. silver conte~tf;l of 

the other sampl~s described by Collins. . All 

seem to have been unaltered or little-altered . . . pri;mary ore. materials~ 

GALENA-SPHALERITE ORES. 

al).d 7.30 ounces of silver to the. :ton,. 0.48 per 

9ent of eoppor, and 65.50 per cent of lead. · So-. 

calle.d "lead ore". from the eleventh level east 

in.the .same· mine .assayed 0.25.oun.ce of gold· and 

15.80 ounces of silver to the ton, 23 .. 45 per cent 

of lead, and 9.35 per. cent of z;inc. 

TELLURIDE ORES. ' Collins's tables show that in ore.s of galena- , ..... 

sphalerit~ type, as in those of the pyritic type, In the telluride type of gold-silver ores some. 

gold is more abundantly associated with. the of the gold (with alloyed silver) occurs free, but 

copper minerals chalcopyrite and tennantite . most of the gold and silyer is combined with 

than with pyrite. · In pla.ces it is abundantly . tell uri~ in the. tellurides. The associated ·suiassociated with sphalerite, although there seems · phide~, particularly tennan.tite, doubtless carry 

to be muoh variability in this regard ... Silver considerable amounts. of the precious· •metals,. 

is associated in particular abundance with ten- but no.data are available on this point. · .. 

nantite and galena and locally to a. notable extent with chalcopyrite' and sphalerite. It is a . FINENE~S OF ~OLD A.ND SIL~R. 

general rule that the veins of the galena- · .The. following table, showing· the fineness of· 

sphalerite type are richer' in silver' than those 0~ :the gold saved by amalgamation in. a number· 

the pyritic type; they may or may not be . of mines of the Central City quadrangle that· 

poorer in gold. produce sulphide ores; .is given by Collins: 1 

Silver seems to be more characteristically 

asso,..iated with sphalerite than has been gener- Gold and sil-ver fineness of retort bullion from representative v · mines. · 

ally recognized: Sphalerite concent}.'ate from 

ore from the eleventh and twelfth levels of the . 

Gem mine which originally contained some 

galena, pyrite, chalcopyrite, rhodochrosite, and 

quartz was picked under the lens as free as 

practicable from these minerals. On assay it 

yielded 1.10 ounces of golQ. and 22.62 ounces of 

silver to the ton, 12.20 per cent of lead, and 

24.17 per cent of· zinc. A specimen from the 

dump of the American Sisters mine, near Lawson, which was mainly sphalerite with a little 

galena, showed on assay a trace of gold, 79.20 -

ounces of silver to the ton, 9 per cent of lead, 

and 46.60 per cent of zinc. 

1870-1880· 1880-1900 

Galena in general appears to be comparable 

with pyrite as a gold Cfl;rrier and of varying importance as a silver carrier. A sample from the 

dump of the American Sisters mine that appeared to be -\vholly fine-grained galena gave on 

assay a trace of gold, 6.24 ounces of silver to the 

ton, 61 per cent of lead, and 2.10 per cent of 

zinc. ''Steel'' galena from the Elida tunnel, 

near Lawson, that appeared to carry no other 

minerals, assayed, according to R. B. Morton, 

14 ounces of silver to the ton and 73 per cent of 

lead. Ore from the Gem mine, 250 feet east of 

the shaft on the Argo lateral, consisting mainly 

of fine-grained galena with a little chalcopyrite and pyrite, assayed 0.06 ounc~ of ~old 

·' 

Mine. 

Gold. Silver. Gold. Silver. 

Bates .......... 0. 746 0.241 0.757 0.214 

Bobtail.· ....... . 858 .134 . 861 .118 

nuell. ......... 0.800-.860 0.120-.140 . 780. '. 200 

Burroughs ..... . 827 .162 . 834 .146 

Gregory_ ... _ .. _ . 810 .176 . 803 .174 

Kansas._._ ... _ a, 770 a.200 . 758 . 215 

Kent County. _ a. no .. a.240 . 700 . 277 

Gold Dirt .. -. _· _ . 870 .100 . 878 .105 

Perigo. ____ .. _. a.860 a. no .,873 .105 

a Approximate. 

The last. two mines (at Perigo) yield exclusively ores of the pyritic type; the others have 

yielded ores of both the pyritic and galenasphalerite types. . 

Four tests of bullion obtained by amalgamation from ore of the Gunnell mines are as 

follows: 

Gold. Silver. 

0.805 0.154 . 823 .163 . 825 .162 . 825 .162 

1 Collins, G. E., op. cit., pp. 492-493. 
120 GEOLOGY OF GILPIN, CLEAR CREEK, AND BOULDER COUNTIES, COLO. 

The Gunnell vein has yielded both pyritic 

and galena-sphalerite ores. . The :fineness of 

the bullion obtained by amalgamation from 

the pyritic ores of the St. Louis mine, near 

Caribou, varies from 0.582 to 0.655 for gold 

and from 0.315 to 0.378 for silver. 

The average :fineness of Gilpin County retort 

bullion is given by Collins as gold 0.787, silver 

0.198, and copper 0.015 for 1870 to 1880, and 

gold 0.778 and silver 0.207 for 1880 to 1900. 

PLACERS. 

Although placer mining has persisted in the 

region covered by thls report from the first 

discovery of placer gold near Idaho Springs to 

the present day, it ceased to be of much importance: before the end ·of the sixties. In th~ 

early days North Clear Creek, Russell Gulch, 

and Gamble Gulch near Perigo were the scenes. 

of .active gravel mining, and for some time 

after the discovery of the first lodes placermining methods were applied in working their 

oxidized surface portions. Even as late as 

1876 the stream gravels in the lower part of 

Russell Gulch and in Clear Creek below Blackhawk .were yielding some gold to placer 

mmers. · 

The most extensive placer workings were 

in the valleys of Chicago Creek and Clear Creek 

near Idaho Springs and developed not only the 

present stream gravels but also glacial outwash 

gravels and gravels. of possible preglacial age. 

These deposits have been fully described by 

Spurr and Garrey .

1 

The surface ·portions of the great stockwork 

of the Alice mine, near Alice, although not 

forming a placer deposit in the stricter sense 

of the term, were worked by placer-mining 

methods. · Burchard 2 describes these ' w.orkings as follows: 

At Fall River the hydraulic mines of the Alice Mining 

Co. are the most extensive placers in the county. ThiS 

·company owns 1,500 acres of" placer land in the forks of 

Fall River and Silver Creek. * * * A high ridge lies 

between the streams, and, it is on the eastern slope of this 

ridge that operations are being carried on. About 700 

feet of pipe is used 'to carry water to the giant, which is 

8 inches in diameter at the sand box. The debris removed 

consists of from 3 to 6 feet of coarse gravel and soil, 2 feet 

of fine yellow dirt, and abo.ut 3 feet of shattered bedrock, 

which consists of white and gray talcose rock, filled with 

vugs of quartz crystals and iron pyrites. This talcose 

rock has been uncovered for a distance of about 500 feet 

in length and 200 feet in width. * * * The yellow 

dirt immediately overlying the talc is said to be quite 

rich and will wash an inch string of gold to the pan. The 

debris is easily removed, and but few large bowlders met 

with. On account of the precipitous ground the flume is 

less than 100 feet in length, with a dip of 5 inches i.n 12 feet. 

The ground washed at present is known to be much 

richer than any heretofore washed, and the gold coarser. 

* * * Work is kept up day and night, several large 

locomotive headlights being used at night. The company 

has a line of pipes laid at the lower end of the placer, but 

no work is being done at that point. 

1 Spurr, J. E., and Garrey, G. H., op. cit., pp. 311-314. 

2 Burchard, H. C., Production of precious metals in the United States 

during the calendar year 1883, p. 280, 1884. 
CHAPTER VIII.-URANIUM ORES. 

INTRODUCTION. 

·The large amount of public interes.t that has 

recently been ~anifested in radium because of 

its apparently beneficial influence in certain 

cases of cancer lends particular importance to 

the study of t~e · uranium ores from which 

radium is derived. 

The quantity of urani11;m ore mined in the 

United States is exceedingly small and in 1913 

appears to have been equival~nt to about 3.8 

short tons of uranium oxide (U 30 8), or approximately 32 tons of metallic uranium. 1 This is 

considerably larger than the production in 1912, 

which was equivalent to about 26 short tons of 

uranium oxide, or in 1911, which was equivalent to about 25 short tons. Practically the 

entire quantity produced in 1911 and 1912 and 

about half that in 1913 went to foreign 

countries. Of this tonnage nearly all came 

. from sandstones of the high plateau regions 

of southwestern Colorado and southeastern 

Utah, in which the uranium occurs dis~eip.inated as the canary-yellow mineral carnotite 

(2U03.V20 5.K20.xH20) or its calcium-bearing 

· equivalenttyuyamunite (2U03.V20 5.CaO.xH20). 

The small remaining· portion of uranium ore 

mined in the United States, amounting in 1912 

to only 275 pounds, was uraninite, or pitchblende, a complex uranate of variable composition to which a definite chemical formula 

can not yet be assigned. This mineral occurs 

in two distinct ways-in small amounts in 

graJ.}ite pegmatites, notably in North Carolina, 

and in intimate association with metallic 

sulphides in certain mineral veins, most of 

which are in. Quartz Hill, within the area 

covered by this report. For many years a 

small and sporadic production has come from 

this group and has been used mainly for 

specimens and for experiments. Quartz Hill 

is not only the one i;mportant locality in the 

United States where pitchblende occurs in 

mineral veins but one of the few in the world. 

As the geologic relations at Quartz Hill differ 

in important particulars from those at foreign 

1 Ross, ·:F. L., Preliminary statement of the production of uranium 

and vanadium: U. S. Geol. Survey Press ~ulletin, January, 1914. 

localities, a summary of the genetically important features of the principal E~ropean 

occurrences is given below for purposes of 

comparison. The writer's thanks are due to 

Mr. FrankL. Hess, of the Geological Survey, for 

_placing .at his disposal additional specimens for 

study, and to Mr. Forbes Rickard for the loan, 

through the Bureau of Mines, of many particularly fine specimens. 

PRINCIPAL FOREIGN OCCURRENCES OF 

PITCHBLENDE. 

In preparing the following summary of the 

principal foreign occurrences the writer has so 

far as possible consulted original sources. The 

chief localities outside of the United States at 

which pitchblende has been found in mineral 

veins are the western part of· the Erzgebirge, 

near the Germ~n-Austrian boundary, and the 

Cornwall district, in England. A brief ·summary ·of the geologic occurrence of uranium 

minerals is also given in a recen:t art~cle by 

P. Krusch. 2 

THE ERZGEBmGE. 

TYPES. OF DEPOSITS. 

, Muller 3 recognized in and near the granite 

batholiths of the western Erzgebirge in Bohe-. 

mia and Saxony four types of ore deposits, 

which he classified as follows: 

A. Older ore-forming period: 

1. Veins of the tin type. 

2. Veins of the pyritic lead-zinc type. 

B. Younger ore-forming period: 

3. Veins of the cobalt-silver type. 

4. Veins ofthe iron and manganese· type. 

Deposits of types 1 and 2 are connected by 

transitions. The tin ores are confined to the 

granite and its immediate vicinity; the pyritic 

lead-zinc veins are a little farther removed 

from the granite batholiths. The veins· of 

types 3 and 4 are later than those of types 1 

and 2. 

At Joachimsth&l, in Bohemia, and at Schneeberg, Annaberg, and Johanngeorgenstadt, 

2 tiber die nutzburen Radium-Lagerstiitten und die Zukunft 'des 

Radium-Murktes: Zeitschr. prukt. Geologie, vol. 19, pp. 83-90, 1911. 

a Miiller, Hermann, Die Erzgange des Annaberger Bergrevieres, · 

Erliiuterungen zur geologischen Specialkurte des Konigreichs Sachsen, 

p. 66, Leipzig, 1894. 

121 
122 GEOLOGY OF GILPIN, CLEAR CREEK, AND BOULDER COUNTIES, COLO. 

across the border in Saxony, the veins of principal economic importance be_lo~g. to Muller's 

cobalt-silver type (No.3). It is with the veins 

of this type th~t the pitchblende is exclusively 

associated. 

pact spherulitic or grapelike masses, some of 

.which have shell-like or concentric structure, 

as a 'coating on siderite and fluorspar. Rarely 

it forms layers as much .as 7 centimeters thick. 

The primary minerals of the cobalt-nickel 

veins· are, according to MUller, barite, fluorite, 

JOACHIMSTHAL, BOHEMIA. quartz;· siderite, rammelsbergite (NiAs'2), niccoAccording to St~p and Becke 1 the ·ores of th~ lite; chloanthite, ·smaltite, native bismuth, tetcobalt-silver type in the Joachimsthal di~trict rahedrite, stibnite, chalcopyrite, pyTite, redinay be fur.ther subdivided int.o two classes- dish sphalerite, ·and berthierite (FeS.Sb2

8 3). 

cobalt-nickel-arsenic ores and rich silver ores. The pitchb1ende, together with siderite, calcite, 

In the writer's opinion the ores of the first class and some pyrite and chalcopyrite, is later than 

represent the primary ore deposition and those :the cobalt-nickel group of minerals, but earlier 

of the second class are in all probability the ·than the Tich silver minerals, whose origin, as 

result of downward enrichment acting on the at Joachimsthal, may be attributed with niuch · 

primary ore. The pitchblende, with its accom- :probability to downward enrichment. 

panying gangue minerals, quartz and dolomite, · 

has rarely been observed in actu.al contact JOHANNGEORGENSTADT, SAXONY. 

either with the rich .silver ores .or with the co- . In ·the J9

hanngeorgenstadt district, which 

halt-nickel-arsenic ores. Usually the pitch7 h b d ·b d b ~T· b' 3 th t as een escn e y v 1e 1g, e mos 

blende and its gangue :r;ninerals. have as metallic valuable uraniun1 ores are also associated with 

associates only.v~dab. le amount~ of pyrite a~d MUller's cobalt-silver type, but the latter are 

chalcopyrite, which appear to be in part earlier h t · d b 1 b d f c arac enze y an unusua a un ance o 

and in part later. than th~ pitchblende. In a native bismuth and bismuth compounds and 

few places, however, the pitchblende, quartz, . are. valuable mainly as a source of that metal 

and dolomite coat ore containing cobalt or and only subordinately for the nickel, cobalt, 

nickel minerals (smaltite, chloanthite, or nicco- .

1

. th Th · · 1 · or si ver ey carry. e pnnCipa pnmary lite), and therefore apparently are later than ·minerals of these veins are arsenopyrite, cothose minerals. The relation of the uranium · baltite, chloanthite!. native bismuth, quartz, 

ores to· the rich silver ores can be inferred only dolo~te, siderite, calcite_. and rarely barite 

from inuseuni specimens in which ruby silver or ·and fluorite. The pitchblende is invariably 

proustite occurs in vugs in the pitchblende ore associated with th.e veins of this type. It is in 

and in minute veinlets traversing· it. It ap- ·part disseminated and in part in solid crusts 

·pears fairly well established, therefore, that the or bands, some of which r~ach a thickness of 

uranium ores. of Joachiinsthal were deposited .

6 to 8 centimeters. Kidney-shaped and consomewhat .later than the. nickel-cobalt-arsenic centric forms . are common. Characteristic 

ores, but before the de:velopment of rich silver metallic associates are. fine-grained galena and 

sulphides, ·which in these deposits were prob- :chalcopyrite and native bismuth, small masses 

ably form.ed by .much later enrichment due to of these ·minerals being locally inclosed in the 

the action of meteoric waters. pitchblende ore. The common. gangue mineral Is ~n iron-manganese carbonate. In other 

parts of the'Erzgebirge the pitchblende is. irregANNAB.ERG, SAXONY. 

In the ~aberg r~gion also. the .c~balt-silver ularly distributed in nests, but in the Gottes 

type of ore 1s economically the most nnportant, 8 ·

8 . t · ·· · ·· thi · ·t · 

d . · . . egen pa nnne, In s regwn, I occurs In an Its vems In many places cut or even mate-. , . . · · . . . · · ll d' 1 th 1

. t' d considerable quantities and With much regu- ria y Isp ace e ear Ier. In, copper, an py- 1 ·. t · · · · 

ritic lead-zinc yeins. Acc.ording to Muller 2 the an Y· · · · · 

pitchblende is characteristically though noSCHNEEBERG, SAXONY. 

where abundantly associated with the cobalt- In· the Scl.llieeberg district:, according to 

silver type o~ veins. It. usually forms com- Miiller/ pitchble:q.de is a characteristic though 

1 St~p, Josef, and Becke, F., Das Vorkommen des Uranpecherzes zu 

St. Joachimsthal: K. Akad. 'Wiss. Wien _Sitzungsber., vol. 113, pp. 

585-618, 1904. . 

2 MUller, ~ermann, op. cit., pp. 94, 98-100. 

a Viebig, W., Die Silber-Wismutgii.nge von Johanngeorgenstadt in 

Erzgebirge: Zeitschr. prakt. ,Geologie, vol. 13, pp. 89-115, 1905. · 

• Milller, Hermann, Der Erzdistrikt von Schneeberg in Brzgebirge, in 

B. von Cotta's Gangstudien, vol. 3, pp. 129-138, 1860. 
URANIUM ORES. 123 

not an abundant accompaniment: of the co·balt- uranium ore is confined to a leader a few inches 

silver typo, of .veins. Its.· kid1~ey-shaped ·or in .width, -consisting partly of. pitchblende and 

rounded shell-like .masses are ordinarily· asso- ·calc tmd copper uranites with. copper py:rites, 

cin.ted with chalcopyrite, galena, and ·brown mispickel, and galena, and small quantities of 

.. carbonate.· 1\fuller regarded tho pitchblende nickel,. cobalt, and chromium. ore. in a· veinand its accompanying minerals as of..slightly stone of-quartz and green garnet rock.'!· 

• 

later formation. than the primary cobalt and 

nickel n1inerals and earlier than the -rich silver 

Ininerals .. 

. ' . 

PITCHBLENDE IN THE CENTRAL CI'fY 

_QUADRANGLE. 

Within· the area of ·the Central City quad- CORNWALL DISTRiCT, ENGLAND. . . . . . rangle .pitchblende has been reported from. the 

.· In and near the granite batholiths of Com- Alps, Belcher, Calhoun, German, Kirk, Mitchwall occur not only till. and copper lodes but ell, and Wood -mines,. on Quartz Hill; from 

also, usually at a great~r distance from t_he the 200-foot level west, in the Pewabic mine, 

granite, younger lodes of two types-(1) those in Russell Gulch; and from the Jo Reynolds 

containing uranium and nickel ores and (2) mine, near Lawson. The pitchblende occurs 

iron-manganese lodes.~ ·In the vicinity of as a minor component of gold-silver ores, and 

Bodmin, for example, there occur certain lodes most of the n1ines mentioned above have been 

containing arsenic and copper miner!1ls and 

smaller quantities of uranium, cobalt, and 

nickel ores. These lodes cross the tin and 

copper lodes thn.t ar~ .the main mineral resources of the district and are therefore some-

. what younger, although it is believed that all 

the lodes are genetically connected with the 

granitic intrusives of the region. 

In the St. Austle Consols mine, according to 

Williams 2 urn.nium minerals h.a ve been found ' . in certain small veins that cross the main tincopper lode. The assoc~ate~ of the uranium 

minerals in the cross veins are locally copper 

ores but mol'e commonly ores of nickel and 

cobnlt. 'I'he uranium minerals also occur on FIGURE 11.-Camera lucida drawing of polished section or ore from tbe 

the sides of the veins. Wood mine, Quartz Hill, show~g 9ontemporaneous intergrowtb of 

At Dolcoath, ·~Gcordin,g to Pearce,s pitch- pitchble~de,cbalcopyrite,andpyrite . 

blende occurred "associated with native bis- worked primarily for gold and silver rather 

muth and arsenical cobalt in a matrix of red than for pitchblende. 

cmnpact quartz and purple fluorspar."' At Although few opportunities were af}:orded 

·South Tresavean . it· occurs with "kupfer- for studying the richer pitchbl~nde ores in 

nickel, native- silver; and .rich· argentiferous place, because of suspension of mining at most 

. galena." "I believe,"-says Pearce, (.(.in all the ··of the mines·, many excellent specimens from 

localities I have named, it was found· in little these mines were· polished and studied under 

. veins crossing thelodes" (that is, the tin lodes). the reflecting microscope and found . to show 

At the South Terras or Uranium mine, in clearly the relations of the pitchblende· to the 

. Cornwall; 4 "The uranium lode .* * * is sulphides which accompany it in the veins . 

. said to. vary in width from 3 to 5 feet., but the In a number of specimens ·it is evident that , 

1 Usshcr,\v. A. E., Barrow, a., ,and :MacAiister, n. A:, The geology the ·pitchblende crystallized contemporane- or thecol.mtry~rowtd Bodmin and st. Austell: Geol. Survey England ously with -chalcopyrite, pyrite, and probably 

and Wales Mem., Expl. Sheet 347, .p. 134, 1909. . · · 'A · · f th W d 

2Williams, R. H.;·Noilce o(the occurrimcc 'ofriickel arid cobalt at St. gray quartz. speCimen rom e' 00 

Austle Consols mine, neal' •at. Austle, Cornwall: Roy. Inst. Cornwall mine, obtained through the courtesy of . Mr. 

· ~':'~?;;~~nt~~~~a~d ~~~~·~::P~~~~!!~~·i~\::ornwall: Roy. Geol. soc~ · W; C;: ·•Denison, presented, when polished, the 

cornwau1'rans., v~I. 9, pp. 103, 1ot, 1875.. · '· · 1 appearan·ce shown in figures 11 and 12.: Some • Ussher, W. A. E., Barrow, G.~ and MacAlister, D. A., op. cit., p .. of the inter_grown chalcopyrite and pitch- 157. 
124 GEOLOGY OF GILPIN; CLEAR CREEK, AN~ ··BOULDE~ COUNTIES, COLO. 

blende of this specimen show angular outlines, 

as indicated in figure 11, but more commonly 

the pitchblende areas are ringlike in cross 

section, chalcopyrite occupying the center of 

the ring and inclosing it, as indicated in figure 

12. Pyrite and gray quartz, apparently contemporaneous with th(;} pitchblende and chalcopyrite, are presen~ in small amounts. Specimens from the Wood and German mines in the 

mineral collections at ·the State Capitol in 

Denver show chalcopyrite and pitchblende so 

intimately intergrown as to leave little ·doubt 

of their contemporaneous crystallization. In 

other specimens from the Wood mine botryoidal 

FIGURE 12.-camera Iucida drawing of polished surface of pitchblende 

ore from the Wood mine, Quartz Hill, showing contemporaneous intergrowth of pitchblende, chalcopyrite, and pyrite. In contrast with 

figure 11, which was drawn from another part of the same specimen, 

the pitchblende areas show rounded outlines. 

pitchblende has cores of pyrite and is in places 

fringed with pyrite, as shown in Plate XV, A. 

To summarize, the· manner in which the minerals are intergrown in several specimens 

shows conclusively that pitchblende crystallized contemporaneously with chalcopyrite and 

probably with minor amounts of pyrite and 

gray quartz. 

Other specimens carry sulphides which are. 

later than t.he pitchblende. A specimen of 

rich ore from the Calhoun mine, obtained· 

through the courtesy of Mr._ Hugh C. Brown, 

consists principally of pitchblende, but ~h.is 

mineral is sharply cut by veinlets one-eighth 

inch or less in width, composed of sphalerite, 

pyrite, and some g~lena. The form of some 

of these vein lets is shown in figure 13. Similar 

relations in a specimen from the GermanBelcher mille, lent by Mr. Forbes Rickard, 

are shown in. Plate XVI, B. Another specimen from' the Calhoun mine s~ows pitchblende 

shattered to minute fragments which lie in amatrix of pyrite and chalcopyrite with some 

galena, sphalerite, and quartz. Similar brecciation of pitchblende in ore from the GermanBelcher mine is shown in Plate XVI, A. 

Specimens of pitchblende ore- from the J o 

Reynolds · mine near Empire were kindly 

lent by Mr .. R. B. :Morton. They came fro'm 

the tunnel level near the bottom of the old 

IMM. • 

FIGURE 13.-camera Iucida drawing of polished face of ore from the Calhoun mine, showing pitchblende (white) traversed by later veinlets or 

pyrite, sphalerite, and ·galena (patterned). . ' 

shaft, from a point about 1,000 feet below the 

surface. Microscopic examination of polished 

surfaces of the ore showed fragments of pitchblende having characteristic botryoidal forms 

embedded in a matrix of quartz, siderite, s.phalerite, galena, and chalcopyrite. In places 

minute· veinlets of one or more of these min-· 

erals traverse the pitchblende. It is clear from . 

the study of these specimens that after the 

period ·of pitchblende deposition th~ ores were 

fractured and the fractures filled with quartz,. 

sphalerite, galena, chalcopyrite, pyrite, and, in 

the Jo Reynol4.s ore, siderite. In the Jo Reynolds ore no sulphides contemporaneous with 

the pitchblende were noted. 
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 94 PLATE XV 

A. POLISHED SECTION OF PITCHBLENDE ORE FROM 

THE WOOD MINE, QUARTZ HILL, GILPIN COUNTY. 

Show ing botryoidal forms characteristic of much of th e pitchblende. Py, intergrown pyrite. 

B. DIKE ROCK FROM EVERGREEN MINE, PINE CREEK VALLEY, GILPIN COUNTY. 

Cl ear-white to light-gray minera l is quartz; cloudy light-gray m ineral in irregular grains is 

feldspar; fibrous prismatic mineral is wo ll astonrte ; mottled dark-gray and blac k min era l 

is principal ly gree n augite ; s mal l black areas in the lower south east pa rt of photograph 

are bornite and cha lcopyrite. Note th e sharp co ntact of th e last t wo min erals with the 

others a nd the ge nerally fresh character of th e rock. Enl arged 15 d iameters. 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 94 PLATE XVI 

A. URANINITE OR PITCHBLENDE (U ) FRACTURED AND BRECCIATED 

AND INTERSPACES FILLED WITH ORE COMPOSED PRINCIPALLY OF 

CHALCOPYRITE .( C), WITH SOME GALENA, PYRITE, AND SPHALERITE. 

Ore taken from German-Belcher mine. En larged 100 d iameters. 

B. URAN INITE OR PITCHBLENDE (U) TRAVERSED BY SULPHIDE VEINLETS. 

Ore take n from Germa n-Be lcher mine. C, Cha lcopyrite; S, s ph a lerite ; Py, pyrite. Enl arged 11 0 diameters. 
URANIUM ORES. 125 

The significance of the contra~ting .. and appa- pitchblende min~ralization is genetically- conrently contradictory modes of association of nected with the intrusion of. the pre-Cambrian 

the pitchblende with th~ sulphide minerals granitic rocks/ on the contrary, the writer 

becomes apparent when it is recalled that there believes that,_ together with the sulphides that 

have been in this region_ two periods 'of miner- accompany them, they are genetically related 

alization, an earlier pyritic mineralization and to the Tertiary· ( n monzonite intrusives. 

a later galena-sphalerite mineralization. The The general geologic relations and the abminerals intergrown contemporaneously with sence of characteristic high-temperature min-

.the pitchblende are those characteristic of the erals in the deposits o~ Quartz Hill, as well as 

pyritic mineralization; those which are later in those of Cornwall and the Erzgebirge, indicate 

than the pitchblende are characteristic of the that the pitchblende was deposited under congalena-sphalerite mineralization. On this evi- ditions of moderate temperature and pressure. 

dence it is believed that the pitchblende ores Unlike the European pitchblende, however, the 

were deposited during the earlier or pyritic min- pitchblende of Quartz Hill is not associated 

eralization; that they were later fractured; and with nickel and cobalt minerals, which so far 

that ores of t.he later or galena-sphalerite type as known have never been found in that region 

were deposited in the fractures. They are,· ac- even in small quantities. The occurrence of 

cording to this interpretation, merely a local and pitchblende in pegmatite as well as in miner.al 

' unusual variation in the main sulphide miner- veins of the type here described shows that the 

alization of this region-a variation of the same mineral may also form under conditions of 

order as the occurrence of enargite in a neigh- high temperature and pressure. 

boring group of veins near South Willis Gulch. 

N 0 evidence was found to indicate that the 1 See Rickard, Forbes, Pitchblende from Quartz Hill, Gilpin County, Colo.: Min. and Sci. Press, vol. 106, pp. 851-856, 1913. 
.... '· 

. ~·CHAPTER IX.-TUNGSTEN, COP.PE~~ AND. ~~~N <?~ES. . . .•. : . ,. ,·. .. . . . . 

·. TUN.GSTEN ORES.· . ' 

The tungs te:ri . ores of . the Cen traf Qi ty quadrangle. are con~ed to. the· regi~n betw~en 

Rollinsville ·and Nederland and betwe.~n N ederhmd and Caribo'u. · Just· outside of the q~adrangle tungsten ores are found near ~~¥arloa:f, 

Ward and Magnolia. Although mmmg for 

gold ~nd silver had been in pr?gres~. in t.his 

part of the region ~m.ce 1870, the _tr~e natu~~ 

of t4e tungsten minerals and. ~hmr economic 

value was not, realized until 1900, when tungsten mining was begun .. The ores were not 

studied by. the writer, and the following su~­

inary of their occurrence' is abstracted· from a 

report by George and Crawford. 1 .• 

COPPER ORES. 

' . GENERAL FEATURES. :· . . 

In a region where n1ost of the ore deposits are. 

typical :fissure veins whose principal val':es 

are in gold ·and silver, the Evergree~ m~e 

stands unique becaus~ it is worke~ prrmarily , 

for copper and because the ore minerals are. 

not in .a· fissure .vein but are disseminated 

through an igneous rock. It is situated in 

the valley of Pine Creek about half. a mile south 

of the little mining camp of Apex.· Its unusual 

features attracted . the attention of Etienne 

Ritter, 4 who described the mine in an interest-_ 

ing article in which ·he showed that the .cop~er 

sulphides crystallized ·contemporaneously With 

the other Ininerals of the igneous rock. · The only abun~ant tungste!l mmer~l of the 

deposits is ferberite, a tu~gstat~ of ~on and 

manganese. This occurs· m· vems With ~re- GEOLOGIC RELATIONS. 

vailing northeasterly trends and steep dips. The prevailing rocks at the Evergreen mine 

The veins are zones of brecciation, and most are schists of the Idaho Springs formation 

of the ferberite occurs in the matrix of these injected by small amounts of gr~nite pegmafriction breccias. Small amounts of one o_r tite. Both schist and pegmatite have been 

more of the minerals scheelite, pyrite,· chal- intruded by. dikes of light-gray rock, which are 

copyrite, galena, sphalerite, ~olybdenite, go~d probably offshoots from the large stock _of 

tellurides, and possibly fluorite and adulana monzonite that crops out less than half a mile 

have been found in association with the fer- north and east of the mine. (See Pl. I.) The 

berite. In some of the veins earlier formed ore minerals, which are chalcopyrite and bornferberite has been brecciated and cemented by ite, are largely confined to the dikes and ~o ~he 

later ferberite. igneous breccias formed _by t~e shattenn_g of 

The relation of the tungsten ores to ores of the wall rocks during the IntrusiOn of the d1kes. 

other types is further discussed on page 132. The mineralization is commonly greatest in the 

The ores are treated at two large mills at breccias, but in these the sulphides are confined 

Lakewood and Nederland and at a number of to the igneous matrix and are wholly absent 

smaller mills. The production of the ent~re from the contained fragments of waH rock. 

Boulder County tungsten field in 1915 .amounted These fragments are angular and show little 

to 960 short tons of 60 per cent tungstic oxide. evidence of metamorphis1n by the dikes. As a 

For further information in regard to the consequence of this distribution of the ore most 

tungsten deposits the reader is referred to_ th.e of the development work has followed the 

report by George and Crawford already cited, dikes though some exploratory workings are 

to a report by Hess and Schaller, 2 and to ~he· mainly in schist. The north drift on the 200-

annual reports by Hess 3 on the productiOn foot level follows a dike for about 250 feet. 

of tungsten. This dike is 1 to 1! feet wide, strikes on the 

I George, R. D., and Crawford, R. D., The main tungsten area of average about N. ~5° w., and dips about 50° E. 

Boulder County, Colo.: Colorado Geol. Survey First Rept., pp. 7-103, The drift on the 150-foot level follows what 

1909. ' ' 2 Hess, F. L., and Schaller, w. T., Colorado ferberite and the wolf· \. 

1 

t 

ramite series: u. s. Geol. Smvey Bull. 583, 1914. 4 Ritter, E. A., The Evergreen copper deposit, Colorado: .1 m. ns • 

a U. S. Geol.. Survey Mineral Resourc_es, 190&-1914 . 1\fin. Eng. Trans., vol. 38, pp. 751-i65, 1908. 

126 
TUNGSTEN, COPPER, AND IRON ORES. 127 

may be the sam:e dike for 130 feet. On this the lo~g prisms ~f that mineral, but in others 

level the dike·rock has· intensely brecciated its the calcite forms-irregular masses showing sharp 

host and the igneous breccia iS' in places 4 feet contacts '?~h fresh feldspar ··an~· augite ·and 

wide. In the tunnel dikes are- encountered at may be· OriginaL· Most of the ·dike roc~ conseveral places .. They .are . .interrupted by nu-. tains no opaque :IDnerals with ·~he exce~twn of 

1nerous faults and their exact relations to one· some small -graans of ·.magnetite? but locally 

another are thus rendered uncertain .. The . chalcopyrite· and ·:bornite occur In s~all and 

narrower dikes exposed in this tunnel are 2 .to 3 ver~ irregular patches. These sulp~1des are 

feet wide while larger Inasses exceed the Width particularly abundant where the dike rock 

of the tu~nel by an .indeterminate amount.. incloses numerous fragments of wall rock and 

thus forms an igneous breccia. The chalcoPETROLOGY OF THE ORE-BEARING DIKES. pyrite and ·bornite are contemporaneous and 

The dike rocks exposed 'in various portions are irregularly intergrown with each other, and 

of this mine are in general of similar ~haracter. they are commonly accompanied by garnet, a 

They are light-gray rocks, in_ placesjwrphyroid mineral which is rare elsewhere. The garnet 

in texture through the deve~opment of pink and sulphides are unquestionably contempofeldspar crystals above the averag~ in size. raneous with the other minerals of the rock~ 

The porphyroid phases t<? the unaided eye being in sharp contact with perfectly fresh 

appear closely similar to ~he monzonite of the individuals· of all ~the principal constituents. 

neighboring stock, but when studied micro- In some places the bornite incloses augite and 

scopically they show notable differences. In wollastonite. ·Needles of wollastonite also pena common type which is even grained a great etrate bornite. In other places bornite is 

abundance of mip.ute colorless prisms are recog- wholly inClosed by quartz. Chalcopyrite and 

nizable with the unaided ·eye. Under the. bornite· occur inclosed between pri~ms of 

·m.icroscope the porphyroid phases . are found· wollastonite. 

to be alm.ost perfectly fresh, granular in texture, Rogers 1 in a recent paper figures chalcocite 

and con1posed dominantly of feldspar, augite,. associated with bornite from the Evergreen 

and wollastonite. (See Pl. XV, B, P· 125.) mine and suggests that the chalcocite is a 

Tlie feldspars are mainly of the ~r~hoc]as~ and product of upward enrichment. ·Chalcocite is 

microcline varieties, finely (per~hitiCally) Inter- a very inconspicuo~s·mineral at this mine and is 

_grown with albite, and the ~r~ns are .of n::any generally not recognizable except under. the 

sizes, the largest ab<_:>ut 5 nnllimeters In diam-·. microscope·. In one of the specimens exanuiled 

eter. I-Iere a:nq there is a ~mall crystal ?f by the present ,v'fiter chalcocite is irregularly 

plagioclase (oligoclase or andesine). Quartz In associated with chalcopyrite and bornite. The 

S11111ller grains is very abundant. The gras.s-: origin of this particular chalcocite is indetergreen augite is nearly equal to quartz In minable. In most other specimens, however, 

abundance. Its crystals are as a rule not over chalcocite has developed along incipient· fra~-

5 1nillimeters long, but .in the matrix. of some tures in the bornite and along contacts between 

<;>f the igneous breccias. augite prisms 5 milli- bornite and silicate minerals. This relation 

meters. wide and 8 millimeters long occur. between chalcocite arid bornite.is totally differWollastonite forms abundant prisms com- ent from the relation between bornite and chal.:. 

n1only less. than 1 i:nillimeter in length. In copyrite and indicates that the chalcocite is 

portions of the dikes ~ t is nearly e~ual to feld- secondary. As ·the mine workings are all shal-

.spar in amount and 1n a few. specu~ens from low, it appea ~s impossible to say whether the 

the dump it formed needles 1 cent1me~er. or chalcocite was deposited by ascending or by 

.less in length. It is the white fibrous ~1neral descending solutions. · The writer is much 

so characteristic of· certain hand speCimens. inclined to the latter and in ore usual origin. 

Titanite, usually . showing · crystal outlines, · The richest· pre that has been produced at 

garnet crystals of irregular outline, and sm~ll this mine was t'aken from a large chamber stope 

.zircons are accessory minerals.. Small amounts about· 120 feet .from tho mouth of the tunnel. 

of calcite are present locally. In soJ:p.e speci- · ·· .. · .. · _ 1 • d t 1 Rogers, A. F., Secondary sulphide enrichment of copper ores with 

mens the calcite is plainly an w~erat10n pro UC special reference to microscopic study: Min. and Sci. Press, vol. 109, 

of wollastonite, being pseudomorphous after p. 686,1914. 
128 GEOLOGY OF GILPIN,. CLEAR CREEK, AND BOULDER COUNTIES, COLO. 

The stope is near the surface, and the geologic RELATIONS OF ORE-BEARING DIXES TO NEIGH;. 

BORING MONZONITE STOCK. relations are much obscured by oxidation, but 

two distinct dikes are recognizable. Much of The mineralogy of the porphyry stock near 

the ore from this stope is a breccia of angular the Evergreen mine shows beyond reasonable 

fragments of gray quartz in a matrix of dike doubt that the dikes at this mine are related 

rock. To the unaided eye the sulphides, which to it. The rock as exposed 1 mile southeast 

are abundant, appeared to be confined to the of the mine is a monzonite which, like the dike 

matrix. Under the microscope this matrix rock, is characterized by predominant orthoshows no important. differences from the ordi- clase in perthitic intergrowth with albite and 

nary dike rock of other parts of the mine. The, by abundant grass-green augite. It differs 

quartz of the fragments interlocks at its borders from the dike rock in the absence of quartz, 

with the minerals of the rriatrix, indicating garnet, wollastonite, and copper sulphides and 

some recrystallization and welding at the time in the presence of abundant magnetite. In 

of the intrusion, but matrix and quartz frag- other phases quartz is fairly abundant. Porments are very distinct when viewed in the phyry occurring on the hill northwest of. the 

hand specimen. In the slide the matrix is seen Evergreen mine and probably a continuation 

to send off small branches or stringers of bornite of the Evergreen dikes is similar in every way 

and feldspar into minute cracks which traverse to the dike rock of the mine except for the 

a single quartz crystal or penetrate between two absence of sulphides, garnet, and wollastonite. 

crystals of the fragments. The origin of the 

quartz that forms the fragments of this brec- ORIGIN OF THE ORE. 

cia is uncertain, but it probably represents a The origin of the copper sulphides, which are 

quartzose phase of the pegmatite which is so the valuable minerals at this mine, is somewhat 

. abundantly associated with the schists. of t.he uncertain. They ynquestionably crystallized 

Idaho Springs formation. That the large quartz contemporaneously with the other minerals of 

masses do not represent coarse crystallizations the dikes, and the dikes are without doubt 

of quartz within the dike rock is apparent from offshoots from the large neighboring monzonite 

their commonly angular character, from the stock. Several hypotheses of origin niay be 

absence of comparably coarse crystallizations stated: 

of the other dike minerals, ·and from the great 1. The sulphide-bearing dike rocks may have 

contrast in size (several inches as compared been formed solely through magmatic differenwith 1 millimeter or so) between the 'large tiation from the monzonite mass. 

quartz. masses and the quartz of the matrix. 2. Sulphides and the materials necessary to 

Ritter 1 called the dike rock evergreenite. form the minerals wollastonite and' garnet, 

The long prisms of a colorless mineral were which are characteristic of the dikes, may have 

identified by him as enstatite or diallage. Their been absorbed from the immediate wall rocks. 

optical properties, however, show unquestion- This view is made hardly tenable by the sharp 

ably that they are wollastonite. ·These proper- contacts between dike and wall rock, even 

ties may be summarized as follows: Inclined where the latter is much brecciated, and the 

extinction; ind~x of refraction notably greater absence of variation in the composition of the 

than that of quartz; double refraction low for dike toward the walls. · 

sections parallel to the prism and high for sec- 3. The sulphides and materials necessary to 

. tions across the prism axis; cleavage parallel form the wollastonite and ·garnet that are 

to prism, intersecting at nearly right angles; especially characteristic of the dikes as disbiaxial; optically negative; plane of the optic tinct from the typical monzonite may have 

axes perpendicular to prism axis. The occur- been absorbed by relatively deep-lying porrence of garnet in association with the sulphides tions of the monzonite magma from wall rocks 

is not mentioned by Ritter. Covellite is de- . or veins with which it came into contact. The 

scribed by him as an alteration product· of magm~ thus modified in composition moved 

bornite in a few speqimens, into fissures I in the wall rocks and there crys1 Op. cit., p. 751. tallized as dikes. By the time it had reached 
TUNGSTEN, COPPER, AND IRON ORES. 129 

its present position it was so cooled and formed 

masses relatively so narrow that its ab~orption 

of the wall rock was slight. · 

4. The ore-bearing dikes may represent the 

combined effect of n1agmatic differentiation 

and digestion of wall rock. 

In the opinion of the writer the abundance of 

garnet and wollastonite, minerals particularly 

characteristic of contact metamorphism, in the 

dikes is strongly suggestive of digestion of calcareous wall rock, wollastonite in particular 

never having been described as occurring so 

abundantly in rocks of purely magmatic origin. 

Such digestion of material probably took place 

before the rock reached its present position, as 

suggested under hypothesis No. 3. The sulphides may have been derived either from the 

wall rocks through absorption or from' the 

magma by magmatic differentiation. The deposit under this view represents an endomorphic e·ffect produced by contact metamorphism 

at the bo:rder of a large intrusion of monzonito. 

LATER FRACTURING AND MINERALIZATION. 

Subsequent to the intrusion of the ore-bearing dikes the rocks of this vicinity were broken 

by numerous fractures and faults. These in..: 

crease the difficulties of mining by displacing 

the ore-bearing dikes and forming water channels. They are not in general mineralized, 

though some are quartz-filled and bordered by 

narrow leached zones. At one place narrow 

seams of calcite and quartz cut both dike and 

schist. One fracture plane traversing ·the 

schists in the tunnel showed about an inch of 

·quartz and c~lcite with a little chalcopyrite. 

On the dumps a number of fragments were 

found which showed narrow veins as much as a 

quarter of an inch wide composed almost 

· wholly of chalcopyrite,. traversing the schist. 

In one specimen such a veinlet of chalcopyrite 

cut sharply through typical dike rock bearing 

chalcopyrite and bornite' and inclosing schist 

fragments. Other fragmen.ts from the dump 

are fine-grained aggregates of quartz, calcite, 

chalcopyrite, specularite, pyrite, and sphalerite. 

(in part resinous), with a little g.alena and bornite. Some of the specularite blades penetrate 

calcite crystals, and a few are half an inch 

across. The mineralization recorded by some 

and probably by all of these occurrences is primary .and of the vein type andis later than the 

44214°-17-9 

intrusion of the or~-bearing dikes. Economi9-

.ally it appears to be unimportant. No evidences of downward sulphide enrichment were 

noted, although, as already stated, the upper 

or 60-foot level w=as not accessible. 

TITANIFEROUS IRON ORES. 

Several deposits of titaniferous iron ore 

occur on the northeast and south slopes of 

Caribou Hill, in the northern part of the Central City quadrangle. The iron ore forms 

irregul~r bodies within masses ·of gabbro and 

pyroxenite, which in turn are within ,a large 

stock of monionite. The gabbros and pyi-oxeni tes and the ores are believed to have been 

formed by a process of differentiation within 

the monzonite magma, as has already been 

discussed· in detail on pages 42-49. Even 

before 1880 the ores had, according to Putnam,t 

attracted the ,attention of miners, and sample 

shipments had been hauled· to the smelter at 

Boulder. Putnam also state~: · 

All the ore is very magnetic and exhibits polarity to so 

marked a degree that the dip of the needle changes from 

+90° (north end down) to -50° (south end down) in the 

distance of 10 paces. There is undoubtedly a large amount 

of iron ore in the hill, but it is probable that the rich ore 

is too irregularly distributed through the rocks to permit 

of its being economically mined. 

Recently the deposit has been studied in 

detail by Jennings,·2 and his analysis of the ore 

with two analyses of the associated rocks are 

quo~ed in the table on page 43. The more 

extended studies of the present writer show 

the presence of olivine-rich iron ores and 

olivine monzonites not described by Jennings. 

In regard to the utility and orig~n of the 

ores Jennings says: "These interesting deposits have little or no economic importance 

but are excellent examples of iron ores of 

igneous origin.'' 

The locality has recently been studied also 

by Singewald,3 and· the following excerpts are 

quoted from his report: 

On Caribou Hill are several intrusions of basic material, 

and it is within these that the ore occurs. The most important one is the dike on the northeast slope of the hill, which 

can be traced for over 1,500 feet. It begins at a point 500 

·yards west of Caribou and runs up the hill slope in a south1 Putnam, B. T., Tenth census, vol. 15, p. 476, 1886. 

2 Jennings, E. P., A titaniferous iron-ore deposit in Boulder County, 

Colo.: Am. Inst. Min. Eng. Trans., vol. 44, pp. 14-25, 1913. Illustrated 

by microphotographs of ores and rocks. 

a Singewald, J. T., jr., The titaniferous iron ores in the United States: , 

U. S. Bur. Mines Bull. 64, pp. 126-128, 1913. 
130 GEOLOGY OF 9-ILPIN, CLEAR. CHEEK, AND BOULDER COUNTI~S, COLO. 

easterly direction for about 400 feet, where it bends sharply 

to the east and coutinues for about 1,000 feet to the edge 

of Caribou. A second intrusion, having more of a stock 

shape, 'occurs on the southeast slope of the hill, half a mile 

southwest of Caribou. A third smaller outcrop occurs 

near the top of the hill about 100 yards southeast of the 

summit. These rocks show considerable local variations 

but are essentially py:roxenitic in character. Associated 

with the pyroxene in places is feldspar and.biotite. The 

texture ranges from that of a coa:r:se py:r:oxenite to a very 

fine grained rock. _ 

Some magnetite occurs as an accessory constituent of 

the basic rocks, and this becomes segregated into richer 

pockets, forming a.medium grade ore. But even in the 

ore-bearing parts of the rock the composition i.s not uniform. It is rather a rock rich in {nagnetite, with numerous 

stringers and veinlets of almost pure magnetite. The 

magnetite is highly magnetic· ~nd. much of it is natural 

lodestone. These stringers of pure ore never exceed 6 

inches in thickness and seldom measure more than an 

inch or two They may form such a network within the 

leaner rock as to constitute a medium-grade ore. Such 

ore bodies do not reach a width of more than a foot or two 

or a length of more than a few feet. The ore in the pits 

and trenches that have been made along the western. end 

of the dike northwest of Caribou consists of a series of 

closely crowded lenses of that character. The dike has a 

width of 50 to 100 feet or over, but only a small part consists of ore of even this grade. The ore in the other two 

occurrences is still leaner and there is still less of it. Thin 

sections of the ore show that it CC?nsists essentially of the 

ore minerals ·and pyroxene, the latter ranging in composition from cliopsicle to augite. Tl;le pyroxene is . frequently altered to serpentine and in part to hornblende. 

Some biotite is also usually present. Inclusions of clarkgreen spinel in the magnetite are common. * * * 

A metallograph.ic study of the ore show!" little of interest. 

The richer veinlets consist of medium-grained aggregates 

of magnetite and ilmenite with a little gangue. The 

ilmenite is far less abundant than the magnetite and occurs 

in smaller grains, in many places as small particles filling 

interstices between the magnetite and the gangue grains. 

The leaner ore, which grades over into the country i·ock, 

contains scat~ered grains of magnetite and ilmenite, with 

the femic minerals in excess. 

Intergrowths of ilmenite in the· magnetite are not 

abundant .. Most frequently they consist of clots and small· 

particles scattered irregularly through the magnetite. 

Regular intergrowths of tabular ilmenite in the magnetite 

are not J;l.Umerous .. * * * The best of.the ore is only 

medium graCle and the ore lenses are very small. On 

accou~t of its small size the deposit can never have any 

economic value. ·· 

To these descriptions the present writer has 

little to add that is of economic significance. 

According to his field studies the iron-ore 

occurrences in and north of Caribou form two 

closely adjacent bodies rather than a single one 

and are not dikelike in forn1. The deposit 

half a mile south of Caribou also consists of two 

irregular bodies. All these features are brought 

out on the map (Pl. I). The deposit n~ar the 

summit of Caribou Hill is too small to appe~r 

on a map of this scale. 

As is well known no iron ores containing 

notable amounts of titanium are at present 

used in the iron industry, though experiments 

looking toward their utilization are now in 

progress. The presence of titanium is not injurious in steels used for certain purposes; in 

fact, titanium is the material most widely used 

to give steel certain desired properties. Its detrimental 'effect in an iron ore is due to the fact 

that it produces a refractory slag that is difficult 

to handle in the blast furnace, and 0.5 per cent 

seems to be almost as detrimental as 10 or 15 

per cent. The percentages of magnetite and 

titanic oxide in samples of the Caribou ore 

analyzed by Jennings and by this Survey a.re 

as follows: 

--~---...,..------ ---------

Magnetite (Fes04)...................... 64. i3 Titanic oxide ('l'i02) ....... '............. 4. 48 

30.55 

2.69 

1, E. P. Jennings, ~alyst; 2, 3, lean ore, George Steiger,·analyst. 

The ·high titanium content ·reported by 

Chauvenet 1 (36 per cent of titanic acid, with 

36 to 38 per cent ·of iron) is probably exceptional or in error. 

Ev(:m if the .metallurgic difficulties involved 

in the high titanium content can be overcon1e, 

the inaccessibility and small size of these de- · 

posits preclude all possibility of successful 

exploitation. 

t Chauvenet, Regis, Preliminary notes on the iron resources of Colorado: 

Colorado School of M:ines Bienn. Rept., .for 1886, p. 16, 1888. 
CHAPTER X.-GENESIS OF THE PRIMARY ORES~ 

PURPOSE O.F THE DISCUSSION. 

the genesis of the ores has · already been 

touched upon at several points in the descriptions of the several ore classes. It is · the 

writer's desire in this chapter to place each· of 

the ore classes in its proper genetic position\v:lth 

respect to the others and to eniphasize certain 

features in the nrineralizatioh of this region that 

are of particular genetic significance.:·. 

RELATION BETWEEN MINERALIZATION AND 

VOLCANISM. 

The nrineralized portions of the Central City 

quadrangle, as has been shown on pages 93..,...94, 

form part of a large nrineralized belt that includes nearly all the in:lportant· nuning ca1nps 

of Colorado. Within this belt the ores exhibit 

great variations in mineral con1position and in 

, 1node of OCCUrrence, their only unifying fetllture 

being their invariable areal association with 

intrusive igneous rocks of probable Tertiary 

age, the ."porphyries'' of the 1niners; (See 

fig. 4.) Beyond the areas containing "·poi!-

phyry" intrusions the: ore deposits also .disappear. This association, suggestive . as it 

might be, would certaicly not be a sufficient 

basis for concluding .·that the ores .and the 

"porphyries" are genetically related were it 

not for the fact that a similar. intin1ate association of ores and igneous rocks has been noted 

in practically every r~gion where lode deposits 

of gold. and silver ores have been studied 

geologically. Further., it is . probable from 

geolo.gic observations in this quadrangle that 

the nrineral veins were formed late in the period 

, of "porphyry" intrusions; the veins are 

younger than the bulk of the." porphyry" but 

older than a few. scattered "porphyry" dikes. 

It is known also that the titaniferous.iron.ores 

are strictly of igneous origin, having been 

forn1ed by 1nag1natic . differentiation: within a 

monzonite stock. It is confi.demtly believed, 

therefore, .that a .genetic connection exists 

between the mineral veins· of this region and 

the Tertiary ( ~) intrusive rocks. 

The precise natur~ of tlus gen~tic connection is largely a n1·atter ?f infereh9e. on the basis '•' : ....... 

of well-established principles of ore deposition 

rather than of direct. ob~er.vat~on. It is not 

practicable to expound here many of the 

fundan1ental · principles th~t ar!3 .involved; to 

students of the science ·of ore deposits they are 

a~.ready farinliar and they have been admirably 

set _forth by Lindgren/ ·to whose .book the lay 

re!}.der is referre<;l .... The recognized principles 

of ore depos~~ion will therefore not be discussed 

in detail,. althougl~ speqific evidence of genesis 

afforded by .. this distr~ct will be pr!3sen~ed .. 

AGENT OF ORE DEPOSITION. 

,With th~. e~qeption of the Caribou iron ores· 

a11:d , ~he cq.pper. ores of the Ev~rgreen rine, 

w~hic~.:~r~. integral parts of the Tert~ary_ ( ~). 

i~trlfs~~es, ·.an the ore depo~its of t~H~. Central 

Ci~y ,q\Hl:drangle are believed to __ ·have been 

dep,o~~ted by thern1~ solutions. th&.t ~scape4 

fr.orp. ~)le "porphyry" 1nagmas proJ:>al?ly during 

t4e~r. crystallization. The "porpl).yries." now, 

·exposed ·at the surface 1nay have: given off 

s9lutions which deposited <?res ·a.t hig~er ~orizo,ns in the portions of the crust now rmnoved 

by erosion, ·but the existing .vein~ and sto.ck: 

works were deposited by solutions mnanating 

far below the present surface. This is shown 

by tp.e fact that the ore deposits, with a fe'~ 

nril).or exceptions, cut. ~he "porphyries" now 

exposed... There a.ppears to. be no basis for the 

belief locally current that· tl{e occurrence of a~ 

ore deposit in or within a short distan:ce ·of 

"porphyry" is a favorabl~ indicatio~; the 

r~lations between ores and ''porphyries'' are 

of a much larg~r and n1or~ generalized order 

tha~ that in~plied in any such concept. 

REGIONAL'VARIATIONS IN MINERALIZING 

SOLUTIONS. 

~he~e {~ ample ·evidence, as explained later, 

of progressive changes in the character of 

the ore-depositing solutions' during the general 

1nineralizing period. In addition there is • • ) I 

evidence . that even solutions which were· 

strictly contemporaneous were of different 

character in different parts of the district. 

. i Lindgren, Walde~.~r, Mineral deposits, 1913. 

131 
132 GEOLOGY OF GILPIN, CLEAR CREEK, AND BOULDER COUNTIES, COLO. 

The ores of the· pyritic type appear to have Although no conclusive proofs have been 

formed for the most part contemporaneously obtained, it has been the opinion of mo~t 

in the earlier part of the mineralizing period, geologists who have studied the tungsten 

yet among these there are several subtypes deposits that they are closely related to the 

showing mineralogic peculiarities and confined gold-silver deposits and probably of nearly the 

to small areas. Such are the group of enargite- same age. This opinion has been expressed by 

bearing veins, all of which lie within a radius of Lindgren 3 and by Hess.4 · Hess says: 

three-quarters of a mile of the Hazeltine mine, Although the data at hand are not very extensive, it 

in South Willis Gulch.· (Seep. 105.) Many of seems probable that the connection between the three 

the pyritic veins .of that vicinity also carry classes of veins [sulphide, telluride, and tungsten veins] 

fluorite, a mineral rarely noted elsewhere in may be fairly close and that there may not be a great 

veins of this type. The presence of pitch- difference in the ages of the several types. 

b~ende (uraninite) in a group of veins on George and Crawford 5 have given no very 

Quartz H~ appears to be another case in poi~t. definite opinion, but from the following ·stateThe. study of polished specimens of these ores ment it. appears that they also believe that 

indioates that the urap.inite crystallized con- the tungsten deposits are in some way contemporaneously with a . suite of mrnerals nected with the gold-silver veins in origin. 

identical with those characteristic of the They say: . 

pyritic gold-silver ores and tp.at it is cut by While the gold and silver deposits and the tungsten 

veinlets mineralogically similar to the galena- deposits are not intimately associated, the two seem to 

sphalerite gold-silver ores. The evidence of. conform roughly to the trend of the belt of intruded 

porphyrie(:l which extends from the middle of Boulder 

these relations is set forth at length on pages County in. a southwesterly direction into Gilpin, Clear 

121-125. The uranium ores are therefore be- Creek, Summit, and Lake counties. Tungsten is known 

lieved to be merely a local and unusual variety within this belt in Boulder, Gilpin., and Clear Creek. 

of the gold-silver ores and, like them, probably counties. 

of Tertiary age. Analogous variations occur in Three features of the occurrence of these 

veins of the galena-sphalerite type-for ex- ores appear to the writer to have an important 

ample, the occurrence of rhodochrosite in a bearing on their origin and their relation to 

few veins on Seaton Mountain and near the other classes of ores. (1) In the region where 

head of Gilson Gulch. Such variations can not they are most abundant they almost wholly 

be satisfactorily ~xplained by differences in the supplant other types of ores.· (2) They occur 

nature of the wall rocks or in any other external in the only part of the C'entral City quadrangle 

conditions and must be attributed to local in which Tertia;ry ( ~) dikes of intermediate and 

peculiarities in the composition of the solu- mafic (basic) composition are abundant and 

tion~ that rose through fissures and deposited adjacent to the only monzonite stock which 

the ores. exhibits extreme mafic differentiation (the 

The tungsten ores of the quadrangle, though Caribou stock with its iron ores). (3) The 

not studied in detail by the writer, appear tungsten district lies between an area of 

from all available geologic evidence to present productive gold-silver veins on the west and a 

an example of regional variation of a different region barren of valuable mineral deposits on 

sort and on a somewhat larger scale. These the east. These facts and the mineral associadeposits form the subject of a. special report tions already cited are in harmony with the 

by George and Crawford.1 According to these view provisionally adopted. by the present 

writers,2 minerals characteristic of the gold- writer ·that the tungsten ores represent an 

silver deposits are· exceedingly rare in the unusual phase of the Tertiary ( ~) mineralitungsten veins. Small amounts of pyrite, zation of the region and are possibly connected 

chalcopyrite, galena, sphalerite, and sylvanite in some way with the pronounced mafic 

have, however, been noted in some of the veins, (basic) differentiation exhibited by the monzoand in places their relations suggest con- nite magmas of ~his vicinity. 

temporaneity ·with the tungsten minerals. 

1 George, R. D., and Crawford, R. D., The main tungsten area of 

Boulder County, Colo.: Colorado Geol. Survey First Rept., pp. 7-103,1909. 

2 Idem, pp. 75-76. 

3 Lindgren, Waldemar, Some gold and tungsten deposits of Boulder 

County, Colo.: Econ. Geology, vol. 2, p. 462, 1907. 4 Hess, F. L., and Schaller, W. T., Colorado ferberite and the wolframite 

series: U. S. Geol. Survey Bull. 583, p. 10, 19~.4. 

6 George, R. D., and Crawford, R. D., op. cit., p. 85. 
GENESIS OF THE PRIMARY ORES. 

DIFFERENCES IN COMPOSITION OF ORE- erosion in a large number of mining districts. 

FORMING SOLUTIONS IN DIFFERENT PAllTS Only meager laboratory data are yet available, 

OF MINERALIZING PERIOD. but through the application of one or both of 

The two distinct types of sulphide ores of the other criteria it is generally possible to 

gold and silver recognizable in this region have determine whether the ores were formed u:nder 

been termed the. pyritic t)rpe and the galena- conditions of great, moderate, or slight intensphalerite type, and it has been shown by a sity as regards temperature or pressure or botl'l;, 

large number of observations that where ores even though· it may not be possible to express· 

of the two types occur together the galena- these conditions accurately in the dynamic 

spha~erite ores are the later. The interval units of degr~es of temperature or pounds per 

between the deposition of one type and. that of square inch of pressure. 

the other was sufficient for the fracturing of The application of the first of these criteria 

the pyritic ores by renewed movement along to the deposits of this region is attended by 

some of the veins and for the development of many uncertainties. The intrusive "porphysome new fractures. It ;may not everywhere ries" are believed to be of Tertiary age; i.nashave been of the same duration, but probably n1uch as effusive rocks that may reasonably 

in geologic terms it was short and is to be be regarded as their equivalent first appear on 

interpreted as an episode in a single gene},'al the· flanks of the range in the Dawson arkose, 

ore-forming period rather than as a notable of Tertiary age, and there are other reasons, 

interval between two distinct periods. Cer- set forth on page 39, for regarding then1 as 

tainly the ores of both types were deposited Ter~iary. Ball recognized in the Georgetown 

·under similar general conditions of depth and quadrangle small masses of sandstone ~hat 

temperature, followed the same or parallel ·he regarded as probable remnants of the Founlines of fracturing,' and appear to have broadly tain formation (Pennsylv~nian) of the foothills. 

the same geographic distribution. Moreover, 'If these correlations, the latter admittedly unaccording to J.D. Irving/ at Leadville, within certain, are accepted, it is quite probable that 

the same great metaUogenetic province, where the entire series of sediments, from the Founores similar to the pyritic and galena-sphalerite tain to the Laramie formation, inclusive, now 

ores of this region are also present, although the upturned along t'l?.e east flank of the range, 

pyritic portions of the ~res were in general the covered the Georgetown and Central City 

first to be deposited, there is no evidence of an quadrangles not long before the intrusion of 

interval between therri and the po;rtions of the the Tertiary 0) "porphyries." The thickness 

ores rich in galena and sphalerite. Evidence of th~se sediments between Boulder and Castle 

of such an interval would presumably b~ less Rock has been variously estimated at 8,000 to 

readily recognizable in replacement ores like 10,000 feet. 1 To this, in estimating the· depth 

those of Leadville than in ores that are fissure of,formation of the ore deposits, must be added 

fillings, or it may be that the mineralization an unia:own amount for the thickness of the 

which progressed pulsatingly in Gilpin County pre-Cambrian rocks that have since been 

progressed more uniformly at Leadville. eroded, and it may be, another amount for the 1 

• thickness of possible effusive phases of the 

TEMPERATURE AND PRESSURE OF ORE FORMATION. ·"porphyries." The possibility of erosion on 

a considerable scale during the interval between 

the deposition of the Pennsylvanian F9ru:itain 

formation and the Tertiary ( ~) volcanism can 

not.be excluded, but the scarcity of coarse sediments in the formation representing this time 

interval along the flank of the range points 

rather to fairly continuous sedimentation. 

For his concept of the temperature and pressure under which ore deposits were forrr1ed the 

geologist is dependent' upon (1) physiographic 

and stratigraphic evidences of the extent of 

erosion subsequent to mineralization; (2) direct 

laboratory data in regard to the range of 

stability of various ore minerals; and (3) 

indirect knowledge of the ·conditions under 

which certain ore minerals are stable, derived 

fr01n estimates of the amount of post-~ineral 

I Oral COfllmunication. 

Geologic observations within the Central 

City quadrangle show that the gold-silver ores 

I Richardson, G. B., U. S. Geol. Survey Geol. Atlas, Castle Rock 

folio (No. 198), 1916. Martin, G. C., The Niobrara limestone of northern 

Colorado as a possibl~ source of Portland cement: U. S. Geol. Survey 

Bull. 380, pp. 314-318, 1909. 
134 GEOLOGY OF GILPIN, CLEAR CREEK, AND BOULDER COUNTIES, COLO. 

extend without notable changes in character 

. from an elevation of about 7,500 feet near the 

mouth of the Argo tlinnel to an elevation of 

about 11,000 feet near Alice, a range of 3,500 

feet. A part of this difference is probably the 

result of differential uplift since the ores were 

formed, but individual lodes have been followed 

·in n1in.ing to depths of more than 2,500 feet 

without revealing changes indicative of markedly different conditions of formation. 

The s01newhat uncertain evidence available 

therefore points to the formation of the ore 

deposits of this region at depths between 7,000 

and 11,000 feet. At a depth of 9,840 feet 

(3,000 meters) the hydrostatic .pressure would 

be about 300 atmospheres and the rock pressure .about 810 atmospheres. Under the normal increment of temperature with increasing 

depth a temperature of 100° C. should be 

reached at a depth of about 9,000 feet, but in a 

region like that under discussion, owing to the 

presence of Tertiary ( ~) intrusive rocks, the 

temperature would presumably increase more 

rapidly. More probably it lay between 150° 

and 300° C. 

Laboratory observations on the range of 

stability of minerals offer no data applicable 

to the ores of this region, but the mineral character of the ores,. interpreted in the light of 

what is known of' conditions of ore deposition 

elsewhere, is of much significance. The mineral 

composition of the ores has been summarized 

in tabular form on page 100, and this table 

brings out clearly the fact that all the ores 

.listed as deposits from ascending thermal 

waters are lacking in mmerals indicative of 

very high temperature, high pressure, or both, 

or of low te1nperature and shallow condition. 

The absence of silicates, except feldspar and 

sericite, is noteworthy. Oxides; except silica, 

are not pr~sent as primary minerals. Pyrrhotite, a sulphide characteristic qf intense conditions; is absent. Chalcedony, a mineral occurring usually ~n deposits of shallow origin though 

locally in those formed under conditions of 

moderate intensity, is present only in small 

amounts in a few· telluride veins. Realgar, 

orpiment, stibnite, and many other minerals 

characteristic of deposits formed ~t slight 

depths are absent. On the other hand, tennantite and enargite, which find their principal 

habitat in deposits forn1ed under n1oderately 

intense conditions, are fairly abundant in certain of the deposits of this region. The nlineralogic as well as the physiographic and stratigraphic evidence therefore points to the fornlation of the gold-:-silver ores, the pitchblende ores, 

and probably also the tungsten ores under conditions of moderate intensity. 

COMPOSITIO~ OF MINERALIZING SOLUTIONS. 

The . composition of the solutions that 

deposited the gold-silver ores and the pitchblende ores of the Central City quadrangle 

may be inferred in a qualitative·way fron1 the 

n1ineralogy of the ores and the alterations 

produced in the wall rocks by the oreforming solutions. As the thermal-spring 

waters of Idaho Springs and the gaseous 

emanations in certain mines are regarded 

as the· last phases in the activity of the oredepositing solutions, their composition should 

also be taken into account. On theoretical 

grounds the solutions are believed to have 

been aqueous and heated, their temperature 

probably not exceeding 350° C. 

The following list shows the components 

present and calls attention to certain substances whose absence is note\vorth)r. 

Alumina (Al20 3), not abundant; presence indicated by 

rare occurrences of feldspar in fissure fillings. 

Antimony (Sb), not nearly so abundant as arsenic. 

Arsenic (As), moderately abundant. 

Barium (Ba), locally fairlfabundant, as shown by occurrence of barite in many veins and recent deposition of 

barite from hot springs at Idaho Springs. 

Bicarbonic acid (HC03), abundant in thermal waters 

at Idaho Springs. · 

Bismuth (Bi), rare. 

Boron (B), only in minute amounts in thermal waters 

at Idaho Springs. 

Bromine (Br), not definitely known. 

Calcium (Ca), abundant. 

Carbon dioxide (C02), abundant as shown by carbonates 

i1r veins and al·tered walls and C02 emanations in some 

mines. 

Chlorine (Cl), not abundant; small amounts in thermal 

waters at Idaho Springs. 

Copper (Cu), moderately abundant. 

Fluorine (F), abundant locally. 

Gold (Au), universally present in small amounts. 

Iodine (I), not definitely known. 

Iron (Fe), abundan~. 

Lead (Pb), abundant. 

Lithium (Li), rare; traces in thermal waters at Idaho 

Springs. . • 

Magnesi~m (.Mg), not abundant; small amounts in 

thermal waters at Idah9 Springs. 
GENESIS OF THE PRIMARY ORES. 135 

Manganese (Mn), locally abundant (rhodochrosite). 

Mercury (Hg),' absent. 

Molybdenum (Mo), rare. 

Nickel (Ni), rare~ small amounts in matte from smelters. 

Phosphorus (P), not noted. 

Potassium (K), abundant. 

Radium (Ra), locally present as shown by pitchblende. 

Silica (Si02), abund'ant. 

Silver (Ag), universally present in small amounts. 

Sodium (Na), abundant in thermal waters at Idaho 

Spl'in.gs. 

Strontium (Sr), traces in thermal waters at Idaho 

Springs. 

Sulphate radicle (SO~), present in small amounts as 

shown by local btu·ite. 

Sulphtu· (S), abundant. 

Tellurium (Te), present locally in fair abundance. 

Tungsten (W), locally abundant·. 

Uranium (U), locally present in minor amounts. 

Vanadium (V), locally present in minute amounts. 

Zinc (Zh), abundant. · 

To summarize, it appears· that the solutions which deposited the ores were alkaline 

or neutral in character and that they ·were 

rich in alkalies, silica, carbonic, and bicarbonic acids, iron, lead, zinc, and arsenic and 

carried lesser amoull.ts of copper, antimony, 

gold, and silver. Locally they carried manganese, the sulphate radicle, barium, tellurium, 

fluorine, uranium, and vanadium. 

' ~ ~ . • t . 
CHAPTER XL-PROCESSES AFFECTING THE ORES SUBSEQUENT TO PRIMARY 

. MINERALIZATION. 

POSTMINERAL FAULTING AND FRACTURING. 

Subsequent to the primary mineralization 

faulting occurred in many parts of the region. 

Many of the fault fractures followed veins for 

a part or all of their length and produced local 

brecciation· of the ores. Other faults cut across' 

and displaced mineral veins, but the displacements as a rule do not exceed a few feet or tens 

of feet. Examples of postmineral brecciation 

were noted on the western part of the California 

vein, in the Ivanhoe vein (Pl. XIV, B, p. 97), 

· ~n the Homes take vein of the East N qtaway 

- ·!lline; and at many other places. An example 

of vein displacement by a postmineral fault 

making a small angle with the vein is the off:;;et 

of the Frontenac vein ·by the barren "flat 

vein"; in this case the continuation of the 

vein beyond the fault had not at the time of 

this survey been found. The Chase vein is 

displaced by a cross fault that is well exposed 

on the 300-foot level about 520 feet east of the 

shaft. 

By facilitating the desc·ent of meteoric waters 

along the veins postmineral fracturing has had 

an important influence oil downward enrichment. 

POSTMINERAL DEPOSITION OF QUARTZ AND 

CARBONATE. 

Postmineral . fracturing has been followed 

in certain places by the deposition .of white 

or . gray quartz, much of which is very fine 

grained and of cherty appearance, though 

microscopic examination shows it to be crystalline. This quartz does not appear to be confined to the portions of the ore deposits near 

the surface or.to be particularly more abundant 

there than at greater depths.· It seems 

probable, therefore, that the quar~z is a dep.osit 

from ascending, probably thermal, waters 

rather than descending waters. So far as 

known it carries no valuable metals, although it 

is very similar in appearance to the finegrained quartz of certain telluride veins such 

as the Notaway. The postmineral quartz is 

nowhere abundant; it wa3 ·noted more fre136 

quently in the region just southea.st of Central 

City than elsewhere. In the composite ore of 

the Specie Payment mine, on Bellevue Mountain, gray quartz' is clearly later than both 

pfi}riods of sulphide mineralization. 

In the Hayseed -mine, in Chase Gulch, 

coatings composed of an association of siderite 

and small ·needles of quartz occur on the 

galena, chalcopyrite, and pyrite of some vugs. 

Some of the siderite is contemporaneous with 

and some .Later than the qu;;trtz. These nlinerals appear to have been deposited at a distinctly later period than the sulphides, for they 

coat their free crystal faces, and, as explained 

in the next section, their deposition seems to 

have been synchronous with etching of the 

galena.· In the Pettibone mine, on Silver 

Creek, ore of the galena-sphalerite type has 

been brecciated, and the fractures and vugs have 

been partly or wholly filled with quartz and 

some siderite. The central portion of the later 

veinlets is in general coarsely crystalline quartz, 

and the one-eighth of an inch or so next to the 

walls consists of cherty-looking silica or of 

siderite. Thin layers of white quartz coat the 

sulphides in vugs. 

ETCHING OF PRIMARY MINERALS. 

Etching of the primary ore·minerals below the 

ground-water level is nowhere conspicuous. 

In one mine-the Hayseed, in. Chase Gulch-it 

has locally produced somewhat striking effects, 

which are shown in Plate XVII, A. In the 

Hayseed vein vugs are of rather common occurrence, and some are several inches long in the 

_plane of the vein and contain very beautiful 

crystals of sulphides and of quartz. In some 

of. these vugs the solvent action of solutions 

circulating through the ore is shown by conspicuous etching of the galena, as shown in 

Plate XVII, A. It is significant to note that 

the pyrite and chalcopyrite associated with the 

galena have not been etched and that the quartz 

and siderite referred to in the preceding paragraph as deposited on crystals of galena, pyrite, and chalcopyrite do not occur on the 
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 94 PLATE XVII 

A. ETCHED CRYSTALS OF GALENA FROM VUG IN HAYSEED VEIN, NEAR CENTRAL CITY. 

Crystals were coated with film of ammonium chloride to avoid reflections in photograph ing. 

B. CARIBOU, LOOKING WEST FROM BOULDER COUNTY HILL. 

.. 
PROCESSES AFFECTING THE ORES. 137 

etched sw·faces. If the quartz and siderite represent a residuum from tens, then hundreds, 

had once coated all parts of the'galena crystals and perhaps thousands of feet of ore that has 

and had been dissolved by- the solutions that been erpded away. To use a commercial 

etched the galen~, it is difficult to see why the simile, the value of the ore in the upper part 

quartz and siderite shoul~ have remained on of a deposit may thus increase "at compound 

other parts of the galena crystals in so great ·interest." Such a process is termed downward 

abundance and in perfect crystals that show enrichment, the adjective being used to .disno signs of solvent action. It must be con- tinguish it from enrichment caused by ascendeluded, therefore, that the same solution that ing thermal solutions. 

deposited the quartz and siderite was instrumental in etching the galena, the two processes 

RELATION TO GROUND-WATER LEVEL .. 

being synchronous .. Waters depositing quartz In general the openings in rocks reach a 

and siderite must haye been alkaline or at least maximum at the surface and gradually deneutral. It is interesting to note that C. E. crease downward, and the water-holding caS:iebenthal, 1 from his study of the lead and pacity of rocks, being dependent on the space 

zinc ores of the Joplin distric~, in Missouri, con- available in openings, exhibits a corresponding 

eludes that slightly alkaline or neutral solu- decrease with increasing depth. There is 

t:ions have been active solvents of galena. The 'reason to believe that at depths of a few · 

writer believes that the n,ctive solutions which thousand feet the openings in most rocks are 

produced these effects were ascending, proba- so small and discontinuous that the rocks are 

bly thermal, and came from the same general essentially dry. 2 Between the dry rocks and 

source fl:S the solutions which deposited the the surface the rock openings are in some 

ore, though they were given off later and had places entirely filled with water; but in most 

a different cornpos:ition. places the water filling extends only within 

DOWNWARD ENRICHMENT. 

GENERAL F~ATURES. 

It is well known· that when the superficial 

parts of ore deposits are attacked by the gases 

of the atmosphere and by water of surface 

origin and the dissolved substances it contains, 

smne of the ore is carried away either mechanically or in solution and some remains behind. 

The metals carried away may become widely 

scattered and lost, so far as concerns the miner 

of to-day, or they may be concentrated elsewhere in ore deposits of different types, such 

as the gold-bearing gravels . of the district 

here described or the copper ores found in 

surface sandstones in other districts. The 

metals that remain behind work their way 

downward into the ore body either mechanically or in solution; those carried mechanically 

do not penetrate far and those descending in 

solution are subject to reprecipitation through 

agencies that will be noted later. 

Such processes as those outlined above must 

at their inception, as when erosion first exposes an ore body, result in a depletion in the 

value of the surficial ore, but as erosion progresses the metals left. behind come in time to 

1 Oral communication. 

a few tens or hundreds of feet of the surface. 

The upper .limit of saturation is termed the 

ground-water level or the water table. Its 

depth below the surface is,: most variable in 

regions of high relief, like that under discussion. It is not absolutely fixed but rises 

and falls with climatic variations; it may also 

be. lowered artificially by mine workings 

that afford deep drainage, as in parts of the 

region under discussion, and in such places 

its natural position J!lUSt be inferred from the 

depth to which alterations attributable, in 

part at least, to the atmosphere (oxidation) 

extend, or ·from early records of the depth- at 

which standing water was found in the :fi..--st 

shafts sunk. In most parts of the· Central 

City quadrangle its natural position appears to 

have been from 50 to 150 feet below the surface. 

Raymond, in an early report on the Gilpin 

County mines, states that oxidized ore in the 

California-Gardner vein extended 85 to 95 

feet below the surface and that in a number 

of other veins oxidation extended to depths 

of 70 to 80 feet. In the Aurora vein oxidation 

extended to depths ~f about 150 feet. In the 

Little Giant mine, near Lawson, the original 

2 Evidence summarized by J. F. Kemp (The ground-waters: Am. 

lnst. Min. Eng. Trans., vol. 45, pp. 3-24, 1914). 

I 
138 GEOLOGY OF GILPIN, CLEAR CR.EEK, AND BOULDER. COUNTIES, COLO. 

ground-water level was within 60 feet of the 

surface. 

GOLD ENRICHMENT. 

GENERAL CONDITIONS. 

In some of the ore deposits of the Central 

City quadrangle enrichment is practically Gold-silver ores of all the types-the pyritic 

'confined to the zone between the surface and type, the galena-sphalerite type, the composite 

th\3 ground-water level, which is subject to· type, and the telluride type-have been notably 

alternate wetting and drying and to the direct enriched in gold in the oxidized zone. The 

influence of oxygen and other atmospheric effects of enrichment are most striking, howgases and which is known as the oxidized z.one. ever, in certain ores of the galena-sphalerite 

In other ore deposits enrichment extends type which, where not oxidized, carry ncglidownward for over 600 feet into the zone below gible amounts of gold, usually less than 0.1 ounce 

the ground-water level. Because the enrich- to the ton, and where oxidized may carry 1.5 to 

ing minerals below the ground-water level are 3 ounces of gold to the ,ton. These are the 

mainly sulphides, this lower zone has been so-called "silver veins,'.' whose surface portions 

called the. zone of downward sulphide enrich- were worked by the pioneers for gold alone. 

·ment .. For brevity it will be referred to in Although data showing in a systemat~c ·way 

this discussion as the secondary sulphide zone, the distribution of gold below the ground-water 

with the understanding that the secondary level are rather meager, such information as is 

sulphides were deposited by downward-moving available fails to indicate any considerable ensolutions. richment in gold below that level. 

CLASSES OF ORES AFFECTED. 

Of the classes of ores represented in this 

region the tungsten ores of Boulder County 

· have been son1ewhat enriched in the oxidized 

zone, owing to the fact that the tungsten 

minerals are heavy and are less readily decomposed than most of the associated ore 

minerals. These ores were not studied in 

detail by the writer. Oxidized ores of uranium 

were not exposed at any of the mines on Quartz 

Hill, but so far as could be learned there has 

been little, if any, enrichment of these ores 

in uranium either above or below the·groundwater level. The copper ores of the Evergreen mine, near Apex, have been enriched 

in the manner usual in copper deposits, but 

on so small·a scale that the value of the ore 

has not been·. greatly au~mented. The iron 

ores of Caribou have not been enriched. It 

is in the predominant ores of the region, the 

gold-silver ores, that enrichment has.been most 

effective. ·Enrichment in gold in the oxidized 

zone has occurred in all types of the gold-silver 

ores; enrichment in silver is largely confined 

to the secondary sulphide zone of the ores of 

the galena-sphalerite type; enrichment in 

copper, always on a small scale, has affected 

ma,inly the pyritic type of gold-silver ores. 

Enrichment in-lead is insignificant, and enrich-

.ment in zinc was nowhere observed. The 

phenomena of enrichment will· be further 

discussed with individual reference to gold, 

silver, copper, and other metals. 

In the unaltered gold-silver ·ores the gold 

Inay OCCUr (1) in particles Of micrOSCOpic Or 

submicroscopic size in the sulphides or gangue 

minerals; (2) in masses large enough .to be seen 

with the unaided eye, embedded in quartz or 

more rarely in calcite or sulphides; or (3) as a 

gold-silver telluride. The first-n:amed mode of 

occurrence is by far the most common, and in 

most of the gold ores of the region visible gold 

is. a rarity. In the oxidized zone such ores 

suffered partial disintegration, which was accompanied by the conspicuous development of 

brown hydrous oxides of iron, an increase in 

porosity, and many other less conspicuous but 

very important changes. Among these changes 

was the partial freeing of the gold through the 

oxidation of its sulphide matrix, thus exposing 

it to the action of the solutions that entered the 

upper part of the lode. 

SQLUTION AND REDEPOSITION OF GOLD. 

:Much of the gold that was partly or wholly 

freed from its matrix during the processes of 

oxidation probab~y remained unattacked by 

the solutions descending from the surface 

through the ore, and a large part of the enrichment in gold in the oxidized zone is doubtless 

due to the residual concentration of such gold 

during long-continued weathering. A part of 

the gold freed by oxidation, however, was unquestionably taken into solution. It has been 

generally assumed that chlorine was the agent 

which effected the solution of gold, but the 

paucity of chlorine in the surface waters of 
PROCESSES AFFECTING. THE ORES. 139 

regions of crystalline rocks like that here un~er 

consideration suggests . that if gold was ~Issolved at all some other solvent was the active 

agent. I-Iowever tbis may ?e, it see~s probable that if O'Old was taken mto solutiOn most 

of it was pl~Omptly reprecipitated within t~e oxidized zone itself or immediately b~low 1t. 

Paln~er and Bastin 1 have. sho·wn that .most of 

the n1etallic minerals common in ore deposits, 

including pyTite, chalcopyrite, arid galena, ~re 

also effective precipitants of gold from chlonde 

solutions. It' is well lmown t}:lat ferrous sulphate is also an effective precipitant of gold 

frotn chloride solutions. Consequently, wherever ferrous sulphate is abundant gold is likely 

to be precipitated. It is doubtful, therefore, 

whether 1nuch gold in solution could travel far 

below tho ground-water level without being precipitated. The available records of the early 

mining of oxidized gold ores show not. only that 

tho oxidized portions of the gold-silver veins 

wore richer in gold than the unaltered ores 

bolow but appear to show also that the gold 

was on tho ·a~erage coarser, a faot explainableonly upon tho assumption that some of it was 

dissolved and redeposited. The oxidized gold 

ores were ''free Inilling"-that is, most of the 

O'Old was recoverable by amalgamation, whereas 

tho gold of tho unaltered ores is only~ small 

part recoverable by this process. It was mcleod 

fortunate that the ore found at first, when 

elaborate mills and smelters were not available, 

was of a sort amenable to sin1ple and inexpensive treattnent. 

EVIDENCE C>l!"' GOLD ENRICHMENT IN OXIDIZED 

ZONE. 

Although enrichment in gold in the oxidized 

~one of tho ores of this region is generally recognized to have been an important process, 

specific data exemplifying it are difficult to proc1.n·e now that tho oxidized ores have for many 

years boon entirely worked out. T~e m?st 

·striking examples are afforded by certau1 vmns 

which, just below tho oxidized zone, were valuable mainly for silver. In speaking of tho condition ·in 1872 of certain mines on or near 

Seaton :Mountain, Raymond 2 .says; 

'l'he mines in the eastern end of Clear Creek County have 

·been worked to a greater extent than in a,ny year since 

--- . 1 Palmer, Chose, 1\nd BMtin, K S., Metl\llic minerals as precipitants of 

silver 1\nd gold: l~con. Geology, vol. 8, pp. 156-IQO, l!l1.3. 

~ H.llymond, n.. W., Stlltistics of minos and mining in the Stlltes and 

''l'orritorlos wost of tho B.ocky Mountains fm· 18i2, p. 2iQ, 18i3. 

their surface ores were treated for the gold they contained. 

The ores still contain more or less gold, :but notwithstanding this fact the lodes now carry mainly silver ores. * * * 

The principal mines are the ~eaton, Crystal, Edgar, ''Tb.ale, 

Hukill, Veto, Que~n, and Franklin. 

The Blue Ridge vein, near Dumont, is .char~ 

acteristically a silver vein, the primary ore in 

general carrying less than 0.1 ounce of gold to 

the ton. Oxidized ore from the surface, how-, 

ever, in places carried several ounces of gold 

and was characteristically poor in silver. Two 

shipments of suoh ore assayed respectively 1.60 

and 2.55 ounces of gold and 3 and 6 ounces 

of silver to the ton. 

In the gold-silver ores of the telluride type 

some primary gold is associated with the tellurides, but it is believed that much of the gold 

of the oxiaized ore has been freed by oxidation 

from combination with tellurium. 

PROBABLE UNIMPORTANCE OF GOLD ENRICHMENT BELOW GROUND-WATER LEVEL. 

There w~ere few opportunities for the study 

of gold-silver ores occurring not far below the 

oxidized zone,· but such data ,as are available 

afford no certain evidence of notable enrichment in gold below the ground-water level. 

The records of careful sampling of all parts of 

a typical pyritic vein in the Iron mine, in Russell Gulch, for example, failed to show any 

systematic change in the gold content below 

the oxidized zone. 

A specimen in the collections of the Colorado 

Bureau of Mines in the State House at Denver 

showed wires of gold on well-formed crystals 

of galena from the Prize vein, near Central 

City, but the depth from wbich the specimens 

came is not known. Another specimen in the 

same collection, from the Cook mine, showed 

wires of gold on crystals of chalcopyrite in a 

vuO' · the location in the mine was not given. bl 

At one point on the 392-foot level of th~ Aurora 

mine free gold occurred as small wires and. 

grains on quartz crystals in a small watercourse 

entering the vein from its north wall,· but 

undoubted primary gold intergrown with 

pyrite and chalcopyrite occurs near by in the 

·same level. In all these cases, therefore, it is 

uncertain whether the gold was deposited ,by 

descending· solutions or by ascending solutions 

belonging to the lat~ stages of primary mineralization. Other relations noted in the Aurora 

vein are unfavorable to the idea of much enrichment in gold below the ground-water 
140 GEOLOGY OF GILPIN, CLEAR CREEK; A~D BOULDER COUNTIES, COLO. 

level. This vein was rich in its oxidized portion, between the ~urface and a depth of about 

150 feet, assaying as much as $300 a ton; 

between 150 and· 325 feet, however, the ore 

was of comparatively low grade; at still 

greater depth its value was locally increased 

by oertain !?tringers that joined it, from the 

hanging wall. 

SILVER ENRICHMEN~. 

Silver enrichment contrasts strongly with 

gold enrichment in this district in that there 

is commonly impoverishment rather than 

enrichment of silver in the oxidized zone and 

notable .enrichment below the oxidized zone. 

Furthermore, silver enrichment is practically 

confined to the ores of the galena-sphalerite 

tyl?e. 

SOLUTION 0~ SILVER IN OXIDIZED ZONE. 

THE SILVER MINERALS AND THE ACTIVE SOLUTIONS. 

The silver minerals of the oxidized ores may 

be either primary or secondary. The primary 

minerals of this region are (1) silver alloyed 

with gold, which though locally visible is 

usually in particles of microscopic or submicroscopic size, and (2) silver-gold tellurides. Argentite has not been authoritatively reported, either as a primary or as a 

secondary mineral. Among the secondary 

silver minerals are native silv~r, cerargyrite, 

pearceite, polybasite,· and proustite. · 

In the weathering of the ore in the zone of 

oxidation the. silver finely disseminated through 

sulphides and gangue minerals is in part freed 

from its matri;X and, with other silver minerals 

present, becomes exposed to the action of 

meteoric water and its dissolved substances. 

In most mine waters of surface origin the 

·principal negative radicles present are chlorine (sometimes witp. bromine and · iodine), 

carbonate, bicarbonate, and sulphate, the 

sulphate as a rule greatly predominating. As 

compounds of silver with all these ·radicles are 

known; it is customary to consider the dissolved silver as existing in distributed balance 

with as many of these radicles as may be 

.present. 

SILVER BALANCED BY THE SULPHATE RADICLE. 

Silver sulphate is, as shown by the following 

table, by far the most soluble of ·an the silver. 

salts of probable economic importancE) in 

nature1 unless it is exceeded by the thiosulphate, whose possible presence in minewaterSl 

has not yet been investigated. 

Sol·ubilities of silver salts.a 

Tempera- Solubility· 

Salt. Solvent. ture (grams 

(oC.). per liter). 

Silver bromide ..... Pure water ... 25 0. 000137" 

Silver chloride ..... ..... do ....... 25 . 002 

Silver carbonate .... ..... do ....... 25 . 033 

Do ............ ..... do ....... 15 . 031 

Do .•........ :. Water satu- 15 . 846 

rated with 

Silver sulphate ..... ·C02• 

Pure water ... 25 8.01 

a Cox, A. J., and Abegg6R., Zeitschr. physikal. ChemiP, vol. 46, P11, 1903. Johnson, G. S., hem. News, vol. 54, p. 75, 1886. 

The solubility of the sulphate is slightly in-· 

creased by the presence of free sulphuric acid. 

It is well known that the sulphate radicle is. 

formed abundantly through the oxidation of 

sulphides and that the mine waters of the, 

upper parts of sulphide ore bodies are charac-· 

teristically "sulphate" waters; . furthermore, 

I-I. C. Cooke 1 has shown that native silver and. 

all the commoner silver compounds, except the, 

chloride, are soluble in dilute sulphuric acid, 

~specially in the presence of ferric sulphat'e .. 

It is believed, therefore, that most of the silver in. 

solution in such waters is in b&lance with the. 

sulphate radicle. 

SILVER BALANCED BY THE CARBONATE OR THE BICAR_;· 

BONATE RADICLE. 

Silver carbonate, being a somewhat unstable: 

compound, has never been certainly recognized .. 

in nature. It may, however, be readily prepared in the laboratory by the interaction a:t. 

ordinary temperatures of solutions of silver· 

nitrate and of an alkali carbonate, as shown by· 

G. S: Johnson. 2 The writer has also obtained. 

it at ordinary temperatures by precipitation. 

from silver sulphate solution with either sodium. 

carbonate or magnesiun1 bicarbonate. The, 

carbonate thus obtained is only slightly,soluble· 

in pure water, although more soluble than the:. 

chloride, but it is readily dissolved by watersaturated with carbon dioxide, its solubilityunder these conditions being almost exactly· 

that of calcium carbonate. 2 . Carbonates are: 

1 Cooke, H. C., The secondary enrichment of silver ores: Jour. Geology,.. 

vol. 21, pp.1Q-15, 1913. 

2 Johnson, G. S., On silver carbonat2: Chern. News, vol. 54, p. 75, 1886. 
PROCESSES AFFECTING THE ORES. · 141 

:abundant as gangue minerals in certain of the 

;gold-silver deposits of this region and are taken 

::into solution n1ainly as bicarbonates. It is 

therefore pr_obable that a portion of the silver 

·dissolved in the oxidized zone of certain depos-

::its was balanced by the bicarbonate radiCle 

-(I-IC03). 

SILVER BALANCED BY CHLORINE. 

The chlorine content of most surface waters, 

-especially those in areas of crystalline rocks, is 

·extremely small. In the river waters of the 

:Piedmont Plateau region of Virginia, the 

· ·Cn,rolinas, and Georgia it ranges from 0.048 to 

cQ.128Inilligran1 to the liter; the average of three 

:analyses of the waters· of Lake Champlain, 

who,se drainage basin is . composed almost 

-exclusively of crystalline rocks, shows only 

<>.034 milligran1 to the liter. These waters 

1nay be contrasted with normal sea water, 

which contains 19,350 milligrams to the liter. 

No similar determinations are available for the 

.area under discussion, but it. is almost certain 

"that the chlorine content of the surface waters 

]s of a correspondingly small magnitude. As 

the ores of this region carry no chlorine min-

·erals, there is no reason why the waters of the 

upper parts of the ore bodies should be appre-

-ciably richer in chlorine than the surface waters. 

The few available analyses of waters of surface 

-origin in the upper levels of 1nines in regions of 

-crystalline rocks also show a low content of 

-chlorine. 1 That son1e chlorine was present 

:and entered into combination with silver is indi-

-cated, however, by the reported presence of 

-cerargyrite (horn silver) in the oxidized zone 

<>f a few deposits. Compounds of silver with 

bromine and iodine have not been noted. 

U.EPREOIPITATION OF SILVEU IN OXIDIZED 

ZONE. 

From the foregoing. considerations it is 

~vident that silver is readily taken into solution 

in the oxidized zone of sulphide ore bodies and 

that in the mine waters it is mainly in balance 

with the sulphate radicle bUlt to some extent in 

bahtnce with th~ carbonate, bicarbonate, and 

-chlorine radicles. Cerarg'yrite is an extrem'ely 

stable mineral under the conditions that prevail 

in the oxidized zone 2 and is very muph less 

soluble than either the bicarbonate or the sulphate of silver. It may be readily precipitated 

in the laboratory by sodium chloride from 

solutions of either. silver bicarbonate or silver 

sulphate. It is probable, therefore, that most 

of the silver balanced by chlorine is promptly 

precipitated within the oxidized zone as cerargyrite (horn silver). The rarity of this mineral 

in the region under discussion is attributable 

to the paucity of chlorine in its surface waters. 

It may be that a small amount of silver balanced 

by chlorine escaped precipitation in the oxidized 

zone and, descending below the water level, 

contributed to the formation of secondary 

silver sUlphides.· 

Native silver as wires or small plates is 

occasionally found in the oxidized ores of this 

region. Some of it may have been deposited 

below the oxidized zone and merely have 

resisted complete oxidation, but some was 

probably deposited within the' oxidized zone, 

either through the agency of ferrous sulphate 3 

or of metallic sulphides. Unaltered residual 

·chalcocite, .enargite, and tennantite remaining 

in the lower part of the oxidized zone may also 

reprecipitate silver ·in part as native silver and 

in part as its compounds. Chalcopyrite may 

also reprecipitate silver from sulphate solution, 

not as the native metal, but as a compound 

whose exact nature has not been determined. 

The preliminary experiments of Palmer and 

Bastin,4 in · which the formation of small 

amounts of silver on chalcopyrite immersed in 

s~lver sulphate solution was reported, must be 

corrected by later observations which show 

that perfectly . clean surfaces of chalcopyrite 

do not precipitate metallic silver. The precipitations previously obtained were due to 

inconspicuous films of secondary copper mine:als on parts of the chalcopyrite surface. 

DEPOSITION OF SECONDARY SILVER l\IINEUALS 

BELOW THE GROUND-WATER LEVEL. 

GENERAL CONDITIONS. 

Silver taken into solution in the zone of 

oxidation, if it escapes reprecipitation within 

that. zone, descends into the ground-water 

zone, where in the presence of certain precipitating agents· it is deposited either as the native 1 Soo Emmons, W. H., 'l'ho enrichment or sulphide ores: U.S. Geol. 

Survoy Bull. 52!:1, pp. 00-61, 1913. a H. N. Stokes (Econ. Geology, vol. 1, p. 649, 1906) showed that the 11 Accordh~g to Cooko (op. cit.) sliver. chloride is the only one of the reaction Fe2(S04)J+2Ag=Ag2S04+2FeS04 was reve;-sible, silver being 

<:ommon sflvor minornls that is not appreciably attacked by sulphuric dissolved on heating and reprecipftated on cooling. 

ocid. • Econ. Geology, vol. 8, pp. 146-147, 1913. 
·' 

142 GEOLOGY OF GILPIN, CLEAR CREEK, _A;~D BOU:LDER COUNTIES, COLO. 

metal or in compounds. ·In the aosence of 

these agents it enters the general ground-water 

circulation and is lost so far as ·these ore deposits are concerned. In the ores 'of this 

region silver enrichment below the groundwater level exhibits an Interesting dependence 

on the primary 'niineral con1position of the 

ores. Furthermore, two contr~sted types of 

silver enrichment were noted; in one the silver 

was redeposited as sulpha-compounds (proustite or ruby silver, pearce!te, and polybasite) 

in association with .seeondary chalcopyrite; 

in the other it was redeposited as native silver 

in association ·with chalcocite, bornite, and 

covellite. In deposits of both types t4e secondary silver D;linerals are associated with carbonates and were not therefore deposited by 

strongly acid solutions. 

DEPENDENCE ON PRIMARY MINERAL COMPOSITION. 

A significant feature of silver· enrichment as 

displayed in the Central City quadrangle is the 

fact that secondary silver minerals, with the 

exception of native silver, have never been 

recognized, so far as known, ill the ores of the 

·pyritic type, in spite of the fact that silver is 

fairly abundant as a primary constituent of 

these ores. 

Native silver has been noted only in the 

oxidized upper portions of the ore deposits; 

its occurrence below the ground-water level in 

a finely divided form, ~xpecially in association 

with rich copper minerals, must be recognized 

as possible and perhaps probable, but if present it is so inconspicuous as to have escaped 

recognition. Although silver is less abundant 

as a primary constituent in the ores of the 

pyritic type, in which it rarely exceeds 10 

ounces to the ton, than in those of the galenasphalerite type, in which a content of 20 to 30 

ounces to· the ton is common, the complete 

absence of secondary silver ·.compounds is a 

fact demanding explanation. 

T:lw pyritic ores consist pred~minantly of 

pyrite in a gangue of quartz, sericite, or both, 

with subordinate amounts of chalcopyrite and 

terrnantite (in part antimoniacal); enargite is 

abundant in some veins, and secondary chalcocite and bornite are present in certain deposits. (See p. 151.) Carbonates are commonly absent•or if present are very minor constituents. In the ga\ena-sphalerite ores galena. 

and sphalerite are the predominant minerals, 

with subordinate amounts of' pyrite,. chalcopyrit~, tennantite (in part antimoniacal), 

~ornite, _quartz, and calcite or siderite. Sec-:-

ondary chalcocite is generally not present. 

The ores ·of both types contain in -their primary 

minerals. all the elements necessary to the 

foqnation. of compounds of silver with sulphur 

and arsenic or antimony, and in deposits ~f 

both types silver is undoubtedly taken into 

solution in the oxidized zone, probably through 

the agency of sulphuric acid and ferric sulphate. 

The causes for this restriction of silver enrichment to veins of a certain mineral composition 

are undoubtedly complex, but the presence of 

carbonate gangue minerals in the ores that 

carry $econdary silver sulphides is believed to 

be a most important factor. 1 Their pr~sence 

has led to an early neutralizatioti of the free 

sulphuric acid in the descending silver-bearing 

solutions. 

Much of the carbonate in these veins is ferruginous (siderite and ferruginous calcite)' and 

this by reaction with sulphuric acid yields fer..: 

rous sulphate·, an effective silver precipit.a.nt. 

In a timely and suggestive paper Nishihara 2 has 

compared the neutralizing effect of various carbonates, silicates, a.nd sulphides on sulphuric 

acid. and their activity in reducing ferric sulphate to ferrous sulphate. It is very significant that pyrite, quartz, and chalcopyrite, the 

principal .minerals of the ores of the pyritic 

type, were in Nishihara's experiments comparatively ineffective in neutralizing sulphuric acid 

and in reducing ferric to ferrous sul.phate. 

Galena and ·sphalerite and, of course, the carb.onates, are comparatively efficient inneutralizing sulphuric acid, and galena is fairly active in 

reducing ferric sulphate. Furthermore, galena 

and sphalerite in solutions of sulphuric acid or 

of ferric sulphate generate hydrogen sulphide, 

which may precipitate secondary sulphides. 

Nishihara has also shown that apparently pure 

galena from several localities, among them 

Idaho Springs, carries small percentages of manganese, which presu1nably occurs as the manganese sulphide alabandite in isomorphous mi.'\:-

ture with the galena. Alabandite evolves 

hydrogen sulphide very actively when in contact with acid sulphate solutions and if present 

1 A large number of field tests of mine waters made by the writer in 

the San Juan Mountains of Colorado durkg the su~mer of 1913 showed 

that in many silver veins secondary sulpho-compounds of silver were 

present far below a le~el where all free acid in the descending mine waters. 

had been neutralized. 

2 Nishihara, G. S. ~ The rate of reduction or'acidity of descending waters 

by 'certain ore and gangue minerals and its bearing on secondary sui p~ide, 

enrichment: Econ. Geology, vol. 9, pp. 743-757, 1914. 
PROCESSES AFFECTING THE ORES. 143 

in the enriched veins of this region nut y have 

exerted a considerable precipitative influence. 

It appears, therefore, that the mineral composition of the galmia-sphalerite veins t.hat 

show enrich1nent is such as to favor ready neutralization of sulphuric acid of the silver-bearing 

sulphate solutions descending from the oxidized 

zone, the formation of ferrous sulpha.te at the 

expense of ferric sulphate and sulphuric acid, 

and the developn1ent of hydrogen sulphide. 

All these features :ft1vor silver precipitation. In 

the ores of the pyritic type, on the. other hand, 

conditions favor the persistence of acidity a.nd 

the retention of the iron in the fenic state; silYer taken into solution in the oxidized zone is 

therefore likely to remain. in solution and 

eventun.lly to enter the general ground-water 

circulation and. be lost so far as the local ore 

deposit is conc~rned .. 

Secondary silver 1ninerals are not, however, 

equally abundant in all veins of the galenasphulerite type. The variations in abundance 

are not clue entirely to physical cause!3, such 

as the degree of fracturing of the ore, but appear to be dependent on differences in mineral 

composition. In certain of the veins near 

Cardinal, such as the Boulder County, Jack 

Pot, Pine Grove, and Gold King, silver enrichJnent appears to have been lacking or to have 

occurred only near the surface. Ore froin a 

cl0pth of 120 feet or less in the Gold King vein 

showed no silver 1ninerals. None were found 

in ore frmn n1oderate depths on the Pine Grove 

and J·ack Pot veins, and in the Boulder County 

mine they appear to have extended. only to 

slight deptl1s. Raymond/ writing in 1870, 

when doYelopn1ent could hardly have extended 

to cleptha of n1ore than 100 feet, says: 

As a greater depth was reached on this lode, the gold 

seemed gradually to be running out and the silver increasing in quantity. In much of the ore gold was found associated with large flakes of silver. Specimens had frequently been taken from the mine in which brittle silver 

and wire silver were visible in large quantities, with a 

smaller sprinkling of gold. · · 

No sihrer 1ninernls were noted by the writer 

in this Yein as exposed in the Boulder County 

tunnel. The absence of carbonates seen1s to be 

tho only important 1nineralogic difference between these veins and those in which ·silver 

enrichment is very prominent. 

Silv-er enriclunent seen1s to hav-e been of 

slight value or at least to hnve extended 'to 

1 Itnymond, R. W., Stntlstlcs or mines nnd mining in the States and 

'!'errftorlos wost or tho Rocky Mountains. 1870, pp. 327-328, 1872. 

only slight depths in certain other v-eins of the 

galena-sphalerite type, such as the Albro, near. 

Dmnont; the Gladstone, near Idaho Springs; 

and the Topeka, near Russell Gulch. In these 

v-eins also carbonates are rare and chalcopyrite 

and in places pyrite ~re unusually abundant. 

It is likewise noteworthy that few ores of the 

cmnposite type show 1nuch sulphide enrichment in silv-er. The scarcity of carbonates and 

the abundance of pyrite and chalcopyrite in 

the con1posite v-eins ·and those v-eins of the 

galena-sphalerite type in which thoro is little 

enrichment cause these v-eins to approach the 

pyritio ore type as regards susceptibility to 

downward sulphide enrichn1ent. 

RUBY SILVER AND CHALCOPYRITE TYPE OF ENRICHMENT .. 

Minerals.~ The minerals recognized as forn1ed 

secondarily in the n1ore comn1on type of 

silv-er enrichn1ent ·are pearceito (in part antimoniacal), proustite (ruby silv-er), polybasite, 

nativ-e silver, chalcopyrite, and rarely galena. 

The primary sulphides are galena and sphale-· 

rite, with subordinate pyrite and chalcopyrite 

and rare tennantite (in part antin1oniacal). 

The gangue· minerals in fissure fillings are 

quartz, carbonates (usually siderite or calcite 

but in plac.es rhodochrosite), and so~1e barite· 

In ·ores .forn1ed by replacen1ent the gangue 

n1:ill.erals are quartz, sericite, and calcite or 

siderite, with. renlnants of unaltered wall-rock 

minerals. 

Secondary minerals in fractures and vugs in 

primary ore.-N aturally tho secondary galena 

and chalcopyrite can not always be differentiated from the priinary, but where these 

n1inerals incrust primary n1inerals in vugs or 

open fractures or completely fill cracks trav-ersing the primary ore their secondary origin is 

clear. The study of polished specin1ens of ore 

under the reflecting n1icroscope shows that the 

secondary sulphides occur in two ways-as 

fillings or lining of fractures or vugs in the 

primary ore and as metasmnatic replacements 

of prin1ary sulphides and quartz. The second 

1node of occurrence, though familiar enough in 

copper enrichment, has seldom been noted in 

silver enrichment, not because it is a rare 

·phenon1enon, but because few secondary silv-er 

ores have been studied by the microscopic 

methods necessary to rev-eal it. 

The. ~eposition o~ secondary silver nrinerals 

along fract~res was ~ell sho~ in specimens 

fron1 the Ahnadeh mine, on Fall Riv-er, where 
144 GEOLOGY OF GILPIN, CLEAR CREEK, AND BOULDER COUNTIES, COLO. 

narrow fractures traversing the primary ore 

were coated with a mammillary deposit of 

pearceite and chalcopyrite, the latter in part 

intercrystallized with the pearceite and in part 

coating it as small crystals. Other fractures 

are coated ·with good-sized crystals of proustite 

associated with finely crystalline secondary 

cp.alcopyrite. One specimen from a depth of 

200 feet showed a fracture one-quarter of an 

inch wide in galena entirely filled with pearceite. 

A few specimens from this mine are among the 

finest examples of rich silver ore that the district has produced. One in a mineral collection in the public library at Idaho Springs was 

a mass of pure ruby silver several inches across; 

another showed a width of 1 inch of ruby silver associated with a !-inch to !-inch band of 

l • ·~ - . .• I ./I /- •• 1, -''-( 

' · -J Quartz ..... ' ..., • r ' . ·r. 

- .., • J { ',, I 

Qu~rtz '' : r·. , .... r -

I J 

5 MM. 

r· , ' , ·. \ ' .. (, 

•,..r ,...; -\...~ 

FIGURE 14.-Camera lucida drawing of poli~hed surface of ore from the 

Princess of India tunnel, Lawson. The areas marked SS show a silver 

sulphide, probably pearceite developed by metasomatic replacement 

of quartz and of galena. · 

pearceite. Wires of native silver were common 

in vugs in the upper parts of the Almaden vein. 

Pearceite and secondary chalcopyrite were 

noted in vugs in ore from the dump of the 

·American Sisters mine, south of Lawson, and 

pearceite in vugs in the White vein, on Red 

Elephant Hill. 

Secondary minerals as replacements of primary 

ore.-One of the best examples of enrichment 

by metasomatic replacement is furnished by 

ore from the Princess of India tunnel, near 

Lawson. Under the reflecting microscope with 

relatively low magnification portions of this ore 

present the appearance shown in figure 14. 

Between original quart?' and galena t4ere has 

develop~d a narrow band of a metallic ·mineral 

which is. somewhat darker gray than galena. 

Larger irregular areas of the same mineral occur 

within the galena. ·The mineral upon testing 

proved to be a sulpharsenide of silver, probaMM. 

I I ~. ·' "') \ "·/ ... 1 '":',. '-r 

Z.....•" ( ~ " - Jl., '\ ( ~ I .,/ -, -, 

....... ~. r '· Quartz' 

• ,-1. '. .... ·' .... ~ 

..... ~ 

B 

FIGURE 15.-Portions of specimen shown in •figure 14, more highly 

magnified. Portions marked ssg and ssq are a silver sulphide, 

probably pearceite. Note the double character of the bands of silver 

sulphide locally, as at a' in A. The portions marked ssg have been 

formed by replacement of galena; those marked ssq by replacement 

of quartz. 

hly pearceite,t carrying son1e ant~mony ·and 

copper. 

1 Fragments of the mineral were isolated from certain specimens. 

They were dark gray and somewhat seetHe and reacted in the closed 

tube for arsenic, antimony, and sulphur. When dissolved in nitric 

acid, they reacted with hydrochloric acid for silver and with ammonia 

for copper. The freshly polished surface has much the appearance of 

chalcocite under the metallographic microscope, but, unliKe chalcocite, 

it does not tarnish or etch readily when treated with nitric acid. When 

treated with concentrated nitric acid this mineral begins to show a 

tarnish at about the same time it appears on the chalcopyrite of the ore. 

When the chalcopyrite shows a faint peacock tarnish, the pearceite 

exhibits a yello:wish-brown color, in places showing slight iridescence. 

In specimens where the pearceite is present in too small amounts to 

be isolated it may be identified with a considerable degree of probability 

in the polished section by its behavior with nitr-ic acid. 
• 

PROCESSES AFFECTING THE ORES. 145 

The absence of any bands of pearceite between the sphalerite and any of the other 

minerals is noteworthy. Under higher magnification these borders present the appearance shown in figure 15, from which it may be 

seen that the bands of pearceite are in places 

single and in places double. Where the bands 

are single the pearceite has locally replaced 

quartz, as in the lower part of the specin1en 

shown in figure 15, B, where the contact between quartz and pearceite is exceedingly 

ragged; elsewhere it has replaced galena, as in 

the lower part of the specimen shown in 

figure 14, where the original crystal faces of 

the quartz are still intact. I-Im·e also the 

pearceite has replaced larger areas in the inFIOUHE 16.-Camera lucida drawing of polished surface of ore from 

Senator voin, noar Lawson, showing metasomatic replacement of 

The sulphides shown in figures 14 and 15 

appear fresh, and there is no evidence that any 

of them represent fillings of fractures or cavities. There seen1s to be no way of accounting 

for the occurrence of the pearceite in this 

manner except by metasomatic replacement 

of the primary quartz and galena. The extremely irregular borders which it exhibits 

bear out this conclusion. 

In a specimen of ore frmn the Senator mine, 

near Lawson, shown in .:figure 16, replacement 

of galena by pearceite is again illustrated. It 

is believed that the whole space represented 

in this figure was originally occupied by 

galena hy pearcelto and some chalcopyrite. c=chalcopyrite. Note 1 a.:...k---·-;.._ __ __..;...:....::;.,.:_;. ___ _;_....:...__......;.,;....:........;._;:.......J~~~ 

tho very irregular borders which characterize such reolacement in 

som9 places. • 

terim· of the galena mass. When the bands 

are double, as shown in figure 15, A, the two 

portions of the bands are separable because 

of a ·very slight difference in shade. The 

fairly regular boundary between the two 

parts of the bands is believed to rep resent .the 

original boundary between the quartz and 

galena. One part of the double band appears to. have been developed by the replacenlell t of galena and the other by the replaceInent of quartz. Both are believed to be 

pearceite, but a slight difference in mineral 

structure or composition has resulted in a 

recognizable difference in shade. Probably 

son1e constituent of the original galena entered into the cmnposition of pearceite during 

the replacmnent of that mineral. 

44214°-17--10 

2MM. 

FIGURE 17.-Cnmera Iucida drawing of polished section of ore from 

Maud S. mine, near Empire station. Shows pearceite fllling fractures 

in brecciated sphalerite and metasomatically replacing quartz. 

galena and sphalerite. The sphalerite, as in 

the specimen already described, has renlained 

unaltered, while the galena has been extensively replaced by pearceite and a very ragged boundary has been developed between 

the two minerals. A little secondary chalcopyrite is associated with the pearceite. 

Unreplaced particles of galena occur within 

the pearceite. 

Figure 17 shows ore fron1 . the Maud S. 

mine, near Empire station. The silver mineral, apparently pearceite, is in part a replacenlent of quart~, as indicated by the 

ragged outline of some of the quartz, but· is 

also in part a filling in a brecciated portion of 
146 GEOLOGY OF GILPIN, CLEAR CREEK, AND BOULDER COUNTIES, COLO. 

the primary ore. The specimen illustrates 

particularly· well the total absence of replacement of the sphalerite. 

A sn1all specimen of ore· from: the American 

Sisters mine, obtained through the courtesy of 

Mr. Philip R. Stf:Lnhope, proved of especial 

interest when polished and examined under 

the reflecting microscope. One face of thia 

specimen is incrusted with a layer of secondary 

chalcopyrite showing a more or less mamlnillary surface. Intermixed irregularly with the 

chalcopyrite and plainly contemporaneous are 

minor amounts of pearceite, reacting strongly 

·for silver, sulphur, and arse:p.ic. _The minerals 

of the primary ore are galena, sphalerite, siderite, gray quartz, pyrite, and chalcopyrite, the 

last two as a rule closely associated. All these 

appe.ar to b,e essentially contemporaneous. 

Subsequent to the primary mineralizatio;n the 

ore has be~n fractured, and along the. fractures 

secondary galena chalcopyrite and pearceite 

h~ve been deposited. In the adjact'mt lessfractured .portions secondary chalcopyrite and 

pearceite have metasomatically replaced primary galena. In the unfractured ore pearceite 

if present usually occupies a position similar to 

that shown in figure 14, being definitely related 

to the contact between galena and other minerals and representing a met~somatic replacement of the galena, similar to that observed in 

the Princess of India and Senator ores. The 

presence of very firie intergrowths of pearceite 

and galena that resemble eutectic intergrowths 

but can be conClusively shown to mark a stage 

in the gradual replacement,of the galena by the 

pearceite is of much significance in the interpretation of ore textures. A true appreciation 

of their significance. was not arrived at until 

this report was in proof, so that their detailed 

description can not be presented here. The 

writer hopes to describe and illustrate them 

later in a short paper. 

Although some of the chalcopyrite in these 

specimens is contemporaneous with secondary 

galena and pearceite, some is distinctly later, 

occurring in cracks in them or replacing them 

metasomatically along their · contacts with 

quartz or sphalerite. · 

Depth of silver enrichment.-General experience in the operation of the silver miries of 

this region has shown that the rich silver ores 

were reached at or near the ground-water 

level, attained their richest development in the 

first 100 or 200 feet below this level, and thence 

downward gradually decreased in abundance 

until at vertical depths of 500 to 600 feet evidences of enrichment were rare or absent and 

the metal values were essentially those of the 

primary ore. In .the Seaton mine secondary 

silver minerals were noted to depths of 450 

feet, and in the Senator vein locally to dep~hs 

of 600 feet. In. the Joe Reynolds vein the. 

richest· silver was found above the third level, 

although ore high in silver was obtained at 

intervals as far down as the eighth level, and 

some flakes of native silver in talclike material 

have been reported fron1 the ninth level. The 

greatest vertical depth at · which secondary 

silver minerals were observed by the writer was 

700 fee~ in the White vein, near Lawson. At 

that depth a few small crystals of pearceite 

were noted on the quartz of a small vug. The 

gradual disappearance in depth of the rich 

silver !1finerals, such as ·native silver, proustite, 

and pearceite, taken in connection with the 

occurrence of these minerals in fractures in the 

primary ore and as replacements of the primary 

ore minerals, forms conclusive evidence of 

their· origin by downward enrichment. 

Geographic distribution.-It has already been 

noted that enrichment in . silver below the 

ground-water level has been recognized only 

in or~s belonging to the galena-sphalerite type. 

In some of these-for example, the ores of the 

Topeka and Seaton veins-the primary ores 

are of w01kable grade, but in many othersf.9r example, those near Lawson and on Silver 

Hill north of Blackhawk-only the ores that 

have been enriched in silver can be profitably 

mined. TP.e latter form the typical silver ores 

of the miners of this region, their gold content 

being characteristically small. The primary 

ores that are workable usually have the primary gold content, rather than the primary· 

silver content, above the average. 

Veins in which silver enrichment of the type 

here discussed has taken place to a considerable 

extent occur principally in four localitie~-(1) 

near Lawson and Empire station, (2) on or near 

Seaton Mountain, north of Idaho Springs, (3) 

on Silver Hill, near Blackhawk, and (4) near 

Caribou, with scattered occurrences elsewhere. 

The characteristics of most of these veins are 

described in detail in :Part III of this report. 

As most of the rich silver ores were worked out 

many years ago, the information con·cerning 
PROCESSES AFFECTING THE ORES. 147 

their OCCUrrence has been gained mainly frOn1 NATIVE SILVER AND CHALCOCITE TYPE OF ENRICH- MENT. specin1ens in collections, from old dumps, or 

fron1 the records of early mining. Specimens from the l)ardanell No. 2 vein, 

Silver content of enriche(l ores.-The· silver obtained from the ore bins at the Up to Date 

content of the enriched ores shows much more tunnel, near Caribou, are of peculiar interest 

variability than that of the primary ores. This because in them silver occurs not in sulphois obviously due to the occurrence of the sec- compounds but in native form and is cononclary silver minerals in fractures and as local- temporaneously intergrown with chalcocite, 

ized replacements rather than in even distribu- bornite, and a little covellite. Stephanite has 

tion through the ore. The silver content of been reported from some parts of the mine, 

ores of smelting grade varied from a few tens of but none was seen by the writer. Unfortuounces up to a thousand ounces to the ton, or ·nately the exposures in the mine were not espeeven more in picked lots; 6! tons shipped in cially good, and the observations are not as 

1870 from the Idaho mine, near Caribou, aver- complete as might be wished in view of the 

aged 977.5 ounces of silver to the ton, and two unusual mi:t;1eral relationships. 

lots of ore frmn the Almaden mine, on Fall The rich silver ores studied occurred as reRiver, gave on assay, according to the manager placements and to some extent as fissure fillings 

of the property, the following extraordinary in altered pyroxenite. All thus far found were 

within 50 or 100 feet of the surface. Some of results, in ounces to the ton: 

Gold. 

149 pounds............. . . 0. 38 

510 pounds............. . . . ~87 

Silver. 

5,810.30 

4,084.92 

In ore shipn1ents aggregating 1 ton or more, 

the silver seldmn exceeds 200. ounces to the 

ton. About 108 tons of enriched ore fron1 the 

:Murray vein near Lawson averaged 0.35 ounce 

of gold and 55 ounces of silver, and 150 tons 

shipped at a different period averagec.l' 0.44 

ounce of gold and 52 ounces of silver. The 

average precious-metal content of the ores 

between the third and ninth levels in the Jo 

Reynolds mine has been estimated by the manage~nent as 0.10 ounce· of gold and 100 ounces 

of silver to the ton. Fuller details in regard to 

silver content is given in tho individual mine 

descriptions. 

The decrease in sil'\fer content of the enriched 

ores with increasing depth has been the prime 

factor in the decline in importance of the silver 

n1ines of this district, but a factor of subsidiary 

importance was the great decline in the market 

value of silver, from $1.32 an ounce in 1R72 to 

63 cents in 1894, a fall of about 50 per cent. 

In this connection the curve showing the average market price of silver from 1859 to 1915 

shown in figure 18 (p. 148) is of interest. 

The gold, copper, lead, and zinc content of 

the ores of this type seems to have been but 

slightly affected by enrichment below the oxidized zone; for information concerning these 

metals the reader is referred to the section on 

metal content of the primary ore (pp. 109-110). 

the· rich veins are· an inch or so in width and 

from this size they grade downward to exceedingly minute veinlets less than 1 millimeter in 

width. One of the latter, greatly magnified, 

is shown in figure 19. 

A specimen of ore taken from the bins but 

said to have been obtained about 60 feet below 

the surface in stopes on the Dardanell No. 2 

vein (see fig. 20) illustrates especially well.the 

mode of silver occurrence. This ~pecimen is 

1 ~ to ·z inches thick and shows one wall of a 

small open fracture traversing altered pyroxenite. This fracture face is coated with an 

intergrowth of chalcocite, bornite, covellite, · 

calcite, and native silver, one-fourth to onehalf inch in thickness. The silver in places 

forms rough projecting knobs, and the. chalcocite, bornite, and covellite are somewhat 

tarnished and not readily distinguishable from 

one another except in the polished section. 

When the polished section is examined under 

the microscope the chalcocite and bornite are 

seen to be about equally abundant and to ,be 

intimately and irregularly intergrown, showing 

beyond doubt that they crystallized contemporaneously. Covellite is present only in subordinate amounts and is in places in~losed by 

bornite and in places by chalcocite. It is 

irregularly associated with these minerals and 

appears to have crystallized contemporaneously 

with them, not being confined to the vicinity 

of vugs or fractures. Native silver is nearly 

as abundant as bornite; it occurs in very irregular masses, in some places inclosed in calcite, 
148 GEOLOGY OF GILPIN, CLEAR CREEK, AND BOULDER COUNTIES, COLO. 

DOLL Ad CALENDAR YEAR DOLLAR 

1860 1865 1870 1875 1880 1885 1890 1895 1900 1905 1910 1915 1.38 1.38 

1.36 I" 1.36 

1.34 1\ ~~ 1.34 :\. 

1.32 ..... 1.32 

1.30 ' 1.30 

1.28 1\ 1.28 

1.26 1\ 1.26 \ 

1.24 1.24 

1.22 \ 1.22 

1.20 \ 1.20 ' 1.18 ' /I\ 1.18 \ 

1.16 \ 1.16 

1.14 ~ 1.14 '" .... 1.12 \ i.J2 ' 1.10 1\ 1.10 

1.08 \ 1.08 

1.06 1.06 

1.04 \ 1.04 

1.02 ' ' 1\ 1.02 ' \ 

1.00 1.00 

.98 1\ .98 

.96 \ .96 \ 

.94 ..... .94 

.92 .92 

.90 .90 

.88 .88 

.86 .86 

.84 .84 

'.82 .82 

.80 .80 

.78 .78 

. 76 . 76 . 

.74 .74 

.72 .72 

.70 .70 

.68 ·.68 

.66 I 1". .66 I 

.64 I ' I .64 ' II 

.62 ' II .62 I 

.60 ~ 1\ .. 60. ~IL' L 

.58 I 1\ .58 I \ 

.56 ' I I .56 \ I 

.54 ' .54 / 1"- 1\ 

.52 1"- \I .52 

.so .50 1860 1865 1870 1875 1880 1885 1890 1895 1900 1905 1910 1915 

DOl LA~ CALENDAR YEAR DOLLAR~ 

FIGURE 18.-Diagram showing average market price of silver in the United States for the years 1859 to 1915, inclusive. Figures 

. taken from Annual Report of Director of the Mint for 1915. 
PROCESSES AFFECTING THE ORES. 149 

but in others iiTegularly intergrown with the 

sulphides, so that there can be no question that 

it crystallized contemporaneously with them. 

The pyroxenite bordering this vein has been 

extensively calcitized, and veinlets and small 

iiTegular masses of all the minerals described 

above are scattered iiTegularly through it. 

The iiTegular form of these veinlets and aggregn.tcs shows that they were developed by 

mot11somatic replacement. The replacement 

v-einlct shown in fig~re 19 illustrates also the 

contemporaneity of the silver and the copper 

sulphides. 

In the absence of any opportunity to study 

the high-grade ore in place, its origin by downward enrichment can not be said to have been 

proved. Its position in the mine, between 50 

Quartz and calcite 

b =bornite 

c .. chalcocite 

s =native silver 

was noted; in this material native silver had 

been deposited along minute fractures. The 

abundance of calcite in association with the 

silver of these ores shows that the solutions 

depositing the silver were neutral or alkaline. 

It appears probable that whatever enrichment in silver takes place in the ores of the 

pyritic type is closely related to the sort of 

silver enrichment here described, much of the 

silver being deposited in nH.tive form in close 

association with secondary chalcocite and 

bornite. 

RELATION BETWEEN THE TWO TYPES OF SILVER 

' ENRICHMENT. 

In recognizing two types of silver enrichment 

the writer's main purpose is to emphasize the 

marked dependence of the process on physical 

YzMM. 

'FIOURI~ 19.-Camcra Iucida drawing of replacement veinlet of silver, bornite, and chalcocite in altered pyroxenite from Up to Date tunnel, 

Caribou. 'rhe average width of this veinlet is 0.25 millimeter and its length 2 centimet.ers. A neighboring veinlet of similar character 

Is traceable for a length of 8 centimeters. 

and 100 feet below the present surface, and . and chemical environment, one set of secondary 

·the fact that the silver is not associated with minerals forming under certain conditions and 

the usual primary ore minerals of this district an entirely different set under other conditions. 

but with rich copper sulphides that in other What the controlling conditions are can not be 

regions are commonly secondary point strongly definitely set forth in the present state of knowlto an origin by downward enrichment. The edge, but it sho'uld be sufficiently apparent 

nature of the wall-rock alteration furnishes from what has already been said that the comconfirmatory evidence of such an origin, for position of the primary ore is of the utmost imcalcite and quartz are the characteristic portance. Both types of enrichment were 

minerals developed in the wall rocks near the effected by alkaline, neutral, or at most only 

rich silver ores, whereas near the primary ores slightly acid waters, as is shown ·by the abunsericite is abundantly developed in rocks of dant presence of carbonates. Some insight in.to 

similar type. An adequate source for the the reason for the abundance of silver in the 

secondary minerals is found in ores of both the native state in association with chalcocite may 

galena-sphalerite and pyritic types that occur be gained from the results of earlier studies by 

in this mine. In the particular stope which Chase Palmer and the writer,• which showed 

yielded the rich silver specimens described 1 Palmer, Chase, and Bastin, E. S., Metallic minerals as precipitants 

pyroxenite heavily impregnated with galena of silver and gold: Econ. Geology, vol. 8, pp. 140-liO, 1913. 
150 GEOLOGY OF GILPIN, CLEAR CREEK, AND BOULDER COUNTIES, COLO. . 

that chalcocite is very efficient in reducing 

silver from a dilute solution of its sulphate, 

precipitating it mainly in the metallic form. 

It is not surprising, therefore, that where chalcocite and silver were deposited contemporaneously from the same solution most of the silver 

should occur native. 

The two types are established merely to simplify description and facilitate discussion of the 

deposits of this region. They may not apply 

to other regions, and conditions intermediate 

between those here existing may produce transition types. What appeared to be secondary 

bornite was in fact observed by the writer intergrown with secondary chalcopyrite in rich ore 

of the ruby silver and chalcopyrite type from 

the American Sisters mine. It is clear, nevertheless, that the conditions which were favorable for the precipitation of the sulpha-compounds of silver also favored the precipitation 

of chalcopyrite, and that u_nder conditions in 

·which the copper was precip(itated as the richer 

. sulphides bornite and chalcocite the silver was 

more likely to be precipitated in native form. 

A determination of the conditions that favor the 

precipitation of copper seco_ndarily· as chalcopyrite rather than as bornite or chalcocite 

should be a material aid to the understanding 

of the phenomena of silver enrichment. 

COPPER ENRICHMENT. 

Downward enrichment in copper .is not conspicuous in any of the mines of the Central City 

quadrangle and is of slight economic importance. Commonly it is restricted to the devel-. 

opment of thin films of chalcocite or bornite on 

chalcopyrite in the upper par~s of the ore 

bodies, but in some places small amounts of 

secondary chalcopyrite or very rarely native 

copper may be developed. 

SOLUTION AND REDEPOSITION OF COPPER IN 

THE ·OXIDIZED ZONE. 

In most sulphide ores the common sulphides 

of copper readily break down in the oxidized 

zone, the copper dissolved ·being balanced 

mainly by the sulphate radicle. If the common carbonates are abundant either as wall 

rocks or as gangue minerals, much of the copper dissolved may by reaction with them be 

temporarily fixed in the oxidized zone as the 

copper carbonates· azurite and malachite; some 

copper may also by reaction with. silicates 

become fixed in the oxidized . zone as chrysocolla. If carbonates are rare or absent most 

of the copper in solution will be precipitated 

only below the oXidized zone, through the reducing influence mainly of the primary sulphides. In the region under discussion limestones are absent and carbonates as gangue 

minerals are abundant only in those ore types 

in which copper minerals are least abundant; 

as a consequence copper carbonates, though 

present in small a1nounts in most of the oxidized ores, are nowhere conspicuous. Chrysocolla was not .observed. In a few of the old 

inine workings, such as those of the Kokomo 

mine, the copper has been temporarily checked 

in its downward progress by the process of 

evaporation and is deposited on the roofs, 

walls, and floors of old drifts as blue-green 

translucent stalactites, coatings, and stalagmites of a hydrous sulphate of iron and copper. 

In the Barnes mine waters carrying cupric 

sulphide descending from the oxidized zone 

have reacted with the iron rails on one of the 

levels and produced metallic copper. Films of 

native copper were also noted along seams in 

the pyrite-chalcopyrite ore of the Gladstone 

mine at depths of less than 75 feet. Copper 

oxides have been reported but are very rare. 

REDEPOSITION OF COPPER BELOW GROUNDWATER LEVEL. 

Copper may be secondarily deposited below 

the oxidized zone, either as chalcopyrite o~ as 

the richer copper sulphides chalcocite, bornite, 

and rarely covellite. The secondary copper 

minerals may line fractures or vugs in the. 

primary ore or may metasomatically replace 

the primary ore minerals. In the section on 

silver enrichment attention has been called to 

the characteristic association of secondary chalcopyrite with the sulpho-compounds of silver, 

and chalcopyrite has also been noted in other 

veins of the galena-sphalerite type in which no 

silver minerals were recognizable. Now here is 

it sufficiently abundant to add greatly to the 

value of the ore. 

The occurrence of chalcocite, bornite, and 

some covellite, probably secondary, in contemporaneous intergrowth with native silver in 

the Up to Date mine has been described (pp. 

147, 149). In this occurrence all the copper 

minerals are contemporaneous. 

The most notable instances of copper enrichment are found in veins of the pyritic type, ' 
PROCESSES AFFECTING THE ORES. 151 

gray films of chalcocite, mainly on chalcopy,rite. 

In son1e places the films show colors suggestive 

of covellite or bornite rather than of chalcocite. Although such films effect only slight 

enrichment in copper, they ·may . exert an 

in1portant influence in the precipitation of 

silver and gold from descending solutions. 

(See p. 114. ) . 

It is noteworthy that in the Evergreen copper 

mine, near Apex, where. the principal metallic 

mineral of the ore is bon1ite, little enrichn1ent 

seems to have taken place. This is doubtless 

attributable to the fact that the bornite, being 

a constituent of monzonite dikes, is comparatively little exposed to active water circulation. 

In at least some· places the secondary 

chalcocite, bornite,- and covellite were deposited from solutions that were alkaline, 

neutral, or only faintly acid, for they are 

associated locally with abundant siderite or 

cal9ite. 

particularly those that carry more than the 

average amount of primary chalcopyrite. Certain ores in the Pittsburgh vein, near Central 

City, furnish the best illustration. The ore of 

this vein is unusually rich in primary copper minerals, principally chalcopyrite, with some tennantite and enargite. It has undergone some 

fracturing subsequent to the primary mineralization, and the fractures have served as channels for copper-bearing solutions descending 

from the oxidized surface portions of the vein. 

Chalcocite was abundant only in the highest 

pn.rts of the vein accessible-that is, a short 

distance above the 500-foot level-but minute 

amounts were noted to depths slightly greater 

than 700 feet. In a stope above the 500-foot 

level the vein consists of 5 inches of. pyrite, 

chalcopyrite, tennantite, gray quartz, and chalcocite, and the texture is. somewhat, porous. 

Examination of a polished section with thereflecting microscope showed that the chalcocite 

was developed by the metasomatic replacement 

of chalcopyrite and to a lesser degree of pyrite. 

f ENRICHMENT IN OTHER METALS. The replacement began along the contacts o 

chalcopyrite with quartz or pyrite or along Sphalerite, the primary zinc mineral of the 

minute fractures traversing the chalcopyrite. ores of this region, breaks down readily in the 

Portions of the ore not far away show much oxidized ores and is taken into solution mainly 

black pulverulent chalcocite in vugs,. and in in balance with. the sulphate radicle. In the 

places the ore is honeycombed with irregular scarcity of carbonates little of it is reprevugs one-eighth to one-fourth inch across. cipitated as zinc earbonate (smithsonite), and 

Ore from this stope averaged about 10 per as sphalerite was nowhere observed to be 

cent of copper. In an underhand stope just clearly secondary, most of the zinc appears to 

below the 700-foot level the vein, which has a enter the ground-water circulation and be lost 

total width of only 2 to 2! inches, consists of a so far as these ore deposits are concerned .. It 

central band made up of chalcopyrite and a is noteworthy that in 'those veins in whicP, 

little tennantite, 1 to 1! inches wide, bordered secondary sulpho-compounds of silver are 

on each side by half an inch of silicified granite developed below the ground-water level as 

· gneiss carrying pyrite.· Shearing movements replacements of the primary ore minerals, 

along the \

7 ein have produced minute fractures galena is commonly replaced but sphalerite 

in the chalcopyrite and tennantite,. and these apparently is not. 

have been filled with gray quartz. Starting Galena ordinarily oxidizes more slowly than 

fron1 the border of these minute quartz vein- sphalerite, .pjrite, or chalcopyrite. The diffilets the chalcopyrite has been replaced by chal- cultly sqluble lead sulphate anglesite was noted 

cocite, narrow rims of which border the quartz. in a few ores, and the carbonate cerusite in a 

Black pulverulent chalcocite was noted on few others, but little opportunity was afforded 

the chalcopyrite of pyritic ore in the 150-foot for the study of oxidation in ores of the galenalevel of the Barnes ml.ne. Films of chalcocite sphalerite type. Secondary galena was nowere noted on chalcopyrite in a stope 100 feet . where observed. 

above the 300-foot level of the Egyptian mine in In the few mines in which pitchblende occurs. 

ore of the galena-sphalerite type, but in general the oxidized ores have been wholly mined out. 

chalcocite is not abundant in ore of this type. A sulphate of uranium whose exact composition. 

In most of the ores copper enrichment mani-. is uncertain has been noted in some of the 

fests itself 111,erely in the development of dark- pitchblende ores, but in ins.ignificant amounts. 
152. GEQLOGY OF GILPIN, CLEAR. CREEK, AND BOULDER COUNTIES, COLO. 

SUMMARY OF ENRICHMENT. is most extensive in the first 100 or 200 feet 

The phenomena of enrich.rnent in the Central below the natural ground-water level and shows 

City qu~drangle are of economic in1portance a progressive decrease with increasing depth. 

mainly in the gold-silver ores, in which enrich- The maximum depth at which secondary silver 

ment in gold and silver has been considerable minerals were noted was 700 feet below the surenrichment in copper of minor a1nount, and face, or about 650 feet below the water level. 

enricrunent in lead and zinc negligible. Two types of n1ineral association were noted 

Enrichment in gold appea;rs to be confined in the rich silver ores; in one secondary sulphoalnlost exclusively to portions of the ore de-· compounds of silver were associated with secposits above or hnn1ediately below the ground- ondary chalcopyrite, and in the other native 

water level; it has affected all types of O'old- silver was associated with abundant chalcocite 

silver ores and has caused a material incre~ent and bornite and some covellite. The secondary 

in the value of the ore in the oxidized zone. silver minerals are deposited in fractures in the 

Enrichment in silver is confined n1ainly to primary ore and also as n1etason1atic replacethe ores of the galena-sphalerite type. It ap- ments of the primary n1inerals. 

pears prob~ble that the relative scarcity of Enrich.J:n.ent in copper is nowhere conspicuous 

pyritic minerals in the galena-sphalerite ores and is confined almost wholly to the groundand the presence of a carbonate gangue. favoring water zone of ores of the pyritic type. ./The oxineutral or alkaline rather than acid conditions dized ores underw.ent impoverishment in cop~ in the secondary sulphide zone are important per. Enrichment in copper is n1ost extensive 

f.actors in restricting silver enrichment below in those deposits whose ores are unusually rich 

the water table to ores of this type. Although in primary copper mineraJs. Chalcocite is the 

in the oxidized.zone of these ores there has been principal secondary copper mineral and is deenrichment in gold, silver seems to have suffered veloped in part as a filling in fractures or a coatimpoverishment. Silver· enrichment is con- ing in vugs and in part by metasomatic replacefined to the ground.:.water zone ~nd consists in ment of chalcopyrite and pyrite. · 

the secondary deposition of pearceite and Enrichment in lead or zinc was not 

proustite and more rarely of native silver. It observed. 

, I 
CHAPTER XII.-ORE TREATMENT, LABOR AND ROYALTIES, FREIGHT RATES. 

By E. S. BASTIN, C. W. HENDERSON, and J. M. HILL. 

ORE TREATMENT. 

HISTORY. 

Entering the' 1nountains with little equiptncnt beyond sho,,el, pick, and pan, the first 

1nincrs in this district saved the gold by the 

usual pioneer 1nethods -of sluicing, cradl~ng, 

and panning. These n1ethods were fmrly 

satisfactory when applied to the stream gravels 

and the o~idized surface ore of the veins, but 

·the 1niners soon discovered that as depth was 

gained on the veins the yield of gold fell off 

rapidly. For this there is an excellent geoloO'ic reason, as the early workings were in the 

o;tcrops of the veins, in which the action of 

air and water had disintegrated the ore, freed 

n1uch of the gold from its sulphide n1atrix, and 

converted it by solution and redeposition into a 

coarser forn1. In the deeper P.O!tions of the 

veins the ore was harder, and most of the gold 

being finely distributed through sulphides 

was n1uch less readily amalgamated. 

• 

Appreciating the difficulty, even if not 

coO'nizant of its causes, the miners sought a 

re~edy in various appliances for fine crushing 

of the ore. An early· device consisted of a 

small mortar whose pestle was attached· to a 

sapling, the spring of the sapling raising the 

pestle. Another device was the "woodpeck~r 

n1ill" which was an iron-shod wooden tnp ' ha1nmer, worked by water power, which fell 

in a wooden iron-lined trough. The arrastre 

early made its appearance, the first one being 

constructed near the mouth of Gregory Gulch 

in July, 1859. Five of them, each 6 feet in 

diameter and constructed of granite, may still 

be seen in the valley of Clear Creek just below 

Dun1ont. This device was followed the same 

summer by the first stamp mill, a homemade 

affair with six stan1ps·, set up at the mouth of 

Chase Gulch and run by water power. It had 

wooden stems, sho~s, and dies, but the dies 

were shod with iron plates. Its operation in 

the summer and fall of 1859 is said to have 

netted its owner about $6,000. The first imported mill appears to have been a little 

3-stamp mill erected in 1859 by T. T. Prosser 

in Prosser Gulch . 

During the first year of the development of 

the region near Central City the scarcity of 

water for ore treatment became troublesome, 

and a company was formed to bring water in 

from Fall River. The ditch built to accoinplish this end had its head above the 1nouth of 

Silver Creek, at the base of the high peaks .of 

the range, was 12 miles long, and traversed 

some rough country. The early n1iners, however, were deterred by no obstacles and had the 

work completed and water flowing at Russell 

Gulch, Nevada ville, and BlaGkhawk early in the 

spring of 1860. The ditch later came under the 

control of New York people, who, through shortsighted management, so antagonized the miners 

that the enterprise was of short usefulness. 

During the summer of 1860 there were 60 · 

stamp mills and 30 arrastres run by water 

power in operation between Nevadaville and 

Blackhawk. These were all working on oxidized ores, but bytheendof that year the heavier 

sulphide ores were reached and the percentage 

of savings. by the mills immediately dropped. 

The year 1861 saw the construction of the 

first mill on South Clear Creek. In Gilpin 

County the savings from sui phi de ores continued 

to diminish, and during 1861 it was found 

necessary to close mine after mine which could 

not be made to pay. Numerous experiments 

were tried, both with stamp mills and leaching 

processes, none of which' was markedly suCcessful. In fact, this change at so shallow a 

depth from free-milling ores to stub born sulphides was a calamity that crushed the hopes 

of many prospectors and caused a suspensiOn 

of operations by numerous companies operating 

in the district. 

In 1861 Caleb S. Burdsall built the first smelter of the region at N evadavillc. This was a 

crude affair that was unfortunately destroyed 

too soon after its erection to prove its worth. 

The difficulty in amalgamating the sulphide 

ores led to what Raymond 1 has called the 

'' process mania.'' 

The process mania, commencing in 1864 and lasting till . 

1867, was one of the main causes which damaged the tepu1 Raymond, R. W ., Statistics of mines and mining in the Sta~ and 

Territories west of the Rocky Mountains, 1869, pp. 347-348, 1870. 
154 GEOLOGY OF GILPIN, CLEAR CREEK, AND BOULDER COUNTIES, COLO. 

tation of the mines to such a degree that the cduntry was 

nearly ruined by the reaction. Upon the first failure of 

the" stamp mills, the people came to the conclusion that the 

ore must be roasted before the gold could be amalgamated. 

One ".invention for this purpose followed another; desulphurization became the abracadabra of the new alchemists, 

and millions of dollars were wasted in speculations based on 

sweeping claims of perfect successes put forward by 

deluded or deluding proprietors of patents. 

In 1866 hope was revived by the successful 

experiments of Nathaniel P. Hill, of Blackhawk, on the smelting of Gilpin County ores. 

In 1867 several of the idle mines were reopened 

in ·anticipation 'of the opening of the Hill 

smelter, whose construction was started in the 

fall of that year. It was opened for business in 

January, 1"868, and consisted of a calcining 

furnace and a small reverberatory. The fire 

brick were shipped by rail from St. Louis to the 

terminus of the road and then 600 miles by 

wagon. The iron cost 22 cents a pound and 

skilled labor $8 to $10 a day. Th~ sm.elting 

charges were $20 to $45 a ton, and the matte 

was hauled to the Missouri and shipped by way 

of New York to Sw.an~ea, in Wales, for resmelting. The plant. was in operation until 1878, 

when it was removed to Argo, near Denver. 

A very complete description of this plant has 

bee~ given by Egleston.1 · 

MILLING OF GOLD ORES. 

In Gilpin, Clear Creek, and Boulder counties,. 

as in many other mining districts, the goldsilver. ore .as mined can be divided into two 

parts. The larger part is called concentrating 

ore, milling ore, or ''mill dirt,'' and is of such 

character that its metal content.is most economically saved by some form of amalgamation 

or concentration. The smaller part, called 

"smelting ore," is of such character that its 

metal content is best recovered by smelting. 

After the establishment of the Blackhawk 

smelter the mill men of the region were not idle, 

h11:t continued to strive actively to improve 

methods of amalgamation and concent:r:ation; 

In May, 1869, over 800 stamps were dropping 

in Gilpin County. Supplies were necessarily 

. expensive on account of the long wagon haul 

from Denver, but· this difficulty was largely 

alleviated by the completion of the Colorado & 

Southern Railway to Blackhawk in 1872 and to 

Floyd Hill, on South Clear Creek, in 1873. 

1 Egleston, T., Boston and Colorado smelting works: Am. Inst. Min. 

Eng. Trans.1 vol. 4, pp. 276-298, 1876. 

The mills now in use are of three principal 

types: (1) The old style Gilpin County stamp ,, 

mill, in which battery amalgamation has been · 

brought to a high degree of perfection,· at the . 

sacrifice· of crushing efficiency; (2) the fastdrop stamp mill of the California type, depending on outside plate amalgamation, the in,ferior 

amalgamating efficiency being compensated for 

by more effective conce~tration; and (3) the 

plant in which amalgamation is wholly discarded and concentration may be supplemented 

by cyanidat.ion or flotation. 

The first stamp mills· extensively used in the 

district were of t4e California pattern, and in 

the middle of 1860, according toT. A. Rickard, 

there were 60 stamp mills of this pattern in 

operation near Central City. While heavily 

oxidized surface ores were being milled, this type 

of stamp did fairly well, effecting savings as high 

as 75 per cent of the gold content. When the 

sulphide ores were reached, the extraction fell to 

an average of but 30 per cent of the gold content. 

To meet these changed conditions the California 

practice was modified, and what is now known 

as the Gilpiri County practice was gradually 

evolved. In the following tabulation of data, 

published· by T. A. Rickard, the California 

and Gilpin County practices are concisely contrasted, the figures in the table representi.pg 

the extremes of both practices: 

Comparison of Gilpin County and California. stamp-rn~ll 

practices. 

Gilpin County. California. 

Weight of stamps ... lbs.·. 500-600 ......... 750-850. 

Number of drops per 30 ............. 90-105. 

minute. 

Height of drop .. inches .. 18-20 .......... 4-6. 

Size of mortars ......... .- Roomy...... . . . Small a n d narrow. Amalgamation plates.... Insl.de and out- Outside. 

side. 

Height of discharge, 14 .. ~ ..•....... 4. 

inches. 

Size of· screens .. mesh .. 60-70 .......... 40. 

Ore crushed in 24 hours 1. . . . . . . . . . . . . . 2,-3. 

per stamp ...... tons .. Pyrite in the ore, per 15 ....... ~----- 1-2. 

cent. , Gangue ................ . 

Distribution of gold .... 

Cost per ton with free 

water power: .. cents .. Gold saved by amaJgamation ..... per cent .. 

Altered granite 

gneiss, some quartz. 

Very fine and 

intimately as- sociated with 

the sulphides. 

Quartz, some slate . 

Coarse and 

p r actically 

free. 

70 .... -....... - 35. 

75 ............ - 70. 
ORE TREATMENT, LABOR AND ROYALTIES, FREIGHT RATES. 

·Reasons for· the differences· between Cali- mills constructed in the last 10 or 15 years the 

fornia and Gilpin Co:unty practice lie in differ- pulp after leaving the plates is classified, and 

ences ill the ores. In the California deposits the fragments of different sizes are concentrated 

the gold is usually free in quartz and amalga- on tables adjusted to these sizes. 

mates readily. In Gilpin County most of the Within the last few years amalgamation has 

gold is finely divided in sulphides and aJ?l~lga- been ~ntirely discarded in a number of mills, 

n1.ates much less readily. T.o effect a reason-. and stamps if used at all are employed only for 

abb saving on Gilpin County ores it is necessary crushing. An example is the Frontenac mill, 

tq prolong the period of amalgamation by hold- in which, accqrding to Downey/ the recovery 

ing the m.ateriallonger in the stamp n1ort.ars, is about 85 per cent of the gold and 78 per cent 

which are provided with amalgamating plates. of the silver content of the p,verage ore, whose , 

This is accon1plished by increasing the depth value is between $8 and $10 a ton .. 

of the n1ortars, decreasing the size of the dis- Although it is hazardous to attempt to give 

charge s9reen, decreasing the weight of the any figure for the average extraction effected 

stamps, increasing tl;w height fron1 which they by the mills employing amalgama~ion and condrop, and decreasing the nun1ber of drops per centration, becau~e of the vru·iation in mill 

n1inute. The Gilpin County stamps are there- practice and in the character of the ores, it is 

fore used both for crushing and for amalgama- probably not wide of the truth to say that it 

tion, whereas the CnJifornia stamps are used seldom exceeds 75 per cent of the gold and 40 

pritnarily for crushing, the principal amalgama- per cent of the silver in ores having a value betion taking place subsequently on the plate tween $5 and $10 a ton. The ratio of concentables.1 tration varies from 30 into 1 to 4 into 1. This 

~ . Many of the mills of the district are still of saving may seem small compared with that obthe old Gilpin County type, but with the im- tained in some other district~, but it should be 

provement in concentrating deVices there has recalled that most of the mines of this region 

been a tendency to depend 1nore on conce~tra- have always been dependent on custom mills 

tion and less on amalgamation. This tendency and that these mills have ·of necessity been dehas n1anifested itself in the adoption· in soine signed to suit. a number of ores approximately · 

mills of heavier and faster stamps (a partial rather than a single one exactly. When it is 

return to tho California prn.ctioQ) and the addi- remembered that in a single mine ores of the 

tion of n1oro concentrating machinery. In pyritic type may predominate at one place and 

1899, out of 600 stamps in 14 mills in Gilpin ores of the galena-sphalerite type at another, 

County there were 140 which had a rapid drop and that each of these types is itself somewhat 

and mediun1 discharge. The old Gilpin County variable, it is not surprising that the milling 

practice, although yielding a high percentage processes are not always closely adjusted to 

of the procious-metal content in the readily the ore being treated and that savings effected 

1narketablo form of amalgam, produced large do not always compare favorably with those 

an1ou.nts of slilnes from which there could not obtained ,elsewhere in ores of more uniform 

be ·a good saving by concentration. In the character. Some of the custom mills continue 

newer n1ills there is still son1e slime to handle, the former general practice of treating each lot 

but the ore as a whole is not crushed so fine, of ore separately, at a certain rate (average, $9) 

and much better concentration is possible. In per cord (8 to 9 tons), turning over to the miner 

the early n1ills 'the pulp after leaving the the gold and silver bullion saved by amalgamaanutlganlation plates was usually run, over tion. The concentrates are also turned over to 

Gilpin County bumping tables without any t~e n1iner, who moves them to the sampler or 

attempt at sizing, and a large part of the finely smelter. Sometimes the custom. n1ill acts as 

crushed sulphides, carrying valuable amounts agent for the miner,· selling the bullion to the 

, of n1etals, went down the strean1s~ In the bank or to the United States .Mint and ~oiling 

•• 1 'The C!_\lifornla and Gilpin County stamp-mill practices are discussed 

In tho following papers, which have been freely drawn upon in this 

doscrip~ion: Rogers, A. N., Tho minos and mills of Gilpin County, 

Colo.: Am. Inst. !I:Un. Erig. Trans., vol. 11, pp. 29-55, 1883. Rickard, 

··r: A.,"'l'he llmit~tions of the gold stumr:i milE Idem, vol. 23, pp. 137-147, 

~~ . 

the concentrates. Sometimes tho mill acts also 

as agent for the ore hauler and distributes the 

proceeds frmn the sale of bullion and concen-

• 2 Downey, C. J., A modern type of concentrator in Gilpin County: 

Min. Sci., vol. G4, p. 52, 1911. 
156 GEOLOGY OF GILPIN, CLEAR.-CR.EEK, AND BOULDER COUNTIES, COLO. 

trates between the miner, hauler, and mill. If charge of the remodeling and subsequent opera-· 

the ore is mined by lessees the custom n1ill may tion. In the later part of 1913 this mill enalso pay ·the royalty to the mine owner. Some tirely discarded amalgamation. 

of the newest custom mills purchase the· ore The latest development in ore treatment in 

outright from the miner, paying on the basis of the district is the installation in 1915 and 1916 

the assay value. , of flotation cells at the Hudson and Argo mills. 

The successful tTeatment of gold-silver ores 

in nlany districts by the cyanide process natu- ·MILLING OF SILVER AND OTHER ORES. 

rally led to experiments on the ores of this re- Much of the rich silver ore mined in this 

gion. There have been a number of experi- region has been shipped direct to the smelter, 

menters. The Collins brothers 1 from their but a few mills have -been erected to treat the 

work decided that it was not economically pos- lower grades. One of the first silver mills was 

sible to cyanide concentrates, and that "the that erected by A. D. Breed at. ~ederh1nd in 

game was not worth the candle" for tailings. 1871. This mill was equipped with Blake 

Later experiments by Alsdorf, Draper, and crusher, stamps for dry-crushing the ore,· 

others on Gilpin County ores led them to con- Bruckner cylinders for chloridizing roasting, 

elude "that there was no particular difficulty and amalgamating pans. A few years later 

in the cyanidation of the ores, and crude con- another mill, also employing c}lloridizing roastcentrates containing 2 per cent copper and ing, was erected at Caribou to treat the ores 

only 10 to 12 per cent silica could be cyanided of the Native Silver mine. After long 'cessadirect without undue cyanide consumption tion of milling in the Caribou district the dump 

and with a high extraction." 2 and stope fillings of the old Caribou mine are 

These experimenters were not in a position now being re-treated by oonoentration and 

to install a mill to put their faith into practice, cyanidation at the Cariman mill, of 25 tons 

and it was left to the Hudson Reduction Co., of daily capacity, at Caribou. A complete descripIdaho Springs, to demonstrate on a commer- tion of this mill has been given by Parmelee.5 

cial scale the possibility of this· metallurgic The Jo Reynolds mill, erected between 

process. This company in 1911 rebuilt its Dumont and Lawson in 1900 to treat the silver 

amalgamation and concentration mill to in- ores of the Jo Reynolds mine, is purely a conclude cyanidation. Parmelee 3 has described . c(mtrating. mill, stamps being used only for 

this mill in detail, giving the recovery in amal- regrinding. It. has a capacity of 40 tons in 24 

gam, concentrates, and cyanide precipitates as hours and yields a lead and zinc concentrate. 

88 per cent of the value of the ore. In 1913 the The treatment of the Boulder County tungArgo mill, at the mouth of the Argo tunnel, was sten ores is entirely one of concentration. 

put into operation. In its. construction the Hills 6 has described the methods and has 

practice developed at the Hudson mill was fol-1 pointed out that the chief difficulty is the large 

lowed closely, but changes have been made in loss due to excessive sliming. Parmelee 7 in 

details which have increased' the extraction. 1911 further discussed the problems of tungThis mill has been described by several writers/ sten concentration. 

including_ Roller and Curran, designers and first. The Delano chlorina.tion plant 8 for the treatoperators, and Heizer and Pearce, who had ment of Boulder County telluride ores was 

1 Collins, G. E., Lessons from Gilpin County practice: Min. and Sci. 

Press, vol. 101, pp. 366-371, 1910. 

2 Draper, M. D., Cyanidation in Colorado: Min. and Sci. Press, vol. 

103, p. 684, 1911. 

1 a Parmelee, H. C., Cyaniding by continuous decantation in Clear 

Creek County, Colo.: Met. and Chern. Eng.,vol. 10, pp. 27-31, 1912. 

4 Goodale, S. L., Eng. and Min. Jour., vol. 00, pp. 385-389, 1913: Colorado State Bur. Mines Twelfth Bienn. Rept., p. 80, 1913. 

Roller, A. H., and Curran, H. T., Ore treatment at the Argo mill: 

Eng. and Min. Jour., vol. 98, p. 1, 1914; idem, p. 217. 

Pearce, J. A., Cyanidation of Clear Creek and Gilpin County sulphides: Min. and Sci. Press, vol. 109, pp. 833-837, 1914; Refining cupriferous precipitate: Min. and Sci. Press, vol. 112, pp. 270--272, 1916. 

Heizer, 0. F., Colorado State Bur. Mines Thirteenth Bienn. Rept., 

pp. 87-90, 1914. 

Parmelee, H. C., Cyanidation of low-grade sulphide ores in Colorado: 

Met. and Chern. Eng., vol. 13, pp. 421-425, 1915. 

successfully operated for some years. 

In thefollowingtable brief information is given 

in regard to most of the mills of the district. In 

consulting it the reader should -remember that 

the equipment of many of the active mills is 

undergoing frequent modification. 1 

6 Parmelee, H. C., Caribou, Boulder County; cyaniding of low-grade j sulphide ores in Colorado: Met. and Chern. Eng., vol. 13, pp. 477-479, 1915. 

o Hills, V. C., Tungsten mining and milling: Colorado Sci. Soc. Proc., 

vol. 9, pp. 135-153, 1900. v / 

7 Parmelee, H. C., The problems of tungsten concentration: Met. and ./ 

Chern. Eng., vol. 9, pp. 341-342, 409-411, 1911. ;' 

s Burger, C. C., Ore treatment in Boulder County: Eng. and Min. 

Jour., vol. 65, pp. 129-130, 1898. 

... 
ORE TREA~MENT, LABOR AND ROYALTIES, FREIGHT RATES. 157 

Mills in Central City region treating gold-silver or silver ore$. 

Name. Location. 

Alton ................. North Beaver Creek, 

2 miles west of N ederland. 

13ailey ................. ' Middle Boulder Creek, 

1! miles west of Eldora. 

Caribou (old' mill) ... t mile west of Oaribou ... 

Caribou (new mill, Caribou ....... · ........ . 19~4). 

Boulder County.... . . CardinaL. ............. . 

Alice................ Silver Creek, t miles sou~hwest of Alice. 

Gold Anchor ....... · .. 

Ninety Four ........ . 

Lombard ........... . 

Silver Creek, ! mile 

northwest of Alice. 

Silver Creek, i mile 

northeast of Alice. 

Cumberland Gulch, 1 

·mile south of Yankee. 

Lalla................. Silver Creek, 1 mile 

northeast of Alice. 

Standard ....... :.: .. Fall l~iver, 1 mile east 

of Hamlin Gulch. 

Phillips.............. Fall River,~ mile northwest of York Gulch. 

United Gold......... Fall River, t mile north 

of South Clear Creek. 

Brighton............ Mouth of Fall River .... 

Silver' Mountain. . . . . Empire Station ......... . 

Boulder County. 

Capacity 

(tons in 

24 hours). 

25 

30 

40 

100 

35 

Process. 

Amalgamation and con- centration. Expect 

to install cyanidation. 

Cyanidation ............ . 

Concentration ......... . 

Cyanidation ............ . 

Amalgamation and con- centration. 

Clear Creek County. 

20 Amalgamation and con- centration. 

40 Amalgamation ......... . 

25 Dry concentration ..... . I 

100 Amalgamation and con- centration. 

25 ..... do ................ . 

30-40 ..... do .. ~ ............. . 

20 · ..... do ................. . 

50 ..... do .... ~ .......... . 

40 Concentration ........ . 

50 ..... do ........... · ... . 

Equipment. 

1 jaw crusher, 15 quick-drop 

850-pound stamps, :3 outside 

amalgamation plates, 1 classifier, 2 Wilfley and 2 Card 

tables, 2 Monell slimers, 3 canvas tables, 1 Hartz jig. 

Crusher, 2 sets rolls, tube mill, 

Portland filter press, 3 re- volving barrels. Never operated. 

1 crusher, 10 stamps, classifier, 

1 Wilfley table, 1 canvas table. 

Crushers, screens, 2 Hardinge 

mills, Flood classifiers, Card 

tables, Dorr classifiers, leaching vats, 3 Dorr agitators, 1 

Dorr thickener, Portland 

filter. 

Blake crusher; 10 stamps, Wilfley tables, etc. Former 

gold-silver mill transformed 

to tungsten concentration 

and back to gold-silver. 

Now dismantled. 'Equipment 

last used was 1 jaw crusher, 

5 rapid-drop 950-pound 

stamps, outside amalgamation plates, patent amalgamator, 1 Gilpin County 

bumper, 1 classifier, 2 Card 

tables. 

1 jaw crusher, 10 stamps. 

1 ']aw crusher, 3 sets rolls, 4 

Waugh dry tables. 

1 jaw cru·sher, 20 quick-drop 

1,000-pound stamps, 3 outside amalgamation plates, 1 

box classifier, 3 Wilfley 

tables, 3 Card tables. 

5 stamps, 1 outside amalgamation plate, 1 Gilpin County 

bumper. 

1 jaw crusher, 20 quick-drop 

stamps, 1 box classifier, 2 

outside amalgamation plates 

4 \Vilfley tables. 

1 set rolls, 5 stamps, 1 outside 

amalgamation plate, 1 Wilfley table. 

1 jaw crusher, 10 quick-drop 

stamps, 2 outside amalgamation plates, 1 Gilpin 

County bumper, 1 Wilfley 

table. 

1 ja,w crusher, 1 set rolls, 1 

Huntington mill, 4 trammels, 

settli1ig box, 4 jigs, 3 Wilfley tables, 1 Card slimer, 1 

Roberts belt table. 

1 jaw crusher, l Huntington 

mill, l set rolls, :3 trammels, 1 

classifier, 2 jigs, 3 Frue 

vanners, 1 Cammett table. 
158 GEOLOGY OF GILPIN, CLEAR CREEK, AND BOULDER COUNTIES, COLO. 

Mills in Central City region treating gold-silver or silver ores-Continued. 

Clear Creek C~unty-Continued. 

Name. Location. 

American Sisters ..... Silver Creek, 1 mile 

south of Lawson. 

Jo Reynolds ......... South Clear Creek, 1 

mile west of Dumont. 

Blue Ridge..... . . . . . South Clear Creek, neax Dumont. 

Syndicate ................. do ............... . 

Clear Creek and Gilpin. 

Clear Creek, i mile east 

of Dumont. 

Mountain Queen...... South Clear Creek, Dumont. 

Capacity 

(tons in 

24 hours). 

Process. 

30 Amalgamation and con- centration. 

40 ..... do ................ . 

40 ..... do ............ ." ... . 

100 Amalgamation and con- centration. · 40 Concentration ......... . 

5-8 Amalgamation and con- centration. 

Donelson............. South Clear· Creek, at ............... do ............... .. mouth of Fall River. 

Hoosac............... South Clear Creek, i 

mile east of Fall 

River. 

Stanley ............. : South Clear Creek, ! 

mile east of Trail 

Creek. 

Argo ................. South Clear Creek, 

mouth of Argo tunnel. 

Combination (Staley) South Clear Creek, 

Idaho Springs. 

Lincoln.......... .. . .. Soutl:). Clear Creek, t 

mile east of Trail 

Creek. , Mixsell.. ............. South Clear Creek, Icl~o Springs. 

Waltham ............ ChicagoCreekandSouth 

Clear Creek. 

Idaho Springs Re- South Clear Creek, 

duction Co. Idaho Springs. 

Jackson ........... ". Chicago Creek and 

South Clear Creek. 

Hudson .................. do ................. . 

35 ..... do ................ . 

50 ..... do ................ . 

100 Cyanidation and con- centration. Flotation 

added in 1916. 

50 Amalgamation and con- centration. 

50 ~ .... do ... ~ ....•........ 

20 ..... do ....... · ......... . 

30 ..... do ................ . 

20 ..... do ................ . 

50 Concentration ......... . 

88 Amalgamation, concen- tration, and cyaniclation; flotation added 

in 1915-16. 

Equipment. 

1 jaw crusher, 1 set rolls, 10 

stamr.s, 3 trommels, 2 cone classifiers, 2 sand classifiers, 2 

jigs, 2 Wilfley tables, 2 Card 

tables, 1 Frue vanner. 1 jaw crusher, 2 sets rolls, 10 

rapid-drop stamps, 4 trommels, 3 Hartz jigs, 1 settling 

box, 1 Callow tank, 2 Carel . tables, 1 spiral plane table, 

1 Frue vanner. Crusher, 2 sets rolls, 3 Card 

tables. Completed 1913. 

30 stamps, tables. 

1 jaw crusher, 10 quick-drop 

stamps, 1 set rolls, 3 trommels, 

3 Wilfley tables, 3 jigs. 

1 jaw crusher, 10 stamps; 2 outside amalgamation plates, 

1 Wilfley table. 

1 jaw crusher, 4 trommels, 

5 jigs, 50 slow-drop stamps, 

10 outside amalgamation 

plates. Remainder dismantled. 

10 rapid-drop 1,050-pound 

stamps, 2 outside amalgamation plates, classifiers, 3. 

Wilfley tables. Built, 1912. 

1 jaw crusher, 1 set rolls, 8 jigs, 

10 stamps, 2 amalgamation 

plates, 3 trommels, 3 classifiers, 2 Cammett tables. 

1 gyratory crusher, 20 1,050-

pouncl stamps, 6 Dorr classifiers, 7 Dorr thickeners, 9 

Carel· tables, Parrall and Dorr 

agitators, Portland filter. 

15 1,050-pouncl stamps with 

outside and inside amalgamation plates, classifier, 1 

tube mill, 4 Wilfley and 2 

Card tables, 1 Deister slimer. 

10 stamps, etc. 

·1 jaw crusher,. 10 stamps, 2' 

outside amalgamation plates 

3 Gilpin County bumpers, 1 

Card table. 

Partly dismantled. 10 slowdrop stamps remain; 

5 stamps and tube mill left of 

former equipment of 30· 

stamps (1,050-pouncl), 3 ball 

mills, amalgamation plates, 

8 Wilfley tables, 3 Frue van-· ners. Dismantled. 

l jaw crusher, l set rolls, 2 

Huntington mills,3 trommels, 

3 jigs, 3 classifiers, 3 Card 

tables, 1 Roberts huddle, 1 

belt table, 2 Callow cones .. 1 jaw crusher, 20 stamps and. 

outside amalgamation plates,· 

3 Ca.rd.tables, 2 Wilfl.ey tables,. 

2 Aiken classifiers, 3 Dorr 

thickeners, 2 Callow cones~ 

agitators, etc. 
. ( 

ORE TREATMENT, LABOR AND ROYALTIES, FREIGHT RATES. 159 

Mills in Central City region treating gold-silver or silver ores~Continuecl. 

Clear Creek County-Continued. 

Name. 

Gem (Newton), east 

section. 

Gem (Newton), west 

sectwn. 

Gem(Newton annex), 

east section. 

Gem (Newton annex), 

west section. 

Bertha ............... 

Wilkie .............. 

Black Rills and 

Denver. 

Golden Sun ........ . 

Location. 

C hi c a g o Creek and 

South Clear Creek. 

..... do ................. 

..... do ............. : ... 

.. ~ .. do ..........•.... 

South Clear Creek, 

mouth 

Canyon. 

of Virginia 

South Clear Creek, 1 

mile below Idaho 

Springs. 

South Boulder Creek, 

l! miles east of Tolland. 

South Boulder Creek 1 

mile east of Boulder 

Park. 

Smuggler ....... ~ .... SouthForkMoonGulCh, 

2 miles south-southwest of Rollinsville. 

Mountain Monarch... Gamble Gulch, 2 miles 

south- southwest of· 

Rollinsville. 

Penobscot........... Gamble Gulch, 2! miles 

south- southwest of 

Rollinsville. 

Perigo............... Gamble Gulch at Perigo. 

Golden Flint .............. do.- ...... : ....... . 

Gettysburg .......... . 

Reform ............. . 

Pine Cone ........... . 

i mile southwest of Gilpin. 

Silver Creek, 2! miles 

north of junction with 

North Clear Creek. 

Missouri Creek, ! mile 

south of Wide Awake. 

Capacity 

(tons in Process. 

24 hours). 

-

150 Concentration .......... 

............ . .... do ................. 

Not used. Amalgamation and con- centration. 

250 Concentration .......... 

20 Amalgamation and con- · centration. 

40 Concentration .......... 

Gilpin County. 

50 Amalgamation and con- centration. 

50 Concentration ......... . 

30 Amalgamation and con- centration 

30 ..... do ................ . 

30 .. __ .do. _____ .......... . 

100 ...•• do. ______ .•.... ·- ... I 

100 Cyanidation _ ...... ·: .. 

Concentration ......... . 

Amalgamation and con- centration. 

I 

Equipment. 

1 jaw crusher, 1 set rolls, 10 

quick-drop stamys, 3 trommels, 3 jigs, 5 \Vi fley tables, 

4 cone . classifiers, 1 Frue 

'~nner . 1 jaw crusher, 1 set rolls, 10 

quick-drop stamps, 3 trommels, 3 jigs, 1 box' classifier, 5 

\Vilfleytables, l Fruevanner. 

10 stamps with amalgamation 

hlates, 3 Wilfley tables, 1 Wiley slimer. 

1 jaw crusher, 1 set rolls, 40 

quick-drop stamys, 3 trommels, 6 jigs, 8 Wi fley tables, 

1 Wilfley slimer. 

1 jaw crusher, 3 Kinkaid (Virginia City, Nev.~ mills, 5 

quick-drop stamp , 2 outside 

amalgamation plates, 3 Giltn 

County bumpers, 2 Wil ey 

tables; idle for years; partly 

cl isman tl eel. 

Crusher, stamps, jigs, \Vilfley 

tables; partly dismantled. 

1 Sampson crusher, 1 Elspass 

roller mill, 1 Pierce amalgamator, 6 Dixon tables. 

1 jaw crusher, 2 sets rolls, 1 

King classifier, ~box classifiers, 2 Wilfley tables, 2 Frue 

slime tables. 

1 jaw crusher, 10 stamps (60 

drops a minute) with amalgamation plates, 2 Gilpin 

County bumpers, 1 \Vilfley 

table. 

1 jaw crusher, 10 quick-drop 

stamps, 2 outside amalg~mation plates, 4 Gilpin County 

bumpers, 1 Bartlet table. 

1 jaw crusher, 10 quick-drop 

stamps, 2 outside amalgamation plates, 4 Gilpin County 

bumpers, 1 Standard table. 

1 jaw crusher, 30 stamps with 

outside amalgamation plates, 

12 Gilpin Cotinty bumpers. 

25 stamps. amalgamation plates, 

Pierce· amalgamator, Card tables. This mill abandoned 

in 1912 a,nd new mill with 

rolls, tube mill, Card tables, 

and cyanide agitation tank 

commenced1913. 

3 rolls, 3 air concentrators. 

10 stamps, King-Darrough table. 

30 ..... do ................. 20 stamps, 4 outside amalgamation plates, 2 Gilpin County 

bumpers. 
160 GEOLOGY OF GILPIN, CLEAR CR.EEK, AND BOULDER COUNTIES, COLO. 

Mills in Central City region treating gold-silver or silver ores-Continued. 

Name Location. 

Annie H ............. Elk Creek, 2 miles west 

of Apex. 

Gilpin County-Continued. 

Capacity 

(tons in 

24hours). 

30 

·Process. Eq1:1iptment. 

Amalgamation and con- 1 jaw crusher, 10 stamps, 3 Gilcentration. pin County bumpers, 3 Frue vanners. Mackey .................. do .......................... . Amalgamationandcyan- 10 stamps, cyanide tanks, etc. 

idation. 

Pioneer ............. . 

Booster ............. . 

Junction North Clear 

Creek and Pine Creek, 

2 miles south of Apex. 

South of Evergreen mill, 

Apex. 

Evergreen............ ! mile south of Apex .... 

North Star ......... . 

Wheeler ....... : .... . 

Pecks Flat, 1! miles 

east of Yankee Hill. 

North Clear Creek, 1! 

miles northwest of 

Blackhawk. 

Amalgamation and con- 10 1,000-pound stamps. In 

centration. construction 191~. 

40 

? ..... do ................ . 15 stamps with outside amalgamation plates, 1GilpinCounty 

bumper. 

60 . Concentration (copper 1 jaw crusher, 2 sets rolls, 2 

ore). trommels, 1 Callow cone, 1 

Richards classifier, 3 Card I tables. .. , ....... Amalgam:=ttion and con- 110 stamps. 

centrat10n. ............... do................. 25 slow-drop stamps with outside amalgamation plates, 5 

Gilpin County bumpers. Mill 

Brooklyn ............. North Clear Creek, 1 ............... do ......... ~ ...... . mile northwest of 

partly dismantled. 

1 Jaw crusher, 10 stamps with 

outside amalgamation plates, 

jigs, and Gilpin County 

bumpers. 

Hidden Treasure .... 

Polar Star ......... . 

" Fifty " ........ -.. - -

Rocky Mountain ..... 

Frontenac .......... . 

Tucker ............. . 

U. P.R. (Buell) 1\'fill. 

Blackhawk. 

North Clear Creek, ! 

niile north of Black-

' hawk. 

North Clear Creek, 

mouth· of Chase 

Gulch. 

North · Clear Creek, 

mouth of Gregory 

Gulch. 

North Clear Creek, ! 

mile east of Blackhawk. 

North Clear Creek, f 

mile east of Blackhawk. 

Chase Gulch, i mile 

northwest of Blackhawk. 

Gregory Gulch, east end 

of Central City. 

Gilpin-Eureka....... Prosser Gulch, i mile 

west of Central City. 

Casto................ Winnebago Hill, north 

of Teller House, Central City. 

. .............. do ................ . 

49 ..... do ................ . 

350 ..... do ................ . 

.......... Concentration ......... .. 

250 ..... do ................ . 

' 50 ..... do ................ . 

150 Amalgamation and con- centration. · 

50 ..... do ................. . 

30 ..... do ................ . 

Pleasant Valley ...... Elkhorn Gulch, 3 iniles ............. ~.do ............... .. southeast of Blackhawk. 

A von. . . . . . . . . . . . . . . Nevada Gulch, east end 

of N evadaville. 

60-100 ..... do ................ . 

Gold Coin .......... Nevada Gulch, south of ............... do ............... .. N evadaville. 

10 stamps (originally 40) 2 outside amalgamation plates, 2 

·Wilfley tables. 

40 slow-drop 500-pound stamps 

with amalgamation plates, 8 

Gilpin County bumpers. 

80 stamps with outside amal- ~amatiOn plates, concentratmg tables. 

Machinery removed. . New 

process to b.e installed in 

building in 1916. 

1 jaw crusher, 3 sets rolls, 3 

trommels, 3 jigs, 3 cone thickeners, 9 Flood classifiers, 20 Card tables,_ 4 Deister 

tables. 

1 jaw crusher, 1 set rolls, 3 

trommels, 5 Hartz i'igs, 10 

stamps, 3 Wilfiey tab es. 1 jaw crusher, 45 rapid-drop 

stamps with outside amalgamation plates, 5 Gilpin 

County bumpers, 3 Wilfley 

tables, 1 Standard table. 

1 jaw crusher, 1 set rolls, 10 

stamps with outside amalgamation plates, Pierce amalgamator, 2 Wilfley tables, 2 

Callow cones, 1 Deister 

slimer, 1 Frue vanner. 1 jaw crusher, 10 stamps with 

outside amalgamation plates, 

1 classifier, 2 cqncentrating 

tables, 1 Horn slimer. 

1 jaw crusher, 2 sets rolls, 20 

stamps with outside amal 

gamation plates, 4 Gilpin 

County bumpers. 

1.jaw crusher, 30 stamps with 

outside amalgamation plates, 

6 Gilpin County bumpers, 

1 Wilfiey table. 

25 stamps, 18 amalgamation 

pans. Partly dismantled. 

~· 
ORE TREATMENT, LABOR AND ROYALTIES, FREIGHT RATES. 161 

Mills in Central City region treating gold-silver or silver ores-Continued. 

Gilpin County-Continued. 

I 

Name. Location. 

Capacity 

(tons in 

24 hours). 

Clear Creek Mining Blackhawk .............. .............. & Milling Co. 

Eagle ............... .. ... do ................. ............ 

Oliver ............... . .... do ................. ............... 

New York .......... ..... do ................. 150 

Randolph •.......... ..... do ................. 100 

Iron City ............ North Clear Creek, f 75 

mile east of Blackhawk (immediately 

adjacent to Frontenac). 

SMELTING. 

HISTOll.Y. 

· After two unsuccessful· attempts to smelt 

the ores of Gilpin County in 1861 and 1866/ a 

successful stnelter was opened for business in 

January, 1868, at Blackhawk by Nathaniel P. 

I-Iill, 2 with two reverberatory furnaces, one for 

calcining and one for smelting.3 In 1869 the 

works consisted of two ·reverberatories for 

roasting and two for smelting, together with 

roast heaps in the open air. There was also 

a terrace furnace, not used. Early. in 1871 

the plant consisted of two calcining furnaces for tailings, which are too finely pulverized to be roasted in heaps, two Gerstenhofer 

or terrace furnaces for calcining (riever satisfactorily operated), and two reverberatory 

smelt~g furnaces.4 The plant was enlarged 

during the summer of 1871 by one smelting 

'Haymond, R. W., Lyon's smelting works: Statistics of Mines and 

Mining in the States and Territories west of the Rocky Mountains, 1869, 

p. 359, 1870. 

D rrm smelter or Boston & Colorado Smelting Co. organized in 1867; 

first experimental plant erected at Blackhawk in June, 1867; establish· 

mont opened for business January, 1868; first shipment or matte June, 

1808. 

a l3aln, lJ. F., Matte smelting at Denver: Min. and Sci. Press, vol. 100, 

p. 251, 1010. 

'}'or detailed description of process, see Raymond, R. W., Metal· 

lurgical processes (smelting): Statistics of mines and 'mining in the 

States and Territories west of the Rocky Mountains, 1869, pp. 362-363, 

1870; 1870, pp. 368-370, 1872; also Hague, J.D., Mining industry: U.S. 

Geol. Expl. 40th Par. H.ept., vol. 3, pp. 577-586, 1870. 

44214°-17--11 

Process. Equipment. 

_9oncentrate mill waste ... 48 canvas tables, 2 Frue van- ners, 2 Wilfley tables. 

Amalgamation and con- 25 stamps·, Gilpin County 

centration. bumpers. . .... do ................. Stamr,s, amalgamation plates, tabes. ..... do ................. 70 stamps and amalgamation 

hlates, 20 Gilpin County 

umpers., . .... do ......•.......... Originally 50 stamps, 10 plates, 

10 bumling tables, water 

power. n 1914 operating 

part of mill consisted of 

crusher, Challenge feeders, 

10 750-pound stamps (53 

drops a minute), amalgamation plates, 2 Gilpin County 

bumping tables, 6 Wilfley 

Concentration and subtables; electric power. 

1 jaw crusher, 25 rapid-drop sidiary amalgamation. stamps, Flood classifiers, 5 

Card tables, 2 Deister tables, 

regrinding pan, 2 Callow cones. 

furnace, a reverb era tory of the same type as 

the two older ones. In 1872 a blast furnace 

was added for reworking slags obtained by 

the treatment of zinciferous silver ores. 

From the beginning of operations this company had shipped its copper matte to Swansea, 

Wales, for separation, but in the summer of 

1873 Richard Pearce 5 built separating works 

at Blackhawk for this smelter, and the first 

silver bullion, 0. 998 fine, was turned out early 

in November. The residue was shipped to 

Boston for the recovery of the gold and copper. 6 

In 1875 :Mr. Pearce invented a process for 

the separation of the gold, "silver, and copper, 

at Blackhawk. 7 This process 8 was not made 

5 In April, 1872, Richard Pearce, of Swansea, Wales, built the Swansea 

smelter (capacity 8 tons in 24 hours) ncar Empire, Clear Crook County, 

similar in design to tho Hill smelter. Owing to the deficiency of iron 

pyrite the smelter was operated steadily only about one month in 1872, 

but in 1873·it was operated intermittently, tho deficiency being supplied 

from Gilpin County. No mention of tho Swansea smelter is made in 

reports subsequent to 1874, and it was probably closed when Mr. Pearce 

took over tho superintendency of the plant at Blackhawk and lead 

smelters were erected at Golden. Mr. Pearce apparently started at the 

Swansea smelter his experiments for tho extraction of silver from the 

matte and carried tho results of those experiments to Blackhawk. 

e Raymond, R. W., op. cit., 1874, p. 361, 1875. 

7 For description of the Blackhawk plant and process, smelting charges, 

capacity, otc., seo Egleston,. T., The Roston and Colorado smelting 

works, in Raymond, R. W., Statistics of mines and mining in the 

States and Territories west of the Rocky Mountains, 1873, pp. 294-295, 

379-394. 1877; Am. Inst. Min. Eng. Trans., vol. 4, pp. 276 ot soq., 1876. 

s The 'revelation of a metallurgical secret: Eng. and Min. Jour., vol. 87, 

pp. 464, 963, 1909. Pearce, 11. V., Am. Inst. Min. Eng. Trans., vol. 39, 

pp. 722-734, 1908. . 
162 GEOLOGY 01!, GILPIN, CLEAR CREEK, AND BOULDER, COUNTIES, COLO. 

public until after the decision in 1908 to close supply of ,galena proved inadequate, it was 

and dismantle the smelter at Argo, a suburb altered to a copper-matte, smelter. Golden 

of Denver to which the smelter had be(m became for a short time a smelting cet) ter of 

removed in 1878 from Blackhawk, because of sonw importance. In 1880 three plants were 

the expansion of business and ·the need of in operation there, but from 1884 to 1888 

closer accessibility to fuel supplies. The re- inclusive, only one was in operation. In 1901 

:finery at Argo was destroyed by fire in 1906 and the Golden semipyritic plant was built by 

was not rebuilt. The fires of the smelting fur- F. R. Carpenter according to plans developed 

naces were finally" out" on March 17, 1910. at Rapid City and Deadwood, S. Dak., for 

It was at. the Argo smelter that Richard the purpose of treating highly pyritic ores 

Pearce developed the smelting of copper ore from Gilpin and Clear Creek counties. The 

in reverberatories, gradually working up from smelter, operated for several years by the 

5-tcm to 100-ton furnaces. The works at one Clear Creek Mining & Reduction Co., s1nelted 

time included five furnaces, later reduced to large quantities of ore from the Saratoga mine, 

two, and finally to one (1909-10). In 1900 the which the company controlled, also ore b~ught 

AI:go works were the only works in the United in the open market. In April, 1910, this 

States that smelted gold and silver ores to plant, after the addition of a reverberatory, 

matte exclusively in reverberatory furnaces. was reopened as the North American semiCopper at Argo was merely a vehicle, and only pyritic plant for the treatment of copper and 

sufficient cupriferous ore was employed to pyritic ores of Gilp~, Clear Creek, and other 

make sure of thoroughly collecting the precious counties, · and was operated intermittently 

metals; the .average charge smelted containing until November, 1911. Its building is still 

less than 2 per cent copper. The ores treated intact, but none of the other plants at Golden 

comprised pyritic (auriferous) ores and con- are standing. 

centrates .from Gilpin County and elsewhere, About the time the owners of the Argo plant 

barytic silver ores from Aspen and Creede, were planning to go put of business, a new 

siliceous telluride and other gold ores from matte smelter, styled the Modern, . with 

Cripple Creek, and any and every kind of ore McDonald furnace, went into blast on October 

containing gold and silver and not too rich in 22, 1909, at Utah Junction, a short distance 

lead. 1 ' from Globeville, on ores purcha$ed in the 

While the Hill smelter at Blackhawk had market from Clear Creek~ Gilpin, Lake, and 

the distinction of being the first successful other counties, but it was closed in April, 1910, 

smelter of the district and with its successor at and was never operated again, being dismantled 

Argo played ·a most important part in the in 1915-16. 

development of this region, several other The American Smelting & Refining Co.'s 

smelters were also in operation at different Globe plant, at Denver, Iiow treats most of the 

times. In 1872 there were in operation the ores of this region .. ,Some ore from GeorgeSwansea matte smelter at Swansea, near town and Rollinsville goes to· the Ohio & ' 

Empire; a matte smelter at the Whale mill Colorado Smelting & Refining Co.'s plant, 

(now a part of the Stanley mill), near Idaho at Salida. Zinc ores and concentrates from 

Springs; and a lead smelter at Golden (Bayley Georgetown and . Idaho Springs go to the 

& Sons or Golden City Smelting Works). In United States Zinc Co.'s plant, at Blende, and 

1873 a lead smelter (Denver Smelting Works) to spelter plants in Kansas and Oklahoma. 

was established at Denver. In 1875 the 

Collom Co., which already had separating and 

concentrating works at Idaho Springs and 

Blackhawk, completed a lead smelter at 

Goldep.. •The Golden Smelting Co.'s plant was 

constructed at Golden in the same ye~r. 

This plant, which started in .September, was 

first operated fl.s a lead smelter, lmt as the 

1 Collins, H. F., Silver, pp. 181, 299-303, 314-315, 1900. 

EARLY SMELTING AND 1\HI. .. LING CHARGES. 

The smelting and milling charges in the early 

days· of the development of the region seen1 

prohibitive compared with those now in vogue. 

The prices paid by the Blackhawk smelter 

previous to January 1, 1870, are shown in the 

following schedule, which was not, however, 

invariably adhered to .. 
ORE· TREATMENT, LABOR AND ROYALTIES, FEEIGHT RATES. 163 

Prices paid by Blaclchawk smelter before 1870. 

Ounces of ,Percentage Ounces of ·Percentage 

fine gold of the value fine gold of the value 

per ton of the gold per ton of the gold 

of 2,000· and copper of 2,000 and copper 

pounds. paid. pounds. · paid. 

10 GO 5 45 

9 58 4 40 

8 5G 3 30 

7 52.G 

I 

2 20 

6 \ 50 

In calculating the value of ore according to 

the above scale; tl;t.e ounce of fine gold was 

reckoned at $20 coin, and the unit (1 per ceht) 

of copper at $2. The copper unit, however, 

was reckoned on the ·English ton; and as the 

ores were assayed and purchased by the short 

ton, a deduction of 12 per cent was made from 

the copper assay. Thus, if an ore was found 

to contain 8 per. cent (or 8 units) of copper, 

worth according to the above scale $16, a deduction of 12 per- cent was m·ade, to adapt it 

to the En,glish ton. Moreover, the copper was 

determi~ed by wet assay, from which 1.5 per 

cent wa~ deducted for working loss, so that if 

the percentage of copper contained in an ore 

did not exceed 1.5, no account was taken of it 

in paying for the ore. The silver in the ore 

was paid for at the rate of 75 cents an ounce, 

after deducting J ounce of silver for each unit 

or per cent of copper present. 

Raymond/ in discussing the smelter charges 

,at this time, says: 

The complicated system of prices, p~rquisites, and deductions employed by smelters in calculating their payment for ores is justly complained of b'y the miners, as 

serving merely to bewilder the seller and conceal the 

profits of the buyer. Many items might be simplified in 

the interest of fair dealing. The theory, however, is correct that the prices paid for ores must be graduated not 

merely according to their actual contents in valuable 

metals, but with reference also to the grade and character 

of ore, as influencing the cost of reduction. It is probable that on the foregoing schedule Prof. Hill lost something in the purchase of the lowest grades and made it up 

on the rich ores. Indeed, he would doubtless refuse to 

purchase 2-ounce gold ores, did he not require them, in 

the absence of cheaper fluxes, to mix with the others. 

* * * At the time of my visit, in the autumn of 1870, 

I was told that no regular schedule was followed. I heard 

of in~tances in which $5 a ton was paid for tailings, cont~ining from 1 to 1! QU~ces of gold. The developments in 

Grand Island district [Caribou] having made silver ores 

1 Raymond, R. W., Statistics of mines. and mining in the States and 

Territories west of the Rocky Mountains, 18i0, p. 3i2, 1872. 

an important part of the supply of th~ works, the prices 

paid for silver had been advanced, possibly to prevent 

shipments of ore to the East. For 100-ounce silver ores 

80 cents per ounce was paid, and fqr very rich ores a8 high 

as $~.30 currency-a deduction of $50 per ton being made, 

however, for the cost of reduction. Probably these works, 

being well established and commanding large capital, 

could afford to advance prices still further, if competition 

should require it-a consideration full of warning to the 

eager projectors of -rival establishments. 

The precious metals. in .the ores were up to 

1874 never paid for below a certain minimum, 

which for, silver was 40 ounces and for gold 

1! ounces. In July, 1874, an arrangement was' 

adopted whereby the Blackhawk smelter paid 

for gold ores at the· rate ·of 85 per cent of the 

total value of the gold and silver contained 

after deducting $35 (currency) a ton for treatment. The gold was estimated at $20 an ounce 

and the silver at $1.25 (gold) an ounce, with 

the premium (3 per c(mt below New York quotations) added. 

Schedules for silver ores are given in the 

table below,· the minimum of 40 ounces still 

holding.· The prices are based on the premium 

on gold in New York, ranging between $l.l0 

and $1.15. 

Schedule of prices paid for silver ores by Blackhawk smelter 

July, 1874. · 

Silver content Price paid of ore (in 'cur-

(ounces per rency) per ounce of 

ton). silver. 

40 .........•. '. 

50 ........... . 60 ........... . 70 ........... . 80 ........... . 90 ........... . 

100 ........... . 125 .......... . 150 .. ·.· ...... . 175 .......... . 200 ......... .. 250 .......... . 

$0.34 . 44 

. 52 

. 60 

. 66 

. 70 

. 74 

. 82 

. 89 

. 93 

. 97 

. 99 

I . 

I

. Silver content 

of ore (ounces per 

ton). 

j3oo ....... · ... 350 ......... : 400 ........ .. 450 ........ .. 500 ......... . 600 .......... . 70.0 ......... . 

800 .. ~ ...... . 900 ......... . 

1, 000 ....... . 

12, 000 ........ . 

----------~--------~--

Price paid 

(in cur- rency) per ounce of 

silver. 

$1.01 

·1. 03 

1. 05 

1.06 

1.07 

1.08 

1.09 

1. 10 

1. 11 

1. 12 

1. 16 

Copper was paid for at. $1.50 currency for 

each unit by the dry Cornish assay. 

SAMPLING WORKS. 

DEVELOPMENT. 

While ·not confined to this district nor ~o the 

State of Colorado, public sampling w0rks for. 

the purchase of ores were-probably first established in this district and to this ·day have 
164 GEOLOGY OF GILPIN, CLEAR. CREEK, AND BOULDER. COUNTIES, COLO. 

continued to be a vitai factor in its mining 

industry. These works in the· early days 

served as agents or brokers for smelters at 

Swansea, Wales, ill Germany, and in the middle Western and Eastern States of this country. Later they acted as agents for or sold 

ores to the Blackhawk smelter, and still more 

recently have acted as agents or middlemen 

for smelters_ at Denver, Pueblo, and other lo-

~alities within and without the State. The 

Chamberlain sampling works at Blackhawk 

was built on the site of the Hill smelter soon 

.after its removal to Argo in 1878 and has been 

operated continuously since that time, selling 

the pur<;hased ores both to the Argo smelter 

.and to other smelters, according to the char-

.acter of the ore. The Chamberlain sampling 

works at Idaho Springs was opened in ~883. 

At the present day the Chamberlain sampling 

works at Georgetown, Idaho Springs, and 

Blackhawk are the only ones remaining in 

operation, although during the _time of the 

operation of the North American smelter at 

Golden the smelter company had its own 

sampling works at Idaho Springs, and for 

some time previous to 1910 the Santiago 

Mining Co. operated a sampling plant at 

Georgetown. 

PAYMENT FOR. ORES. 

The sampling works pays the n1iner for his 

ore according to certain schedules or contracts 

based on the assay of the ore for the precious 

metals, the base metals, and other components 

that aid or interfere with smelting, the charges 

for sampling, freight, and smelting being deducted. An attempt is made to crush, sample, 

assay, and pay for the ore in one or two days, 

and in this promptness of payment lies the 

great advantage of the sampling works to the 

small producer. The n1iner can, if he so desires, watch all the operations of the sampler, 

and he has his own or a public assayer check 

the assaying of the sampler. If the ore is 

shipped direct to the smelter a much longer 

time elapses before payment for it can. be received, and as a rule only the larger producers 

can brook this delay; moreover, the smelters 

do not handle less than carload lots. A considerable quantity of the ore received by the 

samplers is delivered irregularly in small lots, 

by the wagon load, with no contract as to 

grade, tonnage, price, or time of delivery, 

and in acting as a purchasing agent for ore of 

this class the sampler-·serves perhaps its n1ost 

useful purpose. The engineer may use the 

sampler as a testing plant for small lots of ore 

of questionable grade; if those small lots do 

not carry sufficient quantities of metals to pay. 

freight and treatment charges, he is out only 

the price of sampling, and the ore or rock can 

be transferred to an amalgamating or con-

.centrating mill or thrown on the dump. 

At present the Chamberlain sampling works 

act almost exclusively as agents for the American Smelting & Refining Co., although they 

have recently disposed of certain lead-zinc 

sulphide ores and uraniun1 ores to other concerns. The sampling works have many contracts with milling companies whereby the 

latter can ship their ore either to the sampling works or direct. to the American Smelting 

& Refining Co.; any contracts made with the 

American Smelting ~- Refining Co. will be 

fulfilled by the sampling works if the ore is 

shipped to the latter. The ·bulk of the ore 

from this district goes through the sampling 

works before going to the f?melter. For the 

purchase of ores in this district the following 

publicly posted or ''open'' schedules were in 

use in February, 1916. The smelting charges 

given include sampling. If a contract is made 

to deliver a certain monthly tonnage, the 

smelting charge is $1 a ton less than the 

''open'' schedule. If less than carload lots 

are delivered at the sampler, an additional $1 

a ton is charged for sampling. Of the several 

schedules, payment is made in accordance with 

the one most favorable to the miner. 

General schedule for all classes of ores and concentrates, 

Clear Creek, Gilpin, and Boulder districts, e.ffective July 1, 

1912. 

[All rates f. o. b. cars Denver. Lots to contain not less than one 

carload. Subject to change without notice.) 

Upon all classes of ore: 

Gold, $19 per ounce if 0.05 to 2 ounces per ton; $19.50 

if over 2 ounces per ton. 

Silver, 95 per c·ent of the New York quotation on 

date of assay, when ore 1\ssays 2 ounces or over per 

ton. 

Copper, for dry copper (1.5 per cent off wet assay) up 

to and including 5 per cent, 6 cents off ·western 

Union quotation for casting copper. Over 5 per cent 

to 10 per cent dry, 5 cents off quotation; over 10 per 

cent dry, 4 cents off quotation. 

Zinc, limit 10 per cent: Penalty 50 cents for every 

unit over 10 per cent. 

$14 gross value and under, $5 treatment charge. 
·< 

ORl~ TREATMENT, LABOR AND ROYALTIES, FREIGHT RATES .. 165 

Upon all classes of ore-Continued. 

Over $14 to $20 gross value, $6 treat~ent charge. 

Over $20 to $25 gross value, $6.50 treatment charge. 

Over $25 to $30 gross value, $7 treatment charge. · 

Over $30 to $35 gross value, $7.50 treatment charge. 

Over $35 to $'10 gross value, $8 treatment charge. 

Over $40 to $45 gross value, $8.50 treatment charge. 

Over $45 to $50 gross value, $9 treatment charge. 

Over $50 gross value, $10 treatment charge. 

Pay 25 cents per unit for lead if 5 per cent or over. 

Apply to lead ores "neutral schedule" or "flat schedule" of July 1, 1912, if either figures better for shipper than·above schedule. 

Apply to dry ores, $7 treatment charge, neutral basis, 

10 cents adcled or subtracted for each unit of variation up or down from the neutral basis, when this 

figures bettor for shipper than ·the "flat schedule." 

Dry concentrates: 

Gold, silver, and copper as above. 

Silica (insoluble matter), 10 per cent limit; penalty of 

10 cents for every unit above 10 per cent. 

Zinc, 5 per cent limit; penalty of 30 cents for every 

unit over 5 per cent. 

$35 gross value and under, $3.50 treatment. 

$36 to $80 gross value, $4 treatment charge. 

Over $80 gross value, $4.50 treatment charge. 

1.'he maximum treatment charge upon concentrate!'!, 

including silica penalty but not zinc penalty, shall not 

exceed the maximum charge upon crude ores of the same 

grade. 

S1Jecial schedule for lead ores and concentrates: Clear Creek 

and Gilpin counties, effective J'u.ly 1, 1912. 

[All rates f. o. b. cars Denver. Subject to change without notice. 

Lots to contain not less than one carload.) 

J.,ead ores: 

Gold, $19.50 per ounce if 0.05 ounce or over per ton. 

Silver, 95 per cent of the New York quotation on date 

of assay. 

:Lead, prices based upon $4 per 100 pou:nds and based 

on dry lead (1.5 per cent off wet assay). 

CopperJ for dry copper (1.5 per cent off wet assay) 6 

cents off Western Union quotation for.casting copper. 

Zinc, 10 per cent limit; penalty 50 cents for every unit 

over 10 per cent. 

Neutral schedule. 

Per cent of lead (dry). 

5 to 10, inclusive ................ . Over 10 to 15, inclusive ......... . Over 15 to 20, inclusive .......... . Over 20 to 25, inclusive ......... . Over 25 to 30, inclusive ......... . Over 30 to 35, inclusive ......... . Over 35 to 40, inclusive ......... . Over 40 to 45, inclusive ......... . Over 45 to 50, inclusive ......... . Over 50 to 55, inclusive ......... . Over 55 ......................... . 

Price 

paid 

(cents per 

unit of 

lead). 

40 

43 

45 

47 

49 

51 

52 

52 

53 

54 

55 

Working 

charge 

per ton. 

$6.00 

5.00 

4.00 

3.00 

3.00 

2.00 

1.50 

1.00 

1. 00 

1. 00 

1. 00 

---------------------------~------~-------

Neutral basis.: 10 cents added or subtracted for each unit 

of variation up or down from the neutral basis .. 

Flat schedule. 

Per cent,of lead (dry). 

5 to 10, inclusive .............. : .. . Over 10 to 15, inclusive ..... : ... . Over 15 to 20, inclusive ......... . Over 20 to 25, in~lusive ......... . Over 25 to 30, inclusive .......... . Over 30 to 35, inclusive .......... . Over 35 to 40, inclusive ......... . Over 40 to 45, inclusive ......... . Over 45 to 50, inclusive .. : . ..... . Over 50 to 55, inclusive ......... . Over 55 ......................... . 

Price 

paid 

(cents per 

unit of 

lead). 

40 

43 

45 

47 

49 

51 

•52 

52 

53 

54 

55 

Working 

charge 

per ton .. 

$10.001 

8. 50• 

7.·00· 

5. 50• 

4. 50, 

3. 501 

2.00' 

1.00 

] . ()() 

1.00 

1. ()(), 

"Neutral schedule" to be used when it figures. better 

for shipper. 

Lead concentrates: 

Gold, $19 per ounce if 0.05 ounce to 2 ounces per ton; 

$19.50 if over 2 ounces. 

.Silver and· copper, as in lead ores. 

Lead, prices based on $4 per 100 pounds. 

Silica, limit 10 per cent; penalty of 10 cents for every 

unit over 10 per cent. 

Zinc, limit 10 per cent; penalty of 50 cents for every 

unit over 10 per cent. 

Per cent of lead (dry). 

5 to 10, inclusive ................ . Over 10 to 15, inclusive .......... . Over 15 to 20, inclusive .......... . Over 20 to 25, inclusive .......... . Over 25 t? 30, inclusive .......... . 

Price 

paid 

(cents per 

unit of 

lead). 

40 

43 

45 

47 

49 

Working 

charge 

per ton. 

$3.7& 

3. oo2. 5()-

2. 25· 

2. 25· 

Upon concentrates assaying over 30 per cent lead, apply 

"neutral schedule" or "flat schedule," whichever figures: 

better for shipper; gold, $19 per ounce up to 2 ounces~ 

$19.50 if over 2 ounces per ton. 

LEAD QUOTATION. 

The prices paid per unit for lead in all ores and concentrates are based upon a quotation of $4 per 100 pounds, 

1 cent up or clown for each change of 5 cents in the quotation. 

The quotation used as a basis of settlement shall be 

figured as follows from the New York sales price of the 

American Smelting & Refining Co. on date of settlement. 

When the sales price does not exceed $4 per 100 pounds: 

take 90 per cent of the·sales price. Whe:tJ. it does exceed 

$4, add to $3.60 per 100 pounds one-half of the excess of 

the New York sales price above $4. 

As the name implies, the neutral schedule 

refers to the balance between iron and silica, 

and "neutral basis, 10 cents up or d·own"· 

means that 10 cents per unit is paid for the iron 

excess over silica and 10 cents is deducted per 

·unit of silica excess over Iron. 

The use of the scheduies given ·above n1ay be 

illustrated by the following examples. 
166 GEOLOGY OF GILPIN, CLEAR CI_tEEK, AND BOULDER COUNTIES, COLO. 

EXAMPLE I. 

Calculation of the net value of a sulpillde ore carrying 

Q.3 ounce of gold and 29 ounces of silver to the ton, 26 per 

cent of dry lead, 12 per cent of zinc, 18 p.er cent of silica, 

and 11 per cent of iron. Date, October 1, 1914. 

A.. Under neutral schedule. 

Gold, 0.3 ounce at $19.50 per ounce. Silver, 29 ounces at 95 I?er cent of 

the New York quotatiOn for the 

date of assay (which was 52i 

. cents per ounce) .............. . Lead, 27.50 per cent wet assay, 26 

per cent dry (26 units). Lead 

quotation $3.75 per 100 pounds; 

90 per cent of $3.75 is $3.375; 

$4.00 less $3.375 is $0.625. For 

each change of 5 cents in the 

quotation, 1 cent up or down, so subtract 12.5 cents from 49 

cents, making 36.5 cents per 

Credit. Debit. 

$5.85 

14.43 ......... . 

unit. 26 times 36.5 is........... 9. 49 .......... 

Smelting charges ......................... .. Silica excess over iron." ................... . Zinc excess ................................ . 

29. 77 

4. 7() 

Net value per ton. . . . . . . . . . 25. 07 

B. Under flat schedule. 

Credit. 

$3.00 

• . 70 

. . 1. 00 

4. 70 

Debit. 

Credits as in neutral schedule...... $29. 77 ...... _ .. _ 

Smelting charges........................... $4.50 

Silica (no premium or penalty) ............ _ ..... __ .. _. Zinc excess. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1. 00 

Net value per ton ......... . 

29.77 

5.50 

24.27 

5.50 

As tlus is a lead ore the general schedule for all classes 

of ore would not be best, for there would be a smelting 

charge of $7 alone for an ore of gross value between $25 

and $30, and in addition there would be a penalty of $1 

for zinc excess; moreover, gold would be paid for at $19 

an ounce instead of $19.50. In tills case, therefore, the 

neutral schedule for lead ores figures best for the shipper 

and is the one adopted. 

EXAMPLE II. 

Calculation of the value of ore carrying 45 per cent 

silica and 15 per cent 'iron, the other constituents being 

as in Example I. 

A. Under neutral schedule. 

Credit. Debit. 

Credits as under neutral schedule 

in ~xample I ........... .-....... $29. 77 .... ~·- ... . Smeltmg charges................. .. .. .. .. .. $3.00 

Penalty for silica excess over iron ....... _.... ·3. 00 

Penalty for zinc excess ............... _...... 1. 00 

29. 77 7. 00 

7.00 ......... . 

Net value per ton ......... _ 22.77 ......... . 

Under flat schedule the net value would be $24.27, as 

in Example I under the flat schedule. In tills case, 

therefore, the flat schedule figures better for the shipper 

and is the one adopted. ' 

SETT.LE.M:ENT SHEET. 

If a producer shipped to the sampler a lot of 12,720 

pounds (6.36 tons), gross weight (4 per cent moisture, net 

weight 12,221 pounds, 6.11 tons), of the ore shown in 

Example I the sampler settlement sheet would be as· follows, $1.50 a ton being charged for freight and $1 a ton 

for sampling (the sillpment being· less than, a carload; 

see p. 164). The value of the ore is figured on the net 

weight. · 

.••••••••••.•••• ~ ••••••...••••.•••••• OnE SAMPLING Co., 

Blackhawk, Colo., October 1, 1914. _ ................................... nline .. 

I I 

I Assay. Gross Mine lot Sampler Gross Per cent Net weight. per Net per Total 

No. lot No. weight. H20. ton. net. 

Au. Ag. Pb. Cu. ton. 

------

1 4360 12, 720 4.0 12,211 0.03 29.00 26.0 ........ $29. 77 S25.07 $153.06 

Freight .... 9.54 

143.52 

Sampling .. 6.36 

137.16 

Quotations. Fe. Si02 • Zn. S. 

Ag. 52i- ... 11.00 18.00 12.00 a Sul. 

Pb. 3.75 ............ 'I' .................. 'i'.- ......... Signed ............................... 

·--- Manager. 

a ''Sui" means over 6 or 7 per c·ent sulphur. 
OUE TREATMENT, LABOR. AND ROYALTIES, FREIGHT RATES. 167 

Zinc frmn this district goes to the smelter 

1nostly in the fonn of concentrates, although a 

s1nall quantity of zinc ore is produced in Clear 

Creek County. The ore runs 36 to 54 per cent 

in zinc, and the zinc concentrates fro1n Gilpin 

County seldorn exceed 25 per cent in zinc. The 

following schedule was in use in October, 1914: 

S])ecialscheclulejor Clear Creek and Gilpin counties for zinc ore and concentrates of sntelting grad~. 

Bn.se, f. o. b. Denver, 

carloads, $16.50 per 

ton. 

Unit variation for 1 

per cent or 1 ounce up or down 

from base. 

Premium or penalty 

with variations in 

market price. 

Spelter. St. Louis ........... ·...... 5 cents per ton for 

$5 a hundre~weight. each variation of 

1 cent from $5. 

Lead, New York ............... .. $4 a h i.md red weight. 

Zinc, 40 per cent ..... . Wet lead,6.50percent. 

Silver, 10 ounces .... . Gold, 0.05 ounce .... . CaO+MgO, J percent. 

$1.00 . 30 

. 40 I 19,00 

1.00 

EXAMPLI~ III. 

None. 

Cn.lculation of the value of an ore carrying 0.42 ounce of 

gold, 12.50 ounces of silver, 8.70 per cent of wet lead, 45 

per cent of zinc, and 1 per cent of CaO. lTor this ore the 

zinc schedule would be the most advantageous, the calcnlation being as follows: 

I 

Assay and Variation Base. market Credit.!Debit. from base. values. I 

$16.50 ......... .................. ....................... $16.501= 

Spelter, $5 .... Assume -$0.10 at 5 ...... $0.50 

$4.90. cents. 

J.Jead, $4 ...... .................. None ...... ~ None. None. 

Zinc, 40 per 45 per cent + 5.00 at $1.. 5.00 ........ cent. 

Wet lead, 6.50 8.70 per +2. 20 at 30 . 66 .......... per cent. cent. cents. 

S 11 v e r, 10 12.50 ounces +2. 50 at 40 1.00 ........... ounces. cents. 

Go 1 d, 0.05 0.42 ounce. +O. 37 at $19. 7.03 ------ ounce. 

CaO+MgO, 1 1 per cent .. None at $1. .. None. .......... per cent. ----

30. 19 0. 50 . 50 ............ 

----- Net value ................... .................. 29. 69 ............ 

per ton. 

ExAMPLE IV. 

Ca.lculation of the value of an ore 'carrying no gold, 112 

ounces of silver, 13.50 per cent of wet lead, 32 per cent of 

zinc, 10 per cent of silica, and 10 per cent of iron. 

A. Under zinc schedule. 

Base. 

Assay or Variation market [Credit from base. Debit. 

values. 

1---

$16.50 ......... ........................ . ............. $16. 50 

Spelter, $5 .... $6 ......... +$1 at 5 cents 5.00 ............ Lead, $4 ...... $5.10 ....... No variation. .. .......... Zinc, 40 per 32 per cent. -8 at $1. .... $8.00 

cent. 

Wet lead, 6.50 13.50 per + 7 at 30 2. 10 ............ per cent. cent. . cents. 

S 1 1 v e r, 10 · 112 ounces. +102 at 40 40. 80 ............ ounces. cents. 

Go 1 d, 0.05 None ..... .-0.05 at $19. ............ ..95 o~nce. 

Iron, 10 ... .. .......................... ............ ............ Silica, 10 .. .. .......................... ............ ............ 

----

64. 40 8. 95 

8. n5 ........... ----- Net value .................... ........................... 55. 45 .. ........ per ton. 

B. Under neutral lead schedule. 

[Assumed market values, silver $0.64, lead $5.10.] 

CreditJDebit. 

----------------1------

Gold, 0.05 ounce, not paid for ....................... . Silver, 112 ounces, at $0.608 (95 per cent 

of $0.64) per ounce ..................... $68. 10 

Lead, ~2 per cent dry assay, at $0.46 per Ulllt................................ 5. 52 

NoTE.-The lead price is arrived at as follows: To $3.60 add 

$5.10-$4.00 or$0.55, making 

2 .' $4.15. To ·the 

43 cents per unit shown in 

the schedule for ores with 10 

to 15 per cent lead, add 3 

cents, or 1 cent for each 5 

cents difference between $4.15 , and $4.00. 

Smelting charge. . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . $5. 00 

Penalty for zinc (22 excess over 10 per 

cent). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11. 00 

73.62 16.00 

16.00 ..... . 

Net value of ore per ton............. 57. 62 ..... . 

For this ore the neutral lead schedule is more advan-· 

tageous to the shipper than the zinc schedule and is the 

one· adopted. 

Had silver been 52 cents and lead $3.50, the credits I 

under the neutral lead schedule would have been $55.33 

for silver. and $3.12 for lead, a total of $58.45 credits, from 

which the debit of $16 leaves a net credit of $42.45 . 

In this case the zinc schedule would be better, with zinc 

market at $6. It is possible that for the ore represented 

above some. reduction would be made in the $11 zinc 

penalty. 

On October 14, 1914, · the sampler had ·no 

schedule for zinc ore, concentrates, and 1nid-
168 GEOLOGY OF GILPIN, CLEAR CREEK, AND BOULDER. COUNTIES, COLO. 

dlings that must be reconcentrated, but for 

any such material a special price can be obtained on request. 

On January 24, 1916, the following zinc 

schedule was issued: . · 

United States Zinc Co.'s publicly posted zinc schedule January 24, 1916, for Georgetown, Idaho Springs, and Blackhawk, Colo. 

Base: $20 f. o. b. Blende ($1 per ton additional freight 

Denver to Blende). 

6.11 ounces gold. 

13 ounces silver. 

30 per cent zinc. 

No regard for spelter quotations. 

Premiums or penalties for variations up and down from 

base: · · 

Gold $19 per ounce. 

Silver $0.45 per ounce. 

Zinc $1.50 per unit over 3Q per cent; $2 per unit under 

30 per cent; no zinc leBB than 29 per cent. 

1 per cent lime allowed, penalty of $1 per unit for 

excess. 

The ores and concentrates purchased by 

the sampling .works are kept in· separate · 

bins, and after the metal content of each lot 

has been calculated they are mixed in such 

proportion as to make the best charge for the 

blast furnace. The sma:ll quantity of copper 

ores produced in this region is not sent to 

copper plants, for there are no exclusivel:x 

copper smelters in Colorado; such ore is mixed 

with the other ores and sent to the lead smelters. 

Copper, lead,. and siliceous or dry. ores are 

smelted at Denver, Pueblo, and Salida. The 

zinc ·and lead-zinc ores are treated at zinc 

smelters at Pueblo and at different localities 

in Kansas, Oklahoma, and Illinois. Formerly 

·zinc-lead middlings were treated at the Western 

·Chemical Co.'s sulphuric acid, wet concentration, and dry magnetic separation plant. 

The following schedule of the Argo mill'at 

Idaho Springs· for the purchase of gold-silver 

ores from Gilpin and Clear. Creek counties was 

still in. effect February 21, 1916. The ores 

treated in 1914-15 ranged from strictly gold 

ores from Empire to silver-lead-gold, silvergold-copper, and other complex ores from mines 

near the line of the Argo tunnel. 

Schedule D, The Argo Reduction & Ore Purchasing C<!., 

Idaho Springs, Colo., purchase of ores f. o. b. Argo Mtll, 

November 10, 1914. 

[Subject to change without notice.) 

Gold: Pay $19 per otmce, if 0.05 to 1.5 ounces per ton; 

$19.50 per ounce if over 1.5 ounces per ton. 

Silver: Pay New York quotation, date of as~y, for 60 

per cent of the silver assay, if 1 ounce or over per ton. 

Lead: Deduct 2 units from the fire assay and pay 25 cents 

per unit for the balance. 

Copper: Deduct 1.5 per cent from the wet assay and pay 

$1 per unit for the balance. 

Zinc: No pay; no penalty. 

Sampling: No charge. 

No lots less than 10 tons received. 

Treatment charges. 

TreatGross value per · ment I Groea value per 

ton. charge ton. 

per ton. 

Up to $5. __ .... $3.50 Over $20 to $25. 

Over $5 to $6 .... 3.75 Over $25 to $30 . Over $6 to $7 .... 4.00 Over $30 to $35 _ Over $7 to $8 .... 4.25 Over $35 to $40 _ Over $8 to $9 .... 4.50 Over$40to$45 .. Over $9 to $10 ... 4.75 Over $45 to $50 . Over $10 to $11 .. 5.00 Over $50 to $7 5 . 

Over $11 to $14 .. 5.25 Over $75 ....... Over $14 to $20 .. 5.50 

LABOR AND ROYALTIES. 

Treatment 

charge 

per ton. 

$6.25 

7.50 

8.00 

9.00 

9.50 

10.00 

11.00 

12.00 

For many years 1 the leasing system has been 

prevalent in mining in this region, and at one 

time or another has been operative in nearly 

every mine of the region. Under this system 

certain portions of a mine or more rarely the 

entire mine are leased for short terms to a 

miner or group of miners who assun1e the costs 

of operation and pay to the owners a royalty· 

on the ore extracted .. An effect of this system 

has been to give a large number of the miners 

of the region the status of independent operators and to exempt the region from the labor 

troubles that have afflicted many camps whose 

mines were under company operation. It has 

also permitted a large number of mines that 

might otherwise have been closed to continue 

operation, though ra~ely to their full capacity. 

On the other hand, the methods employed have 

not been as economical and far-sighted from the 

standpoint of the mining technologist as they 

might have been under company management, 

lessees naturally being more concerned in obtaining a quick and sure return on their investment than in safeguarding the interests of the 

owners or of future lessees. This difficulty has 

been obviated in some mines by the maintenance of a certain .amount of company supervision over the operations of lessees, the com1 As early as 1871 Raymond recorded that the larger number of the 

older claims which had been idle for several years had been taken up 

under lease by miners, almost every one of whom made good money, 

and some of them small fortunes. 
J 

ORE TREATMENT, LABOR AND ROYALTIES, FREIGHT RATES •. 169 

pany under some contracts operating the hoists 

and furnishing rails arid certain other ~quipment and maintaining thro-q.gh a superintendent some inspection of the methods of mining. 

On ores of fairly uniform character, such as 

those of the Old Town and Saratoga mines, a 

fiat royalty based on the net return~ is charged. 

In many mines this amounts to 25 per cent for 

smelting ore, bu:t in' the Old Town, where the 

company hoists the ore and furnishes rails, etc., 

a royalty of one-third is charged. In the 

Perigo mine 25 per cent is charged on smeltingore and 10 to 15 per cent on concentrating ore. 

In the Ophir-Burroughs 10 per cent is charg.ed 

on concentrating ores. In mines where the ore 

is more variable in metal content the charges 

are graded to the value of the ore. In the San 

Juan mine, for example, the royalties are as 

follows: 

Net return on ore. Royalty 

(per cent). 

FREIGHT RATES. · 

The. freight· rates on the Gilpin' Tr~mw~y, _a \ 

road of 24-inch gage that connects the pnnmpal 1nines of Gilpin County with Blackhawk, . \ 

range from 35 to 75 cents a ton for smelting 

ore and concentrates, depending on the distance of the mine from Blackhawk. Minimum charges of $3 to. $6 a car (holding about 9 

tons) are fixed to prevent the· ship~ent of 

only small lots in a car. For concentrating 

ore the rates are somewhat lower, ranging from 

$2.5.0 to $5 a ·car according to distance from 

Blackhawk. 

Hauling charges in the Argo tunnel in February, 1916, were as follows: Waste 51 cents a 

car (of about 51 cubic feet capacity), or approximately 17 to 20 cents a ton; concentrating ore (under $20 in value) 60 to 75 cents a 

ton, according to quantity. 

·Switching charges from the mouth of the 

Argo tunnel to mills or sampling works at 

Idaho Springs are 15 cents a ton for lots of 20 

tons or over. 

$40 or over ................................ . $25to $40 ................................. . 25 Freight rates over the Colorado & Southern 20 

Less than $25 .............................. . 15 Railway are proportioned to the value· ?f ·the 

smelting ore or concentrate. From the principal ~hipping points to either ·Gol~en or Denver 

they are as follows: In the Gmn mine there is a graded royalty· 

of 25 ~o 60 per cent, depending on the value of 

the ore, on ore mined through the shaft, and 

a flat rate of $1.25 a ton on smelting ore and 

$1 o~ concentrating ore taken out t~ough the 

Argo tunnel, the company in the latter case 

paying the haulage charges. . 

Occasionally the royalties are graded accordin()' to the difficulties of 1nining. Thus in the 

Chase 1nine 15 per cent· is charged on smelting 

ore and 10 per cent on concentrating ore when: 

development work is necessary and 20 to 30 

per cent on smelting ore taken fronl·portions of 

the veins already opened. . 

Although wages are of course subject to 

n1uch variation the following figures approxinlate the average: I-Iand-drill men, $2~75. to $3 

a clay; 1nachine stoper men,'$3 to $3.50; drifting-Inachine drill men, $q.50 to $4; engineers, 

$3.25 to $3.50; and muckers, trammers, etc., 

$3. The wages paid commonly increase somewhat with the distance of the mine from the 

principal towns. 

Freight rates to Golden or Denver by Colo.rado & Southern 

Railway. 

From Blackhawk and Idaho Springs. 

Ore value. 

$9 or less ................................... . $9 to $20 ................................... . $20 to $30 .................................. . Over $30 .............................. · .... . 

From Dumont. 

Ore value. 

$9 or less .. ~ ................... ~ ............ . $9 to $20 ............. ~ ... : ................. . $20 to $30 .................................. . $30 to $100 ................................. . 

Charges 

per ton. 

$0.75 

r.oo 

1 .. 50 

2.00 

Charges 

per hundredweight. 

$0.05 . 06t 

. 08! 

.11! 
170 GEOLOGY OF GILPIN, CLEAR CREEK, ~ND BOULDER COUNTIES, COLO. 

From Empire station and,Lawson. 

Ore value. 

$9 or less ................................... . $9 to $20 ................................... . $20 to $30 ..................... ~ ............ . $30 to $100 ................................. . 

The freight, rates for carload lots over the 

Denv~r & Salt L,ake Railroad are as follows: 

Charges 

per hun- Freight rates from Tolland or Rollinsville to Denver by Dendred- ver & Salt Lake Railroad. 

weight. 

$0.051 

.07 

. 09! 

Ore value. 

I 

. 13 $20 or less ........................ · .......... . $20 to $30 ........... : ...................... . $30 to $40 ................... ; .............. . 

Charges 

per ton. 

When the value exceeds $100 ·the b $40 to $100···· · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · a ove · Over $100 ................................... . 

$1.00 

1. 50 

2.00 

2.75 

5.50 

rates are doubled. 
' 

CHAPTER XIII.-PRODUCTION. 

'By CHARLES \V. HENDERSON. 

The following tables of proquction have been total pr~duction of the State, particularly for 

compiled from the best sources available and lead and copper, have always been more reliable 

revised· to date. Footnotes show the exact than county figures, and where th~re are dissource of each figure used. These data are crepancies the county figures have been protaken from a report showing similar data for the rated on a basis of the State total. For ID;any 

State of Colorado, by counties, the statistical items the aggregate of all counties was much 

part of which is. compl~ted. Figures for the more than the total for ·the State as a whole. 

171 
Year. Ore (short tons). 

Placer. 

Gold (value). 

Lode. Total. 

Metals produced in Clear Creek County, Colo., 1859-1914. 

Quantity 

(fine 

ounces). 

Silver. 

Value. 

Average 

per ounce.a Total. 

Copper. 

Value. 

Quantity 

(pounds). I Average 

per pound.a 

Total. 

Quantity 

(pounds). 

Lead. 

Vaiue. 

Average 

per I Total. 

pound.a 

Quantity 

(pounds). 

Zinc. 

Value. 

Average 

per I Total. 

pound.a 

I I ... so:~· ::::: ::::J ::::::::::: ::::::::: J: :::::::: 

'---1 I 1---1 I 1----1---1 1---1 

1859-I865 ................ b$}000,000 ............ bc$2,000,000 ............ 1 ...................... , ...................... , .......... • 

1866... ... ... ............ 50,000 ............ c d 50,000 15,I23 $1.339 b $20,250 ............ $0.3425 .......... . 1867......... ............ d50,000 ............ cd50,000 I5,226 1.33 b20,251 ............ .2537 ...................... . 1868... ...... ............ d 50,000 ............ d 50,000 106,953 1.326 b 141,820 1............ .23 ..................... ·.1 

1869... ...... ............ d50,000 ............ d50,000 377,359 1.325 d500,000 d 2,000 .2425 3485 de 100,000 1870.. .... ... I 2,000 d 80,000 ............ d 80,000 362,465 · 1.328 b 481,354 d 2,500 .2118 530 de 2,000,000 1871......... ............ b20,000 ............ b20,000 640,790 1.325 b849,047 d3,000 .2412 724 cle550,000 1872... ...... g 5,888 b 25,000 ............ b 25,000 1,118,299 1.322 b 478,391 d 4,000 .3556 1,422 de 1,000,000 1873......... h5,421 b34,000 ............ b34,000 902,668 1.297 b170,760 d10,000 .28 2,800 de1,000,000 1874......... i9,490 b42,500 ............ b42,500 d1,634,434 1.278 2,088,807 d15,000 .22 3,300 dej8Q3,983 

1875......... k12,000 b68,960 $3,448 b72,408 d1;343,610 1.24 - I,666,076 di5,000 .227 3,405 de1,300,000 1876 ..................... b40,000 55,161 b95,161 di,421,104 1.16 1,648,481 di5,000 .21 3,150 de819,672 1877......... ............ b20,000 76,500 b96,500 d1,534,560 1.20 1,84I,472 d15,000 .19 2,850 2,236,364 1878. ........ ............ b 10,000 124,000 b 134,000 d I, 759,652 1.15 2,023,600 d 25,000 .I66 4,150 2, 722,222 

1879......... . . . . . . . . . . . . d 10,000 110,000 m 120,000 m I, 546,875 1.12 1, 732,500 d 100,000 .186 18,600 1951,219 1880......... ............ d5,000 191,000 n 196,000 n 1,902,656 l.I5 2,188,054 d 200,000 .214 42,800 517,500. 1881......... ............ o5,000 195,000 o20Q,OOO o1,546,875 1.13 1,747,969 d200,000 .182 36,400 d815,000 1882 ..................... o6,000 214,000 o220,000 o1,299,375 1.14 1,481,288 o300,000 .191 57,300 d815,000 1883......... ............ d 10,000 240,000 0 250,000 01,222,031 1.11 1,356,454 d 300,000 .165 49,500 d 815,000 1884 ..................... oi2,55I 587,449 o600,000 oi,3I4,844 1.11 1,459,477 d300,000 .13 39,000 d1,038,273 I885 ................ : .... diO,OOO 490,000 P500,000 P1,356,000 1.07 1,450,920 d200,000 .108 21,600 q1,038,273 1886......... ............ d10,000 599,070 r609,070 Tl,396,364 .99 I,382,400 dr200,000 .111 22,200 d I,630,000 1887......... ............ d 15,000 302,2I4 r3I7,2I4 rl,284,083 .98 1,258,40I dr200,000 .I38 27,600 ri,847,930 1888......... .. .. .. .. .. .. d 20,000 399, 82I r 4I9, 82I rl, 148,190 . 94 1, 079,299 d r 200,000 .168 33,600 r 3, 76I, 246 .I889......... ............ o25,000 496,909 r521,909 ri,770,875 .94 I,664,623 r9I,73I .135 12,384 r5,357,906 

1890.. ....... ............ o 24,336 418,032 r442,368 r1,8I9,682 1.05 I,9I0,666 ri24,I02 .156 19,360 ri2,029,217 

1891......... ............ d22,875 4I5,692 r438,567 ri,771,055 .99 1,753,344 r57,572 .128 7,369 r7,947,786 

I892......... ............ 0 5,340 308,701 r3I4,04I ri,69I,579 .87 1,471,674 d40,424 .116 4,689 r7,916,672 

1893......... ............ d_5,000 579,I87 r584,I87 r2,218,377 .78 I,73o;·334 r40,000 .IOS 4,320 dr8,000,000 

1894......... ............ d5,000 657,649 r662,649 r2,228,846 .63 I,404,173 r40,000 .095 3,800 drS,OOO,OOO 

1895......... ............ o5,000 669,210 r674,2IO ri,585,48J .65 I,030,564 r44,168 .I07 4,726 r6,415,936 

1896......... ............ o5,000 787,631 r792,631 rl,626,828 .68 I,106,243 r204,519 .108 · 22,088 r6,438,672 

1897 ...................... 050,000 732,649 t782,649 t1,442,583 .60 865,550 t516,034 .12 6I,924 t5,263,116 

I898... ...... ............ d 5,000 600,528 t 605,528 t I,569,0I2 .59 925,717 t 3I7,423 .124 39,360 t 5,843, 769 1899......... ............ d5,000 541,825 t 546,825 t 1,502,900 .60 901,740 t 292,966 .I71 50,097 t 7,2I6,260 

1900......... ............ d5,000 460,447 t465,447 ti,358,143 .62 842,049 t244,092 .I66 40,5I9 t4,994,263 

I901......... .. .. .. .. .. .. d 5, 000 53;>, 975 t 540,975 t I, 271,227 . 60 762,736 t 374,534 .I67 62,547 t 3, 890, 2I6 1902 ......... '............ d5,000 925,481 t 930,483 t I,279,050 .53 677,897 t 473,754 .I22 57,798. t3,282,270 

I903 ..................... d5,000 467,06I t472,06I t85I,638 .54 459,885 t289,876 .I37 39,713 t3,45I,849 

1904......... u62,661 u.2,398 634,2I7 t636,615 t873,949 .58 506,890 t401,180 .128 51,35I t3,913,976 

I905......... u58,7i5 u.I,881 50I,8I7 u.503,698 u.692,437 .61 422,387 u.235,669 .I56 36,764 u.3,270,211 

1906......... u64,774 u.I,568 528,I85 U.529,753 u.652,796 .68 443,901 u.235,375 .193 45,427 u.3,307,001 

1907......... U 79,548 Uti 11,511 511,385 U.522,896 u.518,364 .66 342,120 U.171,34Q ,20 34,268 U.2,804,172 

1908 ......... u.109,6i2 u.2,610 656,506 U659,116 u.503,551 .53 266,882 u.264,994 .132 34,979 u2,015,010 

1909......... u. 116,753 u. 3, 846 532, 56I u. 536,407 u. 448,535 • 52 233,238 u 299,546 .13 38,941 u 3, 254,675 

1910 ......... u109,954 u.3,678 5I8,846 u.522,524 u475,I74 .54 256.594 u.595,795 .127 75,666 u.2,434,476 

I911......... u.I05, 774 u.1, 754 5I7,453 u. 5I9,207 u.437,84I .53 232,056 u. 650,368 .125 81,296 u.3,325,222 

1912......... u. I02, 892 u. 33I 445, 463 u. 445, 794 u. 373, 940 . 6I5 229,973 u. 449,401 .165 74, 151 u. 3, 523, 733 1913 ......... u.104,892 (u) 432,489 u.432,489 u.408,527 .604 246,750 u.426,393 .155 66,091 u.3,999,614 

19I4 ......... u.101,366 ........... 495,275 u.495,275 u.345,387 .553 190,999 u.367,790 .133 48,916 u.2,435,692 

if ---§tl- i!YH~i ~[~~:~~:~1:~:~~~/ .058 75,400 ........ :... $0.07 ......... . 

.061 l50,000 ............ .072 ·········· .055 li23,000 ............ .06 ........ .. .036 l98,000 ............ .049 ........ .. .041 l 80,000 ............ .052 ........ .. .05 25,875 ............ .055 ........ .. .048 39,I20 ............ .052 ......... . . 049 39, 935 .. .. . .. .. . .. . 053 ........ .. .043 35,045 ............ .045 ........ .. . 037 38, 4I6 .. .. .. .. .. .. . 044 

. 039 40,4931 cl 25,000 . 043 .046 74,980 cl25,000 .044 . 045 83, I57 cl 25,000 . 046 • 044 I65, 495 cl 75,000 . 049 • 039 208,958 cl 75, 000 . 05 .045 54I,3I5 ·d 75,000 .055 .043 341,755 d 75,000 .05 . 04 316, 667 .cl 250, 000 . 046 .037 296,000 d400,000 .04 .033 264,000 d200,000 .035 .032 205,310 8 200,000 .036 .03 193,160 d4.00,000 .039 .036 189,472 d 300,000 .041 .038 222,063 d300,000 .046 .045 324,732 d300,000 .058 .044 219,748 d300,000 .044 .043 167,279 d300,000 .041 .041 134,573 t 3P, 705 .048 .042 144,978 t 656,000 .054 . 043 168, 30I t 906, 705 . 051 .047 153,700 t I,I02,301 .069 .057 I88,499 t I, 733,477 .061 .053 148,621 t 2, 77I,960 .059 .042 84,630 u 836,411 .047 . 043 139, 951 u 758,074 . 054 .044 107,117 u1,247,389 .054 .045 149,635 u.1,417,544 .057 . 045 158,568 U.1, 734,493 . 069 .044 175,983 u.1,489,518 .056 .039 94,992 ui,067,314 .051 

... ii;o7~-~ I,IOO 

I, I50 3,675 

3, 750 4,I25 

3, 750 11,500 

I6,000 

7,000 

7,200 

I5,600 

I2,300 

I3,800 

I7,400 

I3,200 

I2,300 

I5, 250 35,424 

46,242 

65,036 

I05, 742 I63,546 

39,311 

40,936 

67,359 

80,800 

119,680 

83,4I3 

54,433 

Total 

value. 

$2,000,000 

70,250 

70,25I 

I9I,820 

556,485 

573,884 

902,771 

1,568,813 

1,267,560 

2, I82,846 

I, 8I7, 289 

I, 796,792 

2,063,822 

2,259, 750 I, 951, IOO 2,452, 729 

2,023,489 

I, 798,523 

I,690,999 

2, I36,893 

2,0I4,088 

2,089, 750 I,687,522 

I, 70I,890 

2,411,624 

2,9I7,834 

2,544, 785 2,118,57I 

2, 630,841 

2,34I,622 

I,922,010 

2, 129,722 

I,911,895 

I,806,468 

I,840, 794 

I,580,963 

I,545,837 

I,8I5,999 

I, I52,06I 

I,409,399 

I, 18I, 585 

I,313,322 

I,211,45I 

I, 084, 9I8 

989,473 

I,029,260 

I,062,994 

I,028, I66 I,OOl, 726 884,6I5 

2,85I,I39 I7,958,837 . 20,809,976154,967,315 .......... ,49,946,0561 9,555,546 .......... 1,389,960 1155,293,394 .......... ,6, 532, I62 ji9, 363; 89I ........... 1, 062,097 1 79, 740, 251 

a McCaskey, H. D., Prices of silver, copper, le;1d, and zinc, I850-19I3, U. S. Geol. Survey Mineral Resources, I9I3, pt. 1, p. clxxili, 1914. · · b Director Mint R~_!pt. for 1887, p, 153, value of gold and silver. Gold and silver prorated by Charles W. Henderson on basis of subsequent figures or from reports of R. W. Raymond on States and Terri~ories west of the Rocky Mountains for I869 to 1875. 

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e From placers at Idaho Springs and surface workings of lode deposits at Empire. d Estimated by Charles W. Henderson. e Represents lead in ores shipped to Eastern States, to England, and to Germany. I Raymond, R. W., op. cit., 1870, p. 316, 1872. g Idem, 1872, pp. 277-278, 1873. h Idem, 1873, p. 287, 1874. l Idem, 1874, p. 365, 1875. Idem, 1874, p. 365. 1: Idem, 1875, p. 295, 18n. l U.S. Geol. Survey Prof. Paper 63, p. 175, 1908. m Burchard, H. C., Director Mint Rept. for 1880, p. 156. n Idem, p. 157. o Director Mint reports. 

:.._ 

P Interpolation by Charles W. Henderson to agree with total for State in Director Mint reports. q U.·S. Geol. Survey Mineral Resources, 1885, p. 257, figuring 15 per cent reduction correctly. ,. From reports of the agents of the mint, the gold and Silver being prorated to correspond with the corrected figures of the total production of the State by the Director of the Mint, the lead production being prorated to correspond with the total production of the State in annual volumes of U. S. Geol. Survey Mineral Resources, and any "unlrnown production" of the State being· distributed proportionately to the · several counties. Copper treated similarly to lead, but as Mineral Resources figures for copper included copper from matte and ores treated in Colorado smelters from other States, the copper figures are subject to revision. 

• Ore receipts of American Zinc-Lead Co., Canon City. t Colorado State Bureau of Mines, figures being smelter and mint receipts. u U. S. Geol. Survey Mineral Resources, being figures collected from mines. 11 Includes 87,628 "unknown gold," probably stamp gold not placer. 

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Metals produced in Gilpin Co~nty, Colo., 1859-1914. ~ 

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Silver. I Copper. Lead. Zinc. 

1 

Gold, lode Value. Value. Value. Value. 

Year. I Ore (short and frlacer Total value. 

tons). (va ue).a Quantity 

.Average I Quantity Quantity Quantity (fine 0 

ounces). (pounds). Avomgel (pounds). Avomgel (pounds). Avemgel Total. t_::j 

per Total. per Total. per Total. per 0 ounce.b · pound.b pound.b pound.b t-t 

0 

Q 

c $241,918 5,943 $1.36 c $8,0821·············· $0.22 ................ .................... $0.55 

::-: :: :~ I<:Y:: I<> :.t:::::-:::1 

$250,000 ~ 

c 870,903 21,553 1. 35 c29,097 .............. .23 ..................... ......................... .055 900,000 0 c 725,753 18,231 l. 33 c 24,247 .............. .22 ..................... ...................... .05 750,000 bj c 1,161,204 28,738 1. 35 c 38,796 ......................... .22 ..................... . ..................... .06 1,200,000 

c 1, 548,272 38,460 1.345 c 51,728 ........................ .34 .. .................. ........................... .06 1, 600,000 Q c 1, 741,806 43,267 1. 345 c 58,194 ......................... .47 .. ..................... ........ , ................. .07 1,800,000 1-1 

c 1, 451,505 36,272 1. 337 c 48,495 .3925 .066 1,500,000 t-t . . . . . . (d) ..... .................... ....................... ...................... -----------· ........................................ c 725,753 I-'d 18,108 1.339 c 24,247 .3425 ----------·- ........................ .07 ................... .................... ------------ 750,000 1-1 c 967,670 24,308 1.33 c 32,330 (d) .2537 ------------ -------------· .065 ..................... ..................... ·········· ............. 1, 000,000 __ z ............ 

1 

n,64o,ooo 93,311 1. 326 ~ 123,730 I 50,000 .23 $11,500 -------------- .065 ................. ................. ---------- ------------ 1,775,236 

•••.•.•••••. ...--e 2,690,000 86,340 1. 325 e 114,400 I 100,000 .2425 24,250 -------------- .06 .................... ------------ ---------- ------------ 2,828,650 

e 2,120,000 0 65,910 1. 328 ~ 87,528 f 180,000 0 2118 38,124 -------------- .06 ------------ ------------ ---------- ------------ 2, 245,652 t-t e 3, 237,346 59,229 1.325 ~ 78,478 f 180,000 .2412 43,416 -------------- .06 ................ ------------ ---------- ------------ 3,359,240 t_::j e 2, 083,611 52,911 1. 322 e 69,948 I 200,000 .3556 71,120 · ··· ·h5;ooo· .064 ................. ................... ------------ 2,224,679 ·> t 1,393,931 35,907 1. 297 c 46,571 I 200,000 .28 56,000 .06 $1,500 ----------·- ---------- ------------ 1,498,002 t;:d g 1,525,447 g 39,418 1. 278 50,376 g 252,050 .22 55,451 I 50,000 .06 3,000 ------------ .............. ................. 1,634,274 

h 1,395,566 h 62,670 1.24 77,711 i 193,665 .227 43,962 I 50,000 .058 2,900 ------------ $0.07 ------------ 1,520,139 0 j 1,990,002 j 89,365 1.16 103,663 /250,000 0 21 52,500 f 50,000 .061 3,050 ------------ .072 ------------ 2, 149,215 :::0 j 2,086,871 j 93,714 1. 20 112,457 f 300,000 .19- 57,000 f 50,000 .055 2, 750 ------------ ~06 ------------ 2,259,078 f;j 

j 2, 155,708 j 96,806 1.15 111,327 I 300,000 .166 49,800 f 50,000 .036 1,800 .................... .049 ....................... 2, 318,635 t_::j 

k 2,260,000 k 232,031 1.12 259,875 f 300,000 .186 55,800 f 100,000 .041 4,100 ................. .052 ------------ 12,380,000 l 232,031 1.15 266,836 I 300,000 . 214 64,200 f 100,000 .05 5,000 .................. .055 

2,579, 775 ~ ----·------·- 2, 716,036 

m 1,850,000 I m 201,094 1.13 227,236 I 300,000 .182 54,600 f 100,000 .048 4,800 ------------ .052 ------------ 2, 136,636 > 'll 1,600,000 '11201,094 1.14 229,247 I 400;000 .191 76,40Q I 100,000 .049 4,900 .................... .053 ................... 1,910,547 z 01,650,000 0 154,688 1.11 171,704 f 200,000 .165 33,000 f 100,000 .043 4,300 ------------ .045 ---·-------- 1,859,004 l:j p 1,950,000 p 278,438 1.11 309,066 f 600,000 .13 78,000 f 128,411 .037 4, 751 ................. .044 ------------ 2,341,817 

q 2,051,000 q 300,000 1. 07 321,000 f 300,000 .108 32,400 r 128,411 .039 5,008 ------------ .043 ------------ 2,409,408 td 81,337,061 8 101,784 .99 100,766 J-300, 000 .111 33,300 t 200,000 .046 9,200 ------------ .044 ------------ 1,480,327 0 

81,134,476 8266,281 .98 260,955 f 600,000 .138 82,800 8 228,622 .045 10,288 ------------ .046 ------------ 1, 488,519 q 8 1, 250,756 8 174,364 .94 163,902 f 400,000 / 

.168 67,200 81,288,825 .044 56,708 ------------ .049 ------------ 1,538,566 8 1,054,065 8 313,071 .94 294,287 8 250,110 .135 33,765 81,411,926 .039 55,065 ----········ .05 ------------ G 1,437,182 

8 805,236 8 292,495 1. 05 307,120 8 620,927 .156 96,865 81,130,453 .045 50,870 ··---------· .055 ------------ 1, 260,091 t_::j 

8 938,016 8 232,001 .99 229,681 8 558,298 .128 71,462 8 779,837 .043 33,533 ------------ .05 ............... 1, 272,692 t;:d 8 1,358,157 8 134,462 .87 116,982 8 538,988 .116 62,523 8 2, 232,158 .04 89,286 ............... .046 ------------ 1,626,948 8 1, 218,626 8135,850 0 78 105,963 t 600,000 .108 64,800 t 2,000,000 .037 74,000 ................. .04 ------------ 1,463,389 0 

&1,915,863 8 228,927 .63 144,224 t 400,000 .095 38,000 t 2, 200,000 .033 72,600 .................. .035 ------------ 2, 170,687 0 

81 1 196,319 8 190,256 .65 123,666 q 209,414 ~ 107 2.2, 407 8 844,037 .032 27,009 ······------ .036 ------------ 1,369,401 q 8 1,534,358 8 295,182 .68 200,724 q435,838 .108 47,071 8 1, 948,756 .03 58,462 ............... .039 ------------ 1,840,615 z !.£ 2,086,471 u 374,417 .60 224,650 u 1,018,595 . 72 122,231 !.£ 2,007,698 .036 72,277 ............... .041 ------------ 2,505,629 8 !.£ 1,983,514 u 305,687 .59 180,355 !.£ 633,707 .124 78,580 u 1,216,338 .038 46,221 ................ .046 ................. 2,288,670 1-1 

t_::j "1, 996,061 u'340,652 .60 204,391 !.£ 1,037,421 .171 177,399 "1,312,312 .045 59,054 ............... :058 ------------ 2,436,905 Jfl "1,655,502 !.£ 236,400 .62 146,568 !.£ 799,478 .166 132,713 !.£ 735,773 .043 32,374 ................ .044 ................. 1,967,157 11 1,638,966 U271,638 .60 162,983 !.£ 731,194 .167 122,109 !.£ 670,018 .043 28,811 .............. .041 ............... 1, 952,869 0 !.£ 1,551,035 t£303,638 .53 160,928 !.£ 765,516 .122 193,393 !.£ 497,366 .041 20,392 ............... .048 ............... 1, 925,748 0 u1,346,113 u 375,238 .54 202,629 u 611,988 .137 83,842 u 945,975 .042 39,731 ............. •. 054 .............. 1,672,315 t-t 11109,557 v 1,403,865 v 318,406 .58 184,675 v 638,945 .128 81,785 v 859,293 .043 36,950 ------------ .051 ................ 1, 707,275 9 v 182,873 v 1,450,033 v 340,901 . 61 207,950 v 512,276 .156 79,915 v 519,841 .047 24,433 !.£ 33,090 .059 $1,952 1, 764,283 v 114,662 v 1, 115,902 11242,478 .68 164,885 v 638,002 .193 123,134 v 510,791 .057 29,115 !.£ 46,000 .061 2,806 1,435,842 

•87,887 v 938,488 v 209,347 .66 138,169 v 874,060 .20 174,812 v 611,060 .053 32,386 ............... .059 .............. 1,283,855 v 120,761 v 1,075,808 .v 187,030 .53 99,126 v 636,371 .132 84,001 11538,143 .043 22,602 ................. .047 -----···---- 1, 281.532 II 111,118 11887,311 11172,010 .52 89,445 v 499,146 .13 64,889 v 664,581 .043 28,577 ..................... .054 .............. 1,070, 225 v 83,631 v 687,902 v 132,635 .54 71,623 II 534,244 .127 67,849 v 575,477 .044 25,321 ........... 0 .054 ············ 852,695 
1911. ______________ .

1 

. ~ ...... I "7i8, 7i4 • 292 ... , .M I 155,1 ... I . ""· ... I 125 I 118,780 "1,~,3561 .04~. 55, 7i1 . p 23,088 I .057. 1,316 . 1,109, 705 1912 ................ "118,652 "904,505 "316;205 . 615 194,466 "1,025, no .165 169,252 "1,351,600 I .04,') : 60,822 . "25,377 i .069 1, 751 . 1,330, 796 1913 ................ "94,156 0 687,101 "273, 207 .604 165,017 "837,974 .155 129,886 "1,210,341 .044' 53,255 t>8,5S91 .056 481 1,035, 740 1914 .•••............ "52,839 "573,553 "145,237 .553 80,316 "726,579 .133 . 96,635 t>499, 718. .0391 19,4891 "12,980 .051 1 662 . 770,655 

············! 81,998,103 9,812,2951-·········1 7,957,9241 22,990, 7961··········1 3,613,921 31,262,11~ 1······----1 1,272,461 1 149,1241- ..... _ .. ·I 8,968 I 94,856~377 

a How much of the early gold Production should be credited to placers can not be estimated. While the greater part for the first few years was taken out by placer methods, the bulk of the material treated was the oxidized decomposed portion of the lodes, and not placer deposits in the true sense of the word. In later years no placer gold worth mentioning has been taken out, although there are placer deposits worthy of exploration-near Perigo and Rollinsville. b McCaskey, H. D., Prices of silver, copper lead, and zinc, 1850-1913, U. S. Geol. Survey Mineral Resources, 1913, pt. 1, p. clxxili, 1914. c Director Mint Rept., 1887, p. 151, value of gold and silver. Gold and silver separated by Charles W. Henderson on proportion of figures for 1874. d 0. J. Hollister,~. The mines of Colorado,·p. 357, 1867, credits J. E. Lyons smelter with 100 to 200 tons of matte on hand. R. W. Raymond, op. cit., 1869, credits J. E. Lyons smelter with 80 to "100 tons of matte produced in ~ months, beginning in the summer of 1866, and with the discovery of 100 tons additional, which was found later when plant was tom down. No record of assay of copper in this matte or record of sale of this matte is given. e Increased by Charles W. Henderson to agree with R. W. Raymond's figures for Colorado for these years. · f Estimated by Charles W. Henderson, from U.S. Geol. Survey Mineral Resources, 1881-82, p. 228, and subsequent volumes; and Raymond, R. W., op. cit., 1870, p. 3i2. Raymond's figures for 1868, 1869, 

and 1870 are stated to be estimates which he himself thinks high. From Raymond's 1874 and 1875 data, said to be a statement from the Blackhawk smelter, it is seen that the small plant of 1868, 1869, and 1870 could not have produced more than the ·enlarged plant of 1874-75. In 1868, 1869, and 1870 Raymond estimates matte averaged 40 per cent copper. In 1875 Egleson gives more authentic data, including matte 25 to 30 per cent copper. · - · g Raymond, R. W., Statistics of mines and mining in the States and Territories west of the Rocky Mountains, 1874, p. 360, 1875. h Idem, 1875, p. 289, 1877. • - i Idem, p. 294. 

J Director Mint Rept., 1887, p. 151, value of gold and silver. Gold and silver separated by Charles W. Henderson on proportion of figures for 1879. k Burchard, H. C., Director Mint Rept., 1880, p. 156. lldem, p. 157. midem, 1881, p. 355. · n Idem, 1882, p. 394. o Idem, 1883, p. 240. pidem, 1884, p. 177. q Director Mint Rept., 1887, p. 151, value of gold and silver. Gold and silver prorated to correspond with total production of State. . r U.S. Geol. Survey Mineral Resources, 1885, p. 257, figuring 15 per cent reduction correctly. . s From reports of the agents of the mint in annual reports of the Director of the 1\lint, the gold and silver being prorated to correspond with the corrected figures of the total production of the State by the 

Director of the 1\lint, the lead production being prorated to correspond with the total production of lead in the State in annual volumes of U. S. Geol. Survey Mineral Resources, and any "tmknown production" 

of the State being distributed proportionately to the several counties. Copper treated similarly as lead, but as Mineral Resources figures for copper include copper from matte and ores treated in Colorado 

smelters from other States, the copper figures are subject to revision. · t Estimated by Charles W. Henderson. · u Colorado State Bureau of Mines figures, being smelter and mint receipts. 

"U. S. Geol. Survey Mineral Resources, being figures collected from mines. 

~ 

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.I 

PART ill.--o-THE MINES. 

By EDSON S. BASTIN and JAMES M. HILL. 

CHAPTER XIV.-BOULDER COUNTY . 

CARIBOU, NEDERLAND, AND VICINITY. 

GENERAL FEATURES. 

Some prospecting for gold had been done in 

the Caribou, or Grand Islnnd district (as it was 

called in the early. sixties), but the ea'rly prospectors were not on the lookout for silver ores 

and it was not until 1869 that the presence of 

this metal was recognized. In that year Samuel Conger discoyered the outcroppings of a 

ve:in which he cu,Ued the Poor ~{an; and William Martin and George 'Lytle found a lode a 

little farther up the hill which they named the 

Caribou. Assays showed that both veins contained large amounts of silver, and before 

winter a wagon load of ore had been mined and 

sent to the smelter at Blackhawk. In the 

succeeding sum1ner (1870) a wagon road was 

constructed to the mine and regular shipments 

were begun to Blackhawk, 20 miles away. The 

success of these ventures caused a rush to the 

district and resulted in the discovery of numerous other veins, inchl.ding the Boulder County, 

Idaho, Sherman, No Name, and Seven-Thirty, 

and led to the founding of the town of Caribou, 

which in Noven1ber, 1870, hn,d about 30 houses 

aild 125 voters. The great development of 

mining at Caribou may be said to date from the 

completion in 1871 of a mill at Nederland (then 

called Middle Boulder) for the treatment of the 

silver ores from the Caribou mine. This mill 

was built by A. D. Breed, who had purchased 

the western portion of the Caribou lode from its 

discoverers. · ' 

rrhe ess~ntial features of the milling process 

were chloridizing roasting in Bruchner cylinders, followed by pan an1algan1ation, and the 

capacity of the works was 18 to 20 tons per day. 

The bullion recovered had a fineness in silver of 

0.850 to 0.050. Shortly after the completion of 

this mill Breed obtained control of the whole 

Caribou l~de and sold it to a Dutch company for 

44214°-17-12 

~ ' 

the exorbitant a1nount of $3,000,000. According to Rayn1ond 1 Caribou was very active in 

1875, its gross production amounting to 

$450,000, an increase of more than $100,000 

over the figures for 1874. The Caribou mine 

was the largest producer, other mines operated 

being the Sherman, No N arne, Poor Man, Grand 

View, Native Silver, Seven-Thirty, Idaho, 

Potosi, and Sovereign People. In the winter of 

1875-76 the Dutch company operating the 

Caribou mine failed, causing a temporary setback thn,t was offset in ·a measure by the completion at Caribou of a new mill, operated on the 

same principle as that at Nederlap.d, for the 

treatment of ore from the Native Silver mine. 

The silver ores yielded by the camp in early 

days were very rich. For instance, assorted 

lots of from 1 to ·7 tons sent to the smelter from 

the Caribou mine are said to have assayed from 

235 to 666 ounces of silver to the ton, and 39 

tons to have averaged over 300 ounces. Raymond 2 gives the following table of assays of 

silver ore shipped from the Idaho mine to the 

Blackhawk smelter in 1870: 

Assays of ship~~ents of silver ore from the Idaho mine, 1870. 

Tons. Ounces per ton. 

3.25 874 . 56 103 

6. 5 977.5 

4.35 922.4 

1. 28 618.2 

15. 94 3,115.1 

A vet age per ton, 195.4 ounces. 

Up to July, 1880, ,the 'total yield of the Car:i- , 

bou mine is said to have been about $1,168,000. 

1 Raymond, R. W., Statistics of mines and mining in tho States and. 

Territories west of the Rocky Mountains, 1875, pp. 306-307, 1877. 

2 Idem, p. 327. 

177 
178 GEOLOGY OF GILPIN, CLEAR CR.EEK, AND BOULDER COUNTIES, COLO. 

SILVER VEINS OF BALD MOUNTAIN AND CARl- is 3 feet wide and, in addition to c3lcite stringBOU HILL. ers, contains lens-shaped masses of white 

UP TO DATE MINE. quartz, carrying pyrite and chalcopyrite and a 

The Up to Date mine is at the southeast base 

of Bald Mountain, about a mile northwest of 

the small mining camp of Caribou. The main 

development consists of a tunnel about 1,900 

feet in length. The principal geologic features 

are· shown in figure 20, to which the letteri:Qg 

used below refers. . 

Vein A: A highly oxidized vein 2! feet 1n 

width, carrying some white quartz. 

Vein B: A It-inch veinlet of calcite. 

Dardanell No. 1: A vein 4 feet in width, 

composed of sman subparallel veinlets of calcite locally carrying some chalcopyrite. 

Dardanell No. 2: A vein which, at the face 

of the north drift, contains in a width of 8 feet 

numerous veinlets of calcite, most of them less 

than three-quarters of an inGh wide. At the 

face of the south drift monzonite is traversed 

, by a single l-inch · veinlet of calcite, locally 

. carrying a little galena. In the stope on this 

vein, just south of the line of the turinel, the 

vein is more or less oxidized, being only about 

60 feet frorp. the surface, and shows much calcite and some vugs lined with quartz. The 

vein here shows no metallic minerals, but a 

specimen taken from the ore bin and reported 

to have come from this stope showed numerous 

small veinlets, consisting predominantly of 

'bornite and chalcocite, with subordinate cal-

. cite and native silver. Another specimen from 

this stope shows pyroxenite heavily impregnated with galena and traversed by minute 

fractures along which native silver has been 

deposited. This rich silver ore is believed to 

have been formed by downward enrichment. 

(See pp. 147-149;) 

Vein C: A ~ to 2! inch calcite vein. 

- Vein D: A calcite veinlet three-quarters of an 

inch wide. 

Vein E: A zone of altered monzonite 1 foot 

wide traversed by several narrow stringers of 

calcite. 

. Eureka vein: An indefuite zone of fracturing 

characterized locally by sharp-walled veinlets 

0 100 

LEGEND 

-~· Idaho SP.rin~s 

formation 

Pyroxenite 

E2J 

Veins 

~ Barren 

fractures 

(Arrows indicate direction of dip) 

2ooFeet 

of quartz and chalcopyrite or of calcite. In. FIGURE 20.-Geologic plan of Up to Date tunnel, Caribou. Surveyed 

by ~and compass and pacing. 

a stope north of the line of the tunnel level a 

11-Aoot zone of soft much-altered pyroxenite 

is traversed by numerous small calcite stringers. 

At another place in this stope the fractured zone 

few flakes of molybdenite. In places the calcite stringers cut sharply across· the quartzpyrite-chalcopyrite masses. In the tunnel a 
j 

BOULDBR COUNTY. . 179 

few feet beyond the Eureka vein the pyroxenite 

carries abundant dissen1inated pyrite. 

Ve.in F: A network of calcite veinlets, which 

is reported to carry locally some chalcopyrite. 

Vein G: A vein exposed in a short crosscut, 

which shows 7 feet of schist traversed by subparallel stringers of quartz and pale-pink calcite, some of which carry sphalerite, galena, 

and n.little chalcopyrite. 

In genern.l the ore taken from the veins· in 

the Up to Date tunnel as well as t?-at obtained 

in the past from shallow workings now long 

abandoned in the Eureka and neigh boring 

veins was yaluable principally for its silver 

content. Chalcopyrite ore from the Eureka 

vein is said, however, to carry in places as 

much as 2 otmces in gold. Most of the silver 

occurs native and one mass of silver measured 6 by 8 inches by one-fourth to 1 inch 

thick. . What appeared to be polybasite or 

pen,rceite, although no opportunity was 

afforded for testing it, was associated with 

native silver in one specimen seen by the writer. 

Stephanit~ is also reported to have been ob· 

. served in the ore. All these silver minerals, 

as well as the bornite, covellite, and chalcocite 

locally ttssociated with the native silver, are 

believed to have been forn1ed through the 

process of downward enrichment. (See pp.147-

149.) Galena and chalcopyrite are sufficiently 

abundant to forn1 by their weathering in the 

gossan an adequate source for the rich ores, 

especially \vhen the original extension of the 

veins above the present surfnc.e is taken into 

account. 

The pred01ninant metasomatic alteration in 

the wall r0cks next the primary ore is the deoxide of iron. Secondary quartz forms irregular aggregates of small grains. Irregular 

masses of galena and some sphalerite appe'ar to 

replace indiscriminately all . the original constituents except apatite, which remains wholly 

unaltered. In short, in these places, in addition to the development of calcite, sericitization 

is an important 1netasomatic process. 

In contrast, the wall rack near veinlets of 

chalcocite, bornite, and . native silver and 

calcite show no sericite. The rock studied was 

similar to that lastdescribed and was taken from 

another part of the same stope in the Darqanell . 

vein No.2; it has been altered to an associt,t.tion 

of calcite and quartz, through which chalcocite, bornite, and native silver are distributed 

as isolated irregular patches or as irregular replacement veinlets. (See fig.19, p.149.) In the 

portions in which these sulphides are most abundant sericite is entirely absent. The absence 

of sericitization, so characteristic of galenasphalerite mineralization, is additional evidence 

that the deposition of the native silver and 

the rich copper nunerals was not a phase of 

the primary mineralization but was a distinct 

process, probably attributable to descending 

surface waters. The abundant intergrowth 

of calcite with the native silver, chalcocite, and 

bornite of these veins shows conclusively that 

the depositing waters were not acidic in 

character. 

Mining through the Up to Date tunnel had 

up to the time of this survey been mainly · 

exploratory in character, and the total output 

had as yet been small. 

CARIBOU MINE. 

velopnlent of sericite, as is well shown in the All the workings of the famous Caribou 

walls of the Eureka vein. T~e alteration of mine, on the north side of Caribou Hill, were 

pyroxenite carrying abund11nt disseminated inaccessible at the time of this survey, the 

galena, as seen in a stope on the Dardanell No. mine having been idle for many years. From 

2 vein, is instructive. This rock ,consisted the discovery of the property in 1869 until 

originally ·of biotite, pyroxene, apatite, and . 1880 the mine was in almost consta1,1t operation; 

titaniferous magnetite. The biotite has been in 1873 its main shaft was 370 feet d~ep; at th~ 

·bleached and small grains of iron oxide have close of 1875 it was a little over 500 feet deep; 

been developed in it so that it is nearly color- and at present it is said to be about 800 feet 

less and shows only faint pleochroism. In deep. . 

smttli part it ~as been replaced by calcite. Lawrence Thompson 1 describes the appearOriginal pyroxene has been replaced by a mix- ance of the vein in 1871 as follows: · 

ture of calcite and sericite-in some areas . The vein does not show well-defined walls. A hanging 

wholly by sericite. Titaniferous magnetite wall especially can never be recognized, while a footwall 

has wholly disappeared, its place being apparently taken by a 1nixture of carbonate and red I Raymond, R'. W., Statistics of mines and mining in States and 

Territories west of the Rocky :Mountains, 1872, p. 359, 1873. 
18.0 GEOLOGY OF GILPIN, CLEAR. CREEK, AND BOULDER. COUNTIES, COLO. 

shows itself in spots, being separated from the vein by a 

very thin selvage: But in the greater part of the workings 

there was nothing found .to define the vein sharply. The 

gangue is ~ very hard and tough quartz. There is sometimes only one pay streak, from one-half to 4 or 5 inches 

wide, and in these cases this is exceedingly rich. At other 

times there are a great many thin seams of high-grade ore 

running through the vein. But very rarely is the quartz 

interspersed with silver-bearing minerals throughout its 

width,· or even its greater part. 

taken in a new mill which was constructed in 

1914. The equipment of this mill is given 

in the table on page 157. 

The total production of the mine is not · 

accurately known but is believed to be somewhat more than $1,000,000. 

WIGWAM MINE. 

The Wigwam mine is on ·the east side of 

Writing in 1872, Thompson 1 says further: Caribou Hill. The development consists of ~ 

There are in this mine 11 shafts, aggregating 1,248 feet shaft 215 feet deep, with levels at 75, 125, and 

in depth. The main or working shaft is 329 feet deep, 200 feet. The vein strikes about N. 75° E. 

another is 229, a third is 129, and eight others are from 20 At the surface it dips steeply north, but in 

to .100 feet deep. There are also four levels, aggregating 

1,678 feet in length. The crevice may be stated to be from depth shifts to southerly· Work was tern- · 

6 to 8 feet in width, and the paying part of the vein from porarily suspended at the time of this survey 

6 inches to 4 feet wide. The ores of this mine are sulphu- and the mine could not be entered, but speci:-

rets of silver, argentiferous galena, brittle and n·ative mens taken froni a depth of about 200 feet 

silver, with but little zinc blende. were obtained fronl the ore bin and showed 

Examination of the dump shows galena, very well the character of the 1nineralization. 

sphalerite (in ·part resinous), chalcopyrite, The primary n1inerals of this ore are ·galena, 

pyrite; quartz, and barite as primary vein sphalerite (in part resinous); very minor 

minerals, and native silver in wire and leaf amounts of chalcopyrite and pyrite, quartz, and 

form, malachite, azuri~e, limonite, and h~ma- · pink. and white calcite and barite. Along 

tite as secondary mrnerals. One specrmen fracture seams and in small vugs in this ore 

showed jasper developed in vugs with· iron- secondary deposits of very. finely crystalline 

stained quartz and in one place inclosin.g a wire chalcopyrite, proustite or ruby silver, and 

of native silver. Argeqtite, pyrargynte, and pearceite were recognized. Where high silver 

cerusite have been reported. values are present they are evidently the result 

The Caribou mine has in the past yielded of downward enrichn1ent. 

large amounts of very rich silver ores, most of A small shipn1ent fron1 this mine in 1911 

which were a product of downward enrich- assayed gold 0.02 ounce, silver 31.33 ounces, 

mont. According ~o Raymond 2 a fal~in~ off lead 7.58 per cent, and copper 0.1 per cent. 

in silver content rn depth, charactenst1c of 

such enrichment, was noted as early as 1874. 

The unenriched primary ore appears not to be 

of workable grade. 

The ore mined from near the surface was 

very rich. Twenty-six tons shipped in 1869 

had an average assay value of about $124, and 

425 tons of smelting ore extracted in 1870 had 

·an average value of about $173.3 

According to a statement made by Mr. 

A. D. Breed, then owner of the mine, the number of tons inined and milled between September 21, 1870, and October 1, 1872, was 3,650!, 

and the net profit was $90 a ton. Most of the 

ore obtained during 1874 is said to have carried 60 to 90 ounces of silver to the ton. 

Recently reworking of the old dump and 

stope fillings by cyanidation · has been underl Raymond, R. W., Statistics of mines and mining in States and 

Territories west of the Rocky Mountains, 1872, p. 291, 1873. 

2 Idem, 1874, pp. 370-371, 1875. 

a Idem, 1870, p. 320, 1872. 

COMSTOCK MINE. 

The Comstock mine, which was in operation 

at the time of this survey, is in Caribou village 

and is developed by a shaft 212 feet deep. 

Only the 45-foot level was accessible for inspection. On this level the vein, which 

strikes nearly east and west and dips about 

70° S., has been drifted upon for 112 feet west 

and 20 feet east of the shaft. West of the 

shaft the wall rock is monzonite, but just east 

of the shaft it is dark-green gabbro. The 

highest values are reported to have been found 

in the gabbro, but the drift in this rock was 

boarded up and could not be inspected. 

The Comstock vein may be described as a 

zone of fracturing from 1! to 6 feet in width, 

within which galena and calcite and chalcopyrite have been sparsely deposited in small 

·.irregular veinlets and disseminated through 

the rock. Few of the veinlets exceed one-
BOULDER. COUNTY. 181 

fourth inch in width, but one an inch wide was 

observed. 

About 80 feet west of the shaft on the- 45-

foot level the Comstock vein is joined by 

another, said to be the No Name vein, which 

consists of three subparallel veinlets of :finegrained galena and calcite sepm·ated fr;om 

each other by 3 feet of wall rock. The junction of t4e two veins is also exposed in the 

shaft at a depth of about 65 feet, the combined vein there having a width of about 1.0 

feet. 

While none of the rich ore could be seen, it 

is practically certain that like the ore of neighboring mines it owed its high silver value 

largely to downward enrichment. Ore fron1 

a depth of 212 feet"in the shaft is said to have 

assayed 700 ounces·of silver to the ton. 

SHE):tMAN VEIN. 

The Shern1an vein 1 was in 1874 developed 

by a shaft 160 feet deep, from which levels had 

been run to a total length of 310 feet. Its 

production for 187 4 was 220 tons of first-class 

ore of an estimated value of $40,000. Early 

in 1874 this vein was cut by the Caribou tunnel and was found to be productive at ~hat 

depth. It was not accessible for study at the 

time of this survey. 

NO N Al\fE VEIN. 

CROSS LODE TUNNEL. 

The Cross Lode tunnel, just east of Caribou, 

was inaccessible at. the time of this survey. 

Ore on the dump showed pyrite, chalcopyrite, 

galena, and sphalerite of the resinous variety 

in a quartz and calcite gangue. 

GOLD ORES OF IDAHO MOUNTAIN. 

ST. LOUIS MINE. 

The St. Louis rnine is on the southwest 

slope of Idaho Mountain, near Caribou, at a.n· 

elevation of about 10,000 feet. It was discovered in the· early seventies, but was not 

worked until many years later. The mine· 

has been idle since 1905 and the workings 

could not be entered. The vein, which appears 

to strike about N. 60° W., is developed by a 

shaft· 335 feet . deep., The ore seen on the 

dump shows predominant pyrite and quartz, 

with subordinate galena, sphalerite, and a 

little siderite. Most of the ore mined was 

treated in a near-by mill equipped with 10 

stamps and Wilfl.ey tables. 

The ore treated was free milling and the 

value was mainly in gold. Sixteen tons 

shipped in 1905 are said to have shown an . 

average content of gold, 3.28 ounces; silver, 

9 ounces; and silica, 17 per cent. Two tons 

shipped in 1904 are said to have assayed gold, 

5.81 ounces; $ilver, 8.5 ounces; silica, 41.7 

per cent. Sampling-works assays of several 

lots of smelting ore shipped in 1908 are as 

follows: 

Assays of oresfrorn the St. Louis 1nine, 1908. 

Ore. Gold. Silver. Silica. 

Net tons. Ounces. Ounces. Per cent. 

5. 435 1. 82 3. 60 79. 50 

1. 830 3.06 6. 50 26. 50 . 884 5. 59 5. 20 42. 90 

The No Nmne vein had in 1874 been n1ore 

extensively developed than any ·other of the 

region except the Caribou. 1 The main shaft in 

1874 was· 320 feet deep, and the total length 

of shafts and drifts was nearly 800 feet. The 

product for the year was estimated at 4,000 

tons, one~half of which was low-grade concentrating ore that was not then available, and 

the remainder higher grade ore, which was I 

shipped to the smelter at Blackhawk or to the 

Caribou mill at N ederlm).d. The total· value 

of the ore n1ined up to that time v.ras estirnated 

·by the owner at $400,000. The :fineness of the gold ranges from 0.582 

In 1873 a very rich shoot carrying silver to 0.655. 

and horn silver was opened.2 First-class ore BOSTON AND IDAHO TUNNEL. 

from this l.Iline had been sold for more than · $1.,300 per ton, second-class for $250 to $400, . The portal of th~ B~sto~1 and Idaho t~nnel 

and third-class for $30 to $75. . rs near the St. Lours rnill, JUSt east of Canbou. 

The tunnel was inaccessible and the dump t H.£\ymond, H.. W., Statistics or minos m~d mining in tho States and showed only pyritic ore and brecciated peg- 1'erritorlos wost or the Hocky Mountains, 1874, p. 370, 1875. 

2 Idem, 1873, p. 299, 1874. matite. 
182 GEOLOGY OF GILPIN, CLEAR. CREEK, AND BOULDER COUNTIES, COLO. 

EAGLE BIRD MINE. 

The Eagle Bird min:e is near Caribou, in the 

south slope of Idaho Mountain .. The vein 

appears to strike about N. 65° W. and to dip 

about 65 ° NE. Ore seen on the dump was 

oxidized and of the pyritic type. The mine 

was idle and could not be entered. 

development was through a shaft 400 feet deep 

on the south side of Boulder Co11nty Hill at an 

elevation of about 9,500 feet. These workings, 

which include about 5,000 feet of drifts on 

three levels, have been abandoned for many 

years and are now inaccessible. According to 

Mr. Charles Sherman, a former owner,t there 

were in 1872 eight shafts on the Boulder 

. GREAT NORTHERN MINE. County vein, aggregating 250 feet in depth, 

and 225 feet of levels and tunnels. 

The Great Northern shaft, now abandoned, The present management, which assu1ned · 

is on the east side of Caribou Park, about a mile control in 1901, operated exclusively through 

north of the town of Caribou. The shaft house a crosscut known as the· Boulder County 

is just east of the contact between monzonite tm:inel, whose portal is in the valley of Coon 

porphyry and Idaho Springs formation; most Trail Creek, ·a short distance above Cardinal 

of the rock on the dUm.p is porphyry. The station. This tunnel, which was accessible for 

vein apparently strikes east· and west. The study, trends about N. 18° W. and intersects 

greater part of the ore on the dump is the Boulder County vein about 3,200 feet from 

oxidized and consists of iron-stained porphyry the portal. The west drift on the vein, which 

cut in many directions by narrow stringers of is about 1,500 feet long, was unsafe, but the 

limonite containing some sphalerite in their east drift was studied for its entire length of 

centers. Someoreshowsmassivewhitequartz, about 650 feet. Near its east end it is conwith some limonite-coated pyrite and sphal- nected by a 500-foot raise with the shaft 

erite, and here and there some copper carbon- workings. 

ates. A small part of the ore ·consists of veins The Boulder County tunnel cuts no veins of 

of white quartz carrying pyrite, chalcopyrite, importance until the Boulder County vein is 

and subordinate sphalerite and galena. In reached, and is of interest mainly becau:::;e of 

general the massive pjrite ore carries very the number and variety of the porphyry dikes 

little of the other sulphides, but where chalcopy- which it exposes. The dikes and minor veins 

rite appears the lead and zinc sulphides are also int~rsected are described briefly below. The 

present. Some specimens seem to show that distances are from the portal and were deterthe lead ~nd zinc were deposited later than the. mined by pacing. 

chalcopyrite in small seams that in places cut ' At 142 feet: A 3-foot dike. of fine-grained, 

masBes of that mineral. very dark gray biotite diorite. Strike, N. 60° 

GOLD-SILVER VEINS OF BOULDER COUNTY HILL 

AND SHERWOOD CREEK. 

E.; dip, 80° N. 

At 382 feet: A barren fault zone in schist of 

the Idaho Springs formation. Wet. Strike; 

The ores of Boulder County Hill and the N. 70° E.; dip, 80° N. 

upper valley of Sherwood Creek belong to the At 409 feet: A 4-foot dike, probably of horngalena-sphalerite type of gold-silver ores, but blende andesite. Strike, N. 65° E.; vertical. · 

differ from those of Caribou Hill in being At 700 feet: A 4-foot dike of fine-grained and 

practically devoid of carbonates and in con-.· sparsely porphyritic hornblende ,andesite. 

taining a great abundance of gangue quartz. At 725 feet: A 6-inch dike of black biotite 

They show much less downw~rd enrichment diorite showing biotite phenocrysts, some of 

in silver than the Caribou Hill group. Ore which are 5 millimeters across, though most of 

from a depth of only 120 feet in the Gold,King them are under 2 millimeters. This dike cuts 

vein, for example, showed no evidence of sharply through a 15-foot dike of gray porphyry, 

enrichment. which is shown by the microscope to be much 

BOULDER COUNTY MINE. 

The Boulder County vein was discovered by 

S. P. Conger about 1870 and was mined intermittently until a few years ago. The early 

altered, but which was probably originally a 

hornblende-biotite andesite. The biotite diorite is finer grained and nonporphyritic for ono1 Raymond, H.. W., Statistics of mines and mining in the States and 

Territories west of the Rocky Mountains, 1872, p. 291, 1873. 
BOULDER COUNTY. - 183 

fourth inch next its "frozen" contact with the 

andesite. 

At 890 feet: A nearly east-west vertical dike 

of biotite diorite, 2 feet in width.· 

At 1,120 feet: A barren fracture zone 4 feet 

wide. Strike, N. 75° W.; vertical. 

At 1,130 feet: A 4-foot vertical dike of 

hornblende latite. Strike, N. 75° W. . 

At 1,220 feet: An open vein of white quartz 

with a little pyrite, having a maximum width 

of6inch.es. Strike,N.60°-75°W.; dip, 60°-80° 

N. The vein was followed by drifts till it 

pinched out at points 115 feet east and 30 feet 

west of the tunnel. · 

At 1,270 feet: An 8-foot dike. of altered 

hornblende-biotite andesite carrying some 

quartz. Strike, N. 80° W.; vertical. The dike 

is cut by a narrow dike of black biotite diorite 

porphyTy, which is finer grained and nonporphyritic next its contact with the andesite. 

At 1,340 feet: A 10-foot dike of typical hornblende-andesite porphyry. Strike, N. 60° W. 

At 1,730 feet: Fracture zone, unm.ineralized. 

Strike, N. 55 ° E.; vertical. 

At· 1,870 feet: A 4-foot dike of a nearly 

black rock, probably hornblende-biotite diorite. 

Strike, N. 80° E.; vertical. 

At 1,900 feet: A.1-foot dike of biotite diorite. 

Strike, N. 60° E.; vertical. 

At 2,490 feet: A 1-foot dike which is much 

altered but appears to be diorite porph)71'y 

showing altered feldspar phenocrysts.· This 

dike is parallel and in contact with a 6-inch 

light-gray dike, which is also much altered but 

is prQbably an andesite porphyry. The dike 

of diorite ( ~) is finer and nonporphyritic next 

the andesite) which it appears to intrude. 

At 2,920.feet: A 14-inch dike of biotite diorite. Strike, N. 65° W.; vertical. 

The exposures in this tunnel are the only 

ones found in the district that clearly show the 

age relations betwe9n the diodte and andesite 

dikes. The· repetition of the same relations in 

several exposures in this tunnel unquestionably 

determines the diorites as somewhat younger 

than the andesites. 

The strike of the Boulder County vein as exposed in the tunnel workings is about N. 70° W., 

and its dip is 60°-70° N. Its width varies from 

1 inch to 3 feet and in one place to 4! feet; it 

shows many abrupt enlargements, in one place 

widening from 4 inches to .4 feet within a distance of 10 feet. · 

The following statement regarding the appearance of the upper part of the vein is taken 

from Raymond: 1 

As it appeared in A1._1gust, 1870, it presented a 2!-foot 

crevice, one side of which was rich in gold and the other 

still·richer in silver. As a greater depth was reached on 

this lode, the gold seemed gradually to be running out and 

the silver increa.Sing in quantity. In much of the ore gold 

was found associated with large flakes of silver. Speci- · 

mens had frequently been taken from the mine in wh~ch 

brittle silver and wire silver were visible in large quantities, with a smaller sprinkling of gold. 

As now exposed on the tunnel level, the vein 

is, in general, highly quartzose, quartz in places 

constituting the whole vein and commonly 

forming over half of the ore. .In a few places, 

however, quartz is practically absent, t~e vein 

at one point consisting of 3 inches of solid galena 

and chalcopyrite with only a little quartz and 

p)71'ite next the walls. Where wid~st the vein 

consists of a 6-inch border of white quartz on 

both footwall and hanging wall and a core of 

3! 'feet of altered wall rock which is cut by a 

network of quartz veinlets not more than 1 

inch in width and which carries irregular masses 

of sulphides not more than 2 inches aoross. In 

general the l.lljnerals · of the vein in order of 

abundance are white quartz, galena, sphfllerite, 

pyrite, and chalcopyrite. Vugs are con1mon 

and are usually lined with crystals of galena 

and t~ansparent quartz. No c·arbonates were 

observed. 

No evidence of downward enrichment was 

apparent in the vein at the level of the tunnel; 

enrichment was probably operative near the surface (seep. 139), but. does not seem to have been 

extensive far below the oxidized zone or to have 

produced ore extraordinarily rich in silver, the 

ore mined in 1872 being valued, according to a 

former owner, at $20 to. $150 per ton in gold 

and silver. 

The nature of the wall-rock alterations near 

the Boulder County vein has already been discussed. (See p. 52.) 

The ore mined by the present c01npany was 

treated in a mill located at the 1nouth of the 

tunnel which has since been remodeled for the 

treatment of tungsten ores. Th~ richest ore 

yielded $400 per ton and the average between 

$15 and $18. The average gold content is 

placed at about 0.6 ounce, and the usual lead 

content at 3 to 4 per cent, occasionally reaching 

1 Raymond, R. W., Statistics or mines and mining in the States and 

Territories west or the Rocky Mountains, 1870, pp. 327-328, 1872. 
184 GEOLOGY OF GILPIN, CLEAR CR.EEK, AND .BOULDER. COUNTIES, COLO. 

16 to 18 per· cent. Zinc was present only in 

minor amounts. There has been no production since 1906. 

JACK POT TUNNEL. I 

The Jack Pot tunnel is on the southwest 

slope of. Idaho Mountain ttbout one-fifth mile 

southeast of the Boulder County shaft. At 

the time of this survey it had been idle for 

some time but was accessible throughout. It 

is about 670 feet long and develops two nearly 

parallel veins. · 

The first vein, which is tapped by the tunnel 

200 feet fro1n the portal and is followed by it 

for I50 feet, strikes slightly north of west and 

is about vertical. It is for the most part barren, but in one place it shows I! inches of gray 

quartz carrying .some pyrite. There has been 

postmineral movement along this vein. 

The main vein is tapped by the tlinnel 400 

feet from the portal and is followed·by it to the 

face, a distance of about 270 feet. The vein 

strikes about N. 70° W., and dips 35°-70° N. 

It varies in width from 5 inches to 2 feet ttnd is 

mainly in granite, though it traverses some 

Idaho Springs schist. In some places the vein 

shows several subparallel sharp-wall~d veinlets 

of quartz and sulphides, between which the 

wall rock has been only slightly mineralized. 

In other places the rock between small fracture 

planes has been entirely replaced by quartz 

and sulphides which ·form lenses of ore 6 to 8 

inches in width. Elsewhere the only mineralization consists in the development of quartz 

and disseminated sUlphides in the granite immediately adjacent to fracture planes. 

The ore minerals are pyrite, galena, chalcopyri~e, and quartz. The ore is of the same 

type as that from the Boulder County vein, 

being chiefly characterized by the predominance of quartz gangue over sulphides and the 

abundance of vugs .. 

PINE GROVE MINE. 

Boulder County vein, consisting preclmninantly 

of white and. gray . quartz, through which 

sphalerite, galena, and chalcopyrite are scattered. V ugs are very common and are usually 

lined with crystals of quartz and sphalerite. 

A few crystals of calcite and siderite were observed on the quartz crystals of some vugs, 

and in one vug a little secondary chalcopyrite 

deposited on galena was seen. One specimen 

shows 5 inches of such vein material bordered 

by 5 inches of altered wall rock traversed by 

numerous small branches from the main vein. 

Locally the vein proper is bordered by a 

breccia of fragments of wall rock in a matrix of 

quartz and sulphides. No evidence of postmineral fracturing or of downward enrichment 

was observed. The wall-rock alterations are 

sericitization and, close to the vein, silicification. 

The average metal content of smelting ore 

shipped from this mine from 1906 to 1908 was 

as follows: 

}fetal content of smelting ore from Pine Grove rnine, 1906- ~ 1908. 

Gold. Silver. 

Ounce. 

1906 ...... -.- ----............. 0. 24 

1907 and 1908................. . 28 

The total production is not known. 

GOLD KING MINE. 

Ounces. 

35 

24 

The Gold King mine is about 1! miles northwest of Nederland, just north of Sherwood 

Creek, and only a short distance northeast of 

the Pine Grove shaft. The vein ha~ been 

developed by a shaft 120 feet deep, now idle 

and inaccessible. The ore fragments in the 

shaft house show that the vein locally attained 

a width of at least IO inches. The ore . is 

highly quartzose and full of vugs and closely 

resembles that from the neighboring Pine 

The Pine·Grove mine is in the valley of Sher- Grove and Boulder ·county veins. Sphalerite 

wood Creek about It miles west-northwest of is the principal sulphide with galena subordiNederland and about one-half mile northeast nate; pyrite and chalcopyrite were not obof Cardinal station. The shaft, which con- served .. ·The sulphides form from IO to 60 per 

nects with at least three levels, could not be cent by ':olume of the ore. Quartz is the only 

entered, the.mine peing idle at the time of this gangue observed. No evidence of postmineral 

survey. moveme:o.t or of downward enrichment was 

As shown by specimens on the dump and in observed in this ore, which appeared very 

the ore bin the ore ·is very similar to that of the . fresh even though it could not have come froni 
•. 1 

I·~ 

BOULDER COUNTY. 185 

a depth greater than 120 feet. At the time 

of survey a crossc~t tunnel was being driven 

to intersect the vein at a depth· of 100 to 200 

feet. 

MINES NEAR NEDERLAND. 

BLUE BI~D MINE. 

ticularly abundant on the second · and third 

levels in the north tunnel. In all parts of the 

vein druses are common. Metallic minerals, 

though in few places wholly absent, are generally much subordinate to quartz and barite; 

rarely, however, galena constitutes over half 

the vein. The sulphides (galena, chalcopyrite, 

The Blue Bird vein is on the west side of and rarely gray copper) usually form irregular 

North Boulder Creek 2} n1iles west of Neder- bands or bunches. Specularite was observed 

land. The workings consist of three drift in one place intergrown with clear hexagonal 

tunnels, but as the vein is unusually flat, with quartz in a vug in the vein and is probably 

dips of 2° to 17°, the workings bear little primary. Much of the ore is oxidized. Limoresemblance to those on most of the metallifer- nite, malachite, and azurite were observed in 

ous veins of the district. The tunnels are 380, seams and cavities. Films of native silver 

150, and 370 feet long and c01mect with nu- occur on. fractures in quartz in oxidized ore, 

merous drifts and stopes. and smaJl irregular masses of the metal appear 

The country rock is a rather coarse-grained in cavities. Small wires of native gold were 

biotite granite, porphyritic in places, which is observed in cavities in quartz; and cerargyrite 

intruded by granite pegmatite and which con,- was noted in oxidized ore. 

tains several lenses of schist of ·the Idaho The stopes on this vein are low, roomlike, 

Springs forn1ation near its borders. North of and very irregular, following the more heavily 

the Blue Bird tunnels a small dike of gray mineralized parts of the vein and leaving the 

fine-grained biotite andesite porphyry crops leaner parts as pillars. They are all near the 

out; and the Saine porphyry is cut by the third surface. The vein with increased depth under 

level of the north tunnel. The dike was in- the mountain is apparently narrower and not 

truded after the formation of the Blue Bird so well mineralized. This was particularly 

vein and distinctly cuts the latter at the third noticeable at the face of the incline tunnel. 

level of the north tunnel. The relation of this Development work on the Blue Bird property 

andesite to the other andesites of this reg!on was in progress in 1875, when some ore was 

is not known. shipped that yielded over $200 a ton in mill 

The vein strikes north-northwest and dips returns.1 The high value of some of the ore 

2°-17° SW. The steeper dips are seen in the was evidently due to downward enrichment. 

north tunnel, the dips in the lower south tun- . The property has now been idle for many years. 

nel being in plnces scarcely noticeable.. In the 

third level of the north tunnel there is a saddle 

over which the vein curves. At th~ north end 

of the third level the vein dips 7° NW., and 

near the tutmel it dips· about 7° SW. 

The vein varies from 2 inches to 3 feet in 

width but commonly measures 4 to 6 inches. 

In some places it is a single fissure filling and in 

other places it splits into· several narrow subparallel veinlets. The ore is generally" frozen" 

to the walls but here and there breaks free, 

though the parting is hardly noticeable. No 

gouge was seen in any part of the vein. 

The gangue miner~ls are barite and white 

quartz. Most of the quartz is opaque, but 

some crystals of it in vugs are transparent. In 

places quartz is the sole gangue,· but where 

barite also occurs the two minerals are irregularly intergrown. In pJaces barite forms 

fully half of the vein material, being parALTON TUNNEL. 

The mouth of the Alton tunnel is on the 

north side of Coon Trail Creek, about one-half 

mile east of Cardinal station. It is a crosscut 

tunnel, running due north for about 2,060 feet. 

For the first 1,800 feet the tunnel traverses the 

Idaho Springs formation, cutting _numerous· 

lenses of granite pegmatite, the largest of which 

forms the wall for 420 feet in the central part 

of the tunnel. (See fig. 21.) Beyond 1,800 

feet the tunnel is driven in coarse porphyritic 

biotite granite (Silver Plume granite). ·At 

2,060 feet the tunnel turns northwest and by 

the fall of 1911 had been driven about 100 feet 

toward the Pine Grove shaft. 

Four porphyry dikes are cut by the tunnel. 

The first is 410 feet from the mouth and has 

1 Raymond, R. W., Statistics or mines and mining in the States 

and Territories west or the Rocky Mountains, 1875, p. 307, 1877. · 

. I 
186 GEOLOGY OF GILPIN, CLEAR' CR.EEK, AND BOULDER COUNTIES, COLO. 

aiso been followed for about 80 feet by the west 

Skipper drift. I_t varies from 14 inches to 2 

feet in width and is nearly vertical. It is a 

fine-grained dark biotite andesite containing a 

few feldspar phenocrysts about one-eighth 

vein and is somewhat mineralized~ The third 

dike, about 2 fee~ wide, is cut 1,270 feet from the 

mouth of the tunnel, where 'it traverses granite 

pegmatite. It is·a very fine grained light-gray 

much-altered porphyry containing a little 

disseminated fine-grained pyrite and is probably a hornblende andesite. The fourth dike, 

about 3 feet wide, trends east and west, cutting 

granite 1,960 feet from the mouth and 100 .feet 

south of the turn of the tunnel. It is a darkgray, fine-grained, highly altered rock, probably originally a bio'tite diorite. Its outcrop 

was not located. 

LEGEND 

. 

~ . Hornblende ·andesite 

Biotite ~ andesite 

~ Probably biotite diorite 

;{s"A-J~."': L.-,t.-·"!."'"'11 Granite pegmatite 

Granite 

~ 

~ (porphyritic) 

(2] 

Tungsten vein 

B 

Galena-pyrite vein 

1-L/1 Unmineralized fr<!Cture 

There are only three drifts of' consequence 

from this tunnel. The first starts 85 feet from 

the mov.th and extends east for 150 feet about 

parallel to the foliation of the schist walls. 

About 80 feet east of the crosscut there is a 

70-foot raise, from which a small pocket of 

tungsten ore is said to have been taken, 

though no ore and nothing that resembled a 

vein was seen in the drift. 

The Skipper vein is cut 540 feet from the 

I -:~ f mouth of the tunnel and has been followe'd 

Workings inaccessible east for 250 feet and WeSt for' 80 feet. This 

I _t.--j vein strikes N. _63° E. and is about vertical, 

c~r;~~i~~~W;~) traversing Idaho Springs formation. In most 

Note: Wall rock is sch>stof placeS it is a barren fracture ZOlle 2 tO 4 inches Idaho _Springs· for~ation ' 

unless· other:wlse mdlcat.ed wide, containing gouge; brecciated schist, and 

'

0

._

0 .....J5

._

0 .....Jo'--_,_.~' 0 _..Jzoofeet in some places small lenses and stringers. of 

N 

FIGURE 21.-Geologic plan of Alton ttiimel. · 

gray and buff· cherty silica. Eighty feet west 

of the tunnel the fracture splits on entering a 

small lens of granite pegmatite. In this place 

the pegmatite is iron stained and contains 

small pockets and. seams of ferberite which 

form the matrix of a breccia of pegmatite and 

chert fragments. West of .this ore pocket the 

drift did not follow the fracture but turned 

south·for 80 feet, then west along the 14-inch 

andesite'. dike mentioned above, and finally 

north. A little brecciated pegmatite and schist · 

along a northeast-southwe~t fracture at its end 

may be the continuation- of the Skipper. vein, 

but so fa:r as seen it is barren at this place. 

The Little Jimmie vein, which is cut 1,050 

feet from the mouth of the tunnel, strikes N. 

88° W .. and dips 75° N. In the tunnel it cuts 

granite pegmatite l;>ut enters schist 50 feet to 

inch in maximum diameter. The second dil\-e, the west .. The west drift is caved 370 feet 

32 feet wide, is cut 1,000 feet from the mouth from th~ .·tuim~l, a~d !ts iast 150 feet are south 

of the tunnel and is also exposed in a crosscut of the vein. ·The .. east drift is north of the vein 

to the south from the west Little Jimmie .drift. ·but exposes a nearly parallel barren fracture.· 

The rock is a much-altered hornblende· andes- Iii the west drift the vein, which varies from 

ite; it lies a few feet south of the Little Jimmie a few inches to a foot Ill width, consists of 

.,. 
' ... 

BOULDER COUNTY. 187 

narrow stringerS of gray cherty silica about 

one-fourth inch wide running about paro.llel 

to the foliation of tho schists. ;These stringers 

are nearly barren in the schist, but in tho pegmatite near tho tunnel a s1nall stope, showing 

some ore, consists of stringers o~ gray and buff 

chert carrying pyrite, chalcopyr~to, galena, and 

light-colored sphalerite. Astnall quantity of ore 

taken fro1n this place is said to have assayed 

$100. a ton, principally silver with a little gold. 

Although both lead-silver veins and tungsten veins are cut in this tunnel the production 

frmn all of them has been small. 

The Alton mill is near the mouth of the 

tunnel and can be used for treating either gold, 

silver, or tungsten ores. It is equipped with a 

crusher, 15 quick-drop stan1ps, an1algamation 

plates~ con,ce.ntrating tables, and canvas tables. 

' I 

Crystals of the gangue very ~requently project mto the 

vugs. 

The ores contain chiefly gold, with very little silver, 

and the principal valuable mineral is a telluride of gold 

believed to be sylvanite. The tellurides usually occur in 

a flinty vein matter or in the greenish roscoelite distributed 

as small specks, hardly ever as well crystallized minerals. 

Pyrite is present in small amounts, chiefly as small grains 

in the altered country rock. Molybdenite occurs in 

abundance, but is usually extremely fine grained and 

intergrown with barite. On the dump its presence is 

indicated by deep-blue stains on the ore fragments. This 

blue molybdenite stain, to which attention has been 

drawn in the Cripple Creek report,3 is believed to be the 

rare mineral, ilsemannite, a compound of the' oxides of 

molybdenum (Mo02 .4Mo03 ). . 

Characteristic among the gangue minerals of the telluride 

veins are barite, quartz, roscoelite and chalcedony. The 

quartz occurs in moderate amounts, and more frequently 

chalcedony takes its place, forming jasperoid masses of 

brown or black color, locally called hornstone. Barite is 

also very ab.undant and often appears crystallized in small 

ELDORA AND VICINITY. , and thin plates. 

Mr. Rickard, in the article mentioned, 4 has called 

attention to the general occurrence of roscoelite in the 

' Boulder County mines-an interesting fact not elsewhere 

As most of the mines in the vicinity of recorded. Roscoelite is very abundant in the ores of the 

Eldora were idle at the time of this survey and Mogul tunnel and the Enterprise mine. It forms dark 

yellow-green masses intergrown with quartz or irregularly 

as admission w.as denied to the only one that distributed in the ore, and, as stated above, very freGENERAL FEATURES. 

was in operation the. data c.ollected in regard quently contains specks of gold tellurides. Sections of 

to' the district are not· extensive. Most of the this greenish material show the roscoelite as minute 

1ve.ins belong to a different type from those about greenish-yellow scales of micaceous character, intergrown 

Caribou, their distinguishing character being with pyrite in small crystals. This mixture of roscoelite 

and pyrite is surrounded and invaded by a later deposited the presence of tellurides of gold. · In regard mass .of fine granular quartz, with some adularia in the 

to the relative ages of the telluride and sui- rhombic crystals which are so characteristic in the variety 

phicle veins Lindgren says :

1 of this mineral called valencianite. 

It is believed that the sulphide veins are later than the 

telluride veins, and one instance was noted in the Mogul 

. tunnel which seemed to confum this, but the subject 

requires further examination. 

'1.1.le present writer was not able to obtam 

any evidence bearing upon this point. As no 

rich portions of the telluride veins were exposed at ~he time of this survey, Lindgren's 

description of them may here be quoted at 

length.2 

In general, the veins consist of several narrow seams 

forming a more or less regularly sheeted zone, along which 

partial filling and some replacement have taken place. 

A gouge separating the vein from the country rock on one 

side is sometimes present, but more commonly the vein is 

cc frozen to the wall, and the vein matter changes gradually into the country rock. The width of the vein is 

usually confmed to from one to three feet. Within the 

sheeted zone crushed rock very commonly appears partly 

cemented by the vein matter. Vugs are of very frequent 

occurrence and really characteristic of the deposits. 

t Lindgren, Waldemar, Somo gold and tungsten deposits of Boulder 

County, Colo.: 1~con. Geology, vol. 2, P- 453, 1907. 

. I Idom, pp. 458-4()0. 

Thin sections of the crusted ore show that the granitic 

rock on which it was deposited is extensively altered to 

fine scales of sericite, and in part also replaced by grains 

of barite. Neither calcite nor chlorite is present, but a 

little pyrite is distributed through the partially altered 

granitic rock. The crusted material consists of tabular . 

crystals of barite, on which a layer of very fine grained 

molybdenite is deposited. This again is covered by 

concentric deposits of chalcedonic silica. Next to the 

crust the silica is of a brownish color, but gradually lightens 

toward the center, in which large barite crystals are 

cont::J,ined. Another specimen of country rock, originally 

an amphibolitic schist, is found to be converted into a 

greenish-gray soft rock which chiefly consists of extremely 

fine and felted sericite, with a little iron pyrite. 

Summing up these statements, it will be seen that the 

telluride veins at Eldora have a very remarkable structure 

and composition. The structure is char~cterized by 

narrow shear zones, vug holes, and incomplete deposition. 

The characteristic minerals are gold tellurides, molyb~ 

denite,. roscoelite, barite, adularia, and chalcedonic 

silica. The intimate relationship to the Cripple Creek 

SLindgren, Waldemar, a.nd Ra.nsomo, L. F., Geology and gold do. 

posits of tho Cripple Creek district, Colo.: U. S. Geol. Survey Prof. 

Paper 54, pp. 114, 123, 1906. 

c Rickard, T. A., The veins of Boulder and Kalgoorlle: Am. Inst. Min . 

Eng. Trans., vol. 33. p. 558, 1908. 

\. 
188 GEOLOGY OF GILPIN, CLEAR. CR.EEK, AND BOULDER COUNTIES, COLO. 

veins is clearly apparent, and the structure here, as there, 

points to deposition comparatively near the surface. 

These deposits are emphatically not formed at great 

depths. The original surface can not have been much 

different from that general surface of erosion which is 

marked by the high ridge lines of this part of the Rocky 

Mountains and which is supposed to be of late Tertiary age. 

A specimen of rich ore from the Village Belle 

mine in the collections of the State Bureau of 

Mines in Denver shows specks of sylvanite with 

a maximum width of one-sixteenth inch in a 

matrix of porous gray quartz. Another specimen shows a silvery-looking telluride coating 

fracture seams in cherty-looking silica. 

ENTERPRISE MINE. 

The Enterprise vein outcrops at an elevation of about 9,400 feet on the north side of 

Spencer Mountain and is developed by a shaft 

which could not be safely entered at the time 

of this survey. The shaft is 400 feet doep, 

with five levels and about 1,200 feet of drifting. 

At greater depths what is bslieved to be the 

Enterprise vein is cut by both the Mogul and 

Swathmore tunnels. 

Rickard 1 has published an instructive sketch 

and a description of the Enterprise -vein. 

Where studied by him it was a zone of fractured and crushed wall rock about 5 feet 

wide traversed in its central portion by 

numerous subparallel threads of dark flinty 

silica. · He says: '' The dark quartz carries 

finely disseminated tellurides, chiefly petzite, 

which renders a width of 2 to 2! feet sufficiently 

rich to yield an average· of 2 ounces of gold 

per ton.'' 

Only a part of the drifts· on the so-called 

Enterprise vein in the Mogul tunnel was 

accessible, and in this part no mineralization 

was observed. The vein was not studied in the 

Swathmore tunnel. 

About 1,800 tons taken from the Enterprise 

shaft in 1896 and 1897 and treated by chlorination in the Bailey mill at Eldora are said 

to have averaged about $10.80 a ton, mainly 

in gold. 

MOGUL TUNNEL. 

The portal of the Mogul tunnel is near Eldora station. No mining through it was being 

done at thetime of survey, but it was entered 

and all the accessible workings examined. Its 

general direction for about 835 feet from the 

portal is southwesterly; l;>eyond that it trends 

approxin1ately S. 18° E. for 530 feet to a point 

'where it -is caved. In this distance three fracture zones occur. 

The Little Charlie vein, which strikes nearly 

east and west, is cut about 680 feet fron1 the 

portal and has been drifted on for about 100 

feet to the e9>st and 200 feet to the west. 

Although it has been stoped somewhat at one 

point, the stope was not access~ble and no ore 

was seen in the drifts, the vein being si1nply 

a zone of slight fracturing. 

A vein which strikes about N. 60° E., and 

which is said to be the Enterprise, has been cut 

by the tunnel about 935 feet fron1 the portal. 

Considerable drifting has been done upon it,. 

but the drifts were caved 130 feet east and 1.Q.Q. 

feet west of the tunnel. In the part acces.,., 

sible for inspection no ore was observed, the 

vein being a zone of slightly fractured country 

rock showing local stringers of red j aspery 

silica one-half to 1 inch wide. 

A third fracture zone, striking about N. 70° 

E., is cut about 1,185 feet from the portal. 

The drifts were caved a short distance on each 

side of the tunnel. No mineral was seen, 

although 1 to 2 inches of gouge was. observed 

at one place. 

Lindgren, who examined the tunnel in 1906 

when the veins were better exposed, says: 2 

The Mogul tunnel at Eldora, 900 feet below the croppings of the Enterprise vein, cuts a number of parallel 

veins, most of which belong to the telluride class; some of 

them, however, are regarded as belonging to the sulphide 

veins. The tunnel cuts the eastern extension of the Village 

Belle, which is thought to be the extension of the Enterprise. 

* * * No accurate data of the production of these veins 

are available. A considerable amount was, as stated, 

obtained' from the upper portion of the Enterprise vein, 

and in the tunnel much stoping has been done along one 

of the telluride veins for a distance of about 400 feet. 

O~e shipped from the Mogul tunnel in 1905 

is said to have averaged about 1 ounce per ton 

in gold. Ore from the tunnel workings on the · 

Enterprise vein is said to have ranged from 

$24 to $40 per ton in gold. 

SWATHMORE MINE. 

The Swathmore shaft, near the station at 

Eldora and close to the mouth. of the Mogul 

tunnel, was idle at the time of this survey and 

could not be entered. The only ore seen on 

the dump showed either fine-grained pyrite in a 

quartz gangue or specularite and cherty1 Rickard, T. A., The veins Of Boulder and Kalgoorlie: Am. Inst. Min. 2 Lindgren, Waldemar, Some gold and tungsten deposits of Boulder 

Eng. Trans., vol. 33, p. 5G8, 1908. County, Colo.: Econ. Geology, vol. 2, pp. 457-458, 1907. 
BOULDER COUNTY. 189 

looking silica presumably derived from the 

pyrite and quartz tlu·ough surficial alteration. 

Admittance to the Swathmore tunnel, lo.cated 

a short distance above the village of Eidora 

was denied. 'rhree other veins carrying ore 

similar to that of the Enterprise are said to 

hnve been cut by this tunnel before the Enterprise vein was reached. Ore seen in the bins 

is an association of cherty silica, fine-grained 

pyrite, and a greenish mineral that is probably 

roscoelite. The tellurides are said to be carried in narrow seams (those seen measured onesixteenth to one-eighth inch) of dark-gray 

quartz that traverse the greenish aggregate. 

Upon exposure the ore becomes coated with a 

blue f.tlm of oxides of molybdenum formed from 

the molybdenite in the ore. 

XOH-1-NOOR TUNNEL. 

The K.oh-I-Noor tunnel extends nor~hwa~·d 

into the north vnlley wall of Middle Boulder 

Creek from a point about a mile west of 

Eldora. From the size of t:!le dump it is infen·ecl that there n1ust be several hundred feet 

of development, but the workings could not he 

entered. The clump consists of altered schist 

and pegmatite; some of the schi$t shows small 

stringers of gray cherty quartz, accompanied 

·by a little siderite, which generally occurs in 

· nUJ'l'OW bands, but in places a8 coatings on 

small ch·uses. The material is all somewhat 

iron stained, but no metallic · minerals were 

noted. 

SCANDIA VEIN. 

The Scandia vein is on the south side of 

l\1iddle Boulder Creek about three-fourths of a 

mile east of I-Iessie and 1.!: miles west of Eldor~. 

It is opened by a tunnel now inaccessible and 

by several pits. The vein apparently strikes N. 

80° E. and is entirely in Idaho Springs formation. The mouth of the tunnel is near the 

east edge of a large mass of monzonite porphyry, and some of this rock is on the dump, 

which also carries some crushed highly altered 

silicified schist containing a small amount of 

disseminated pyrite. Mineralization along this 

vein was apparently weak. 

JASPER TUNNEL. 

The portal of the Jasper tunnel is on the 

north side of I-Iicks Gulch at an elevation of 

about 9,250 feet. The development work consists o:f a crosscut tunnel about 680 feet in 

length trending slightly west of north. A. 3-

foot vertical dike of felsite porphyry is cut 385 

feet from' the portal. Two other dikes of similar felsite appear to cut a broad dike of hornblende andesite porphyry, which is intersected 

by the tunnel about 490 feet from the portal. 

The exact nature of the felsite was not determined. 

About 520 feet from the portal a drift to the 

northwest exposes about 320 feet of what is 

known as the Anything vein. The average 

strike of this vein is N. 45° W. and its dip 

30°-:45° NE. This vein is well defined but 

varies from a mere knife-edge fracture to 1! 

feet in width. In most 'places it consists of 

altered wall rock which carries disseminated 

pyrite and is traversed by stringers of quartz 

and pyrite. Most of the pyrite is fine-grained. 

Some small vugs are lined with quartz crystals. 

The vein shows no evidence of longitudinal 

postmineral movement nor of the development 

of secondary minerals. Its walls are in part 

pegmatite and in part hornblende andesite porphyry. It cuts the porphyry and is distinctly 

younger. 

About 560 feet from the portal an east drift 

about 160 feet in length leaves the tu1mel. 

After following several barren postmineral fractures it cuts a vein similar to the Anything but 

with ~more westerly trend (about N. 75° W.) 

and a dip of 45° N. It is uncertain whether 

this is the Anything yein or another vein of 

similar character. The average value of the 

total width of the Anything vein is said to vary 

from $18 to $27.50, mainly in gold. 

A second ve~n, known as the Rosalind, which 

has not yet been reached by the tunnel, is developed by a 60-foot shaft and is said to have 

yielded rich silver ore near the surface. 

Mining on this property was begun about 

1903 and was in progress at the time of this 

survey. 

SUMMIT PROSPECT. 

The Summit prospect is on Mineral Mountain between Eldora and Caribou. A shaft 90 

feet deep has been sunk in granite gneiss but 

could not be entered. The ore seen consisted 

of small stringers of pyrite in the gneiss. 

OTHER PROSPECTS. · 

In the small valley between Hicks Gulch and 

Coon Trail Creek there are three prospect tunnels which are now idle and which were not entered. Ore on the dump consi~ted of pyrite, 

galena, and white quartz. Vugs arn common. 
CHAPTER XV.-GILPIN COUNTY. 

SOUTH BOULDER CREEK, JENNIE LIND GULCH, 1 AND PHOENIX. · . 

BLATERNICK TUNNEL. 

The Blatemick tunnel is on the northwest 

side of Black Canyon about 1! miles southeast 

of Tolland. It could not be entered, but it is 

said to be 300 feet long and to follow a tight 

unmineralized slip · plane. Two small veins 

carrying pyrite in a quartz gangue are said to 

have been ·cut in this tunnel. 

HILL AND GOLD TUNNEL.· 

The Hill and Gold tunnel is on the southeast 

side of Black Canyon 1! miles southeast of 

Tolland. It is a 600-foot crosscut but was 

inaccessible on account of caving. It is reported to have cut no veins. ·All the rock on 

the dump is schist from the Idaho Springs 

formation. Some of it shows a little pyrite 

along joints. 

ROOK~ CO.UNTY MINE. 

The Rooks County mine is about It miles 

north-northwest of Apex, in a gulch ·on the 

north side of Colorado Mountain. It is 

developed by a tunnel about 700 feet long, 

. which is somewhat crooked but which as a 

whole trends southeast. 

No large veins have yet been found, but the 

tunnel is still being (3xtended. The wall rock is 

pegmatite for the first 450 feet from the portal, 

but beyond 450 feet is Idaho Springs formation. 

The small veins intersected belong to the 

pyritic and the galena-sphalerite. types. The 

principal pyritic vein is reached about 570 feet 

from the portal and is exposed for 5o feet to 

the face of the drift. ~t strikes about N. 65° W. 

and dips 30° N. It consists of several subparallel pyrite veinlets, the largest 7 inches 

wide, commonly in a quartz gangue. All these 

vein lets lie in the plane of foliation of the schist. 

Vugs in the .larger pyrite veinlets are lined' 

with crystals of octahedral pyrite, a form 

which is rare in this district. Implanted on 

these pyrite crystals and evidently formed 

later is a mixture of crystals of light-brown 

siderite and snowy-white feldspar (probably 

190 

sodtt orthoclase). Under the microscope this 

feldspar shows no twinning. Its index of re-

'fraction as determined by the im1nersion 

method is about 1.520. It gives strong flame 

reaction for both soda and potash. Closely associated with and apparently contemporaneous 

with the siderite and feldspar is a little sphnJerite and galena. In some places both these 

sulphides form crystals which are olearly 

implanted on pyrite crystals, and in other 

places the galena forms thin films in fractures 

in the pyritic ore. The post-pyritic vug 

minerals were presumably deposited in the. 

more porous portions of the pyritic vein at a 

slightly later stage in the process of mineralization. Some of the sphalerite crystals in these 

vugs are in turn coated with minute crystals 

of chalcopyrite, possibly deposited by descending solutions. Ore from this vein is said to 

assay about $5 a ton. 

A small vein cut about· 500 feet from th~ 

portal is composed of galena, sphalerite, and·-

chalcopyrite. in a calcite gangue. It varies 

from one-half to 2 inches wide and lies in general parallel. to the foliation of the schist, 

which st~ikes N. 55° W. and dips 30° NE. The 

contac.t between ore and wall rock is of ex:.. 

treme sharpness and the· walls are free from 

disseminated sulphides. Ore from. this vein 

is said to. have assayed. gold 0.25 ounce, silver 

11 ounces, copper 8 per cent, and lead 40 per 

cent. 

Mining to the time of survey had been entirely exploratory. 

MELROSE TUNNEL. 

· The Melrose tunnel, on the east side of 

Jenny Lind Gulch, three-quarters of a mile 

south of South Boulder Creek, intersects two 

veins, the Melro~e striking N. 20° E. and dipping 65° W. and the Bonanza striking N. 65° 

E. and dipping 70° N. The two veins intersect about 30· feet from the mouth of the 

tunnel and 15 feet below the surface. The 

drift on the Melrose is 80 feet and that on the 

Bonanza 125 feet long. These ve~ns, so far as . 

exposed, cut only Idaho Springs formation 
GILPIN COUNTY. 191 

injected by granite pegmatite. They both a little' disseminated pyrite, and both sides of 

vru·y from a few inches to a foot in width and the dike are bordered by pyrite in bands 1 to 

consist largely of crushed wall rock· carrying 2 iriches wide, which locally expand into lenses 

disseminated pyrite; The Bonanza· comprises as wide as 8 inches. The ore to ·a· depth of 

several lenses of quartz carrying pyrite and a 15 feet was oxidized and is said to have been 

little chalcopyrite; its ore is all o;xidized to a rich,, but below 15 feet the sulphides carry only' 

depth of 50 feet, and its face in the southeast $2 to $3 a ton in gold. · 

chift a.bout 100 feet below the surface shows A few shallow pits on a group of claims south 

a small a.mount of limonite. of the Buckeye show several s1nall veins, all 

'l'he ore is said to average about $30 a ton in oxidized, with a general east-west strike. 

gold, silver, and copper, in the proportion of 

l to 2 ounce~ of gold to each ounce of silver. GOLDEN SUN TUNNEL. 

~here ~as been no production from the property. .The Golden Sun crosscut tunnel starts on 

EARLY Bmn TUNNEL. the south side of South Boulder Creek, threefourths of a mile east of the mouth of Jenny 

The Early Bird tunnel is on the east side of Lind Gulch. In August, 1911, this tunnel was 

Jenny Creek just north o.f Boulder Park. The 2,410 feet long, extending under Jumbo Mountunnel, a crosscut, is said to be 125 feet long tain toward Perigo, through Idaho Springs 

and to intersect two small and uni'mportant schist, which in this vicinity is· not ordinarily 

stringers of pyritic ore. The country· rock is. much fractured. Several small zones of slight 

Idaho Springs schist with abundant lenses of crushing exposed in the tunnel trend in general 

granite pegmatite. about parallel to the foliation of the schist and 

BLACK HILLS VEIN. cominonly dip with it north or northwest. A 

The Black I-Iills vein is on the crest of the few of these fractures are slightly mineralized 

ridge between Jenny Creek and the drainage with pyrite, which is disseminated in the schist 

into Peterson Lake, about 1! miles north of for a few inches on either side of the plane of 

the east end of Boulder Park. It is developed fracture, but most of them are. barren. The 

by a shaft which follows the vein to an un- workings are shown in figure 22. 

lmown depth. A crosscut tunnel has been ·About 1,200 feet from the portal of the tunnel 

started from Bouldt;}r Park, but· is not very an 8-foot dike of monzonite porphyry strikes 

long, for the dump is small. The· shaft is in aboutN. 46° E. and dips 50° N. The two pringranite gneiss just east of a contact with Idaho cipal veins of the tunnel are short distances 

. Springs formation. Two kinds of ore, both north and south 'of this dike. 

apparently low grade, are stored in the bins; The more southerly vein (.A, fig. 22) strikes 

one is a silicified granite gneiss containing N. 85° E. and dips 60-65° N. This vein has 

sparsely disseminated galena, sphalerite, and faulted the monzonite porphyry dike, which it 

subordinate pyrite; the other is a breccia of cuts about 125 feet west of tlie tunnel, displacing 

dark-gray quartz containing small amounts of it by about 20 feet. The vein consists of 2 to 

sulphides in a matrix of buff-colored cherty 10 inches of crushed schist containing a little 

silica. All the cavities are not completely disseminated pyrite and chalcopyrite. Next 

filled; and the ru·uses that remain contain the hanging wall there is from 2 to 8 inches 

small crystals of barite and yellowish quartz of gouge. . coo.ted with a little limonite. The vmn ap- The vein north of the dike (B, fig. 22) strikes 

pn.rently strikes N. 60o E. N. 47° E. and dips 80° NW., parallel to the 

foliation of the schist. In most places this 

BUCKEYE MINE. vein consists of 3 to 4 inches· of crushed schist 

The Buckeye mine is on the north ·side of with disseminated pyrit~ and scattered chalSouth Boulder Creek about three-quarters of a copyrite. A few small lenses· of white quartz 

mile north of Jenny Gulch: The old shaft, with the same sulphides are found in the 

now abandoned, is said to be 80 feet deep. The crushed material. This· vein intersects the 

country rock is granite gneiss cut by a coarse- east-west vein 190 feet west of the tunnel. 

grained n1onzonite porphyry dike 8 feet wide Postmineral movement along vein B has offset 

that strikes N. 75° w. The porphyry contains vern .A about 10 feet. I I 
192 GEOLOGY OF GILPIN, CLEAR CREEK, AND BOULDER COUNTIES, COLO . 

. At the mouth of the Golden S11;n tunnel there linsville, in a region underlain by Idaho 

is a power house and 50-ton mill equipped with Sp;rings formation containing some small lenses 

crus4er, rolls, Wilfley tables, and Frue vanners. of granite-pegmatite. This tunnel is 550 

feet l~ng, following a fracture 

which strikes N. 809 E. and dips 

55°-70° N. It is in most places 

barren, but near the face shows 

a little pyrite largely altered to 

soft earthy limonite in an -open 

part of the vein. About 210 feet 

from the face an opening 4 feet 

long and 2 inches wide contains 

crystals of hematite and siderite 

in druses~ Old abandoned workings on this vein are on top of 

the ridge east of the mouth of 

the tunnel. The dump at the 

tunnel shows a little pyrite in 

a quartz- hem at it e-siderite 

gangue. This vein was worked 

in the early days of the camp, 

but its production is not known. 

What little ore is found in the 

tunnel is said to assay about $18 

a ton in gold and silver. 

N 

200 100 0 200 

LEG~ND 

[2] 

Monzonite porphyry dikes 

EE3 

Pyritic veins 

EJ 

Unmineralized fracture 

Arrows indicate direction of dip 

·' 

Note:. Co4ntry rqck is all lda)1o Sprrngs format1on ·except·drkes 

300 Feet 

FIGURE 22.-Geologic plan of Golden Sun tunnel. Surveyed by hand compass and pacing. 

I 

JOHNSON TUNNEL. 

The Johnson tunnel, on the 

south side of South Boulder 

Creek, 1! miles west of Rollinsville, is 270 feet long, running S. 

70° W., parallel to the foliation 

·of the Idaho Springs formation, 

which forms the wall rock. No" 

vein or fracture is to be seen in 

this tunnel. 

FAIRHAVEN VEIN. 

The Fairhaven vein, on the 

ridge between Beaver and South 

Boulder creeks, about a mile 

south of Phoenix, is developed 

by a 40-foot shaf~ and sev- · 

eral pits. Th~ vein strikes about 

N. 80° W. and_dips steeply north, 

cutting Idaho Springs formation. 

All of the ore is oxidized, limonite replacing pyrite. · The principal ore to be seen at present ·is 

very much iron-stained quartz 

GRAND UNION TUNNEL. 

The Grand Union tunnel is on the south side 

of South Boulder Creek, 21 miles west of Roland schist cut by stringers of limonite. It is 

said that 500 pounds of float from this vein ran 

42 ounces gold to the ton. 

\ .. , 
1 ..._ 

GILPIN COUNTY. 193 

:MELETT VEIN. 

Tho Melott vein is opened by a whim shaft, 

now water filled, on tho crest of tho ridge 

botwoon South Boulder and Beaver creeks, 

about a 1nilo southwest of Pho~nix. The 

vein apparently strikes about N. 70° E., about 

parallel to a monzonite porphyry dike. It is 

about· 300 foot west of tho dike in Idaho 

Springs formation. Tho ore on tho dump 

is n1uch oxidized, but a little pyrite remains 

in a quartz gangue and disseminated through 

schist. 

LONE STAR VEIN. 

trating ore, which' is reported to assay $8 to $19 

per ton. Smelting ore shipped in 1910·averaged 'gold 1.51 ounces, silver 1.98 ounces, and 

copper 0.96 per cent. 

The claim was located in the late sixties and 

much of the surface ore was removed d~ing the 

next few years. Free-milling ore was found to 

a depth of about 40 feet, but below 50 feet 

sulphides were encountered and work was 

abandoned for many years. In 1900 the 

present shaft house was built and sinking 

resumed, and the property has been worked at 

intervals during the last ten years. In 1909-1.0 

it was worked by lessees, who report that they 

'l"'he Lone Star vein near Phoenix is opened have produced about $4,000 worth of ore. 

by a shaft and several pits on the ridge 

between the north and south forks of Beaver CHAMPION VEIN.· 

Creek. In this vicinity the Idaho Springs The Champion vein lies just east of Phoenix 

formation is intruded by a large mass of granite and 2! miles northwest of Rollinsville. It 

pegn1atite. The pegmatite has the greatest strikes N. 70° W. and follows the northeast 

surface exposure, but it includes many small side of a ~ass of white quartz 15 to 20 feet in 

and a few large lenses of schist. width. This quartz is probably an offshoot 

The shaft is 260 feet deep with levels at 60, from the pre-Cambrian pegmatite, for it 

150, and 250 feet. The drifts are practically seems to be cut by a 25-foot dike of monall east of the shaft, except on the second level zonite porphyry and appea·rs to be barren. 

where a short ch·ift runs west, with an explora- The vein is developed by a shaft said to be 

tory crosscut to the south. The ground above 250 feet ,deep with about 500 feet of drifts. 

the 60-foot level is stoped 'to the surface for 100 At the time of this survey, in September, 1910, 

feet east of the shaft, at which point the drift it was water filled. 

connects with an old shaft. On the 150-foot The ore on the dun1p consists of pyrite and 

level a 30-foot stope about 200 feet east of the chalcopyrite in a gangue of quartz and sidershaft has been carried to the surface. On the ito, in many specimens forming the matri.x 

third level a stope beginning near the shaft of a breccia of schist fragments. Films of 

has been carried to a height of 60 feet for 20 to chalcocite and bornite coat the pyritic min30 feet along the vein. orals locally. N ea'r ·the surface much of the 

Throughout the drifts and stopes the wall ore has been brecciated and the fractures filled 

rock is pegmatite. The vern proper ranges with hematite deposited by oxidizing surface 

frotn 4 inches to 2 feet in width and averages 12 waters. 

to 14 inches. It strikes N. 78° E. and stands This property was located in the eighties, 

nearly vertical to a depth of 150 feet, below but as far as can.be learned has made no prowhich it dips 80° N. It ~s composed of white duction. Some surface ore is reported to have 

quartz and massive pyrite and chalcopyrite been rich, but the sulphide ore is said to be of 

without other metallic minerals. Almost no low grade. The shaft is equipped with a 

banded structure and no evidence of post- stean1 hoist, and the .company owns a mill 

mineral shattering was seen. The wall rock situated on Beaver Creek just south of Phoeni.xon either side of the vein is heavily impregnated ville. The mill is equipped with 10 stamps, 

with pyrite to a maximu1n width of 2 feet. amalgamating plates, and Gilpin County 

On ·account of' the size of the vein most of the bumpers. 

material broken is ore. The massive pyritic 

material is sent to the smelter and is said to TUNNELS WEST OF ROLLINSVILLE. 

bring from $30 to $100 per ton, mainly in gold On the south side of Boulder Creek about 1! 

w.ith some silver. The less heavily n1ineral- miles west of Rollinsville two crosscut tunnels 

ized portions of the vein constitute the concen- are driven south through the Idaho Springs for442140-17-13 
194 GEOLOGY OF GILPIN, CLEAR CREE!{, AND BOULDER COUNTIES, COLO. 

mation. As neither of these crosscuts could be 

entered. the position and character of the veins 

·cut are unknown. From the size of the dumps 

the tunnels are judged to be rather long. They 

are only 150 feet apart, the western one being 

50 feet higher tha_n the eastern. There is very 

little ore on either dump, though it is evident 

that some pyritic ore has come from the 

upper western tunneL 

~ERIGO, GILPIN, GAMBLE GULCH, AND MOON 

GU~CH. 

PIONEER TUNNEL. 

:. The. Pioneer tunnel, on the south side of 

Moon Gulch, a mile west-southwest of Rollinsville, is a crosscut 1,270 feet long bearmg 

S. 8° E. It is entirely in granite gneiss, which 

shows little fracturing. It exposes no valuable 

veins, but in its first 290 feet cuts three small 

fractures striking abd'ut N. 60° E. These fractures are tight slips . with a maximum of 4 

inches of crushed granite gneiss along them. 

Two of them show !:-inch stringers of pyrite. 

Two other fractu,res with about the. same 

strike intersect the central part of ·the tunnel. One of these is unmineraliz.ed and the 

other shows a !-inch veinlet of white quartz 

with a little pyrite .. 

QUINDARO TUNNEL. 

The Quindaro tunnel is on the south side of 

Moon Gulch. about a mile southwest of Rollinsville and just west of the Smuggler tunnel. It 

is a crosscut running S. 27° E. for 270 feet 

through the Idaho S.prings formation. At 95 

feet from the mouth of the tunnel a barren slip 

plane strikes N. 48° E. and dips 85° SE.; 

at 210 feet a 1-foot zone of unmineralized 

brecciated schist strikes N. 15° E., and at 

260 feet another brecciated zone strikes N. 78° 

E. The two zones join 50 feet west of the line 

of the tunnel. Some iron-stained float lies on 

the surface above the line of this tunnel, but the 

development has not y~t reached this part of 

the ground. 

GOLD QUEEN VEIN. 

The Gold Queen vein is on the north side of 

Moon. Gulch west of the mouth of the south 

fork. It is developed by a short crosscut t1mnel 

and 100-foot drift and by a shaft now abandoned .. 

The country rock is schist of the Idaho 

Springs formation with abundant pegmatite 

cut by a 6 to 8 foot mafic (basic) dike that 

strikes N. 20° E. and stands nearly vertical. 

This dike is presumably very old, for it is 

intruded by pegmatite and has a rather distinct 

schistose structure parallel to the general structure in the vicinity. A very narrow dike of 

quartz monzonite. porphyry with an east-west 

strike cuts both schist and the mafic dike.· 

Movement along the dike since the intrusion of 

the quartz monzonite dike has offset the latter, 

the north side now being ·about 10 feet northeast 

of the south side. Pyrite, chalcopyrite, and 

hematite have been deposited in fractures and 

joints in all the formations, but the chief seat 

of mineralization seems to have been the 

much-jointed dike, which has been altered and 

contains more or less abundantly disseminated 

pyrite throughout. 

SMUGGLER VEIN. 

The Smuggler vein is on the south side of a 

ridge between two forks of Moon Gulch about 

one-half mile so:uthwest of the head of Traverse 

Gulch. It is developed by a drift tunnel 797 

feet long and by a shaft 150 feet deep. The 

shaft was under water during the summer of 

1911. 

The co~try rock is Idaho Springs for~ation, containing numerous small tongues of 

granite gneiss, offshoots from the large n1ass 

of that rock on the south side of Moon Gulch. 

The vein strikes N. 75° E. and dips about 65° 

N. Its width ranges from a small barren fracture to 8 feet and averages between 2 and 3 feet. 

The wider parts consist of crushed wall rock 

carrying more o:r less abundant disseminated 

pyrite and lenses of coarse pyrite, most ·of which 

are about 2 inches wide but some of which 

reach 10 inches. Dark cherty silica, siderite, 

and hematite appear to have been deposited 

subsequent to the main mineralization. 

Mineralization was slirong everywhere except 

for about 100 feet near the face of the drift. 

The largest body of ore seems to have begun 

about 300 feet in from the mouth and to have 

extended for 290 feet. It has been stoped' for 

209 feet to a height of 80 feet and an average 

width of 4 feet. · 

The coarse pyrite·. is said to carry only about 

$2 a ton in gold, whereas the general rmi of 

mine has a value of $10 a ton. The ore thus 

far mined has been valuable mainly for its 

gold. In 1910 the average content of all con-
r"':_, 

GILPIN COUNTY. 195 

I 

centrates sold to the smelter was 0.75 ounce 

gold to the ton. In 19~1 the smelter returns 

gave an average of 1 ounce gold and 1 ounce 

silver a ton. A 10-stn.mp mill is situated at 

the 1nine. 

The total production is estimated at between 

$50,000 and $75,000. 

BONANZA TUNNEL. 

'"l"'he mouth of the Bonanza tunnel is about 

500 feet south of that of the Smuggler tunnel. 

The tunnel, which is approximately 845 feet in 

total length, follows a rather winding but generally westerly course. Most of it is crosscut. 

Four zones of fru.cturing, some of which have 

been drifted on for short distances, strike 

northeast-southwest and dip 40°-50° NW., 

about parallel to the schistose· structure of the 

Idaho Springs· formation. A little disseminated pyrite occurs in the crushed country 

rock between their walls. At one place calcite 

was f01md in a small drusy cavity, bu·t in general the gangue is silicified COl.llltry rock. The 

west end of the Bonanza tunnel breaks into the 

stopes on the Smuggler vein about 45 feet 

above the Smuggler tunnel level. 

DIAMOND BILL GROUP. 

The Diamond Bill clain1s are on the north 

side of :Moon Gulch about 2~ miles southwest of 

Rollinsville. Two nearly parallel veins that 

strike N. 50° E. are shown in numerous pits on 

the surface. The northern vein dips 55° N. 

and the southern vein a little more steeply. 

Both are quartz~pyrite veins cutting Idaho 

Springs formation. A crosscut tunnel at the 

level of the road has been started to intersect 

them. 

OFFICER TUNNEL. 

The Officer tunnel is ·on the south side of 

Moon Gulch about a mile from its head. The 

tunnel, which runs south-southeast through 

Idaho Springs formation, cuts near its· mouth 

a narrow east-west dike of monzonite porphyry 

and also exposes ·a very narrow (1 to 2 inch) 

nearly barren fracture, in most places filled with. 

gouge. S~me rather coarse pyrite is seen on 

joint planes. near the fracture, and at several 

places the schist for 2 inches on either side of 

the fracture contains a little disseminated pyrite. Many of the small pegmatite "eyes" in 

the schist near the fracture are more mineral-

. ized than the inclosing schist. 

S~A BmD TUNNEL. 

The Sea Bird tunnel, on the north side of I 

Moon Gulch about a mile east of the sum.rillt of 

Jumbo :Mountain, runs west-northwest for 385 

feet. Between 90 and180 feet from the portal 

it cuts the only vein exposed-a lens of ore 

striking N. 85° W. and dipping 34° N. At its 

widest place this lens measures 4 feet, but its 

usual width 'is less than 1 foot. It consists of 

silicified schist carrying disseminated pyrite 

cut by narrow stringers of quartz and pyrite 

and little scattered chalcopyrite. An incline 

shaft sunk from the t~el level in the widest 

part of the ore lens was full of water at. the. 

time of this survey. 

t---jj . Pyr:itic vein · 

0 

Barren fracture 

N 

Note: Wall rock throughout is Idaho Springs formation 

100 200 400 Feet 

(Arrows indicate directionofdip) 

FIGURE 23.-Geologic plan of 1\fotmtain Monarch tunnel. Surveyed·. 

by"hand compass and pacing. 

MOUNTAIN MONARCH TUNNEL. 

The Mountain Monarch tunnel, on the north. 

side of Gamble Gulch 2 miles south of Rollins-· 

ville, is a ~00-fopt crosscut bearing N. 25° W .. 

It intersects two veins and two barren fractures .. 

(See fig. 23.) The wall rock is schist of the, 

Idaho Springs formation. 

The Chieftain vein strikes N. 45° E. and. 

dips about 56° NW. It is a well-marked 

fracture zone varying from 10 inches to 4 feet; 

wide but is not well mineralized except for 

about 110 feet l).ear its junction with the Twelvefoot vein.· The latter vein, where cut by the 

tunnel, is a 12-foot zone of schist bounded by 

well-marked fractures, carrying abundant disseminated pyrite, and cut in all directions by 

small pyrite stringers. It narrows to about 

18 inches as .it approaehes the Chieftain vein . 

,' 
196 GEOLOGY OF GILPIN, CLEAR CREEK, AND BOULDER COUNTIES, COLO. 

Where the two veins come together they form formation injected by small lenses of granite 

-:an ore . shoot ~bout 3 feet wide of crushed pegmatite. 

:silicified schist heavily impregri~ted with pyrite 

·which continues 110 feet along the Chieftain 

·vein with fairly constant width and minerali-

.zation. In the ore shoot the gangue is crushed 

silicified wall rock and the principal metallic 

mineral is pyrite, though in places a small 

amount of chalcopyrite was n_oted. The northwest end of the ore body is marked by a welldefined but feebly mi.neralized fracture making 

off into the hanging wall at an acute: angle. 

Beyond the main ore body the Chieftain vein 

consists of about 18 ·inches of crushed schist 

'between gouge-covered walls and contains n 

few small lenses of ore. 

.The Lutey drift is on a fracture, striking 

N. 25° E. and dipping 79° W. The fracture, 

which contains about 7 inche~ of crushed 

schist carrying a little disseminated pyrite, is 

bounded by gouge-covered walls. 

The Jake and Cutler drifts are on unmineralized fractures. 

A .few hundred tons or" ore, said to have 

assayed $10 to $16 in gold and silver, have 

been stoped above the t,unnel level from the 

shoot on the Chieftain vein. 

A mill at the mouth of the tunnel is equipped 

with 10 stamps, an1algamation plates, 4 

Gilpin County bumping tables, and a Bartlett 

table. 

SWISS TUNNEL. 

The Swiss tunnel, on thesouth side of Moon 

Gulch about 1t miles northwest of Perigo, 

is a crosscut extending south for · 880 feet. 

The general country rock of the tunnel is 

I_daho Springs.formation with abundant lenses 

Df granite pegmatite, but the last 150 feet 

is largely in n1onzmlite porphyry. Near the 

mouth of the tunnel a small dike of monzonite 

porphyry bears about east and west. No· 

veins and only a few unmineralized slip planes 

parallel to the schistosity were seen. 

PENOBSCOT TUNNEL. 

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The Penobscot tunnel is on: the· west side of 

Gamble Gulch 2! miles southwest of Rollinsville 

and ·about a mile north of Perigo. The tunnel 

is a drift about 2,100 feet long on the Myrtie 

Bell vein, with other drifts on the Gold Dirt 

vein, and a 330-foot crosscut northwest to the 

Penobscot vein. (See fig. 24.) The country 

rock throughout is schist of the Idaho Springs 

The Myrtie Bell vein §trikes N. 47° E. 

and dips on an average 75° NW. Its width 

·r-
GILPIN COUNTY. 197 

varies fro1n 2 inches to 4 feet, the average 

being about a foot. Both walls are marked 

by heavy postmineral gouge which in some 

places is 4 inches thick. 'rhe vein consists of 

somewhat crushed altered country rock carrying disseminated pyrite and here and there 

a little chalcopyrite. Just west of where it. 

crosses the Gold Dirt vein the Myrtie Bell 

vein, here about 18 inches wide, incloses a 

lens 5 inches wide of solid chalcopyrite. The 

mineralization is in general not strong,. but 

several small lenses yield concentrating ore. 

The spm·s from this vein shown on the map 

(fig. 24) are rather small and are mineralized 

similarly to the Myrtie Bell. 

'l"'he Gold Dirt vein cut near the end of the 

main tunnel strikes N. 78° E. and dips 50°-

650 SSW. It varies in width from 4 inches 

to 4 feet, widths of 2 to 4 feet being most 

common. This vein: consists of a number of 

subparallel fractures between which the country 

rock is altered and contains abundant disseminated pyrite. This disseminated ore is 

cut in all dn:ections by stringers of solid 

pyrite, some of which are one-half inch in 

width, and by stringers of dark quartz and 

siderite carrying pyrite, chalcopyrite, and 

galena. The age relations of this galenabearing ore are not clear from the exposm·es 

seen in this mine. The Gold Dirt vein has 

been offset for 50 feet by the .Myrtie Bell. 

This movement probably took place after the 

mineralization of both. veins for the postmineral gouge of the Myrtie Bell vein shows 

h9rizontal strire. Postmineral movement along 

the Gold Dirt fracture has. produced a little 

gouge and some strire parallel to the dip of 

the vein. 

The Penobscot vein, as exposed at the end 

of the crosscut from the Myrtie Bell drift, is a 

zone of fractured rock about 4 feet wide, carrying a little disseminated pyrite. The drift 

to the west is caved, but is said to be 300 feet 

long. 

The Penobscot tunnel was intended as a 

chainage and transportation tunnel for the 

mines on Tip Top :Hill west of Perigo, and very 

little stoping has been done on any of the veins 

it exposes. In 1911 the owners were drifting 

west on the Gold Dirt vein and had found 

some good ore. A 10-stamp amalgamation and 

concentration n1ill is situated north of the 

tunnel n1outh in Ga1nble Gulch. 

Some ass a )Ts of ore from the west Gold Dirt 

drift are reported to show 0.68 ounce gold, 4.5 

ounces silver, and 10.5 per cent copper per ton, 

though the averageore does not appear to contain so n1uch copper. Some of the chalcopyrite in this drift has altered to soft black chalcocite. Ore from the small stope on the Penobscot vein is said to have carried $30 in gold 

and silver. The copper ore·from the shoot on 

the Myrtie Bell southwest of the Gold Drrt 

crossing is said to have had a value of $30 a 

ton. The ore of the Myrtie Bell northeast of 

the crossing is generally of low grade. 

GOLD DmT MINE. 

The Gold Dirt, one of the first mines discovered in this district, is about a mile northeast 

of the village of Perigo. It i~ developed by a 

drift tunnel starting eastward from Gamble 

Gulch and by several shafts, the main one ·of 

which, 700 feet deep, is sunk beside the road 

from Perigo to Gilpin. The vein strikes N. 

80°-85° E. and dips 80°-85° S. 

The ore could b~ studied only" on .the shaft 

dump and in the tuni:tel, which was entered for 

570 feet. That on the dump is composed 

mainly of coarse pyrite, some of which is copper stained. Near the surface the ore is much 

altered and secondary hematite is developed, 

but as exposed in the tunnel about 450 feet 

from the face it forms a vein of nearly sol~d 

coarse pyrite 8 inches thick. Postmineral move- . 

ment along the vein has crushed and sheared 

the ore in places. According to Hollister 1 the 

upper portions of the vein were very rich: 

During the spring [of 1860] the Gold Dirt lode had been 

struck, and very rich it was. By the end of the year six 

quartz mills were running from it. One sluice took out 

in 17 days $2,227. 

Hurlbut & Co.'s six-stamp mill started October 1 and 

up to January 5, 1861, had taken out $11,526.94 and 

had been idle four weeks of the time. Between June 

and November two men realized from the lode, over and 

above all expenses, $35,000. Hollister & Co. struck 

pyr~tes on the lode 70 feet from the surface. Before that 

they had been working 60 hands, and their weekly yield 

of gold was from $1,500 to $2,000. Upon striking the 

pyrites, a run of 18 hours gave but $1.40. 

The ore below the oxidized-surface portions 

of the vein is said to average ,.about $13 a ton 

for concentrating ore and..,$20 to $60 for smeltipg ore. A 50-ton cyanide mill is near the 

mouth of the tunnel. 

1 Hollister, 0. J., The mines of Colorado, p. 113, 1867. 
198 GEOLOGY OF GILPIN, CLEAR. CREEK, AND BOULDER COUNTIES, COLO. 

COLORADO TUNNEL. 

The Colorado tunnel, whose portal is in 

Gamble Gulch ab<?ut 100 yards below th~ portal 

of the Gold Dirt, extends northeast for about 

630 feet through schist of the Idaho Springs 

formation and pegmatite. From a point 200 

feet from the portal to the face it follows a vein. 

The first 250 feet of this vein is practically bar-

:ren, but beyond that it is well mineralized and 

in one place shows 8 inches of coarse pyrite ~nd 

gray quartz between sharp walls. At 500 feet 

from the portal the vein is made up of 4 feet 

of somewhat brecciated achist and pegmatite 

carrying more or less disseminated pyrite 

.and traversed by a 4-inch sharp-walled pyrite 

-veinlet. 

The tunnel forms part of the Gold Dirt group 

·of workings. No shipments have been made 

from it. 

WAR EAGLE MINE. 

The War Eagle vein is oil the ridge east of 

Gamble Gulch about a mile northeast of Perigo .. 

It is developed by a shaft said to be 200 feet 

'deep and to have short drifts on three levels. 

The country rock· is granite gneiss. 

The vein strikes N. 60° E. through a saddle 

in the ridge. The ore on the dump is pyriteimpregnated country rock traversed by veins 

as much as 1! inches wide of coarse-grained 

pyrite with a little white quartz. In these sulphide veins individual pyrite crystals attaip. a 

maximum size of one-half inch. Some of the 

ore contains a little specularite and some, it is 

reported, a very small amount of chalcopyrite. 

Some ore shows a little· postmineral crushing 

with blackened slickensided faces cutting pyrite 

stringers. 

The ore is said to average about $15 a ton in 

gold. 

PERIGO MINE. 

The Perigo is the largest mine in the Perigo 

region and one of .the oldest, having been 

·Opened in 1860. The principal development· 

work consists of two tunnels (see figs. 25 

:and 26) and the stopes connected with them. 

Several old shafts could not be entered. In 

general, as may be seen from the maps, the 

workings develop a complicated set of veins 

with a general trend somewhat north of east. 

Toward the southwest the branches unite to 

form a single fracture zone, which, however, is 

not so strong nor so heavily mineralized as 

might be expected. from the union of so many 

branches. All of the veins of this system are 

similar mineralogically and were plainly formed 

at the same time. The wall rocks are schist of 

the Idaho Springs formation, granite gneiss, 

and pegmatite. (See figs. 25 and 26.) Much of 

the granite gneiss is unusually coarse grained, 

approaching pegmatite in texture. 

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The veins may be described in general as 

disseminations of pyrite in the wall rocks along 

zones of fracturing; with the s~ngle exception 

of the vein at locality A, figu:r~e 25, in which 

fissure filling seems to have been very subordinate. The relations ·are complex and the degree of minetalization ~xtremely variable. 

\,.l 

,... 
GILPIN COUNTY. 199 I 

Although most rite for a maximum width of 6 feet. Some of 

of the ore of the the pyrite is very fine grai~ed and some of it is 

upper tunnel seen coars·e, occurring in cubical crystals with maxi-

, in phtce was py- mum widths of three-fourths. of an inch. 

ritic, some of that Vein A, exposed in a branch drift, shows 

· on the dump car- pyrite disseminated through schist bordering a 

ried a little fine- fracture zone. At the east face it is 4 feet wide. 

grained galena. What is probably the Daisy vein (locality B, 

The ore, though fig. 26) consists of 3 to 5 feet of fractured gneiss 

commonly a dis- and pegmatite carrying disseminated pyrite. 

semination of py- . The Red Pocket vei~ at the west· end of the 

rite +,hrough frac- drift which follows it is a zone of schis~ -and 

tured wall rock, pegmatite 4 feet wide cut by several small 

locally occurs in pyrite stringers and carrying some disseminated 

sharp-walled pyrite. Alittlestoping has been done upon it. 

veill.lets which Vein B consists of 2 feet of schist and pegmay be true fis- matite trav~rseci by irregular stringers of 

sure filling s . coarse pyrite some of which are an inch wide. 

Thus, at locality The Ladysmith vein, which consists in places 

A, figure 25, the of 6 to 8 inches of crushed but unmineralized 

granite ·gneiss, schist, shows near the mai~ tunnel 2 feet of 

.~ which carries dis- crushed schist and pegmatite traversed by 

·~ seminated pyrite two 2 to ·3 inch veinlets of quartz and pyrite. 

~ for a width of 2! Vein C is a strong sharp-walled, vein of 

~ feet, is cut by sev- white quartz which carries irregular masses of 

_g eral fairly sharp pyrite and is traversed by a band of coarse, 

~ walled subparal- pyrite ·1! inches wide. Pyrite locally forms 

~ lel veinlets of py- half the 'vein but in most places is much 

§ r i t e , s o ll:i e· of subordinate to quartz. Vugs aro common; 

P. 'Yhich are 3 i'nches one a: foot across is lined with quartz crystals 'So -§ in width.· The three-fourths of an inch and less in diameter. 

~ northern vein de:.. The vein has not been developed. 

~ veloped in 'the up- The shipping point for ore and concentrates 

~ per tunnel is from the Perigo mine is :Jlollinsville, 3 miles by 

~ known as the road fron1 the mine. The lower grades of ore 

Daisy;otherveins are treated at Perigo in a stamp mill of 100 

have been named . tons capacity. At present mining on a small 

the Baker and the scale ois in progress in several parts of the mine 

Perigo, but as by lessees, who pay a royalty of 25 per cent 

their identifica- on smelting ore and from 10 to 15 per cent 

tion is uncertajn on concentrating ore. Short mill runs . are 

these names have made at intervals as sufficient ore accumulates. 

be en omi ~ted Fourteen ~ots of sn1elting ore aggregating 42! 

from the map. tons, shipped at different times from 1901 to 

In the ,lower 1909, showed by sampling-works assays gold 

tunnel, at one of 0.44 to 3.16 (average, 1.23) ounces, and silver 

the best expos- 1.20 to 4. 70 ounces. 

ures, the main 

vein (locality A, 

fig. 26) consists 

of schist and pegmatite carrying 

disseminated pyFREE GOLD AND MAREAU VEINS. 

The Free Gold and Mareau veins, on the hill 

just ;west of Perigo village, are developed by 

shafts 310 and 190 feet deep, respectively. The 

properties were opened about 1900. 
200 GEOLOGY OF GILPIN, CLEAR CREEK, AND BOULDER COUNTIES, COLO .. 

The Free Gold had long been idle at the time 

of this survey. The vein is at or near the contact between schist of the Idaho Springs formation and monzonite porphyry. The only mineral seen was coarse pyrite in bunches or irregularly disseminated in pegmatite. The average 

metal content of the ore treated in 1910 was 

0.368 ounce of gold and 0.21 ounce of silver. 

About 96 tons of ore, obtained recently from 

the Mareau shaft, were 1nilled in the Daisy mill 

at Perigo and are said to have averaged about 

1 ounce in gold. 

The Daisy mill, connected with these properties, is equipped with three batteries of slowdrop ;4.50-pound stamps ~nd three Gilpin 

County bumpers. 

GOLDEN FLINT vEIN. 

The, Golden Flin,t vein is about three-fourths 

of a mile south-southwest of Perigo. It 'strikes 

N. 85° W., and appears to dip about 80° N. 

It is developed by a shaft 400 feet deep, now 

water filled. The ore is entirely pyrite in a 

quartz gangue. The mine was an important 

gold producer in the early days of the district 

but has been idle for many years. 

MOUNTAIN CHIEF MINE. 

The Mountain Chief mine is about 11 miles 

northeast of Apex, on a north spur of Dakota 

Hill, within a large stock of monzonite porphyry. The shaft, now long abandoned, is 

said to be about 300 feet deep. The surface 

, exposures and the remnants of ore on the dump 

suggest that the deposit represents mineralization along a large· number of small subparallel 

fractures rather than along a wide fissure. In 

places the porphyry is traversed by an irregular 

network of pyrite veinlets th.at range in width 

from one-fourth inch · to paper thinness. 

Pyrite in disseminated grains and minute 

lenses is abundant in all of the ore. The only 

vein mineral observed besides pyrite.was hematite, probably formed by oxidation from the 

pyrite. Some of the oxidized surface ore fro:p1 

this mine is said to have run about 2 to 3 ounces 

in gold, but the unaltered material was not of 

profitable grade. 

VICTORIA VEIN. 

The Victoria vein, on the south side of Lump 

Gulcl;t, one-fourth mile south and a little east 

of Gilpin, strikes about N. 22° E. and dips 

65° NW. The.shaft, now full of water, is said 

to be 150 feet deep and to have about 290 feet 

of drifting on the 11 0-foot level. The vein is 

largely stoped at the surface for a distance of 

250 feet south of the shaft. . 

The ore is pyrite and chalcopyrite in a quartz 

gangue. A relatively narrow streak· of solid 

sulphides constituted the higher-grade material, and the country rock impregnated with 

sulphides for 3 to 11 feet on either side of the 

vein was considered concentrating ore. It is 

claimed that the smelting oi:e averaged about 

$54 per ton and the concentrating ore about $6. 

The property, consisting of two claims on the 

vein and a placer in Lump Gulch, was located 

in 1879 or 1880 and was worked intermit-· 

tently untill906. To that time the gross production is said to have been about $20,000. 

GETTYSBURGH' VEIN. 

The Gettys burgh vein, forn1erly called the Illinois, is about one-half nnle south of the town 

of Gilpin. Its trend is slightly north of east 

and its dip apparently about vertical. It has 

been developed by several pits and by a shaft, 

now inaccessible, said to be 225 feet deep. 

The ore on the dump shows a pyritic vein in 

places as much as 6 inches wide though gener-

·ally much narrower. Gangue minerals are 

siderite and quartz. Specimens of oxidized 

ore show limonite and some n1alachite with 

remnants of unaltered chalcopyrite. The value 

of the unaltered ore is said to have been low, 

but that of the oxidized free-milling ore in 

surface pockets is said to have been $50 to $60 

in gold. 

The mine was discovered in 1860. The 

present company has installed three sets of 

crushing rolls and Crane dry concentrators, 

which, however, appear to have been but little 

used. 

APEX, AMERICAN CITY, AND KINGSTON. 

CHARCOAL CHARLIE .VEIN. 

The Charcoal Charlie vein, on the north side 

of Freeman Gulch about half a n1ile above its 

junction with North Clear Creek, is opened by 

a shaft of unknown depth. The vein strikes 

about N. 55° E. through Idaho Springs formation. Very little ore appears on the dump, 

but what there is shows a banded- vein at least 

3 inches wide. Next the walls there is about 

an inch of siderite carrying pyrite and a little 

'-; 
GILPIN COUNTY. 201 

scattered chalcopyrite. The central part of 

. the vein is filled with white quartz free fr01n 

sulphides. 

SCHULTZ WONDER MINE. 

'rhe Schultz Wonder 1nine is on the south 

side of North Clear Creek just above the junction of Pine Creek, about 2 n1il~s south of Apex. 

The principal vein strikes N. 20°-:-35° E. and 

clips 75° W. The main develop1nent is a tunnel following this vein for about 700 feet 

through schist of the Idaho Springs for1nation 

and subordinate pegmatite. The vein commonly cuts the schist foliation at sn1all angles 

but in a few places• parallels it. A bostonite 

dike outcrops a short distance west of the vein. 

The Schultz Wonder vein is irregular in size 

and decrree of mineralization and exposes no 0 

ore shoots of workable size. The largest ore 

body seen was fr01n 4 to 30 inches wide and 

persisted for about 125 feet along the adit. It 

consists of a heterogeneous nuxture of chalcopyrite, pyrite, sphalerite, and a little galena 

in a white to gray quartz gangue. In the 

narrower portions of the vein there is conlmonly a band of c01nb qua:ctz next the walls. 

Siderite occurs in places, generally in the central portion of the vein. 1'he vein is cut off at 

the face of the tunnel by a fault striking N. 45° 

W. and dipping 70° S. 

The tunnel cuts a nun1ber of lean or barren 

cross fractures, some of which have been 

drifted upon. 

The clain1s of this group were located in 1894 

and s1nall a1nounts of ore, said· to have averaged about $15 a ton in gold and silver, have 

been shipped. 

PIONEER ,TUNNEL .. 

The Pioneer crosscut tunnel, started in the 

fall of 1910 on the north side of North Clear 

Creek at the junction of Pine Creek, about 2 

miles south of Apex, is designed to. run northwest under Arizona and Montana hills. The 

tunnel is for drainage and transportation and 

is 8 by 9 feet in the clear. In 1911 a 10-stamp 

mill was under construction at the mouth of 

the tunnel. The company owns only a few 

claims on the ·southeast slope of Arizona Hill, 

and no veins have yet been intersected. 

"GEIGER VEIN. 

The Geiger vein is exposed on the west side of 

Michigan I-~ill, 1t miles south of Apex and about 

opposite the mouth of Pine Creek. It has been 

opened by shafts, pits, and tunnels from the 

creek bottom to the top of the hill, a ~listance of 

nearly three-fourths of a mile. Owing to 

caving and flooding, none of the workings are 

now accessible. 

At the outcrop the vei1~ strikes about N. 50° 

E. and is nearly vertical. 

On the top of Michigan Hill the vein, which 

here cuts granite gneiss, is about 4 to 6 feet 

wide and consists of white quartz stained yellowish along fractures and traversed by many 

small veinlets of pyrite. Much disseminated 

pyrite occurs in the vein material and -the adjacent wall rock. Bands of reddish-gray cherty 

quartz containing a little chalcopyrite and 

p'yrite appear to cut the white quartz. Ore on 

the large dump of the lower tunnel, just above 

the road in North Clear Creek opposite the 

mouth of Pine Creek, shows two distinct periods 

of mineraFzation. The first is represented by a 

vein consisting largely of pyrite in a quartz 

gangue and by associated pyritic replacement 

of the schist wall rocks. This vein was fractured and the fractures filled during. a second 

mineralization by an abundant white gangue of 

quartz carrying chalcopyrite, some pyrite, and 

scattered sphalerite and galena. Siderite is 

generally present in the later veinlets as a thin 

crust next their walls. Vugs lined With quartz 

crystals are common. 

Subsequent to both mineralizations some 

fracturing of the vein took place, and the fractures were filled with cherty-looking silica, 

which has also been deposited upon the quartz 

crystals in some of the vugs. 

INGRAM VEIN. 

The Ingram vein cuts across the ridge 

between North Clear Creek and Elk Creek 

about a mile south of Apex. It was open.ed in 

1896 by a shaft starting on the top of the ridge 

at an elevation of 10,150 feet. This shaft is 

said to be 270 feet deep and to be connected 

with a large amount of drifting. It was last 

worked in 1909 and could not be entered on 

.account of water. A tunnel from Elk Creek, 

starting about 50 feet above tl~w valley bottom, 

was at the time of survey about 120 feet long. 

The last 70 feet follows an unmineralized fracture. zone that strikes N. 55° E. and clips 55° W. 

Whether this represents the Ingram vein itl 

doubtful. . 
202 GEOLOGY OF GILPIN, CLEAR CREEK, AND BOULDER. COUNTIES, COLO. 

At the shaft the vein apparently strikes 

N. 65° E. and dips 70° NW., cutting the foliation of granite gneiss at very acute angles. 

Some rather obscure outcrops of bostonite 

porphyry just east of the vein are probably 

part of a long dike which extends southeast 

nearly to N evadaville, a distance of 4 miles. 

The ore on the dump is largely chalcopyrite 

and pyrite in a bluish quartz gangue. Portions 

of the vein are said to carry galena containing 

some gold and silver. 'Much of the massive 

sulphide ore is crushed and fractured, and ·the 

vein material is separated from the wa~l rock 

by gouge blackened by an abundance of 

crushed pyrite. In places a dull black earthy 

coating, probably chalcocite, appears on the 

pyrite and chalcopyrite. 

The owners estimate the production of the 

property at· about $10,000 from ore running 

between 14 and 22 per cent copper per ton. 

EVERGREL ... ~ MINE. 

The Evergreen mine in the valley of Pine 

Creek, about half a mile south of Apex post 

office, is unique for this district in the nature 

and mode of occurrence of its ore .. The ore is 

valuable largely for its copper content, and the 

sulphides occur not in a vein but disseminated 

through monzonite as an original constituent. 

The property was worked in the early eighties, 

but its modern development began with its 

acquisition by the present company in 1904. 

The · mine is developed by a vertical shaft 

with levels at 60, 150, and 200 feet. The 

60-foot level was inaccessible at the time of the 

survey. The drift on the 150-foot ·level extends about 130 feet north-northeast from the 

shaft. At the 200-foot level the maiD. drifts 

are connected with the shaft by a crosscut 

· about 100 feet long, from which drifting has 

~ 

The plant, which is operated by steam power, 

consists of a shaft house and mill. The shaft · 

is equipped with· bucket hoist. In the mill, 

which has a capacity of about 60 tons in 24 

hours, the ore, after crushing, goes·to a conical 

settling tank and then to Richards pulsating 

jigs and Card tables. The concentrate is 

hauled by team 8 miles to Black Hawk. 

· The geologic relations at the Evergreen mine 

and the mineral character and origin of the 

ore have already been fully described on pages 

.126-129. 

The ore obtained at this mine is said to average about 3 per cent copper and $4 to $5 in 

gold and silver per ton. Its distribution, 

however, is sporadic, and with the exception 

of that in the large chamber stope on the 

tunnel level no large bodies of it have been 

found. Only a few carloads have been shipped. 

and work is still largely exploratory. The 

ore is unquestionably. to be sought in and 

near the dikes, but as the sulphides are so 

unevenly distributed in the dike rock no 

prediction of its probable value or extent can 

be made. 

GOLD STANDARD AND NANCY LEE VEINS. 

The Gold Standard and Nancy Lee veins are 

on the south side of Pine Creek about threefourths of a mile south of Apex. There are. 

shafts on both veins, said to be over 100 feet 

deep, and a tunnel now caved has been driven 

on the Nancy Lee vein. ·The ore near the 

surface was free milling as a result of oxidation 

but passed with depth into pyritic ore with 

quartz gangue which does not appear to have 

been payable. A sniall stamp mill with Gilpin 

Count'y bumpers is located near the mouth of 

the tunnel. The gross production is said to 

have been about $10,000, mainly from oxidized 

been extended for &bout 270 feet to the north ore. 

and 220 feet to the south. A tunnel, whose BULLION TU:N'NEL. 

mouth is about 50 feet north 'of the shaft, Several small pyritic veins are cut by a prosruns for about 565 feet a little west of north. pect tunnel known as the Bullion (925 feet 

Mining has been largely exploratory; no long) in Whites Gulch about one-fourth mile 

stoping has been done on the 200-foot level west of Apex. This tunnel through most of its ' . and only 50 feet of stoping, locally to a height, length runs somewhat west of north and is 

of 15 feet, has been done on the 150-foot level. almost entirely.in Idaho Springs formation. It 

Almost the only stoping in the tunnel is at a cuts five fracture planes, which strike N. 70° E. 

point about 120 feet from the mouth, where a to N. 80° W. and dip from 40° N. to vertical. 

large chamber stope, about 40 ·feet long,. 30 Some of these fractures are barren throughout, 

feet wide, and from 2 to 12 feet high has been but others, though barren locally, carry pyrite 

excavated. in lenticles 2 inches or less across. The pyrite 
'· 

GILPIN COUNTY. 203 

is con,rse and is associated with some gangue Most of the ore was treated at the mine in a 

quartz; none of the sean1s have been worked. 1nill equipped with automatic feeders, 10 

A dike of monzonite porphyry is cut by this stamps, 2 Gilpin County bumpers, and 3 Frue 

tunnel about 420 feet from the mouth and is vanners. 

MACKEY VEQJ. exposed for 90 feet. It contains much disserrii- ' 

nated pyrite in small particles, which are most 

abundant along and near small fracture planes. 

Some of these pyritized seams traverse porphyry and schist indiscriminately. A barren 

fracture similar in trend to the pyritic seams 

cuts the porphyry, indicating that the pyritic 

nuneralization is probably later than the intruThe Mackey mine, about a mile west of 

Apex near the head of Elk Creek, was idle at 

the time of this survey,· and only a portion of it 

was accessible. The workings consist · of a 

shaft connecting with two .accessible levels at 

25 feet and 140 feet and a third, at a greater 

depth, which was water filled. The · vein 

strikes N. 50°-75° E~ and dips 30° t.o 50° N. 

The shaft follows tne vein. 

sion of the monzonite porphyry. 

A specimen from the turu1el dump shows a 

coarse pyrite vein cutting sharply across· the 

foliation of schists of the Idaho Springs formation but shows practically no dissemination 

of pyrite in the schist. Another .. dump specimen, evidently from a vug in one of the pyritic 

veins, shows pyrite cubes. etcl;wd or corroded to 

steplike or ragged surfaces. Upon portions of 

these pyrite crystals coatings of siderite, chalcopyrite, and bornite in small crystals were 

deposited either contemporaneously with or 

prio~ to the etching. 

ANNIE H. VEIN. 

The Annie I-I. mine, on Elk Creek near Nugget and just southwest of the Mackey mine, 

was last operated about 1908 and could not be 

entered. The workings consist of two shafts 

known as No. 1 and No. 2, 300 and 225 feet 

deep respectively and 310 feet apart. The 

most extensive drifting is on the upper or 

tunnel level, which is 572 feet long and is cut 

by the No. 2 shaft at a depth of 155 feet. 

The deeper levels connect only with the No. 2 

shaft; one at a depth of 205 feet extends about 

60 feet on each side Qf the shaft, and another 

at 255 feet extends about 75 feet on each. side. 

The vein strikes about N. 60° E. Its dip 

may be inferred from the inclination of the· 

shaft, which, between the surface and the first 

level, dips 50° N ., and between the first and 

second levels to about 35° N. From the bottom of the shaft a crosscut has been driven 

northward for about 125 'feet. 

. The ore, which is of the pyritic type, is similar in general to that· of the Mackey vein. 

.Available assays. of the ore show $4 to $50, 

mainly gold; most of them show $16 to $20. 

Son1e picked lots assayed as high as 6 per cent 

copper. 

The 25-foot level is about 200 feet in length 

and has been considerably stoped. The vein 

material, however, is highly oxidized and the 

exposures are not favorable for study. The 

140-foot level (see fig. 27) cuts mainly Idaho 

N 

0 so 10oFeet 

L:.:::J 

~ 

Pyritic veins 

F.IGURE 27.-Plan of 140-foot level, Mackey mine, ncar Apex, Colo. 

Springs formation intruded by small amounts 

of pegmatite. The vein is a well-defined fracture zone, which on the west of the level is 

practically barren but at most other points 

is well mineralized. Where widest the heavily 

mineralized portion is about 2 feet across and . 

appears to be a true fissure filling composed 

of white quartz and pyrite in nearly equal 

amounts. Som.e of the quartz shows comb 

structure. This is bordered on each side by a 

foot or so of wall rock carrying some disseminated pyrite. In stope A (fig. 27), which 

connects with the 25-foot ~evel, the vein is 

commonly about 1! feet wide. At one place 

it shows about a fo.ot of nearly solid pyrite, 

below which, for 2! feet, scattered stringers 

of pyrite traverse the. schist. 

A relatively narrow branch vein, said to be 

of much higher grade, joins the main vein a 
204 GEOLOGY OF GILPIN, CLEAR CREEK, AND BOULDER COUNTIES, COLO. 

short distance west of _the shaft. Stope B, on 

this branch vein, extends 15 to 20 feet above 

the level an~ shows that it is of very uneven 

or pockety character and is in place3 6 inches 

wide. though commonly narrower. Its richest portions carry chalcopyrite, which is 

coated along fractures with secondary films 

that show peacock colors where thin, and 

where thicker the blue-color characteristic of 

covellite. 

The sh~ft house is conne·cted by a short 

tramway with a 10-stamp mill which is also 

equipped with cyanide tanks. Only experimental runs seem to have been made. 

Gold is the principal valuable metal of the 

ore, but no reliable figures showing the tenor 

of the ore were accessible. Exceptionally as 

much as 5 per cent of copper is present. The 

total product~on is said to have been about 

2,000 tons. 

FISH VEIN. 

The Fish vein, in the. valley of Elk Creek 

about due west of the summit of Idaho Hill, is 

opened by a tunnel which is caved 460 feet 

from . the portal. For the first. 300 feet the 

tunnel expos~s no important veins, but from 

the 300-foot point to .where it is caved it fol-

. lows a vein striking N. 60° E. and dipping 

50° NW. This vein is typically pyritic, carrying pyrite, some chalcopyrite, and a quartz 

gangue. Much gouge is present, and the vein 

is soft and wet. Near the surface some hematite has developed from oxidation of pyrite. 

The ore .appears to be low grade and little has 

been shipped. · 

PLATEAU VEIN .. 

The Plateau vein is on the south side of 

Colorado Mountain near its crest, about onefourth mile north of American City. It strikes 

about east and west and at the slirface apparently dips 45° N., but in the lower levels is 

said to be almost vertical. The main shaft, 

now full of water, is said to be 640 feet deep, 

with about 1,000 feet of. drifts. The ore on 

the dump is entirely pyrite and white quartz 

and is said· to carry about $20 per ton in gold 

and silver. No production figures were obtainable. 

City. · The shaft, now full of water, is said to 

be about 150. feet deep. The vein strikes 

northwest and· consists of quartz and pyrite; 

it is said to have been oxidized to a depth of 

35 feet. . 

ANNIE TUNNEL. 

The Annie tunnel is in the gulch between 

Pile Hill and Montana Mountain, about 2 'miles 

west-southwest of Apex. The property was 

being worked in 1910, the development consisting of a tunnel about 250 feet long, trending N. 60-65° E. for the first 220 f.eet and thence 

N. 4.0° E. to the face. Almost the whole tun-· 

nel is in schist of the Idaho Springs formation 

and pegmatite. At the face is exposed a broad 

fracture zone, 7 to 8 feet wide, striking about 

N. 85° E. and dipping 85° N. This fracture 

zone shows over a foot of gouge and nume~ous 

subparallel veinlets of pyrite one-half inch or 

less in width and of quartz. Some chalcopyrite is present in these veinlets and much 

pyrite is disseminated in the altered schist 

between them~ Tennantite occurs here and 

-there in small veinlets within the fracture zone. 

The ore of this vein is said to have an average 

value of $8 a ton, but picked portions show $26 

in copper and $60 in gold. No shipments 

have been made. 

METEOR TUNNEL. 

The Meteor tunnel, at the southwest corner 

of Elk Park, is 225 feet long. It runs S. 67° W. 

through Idaho Springs formation, following. a 

2 to 8 inch fracture which dips 35° N. This 

fracture. contains brecciated silicified schist 

carrying some disseminated pyrite. The vein 

is partly oxidized throughout its entire exposure, for even at the face the depth attained is 

only about 75 feet. · 

GOLD RESERVE VEIN. 

The outcrop of the Gold Reserve vein trends 

east-northeast along the southwest slope of 

Montana Hiil, south of and about parallel to a 

bostonite p~rphyry dike. The vein consists of 

quar~z with a little pyrite and chalcopyrite, 

and its higher-grade ore is said to average 

about $15 to $20. The shaft ls said to be 90 

HUBERNOCKER VEIN. feet deep but is full of water. .A crosscut tunnel 

The Hubernocker shaft is at the north side now 140 feet long, whose mouth if below the 

of Elk Park near the divide into Black Canyon," junction of Mosquito Gulch and North Clear · 

about one-half mile northwest of American Creek,.has not yet intersected the vein .. 
GILPIN COUNTY. 205 

MONTANA HILL TUNNEL. ·MOOSE VEIN. 

'fho Montana I-fill tunnel is on the north side The Moose mine in Kingston Camp has been 

of North Clear Creek about one-fourth mile long abandoned. It was worked through a 

above tho mouth of Miners Gulch. It is a 'shaft now inaccessible. The strike of the vein 

crosscut, at present about 300 feet long, that is about N. 75° W. and the dip near the surface 

bears N. 2° W. It' is driven through dense is 70° N. The unaltered ore shows pyrite and 

quartz diorite and hornblendite without joints subordinate chalcopyrite; the oxidized surface 

or fractures and exposes no orQ. ore carries specular hematite. 

'J. W. PROSPECT. 

Tho J. W. prospect, in Kingston rmn1ng 

camp, consists of a single tunnel 125 feet long 

from which a branch tunnel 60 feet long has 

been driven. The main tunnel trends N. 25° 

E. and the branch tunnel diverges at only a 

small angle. The 1nain tunnel at one point cuts 

a breccia of schist; fragments in a partly oxidized n1atrix: carrying chalcopyrite, tennantite, 

sphalerite, quartz, and barite. The 60-foot 

drift follows a quartz stringer which locally 

carries some chalcopyrite and tennantite. 

Work at this property was begun in 1904, but 

no ore has as yet been shipped. 

LONDON VEIN. 

The London vein, in the n1ining camp of 

Kingston about 3! miles west-southwest of 

Apex, strikes N. 80° E. and dips about 

70° N. It is developed by a shaft 100 feet 

deep, from the bottom of which some drifting 

has been clone. The shaft was sunk 12 to 14 

years ago, and after lying idle for many years 

the property was again being worked (by 

lessees) in 1910. The wall rock is schist of the 

Idaho Springs formation. 'fhe drift on the 

100-foot level follows the vein westward from 

tho shaft for about 50 feet, then leaves t>the 

main vein and for 50 f~et follows a branch, 

which strikes N. 60° E. and dips 70° NW., to 

a point where it is cut off by a fractured mass 

of soft barren schist, into which the drift penetrates for 40 feet. 

The ore is py'rite with a little chalcopyrite and 

is said to avei·uge $15 to $20 a ton, principally 

in gold. Oxidized portions show specular 

hematite in aggregates of small flakes. Assays 

as high as $170 have been obtained. The averago content per ton of small lots of smelting 

· oro shipped in 1910 was gold 0.97 ounce and 

silver 3 ounces, and of concentrating ore, gold 

0.23 ounce and silver 1 ounce. 

ILLINOIS VEIN. 

The Illinois vein is in Kingston camp on the 

northwest slope of Pile Hill. The shaft could 

not be entered·, but from surface appearances 

the vein appears to strike about N. 50° E. 

The ore, which is in general similar to that of 

the Annie H. vein, consists of pyrite and subordinate chalcopyrite. 

SILVER CREEK A~D STEW ART GULCH. 

SHERMAN-MACON TUNNEL. 

The Shern1an-:Macon ttulnel, on the west 

side -of Silver Creek about three-fourths of a· 

Tnile north of its junction with Clear Creek, is 

a crosscut 1,240 feet long trending' N. 55° W. 

through granite gneiss injected by pegmatite. 

Two systems of fractures cutting the gneiss 

are shown, one striking about N. 20°-40° E. 

and the other abqut 80° E. The northeastsouthwest fractures dip steeply west or stand 

vertical, an.d the east-west ones dip 40°-70° 

N. Both systems are mineralized in a few 

places,. but for the n1ost part are nearly barren. 

The 1nineralization is pyritic, the pyrite occurring as disconnected lenses .and stringers onefourth to 1 inch wide. Locally the walls are 

son1ewhat silicified. 

The n1ost prorninent and best mineralized 

fracture is cut about 1,000 feet in from tho 

mouth of the tutln~l. It belongs to the eastwest system. Drifts have been run both ways 

on this fracture for about 100 feet from the 

tunnel, and an SO-foot raise has been excavated 

at the tunnel. Parallel to the vein and about 

10 feet northwest of it a nearly vertical open 

watercourse is filled with breccia and gouge. 

No ore had been produced up to the time of 

this survey. 

PETTIBONE MINE. 

The Pettibone nline is on the east slope of 

Oregon Hill about 1! n1iles north of the junction of Silver Creek with North Clear Creek. 
. 206 GEOLOGY OF GILPIN, CLEAR. CREEK, AND BOULDER. COUNTIES, COLO. 

rhe workings consist of an upper and a lower County bu1nping table, and a King-Danough 

· tunnel, about 200 feet apart vertically, located , concentrator. 

a few hundred feet above the level of Silver 

Creek. The mine has been closed for several GOLDEN ROD MINE. 

years, both tunnels were caved near the por- The Golden Rod mine, on Silver Creek about 

tals, and the·information in regard to the ores 1! miles above its junction with North Clear 

was derived solely from an examination of the Creek, is developed by a shaft and tunnel. 

dumps. The size of these ,indicates that the The tunnel, which was started in 1902, is about 

workill.gs were extensive.· 50 feet above the level of 'Silver Creek and 

The ore on the dumps belongs to two distinct extends for about 825 feet into Oregon 'Hill. 

types, pres..imably coming from different veins. Its· average direction is about N. 60° W. For 

The first type shows pyrite in solid veinlets 2 its whole length the tunnel is in Idaho Springs 

inches or less in width. A small copper con- formation highly injected with pegmatite. 

tent is indicated by films of chalcopyrite on (See PL X, A, p. 21.) The tunnel cuts· a 

the pyrite crystals. The second type of ore number of small pyrite veinlets but exposes no 

consists of galena and resinous sphalerite with important veins in its first 700 feet; beyond 

very small amounts of chalcopyrite, com- this it follows a well-defined vein for 125 feet 

monly in qoarse crystals without any impor- to the face. This vein strikes N. 85° E. and 

tant amount of gangue. In some specimens dips 30° N., about parallel to the foliation of 

quartz and barite are present as gangue, the inclosing Idaho Springs formation. A 

minerals. Vugs are lined with well-formed small amount of.stoping has been done on this 

crystals of galena, sphalerite, and transparent vein, disclosing 1! feet of fractured schist travquartz. The contacts of ore and wall rocks ersed by numerous one-eighth inch stringers of 

are very sharp, and the walls show almost no pyrite, all lying about parallel to the schist 

disseminated sulphides. - foliation. Specimen.s from the dun1p show 

The galena-sphalerite vein has.been reopened abundant chalcopyrite locally associated with 

and brecciated, and the breccia spaces as well pyrite. In other specimens chalcopyrite ocas the vugs have been partly or wholly filled cupies the center and pyrite the walls of the 

witl;l silica and some siderite. Most of these veinlets. The gangue where present is usually 

later veinlets have a central portion of cry~tal- quartz. The same vein has been developed 

line quartz and one-eighth inch borders of by a shaft 240 feet deep from which some 

cherty silica or siderite. The smaller veinlets drifting has been done. The collar bf the 

also are commonly cherty. Thin layers of shaft is about 200 feet vertically above the 

white quartz coat the galena, sphalerite, and tunnel level. The tunnel and shaft workings 

the original quartz crystals of some of the vugs. do not connect and the latter were filled with 

REFORM VEIN. 

The Reform vein is on the east side of Silver 

Creek 1! miles above its junction with North 

Clear Creek. The vein strikes N. 11° E. and 

dips steeply east, cutting granite gneiss. The 

shaft could not be entered, and no ore was 

to be seen on the dump, though a little pyrite 

disseminated through the gneiss was found. 

The shaft is said to be 160 feet deep with a 

total of 108 feet of drifting on both the 35 and 

130 foot levels. A small seam of smelting 

ore, largely pyrite, is reported to have run from 

$20 to $60, but most of the ore averaged from 

$3 to $8 per ton. · 

A partly dismantled mill just below the 

mine was equipped with ten 700-pound slowdrop stamps dropping 16 inches, a Gilpin 

water. ·The work on this property has thus far 

been largely exploratory. 

SNOWDEN VEIN. 

The Snowden vein cuts across the low divide 

between Stewart Gulch and Silver Creek. The 

shaft and tunnels are on the east side of Silver 

Creek about 2 miles north of its junction with 

North Clear Creek. The workings a:re in rather 

poor condition and the lower tunnel, the ,only 

one accessible, could be penetrated. for a distance of only about 60 feet. In this tunnel the 

vein strikes N. 55° E. and is vertical. The 

walls are granite gneiss, and on the surface the 

vein cuts this formation throughout. The 

shaft, which follows the vein, is said to be 140· 

feet deep. Near the surface it is said a 500-foo J 

drift runs east on the vein. 
I' 

·, 

GILPIN COUNTY. 207 

rl'he ore on the dump is entirely coarse pyrite 

with some Cf}artz. From the size of the blocks 

it would seem that the vein is in some places at 

least 10 inches wide. It is said that its average width is about 6 inches, but that in one 

place it opened out to form. about 4 feet of solid 

pyrite· ore. Postmineral movement has brecciated and ground some of the pyrite. 

The ore is s~id to average about $10 to $12 

per ton, some pockets running as high as $40. 

OLD KENTUCKY MINE. 

The Old Kentucky mine, near the divide between Stewart and Pickle gulches, had been idle 

for several years at the time of this survey and 

could not be entered. The claims were located 

in 1893 and 1894. The vein, which appears to 

strike about N. 60° E. and to dip northwest, is 

developed by a shaft about 600 feet deep. The 

extent of the drifting could not be learned, but 

the mine has not been a large producer. · 

STEW~RT VEIN. 

The Stewart vein, about three-quarters of a 

mile southwest of Wide Awake on the hill north 

of Stewart Gulch, strikes about N. 30° W. and 

appears to dip about ver'tical. The main shaft 

and a tunnel 200 feet below it lie south of the 

crest of the hill, but the vein can also be traced 

along the north side of the hill and has been 

opened there by three small. shafts. All the 

workings are inaccessible, the mine having been 

idle for several years. 

, The remnants of ore on the dump and in the 

bin indicate that the mineralization was in part, 

at least, similar to that at the neighboring Cale-

, doni a 'mine. Sn,mpling works assays show the 

presence of lead and zinc minerals, which were 

not seen on the dump. The yein in places is 

a typical fissure filling showing comb quartz 

next the walls. Small sharp-walled stringers 

of spe<'ular hematite carrying some quartz and 

pyrite cut .the granite gneiss, as at the Caledonia mine. 

CALEDONIA VEIN. 

The Caledonia vein is opened by several 

· abandoned shafts on the hill west of Missouri 

Gulch, about 7 miles northwest of ·Blfackhawk 

and one-half mile southwest of Wide Awake. 

The vein strikes, N. 45°-50° 'w. and ·dips 

65°-70° NE. 

The shaft houses are in ruins and the workings could not be entered, but the size of the 

dumps indicates that they are extensive. The 

ore in the bins shows that t~e vein is a sharpwalled· fissure_ filling in granite gneiss. The 

minerals seen were pyrite and chalcopyrite in 

a quartz gangue. Small grains of pyrite are 

disseminated in the wall rock near the vein. 

Some specularite was also observed in yeinlets 

or as· disseminations in the wall. 

It is reported that some rich free-milling ore 

from stopes near the surface in this vein was 

milled at a 20-stainp mill in ·Wide Awake. 

This mill, called the Douglas, is now leased to 

the Pine Cone Gold Mining Co., which is working some properties just south of the camp. 

PINE CONE TUNNEL. 

The Pine Cone tunnel is located on the west 

side of Missouri Gulch about one-half mile 

south of Wide Awake. It trends northwest 

and southeast for about 270 feet, cutting veins 

130 and 220 feet from the portal. Short drifts 

have been run on both veins. 

The vein cut 130 feet from the portal is at 

slight depth and is much oxidized. It strikes 

N. 20° E. and in general· dips about 80° SE. 

It shows sparse mineralization with pyrite and 

chalcopyrite·, the largest observed streaks 

being 2 inches wide and having a rather abundant gangue of white quartz and calcite. Drifts 

are being run on the tunnel level to connect 

with a shaft 100 feet deep, with a level and 

short drifts at 94 feet, that has been sunk on 

this vein. · 

The vein cut 220 feet from the portal strikes 

N. 55° E. and dips from vertical to 80° SE. 

It is a fracture zone 1! to 2 feet wide, near 

which there is some dissemination of pyrite. 

Small amounts of ore from this property 

have been milled at a small stamp mill at Wide 

Awake. 

JOHNSON PROSPECT. 

A prospect about three-fourths of a. mile 

south of Missouri Lake, on what is said to be a 

continuation of the Bass lode, was being 

developed by a tunnel at the time of this survey. 

A gangue-:fille3d :fissure had been exposed, but 

no sulphides of consequence had yet be~n 

found. Assays on surface ore from the claims 

of this group are said to have shown as high as 

250 ounces in silver. 
208 GEOLOGY OF GILPIN, CLEAR CREEK, AND BOULDER COUNTIES, COLO. 

NIGGER AND WINNEBAGO HILLS. 

CASTO VEIN. 

The Casto vein. cuts across Winnebago Hill 

half a mile north of Centra1 City and is supposed to connect with the Winnebago. The 

shaft is 420 feet deep along the dip of the vein 

with levels aggregating 1,000 feet at· 178, 214, 

283, 334, and 402 feet beiow the collar. The 

283-foot level connects eastward with the 

Belden tunnel (fig. 28), which has its mouth in 

Chase Gulch. A drift trom the ·Review shaft 

connects with the fourth level. 

The country rock throughout the· mine is 

granite gneiss. The Casto vein strikes about 

~. 70° E. and has an average dip of about 

80° S. It varies in width from 2 inches to 4 

feet, the average being about 2 feet. The main 

ore shoot of the mine seems to follow in a general way the junction of a northern vein, which 

is traceable into the Review workings and 

which has a branch vein coming in at a small 

angle from the south. The exact junction is 

not readily determined but seems to lie about 

60 feet west of the shaft on the second level, 

4.5 feet west on the fourth level, and in the 

shaft between the fourth and fifth levels: This 

ore shoot has been stoped for 100 feet west of 

the shaft more or less continuously to the fifth 

, level and has also been stoped east of the shaft 

between the third and fifth levels. At the 

junction on the fourth level a width of 10 feet 

of ore has be~n stoped. 

The vein consists of crushed granite gneiss 

somewhat silicified and containing rather coarse 

disseminated pyrite. A few specks of galena 

were seen in ·the ore . but are .very scarce: 

Throughout the ore shoot there are numerous 

small branching stringers of pyrite, few of 

which are over 1 inch in width and most of 

which lie near the footwall. 

Some postmineral movement has taken 

place along the Casto vein, but. most 'of the 

gouge is very thin. In the shaft between the 

fo:urth and fifth levels some strire on the hanging wall showed that the movement was in 

part horizontal. 

A 10-stamp mill at the shaft treats all of the 

ore mined. The coarse concentrates from the 

table carry a very small amount of galena, and 

. it is s~id that occasionally a· little ore that 

carries chalcopyrite is milled. 

SPUR DAISY GROUP. 

The Spur Daisy group of claims is on the 

north side of Nigger Hill near the head of 

Eureka Gulch. The country rock in this 

vicinity is granite gneiss cut by several veins, 

the most pronounced of which trends a few . 

degrees west of north and the others northeast. 

Several shafts and pits have been sunk on 

these veins, but none of the exposures are good 

and the shafts can not be entered: The veins 

are all of the galena-sphalerite type. 

The total production from this group of 20 

claims is said to be about $200,000. The ore is 

said to average from $25 to $30 a ton in gold 

and silver. 

BELDEN TUNNEL. 

The Belden tunnel starts on the ·south side 

of Chase Gulch a mile above Blackhawk and 

about 1,000 feet east of Castle Rock. It appears to have been begun in 1875. The first 

690 feet i~ crosscut, running south-southeast 

into Winnebago. Hill. Beyond this distance . 

the tunnel turns southwest and follows a vein 

which eventually joins the Casto vein, the 

Casto shaft being about 1,680 feet fro:rn the 

mouth of the Belden tunnel. (See fig. 28.) 

Granite gneiss i~S the only rock seen in the 

workings. 

The Ellery vei~, cut 115 feet fro~ the ·portal, 

has been developed by a drift on the tunnel 

level and by a shaft of unknown depth just 

east of the tunilel. The vein strikes about 

N. 62° E. and dips 63°-80° (average about 

7 5°) S. Thotl.gh ranging from a few inches to 

4 feet in width, it consists in most places of 

8 to 10 inches of crushed bleached granite 

gneiss carrying here and there a small amount 

of disseminated pyrite. In the west ·end of 

the drift the vein is practically barren. Two 

hundred and ninety feet in from the tunnel a 

small, feebly mineralized branch comes into 

the vein from the north, and just east of this 

junction a small stope has been excavated on 

a 4-foot portion of the vein. Here the granite 

gneiss is brecciated, bleached, and rather heavily impregnated with pyrite. Other stopes, 

both underhand and overhand, are -excavated 

for 110 feet west of the tunnel; they are fron1 

3 to 4 feet wide and are all timbered, so that 

the vein can not be seen. 

A vein 2 to 4 feet wide, cut 210. feet from 

the portal, consists of several subparallel 
GILPIN COUNTY. 209 

quartz stringers three-fourths of an inch or less I' At 370 feet from the mouth of the tunnel. 

in width carrying a little pyrite. The granite short drifts run east and west on a relatively 

gneisc;_; is bleached near the veinlets. . barren vein, along which the granite gneiss is 

N 

LEGEND 

Note: Wall rock is granite gneiss throughout 

Pyritic 

F--Ti 

vein Composite 

b·~·-·j vein Galena-sphalerite 

EJ 

vein Workings ~ inaccessible 

(Arrows indicate 

direction of dip) 

0 50 100 2.00 3QO 400 

FIGURE 28.-Geologic plan of _Belden tunnel. Surveyed by hand compass and pacing. 

Between 260 and 300 feet from the· mouth bleached and is locally traversed by. lensthe tunnel cuts three narrow seams of rather ·shaped veinlets of coarsely crystalline pyrite 

coarse pyrite, near which the granite gneiss has and white· quartz, none of ·which are more than 

been bleached for a width of 1 to 2 inches. 5 inches wide. 

44214°-17-14 
210 GEOLOGY OF GILPIN, CLEAR CREEK, AND BOULDER COUNTIES, COLO. 

Short drifts 590 feet from the mouth show a Eighty feet east of the Casto shaft the 

vein' 6 inches to 1 foot in width, consisting of vein which has been followed by the Belden 

crushed decomposed granite gneiss carrying a . tunnel joins the Casto vein. Near the shaft 

small amount of disseminated pyrite and locally the Casto vein; which here consisted of granite 

cut by stringers of coarse pyrita and quartz 1! gneiss carrying disseminated pyrite and cut 

inches or les>; in width. by stringers of coarse pyrite, has been stopecl 

At 690 feet from the mouth the tunnel turns for a width of 5 feet. Froze11 to the walls are 

southwest and follows a vein which in most small stringers of galena, sphalerite, pyrite, and 

places is from 6 to 10 inches in width and chalcopyrite. 

nearly barren, though commonly a small 

amount of fine pyrite is disseminated through MONT D'ORO TUNNEL. 

the granite gp.eiss along it. The Mont d'Oro is a drift· tunnel ri1nning 

Although the dominant mineralization in this nearly clue west on the Delight vein. Its 

mine belongs to the ea.rlier pyritic type, some mouth is on the west side of Chase Gulch, about 

later galena-sphalerite mineralization was noted. 2 miles northwest of Blackhawk. The tunnel 

At a point 140 feet west of the southwest turn is 590 feet long and has three short branch 

in the tunnel CA, fig. 28), a small stringer of drifts. The country rock is entirely granite 

galena, sphalerite, and chalcopyrite cuts across gneiss. 

the main vein at an acute angle, but its relations The Delight vein stands nearly vertical and 

are obscured by a raise lately started at this is for the most part a barren fracture zone 

place. Near by a small pyritio veinlet enlarges 2 inches to 21 feet in width. It is, however, 

to a lens of galena and sphalerite with a vuggy locally mineralized, at one place showing as 

center. Another occurrence is noted 'below. much as 6· inches of gray quartz bearing scatAt 250 feet west of the southwest turn 'of the tered crystals of pyrite and bordered by altered 

t~mnel crosscuts run 80 feet north and 140 feet gneiss carrying disseminated pyrite cut by 

south from the drift. Forty feet froin the drift small stringers of sphalerite and galena. At 

vein the south crosscut cuts a 2-foot vein which another place it consists of 21 feet of altered 

strikes about parallel to the drift vein but dips gneiss cut by several small subparallel stringers 

87° N. This vein has been stoped to some ex- of white and gray quartz. carrying pyrite and 

tent, both underhand and overhand, for about sphalerite. 

60 feet either way from the crosscut. The ore The New Century .vein joins the Delight 

is crushed granite gneiss carrying some dis- about 500 feet from the mouth of the tunnel. 

seminated pyrite and cut by a few small vein- It strikes on the average N. 45° E. and dips 

lets of pyrite. 55° NW. It consists of 1 to 2 feet of altered 

At 200 feet east of the Casto shaft a branch country rock containing disseminated pyrite 

vein leaves the drift vein on the south· or and trav.ersed by small stringers and bunches 

hanging-wall side. Neat the junction there is of galena and sphalerite~· 

a 5-foot zone of crushed bleached granite gneiss A short branch drift leaving the· main drift 

> which carries rather abundant disseminated about 400 feet from the portal exposes two 

pyrite and is cut by numerous l-inch to l-inch small sphalerite veinlets nearly parallel to the 

stringers of coarse pyrite. There has been Delight vein. A short crosscut 40 feet ·long 

some drifting and stoping on this· vein, but starting about 280 feet fron1 the portal crosses 

. the workings are all caved. At the junction three small parallel veins carrying quartz, 

of the two veins a barren fracture, which is pyrite, and sphalerite. They are probably 

cut by the drift vein without appar~nt dis- offshoots from the main vein . 

. placement, crosses the drift. Some mill runs of cord lots of ore show a 

· A crosscut starting 130 feet east of the Casto rather consistent saving of ·1 ounce gold a 

shaft runs northwest for 170 feet through cord on the plates. The concentrates vary 

granite gneiss. Seventy feet from the drift vein from 0.4. to 0.64 ounce gold and 2.4 to 19 

it cuts a fracture which is about 4 inches in aver- ounces silver a ton. · The ratio of concentration 

age width and carries coarse pyrite with some is abo~t 7 to 1. The vein has had as yet no 

small scattered lenses of galena and sphalerite: production. 

't· 
~I 

GILPIN COUNTY. 211 

FREEDOM VEIN. 

1'he Freed01n vein, discovered in 1865 or 

1866, outcrops on the southeast part of Winne-, 

· bago I:Iill. It trends about N. 40°. E. and is 

developed by severnl drift tunnels, one of which 

is 94:0 feet long, and by a shaft over 800 feet 

deep. The workings were not accessible at 

the time of this survey. The· ore seen on 

the dmnps belongs to the galena-sphalerite 

type. 

'I'he following are sampling-works assays of 

son1e of the stnelting ore shipped fron1 the Freedmn rnine between 1899 and 1904: 

Sampling-works assays of ore from Cyclops vein, 1890-91. 

Ore. Gold. Silver. 

Net pounds. Ounces. Ounces. 

2,400 ....................... 87.00 

3,060 ...................... 31.00 . 

1, 930 ............. 22.00 

3, 790 0.05 52.00 

2,332 ................ 79.00 

1, 584 ............... 31.00 

1, 793 .................. 27.00 

1,008 .............. 41.50 

3,263 ................ 40.27 

2,342 ............ 75.00 

1,575 .............. 87.00 

582 ................. 48.00 

2,413 .08 26.00 

Sam pliny-works assays of smelting ore from Freedom mine, 

1899-1904. · Little detailed information concerning the 

Ore. Gold. Silver. Silica. 

Net lbs. Ounce.~. Ounces. Per cent. 

4, 640 1.60 2.40 21 

7, 300. 3.24 5.00 22 

14,874 l. 30 2. 70 22 

5,1364 1.30 3. 70 30 

20,390 4.59 6.17 29 

22, 275 3.89 6.23 34 

20,414 1.40 3.80 42 

12.444 1.53 4.20 40 

6, 905 2.28 5. 70 34 

19, 135 1.36 4. 70 ·········· 22, 687 1.56 4.50 ·········· 

SILVER l;IILL. 

Fannie vein was available, but seven. lots of 

smelting· ore shipped between 18S8 and 1904 

gave the following sampling-w?rks assays:. 

Sampling-works.assays of ore from Fannie vein, 1888-1904. 

Year. Ore. Gold. Silver. Lead. 

Net lbs. Ounces. Ounces. Per cent. 

1888 ........ - 1,950 ·········· 115.00 6 

1889 ........ - 1,123 0.12 78.20 ........... 

1889 ........ - 4,669 . 25 140.00 ............ 

1903 .... ·- .. - 1,.497 .10 308.00 14 

1903 ...... --- 3,270 . 07 148.30 ........... 

1903 ...... --- 2,472 .10 75.00 8 

1904 ...... --- 2,462 .14 176.00 ........... 

The silver veins of Silver Hill appear to have That the ores of Silv.er Hill owed their workabeen discovered in 1877 or 1878 and are said bility to the process of downward enrichment is 

to have yielded about $150,000 annually for attested by the nature of the silver minerals, 

several succeeding years. All of the mmes of the high local silver conte;nt, and the falling off 

Silver I-Iill have been idle for many years and in the silver value of the ore in depth. The 

only 1neager -information concerning them is process of silver ·enrichment is more fully 

available. · considered on pages 140-149. 

The Cyclops vein was first worked in 1877 

or 1878 and has been little worked since 1886. MARYLAND MOUNTAIN. 

The ore is said to have been rich to a depth of HAYSEED VEIN. 

about 300 feet and notably lower grade below The Hayseed vein is developed by the Haythat. The rich ore carried wire silv_~r and seed adit-tunnel a mile north of Central City on 

nniChso-called "brittle silver" (possiblypearce- .the east side of Chase Gulch. It is close to the 

ite) and a very little ruby silver (proustite). · Tucker mill and is passed by a spur of the 

The native silver is said to have been con:firied Gilpiri tramway. 

1nainly to the uppe1; 100 feet of the vein. The The adit is 540 feet long and follows the vein 

gold content was negligible. . throughout. The vein has an average strike 

';l'he following smnpling-works assays give an of N. 70° E. and dips 55°-57° S. It is strongly 

idea of the value of some of the ore mined in defined throughout,.but in width and degree of 

1890 and 1891. The ore obtained in earlier mineralization is extremely variable. At one 

yen.rs was pre~umably somewhat richer. place the vein changes in a distance of only 10 
212 GEOLOGY OF. GILPIN, CLEAR CREEK, AND BOULDER COUNTIES, COLO. 

feet from a well-mineralized zone 2! feet wide 

to a tight and nearly barren fracture. At 

about 275 feet from the tunnel mouth the vein 

forks, the branches' joining again about 50 feet 

farther on. Near this point also a branch about 

4 inches wide diverges in to the north wall. 

Stopi~g has extended over about half of ·the 

vein as exposed in the tunnel, but only portions 

particularly rich in sulphides have been worked. 

Th~ best exposures are in stopes 300 and 400 

feet from the tunnel mouth. As exposed in the 

400-foot stope, the vein attains in places a width 

of 1 foot, about 5 inches next the hanging-wall 

being solid sulphides, galena, chalcopyrite, and 

some sphalerite. Although the proportions 

between the sulphides are variable, galena is in 

general the most abundant and sphalerite is 

next; chalcopyrite and pyrite are subordinate. 

Commonly more or less altered wall rock is 

present in the vein. In some places more or 

less silicified wall rock is penetrated by a network of sulphide stringers, but in most places 

the sulphides form a single band, or two or three 

nearly parallel bands, penetrating the altered 

wall rock which makes up the remainder of the 

vein. The greatest observed width in the sulphide bands or veins proper was in the stopes, 

where 5 inches of solid galena and chalcopyrite 

with some sphalerite occurs in places. 

The various sulphides are intercrystallized 

in such J1 way as to· indicate that they were 

deposited during a single period of mineralization. S01ne crusti.fication -is locally apparent 

and indicates that in a few places most of the 

sphalerite was deposited before most of the 

galena and chalcopyrite, and that in certain 

. places the chalcopyrite was later than both 

sphalerite and galena. 

Vugs are rather common, some being several 

inches across in the plane of the vein. Some 

contain very beautiful step crystals of galena, 

and the walls of others carry · crystals of 

transparent quartz associated with galena. 

Coatings composed· of siderite or of an association of siderite and small needle quartz 

crystals ·occur on the galena, chalcopyrite, 

and pyrite of _some of the vugs. In places 

siderite coats the quartz crystals. Dissolving 

action manifests itself in extensive etching of 

some of the galena crystals (see Pl. XVII, 

A, p. 136) but not of the chalcopyrite 

and pyrite. Although a few slightly etched 

surfaces of the galena have been coated by the 

siderite and quartz, most of the etched surfaces 

are free from such coatings, and this suggests 

that the same waters which deposited the carbonate also dissolved the galena.· These effects 

were presumably the work of ascending solutions from the same general source as, but of 

different composition from, the earlier ones 

that deposited the ore. 

Work on the property has been in the main 

exploratory, and stoping has not been extensive. The two claims of this group were located in 1897 and have been worked intermittently since then either by the owners or 

under lease: The ore is all handcobbed and 

sorted and is then sent to the smelter. It is 

said to· average 45 to 55 per cent lead., 12 

ounces in silver, and 0.75. ounce in gold. 

Picked ore is said to have given $40 smelting 

returns. The total production since the open..: 

ing of the mine was given as $7,000. 

ROB~RT EMMET MINE. 

The Robert Emmet shaft, on the north side 

of Chase Gulch, was being unwatered at the 

time of the survey, but the work had not 

progressed sufficiently to permit an examination. The workings consist of an abandoned 

shaft 270 feet deep and a main shaft 525 feet 

deep, which has levels at 100, 200, 335, and 

425 feet. The vein strikes about N. 45° E. 

and dips about 85° SE. The ore on the dump 

is of the galena-sphalerite type. 

The following sampling-works assays of a 

number of shipments of smelting ore will 

give some idea of its range in value: 

Sampling-works assays of ore j1'om the Robert Emmet mine, 

1889-1904. 

Year. Ore. Gold. Silver. Cop- Lead. Zinc. Silica. per. 

----------

Lbs. Oz .. Oz. P.ct. P. ct. P.ct. P. ct. 

1889 .... 2,436 1. 80 11.30 . ....... ........ ......... ........... 1889 .... 2,758 2.10 18.50 ......... ......... ........... ........... 1889 .... 2,040 7.20 38.00 4.50 ........... ............ .......... 1889 .... 2,118 2.26 3.00 .................. ............ ........... 1896 .... 13,820 1. 93 7.50 I ........... ....... ........... ........... 1898 .... 3,606 1. 42 5.60 .......... .......... 8 53 

1898 .... 5,822 5.25 33.60 .......... 20 12 .. ......... 

1898 .. -- 5,102 3.56 24.00 

:::::: ( ~~: J: /~: ........... 1902 .... 7,033 2.36 21.80 45 

1902 .... 5,792 1. 52 4.50 53 

1902 .... 2,187 1. 53 13.35 51 

1904 .... 1,351 3.17 4.00 ::::::::::::1:::::: 58 

The gross production of the mine is reported 

to be about $263,000. 
~· 

GILPIN COUNTY. 213 

NEVADA HILI .. AND PROSSER GULCH .. 

GILPIN EUREKA MINE. 

Tho Eureka vein is on the nortl;l side. of 

Prosser Gulch about half a mile west of Eureka 

Gulch. The shaft, an incline on the vein, is 

about 700 feet deep with levels at vertical 

depths of 130, 200, 350, 400, 500, and 600 feet. 

'rho fu-st level could not be entered. The 

coutitry rock throughout the mine is granite 

gneiss, except for one small lens of schist on 

the west third level. 

Four veins are exposed in this mine. The 

North vein bea1-s east and the Eureka vein 

north of east; they converge tow.ard the_ east 

and unite near the shaft. About 300 feet 

west of the· shaft a second ~~~r!y east-west 

vein, exposed on two levels, is known as the 

South vein. On the surface and on the 350-

foot level east of the shaft is the Spur vein, 

which bear-s northwest. · 

'.rhe Eureka vein as exposed in all of the 

levels has an average strike of N. 70° E. The 

dip rftnges from 45° to 70° N., being more nearly 

vertical east of the shaft, where .. it averages 

65°, than west of it. The vein ranges in width 

from 1 to 6 feet with an average of about 2! 

feet. East of the shaft the vein is strongly 

n1arkod' but is not particularly well mineralized, though on the third level it carries small 

lenses of ore, some of which have been stoped. 

Tho principal ore body is west of the shaft 

1 and extends along the vein to its junction 

\ with the South vein. 

The South vein on the third level joins the 

Eureka vein 200 feet west of the shaft, follows 

that vein westward for about 50 feet and then 

rosun1os its independent cou1-se. Normally it 

strikes N. 85° E. and dips 65°-70° N. It 

intersects the E~·el\:a about· 280 feet west of 

tho shaft on the fourth level and about 300 

feet west on the fifth level. The ~~ is from 

12 to 18 inches in width but ncar the junction 

widens to 2 feet. Where it joins the Eureka 

a large body of oro occurs. 

The Spur vein is intersected only on the third 

level about 450 feet east of the shaft. It 

strikes N. 68° W. and dips 80° SW. Ordinarily it is rather narrow, b~t near the junction 

with the Eureka it carries a small ore bbdy 

whose n1aximun1 width is about 2 feet. 

Tho North vein strikes about N. 85° E., 

joining the Eureka at or near the shaft, and 

dips very steeply north. It is ·about 10 inches 

wide and is not heavily mineralized except for 

a lens of ore 80 feet long between the second ___ _ 

and fifth levels and west of the shaft. At the-~ 

sixth level the North and Eureka veins are . 

about 12 feet apart near the shaft. The drift 

has been carried 12 feet wide for a short dis- · 

tance and shows the granite gneiss bet'Yeen the 

two fractures to be more or less mineralized '. 

throughout. There is, however, no particularly good ore on this level. 

The mineralization in this mine was particularly strong west of the shaft to a point on 

the Eureka vein a little beyond the junction 

with the South vein. In this ore body the 

lead-zinc sulphides occur in places in solid 

streaks 8 to 10 inches wide and i1~ sparse dissemination through -the intervening parts of 

the vein. 

Two distinct periods of mineralization are 

shown in the mine. All four of the veins exposed show ore of the pyritic type cut by 

stringers and lenses of ore. consisting of darkgray quartz, dark sphalerite, galena, and chalcopyrite. Pyrite is by· far the most abundant 

metallic mineral, but is said to carry only small 

amounts of gold and silver. Of the minerals of 

the later mineralization sphalerite is by far the 

most abundant, galena and chalcopyrite com- \ 

monly forming less than 5 per cent. The principal gangue is quartz and silicified granite 

gneiSS. 

Postmineral movement is shown by heavy 

gouge along the walls throughout the mine and 

by .clay partings in the ore itsel~. On the 

fourth level and at the west face of the third 

level slickensides on the wall pitch 7 5° E. 

The Spur vein north of the Eurekq, has been 

offset about 2 feet to the west by this movement. On the third level a breccia of fragments of both pyritic and galena-sphalerite ore 

is partly cemented by bluish-gray cherty silica. 

In late years the entire vein has been mined 

and milled irrespective of the mineral_s contained. The highest-grade ore was obtained 

above the second level, but some gold ore has 

been taken from the junction of the South and 

Eureka veins on the lower levels. The company has a 10-stamp mill eq~pped for amalgamation and concentration. This mill produces 

a lead-zinc concentrate said to have a value of 

about $90 a ton and an iron-zinc product whicli 

carries about $10 i11.gold and silver. 
214 GEOLOGY OF GILPIN, CLEAR CREEK, AND BOULDER COUNTIES, COLO. 

From 1897 to 1908 ~4 lots of smelting ore 

aggregating 30 tons averaged· 1. 91 ounces 

gold and 12.37 ounces silver per ton. Most 

of this ore carried about 16 per cent lead and 

from 8 to 12 per cent zinc. · One shipment of 

smelting ore mined in 1910 carried 1.58 ounces 

gold, 10.6 ounces silver and 49.2 per cent lead. 

" In 1910 the average metal content of the 

concentrating ore was 0.4 . ounce gold, 0.4 7 

ounce silver, and 0.47 per cent lead. 

The total production is estimated at about 

$467,000, of which $400,000 is reported to 

have come from a zone 400 feet long and 

within 90 feet of the surface. 

GOLD COLLAR MINE. 

this level there are a few small · lenses of 

workable ore. In the 257-foot level the ·shoot 

extends the entire length of the drifts now 

open, but. the ore has been entirely removed. 

At the back of the stope at the west end of the 

drift the ore is playing out. 

The vein £lling is somewhat altered granite 

gneiss, usually barren of 'mineral but cut in· a 

few places· by stringers containing dar;k sphalerite, chalcopyrite, pyrite, and a little galena, 

with quartz and some siderite. The sphalerite is by far th~ most abundant sulphide. 

These stringers vary from a fraction of an 

inch to at least 6 inches in width. 

Microscopic examination of the wall rock in 

con~act with one of the galena-sphalerite veinlets shows that it has been altered to an irregular aggregate of quartz, carbonate, and chlorite. 

The quartz forms good-sized grains, and the 

carbonate and chlorite occur as aggregates of 

minute plates. Through this rock pyrite is 

scattered in small grains, and grains of galena 

and sphalerite occur sparsely. The abundance 

of chlorite gives the rock a green ·color. 

The smelting ore is said to be only about 2 to' 

4 per cent of the material mined. This grade 

of ore, as shipped for 12 to 14 years, h.as 

averaged about $70 per ton in gold and silver 

and is said to contain about 2! ounces of silver · 

for each ounce of gold. The total production 

of the mine is said to be about $250,000, all of 

which has come from the Hydrant vein. 

CONCRETE MINE. 

The Gold Collar mine on the Hydrant vein 

is on the north side of· Prosser Gulch just 

above its junction with Eureka Gulch. The 

shaft is said to be 712 feet deep but has been 

idle for some years and could be descended 

only to the 332-foot level. Lessees had just 

begun, in September, 1911, to reopen the 

332, 257, and 200 foot levels. On the 200-foot 

level the face of the e~t drift .is 670 feet from 

the shaft and the west drift is caved 50 feet 

from the shaft. On -the 257-foot · level the 

east drift is caved 50 feet from the shaft but 

the west drift can be traversed to its face, a 

distance of 200 feet. · The 332-foot level has 

been run east 80 feet and west 300 feet from the 

shaft and was open throughout. The wall 

rock of all of these levels is granite gneiss 

except for a lens of schist at the end of the 

·332-foot lever east. The Concrete vein, a westward continuation 

The vein strikes N. 76° E. and dips steeply of the Gunnell, is on the south side of Prosser 

south, the lowest dip noted being 65° S., near Gulch. The shaft house is about half a mile 

the shaft at the third level. Commonly the w.est of Eureka Gulch, a short distance south 

dip is 75° to 85° S. with an average of about of the Gilpin-Eureka shaft. The shaft is an 

80°. In the granite gneiss the vein ranges incline following the vein and is equipped with 

in width from a fewinches to 2 feet, but where bucket hoist. It is about 1,285 feet deep, but 

it passes from granite gneiss into schist on the the lower 150 feet were under water at the 

third level it dies out in a series of small branch- time of this survey. As the shaft is near the 

ing fractures parallel to the schistose struc-1 east line of the Concrete ground the dev~lop­ tl).re. The principal ore body as far as could ment work lies almost entirely to the west. 

be ascertained lay on both sides of the shaft The Golden Treasure shaft following the 

and extended from the surface to some point Golden Treasure-Slaughter House vein enters 

between the 257 and 332 foot levels, the latter the Concrete workings 540 feet west of the. 

showing only a small amount or ore. In the Concrete shaft at a depth on the incline of 674 

200-foot level the shoot extends for an un- feet. Below this the Golden Treasure shaft 

known distance west of the shaft and 250 follows the Conerete vein, the total depth of 

feet east of it. East of the main shoot on the shaft being over 1,300 feet. 
GILPIN COUNTY. 215 

Levels have been driven from the Concrete and 681 foot levels and for 200 feet below the 

shaft at depths of 530, 608, 681, 761, 900; 937, 761-foot level. This shoot probably crosses 

1,000, 1,033, 1,127, and 1,208 feet. A level the Concl'ete shaft at or near the 761-foot 

between 681 and 761 feet connects with the level and joins the large shoot last described. 

Slaughter llouse workings, and the 1,127-foot The Concrete vein consists of somewhat 

level con1,1ects with the .Gunnell wqrkings. crushed silicified granite gneiss which in the 

The 761-foot level from the Concrete shaft ore shoots has been impregnated with small 

connects by a winze near its west end with a scattered crystals of sulphides and is cut by a 

drift fr01n the Golden Treasure shaft. network of · veinlet~ of solid sulphides from 

The . cou1~try rock throughout the entire knife-blade thinness to several inches in 

mine is· granite gneiss. width. They are in general more numerous 

The vein strikes fron1 N., 74°-85° E., with in the lower half of the vein, though in some 

an a-verage of about N. 78° E. Fron1 the places they occur next to the hanging wall. 

collar to the ·530-foot level the shaft dips The sulphides in general order of abundance 

about 50° S., though in detail the vein flat- are dark sphalerite, galena, pyrite, and cbaltens and steepens in short distances. On the copyrite, but some veinlets consist almost ex530-foot level the vein dips 65° S., on the elusively of galena and sphalerite and others 

750-foot level 64° s. at the shaft, and about. are co~posed mairuy of sphalerite and chal820 S. farther west; and on the 1,033-foot level copyrite. Pyrite is the most abundant suiabout 57° N., below which it is nearly vertical. phide in ~he wall rock adjacent to the veinlets. 

Above the 1,033-foot level the vein is in few Quartz is the common gangue mineral. 

places over 8 feet wide. Its general width is Postmineral movement along this vein is 

1 to 3 feet, but in some places it i~ represented shown by tight fractures cutting the ore and 

by a single narrow slip plane. Below the in a few places by slickensided surfaces on the 

1,033-foot level the vein widens rapidly to a walls .. The strire · are either parallel to the 

maximum of 25 feet at the 1,127'-foot level. dip or pitch · at 80° E.· . On the 761-foot 

'1\vo main ore bodies have been developed, level near the west end of the drift an open 

both of them west of the shaft. The upper watercourse follows the ·vein for about 150 

has been stoped from about 450 feet down to feet. Along this zone somewhat rounded pebthe 761-foot level. On the 761-foot level it bles of ore and wall rock are partly cemented , 

begins about 230 feet west of the shaft and by bluish-gray cherty silica. 

extends to the Golden Treasure shaft, a dis- In mining the ore bodies it seems to have 

tance of 300 feet. As exposed on the higher been the practice to avoid, as much as possible, 

levCls the shoot is not so long nor so continu- breaking the ground in which solid sulphide 

ous. Above the 530-foot level the ground has veinlets were small or few in number. The 

not been prospected, though a 100-foot whi~ concentrating ore after a concentration of 

shaft sunk 400 feet west of the Concrete shaft about 18 into 1 yields a product .having an 

is said to be in good ore. The Slaughter average con ten~ of 0.64 ounce gold, 5.80 ounces 

IIo~se-Golden Treasure vein is said to join silver, 12.30 per cent lead, 11.20 per cent zinc, 

the Concrete vein between the 608 and 761 and 12.10 per cent silica a ton. About 12 per 

foot levels. As it is common for a vein to cent of the ore mined is shipped direct to the 

become heavily mineralized near its junction !:nnelter. The average assay content for about 

with another vein this union may, in part at 307 tons of JSmelting ore was 1.03 ounces gold, 

least, explain the formation of the ore shoot. 8 ounces silver, 23.80 per cent lead, and 10.60 · 

The second large ore shoot extends from the per cent zinc. Most of the smelting ore carries 

937 to the 1,127 foot level west of the shaft, so little copper that it is not shown on the assay 

and is developed by workings from the Golden sheets. In some stopes it was found practicaTreasure shaft. · The most productive por- ble to separate the smelting ore into two 

tions of this .shoot appear to lie at or near the classes, one a typical lead-zinc ore, and the 

junction of the Concrete with the Elizabeth other a zinc-copper-~ead ore. Some assays of 

vein. Another ore shoot east of the Concrete the zinc-copper-lead ore show about as many 

shaft on Gunnel' ground is stoped at the 608 ounces of gold as units of copper and a gold 
216 GEOLOGY OF GILPIN,. c·LEAR CREEK, AND BOULDER COUNTIES, COLO. 

valu~ about three times as great as in the lead- ,tion. ·From it levels have been dl'iven at 

zinc ore, though the silver content is about the about 100-foot. intervals. A winze from the 

same in both classes. According to sampling- 1,100-foot level connects with a raise from the 

works assays 32 lots of smelting ore shipped Argo tunnel workings. (See fig. 29.) The 

at different times from 1893 to 1909 inclusive workings develop the Gunnell North, Gunnell 

showed: Gold, 0.40 to 4.13 ounces; silver, 3.08 Middle, Gunnell South, Hattie,, Wheeler, Elizato 15.80 ounces; copper, less than 1.5 to 3. 70 beth, and Slaughter House veins. The ore 

per cent; and lead, less than 5 to 64 per c(mt. above the 900-foot level is said to be nearly exThe Concrete claim was located in 1879 and hausted, and most of the workings above the 

its gross production has been ·about $800,000. 700-foot level are inaccessible. 

GUNNELL-GRAND ARMY MINE. 

It was manifestly impossible in the present 

condition of the mine and the brief :time availThe Gunnell-Grand Army mine is on the able for the work to determine the exact 

south side of Prosser Gulch just west of relationships of all the veins. The following 

Central City. The vein was 1 discovered in the account is confined therefore to a description 

early sixties, but extensive development was· of the general character of the mineralization 

Idaho Springs formation 

Grsnd Army shaft 

0 so 100 

LEGEND 

G B EZJ Pyritic veins Galena-sphalerite ComRosite vein ve1ns 

(Arrows indicate direction of dip) 

N 

I 

200 

rn 

Workings 

inaccess•ble 

Pump shaft. 

300 400 Feet 

FIGURE 29.-Sketch showing Argo tunnel level and 1,100-foot level of Gunnell-Grand Army mine. 

not begun until1874. At the close of 1875 the and to a few of the more salient structural 

Gunnell shaft was 700feet deep. The property features. . 

was operated intermittently from 1874 until , The Gynnell group of veins presents one of 

1904 when the pump shaft burned and the. the best examples of composite mineralization 

. mine flooded. Not until 1910, when the mine in this district. The Gunnell-Orand Army 

was iliained by tho. Argo tunnel, was work system of veins is predominantly pyritic, but 

resumed. · . some of the smaller veins are of the galenaThe mine has been one of the most produc- sphalerite type, and the larger veins have 

tive in the district and tho total development locally been reopened and further mineralized 

work approximates 25,000 feet. The eastern with this type of ore. As the lode is followed 

shaft on the main lode is known as the Pump westward into the Concrete workings the minshaft, and the western as the . Grand Army eralization becomes almost exclusively of the 

shaft. The Slaughter House shaft, farther galena-sphalerite type. On the Argo tunnel 

south, follows a vein which joins the Gunnell level only pyritic ore was observed. The Gunworkings at depth. The Grand Army shaft, nell-Grand Army-Concrete lode therefore forms 

1,200 feet deep, is the only one now in opera- an example of a fracture system whos~ min-
GILPIN COUNTY. 217 

erulization in son1e parts is exclusively pyritic, age interval between the seams and veinlets is 

in other parts galena-sphaleritic, and elsewhere 4 to 5 inches. · 

con1posite. Exposures showing clearly the rela- Two sublevels have been driven on the Guntionships between the two types of mineraliza- nell South vein between the Argo ht;teral and 

tion are not nun1erous. On the 700-foot level, the 1,100-foot level. These are not shown on 

720 feet east of the Grand Army shaft, an figure 29, but start from tP,e raise which conexposure in a stope shows a 10-inch vein of nects .the Argo lateral and the shaft workings. 

nearly solid :fine-grained p}rrite. Between The sublevel 80 feet above the Argo lateral is 

this and the wall occurs a lens of sphalerite 300 feet long. The vein averages.about 3 feet 

and some galena sharply demarked from the in width and shows several veinlets, none more 

pyrite. In other parts of the mine galena than 3. inches wide, of pyrite and chalcopyrite 

and sphalerite are common in vugs in the bordered by wall rock carrying disseminations 

pyritic ore. At one point on the Gunnell of these minerals. 

Middle vein on the 1 ,000-foot level the vein is Another short sublevel about 70 feet below 

6 feet wide and consists of a number of pyritic the 1,100-foot level shows galena, sphalerite, 

veins 6 inches or less in width, bordered by chalcopyrite, and pyrite as the predominant 

granite gneiss carrying disseminated pyrite. sulphides in sharp contrast to the pyritic charCutting across the trend of the pyrite veins are acter of the vein f~uther down. . 

s'everal sn1all stringers of galena, sphalerite, As exposed on' the 1,1 00-foot level the Gunchalcopyrite, and quart,z. nell South vein is also in the ma_in. pyritic, 

'l"he detailed descriptions, tnough confined though showing ore of the galena-sphalerite 

mainly to the 1,100-foot and Argo tunnellevels,< type in a few places. 

serve to illustrate the general character of the The Gunnell Mi.ddle vein is cut· by the Argo 

1nineralization in the portions of the mine now tunnel about 90 feet north of the Gunnell South 

being worked. vein. As exposed in the lateral on the Argo 

rJ,1e Gunnell South vein, as exposed in the tunnel level it is in places a barren fracture zone 

Argo laterals, though locally barren, is goner- and elsewhere is not heavily mineralized. The 

ally well mineralized; the mineralization is, most highly mineralized portion shows 5 pyritic 

however, somewhat weaker than on the higher veinlets, the widest 1~ inches acrosa, distr:ibuted 

levels. The width varies from 6 inches to 2~ through a width of 15 inches of granite gneiss. 

feet. 'About 150 feet east of the tunnel the vein Another exposure shows 7 inches of gray quartz 

consists of a 6-inch streak of pyrite and gray and pyrite. At the· extreme west end of the 

quartz next the north or hanging wall, below drift (see fig. 29) a tight vein of fine-grained 

which for 2 feet small stringers of pyrite trav- pyrite ·and chalcopyrite possibly indicates the 

erse the schist. About 700 feet east of the tun- proximity of a junction with the Elizabeth vein. 

1~ol the vein shows, next the north wall, 8 inches As exposed on the 1,100-foot level the middle 

of rather coarse pyrite, bordered by 2 to 4. vein is predominantly pyritic,.but carries locally 

inches of gouge. T4e pyrite shows local crush- a little galena. It varies from 6 inches to 2· feet· 

ing due to postmineral motion along the vein. in width. At A, figure 29, it includes. two veinExposru·es on the walls of the Argo tunnel lets of nearly solid pyrite 3 and 5 inches wide, 

show that the rocks for 60 feet south of the Gun- which a little farther along unite in a single 

nell South vein are more or less mineralized. 8-inch vein, bordered by wall rock carrying dis-

'111o walls are granite gneiss with subordinate seminated pyrite, making the total width of the 

an1ounts of Idaho Springs schist and pegmatite. vein about 2 feet. At the east end of the drift 

These are traversed by a large number of frac- on the 1,100-foot level this vein splits into three 

ture seams and pyritic veinlets which trend ,branches, none of which are of sufficient size to 

nearly east and west, and dip about 80° N., be WQrked. 

crossing the foliation of the granite gneiss a.t The Elizabeth vein joins the Gunnell North. 

large angles. One of the veinlets shows 1 to vein in the Argo tunnel. As exposed on the 

1! inches of coarse pyrite, but most of them are Argo tunnel level, it is not heavily mineralized, 

smaller. The granite gneiss bordering the vein- showing merely a few stringers of pyrite and 

lets and seams has been leached, its biotite los- quartz which parallel the foliati9n of the schist. 

ing its color, and has been silicified. The aver- It has not been developed on this level. In gen-
218 GEOLOGY OF GILPIN, CLEAR CREEl{, AND BOULDER COUNTIES, COLO. 

eral~ the Eliz~beth vein has not yielded muoh ore The Elizabeth vein on the Argo tunnel level 

inanyportionof the mine, butnearitsintersec- gave $1.14 to $5.85 per ton for widths of 7 to 

tion with more productive veins it has probably 24 inches. The Gunnell North vein on the 

caused an erilargement of the ore bodies. ' Argo tunnel level averaged $6:,57 for widths of 

The Gunnell North vein as exposed in the 11 to 20 inches. The Gunnell South vein on 

Argo lateral is nearly barren, showing only the Argo tunnel level showed some barren 

from 2 to 6 inches of bleached schist carrying stretches, but in one block of ground 235 feet. 

disseminated pyrite. long it averaged $12.20 per ton for an average 

At B, figure 29, a crosscut on the 1,100-foot width of 22 inches; in another block 115 feet 

level intersects· a quartz-pyrite vein 4 to 5 long $8.50 for an average width of 10 inches; 

inches wide. A short distance farther north, at and in a third block 120 feet long $15.20 for 

c, figure 29, is another vein 2 to 6 inches' wide, an average width of 25! mches. 

consisting of pyrite, galena, and sphalerite in a In the raiae on the Gunnell South vein to the 

white quartz gangue. A vein that may be a 1,100-foot level much better values were found. 

continuation of that last described is exposed j The sublevel75 feet above the Argo lateral averin another crosscut at D, figure 29 .. It has a i aged $18.20 for an average width of 22 inches, 

maximum width of 4 inches and shows galena, and in some blocks of ground averaged $34 to · 

sphalerite, and pyrite in irregular stringers and $36 for widtha of 26 to 35 inches. 

disseminated through the bordering gneiss. Computations made for the· company from· 

The value .of the smelting ore from different the records of shipments show that fron1 1874 

parts of the mine is indicated by the following to 1889 the average value of the smelting ore 

- selected sampling-works ·assays. The la~ge was $56.59 and of the ~oncentrating ore $14.02. 

number of vmns ,developed and the c0mposite As the price of silver for these years ranged 

character of the mineralization render the value from $0.93 to $1.28 the value of the returns of 

of the ore extremely. variable. course can not be duplicated at the present time. 

·Sampling-works assays of ore from the Gunnell-Grand Army The total gross production of the mine from 

·mine. 1874 to the close of 1911 was about $2,760,000. 

Location. Ore. Gold. Silver. Copper 

(wet). 

Gunnell: Gross Per 

400-foot level, west tons. Ounces. Ounces. cent. 

spD~. ·. ·. ~ : : : : : : : : 8.080 2.40 4.35 ........... 4.015 2.24 8.80 ......... Do ............ 1. 375 . 69 2.17 .......... 600-foot ]evel, \lest 

spD~. ~- : : : : : : : : : : 5.570 1. 09 ·3.80 ......... 2.620 . 93 2.00 ........... 

Grand Army: 

700-foot Jevel, west 

spur ............. 1. 705 . 55 4.80 .. ....... 1,000-foot level, 

North vein ...... 8.170 1. 26 13. 73 1.40 

Do ............ 3.300 2.05 19.17 3.60 

Do ............ 3.235 l. 68 8.92 .90 

Do ....... ·--~- 4.530 1.08 9.44 . 70 

1,100-foot level, 

north ............ 5.485 .74 2. 77 .. ........ 1,100-foot level, 

north spur ....... 1.960 1. 37 4.15 ............ 

1,100-foot level, 

North vein ...... 2.585 1. 95 5.50 .......... Raise from Argo lateral, Gunnell South 

vein ............... 24.130 . 91 2.12 ............. Do ............ 28.690 1. 23 3.04 Trace: 

The copper values in son1e lots of ore arc 

negligible but in some smelting ore .reach 5 

per cent. 

Tho sampling of the v:eins in the lower 

ovels of the 1nine show interesting results. 

Three mills are owned by the companythe Fullerton 40-stamp mill on North Clear 

Cr~ek above Blackhawk,. the Mead mill in 

Blackhawk, now in ·poor shape, and· the · 

Polar Star mill in Blackhawk, now operating. 

The last· named was originally equipped with 

40 stamps but 15 have been removed. 

Three determinations of the fineness of the 

bullion obtained by amalgamation ·show gold 

0.805, silver 0.154; gold 0.823, silver 0.163; 

and gold 0.825, silver 0.162: 

WHITING VEIN. 

The Whiting vein is on the hill due west of 

Central 'City about 500 feet southwest of the 

Gunnell shaft. It is developed by a shaft 

that has levels at depths of 200, 300, 400, and 

500 feet and follows a vein trending nearly 

el¥3t and west and dipping about 75° S. rhe 

mine wa;:; idle at the time of this survey . 

Ore ·seen o~ the dump showed· only pyrite and 

chalcopyrite. 

HUBERT MINE. 

The Hubert mine is on the south slope of 

Nevada Hill just north of N evadaville. The 

workings develop tw? principal veins (the 

I -
GILPIN COUNTY. 219 

North and South) and several branch veins. Fifteen feet west of the shaft on the 850-foot 

On the North vein a shaft now used only for level the vein consists of 2 feet of ~ltered 

ventilat.ion descends. to the 370-foot level. granite gneiss carrying dissemin~ted pyrite 

The n1ain shaft, through which all ore is 

'hoisted, is about 280 feet. west of the North 

vein shaft; it follows the South vein to the 

600-foot level, where it branches;· one branch 

. continuing on ~he South vein to the 1,250-foot 

level and the other crossiJJg to the North vein 

and following it to the 975-foot level. (See 

-fig. 30.) 

All workings above the 500-foot level and 

below the 950-foot level were inaccessible at 

the ti1ne of this survey, and n1ost of the ground 

east of the shaft between these levels is stoped 

out and could not be entered. Above the 450-

foot level the stoping has been practically 

confined to the North vein; and between the 

450 and 900 foot levels most of it has been done 

on the South vein. Some of the stopes are large 

and contiJ1uous, but the ore shoots seem to 

'possess little regularity. 

As a plan showing all of the levels would be 

extremely complicated figure 31 shows only 

the vein systems exposed on the 800, 850, and 

950 foot levels. Time was not available. for·ascertaining all of the structural relationships of 

the complex vein syste1n, and only a few of the 

salient features are here described. 

The North yein was worked mainly in the 

upper portions of the mine not now accessible; 

where exposed on the 60!)-foot level it is in most 

places a nearly barren fracture zone a few inches 

to 3 feet in width. The Middle vein was exposed only on the 800-foot level (fig. 31), where 

it is only feebly mineralized, showing at. the 

east face of the drift a single one-half inch veinlet of white quartz, sphalerite, and ch9.lcopyrite. Exposures of the South vein and its 

branches are numerous and excellent. One of 

the best ore bodies is on the 950-foot level 

(see A, :fig. 31), where it dips 65° S. and shows 

the following succession from hanging wall to 

footwall: 

Sect·ion of South vein on 950-joot level of Hubert mine. 

iianging .wall. Inches. 

5 

.c: 

... 

:J, 

'J>\ t· C.==~C;:;/)~T 35:;;4~rg:T~SO~U;;;=TH~~ ==:·.~:~· /OSQ-rOOT LEVEL 

1/SO·F'OOT LEVEL 7 /25()-F'OOT LEVEL_Ji====:f 

OLD NORTH 

SHAFT N 

so._, _.___..___._!jo _ _.'9_o -...J1~o feet 

White quartz ...... :.............................. 1 

SphaJerite w:i th some chalcopyrite.-.. .. .. . . . . . . . . . . . . 3 FIGURE 30.-Cross section showing relations of Hubert North and south 

veins and the shafts which develop them. From map prepared by 

White quartz carrying some sitlphides. . . .. . . . . . . . . . 2 Percy n. Alsdorf. · 

Sphalerite and chalcopyrite......................... 3 

Granite gneiss carrying disseminated pyrite and trav- and traversed by a network of galena-sphalerite 

erscd by .t; to~ inch stringers of sphalerite........ 18 stringers, most of which are less than oneFootwall. . eighth inch in ·width. . 
GEOLOGY OF GILPIN, CLEAR CREEK, AND BOULDER COUNTIES, COLO. 

One of the most instructive parts of the I a network of sulphide stringers traversing the 

mine is the large stope near the west end of gneiss in all directions; this passes locally int() 

a true filled breccia. (See fig. 6, p. 97.) 

The fragments have plainly been n1oved• 

z~------· 

w 

~ rn~ ~ 0 

(.!) c 

w :~ _.1 > .,., 

N 

0 

,., 

·from their original position. The largest 

are not more than 3 inches in dian1eter 

and most of them show sharp angular outlines. Many of the sulphide aggregates. 

between the fragments show roughly triangular cross sections and a central vug 

lined with quartz, galena, and sphalerite 

crystals. The large stope at the west end 

of the 850-foot level is about 35 feet in. · 

width. The ore breccia extep.ds upward 

to the 700-foot level but apparently does. 

not extend downward to the 950-foot level, 

the vein at A, figure 31, in that level 

brancl;t.ing in a normal manner without. 

notable brecciation. The ore breccia of 

the I-Iubert mine is identical in appearance 

.§ with certain portions of the Patch (see 

~ pp. 96-97), and was probably formed by 

~ similar processes acting on a much smaller-

::= scale. Stress initiated along the South. 0 

~ vein fracture and, along several branches 

j leaving it at nearly the same point appar-

~ ently became more or less distributed 0 

~ through the intervening rock, fracturing 

s it irregularly and in places moving the frag- ~=~< 

'E ments among themselves. This· fractured 

~ and porous mass became a favorable locus. 

J for ore deposition. e<:> 

r.1 The underground workings, and the ore i on the dump and in the bins show that the 

great bulk of the sulphides were deposited 

in open spaces, either in cracks or between 

the· fragments of a breccia. In places, 

however, the sulphides are replacements 

formed by solutions penetrating· along 

hardly perceptible fractures in the granite 

gneiss. Some irregular areas heavily ilnpregnated with sulphides are not associated 

with visible fractures. 

The ore of this mine is entirely of the 

galena-sphalerite type, being composed of 

galena, sphalerite, pyrite, chalcopyrite, and 

some quartz and siderite. 

Sampling-works assays of 41lots ofsmelt-· 

ing· ore. aggregating 131 tons, shipped be- · 

tween 1888 and 1909, show gold, 0.74 to 5.S. 

(average 2.39) ounces per ton; silver, 2 t() 

17.6 (average 13.16) ounces per ton; copper, 

the 850-foot level. Near locality B, figure 31, \less. than 6.5 and generally.less than 1.5 perthe vein begins to split up and eventually forms cent; lea~, less than 5 to 37 per cent.; zinc, less 
GILPIN COUNTY. 221 

than 32 per cent. Similar assays of smelting 

Qre, aggregating 72 tons, shipped in 1910, show 

gold, 1.04 to 1.7 (average 1.38) ounces per ton; 

silver 8 to 15.9(average 14)ounces per ton; lead, 

less than 5 to 30 per cent. The average content 

-of concentrating ore shipped in 1910 in bullion 

and concentrates was gold, 0.21 ounce; silver, 

1.8 ounces; lead, 1.3 per cent. 

Barnpling-works assays of concentrates frorn H'ubert rnine. 

Gold. Silver. Lead. Zinc. 

Ounce,<J' Ounces! 

per ton. per ton. Per cent. Per cent. 

] Jead concentrate .... 0.58 9.60 16.80 

'Zinc concentrate ..... { . 39 6.50 ........ 19.40 . 55 3.57 29.80 

The n1ine contains considerable reserves of 

·concentrating ore of the filled-breccia or Patch 

type. The total gross production of the mine 

"is said to have been about $1,000,000. · 

PRIZE VEIN. 

The Prize vein is . on the south slope of 

Nevada I-Iill about 600 feet north of the main 

'street of Nevadaville. It is opened by a longabandoned shaft said to be 870 feet deep. 

'The vein strikes about east and west, with 

local vu,riations. A l11ter~ from the Newhouse 

tunnel has been run on what is supposed to be 

the Prize vein for a few hundred feet, exposing 

1 to 4 feet of crushed altered granite gneiss 

and schist carrying disseminated pyrite and 

cut by stringers of coarse pyrite 3! inches and 

.less across. 

The ore carries from 0.5 to 2 ounces gold 

.and from 3 . to 16 ounces silver a ton. Some 

·assays show as high as 4.5 per cent copper 

thoi.1gh n1ost of the ore appe11rs -to hav·e no 

·-copper of value. 

The original owners are reported to have 

taken out between $400,000 and $500,000 

-worth of ore. 

C<E"JR D'ALENE MINE. 

The Creur d'Alene mine is in the west part 

·of Central City close to the Catholic school. 

'The mine is developed by a shaft with l~vels 

at intervals of 50 or 100 feet. The accessible 

:.levels are at vertical depths of about 200, 400, 

-450, 550, 600, and 700 feet. Most of them are 

:~short, the longest being accessible for only 

.about 250 feet. 

The workings . develop a zone of fracturing 

-that has been locally mineralized, but only a 

few parts of which can be termed a true vein. 

The strike ranges from about N. 70° E. in the 

upper levels to about N. 70° W. in parts of the 

600-foot level. The general dip is nearly vertical. In places the wall rock is schist of the 

Idaho Springs formation with some associated 

pegmatite and elsewhere is granite gneiss. 

Throughout the mine the character of the 

mineralization is strikingly dependent upon the 

nature of the wall rock. Where the wall rock 

is granite gneiss, as on the 200-foot level east, 

the 400-foot level west, and the 700-foot level, 

most of the mineralization is of the fissure-vein 

type characteristic of this district, one or more 

sharp-walled sulphide veinlets 2 inches or less 

in width being distributed through several feet 

of granite gneiss carrying disseminated .pyrite. 

The veinlets in places inclose numerous fragments of 11ltered wall rock. Their predominant 

ore minerals are pyrite and gray quartz in some 

parts of the mine, and galena, sphalerite, 

pyrite, and white quartz in other parts, a variation due probably to double mineralization. 

The ore now being mined is of this type. 

Where the wall rock is schist of the Idaho 

Springs formation, sulphide veinlets are commonly absent and the fractured zone is either 

barren or carries irregular disseminations of 

sulphides through a width of 10 to 20 feet. 

In the past bodies of such disseminated ore 

were an important resource. One of the largest of the old stopes in this type of ore, on the 

200-foot level just west of the shaft, measured 

about 15 by 20 feet horizontally and extended 

'nearly to the surface. Its average gold content is said to have been about 2 ounces to the 

ton. In this ore, grains of pyrite, many of 

them with perfect crystal forms, are disseminated through altered schist now consisting 

mainly of quartz, sericite, and some siderite, 

the nonmetallic minerals being stained bluegreen by iron sulphate. The ore also carries 

some sparsely disseminated sphalerite and in 

places small stringers of galena and sphalerite. 

Similar ore, but of lower grade, forms a body 

10 feet wide on the 600-foot level about 80 

feet east of the shaft. Here in places one-half 

the volume of the ore is pyrite. 

NEWFOUNDLAND VEIN. 

The Newfoundland vein, on the north side 

of Nevada Gulch about 1,400 feet west of the 

railroad station at Central City, is opened by 

an inclined shaft on the vein, said to be 1,500 

feet deep. The shaft could not be entered. 
222 GEOLOGY OF GILPIN, CLEAR CREEK, AND BOULDER COUNTIES, COLO. 

The vein on the surface strikes about N. 70° E. 

and is reported to ·have a very variable dip. 

All the ore is pyritic. Some picked smelting 

ore is said to have carried from $150 to $200 

a ton in gold. Sampling-works assays of seven 

lots of smelting ore shipped between 1898. and 

1906 show gold, 2.01 to 10.04 ounces; silver, 1.50 

to 5.25 ounces; and silica, 30 to 56 per cent. 

The total production of the vein is· estimated 

to be between $225,000 and $275,000, of which 

$75,000 was taken out between 1891 and 1911. 

CORYDON VEIN. 

The Corydon vein is opened by several short 

tunnels on the west side of Nevada Gulch' and 

by an inclined shaft, said to be 700 feet deep, 

situated 1,000 feet west of the railway station 

at Central City. In 1911 some lessees were 

reopening/ the shaft, much of which was inaccessible, though the vein could be seen on the 

100, 200, 260, and 320 foot levels. The country rock is granite gneiss in all accessible 

workings. . 

and ·8 per cent or less of copper, the average 

content being 1.74 ounces g9ld and 5.63 ounces. 

silver. The ore from the large stope east of the 

shaft b~tween the second and third levels is. 

said to have averaged 2 to 3 ounces gold per 

ton, with only a little silver. The total pro,... 

duetion of the mine is unknown. 

CENTRAL, MAMMOTH, GREGORY, BOBTAIL, 1 

AND BATES HILLS. 

MAINE HAMLET MINE. 

The Maine Hamlet_ mine is just southeast of 

Central City in the northeast slope of Central 

Hill. The development conl?ists of ~ shaft 

with levels at 178, 210, 310, and 410 feet. 

A tum1el, now caved, connects with the 178-

foot level. Tlte workings (see fig. 32), develop 

N 

The Corydon vein strikes N. 56° E., dips 70° 

SE., and is from 18 inches to 8 feet in width. 

It consists of. crushed silicified granite gneiss, 

rather heavily impregnated with fine pyrite ' 

and cut by veins of solid coarsely crystalline 

pyrite and chalcopyrite with a little ~hite 

quartz. In places some of the chalcopyrite 

crystals are coated with a thin black film of 

chalcocite. Some of the sulphide veinlets ar~ 

as much as 10 inches wide, but their average 

width is only 3 to 4 inches. 

1 

f-;::j 

Pyritic veins 

. 0 so roo F'eet (Arrow indicates direction of dip) 

Note: Wallsare mainly ~ranite ~neiss 

FIGURE 32.-Vein system on 17S.foot level of Maine Hamlet mine. Stir 

veyed by hand compass and pacing. 

Evidence of postmineral movement is found 

in the crushing of a coarse pyrite stringer at one 

. place and in the occurrence of horizontal strire 

. on· the hanging wall on the 320-foot level. 

The ground above . the 320-foot level has 

practically all been stoped, though a few fairly 

large pillars remain. . . 

Exposures near the shaft on the 260 and 329 

foot levels show the junction of the ·Corydon 

vein with a branch striking N. 45° W. and 

standing nearly vertical. This branch vein 

where exposed has an average width of about 

18 inches. The horse b~tween the two veins is 

all more or less mineralized and near the junction is traversed by several cross veinlets. · 

. Impartially selected sampling-works ass_ay's 

of 16 lots of smelting ore aggregating 51 tons 

shipped between 1892 and 1897, show 1.08 to 

· 2.62 ounces of' gold, 2 to 15 ounces of silver, 

two steeply dipping veins, the shaft being on 

the northerp. one. The 178 and 410 foot levels 

develop both veins and the 210 and 310 foot 

levels only the North vein. Botli veins are of 

the same a.ge and mineral character and are· 

connected by branch veinlets. The prevailing. 

wall rock is granite gneiss, but lenses of schist of 

the 1ldaho Springs formation are locally present. The mineralization is of the true fissure-

·vein type, ·consisting characteristically of several sharp-walled sulphide veinlets, in places 

uniting to form a single larger one. The predomina~t vein materials are quartz and pyrite, 

but in·a· few places galena, sphalerite, and chalcopvrite are present and notably increase th~ 

value of the ore. The North vein 10 feet west 

of the shaft on the 210-foot level is more or 

less typical of the pyritic portions, showing'. 

pyritic veinlet~ with a maximum width of 3. .. 

'\... 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 94 PLATE XVIII 

A. MAMMOTH HILL FROM EAST, SHOWING OPEN 

PITS MARKING OUTCROP OF MAMMOTH VEIN. 

B. DUMP AND ORE BINS AT MOUTH OF ARGO TUNNEL BELOW IDAHO SPRINGS, CLEAR CREEK 

COUNTY. 

Photograph by R. B. Morton. 
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 94 PLAT E XIX 

MINES OF GREGORY HILL AND PACKARD GULCH, FROM BATES HILL. 
GILPIN COUNTY. 223 

inches forming a network through a thickness· City. (See Pl. XVIII, A.) It can be traced 

of 4 feet ·of granite gneiss. .· continuo.usly fron1 a point near the Cook shaft 

The distribution of the pyritic and the ga- southwestward until obscured by the alluvium. 

lena-sphalerite types of ore is such as to sug- of Spring Gulch. The san1e · gel}eral mineralgest a difference in age. On the 210-foot level, ized zone continues west of Spring Gulch, where 

for example, the ore for 40 feet 'east Qf the shaft it is represented· by the· National and I-Iecla 

is entirely pyritic and beyond· that point is veins, and finally-.enters the Patch, fron1 which 

entirely of the galena-sphalerite type. The it emerges as the great California-Ilidden 

1nutual relations are not definite~y shown. Treasure lode. The eastern part of the Maml\1ovement later than the 1nineralization has moth vein was. developed in the workings of 

in places followed the veins and has produced. the Fifty Gold Mines Co. On Manunoth I-Iill 

gouge and crushed ore . .' the lode is developed by an almost continuous 

Su:fEicient data are not .at hand from which to series of shafts and pits, the principal one being . 

estimate the average value of the ore, but the the Great Mammoth shaft on the east side of 

following selected sa1npling-works returns give the hill. A lateral has also been driven under 

some idea of its range: Mammoth ground from the Argo tunnel. 

Sampling-works assays of ore from the ~Maine Hamlet mine. Little statistical data is available in regard 

to the ore of the Mammoth lode. It is well 

Date. Ore. Gold. Silver. Copper. 

..... 

Net lbs. Ounces. Ounces. Percent. 

1888 ................ 1,544 11.95 22.00 6.00 

1888 ................ 2,584 2.30 11.00 4.50 

1888.---.-.---.- .... 2,822 3.20 6.00 3.00 

1896 -- ...... -.. -.... 6,777 . 67 5.50 ........ 1899-- ....... ---- .. - 20,370 .48 1. 50 ........ 

0. K. MINE. 

The 0. K. mine, on Central I-Iill just southeast 

of Central City, is developed by a shaft which, 

according to the maps available, connects with 

levels at depths of 200, 400, and 500 feet. The 

400-foot level connects with the Bobtail tunnel. 

The map shows a single vein striking about 

N. 45 ° E. and dipping nearly vertical. The 

ore appears from the available assays to be~?ng 

largely to the pyritic type, but a little sphalerite was seen on the dump. 

Sampling-works assays of 29 lots of smelting 

ore aggregating 185 tons, shipped at various 

times fron1 1893 to 1908, inclusive, show gold, 

0.30 to 4.28 (average 1.13) ounces per ton; silver, 3.40 to 10.20 (average 5.59) ounces per ton; 

copper, 2 to 10.25 per cent. Thirty-five tons of 

smelting ore shipped in 1910 averaged gold 1.13 

ounces and silver 5.37 ounces. The average 

recovery as bullion and concentrates from concentrating ore shipped in 1910 was g9ld 0.166 

ounce and silver 0.32 ounce per ton treated. 

MAMMOTH VEIN. 

The Mammoth, sometimes called the :Great 

MalnJnoth lode, is probably the widest· and 

most conspicuous lode in the vicinity of Central 

lmown ·that the free-1nilling surface ore mined 

in the early days gave good returns. Hollister 1 

states that a 4-weeks' run on Mammoth sur-

'face ore yielded $5,250. Ore mined in 1875 

within 200 feet of the surface is said 2 to have 

averaged about $10 per ton. The ore from the 

deeper portions of the lode, on the contrary, is 

lmown to be low grade. Careful sampling has 

been done by several persons interested, but 

the results do not appear to have encouraged 

further development under present conditions, 

and within recent years the lode has no't been 

worked. 

Outcrops on top of Mammoth Hill show that 

the granite gneiss bordering the vein has been 

1nuch silicified; it has weathered· whiter than 

the normal granite gneiss and is more resistant. 

BROOKLYN MINE. 

The Brooklyn mine is in the depression between Mammoth and Bobtail hills. The claims 

of the Brooklyn group cover the outcrop of se.veral veins, but the main shaft and most of the 

development is in the Washington vein. The 

shaft, which is about 570 feet deep, follows this 

vein down to the 3 70-foot level, below which 

the shaft is vertical and lies in the footwall 

country rock. Levels have been driven at 

vertical depths of 81, 156, 249, 370, and 470 

feet; A crosscut north from the 249-foot level 

at a point 20 feet west of the shaft cuts the 

.Cashier vein 60 feet from the Washington vein 

1 :Mines of Colorado, p. 112, 1867. 

2 Raymond, R. W., Statistics of mines ancl mining in the States and 

Territories west of the Rocky Mountains, 1875, p. 290, 1877. 
224 GEOLOGY OF GILPIN, CLEAR CR.EEK, AND BOULDER COUNTIES, COLO. 

and serves as a starting point of short drift~ on 

the Cashier. vein. 

The average dip of the Washington vein is 

about 70° S. The average strike is nearly east 

and west. The workings were closed temporarily at the time of this survey anp. could not 

be entered, but an examination of material on 

the dump indicates that the veins belong to the 

pyritic type, the ore showing pyrite, chalcopyrite, and tennantite as its metallic minerals. A 

polished specin1en showed minute veinlets of a 

gray secondary mineral, probably c~alcocite developed in the. chalcopyrite. · 

The Brooklyn mill, not now being operated, 

is on North ]..;ork of Clear Creek, about threefourths of a mile above Blackhawk. It is 

equipped with 10 rapid-drop 1,000-pound 

stamps, Hartz jigs, and Woodbury concentrating tables. The capacity is stated to be 

3Q to 40 tons daily. 

NEXT PRESIDENT MINE. 

The Next President mine, on the east side of 

Packard Gulch at the side of tlie Colorado & 

Southern Railway track, is developed by a 

shaft with levels at 100, 160, 260, 360, and 

460 feet. The mine was not in operation and 

th~ workings were not examined. The map 

shows a vein (followed by the shaft to a depth 

of 350 feet) that has a general northeast to 

southwest strike, and another vein, intersecting the first, that strikes about N. 70° E. The 

junction of the two shifts eastward in dept.~. 

The mine is reported to have been worked 

fairly continuously from 1865 to 1878, spasmodically from 1878 to 1908, and continuously again from 19Q8 to 1910. Since 1910 it 

has been idle. There is no reliable record of 

the production. The Eagle Mill at Blackhawk 

is owned by the company owning this mine. 

The following sampling-works assays are of 

ore shipments from this mine: 

Sampling-works assays of ore from Next President mine, 

1901-1910. 

Year. Ore. Gold. Silver. Copper. Silica.· 

Net.lbs. Oz. Oz. P. ct. P. ct. 

1901 ........ 5,556 l. 34 4.00 3.20 37 

1902 ........ 5, 220 1.42 2.60 . ............... 78 

1902 ........ 4,600 . 89 6.90 3.60 ........ 1907 ........ 1, 182 .78 2.30 ............. ····---- 1907 ........ 1,636 .48 2.50 ......... .. ........ 

1910 ........ 4,413 1. 34 4.20 . 70 .......... 

VASA VEIN. 

The Vasa shaft, about 400 feet southwest of 

the Gregory-Buell mill in. Central City, is over 

260 feet deep, but only the 260-foot level was 

accessible. The vein strikes N. 42° E. and 

dips on an average 80° SE. It varies from 4 to 

10 feet in width and so far as seen is in granite 

gneiss. This vein has been stoped from th~ 

surface to the water level (some distance below 

the 260-foot level) for at least 250 feet northeast of the shaft and for an unknown distance 

southwest of it. At the northeast end of the 

260-foot level, about 200 feet from the shaft, 

lessees were working in a small bl<?ck of unstoped ground. At this place the vein, 10 feet 

between walls, is composed of silicified granite 

gneiss heavily impregnated with rather coarse 

pyrite. Numerous small stringers of white 

quartz and pyrite cut the disseminated ore. 

On the northwest side of the vein next the 

wall a 10-inch streak of coarse pyrite and 

quartz is cut by a one-half to 1 inch stringer of 

dark-gray quartz carrying black sphalerite, 

galena, pyrite, and chalcopyrite. 

About 75 feet from the face ·of this drift a 

branch vein of pyritic ore goes into the southeast wall at a very small angle with the n1ain 

vein. This branch vein is about 4 feet wide 

and stands nearly vertical, though near its 

junction with the Vasa it dips 75° SE. It is 

well 1nineralized and has a narrow streak of 

smelting ore near each wall. Between this 

junction and the shaft the Vas a vein is 4 to 5 

feet wide and has been entirely stoped above 

and below the level. 

The ore is cut by a number of postnlineral 

slip planes, along none of which has there been 

much movement. 

· The lessees stated that the 10 feet of material 

which they are working includes both concentrating and smelting ore and average~ about 3 

ounces gold a cord (8 tons). ~ -~·: ~- rJ /T) 

O'NEIL VEIN. 

The O'Neil lode, which is said to be a westward . continuation of the Gregory lode, is 

opened by a 986-foot shaft on the top of the 

ridge between Bobtail and Packard gulches. 

The mine was inaccessible at the time of survey and maps were not available. The workings are said to develop two veins winch bifurcate and then rejoin. The 358-foot level connects with the Bobtail tunnel. Ore on the 

.. , 
U. S. GEOLOGICAL SURVEY 

LEGEND 

,... - Pyritic veins 

(Ar.row indicates 

tlirectio" of dip) 

Workings ~ inaccessible 

sLo~~~o ______ s~o _____ ,_o~~-----·•s~o _____ z_o~o _____ z~soFEET 

N 

Tight vein 

locally 3 inches wide/ 

,·0 

~ 

~ 

0 

~ 

~ 

~ 

0 

0 

'/, 

~ 

r.-0Drift extends abollt .(__ 100 feet beyon.d tllis point 

PROFESSIONAL PAPER 94 PLATE XX 

PI..AN OF A PART OF BOBTAil. TUNNEL • 

• 
GILPIN COUNTY. 225 

dun1p consisted n1ainly of pyrite and chalcopyrite, with in places a very little galena. Free 

gold inclosed in galena and quartz is reported 

to have been found at a depth of 866 feet. 

The average value of nearly 600 tons of smelting·ore mined between 1897 and 1906 is said to 

have been about $70 per ton. Twenty-one lots 

of sm.elting ore, aggregating about 48 tons, sold 

between 1897 and 1908, averaged 3.10 ounces 

gold, 7.13 ounces silver, and 5 per cent copper 

a ton, according to smnpling-works assays. The 

concentrating ore for the same period is said 

to have averaged about $10 per· ton. 

The gross output between 1897 and 1906 is 

said to have been $150,000. 

PROPERTY OF FIFTY GOLD MINES CO. 

Mining near Blackhawk, on the Gregory, 

Fisk, Cook, Bobtail, and Mammoth veins and 

thei1: branches, and on several minor veins, has 

in recent years been controlled by the Fifty 

Gold 1\1ines Co. The properties under this 

managmnent have been among the most productive in the district, but were un±:ortunately 

closed down at the time of this survey, and 

access could be had to only a small part of the 

workings. The Gregory, in this group, has the 

distinction of being the first gold lode discovered 

in Colorado (May 6, 1859). (See Pl. XIX.) 

In recent years development has been 

mainly through the Cook ·shaft, the Bobtail 

ttmnel, and the Gregory incline. The Cook 

is a large vertical shaft 1,450 feet deep, 

equipped with cages. It connects with 14 

levels, and from the surface to the eighth level 

is close to the Cook vein. Below this the Cook 

vein lies a short distance to the south of the 

shaft and the Fisk vein to the north. The 

Bobtail tunnel, begun in 1863, starts in Blackhawk, on the north side of Bates Hill, follows 

the Gregory vein through the hill, crosses beneath the road from Central City to Blackhawk, and enters the hill south of Gregory 

Gulch, where it intersects the Fisk and Co.ok 

veins. (See·Pl. L\::.) Tlie Cook shaft is connected with the mill at Blackhawk by a motor 

railroad run_ning through the Bobtail tunnel. 

Ore is hoisted to the tunnel lev-el, deposited in 

ore bins, and aut01natically loaded onto the 

motor cars for transportation to the mill 4,200 

feet distant. The Gregory incline slopes downward for 1,709 feet at about 25° from the large 

null of the company in Blackhawk to a point 

44214°-17-15 

on the Gregory vein 700 feet below the surface. Crosscuts on the eleventh level connect 

the Gregory vein with the Cook vein and with 

the Mammoth vein. · 

The relations between the veins of the group 

are complex. In general, as exposed on the 

surface, the Cook, Fisk, Sleepy Hollow, and 

After Supper (Banzai) shafts seem to be on 

one great lode, which. preser:ves a fairly constant trend of about N. 40° E. Near the Cook 

shaft this main lode is joined from the west by 

the Mammoth lode and from the east by the 

Bobtail lode, and the relations are very complicated. (See Pl. XX.) On the hill east of 

the Cook shaft a large nu:fnber of minor veins, 

such as the Warwick and Nemeha, are probably branches from the larger lodes. 

The first vein cut in the Bobtail tunnel is 

the Fisk (Pl. XX), which, where cut by the 

tunnel, is 2 feet wide . and shows numerous 

irregular veinlets of pyrite traversing silicified 

granite gneiss. As exposed in the drift extending southwestward from the tunnel it 

ranges fron1 2 to 6 feet in width. The vein 

has been fractured subsequent to mineralization and the fractures filled with cherty silica. 

A short distance east of the tunnel the Fisk 

vein is crossed by the east-west Ground Hog 

vein, which is mineralized in the same manner 

but less heavily than the Fisk. As exposed, 

175 feet west of tb.is junction the Ground Hog 

is 16 inches wide and includes at-inch veinlet 

of solid pyrite bordered by 2 inches of silicified 

granite gneiss, the remainder of the vein being 

gneiss carrying disseminated pyrite. 

From the Bobtail tunnel the Cook shaft was 

descended, and portions of the next three levels 

were examined. On each level several veins· 

complexly related were exposed near the shaft, 

but could not be followed far because of caving 

of the roofs or floors. The veins are all highly 

pyritic and reP,resent the contemporaneous 

mineraliz,ation of a number of more or less connected fracture zones. Their character may 

be typified by an exposure 300 feet west of the 

shaft on the second level below the Bobtail 

tunnel, where the mineralized zone is about 6 

feet wide and consists of granite gneiss carrying 

disseminated pyrite and traversed by a number 

of sharp-walled v-uggy veins of pyrite 3 inches 

and less in width. 

The northeast part of the Gregory vein, under 

Bates· Hill, is developed by a drift tunnel ex-
226 Ci-EOLOGY OF G~LPIN, CLEAR CREEK, AND BOULDER COUNTIES, COLO. 

tending entirely through the hill. The average 

strike of this part of the vein is about N. 45 ° E. 

and its dip is 80°-8~ 0 SE. The mineralization is predominantly pyritic but locally has 

been supplemented by ore of the galenasphalerite type. The vein varies in width from 

2 to 5 feet, and its appearance. in the purely 

pyritic portions is well illustrated 300 feet from 

the south entrance to the tunnel, where it is 

2 feet wide and contains several veinlets which 

are about half pyrite and half quartz and are 

sharply bounded by granite gneiss carrying an 

abundance of disseminated pyrite. In a stope 

about 670 feet from the south portal, the vein 

is about 4 feet in width and consists mainly of 

granite gneiss carrying varying amounts of disseminated pyrite, which in some places constitutes 90 per cent of the vein material. In the 

more pyritic portions a few vugs are lined. with 

crystals of quartz, pyrite, and chalcopyrite. 

· The pyritic· vein material is traversed by a 

veinlet of galena, sphalerite, and chalcopyrite 

that appears to be of later origin. This vein 

usually shows a sharp contact against the 

pyritic material. 

The ores of this. group of veins belong ·almost 

exclusively to the pyritic· type, though in a 

few places, most of them in the eastern portions 

of the veins, galena-sphalerite ore also occurs. 

Pearce 1 recognized the presence of tellurium 

in certain ores from the Gregory mine, and 

·although it has not been demonstrated that 

this metal occurs here in combination with 

gold, the possible existence of tellurides of gold 

must be recognized and may account for the 

richness of certain portions of the ore bodies. 

Raymond mentions the discovery in the 

Gregory vein in 18'74 of a pocket of ore carrying 

a large ·amount of free gold, and a specime:u 

·from this vein in the collection of the Colorado 

Bureau of Mines in the State capitol at Denver 

shows small masses of gold inclosed in light 

gray quartz. . 

Sampling-works assays of 100 lots of smelting ore from. the Gregory, Fisk, Bobtail, and 

Cook veins aggregating 410 tons, shipped at 

different times from 1888 to 1909 l.nclusive, 

show gold, 0.52 to 26.4 (average 2.58) ounces; 

silv~r, 1.50 to 21 (average 5.4) ounces; copper 

(wet), less than 1.5 to 13.75 per cent; silica, 

36' to 70. per cent. 

1 Pearce, Richard, The association of gold with other metals in the 

West: Am. Inst. Min. Eng. Trans., vol.18, p. 449,1890. 

According to a private report by William A. 

Farish, the books of the Cook and Fisk mines 

show an average yield of $7.03 per ton from 

177,717 tons of ore, 2.6 per cent of which was 

smelting ore and the remainder concentrating 

ore. The ratio of concentration was about· 9 

to 1. 1 Very few data are available for a coml?arison 

of the metal contents in the deeper workings 

with those near the surface. Sampling of the 

so-called Fisk-Mammoth vein on the fourteenth 

level of .the Cook shaft shows 0.1'2 to 0.52 

ounce gold and 0.4 to 4.28 ounces sil.ver, with 

an average of about ·0.3 ·ounce· gold and 2 

ounces silver. These sarp.ples, taken over 

vein widths of 3 to 6 feet, included both solid 

sulphide veinlets and gneiss carrying disseminated pyrite. Assays of the solid sulphide 

veinlets showed a maximum of 5 ounces gold 

and 11 ounces silver. 

According to Farish's report, already cited, 

samples of ore {rom every 10 feet in the lower 

levels of the Cook 'shaft showed the following "' 

results, gold being computed at $20.6.7 and silver at $0.55 per· mpice. 

Results of ore sampling from lower, levels, Coole shaft. 

Length. Average 

width .. Value. 

Tenth level: Feet. Feet. 

First block ......... 290 3.87 $1.42 

Second block ....... 138 4.1 10.23 

Twelfth level: 

First block ......... no 4.13 4.33 

Second block ....... 210 4.94 1.53 

Third biock ....... 130 3.00 6.86 

Thirteenth level: 

First block ......... 120 2.4 11.25 

Second block ....... 152 3.53 4.30 

There is little doubt that the percentage of 

gold in the ores near the surface was augmented by oxidation, but it is equally certain 

that high gold contents are occasionally 

found at depths far below the reach of this 

process. . 

The concentrating ores from the Fifty Gold 

Mines properties were treated at a large and 

well-equipped 80-stamp mill in Blackhawk. 

.t\FTER SUPPER-SLEEPY HOLLOW VEIN. 

The Sleepy Hollow vein crosses North Clear 

Creek at the mouth of Gregory Gulch and 

appears to be a northeastward extension of 

the Fisk lode. The After Supper or Banzai 
GILPIN COUNTY. 227 

shaft, north of Blackhawk, is down 714 feet. · CARR VEIN. 

The Sleepy I-Iollow shaft, about 700 feet south The Carr vein, which crosses Gregory Hill 

of Blackhawk post office, is over 1,000 feet just south of the !;lUmmit with a general strike 

deep. The American shaft is on the same vein, of about N. 45° E., is clearly traceable on the 

500 feet southwest of the Sleepy Hollow. · surface for. about 2,500 feet. It has been 

'rhe outcrop of the vein strikes N. 45o E. developed through two principal shafts, a 

The dip, as,shown by the vertical plan of th~ western one, the Colorado-Carr, on· top of 

Sleepy IIollow shaft, varies greatly. This Gregory Hill, and an east~rn one, the Chicagoshaft dips 80° S .. as far as the se?ond. level, Carr, in Bobtail Gulch. The vein is not now · 

then about 80° N. to a little below the fourth worked and the old workings ·are inaccessible 

level, where a vertical vein joins . the vein and the only information in regard to the ore. 

which it has been followin~, below which it was obtained from the sampling-works assays. 

is about vertical to the ninth level. Below and from examination of the dumps. The· 

the ninth level the vein splits, one part con- latter, however, revealed some interesting 

tinning about vertical and the other, which the relationships. . 

shaft follows, dipping 70° N. The vein cuts The principal minerals in the vein rock are, 

schist, peg1natite, and granite gneiss. pyrite and chalcopyrite, the proportim~ of' 

Fron1 the ore on different dumps it is ap- chalcopyrite apparently being above the averparent that two periods of mineralization have age for most veins in this vicinity. The 

occurred. The original vein consisted of sulphides occur both as sharp-walled fissure 

crushed silicified wall rock with abundant fillings with a quartz gangue and as dissemiclisseininated pyrite cut by veinlets of rather nations. in the altered wall rock within the 

coarse pyrite. This vein was reopened, and fracture zone. Galena and sphalerite, in 

white to gray quartz with galena, dark sphaler- association with pyrite, chalcopyrite, and 

ite, and chalcopjrite was deposited in the quartz, were observed in a few specimens and 

fractures. The younger veins cut the older in at least some of these were formed after the 

ore in all directions but few of them are very pyritic mineralization, cutting sharply through 

wide. Ore frmn the Sleepy Hollow mine is the pyritic ore. Later than the pyritic 

said to have carried tellurides of gold locally, mineralization and possibly also later than the. 

and the high gold content 'of certai~ shipments galena-sphalerite mineralization portions of the: 

may be due to their presence. The high silver vein were again opened, more or less brecciated,. 

• content of certain shipments, as high as 492 and wholly or partially filled with gray cherty 

ounces, is probably a result of downward en- silica, commonly inclosing angular fragments of 

richment in this metal. pyrite, chalcopyrite, and quartz of the original 

On the stope maps of the Sleepy Hollow vein. Some of the cherty silica is pure white~ mine the vein is shown to have been ex- In a few specimens the pyrite and chalcopyrite: 

tensively stoped from the second to the eighth are cut by small veinlets which show galena and. 

levels for 150 to 300 feet east of the shaft. sphalerite next the walls and a center of cherty 

Above the first level the workings are. not silica .. 

shown but are supposed to be extensive. The Eighty-five lots of sm~lting ore, aggregating 

precious-n1etal content ranges from 0.28 to 400 tops, shipped at v.arious times from 1893 t() 

34.25 ounces gold and from 2 to ,492 ounces 1910, show, ... according to . sampling-works 

silver per ton. In most of the lots of smelting ~ssays, 0. 72 to 9.06 ounces in gold, 2 to 21.2: 

ore the gold content is about 2 ounces and the ounces in silver, and as much as 11.7 per cent of 

silver content 10 ounces per ton. Few assay Th 

2 88 · ld 

returns record any copper or lead, although a , copper. e aver.age :was · ounces ill go 

few lots of smelting ore carried as high as 20 an.d 7.62 o~ces ill silver. The silica in 21 

per cent lead, and other lots as much as 5.7 sh1pmentsvaned from 33 to 79 per cent but was 

per cent copper per ton. commo~ly betwe~n 45 and 55 per c~nt. ConThe total production of the Sleepy Hollow centratm¥ ore shipped from the Chicago-Carr 

mine is stated to be about $800,000 and that n1ine durmg 1910 averaged about 0~1.8 ounce 

of the After Supper about $80,000. in gold and 0.3 ounce in silver. ' 
228 GEOLOGY OF GILPIN, CLEAR CREEK, AND BOULDER COUNTIES, COLO. 

GOLDEN EAGLE VEIN. 

The Golden Eagle vein, a short distance east 

of Bobtail Hill, is developed by several shafts 

and pits now abandoned. The ore is said to 

have consisted mainly of coarse pyrite and 

chalcopyrite of low grade. 

UNEXPECTED VEIN. 

The Unexpected vein crops out about a mile 

southeast of Central City and is developed by 

three shafts now abandoned. Ore on the 

dun1ps was mainly coarse pyrite with some 

white quartz gangue. Small amounts of 

galena and sphalerite_ were noted. 

CLAY COUNTY VEIN. 

The Clay County vein, on the north side of 

Lake Gulch about three-fourths mile southsoutheast of Blackhawk, is developed by a 

shaft which has · not been used for several 

years. It is also cut at the sixth level by the 

New National tunnel, which starts below the 

mouth of.Fourmile Gulch on the south side of 

Clear Creek and also develops the Hors~shoe 

vein. This tunnel was not entered. 

On the surface the country rock near the 

vein is Idaho Springs formation, which contains numerous fairly large lenses of granite 

pegmatite·and is cut by a monzonite porphyry 

dike. 

The vein strikes about N. 21° E. and dips 

steeply northwest. The ore seen on the dump 

shows two periods of mineralization: A pyritic 

vein, consisting of country rock, with fine disseminated pyrite and stringers of -coarse 

pyrite, enargite, tennantite, and quartz, has 

been breccia ted and the fragments have been 

recemented by ore carrying galena, sphaierite, 

and chalcopyrite. 

Sampling-works assays of 12 lots of smelting 

ore,aggregating57.5 tons, shipped between 1891 

and 1899, s4ow gold, 0.40 to 1.15 (average 0.65) 

ounces; silver, 5 to 91 (average 11.28) ounces; 

and copper (wet), from less than 1.5 to 6 per 

cent. No lead is quoted. 

The gross production of the mine is said to 

be $600,000 to $700,000, derived almost entirely from ore that came from above the third 

level of the Clay County shaft. 

CHEMUNG-BELMONT MINE. 

The Chemung-Beln1ont mine, about one-half 

mile south of Blackhawk, develops a lode which 

forks near the shaft house, but reunites farther 

west, as well as in the deeper levels of the mine. 

The north fork is termed the Chemung and the 

south fork the Belmont. The main shaJt is on 

the south or Belmont vein for the upper 600 

feet, but below that follows the united veins 

to a depth of 820 feet. There are 10 levels; 

the main development has been on the Chemung vein above the 620-foot level. The mine 

was last worked in 1907, and the workings were · 

not accessible at the tin1e of survey. 

Ore on the shaft dump was in general similar 

to that of the Clay County vein, showing pyrite 

and tennantite but also galena, sphalerite, and 

some chalcopyrite. 

Sampling-works assays of 29 lots of sn1elting 

ore, aggregating 95 tons, shipped from this 

mine at various times from 1889. to 1902, show 

gold, 0.52 to 5.5 (average 1. 7 4) ounces; silver, 7.3 

to 28.6 (average 16.03) ounces; copper (wet),less 

than 1.5 to 7.5 per cent; silica, 23 to 62 per cent 

in 16 lots. 

The shipments of smelting ore in. various 

years showed the following ranges in metal 

content, according to the records in the books 

of the company: · 

Metal contents of smelting ore, Chemung-Belmont mine, 

1890-1894. 

Date. Gold. Silver. Copper 

(wet). 

Ounce.c;. Ounces. Per cent. 

1890.- .. ----.---- 0.60-3.90 6.47-63.00 6.50 or less. 

1891 .......... --. .90-4.95 7.90-47.60 7.50 or less. 

1892-93 .......... . 50-4.10 7.00-29.50 7 .10 or less . 18~3-94 .......... . 32-4.50 7.10-64.30 3.10 or less . 

The gross production of the mine is estimated · 

to be at least $500,000. The net output from 

1887 to 1902, as recorded in the company's 

books, was $147,366. 

ALPS AND QUARTZ HILLS. 

KANSAS VEIN. 

The Kansas lode on the north slope of 

Quartz Hill is developed by seven principal 

shafts which, named in order from east to west, 

.are the Alger-Kansas, English-Kansas, PeaseKansas, University-Kansas, First NationalKansas, Mammoth-Kansas, and Gold Coinl(ansas. All except the Alger-Kansas 'were 

i<!le at the time of survey, but the Kansas vein 
GILPIN COUNTY. 229 

w11s observed where cut by the La Crosse 

Tunnel. 

r:rho Alger-Kansas ve41, on the northeast 

slope of Qtutrtz I-Iill, about 1,000 feet northeast 

· of tho Fourth of July shaft, is opened by two 

tunnels and by a shaft said to be 390 feet deep. 

· Only the SO-foot west drift of this mine was 

accessible. The ground east of the shaft is said 

to be stoped for 100 feet from the surface to the 

300-foot level. The ground west of the shaft 

has been stoped from the 135-foot level to the 

surface. It is said that on the 300-foot level 

the II.linois-Kansas vein is exposed in a crosscut 

68 feet north of the Alger-Kansas. On the SOfoot lev~l a 25-foot crosscut 135 feet west of the 

shaft has broken h.1to the south wnll of the Illinois-ICansas vein. At the surface the two 

veins are about .15 feet apart. The AlgerKansas vein at the shaft strikes N. 60° E. and 

dips 80° S. On the· SO-foot level it varies from 

IS inches to 4 feet in width and is entirely in 

granite gneiss. The vein consists of pyriteinlpregnated wall rock, cut by stringers of 

almost solid pyrite 1 inch and. less in width and 

~y a series of veinlets ·of dark quartz, galena, 

sph11lerite, and chalcopyrite, which are apparently of later origin. 

The south wnll of the Illinois-Kansas vein was 

shown in the face of the crosscut at the 80-foot 

level. It is apparently similar in mineralization to the Alger-Kansas; having a 2-inch 

streak of galena, sphalerite, and pyrite just 

below the tight south-wall slip. 

The Kansas vein, where cut by the La Crosse 

tunnel about ISO feet from the portal, is nearly 

vertical and shows several sharp-walled quartzpyrite veinlets up to 2 inches wide through a 

.width of 2 feet of granite gneiss. 

From all the information available it appears 

that the ore of the Kansas lode as a whole was 

predon1inantly of the pyritic type, although in 

places the galena-sphalerite .type was · also 

present. 

Tho pyritic ore of the Alger-ICansas vein is 

said to average about $45 a ton in gold and 

silver. In 1910 the average conce1;1trating ore 

carried 0.15 ounce gold and 0.16 ounce silver 

per ton. Six selected sampling-works assays of 

shipments of smelting ore between 1SS9 and 

1904 showed from 0.32 to 3.5 ounces gold, from 

2 to 7.6 ounces silver, and 5.5 per. cent or less of 

copper. The metal content appears extremely 

variable, owing perhaps to the variable proportions in which the pyritic and galena-sphalerite 

ore types are associated in the vein. 

Sampling works assays of 57 lots of smelting 

ore aggregating 34S. tons, shipped from mines 

in the central part of the Kansas lode between 

1S94 and 1905, show gold, 0.35 to 5.56 (average 

1.62) ounces; silver, 2.25 to 14.7 (average 6.50) 

ounces; copper, 5.5 per cent or less; silica, 

commonly, 25 to 50 per cent. None of these 

shipments showed lead in commercial amounts 

but one showed S.5 per cent of zinc. 

BURROUG~S VEIN. 

The Burroughs vein outcrops on the north 

side of Quartz Hill opposite Nevada ville. It 

is developed by four main shafts, the ConleyBurroughs, Mackey-Burroughs, Ophir-Burroughs, and Phoenix-Burroughs. AU of these 

were idle at the time of survey and could not 

be entered. The Ophir-~Burroughs shaft is said 

to be 1,200 feet deep. The Phoenix-Burroughs 

shaft, according to the available maps, connects with 12levels. The Mackey and Conley 

shafts are less important. 

The appearance of. the Burroughs vein in 

1870 as exposed in the Ophir workings is described by J. D. Hague 1 as follows: · 

The walls are usually well defined, smooth, and regular, 

sometimes carrying a thin gouge of clay, sometimes having 

the seam of ore resting directly upon it without anything 

intervening. The vein, however, is not wide as compared 

with other leading veins, varying from 8 to 10 inches to 3 

or 4 feet, seldom exceeding the latter. 

The vein matter and the ore, consisting usually of a solid 

seam of the latter from a few inches to more than 1 foot in 

thickness and associated with a belt of siliceous and feldspathic material highly charged with pyrites, present the 

same general features in mode of occurrence and distribution that have been already noted in connection with the 

other lodes, but the pyritous ore is more exclusively iron 

rather than copper pyrites; in fact, the small proportion 

of the latter, at least in the Ophir, is very marked, and 

the iron pyrites is not only gold bearing but the Ophir 

ore carries more silver than is generally associated with 

the ores of the district similar to these in other respects, 

the average assay of the first-class ores S«?ld at the smelting 

works showing about 6 ounces of fine gold and 12 ounces 

of :fine silver to the ton. The ground is generally hard, 

requiring the aid of powder for its removal. Very little 

of it can be picked down. * * * 

The :first-Class ore, sold at the smelting works, netted 

the mine, in the month of May, 1868, $93; in July, $98; 

and in August, $104 per ton, in currency. The yield of 

the stamp rock, including that treated in the company's 

mill and in custom mills, was, in May, $24.50; in June, 

$15; in July, $12; and in August, $19 per ton, in currency. 

1 U.S. Gool. Expl. 40th Par. Rept., vol. 3, pp. 532-536, 1870. 

' 
230 GEOLOGY OF GILPIN, CLEAR CR.EEK, AND BOULDER COUNTIES, COLO. 

The proportion of first-class or smelting ore to second- Granite gneiss was the only rock seen along 

-class or concentrating ore appears from the accounts to be the walls of the mine. The :vein consists of 

about 1 to 50. 

Thus we have inApriL ........ 8 in 

May ......... :. 15 in 

June........... 6 ln. 

July .......... 4.5in 

August ........ 12 in 

374, or 1 in 46 

445, or 1 in 30 , 

592, or 1 in 97 

598. 5, or 1 in 13.3 

428, or 1 in 35i 

crushed silicified granite gneiss through which 

is disseminated fine-grained pyrite with a little 

scattered chalcopyrite. West of the shaft ore· 

of this kind has been brecciated and recemented 

by gray quartz carrying an abundance of 

sphalerite, galena, and chalcopyrite. (See 

For 5 months .. 45.5 in 2, 437. 5, or 1 in 53.6 Pl. XIII,-0, p. 96.) In some places the second 

The ore on the Ophir and Phoenix dumps mineralization has not completely filled the 

was composed mainly of. quartz and pyrite open spaces, and small vugs remain which are 

with, in places, some chalcopyrite and very lined with crystals of galena and sphalerite. 

little tetrahedrite. Coarse pyrite was the only In places the sulphides are covered with a later 

sulphide noted in the LaCrosse tunnel workings coating._of dark-gray .cherty silica. 

· on this vein. (Seep. 237.) Galena and sphal- Horizont~l postmineral movement along the 

. ·erite, though occasionally noted., appear in gen- fractur!3 subsequent to the last mineralization 

eral to be rare. · is shown by shearing in the ore and by slickSampling works assays of 71 shipments of ensided gouge in the west 450-foot level. 

smelting ore, aggregating 251 tons, shipped · The main ore shoot pitches westward. At 

from 1893 to .1899 from the Conley, Mackey, the surface the shaft marks a~out its center, but 

Ophir, and Phoenix workings on the Burroughs on the 250-foot level the shoot was reached 80 

vein, show gold, 0.88 to 12 (average 4.3) feet west of the shaft, and on the 450-foot level 

ounces; silver, 2.1 to 25.5 (average 9.97) ounces; the west drift appears to be just entering the 

copper, not more than 4.3 and commonly less shoot at its face, 200 feet from the shaft. On 

than 3 per cent. Ten tons of smelting ore , the second level the shoot extends for at least 

shipped in 1910 averaged gold, 3.31 ounces 150 feet along the vein. 

and silver, 5.9 ounces. The pyritic ore is reported to be of low grade. 

FOURTH OF JULY VEIN. 

The Fourth of July shaft is on the northeast 

slope of Quartz Hill about half a mile south-· 

west of the railroad station at Central City. 

Tlie shaft is said to be 600 feet deep, but the 

only accessible levels were 250 and 450 feet 

below the collar. On the upper level the east 

drift is caved near the shaft and the west drift 

about 250 feet from it. On the lower level the 

drift east was 210 feet and the west drift 190 

feet long. 

The vein strikes approximately east and 

·west, but in the 450-foot east drift it strikes 

:N. 75° W. for about 180 feet, beyond which it 

trends N. 80° E. From the surface to a depth 

·of 360 feet the average dip is 87° S.; below 360 

feet it is commonly about 85° N., though in 

many places it stand~ vertical. It varies from 

6. inches to 10 feet in width with an average of 

about 2! feet. On the 450-foot level 140 feet 

east of the shaft a small cross fracture striking 

N. 70° E. and dipping 73° S. runs into the 

Fourth of July ·vein. 

The concentrating ore, containing a little· 

galena and sphalerite, carries about 0.75 

ounce of gold to the ton. Three lots of smelting ore shipped in 1896 assayed from 0.4 to 

1.16 ounces gold and 2:6 to 14.2 ounces silver. 

The total production of the mine is not 

known, but it is reported that $250,000 worth 

of ore was taken from the stope connecting 

with the 250-foot level. 

QUARTZ HILL TUNNEL. 

The Quartz Hill tunnel, started in the late· 

sixties, has its portal on the south side of 

Nevada Gulch about 1,000 feet southwest 

of the railroad station at C@ntral City. The 

first 1,480 feet (see fig. 33) is a crosscut running 

south-southwest tl;trough granite gneiss containing a few small lenses of schist of the Idaho 

Springs formation. At 1,480 feet the Hecla 

vein is cut and the remainder of the workings 

are drifts on· this and on the Barnes vein. 

At 155 feet from the mouth the tunnel cuts 

a very small vein of crushed granite gneiss, 

which is almost barren except for ~· !-inch 

stringer of coarse pyrite near the center. At 
GILPIN COUNTY. 231 

310feetfrom the mouth an 8 to 18 inch vein has streak of quartz with some pyrite is cut. 

been drifted on west of the· shaft for 120 feet to a Between the 450-foot point and ,the Hecla v~in 

winze (W,·fig. 33) and for an undetermined dis- the granite gneiss is barren except for a vein 

tance beyond; it varies from 6 to 8 inches in which is cu~ about 50 feet north of the Hecla. 

width and consists of 3 to 4 inches of quartz This vein is about one foot wide and is comwith pyrite and chalcopyrite, the laJter mineral posed of crushed granite gnerss carrying disbeing most abundant near the winze. In some seminated pyrite and cut by stringers of pyrite 

LE~END 

a 

Pyritic vein 

B Unmineralized fracture 

(Arrows indicate direction of dip) 

~orkin~s 

~ inaccessible 

Note:\A{arl rock Is ~ranite ~neis.s except a few small lenses or. sch1st 

N 

o&"""""a:m::iiQ;co:=:::===::e3!so~ ...... !!i;I300 Feet 

FIGURE 33 . ..:_Geologic plan or Quartz Hill tunnel. Surveyed by hand compass and pacing. 

places the granite gneiss for 6 to 8 inches on 

either side ·of thi$ ore contains ·a little dissmninated fine-grained pyrite; 20 feet north 

of this vein is an east-west barren fracture. 

About 400 feet in from the mouth there is a 

1-foot zone of bleached granite gneiss along a 

bn,rren fracture; 30 feet farther in a 3-inch 

and some later veinlets of galena, sphalerite, 

and chalcopyrite. There are short drifts and 

small stopes on this vein both east and west 

of the tunnel. 

The Hecla vein averages· about 3! feet between walls, and· that part of it which could 

be seen. consists of, pyrite-impregnated granite 
232 GEOLOGY OF GILPIN, CLEAR CREE_K, AND BOULDER COUNTIES, COLO. 

gneiss cut by narrow subparallel stringers of 

quartz and pyrite. The ore is said to be 

largely concentrating ore carrying about 0.2 

ounce of gold per ton. The walls of the drift 

are coated with limonite;· stalactites of it are 

pendant from the roof; and a deposit of it 2 

to 6 inches thick covers the floor. The east 

drift was inaccessible and the west drift 

. could be followed for only 275 feet before the 

air became bad. A 150-foot crosscut to the 

south, starting from the Hecla -drift 125 

feet west of the line of the tunnel intersects 

the Barnes vein 60 feet from the Hecla drift 

and follows it ·west for at least 180 feet, to a 

shaft full of-water, beyond ,which progress was 

impossible. 

The Barnes vein, where cut in the crosscut, 

is an 8-inch vertical vein of crushed granite 

gneiss carrying a little pyrite; toward the 

shaft .it widens to 2 feet of heavily pyriteimpregnated granite gneiss. The crosscut also 

intersects, 40 feet south of the Hecla vein, a 

2-foot zone. of crushed pyrite-impregnated 

granite gneiss. 

COLUMB~ TUNNEL. 

portions contain a little sphalerite and some 

galena. Some of the copper-rich bands are 

1 to 3 inches across, and they constitute the 

richest ore. Microscopic examination shows 

that the association of chalcopyrite, tennantite, reddish-brown sphalerite, galena, and 

white quartz present in the richer portions of 

the ore is later than the pyrite which forms 

the main mass of the vein. Some speCimens of 

open portions of the pyritic ore show these 

minerals forming incrustations, in which the 

tennantite and ·quartz form well-developed 

crystals that line the vugs. The Colun1bia 

vein, like other pyritic veins, carries minor 

amounts of chalcopyrite and tennantite belonging to the earlier or pyritic mineralization. · One hundred feet east of the shaft on 

the 200-foot level the vein is 4 feet wide and 

shows in one place 2~ feet of solid sulphides. 

At 370 feet from the _portal the Columbia 

tunnel cuts a vein dipping 60° SE. and follows 

it for 60 feet to the point where it is cut off by 

an east-west fault. This vein is a 3 to 8 inch 

zone of fractured schist that carries disseminated pyrite and is traversed by a few veinlets 

of nearly solid pyrite not more than 3 inches 

wide. It has not been developed and is presumably of low grade. 

Sampling-works assays of 27 lots- of smelting 

ore aggregating 193 tons, shipped from the 

Columbia vein in 1910, show gold, 0.68 to 5 .. 52 

(average, 2.41) ounces; silver, trace to 13.33 

(average, 3.93) ounces; and copper not exceeding 4.8-per cent. 

The Columbia tunnel, on the south side of 

Nevada Gulch in the southwest part of Central 

City, extends generally S. 30° W. for about 

500 feet to the Columbia vein. On the tunnel 'level a drift on ,the vein extends 130 feet 

west of the tunnel, and a winze provided with 

a gasolin~ hoist descends to the 100 and 200 

foot levels. The vein strikes on the average 

about N. 70° to 75° E., and dips about 75° S. 

The best exposures were on the levels below BAXTER MINE. 

the tunnel, where mining was in progress at The Baxter mine is situated in Spring Gulch 

the time of survey. on. the southern outskirts of Central Citv. It 

The 100-foot level extends 35 feet west and is developed by a shaft, said to be 300 feet deep, 

130 feet east of the winze. The 200-foot level which was idle at the time of survey. 

extends 50 feet west and 160 feet east of the Sampling-works assays of 17 lots of smeltwinze. West of the Winze the vein splits into ing ore aggregating 45 tons, ~hipped in 1910, 

two branches diverging at a small angle. In a show gold, 0.29 to 4. 78 (average, 2.52) ounces; 

stope on the north fork the vein is about 3 silver, 2. 7 to 10.4 (average, 6.55) ounces; copfeet wide and consists of an irregular network per, 1.6 to 6 per cent. The mine is credited 

of stringers of nearly solid pyrite traversing . with a gross production of $120,000. 

altered granite gneiss which carries some 

disseminated pyrite. Certain parts of these 

veinlets not sharply bounded from the pyritic portions consist mainly of chalcopyrite 

and tennantite and in some of the more open 

CLIMAX MINE. 

The Climax mine is on Quartz Hill about 

three-fourths of a mile southwest of Central 

City. The development work consists of a 
GILPIN COUNTY. 23.3· 

shaft 532 feet deep connecting with 11 levels. 

The 263-foot level connects w1th the La Crosse 

tunnel. The shaft, which has an average dip 

of 75° S., follows a vein striking about N. 65° 

E. The Clima."'{ vein becomes dissipated in the 

Patch a short distance west of the shaft. 

Mineralization is of the composite type. 

tunately inaccessible at the time. of this survey. 

The stope map (fig. 34) shows their very extensive character. 

The vein as exposed on the surface parallels 

for most of its length a dike qf bostonite porphyry. (See Pl. IIIJ This relationship is 

apparent throughout most of the workings 

Hidden TN!i1SI/Le 

short 

o so 100 zoo 300 400 soo F'eet 

s. 

FIGURE 34.-Stopo map and north-south sections through shafts, California-Hidden .'I'rcasure lode. 

HIDDEN TREASURE-CALIFORNIA-GARDNER 

LODE. 

The I-Iidden Treasure-California-Gardner 

lode, on tl}e north side of Quartz Hill opposite 

N evaclavilie, is one of the strongest and most 

persistent in the district. It has been developed to a depth of 2,250 feet by the California 

. shaft, the deepest in the district. All t:P.e 

workings except the Gardner lateral from the 

Argo tunnel and a portion of the Gard:::J.er vein 

reaehed through the San Juan mine were unforand persists even as far down as the Gardner 

lateral on the Argo tunnel level. The vein 

appears to fur11ish an excellent example of 

composite mineralization, for, according to Mr. 

Geo. E. Collins, the mineralization was mainly 

of the galena-sphalerite type in the Hidden 

Treasure workings and almost exclusively of 

the pyrit.ic type in the California workings . 

Fragments on several of the clumps clearly 

show that both types of ore are later than 

the bostonite porphyry dike. . . 
234 'GEOLOGY OF GILPIN, CLEAR CREEK, AND BOULDER COUNTIES, COLO. 

As regards the distribution of pr~cious metals 

in the different ore minerals the following test 

by Rickard is· of interest: 1 · 

Metallic content of ore from Hidden Treasure-CaliforniaGardner lode. 

· Gold. Silver. 

stockwork, the ore minerals being deposited 

in spaces between the 'fragments of a breccia 

or in an irregular network of fractures. The 

area characterized by mineralization of this 

sort is known locally as the Patch and its 

origin has been the subject of much interest 

and speculation among those familiar with the 

Iron pyrites ......... : .. · ..... . 

Oz. per ton. 

0.65 

. 85 

. 90 

district. Though opened in the fall of 1888 

Oz. per ton. the main period of activity of the San Juan 4.85 

Copper pyrites ............... . 53.50 mine was from 1890 to 1894. From 1894 to 

Gray copper ................. . Blende ....................... . .16 

3.32 

3.56 

.18 

88· 65 1900 it was worked by lessees and after a 6.45, 

White quartz................. I 7. 35 period of idleness was taken over by the present Bluish quartz ................ . Flinty quartz ..... · ......... ~ .. 5· 

84 company in 1906. In 1911 a little work by 1.90 

Feldspathic gangue .......... . . 90 2. 35 lessees was in progress. 

The Gardner workings cari. be reached 

through one of the large stopes on the La 

Crosse tunnel level of the San Juan mine. 

As the workings are in bad shape the Gardner 

vein could only be explored for a short distance, 

but the exposures are particularly instructive 

in showing the transition from the true fissure 

type of mineralization to the breccia-filled type 

exemplified in the Patch. (See pp. 96-97 .) 

The Gardner lateral connecting with the 

Argo tunnel extends 250 feet east and an equal 

distance west ·of the tunnel. The vein varies 

in dip ·from 75° S. to 80° N. It follows the 

south side of a dike of bostonite porphyry. 

The other wall is schist. The mineralization in 

these laterals is entirely pyritic. At 130 feet 

west of the tunnel the vein consists of 14 inches 

o:i' pyritized and silicified porphyry, somewhat 

crushed by postmineral movement. At 120 

feet east of the tunnel it consists of 6 inches of 

crushed, pyritized schist. Sampling along 

these laterals shows in most places a gold content between 0.05 and 0.50 ounce and a silver 

content between 0.50 and 3.50 ounces. Ore 

with noticeable amounts of chalcopyrite or of 

"gray copper" (presumably tennantite) showed 

gold not exceeding 3.24 ounces and silver not 

exceeding 9 ounces per ton. I · 

SAN JUAN ,MINE, LA CROSSE TUNNEL, AND THE 

PATCH. 

The San Juan mine, about a mile southwest 

of Central City on the crest of Quartz Hill, 

is unique for the district in that most of the ore 

occurs not in fissure veins but in an irregular 

1 Rickard, T. A., The stamp milling of gold ores, p. 26, 1898. 

The San Juan mine is developed by a shaft 

916 feet deep connecting with 11 levels,· 

P.~-~~ ... ....... •o '"~- co·-~- w ~ ·z~ ff! .... " r--. w N 

W, winze 

FIGURE 35.-Plans of levels of San Juan mine, Quartz Hill. 

whose form, ta~eh from plans furnished by 

Mr~ W. C. Denison, is shown in figure 35. 

From this the large size and irregularity of 

many of the stopes is apparent and also 

(especially in levels 1 to 5) the presence of 

several northeast-southwest zones of maximum 

mineralization which have been followed by the 

development work. The San Juan workings 

could be entered only through the La Crosse 

tuimel. The chamber stopes connecting with 

the tunnel are of immense size and form one of 

the most interesting features of the district. 

The principal geologic features of the San Juan 

mine as· shown in the La Crosse tunnel workings may be understood from the following 

brief descriptions and from the plan shown in 

figure 36. · 
GILPIN COUNTY. 235 

About 585 feet from the portal of the La 

Crosse tunnel and 60 feet south of the Misf:;ouri 

vein are two pyrite veinlets one-half inc~ in 

width separated by 4 feet of brecciated mineralof clear white quartz occur in abundance. 

In the northern part of the Patch, as exposed 

in the La Crosse workings, the mineralization 

is almost exclusively of the galena-sphalerite 

~ed~anilegne~s. Thegrnn- ~~~·~~~~~~~~~~~~~~~~~~~~~ 

ite gneiss to the south is also 

'brecciated and carries quartz 

and pyrite in the interspaces 

between the fragments. This is 

the beginning of the Patch type 

of mineralization which (see fig. 

36) characterizes all of the remaining accessible parts of the 

La Crosse workings. The prevailing wall rock of the Patch 

is granite gneiss, but bostonite 

porphyry occurs at several plac·es. These rocks have been cut 

by a most irregular network of 

:fractures, forming blocks that 

in places show little differential 

movement but that elsewhere 

have been moved over each 

other and more or less rounded, 

blocks of gneiss becoming mixed 

with blocks of pegmatite or porphyry. These relations show· 

conclusively that' the mineralization was later than the intrusion of the bostonite porphyry. 

Not all portions of the breccia are mineralized. The sulphides and quartz gangue occur 

principally between the fragments of the breccia, in part as 

true fissure fillings and in part 

as replaceinen ts of the blocks 

of their crushed fl1,atrix. Where 

'the fragments have not ,been 

much shifted the replacement 

reaches a maxin1un1 at places 

·where several fractures inter-

.sect. Disseminated sulphides 

rna y be present even in the 

centers of the blocks. In one 

type of ore sphalerite is predom-

....... 

Q) 

c: 

c: 

~ ., 

0 

to 

~ 

-~ 

N 

80° 

so 100 

LEGE NO 

'EJ 

Pyritic vein 

Composite 

c.=:! 

~ veins 

(Arrows indicete direction of dip) 

The Patch 

~ Workin~ 

lnaccessf61e 

200 300Ft 

inant With a little associated FIGURE 36.-Gcologic plan showing veins and the Patch as exposed in the La Crosse tunnel 

·pyrite,'~ galena, and quartz; in and positions of the Patch on the surface and in the Argo tunnel. 

the other type the minerals are pyrite, type. Some galena-sphalerite ore persists as 

chalcopyrite, and quartz with a little anti- far as the crosscut leading into the San Juan 

·moniacal tennantite. Vugs 2 to 3 inches workings, but in the latter the pyritic type of 

.across are common, and in. them crystals ore is almost exclusively present. 
236 GEOLOGY OF GILPIN, CLEAR CREEK, AND BOULDER COUNTIES, COLQ, 

The general conclusions of the authors in across the foliation of the undjsturbed schist 

regard to the origin of the Patch have been that forms its south wall. In places along 

summarized on pages 96-97. the tunnel the Patch is a breccia of rock frag-. 

Sampling-works assays of 42 lots of smelting ments not larger than 4 feet in diameter in an 

ore aggregating 117 tons, shipped from the arkose-like matrix. The fragments are heteroSan Juan mine between 1888 and 1909, show geneous in size, in lithologic character, and in 

gold, a trace to 12.2 (average 2.09) ounces; sil- degree of rounding, most of them being anguver, 2.15 to 34 (average 6.81) ounces; copper, lar and a few perfectly rounded. Fifty fe'et 

from less than 1.5 to 9 per cent. These figures from the south border of the Patch a bowlderrepresent, of course, only the richer ore. The like mass of schist measuring 3 by 4 feet is 

gold content of :p10st of the ore in the largest of bordered by another of schi8t and pegmatite 

the San Juan.stopes is said to have ranged from 1! feet long by 6 inches wide. The surround0.44 to 0. 78 Oll.JfCe. The average value inay be ing smaller fragments are mostly granite 

placed at about $15 per ton. Ore not suffi- gneiss with their foliation oriented in different 

ciently rich to ship directly to the smelter was directions. The Patch as expos.ed in the tunnel 

treated in the Avon mill near the mouth of the is practically barren as comp.ared with tlie 

La Crosse tunnel. In this n1ill, which is San Juan :workings, sulphides being present 

equipped with 30 stamps, 6 Gilpin County in only a few small areas. 

bumpers, and 1 Wilfley table, a concentration As shown in Plate XXI,' A (in pocket), the 

of about 10 into 1 was effected. The average Patch ·is traversed on the Argo tunnel level 

value of the concentrates is said to have been by a number of pyritic ':'eins. The first of 

about $26 per ton, the larger share of the these, cut 130 feet north of the south border 

precious metal content being recovered in the of the Patch, is a l-inch seam of quartz and 

plates. · · pyrite that cuts across both "bowlders" and 

Most of the ore mined in recent years is of matrix .. The second, 50 feet farther north, is 

comparatively low grade. Ore shipped in 1910 similar in size and character. In the northern 

had the following metal content: part of the Patch 'three veins form the Kansas-

. Burroug4s group. The south member of this 

Metal content of ore shipped from the San Juan mine, 1910. group is· a 4-foot vein which is sparsely minerGold. Silver. Copper. 

Ounces. Ounces. Per cent. 

Small lot of smelting ore. · 1. 27 4.54 0.85 

Recovered as bullion 

and cone en trates 

from concentrating ore .•••••.•••.•...... . 226 . 31 --········ 

The gross production of the rnine is said to 

have been about $600,000. 

The Patch where traversed by the Argo 

tunnel has yielded no workable ore, but the 

unusually complete and fresh section there 

afforded gives a clear insight into its nature 

and origin. The Argo tu1mel traverses the 

~atch between 18,867 and 19,412 feet·from the 

portal-a distance of 545 feet. The tunnel 

lies about 1,600 feet below the collar of the 

San Juan shaft. The south border of the 

Patch is a nearly vertical northwest-southeast 

fault plane about a foot wide, of soft, crushed, 

bleached schist, carrying bowlder-like masses 

of pegmatite and gneiss. It cuts sharply 

alized with quartz and pyrite and in which an 

active water circulation is depositing limonite. 

The middle member shows 4 inches of crushed. 

gneiss carrying disseminated pyrite. The northern member shows 4 feet of quartz and finegrained pyrite. No development work has. 

been done on any of these veins. Two assays . 

of the ore showed gold 0.12 and 0.36 ounce 

and ·silver 1.4 and 3.6 ounces. Assays of 

mineralized portions of the Patch in the Argo 

tunnel show from a trace to 0.14 ounce in. 

gold and from 0.2 to 0.8 ounce in silver. 

- The Pease-Kansas vein, the first cut by 

the La Crosse tunnel, is intersected about 180 

feet from the portal. It is nearly vertical. 

and shows several sharp-walled quartz-pyrite 

veinlets 2 inches .or less in width distributed. 

through 2 feet of granite gneiss. 

The Phoenix-Burroughs vein is cut about. 

500 feet from the portal. Near its junction. 

with the Missouri vein it shows 4. incbes of 

sulphides. · In a stope about 30 feet above. 

the level of the tunnel and 75 feet east of it. 

one branch of the Phoemx-Burroughs is a. 
GILPIN COUNTY. 237 

tight vein 1 to 4 inches Wide composed of 

com·se pyrite and chalcopyrite, the latter 

coated along fractures with thin films of secondary bornite and chalcocite. 

The Missom·i vein is cut about 525 fe3et from 

the portal. It joins the Phoenix-Burroughs 

vein about 70 feet west of the tunnel and the 

Baker vein about 50 feet east of the tunnel. 

In a stope 60 feet above the tunnel level in the 

junction of the Baker and Missouri veins a 

width of 5 feet of granite gneiss is cut by an 

irregular network of.· pyrite veinlets mostly 

under 1! inches across. A veinlet of galena, 

sphalerite, and chalcopyrite one-half to 1 

inch wide traverses the center of this zone. 

In a winze at the east end of the Baker drift 

the Baker vein is 8 inches wide and shows H. 

pyrite veinlet 2 to 3 inches wide paralleled 

by several smaller ones. . At another place in 

this winze a small, sharp-walled veinlet of 

galena, sphalerite, chalcopyrite, and tennantioo 

cuts the pyrite veinlets at a small angle. 

The La Crosse l~vel of the San ,Juan mine 

connects with the workings on the Gardner 

vein, but these being in bad shape could only be 

entered for a short distance. The Gardner 

vein as exposed just west of the Patch is a 

sharp-walled fracture filled with pyrite and 

chalcopyrite. As the Patch is approached the 

vein sends off branches into the walls, .and 

these branches break up within a short distance 

into a netwqrk of very sn1all veins traversing 

the wall rock in all directions and dividing it 

into a n1ultitude of angular blocks which have 

not, however, suffered n1uch n1oven1ent with 

respect to each other. This network of veins 

passes into tho Patch, composed of angular 

fragments that have been more or less moved 

upon each other, the interspaces being partly 

or wholly filled with ore minerals and the 

fragn1ents then1selves partly replaced by sulphides. 

NATIONAL MINE. 

The N ational1nine is about half a mile southsouthwest of Central City, on the west side of 

Spring Gulch, and appears to be on the westward continuation of the Mammoth vein. The 

shaft follows the vein, whose dip in general 

varies ·from vertical to 80° S. Three levels 

were studied at depths of 290, 350, and 400 

feet, their lengths being 490~ 280, and 200 feet 

respectively. The vein as exposed in these 

workings ranges from 2 to 8 feet in width and is 

one of the most heavily mineralized fractures 

seen in the district. A particularly clean exposure in a stope above the 35o:..foot level 50 feet 

west of the shaft showed the follo~ing sequence 

from north to south: 

Section of National mine on 350foot level. 

North wall. Inches. 

Post mineral slip plane composed of crushed gneiss 

and pyrite ............................ ---.--.. 1-2 

Gneiss, brecciated and carrying some fine disaeminated pyrite .... ____ .. __ . __ ...................... 6-12 

Granite ·gneiss, silicified and carrying abundant disseminated pyrite. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 

Nearly solid pyrite, with small amounts of gray 

quartz, chalcopyrite, and tennantite............ 36· 

South wall; gneiss carrying disseminated pyrite. 

Other exposures of the vein show similar 

features but generally lesser widths. In places 

there are several bands of nearly solid sulphides 

instead of one. In many places vugs are 

numerous, and the copper minerals seem to be 

more abundant near them than elsewhere. 

One vug on the 400-foot level, measuring 6 by 

4 inches by 2 feet, lies in gneiss carrying 

disseminated pyrite and is lined with quartz 

crystals, some of which are one-half inch in 

diameter. 

The highly pyritic ore of this vein is too low 

grade to·be worked at a profit. By the present 

operators the ore as hoisted is sorted, the purely 

pyritic portions are discarded, and only the 

portions carrying chalcopyrite, tennantite, or 

both, are saved. 

IVANHOE VEIN. 

The· Ivanhoe vein is on the north slope of 

Alps Hill south of the east end of Kings Flat. 

It is developed by several shafts, none of which 

could be entered in 1911. The vein strikes a 

few degrees north of east and on the surface 

dips 75° N. It is strongly 1narked in the 

granite gneiss, but just west of the Ivanhoe 

shalt it dies out on entering an area of schist 

of the Idaho Springs formation. 

All ore seen on the dumps is of the. galenasphale.rite type, carrying dark sphalerite, galena 

chalcopyrite, and a little pyrite, associated with 

dark-gray cherty· silica. Some of the ore has 

been brecciated, angular fragments of sulphides 

lying embedded in a matrix of altered country 

rock. (See Pl. XIV, B, p. 97 .) 

Ten lots of smelting ore aggregating 11 tons, 

shipped between 1898 and 1902, showed, accord-
I ' 

238 GEOLOGY OF GILPIN, CLEAR CR.EEK, AND BOULDER COU~TIES, COLO. 

ing to sampling-works returns, gold, 0.1 to 

0.9 (average 0.59) ounce; silver, 7.62 to 21.4 

(average 13.95) ounces; lead, 10.9 to 54.1 per 

cent; and zinc, 8 to 18 per cent. 

KENT COUNTY VEIN. 

The Kent County vein, on the north slope of 

Quartz Hill south of the California vein, was 

one· of the first to be discovered in the district 

(1859). It is opened by several shafts, none 

of which were accessible in 1911. The vein 

trends about east and west and appears to be 

the westward extension of the Ralls County 

and East Kent veins. The surface rock is 

granite gneiss, though it is reported that 

porphyry is found on the hanging wall of the 

fifth level and possibly elsewhere. The main 

shaft is said to be 1,17 5 feet deep along the 

dip of the vein and to have 12levels, the longest 

of which, the fifth or 500-foot level, extends 

1,500 feet west of the shaft. It is reported 

that the vein is from 2 to 20 feet wide, consisting of altered wall rock carrying disseminated pyrite and. traversed by veinlets composed of galena, sphalerite, and chalcopyrite. 

Several branches; making in to both foot and 

hanging walls, strike about parallel to the 

Kent County vein but dip more steeply. The 

main ore shoot is said to have begun on the 

second level west. of the shaft and to have 

extended nearly to the eighth level. 

Data are not at hand for a satisfactory estimate of the value of the ore. . The gross production of the mine is variously estimated at 

$500,000 to $800,00'0, but the higher figure is 

possibly more. nearly correct. 

RALLS COUNTY MINE. 

The Ralls County vein is developed by the 

lEtna and Ralls County shafts on the north 

side of Quartz Hill near its summit. The 

' lEtna shaft was idle at the time of this survey, 

but the Ralls County shaft, said to be 700 feet 

deep, was accessible on three levels, of which 

the 500-foot level was the lowest. In 1911 

some work was being done on the 300-foot 

level, and the 180-foot level could be entered 

for a short distance west of the shaft. 

The country rock throughout the mine is 

granite gneiss. The vein in general strikes 

nearly east·and· west and dips 62°-75° S. It 

ranges in width from 1 to 6 feet, with an average of about 3 feet. On the 180-footlevel, 200 

feet west of the shaft, a small branch vein 

dipping 60° S. goes into the south or hanging 

wall. On the 300-foot level the vein splits 230 

feet west of the shaft and comes together again 

170 feet farther west, the horse between the 

two portions, being about ·15 feet wide and 

somewhat mineralized throughout. On the 

500-foot level the drifts are caved 240 feet east 

and 120 feet west of the shaft. 

The vein may be described as a zone of 

crushed and altered ·granite gneiss impregnated 

with pyri~e and cut here and there by stringers, 

composed of chalcopyrite and a lit'tle gray 

copper. In so·me parts of the vein a later 

mineralization took place, as is particularly 

well shown west of the shaft in the main ore 

shoot, where the pyritic vein is cut in several · 

places by veins 8 inches ·or less in width composed of· dark-gray quartz, galena, sphalerite, 

and chalcopyrite. This ore shoot presumably 

extends above the third level in the stopes now 

inaccessible and appears again on the 180-foot 

level, where the vein is stoped to the shaft. 

The shoot is not cut in the part of the fifth 

level now accessible, but it may have been cut · 

west of the shaft at some point beyond the 

cave in the drift. 

Some postmineral movement along the vein 

subsequent to the galena-sphalerite mineralization is indicated by the blackened gouge observed along both foot and hanging walls at 

many parts of the mine. The ore itself is 

sheared in some places, or is cut by small slip 

planes. 

· The gneiss carrying disseminated pyrite 

which forms the concentrating ore is said 

to carry' in the west fifth level about 0.37 

ounce gold per ton. Some smelting ore, presumably the chalcopyrite-rich ore from the 

stope on the south part of the vein in the 

west third level, carried about 0.75 ounce 

gold, 13 ounces silver, and 9 per cent copper 

per ton. In a number of shipments of smelting 

ore made in 1905 and 1907 the sampling-works 

assays showed from 0.54 ounce to 2.08 ounces 

of gold, 9.1 to 16 ounces of silver, and from 2.5 to 

10. 3 per cent of copper. No figures are available for a comparison between the value of the 

purely pyritic ore and that containing galena 

and sphalerite of t4e second mineralization. 

The total production of the Ralls County 

mine is estimated by the company to be about 

$225,000, most of which has come from: the 
GILPIN COUNTY. 239 

westward-pitching ore shoot above the. third 

level. 

EGYPTIAN MINE. 

The Egyptian mine is about a mile southwest 

of Central City near the summit of Quartz 

I-Iill. It is developed by an inclined shaft 

880 feet deep, connecting with levels at 100, 

200,. 300, 400, 500, 600, and 700 feet. The 500, · 

600, and 700 foot levels were UJ1der water at 

the time the mine was studied, and the 100 

and 400 foot levels could not be entered for 

other reasons. The wall rock exposed on the 

200 and 300 foot levels (see fig. 37) is almost 

exclusively granite gneiss. · 

As exposed at the shaft on the 300-foot level 

the North or Shaft vein is 8 to 14 inches wide 

and consists of several subparallel veinlets 

of pyrite, sphalerite, and gray quartz. The 

widest of these veinlets is 3! inches. The 

Sh~t vein has not been extensively worked. 

R, re'ose 

!;0 

I 

100 

I 

Well rock is meinly 

grenite gneiss 

1 

FIGURE 37.-Plan of 200-foot. and 300-foot levels of Egyptui.n mine. 

Surveyed by lland compass and pacing. 

Between it and the South vein occur a number 

of unimportant branch veins. 

The South vein, which· has yielded the bulk 

of the mine's production, is well exposed in a 

stope nearly 100 feet aboye the east end of the 

300-foot level, where at one point it has a width 

of about 5 feet, the ore filling a brecciated zone. 

One vein of solid sulphides is 15 inches wide 

and incloses in places angular fragments of 

the wall rock. The primary ore minerals are 

galena, sphalerite, and chalcopyrite. In the 

more open portions of the vein some chalcocite, 

developed from chalcopyrite, by downward 

sulphide. enrichment, occurs as thin films 

along fractures in the chalcopyrite. · 

Postmineral movement along the South vein 

has in places crushed the ore and neighboring 

wall rock, producing a breccia of angular 

ore fragments in a groundmass of crushed and 

recemented granite gneiss. 

Sampling-works assays of 18 lots of smelting 

ore aggregating 63 tons, shipped between 

1899 and 1909, inclusive, show gold, 0.28 

to 5.77 (average 2.98) ounces; silver, 2.7 to 

22.3 (average ·12.33) ounces; copper, 9.5 per 

cent or less.· Similar assays for 154 ·tons of 

smelting ore shipped during 1910 show gold, 

0.64 to 5.48 (average 2.4) ounces; silver, 2 to 

23.5 (average 17.35) ounces; copper, 4.65 per 

cent or less. 

ILLINO.IS MINE. 

The illinois mine, one of the oldest mines of 

the region, is about a mile southwest of Central 

City near the crest of Quartz Hill. The property, formerly lmown as the North Star, was 

discovered in Mayor June, 1859, and its surfaceoxidized portions yielded large returns in gold 

to placer mining. Its app'earance in 1870 is described in a report. by Hague.1 

The vein appears to have a course of N. 60° E., true, 

though its average course for a longer distance than that 

observed is said to be more to the e~stward, and thus more 

nearly parallel with the other neighboring lodes farther 

south, that trend north 85° E. Its dip is 84° S., and so far 

as sunk upon is very regular. The average width is about 

2 feet, frequently expanding or contracting to greater or 

less dimensions. Its walls are genei·ally smooth and well 

defined, sometimes polished, grooved, or striated, showing 

indications of movement. usually there is a soft "gouge," 

.or seam of clay, between the walls and the filling of the 

vein. The latter is chiefly quartz; sometimes white, hard, 

and amorphous, carrying little or no valuable mineral; 

sometimes showing a sparse distribution of crystalllzed 

iron pyrites throughout its mass; but most commonly the 

vein matter is a :rp.ixture of siliceous and feldspathic material, in which occur small seams or scattered particles of 

pyrites, making a very fair quality of stamp rock, and as 

in the other veins already described associated usually 

with a narrower but solid seam of compact pyritous ore. 

The latter is from 2 or 3 to 10 or 12 inches thick, and furnishes a small proportion of smelting ore. This proportion 

appears, from all available data, to be between one-twentieth and one-tenth of the whole number of tons produced. 

The valuable mineral·in the vein consists chiefly of iron 

pyrites with a lesser proportion of copper pyrites and as a 

characteristic feature some arseuical pyrites; with these 

are associated some zinc blende and galena. The yield of 

this ore in silver is shown by the assays of Prof. Hill to be 

larger than is usual in the pyritous ore veins of the district, 

the average of 42 tons sold by the mine at the smelting 

works during the summer of 1868 being about 4 ounces of 

fine gold and 20 ounces of fine silver to the ton. The yield 

of stamp rock during a run of 34 weeks in the summer of 

1868, when 200 cords, or 1,500 tons, were supposed to have 

been treated, was 1,538 ounces of crude bullion, or about 

1 ounce per ton. The average value of the ounce of this 

bullion is stated at $15.50, coin. 

1 Hague, J.D., U.S. Geol. Expl. 40tll Par. Rapt., vol. 3, pp. 524-525, 

1870 .. 
240 GEOLOGY OF GILPIN, CLEAR CREEK, AND BOULDER COUNTIES, COLO. 

At present the shaft is 635 feet deep with GERMAN AND BELCHER MINES. 

levels about every 100 feet. Most of the ore The German and Belcher mines are, on the 

above the 300-foot level has been stoped. For summit· of Quartz Hill about I! miles souththe past 20 years the property has been worked west of Central City. The underground workonly on a small scale by lessees. It was idle at ings of the two mines are connected at the 

the time of this survey and could not be en- first and second levels and being under one 

tered. The maps indicate that the workings ownership are worked as one mine. The 

develop two and possibly three veins. Ore German shaft is 600 feet deep, with an average 

seen on the dump showed only pyrite and chal- dip of 80° S., and with. levels at 130, 250, 400, 

copyrite. A pyritic vein supposed to be th~ and 50_0 fe~t. Stoping has been confined 

Illinois is cut by the Argo tunnel 18,088 feet principally to ground above the 130-foot level. 

from the portal and has been drifted on for 30 Development work on the uranium ores was in 

feet east and 50 feet west. progress at the time of this survey. The writer 

The following are a ·few sampling-works is indebted to Mr. 'James Force, consulting 

assays of smelting or.e: engrneer in charge at the time of this survey, 

for information as to the ore values and for Sampling-works assays of smelting ore from the Illinois mine. 

personal guidance in the study of the mine: 

The vein as exposed in most parts of the Silver. Copper o · mine strikes about N. 75° E. arid dips 75°-80 Year. Ore. Gold. 

----I----I-----I----I--- S. That mineralization is not confined to this 

Pounds. Ounces. 

1 893 ......... 8,390 2.10 

1 893 ......... 2,305 1. 58 

1 897 ......... 2,1327 2.12 

1 903 ......... 4, 743 1.50 

1 908 ......... 2,450 . 68 

Ounces. 

6.70 

5.50 

8.10 

6.50 

4.80 

Per cent. ................... 

2.90 

3.90 

3.60 ............ 

zone is shown, however, by the occurrence on 

the 130-foot level, 15 to 20 feet west of the 

shaft, of a 6-inch band of pyritized and silicified 

schist that strikes N. 35° E. and dips about 

15° NW. This is said by Mr. Force to assay 

The total gross production is said to be about 0·

39 per cent of uranium oxide. 

The wall rocks of the vein are mainly schists 

$

350,

000· GAUNTLET MINE. of the Idaho Springs formation and associated 

pegmatite. Exceptionally, as on the 400-foot 

level west, there is a small amount of granite 

gneiss. At the face of the 500-foot level west 

a 3 to 6 inch dike of bostoni te porphyry comes 

into the drift from the hanging wall and is 

sharply cut off by the vein, which is cle~rly 

later than the dike. A larger bostonite 

porphyry dike is exposed on the 500-foot 

level about 97 feet west of the shaft and is 

also cut off sharply by the vein; it is followed by 

a crosscut. (Se~ p. 241.) 

In general the mineralization ·in the German 

mine is of the composite type modified by the 

deposition of uraninite. In places, as on the 

Sampling-works assays of smelting ore from the Gauntlet 300-foot level west, the vein is a typical fissure 

mine. filling; but in most parts of the vein metasoThe Gauntlet mine is about .three-fourths of 

a mile southwest of Central City near the head 

of Spring Gulch. The development consists of 

two 500-foot shafts about 300 feet apart, connecting with about 3,000 feet of drifts. None 

of the workings were accessible at the time of 

this survey. Ore seen on the dumps was of the 

pyritic type with some tennant~te, but assays 

show that considerable galena was locally present. The average value is said to be about $10 

per ton. 

The following are sampling-works assays of a 

few l?ts of smelting ore: 

Year. Ore. 

matic replacement proceeding outward from 

Gold. Silver. Copper. Lead. small fractures has been equally as important 

----I----I--- a mineralizing process. Two exposures may 

Net lbs. 

1,644 

3, 778 

2, 512 

6, 742 

1,414 

Ounces. 

1.40 

1.40 

1.54 

3.02 

2.00 

1.10 

2.53 

Ounces. Per cent. Per cent. 

1889 ..... . 8. 80 . . . . . . . . 20.50 

1894 ..... . 1895 ..... . 1895 ..... . 1906 ..... . 1906 ..... . 1906 .... .. 843 

1,463 

8. 00 4. 70 

8. 40 . .. . . . . . 11.00 

12.80 5.35 48.00 

2. 20 12.00 ....... . 6. 50 3. 00 ....... . 21. 70 10. 00 ....... . 

be described to show the commoner characteristics of the vein. 

In the stope 65 feet east of the shaft on. the 

130-foot level the vein forks upward lik~ the 

letter Y, one' · branch · following each wall. 

The footwall branch is only 2 inches wide; the 
GILPIN COUNTY. 241 

hanging-wall branch is 10 inches wide and the Bushwacker vein, a small vein which in 

consists of altered wall rock silicified and heav- places shows only pyrite but elsewhere carries 

. ily ilnpregnated with pyrite and to a less degree also galena and sphalerite. Where cut, at 

with sphalerite. Sphalerite, chalcopyrite, and about 26 feet from the main drift, the Bushpyrite, with son1e galena, form narrow veinlets, wacker strikes N. 80° E. anq dips 65° N. 

near the. hanging wall and irregular lenses or Only low-grade uranium ore, in which the 

bunches elsewhere in the dissen1inated ore. pitchblende could not readily be identified, 

Both the dissetninated or replacen1ent. ore was exposed ~n the workings at the time of this 

and the sulphide veinlets are travei'sed by survey. Such ore cons~stsof schis,torpegmatite 

partly open fracture semns a fraction of an filtered and highly impregnated with pyrite, 

inch wide, .lined with crusts one-sixteenth to with lesser amounts of sphalerite, and with 

one-foutth inch thick, of which the inner or still sma.ller amounts of pitchblende, giving 

under part is conunonly rosin sphalerite fVlely it a content commonly of from 0.25 to 0.5 per 

banded parallel to the walls and the outer cent of uranium oxide. It forms an intimate 

part finely crystalline pyrite con1n1only showing part of the sulphide vein and would. form the 

botryoidal surfaces and in cross. secti~n a concentrating ore of the mine. A specimen of 

radiate structure .. 'The free surface of the such ore from the 130-foot level west, said to 

pyrite is a 1nass of 1ninute crystals. assay about 0.39 per cent uranium oxide, was. 

No pitchblende was seen by the writer in altered schist of the Idaho Springs formation, 

place on this level, but one san1ple across the highly impr~gnated with pyrite (in many 

entire vein in the stope 130 feet east of the places in well-formed crystals) and with some 

. shaft is Sttid by :Mr. Force to have assayed 0:39 sphalerite. The foliated structure was .still. 

per cent urn.nium oxide, and a second' san1ple preserved in places. Microscopic study showed 

across 3.3 feet of vein 1naterial assayed 0.5 per that the· rock had suffered practically comcent uraniun1 oxide, 0.02 ounce in gold, and plete recrystallization, the .principal changes 

0.2 ounce in silver. being the extensive development of pyrite, 

At the face of tho 250-foot level, 124 feet the alteration of biotite to chlorite, and tho 

west of tho shaft, tho vein clips 75° S. between replacement of feldspar by sericite and chlorite. 

walls of pegmatite. Next tho south or hang- 'To judge from the statements of thos(:} faing wall is a 1 to 1i inch band of clark-gray miliar with the mine and by .analogy with 

highly siliceous material, probably altered neighboring veins bearing uranium, .tho highpegmatite, highly impregnated with pyrite, grade pitchblende ore occurs as irregular 

usually in s1nall cubes, and carrying a little masses in the low-grade dissemina~ed ore just 

sphalerite. Below this is 10 inches of peg- described. 'The largest piece known to have 

matite less heavily impregnated with pyrite; been found in the mine came from the 130-

succeedod by a 1!-inch vein of solid pyrite and foot level west, weighed 240 pounds, and was 

sphalerite. Where pyrite impregnates the 88 per cent uranium oxide. According· to 

pog1natito it is usually in well-formed crystals Rickard 1 ''the more solid pitchblende, either · 

lying in a matrix of quartz and altered feldspar. in lens form or in a well-defined streak, seldom 

Whore sphalerite is also present in sucli ore it exceeds 3 to 4 inches in width." 

partly or completely replaces this matrix and A specimen of the rich pitchblende ore of 

was apparently introduce,d later than the py- this mine presented to the Geological Sur:vey , 

'rite. On tho 300-foot level west tho vein is a by Mr. Hugh C. Brown is particularly inmore typical fissure filling, and· galena and structive. It consists ,principally of pitchsphalerite are the principal sulphides. An blonde, but this mineral is sharply cut by 

assay of a band of ore from the south wall gave, veinlets one-eighth i:Ifch or less in width comaccording to Mr. Force, gold, 2.12 ounces; silver, posed of sphalerite, pyrite, and some galena. 

10.9 ounces; and uranium oxide, 0.015 per cent. An enlarged view of some of ·the smaller veinOn the 500-foot level 97 feet west of the lets as seen under the reflecting microscope 

shaft a crosscut extends N. 35° W. for 102 is shown in figure 13 (p. 124). Similar relations 

feet. It follows a fracture zone along the in another specimen are shown in Plate XIV, B. 

west side of a dike of bostonite porphyry and al ll 1 Rickard, Forbes, Pitchblende from Quartz Hiii, Gilpin l.)•,tmty, 

cuts sever Sina unin1portant ,veinlets and Colo.: Min. and Sci.. Press, vol.IOG, p. 854,1913. 

44214°--17----16 
242 GEOLQGY OF GILPIN, CLEAR CREEK, AND BOULDER COUNTIES, COLO. 

Another specin1en of rich ore from the 130-

foot level west, presented by :Mr. Force, shows 

under the reflecting microscope pitchblende in 

botryoidal forms, fractured and traversed by 

minute later veinlets that are predominantly 

pyrite, chalcopyrite, and dark-gray quartz, but 

that contain also some galena and sphalerite. 

In the more shattered portions fragments of 

pitchblende lie in a matrix of these sulphides. 

A specimen presented by Mr. W. C. Denison 

of Central City shows portions of a vein at least 

2 inches wide consisting of a granular aggregate 

of pyrite and gray quartz inclosing broken 

fragments of pitchblende which locally form 

as much as 25 per cent of the materinJ.. Neither 

the pyrite not the quartz is shattered, .but the 

pitchblende fragments have clearly been broken 

from larger botryoidal or globular masses, for 

some of them show very ragged fractured faces. 

A specimen from the German mine in the 

mineral collection at tl~e State capitol in Denver 

shows pitchblende and chalcopyrite so intimately intergrown as to leave little doubt of 

their contemporaneity. 

All these relations indicate that after pitchblende (sometimes accompanied by pyrite) 

was deposited the vein was fractured and later 

galena, sphalerite, chalcopyrite, and pyrite 

were introduced. 

In regard to the content of the ore in uranium 

and other metals Rickard 1 says: · 

Where the vein reaches its maximum width, the proportion of uraninite is inversely small, though for the 

whole width (apart from the high-grade bunches) the vein 

carries sufficient pitchblende to constitute a grade of ore 

for concentration; from 2! to 4 per cent U30 8 • Concentration tests now in progress are proving satisfactory and give 

encouragement for the erection of a reduction plant on the 

mine premises. 

Assays of concentrates of ores from German and Belcher 

mines. 

Weight. Gold. Silver. Copper. 

Uranium 

oxide. 

Slime con- Pounds. Ounces. Ounces. Per cent. Per cent. 

centrate .. 140 21. 75 12.40 0.61 18.79 

Jig concentrate ...... 300 6.49 6.00 1. 17 2.34 

Slime tailings ....... 160 . 43 4.30 1.58 2.20 

Assay of coarse concentrates from German and Belcher 1nines. 

Gold .................................... ounces.. l. 50 

Silver ...................................... do.... 3. 7l 

Copper ................................ per cent. . l. 42 

Lead ... ---- ............................... do.... . 65 

Silica ..................................... do .... 10. 60 

Iron ...................................... do .... 36.69 

Sulphur .................................... do .... 41.05 

Uranium oxide ............................. do.... 3. 22 

Assays of uranium ores from, German and Belcher mines. 

UraGold .. Silver. Zinc. nium 

oxide. 

130-foot level: Otmces. Ounces. Per ct. Per ct. 

90 feet east of 

shaft ........... None. None. ........... l. 47 

10 feet east of 

shaft ........... 0. 12 0.60 ............. 1.'38 

500-foot level ........ l. 20 21. so 12. 95 l. 10 

Sampling-works assays of sn1elting ore 

shipped in 1909 are given below. This ore was 

sold solely for its precious-n1etal content, the 

uranium content not being detern1inecl. 

Sampling-works assays of smelting ores from German and 

Belcher mines, 1909. 

.--------~------~·--------~------~----~-

Ore. Gold. Silver. Copper. L Lead. 

Net tons. Otthces. Ounces.. Per cent. Per cent. 

3. 122 2.09 7.44 ................... .................... 

l. 596 2.86 9.60 ................... .................. 

1. 305 . 46 6. 90 .................. 9. 70 

3. 337 . 31 4.00 ................. ................ 

1. 286 3.40 9.00 0.50 .............. 

2.413 5. 99 13. 64 . 95 ............... 

3.580 2.00 12.00 1.80 ............. 

6. 205 l. 30 2. 30 ................ .............. 

. 907 4.00 21. 60 1. 90 ............... 

1.443 3. 46 11. 30 1.50 ·--------· 3. 270 . 76 2.00 ---------- ................. 

Outside of the general policy of development adopted 

by the management, a small amount of pitchblende ore 

is being mined. By crude hand sorting within the shaft 

hol~se, there is now being produced, in small but increasing 

quantity, a selected grade of pitchblende carrying 15 to 

60 per cent uranium oxide (U30 8). An average of approximately 30 per cent U30 8 is established and can probably 

be maintained in quantity of several tons per annum. 

The bulk of ore suitable for ffiin treatment accumulates 

in the proportion of something like 40 tons to 1 ton of 

"selected pitchblende." According to a recent report by the Bureau 

According to Mr. Force various classes ·of of Mines: 1 

concentrates obtained in milling tests on the ' The total production of pitchblende ore from the two 

lower grades of ore from the mine assayed as mines from the fall of 1911 to January 1, 1913, has been 240 

follows: 

1 Rickard, Forbes, op. cit., p. 854. 

1 :Moore, R. D., and Kithil, K. L., A preliminary report on uranium, 

radium, and vanadium: Bur. :Mines Dull. 70, p. 45, 1913. 
GILPIN COUNTY. 243 

pounds of high-grade ore containing·more than 70 per cent The Barnes vein, as exposed on the 100-foot 

UaOs, 220 pounds of ore containing 20 per cent U30s, 5 tons level, is most heavily mineralized near.its june::. 

of ore carrying 2.6 per cent UaOs, and 1 ton of ore carrying tion with the Gibson vein and south of this 

2 per cent U308• 

MITCHELL MINE. 

The Mitchell mine is in the southeast side of 

Quartz I-Iill about a 1nile southwest of Central 

City. Tho vein, which appears to strike nearly 

east and west, is developed by a shaft said to be 

500 feet deep. Ore seen in the bins consisted 

of pyrite· and chalcopyrit(;) in granite gneiss 

wall rock. Smne pitchblende ore is said to 

hu,ve been found in tho western part of the 

vein. 

SCANDIA MINE. 

The Scandia Inine is on the east slope Of 

Quartz I-Iill a little over a 1nile southwest of 

Central City. The developn1ent consists of a 

shaft and a tunnel, neither of 'vhich could be 

entered at the time of survey. The only ore 

seen on the dmnp consisted of pyrite in a 

quu,rtz gangue. The 1nine has been idle for 

many years. 

BARNES MINE. 

junction is practically b~rren. The same junction is exposed on the 150-foot level about 

7 5 feet southwest of the shaft. The east-west 

vein near this junction is 6 inches to 1 t feet in 

width, is sharp walled, and consists of pyrite 

and some chalcopyrite; pyrite is also disseminated in the bordering granite gneiss. At A, 

figure 38, a little farther west, a mass of 

smelting ore left along the south wall of the vein 

is 7 inches in 'vidth and shows sharp walls. It 

consists of pyrite and chalcopyrite, the latter 

in many places covered with a black pulverulent 

coating, probably chalcocite. Exceptionally 

son1e 1nalachi te and tennan ti te are present. 

Vugs are lined with quartz and very perfect 

cubes of pyrite. On the 200-foot level the 

junction between the two veins is not clearly 

shown. At a point 40 feet east of the shaft on 

tllis level the vein is lincommonly wide and 

consists of 5 feet of granite gneiss cut by a network of sharp-walled veinlets of pyrite and 

The Barnes 1nine is at the east end of Quartz chalcopyrite 2 inches and less in width.· 

I-Iill near the main road fron1 Central City to At the time. of survey the mine was bei~g 

ISO -f'oot level 

placGd in shape for further work after a long 

period of idleness. It was instructive to note 

that during the shutdown iron rails on the 

200-foot level.had in places been eaten away 

and in part replaced by native copper through 

the action of strong 111ine waters descending 

through the vein and collecting in pools on the 

floor of the drifts. These pools were deep blue~ 

l~IG\Jltl~ 38.-Plan or upper levels of Barnes mine. Surveyed by hand green in COlOr and probably Carried COpper and 

compass and pacing. iron sulphates in abtlndance. 

Russell Gulch. The developmei1t work consists In working the upper levels of this mine only 

of a shaft with levels at depths of 100, 150, 200, the richest ore was saved and 1nuch material 

·250, 325, 400, and·500 feet. After a period of carrying abundant sulphides was left as stope 

idleness the mine was being reopened in 1911, filling. It is the intention of the present 

but at the tin1e of this survey the 400 and 500 operators to ship much of this filling. Films 

foot levels, the longest in the mine, were still of pulverulent secondary chalcocite were recogunder water. The wall rock is entirely granite nized on fractured chalcopyrite in n1any of the 

gneiss. drifts, and it is evident that chalcocitization has 

In general the workings clown to the 325-foot inereasecl somewhat the copper content of the 

level 1nay be said to develop an ore shoot ores. 

fonned by the junction of the northeast- Sampling-works assays of 14 lots of s1nelting 

trending Barnes vein and an eastward-trending ore aggregating 108 tons, shipped from this 

lode. The latter lode, as exposed on the surface, mine bet\veen 1893 and 1907, showed gold, 

consists of the Gibson and the Stark County 0~27 to 2.68 (average 1.19) ounces; silver, 4 to 

veins, nearly parallel in strike but with slightly' 17.4 (average 11.81) ounces; copper (wet), 3 to 

divergent clip, which unite a short distance 9.55 per cent; silica, 31 to 52 per cent in Slots. 

below the surface. The gross production of the mine is not known. 
'244 GEOLOGY OF GILPIN, CLEAR CREEK, AND BOULDER COUNTIES, COLO. 

DELMONICO VEIN. 

The Delmonico vein crops out near the summit of Alps Hill and is· developed by a shaft 

which is said to be 1,100 feet deep but which 

was idle and inaccessible at the time of this 

survey. The ore seen' on the dump showed 

pyrite, sphalerite, galena, and chalcopyrite. A 

few sampling-works assays of smelting ore 

follow. 

Sarnpling-works assays of smelting ore frorn the Delmonico 

vein. 

Year. Ore. Gold. Silver. Copper. Zinc. Silica. 

-------------------

Net lbs. Ounces. Ounces. Per cent. Per cent. Per ct. 

1903 .. 8, 727 4. 36 3. 10 4.50 . ......... 36 

1904 .. 4, 738 4.04 24.40 4.60 . ....... 32 

1907 .. 6,028 5. 15 46.55 8.50 11. 00 .. ...... 

1907 .. 4,236 3.40 48.60 10.00 ............. ........ 

been mined, but none of the ore was seen by 

the writer. The following account of the occurrence and production of the uranium ores 

is taken from a recent report of the Bureau of 

Mines: 1 

The original workings of the Kirk mine are about 100 

feet deep. The majority of these have been filled up. 

In this manner the larger part of the 500 feet of the lode 

to the east of the shaft has been worked out to the above 

depth, but the 1,000 feet to the west has not been opened 

except by prospect holes. An old shaft and part of the 

workings are still open. In this shaft and workings a 

considerable amount of pitchblende was mined in the 

early days. The miners did not know at the time. what 

the ore was and it was wasted in an attempted treatment 

for gold. When the pitchblende was found the gold gave 

out, and therefore the owner left his shaft and started a 

new one 185 feet to the west, which is now the main shaft. 

The next owners knew the value of pitchblende and about 

1898 took out several tons of good ore. When further 

development was unsuccessful the mine was bought by 

the present owner. The mine is_more than 400 feet deep. 

ALPS MINE. The vein strikes almost clue east and west and dips-about 

80° S. The shaft follows the vein. The main levels are 

The Alps inin·e, on the summit of Quartz at 97, 140, 200, 300, and 400 feet. 

Hill on what appears to be the eastward con- The Kirk lode is 3 to 6 feet wide, and seems to be a fistinuation of the Deimonico vein, was inacces- sure vein in gneiss and mica sclpst. It carries gold, silver, 

and copper in addition to pitchblende. The best pitchsible at the time of this survey. Although blende ·was- found between the 140-foot level and the 250-

only ore of the galena-sphalerite type was seen foot level on the east side of the shaft. Ore was als~ found 

on the dump it is said that the ore of the at other places, notably ju.st above the 400-foot level an.d 

deeper levels was mainly of pyritic type. The in this level. The ore shoot seems to pitch from east to · west. Except in one place the ore was everywhere against principal development is said to have followed the country rock on the hanging wall. There were pracnot the Alps vein but a vein with more north- tically no stringers, spurs, or other indications that the 

erly dip develope.d by a winze 520 feet deep vein was near except that the country rock carried some 

·on the 800-foot level, 360 feet west of the shaft. uranium. Much of the ore was exceedingly rich, some 

Some uraninite is reported to have been found assaying 60 to 80 per cent U30;. At places this rich ore was a foot thick; one single piece was removed that meas-' 

in this mine, but no important amounts of ured 2 feet 8 inches by 1 foot 4 inches by 1 foot. 

that mineral have been shipped. Reliable data on the production of pitchblende from the 

Sampling-works assays of 43 lots of smelting Kirk mine before the present ownership could not be deore aggregating 148t tons, shipped from the termined. Since the present owner has had the mine, in 

Alps mine between 1888 and 1909, show gold, ·round numbers about 20 tons of ore wlth an average con- tent of 35 per cent U30 8 and something over 100 tons of ore 1.92 to 11.45 (average 4.79) ounces; silver, 2.3 with a content of 3 to 4 per cent U30 8 have been mined. 

to 38.33 (average 23.07) ounces; copper from Most ofthis ore was produced in 1905-6, and practically all 

less than 1.5 to 9.6 per cent. The average of the high-grade ore was sold abroad. 

value of 77 tons of smelting ore shipped in 1909 Therefore, at a tjme when the Austrian mines were apwas gold 4.53 ounces, anQ. silver 17.

28 ounces. parently the only producers of uranium ore the Kirk mine , was sending pitchblende abroad and· supplying a large 

KIRK VEIN. proportion of the radium that was sold on the open market. 

Dur~ng the last few years the Kirk has not been worked 

The Kirk vein is on the south side of Quartz regularly; therefore the production of ore has been small. 

Hill. Access could not be had to the under- Several ·lots of gold-silver smelting ore 

ground workings, but the dumps and surface shipped from the Kirk mine at various times 

exposures were examined. The ore on the between 1905 and 1910 gave the following 

dump consisted dominantly of pyrite, chalco- sampling-works assttys: 

pyrite, and tetrahedrite, but a few specimens ------~--------------

1 M:oore, R. B., and Kithil, K. L., A preliminary report on uranium, 

carried a little galena. Uranium minerals have radium, and vanadium: Bur. Mines Bull. 70, pp. 43-44,1913. 
GILPIN ·COUNTY. 245 

Sarn1Jling-1.oo·rks assays of smelting ores front Kirlc rnine, 

1905-1910. . 

Year. Ore. Gold. Silver. Copper. Silica. 

Net lbs. Otmces. Ounces. Per ct .. Per ct. 

1905 ........ 4,520 2.00 3. 00 46 

1905 .......... 5,506 . 30 7. 70 . ........ ......... 1900 ........ 1,970 1. 75 16.25 9.00 45 

1908 .... · .... 25,443 1. 46 14. 45 4. 70 33 

1908 ........ 9,457 .43 3. 09 . ........ ........ 1910 ........ 1, 724 . 86 16. 70 . 60 

1910 ........ 4.689 . 69 11.. 29 2.:10 

1910 ........ 1;606 . 81 11. 1.9 3.32 ········ 

Concentrating ore shipped in 1910 is said to 

hn,:vo n,:verugecl gold 0.10 ounce and silver 0.50 

ounce. 

NORTH MINE. 

Tho North n1ino is on the east slope of Quartz 

flill about a mile southwest of Central City. A 

shnJt now :in ruins .develops a pyritic vein striking nbout N. 70° E. and dipping about 85° S. 

Tho walls are granite gneiss. 

GEM MINE. 

to 5 tons in weight in the sulphide ore. The 

relations of the pitchblende to sulphides in the 

ore from this mine have already been described 

on pages 123-124 and illustrated in figures 11 

and 12 and Plate XV, A (p. 124). 

No record exists of the· total production 'of 

this mine, although the output of crude 

uranium ore is said to have been about 150 

tons. The gold ~~ntent in the ore extracted 

in driving the 200-foot level east is said to have 

n,veraged $10 per ton. Exceptionally the gold 

conte~t is very high, one assay showing 25 

ounces. During the last few years about 1 ton 

of medium-grade pitchblende ore has been 

mined, mainly from between the 135-foot and 

200-foot levels. 

JEFFERSON-CALHOUN VEIN. 

. The Calhoun vein, on the south slope of 

Quartz I-Iill n,bout 1! to 2 miles southwest of 

Central City, is developed by several shafts 

whose position and depth are shown in figure 

39, taken from a map obtained through the 

courtesy of Mr. Percy R. Alsdorf, engineer in 

Tho G01n nune, on the south slope of Alps charge. N on<3 of the shaft workings could be 

flill a short distance northwest of Russell Gulch. entered at the time of this survey. The wall 

viHage, appen,rs to be on the eastern continua.:. rock along the apex of the vein is granite gneiss, 

t:ion of the Gold Dollar vein. It is developed with a few lenses of hornblende schist which 

b~ a s~utft which ~ould not .be entered, thQ ~ine represe~t 1lletamorphosed portions of the 

bmng 1~lle ut the t1me of th1~ surve~, but which, Idaho Springs formation. Considerable bodies 

accorchng to tho maps avmlable, IS about 270 of schist were, however, intersected in some of 

feet deep, with short levels at depths of 50, the workings, as described in the following 

100, 125, 150, 200, a~1d 250 feet. Ore on tho statement from a repo:r;t by Mr. Alsdorf: 

clump wus of tho galena-sphalerite type. Tho 

\'fLluo of tho early output of th0 n1ine is .not 

known, but its output since its acquisition by 

tho present company is said to hav<:) been about 

$6,000. 

WOOD MINE. 

I note that the ViTest Calhoun ore body, which was 

profitable, ended with depth when the vein fracture went 

into the formation known as the Idaho Springs schist. 

I also note [that] the Kemp ore body west stopped when 

this same schist was encountered; that no values were 

found in the Jefferson vein after it went into this sam:e 

formation. From what I can gather, the East Calhoun 

The Wood n1ine, neu.r the head of Leaven- shaft encountered this, and all work did not yield any 

worth Gulch, was idle at the time 'of this surv~y encouragement for a distance of 340 feet, when the granite' 

and was not entered. The vein, which lies just gneiss w~s again e~counter~d, _and with it_ th~ regularity 

north of the Calhoun vein and strikes .somewhat. of the. vem fractur~ and, comc1dent, ore y1elcli~~ a profit 

· tl f t · · · cl t f ·

6· · h t to the operators. 

nor l ~ ea~ ' IS Sal O r~ng~ rom l~C es 0 Other adjacent 1nines have sunk through this formation 

2 feet 1n Width. The prinCipal sulphide!? are and have been quite discouraged while in this schist, 

pyrite and chalcopyrite with local stri:p_gers owing to almost totai lack of pay val~es, but.ha,~e found 

carrying galena and sphalerite. Two sha~ts, much bette~ condi:lons below in the gra~te g~eiss. My 

90 foot apart on the vein, are connected by data approXImates 1t from 250 to 350 feet m thickness, so 

· d f far as proven. levels at depths of 50, 135, 160, an 200 eet. 

Tho mine is noted principally for ·its pitch- Mr. Alsdorf's observ~tion~ in regard to the 

blonde, having been worked for this mineral as marked falling off in the mineralization where 

early as 1872. The pitchblende .ore ~s said to the vein passes into considerable areas of schi~t 

occur in bunches and pockets from a few pounds of the Idaho Springs formation is in entire 
·246 GEOLOGY OF GILPIN, CLEAR CREEK, AND BOULDER COUNTIES, COLO. 

accord with the writer's observations in many 

mines of this district. (See p. 104.) His 

opinion that stronger mineralization will be 

found when the vein has been followed through 

the schist into the gneiss again appetlifs to be 

well founded.· 

Ore on the various dumps along this vein 

belongs principally to the galena-sphalerite 

type. One specimen from the West Calhoun 

dump showed gneiss carrying abundant disseminated pyrite, in places wholly replaced by 

JEFFERSON SHAi"r 

0 

covellite. Such coa.tings are evidently the 

result of downward sulphide enrichment and 

indicate that the copper content has locally 

been slightly augmented through this process. 

A feature of especial interest is the presence 

of uranium ore in the West Calhoun 387 -foot 

level west. To quote from a report by .. Mr. 

Alsdorf: 

This level is driven on a vein whose course is 40° north 

of the regular course of the Calhoun vein and whose dip 

is 15° flatter. * * * 

Horizontal scale 0 sooF"eet 

Vert;cal scale sooFeet 

Shaded areas repre$ent stop~ · 

LEVEL OF PI?OPOSEO LATEI?AL FROM AI?GO TVIVN£L 

FIGURE 39.-Section showing workings along Jefferson-Calhoun vein. From maps furnished by P.R. Alsdorf. 

quartz· and pyrite, cut obliquely by a narrow 

veinlet of dark sphalerite. Another specimen 

from the same dump shows somewhat porous 

ore composed of chalcopyrite and sphalerite 

with subordinate pyrite; the free faces of the 

chalcopyrite are. coated with a black film, 

probably chalcocite, and the sphalerite is 

cqated with a steel-blue coating resembling 

This vein is followed by the level a clis.tance of 179 feet; 

the first 35 feet returning negative commercial results, the 

next 35 feet returned average values of $104 in gold and 

silver, from 2.4 per cent to 29 per cent uranium oxide, 

which averaged 6.1 per cent, worth approximately $360· 

per ton, or a total gross value of $464 per ton, averaging 3.1 

inches in width. The next 40 feet gave a gold and silver 

value of $70 per ton, with small percentages of uranium, 

while the ~ast 60 feet returned no commercial profit from 

the ore in sight.· 
GILPIN COUNTY. 247 

Specimens of the wall rock of the uraniun1 

stope forwarded to the Geological Survey are 

altered Idaho Springs formation carrying ·dissetninated grains of p)7Tite. 

The following assays of the uranmn1 ore 

were furnished by Mr. Alsdorf: 

Assays of uraniurn ores front Calhoun vein. 

Character. Uranium Gold. Silver. oxide. 

Vein material: Per cent. Ounces. Ounces. 

2 inches wide ....... 28.0 14.20 1.80 

4 .inches wide ....... 14.4 12.60 1. 20 l~ inches wide ...... 10.8 6.40 1.00 

Selected piece .......... 46.6 .............. ............... }!fainly sphalerite ...... 3.4 3.40 1.60 

Mainly pyrite ........... 1.2 .08 • JG 

A noteworthy feature is the n1arked association of high gold content with high uraniu1n 

content. 

A specin1en of high-grade 'pitchblende ore 

frmn 45 feet west of the West Calhoun shaft 

on the 387-foot level, furnished by :Mr. Alsdorf, 

showed siinilar relations to those described in 

specin1ens fron1 the Gennan-Belcher lode, the 

pitchblende having been 'brecciated and. penetrated by nun1erous later veinlets composed 

of pyrite, sphalerite, quartz, and some galena. 

A specin1en frmn 50 feet west of the shaft on 

the · smne level shows altered schist · of the 

Idaho Springs for1nation traversed across its 

foliation by a !-inch to 1

3

6 -inch veinlet of 

pitchblende. A polished section of this veinlet was studied under the reflecting microscope. It shows that the pitchblende has in 

places· been shattered and that fragments of 

it lie in a n1atrix of galena, sphalerite, chalcopyrite, and gray quartz, and that other parts 

are traversed by veinlets of galena. 

During 1912 a small.quantity of pitchblende 

· was n1ined frmn the West Calhoun workings 

and sold for about $1,300, mostly for experimentalpurposesandasspecinlCiis. Itissaid tohave 

averaged about 37.5 per cent uraniu1n oxide. 

A lateral started fr01n the Argo tunnel, 

about 16,506 feet fr01n the portal, on what is 

supposed to be the Calhoun vein, extends for 

about 800 feet, of which only the first 350 feet 

were accessible. If extended it will intersect 

the Jefferson shaft at a vertical depth of 1,820 

feet below the collar. The n1eager exposures 

in the lateral are described on page 305. 

In periods of idleness .the water level in the 

Calhoun workings stands 300 to 400 feet-below 

the surface. Thus, on December 20, 1912, the 

water level in the East Calhoun shaft stood, 

according to AlsdorfJ 380 feet below the coll~I'. 

Data . are not at hand for detern1ining the 

average value of the ore in the Calhoun vein, 

but the following selected sampling-works 

assays give son1e idea of the n1etallic content 

of smelting ore fr01n the Jefferson portion of 

the vein: 

Sarnpling-works assays of smelting ore from Jefferson vein. 

Year. Ore. Gold. Silver. Copper. Lead. 

Net l7>s. Ounces. Ounces. Per ct. Per ct. 

1889 ........ 2,_911 1.15 22.90 .............. ............. 1889 ........ 1,911 1. 50 4.20 . ............ ............... 1889 .. .' ..... 2, 653 3.10 22.00 3.50 .............. 1894 ........ 2, 700 2.12 15.00 ............. 27.70 

1894 ........ 1, 220 3.00 12.00 2.50 ............... 1908 ........ 14,096 . 97 6. 10 ............. ............... 1908 ........ 15, 928 2.98 25.25 6.00 ............. 1909 ........ 19,464 2.21 23.55 8.10 ............... 1909 ........ 14, 918 . 60' 3.80 .. ........... ........ 1910 ...... -. 4,472 3.72 36.34 15.40 ........ 1910 ........ 6,008 3.33 42.85 14.05 ............ 1910 ........ 14, 174 . 63 5.10 .50 ............. 1910 ........ 16,922 1. 04 6.24 .10 ........... 

I-Iigh copper content (as cha1copyrite) is 

almost invariably accompanied by high content in both gold and silver. 

The average precious metal content ~f 54 

tons of smelting ore shipped in 191.0 was gold 

1.07 ounces and silver 10.10 ounces. 

PROMPT PAY MINE. 

The Prompt Pay shaft is. about one-fourth 

mile northwest of the village of Russell Gulch 

on a short north~ast-southwest vein just south 

of the JefferRon-Calhoun vein. It is developed 

by a shaft 17 5 feet deep connecting with four 

short levels. The mine had been idle since 

1905, and the workings could not be entered. 

Ore on the dump was predominantly pyritic 

but carried a little sphalerite and galena. 

Very few data are available in regard to the 

metal content of the ores. The following are 

sampling-works assays of a few shipments of 

smelting ore: 

Sampling-works assays of S?rfelting ore from Prompt Pay m~ne. -

Year. Ore. Gold. Silver. Gopper. Leaq. 

Net lbs. Ounces. Ounces. Percent. Percent. 

1895 ........ 1,812 10.80 36.00 .......... 18.20 

1895 ........ 2,069 5.14 16.00 2.50 16.00 

1895 ........ 2,293 5.79 26.80 . .......... 18.00 

1899 ........ 6,797 . 32 3.00 ............ ········ 

The . total production of the mine is said to 

have been about $30,000. 
I I 

248 GEOLOGY OF GILPIN, CLEAR CREEK, AND BOULDER. COUNTIES, COLO. 

BEZANT OR QUARTZ ~ULL MINE. I 

The Bezant or Quartz Mill mine is on the 

south side of Leavenworth Gulch, a short distance west of the Russell Gulch and Central 

City wagon road. The development consists 

of a shaft 485 feet deep with levels at depths of 

75, 165, 250, and 420 feet. The mine was 

opened in 1864 and was taken over by the 

present company in 1908. It was closed at 

the time of this survey, and there were no surface exposures of the vein. Vein material on 

the duinp showed galena, sphalerite, chalcopyrite, and pyrite. 

HARSH VEIN. 

The I-Iarsh vein shaft is in Leavenworth 

Gulch about 50 feet west and 100 feet north of 

the Central City and Russell Gulch road culvert. In the underground workings only 

granite gneiss is exposed. The shaft is 80 feet 

deep with drifts 50 feet west and 10 feet east 

at the bottom. 

The vein ranges from 4 to 6 feet in width, 

strikes N. 61° E., and is nearly vertical. The 

ore is crushe~ silicified granite gnci~s carrying 

abundant rather coarse grained disseminated 

pyrite. Some 4-inch stringers of nearly pure 

pyrite are seen cutting the disseminated ore. 

Very rarely small crystals of dark sphalerite 

and galena are seen. 

A crushed zone 1 to 1! feet wide, formed near 

the center of the vein by p<;>stmineral movement, is filled with angular fragments of ore 

cemented by a grayish siliceous.matrix, which 

appears to consist of finely ground granite 

gneiss . highly silicified and commonly quite 

barren although in places containing a very 

llttle ·fine pyrite. Slickensides in the gouge 

at one place on the south wall of the vein show 

a horizC!~tal movement along that wall. 

The shaft has been opened only recently and 

little stoping has been done. A shipment of 3 

tons of smelting ore in 1910 averaged 0.48 

ounce gold and 2.1 ounces silver a ton, which 

is probably about the average grade of ore. 

During the same y~ar a small shipment of 

smelting ore carried 2 per cent copper beside 

the common gold an~ silver values. 

TOPEKA MINE. 

inclined shaft connecting with 15 levels and 

the West Topeka shaft reaching only to the 

seventh level and used only for ventilation. 

Levels above the seventh were not accessible 

for study. Most of the workings are in a single 

strong vein of the galena-sphalerite type, 

striking about N. 50° E. and clipping 35°-60° 

NW. (average about 40°). The vein, which 

varies from a few inches to 7 feet in width, 

in places shows only small amounts of dis• 

seminated pyrite and elsewhere shows 15 

inches of solid sulphides, bordered by several 

·feet of disseminated ore. The wall rock is 

mostly granite gneiss but in a few places is 

hornblende schist, a phase of the Idaho Springs 

formation; the twelfth level is almost entirely 

in hornblende schist. Some pegmatite is 

associated with the schist. The mineral character of the vein does not seem to be closely 

dependent upon the nature of the waU rock. 

The hornblende schist, unlike the commoner 

and less rigid phases of the Idaho Springs formation, shows no tendency to dissipate the 

vein fracturing along a number of minor slips, 

but carries the fracture as firmly as the granite 

gneiss does. 

At a particularly good exposure of one of the 

wide portions of the vein 20 feet east of the . 

shaft on the thirteenth level two veins of 

solid sulphides, 12 inches and '14 inches wide, 

traverse a zone of altered biotite-hornblende 

schist 5 feet wide. The veins consist of about 

50 to 75 per cent pyrite and 25 to 50 per ·cent 

sphalerite, irregularly intercrystallized. The 

altered schist between and on either side of 

the solid sulphide veins carries disseminated 

pyrite and is traversed by srr1all scattered 

pyrite or pyrite-sphalerite veinlets commonly 

less than one-fourth inch across. Slip planes 

occur along the hanging wall and the footwall. 

In most places the ore minerals are irregularly mingled but at.some points the sphalerite, 

or sphalerite and calcite, tend to occupy the 

center of the sulphide veinlets, with pyrite 

next the walls. 

Vugs are small and rather uncommon: The 

largest observed was 5· inches across, parallel 

to the vein. Most of them are lined with 

crystals of quartz, pyrite, and sphalerite; 

but one on the fourteenth level was lined with 

The Topeka mine is about one-fourth of calcite. A specimen from the dump showed an 

a mile north of the village of Russell Gulch. aggregate of small pyrite and some sphalerite 

The development . consists of the Topeka crystals coated with a layer of sphalerite crys-
GILPIN COUNTY.· 249 

tnls one-half inch and less in diameter, showing seventh and eighth levels, however, it was comwell-developed crystal faces. These in ·turn . monly 6 inches to 2 feet wide, and near its juncwei·e coated with a n-inch to l-inch crust of tion with the Topeka vein expanded to a width 

siderite cttrrying minute intergrown crystals of 10 to 15 feet and carried rich ore. The hoof galena and sphalerite. nanza ore had all been worked out at the time 

In genernl the relations that have· been of this survey, but except for the absence of 

described, though not iinplying more than one free gold some of the ore now in place resembles 

general period of vein formation, indicate that rather closely that extracted from the richer 

the character of the solutions changed some- portions of the stope. Some portions of the 

what during that period, pyrite depositing Klondike vein are entirely similar to the Topeka 

most fLbunclantly at the beginning and sphaler- vein in appearance. The same minerals charite and carbonates depositing in proportion- acterize both veins but commonl;y in somewhat 

ately greater abundance later. The presence different proportions, white quartz and calcite 

of resin sphalerite as a late crystallization in being prominent constituents in many portions 

a few places is perhaps another indication of of the Klondike vein and being less conspicuous 

0 50 100 200 Feet 

LEGEND 

Galena-sohalerite 

~ 

~ veins 

(Arrow indicates direction of dip) 

~ranite gneiss 

Idaho 

~ 

~ Springs formation 

N 

FIGURJ<~ 40.-Goologic plan of portions of tho seventh and eighth levels of the Topeka mine. 

a decrease in the iron content of the ore-forming 

solutions as deposition progressed. 

Although the greater part of the mine workings are in the Topeka vein, the richest ore of 

the mine has come from another vein, ~nown as 

the Klondike. This vein, which has in places 

proved fabulously rich in free gold, joins the 

Topeka on the seventh level about 380 'feet 

west of the shaft. (See fig. 40.) It is also exposed in a drift reached by a crosscut from the 

eighth level and in extensive stopes between 

these· two levels. It strikes on an average 

about N. 35° E. and dips 25°-40° NW. As exposed on the seventh level the Klondike vein is 

only feebly mineralized and nowhere exceeds· 4 

inches in width. In the ~topes between the 

in most parts of the Topeka vein. One exposure showed a lens of white quartz 1 foot across, 

carrying pyrite and sphalerite scattered sparsely 

and irregularly through it .. In one place the 

vein consists of a number of subparallel bands. 

of white quartz, carrying pyrite, separated by 

barren fracture seams. The pyrite becomes 

copper stained on weathering, and is probably 

cupriferous. The 'wider portions of the vein 

are granite gneiss impregnated with pyrite and 

sphalerite and traversed by those sulphides in 

somewhat indefinitely bounded veinlets 2! 

inches and less across. 

The bonanza ore of the Klondike vein was 

found mainly between the seventh and eighth 

levels. A raise above' the seventh level and n. 
'' 

250. GEOLOGY OF GILPIN, CLEAR CREEK, AND BOULDER COUNTIES, COLO. 

winze below the eighth both failed to disclose 

a continuation o~ the rich ores. The writers' 

examination, furthermore, yielded no criteria by 

which the occurrence of other bodies of similar 

bonanza ore could be predicted. It is reasonably certain, however, that the Klondike vein 

does not cross the Topeka vein, but is rather a 

branch ·from the Topeka mineralized with the 

same vein minerals and probably during the 

same mineral-forming period. That it is actually a branch of the Topeka is indicated not 

only by its position and its general mineralogic 

similarity to the latter, but also by the presence 

of uncommon amounts of white quartz in the 

Topeka vein for some distance west of its junction with the Klondike. A possible explanation for the peculiar richness of the Klondike 

vein has been suggested on page 110. 

The predominant metallic minerals of the 

Topeka vein ar·e pyrite and sphalerite, with 

chalcopyrite and galena subordinate. Quartz 

and altered wall rock and exceptionally calcite 

are the principal gangues. The vein therefore 

bel~ngs to the galena-sphalerite type but is 

characterized by an uncommon preponderance 

of sphalerite. Most of the sphalerite is darkcolored, but the resin variety was observed at a 

few places; thus on the seventh level 100 feet 

west of the shaft a coarse-grained association of 

resin sphalerite, pyrite, chalcopyrite, and 

slightly-ferruginous calcite appears to have 

been the last-formed part of the vein. Small 

amounts of native bismuth are reported from 

the fourteenth level. · 

The sulphides of the Klondike vein, like those 

of the Topeka, carry important amounts of the 

precious metals, but the bonanza character of 

the stopes was due to free gold. This occurred in some places in the white quartz, b~t 

elsewhere was intimately associated with sphalerite, chalcopyrite, galena, and pyrite in ·an 

irregular manner that showed beyond question 

that it was a primary constituent that crystal~ 

lized simultaneously with. these sulphides. 

·Microscopic examin_ation of polished pieces of 

rich gold-bearing quartz courteously donated 

by Mr. Henry 1;'. Lowe showedthatthegold bore 

no relation to fracture planes in the quartz, but 

occurred in highly irregular masses which, if 

their matrix were dissolved·, would constitute a 

veritable sponge of gold. Small amounts of 

sphalerite and exceptionally a bit of galena are 

in plac~s intercrystallized with the gold. Like 

the gold, they are very irregular in form, and 

they bear the s~me relation to the quartz that 

the gold does. 

Metasomatic alteration of the granite gD.eiss 

bordering the Topeka vein consists in a 

sericitization of the feldspars and an impregnation of the ro~k with small grains of pyrite and 

sphalerite. The sulphides replace feldspar 

almost exclusively; many of the grains of 

pyrite show crystal form; 'the sphalerite grains 

are commonly smaller and always i~regular. 

The stope on the Klondike vein, 280 feet 

long, 44 feet high, and 16 feet in m~ximum 

width, yielded about $480,000. A particularly 

rich piece of ore, which received an award at 

the Paris Exposition, weighed 88 pounds, and 

when subsequently melted yielded $5,449. 

Where this specimen was obtained the vein 

was 5 to 13 inches in width. 

·Practically all the present output of the mine 

is treated at the Penn mill, in Blackhawk, 

owned by the company owning the mine. This 

mill is now producing a zinc concentrate which 

is said to carry about 0.3 to 0.4 ounce in gold, 

2 to 4 ounces in silver, and 20 to 30 per cent 

of zinc. 

The total production of the. mine is said to 

have been about $1,850,000. 

ROCKFORD MINE. 

The Rockford mine is just north of the 

village of Russell Gulch. The shaft, which is 

230 feet deep, and develops a vein of the 

pyrite type, was idle at the time of this survey. 

The smelting ore shipped in 1910 carried an 

average of 1.09 ounces of gold and 4.35 ounces 

of silver. 

UPPER RUSSELL GULCH. 

Russell Gulch was the scene of some of the 

earliest gold discoverjes in the district, and was 

an important placer-mining camp in 1859 and 

for several years following.· Most of the ores 

belong to the pyritic type and below the 

oxidized zone are on the whole of comparatively 

low- grade. Some of the veins, however, such 

as the Old Town, Iron, and Pewabic, are uncommonly strong and persistent, and have 

yielded· large tonnages of ore. A few veins, 

such as the Belmont and Livingston, are of 

the galena-sphalerite type. 

GOLDEN CLOUD MINE. 

The Golden Cloud mine is about one-half 

mile· south of. Russell Gulch yi~lage, .just west of 
GILPIN COUNTY. 251 I 

the Idaho Springs road. The shaft dips about 

45° N., following the vein. According to the 

maps it is 670 feet deep on the incline with 

levels every 100 feet. The ore is entirely of 

the pyritic type. The two prjncipal stopes 

are above the 400-foot level and are credited 

·with a production of $25,000 · and $14,000 

Tespectively. 'rhe n1ine was. first worked in 

1860 and the last work was done in 1906. 

NASHVILLE MINE. 

The N ash,,ille 1nine is just southeast of the 

Golden Cloud mine and is owned by the same 

eon1pany. The vein is of the pyritic type and 

is developed by a shaft 200 feet deep. 

LIVINGSTON MINE. 

The Livingston rnine is developed by a shaft 

just east of the Idaho Springs road about one-

'half n1ile south of Russell Gulch village. The 

·vein; from surface exposures, appears to strike 

.about N. 55° E. and to dip 70° NW. Unlike 

. n10st of the neighboring veins it is of the 

galena-sphalerite type. 

ROCKY MOUNTAIN TERROR MINE. 

The abandoned Rocky ~1ountain Terror 

:mine, in Russell Gulch just west of the n1a.in 

road to IdnJ10 Springs,.is developed by a shaft 

-connecting with six levels. '.('he north-dipping 

vein strikes slightly north of east. 

The ore on the dump was n1ostly of the 

pyritic type but is cut in a few specin1ens by 

s1nall later veinlets of galena and sphalerite 

Slickensides show pos tn1ineral ,n1ovemen t along 

the vein. 

Smnpling-works assays of 8,304 and 5,122 

pounds of ore, shipped in ~898, show respectively 1. 74 ounces of gold and 8 ounces of silver 

.and 1.9 ounces of gold and 8 ounces 'of silver 

FEDERAL MINE. 

feet below the 400-foot level. The wall rock 

exposed is mainly granite gneiss. 

As exposed in these workings the n1ain veiri 

shows frorn 3 inches to 2 feet.of granite gneiss, 

which carnes clisserninated sulphides and is 

traversed in a few places by irregular veinlets, n1ostly sulphides, whose n1axin1um width 

rs 1! inches. The great bulk of the vein 

material, however, is ofthe dissen1inated type. 

The sulphides are pyrite with Slualler amounts 

of chalcopyrite arid tennantite. ·The best ore 

is that carrying the copper n1inerals in abUJ1-

dance. 

A few sampling-works assays of shipments of 

sn1elting ore are given below: 

Sampling-works assays of smelting ore from Federal rnine. 

Year. Ore. Gold. Silver. Copper. 

Net tons. O·unces. Ounces. Per cent. 

1907 ......... 1,659 2.88 7.10 . ........... 1907 ......... 15,536 . 76 4.40 2.40 

1907 ......... 15,044 . 79 6.14 2.65 

1910 ......... 9,525 . 57 3.20 . 25 

1910 .......... 30,437 . 80 2.20 .20 

1910 ......... 7,702 . 58 2.71 . ......... 

RUSSELL VEIN. 

The Russell vein, which crosses the Idaho 

Springs road just south of Russell Gulch village, is developed by the East and West R ussell shafts. None of the workings could be 

entered. The West shaft is 500 feet deep and 

connects with five levels. The East· shaft is 

200 feet deep and at the bottmu connects with 

the Old Town workings. Levels have been 

driven at 100 and 200 feet depths. The vein, 

which appears to be nearly vertical, is of. the 

pyritic type . 

Sn1elting ore shipped frmn t4e Russell mine 

in 1910 averaged gold 0.51 ounce, silver 6.23 

ounces, and copper 1.41 per cent. Three 

earlier shipments of smelting ore gave the 

following sampling-works returns: 

Sampling-work$ assays ,of smelting ore from Russell vein . 

Year. Ore. ~ Gold. Silver. Copper. 

Net lbs. Ounces. Ounces. Per cent. 

1907 ......... 1, 322 3.22 10.75 7.65 

1908 ......... 6, 182 .56 2.00 ............. 1909 ......... .32 3.30 . ........... 

The Feclernl 1ni.ne is in Russell Gulch a 

-short distance east of the 1nain road to Idaho 

Springs. I11 the older workings above the 

. 300-foot level n1ore than one vein see1ns to be 

·present, and their relationship to each other 

is smnewhat obscure. The newer workings 

frmn the 300-foot level to the lowest or 400-

foot level· are all on one vein, which strikes 

nearly east and west and clips 35-65° N. It is 

exposed in short drifts on the 300 and 400 foot 

levels and in a winze which extends about 100 ____ ___:_ ___ -'-----'----------'----

5,096 
252 GEOLOGY OF GILPIN, CLEAR CREEK, AND BOULDER COUNTIES, COLO. 

· The Old Town mine, whose shaft is in the tliat dips steeply south and joins the Old 

OLD TOWN MINE. ~~e Old Town shaft, which was sunk on a vein 

village· of Russell Gulch, develops one of the Town vein .at the Wautauga fifth level (Old 

largest and most persistent pyritic lodes of To~ new sixth level). The usual controversy 

1n regard to apex rights began when· the 

juncture was discovered but wa~ settled by 

a consolidation of interests. TheW autauga 

shaft is now abandoned. The Old Town shaft 

is 2,205 feet long on the incline and con-

. nects with 21levels. The lowest or twentyfirst level is the Hot Tin1e lateral, 14,306 

feet long, which connects with the Argo 

tunnel and is at present used only for 

drainage and ventilation, but which, if 

the mine were operated on a large scale, 

would presumably be used for .electric ore 

s haulage, for which it is already equipped. 

~ .The wall rock on the first and second ~ 

t . .s levels is schist of the Idaho Springs forma-· 

~ ~ tion, but below tlus the shaft workings are 

~ ~ almost exclusively in granite gneiss. 

~ ~ The upper levels (see fig. 41) expose a .0 

.Ef branching vein system whose components 

~ show considerable variety in b~th stri¥e and 

'51 ~ dip~ The eleventh to twentieth levels in-

·§ elusive are shorter and reveal no forking of 

~ the vein. 0 

~ The mineralization belongs to the pyritic. 

~f==~~~~~ ~ o type and in places, as on the fourteenth and VJ~ {ij c; "' fifteenth levels west of. the shaft, extends 

~ through a width of 6 to 8 feet of granite 

~ gneiss. A characteristic exp~sure oil the . 

. ! fourth level about 800 feet Wef?t of the shaft. 

§ shows about 4! feet of granite gneiss heavily 

P:: impregnated with pyrite and traversed by 

~ numerous· pyrite-chalcopyrite veinlets one-

~ fourth inch or less in width and by four or 

. ~ £ five postmineral slip planes showing gouge. 

~ and slickensides. On the seventh level about. 

0 

0 

0 

the district. The Old Town or Kimball shaft 

follows the lode, dipping 35°-50° NW. Some 

of the earliest development was done through 

the Wautauga shaft, about 600 feet north of 

380 feet west of the s~1aft similar sulphide 

veinlets 1!inches and less in width that trav-· 

erse the pyrite-impregnated gneiss are al-· 

most wholly chalcopyrite. 

What appears to be the junction of the. 

Wautauga and Old Town veins is exposed 

op. the new sixth level about 20 feet east of 

the Wautauga shaft. The Wautauga vein. 

descends with a dip of about 78° S. ~ithin 

5 or 6 feet of the Old Town vein and then 

swings into it. 

The Hot Time lateral, otherwise the twenty-· 

first ievel on the Old Town shaft, follows the· 

Old Town vein to about 1, 7 50 feet east of 

the Old Town shaft and then shifts a short. 
GILPIN COUNTY. 253 

distance north to a nearly parallel vein, s.aid to 

be the Columbus. This it follows to a point 

about 2,850. feet ·east of the Old Town shaft; 

then shifts south' again to the Old Town vein, 

w. 

Mineralization of the Old Town vein on the 

Hot Time lateral is similar in character to that 

in the shaft workings but ·is less pronounced. 

In an exposure about 70 feet west of the shaft 

FIGURE 43.-Sectiop in plano of Old Town vein, showing portions that havo been stopcd. 

on which it continues to the Argo tunnel. The 

·prevailing wall rock is granite. gneiss,, interspersed with a few small patches of schist of 

the Idaho Springs formation. 

the vein is about 4 feet wide and is not strongly 

mineralized. The granite gneiss carrying disseminat.ed pyrite is traversed by a network of 

sulphide stringers, which are commonly not 
254 GEOLOGY OF GILPIN, CLEAR CREEK, AND BOULDER. COUNTIES, COLO. 

more than one-eighth of an inch wide but which 

locally swell to 1 inch. The narrower stringers 

are pyrite with a little chalcopyrite; the wider 

ones carry also some quartz. In the eastern 

part of the lateral the veinlets of solid pyrite 

that traverse the pyrite-impregnated gneiss 

are sharp walled and are plainly fissure fillings. 

In one place there is 1 foot of solid pyrite. 

The so-called Columbus vein exposed on the 

Hot Time lateral is also pyritic but is only 

feebly mineralized. It is a fractured zone from 

a few inches to 2 feet in width carrying here 

and there a small stringer of pyrite and a little 

disseminated pyrite. 

All ore is now mined through the shaft and 

is carried 3 miles to .Blackhawk by the Gilpin 

Tramway. Smelting ore is sold to the sampling works at Blackhawk and concentrating 

N 

L...-.L...-2s ---~.-so -.:.......~'" r,.t ) 

average width sampled was 3.8 feet. In these 

samples the gold ranged from 0.1 to 6.44 

ounces, the silver from 0.3 to 22.1 ounces, and 

the copper from a trace to 8.8 per cent. 

From sh11ft workings below the fifteenth level 

124 samples ofore taken by Mr. Wiley showed. 

gold contents from a trace to 4.22 (average: 

0.29) ounces and silver from a trace to 5. 7 

(average 0.78) ounces. The ore of the Old 

Town vein on the Hot Time lateral is said 

to average only $0.80 to $1 per ton. 

The gross produc.tion of the mine is said to 

have been about $2,700,000. 

BECKY·SHARP MINE. 

The Becky Sharp 1nine is a short distance 

southeast of Russell Gulch village, apparently 

on the westward extension of the Pewabic vei'n. 

The development consists of 

three shafts 120, 135, and 

160 feet deep, with connecting drifts. All of the oro is 

of the pyritic type and of 

concentrating grade and is 

sent to the Jackson mill at 

Idaho Springs, where a con-· 

· centration of about 3! into· 

1 is effected. The value is 

said to be $8 to $10 per ton .. 

. mON MINE. 

The Iron mine, on the 

south side of Russell Gulch. 

FIGURE 43.-Plans of portions of the 4JO-foot and 500-foot levels of the Iron mine, showing charac· near the tOWn Of that nan1e, 

teristic branching vein systems. is m a in 1 y de v e 1 0 p e d 

ore shipped via the Colorado & Southern Railway to the Jackson mill at Idaho Springs. It 

has already been pointed out that the strength 

of the mineralization decreases in the deeper 

workings, a fact reflected in decreased value of 

the ore. An example of the richer portion of 

the lode is a shoot between the surface and the 

third level, in which the o;re averaged about $59 

per ton. A lens between the fifteenth and sixteenth levels averaged $40 per ton, mainly in 

gold. Chalcopyrite is, as a rule, much richer in 

gold than pyrite, and the better grades of ore 

commonly carry about 3 per cent of copper. 

Sampling of the fourteenth and fifteenth levels 

by l\fr. W. H. Wiley gave an average ore value 

of $40.58 for one block and $32.01 for another, 

gold being reckoned at $20 and silver at $0.65 

an ounce and copper at $0.18 a pound. The 

through an inclined shaft following the, 

vein, with levels . at 120, 250, ~00, 400, 500, 

600, and 700 feet. The wall rock is granite 

gneiss except for a small amount of bostonite 

porphyry. The workings, which are very 

extensive, are mainly on the Iron vein, whose 

average strike is nearly east and west and 

whose dip ranges from vertical to 7 5° S. On 

the 300 and 400 foot levels east the junctiqn of 

the Iron vein with the. Richardson and Grasshopper veins is exposed. (See fig. 43.) The 

300,. 400, and 500 foot levels were examined so 

far as they were accessible. 

The commonest type of mineralization in the· 

Iron vein is a dissemination of pyrite through. 

the altered granite gneiss of a zone of fracturing. · 

This zone may vary in width from a few inches 

to several feet, the stopes near the shaft on the 
GILPIN COUNTY. 255 

400-foot level being 12 feet in width. In a few 

places this dissmninn,ted ore is traversed by a 

net of 1ninuto pyrite stringers and n1ore rarely 

by several inches of nearly solid pyrite. On 

the 400-foot level east the vein enters a dike of 

bostonito porphyry and divides into nun1erous 

s1nall stringers, son1e of which are very vuggy. 

'fho 1ninernJizationis clearly later than this dike, 

but in the dike the ore is said to assay only 

$3 to $4 a ton. 

At the tin1o of this survey the n1ine was being 

worked by several sets of lessees. Little work 

was in progress on the Iron vein, the n1ain 

activity being on branch or subsidiary· veins 

exposed on the 500-foot level1nore than 800 feet 

west .of the shaft. At the face on this level 

(A, fig. 43) 1 foot of nearly solid fine-grained 

pyrite is exposed in a narrow sto.pe; and at a 

place 320 feet west of the shaft a breccia of 

gneiss fragments is cmnented by pyrite in 

crystals a quarter of an inch in nh1.ximun1 size. 

Beautiful green crystals of hydrous iron sulphate 

are now forming in places on the walls on this 

level by deposition fro1n surface waters descend.:. 

ing along the vein. The waters of this 1nine are 

so corrosive that the overalls of 1niners working 

in wet places are son1etimes oaten to shreds in a 

day or two, and iron rails, pipes, and nails 

must be frequently replaced. 

The Richardson shaft, about 300 feet northeast of the Iron shaft, was inaccessible. The 

Richardson vein, however) was studied on the 

400-foot level,· whicli connects with the 400-foot 

level of the Iron 1nine (fig. 43). The average 

strike of the Richardson vein is about N. 40° E. 

and the dip is 65°-~0° SE. A shaft with short 

levels at 160, 200, 300, and 400 feet descends 

on the vein. East of the shaft the ~ein was 

not traced far, but west of the shaft it forms 

a true junction with the Iron vein. One of 

the best exposures of the Richardson vein is in 

a stope 20 feet east of the shaft, where a width 

of 6 feet of altered granite gneiss is traversed 

by a network of irregular but sharp-walled 

sulphide veinlets 5 inches and less in width. 

These veinlets consist ahnost wholly of pyrite 

in crystals whose maxin1un1 size is 1 ?!- inches. 

The vein here is said to s~u11ple about $7 per 

ton, the coarse pyrite being characteristicu1ly 

of low value. 

The Gntsshopper. vein was accessible only 

on the·400-foot level (fig. 43), where it forms a 

true junction with.the Iron vein about 180 feet 

east of the Iron shaft. As exposed it strikes 

nearly east and west and stands about vertical. 

Its n1ineralization is feeble. A vein between 

the Grasshopper and the Richardson (fig. 43) 

is 1! feet wide and is sin1ilarly but n1ore heavily 

mineralized. 

The lVIars vein, which strikes nearly east and 

'vest and dips 50°-80° N., is exposed on the 

300-foot level of the Iron mine by a crosscut 

extending south-southeast. It lies about 115 

feet south of the Iron vein and has been drifted 

upon for 85 feet and developed by a stope and 

winze. The vein shows fro In 1! to 3 inches of 

solid pyrite bordered by granite gneiss carrying 

disse1ninated pyrite. 

All of the veins described above are sin1ilar 

in mineral character and were formed at the 

sa1ne time .. Although pyrite is the principal 

ore mineral, chalcopyrite and t01mantite also 

occur in more or less pockety distribution and 

commonly indicate con1parative richness. In 

n1ost places where the ore carries over 2 ounces 

in gold it also carries copper in comnlercial 

an1ounts (over 1.5 per cent). The coarse pyrite 

is prevailingly of low grade, but much of the fn1e 

pyrite is fairly rich in ·gold. 

The Iron and Pewabic n1inAs being under one 

managen1ent and carrying ore entirely si1nil~u 

in character, the tenor and production of the 

two may be considered together. Records of 

shipments show that the sn1elting ore shipped 

fro1n February ~9, 1910, to December 28, 1910, 

had an average value of $58.40 per ton. The 

poorest shipnlent showed 0.14 ounce in gold 

and negligible a1nounts of other n1etals; the 

richest showed gold, 10.47 ounces; silver, 15.25 

ounces; and copper, 11.65 per cent. 

One shipment which approaches the average 

in value showed gold, 2.62 ounces; silver, 5.75 

ounces; and copper, 1.55 per cent. The average value of the concentrating ore is stated 

to be about $11 per ton, n1ainly in gold. 

The gross production of the Iron and 

Pewabic mines from 1904 to 1910 inclusive 

was $526,000. The production before· ' ' this 

period is estimated at $1,500,000 to $2,000,000. 

The records of careful samplings fail to show 

any regular decrease in ore values dependent 

upon depth, and development has failed to 

reveal any regularity in the shape or attitude 

of the richer ore shoots. 
256 GEOLOGY OF GILPIN, CLEAR CREEK, AND BOULDER COUNTIES, COLO. 

PEWABIC VEIN. 

The Pewabic vein outcrops about 100 feet 

. north of the Iron vein and nearly parallels 

it in strike. It dips, however, in the opposite 

direction; that is, northward. The vein is 

developed by the Pewabic shaft, over 900 feet 

deep, and by the East Pewabic shaft, 700 feet 

deep, each shaft having levels at 100-foot 

intervals. The amount of drifting done on 

this vein is much less than that in the Iron 

mine. 

. Both shafts having been idle for some 

time the mine was not entered. The ore is 

entirely similar in character to that from the 

Iron vein, except that it is reported to carry 

Sampling-works assays of smelting ore from the Hall mine, 

1910. 

Ore. Gold . Silver. . Copper. 

Net pounds. Ounces. Ounces. Per cent. 

7,223 1.69 ll.56 9.20 

463 1. 16 6.80 ............... 

6,441 1.66 8.60 3.55 

3,674 .44 2.90 ............... 591 1.14 2.60 2. 00. 

462 . 76 7.30 4.00 

All the ore is of the pyritic t}rpe . 

LOTUS MINE. 

The Lotus mine, iii the eastern part of . the 

village of Russell Gulch, was not being worked 

uranium in the foot wall on the 20.0-foot level r----------~--------,----, 

west. The value of the ore and the production have already been considered in conjunction with the Iron mine. 

BANGOR MINE. 

The Bangor shaft, which is about 800 feet 

west-southwest of the Iron shaft, appears to be 

on the westward continuation of the Iron vein 

or one of its branches. The shaft is equipped 

with a whim but could not be entered. The 

ore seen on the dump was mainly coarse pyrite 

and some chalcopyrite disseminated in altered 

schist. A few specimens show vuggy veinlets of galena and sphalerite cutting the'pyritic 

ore sharply and evidently of later formation. 

Some narrow Vtigs are lined with crystals of 

quartz and sphalerite, the latter coated with 

a thin film of later quartz. 

· mON DUKE MINE. 

The Iron Duke mip.e, a short distance southeast of Russell Gulch village, is developed by a 

shaft 510 feet deep, but was idle at the time 

of survey. The underground workings are 

said to'total2,664 feet. The ore is of the pyritic 

type and appears to be entirely similar tq that 

of the Iron mine. 

HALL MINE. 

The Hall mine, in the eastern part of Russell 

Gulch village, is developed by a shaft 260 feet 

deep, connecting with short levels at depths 

of 50, 100, and 200 feet--. It was idle at the 

time of survey. The following are samplingworks assays of smelting ore shipped in 1910. 

N 

Pyritic 

1---] 

veins Workings 

~ inaccessible 

Note: Wall rock is granite gneiss 

ot::::, et=Ea:::.s!2o =i'==i:::i'ot:::o===239o Feet 

FIGURE 44.-Geologic plan of the 450-foot level on the Lotus vein and 

connecting workings on other veins. Surveyed .by hand compass 

and pacing. 

at the tin1e of survey but was accessible through 

the first or tunnel level, at the side of the lower 

road between Russell Gulch and Central City. 

The Lotus s4aft, 810 feet deep, follows the 

Lotus vein, which strikes in general about 

N. 70° E. and dips 65°-75° SE. There are 

seven levels at intervals of approximately 100 

feet. Most of these develop only the Lotus 

vein, but the 450-foot level (fig. 44) develops 

also the Royal, Minnesota, and Niagara veins. 

The wall rock in the workings is almost exclusively granite · g~eiss but includes some 
GILPIN COUNTY. 257 

smull lenses of schist. The several veins ex-· 

posed in the workings all belong to the pyritic 

type and show don1inant pyrite with subordinate chulcopyrite and tennantite. 

The Lotus vein as exposed on the tunnel 

level is in a few places a barren fracture seam; 

in other places it consists of 2 feet or so of fractured granite gneiss carrying disseminated 

pyrite; where n1ost heavily mineralized it may 

show as much us 7 feet of pyrite-impregnated 

granite gneiss traversed by numerous subparallel voinlots of pyrite and quartz whose 

tnaximum width is about 1 inch. In places 

both tho voinlets and the impregnated gneiss 

contain abundant tennantite associated with 

tho pyrite. On tho 210-foot level east the vein 

in places contains largo arnounts of coarse 

· pyrite, evidently of low grade. About 250 feet 

enst of the shaft on this level the vein, which is 

over 3 feet wide, shows 3 to 4 inches of gouge 

next tho hanging wall, then 1 t feet of granite 

gneiss containing more or less disseminated 

pyrite, then a 1 !-foot vein about one-third 

quartz and two-thirds pyrite, the latter in very 

·. ooarso crystals exceptionally 2 inches across. 

'rho Royal vein, as exposed on tho 450-foot 

level about 100 foot east of its junction with 

tho Lotus vein, is about 4 inches wide and is 

composed of nearly solid pyrite. Tho granite 

gneiss wulls carry disseminated' pyrite in 

amounts that gradually decrease from the vein 

outward. Locally son1e chalcopyrite occurs 

with tho pyrite. 

The Niagara vein, as exposed on the 450-foot 

level, shows in places 3 feet of altered granite 

gneiss carrying disseminated pyrite and is cut 

by a number of indefinitely bounded pyrite 

stringers. In one place a single sharp veinlet of 

solid pyrite is 1! inches wide. Near its junction with the Minnesota vein the rock between 

the two veins is n1ineralized in a similar manner 

for a width of 4 feet, some' of· the solid pyrite 

veinlets being 5 inches wide. 

The exposures in the Lotus mine were the 

only places at which the Niagara vein could be 

has been movement 1 along the vein subsequent 

to mineralization. 

The smelting ore from the Lotus vein is said 

to have an average value of $14 per ton, mainly 

in gold. 

HILLHOUSE-COLUMBUS VEIN. 

The I-Iillhouse-Columbus vein, in the eastern 

part of Russell Gulch village, is developed by 

three principal shafts known as the Hillhouse, 

Columbus, and Ipavia, none of which could be 

entered at the time of this survey, and by several smaller shafts. 

The Hillho~se portion of the vein is developed 

by two shafts 200 and 600 feet deep with levels 

every 100 feet. It has been idle since 1908. 

The average value of the ore is said to have been 

between $15 and $20 per ton and the gross 

production about $50,000. 

The following are sampling-works assays of 

smelting ore: 

Sampling-works assays of smelting ore from Hillhottse vein. 

Year. Ore. Gold. Silver. Copper. Silica. 

. Net lbs. Ounces . Ounces. Fer ct. Per ct. 

1903 .... 5,588 1.25 14. 70 ................ 74 

1903 .... 5,910 . 95 9.05 .................. 76 

1903 .... 16,110 1. 08 5.00 ................. 70 

1904 .... 5,180 1. 10 8.00 ............. 65 

1906 .... 6,944 2. 28 19.40 4. 25 43 

1907 .... 5,645 5.35 17.80 13.00 26 

·The Columbus shaft, according to available 

maps, is a little over 300 feet deep', with short 

levels at 110, 144, 192, and 300 feet. The 

following are san1pling-works assays of smelting 

ore shipped in December, 1888: 

Sampling-works assays of smelting ores from Columbus vein, 

1888. 

Ore. Gold. I Silver.' Copper. 

Net pounds. Ounces. Ounces. Per cent. 

5, 603 1. 70 9.10 5.30 

3,455 1. 90 10.30 9.50 

4, 535 1.60 10.90 6.00 

studied. The Niagara shaft beside the lower The Ipavia shaft is 717 feet east of the Coroad from Russell Gulch to Central City was 'not lun1bus shaft and is also on the Columbus vein. 

accessible. · ' At 8: depth of 280 feet a long. level extends 

The Minnesota vein, as exposed on the 450- eastward for several hundred feet and westfoot level, consists at one point of 5 feet of gran- ward beyond the Columbus shaft._ Little ore 

ite gneiss carrying varying amounts of dissemi- appears to have been taken from the Ipavia 

natcd pyl'ite. At another place a It-foot band workings. Smelting ore shipped in 1889 gave 

of gray quartz caiTies rather fine pyrite. There/ the following sa1npling-works assays. 

44214°-17-17 
258 GEOLOGY OF G~LPIN, CLEAR CREEK, AND BOULDER COUNTIES, COLO. 

Sampling-works assays of smelting ore from Ipavia shaft 

(Columbus vein), 1889. . · 

I Ore. Gold. Silver. Copper. 

n 

Net pounds. Ounces. Ounces. Per cent. 

2,058 1.05 5.30 3.00 . 3,507 .80 2.20 ·-·········· 436 3.00 13.00 9.50 

GETTYSBURGH VEIN. 

The Gettysburgh vein lies between L~avenworth and Illinois gulches just west of the 

Central City-Russell Gulch wagon road. Its 

shaft was idle at the time of this survey, and no 

information concerning the workings was obtained. As exposed on the surface the vein 

strikes about N. 25° E. and dips steeply .. 

All the ore in the bi;ns at the shaft house was 

of the p.yritic type, consisting mainly of pyrite 

and chalcopyrite· with subordinate amounts of 

te~antite in a quartz matrix. Vugs are 

common. 

Sampling-works assays of two shipments of 

436 and 1,941 pounds show, respectively, gold, 

0.55 ounce and silver 3.5 ounces, and gold 2 

ounces, silver 7 .5, ounces, and copper 3 per cent. 

LUTZ VEIN. 

The Lutz vein, in the eastern part of Russell 

Gulch village, is developed ·by the Lutz, the 

I. 'X. L., and several subsidiary shafts. The 

principal (Lutz) shaft, 530 feet deep, follows 

the vein and connects with six levels. It 

dips about 70° N. between the 245 and 325foot 

levels, but elsewhere is nearly vertical. The 

vein strikes nearly east and west. 

The mine was idle and none of the workings 

could be entered. . The ore on the dump was 

all of the pyritic variety, locally brecciated and 

recemented by gr~y quartz. 

. SLIDE VEIN. 

The Slide vein on the Wellington No. 2 claim 

outcrops a short distance southeast of the 

village of Russell Gulch. It is developed by a 

shaft that was being sunk below the 200-foot 

level at the time of this survey, at which time 

the 100-foot level extended 40 feet east and 50 

feet west and the 200-foot Ievell 0 feet east and 

20 feet west of the shaft. The vein is of the 

pyritic type; it st~ikes about N. 75° E. and 

dips from 75° N. to 75° S. Its width ranges 

from 3 to 8 inches. The richer ore carries 

chalcopyrite and tennantite in addition to 

pyrite and may reach $60 per ton in value. In 

the richest ore the copper may run as high as 14 

per cent. In places the coarse pyrite is cut by 

later veinlets of white quartz. 

MISSOURI MINE. 

The Missouri mine is about half a mile due 

e-ast· of Russell Gulch· village. There are two 

shafts on the property, the Missouri shaft with 

four levels, now idle, and the East Missouri 

·shaft, through which lessees were doing some 

mining at the time of this survey. These two 

shafts are on nearly parallel veins about 40 feet 

apart. . 

The northernmost vein is developed by the 

East Missouri shaft, 250 feet deep. As exposed 

15 feet east of the shaft on a level 158 feet 

below the s:urface it dips .65° N. and consists of 

3 feet of granite gneiss traversed by a network 

of sharp-walled veinlets of coarse pyrite. A 

postmineral slip plane follows the vein and has 

crushed the ore in places. 

The southern vein is developed by the Missouri shaft and by a crosscut 40 feet long f~om 

the 158-foot level on the northern vein. The 

drift on the south vein on this level is 130 feet 

long; at its east end it exposes a tight sulphide 

vein 2 inches to 2 feet wide, mainly pyrite, but 

carrying also some tennantite and chalcopyrite. 

The vein strikes N. 75°-80° E. and dips about 

55 ° . N. The ore in this drift is said to carry 

about 1 to 3 ounces in gold and 2 to 3 ounces 

in silver. 

The following are a few sampling-works 

assays of shipments of smelting ore fron1 the 

East Missouri mine: 

Sampling-works assays of smelting orefrom the East ~Missouri 

mine. · 

Y~ar . I Ore. Gold. Silver. Copper. Silica. 

·Net lbs. Ounces. Ounces. Percent. Percent. 

1903 ........ 7,252 3. 22 ~.80 2.50 32 

1904 ........ 8,000 2.40 6. 23 .............. 34 

1905 ........ 6,125 3. 33 5.80 ............... 17 

1906 ........ 7,282 4. 36 8. 70 ................ 23 

1907! ....... 13,988 1.27 2. 35 ................. 58 

1908 ....... ,. 8,116 . 65 2. 90 ................ .............. 

1908 ........ 5,498 3.61 8.20 ................ -------- 1908 .. ; ..... 6,989 1. 20 .3.80 ................. ............ 

The smelting ore shipped in 1910 had an 

average content of 2.91 ounces gold and about 

6 ounces silver, according to sampling-works 

assays. 
GILPIN COUNTY • 259 

. JUSTICE HILL AND LOWER PART OF much displacement, and in such shattered parRUSSELL GULCH. tions white quartz containing a little antinlOnGLADSTONE VEIN. iacal tennantite occurs in small irregular lenses. 

The Gladstone vein outcrops on the ridge which send off minute stringers between the, 

between· Spring and Russell gulches about one- chalcopyrite fragments. 

half 1nile due south of the railroad station at Although the principal ore n:;tineral of the: 

Central City. It is developed by a shaft, which Gladstone vein is chalcopyrite, the value of the 

dips steeply north, fol).owing the vein, and is ore is mainly in gold and silver, and picked ore 

somewhat over 220 feet deep, with levels at 72, is said to have run as high as 11 ounces in gold. 

160, and 220 feet. On the 72-foot levei the vein, The metal content of 29 tons of smelting ore 

is drifted on for about 280 feet and is stoped to shipped at different times between 1893 and 

the surface for 120 feet west and 50 feet east of 1910, as recorded in sampling-works assays, 

the shaft. On the 160-foot level drifts extend was gold, 0.56 to 8.1 (average 1.49) ounces; 

200 feet west and 160 feet east of the shaft, and silver, 2.4 to 14. (average 5.35) ounces; copper, 

the vein is stoped to the :fust level for about 90 10 per cent or less. All the ore mined is of 

feet west and 25 feet east. On the 220-foot smelting grade. 

level a 60-foot stope 10 to 20 feet high has been Three veins exposed in the crosscut on the 

started in the short west drift; the unstoped 220-foot level differ in character from the Gladeast drift is about 50 feet long. From this stone vein. Two of these, lying about 40 and 

level an exploratory crosscut extends 210 feet. 50 feet south of the Gladstone vein, strike 

south of the Gladstone vein. nearly east and west and dip, respectively, verThe Gladstone vein strikes a few degrees tical and 65° N. They are tight fissure veins 

northofeastanddips65°-80°N. Granitegneiss consisting almost wholly of coarse pyrite in 

is the only country rock exposed. The yein crystals up to three-fourths inch in diameter, 

is a tight, sharply bounded, extremely narrow with 'very little gangue. The third vein 

fissure vein, which varies irregularly from a bar- strikes about N. 30° E. and dips 65° SE. and 

ren fracture to 4 inches in width, with an aver- intersects the Gladstone vein about 50 feet 

ago of about 2! inches, and which locally cuts west of the s4aft, the exact contact not being 

sharply across the foliation of. the granite exposed. The drift follows it for about 25 feet. 

gneiss. In places it consists of a single ore· This vein is 2 to 3 inches wide and consists 

stringer and in other places of several nearly mainly of pyrite with a little gray copper ill. . 

parallel ones. Several branches digress into places. All three veins are low grade and none 

the walls. of them have been worked. 

The principal vein mineral in most places 

is chalcopyrite, though locally pyrite is dominant. Very rarely a little resinous sphalerite 

is present. As a rule the vein contains no 

gangue, but in placesitshowssomequartz. · At 

one place, for example, it consists of white 

drusy quartz at the center with chalcopyrite on 

both walls, and a few feet away it is wholly 

chalcopyrite. At another place light-gray 

quartz occurs on both walls with chalcopyrite 

in the center. Pyrite in small disseminated 

grains is the only sulphide noted in the wall 

rock; it is especially abundant within 6 inches 

or so of the vein. 

Changes subsequent to the principal n1ineralization appear to have been slight. No large 

fracture-planes follow the vein, and no evidence 

of enriclnnent was found on the two accessible 

AURORA MINE. 

The Aurora mine, in Russell Gulch about a 

mile south of Central City, is developed by a. 

shaft 578 feet deep with levels at · vertical · 

depths of 85, 183, 258, 316, 392, and SOl feet. 

The workings develop portions of two nearly 

parallel veins, striking in general nearly east 

and west, which are known as the North, or 

Aurora, and the South v-eins. In general 

these veins appear to converge from the surface 

to the 258-foot level, where they are only 10 

feet apart, and thence to diverge. Down to 

the third or 258-foot level the shaft fqllows 

the North vein. Below this there are two 

shafts, an.old·one, now closed, which followed 

the North vein, and a new one, which follows 

the South vein. · 

levels (160 and 220 feet). In a few places the The Aurora, or North, vein, in which most of 

v-ein 1naterial shows a little shattering without the mining has been done, was discov·ere~ by 
'260 GEOLOGY OF GILPIN, CLEAR. CHEEK, AND BOULDER COUNTIES, COLO. 

·placer miners working in the bottom of Russell Gulch. For about 100 feet below the 

·collar of the shaft it dips steeply south, but 

·below 100 feet it dips about 70° N. Its most 

~ontinuous exposures are on the 180-foot level, 

on which it has been followed for about 280 

feet east and 300 feet west of the shaft. Here 

it is a true fissure vein showing one or more 

small stringers of pyrite and white quartz in a 

width of several feet of altered wall rock. 

Some distance east of the shaft the Aurora 

vein crosses the Baldwin vein, but the intersection failed to yield high-grade ore. The 

South :vein is exposed in a short crosscut from 

the 183-foot level east and on all lower levels. 

Where exposed in the 183-foot level the walls 

are mainly pegmatite. The vein dips 60°_ N. 

and where widest shows a network of pyritic 

veinlets (maximum width, 4" inches) through a 

width of 4 feet of pegmatite. 

The ores of the Aurora mine belong to the 

pyritic gold-silver type. In both the North 

and South veins the richer ores carry ill addition to pyrite much chalcopyrite and tetra-

·hedrite; the latter being in some places the last 

-of the primary minerals to crystallize. Free 

gold, in places forming small ·nugge~s, was 

abundant in the oxidized ore above the second 

level and was found in ·small amounts in the 

unoxidized ore to the greatest depths to which 

·the veins have been worked. Local oxidation 

was noted at several places in the 183-foot 

level. In a specimen obtained from the 392-

. foot level the gold is irregularly associated 

·with pyrite, tetrahedrite, and quartz and is 

probably a primary crystallization; at one 

. point on this level free gold was deposited in a 

narrow watercourse which entered the vein 

:from the north wall. It forms small wires 

:and grains upon the quartz crystals and is 

·plainly later than the quartz ·and probably 

~ater than the' pyrite associated with the quartz. 

It is uncertain whether this gold was deposited 

by solutions descending from the surface. or by 

· :Solutions ascending in the later stages of the 

:sulphide mineraiization. 

The oxidized ores above the second level 

:appear to ~ave been notably richer in gold 

than the unoxidized ores below; smelter returns 

:in the early eighties showed as high as 20 

ounces in gold. In the Aurora vein the rich 

<>re in general extended to a vertica1 dept4- of 

about 150 feet; between 150 and 325 feet the 

ore was of comparatively lqw grade; but oelow 

325· feet stringers coming in from the footwall 

carried, locally, ore of good grade, in some 

places assaying $100 to $200 per ton. Many 

parts of the South vein are low grade; for 

instance, in places on the 183-foot level, where 

it attains the unusual width of 4 feet, it assays 

only 0.3 ounce in gold and less than 2 ounces 

in silver. On the 258-foot level an underhand 

stope on· the South vein shortly west of the 

shaft yielded rich ore, one 5!-ton lot netting 

$112 per ton. Ore for some distance along the 

bottom of the 316-foot l~vel had, according to 

Mr. Percy Alsdorf, an average metal content 

of gold 1.2 ounces, silver 4 ounces, and copper 

4 per cent. At the time of this survey ore of 

good grade was being obtained from the 392-

foot level, assays of $95 to $125- per ton being 

common. At a point about 50 feet east· of 

the shaft ·on that level the vein consisted of 3 

inches of sulphides, assaying gold 3.1 ounces, 

silver 2 ounces, and copper 1 per cent. 

Twenty-three lots of smelting ore, aggregating 114 tons, shipped from the Aurora mine 

at variotls times· from 1889 to 1910, showed 

gold. 0.87 to 4.48 (average 2.24) ounces, sliver 

1.3 to 17.15 (average 6.3) ounces, copper 13.65 

per cent or less. 

ARGO VEIN. 

The Argo vein, on the south side of lower 

Russell Gulch, nearly due south of Gregory 

Hill, is developed by a shaft 340 feet deep with 

short drifts on the 150, 200, 265, and 340 foot 

levels. The country rock is schist of the Idaho 

Springs formation, heavily injected by granite 

pegmatite. 

At the Argo shaft· the vein strikes N. 87° E . 

and dips 55°-70° N. It varies from a single 

tight unmineralized fracture to a well-mineralized fracture zone 2 feet in width. The mineralized· portions commonly consist of schist 

carrying disseminated pyrite traversed by 

veinlets and irregular lenses, 6 inches or less 

in width, of nearly solid sulphides. On the 

200-foot level west the vein splits and shows 

nearly parallel hanging-wall and footwall 

branches 2-~ to 6 feet apart. 

·The ore belongs to the pyritic type and is 

very similar to that of the Aurora mine, except 

'that in places it carries some enargite. Pyrite, 

coarse in cplaces, is the principal vein mineral, 

but is locally associated with chalcopyrite, enargite, and antimoniacal tennantite, appar-
GILPIN COUNTY. 261 

ently all contemporaneous. Posttnineral slipping along the \

7 ein has developed slickensides. 

Little of the ore containing only coarse pyrite carries over 0.12 ounce .in gold and most 

of :it carries less. The richest is that carrying 

tennantite, chalcopyrite, and enargite. 

Shipments between 1889 and 1908 of 12 lots 

of smelting ore, aggregating over 30 tons, showed 

according to sMupling-works assays, gold 0.5 to 

5 (average 2.39) ounces, silver 2.5 to 12.13 (average 7.31) ounces, and copper 2.1 to 16 per 

cent. The avernge value of the smelting ore 

shipped during 1910 according to samplingworks assn.ys was gold 1.-18 ounces, silver 5 

ounces, copper 6.1 per cent. 

the shaft and is caved 40 feet east of the shaft; 

the waH rock for this 40 feet is schist. The 

700-foot level has not been driven west. The. 

800-foot level extends west of the shaft for 

about 120 feet, aU in granite gneiss. It has no· 

good expos,ures of tbe vein and was not mapped .. 

The 900-foot level is driven about 110 feet east. 

of the shaft, the walls being wholly granite) 

gneiss. It was not mapped. The 1,000-foot·. 

level was not accessible during this survey, but 

ore from it in the ore bins was examined. 

The Pittsburg vein strik~s in general aoout; 

N. 65° to 70° E. and dips 45°-65° N. Unlike' 

most of the veins of this district, it shows only· 

slight postn1ineral movement. The vein 1s: 

LEGEND 

Vein 

(Arrow indicates direc.tionofdip) 

]~IOUIU~ 45.-0oologlc plans or 500-foot, 70()-foot, and soo-root levels of Pittsburg mine. Su~veyed by hand compass and pacing. 

PITTSBURG MINE. 

The Pittsburg 1nine is on the north side of 

Russell Gulch about a mile southeast of Central City. The shaft dips steeply north, following the vein. Only tbe lower levels, at depths 

of 500, 600, 700, 800, 900, and 1,000 feet were 

accessible for study. The relntions in some of 

the levels east of the shaft are shown in figure 

45. The 500-foot level west was inaccessible, 

a pumping station being located t4ere. A sublevel u.bout 200 feet long has been driven 50 

feet above the 500-foot level and is reached by 

an inclined raise from the east end of that 

level. The 600-foot level is not driven west of 

characteristically tight, the workable ore in 

many places being only 3 to 4 inches in width; 

it is, however, composed almost wholly· of 

sulphides of comparatively high grade. 

A rough and not very persistent banding 

occurs in some portions of the vein .. In many 

places coarse pyrite occurs along t];u:) wall~ 

with copper-bearing sulphides in the center; 

elsewhere the pyritic and the copper-rich portions form separate bands. At one place, for 

example, the hanging-wall po~tion of the vein 

is composed entirely of coarse pyrite, and the 

2 to 4 inches next the footwall conaists of pyrite 

and. tennantite. A short distance away along 
. 262 GEOLOGY OF GILP'rN, CLEAR CREEl{, ~\.ND· BOULDER COUNTIES, COLO. 

the vein the two· streaks merge. In a stope 25 pyrite or along minute fractures traversing tho 

:feet above the 800-foot level and about 750 chalcopyrite. Portions of the vein not far 

feet east of _the shaft the lower 2 to 2! inch,es away show much black pulverulent chalcocite 

<>f the vein is an irregular association .of pyrite in vugs, and in places the ore is honeycombed 

and gray quartz, the next '2 to 3 inches is with irregular vugs one-eighth to one-fourth 

mainly tennantite, and the upper 1 inch is inch across. According to miners working in 

pyrite and gray quartz. In spite of this band- this stope abundance of the black pulverulent 

ing all of the primary minerals are believed to chalcocite means an increase in copper but not 

belong to the same period of mineralization, in the precious metals. Ore from this chalfor in many places they are intimately inter- cocite-bearing stope is said to have an average 

grown. value of about $40 per ton, carrying about 1.5 

The'ores of the Pittsburg mine belong to the ounces gold, 15 ounces silver, and 10 per c~nt 

pyritic type but are unusually rich in copper-· copper. 

'bearing minerals. Some portions of the ore In an underhand stope just below the 700-

consist mainly of coarse pyrite with a little foot level about 550 feet east of the shaft the 

quartz gangue, but in others pyrite is asso- total width of the vein is only about 2 inches. 

dated with chalcopyrite, antimoniacal ten- A central band of chalcopyrite and a little tennantite, and in places with some enargite. n~ntite 1.to 1! inches wide is bordered on each 

Microscopic study of polished sections of· side by one-half inch of silicified granite gneiss 

· 'copper-rich ore. from the 800-foot level showed carrying pyrite. Shearing movements along 

.that the pyrite, antimoniacal tennantite, and the vein have produced minute fractures in 

·quartz are contemporaneous crystallizations the chalcopyrite and tenn~ntite that have been 

;and that with them, also contemporaneous, filled with gray quartz. 

:occur very minor amounts of chalcopyrite and ·Starting from the border of these minute 

galena; This is one of the few instances ob- quartz veinlets the chalcopyrite has been reserved of the crystallization of galena contem- placed by chalcocite, so that narrow veins of 

. poraneously with the minerals characteristic the latter mineral border the quartz. The deof the pyritic-ore type. According to Mr. velopment of chalcocite, however, is so slight in 

Percy Alsdorf some quartz-tennantite ore amourit that the·copper content of the ore can 

from this mille developed globules of gold on not have been greatly increased thereby. This 

its surface when roasted, indicating the possi- is the greatest depth at which enrichment was 

ble presence of a telluride of gold. noted in this mine. 

As the Pittsburg vein is richer in primary The "tight" ·character of the Pittsburg vein 

copper minerals than most of the veins of this indicates the absence. of extensive postmineral 

region, it is natural that it should be one of movement along it. A small amount of postthe few veins to show an important amount mineral movement, however, is indicated by 

of enrichment in copper through the develop- the minute quartz veinlets described above and 

ment of the rich copper sulphide chalcocite. by shear planes in· ore from other parts of the 

Chalcocite. was abundant only in the highest vein. This fracturing has sufficed to render 

portions of the vein accessible for study the ore permeable to descending copper-bearing 

(shortly above the 500-foot level), but minute solutions, thus facilitating chalcocitization. 

amounts were noted just· below the 700-foot Sampling-works assays of 50 lots of smelting 

level. · In stopes 50 to 60 feet above the 500- ore, aggregating 243 tons, shipped at various 

foot level and about 460' feet east of the shaft times from 1894 to 1909~ inclusiv~, show gold, 

the vein consists of 5 inches of pyrite, chal- 0.45 to 12.72 (average 2.37) ounces; silver, 1.5 

copyrite,' tennantite, gray quartz, and chal- to 18.3 (average 7 .52) ounces; copper, not to 

cocite; the ore texture is somewhat porous. A exceed 16.6 per cent. Similar assays of 92lots 

polished section showed that the chalcocite of smelting ore aggregating 435 tons, shipped 

.developed by metasomatic replacement of during 1910, show gold, 0.52 to 25.35 (average 

chalcopyrite and to a lesser degree ~y replace- 5.77) ounces; silver, 2 to 22.65 (average 8.9;3) 

ment of pyrite. The replacement began alo:ng ounces; copper, 0:3 to 16.3 (average 6.65) per 

the contacts of chalcopyrite with quartz or cent. 
GILPIN COUNTY. 263 

WEST NOTAWAY ¥1NE. 

The West Notaway mine is on the north side 

of Russell Gulch about 1 mile southeast of 

Central City, on a single vein which is th(( westward continuation of one of those ,developed by 

the East Notaway workings. The development consists of a shaft following the vein and 

c01mecting with levels at vertical depths of 110, 

160, 230, 360, and 440 feet. The vein strikes 

on the average about N. 55°-60° E., and dips 

60°-65° NW. 

The ore is distinctly of two periods of mineralization. That of the first period· consists 

N 

9 

elsewhere the pyritic ore fragmentl? are completely cemented by nearly black cherty silica 

carrying tennantite. Both types of mineralization are. als() shown in the stopes above the 

east end of the 230-foot level, where the main 

mineralization follows the north side of a dike 

of monzonite porphyry for 3 feet, north of 

which· the s·chist is traversed by veins of fairly 

coarse pyrite. The porphyry, schist, and pyrite veins are traversed by irregular stringers of 

gray to brownish cherty silica carrying fme 

pyrite. Both types of ore distinctly cut the 

porphyry at. several places m the workings, · 

50 I 

100 I 

LEGEND 

-~ 

~ 

Idaho ·Springs formation 

0 

Vein 

( f>:rrow indicates direction of dip) 

200 300 Feet I I 

FIGURE 46.-Geologio pll\DS of levels or West Notaway· mine. Surveyed by hand compass and pacing. For convenience in comparing geology 

of successive levels tho shaft intersections arc placed in aliqnmcnt 1 but as no survey was mad~ of the shaft the distl\llce between levels is not 

shown to scale. · 

predominantly of coarse pyrite. Where well 

exposed on the 440-foot level, 70 feet northeast 

of the shaft-, the vein consists of three parallel 

bands of coarse pyrite three-quarters of an inch, 

1 inch, and 6 inches wide. In many places the 

coarse pyritic ore has been brecciated and the 

spaces filled with later ore consisting of gray 

cherty silica carrying very fine grained pyrite 

and in places considerable tennantite. Both 

types of ore are also well exposed on the 110-foot 

level (see A, fig. 46), where there is a strong vein 

1! feet wide of coarse pyrite with some white 

quartz gl\ngue. This vein has been fractured 

and in places is still only slightly cemented, but 

showing conclusively that they are of later 

origin.· 

The property is now being operated by 

lessees. All of the ore mined is shipped direct 

to the smelters. As in the East Notaway mine 

tellurides are present in the siliceous veinlets 

that cut the heavy sulphide ore of the first 

mineralization, and to their presence i~ mainly 

due the high gold value of much of the ore 

mined. As no tellurides were actually seen 

in ore available for study, the reader ~s referred to the description' of the East· Notaway mine 'for a discussion of their mo~'e of occurrence (pp. 264-265). 
264 GEOLOGY OF GILPIN, CLEAR · CR.EEK, AND BOULDER COUNTIES, COLO. 

Few of the sampling-works assays now available, for 1888 to 1910 inclusive, show a gold 

content less than 0.5 ounce or more than 7 

ounces or a. silver content less than -2 or more 

than 10 ounces. Copper varies from less than 

1.5 to about 5 per cent. The following selected 

assays give some idea of the range in metal 

content: 

Sampling-works assays of ore from the West Notaway mine. 

Year. Ore. Gold. Silver. Copper. Silica. 

Net lbs. Ounces. Ounces. Per cent. Per cent. 

1888 ........ . 3, 862 3. 15 6.30 ......... ............. 

1893.--.- ... 4,670 1. 50 6.70 3.8 ............. 

1895.-- ..... 6,319 2.97 8.00 .......... ........... 

1897.--- .. -. 11,042 . 91 2.80 ............ ............... 

1898.---- ... 12,650 1.43 5.60 .............. ............. 

1900.--- .... 6,054 2.00 7.00 4. 7 40 

1905.---- ... 11,958 . 48 2.50 .......... 64 

1906.- .. -... 11,229 . 67 3.20 7.0 49 

1908.--.- ... 5,043 7.34 4.50 2.55 ........... 

On the 488-foot level the Shaft vein is exp~sed f~r about 500 feet but is ~owhere heavily 

nunerahzed, the pyrite stringers never exceeding 3 inches in width. 

Crosscuts south from the Shaft vein on each( 

level cut the H;9mestake and Notaway veins, 

which are closely associated. In an exposure 1 

about 130 fee,t east of the crosscut on the 651-t 

foot· level, which dips 55° N., the. Homestake 1 

vein shows the following section: 

H 

. I . · Inches. 

angmg wa I, a 10-foot dike of monzonite porphyry. 

Postmineral slip pl~ne. · 

Gouge and brecciated pyrite .... : ________ • __ . __ ._._.. 3 

Coarse pyrite in a quartz gangue ....... _._ ..... _.... 6 

Pegmatite, traversed by small pyrite stringers and 

carrying some disseminated pyrite .... _ . __ . _ .. _ . . . 15 

The Notawa:y vein differs entirely from the 

Homestake vein, in size, in value, and in mineral character. It is well shown at the 555-foot 

level about 120 feet east of the crosscut from 

EAST NOTAWAY MINE. the Shaft vein (A, fig. 47), where it consists of 

The East N otaway mine rs about a mile three or four subparallel stringers of cherty 

southeast of Central City on top of the ridge appearance (maximum· width, 1! inches) in a 

between Lake Gulch and Russell Gulch. It 4 ~o ~inch zone. In other places the Notaway 

Was first opened about 37 years ago and has Vein IS represented by a single narrOW Veinlet. 

been worked continuously by the present oper- Small vugs are of exceptional occurrence and 

ating company for the last 14 years. The levels some of them are lined with silica of chalcedaccessible for study were at vertical depths of onic appearance. 

~88,_ 555, and 651 fee.t and were served by an In places, as along most of the 555-foot level 

nclined shaft followrng what -is termed the east; the Notaway vein occurs alone, but elseShaft vein. where, as on the 555-foot level for 80 feet west 

The geologic relations throughout most of the of the crosscut (fig. 47), it lies in or along the 

mine are very complex owing to the intrusion Homestake vein and is mined with it. In such 

of irregular dikes of I):lonzonite porphyry and places the N otaway dark-gray cherty ore cuts 

to the presence of t~~ -~is tinct types of miner- sharply ~hrough the heavy pyritic Homestake 

a:~z!Lti~~· The wall rocks- are monzonite por-: ore and is plainly of later formation.· 

phyry and schist of the Idaho Spr~ngs forma- Both the Homes take and N otaway veins were 

tion with more or less associated pegmatite. f~rmed later. than the monzonite porphyry 

Geologic relations are most clearly exhibited on dikes, the evidence as to the N otaway being 

the 555-foot level. (See fig. 47.) · particularly clear. Eighty feet west of the 

The north or Shaft vein consists predomi- crosscut, for example, on the 555-foot level 

nantly of coarse pyrite, characteristically low (B, fig. 47) the Homestake vein goes into the 

I

. grade, on which little mining has been done. south wall and the N otaway continues· aloncr 

As exposed in the 651-foot level near the shaft the drif~, cutting sharply through the dik~ of· 

this_ vein shows the following section: ' monzonrte porphyry. The Homestake vein is 

later than the monzonite porphyry, but there- · Section of north vein of East Notaway mine. 

Footwall pyrite. ___ ._ ... _. ________ . _____ . ____ Ft. 

Pegmatite, traversed by minute pyrite veinlets 

and carrying some disseminated pyrite...... 3 

P?i~e in a white_ siliceous gangue. _______ , ___ ._ 

Silicified pegmatite ................... _ ... _ . _ 

. Gouge-filled fracture zone, -carrying some disseminated pyrite._ .. _. ___ . ____ ._ ... ____ .__ 4 

in. lations have been masked in most exposures by 

1!± postmineral movements that have crushed or 

shattered both ore and porphyry. The resulting breccia of ore fragments in crushed porphyry bears a deceptive resemblance to certain 

breccias formed when porphyry has intruded 

ore, but careful study reveals the true relations. 

0 

10 

6 

0 
GILPIN COUNTY. 265 

The ores of the Shaft and Homestake veins are present its value may reach $200 per ton. 

belong to the pyritic type and consist predom- The gold content of the Notaway vein is notainantly of pyrite in a gangue of quartz o or bly irregular. One shipment from the 555-foot 

altered wall rock. In the I-Iomestake vein level gave a gold content of 32 ounces, and the 

chalcopyrite and antimoniacal tennantite are ·next, a shipment of similar appearance from ~he 

present in a few places. The N otaway vein same stope, ran only 2 ounces. Another lot 

consists typically of 1 to 3 inches of dark-gray ran 27 ounces and the next, from an adjacent 

cherty-appear:ing silica, fine-grained pyrite, an- part of the stope, only 7 ounces. Such irregutimoniacal tennantite, and varying amoW?-ts of larity is evidently due to irregular distribution 

a telluride of gold-and silver and native gold. of the tellurides, in which most of the preciousA study of polished surfaces of the rich tel- metal content occurs. Where,. ~p.e Notaway 

luricle ore, supplemented by an examination of vein traverses the Homestake it is necessary to 

a thin section by transmitted light shows that mine both ores. 

the predominant constituents near .the border About one~thir9, of the ou~p_l!t of the_JDipe \ 

of the l-inch veinlet are pyrite, antimoniacal is smel~ing. ore and the remainder co:ilcentennantite, and microcrystalline quartz, all trating ore. According to the sampling-works 

~1fi Monzonite porphyry 

~~ Idaho Springs formation 

I /' j Barren fracture 

(Arrows '1ndicate direction of dip)' 

100 50 0 

N 

---- Pyriticve'1n exposed t- ----- Pyriticvein inferred 0 

.~· 

·········· Notaway ve\n ~xposed ............ Notawa_y ve1n mferred -·-·- Compos1te pyritic and Notaway veins exr;1osed -·-·-Composite pyriticand Notaway,veins inferred 

FIGURE 47.-Goologic plan or 555-foot level or East Nota way mine. Surveyed by hand compass and pacing. 

apparently contemporaneous. Toward the 

center of the veinlet the sulphides decrease in 

abundance and a telluride (sylvanite~) appears, 

associated in places with native gold. Most of 

the sylvanite occurs alone, but in places it is 

intergrown, apparently contemporaneously, 

with tennantite. The larger crystals of sylvanite are platelike or bladelike in form. The 

native gold in these specimens appears to be 

primary and not an alteration product of 

sylvanite. 

•. The pyritic ore of the~h~ein is every-

~\ where below workable grade, its average value 

being about $3 per ton. ·¥ost of the ore of the 

I-Iomestake . vein. is likewise befow ---workable 

1grade, but where chalcopyrite and tennantite ·~ ,--- --- .. . 

assays the smelting ore shipped in 1909 

showed gold, 0.39 to 11.6 (average 3.3) ounces; 

silver, 2 to 11.04 (average 5.44) ounces; copper, 6.71 per cent or less. Ore shipped in 1910 

showed gold, 0.27 to 13.3 (average 2.52) ounces; 

silver, 1.8 to 15.25 (average 4) ounces; copper, 

8.5 per cent or less. 

The average metal content of the concentrating ore for 1910, as computed from the 

value of the amalgam and concentrates, was 

gold 0.18 ounce, silver 0.426 ounce. 

GULCH MINE. 

The Gulch mine, about a mile southeast 

of Central City and a short distance northeast 

of the East N otaway mine, is developed by 

' 
2.66 GEOLOGY OF GILPIN, CLEAR CREEK, AND BOULDER COUNTIES, COLO. 

rock is schist of the Idaho Springs formation 

with some pegmatite. The vein, which is a 

true fissure filling, is predominantly of the 

pyritic type; on the 400-foot level 20 feet west 

of the shaft it consists of 1! feet of pyrite and 

quartz, and at the bottom of the shaft it consists of 4 to 5 inches of coarse pyrite with some 

white quartz gangue. In the shaft between the 

300 and :400 foot levels a littie galena and 

sphalerite are associated with pyrite. On the 

200-foot level a barren crosscut extends N. 30° 

W. for 85 feet from the vein, and on the 300-foot 

level a barren crosscut extends S. 35 ° E. for 70 

feet from the vein. 

The ore mined from this property is small in 

amount and its average value is said to have 

been about $12 per ton. · 

a shaft 430 feet deep with short levels at depths 

of 80, 160, and 430 feet. The mineralization 

is greatest on the 430-foot level, and it is there 

that the geologic relations are best shewri. 

The level cuts a 10-foot dike .of monzonite· 

porphyry 50 to 60 feet east of the shaft but 

elsewhere penetrates schist of the Idaho 

Springs formation. One wall of the porphyry 

dike is followed by a barren !-inch :veinlet 

of white quartz, the other wall by a 1 t to 

2 inch veinlet of fine-grained pyrite of low 

value. Both the d-ike and the veins following 

its walls are cut by a tight 1 to 2 inch vein 

of fine chGrty-looking quartz, which carries 

chalcopyrite and fine-grained pyrite and is 

said to have averaged $2 per ton, mainly in 

gold, and exceptionally 28 ounces in gold; 

the drift follows this vein. Elsewhere on this JUSTICE VEIN. level, notably in a winze 115 feet east of the 

shaft, the mineralization consists of coarse The Justice vein, which strikes northeast 

pyrite cut by fractures filled by cherty-looking across the crest of Justice Hill, is developed by 

gray silica, antimoniacal tennantite, and fine. three shafts. · The property had been idle for 

pyrite. These. cherty veinlets are 1 inch and some years at the time of .this survey, and none 

less in width and contain some vugs. They of the workings were entered. The ore on the 

carry gold up to 2 ounces, probably tellurides, dump was mainly of the pyritic type, consistand are similar in appe~rance to the East..Not- ing of pyrite, qua.rtz, and some gray copp~r. 

away vein as exposed in the· East N otaway ExceptiOnally a httle galena and sphalente 

workings. ' ·were not~d. . 

The following selected sainpling-works assays Sampling-w?rks assays of 17: lots of smelting 

of smeltinO' ore from the Gulch mine show its ore, aggregating 60 tons, shipped from the 

considerable variation in metal content: Justice mine between 1888 and 1910: show 

Sampling-works assays of ore from Gulch mine. 

I Silv~r. ' 

Date. Ore. Gold. Copper. Silica. 

Net lbs. Ounces. Ounces. Per cent. Per cent. 

June, 1904 .. 6,156 . 10.00 10. 20 10:6o 39 

July, 1905 .. '. 7,866 . 20 2.00 .............. ........... 

Nov., 1905 .. 3, 103 4.20 6.80 9.00 30 

Nov., 1905 .. 5,880 1. 60 3.60 3.80 45 

Sept., 1906 .. 4,856 8.74 8.00 2.50 ................. Sept., 1906 .. G,314 1. 18 5. 35 5.00 ............. Aug., 1907 .. 8,500 l. 60 5.40 6. 30 ............... July, 1908 ... · 7,289 2.55 8.08 9. 65 ............ 

PEARCE OR MORRIS MINE. 

The Pearce mine is on the northeast side of 

Russell Gulch a short distance above its junction with. South Willis Gulch. The development work consists of a shaft 460 feet deep 

with short levels at vertical depths of 100, 200, 

300, and 4oo feet. The sh,aft follows the vein 

which strikes N. 70°-75° E. and dips in most 

places about 80° S. The predominant wall 

gold, 0.29 to 3 (average 1.33) ounces; silver, 3.4 

to 22.6 (average' 12.88) ounces; copper (wet), 

from l~ss than 1.50 to 7.30 per cent; and silica, 

29 to 50 per ci:mt (in six lots). Similar assays· 

of 15 lots of smelti_ng ore, ·aggregating 50 tons,. 

shipped from the St. Louis. shaft on the Justice 

vein, show gold, 0.7 to 3.87 (average 2.11) 

ounces; silver, 3.8 to 19.2 (average 10.52) 

ounces; copper (wet), from less than 1.5 to 7.1 

per cent; and silica, 28 to 73 per cent (in five 

lots) . 

WILLIS AND SOUTH WILLIS GULCHES AND 

PLEASANT VALLEY. 

TWO-FORTY VEIN. 

The Two-Forty vein is' on the south side of 

Willis Gulch near the main road from Russell 

Gulch to the Frontenac mine, 2,000 feet southwest of the Saratoga shaft. It is developed by 

a shaft over 180 feet deep, with a 700-foot drift 

at 180 feet, and by two drift tunnels. The 

lower tunnel, 1,470 feet long, intersects the 
GILPIN COUNTY. 267 

shaft 530 feet fron1 the mouth and 90· feet 

below the collar. The upper tunnel starts 

15 feet below the shaft house and runs west on 

the vein for 970 feet. The ground fron1 the 

lower tunnel to the surface is practically all 

stoped for 400 feet west of the shaft, and above 

the upper tunnel the stopes continue 800 feet 

west of the shaft. . 

The vein is in Idaho Springs forn1ation and 

is about parallel to the schistosity. It cuts 

diagonally across a bostonite porphyry dike 

near the face of the lower tunnel. The same 

porphyry is seen orr the hanging wall . of the 

·vein 690 feet west of the shaft on tlus level and 

350 feet west of the shaft on the level below. 

On the footwall a small 1nass of bostonite 

porphyry is exposed 490 feet west of the shaft 

on the lower tunnel level. Where the vein distinctly cuts the porphyry that rock is n1uch 

altered, contains son1e dissenunated pyrite, and 

. is traversed' by little veinlets of pyrite, offshoots frOln the vein. 

'fhe Two-Forty vein strikes about N. 63° E. 

and dips 48°-72° N., with an average of about 

60° N. It ranges from 2 inches to 8 feet in 

width, with an average of 2 feet, and shows 

no branches in the workings accessible. The 

vein consists of crushed silicified schist carrying 

in practically all places abundant ~no-grained 

diss01ninated pyrite. Most parts . of the vein 

contain at least one stringer of coarse pyrite 

and gray quartz 1 to 8 inches in width, the 

average being about 2 inches. These sulphide 

streaks are s.een near· the foot and hanging 

walls as well as in the central part of the vein. 

A eross section of the vein is as follows: 

Section of Two-Forty vein. 

Hanging wall. Inches. 

Black gouge, containing crushed pyrite........... l 

Two veins about parallel to the Two-Forty 

ar~ shown by the development work. One 

south of the Two-Forty on the upper tunnel 

level which has been drifted and stoped for 

about 200 feet, is a. 2 to 4 foot fracture, very 

similar in character to the Two-Forty. The 

second vein, which is exposed about 150 feet 

fron1 the mouth of the lower tunnel, strikes 

N. 85° W. and dips 60° N. It is about 8 

inches wide and is filled with .crushed wall rock 

containing a little disseminated pyrite and 

traversed by lenses and stringers of coarse 

pyrite not more than 2 inches wide. 

Lessees working on the Two-Forty vein in 

the lower tunnel ,report a few small pockets of 

coarse pyrite cont.aining chalcopyrite in which 

the gold values are somewhat higher than in the 

average ore. The average content of smelting 

ore for 1910 was 0.95 ounce gold; 5.82 ounces 

silver, and 0.69 per cent copper. Samplingworks assays of 11 lots of smelting ore shipped 

from 1895 to 1905, show gold, 0.58 to 10.9 

ounces; silver, 2.1 to 14.6 ounces; silica, 25 

to 73 per cent. Few of the larger shipments 

contain more than 1' ounce gold and 7 ounces 

silver per ton. 

SARATOGA ~INE. 

The Saratoga vein, whic.h crops out on the 

ridge between Russell and Willis gulches, ];las 

been one of the n1ost productive in the Central 

City district. It is developed by three shaftsNo. 1, 700 feet deep; No. 2, 1,000 feet deep; 

and No.3, 400 feet deep-and by the Saratoga 

lateral. No. 2 shaft, the only one now being 

operated, is vertical, connects with 10 levels, 

and is one of the few shafts in the district 

equipped with a cage. The Saratoga lateral, 

nearly 3,000 feet long, is on the level of the 

Argo "tunnel, nearly 1,300 feet below the collar 

Schist, crushed and siliciftecl, with some disseminated pyrite .................................... . 2 

of No. ·2 shaft. At the time of this survey 

1 mining was being done by the Saratoga Development Co. through the Saratoga lateral and 

4 by lessees on the sixth and tenth levels through 

2 No. 2 shaft. Most· of the workable ore above 

10 the ninth level had been s toped out. 

Pyrite, coarse, intergrown with a little gray quartz .. 

Schist, crushed, silicified, with much disseminated 

pyrite ...................................... , .. . 

Pyrite, coarse, soinewhat sheared ................ . 

Schist, sheared, with abundant disseminated finegrained pyrite ................................ . 

Gouge next the footwall. 

Posbnineral 111ovement has produced abundant blackened gouge containing fragments 

of pp:ite throughout the lei1gth of the vein. 

In n1any places the 1nassive sulphides are 

crushed. A little enargite is reported. 

The sixth and tenth levels were the only 

parts of the upper. workings that ,could be 

entered. The sixth level is open for about 

320 feet· east of the shaft but is caved just 

west of the shaft. In a stope 60 feet ahove 

the level. the vein is 1 to 2 feet wide and con:-

sists mainly of pyrite and a little white quartz 
268 GEOLOGY OF GILPIN, CLEAR CREEK, AND BOULDER. COUNTIES, COLO. 

gangue. The vein walls are not sharp and 

there is much dissemi1iated pyrite in the bordering gneiss. In places the main vein is paralleled by subsidiary veins from three-fourths 

inch to 5 inches wide. The dip is about vertical. Some of the pyrite crystals in this ore 

are as much as three-fourths inch in diameter. 

In a raise about 50 feet above the tenth level 

and 340 feet west of the shaft the vein consists 

of about 5 feet of altered granite .gneiss carrying abundant disseminated pyrite. Several 

inches of soft gouge lie next to each wall, and 

at one place a veinlet of gr~y quartz and pyrite 

traverses the center of the n1ineralized zone. 

before the workings w~re drained by the Argo 

tunnel the groundwater is reported to have 

stood at the fourth level. 

The 1netal content of l,019 tons of smelting 

ore shipped between 1893 and 1909, inclusive, 

as determined from sampling-works assays, 

was gold, 0.12 to 8.41 (average 0.90) ounces; 

silver, 1 to 13.90 (average 2.32) ounces. Copper was nearly always below the commercial 

limit of 1.5 per cent. The ore between the 

ninth and tenth levels is said to average about 

1 ounce in gold, 2 ounces in silver, and 1 per 

cent copper. 

The gross production of the mine is reported 

to be somewhat over $2,500,000. The company owns no mill. ' 

TOGO VEIN. 

· The Saratoga lateral for practically its whole 

length follows the v~in. The wall rock is almost exclusively granite gneiss, though one 

dike of highly altered porphyry (probably 

monzonite) is cut about 2,850 feet from the The Togo vein, in Willis Gulch, just south of 

Argo tunnel. For 800 feet from the tunnel the Saratoga mine, is developed by a shaft 220 

the vein is barren or only feebly mineralized feet deep, with levels at 100, 150, 200, and 220 

and n'o stoping of consequence has been done. feet. The general strike of the vein is nearly 

.Beyond this stapes occur at intervals. About east and west and tlie dip about 65° N. 

810 feet from the tunnel 6 inches to 1! feet of At a depth of about 75 feet in a winze from 

coarse pyrite, exposed on the foot,wall of the the 100-foot level the vein shows next the hangdrift, grades into granite gneiss carrying dis- ing wall a band 2 feet wide of fluorite, white 

seminated pyrite. About 2,900 feet from the quartz, and fine-grained pyrite, succeeded by 

Argo tunnel, in a stope where work was in nearly solid galena,. sphalerite, and some pyrite, 

progress at the time of this survey, there is a in places 1! feet wide. In a stope 40 feet above 

slip plane next the footwall, succeeded by 5 the 200-foot level the vein is about 1! feet wide 

inches of nearly solid pyrite s01newhat sheared and shows galena, sphalerite, and pyrite, with 

in places, and by 2! feet of granite gneiss cut some gray quartz gangue. A little secondary 

by a network of minute pyritic stringers and hematite occurs in ore from near the surface. 

carrying much disseminated pyrite. Sample3 Sampling-works assays of fou:r; lots of smeltof coarse pyrite and of granite gneiss carrying ing ore shipped from this mine in 1907 and 1910 

disseminated· pyrite, collected by the writ~r are as follows: 

from this stope, assayed, for the pyrite, gold . Sampling-works assays of smelting orefrom the Togo vein. 

0.16 ounce, silver 1.84 ounces, copper 10 per 

cent, and for the granite gneiss, gold 0.07 ounce. 

with a trace of silver. 

In general all the ore now exposed in . the 

Saratoga workings is of the pyritic type, but a . 

few old stunpling-works assays show smaU 

amounts of leaP,. The gradual transition observed at several parts of the vein from solid 

Ore. I 

Net pounds. 

3,410 

2,719 

5,076 

3,878 

Gold. Silver. 

Ounces. Ounces. 

2. 93 14.25 

3.05 17.00 . 87 4.00 

1. 59 13.46 

pyrite into gneiss carrying more. or less dis- Ore from a winze from the 200-foot level east 

semina ted pyrite indicates that the vein was is said· to have run 1. 4 ounoes in gold. and 90 

formed mainly by replacement, accompanied, ounces in silver. 

however, by some fissure filling. The ·vein, 

though not in general high grade, is one of the 

most persistent in the district and has been 

stoped throughout large continuous areas. 

During periods when the mine was idle and 

HAZELTINE VEIN. 

The Hazeltine vein, which trends slightly 

south of east across South Willis Gulch, is de:-

veloped by two shafts, the Hazeltine east of the 
GILPIN COUNTY. 269 

gulch and the I-Io.zeltine Extension .west of the 

gulch. Both of these were idle and the workings could not be entered. The ore on the 

dumps indicated that the vein was very similar 

to the Anchor vein in mineral chars.cter. Much 

con.rse pyrite wo.s present, some masses of this 

mineral being 8 inches across. Enargite was 

fairly n.bundant in association with the pyrite. 

Fluorspn.r wo.s present, as were minqr amounts 

of galenn. o.nd sphn.lerite. Vugs are abundant in 

the pyritic ore, one observed being 1 foot in 

length parallel to the vein and 2 inches wide. 

Son1e quartz crystals in this vug are one-half 

· Both pyritic and galena-sphalerite ore types 

are present. The structure of· one of the 

inch in diameter. ' 

FRONTENAC AND ADUDDELL MINES. 

The ]3'rontenac and Aduddell mines at the 

head of South Willis Gulch develop the same 

veins,' are under a single management, and § 

may appropriately be described together. In ~ 

the present development the Frontenac and t> 

., 

the Aduddell east shafts are used for hoisting ~ 

and the Aduddell west shaft for ventilation. s 

a• 

The Frontenac shaft follows the dip of the lode ~-

and connects with eight levels and one sub·- § 

:level (between levels 3 and 4). The Adud- § 

dell shaft also follows the dip of the lode and 8 

·connects with eight levels. The fourth level ( 

of the Frontenac workings connects with the ~­

fifth level of the Aduddell air shaft, which has (!) 

~ the same elevation. The seventh level of the ~ II> 

Frontenac connects thro'ugh a rise with the ~-

fourth level of the main Aduddell shaft. Short ;; 

drifts from the Argo tunnel ·on what is sup- g 

posed to be the Frontenac-Aduddell vein systenl are described elsewhere (pp. 304-305). The 

mineralization in these drifts is feebl~, and no 

·stoping has been done. 

In general the workings develop a compound 

·ve.in system made up of two and in some places 

·of several subparallel veins. The two principal veins are referred to as the North and South 

veins, but their identification in all parts of the 

mine is not certain. The average trend of the 

vein system is about N. 50° E. and the dip is 

50°-80° NW. 

The apex of the lode is in an area of Idaho 

Springs formation· and pegmatite just northwest of a contact with granite gneiss. As the 

lode is followed downward it passes out of 

schist and into granite gneiss, which is the 

prevailing wall rock in most of the workings. 

pyritic veins is well shown at the top of the 

rise connecting the eighth level of the Fron.-
270 ' GEOLOGY. OF GILPIN, CLEAR CR.EEI{, AND BOULDER COUNTIES, COLO. 

tenac with the fifth level of the Aduddell. The 

vein here has a width of about 4 feet; its aver~ 

age width in the Frontenac eighth level east 

is 5 to 6 feet. · 

Section of pyritic vein in the Frontenac-Aduddelllode. 

Hanging wall. Inches. 

Granite gneiss, sheared, carrying some crushed pyrite. 6 

Granite gneiss, somewhat fractured and altered, traversed by a few small stringers of pyrite ............ 14. 

Slip plane. 

Pyrite, cut by stringers of dark-gray cherty silica.... 2 

Pyrite, cqarse, nearly solid, cut by a few stringers of 

gray cherty quartz, some one-fourth inch in width .. 12 

Footwall. 

Another good exposure of the highly pyritic 

ore is at the east face of the Aduddell :fifth 

level, where the width of the vein is about 7 

feet. 

Section of highly pyritic vein in Aduddell mine. 

mines, that the pyritic ore was fractured ahd 

the galena-sphalerite ore later introduced. 

Throughout much of the Aduddell workings 

from the first level of the Aduddell air shaft 

down to the eighth level. of the Aduddell main 

shaft a highly siliceous ore is found, in places 

alone and in places paralleling a vein of the 

pyritic type. Ore of this siliceous type is particularly well exposed along the footwall of the 

sixth levef west. · At the face of .this level, 

about 170 feet west of the shaft, the vein is 

about 5 feet wide and appears to be mainly a 

replacement of the granite gneiss along a zone 

of fracturing rather than a true fissure filling. 

The more quartzose portions . are in general 

richest in sulphides, and there is every gradation from such mixtures of quartz.and sulphides 

into little-altered granite gneiss. Many of the 

portions richest in sulphides are, however, more 

Hanging wall. Ft. in. or less veinlike in form, owing to the replace- Granite gneiss, more or less sheared, with numerous fragments of cherty silica in the upper portion, ment having reached a maximum along anumand of pyrite in the lower portion ................ 2 o her of subparallel fractures. Pyrite is the 

Granite gneiss, carrying in places as much as 70 to 80 predominant sulphide in most of the siliceous 

· per cent (by volume) of pyrite ........... ~........ 8 ore and is in some places the only one present. 

Granite gneiss, cut by several pyrite stringers, three- Elsewhere, however, galena, sphalerite, and 

fourths inch or less in width, generally carrying some chalcopyrite are also present and· are so some quartz .............................. ~ ..... 1 0 

Pyrite, coarse, with some quartz gangue ......... ". 1 o intimately associated with the pyrite as to 

Granite gneiss, more or less silicified, carrying vary- leave little doubt of their contemporaneity. 

ing ai;Uounts of disseminated :fine pyrite ......... 2 0 Rhodochrosite is present in a few 'places as a 

Vein structure where the mineralization is gangue mineral. In general it seems probable 

mainly of the. galena-sphalerite type is well that the siliceous ore is cogenetic with that of 

shown on the Frontenac seventh level in a the Druid !fiine (see pp. 272-273) and is to .be 

stope about 1,125 feet west of the shaft, where regarded as an uncommon phase of the second 

the ,width of the vein varies from 4 to 7 feet. or galena-sphalerite mineralization. 

Both types of ore 'are exposed on the eighth In addition to the veins described above the, 

level of the Frontenac mine about 860 feet Frontenac workings expose what is known as. 

west of the shaft. the Flat vein for nearly the whole length of the. 

Section of vein in Frontenac mine, showing composite miner- tunnel level. (See fig. 48.) The wall rocks. 

alization. as far as the 1 ,000-foot raise are schist of the. 

Hanging wall. Idaho Springs formation and pegmatite, and.. 

Slip plane. . Inches. the vein is a pronounced fault zone only feeBly 

Gouge ........ ----·····:····----~---····:········· 4- 6 · mineralized with disseminated pyrite and a. 

Galena, coarse, and reddiSh-brown sphalerite ........ 3-5 f ll · f 1 d l' · 'Galena, sphalerite, and pyrite, more or less crushed._ 2 ew sma strmgers o ga ena an spha ente. 

Pyrite, coarse, with a little white quartz gangue..... 12 Beyond the 1 ,000-foot raise the wall rock is. 

Footwall of granite gneiss, carrying a little dissem- wholly schist and the fault is much less coinated pyrite. · herent, the movement being distributed among· 

In the preceding section the relations be- many s~all slip planes parallel to the schist 

tween the pyrite and the galena-sphalerite ore folia. This portion of the vein is hardly at all 

are not clearly shown, but elsewhere. in the mineralized. , 

mine and in specimens from the ore bins and The Flat vein as exposed on the fourth level 

dumps the two types were commonly separated west of the Frontenac is in most places inby sharp contacts, a relationship which accords closed in walls of granite gneiss and is a very· 

with the evidence, obtained from neighboring definite zone of gouge and brecciated wall rock. 
GILPIN COUNTY. 271 

6 inches to 1! feet wide. Sulphides are present 

only as sparse disseminations. In the last 

120 feet of this level the wall rock is schist of 

the Idaho Springs formation, and the fault 

breaks up into a zone 5 or 6 feet wide, through 

which there has been slipping between the 

schist folia but neither mineralization nor even 

noticeable alteration of the schist. Although 

the Flat vein has in places been slightly 

mineralized, much of the movement along it 

has been subsequent to its mineralization and 

to that of the Frontenac-Aduddell vein system. 

It cuts across the strike of the latter at a small 

angle (see fig. 48) and dips somewhat more 

gently 'in the same general direction.· The 

contact between the Flat vein and the Frontenac-Aduddell system pitches very gently 

southwest. The crossings are shown in figure 

48 at A on the tunnel level, 8 on the fourth 

level, and C on the sixth level, the exact position of the last being .hard to determine because the two veins are nearly parallel. The 

main interest in the Flat vein centers in the 

fact that it displaces the workable veins of the 

Frontenac system, none of which have been 

found beyond it, though their continuation 

should lie above (or northwest) of the vein. 

The direction of movement along the Flat vein 

is, however, uncertain. If the north wall 

moved upward for a considerable distance with 

respect to the south wall, the ·continuation of 

the Frontenac veins may have been shifted 

upward to· a point above the present surface 

and may have been entirely removed by erosion. A raise on the Flat vein above the tunnel level failed to find its continuation. If, on 

the other hand, the north wall of the Flat vein 

has 1noved down with respect to the south wall, 

or has moved up only for a short distance, then 

a crosscut driven northwest from some point 

well up on the Flat vein should find the faulted 

continuation of the Frontenac-Aduddell system. There is some slight evidence that the 

north wall of the Flat vein has moved downward with respect to the south wall, but it is 

far from conclusive. A drill hole· or crosscut 

driven northwest from the Flat vein would 

appear, however, to be justifiable prospecting. 

Postmineral displacement is not confined to 

the Flat vein, but in places has followed the 

veins of the Frontenac-Aduddell system, brecciating the ore and developing gouge. In some 

places the fractures have been healed ·with 

cherty silica, and in other places the matrix: of · 

crushed gneiss inclosing sulphide fragments 

'Qas apparently been recemented by the solution and redeposition of portions of its own 

substance. 

The mineral character of the ores may be 

summed up as follows: The mineralization is 

of the pyritic type, of the galena-sphalerite 

type, and composite. A highly quartzose ore 

found in portions of the Aduddell mine 1.11ay be 

an uncommon phase of the galena-sphalerite 

mineralization. The· characteristic minerals of 

the galena-sphalerite type of ore are galena, 

sphalerite, chalcopyrite; tennantite, ,and pyrite. 

Some enargite is reported to occur locally, 

probably (as in adjacent mines) in ore of the 

pyritic type. No evidences of downward 

enrichment were noted in any of the workings 

examined. Ore at a depth of 90 feet in the 

Aduddell air shaft was unoxidized. · · 

Accor~ing to Mr. H. P. Lowe, manager of 

the Frontenac-Aduddell property, 27,000 tons 

of smelting ore from the upper levels 'of these 

mines averaged $23.30 per ton. The smelting 

ore being obtained at the time of survey from 

t~e lower levels is estimated to average $25 per 

ton. Below the si.xth level of the Frontenac 

about two-thirds of the value of precious metal 

content is in gold and one-tliird in silver; 

higher up the silver content was proportionately greater, possibly as a result of a small 

amount of downward enrichment in silver. 

The value of the concentrating ore may be 

inferred from the results of a test mill-run on 

3,209 tons of ore taken from all parts of the 

mine below the sixth level of the Frontenac. · 

The net savings per ton were gold, $4.56; silver, 

$3.29; copper and lead, $0.50; total, $8.35 .. 

The Gilpin County tramway carries the 

smelting ore to the sampling works at Blackhawk and the concentrating ore to the 

Frontenac ·and Iron City mills below Blackhawk: These mills are briefly described on 

pages 160-161. 

The Frontenac mine is reported to have had a 

gross production of about $980,000 fr01n above 

the fourth level, exclusive of. the fr~e-milling 

surface ore. The total gross production of 

both the Frontenac and Aduddell mines up to 

the fall of 1911 is estimated by Mr. Lowe at 

about $2,250,000. . 

The following selected sampling-works assays 

show the range of the smelting ore. 
272 GEOLOGY OF GILPIN, CLEAR CREEK, AND BOULDER COUNTIES, COLO. 

Sampling-works assays of ore from Frontenac-Aduddell mines. 

Year. Ore. Gold. Silver. Copper. Lead. Zinc. Iron. Silica. 

1907 ................... : .. . 1909 ...................... . 1909 .............. ·.· ...... . 1909 ...................... . 

Net lbs. 

18,548 

65,010 

94,265 

93,063 

19, 144 

Ounces. 

0. 28 

. 50 

~ 44 

. 37 

. 20 

. 44 

. 45 

. 94 

. 47 

. 35 

. 20 

. 57 

. 52 

. 20 

.19 

. 20. 

. 22 

.18 

. 28 

Ounces. 

11. 70 

18. 24 

22. 00 

19. 60 

Per cent. Per cent. Per cent. Per cent. 

2. 00 6. 00 1. 5 ......... . 4. 45 6. 80 2. 0 ......... . 4. 50 6. 90 .................. .. 3.10 6. 20 .................. .. 

Per cent. 

56 

43 

35 

41 

51 

40 

35 

1907 ...................... . 1908 ...................... . 1894 ...................... . 1894 ...................... . 1908 ...................... . 

108, 720 

18,669 

4,930 

7,496 

20,660 

19, 517 

19, 790 

8. 15 

18. 10 

23. 10 

23. 50 

19. 80 

2. 10 ............................. . 4. 40 .. .. .. .. .. 4. 0 16 

4.10. .......... .......... 20 

3. 70 ....................................... . 1. 85 ....................................... . .1909 ............. ·.· ....... . 9.05 1. 85 ....................................... . 1909 ...................... . 13. 15 2. 65 ... ·.· .................................. . 1909 ...................... . 1907 ...... ~ ................ . 1907 ..................... '. 

1,907 ...................... . 

6,008 

9, 752 

14,066 

22, 893 

18,533 

45,407 

12,682 

14. 43 

12.00 

12. 35 

11. 46 

3.05 : : : : : : : : : : .... ~ r gf : : : : : : i.: ~: : : : : : : : : : : 1: : : : : : : : ~~ . .. .. .. .. . 22. 50 6. 5 .. .. . .. .. . 36 

1907 ...................... . 1907 .................. , .... . 1909 ....................... . 1908 ............. ·.' ........ . 

8. 80 

6. 95 

6. 50 

5.30 

.. .. .. .. .. 11.50 14.8 .. .. .. .. .. 35 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59 . .. . . . . . . . . . . . . .. .. . . . . . . . . . . . . . . .. . . . . . 54 

DRUID MINE. 

The Druid mine is not far from the head of 

South Willis Gulch, on the northeastward 

continuation of the Frontenac-Aduddell lode. 

The workings consist of the Druid shaft, 500 

feet deep, connecting with eight levels, and the 

Searle shaft about 100 feet farther south, 

connecting with levels at depths of 60, 90, and 

140 feet. Conp.ection has been made between 

the Searle and Druid workings. At the time 

of survey mining was in progress by lessees in 

both sets of workings. 

The wall rock down to the 350-foot level of 

the Druid workings is mainly schist of the 

Idaho Springs formation, ,but below this 

granite gneiss predominates. On the 50-foot 

level of the Druid shaft and the 90-foot level of 

the old Searle shaft, a dike of monzonite 

porphyry apparently striking east and west is 

exposed. It is not visible on the surface and 

is not cut on any of the other levels. 

The Druid workings develop a series of 

subparallel mineralized fractures striking N. 

40°-70° E., two or three being exposed on 

most of the levels, and dipping 55°-80° NW. 

Above the 400-foot level the shaft is vertical 

and is not on a vein; below this it follows the 

South vein. of the Druid series. 

The South vein is more regular and persistent 

than the others and is especially well exposed 

on the 150, 200, and 300 foot levels. It shows 

great variation in width, in a few places being 

narrow and nearly barren and elsewhere attaining the uncommon width of 11 feet. On the 

150-foot level east, where it is 11 feet wide, it 

shows the following cross section: 

Section of south vein in Druid mine. 

North or hanging wall. 

Slip plane, dipping 80° N ., bearing slickensides 

which pitch 20° W ......................... . 

Wall rock, soft, gray, crushed, barren .......... . 

Quartz, gray, brecciated, carrying some fine pyrite 

W.all rock,· somewhat fractured, cut by many minute pyrite stringers ........................ . 

Pyrite, coarse, brecciated, the interstices being 

occupied by galena and sphalerite, associated 

with some quartz and barite ................ . 

Schist, .somewhat altered, cut by. a few minute 

stringers of galena and pyrite ................. . 

Wall rock, altered, carrying disseminated pyrite 

and traversed by irregular veins and lenses of 

pyrite, with a very little white quartz as a 

gangue. Many of the pyrite crystals measure 

Ft. in. 

2-4 

6 

6 

1-3 

1 8 

one-half inch and a few 1 inch across. . . . . . . . . 7 0 

In one place on the 300-foot le~el east a vein 

of nearly solid pyrite 1 foot in width is cut by a 

network of minute stringers of gray quartz 

carrying some fine galena. In another place a 

stringer of galena and sphalerite cuts sharply 

across one composed wholly of pyrite at nearly 

a right angle, showing conclusively that it was 

formed later than the pyritic mineralization. 

In places on this level the galena-blende mineralization is very conspicuous, and one exposure 

shows 1 foot of vein material composed almost 

wholly of galena and sphalerite with only a few 

inclosed fragments of pyritic vein n1aterial 'or 
GILPIN COUNTY. 273 

wall rock. Vugs are lined with quartz and latter indicate that the siliceous ore is, probably 

with crystals of galena and sphalerite. to be regarded as a phase of the second or 

Ore similar to that of the Druid South vein galena-sphalerite mineralization, the mechawas characteristic of the Searle vein lying nism of ore deposition being wall rock replacenearly parallel to it but farther south. ment rather than fissure filling. The siliceous 

The Druid veins north of the south vein are ore of the Druid and Searle mines is probably 

narrow and less persistent and in places are cogenetic with that of the Aduddell mine, which 

characterized by a different type of mineraliza- also in places carries galena sphalerite and also 

tion. This mineralization was exemplified in rhodochrosite, minerals characteristic of the 

the principal ore shoot on the north vein, which, second mineralization. 

according to ::Mr. Q-. E. Collins, was irregularly As already intimated the ore of the Druid 

pipelike in form and extended from the surface and Searle workings is of two types. The first, 

to the 300-foot level. This shoot widened which constitutes the typical ore of the Searle 

greatly at intervals where certain layers of the vein and of the South vein of the Druid workgently dipping schists were replaced to an un- ings, is similar in general to the commoner ore 

usual degree by ore minerals. This type of types from the Frontenac and Aduddell iillnes, · 

mineralization is also represented by the ore of being a heavy sulphide ore bordered by more 

a new shoot, opened in 1912 subsequent to this or less disseminated ore. Most of it is conlsurvey, on the middle vein on the 150::-foot posite, consisting of earlier-formed heavy 

level, where it was 30 feet in length and 2 feet in pyritic ore (pyrite and some chalcopyrite and 

average width. According to :Mr. Collins the enargite) and of later-formed ore (galena and 

ore is essentially a. replacement of the more sphalerite and some barite), which in many 

micaceous layers of the schist of the Idaho places occupies. fractures in the pyritic ore or 

Springs formation by pyrite, galena, chalcopy- serves as a 1natrix for pyritic fragments. 

rite, and sphalerite, named in order of their The second or siliceous type of ore, which 

abundance. Most of it is highly siliceous. carries sulphides in much less abundance and is 

Siinilar ore was found in a small chamber stope, highly quartzose, is essentially a replacement 'of 

said to have been the most productive in the schist of the Idaho Springs formation by 

mine, just north of the Searle shaft on the 90- quartz and pyrite and in places also by galena, 

foot level, where the ore remnants still visible chalcopyrite, and sphalerite. The replacement 

are mainly a replacement of certain schist has proceeded outward from narrow and in 

layers by pyrite, .though there are also some 1nany places scarcely perceptible fractures, and 

stringers of gray granular quartz and pyrite so far as could be learned appears to affect the 

that clearly cut coarse pyritic ore. The same schist in preference to the granite gneiss and to 

type of ore is found in what is known as the affect the more micaceous folia of the schist in 

Svoldi lease on a vein distinct from the Searle preference to the n1ore quartzose. 

but worked through the 90-foot level of the Subsequent to both n:uneralizations moveSearle shaft. This vein strikes N. 30° E., dips 1nent took place along a number of the veins, 

about 55° N., and appears to be cut off on the as is shown by slickensided fracture planes on 

north by the Searle vein. Rich ore of the sec- the walls or traversing the ore in many parts of 

ond, more quartzos~ type is· confined so far as the mine. This n1ovement has not been in one 

now lmown to the portions of. the workings direction only but in several, as is shoW]). by one 

above the 300-foot level, where schist of the exposure, where a slip zone on the hanging wall 

Idaho Springs formation is the predominant shows horizontal slickensides on one layer and 

wall rock. The possibility of similar ore occur- vertical ones on another. .The cutting off of 

ring as a replacement of granite gneiss should the siliceous ore of the Svoldi lease at the Searle 

not, however, be lost sight of, for similar sili- ·vein may be due to such postmineral movement 

ceous ore in the Aduddell n1ine (see p. 270) is along that vein. 

in places a replacement of granite gneiss. According to :Mr. Collins, the coarse pyritic 

The occurrences of veinlets of quartz and ore o~ the Searle and South Druid veins is charpyrite cutting heavy pyritic ore near stopes acteristically low grade, carrying from 0.1 to 

which carried the siliceous ore and the occur- 0.2 ounce of gold and 3 to 5 ounces of silver 

renee locally of galena and sphalerite in the per ton. So1newhat higher values obtain when 

44214°--17----18 
274 GEOLOGY. OF GILPIN, CLEAR CREEK, AND BOULDER COUNTIES, COLO. 

copper minerals are present, as in the enargite- 500-foot level about 170 feet southwest of the 

rich ore which shows 0.15 to 0.25 ounce of shaft, where 4 feet of coarse pyrite with very 

gold, 12· to 18 ounces of silver, and 3 to 13 per little gangue is exposed. Material of this kind 

cent of copper. is too low grade to mine. In other portions of 

. The second mineralization introduced galena the vein, as on the 400-foot level 200 feet west· 

and sphalerite and notably increased the con- of the shaft, enargite is an abundant ore mintent of the-ore in both gold and silver. One eral. It is intimately intergrown with pyrite 

assay of galena ore from the Searle vein on the and the two are plainly contemporary. 

300-foot level gave gold 1 ounce and silver 108 In portions of the vein galena and sphalerite 

ounces. A sampling-works assay on. a shipment are present. None of this ore was seen in place; 

fr.om the 300-foot level of smelting ore. rich in and specimens on the dump did not exhibit its 

galena and sphalerite showed gold 0.6 ounce relati<;ms to the pyritic ore. It consists of . 

and silver 70 ounces. galena, sphalerite, gray quartz, and subordinate 

The richest ore of the mine is the siliceous pyrite. One lot of this ore from the 500-foot 

type, which as already stated is in the, main level west averaged about gold 0. 12 ounce and 

a replacement of· the· schist, and this ore has silver 2 to 3 ounces. Some fluorite has .been 

formed the main resource of the mine. Accord- found in the eastern portion of the vein, and 

ing to Mr. Collins, the average metal content of according to Mr. Percy Alsdorf some tellurides 

the siliceous ore shipped from the. Svoldi lease of gold occur. 

in April to July, 1911, inclusive, was gold 3.02 An interesting feature of the older drifts is 

ounces and silver 30.17 ounces. The average the occurrence of incrustations of beautiful 

composition of the siliceous ore shipped up to· soluble salts on the timbers -and wall rock. On 

June, 1912, from the siliceous-ore shoot on the the 400-foot level east of the shaft blue-green 

Druid middle vein was as follows: stalactites of iron and copper sulphates are 

Assay of siliceous ore from shoot of Druid middle 1Jein. 

Ounces. 

Gold. __ ._. ___ . .':.,......... . . . . . . . . . . . 2. 50 

Silver._ .. __ . __ . . . . . . . . . . . . . . . . . . . . . . . 22. 27 

Percent. 

Insolub~e (mainly silica) ....... _ ..... 70.·2 

Iron. __ .. __ ~ ...... ·. . . . . . . . . . . . . . .. . . . 11. 0 

Sulphur .. __________ ._ ................ 12. 7 

Copper_ ... __ . . . . . . . . . . . . . . . . . . . . . . . . . 1. 1 

Lead... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2. 5 

Zinc ........... '........ . . . . . . . . . . . . . . 1. 2 

·An assay of a sample of siliceous ore collected · 

by the writer from the Svoldi lease showed 

gold 1.66 ounces and silver 24.54 ounces. · 

KOKOMO MINE. 

The Kokomo mine is on the east side of 

South w·illis Gulch, at an elevation of 8,950 

feet. The workings are on .the northeastward 

continuation of the Frontenac-Aduddell-Druid 

lode,· on a single vein striking·about N. 55° E.· 

and dipping about 70° NW. The development 

work consists of a shaft which follows the vein, 

with levels at depths of 200, 300, 400, and 500 

feet. The 200-foot level was not accessible 

for study. · 

In mineral character the' vein is very similar 

to those developed in the Druid workings. 

Certain portions are wholly pyritic,· as on the 

locally present and some are 6 inches in length. 

In other places white crystals of alum coat the 

walls,· haV'ing been deposited by sulphate 

waters descending through the vein and evapo-. 

rating on the walls of the drift. 

The following sampling-works returns give 

an idea of the range in value of the ore: 

Sampli~g-works assays of ore from th~ Kokomo rr;ine. 

Year. Ore. Gold. Silver. Copper. Le~d. 

-

Net lbs. Ounces.• Ounces. Per ct. Per ct. 

1893 .. -- ... - 225 1.25 29.00 .............. ................. 

1897 0 -- ~ ---- 6,840 1. 10 16. 90 ····---- -------- 1901. .. ----0. 2,049 .18 12. 80 . ......... 11. 50 

1901.. 0-- ... 20,642 . 34 13. 70 . .............. 7.00 

1901. ....... 5,290 . 32 15. 70 5. 00 .. ............ 

1902.------- 1,330 .46 16. 50 7. 10 -------- 1902.----.-- 590 . 32 24. 60 4.00 .......... 

The last three lots probably represent orecarrying enargite. 

ANCHOR MINE. 

The Anchor mine is on the southeast side of 

South Willis Gulch at an elevation of about 

8,700 feet. At the apex the vein strikes 

slightly east of north and dips 45°to 65°N. The 

vein is developed by a shaft, which is about 50Q· 

feet deep on the incline, but which was idle at 
GILPIN COUNTY. 275 

tho time of this survey, so that the underground 

workings were not seen. 

T,he ore most abundant on the dump was an 

irregular association of white to dark-gray 

quai'tz and pyrite. Another abundant type 

consisted of an irregular association of white 

quart:z, white to pale-purple fluorite, and 

pyritfl. Some specimens showed molybdenite 

in a finely divided state abundantly associated 

with quartz, fluorite, and pyrite; and one specimen, a !-inch veinlet, showed n-inch to l-inch 

bands of molybdenite inclosing a center which 

was largely quartz and pyrite. Other specimens showed abundant enargite intergrown 

with pyrite and fluorite and apparently consilver not exceeding 45.15 ounces. Copper 

is seld01n sufficiently abundant to be paid for, 

being below 1.5 per cent in most of the ore, but 

exceptionally reaches 4.5·per cent. The average metal content of the smelting ore shipped in 

1910 was gold, 0.44 ounce; silver, 12.8 ounces; 

lead, 3.2 per cent; and copper, 0.2 per cent. 

The Anchor mine was opened about 1890, 

a~quired by the present company about 1907, 

and worked by them continuously unti~ the 

spring of I 911. 

CHASE MINE. 

The Chase mine is near the crest of the divide 

between Russell and South Willis gulches. 

The workings are mainly on the Chase vein, 

0 so 100 200 Feet L--.-J-.--L.-----J 

. 

-

Wall roc:k is Idaho Springs ~ r-:±:=1 

Monzonite 

' 

porphyry 

formation 

otherwise 

except 

indicated 

where 

Pyritic 

t:.=.=.J 

veins Unmineralized 

'--=--J 

fractJ:.e ~ Arrows mdicate direction of~ip 

FIGURE 49.-Gcologlc plan or portions of the Chase mine. 

Workings inaccessible · 

temporaneous; and ·still others showed chal- which was first developed through the Pullman 

copyrite abundantly associated with pyrite. shaft but is now worked solely through the 

Some small occurrences of galena and sphalerite Chase shaft 200 feet farther west. The Chase 

in, a quartz gangue were noted, but their rela- shaft, which follows the vein, is 500 feet deep 

tionship to the other vein minerals was not and connects with seven levels, on si.-x: of which 

clearj The smelter returns show that in some the workings develop only the Chase vein 

of the ore shipped they were abundant. and its branches. On the 300-foot level 

There are very wide v~riations in the value there has been some development on the 

of the ore and the proportion of the metals . Bosen-Plume and Decatur veins. 

present. A comparison of sampling-works The prevalent wall rock is Idaho Springs for-) 

assays on 40 lots of smelting ore shows that in mation with minor amounts of pegmatite. Monmost shipments the value is wholly in gold and zonite porphyry is exposed on· the surface north 

·silver. In this typ.e of ore the gold commonly of the shaft, in many places on the 400-foot I 

ranges from 0.2 and 0.7 ounce and the silver level, and less abundantly on the 300-foot and \ 

fron1 8 and 20 ounces. Another type of ore 500-foot levels. Figure 49 shows the g·eologic. 

ca.rries lead not exceeding 30 per cent and relations in the 300-foot and 400-foot levels. 
:27(} GEOLOGY OF GILPIN, CLEAR CREEK, AND BOULDER COUNTIES, COLO. 

1 

The Chase vein occupies a persistent and 

well-defined fracture zone, s~g northeast 

and . varying from verticality 'to steep nort"hwest or southeast dips. In a fe~ places it. 

consists of a narrow and barren fracture, but_it 

1 is usually well mineralized. A characteristic 

!, exposure on the 300-foot level 240 feet east 

of the shaft shows the vein sharp walled 

( and 6 inches wide. It consists mostly of coarse 

pyrite with some white_ quartz gangue. The 

scliist walls carry disseminated pyrite in decreasing abundance for about 6 inches from the 

vein. The Chase vein is particularly well 

·exposed in the stopes on the 500-foot level east, 

:where it varies from 8 to 12 inches in width. 

It consists of cubical pyrite in coarse crystals, 

:some of which are 2 inches across, lying in a 

·white clayey matrix, which, when . examined 

under the microscope, · appears to consist 

wholly of small grains of quartz and minute 

flakes of sericite. Pm::£!.e_t~:P.s1. _g_!~~ll- Al!.orite is 

abundant in places, and tennantite is exceptionally present. In one pia;;eth.ere. 'is nearly 

3. inches of pure fluorite associat~_lY'jth_ very 

CQ!!J:S~tt _pyrite. At another place on the 500-

foot level the Chase vein shows 3 inches of 

f' pyrite traversed through its central part by a 

{ -! to 1 inch streak of galena and sphalerite, 

) probably a later mineralization. 

' It is noteworthy that wherever porphyry is 

associated with the vein the 1nineralization is 

later than the porphyry intrusion. What appears at first sight to be an exception to this 

:rule is found on the 300-foot level east, where 

the vein is cut off by a body of porphyry 50 feet 

through. Close inspection shows, however, 

that the Chase vein penetrates the porphyry 

for 10 feet or so until cut off by a fault (A, 

:fig. 49), and that the porphyry is bounded on 

the east by a fault plane (8, :fig. 49). The vein 

east of this ·porphyry n1ass aligns with the 

·Chase vein and has generally been assu1ned to 

be its eastward continuatibn. According to 

I Mr. H. C. Willis, however, it is characterized by 

\

more coa~e~_pyrit~- an~, fluorite and by 111-uch 

lower values than the Chase vein. The fault 

~~(A,· :fig. 49) is a strong one, showing locally 3 

inches of gouge, ~nd it is quite possible that the 

vein to the east may be the Decatur or some other 

vein faulted into alignment with the Chase. 

Another feature of interest is the presence on 

the 300-foot and 400-foot levels, 450 to 500 

feet east of the shaft, of a series of parallelinineralized cross fractures striking about N. 40° W. 

and dipping 40°-65° NE. For 100 feet wost of 

the fault 15 to 20 of these veinlets from one-half 

inch to 5 inches wide are exposed in the south 

wall. Si1nilar veinlets el).ter the north wall also, 

but these do not all correspond with those iii the 

south wall. The cross fractures occupied by 

the veinlets were formed previous to the mineralization, and were m'ineralized at the. same 

time as the Chase vein, for in places the sulphides 

~an be traced continuously from the Chase fissure into these cross fissures. On the 300-foot . 

Level, at the place (C, fig. 49) where one of the 

cross veins just described is connected by a 

diagonal vein with the Chase vein, one of the 

best ore shoots of the mine extended for son1e 

distance above the level but not far below it. 

In general, the best ore in the Chase vein · 

seems to be· that in which tennantite is most. 

abundant. The presence ~f ~ fl~o~ite- is not an\ 

indication of richness. · \. 

The Bosen-Plume vein (see fig. 49) has been 

developed by short drifts west of the shaft on 

the 300-foot level. As there exposed, it consists of from 1 to 7 inches of coarse pyrite and 

white quartz. 

The Decatur vein is also exposed on the 300-

foot lev(3l, where it is reached by a crosscut 

from the Bosen-Plume drift. It stands nearly 

vertical in most places. At the west face of 

the drift 3 feet ·of coarse pyrite and quartz, bordered by walls of sericitized schist which carry 

disseminated pyrite, is traversed by several 

subsidiary pyrite veinlets, giving a total width 

of vein of 5 feet. Postmineral movement along 

the walls of the vein has locally produced 2 to 3 

inches of gouge and seams of crushed pyrite 

which traverse the main sulphide streak. 

As is apparent from the description already 1 

given, the ore of the Chase mine is of the pyritic • 

type, except for small amounts of galena-sphalerite ore in the Chase vein. The presence· of 

fluorite in the Chase vein and of enargite in ·the 

Boson-Plume ·is noteworthy. 

At the time of this survey only smelting ore 

was shipped from the Chase mine.· . Samplingworks a~says of 34 lots ·of s1nelting ore, aggregating 193 tons, shipped bet~een 1893 and 

1908, show: Gold, 0.29 to 8.2 (average, 1.98) 

ounces; and silver, 1.9 to 28.4 (average, 6.53) 

ounces. The average content of the smelting 

ore shipped in 1910, according to sampling 

works assays, was gold 2 ounces and silver 5 

ounces. Few assays show n1ore than 1.5 per 

cent copper, not enough to be paid for. 
GILPIN·. COUNTY. 277 

WAR DANCE MINE. a connection is by no means proved, and even 

The War Dance mine, on th~ hill between if proved would not preclude the occurrence 

Russell and Willis gulches, was originally of valuable telluride ore along minor fractures 

worked for its sulphide ore, but in February, ~t some· distance from the main veins. The 

1908, gold telluride ores of much higher grade fluoritic ore is not confined to large fracture~ 

were discovered close to the sulphide ore and "zones (see p. 114) but has developed in many 

have since formed the output of the mine. places through replacement of the country 

Son1e valuable telluride ore has also been re- rock by solutions _entering along very minute 

covered from the old dumps. The mine is fractures. It would seem to be the part of 

developed by a shaft connecting with short wisdom therefore to prospect thoroughly the 

levels at 80, 140, 200, 325, and 375 feet. The ground for some distance on either side of the 

irregularity shown in . the distribution of ·the sulphide vein. 

high-grade ore is reflected in the notable The fluoritic vein material occurs in twoirregularity of some of these levels. ways. It forms sharp-walled veins, as on the 

The sulphide vein, though now exposed at 375-foot level 30 feet southwest of the shaft,. 

only a .few points in the mine, strikes in gen- where it occurs in two parallel veins 7 and 4 

eral northeast and is characterized by steep inches wide. The 7 -inc~ vein shows 1 to 

dips. It consists. of pyrite and gray quartz 1 t inches of white quartz next one wall, 5 

with some tennantite. Enargite has also been inches of nearly solid granular purple and red 

reported. Vugs are common and are lined with fluorite, and one-half inch of gray quartz next 

ci:ystals of these minerals. The vein is well the other wall. Near the contact between the 

exposed east of the shaft on the 325-foot level, quartz and fluorite bands occur some aggrewhere it strikes N. 30° E., is vertical, and is gates of pyrite whose maximum width·is one3 feet in width. At the shaft on the 80-foot half inch. The other vein, parallel . to the 

level it strikes N. 55° E. and dips 70° SE. "first, consists mainly of fluorite with a little 

Though no galena and spahlerite were seen pyrite through it, especially near the ·walls. 

in this 1nine by the writer they are known to Tennantite is found. in places in these veins. 

have been present in some of the ore; and lead Both veins send off numerous branches of 

and zinc appear in one of the assays. As in. fluorite and pyrite into the bordering schists. 

other mines of the district where these min- Some vugs in· these branches are lined with 

.eru1s occur in a -vein predominantly pyritic, crystals of quartz and pyrite, and the darkthey were probably introduced at a later gray sqhist bordering them has been bleached 

period of mineralization. Ore from the sui- white. The material of such large fluoritic 

' phide vein shortly below the 80-foot level veins as those described above is characteristiassayed only 0.2 ounce gold and 30 ounces cally of too low grade to pay for mining. 

silver, whereas a ton lot of near-by telluride In the second mode of occurrence the fluorite 

ore ran 20 ounces gold and 3.5 ounces silver. and associated minerals form smaller. veinlets 

The rich ore of the mine, in contrast to the or somewhat irregular replacements of the wall 

sulphide ore, occurs along a complex network rocks. One such occurrence is shown on the 

of fractures, some paralleling the sulphide . 325-foot level 40 feet southwest of the shaft, 

vein and others being highly inclined to it. where the wall rock is mineralized for a width 

The characteristic minerals of this ore ate of 4 to 5 feet by a network of veinlets carrying 

purple fluorite, pyrite, and locally a pale-yellow pyrite, fluorite, quartz, and in places gold 

telluride of gold in platelike crystals not more telluride. 

than 2 mi~limeters or so in length. Explora- In a few places, as on the northeast drift of 

tion, though mainly confined to the vicinity of the 140-foot level, the fine-grained pegmatite 

the sulphide vein, has already shown that rich wall rock has been brecciated, and more or less 

telluride ore may occur at some distance fluorite occurs in the matrix:. At one p8int the 

therefrom and along fractures, some of which brecciated zone is 3 feet in width. · 

are clearly not branches of the main sulphide . It is clear that in general the tellurides· are 

vein and some of which cut acrm;;s it. Though not abundant in either the· sulphide vein 

some evidence suggests a relationship between material or the coarse fluorite but are characthe sulphide and telluride mineralizations such teristically found in the smaller veinlets and in 
. ' 

278 GEOLOGY .OF GILPIN, CLEAR CREEK; AND BO~LDER COUNTIES, COLO. 

the wall rock bordering. coarse fluoritic veins. 

Assays in one place showed th~t the altered 

schist near a coarse fluorite vein averaged 

about $5 per ton in gold and that the coarse 

fluorite contained from a trace to $3 per ton in 

gold. The wall rocks in the mine are ·schist of 

the Idaho Springs formation and granite pegmatite, and valuable ore has been formed by 

the replacement of both. · , 

In general it seems probable from the 

relations shown in this mine and in others in 

· ts vicinity that the fluoritic mineralization is 

·Closely related genetically to the development 

of the pyrite-chalcopyrite-gray copper veins. 

An exposure suggestive of such a connection 

occurs on the 250-foot level northeast of the 

shaft, where a vein I! feet wide consists ·mainly 

of pyrite and gray quartz with some tetrahedrite. The gray quartz gangue contains 

.fluorite in, some places, and quartz coats 

fluorite crystals that line a large vug. 

All the telluride found in the mine is similar 

In appearance. It forms flakes or plates of 

pale brass-yellow color which frequently show 

numerous striations in one direction. In most 

of the ore now being mined ·the plates show no 

evidence either of decomposition· pr of deposition of gold.1 In spite of this fact assays 

show marked variability in the ratios of gold 

and silver in the ore. The telluride was not 

analyzed, but from its physical characters and 

from commercial assays it appears to correspond most closely to sylvanite or krennerite. 

Its silver content is too high. for calaverite. 

The. variable character of the telluride ore 

fron1 this mine is shown by the. following 

.selected sampling-works assays: • 

I 

.Sampling-works· assays of telluride ores from War Dance mine. 

Year. 

1908 ............ . 1908 ............ . 1908 ............ . ll909 ............ . 1909 ............ . 

J Ore. 

Net pounds. 

5,516 

6,491 

13,859 

7,732 

191HL. ........ l 13,495 

2,640 

5,452 

9,360 

571 

8,510 

Gold. 

Ounces. 

14.84 

2.96 I 24.08 

6. 87 I 7. 63 

41.00 

6.48 

21.88 

71. 09 

26.26 

Silver. 

Ounces. . 5. 82 

3. 30 

9. 35 

2.90 

6. 65 

10. 53 

4. 20 

56.72 

28. 10 

11. 18 

1 Lehner and Hall have shown th,at tellurides of gold can precipitate 

·metallic gold from its solutions. See Am. Chem. Soc. Jour., vol. 24, 

.P· 918, 1902. 

The average value of over I,OOO tons of telluride ore shipped from the War Dance mine in 

I9II is reported by the company to have been 

gold, 1.32 ounces and silver 1. 78 ounces. Much 

of this ore was, however, obtained from picking 

over the old dump and was below the average 

of that obtained direct from the mine. 

In sharp contrast to the above are the assays 

of ore from the sulphide vein. 

Assays of sulphide ores from War Dance mine. 

Ore. Gold. Silver. Copper 

(wet). Lead. Zinc. 

Net lbs. Ounces. Ov,nces. Per ct. Per ct. Per ct. 

2, 724 0.43 69.00 7.50 -------- 1,402 . 40 55. 00 -·------ -------- ........... 9,000 . 55 31. 00 5.20 ................ --······ 13,130 l. 20 62.00 8.90 14.00 3.50 

SILVER DOLLAR VEIN.· 

-The Silver Dollar vein is just west of the 

junction of Russell and Willis gulches. It 

strikes about N. 50o_ E. and appears to be 

the westward continua~tion of the Hampton 

vein. The development work consists. of a 

shaft I85 feet deep with levels at 95 feet and 

I85 feet. The 95-foot level extends 35 feet 

west of the shaft, but has no east drift. The 

vein on this level strikes N. 45° E. and dips 

about 60° NW. At the face the vein is tight 

and It feet in width. 

The I85-foot level extends 340 feet west of 

the shaft. The dip on this level is 50°-55° 

NW. The drift east of the shaft is caved. In 

a stope near the face the vein has a width of 

I to It feet and is between tight walls. It 

consists mainly of pyrite and· enargite in neatly 

equal amounts. Vugs not exceeding It inches 

across are common and are lined with crystals 

of quartz, pyrite, and enargit.e. In a stope 

I 70 feet west of the shaft the vein which has a 

width of 2 feet, is mostly coarse pyrite next the 

walls with a central band about I foot wide 

composed of pyrite and abundant enargite. 

In all the polished sections of the ore studied 

these two minerals unquestionably belong to 

the same period of mineralization. 

A little galena and sphalerite were present 

in some of the ore on the dump, but pyrite and 

enargite formed the great bulk of it. Fluorite 

was present locally, generally in vugs with 

quart~ in the pyritic portions of the vein . 

/ 
GILPIN COUNTY. 279 

No reliable data were obtainable in regard 

to the value of the ore or the production. 

HAMPTON MINE. 

The Han1pton mine is in Russell Gulch a 

short distance above its confluence with Willis 

Gulch. The vein, which appears to be the eastwn.rd continuation of the Silver Dollar, str~kes 

about N. 50° E. and near the surface dips 70° 

NW. It is developed by a shaft, which was 

idle at the time of survey and was not entered. 

The ore on the dmnp showed double mineralization, first with coarse pyrite and later with 

pyrite, galena, n.nd tennantite. Some of the 

later veinlets had a center of nearly white 

cherty silica, which appears to have been 

deposited in the last stage of the galena-tennantite mineralization. According to Mr. 

. Percy Alsdorf son1e enargite is locally present 

in the ore fron1 this 1nine. 

POWERS VEIN. 

The Powers vein, just northwest of the junction of Willis and Russell gulches, is developed 

by three shafts, one of which is equipped with 

shaft house and steanl. hoist. At the time of 

this survey the property had been idle for a 

number of years and could not be entered. 

The ore on the dmnp was similar to that of the 

Silver Dollar vein (p. 278), except that fluorite 

appeared to be slightly 1nore abundant and to 

hn,,ro replaced some of the n1inerals of the schist 

wn.lls. Enargite and coarse pyrite are so intergrown in this ore as to show plainly that they 

belong to the sa1ne period of Inineralization. 

The following are sampling-works assays of 

sn1elting ore shipped between 1898 and 1907: 

• 

Sampling-works assays of ore from, Powers vein. 

Ore. G0ld. Silver. Copper. Silica. 

Net lbs. Otmce. Onnces. Per cent. Per cent. 

6,511 0. 28 22.00 19. 10 36 

6,028 .12 19.90 8.00 35 

6, 718 . 20 20. 20 16.00 32 

9,978 .10 10.00 7. 20 59 

13,319 . 08 1. 70 15. 30 30 4,334 . ]<! 16. 80 14. 50 44 

4,216 .12 12.86 11. 60 44 

1,290 . 28 31. 70 18. 50 28 

8,629 . 22 21. 70 16. 90 24 

1,468 . 28 22.70 18. 10 ········· 

mOQUOIS VEIN. 

The Iroquois vein was opened in. the sixties 

but was. not extensively operated. The present company, which has controlled the ·property since ·1908, has done development work 

but has shipped very little ore. The. vein, 

which trends northeast across Russell Gulch 

just abov-e the mouth of Willis Gulch, is developed by a shaft, which was idle at the time of . 

this survey and could not be entered. Some 

of the ore on· the dump consisted wholly of 

coarse pyrite with a little quartz as gangue, 

but the most abundant ore consisted of galena 

and sphalerite, the latter in part resinous 

and in part dark colored. The relations 

between the pyritic and the galena-sphalerite 

ore were not clearly shown. Both types of 

ore are traversed by minute veinlets of quartz 

and cherty-looking silica which are distinctly 

later. Much fluorite, varying from colorless 

to green and purple, is associated with some 

of the pyritic ore. The fluorite, with some 

quartz, occurs in vugs in this ore and as veinlets 

cutting it and therefore appears slightly later. 

Some enargite is also reported. 

Sampling-works assays of two lots of smelting ore, of 4,975 and 8,55.0 pounds, shipped 

from the Iroquois mine in 1910, gave respectively, gold 0.16 ounce, silver 10.9 ounces, lead 

6.45 per cent; and gold 0.36 ounce, silver 12.7 

ounces, lead 10.15. per cent. 

PROSPECTS ON RIDGE BETWEEN ELKHORN 

GULCH AND PLEASANT VALLEY. 

Some abandoned prospects near the summit 

of a hill about 1,000 feet southeast of the 

Moose mine lie within a large area of lllOnzoni te 

porphyry. No well-defined vein is tecognizable on the surface, but the porphyry h.as 

been brecciated and is traversed in many 

directions by sma1l seams (mostly under onefourth inch in width) of green and pink 

fluorite with a little associated pyrite, chalcopyrite, and quartz. In· other seams fluorite 

is rare or ab.sent, only gray quartz, pyrite, 

and cHalcopyrite being present. 

Microscopic study indicates that the fluorite, 

quartz, and pyrite of the veins were formed 

contemporaneously. Theonlywall-rock alterations are sericitization and the development 

of a little fluorite. Inclusions, which are 
280 GEOLOGY OF GILPIN, CLEAR CREEK, AND BOULDER COUNTIES, COLO . 

exceedingly abundant in the vein quartz, are 

in part arranged in bands and in part irregular; 

they show a liquid filling and a bubble but no 

solids. 

HILL AND BUNK HOUSE VEINS. 

The Hill and Bunk House veins are on the 

southeast side of Banta Hill. The two veins 

are developed by the Hill shaft, which is said 

to have a depth of 465 feet, but which was full 

of water below the 150-foot level at the time 

of· this survey. The drifts at the 100 and 150 

foot levels were also largely inaccessible. 

The Hill shaft is sunk in the Idaho Springs· 

formation just south of a large mass of monzonite porphyry, which is also exposed 70 feet 

west of the shaft on the 150-foot level. The 

Hill vein strikes N. 70° W. and dips 58°-60° 

SW. It is in most places a tight barren fracture, about parallel to the schistose structure, 

which continues across the schist-porphyry 

contact. and is therefore younger than the 

porphyry. The Bunk House vein, which 

strikes N. 48° E. across the schistosity and 

stands nearly vertical, cuts the Hill lode about 

50 feet west of the shaft on both levels. It is 

marked by a schist breccia a few inches to 4 

feet wide that is barren except at the ore shoot. 

Both the .100 and the 150 foot levels expose 

a spur which leaves the Hill vein 40 feet west 

of the junctic,>n of the Hill and the Bunk House 

and joins the latter 50 feet to the northeast. 

The principal ore body, which is in this spur 

and along the Bunk House vein where it is 

joined by the spur, contains 3 to 4 feet of more 

or less mineralized brecciated country rock 

cut by stringers of sulphides ·4 inches in maximum width. 

The ore ·consists of galena, light and dark 

sphalerite, and minor amounts of chalcopyrite 

. and pyrite. These metallic minerals are 

accompanied by abundant white quartz, some 

barite, and exceptionally by fluorite. It is 

said that the Hill vein is mineralized in the· 

porphyry beyond the schist contact on the 150-

foot level. The porphyry on the dump does 

carry some disseminated pyrite and joints in 

this rock are coated with a film of the same 

mineral. 

Some small shipments of very siliceous 

smelting ore made in 1900 and 1906 carried 

about 0.20 ounce gold, 20 ounces silver, 24 

per emit lead, and zinc not exceeding about 4 

per cent. A 30-ton mill on the property is now 

largely dismantled and does not appear to have 

seen much service. 

MOOSE MINE. 

The Moose mine, on the south side of 

Pleasant Valley at an elevation of about 8,850 

feet, is developed by a shaft "\yhich was idle' at 

the time of survey, so that the workings could 

not be seen. The mine is at the border of a 

large area of monzonite porphyry, and the 

wall rocks are porphyry and a breccia of schist, 

pegmatite, granite gneiss, and porphyry fragments. The ore belongs mainly to the pyritic 

type and seems in the main to be a metasomatic replacement of the matrix of the breccia. 

Much of the pyrite and chalcopyrite are exceedingly fine grained. An association of 

galena, sphalerite, pyrite, and chalcopyrit~ is 

present in certain specimens, which; however, 

are rather ~harply distinct from the purely 

pyritic ore and were prol?ably mineralized 

somewhat later. Rhodo~hrosite is very abundant in some parts of the mine, but it is uncertain whether it is associated with the pyritic 

or the galena-sphalerite mineralization. 
CHAPTER XVI.-CLEAR CREEK COUNTY. 

BELLEVUE MOUNTAIN AND UPPER PART OF Springs formation. All the wall rock in the 

VIRGINIA CANYON. workings studied is granite gneiss except for 

CROWN POINT AND VmGINIA MINE. 

The Crown Point and Virginia mine is near 

the head of Virginia Canyon, the n1ain shaft 

being at an elevation of about 9,300 feet. ~he 

workincrs could not be entered, but the mme b . . 

n1aps show an inclined shaft dipping northe~st 

and extensive workings apparently dev.elopmg 

at least two veins. All the ore on the dump 

was of the pyritic type. The main or Crown 

Point vein has a strike along the outcrop of 

about N. 50° W. and a dip of about 75° NE. 

It is apparently the continuation of the B~lman vein, which it should closely resemble m 

character. (Se~ pp. 28a-284.) 

Satnpling-works assays of 11lots of smelting 

ore, aggregating 102 tons, shipped between 1897 

and 1901, show gold, 0.24 to .. 3;72 (usually 1 to 

2.50) ounces; silver, 1 to 12 (usually 3 to 6) 

olill.ces; copper (wet), 0.3 to 18 per cent; silica, 

21 to 62 (usually 40 to 60) per cent. 

The following are assays of concentrates 

shipped in 1901: 

the small areas of schist of the Idaho Springs 

formation shown in figure 50. 

Three veins are shown by the development. 

From the strikes and dips of these veins their 

intersections should shift northeast with depth, 

and this is clearly shown to be the case in the 

mine worlqngs. The Clarissa vein strikes on 

the average about N. 85° W. and dips about 

65° N.; it is exposed in all of the levels. The 

Blue Bell vein strikes on the average about 

N. 45° W. and dips 55° NE. in the lowest level 

and 80° NE. in the upper levels. On the 70-

foot level it joins the Clarissa about 80 feet east 

of the shaft, continues with it for about 30 feet, 

and then resumes its independent course. On 

the 135-foot level it is exposed in the crosscut 

about 60 feet east of the shaft. Its junction 

with the Clarissa is presumably somewhere in 

the inaccessible part of this level about 100 

feet east of the shaft. On the 185-foot level 

the Blue Bell vein is cut in a drift about 25 feet 

east of the shaft and again 130 feet east of the 

shaft at a point where it joins the Clarissa vein, 

Assays of concentrates from Grown Point and Virginia mtne, · with which it runs for the last 70 feet of the 

1901. drift. The East vein, possibly the Belman, 

Ore. Gold. 

Net lbs. Ounces. 

22,280 1. 35 

21, 710 1. 12 

39,142 1. 39 

34,666 1. 06 

4,543 1.88 

Silver. 

Ounces. 

3. 70 

2.80 

2.05 

2. 20 

4.00 

strikes on the average about N. 50° W. and dips 

60° NE. It is exposed in the extreme east end 

of the 70 and 135 foot levels and probably in 

the 30-foot level. It has not yet been cut by 

the east ch·ift on the 185-foot level. 

The mineralization is similar and probably 

contemporaneous in all three veins. Postmineral movement and possibly movement previous to mineralization has, however, offsetthe 

The gross total production of the mine is said Blue-Bell fracture along the Clarissa fracture 

to have been about $500,000. and offset the Clarissa along the East vein. 

CLARISSA MINE. 

The Clarissa shaft is 300 feet northeast of the 

Virginia Canyon ·wagon road and about 1,500 

feet southeast of the Gilpin-Olear Creek county 

line. The shaft (see fig. ~0) follows the Clarissa 

vein to the 30-foot level but below that level 

lies north of the vein, necessitating a 50-foot 

crosscut to the south on the 185-foot level. 

·The collar of the shaft is 200 feet west of the 

contact between granite gneiss and Idaho 

The Blue Bell seems to have been offset along the 

Clarissa fracture for 30 feet on the 70-foot level 

and for at least 70 feet on the 185-foot level. 

The Clarissa in turn is sharply cut off by the 

East vein and the offset eastern portion has not 

yet been found. Slickensides striffi on the wall 

pitch 60° NW. On the 135-foot level, where 

the Clarissa vein is cut by the ct'osscut from the 

shaft, a mineralized fracture striking N. 25° W. 

and dipping 70° E. displaces the vein nearly 

1 foot. · 281 
282 GEOLOGY OF GILPIN, CLEAR CREEK, AND BOULDER COUNTIES, COLO. 

The Blue Bell vein has been stoped to some 

extent on all levels.. . The East vein has been 

stoped to an unknown height above the 135-

foot level, and at the east end of the 70-foot 

level, where the stope is caved. In 1911 development was proceeding entirely through the 

lower tunnel-leveL Above the 70-foot level the 

. old shaft is very small and 9an be used only for 

hoisting water; ·below this level it has been enlarged and retimbered. A new working way 

N 

Bl - _"Of'j I EL i 

Pyritic veins 

2.7 ounces silver. Where the copper content 

is low the precious-metal content is low also. 

FAIRMONT TUNNEL. 

The Fairmont tunnel is on the southwest slope 

of Pewabic Mountain at an elevation of a little 

over 9,250 feet. (See fig. 51.) The first vein 

cut in the tunnel is 265 feet from the portal and 

is in general narrow, showing from 1 to 2 inches 

of galena, sphalerite, and pyrite. It has been 

~ 

stoped somewhat for 

40 feet east of the 

tunnel. 

Idaho Springs 

f'ormation (Arrow indicates direction of dip) 

Workin~s 

inaccessible 

The second or main 

vein is- cut about 

430 feet from the 

portal. 'In the stope · 

near the east face 

of the drift this 

vein ranges from 1! 

inches to 1 foot in 

width and shows solid 

galena and resin 

sphalerit~, some of 

the sulphide crys·t~ls 

being 1 inch in diameter. At a point 

about 120 feet west of 

the tunnel a portion 

of the vein goes in to 

the south wall, following the. contact 

between the schist 

and a dike of bostoniteporphyry; 3 inches 

of solid sulphides are 

exposed here. West 

of this point the drift 

Note: Wall rock is granite gneiss 

except where otherwise 

indicated 

0 50 

'VIRGINIA CANYON WAGON li'OAO 

100 200 Feet 

is mainly in porphyry 

and follows a postFIGURE 50.-Geologic plan of portions of the Clarissa mine. mineral f r a c t u r e 

plane and several 

consisting of a winze from the 1S5-foot to the 

185-foot level has been sunk entirely on the 

Clarissa vein. 

The ore from the stopes above ·the 70-foot 

level is said to have carried some galena, but 

that shipped in 1909-10 from the lower levels 

carried only gold, silver, and copper in valuable 

amounts. The average assay value of this ore 

was 1.15 ounces gold, 5.58 ounces silver, copper 

less than 1 to 2. 7 per cent. Some ore assayed 

as high as 3 ~unces gold and 9 ounces silver 

and other ore as low as 0.66 ounce gold and 

small galena-sphalerite veinlets. The veins in 

one place cut the porphyry sharply and are 

plainly younger; elsewhere these relations have 

been obscured by movements which fractured 

both ore and porphyry. The porphyry dike cut 

by this driftis probably the one exposed in the 

main tunnel. This vein has been worked , 

through stopes and winzes for most of the 

length of the drift. . 

A third vein is cut about 650 feet from the 

portal. It is narrow and in places consists 

only of a few inches of gouge, but elsewhere 
Q 

CLEAR 0REEK COUNTY. 283 

shows several veinlets of galena, sphalerite, and 

pyrite from one-half to 1 inch across. Some of 

these have been crushed by postmineral movements parallel to the vein. 

As shown by the underground studies and by 

examination of the dump most of the ore is of 

the galena-sphaleri to type. Small vugs are very 

common and are usually lined with crystals of 

white quartz, some of which are transparent. 

Some of the ore is a breccia of schist fragments 

cemented by sulphides and quartz, and some 

N 

LEGEND 

1~1 Barren 

fracture (Arrows 1ndicate 

direction of dip) 

[?[] 

Inaccessible 

workin~s 

W, winze 

Note: Wall rock is Idaho Springs formation 

except where otlierwise indicated 

0 50 100 zoo Feet 

FlOUim5l.-Geologieplo.n of Fuirmonttnnnel. Surveyed byhandcompass and pacing. 

·Of the schist fragments carry pyrite either irregularly disseminated or arranged in narrow bands. 

·The veinlets of galena and sphalerite truncate 

these bands sharply, a relation which proves 

·some mineralization with pyrite previous to 

further fracturing and mineralization with galena, sphalerite, and pyrite. 

No data were obtained in regard to the value 

.of tho ores. 

BELMAN VEIN. 

The Belman vein, which is exposed on the 

·surface at the head of Virginia Canyon near 

-.the west base of Pewabic Mountain, is developed by several shafts now abandoned. It 

has also bee~ cut at a vertical depth of about 

1,675 feet by the Big Five tunnel, which connects with drifts in both directions, aggregating 800 feet in length. (See Pl. XXI, B, in 

pocket.) In these drifts the vein strikes 

N·. 67° W. and dips 60°-70° NNE. The tunnel cuts an important ore shoot, which extends eastward about 180 feet and westward 

at least to the end of the drift (420 feet). 

Stopes on this shoot are 110 feet in maximum 

height. The drifts have been run on the footwall side of the vein, and its total width is 

seen only where the tunnel crosses it. The 

section of the vein here is as follows: 

Se.ction of Belman vein in Big Five tunnel. 

Gouge, on footwall ............................... . 

Schist, crushed, carrying small lenses of pyrite and 

more ~r less disseminated pyrite ............... . 

Veinlet of quartz, pyrite, and chalcopyrite ....... . 

Gouge .... ~ ...................... : ............. . 

Pyrite and chalcopyrite with a little quartz as 

Ft. in. 

3 

2 

2 

' 

gangue.... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 

Quartz, cut by stringers of darker quartz (maximum 

width, on~half inch), carrying pyrite and chalcopyrite...... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 6 

Tight slip plane. 

Quartz, heavily mineralized with pyrite and chalcopyrite...... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 0 

Gouge, on hanging waiL.......................... 1 

The schist for 30 feet above this vein is cut 

by many parallel slip planes, is considerably 

alte.r;ed, and contains abundant disseminated 

pyrite. A well-marked fracture zone separates 

this altered schist from the schist which is little 

altered and unmineralized. 

The footwall pay streak of the Belman vein 

ranges from 3 to 9 feet· in width and shows very 

similar characters throughout.· Commonly, it 

contains 2 or 3 bands, 2 to 14 inches wide, of 

good pyritic ore in a filling of quartz or of 

silicified crushed schist that contai'ns only disseminated pyrite. Chalcopyrite is subordinate in all of the ore; it is said that little or 

none occurs in the backs of the stopes ea~t of 

the tunnel, and that the ore is much poorer 

than that in the shoot west of the tunnel, 

where chalcopyrite is more abunda,nt. Tennantite is said to have been found in some of 

the richest ore, generally associated with the 

chalcopyrite and with dark-gray quartz. · 

Postmineral movement has produced 

slickensides in the ore and crushed the pyrite 
284 GEOLOGY OF GILPIN, CLEAR. CREEK, AND BOULDER COU~TIES, cor.o. 

and quartz. The slickensided faces show 

polished pyrite in a few places, but are generally blackened by the crushed pyrite. 

Figures for computing a satisfactory average 

for the metal content of the vein are not 

available, but 13 sampling-works assays of 

smelting ore recently shipped show gold, 

0.52 to 1.16 ounces.; silver, 2.2 to 6.4 ounces; 

copper, from less than 1.5 to 3.55 per cent; 

silica, 45 to 62 per cent; and iron, 16.5 to 26.9 

per cent. 

LAKE AND WINDSOR CASTLE VEINS. 

The Windsor Castle shaft is on the east .side 

of Virginia Canyon just above the Two Brothers 

tunnel at an elevation of 8,850 feet. The conso 100 zoo Feet '---"----'------J 

N 

L..E:GE:ND 

were found in any part of the Windsor Castle 

vmn. 

Sufficient figures for computing a satisfactory 

average of the metallic cm:itent of the ore are 

not available, but sampling-works assays of 

seven lots of smelting ore aggregating about 

30 tons, shipped from 1897 to 190Q inclusive, 

show gold, 0.08 to 0.68 ounce;' silver, 8.4 to 

23 ounces; copper (wet), from less than 1.5 to 

2.8 per_ cent; lead, 4 to 16 per cent; zinc, 5 to 

16 per cent. 

Veins marked A and B in figure 52 and the 

Lake vein are not .heavily mineralized where 

~xposed in these workings. The vein at A is 

tight, showing 1 to 2! inches of gray quartz 

carrying some pyrite .. The vein at B shows 4 

inches of gray quartz and silicified granite 

gneiss carrying pyrite. The Lake vein as exposed in the lower tunnel has not been stoped 

and is not heavily mineralized. Locally it is 

barren, but elsewhere it shows for a width of 

2 to 4 inches a little pyrite in altered wall rock 

or gray quartz. In the upper t~nel, which is 

about 700 feet long, the ·Lake vein is in the 

main very soft and wet, consisting of 1 to 3 feet 

of crushed and decomposed wall rock, locally 

carrying a little Q.isseminated pyrite. Small 

bands of dark-gray quartz ca:r:rying some 

~ , ... ~---j , ....... ·:···'! c::q (A~row~indicate pyrite occur locally, and it is reported that some ~ ">-" !t,... L__j dorectlonofd•p) lead ore has been obtained. Local stoping.has Jd1~.:'msJ'{;~~ss P~;i,;~c Gelen~.;';';,h;lente f~!ct:~;'.. been done in the tunnel. , 

What is said to beth~ Lake vern is cut by the 

FwuRE52.-PianofLaketunnelandconnectingworkingsontheWind- Big Five tunnel about 8,345 feet from the por-· sor Castle vein. Surveyed by hand compass and pacing. 

tal at a vertical depth of 1,150 feet.. (See Pl. 

Well rock is granite gne•ss except where otherwise indicated 

necting Lake lower tunnel starts near by at the . XXI, B, in pocket.) Drifts on the vein, extend. 

side of the main wagon road. (See fig,. 52.) 420 feet east and 250 feet west of the Big Five· 

The Windsor Castle vein was examined on tunnel. The average strike is about N. 80° E., 

the lower tunnel level and for a short distance and the dip 32°-52° N. The Windsor Castle, 

below .it in the shaft. It is a strongly and vein is not recognized in the Big Five tunnel, 

eve~ly mineralized vein which has been ·stoped and it may join the Lake vein above the tunnel 

for most- of its length as exposed on the tunnel level. The wall rock is schist of the Idaho 

level.. Several excellent exposures show a Springs formation except ·at the face of the, 

width of 1! feet of nearly solid sulphides- west drift, where a little nwnzonite porphyry 

pyrite and sphalerite in nearly equal·amounts is ·exposed. The principal alterations proand subordinate galena. This portion of the duced in this porphyry by the mineralizing· 

vein is sharp walled and appears to be a. true" solutions are the ·development of sericite and. 

fissure filling. The wall rock, however, carries pyrite. The mineralization is stronger than. 

disseminated pyrite for 1 to 2 feet from the in the Lake upper workings and is wholly py-· 

vein proper. . ritic. Considerable stoping has been done .. 

The Windsor Castle vein appears to be the The vein is a strong fracture zone, in places 5 

eastward continuation of the Bald Eagle vein. feet wide, including much crushed schist and 

According to Mr. Hal Sayre, owner of the prop- one or more slickensided fracture planes. The 

erty, no large amounts of rich silver minerals crushed schist has in most places been greatly 
CLEAR CREEK COUNTY. 285 

altered and carries disseminated pyrite. In 

Jnany places it is ti·{tversed by bands not more 

than a foot wide of quartz carrying pyrite and 

in a :few plu.ces by veinlet.s of coarse pyrite not 

more than 4 inches wide. 

At the face of the east drift the Lake vein 

shows the following detailed sections: 

Section of Lake vein on the Big Five tunnel level. 

Footwall. 

Tight slip. Inches. 

Schist, crushed, bleached, carrying disseminated pyrite and cut by a network of veinlets of quartz and 

pyrite one-eighth inch and less wide.. . . . . . . . . . . . . 24 

Tight slip plane. 

Schist, silicified, carrying a large amount of fine disseminated pyrite. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 

Quartz and coarse pyrite........................... 12 

Schist, carrying abundant disseminated pyrite . . . . . . . 6 

Slip plane with gouge. . . . .. .. . .. .. .. . .. .. . .. .. .. .. 2 

Hanging wall. 

·The gross production of the properties is 

said to be between $250,000 and $350,000. 

TWO BROTHERS TUNNEL AND BALD EAGLE VEIN. 

The Two Brothers tunnel, which starts in 

Virginia Canyon at an elevation of about 

8,740 feet, extends generally westward for 

about 1,300 feet and then northwestward for 

about 1,100 feet to the Specie Payment vein. 

It cuts several veins and follows one for several 

hundred feet. The wall rock is principally 

granite gneiss, but in a few places is schist of 

the Idaho Springs formation. 

About 500 feQt from the portal the tunnel 

cuts the Bald Eagle vein, which is probably a 

continuation of the Windsor Castle vein. A 

short drift north from the tunnel connects with 

a shaft on this vein. As exposed in this drift 

the vein strikes northeast and shows numerous 

stringers of galena, sphalerite, and pyrite 

through a width of about 4 feet of granite 

gneiss. Disseminated pyrite is abundant be-

. tween the stringers. . 

Sufficient data are not at hand for satisfactorily computing the average tenor of the ore 

from the Bald Eagle vein, but samplingworks assays of seven lots of smelting ore, 

aggregating 11 tons, shipped in 1888 and 1889, 

show gold, a trace to 0.3 ounce; silver, 12 to 

172 ounces;lead,5 to 10.8 percent; zinc, 6 to 

17 per cent. The high silver values in certain 

shipments were probably due to downward 

enrichment. 

Between 800 and 1 ;250 feet from the portal 

the Two Brothers tunnel follows a fracture 

zone, 1 inch to 2 feet wide, which strikes 

nearly east and west and dips steeply north. 

Most of this fracture zone is barren, but a few 

parts of it contain sharply bounded veinlets 

of sphalerite and galena one-fourth to onehalf inch across. . 

A little over 1,900 feet from the portal the 

tunnel cuts a dike of monzonite porphyry. A 

hundred feet farther in a mineralized fracture 

zone 2 to 4 feet wide strikes nearly east and 

west and dips 50° N. · This zone includes two 

3-inch veins of nearly solid galena and sphalerite with some pyrite, one next to the hanging wall and the other next to the footwall. 

Between these veins and for a short distance 

outside them the granite gneiss carries some 

disseminated pyrite. . 

The workings on the Specie Payment vein 

on the Two Brothers tunnel level were inaccessible at the time of this survey. They 

are briefly mentioned on pages 286-287. 

MONA VEIN. 

The Mona vein is developed by the Mona 

tunnel, the portal of which is on the east side 

of Bellevue Mountain at an elevation of about 

9,100 feet. The tunnel, which follows the 

vein, was caved about 400 feet from the portal. The vein as exposed in the 400 feet ac~ 

cessible strikes about N. 75° E. and dips 

60°-65° N. In its narrower portions it shows 

1 to 2 inches of somewhat sheared schist carrying fine disseminated pyrite. In other places 

it broadens to 2! or 3 feet, mostly of fractured and somewhat silicified schist carrying 

disseminated pyrite, but including veinlets of 

galena, sphalerite, and subordinate pyrite and 

chalcopyrite from 1 to 2t inches wide on both 

the hanging and foot walls. In ori.e part of 

thevein a 2-inch band of gray quartz contain-· 

ing finely granular pyrite ("steel" pyrite) and 

chalcopyrite is bordered next the hanging wall 

by a one-fourth to 1 inch veinlet of resin 

sphalerite and some chalcopyrite which, a 

little farther along, shifts to the footwall and 

in doing so cuts across the quartz~pyrite band. 

In harmony with evidences elsewhere this 

probably indicates that the quartz-pyrite 

mineralization was somewhat the earlier. 

Few data are at hand in regard to the value 
l -

286 · GEOLOGY OF GILPIN, CLEAR CREEK, AND BOULDER COUNTIES, COLO. 

of the ore from this vein, but the following 

sampling-works assays record the n~etal content of a few shipments·: 

Sampling-works assays of oresf.rom Mona vein. 

Year. Ore. Gold. Silver. Copper Silica. (wet). 

Net lbs. Ounces. Ounces. Per ct. Per ct. 

{ 877 2.10 7.00 ................ ......... 

1904 .. -----. 12,066 1. 71 9.10 .. ............ 50 

5,300 4.85 22.40 4 44 

1,300 3.32 16.00 3 53 

{ 7,000 . 32 3.00 ................ .............. 

1908.------- 6,830 1.49. 7.20 ............. ............... 

4,950 . 46 21.00 ............... .............. 

SPECIE PAYMENT VEIN. 

The Specie Payment vein outcrops on Bellevue Mountain. (See fig. 53.) ~e main inclined shaft descends 585 feet on the vein and 

the "Gasoline incline" 380 feet. The Two 

B:r:others tunnel cuts the vein over 1,000 feet 

. below the collar of the main shaft and connects 

with over 1,400 feet of drifts on the vein, 

mainly on the tunnel level but in part on a 

level 145 feet below. · The drifts on • the Two 

Brothers level could not be entered on account 

of bad air; and the Wolverene tunnel, which 

is probably also on the Specie Payment vein, 

was unsafe on account of caving. Observations were therefore confined to the main shaft 

'and Little Annie workings. 

These workip.gs show two main veins-the 

Specie Payment vein, which has a strike of 

about N. 60° W. in the upper workings, shifting to N. 80° W. in the Two Brothers tunnel 

wor,kings, and an unusually variable dip of 15°-

750 N. (average about 40° N.); and the Cross 

vein, which strikes N. 70 to 80° E. and dips 

30°-75° ~· These two veins intersect without 

· notable displacement of either. The intersec-

-tion is well exposed on thr~e of the levels connecting with the· Gasoline incline and on both 

of the levels connecting with the Two Brothers 

tunnel. 

The Specie· Payment vein is commonly well 

defined. In its leaner portions it shows either 

several nearly parallel unmineralized fractures 

or ~lse narrow quartz-pyrite veinlets di~tributed through 6 inches to 2! feet of more or 

less altered wall rock. The wall rock near 

these fractures and veinlets generally carries 

pyrite in small disseminated crystals. In its 

more heavily mineralized portions the vein 

carries principally pyrite -and chalcopyrite, 

with galena and sphalerite in minor quantitie~. 

As compared with most of the veins of this 

vicinity the Specie Payment vein shows an 

uncommon abundance of , quartz and an uncommon number of vugs. A few des9riptions 

of heavily mineralized portions illustrate its 

character. In a winze on the first level 

below the Little Annie tunnel (A, fig. 53), the 

vein is 3 feet wide. It shows next the hanging wall a 6-inch band of pyrite, chalcopyrite; 

and quartz in nearly equal amounts. Small 

fractures in this portion of the vein show thin 

films of what appears to be chalcocite. Below 

comes 2 feet of schist carrying disseminated 

pyrite and chalcopyrite; and finally, next the 

footwall, is 6 inches of gray quartz and pyrite 

traversed by stringers of galena, sphalerite, 

chalcopyrite, and pyrite. The character of a 

polished specimen from this part of the vein 

when · examined under the microscope has 

already been described on page 113. ,Free gold 

is· reported to occur locally in white quartz in 

this part of the· mine. ' 

Ore from the bins at the Two Brothers tunnel, said to come from the Specie Payinen t 

vein, is uncommon in carrying abundant 

bornite. A polished specimen of this ore shows 

minute stringers of bornite with accompanying chalcopyrite and galena occupying sharp 

fractures in ·the pyrite. Because it is later 

than the pyrite ore and ·carries some galena, 

the bornite-rich ore is regarded as an unusual 

phase of the later mineralization. ·Subsequent 

to both mineralizations there was further 

fracturing and an introduction of gray quartz. 

In a stope on the 360-foot level 130 feet 

east of the main shaft the vein shows 7 inches 

of gray quartz and pyrite in about the proportion of 2 to 1. · Above this for 2! feet pyrite is 

disseminated in pegmatite of the wall. 

1n most of the exposures described above 

pyritic mineralization is predominant, but on 

the 440-foot level the principal minerals are 

galena, sphalerite, and chalcopyrite. About 

110 feet east of the shaft the vein shows in 

places 2 inches· of solid galena and sphalerite 

associated . with pyrite and chalcopyrite. 

Quartz is common as a gangue and is associ a ted 

principally with the pyrite and· chalcopyrite. 

Near the shaft on this level the vein is 6 inches 

wide and consists of several veinlets of white 
OLEAR OR.EEK COUNTY. 287.· 

quartz (2 inches in :rp.aximum width), carrying 

a little pyrite and chalcopyrite, and traversed 

by irregular bands of galena and sphalerite. 

The vugs of the vein are commonly lined 

with quartz crystals, in places accompanied by 

crystals .of pyrite and chalcopyrite. It is particularly noteworthy that small crystals of 

resin sphalerite are deposited on some of the 

quartz and pyrite crystals, in places .completely 

coating them. A specimen fron1 the 360-foot 

level showed this feature. A specimen from 

the Two Brothers tunnel level, seen in a private 

collection, showed quartz crystals in a vug 

beautifully plated at their tips with pyrite. 

Little Annie 

tunnel 

A number of minor veins, which have not 

proved to be of connnercial importance, are 

exposed near the east end of the Little Annie 

tunnel level. (See fig. 53.) They are pyritic, but 

the widest pyritic streak observed was only 2 

inches. They lie about parallel to the schist 

foliation and are nearly parallel to the Cross 

vein in strike. 

Another minor vein, lying a little below the 

Specie Payment vein and dipping about 

65° NE., is exposed on the fifth or 440-foot 

level, for 220 feet southeast of the shaft to a 

point where the drift is caved. Some of the 

drifting on the fifth level beyond the cave 

N 

FIGURE 53.-Geologic plan of a portion of the workings on the Specie Payment and adjacent veins. 

The Cross vein is dominantly pyritic and 

narrower than the Specie Payment vein. 

In a few places it carries some galena and 

sphalerite. As exposed in the Little .A..nnie 

tunnel, 140 feet from the portal, it shows 1~ to 2 

inches of pyrite in a gray quartz gangue, beneath which there is 1 foot of schist carrying 

disseminated pyrite. As exposed on the first 

level below the Little Annie tunnel it shows 

2 to 3 inches of gray quartz carrying pyrite and 

chalcopyrite. Vugs lined with quartz crystals 

are numerous. The vein nearly everywhere 

shows evidence of postmineral movement 

in brecciation and in the presence usually of an 

inch or so of gouge next the hanging wall. 

t1ppears from the map to have followed this 

vein. In ·places this vein is a nearly barren 

fracture plane 2 to 6 inches in width, but in 

other places it is fairly well mineralized with 

pyrite and chalcopyrite in a gray quartz matrix. 

No stoping has been done on it. 

The Specie Payment vein was discovered in 

1875, was first opened in 1876, and was acquired by. the present company in 1903. At 

the time of this surv.ey some work was being 

done by lessees in both the Two Brothers arid 

Little Annie workings. The records ~f output 

are incomplete, but the total gross production is estimated by the company at about 

$1,500,000. Oxidized ore from the early work-
·.288 G~OLOGY OF GILPIN, CLEAR CREEK, AND BOULDER COUNTIES, COLO. 

ings carried much free gold and very little silver. 

' In theunoxidized ores the highest gold and silver 

content is commonly found in the chalcopyriterich portions, though some of those. high in 

pyrite or in galena have proved rich and sphalerite is said to carry gold in places. 

The metal content of 124lots of smelting ore, 

aggregating 506 tons, as determined from 

sampling-works assays, was gold, 0.32 to. 7.09 

(average 1.88) ounces; silver, 0. 7 to 37 (average 

5.8) ounces. In most lots copper was not 

present in sufficient amounts to be paid. for, 

but in a few it ran ,as high as 7 per cent, although 

3 to 5 per cent was more common. Lead and 

zinc are recorded only exceptionally. Silica 

ranges from 42 to · 7 5 per cent. 

The average value of the concentr~ting ore 

. shipped in 1910 was gold, 0.35 ounce; silver, 

3.7 ounces; lead, 1.6 per cent; copper, 0.4 per 

cent. 

CHAMPION-TRIO MINE. 

In 68 lots of smelting ore, shipped fro·m 1888 

to 1911 inclusive, the range in metallic content, 

according to sampling-works returns, was gold, 

0.2 to 6.64 ounces; silver, 1 to 34.5 ounces; 

copper, from less than 1.5 to 7.2 per cent. 

SEATON MOUNTAIN, GILSON GULCH, AND THE 

LOWER PART OF VIRGINIA CANYON. 

EAST LAKE TUNNEL AND OWATONNA VEIN. 

The East Lake tunnel is on the south slope 

of Pewabic Mountain at an elevation of 8,500 

feet. It is a nearly straight tunnel about 550 

feet long driven on a vein striking on the 

average N. 50° E. and dipping northwest. A 

crosscut 30 feet in length· running westward 

from this tunnel connects with the Owatonna 

shaft workings. The workings are all in schist 

of the Idaho Springs formation and pegmatite. 

· One of the best exposures of the East vein, 

on which the tunnel is driven, is at the face, 

where it dips' 50° NW. Idaho Springs schist 

The Champion shaft, on the summit of for a width of 6 feet is more or less altered 

Bellevue Mountain at an elevation of a little and impregnated with small grains of pyrite, 

over 9,600 feet, is abo1;1t 1,130 feet deep on a which in places forms about half of the rock. 

northward-dipping vein. The Trio drift tun- Near the footwall are two veinlets, one-half 

nel, starting in Virginia Canyon at an elevation and 1 inch wide, which consist of galena and 

of about 9,150 feet, is about 1,000 feet long ·sphalerite in a gray quartz matrix. A small 

and connects by a raise ~th the 655-foot level branch vein joining this vein about 160 feet ' 

of the shaft workings. fro·m the portal is said to have assayed gold, 

None of the workings were accessible at the 0.21 ounce; silver, 42 ounces; copper, 2.5 per 

time of thi~ survey, but according to the stope cent. 

maps available most of the ore extracted came No important production has yet been refrom the shaft workings above the 655-foot ported from the East vein. 

level. Between the surface and the 451-foot The west or Owatonna vein, which is conlevel the stoping is confined to the vicinity of nected with the East Lake tunnel by a crossthe shaft, but between the 451-foot and 655- cut, is best exposed on a level 40 feet or so 

foot levels the stopes extend roughly 400 feet above the tunnel .. This vein, which strikes N. 

west and 500 feet east of the shaft. 50°-60° E. and dips 45°-50° NW., shows 

The tenor of the. ore is extremely variable two nearly parallel portions. ·The upper porand for that reason no satisfactory average tion, which the shaft follows, consists of 2 to 5! 

value can be given. The following selected· feet of more or less altered schist and pegmatite 

sampling-works assays give some idea of vari- traversed by galena, sphalerite, and subordiations: nate pyrite in veinlets which are rarely over 

2 inches wide, but which exceptionally unite in 

.Sampling-works assays ·of ore from Champion- Trio mine. lenses of nearly solid sulphides as much as 1 

Ore. Gold. 

Net pounds. Ounces. 

10,840 1.41 

5,500 2.50 

7,820 6.64 

14,360 . 94 I 

Silver. 

Ounces. 

34.50 

3.00 

10.00 

18.50 

Copper. 

Per cent. 

3.6 .................... 

3.0 

4.0 

.foot in width. In many places the sulphides 

form the matrix of a breccia of schist fragments. One to two . inches of gouge is commonly observed next the hanging wall. The 

lower portion of the Owatonna vein is exposed at the northeast .end of the same level,. 

where it ~s reached by a 15-foot cros~cut from 
CLEAR CREEK COUNTY. 289 

the upper or shaft streak. As exposed in the 

face this is a tight 8-inch vein of galena, 

sphalerite, and pyrite; with here and there 

a little gangue quartz. The upper and lower 

branches of the Owatonna vein probably 

tnerge at no great distance northeast of these 

workings. 

Fifteen lots of smelting ore fron1 the 

Owatonna vein, aggregating 117 tons, shipped 

between 1897 and 1910, show, according to 

sarnpling-·works assays, gold, 0.12 to 0.5 

(average 0.23) ounce; silver, 5.7 to 58.8 

(average 27 .57) ounces; lead, 36 per cent or 

less; and zinc, 25 per cent or less. Lead 

con11nonly is slightly in excess of zinc. 

SUN AND MOON VEIN. 

The Sun and Moon vein outcrops at the head 

of Gilson Gulch near the Gilpin-Clear Creek 

county liu.e. It is developed by three shafts 

called, fr01n east to west, the Minott, the Sun 

and Moon, ~nd the Garden. The Sun and 

Moon shnft connects with only stnall and unimportant devolopn1ents. The Garden shaft 

· has nine levels. The :Minott is the main shaft 

and hns twelve levels. Fr01n the twelfth level, 

at a point about 450 feet east of the Minott 

shnft, another shaft with seven levels descends 

to the Argo tunnel lateral, which alone wa.c:; 

accessible nt the time of this survey. 

On tho surface, and presu1nably in n1ost of 

the workings above the Argo tunnel level, the 

wnll rock is grnnite gneiss, but on the Argo 

level it is schist of tho Idaho Springs forn1ation 

with n. little tnonzonito porphyry, granite gneiss 

being present ·only for 100 ·feet or so east of 

tho shaft. 'rho vein in general follows the foliation of 1 the schist. A large area of n1onzonite 

porphyry crops out just enst of the shaft. 

Although the vein was certainly forn1ed later 

than this porphyry it is not traceable on the 

surface for any considerable distance into the 

porphyry. . 

The vein was studied in the Argo lateral for 

1,825 foot enst of tho Argo tunnel, beyond which 

the drift was flooded. The strike averages 

about N: 60° E. and the dip is about 50° NW. 

In n1ost exposures the vein shows 6 to 12 inches 

of sheared and altered schist, locally somewhat 

silicified n.ncl co.nunonly carrying disseminated 

grains of pyrite. In pln.ces tho fracture zone 

is entirely unminern.lized. For about 500 feet 

44214°-17-19 I 

east and west from the shaft the lateral exposes 

at intervals a dike of monzonite porphyry 1! 

to 5 feet wide, which is :q.early parallel to the 

vein. The vein is younger than the dike, cutting across it in several places as the mineralized fracture shifts froln one wall of the dike to 

the other. Veins of solid pyrite from a fraction of an inch up to 6 inches in width are present in a few places along the walls of the fracture zone or along the wall of the monzonite 

dike. In n1ost places the wall rock next such 

coarse pyrite carries disseminated pyrite in 

increasing amounts as the vein is approached. 

vVhere the vein is cut by the Argo tunnel the 

hanging wall is a nearly barren sheared zone 

1 to 1! feet in \vidth. Below this and separated from.it by 6 feet of unmineralized schist 

is 5 feet of fractured and somewhat silicified 

schist carrying pyrite in small disseminated 

grains. 

As indicated in the above descriptions the 

mineralization of the Sun and :Moon v:ein in the 

Argo lateral is wholly of the pyritic type. 

Although the upper workings on the vein were 

not accessible the character of the ore on the 

dumps and the record!3 of the ore shipped show 

that much of it carried galena and some sphalerite. The vein therefore affords another example of the passage in depth of a composite into 

a purely pyritic vein. (See p. 102.) 

Postmirieral movement has taken place along 

the vein, as is shown by the presence in places 

of angular fragments of pyritic ore in a matrix 

of crushed but unmineralized rock, but it is not 

always easy to distinguish its effects from those 

of movements previous to mineralization. In 

one place the fragments in a friction breccia 

were well rounded. 

The mine is at present operated under the 

leasing systein. Practically all of the ore 

shipped goes direc.t to the snielters, the company 

owning no mill. The average metailic content 

of the ore is said to be about gold 1 ounce, 

silver 20 ounces, copper (wet) 2.5 per cent. 

Sampling-works assays of 54 lots of smelting 

ore, aggregating 836 tons, shipped in 1908 and 

1_909, show gold, 0.4 to 8.25 (average 1.31) 

ounces; silver, 3.81 to 37.7 (average 14.49) 

ounce<s; copper (wet), fr01n less than 1.5 to 6.9 

per cent; lead, none to 13 per cent; zinc, none to 

8 per cent. The total gross production is said. 

to be about $2,000,000." 
290 GEOLOGY OF GILPIN, CLEAR CR.EEK, AND BOULDER COUNTIES, COLO. 

SANTA FE VEIN. 

The Santa Fe vein, near the head of Gilson 

Gulch, at an elevation of about 9,250 feet, 

strikes about N. 60° E. and dips about 6P0 N. 

It is developed by several shafts, of which the 

deepest, the Santa Fe, is down about 320 feet 

and connects with 4 short levels. The workings could not be entered at the time of this 

survey, but an examination of the dump 

showed that the ore was mainly if not entirely 

of the galena-sphalerite type. 

Sufficient data are .not at hand for computing the average. value of the ore. Samplingworkc;; assays of 16 lots of smelting ore aggregating 91 tons, shipped between 1888 and 1904, 

show gold, 0.25 to 4 ounces; silver, 2.7 to 38 

ounces; copper (wet), not more than 2.3 per cent; 

lead, not more than 20 pe.r cent; zinc, not more 

than 5 per cent. · 

The property is said to have had a gr,oss 

production of $100,000. 

DE LESSEPS TUNNEL. 

The De Lesseps tunnel, near the village of 

Gilson Gulch, at an elevation of about 8,900 

feet, is about 440 feet long, the .first 50 feet 

being crosscut and the remainder on ·a vein 

with a general N. 80° E. strike and a dip of 

60°-70° N. About 320 feet from. the portal 

the tunnel connects with a shaft. A second 

vein trending about N. 75° W. ·and dipping 

60° N. joins the main vein from the west 20 

feet from the face of the tunnel. The stopes 

are rubble filled and little could be seen of 

the c:P,aracter ·of either vein. In many places 

they are practically barren, ·showing 'only 6 

inches to 1! feet of. fractured and silicified 

gra~te gneiss. The ore found was of the 

galena-sphalerite variety. A s~mpling-works 

assay of 16,508 pounds of ore shipped about 

1893 shows gold, 1.03 ounces; silver, 32 ounces; 

lead, 11.5 per cent; zinc, 12 per cent. 

GEM-FREIGHTER'S FRIEND LODE. 

The veins developed in the Gem and the 

Freighter's Friend mines form part of a welldefined system of mineralized fractures that 

outcrop on the summit of· Seaton Mountain, 

extending slightly south of east fron;:t the Main 

Trunk claim to the Franklin and· Freeman 

claims. The system includes a number of subparallel.branching fractures whose mutual relations could not be accurately worked out from 

the exposures available. The Silver Age tunnel level connects with the fourth level of the 

Freighter's Friend shaft, but a~cess was not 

gained to this part of the workings. 

The Gem workings consist of. a shaft inclined 

to the north and connected with lev~ls numbered from 1 to 18. An interval has be€:m left 

for levels Nos. 10 and 15, but they have not 

yet been driven. On account of the age and 

caved condition of the workings little could be 

seen above the ninth level. The Gem lode was 

cut by the Argo tunnel in 1900 about 7,860 feet 

from the portal and in 1903 a raise was com~ 

pleted connecting the Argo level with the shaft 

workings. The elevation of the collar of the 

Gem shaft is 9,026 feet, and that of the Gem 

lateral on the Argo tunnel level is 7,606 feet, a 

vertical difference of 1,420 feet. A winze·and 

short level below the Argo level increases the 

total vertical extent of the workings to 1,.'504 

feet; their extent measured along the dip of the 

lode is about 1,900 feet. 

The workings of the Freighter's Friend mine 

were not accessible for study; they consist of 

the Freighter's Friend shaft and five levels 

driven from it. 

The average strike of the Gem lode is about . 

N. 70°-75° W. and its dip is 35°-80° N. (aver- · 

age about 50° N.). The prevailing wall rock · 

is granite gneiss, but monzonite porphyry is 

abundant on the ninth, thirteenth, seventeenth, 

eighteenth, and Argo tunnel levels, particularly west of the shaft. On. the ninth level 

about 400 feet west of the shaft the monzonite 

contains feldspar phenocrysts, some of which 

measure 2 by 2! inches. The porphyry is distinctly earlier than the mineralization. 

The lode taken as a whole is remarkable for 

its width and compound character. Though 

in some places composed apparently of a single 

well-mineralized vein, in most of the workings 

it consists of two nearly parallel veins 20 to 30 

feet apart. This compound character is a 

feature also· in the Franklin and Silver Age 

workings. From the surface to about the 

ninth level the shaft in general follows the 

footwall vein and below the ninth level the 

hanging-wall vein, which, as indicated by the 

amount of development on it, becomes increasingly important with depth. One of the 

best and most easterly exposures of the footwall vein is on the eleventh level, about 800 

feet east of the shaft. 
CLEAR CREEK COUNTY. 291 

Section of footwall vein on eleventh level of the Gem rnine. this ore shoot showed sylvanite in a gray quartz 

. matrix. \. Ranging wall. Ft. m. As far as could be learned tho minerals char- Granite gneiss, somewhat sheared ......... ········ 1 0 f . 

Pyrite, coarse, cut by a network of rhodochrosite acteJ"istic of the second period of ore ormatiOn 

veinlets not more than 1 inch wide, which are are more abundantly present in the Freighter's 

plainly later than the pyrite .......... ·········· 1 0 Friend than in the Gem workings, thus forming 

Quartz, gray, carrying disseminated grains and 

6 

a transition to the purely galena-sphalerite \. 

small irregular veinlets of pyrite.··············· 4 type of ore characteristic of the Franklin and Pyrite, coarse, cut by rhodochrosite veinlets ...... . 

Aggregate of gray quartz, galena, pyrite, and chalco- Silver Age workings. 

pyrite......................................... 3 0 Because of the diversity in the mineral charSlip planes showing horizontal slickensided footwall.__ acter of the ore from various parts of this lode: 

5 10 

In contrast to the size and•extensive mineralization of the footwall vein at the locality just 

described is its appearance in a crosscut 80 

feet west of th~ shaft on the eighteenth level, 

where it consists of 4 feet of crushed granite 

gneiss containing only disseminated PY:ite and 

a few small stringers of quartz and pyrite. 

Although the Freighter's Friend workings 

are on the same general lode as those of the 

Gem mine, the two mines have not been connected and the exact correspondence between 

individual veins within the lode is not known. 

Mineralization in the Gem mine is dominantly pyritic . but in many places comprises 

other sulphides. The occurrence of sphalerite 

and chalcopyrite in rhodochrosite veinlets cuttinO' coarse pVTite has already been recorded. b u 

On the fourteenth level the footwall vein 300 

feet west of the shaft exhibited a one-eighth 

inch veinlet of quartz and galena cutting obliquely across a 5-inch band of quartz carrying 

fme pyrite. At one place on the Argo tum1el 

level small veinlets · that consist mn.inly of 

enarO'ite quartz, pyrite, and galena, with b ' • subordinate amounts of very fine grained 

chalcopyrite, rhodochrosite, and bornite, cut 

quartz-pyrite ore. Small enD,rgite crystals 

were observed on the faces of pyrite crystals 

in the pyritic ore. 

These relationships add · to the evidence 

alren.dy set forth (pp. 112-114) of two periods 

of mineralization. The minerals of the second 

period observed in this mine are galena (in part 

"steel" galena), sphalerite (both dark-colored 

and resinous), tetrahedrite, enargite, 'rhodochrosite, and bornite. Chalcopyrite, pyrite, and 

quartz, and possibly tetrahedrite, are common 

to both mineralizations in this mine. 

A pocket about 100 fe~t long by ·100 feet 

high near the Gem shaft on the twelfth level 

carried tellurides of gold. A specimen from 

a better idea of the value of the ore m~y be 

gained from a separate consideration of the 

different types than from, general averages .. 

From an inspection of the complete record of 

smelter returns from 1897 to 1910, inclusiver 

the following summary of the values of. the 

different types~f ore may be made: 

The pyritic ores, consisting largely of pyrite 

with very subordinate chalcopyrite, are quantitatively the most abundant. In most of the 

smelting ore of this type the gold content lies 

between 0.3 and 3 ounces (generally less than 

1 ounce) per ton, and the silver between 5 and 

30 ounces per ton. Unusually high gold values 

are commonly accompanied by unusually high 

silver values. Copper, although generally below the commercial limit of 1.50 per cent~ 

reaches 5 per cent in a few places. These figures take no cognizance <;>f exceptional values. 

Smelting ores showing lead in quantities' 

sufficient to be paid for (over 5 per cent wet)' 

are more abundant in· the Freighter's Friend 

than in the Gem mine, from which in certain 

years no le~d ores· were shipped. The lead in\ 

some shipments reaches 65 J?er cent and. the\ 

zinc 23 per cent. A comparison of the silver 

1 values in the pyritic an.d lead .ores indicat_es 

that much of the galena IS not highly argentlferous, although it is more so than the pyrite. 

The precious metals seem on the whole to be 

most closely associated with ~he copper minerals, as is suggested by the following assays: 

Assays of ores from the eleventh level east in the Gern rnine. 

Cop- Gold. Silver. per Lead. Zinc. 

(wet). 

--------

Oz. Oz. P. ct. P. ct. P. ct. 

Pyritic ore .......... 0.28 7.85 ........ ............. . ....... Cupriferous pyritic { .93 17. 60 2.30 ........ ...... ore ............... 1. 30 19. 30 4. 10 . ........ 

Lead ore ............. . 25 15. 80 . ...... 23.45 9.35 
292 GEOLOGY OF GILPIN, CLEAR CREEK, AND BOULDER COUNTIES, COLO. 

The follo~g assays are of samples of various 

types of ore collected by tp.e writer.: 

Miscellap,eous assays of oresjrom the Gem mine. 

Number. 

1 .......... . 2 .......... . 

3 .......... . 4' .•.•• · ••.•.• 

5 .......... . 

Gold. Silver. Copper. Lead. Zin.c. 

Ounces. 

2.00 

.08 

. 06 

1. 10 •. 07 

Ounces. 

11.44 

5.40 

7. 30 

22.62 

. 33 

Per cent. Per cent. Per cent. 

0. 54 ............... . . . . . . . . . . . . . . . . . 62.22 

. 48 65. 50 ....... . 12. 20 24. 17 

· l. Ore, mainly of coarse pyrite, from an underhand stope 

100 feet. west of the Gem shaft on the twelfth level. Sylvanit!3 )::la$ been identified in this part of the mine and 

may be the cause of the uncommonly high value of this 

sample as compared with most of the coarse pyritic ore of 

the mine. 

i--·. 

300 Feet L-~--~----~----~ 

0. 50 100 .. 200 

cin!ty of the old Freeman shaft as a cbntinuous well-defined lode. From this point eastward to Silver Age Gulch a number of slightly 

divergent veins are exposed in the Silver Age 

tun:riel.. The apparent position of their outcrops is shown on Plate VI (in pocket), but 

their relations to each other and to the Franklin vein could not be completely worked out on 

account of the inaccessibility of many of the 

old workings. West of Gilson Gulch the 

Franklin vein probably merges with one of the 

veins opened in the Freighter's, Friend and 

Gem w9rkings, but the precise relations are not 

known. -

The ·Franklin vein was seen only in the 

Franldin shaft, which is 200 feet deep and 

has short levels at 100, 135, and 200 feet. The 

LEGEND 

, ....... t... ... , 

Veins E9 

Barren 

fractures 

(Arrows indicate d1rection of dip) N 

I FIGURE 54.-Geologic· plan of Silver Age tunnel. Surveyed by hand compass and pacing • 

. 2. R~sin sphaleri~~ picked. from ore carrying galena, Silver Age tunnel starts in. Silver Age -Gulch 

sphalerite, tetrahe9-rite, ·and a little· pyrite and chalco- at an elevation of 8 440 feet. An inclined 

pyrite; from the same locality a.sl''!'o. l. h f . h 1 ' h · h 1' 1 

3

. 0 ·· · · 1 fi · d 1 ( " t 1, s at at t e tunne mout connects wit eves · . re, mam y ne-grame ga ena some see . · . . 

galena) and chalcopyrite with some pyrite, from the Gem 100 and ?OO feet below the tunne~ but co~ld 

South vein on the· Argo lateral about 250 feet ea.st of ~he not be entered. The tunnel workings, which 

shaft. were studied to a point 75 feet west of the · 4. A sphalerite concentrate from ore from the eleventh Freeman shaft are shown in figure 54. 

and twelfth levels. It originally contained some galena, Th F h 'Fl h ft h'· h t b . . . . e rene ag s a w 1c appears o e 

pynte, chalcopynte, rhodochrosite, and quartz, but wa.s . . ' . . 

picked over to free it as far as possible from these minerals. on a _continuatiOn o~ the F~anklin-Sllver Age 

Its high content in precious metals is in marked contrast lode, IS on the east ·side of S1lver Age Gulch. at 

with the sphalerite of No. 2 and is possibly due to the an elevation of about 8,500 feet. The dip of the 

admixed galena. . vein at the surface· is about 45° N. The work5. Coarse pyrite of the first mineralization, traversed by 

veinlets of rhodochrosite belonging to the later mineralization, from the eleventh level, about 800 feet east of the 

shaft. 

FRANKLIN VEIN AND SILVER AGE TUNNEL. 

The Franklin ·vein, which was discovered in 

1865, l.s traceable on the surface from the 

village of Gilson Gulch ·eastward· to the viiJ-1-gs are inaccessible; 

As exposed in the Franklin shaft and con-

'necting levels ·the Franklin vein dips .. 50°-60° 

N.· Its width is commonly 1-to 1!-ieet. The 

wall rock in most places is granite gneiss with a 

few dikes , of monzonite porphyry. At the 

west face ·of ·the 200-foot le:vel the vein- cuts · 

sharply' through a 1-foot dike of monzonite 
CLEAR CR.EEK COUNTY. 293 

porphyry, than which it is clearly later. The 

135-foot leYel east exposes two nearly parallel 

veins about 20 feet a~a.rt, between which the 

wrul rock is trayersed .by galena, sphale~ite, 

and pyrite in nu:inerous small stringers, few of 

which a.re over one-fourth inch wide and all of 

which are Yery irregular in trend. 

In the SilYer Age tunnel three principal 

veins are exposed. For 400 feet from the 

mouth the main drift follows a vein which is 

generally lean and on which only a small amount 

of stoping has been done. In one of. the more 

heavily mineralized .. portions, 320 feet from 

the portal, the vein is 1 foot wide, consisting 

of 6 inches .of crushe<;l porphyry next the 

footwall and above 6 inches of gray quartz 

· containing fine-grained galena and sphalerite. 

Thjs 1nay be the same vein expo~ed farther in 

A, -figure 54, although at that point it shows 

no nuneralization but is merely a zone of fracturing, within which the schist shows some 

silicification. · ·· , · 

What n1ay be termed for convenience the 

south vein diverges f;rom the vein just described 

about 120 feet from the portal and is exposed 

continuously for about 760 feet. . For the first 

500 feet· or so it··has been stoped extensively, 

but beyond 500 feet it is a barren fracture zone 

6 inches to 2 feet in width, mainly in altered 

porphyry. In an exposure of one of the more 

1nineralized portions, about 540 feet from the 

po·rtal, the Yein is 2 feet wide and consists of 

brecciated and silicified porphyry traversed by 

several stringers of quartz carrying fine-grained 

galena and sphalerite and some pyrite. 

The northern vein, which i.s exposed in the 

drifts near the Freeman shaft, is larger and 

mot·e heavily mineralized than the others and is 

evidently the main. vein opened in the Franklin 

shaft workings. It is followed by the Silver 

Age tunnel for over 1,200 feet west of the 

Freen1an shaft, but this portion of the mine was 

inaccessible. About 200 feet east of the Free-

, man shaft it is 7 inches wide and shows bands 

of galena and resinous sphalerite with subordinate pyrite and chalcopyrite alternating 

with band'3 that are mostly quartz. Vuggy 

portions show what appear to be pseudomorphs 

of quartz after barite. At another point the 

vein shows a 1 to 2 inch streak of rhodochrosite 

containing specks of pyrite, galena, and gray copper. The vein has been stoped continuously 

for 225' feet east from where the drift is caved. 

The mineralization throughout ne.arly all of 

the Franklin and Silver Age workings is of the 

galena-sphalerite type. As exposed in the 

Franklin shaft workings the ore of the Franklin 

vein is an irregular aggregate of galena, sphalerite, and pyrite in a gangue either of gray quartz . 

or of pink rhodochrosite or both. The rhodochrosite plainly crystallized contemporaneously 

with the sulphides and. in places is the most 

abundant vein mineral. A little tetrahedrite 

was observed in small vugs. In a few places 

gruena and sphalerite form a very fine grained 

aggregate. Vugs .. are· common in the more 

quartzose .parts of. the vein. More or . less 

crushed wall rock generally forms either the 

hanging wall or the footwall of 'the vein and in 

places is 1 foot in width. At one place on the 

200-foot level east the hanging wall is followed 

by a band of gray flinty quartz 1 to 5 inches 

in. width; which was formed later than the 

main n1ineralization and contains angular fragments of the ore .. 

. A small amount of ore seen in bins at the 

mouth of the Silver Age tunnel consists mainly 

of gray quartz and pyrite with some sm.all 

stringers and lenses of galena which appear 

to be later. The presence of such composite 

ore shows that there was some ore deposition 

along this lode in the earlier or pyritic mineralization. · 

According to Hollister 1 the ore taken from 

the upper portions of·the Franklin vein in 1867 

was .mainly valuable for its silver. (though also 

carrying considerable copp~r) and yielded assays of $100 to $150 per ton, the average market price of silver being $1.33 per ounce. 

There can be no doubt that the high silver 

content of the upper portions of the lode was 

the result of downward enrichment. In the 

present workings little evidence of enrichment 

was observed. On the 135-foot level of. the 

Franklin shaft workings fractured wall rock 

near the main sulphide vein is reported to have 

carried wire silver in seams and vugs and to 

have been richer than the sulphide ore. This 

silver was probably dissolved from the oxidized zone and redeposited by descending 

waters. 

Sampling-works assays of 130 lots of galenablonde smelting ore, a.ggregating 1,374 tons, 

shipped from this property from 1888 to 1.910 

inclusive, show gold, 0.05 to 1.52 (average 0.146) 

1 Hollister, 0. J., The silver mines of Colorado, p. 70,1807. 
294 GEOLOGY. OF GILPIN, CLEAR CREEK, AND BOULDER COUNTIES, COLO. 

ounces; silver, 4 to 16t' (average 22. 74) ounces; 

lead, 38 per cent or less; zinc, 18 per cent or less; 

'and silica, '67 to 82 per cent (6 determinations 

only). The high silver content of some of these 

shipments is indicative of enrichme_nt. Several 

. small shipments in 1910 which assayed, according to sampler returns, 0.28 to 1.2 ouncAs gold 

and 1 to 1.7 ounces silver, probably represent 

the pyritic type of ore. 

The company owns two mills, the Wilkie and 

Silver Age, in the· valley of Clear Creek below 

Idaho Springs, power being furnished by a 

hydroelectric plant. These 1 mills are capable 

of treating 60 tons of ore per day. 

HUDSON-BURR TUNNEL. 

The portal of the Hudson-Burr tunnel is in 

Silver Age Gulch at an elevation of about 8,500 

ieet. The workings were blocked at the mouth 

:and only the dump could be studied. On the 

dump two types of ore were observed, one 

·showing galena, sphalerite, pyrite, and subcarrying dissmninated pyrite. Locally, however, veinlets up to 2 inches wide of galena, 

sphalerite, and ·subordinate pyrite. in a gray 

quartz gangue occur. An interesting feature 

is the occurrence of a few 1 to 2 inch bands of 

soft white sericite, which represent an extremQ 

phase of n1etasomatic ·alteration by· the mineralizing solutions. No mining is now be~ng 

done in this tunnel. 

Six lots of ore from this mine shipped in 1911 

showed the following metal content.: 

Assays of ores from the Metropolitan tunnel. 

Ore. Gold. Silver. Lead. Zinc. 

Net lbs. Ounces. Ounces. Per cent. Per cent. 

1, 920 1. 40 17 .................. ................. 

2,470 l. 95 64 .................... .................... 

5,150 0 52 14.50 ................... .................. 

4,650 l. 24 41.00 ll 27 

2,470- 0 55 25.00 I .................... ................... 

6, 790 0 20 ll. 50 6 13 

-ordinate chalcopyrite in a gangue of quartz and SEATON VEIN. 

siderite and the other showing only coarse The Seaton vein was first developed through 

pyrite in a quartz gangue. a shaft on the south side of Seaton Mountain 

Some of the pyritic vein material shows at an elevation of about 8,900 feet, but since 

minor amounts of galena, sphalerite, and chal- 1900 has been worked through the Foxhall 

copyrite. A polished specimen 3 inches wide, tunnel. It is also cut by the Tropic tunnel 

the entire width of a vein, showed, when studied about 680 feet frpm the portal and 250 feet 

under the microscope, an irregular central band vertically below the surface. Drifts on it from 

·of coarse pyrite 1 to 1 t inches wide bordered on the Tropic tunnel break into the workings of 

·either side by three-fourths to 1 inch of light- the Pine Shade shaft, which connects with 

gray quartz. The pyrite had been brecciated, 7 levels, all inaccessible except that from the 

a fet_tture especially clear when the polished Tropic tunnel. The Seaton vein is also cut by 

.surface was ·etched with nitric acid, and along the Argo tunnel at a .vertical depth of about 

.small cracks .traversing the pyrite and in small ·1,200 feet at about the point (6,980 feet from 

.irregular spaces between pyrite fragments the portal), whe~e it should be cut if its average 

galena, ~phalerite, chalcopyrite, . and clear dip of 60° N. in the upper workings persists to 

calcite had been deposited. The relations were the tunnel level. 

·entirely clear and indicated beyond any ques- The Seaton shaft follows the vein to a vertion that composite mineraliza,tion had taken tical depth of 450 feet. It has six levels, the 

·place, :first with quartz and pyrite and later lowest of which (seventh) connects through a 

with galena, sphalerite, and chalcopyrite. 1 00-foot raise with the w'orkings in the Foxhall 

tunnel level. About 450 feet east of the main 

METROPOLITAN TUNNEL. shaft a sub~idiary shaft 1s sunk from the 

The Metropolitan tunnel, at an elevation of tunnel level for a vertical depth of 220 feet. 

8,600 feet on the east side of Boomerang Gulch, A room for hoisting engine and head frame has 

follows for about 1,850 feet a vein which strikes been excavated at the top of this shaft and the 

generally N. 60° E. and ·dips 35°-55° NE. The ore is trammed out through the tunnel. Three 

wall rock is schist of the Idaho Springs forma- levels connect with this subsidiary shaft. All 

tion and monzonite porphyry. At some places the levels connecting with the main shaft are 

the mineralization consists of stringers of gray inaccessible except the sixth, which can be 

quartz bearing pyrite which traverse schist reached by the raise from the tunnel. The 
CLEAR CREEK COUNTY. 295 

writer's observations, therefore, were confined 

to the portions of the workings below 450 feet 

in vertical depth. 

On the surface the. vein can be traced with 

certainty for only a short distance west of the 

Seaton shaft, but to the east it can be followed 

for 1,000 feet beyond the Pine Shade shaft to 

the southeast nose of Seaton Mountain overR 

LEGE NO 

W1 winze 

R, raise 

We.ll rock is Idaho Sprmgs formation 

with some peRmatite except where 

otherw•ae Indicated 

9..___.~o-' ..... CJ0 ___ 29.._o-'--_3...,~q_o -----l~o Feet 

SEATON SHAF"T 

portions studied the wall rocks are schists of 

the Idaho Springs formation, with small lenses 

of pegn1atite, and the vein in general lies parallel. to their foliation though occasionally cutting across it at small angles. The vein is in 

places barren but elsewhere is heavily nlineralized. One portion, 130 feet east of the Foxhall tunnel, shows 1. to 2 inches of crushed schist 

N 

FIGURE 55.-Geologic plan of Foxhall tunnel and of Seaton and Casino mines. 

looking Gilson Gulch. The same, or a closely 

parallel lode, probably extends across Gilson 

Gulch. As shown on the surface the Seaton 

vein appears to join the Tropic vein near the 

Pine Shade shaft, and the Tropic is probably 

to be regarded as a branch ·from the Seaton 

lode. 

The Seaton is a strong vein dipping 45°-80° 

N. (average about 60° N.). '1;11roughout the 

and pegmat~te wholly unmineralized. Other 

portions show pyrite as the only mineral 

sparsely disseminated in small grains through 

crushed and altered· scllist. These sparsely 

pyritic portions have not been worked: The 

workable portions. of the vein carry galena and 

sphalerite and minor amounts of other minerals, in places in a single sharp-walled vein but 

1nore conunonly in a network of small sub-
296 I 

GEOLOGY OF GILPIN, CLEAR CR.EEK, AND BOULDER COUNTIES, COLO. 

parallel veins bordered by schist or pegmatite the fine steel-galena variety and carries son1e 

carrying more· or less disseminated pyrite. local antin1ony. The sphalerite is locally 

Only rarely do the walls contain disseminated of the resinous variety but is comn1onlygalena or sphalerite. The vein, mcluding 'the dark. Pyrite is subordinate and chalcopyrite 

gangue and disseminated material, reaches a rare. Quartz is the common gangue mineral, 

width of 5 feet in its stronger portions, but but some rhodochrosite is found locally. 

more commonly measures 1 to 2 feet. As ex- One specimen showed crystals of rhodochrosite 

posed in a winze 330 feet east of the Foxhall as, much as 2 inches across intercrystallized 

tunnel it shows 3 inches of gouge next the foot- with pyrite and evidently of primary deposiwall, a 5-inch band of galena, sphalerite, and tion. Tennantite in small fragments was 

subordinate pyrite and quartz, a small fracture observed on the shaft dump but was not seen 

seam, and 4 inches of so~ewhat altered schist in place. Son1e of the best values in silver 

and pegmatite carrying disseminated fine py- in the lower parts of the mine are said·, howrite. The galena forms crystals locally 1 inch in ever, to have been found in tennantite-rich 

diameter though commonly smaller. Twenty portions· ef the lode. A specimen of "gray 

feet east of the shaft in a stope between the copper" (presumably tennantite) from shortly 

eighth and ninth levels the vein has a width of below the tunnel level assayed 1 ounce in gold 

5 feet and includes a stringer of gray quartz, and 118.4 ounces in silver. Zinc ore from 

one-half to 1 inch wide, carrying abundant the same part of the mine assayed 0.32 ounce 

pyrite, which is cut sharply at 60° by veinlets in gold and 25.9 ounces in silver. 

of galena and sphalerite which are plainly Specimens from the older shaft workings 

younger. Si1nilar evidence of two n1ineraliza- seen in private collections show undoubted 

tions (a relatively unimportant pyritic miner- enrichment in silver with the development of 

alization followed by a very considerable ruby silver, argentite, and native silver. The 

galena-sphalerite one) is found in the winze, richest ore of the mine is said to have come 

330 feet east of the Foxhall tunnel, where a from the fifth level (315 feet vertical depth), 

2-inch quartz-pyrite vein is cut nearly at right but one specimen from the sixth level (450 

angles by the main galena-sphalerite vein. feet vertical depth) showed wires of native 

The appearance of the vein in the Tropic tunnel silver deposited on the quartz crystals in a 

workings (see fig. 56) is described on page 298. small vug, indicating that silver enrichment 

On the Argo tunnel level many portions of the locally extended to that depth. 

vein show only pyrite. Some of the abundant Sampling-works assays of 27 lots of smeltdisseminated pyrite in portions of the vein ing ore, aggregating 202 tons, shipped from ' 

may also' belong to the earlier mineralization. the Seaton mine between 1902 and 1910, show 

On the Argo tunnel level the drifts on the gold, 0.12 to 2.35 (average 1.13) ounces; silver, 

Seaton vein are caved 70 feet east and 170 .feet 7.5 to 105 (average 39.66) ounces; copper (wet), 

west of the tunnel. (See Pl. XXI, A, in 2.55 per cent or less; lead, 26.4 per cent or 

pocket.) Within the 240 feet available for less; zinc, 24 per cent or less. A former 

study the vein dips 55°-60° N. West of the operator estimates the average value of clean 

tunnel the vein is practically barren, and east smelting ore between the fifth and seventh 

of it the largest amount of mineral observed levels at gold 1.6 ounces, silver 55 ounces, lead 

was a 4-inch streak of quartz and pyrite with' 22 to 25 per cent, zinc 18 per cent. 

small local vugs. In one place a little galena A test run made in the Dover mill on 25 

was observed with the pyrite, and s1nelter re- tons of material fr01n the Pine Shade dump 

turns for this lateral show that much of the ore yielded a nearly pure galena concentrate, which 

was rich in both lead and zinc. assayed gold, 5.36 ounces; silver, 20.90 ounces; 

Some postmineral movement along the vein and lead, 66.50 per cent. Zinc concentrates 

is shown in eeveral places .by crushed and weighing 11,900 pounds, shipped in 19l0, 

sheared ore. assayed gold, 0.55 ounce; silver, 20 ounces; 

The dominant minerals of the main mlnerali- lead, 7.50 per cent; zinc, 27 per cent. These 

zation are galena and sphalerite. The galena assays indicate that the gold values are con~ 

commonly forms crystals one-fourth to one- siderably higher in the galena than in the 

half inch in size but in a few places is of sphalerit~. San1pler returns fron1 ore shipped 
CLEAR CREEK COUNTY. 297 

frorn the Seaton lateral in the Argo tunnel ing '\vall in most places there is from 2 to 4. inches 

level show lower values than ore from the of gouge, below which is altered silicified schist 

Shaft and Foxhall tunnel workings, an esti- traversed by bands not more than 10 inches 

mated average for about 45 tons being gold,· wide carrying clark sphalerite, galena, and 

0.5 ounce; silver, 25 ounces; lead, 20 per cent; 

zinc, 15 per cent. Silver contents considerably higher than those recorded above were 

chal'acteristic of the enriched ores in the upper 

levels. Rayn1ond 1 states, for example, that N 

ore obtained just below the oxidized zone in 

1871, containing sphalerite and galena in the 

proportion of 3 to 1 and son1e "gray copper," 

assayed 100 to 243 ounces in silver. 

TROPIC TUNNEL. 

The Tropic tunnel, which was started in 1900, 

runs N. 18° W. for about 1,600 feet under the 

eastern end of Seaton Mountain from an elevation of 8,57 5 feet near the head of Buttermilk 

Gulch. The first 1,000 feet cuts schist of the 

Idaho Springs formation and the last 600 feet 

is in grnnite pegmatite and granite gneiss with 

some schist. (See fig~ 56.) At 600 feet from 

the mouth the tunnel cuts· a monzonite porphyry dike 45 feet wide. 

The Tropic tunnel cuts three main veinsthe Gem, the Tropic, and the Seaton-Pine Shade 

and severul smaller mineralized fractures. The 

Gem vein, as exposed by the Tropic tunnel, is at 

least 20 feet wide. The drift follows its footwall portion (fig. 56), which consists of crushed 

altered granite gneiss, heavily impregnated 

with pyrite anc~ traver~ecl by numerous stringers of rather coarse pyrite, some of which are 8 

inches in width, though most of them are only 

1 to 1! inches. Thirty feet south of the footwall a fracture nearly parallel in strike but 

clipping 69° N. contains 4 inches of gouge. 

The granite gneiss between the Gem vein and 

this fracture is all somewhat altered and contains pyrite sparingly disseminated through it. 

(See alsop. 291.) 

Vein A (fig. 56) is a 4-inch vein of quartz and 

pyrite which is frozen to the walls. 

Vein B is an 18-inch zone of crushed pegma--

tite in which there has been a slight deposition 

of pyrite. 

Vein 0 is a 2 to 4 inch quartz-pyrite vein parallel to the schistosity and frozen to both walls. 

The Tropic vein ranges from 1! to 6 feet in 

width (average about 2 feet). Next the hangJ Raymond, H.. W ., Statistics of mines and mining in the' States and 

'l'erritories west of the Rocky Mountains, 1871, p. 351, 1873. 

LEGEND 

Monzon'•te porphyry. 

_i ___ Pyritic veins 

· ....... t...... Galena-sphaler'•te v~ins 

J._.___ Composite veins 

-----...1.. Unmineralized fractures 

(Arrow indicate -direction of dip) 

100 

.;._~:- Workings blocked 

Note: Wall rock is Idaho Springs formation unless other• ', "Vise indicated 

0 100 200 Feet 

FIGURE 56.-Geologic plan of Tropic tunnel. Surveyed by hand com-

. pass and pacing. 

more or less pyrite and chalcopyrite. In some 

of the ore here a small amount of gray copper is 

closely associated with galena and sphalerite. 

In the Tropic vein on the Argo tunnel level 

some rhodochrosite is found. 
298 GEOLOGY OF GILPIN, CLEAR CREEK, AND BOULDER COUNTIES, COLO. 

Sampling-works assays of a few shipments of 

smelting ore from different parts of the Tropic 

vein give some idea of the metal content. 

Sampling-works assays of ore from the Tropic vein. 

Gold. Silver. Copper 

(wet). Lead. Zinc. 

---

Ounces. Ounces. Per cent. Per cent. Per ct. 

Argo level .... 0.23 29.70 ............. 18.00 20 

Surface ........ .19 53.00 .............. ................ ....... 

Seventh le~el. { 1. 60 24.10 ............. 20.90 23 

1.24 117.80 ............. 13.50. 23 

Tropic tunnel ~ . 26 21.30 ............... ............ 9 

level. ...... . 75 56.40 0.50 . ............ 18 . 70 169.00 4.10 12.00 7 

The tenor of the ore is so variable that it is 

difficult to give a satisfactory average. Sampling-works assays of 25 lots of smelting ore, 

aggregating 68 tons, shipped from 1908 to 

1910, show gold 0.1 to 7 ounces and silver 

0.5 to 118.5 ounces. 

In general the gold content is less than 1 ounce 

and the silve~ less than 50 ounces, though some 

ore from the upper levels contained several 

hundred ounces of silver as a result of downward enrichment. Copper generally is below 

the smelter limit of. 1.5 per cent. Lead averages about 10 per cent. 

The gross production is said to be about 

$200,000. 

Vein D is a· 3-inch fracture in which the 

crushed schist contains a little disseminated 

pyrite. 

The Seaton-PinA Shade vein, as exposed in 

the Tropic tunnel and . in drifts on the vein 

which connect the tunnel with the Pine Shade 

shaft, ranges from 7 inches to 5 feet in width 

(average about 2! feet). The vein consists of 

dark-gray quartz with galena, dark and light 

sphalerite, pyrite, and chalcopyrite. In some 

places the schist has been silicified and contains disseminated sulphides .. · At one place 

about midway between the Tropic tunnel and 

the·Pine Shade shaft the ore'has been brecciated 

and partly recemented and lies in a matrix of 

crushed wall rock and· white quartz. For the 

value of the ore and a· description of other 

development on this vein, see pages 294-297. 

Vein E is a 2-foot zone of crushed altered 

schist,, somewhat silicified, which contains disseminated pyrite. It is about parallel to the 

foliation of the schist and is separated from 

both walls by 1 inch of gouge. 

Vein F comprises 10 feet of shattered and 

bleached schist. On the hanging wall and the 

footwall and pear the center of this zone there 

are 12 to 14 inch bands of quartz and pyrite. 

·Vein G is about 5 ·feet wide. For 8 inQhes 

·above the footwall the crushed schist is silicified 

and contains a little disseminated pyrite. The 

rest of the vein consists of fractured but unmineralized schist . 

CRYSTAL TUNNEL . 

The portal of the Crystal tunnel is on the east 

side of Virginia Cany?n at an elevation of about 

N 

z' 

/ 

/

. ~.€!'-. .' shaf't 

. . . . 

' 

z' z', 

9.__· s_._p _ _._1~o __ __.2)>0 Feet 

L..E:GE:ND. 

Comppsite 

~ vems 

EJ 

Fault 

Stooed 

~ (Arrows indicate 

direction of dip) . 

Wall rock is ' 

Idaho Springs Formation throughout 

FIGURE 57.-Geologic plan or Crystal tunnel. Surveyed by hand . compass and pacing. 

8,250 feet. The vein is strong and without 

branches from the portal to the winze, shown in 

figure 57, and in this distance. varies from 6 

inches to 4 feet in width. An exposure 300 feet 

from the portal shows a tight slip plane next 

the footwall followed successively by 8 inches 

of silicified schist carrying disseminated pyrite, 

a 4-inch vein of quartz, pyrite, and sphalerite, 

3 feet of silicified schist carrying dissemipated 

pyrite, and a tight slip plane next the hanging wall. Near the winze the vein divides 

into three forks, and the principal development follows the middle fork. Specimens from 

near the face of the north fork show clearly that 

the mineralization is composite, coarse pyrite 
CLEAR. CREEK COUNTY, 299 

being traversed by veinlets of quartz, galena, 

and sphuleri to. 

About 600 feet from the portal the middle 

branch is cut without displacement by a fracture zone that parallels the schist foliation and 

shows 2 to 4 inches of gouge. About· 10 feet 

farther on the vein is crossed by vein B, showing from 2 to 6 inches of fractured schist on the 

footwall and a 1 to 4 inch band of quartz, 

pyrite, galena, and sphalerite next the hanging 

wall. Vein 0, at the end of the drift on vein B, 

is a 1 to 2 inch stringer of sphalerite frozen to 

both walls. At the face the schist for 4 inches 

below it is silicified and carries disseminated 

sulphides. 

The metal content of the ore from the Crystal 

tunnel is variable. Sixteen lots of smelting 

ore, aggregating 35 tons, shipped from 1888 

to 1910 inclusive, show, according to samplingworks assays: Gold., 0.15 to 3 (av~rage, 0.76) 

ounces; silver, 5.5 to 95 (average, 37.4) Olll;lces; 

copper (wet) in one lot 3, but usually less than 

1.5 per cent; lead, 3 to 17 per cent; zinc, 6 to 

16 per cent. 

CASINO VEIN AND FOXHALL TUNNEL. 

The portals of the Foxhall and Casino tunnels are near each other and at nearly the same 

elevation (about 8,450 feet) at' the head of 

Seaton Gulch. (See fig. 55.) 

The Foxhall tunnel cuts several minor veins, 

described below in order from portal to face 

and identified by letters in figure 55:. A, a onehalf to 2 inch vein of gray quartz carrying finegrained' pyrite; B, a tight but very vuggy 

quartz vein 1 to 3 inches wide, showing pyrite 

and some galena near and on the walls of vugs; 

C, a zone of fractured schist 4 inches to 1 foot 

in width carrying some disseminated pyrite; 

. D, n one-half to 1 inch veinlet of gray quartz 

·canying pyrite; E, a fracture zone feebly mineralized with galena and sphalerite; F, a sharpwalled vein 1! to 2! inches wide consisting of 

-coarse pyrite in a quartz gangue; G, a tight vein 

1! to 2! inches wide, composed of galena, sphalm·ite and pyrite and pi·obably an offshoot 

from the Seaton vein; H, a vein 1 to 2 inches 

wide, parallel to the foliation of the schist, consisting of pyrite and quartz. The schist for several inches on each side carries disseminated 

pyrite. 

The Total Eclipse vein, as seen in drifts from 

the Foxhall tunnel, is not strongly mineralized. 

In places it is a bar:ren fracture zone 2 inches 

to 2 feet across, but e~sewhere it shows 1 foot 

of gray quartz and somewhat silicified schist 

carrying pyrite. 

The Danube vein, as exposed in the Casino , 

tunnel, is not heavily mineralized and no stoping has been done on it. In many places it is 

a barren fracture zone, 6 inches or so in width, 

about· parallel to the foliation of the ·schist wall 

rock. In a few places small stringers of gray 

to brownish quartz carry fine galena, sphal ... 

erite, and pyrite. 

The Casino vein is less regular than the other 

main veins cut by. the Foxhall and Casino tunnels. It is composed of several branching fracture zones in the schi~t whose relations to each 

other are more or less irregular. The exact 

relations between the portions of the vein exposed in the Casino and Foxhall tunnel workings, respectively, are not c~ear; tp.e relationship is evidently complicated by the presence 

of the Total Eclipse vein. The vein is not now 

being worked in the Casino workings, but at the 

time of survey it was being worked on a short 

level150 feet belo.w the Foxhall tunnel through 

a shaft start~ng underground in the Foxhall 

tunnel.. · On this level, 95 feet west of the shaft, 

the mineralization consists of three tightwalled veinlets one-half to 2 inches wide distributed through a width of 4 feet of schist and 

lying about parallel to its foliation. These 

veinlets consist of rather fine sphalerite, galena, 

and subordinate pyrite in a gangue of gray 

quartz and some pink calcite. The presenc<;l of 

gray· copper in this portion of the vein is said to 

indicate goqd values. 

The Casino vein has in the past yielded considerable amounts of rich telluride ore. The 

silver values in these ores were said to be small, 

and th~ valuable mineral was probably sylvanite. Only roasted specimens of this ore were 

seen by the writer, but some of these were exceedingly rich. 

All the output is smelting ore, but its tenor 

is so uneven that it is impossible to give the 

average metal content. The following sampling-works assays show the high values occasionally found and the extreme irregularity in 

the gold-silver ratio. The first two pro.bably 
300 GEOLOGY OF GILPIN, CLEAR CREEK, AN_D BO"CLDER COUNTIES, COLO. 

represent ores enriched in silver; the third and 

probably the fourth are. certainly of telluride 

ores; ·the last two more nearly represent the 

content of most of the ore. 

Sampling-works assays of ore from Crystal tunnel. 

I Year. Ore. Gold. Silver. 

Net po·unds. Ounces. Ounces. 

1888 ...... 3, 709 4.30 252.65 

1888 ... · ... 1,118 6. 78 241. 66 

1893 ....... 82 76.00 18.00 

1894.: .... 2,750 8. 20 . 25 

1893 ....... 3,674 1. 58 8.34 

1888 ...... 3, 414 2.25 3.00 

EARLY BmD TUNNEL. 

·The Early Bird tunnel, on the west side of 

Virginia Canyon opposite the mouth of Boomerang Gulch, is entirely on the vein and is said 

to be 640 feet long but· could be entered for 

only 510 feet. At 310 feet from the mouth a 

. winze, now full of water, has been sunk; and at 

180 feet a 30-foot crosscut leads south. Schist 

of the Idaho Springs formation is exposed 

throughout the entire workings. 

The vein strikes N. 55° E. and dips on an 

average 85° SE. It is usually from 12 to 18 

inches wide. Branches'into the footwall were 

noted just east of the winze and 80 feet from 

the n;wuth. A small parallel fracture with 

similar mineralization is exposed. at the end of 

the crosscut. · 

The mineralization is entirely pyrit.ic, small 

cubes of pyrite being disseminated in the 

crushed, bleached, and in places silicified schist 

along the fracture zone. At the w1nze the 

mineralized zone is at least 10 feet wide; nearer 

the mouth of the tunnel i~s maximum width is 

about 5 feet. In a few places lenses of white 

quartz with rather coarse pyrite are seen in the 

vein; in most places these are about. 2 inches 

wide and are very short, but in one locality 6 

inches of the material extends for about 20 feet 

along the drift. 

Apparently little work has been done in this 

tunnel for years, and the water, which is considerable, is depositing limonite on the walls 

and floor. Near the winze the floor is covered 

with 2 to 3 inches of soft spongy limonite. 

The Early Bird shaft, 300 feet southeast of 

the tunnel on the Old Proverb vein,, is full of 

water. The dump indicates that this vein· has 

the same constituents as the Early Bird vein. 

BELL VEIN. 

The Bell vein is developed by the Bell tunnel 

with portal in Seaton Gulch at an elevation of 

about 8,200 feet. The tunnel, which is about 

650 feet in length, trends from east to N. 65 ° 

E., following a we~-defined but lean fracture 

zone which only exceptionally shows small 

seams and lenses of pyrite. It is in general 

nearly vertit;al. In several places the fracture 

zone is 3 to 4 feet in width, but the widest 

pyrite stringer observed was only I! inches. \ 

TREASURE VAULT MINE. 

The Treasure Vault vein cuts across the noseof the ridge between Virginia Canyon and But-· 

termilk Gulc:1 about three-quarters of a mile 

north of Idaho Springs, the main shaft and. 

mouth of the tunnel being within 400 and 500 

feet of the road between Central City and Ida4o· 

Springs. This vein has been worked through. 

three shafts, the deepest of which has reached. 

130 feet below the surface. A drift tunnel 45,0 

feet long, start.ing from the draw between But-. 

termilk 'and Seaton gulches, ·runs east to a 

point under the main shaft, with which it is. 

connected by a 50-foot inclined raise. This. 

shaft has levels at 76 and 126 feet and is. 

equipped with a hand windlass. The lowerlevel extends 1:35 feet east and 40 feet west of 

the shaft, the ra.ise from the tunnel being at the 

'extreme west end. The 76-foot level is 210· 

feet long, 50 feet of which is. west of the shaft. 

Most of the .stoping has been done between the. 

first level and the surface, though some ore has. 

been taken from greater depths. 

Granite gneis~ is the only rock seen under--

ground. On the surface a very little monzo--

nite porphyry is exposed just east of the tunnel 

mouth but was not noted in the tunnel. 

The Treasure Vault vein strikes about N. 

60° E. and dips 29°-58° N. It is accompanied 

by two subparallel veins. The first, a rather· 

strongly marked, nearly vertical fissure averaging about 1 foot in width joins the Treasure.' 

Vault on the upper level about 90 feet east of 

the shaft and diverges from it westward. 

Thirty feet west o.f the shaft it is 15 feet south 

of the main vein, and it is probably identical 

with the southern 1 to· 2 foot fracture in the 

tunnel level, where the veins are about 100 feet. 

apart. Between t.he main vein and the first. 

fissure a second fissure appears, about 50 feet 

from each in.the tunnel and about equidistant 
CLEAR CR.EEK COUNTY. 301 

n the upper level. It has a dip of 55°-70° S. 

Cross fractures connect the three main :fissures, 

and the granite gneiss between them is more 

or less silicified and otherwise altered. The 

gently dipping Treasure Vault vein in particular tends to send off small very flat lying 

stringers which seem in some places to out 

across the middle and vertical vein. . These 

"flats," of which there are two and possibly 

three between the surface and the second level, 

seem to have some connection with the bonanza 

pockets. They are generally narrow and of 

short length along the vein, being rarely traceable for 1nore than 30 feet. 

In the tunnel the three :fissures exposed were 

practicu.lly barren fracture zones containing a 

little dissen1inated pyrite. At one locality in 

the north or Treasure Vault drift a stope 100 

feet long and 10 to 15 feet high shows two 

stringers of gray-blue cherty quartz with 

pyt·ite, each about 4 inches wide, separateq by 

4 feet of very slightly altered granite gneiss. 

The ore is silicified granite gneiss cut by 

subparallel branching stringers of blue-gray 

cherty silica, commonly one-fourth to onehalf inch . wide but reaching 4 to 6 inches in a 

few localities, where they are apt to inclose a 

drusy central cavity. On the :first level in the 

stope east of the shaft one of the "flats" 

crossing the drift shows successiYe depositions 

of a thin :fihn of dark-grt~ .. y cherty silica in small 

disconnected patches, a film of violet-colored 

fluorite, one-eighth inch in maximum thickness, and a coating over all of one-eighth to 

one-fourth inch of ferruginous calcite. That 

the fluorite and calcite were deposited in open 

cavities is shown by their drusy surfaces. 

The gangue 1ninerals are frozen to the granite 

gneiss, but there is in most places a tight parting between adjacent layers of the cherty silica 

near the walls. A very minor amount of fine 

pyrite accompanied the silica, but it is more 

abundantly disseminated in the adjacent wall 

rock than in the veins proper. Th~ gold is 

largely native and in tellurides (found thus 

far only to a depth of 126 feet) and is largely 

confrned to the stope at the shaft and the small 

flat stope in the east 76-foot level. The native 

gold occurs as irregular :films on joint planes 

near the flat vein il.nd as stringers up to onefourth inch wide cutting brown-stained altered 

granite gneiss. Th1

e telluride is silver colored 

and is said to contain about equal amoul?.ts of 

gold and silver, being near sylvanite in con1-

position. Tell_urides are not nearly so abundant as natiYe gold, but the two occur in the 

same manner and in close association with each 

other. 

Only two localities show postmineral movement. On the 126-foot level, 115 feet east of 

the shaft, a nearly vertical fault striking northwest has displaced the vein bringing the east 

side down about 2 feet. What is probably the 

same fault is seen in the 76-foot level, but here 

it cut~ the vertical ·vein, and neither the 

direction no'r amount of displacement can be 

determined. 

The ore, where rich enough to mine, is 

generally of bonanza grade, and the work is 

~lone entirely by hand in order to break only 

the good ground.· The ore that has been 

shipped varies exceedingly in value. Some 

of it carried as high as 12 ounces gold per ton, 

though most of it seems to carry one-half to 

1! ounces. Small specimens run higher. The 

silver varies from one-half ounce to 50 ounces 

per ton. Some' ore, low in gold, carries high 

silver, and the ore carrying the most gold had 

only 3 ounces of silver per ton. There seems 

to be no regular relation between the amounts 

of gold and silver present, ratio of gold to· 

silYer by weight ranging from 1 :1! to 1:16. 

The total production of the mine is estimated 

to be at least $30,000. 

IDAHO TUNNEL. 

The Idaho tunnel, whose portal is in Boomerang Gulch at an elevation of approximately 

8,250 feet, extends north-northeast under Seaton Mountain. The veins are shown in :figure 

58, to which the letters used below correspond. 

A. A n·early vertical fracture zone 2 to 4 

inches wide, lying about parallel to the foliation 

of the schist wall rock. In most places it is barren of mineral but in one place shows 1!inches 

of light-gray quartz carrying pyrite. 

B. A vein sho·wing 1 to 3 inches of galena, 

sphalerite, and white quartz. 

0. · Several small veins carrying 1 to 2 inches 

of gray quartz and pyrite. 

D. A tight veinlet, one-half to 3 inches wide, 

of galena, sphalerite, and subordinate pyrite. 

E. Not a distinct vein; a few sm.all stringers 

of gal~na and sphalerite traversing the monzonite porphyry.· , 

F:· A vein in one place about 10 inches wide, 

the. upper 5 inches being nearly solid galena, 

sphalerite, and very subordinate pyrite, and 
302 GEOLOGY OF GILPIN, CLEAR CREEK, AND B,OULDER COUNTIES, COLO. 

the lower 5 inches si]J._cified schist and pegmatite· G. About 4 inches of somewhat silicified 

carrying some disseminated pyrite and a few schist, which carries disseminated pyrite and 

very narrow pyrite stringers. In places the is traversed by several subparallel stringers of 

LEGEND 

Granote 

~ 

~ pegmatote 

1~1 Barren fractures 

t::::.._j ~ 

Pyritic vems 

B 

Galena-sphalerite veins 

(Arrows ondlcate direction of dip) 

Note: Wall roc:k-is'ldaho. Springs formation except where otherwise indicated 

.<:f:r~' 

l;,~l !/(PORTAL 

N 

10._, o_,_-.J,__....J•9._o __ ' _.zpo Fe.et 

FIGURE 58.-Geologic plan of Idaho tunnel. Surveyed by hand com-

. pass and pacing. 

vein has a total width as great as 2 feet and 

includes several galena-sphalerite veinlets. It' 

appears to be the westward continuation of the 

Seaton ve~. It has been stoped to some extent. 

galena and sphalerite not more than one-half 

inch in. width. It lies parallel to the foliation 

of the schist. 

11. A !-inch veinlet of galena, sphalerite, 

and pyrite, bordered on the hanging-wall side 

by 2 inches of gouge carrying some. crushed 

sulphides. 

The Bride vein is the principal vein cut by 

the tunnel. To the· east of the tunnel its wall 

rock is monzonite porphyry and to the west 

granite-pegmatite; the vel.n is strong in both 

rocks. In a stope 25 feet above the drift and 

130 feet east of the line of the tunnel the vein 

varied from 4 i'nches to 1! feet in width and 

was made up of a number of narrow subparallel 

veinlets of galena, sphalerite, and pyrite cutting altered mo:o.zonite porphyry. One of the 

most heavily mineralized portions of the vein 

is exposed in a ~;tope about 40 feet west of the 

line of the tunnel, where it is 2 feet in width 

~nd consists of a network of subparallel veinlets of solid galena, sphalerite, pyrite, and 

rarely a little chalcopyrite. Some of the sphalerite is resinous, though apparently original 

·and contempor~neous with the niore abundant darker variety. Minute fractures in the 

. ore are coated by a varicolored film, probably 

of bornite, and by very minute crystals of 

chalcopyrite. These are plainly secondary depositions, probably from surface waters descending along the vein. In one place' there 

is a width of 1 foot of solid sulphides, parts of 

which are coarsely crystallized with single crystals three-fourths to 1 inch in diameter. 

On account of the high percentage of 

sphalerite present the ore from this vein is 

concentrated befo:re s:hipment to the smelter, 

the ratio of conce:o.tration being about 1 to 3 

or 4. The following sampling-works assays of 

different types of concentrates from shipments 

in 1911 give an idea of the ·metallic content: 

Sampling-works assays of ore from the Bride vein in the Idaho tunnel. 

'Copper I 

Gold. Silver. (wet). Lead. Zinc. Silica. Iron. 

Ounce. Ounces. Per cent. Per cent. Per cent. . Per cent. Per cent . 

Pyriti~ concentrate .......... { 0.31 11 .. 90 ................. 3.00 8.50 21. 10 ............ 

. 59 23. 70 2.60 6. 10 9. 50 51.00 ........... 

Sphalerite concentrate .... -l .49 25. 10 2.35 6. 70 21.50 16.00 --········ .. 47 24.50 2. 70 8.20 23. 75 18.00 ........... . 42 23. 00 2.40 7.40 23. 10 16.00 ........... 

Galena concentrate ......... { . 56 21. 80 1. 80· 45. 10 7.00 4.00 13 . 565 21.20 ············ 34.30 7.00 5.00 20 
CLEAR CREEK COUNTY. 303 

GOLDEN ROD MINE. Developments from the Argo tunnel on veins 

The Golden Rod mine; on the west side of that can be certainly correlated with veins on 

Gilson Gulch at an elevation of about 8,250 the surface are described in other parts of 

feet, is developed by a drift tunnel about 430 the report. The following descriptions include 

feet long on a vein striking N. 60o w. and by only veins and other geologic features riot 

the Bessie M. shaft, 160 feet deep, on a vein elsewhere treated. 1 

f No veins of importance are cut between· the I 

striking about N. 75o E. and dipping rom po.r tal of the Argo tunnel and the Edgardine \ vertical to 65° N. The two veins intersect in 

the tunnel, and short drifts have been driven veTinh. Ed d' . d · h t 

f l l h h f · Th h ft e gar Ine vein, as expose In s or 

rom t.1e tunne on t e s a t vein. e s a d . f . h Ar t · 1 t 'k 1 t 

and tunnel workings, however, do not coru:iect. ri ts In t e . go un~e' s r~ es near Y eas 

Th · f 11 d b th t l · : t and west. It IS barren In places and elsewhere 

e vein o owe y e unne Is In mos h vil . al' d A h t d' t · h f . b f · 1 not ea y· miner Ize . s or IS ance 

exposures a tig t racture seam arren o su - f ·th t 1 · t h 3 · h f b 

h. b · · 'd h · d · hi h west o e unne I s ows Inc es o recp Ides, ut It IS sa1 to ave carrie some g - . t d h' t t d b h d hr 't b t · · · h .. . cia e sc Is cemen e y r o oc os1 e u grade silver ore locally. The s aft vmn In two . th t ul h' d Ab t 80 f t t f th ' · · \.J 

h d · h. f I'd 1 WI ou s p 1 es. ou ee eas o e 

exposures s owe 2 to 2! Inc es o so 1 ga ena, t 1 th h d h' t · t d b · · h 'd b unne e s eare sc Is Is raverse y a sphalente, and pynte, bounded on eac s1 e Y ~ . h . 1 t f a1 d hal 't Th ·~ h d all 1 d rinc vein e o g ena an sp en e. e 

crus e w roc\: an gouge. . outcrop of the Edgardine vein crosses ButterARGO TUNNEL AND VEINS CUT BY IT. milk Canyon at an elevation of about 8,150 

feet, where it dips 60°-70° N. It is developed 

The· Argo tunnel, formerly called the New- by a shaft which could not be entered. Samhouse, is the largest and most important mining piing-works assays of 722 and 930 pounds of 

work in the district covered by this report. It smelting ore shipped in 1897 and 1898 sho~, 

was begun in January, 1904. The work was the ·one, gold 1.25 ounces and silver 4 ounces; 

delayed at several times by negotiations with and the other, gold 0.3 ounce, silver 13 ounces, 

mine owners whose veins it cut, but in spite of lead 2 per cent, and zinc 7 per cent. 

these delays the progress at certain times was The so-called Queen vein is cut by the tunnel 

rapid, the face being advanced 2,759! feet in about 5,794 feet from the portal. It strikes 

pne year and 2,925 feet in another. Its cross slightly north of east and dips about 80° N. 

section is 12 by 12 feet for the first 13,117 feet, As exposed in drifts about 15 feet above the 

beyond which it is 9! by 6 feet, except for level of the Argo tunnel, it is not heavi]y 

occasional widenings to provide passing tr~cks. mineralized. The wall rock is schist of the 

Its total length is 21,968 feet, or about 4.16 Idaho Springs formation throughout, and the 

miles. vein is a sheared zone nearly parallel to the 

The object in driving the tunnel was to inter- schist foliation. In places a little pyrite is 

sect many of the largest veins of the district at disseminated through the schist, and in one 

·depths considerably greater than the deepest place stringers one-half to 1 inch wide of quartz, 

shaft ~orkings, thus decreasing the cost of pyrite, and a little galena were observed. 

deep mining, furnishing cheap and rapid trans- What is commonly called the Tropic vein on 

portation to the mills and railroad at Idaho the Argo level is· cut 6,545 feet from the 

Springs (see Pl. XVIII, B, p. 222), and afford- portal. On the surface the +'ropic vein lies 

. ing natural drainage when the shaft workings about 360 feet north of the Seaton vein, but 

were connected with the tunnel. In ·the case the Seaton, having the gentler dip, is supposed 

of the 014_ Town, Sa,ratog~, and other veins to have crossed the Tropic between the surface 

where the shaft workings were some distance and the Argo· tunnel level so that the relative 

from the line of the tunnel, it was neces.sary to positions are reversed. As exposed on the Argo 

drive long laterals which are not completely level the Tropic vein is wholly in schist of the 

shown in Plate XXI, A (in pocket). Idaho Springs formation. In mo.st places it 

The tunnel is double tracked in the 12-foot is a barren fracture zone 2 to 6 inches wide, 

portion and single tracked with occasional b~t 35 to 40 feet west of the tunnel it opens, 

sidings beyond. I-laulage is in trams· drawn for a distance of about 5 feet, to a width of 2 

by elec~ric locomotives. feet, in which the lower 6 to 8 inches is some-
\J 

304 GEOLOGY OF GIL:PIN, CLEAR CR.EEK, AND BOULDE:R COUNTIES, COLO. 

what fractured but barren schist, and the tight slip on the hanging wall and gradation 

remainder is schist traversed by several sui- into granite gneiss on the footwall. 

phide veinlets 3 inches in maximum width, A vein 9,54a feet from the portal shows a 

mainly of sphalerite and galena with a little tight slip next the hanging wall, below which 

chalcopyrite and pyrite. The strike and dip is 2 inches of crushed barren granite gneiss, 2! 

of this vein are fairly concordant with the inches of sinular material carrying some 

Tropic vein as exposed in the Tropic tunnel. pyrite, and 5 inches of quartz, pyrite, and 

The Seaton vein is cut 6,Q80 feet from the chalcopyrite .. 

portal of the tunnel at about the point· where A 10 to 18 inch vein of quartz at about 9,900 

it should be found if it maintains the average feet carries coarse pyrite. . 

dip of 60° N. that it has in the upper workings. A 1-foot zonE' of crushed schist carrying at 

Its character in the Foxhall tunnel is de- one place a 4-inch wide lens of quartz, pyrite, 

scribed on pages 294-297. and chalcopyrite is cut about 9,978 feet from 

The Gem system ·is cut between 7,790 and the portal and 25 feet south of the Morning 

1

7,900 feet from the portal. (See pp. 290-292.) Star vein. It dips 55° N. 

i The Gem shaft connects with the Argo workings The Morning :3tar vein is cut at 10,003 feet 

1/ 160 feet east of the tunnel, so that the lode and has been drifted on for 280 feet east of the 

has been certainly identified. tunnel. 'It is a narrow zone of crushed and 

The so-called Belman vein is cut a little somewhat silicifi,3d schist carrying a little dismore than 8,500 feet from the portal and is seminated pyrite. 

developed by a drift extending east for about A fractured zone 18 to 20 inches wide, in 

490 feet. The average strike of the vein is schist, carrying some disseminated pyrite, 

about N. 75° E. and the dip is 55°-75° N. is cut at about 10,330 feet. 

The wall rock is mainly schist of the Idaho Two inches of crushed schist, carrying 

Springs formation but in small part is granite lenses of quartz, galena, and sphalerite, is 

gneiss. The vein varies from 6 inches to 1! cut at abop.t 10,~:83 feet. 

feet in width and consists of fractured and The Half and .Half vein, controlled by the 

. somewhat silicified wall rock, usually carrying Bertha Mining Co., is cut 10,511 feet from the 

some disseminated pyrite, locally traversed by portal. The east drift, 120 feet long, is caved 

small veinlets 2 inches and less in width of within a few feet of the tunnel and the west 

galena, sphalerite, and quartz. Some small drift 150 feet wesii of the tunnel. As exposed 

veinlets of coarse pyrite are present, but their in this 150 feet t:he vein is a sheared zone 8 

relations to the galena-sphalerite veinlets are inches to 1 foot wide, mainly in schist. This 

nowhere shown. The surface workings on the zone is locally silicified and carries dissemiBelman vein could not be entered. They con- nated pyrite. In general the mineralization 

sist of a drift tunnel more than 650 feet long is very weak. 

and a shaft with 5 short levels. · The south vein of the Frontenao-Aduddell 

A vein of fair size, though undeveloped, is group is cut at 11,210 feet. (See fig. 59.) 

cut about 8,925 feet from the portal of the The Druid lateral, wl;lich extends northeastArgo tunnel and 90 feet south of the Sun and 1 ward from the Argo tunnel for over 1,300 feet, 

Moon south vein. It shows 20 inches of quartz ! starts on the nort:tt vein, but was flooded 50 

and coarse pyrite frozen to a · monzonite ·feet east of the tunnel and was inaccessible for 

porphyry footwall, above which is 18 inches of study. In general, mineralization along the · 

silicified schist carrying disseminated pyrite. south vein is very meager, only a little disOrr the west side of the tunnel a l-inch vein- ·seminated pyrite appearing locally in. crushed 

let of galena and sphalerite cuts across the porphyry or gneiss. The north vein is more 

coarse pyrite vein. strongly mineralized, showing 30 feet from the 

, The Sun and Moon workings connected with southwest face, 1! inches of sheared granite 

I

. the Argo tunnel have already been described. gneiss next .the: hanging wall, below which 

(Seep. 289.) . · is a veinlet of coarse pyrite 2 to 4 inches 

A vein showing 10 inches to 2 feet of silicified wide, traversed near its center by a t-inch 

gneiss carrying disseminated pyrite is cut; to l-inch sharp-waU3d veinlet of sphalerite and 

about 9,384 feet from the portal. There is a galena. The vein on the north side of the drift 
CLEAR CREEK COUNTY. 305 

(A, fig. 59) is 3 inches to 1 foot in width, with 

sphalerite and galena predominant and some 

pyrite. ' 

'l'he Wellington No. 6 vein, of the King Bee 

Gold Mining Co., is out 12,260 feet from the 

portal. It is developed by a lateral extending 

about 225 feet. east of the tunnel and by another 

which extends over 700 feet west but which 

at the time of this survey was caved 330 feet 

fron1 the tum1el. A winze has been sunk from 

this west drift and a considerable amount of 

stoping done above it. The vein was well 

exposed in a stope 200 feet above the west 

lateral, where mining was in progress at the 

tilne of this survey. There it is a tight vein 

2 to 4 inches wide, between walls of granite 

1-E:GENC 

~~ 

~ 

Monzonite 

porphyry 

~ 

~ 

Idaho Springs formation 

N 

l 

' o so 100 200 Feet ~--~~~----~ 

subparallel fractures without sulphides. On . 

the east wan. it shows 14 inches of quartz 

carrying fine galena and pyrite. 

Four ·feet of crushed and somewhat silicified schist caiTying disseminated pyrite is cut 

about 12,850 feet from the portal. 

The Compensation vein of the King Bee 

group has been provisionally identified as one 

of two veins 20 feet apart which cut the schist 

12,980 to 13,000 feet from the portal .The 

south vein consists of 18 inches of crushed 

schist caiTying disseminated pyrite. The north 

vein is in places a tight barren 'fracture but 

elsewhere shows 6 inches of crushed and silicified schist caiTying disseminated pyrite. 

The Japan vein, cut 13,235 feet from the · 

portal, shows a tight. fracture on the hanging 

wall, below which is 14 inches of highly silici- . 

fied schist carrying disseminated pyrite and 2! 

feet of crushed schist only slightly silicified 

and carrying only a little pyrite. 

The Saratoga vein is cut at 15,080 feet. (See 

pp. 267-268.) 

A large vein at 15,350 feet shows a tight slip 

next the footwall, ·above which is 8 inch~s of 

soft altered gneiss cut by a network of small 

pyrite stringers, 1 inch of coarse pyrite and 

quartz, 14 inches of gneiss carrying disseminated pyrite, 4 feet of quartz with coarse pyrite, 

and 8 inche~ of quartz carrying some pyrite, 

frozen to the porphyry hanging wall .. 

A tight vein consisting of 2 feet of pyritiferous quartz is cut at about 16,336 feet. 

The Calhoun lateral is reached about 16,506 

FIGURE 59.-Geologic plan of workings on Frontennc-Aduddell system feet from the portal, but WaS accessible for only 

of veins on Argo ttuUlellevel. Surveyed by pacing and hand com- 350 feet west, beyond which it was flooded. 

pnss. 

In the 350 feet examined it follows a fractured 

gneiss, consisting of galena, sphalerite, and zone 2 to 2! feet wide in granite gneiss weakly 

pyrite in a gangue of gray quartz and altered mineralized with minute -veinletf? of pyrite and 

gneiss. Vugs lined with quartz and pyrite are some disseminated pyrite. The prevailing 

· numerous, and there are a few lenslike en- dip is about 80° N. 

largements of the vein 1· foot in maximum Three pyritic veins, none of which is heavily 

width. The smelting ore from. this stope is mineralized, are cut in the 150 feet north-of the 

reported to caiTy 2 to 3 ounces in gold and 20 ·calhoun lateral. One of these veins assayed 

to 25 ounces in silver per tOT!. The fine- gold 0.2 ounce and silver 1.2 ounces. 

grained ·pyrite is reported richer than the A 4-foot zone of silicified granite gneiss 

coarse. As exposed in the east lateral the vein 16,780 feet from the portal is traversed by 

is in many places represented by a barren numerous subparallel tight fractures and b:y 

fracture and elsewhere is a tight sulphide vein small stringers of quartz and pyrite. It carries 

not n1ore than 2 inches wide. more or less disseminated pyrite. 

What is called the Compeer vein of the King A zone 10 feet wide in granite gneiss is cut by 

Bee group is cut 12,710 feet from the portal. numerous· subparallel fractures at about 17,020 

On the west wall of the tunnel it is· a series of feet. The gneiss IS silicified and carries dis-

' 44214°--17----20 

.) / 
306 GEOLOGY OF GILPIN, CLEAR CR.EEK, AND BOULDER COUNTIES, COLO. 

· seminated pyrite. About 2 feet above· the footwall is a 1-foot vein of quartz carrying abundant 

fine pyrite. · 

. Three veins are cut between 17,160 and 

17,230 feet. The southernmost vein is an 

8-foot vertical zone of crushed and silicified 

gneiss carrying abundant disseminated pyrite; 

the middle vein dips 80°N. and shows 1 foot 

of crushed granite gneiss next the footwall, 

followed by 1! ·feet of silicified gneiss carrying 

disseminated pyrite; the northei'I! vein dips 

85° N. and shows 1! feet of pyritic quartz. 

The Mammoth lateral leaves the Argo tunnel 

about 17,370 feet from the portal. It was 

studied to a point 1,350 feet east of the tunnel, 

·beyond which flooding prevented further study. 

For the first 700 feet the· lateral follow~ a 

sheared belt 6 inches to 1 foot in width, only 

slightly mineralized with disseminated pyrite. 

Beyond this the mineralization is slightly more 

pronounced and at about 825 feet is strengthened by a branch vein coming i~ from the 

south wall. Beyond 825 feet· the vein shows 

commonly 1 to 2 feet of silicified schist carrying 

abundant disseminated pyrite. The mineralization is not at all comparable in strength 

- with that of the Mammoth vein as exposed in 

higher workings, and no stoping of consequence 

has been done. A sample of heavy pyritic ore 

from the breast of this lateral assayed gold 0.06 

ounce and silver 0.5 ounce. A width of 1 foot 

of the heaviest pyritic ore in the lateral assayed 

gold 0.16 ounce, silver 1.3 ounces. 

The so-called Illinois vein is cut by the Argo 

tunnel 18,088 feet from the portal .and has 

been drifted on for 30 feet east and 50 feet west. 

What is probably the California vein is cut 

18,362 feet from the portal. Its identification 

is based not only on its position but on its 

association With a dike of bostonite porphyry, 

a feature which characterizes it in the shaft 

workings. (See p. 223.) 

. The Paten is traversed between 18,867 and 

19,412 feet from the portal. (Seep. 236.)-

What is supposed to be the Dyke vern is cut 

at about 20,370 feet, where development was 

in progress at the time of this survey. The 

Dyke lateral extends west from the tunnel for 

about soo· feet, following a well-defined vein 

strongly mineralized for the first 700 feet but 

only weakly so in the last 100 feet. In most 

places it is 1 to 2 feet wide, in one place reaching 2! feet. In some places it is merely a 

heavy dissemination of pyrite through a zone 

of fractured gneiss but elsewhere shows one or 

more sharp-walled veins of ·gray quartz and 

pyrite borden:d by gneiss carrying disseminated pyrite. In one place it contains 8 to 10 

inches of neari~y solid pyrite. The prevailing 

wall rock is granite gneiss, but near· the face, 

where the vein becom.es leaner, there is son1e 

schist of the Id.aho Springs formation. 

J\ large num.ber of assays of ore from along 

the Dyke lateral show a gold content of 0.3 

ounc~ to 2 ounces (1naxi1nu1n of 9.8 ounces). 

The silver content is commonly between 3 and 

15 ounces (maximum 36 ounces). The copper. 

content is usually negligible. 

Shipments in 1910 as shown by samplingworks assays were as follows: 

Sampling-works assays of ore fmm Dyke vein, Argo tunnel. 

Ore. Gold. Silver. 

Net pounds. Ounce. Ounces. 

5,306 . 0.62 4.·30 

13,020 . 77 4. 10 

12,673 . 56 3.02 

14,760 . 62 6.20 

16,342 . 275 9.72 

The Dyke shaft is in the east part of Nevada-

·viJle, but little ore has been mined through it. 

The Prize vein is cut· about 20,980 feet from 

the portal and ·has been developed by short 

drifts. (See p. 22:1.) 

The Gunnell South, Gunnell Middle, and 

Gunnell North, and. Elizabeth veins are cut 

21,296 to 21,563 feet from the portal. (See 

fig. 29, p. 216; ah:o pp. 216-218.) 

The Hattie vein, cut about 21,798 feet from 

the portal, is a 2 to 3 inch zone of crushed schist 

carrying disseminated pyrite. 

FALL RIVER. 

DOVER AND PHILADELPHIA TUNNELS . 

The Dover and Philadelphia tunnels are 

near each other on the east side of Fall River 

near its junction with Clear Creek. Parts of 

the workings in both are on the same northwest-striking vein. (See fig. 60.) 

The Dover tunnel is an adit about 840 feet 

long with short branch drifts and crosscuts. 

For about 600 feet from its mouth this adit 

follows a fracture zone which trends about N. 

45° E. and dips 30°-50° ·NW. The vein 1s 
CLEAR CREEK COUNTY. 307 

·conunonly barren, consisting only of crushed 

or silicified wall rock, ehough locally it carries 

pyrite disseminated through gouge or through 

gray quartz probably formed by silicification 

of the wall rock. The greatest width of pyrite 

and quartz observed was 16 inches. 

The 1nain vein is crossed with slight displacenlent 440 feet from the mouth of the aclit by a 

vein striking about N. 40° W. and dipping 

about 60° NE., which shows 6 to 9·inches of 

white and gray quartz, probably formed by 

silicification of the wall rock along a frac.ture 

carries disseminated pyrite. Only a few clist~nct veinlets of pyrite are present, and all are 

small exce-pt in the stoped part of the ·vein, 

300 to 380 feet from the portal, where in one 

place an 8-inch vein of pyrite and quartz was 

exposed. In other places galena-sphalerite 

veinlets one-half and 1 inch wide were noted. 

In one place the Boston vein forks and reunites (see fig. 60), and in another place it is 

offset into one wall of the drift by· eros's faults. 

The ore is of low grade and has been stoped 

at only the one place noted. A little drifting 

Note: Wall rock is granite gneiss except where otherwise indicated 

E:j ·~ ~ ~· Monzonite 

porphyry 

Unmineralized Pyrif1c vein Composite pyritic and Workin~s fracture gatena-splialerite vein inaccess1ble 

·c Arrows indicate direction of dip) 

FIGURE 60.-Geologic plan of Dover and Philadelphia tunnels. 

zone. It is barren of sulphides. About 100 

feet of drifting has been done on this vein. 

The n1ain vein is cut 600 feet from the mouth 

of the ·aclit by a fault striking about N. 60° W. 

and dipping 50° NE. The main adit turns and 

follows this fault but is caved a little beyond 

the turn. The fault where exposed shows· 6 

inches of gouge. It is the same fault (see fig. 

60) on which e~tensive drifting has been d,one 

in the Philadelphia tunnel. 

That portion of the . Philadelphia tunnel 

which trends northeast follows several ·nearly 

parallel fractures comprising the Boston vein, 

along which for a width locally of several feet 

the granite gneiss has been much siliqified and 

has been done on two barren fracture planes 

which cross this vein. 

The part of the Philadelphia tunnel which 

trends northwest and southeast follows a 

fault plane which parallels the general course 

of a dike of· monzonite porphyry. The fault 

plane is characterized by much breccia and 

gouge but is'barren except for scattered grains 

of disseminated pyrite. No stoping has been 

clone on it. 

The Gloria Mundi vein shows a snlall anlOUll t 

of stoping. (See fig. 60.) In one place· it 

carries, frozen to the hanging wall, a 2-inch 

band of quartz, pyrite, and chalcopyrite, below which for about 4 feet the granite gneis3 
308 'GEOLOGY OF GILPIN, CLEAR CREEK, AND BOULD-ER COUNTIES, COLO. 

is cut by small stringers of pyrite one-eighth 

inch to 1! inches wide. This vein is distinctly 

later than the monzonite porphyry dike. A 

vein (A, fig. 60) a short distance northeast of 

the main fault vein, which may be a spur from 

it, shows next the hanging wall 6 inches of 

crushed granite gneiss, below which the gneiss 

.is traversed for a width of 2 inches by pyrite 

stringers· 1 inch and less in width and carries 

disseminated pyrite. 

· A vein (B, fig. 60) about ioo feet below the 

main fault vein shows 4 feet of granite gneiss 

more or less . silicified, containing pyrite in 

disseminated grains and as small stringers. 

Above it lies an open watercourse, along which 

muchdark-grayc4erty silica has been deposited. 

UNITED GOLD TU~L. 

The United Gold tunnel is on the east side 

of Fall Eiver, about one-fourth inile north of 

its junction with South Clear Creek. A 10-

stamp mill, known as the Riste~t mill, is in 

the creek bottom opposite the ·mouth of the 

tunnel, with which it is connected by a short 

trestle over the Fall River road. (See fig. 61.) 

The main. tunnel is a drift 450 feet long. A 

crosscut started about 150 feet fron1 the 

mouth is 600 feet long and intersects six 

narrow fracture seams, which strike 16°-42° 

NW. The mineralization in all ~of them is 

weak, consisting generally of a small amount 

of disseminated pyrite in the walls very close 

to ·the fractures. Lenses of white or lightgray quartz with fairly coarse pyrite occur 

in places, particularly in the fourth fracture 

intersected by the crosscut. 

The first fracture in the crosscut consists of 

4 inches of barren crushed granite gneiss and is 

probably the extension of a fault encountered 

in the main drift. The second fracture consists 

of 1 foot of crushed granite gneiss, with abundant disseminated pyrite separated from both 

south drift ·some pyrite is disseminated in 

the footwall through a width of 20 inches. 

The fifth fraeture is a 1-foot zone of slightly 

silicified granite gneiss containing a very 

minor amoun·t of pyrite. The si..-x:th and last 

fracture showB a 2 to 4 inch stringer of white 

quartz, which carries a few pyrite cubes and 

is usually frozon to the footwall and separated 

from the hang:mg wall by a slip plane. 

From 40 to 3:00 feet from its mouth the main 

drift follows a fiat vein 2 to 6 inches wide of 

light gray quartz with fairly abundant pyrite, 

separated from both walls by an inch or so of 

gouge. At 300 feet from the portal this 

fiat vein is cut without displacement by a vertical barren fracture which the drift follows 

'from that point. This fracture contains :4 to 

6 inches of cru.shed granite gneiss, much of 

N 

LEGEND 

Note: Wall rock is .lranite ~neiss except where otherwise indicated 

ld!!ho ~-Springs Unmineralized w fracture Pyritic w. vein 

tormatoon (Arrows indicate directoon of dip) 

FIGURE 61.-Geol•>gic plan of United Gold tunnel. 

which approaches gouge in fineness. Near the 

face of the drift a kms of white quartz 6 in{{hes 

wide by 5 feet long shows a minor amount of 

pyrite, as does abo ~bout 2 inches of the 

adjacent crushed wall rock. 

There has been no stoping on any of the veins 

exposed by this tlinnel. 

DUBlfQUE MINE. 

walls by gouge; the wall _rock for 4 feet on The Dubuque vein, on the west side of 

either sid~ is impregnated with pyrite. The Fall River a short distance above .its conthird fracture is tight and barren. The fourth fiuence with Clear C:reek, is developed by two 

fracture contains a vein.:filling of white quartz drift t.unnels, the up.Per 120 feet long and the 

2 to 10 inches in width, which carries locally lower over. 400 feet long. The vein strikes 

a minor amount of coarse pyrite and is com- northwest, following the northeast side of a 

monly frozen to the walls, though at one place dike of monzonite porphyry. T~e workings 

it is separated from the hanging wall by 2 could n~t be entered 2.t the time of this survey. 

inches of gouge. The walls are everywhere I Ore on the dump showed pyrite and chalcoslightly silicified, and near tP,e face of the pyrite. 
CLEAR CREEK COUNTY. 309 

L UCANIA TUNNEL. 

The Lucania crosscut tunnel runs N. 40? E. 

for at least 6,240 feet from a point on the east 

' side of Fall River about 1 n1ile. north of South 

Clear Creek. The tunnel, which is one of the 

longest in this district, was designed to cut 

the veins of Russell Gulch and Quartz Hill at 

considerable depths and to reach the Patch 

about 14,800 feet from the portal at a depth of 

about 1,400 feet. In September, 1911, the 

face was under the head of Davenport Gulch. 

'rhe country rock throughout the tunnel is 

granite gneiss, which for the first 4,435 feet is 

n1ore biotitic than it is near the face. The 

line of demarcation between the two. facies is 

fairly sharp and is parallel to the gneissic 

structure. 

In the tunnel the gneiss is cut by a succession 

of small, tight, nearly parallel fractures, 

which strike on the average N. 80° W. ~1ost 

of the:m dip north at rather steep angles (75° 

being 111ost commoi1), but one or two dip 

80°-85 o S. Near the face an ~xceptionally 

large well-mineralized fracture, cut by the 

tunnel, strikes N. 50° W. and dips 70° NE. 

Accompanying this near the south wall is a 

10-foot monzonite porphyry dike. 

Except for the vein just mentioned the 

minernlization of the fractures is weak. In 

about 20 fractures noted in the entire length of 

the tunnel only very 1ninor amounts of pyrite 

occurred, generally dissen1inated in the wall 

rock ~lear the fissu,re but in places occurring 

as strmgers of coarse pyrite and qua~tz in the 

fissure. In three fractures, about two-thirds 

of the ~vay in fron1 the mouth, son1e galena, 

sphalerite, and chalcopyrite associated with 

gray quartz occur in lenses, most of which are 

frozen to the walls above the pyritic.veins. 

The large vein near the face is supposed to be 

the John L. Emerson, opened higher· on the 

hill by the Knickerbocker tunnel. In the 

Lucania tunnel it is 42 feet wide, with- about 

30 feet of the hanging wall slightly n1ineralized. 

The cross section of this vein is as follows: 

Section of John L. Emerson vein(?) in Lucania tunnel. 

Feet. 

Granite gneiss, dark colored,. altered, carrying dis.-

seminated pyrite ................................ 10 

Tight slip plane. 

Quartz, white, carrying~ little pyrite.............. 1! Grani~e gneiss, crushed, with abundant disseminated 

pyr1 te. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . 2 

. Feet. 

Granite gneiss, darker, much altered; cut by numerous 

stringers of white quartz and pyrite with a little 

chalcopyrite. These minerals also occur in small 

grains disseminated through the gneiss. · Several 

slip planes traverse this part of the vein ............ 15 

Quartz, white, containing pyrite. . . . . . . . . . . . . . . . . . . 1 

Quartz, gray, carrying pyrite....................... 1! 

Monzonite porphyry, much altered, carrying dissemina~ecl pyrite and traversed by numer,ous very small 

strmgers of dark quartz locally carrying galena and 

chalcopyrite .................................... 10 

Tight slip plane against footwall. 

A little ore obtained in cross.cutting the vein 

was largely galena and chalcopyrite but apparently came frcm a lens, for similar material 

was not seen along the walls. At the time of 

survey there had been no drifting on the vein. 

The veins underground are numbered from 

the .mouth of the tunnel. An aggregate of 

1,040 feet of drifting has been clone on Nos. 

12, 13, 14, 15, and f7. The longest drifts are 

on No. 16 vein and extend 450 feet west of the 

tunnel and 220 feet east. In the west drift 

there has been some stopi:r;lg, but a cave at the 

east end of the stopes has blocked them. A 

little ore shipped in 1908 and 1909, possibly 

from this stope, carried as high as 1 ounce of 

gold and· 12 ounces of sliver to the ton a:hd 20 

per cent of le9;d. The average content, however, was. about 0.5 ounce gold and 6 ounces 

silver. 

BERRY VEIN. 

On the west side of Fall River 900 feet 

northwest of the mouth of the Lucania tunnel 

two tunnels on the Berry vein strike N. 50° E. 

and .djp. 45° NW. in granite gneiss. The upper 

tunnel IS very short, but the lower one is 620 

feet long with only the first SO feet off the vein. 

The vein fracture is 1 to 6 inches· wide and is 

gouge-filled for its entire length, the gouge in 

most places being slightly mineralized. In a 

fe:W pla.~es narrow stringers of white quartz 

with pynte are seen above the slip. The hangi:qg wall is mineralized for 1 to 2 feet from the 

slip by a small amount of disseminated pyrite 

and by a few narrow stringers of coarse pyrite. 

There has been no st.oping on the vein, and as 

far as known the property has had no production. 

U. P.R. MINE. 

The U. P. R. nline is on the east side of the 

valley of Fall River between Phillips and 

Lucania gulches. The development work com-· 

prises two short drift tunnels, only the lower 

.. 
310 GEOLOGY OF GILPIN, CLEAR CREEK, AND BOULDER COUNTIES, COLO. 

of which is ·accessible. The country rock vein and about parallel to it are two relatively unis granite gneiss with sn1all lenses of granite imp9rtant fract-llres, along which there has been 

pegmatite. a little mineralization. There has been slight 

The general strike of the n1ineralized zone .postmineral moyement along the main vein. 

is about N. 70° E. and the dip 50°-60° N. The first 250 feet of the vein in the middle 

The vein, as seen in the lower tunnel, consists tunnel has been stoped for about 30 feet both 

in niost places of 2 to ·4 feet of wall rock pene- above and below the tunnel. Several smaller 

trated by a network of small stringers of stapes are near .the face of the drift. 

white quartz and pyrite, which in places unite Sampling-wo:rks assays of 45 lots of smelting 

to form· a well-defined vein 1 foot in maxi- ore aggregating 477 tons, shipped in 1908 and 

mum width, bordered by gneiss carrying a lit-. 1909, show gold 0.02 to 1.16 (average 0.5) · 

tie disseminated pyrite. Near the end of the ounces. and silver 1 to 31 (average ·9.5) ounces. 

tunnel the lode forks, forming two veins each Lead is not reported for most of the shipments 

10 inches wide, which in 30 feet from their and seldon1 runs over 10 per cent. One lot 

separation are 15 feet apart. assayed gold l.H6 ounces, silver 31 ounces, and 

No stoping has been done, and no data are lead 23 per cent, showing higher values for the 

at hand regarding the value of the ore. three metals th~n most of the other shipments. 

XINDA VEIN .. 

The Kinda vein, on the east side of Fall 

River valley about three-fourths of a mile 

north of the confluence of Clear Creek, is 

developed by three drift tunnels. at elevations 

of 800, 940, and 1,000 feet above Fall River. 

The upper tunnel_ is connected with the 

surface by a 75-foot shaft and with the midCUe 

tunnel by winzes. Connection is planned 

between the middle and lower tunnels but has 

riot as yet been completed. There is a total 

of a little over 2,000 feet of work on the property, the middle tunnel exposing . 650 feet 

of the vein. 

The country rock is granite gneiss and granite 

pegmatite, the latter rock occtirring as narrow 

offshoots from a large n1ass whose western 

boundary passes between. the portals of the 

upper and middle tunnels. 

The vein strikes about N. 55° E. and dips 

~n an average 50° NW., though dips as low as 

3.9° and as high as 59° were noted. It is a 

zone from 1 to 3 feet wide of fractured pegmatite and granite gneiss, in . which . disseminated pyrite occurs, and in the mo~e open 

portions of. which quartz has been deposited. 

Lenses of coarsely crystallized quartz 8 inches 

-in maximum width but not of great length were 

not~d. The ore is all oxid~zed a~d in a few 

_places shows small bunches of a light-yellowish 

earthy n1aterial which carries a little lead 

probably as an oxide. The pyrite was apparently coarse, but as the orE( is largely· oxidized 

only casts and small remnants of the original 

crystals usually_ remain. South of the main 

The total gross production is said to be 

about $150,000. 

. BOURBON VEIN. 

The Bourbon vein, on the . south side of 

Phillips Gulch a little over one-fourth mile east 

of Fall River, is developed by a tunnel 760 

feet long, o~ which the first 110 feet is a crosscut and the remainder a drift on the vein. 

The country rock throughout is granite gneiss. 

The vein strikes N. 80° W. and dips 25°-78° N. 

(average about 54 °). The vein proper varies 

from knife-blade thinness to 6 inches and 

consists of white quartz with some coarse 

pyrite. In n1ost places the bordering granite 

gneiss is altered and impregnated with pyrite 

for a few inches to 2 feet frmn the vein proper. 

This impregnation is usually in the footwall but 

is locally presEnt in the hanging wall. Sm~ 

stringers of quartz and pyrite branching 

from _the main vein cut the pyrite-impregnated 

walls. Two Enlall branches . run into the· 

hanging wall, one 120 feet from the face of the 

drift and the other 150 feet from its n1outh. 

Near the end of the tunnel a few small stringers 

of dark-gray fine-grained quartz contain a 

very small qua,ntity of galena and are appar- · 

ently younger than the quartz-pyrite mineralization. A very slight amount of postmineral · 

movement is indicated by one-fourth to threefourths of an ·Lnch of gouge next the hanging 

wall. There has been no stoping on the vein, 

and the produetion if any has been very small. 

MANDOLIN A VEIN. 

The Mandolina vein, on the south side of 

York Gulch jw;t east of Fall River, is developed 
CLEAR CREEK COUNTY. 311 

by a tunnel 660 . feet long, of which the first 

30 feet is crosscut and the remainder a drift 

on the vein, which strikes S. 85 ° E. and dips 

50° N., cutting only granite gneiss. It is a 

well-marked fracture zone 1 to 4 feet wide which 

contains abundant disseminated pyrite in 

altered wall rock. In most places a stringer 

of coarse pyrite and quartz lying near the 

center ranges · fron1 2 inches to 6 inches in 

width, the sn1aller size being the more usual. 

Postmineral gouge 1 to 12 inches wide is present 

• on the hanging wall of the vein. A little 

molybdenite was noted in small flakes on 

joints· in son1e ore from the dump. 

So far as could be learned no stoping has 

been done. 

HELEN TUNNEL. 

The I-Ielen tunnel starts on the north side of 

Phillips Gulch one-fourth rnile east ·of Fall 

River opposite the Bourbon tunnel. It is a 

crosscut 530 feet long, which for the first 340 

feet runs generally north and then gradually 

shifts to the right until in its last 20 feet it 

trends southeast. The country rock is granite 

gneiss. At 450 feet fr01n the mouth a 2-inch 

quartz-pyrite stringer frozen to the walls 

and striking N. 21° W. cuts across the tunnel. 

A winze 110 feet from the mouth is sunk to 

an undetermirl.ed depth on a mineralized zone 

striking N. 80° E. and dipping 59° N. This 

zone consists of about 2 feet of pyrite-impregnated granite gneiss cut by very small stringers 

of coarse pyrite; below this and separated from 

it by a tight slip plane is a streak of dark 

quartz one-half to 2 inches in width that carries galena and sphalerite. The galena-sphalerite vein is separated from the footwall by a 

thin film of gouge. 

Eighty feet from the mouth a winze about 

80 feet deep is sunk on a 4-foot zone of pyriteimpregnated granite gneiss cut by stringers 

of quartz a,nd coarse pyrite one-fourth inch 

in Inaximurn width. This zorie strikes about 

parallel to the one last described but dips 

more steeply north. 

So far as known there has been no production frorn this property. 

KNICKERBOCKER TUNNEL. 

The Knickerbocker tunnel is in the east fork 

of York Gulch, about three-fourths of a mile 

southwest of Russell Gulch. In the first 80 

feet it bears N. 84° E., crosscutting through 

granite gneiss to the John L. Emerson vein. It· 

then turns southeast on the vein, which 

strikes N. 46° W. and dips about 60° NW., 

and follows it to the En1erson shaft. The 

tunnel is caved 780 feet beyond the turn. 

The vein, where exposed in the crosscut, 

shows 20 feet of crushed, sheared, granite · 

gneiss which carries fine disseminated pyrite 

and is some.what silicified. A central zone 3 

feet wide contains disseminated quart2; and 

pyrite in greater abundance and is cut by 

stringers of almost solid pyrite. 

Postmineral movement along the hanging 

wall of the vein is shown about 310 feet from 

the turn of the tunnel by strire that pitch 

59° NW. and in several places by small seams 

of gouge that contain finely ground pyrite. 

There has been much stoping along the vein, 

but the production is not known. 

MAGDALENA VEIN. 

The :Magdalena vein is in the lower part of 

the middle fork of York Gulch, about half a 

mile south of Bald Mountain. It is developed 

by an inclined shaft said to be 265 feet deep, 

with short drifts ori the 120 and 200 foot levels, 

and al~o by a 260-foot crosscut tunnel. 

The vein, which strikes N. 40° E. and dips 

on an average 47° NW., cutting Idaho Springs 

formation, varies from one-half inch to 3! feet 

in width, with an average of 10 inches in the 

tunnel and about 16 inch~s in the shaft. It is 

a zone of crushed and altered schist between 

gouge-filled slip planes. The schist is impregnated 'with pyrite and is locally cut by veinlets 

not more than one-half inch wide of pyrite 

with some chalcopyrite. Microscopic examination showed the· presence of calcite· in one 

of the pyritic veinlets but not in the bordering schist. The altered schist wall rock consists exclusively of quartz, sericite,· and scattered grains of pyrite. The shapes of the 

quartz grains suggest recrystallization; the 

sericite probably in the main replaces feldspar; 

and the pyrite was also introduced by the vein 

solutions. 

Very little ore has been taken from the mine. 

A srnall lot sent to the smelter is reported to 

have carried $36 gold and $3 silver per ton. 

MILLIONAIRE VEIN. 

The Millionaire vein, on the east side of 

York Gulch, lies about 500 feet south of the 

. . 
312 GEOLOGY OF GILPIN, CLEAR. CREEK, AND BOULDER COUNTIES, COLO. 

Magdalena, is parallel to it, and has a similar North of .the fault the vein is known as the 

fiat northwest dip. It is developed by a short Gold Rock and has been drifted on and stoped 

tunnel which does not reach a sufficient depth ·for a considerable distance beyond the Gold 

to expose unoxidized ore. A small amount of Rock shaft, but as the drifts were caved it 

ore on the dump is iron-stained, pyrite-impreg- could not be exa1nined. 

nated., silicified schist and in some places con- The Denbigh V·3in has been stoped fronl' the ' 

tains small stringers and lenses of quartz. surface to the lower tunnel to within 30 feet 

of the fault·, an<l the re·mainder was being DENBIGH VEIN. removed in 1911 hy lessees. At this place the 

The Denbigh vein is at the head of the east streak of smelting ore is slightly wider than 

fork of York Gulch about half a mile southwest usual and the wall rock for a foot from the 

of the town of Russell Gulch. The develop- veiri is somewhat mineralized. 

ment consists of two drift tunnels and an in- Sufficient data iB not at hand for con1puting • 

cline shaft, bv.t the lower tunnel and the shaft the average metallic content of the ore. 

were not accessible. In the upper tunnel the Sampling-works assays of 13 lots of smelting 

walls are entirely Idaho Springs forn1ation ore shipped between 1888 and 1910 show gold 

with a little granite pegmatite. A bostonite 0.8 to 7.5 ounces, silver 2.96 to 16 ounces, 

porphyry dike cuts the schist about 350 feet copper Cw:et) 1.5 tc• 6.6 per cent. 

north of the shaft. 

PENNSYLVANIA TUNNEL.' The vein in general strikes N. 47° E., dips 

about 75° NW., and is 2 to 6 inches in width. The Pennsylvania tunnel has ·its .mouth on 

In most places it is frozen to one or both walls, the north side of Fa,U River about one-half mile 

'but in a few localities a very thin clay parting above the mouth of York Gulch. It is a crossseparates it from wall rock. Several small cut, the first 300 feet of which bear N. 41° E. 

branches. entering the footwall dip 75°-80° SE. and the remainder due north, the total length 

The vein filling is white or light-gray sugary being 2,000 feet. The country rock throughout 

quartz, carrying pyrite and in places a -little is Idaho Springs fonnation intruded by granite 

chalcopyrite. Locally, where the fracture is pegmatite. 

slightly wider, there is a suggestion of comb Numerous veins a.re cut by the tunnel. At 

structure,' quartz being frozen to the walls and 1,890 feet from the mouth an unmineralized 

bordered by a central band of coarsely crys- fracture zone 1 foot wide which strikes N. 85° 

talline pyrite. In some places the pyrite is E. and dips 80° N. has been followed east for 7 

coated with a thin film of chalcocite. In one feet. At 1,700 feet a drift 240 feet long runs 

place the schist footwall, somewhat silicified, northeast on a barren fracture, striking N. 69° 

· contained disseminated pyrite for 1 foot from E. and dipping 70° NNW. The fracture is 

the fracture; in most places, however, the commonly about on3-half inch wide and ·is 

walls are unmineralized and· only slightly filled with gouge, but in some. places contains a 

altered. There. is a little _iron stain in the foot of crushed schist. At 1,210 feet a fracture 

fracture, but the ore as a rule is only slightly which strikes N. 50° E. and dips 50° NW. is 

oxidized. · followed by a 90-foot northeast drift, in which 

The Denbigh vein is cut off, 400 feet from the it contains about 1 foot of crushed barren schist 

n1outh of the tunnel, by a fault that strikes above a. half inch of gouge. At 500 feet a fracN. 61° W. and dips 78°-80° SSW. The fault ture striking N. 40° E. is exposed by a 70-foot 

zone is marked by 6 inches to 3 feet of crushed drift running northeast from the tunnel. It is 

schist between walls carrying th:r:ee-fourths to barren and consists of ·1 to 12 inches of crushed 

1 .inch of gouge. There is a small amount of schist and pegmatite. At 385 feet a fracture 

pyrite disseminated in this fault n1aterial and striking N. 45° E. and dipping 50°-70° NW. 

a few. narrow stringers of coarse pyrite cut it has been followed for 40 feet. It is a 2-inch 

in places. The material, however, is said to zone of crushed wall rock above one-half inch 

have almost no value. The displacement of of gouge. At 300 feet a well-mi~eralized vein 

the Denbigh vein along this fault has been which strikes east and dips 55 ° N. is developed 

about 12 feet, the north wall ~oving west with by a long drift to the east which could be exrespect to the south wall. plored for only 140 feet c•n account of the rotten 
CLEAR. CREEK COUNTY. 313 

condition of the timbers. The vein is rather 

wide, consisting of a breccia of wall rock and 

pyrite cemented by dark-gray' quartz and 

crushed rock and containing numerous small 

incompletely filled interstices, some of which 

are lined with yellowish-green barite. From 

this vein to the mouth the tunnel bears S. 41° 

W. At 200 feet the Pennsylvania vein strikes 

N. 86° E. and dips 40° N. A small an1ount,of 

driftincr shows that it is offset 50 feet east of the 

tunnctby a north-south fault which has shift~d its continuation 30 feet to the north. The ve1n 

is on 'the average about a foot in width and 

consists la.rcrely of crushed wall rock, though b 'h in places it contains lenses of :White quartz w~t 

pyrite and, more rarely, strmgers of mass1ve 

pyrite. At 150 feet from.the mouth of t~e 

tunnel a 4-inch east-west ve1n of crushed sch1st 

and white quartz, carrying some pyrite and 

chalcopyrite, dips 60° N. · 

No figure.s showing the values of the ore were 

avn,iln,ble. The output has apparently been 

small. 

WASHINGTON TUNNEL. 

The vV nshington 'tunnel begins on th~ ~orth 

side of FaU River about 1! miles above tho 

n1outh of York Gulch, bears N. 40° E., and is 

1,080 feet iong, all in Idaho Springs formation. 

The first 400 feet follows a fracture zone which 

dips 70°-75° NW .. and is tight and· barren in 

1nost places. _1\t 4.00 feet the fracture turns a 

little east and is follo·wed for about 60 feet by 

a drift, in which there is a 6-inch wide lens of 

quartz carrying a little pyrite and chalc?-

pyrite. A few small branches from the Ina1n 

fracture run into the east wall, and some of 

then1 show a little mineral. At 350 feet a 

fa.irly open cross fracture, striking N. 79° W. 

and dipping 60° N., contains a little local quartz 

with pyrite and chalcopyrite. At 950 feet two 

veins are exposed .. One strikes N. 13° W. 

and dips 80° E.,. is about 6 inches wide, and 

consists of crushed schist with some dissenlinu.ted pyrite. The other, a narrow unmin-

·erulizecl fracture, strikes N. 68° W. and dips 

50° N. 

MOHAWK VEIN. 

The :Mohawk vein is exposed by a 140-foot 

tunnel starting in the snud] draw just north of 

Comstock's house in Fall River. It strikes N. 

75° E. and dips 70° N. Eighty feet from the 

mouth of the tunnel a branch con1ing in fron1 

the north waH is wider arid n1ore strongly n1ineralized than the n1ain vein. The wall rock is 

Idaho Springs forn1ation. The ore is all more 

or less oxidized but shows pyrite in a quartz 

gangue. At the junction of the two veins 

about 2 feet of crushed schist eontains disseminated· pyrite and is cu~ by strings of ironstained quart7. and pyrite. 

LUCKY GROUP AND PHILIPS TUNNEL. 

The Lucky Group of eight clain1s, on the 

south side of Fall River about 1 i miles southeast of the mouth of Woodpecker Gulch, is 

developed by a few shallow pits and by the 

Philips tunnel, 435 feet. long, starting· 25 feet 

above the floor of the valley. The e~tire tunnel, which trends generally west, is contained 

in an irregular-shapeq stock of monzonite porphyry, which intrudes the Idaho Springs 

forn1ation and is exposed on both sides of Fitll 

River. (See Pl. I, in pocket.) The porphyry 

stock is cut by a series of east-southeast joints, 

some of which are occupied by veinlets of dark 

quartz carrying pyrite and occasional chalcopyrite, fron1 which stringers of quartz one-half 

inch in 1ninimun1 width diverge in all directions. 'The porphyry along these quartz bands 

is bleached, altered, 1nuch softened, and generally· contains a little disseminated pyrite. 

There is no regular vein but rather a fractured 

and mineralized zone of unknown width elancrate in a direction a little north of west, as b 

shown by the surface exposures. 

The narrow siliceous and pyritic veinlets, 

together with a little of the near.:.by altered 

porphyry containing disseminated pyrite, constitute the ore, which is said to average about 

$5 a ton in gold. This material is treated in a 

water-driven 10-stanlp null at tho mouth of 

the tunnel. ~ 

STANDARD TUNNEL. 

The Standard tunnel, starting on the, east 

side of Fall River about one-half mile southeast 

of the mouth of Woodpecker Gulch, runs northeast for its first 750 feet and due north for its 

last 500 feet. (See fig. 62.) The main tunnel 

and several drifts connecting with it traverse a 

~tock of monzonite porphyry (see Pl. I, in 

pocket), and cut numerous dike offshoots from 

it. Some feldspar phenocrysts in this porphyry are 1 inch in length. The other wall 

rocks are pegn1atite and schists of the Idaho 

Springs formation. 

All of the veins cut by the t1.nmel belong to 

the pyritic type, except No. 11 vein, 1,180 feet 
,, 

,•,: 

314 GEOLOGY OF . GILPIN, CLEAR CREEK, AND BOULDER {JOUNTIES, COLO. 

~rom the mo~th, which is of the galena-sphaler-~ work of small pyritic veinlets shortly after 

1te type. It 1s noteworthy also that none of the entering the main porphyry mass. 

LEGEND 

Ea 

Pyritic veins 

·~ 

c=J 

Galena- sphalerite veins 

. 1<-1 

Unmineralized fracture 

(Arrow indicates direction of dip} 

·~ LkJ 

Workings inaccessible 

100 0 

ve n 

N 

100 200 Feet 

FIGURE 62.-Geologic plan of Standard tunnel 

veins lying wholly in porphyTy have proved 

of commercial importance, and that the two 

n1ost extensively developed veins split up into 

a number of minu,te subparallel seams or a netThe most important voin is the Standard or 

No. 2, intersected 160 feet from the portal, 

·which has been drifted on for 650 feet and has 

been stoped in some of its wider portions. In 
CLEAR CREEK COUNTY. 315 

;general the mineralization consists of rt dissen1-

.ination of pyrite in sn1all grains through the wall 

.rocks near minute fractures, the boundaries of 

the vein being indefinite. Extensive develop-

. ment of silica. has usually accompanied the 

more intense mineralization, and some of the 

more siliceous portions carry 20 to 50 per cent 

'by volume of pyrite. In th~ wider parts of th~ 

·vein in one of the stopes several !-inch to !-inch 

veinlets of solid pyrite, some of which show a 

'little galena and sphalerite in their wider portions, are exposed within the general mineralized zone. As already stated, the vein breaks 

·up soon after entering the porphyry area into a 

network of small fractures, near which the min-

·crals· of the porphyry have been more or less 

replaced by quartz and pyrite. The ore in the 

])Orphyry is of low concentrating grade. 

The vein cut 300 feet. from the portal has 

'been developed by a drift 4 70 feet in length. 

'The mineralization consists for the ~ost part 

·Of pyritization and accompanying silicification 

·of the wall rocks near a series of small fracture 

-planes, but a few sn1all sharp-walled veinlets, 

·.half an inch to 2! inches wide, of gray quartz 

.and pink calcite carrying pyrite occur. No 

;Stoping has been done. 

The veins cut between 300 and 1,180 feet are 

·small and are mineralized similarly to the 

larger veins already described, except that 

·chalcopyrite and tennantite were observed in 

=some of them. 

Vein No. 11, cut at l,lSOfeet, is unlike all the 

-other veins in the urine, being of the galena-

.sphalerite type. It is a tight vein half an inch 

to 2 inches wide, consisting of galena, sphal-

·CI'ite, and very minor an1ounts of pyrjte. A 

specimen from the dump which probably came 

from this vein showed barite as a gangue 

mineral. 

According. to 14 sampling-works assays the 

·Ore from No. 2 and No. 4 veins is very similar 

in t.enor and in mineral character. It contains 

gold 1.2 to 5.95 ounces, silver 1.75 to 21.4 

ounces, and copper 5 per cent or less. Suffi-

·cient figures are not at hand to furnish a reliable nverage. The silver content is particu-

.lnrly variable, even when only the larger shipments nrc considered, and this is due probably 

to the local presence of gnlena and sphalerite 

:for1ned during the second mineralization. 

.Smne small lots of particularly rich ore assayed 

.as high as 25 ounces in gold and others· as high 

as 53 ounces in silver. About half a ton of ore 

shipped from No. 11 vein in 1910 ran 0.08 

ounce in gold and 100 ounces in silver. A 

single specimen from this vein assayed 400 

ounces in silver . 

There is no record of the gross production, 

but it has been small, in spite. of the fact that 

ore was extracted from the. property as early 

as 1865 . .'A mill near the tunnel mouth, idle 

at the time of this survey, is equipped with 20 

stamps, Wilfley tables, classifiers, etc. 

GOLCONDA MINE. 

The Golconda claims are on the ridge between 

Fall River and Spring Gulch east of south of 

the mouth of Woodpecker Gulch. The old 

~orking~, now inaccessible, are on the Spring 

Creek side of the ridge at an elevation of nbout 

9,050 feet. A crosscut tunnel, whose mouth is 

near Fall River about half a mile southeast of 

Woodpecker Gulch, has been driven southwest 

1,665 feet, intersecting the Golconda vein at a 

vertical depth of 835 feet. The tunnel runs S. 

65° W. for 900 feet, S. 13° W. for 90 feet, a~d 

S. 36° W. for 675 feet to the face. Idaho 

Springs formation forms the wall rock for the 

en tire length. 

About 1,015 feet from the portal what is 

called the Virginia vein strikes N. 50° W. and 

dips about 75° NE. It varies from 4 to 8 

inches in width and is largely ~omposed of 

crushed schist, some white and gray quartz, 

and minor amounts of pyrite and chalcopyrite, 

these sulphides occurri~g disseminated in the 

filling and as small stringers. 

The No.4 vein, cut 1,190 feet from the portal, 

has drifts both west and east. The west drift. 

is caved 70 feet from the crosscut; but the east 

drift can be trnversed to the face, a distance of 

250 feet. The first 60 feet east of the tunnel 

has been stoped to a height of about 60 feet. 

The vein strikes N. 68° W. and dips on an 

average 55° N. It varies from a very narrow 

slip plane west of the crosscut to a max.imum 

width of 2 feet near the center of the east d1:ift. 

The vein filling is crushed schist, wh1ch is 

n1ineralized for 100 feet east of the tunnel but 

which elsewhere. contains prnctically no ore . 

The ore is crushed schist with whlte and gray 

quartz containing some pyrite and chalcopyrite, and is said to have been' of fair .grade 

and to have contained some small lenses of 

high-grade m~terial. 
316 GEOLOG~ OF GILPIN, CLEAR CREEK, AND BOULDER COUNTIES, COLO. 

. The Golconda vein, cut 1,380 feet from the 

mouth of the tunnel, strikes N. 43° W., and in 

general dips 64 °-65° NE. The east drift is 

caved 50 feet from the tunnel. The west drift 

is 475 feet long with a 40-foot winze 180 feet 

west of the tunnel, but shows little of the vein 

above the tunnel except near the end of the 

drift. In a stope· 300 feet west the vein is 4 to 

18 inches wide and consists largely·of crushed 

schist, carrying disseminated pyrite, chalcopyrite, and some galena and sphalerite, the latter 

two usually occurring in small hunches rather 

than scattered through all the ore. The vein 

pinches about 20 feet west of this stope to 3 

inches of unmineralized gouge and continues 

small to the end of the drift. In the winze the 

hanging wall is mar ked by 1 to 3 inches of postmineral gouge with' horizontal strire, below 

which is 10 to 14 inches of crushed schist with 

abundant white and gray quartz, pyrite, chalcopyrite, and some tennantite,. galena, and 

sphalerite. . This is rather hard ore, usually of 

smelting grade. The footwall is not well 

marked and contains, below the vein proper, 

irregular, usually very soft and somewhat porous masses of quartz and sulphides 3 to 4 feet 

across, which are said to carry about 1.16 

ounces gold, 15. ounces silver, and 1 per cent 

copper per ton. Some small lenses of almost· 

pure chalcopyrite in this mass are said to be of 

much higher value. In general this ore shoot 

pitches 75°' NW. and extends about 250 feet 

along the vein at the tunnel level. 

At 240 feet beyond the Golcondn vein short 

drifts run east and west on a fracture that 

strikes N. 53° W. and dips 55° N. and is supposed to be the Logan vein. It is•not mineralized where c11t by the tunnel. 

In 1909 some ore shipped from the Golconda 

ran as high ~s 11.78 oun,ces gold, 98.50 ·ounces 

silver, and 8.6 per cent copper, and some ran 

only 0.85 ounce gold, 10.3 ounces silver, and 

1.3 per cent copper. It is not certain from 

which vein thi~ came. The average content of 

1.3 tons shipped during that year was 3.26 

ounces gold, 31.2 ounces silver, and 2.31 per 

cent copper per ton. The average value of all 

the smelting ore shipped during 1910 was 1.25 

ounces gold, 9 ounces silver, and 1.07 per cent 

copper per ton, which is probably nearer the 

average value of this class of ore for the mine. 

The total production of the property is said 

to be about $4,000. 

AJ~MADEN MINE . 

The Almaden mine is on Fall River about 

one-half mile below· the mouth of Woodpecker 

Gulch. The principal working is a nearly 

straight drift tunnel about 1,300 feet long 

trending slightly north of west. This tunnel 

for its whole lengt.h is on the Colorado No. 1 or 

Blazing Star vein. The workings are in schist 

of the Idaho Springs formation intruded by 

small amounts of granite pegmatite. 

The Blazing Stt,r vein consists of 3 inches to3 feet of fractured and altered schist (in some 

places crushed to a clayey gouge), generally 

barren but in a few places traversed by small 

veinlets carrying a.ne-grained galena, sphalerite, and pyrite in a gray quartz and calcite 

matrix. The wid~~st observed veinlet of this 

kind was 1 t inches. There is some disseminate'd pyrite in the ~chist. Some slipping and 

brecciation along the vein has taken place subsequent to the original n1ineralization. The· 

richer ore was not ::;een in place, but numerous 

specimens saved in the nuning show clearly its 

mode of deposition. Along irregular fractures · 

in the gale:q.a-pyrite ore and the neighboring 

wall rock pr.oustit.e (ruby silver), pearceite 

(9Ag2S.As2S3), and ~:econdary chalcopyrite have 

been deposited. 'I'he secondary chalcopyrite 

forms a characteristic aggregate of very minute 

grains. The pearceite seen ·did not exhibit. 

crystal faces but occurred in massive forms 

intimately intergrmvn ·with the chalcopyrite. 

The proustite is usually well crystallized. Minute crystals of cer.ttrgyrite (horn silver) were 

observed in one specimen. Native silve~ in 

small wires was found in vugs in the upper part 

of the vein. One specimen seen came from a 

depth of 125 feet. 

A polished specim.en of rich silver ore from. 

the Almaden mine was examined under the 

reflecting microscope. In the· portions unaffected by downward enrichment the earlie~t 

sulphide (pyrite) is brecciated by lat.er ore consisting of gray quartz, galena, sphalerite, and 

chalcopyrite. Fracturing subsequent to bot~ 

these mineralizations was followed by the development of secondary sulphides as fillings of 

small fractures, as n1etasomatic replacements 

of galena and quartz, and as incrust~tions on 

the walls of vugs and open fractures·. The· 

secondary sulphides consist of chalcopyrite, 

pearceite, and a little galena. Replacement 

veins between quart<l and galena (similar to 
CLEAR CREEK COUNTY. 317 

those ·shown in figs. 14 and 15, p. 144) are 

comn1on. In son1e of the secondary veinlets 

proustite or rul,y silver is irregularly associated 

with the- pearceite and chalcopyrite. 

Sol'ne specin1ens frorn this n1ine are among 

the finest of their kind that the district has produced. One specimen showed 1 inch of pure 

ruby silver associated with a t to ! .inch band 

of pearceite. A mass of ruby silver several 

inches across, now in the Idaho Springs public 

library, can1e fron1 this tnine. A specin1en fro1n 

200 f~et below the surffice shows galena cut by 

a i-inch veinlet of pearceite. 

The native silver, proustite, pearceite, cerargyrite, and fine-grained chalcopyrite are· all 

shown by their mode of occurrence in fracture 

planes cutting the galena-pyrite ore to have 

been deposited later than the originaltnineralization. They fortn a striking example of the 

enrichment of a vein in silver by the action of 

at1nospheric waters descending through the 

more or less porous vein 1naterial. These 

waters dissolved certain of the n1etaUic ~ninerals 

of the original vein, such as argentiferous galena. 

and chalcopyrite, and redeposited s01ne of their 

constituents in the form of the silve~ sulphides, 

chalcopyrite, etc., fa.rther down. It is this 

process which is largely responsible for the richness of the vein, and without which the vein 

would .not itnprobably have .been too lean to 

work. It is in1probable that the enrichn1ent 

will continue for any great distanee below the 

level of Fall Riv·er. 

The output of the 1nine has been s1nall though 

of high grade. The c01nplete record of sanlpling-works assays on all shipments shows. gold 

0.04 to 0.3 ounce, silver 19.5 to 480.8 ounces, 

and lend not exceeding 1.7.5 per cent. TWo lots 

of ore weighing 1.49 and 51.0 pounds, fr01n a 

shallow winr.e below the tunnel level, showed 

respectively the following extraordinary values: 

Gold 0.38 ounce, silver 5,810.3 ounces, and gold 

0.4.87 ounce, s~ver 4,084.03 ounces. 

SEVEN-FORTY TUNNEL .. 

The Seven-Forty: tunnel is on the south side 

of Fall River about 700 feet southeast of the 

mouth of Woodpecker Gulch. It bears west 

for 80 feet at which distance it intersects a 

g~·oup of minor slip planes which strikeS. 60° E. 

and dip 50° SW. S01ne of these seams contain a little calcite and siderite and rarely a 

small amount of galena as a thin discontinuous 

crust between the carbonates and the wall rock. 

POLAR STAR TUNNEL. 

The Polar Star tunnel, on the north side of 

Fall River 700 feet below the mouth of W,oodpecker Gulch, bears N. 68° E. for 240 feet and 

about N. 45° E. for 160 feet. The wal~ rock 

is schist of the Idaho Springs formation, except for the last 20 feet, which is granite gneiss. 

The tunnel follows the schistosity, which dips 

steeply northwest. Some movem,ent has taken 

place along the foliation, producing a little 

gouge which has not bken mineralized. Where 

the direction of the tunnel changes the schist is 

cut by a fracture plane striking N. 13° W. 

This zone shows about 10 inches of brecciated, 

crus.hed, and. slightly silicified country rock, 

thro.ugh which pyrite is sparsely disseminated. 

In some 'places 'a little quartz and carbGnate 

gangue minerals contain sphalerite, galena, and 

pyrite. 

IDA MAY TUNNEL. 

The Ida May tunnel, on the spur just west of 

the'mouth of Woodpecker Gulch, bears N. 28° 

E. in its first 110 feet along a vein which dips 

65° NW. The ore is all oxidized but shows 

occasional remnants of galena and pyrite and is 

said to average ·about $22 per ton in silver. 

At 110 feet from the portal the tunnel leaves 

the vein and trends N. 7° E. for 130 feet, cutting 

at an acute angle through a bostonite porphyry 

dike for the greater part of that distance. Beyond the porphyry a 20-foot drift is driven on a 

vein that strikes N. 20° W. and dips 65° NE. 

This vein is fairly well mineralized, carrying 

considerable galena and some pyrite. 

CLIFFORD VEIN. 

The Clifford vein runs al<?ng the divide between Woodpecker and York gulches. About 

a mile south-southeast of Mount Pisgah it is 

opened by a shaft which could not be entered, 

but which is shown by mine maps to be an incline a little over 150 feet deep, with 300 feet 

of drifting on the 100-foot and about 400 feet · 

on the 150-foot level. 

The· country rock belongs to the Idaho 

Springs formatio~1, and biotite schist is the 

only rock seen on the dump. On the surface 

the vein is not well exposed but appears to 

strike N. 60° E. The drifts shown on the mine 

n1ap strike about N: 59° E., and the vein dips 

steeply southeast. The ore in the bins consisted of white quartz cut by seams and stringers of dark quartz carrying galena, light and 

dark sphalerite, chalcopyrite, and some pyrite. 
318 GEOLOGY OF GILPIN, CLEAR CR~EK, AND BOULDER COUNTIES, COLO. 

~1ost of the ore is siliceous, but some specimens 

carry barite, which is either embedded· or imphtnted on the walls of vugs and which crystallized with the dark quartz·and the lead and 

zinc minerals. Postmineral movement has 

·crushed some of the ore, producing in some 

places a grayish gouge. 

THOMAS TUNNEL. 

The Thomas tunnel, on the north side of Fal~ 

River about 250 feet west ·of the n1outh of 

Hamlin Gulch, trends generally north for 515 

feet and connects near the face with a 210-foot 

drift that bears N. 75° W. The· country rock 

throughout is schist of the Idaho Springs formation. The first 215 feet of the tunnel cuts 

the schistosity at acute angles, and the following 300 feet trends parallel to the structure 

(about N. 15° E.). This part of the tunnel 

discloses a zone of somewhat silicified schist, 

which dips 65°-70°" W. Sphalerite, galena, and 

pyrite are sparingly disseminated through the 

schist of this 8-inch to 3-foot zone and are locally concentrated in veinlets with a quartz 

gangue. The drift near the face of the tunnel 

is on a vertical barren fracture which has not 

displaced the ore zone shown in the tunnel. 

BOSS TUNNEL. 

The Boss tunnel, on the north side of Fall 

River half a mile west of Hamlin Gulch, at an 

elevation of 8,575 feet, is a crosscut 240 feet 

long, the first 90 feet of which penetrate schist 

and the remainder heavily pegmatized schist 

except for a 30-foot bostonite dike 20 feet north 

of the schist and pegmatite contact. Forty 

f_eet from the face of the tunnel a small fracture 

striking N. 75° E. shows in places a very slight 

galena-pyrite mineralization. 

:MANHATTAN TUNNEL. 

The Manhattan crosscut tunnel starts near 

the head of the west fork of Hamlin Gulch at 

. an elevation of 10,150 feet and runs N. 50° W. 

to pass under Yankee Hill. ·It has been driven 

600 feet, all through granite gneiss. A little 

galena-sphalerite ore seen on the dump was said 

to have come from a northeastward-trending 

stringer. Some pyrite· and chalcopyrite are 

associated with the galena and sphalerite. The 

gangue minerals are white quartz and siderite. 

of Hamlin Gulch. · (See fig. 63.) The wali. 

rock throughout is Idaho Springs formation .. 

The workings expose several barren· fractures. 

and one mineral-bearing fracture (A, Jig. 63),. · 

which shows a central 4-inch band of oxidized. 

sulphides bordered on each side· by about. 

4 inches of altered schist. In the drifts. 

farther west this v-ein shows little mineral on. 

t:qe tunnel level, but in a level 115 higher it. 

shows in one place about 6 inches of more or· 

less silicified schist next the hanging wall, below 

which there is a :3-inch vein of quartz and 

N 

LEGEND 

Galena-sphalerite 

~ 

~ 

veins 

Barren 

fractures 

. (Arrows indicate 

direction of dip) 

Wall rock is schist of 

Idaho Springs formation 

o so 100 200 Feet L---l---....1..----J 

FIGURE 63.-Geologic plan of Wyomed tunnel. Surveyed by hand. 

compa~ s and pacing. 

sulp4ides. 'rhe ore c:uries chalcopyrite, sphal-· 

erite, siderite, quartz,. and subordinate galena~ 

SEAMAN' TUNNEL. 

The Seaman tunnel, on the north side of 

Fall River at an elevt:~tion of about 9,100 feet, 

trends about N. 38° "r., is 3,636 feet in length, 

and was driven •to dra.in at depth the veins at. 

the head of Cumberland Gulch and at Yankee. 

At the time of this s·1rvey bad air prevented. 

its being traversed for more than 1,400 feet,. 

and in this distance only barren fracture> 

planes were seen. 

BONNIE B1tiAR MINE. 

WYOMED TUNNEL. The Bonnie Briar mine is on the south valley· 

The ·wyomed tunnel is on the north side of wall o<f Fall River nearly opposite the mouth of· 

Fall River a little over a mile above the mouth Cumberland Gulch, at an elevation of about 
CLEAR CREEK COUNTY. 319 

9,650 feet. The principal development is a 

tunnel about 400 feet in length, which exposes 

three fracture zones, none of which show any 

important mineralization. A porphyry dike is 

intersected near the face. A second tunnel, 

about 75 feet lower than the first, is short and 

was not accessible. 

MERRY MONARCH TUNNEL. 

The :Merry :Monarch claims are on the ridge 

south of Fall River opposite the n1outh of 

Silver Creek. A crosscut tunnel 380 f~et long 

trends S. 15° W. from a point just west of 

where the Alice-Dumont road crosses Fall 

River. The first 350 feet of the tunnel is 

driven through granite gneiss, which shows 

only two small fractures, both unmin.eralized, 

which strike about N. 70° W. and dip very 

steeply south .. The last 30 feet of the crosscut 

is in schist, which is cut by a fault zone striking 

N. 70° W. and dipping 80° S. This zone has 

been followed westward for more than 7 5 feet 

to· where it is caved. There is apparently very 

little 1nineralization along this fracture, certainly none of any importanee in. the part that 

can be seen. · 

ALICE, YANKEE, AND VICINiTY. 

The ores of Alice and Yankee ar~ n1ainly of 

the pyritic type with the exception of a few, 

such as· those of the Stonewall vein in the 

Ninety-Four mine, and the Cumberland and the 

Lombard veins. The pyritic ores, whose predomin·ant value is in gold, Were rich in the surface oxidized portions, but the unaltered Sl:llphide lower down was generally below workable grade. As a conseque:q.ce few of the 

pyritic deposits are now being mined, except 

where oxidized ore remains. The surface portions of the great pyritic sto~kwork of the Alice 

mine were first worked in the early eighties by 

hydraulic n1ethods and were fairly rich, but 

the unaltered ores below had not to the time of 

this survey Been successfully exploited. 

The few galena-sphalerite veins of the region 

carry i1nportant amounts of silver as well as of 

gold. 

AURA VERDE VEIN. 

The Aura Verde n1ine, at the head of Silver 

Creek at an e-levation of about 10,200 feet, lies 

about 1! n1iles north of the town of Alice. The 

development work consists of a crosscut tun1iel driven generally northwest. The only iJn.:. 

portant vein is the Aura Verde, 70 feet fron1 

the portal, which strikes N. 80° E. and dips 

steeply, and upon which considerable drifting 

has been done. Where the conditions of the 

workings permitted examination, the vein was 

found to be in places a barren fracture and 

elsewhere to contain 4 ii1ehes of ore. On account of the slight depths attained in this tunnel, most of the ore has been oxidized and shows 

alternate bands of siderite, quartz, and hematite. From certain specimens on the dump it is 

judg~d that the unaltered ore was of the pyritic 

type. 

The mine was idle in 1911 and so far as 1 

known its production has been small: No data 

as to the value of the ore .were obtained. 

LITTLE BLANCHE TUNNEL. 

The Little Blanche tunnel, on the northwest 

side of St. Marys Lake, is 460 feet long and 

follows a tight fracture striking S. 87° W. that 

cuts what is probably a dark variety of Silver 

Plume· granite, which is exposed on the surface 

·in this vicinity. At a few places the fracture 

opens to a maximum width of 2 inches. One 

lens of ore 2 inches wide and 10 feet long consists of white quartz, carrying a small amount 

of galena, sphalerite, and chalcopyrite. The 

values are said to be largely in gold but no 

important productionis recorded. 

METEOR VEIN. 

The Meteor vein is exposed on the cliffs on 

the ·southwest side of St. Marys Lake and is' 

developed by 2 tunnels about 10 feet and 260 

feet above the high-water mark of the lake. 

A shallow shaft is sunk from a point above the 

upper tunnel. The lower tunnel is 440 feet 

long, the first 90 feet bei_ng a crosscut and the 

last 350 feet a drift on the vein. The upper 

tunnel consists of 190 feet of crosscut and 60 

feet of dr.ifting on the vein. The country 

rock is a dark, siightly porphyritic granite, 

probably a variety of the Silver. Plume granite. 

. The lode strikes about N. 40° E. and dips 

70°-75° SE. In the upper tunnel it varies 

from 8 inches to 4 feet in width, .but in the 

lower tunnel it is uniformly about 5 feet wide. 

The filling is brecciated wall rock in a matrix 

of cherty-looking silica or very finely crystallized gray quartz with some siderite. The 
320 GEOLOGY OF GILPIN, CLEAR CREE~, AND BOULDER COUNTIES, COLO. 

siderite is more common ·in the upper tunnel, 

but narrow stringers of it occur along more or 

less open fractures in the lower tunnel. Pyrite 

and chalcopyrite are sparsely disseminated 

. throughout the vein, both in the fragments and 

in the matrix of the breccia. The mineralization has been stronger where the brecciation 

was greatest. In the lower tunnel, where the 

fragments are small and few and the vein 

filling is almost entirely quartz, there 1s les.s 

pyrite and almost no chalcopyrite. 

LEGEND 

rn CZJ 

contains a little disseminated pyrite; it is 

traversed by small stringers of dark-gray or 

white quartz and nearly white siderite carrying 

pyrite and chalcopyrite. · 

One of the· wid~3st portions of the ·vein is 

exposed in a stope 15 feet above the Mayflower 

tunne~ level and about 110 feet southwest of 

the line of the tunn~. The general fracture 

zone in this place is about 5 feet wid.e and 

shows the following section fro1n southeast to 

.northwest: 

N 

ldahq Springs formation ~ranite pegmatite Pyr.itic vein Unmineralized .CZB fracture ·C~ Working> inaccessible (Arrow indicate direction of dip) 

Note: Wall ;ock is granite except where otherwise indicated 

FIGURE 64.-Geologic plan of Mayflower tunnel. Surveyed by himd compa~:s and pacing. 

No stoping has been done in either of the 

tunnels, but 90 tons of oxidized material from 

the shaft is sa~d to hav:-e carried about $20 per 

ton in gold. This gold was not free but was 

carried in the pyritic concentrates. 

PURITAN VEIN. 

The Puritan veii1 is on the north side of the 

ridge between Anchor Gulch and St. Marys 

Lake, about half a mile south of the lake. It 

is developed by two drift tunnels and an old 

shaft near the Grest of the ridge and at greater 

depth by the Mayflower tunnel .(see fig. 64), 

which starts in Silver Creek valley about onefourth mile southwest of Silver Lake. 

The vein could be studied only in· the Mayflower tunnel, where it cuts coarse-grained 

biotite granite with a little associated pegmatite. It strikes N. 45° E. and dips very steeply 

southeast or stands vertical. It is a zone varying from ·a few inches to several feet in width, 

in which numerous small subparallel fractures 

have been formed. The granite in this zone 

is altered, bleached, and 1nuch softened and 

Section of P·uritan vein. 

. Ft. in. 

Granite, cut by many subparallel slickensided fractures trending parallel to the course of the vein 

and by several trendin.s across it ............... 3 0 

Granite, bleached, cut by 2 to 3! inch veinlets of 

quartz and siderite carrying pyrite.· ............ 1 0 

Veinlet, of white and gray quartz carrying pyrite 

and chalcopyrite; said to carry most of the metal. 1! 

Strong slickensided fracture parallel to the trend of 

the vein. 

Granite, altered, grading into unaltered granite.. . . 6 

Some postmineral movement has taken place 

along the vein, which is crossed by numerous 

minor slip planes. 

Some surface ore from one of the upper tunnels is said to have as·sayed 7 ounces in gold, 

27 ounces in silver, and 6 per cent• copper. 

Five shipments in 1910, aggregating a little 

over 6 tons, show, according to sampliilgworks assays, gold, 1.12 to 2.6 (average 1.56) 

ounces; silver, 1.5 to 6 (average ·2.27) ounces; 

and .copper, 2 per cent ·or less. 

The total production from the 'Puritan vein 

is said ~o have been about $4,000. 
CLEAR CREEK COUNTY. 321 

GOLD ANCHOR MINE. 

The Gold Anchor n1ine is about one-half mile 

northwest of the village of Alice, at an elevation of about 10,000 feet. The vein, which 

trends northeast-southwest, is developed by a 

shaft 200 feet deep. It could, however, be 

studied only at one point, where it strikes N. 

60° E., dips 80° SE., and is 3 feet in width. 

It consists of more or less altered granite gneiss, 

traversed by veinlets 4 inches or less in width 

of white qu~rtz and pyrite (or iron oxide 

formed by alteration of pyrite). Ore on the 

dump showed bands of quartz and pyrite alternating with bands of nearly pure pyrite. Most 

of the ore is somewhat oxidized, and the freemilling surface ore appears to have been rich in 

gold, which fell off in amount as depth was 

gained and the less altered ore reached. A 

10-stamp mill is at the mine. · 

The gross production is said to have been between $4,000 and $5,000. 

CHESAPEAKE TUNNEL. 

The Chesapeake tunnel starts on the west 

side of Silver Creek about one-half mile southwest of Silver Lake, about 250 feet above the 

bottom of the valley. The tunnel, which trends 

west under the ridge 'between Anchor Gulch 

and St. Marys Lake, is said to be 1,500 feet 

long. The first 260 feet is crosscut and intersects the crossing of two veins at a point about 

100 feet from the portal. Beyond 260 feet .the 

tunnel follows an east-west vein for at least 280 

feet, beyond which it was inaccessible because 

of bad air. 

The two veins cut 100 feet froin the mouth 

of the tunnel are known as the Champion Nos. 

1 and 2. The No. 1 vein strikes N. 70° E. and 

dips 80° SSE. There is a 15-foot drift on it on 

each side of the tunnel. The vein is a zone of 

fracturing in granite along which the rock is 

somewhat silicified and in which there are three 

narrow stringers of white drusy quartz containing some pyrite and locally a little chalcopyrite. The No. 2 vein strikes N. 85° E. and 

dips 80°-85° S. A 25-foot west drift on this 

vein shows it to be a shear zone 2 to 4 feet wide, 

in which the granite is crushed and somewhatsilicified. One persistent ·stringer of white 

quartz with pyrite and chalcopyrite occurs in 

some places near the center of the zone but 

elsewhere shifts to the hanging wall. A smal 

stope 15 feet above the tunnel exposes a dark 

phase of the· granite, which has been sheared 

along the vein and contains disseminated 

pyrite cut by minute pyrite stringers for about 

5 inches next the footwall. 

The America vein, which is cut by the tunnel 

at 260 feet and is followed by it for some distance beyond, strikes N. 85° W. and stands 

nearly vertical. It traverses granite containing lenses of magnetite-bearing pegmatite.· The 

vein varies fron1 a barren gouge-filled slip 

plane one-half· inch in width to a zone of 

crwshed granite 8 inches wide. In the wider · 

portion of the zone the crushed granite between the walls is somewhat silicified and is cut 

by a central veinlet of white quartz carrying a 

little pyrite and exceptionally chalcopyrite. 

All the ore in these three veins was considerably oxidized. It is said to average about 

$20 a ton in gold, 95 per cent of which is in free 

gold that can be saved by amalgamation. It 

carries no notable amount of any other metal. 

NINETY-FOUR TUNNEL. 

The Ninety-Four tunnel is about threefourths of a mile northeast of the village of 

Alice at an elevation of 10,512 feet. (See fig. 

64.) It cuts several veins, one of which, the 

Stonewall, is also developed by a shaft 300 

feet deep, now inaccessible. 

The Yankee Centennial vein, which strikes 

nearly east and w~st, is the first vein intersected. This vein, as exposed, varies from a 

barren fracture an inch or so wide to a band of 

white quartz 10 inches wide which carries 

pyrite, scattered or ·in irregular bands. At 

one place the vein is 8 inches wide, including 

3 inches of alternating bands of white quartz 

and pyrite and 5 inches of ~ractured and altered wall rock. 

The Enterprise vein is best exposed in a 

short drift from the main tunnel 360 feet. from 

the portal, in which it shows at one place two 

veinlets of quartz and pyrite (in part c·opper 

stained) 1 t and 2 inches wide, inclosing 8 

inches of altered wall rock. 

The Stonewall vein, on which the· greatest 

amount of stoping has been done, shows in its 

narrower portions 1 t inches of barren crushed 

wall rock b~t in other portions a8 much as 10 
.322 GEOLOGY OF GILPIN, CLEAR CREEK, AND BOULDER COUNTIES, COLO. 

inches of.white quartz traversed by a number 

1 

inches of brecciated and silicified wall rock 

of irregularly. bounded sulphide stringers of stained in streaks by iron oxide and carrying 

sphalerite, galena, and pyrite, . with subordi- I some disseminated pyrite and a few irregular 

nate chalcopyrite. Vugs 1! inches or less 

across, lined with white quartz, calcite, and 

pyrite are common.. At one place, where the 

vein is over 2 f~et wide, it shows a slip plane 

next the footwall, followed above by about 1 

foot of fractured and altered wall ro~k and. by 

14 inches of similar altered rock traversed by 

a number of veinlets 2 to 3 inches wide of 

white quartz carrying scattered specks of sulphides. The Stonewall vein is cut off (A, fig. 

65) by a barren fault. The vein B-C bemasses of pyrite 1 inch across~ A narrow 

open crevice is lined with quartz. 

All of the veins except the Stonewall carry 

gold almost exclusively.· According to statements of the foreman the smelting ore from the 

Yankee Centennial vein, of which about 50 

tons have been smpped, averaged about 3 

ounces in gold with very little silver. The 

vein 8-:-C (fig. 65) nnd the Hidden Treasure 

vein are said ·to average $4 to $5 per ton, 

almost wholly in gold. 

LEGEND 

E:J 

Pyritic veins 

1······ ... +..1 .1~ I ~~ Galena- sphalerite Unm'meralized Worl\inQs 

Arrows indicate 

direction ~f dip 

vetns fractures inaccessible 

N Note: All w.all roc.k is schist of Idaho Spri~gs formation with lenses of granite pegmatite 

FIGURE 65.-Geologic plan of Ninety-Four tunnel. Surveyed by hand compass and pacing. 

yond the fault is ~pparentl}/··~ot a continua- The ore from the Stonewall .vein is said to 

tion of the Stonewall, for its mineralizati<?n average about 1 ounc(:'l in gold and 10 to 12 

appears to be wholly pyritic. This vein in ounces in silver. Mm:t of this ore has been 

turn is cut off by a fault plane (C, fig. 65). treated in the company's mill near the mouth 

The Last Chance vein, so far as observed, is of the tunnel. Tp,is mill, however, made only 

pyritic. It is commonly narrow .and shows in experimental runs, using a dry process of conone place, 11:ext the hanging wall, 1 inch_ of centration. Smelting ore is hauled by team 

. gouge folfowed by 1 inch of gray quartz carry- 12 miles to sampling works at Idaho Spri1igs. 

ing some fine pyrite. At this point it has · 

been more or less fraetured through a width of 

3 feet. 

The Hidden Treasure vein is only feebly 

mineralized. At one exposure it shows, next 

th.e hanging wall, 1 inch of gouge followed by 8 

LALLA VEIN. 

The Lalla vein, on the east side of Silver 

Creek, one-eighth milo north of the. A.IiceCentral City road, is deYeloped by two 'tunnels. 

The lower, on a level w.ith the road, is 355 feet 
CLEAR CREEK COUNTY. 323 

lohg; and the upper, about 100 feet higher up The Princess Alice vein strikes N. 48° E. 

the hill slope, is shorter. The country rock is and dips 70°-80° SE. It is a strong, wen.:. 

schist of the Idaho Springs formation except mineralized fracture of white quartz and coarse 

for the fu·st 100 feet in the lower tunnel, in pyrite 6 inches to 2 feet wide (average 4 to 10 

which it is porphyritic granite. inches). Part of the vein. filling in the wider por-

'l'he vein is a strong well-mineralized frac- tions is crushed chloritized schist carrying some 

ture which strikes N. 60° E. on the average disseminated pyrite and cut by small stringers 

and dips 70° SSE. It ranges from 1 to 3 feet of quartz and pyrite. At 590 feet fron1 the 

in width and is mainly filled with crushed crosscut the vein receives a 4-inch stringer of 

pyrite-impregnated schist, in most places car- quartz and pyrite froin the footwall. Where 

rying 2 to 4 inches of white quartz and coarse first cut by the tunnel the Princess Alice vein 

pyrite near the walls. In the narrow portions is 18 inches wide and is entirely quartz and 

of the vein these quartz-pyrite bands come pyrite.· At this point 1!-inch crusts of coarse 

together to form the entire filling of 1 foot or pyrite on each si~e of the vein border a 2-incb 

less. In both tunnels there has been much central cavity lined with quartz crystals and 

stoping. The ore is much oxidized and in a few very large pyrite crystals. This lens 

1911 was treated at the mouth of the lower continues southwest along the vein with an. 

tunnel in a 2-stamp mill, which was saving $14 average width of 12 inches for 170 feet and is 

per ton on the plates. Concentrates from a repeated for 150 feet northeast of the crosscut. 

Gilpin County bumper were said to carry In all places the vein quartz is separated from 

about $7.25 in gold .. The average inetal con- the wall rock by a thin parting. Some stoping 

tent of 5.18 tons of. 'oxidized smelting ore has been done· in ·this drift. ·At 395 feet from 

shipped in 1910 was, according to sampling- the crosscut a raise 15 feet high ·has been 

works assays, gold 1. 7 ounces and silver 0.88 driven, and between 210 and 240 feet from the 

. ounce per ton. crosscut a stope is carried at least 30 feet above 

The Little Mary vein lies 15 feet north of the floor of the drift. Northeast of the crossthe Lalla near the mouth of the lower tunnel, cut some stoping has been done, and a winze 

with which it is connected by two short cross- southwest of tqe crosscut, now full of water, 

.cuts. The vein is almost parallel in strike to 'is said to be 20 feet deep all in ore. 

the Lalla but dips 55° SSE. It varies from 6 The ore is said b'y the <?Ompany to assay 

inches to 1 foot in Width but is not strongly from 0.18 to 3.2 ounces gold and 0.5 to 9.3 

mineralized. Some pyrite is disseminated in ounce~ silver per ton with an average content 

crushed wall rock and a few short stringers of of about 1 ounce ~f gold and 3.7 ounces silver: 

, quartz and pyHte were seen. Some smelting ore shipped in 1910 ave~aged 

PRINCESS ALICE VEIN. 

1.14 ounces gold and 4 ounces silver per ton. 

A very minor amount of lead and copper is 

The Princess Alice vein, on the east side of said to occur in son1e places, but none was 

Silver Creek northeast of Silver Lake, is noted either in the vein or on the dump. In 

opened by a crosscut tunnel250 feet long with milling 50 per cent of the gold and silver are 

a 670-foot drift on the vein. ·The crosscut said to be saved by amalgamation. The procontinues eastward beyond the vein for 520 duction as yet has been sn1all. \ 

feet but cuts no other lodes. A second cross- · ') \ ALICE MINE. cut 100 feet lower down the slope has been 

driven 140 feet but has n9t intersected the The Alice mine is about three-fourths mile 

Princess Alice vein. The country rock ex- west-southwest of Alice post office at an eleposed in all of the workings is Idaho Springs . va.tion of about 10,300 feet. The deposit is 

forrnation. not of the vein type but constitutes a large 

Ninety feet· fr01n the n1outh of the crosscut irregular body of more or less mineralized rock 

a vertical vein striking N. 56° E. has been which has been developed by an open pit and 

drifted on for 50 feet either way-. It is fr01n 4 by irregular underground workings. (See fig. 

to 6 inches wide, and the filling is white quartz, 66.) The rocks in the vicinity of the mine 

locally carrying coarse pyrite crystals. are Idaho Sprmgs formation and intrusive 
324 GEOLOGY OF GILPIN, CLEAR CREEK, AND BOULDER COUNTIES, COLO. 

porphyry, the latter forming the wall rock 

·in all the mine workings. 

The porphyry is of two varietie~. The 

coarser an,d more abundant variety is a typical 

quartz monzonite porphyry, so crowded with 

feldspar phenocrysts as to appear granitic in 

texture to the naked eye. When viewed 

·under the microscope, however, it is found 

-.to be truly porphyritic, phenocrysts being 

·crowded in unusual abundance through a 

much finer grained groundmass. The rock is 

gray with locally a pink cast. It shows some 

-variation in coarseness, but in its coarsest 

:phases most of the feldspar, hornblende, and 

biotite phenocrysts are under 3 millimeters in 

, 

/ 

,, ,, ____ .,., 

in char~cter to that in the quartz monzonite 

porphyry. The groundmass has a microgranular texture, and probably consisted 

originally of quartz and feldspar, though the 

latter· mineral has been largely replaced by 

sericite. A few areas having the shape of 

feldspar crystals are n1ade up of minute sericite 

flakes forming an aggregate with low double 

refraction. These areas are probably replaced 

plagioclase phenocryE ts, and other and more 

irreg11lar areas of larger sericite plates may also 

have started as replacements of feldspar phenocrysts. Aside from sericitization metasomatic alteration shows itself in the development of nodular masses of pyrite, few of which 

FIGURE 66 . .:._Plan and section of workings of Alice mine. From surveys made for the owners. 

:greatest dimension. Among· the phenocrysts exceed 5 millimeters in diameter and which, 

plagioclase feldspar (andesine) is most abun- by their distribution, suggest that some of them, 

dant, brown biotite is next, and green horn- in nucleus at least, were replacements of feldblende last. The groundmass shows a granu- spar phenocrysts. In some of the ~egat_es 

lar texture and consists mainly of orthoclase two or ~Lthe mineral~!.,_.~ericite, and 

and quartz, with subordinate amounts of pyrite, and exceptionally apatite, are present 

plagioclase, horriblende,11 biotite, titanite, mag-· in irregular association. The rock in some · 

netite, and apatite. No sulphides were ob- places presents a blotched appearance, owing 

served in the fresh rock. · to the uneven develop1nent of sericite. In the 

The gray quartz monzonite porphyry is absence of perfectly fresh specimens it is not 

intruded by dikes of a light-gray to nearly possible to apply a preciBe name to this roc~, \ . . . 

white poq~hyry, very poor in iron-bearin~ min- but it may provisionally ?e. c~lle? ~n alas kite. C\ \lA~ ·~\~ ,, ' 

erals, whiCh shows a sparse scattering of .,£9.l:RhJ2:y, the term alask1te s1gnifymg merely \ ;_ v l \~t~ 

quartz phenocrysts in an aphanitic ground- the absence of iron-bearing minerals. It 0is 1 

mass. All the specimens collected show a probable that it came from the same general 

large amount of metasomatic alteration similar magmatic source as the nssociated monzonite 
CLEAR CREEK COUNTY. 325 

porphyry but at a slightly later time. The between the h1ineralization and fractures, and 

larger alaskite porphyry dikes send off nar- Plate XIV, A. (p. 97), shows the progressive 

rower branches into the quartz monzonite, alteration of the ore, as exhibited in a hand. 

and the two are usually in welded contact. specimen. The nature of this alteration has al-· 

Typical fissure-vein n1ineralization, so com- ready been described in detail on pages 108-109~ 

mon in tllis vicinity, is represented in the The metallic constituents of the nests and \fy. t·· 1 ~· l£l,. t1 •'· .\ 

Alice mine only on a small scale by a few vugs of ore are predominant pyrite and :· f·t·,-.r'Pt~-t e.-

s~raight and persistent pyrite veinlets, none of subordinate chalcopyrite. Quartz and brown / 1~ :·. ,, ,) ~· \' '{' l (' 

then1 over one-half inch in width and none of siderite are the principal gangue minerals. 1; , • , _ 

them commercially important. The important Intimately associated with the chalcopyrite ; (} r~ ~ ·r._:f' , '( · 

mineralization has been accomplished through in sorn.e places is a sulphide of bismuth which. \ · ; · ·,' · ~· 

the removal in solution of certain constituents is very rich in silver. 

of the porphyries and the deposition in their The form of the mineralized area is not deplaces of metallic sulpllid~s, or, technically terminable from present exposures, but the· 

speaking, by metasomatic replacement which open pit and all of the underground workings 

was initiated along a network of irregular frac- west of the first crosscut on the lower tunnei 

\ 

tures. Both porphyries are mineralized, the level are in mineralized porphyry for most of 

quartz monzonite more extensively than the their length. The scattered character of theal~sJcite, probably because its coarser texture mineralization will probably necessitate the 

·was more favorable to metasomatic replace- mining of all the mineralized porphyry withment and possibly also because of its more ex- out much selection, the limit of profitable 

tensive fracturing. Mineral-bearing solutions extension of the workings being determined by;· 

similar in character to those which deposited assay as in other low-grade disseminated de-· 1 

the typical pyritic veins of the Alice ~istrict posits. The amount of ore available is un- : 

and probably coming from the same source doubtedly very l~rge and has been estimated· 

were the mineralizing agents, but instead of by different eng,ineers :whose reports are accespenetrating along straight and open channels sible to those especially interested. By driv-, 

they worked their way through a network of ing a tunnel on~-half mile in length from the \ 

U?-inute crevices formed by the irregular frac- valley of Fall River the deposit could be cut 

turing of a large body of porphyry. The cause at a depth of 400 to 500 feet below the present 

of this fracturing is ·unknown, but it is not worlcings. The ore may reasonably be exunique in this general district, similar fractur- pected to persist with little if any ·decrease in. 

ing being observed in the Commercial Union value for several hundred feet below the. 

mine near-by and- on a more extensive scale in present workings, though not to indefinite· 

the Patch, near N evadaville. The alteration depths, but an increase in copper content with_ 

of the porphyry is most intense along the depth, as is postulated in some private reports, 

crevices. which formed the main channels of is not to be expected. The somewhat similar· 

circulation and decteases gradually away from mineralization of the Patch near Nevadaville· 

these channels, so that a rock composed wholly becomes negligible on the Argo tunnel level. 

of sulphides and secondary silicate minerals The Alice property was first worked as a.. 

grades gradually into little-altered porphyry. placer with the aid of h~ydraulic giants, and 

The 1naxhnum alteration took place where two' $60:000 is said to have been recovered by these. 

\ 

or n1ore fractures intersected, in which places methods. Later an old-fashioned stamp mill. 1 

"nests" of ore minerals 3 inches or less across wns erected, and a portion of the free gold in. I 

were developed. Less often cavities occur the oxidized ore saved by amalgamation, con- \ 

at such. h1tersections and are partly filled centration not being attempted. The mill ) 

with ore 1ninerals. Some such cavities or vugs operate~ at a pro~t for three seasons until the , 

are a foot in diam~ter. Most of them were relatively free-n1illing. oxidized ore was exprobably formed by the solvent action of solu- hu.usted. Since that tin1e several attempts 

tions, but others may represent open spaces to treat. tho unoxidized ore _by concentration 

.forn1ed by movement between the porphyry have met with indifferent success. ·The ratio 

fragments and only partly filled with ore. of concentration in the earlier attempts at 

Figure ·7 (p. 98) illustrates the general relation milling vary fron1 12 to 1 to 17 to 1. In ox-
326 GEOLOGY OF GILPIN, CLEAR CREEK, AND BpULDER COUNTIES, COLO. 

perimental runs concentration ratios of from tion has. proceeded so far that the rock has 

6.4 into 1 to 13.5 into 1 were obtained. The been wholly converted into a soft aggregate 

concentrates shipped 'do not appear to have of these two minerals. 

exceeded $10,000 in total value. In general the mineralization at this mine is 

The average value of the ore has been accu- similar in character to that at the Alice mine 

rately determined by a number of careful except that the wall rock is schist of the Idaho 

samplings and by experimental runs. Auto- Springs formation im:tead of porphyry. It 

matic head samples of crude ore from five lots represents mineralizat:ion throughout an aFea 

taken from various parts of the mine arid ag- of irregular fracturing rather than along a , 

gregating 587 tons gave an average metallic linear fracture or vei1. The ore values are 

content of gold, 0.167 ounce; silver, 0.82 said to be very similar to those of the Alice 

ounce; and copper, 0.38 per cent. Gold assays mine. 

on 57 samples taken by Mr. E. E. Chase from . GOLD RESl:RVE GROUP. 

various :r:>arts of the mine ranged up to .0.98 , · The Gold Reserve group, which is apparently 

ounce, .with an average of 0.225 ounce. Silver similar in ·character to the Commercial Union 

determinati~ns on· 39 of t~ese samples ~how eel deposit, lies east of ·Alice on the northeast 

values ranging up to 10.3 ounces, With an slope of Bull Hill w~ st of Washoe ·Gulch. 

average of 1:21 o~~es ... · ·.. .Over a large area the, schist and pegmatite 

~_large mill buildmg In good rep a~, but con- have been fractured and traversed by a net-. 

ta~u~g· only· five ~tamrs and a httl~ other work of irregular stringers of specular hemamac~'m.ery for testmg, IS connected With the tite and have also been smnewhat silicified. 

lower ~unnel .by a trestle. A pipe line ~rom The. deposit is exposed only in surface pits, 

FalL River With a head of 350 feet furnishes and as the oxidized zone is passed and depth 

apout 100·horsepower. attained will unquestionably become pyritic. 

Whether the property can be profitably 

worked on a large scale after the manner· of 

low-grade gold ores elsewhere is a question 

involving the tonnage available and the cost 

of mining and treatment, all of which are 

matters to be carefully estimated by engineers. 

Concentrates and supplies must be hauled 10 

miles to and from the railroad at _the mouth 

of Fall River. 

LOMBARD MINE. 

The Lombard mine ·i::; in the upper part of 

Cumberland Gulch. The vein, which trends 

generally N. 55°-60° E. and dips 50°-.75° NW., 

has been de:veloped for about 2,000 feet by a 

shaft 150 feet deep and four drift tunnels. 

.The lower or No. 4 tunnel begins . near the 

Lombard· mill, trends about N. 45° E., an.d 

was about 780 feet long at the time of this surCOMMERCIAL UNION TUNNEL. vey. The wall rock is entirely schist of the 

The Commercial Union tunnel is about one- Idaho Springs formation. The vehi, which ~s 

half mile southwest of Alice at an elevation of reached 350. feet from the portal, branches in 

nearly 10,500 feet. It is a straight crosscut numerous places ·and in general is not strongly 

trending N. 12° W. for about 4 7o' feet, with mineralized. A dike of bostonite porphyry 20 

several short crosscuts. The workings expose feet wide is cut 70 feet f1·om the ·portal. 

no true veins but ·develop an irregular ore , The No. 3 tunnel, next above the· No. 4, is 

body of considerable size. The wall rock is 'about 1,440 feet in length and follows the LornIdaho Springs formation locally highly quartz- bard vein for 1,130 feet of tlus distance. It 

itic. Throughout much of the workings minute cuts a 20-foot dike of bostonite porphyry at 

seams of pyrite traverse this rock in all direc- about 7 50 feet, ~nd both vein and tunnel foltions, but locally the mineralization is strong, low a dike of porphyry from 1,110 to 1,360 

and irregular "bunches" of coarse pyrite 12 feet. This porphyry is too altered for. certahi 

by 18 inches in maximum dimensions are de- determination but is probably bostonite. A 

veloped. In these heavily mineralized por- r-aise to the surface is about 940 feet from the 

· tions the wall rocks become highly altered and portal, In general the Lombard vein as exnearly white in color through the development posed in this tunnel is W,3ll defined and varies 

of quartz and sericite, and locally the altera- from a tight crevice t? about 2 feet in .width. 
CLEAR CREEK COUNTY, 327 

It is barren in places but elsewhere shows one ·and minute amounts· of galena are locally 

or 1nore narrow sean1s of galena, sphalerite,' present. 

chalcopyrite, and pyrite. A 15-stamp mill for the treatment of ore· 

1unnel No.2, about 250 feet higher than No. from the Lombard vein, recently installed 

3, connects through a raise with the Lombard near the mouth of the No.4 tunnel, is operated 

shaft. The wall rock is Idaho Springs forma- electrically by power furnished by·. ·a 7~0-

tion with some pegmatite. The vein is reached horsepower hydroelectric plant in the valley of 

at about 230 feet and is followed for the re- Fall River near the mouth of the Seaman tunnel. 

maining 950 feet of the tunnel. For about 250 According to :Mr. H. I. Seaman ·smelting 

feet beyond where it is first 1net the vein paral- ore fron1 the Lotnbard mine averages about 

lels a 4-foot dike of porphyry, than which it is $65 per ton and milling ore about $1.3. 

distinctly later. The vein as exposed in this 

tunnel varies frmn 2 inches to 2 feet in width 

and shows the usual alternation of barren arid 

mineralized stretches. At one of the widest 

portions it shows 2 inches of gouge next the 

hanging wall, succeeded by 10 inches mostly 

white and gray quartz· in subparallel veinlets 

2 inches in n1axin1u1n width. Quartz predmninates in these veinlets, but locally they carry 

sphalerite, galena, chalcopyrite, ancl. pyrite. 

1"'he highest or No. 1 tunnel is about 75 feet 

above No. 2 and is about 800 feet long, all on 

tho vein. :Most of the ground between No. 1 

and No. 2 tunnels has been stoped. 

In general the ore from the Lombard vein 

consists in order of abundance of white 

quartz, sphalerite, galena, chalcopyrite, . and 

pyrite, with light-colored siderite in certain 

CUMBERLAND MINE. 

The Cumberland mine is in Cumberland 

Gulch near Yankee, about one-fourth mile 

northwest of the Lombard shaft, at an elevation of about.10,650 feet. The mine was being 

unwatered at the time of this survey but could 

not be entered. The shaft is 150 feet deep 

with about 150 feet of drifts. The vein $trikes 

about N. 45°-50° E., nearly parallel to the 

Lombard vein, and dips northwest. ·The ore 

on the dump was pi·actically identical in character with that of the Lombard vein. Some 

pieces showed 3 inches of solid coarse galena. 

The mine was located in 1897 and has been 

worked intermittently. 

GOLD BAND VEIN. 

places. These 1ninerals are usually irregularly The Gold Band vein extends east from the 

associated and all belong to t.he same period of summit of Yankee Hill to the head of Miners 

mineralization. In· son1e plac~s comb quartz Gulch. It has bean developed by a tunnel 

and pyrite were the first minerals deposited 750 feet long, for the first 210 feet of which the 

next the walls, but even these are not inter- walls are granite gneiss and for the remainder 

preted as belonging to an earlier period of Idaho. Springs formation. The contact of these · 

mineralization. As in most veins of this type two formations strikes about north and south 

fine pyrite is con11nonly disseminated through and dips at medium angles to the east.· 

the schist bordering the suli)hide veinlets. The vein strikes N. 80° E. and dips 55° N. 

The n1etasomatic alterations in porphyry It is commonly about 6 to 8 inches wide and 

bordering the Lombard vein consist in .some. consists of crushed wall rock containing displaces in· the development of sericite in the seminated pyrite. Fairly continuous narrow 

feldspm· phenocrysts and the development of stringers of white quartz and pyrite are seen 

calcite in great abunda.nee in the groundmass. either on the walls or near the center of the 

Original 1nagnetite grains have been partly vein. From 550· to 650 feet from the mouth of 

converted to hmnn,tite. In other places, where the tunnel a stope has been carried· up about 

alteration has progressed still farther, the · 30 feet on an, 18-inch wide portion of the vein. 

porphyry has been almost completely serici- The ore here is crushed and bleached schist, 

tized and consists of large flakes of secondary which carries abundant disseminated pyrite and 

n1uscovite mnbedded in a matrix Inade up is· cut nea.r ·the center of the vein by a 2-inch 

mainly of minute sericite flakes. Quartz is quartz-pyrite veinlet. This ore is said to aver~ 

fairly abundant in irregular grains and car- age about $17 per ton; in gold and silver. Postbonn,te less so. Pyrite and sphalerite are mineral movement ·is sho:wn by thin gouge on 

scattered through the rock in il-regular grains, one or both walls. 

/ 
328 GEOLOGY OF GILPIN, CLEAR CREEK, AND BOULDER COUN~~IES, COLO. 

OHIO VEIN. 

A 640.:.foot drift tunnel on the Ohio vein has 

its mouth about 600 feet northeast of the Gold 

Band tunnel. (See p. 327 .) The vein strikes a 

few degrees south of west and traverses granite 

gneiss. The tunnel could not be entered but 

ore on the dump showed a 2 to 4 inch v~in of 

quartz carrying pyrite, some chalcopyrite and 

rarely a little fine galena. It also showed ~yri te 

disseminated in granite gneiss, some of which 

was crushed and had evidently formed part of 

the vein. Druses were lined with crystals of 

pyrite, quartz, and siderite, of which the siderite 

appeared to have been the last deposited. 

erty since that year. Nothing could be seen of 

the trend of the vein or the character of the ore. 

OTHER MINES NEAR YANKEE. 

On the southwest slope of Yankee Hill north 

and northeast of the now abandoned camp of 

Yankee several veins .are opened by shallow 

shafts and tunnels, none of which are now 

accessi?le. The. veins all cut Idaho Springs 

formatwn and with one exception strike northeast and southwest across the schistose structure. They are fairly strong fractures from 

~everal inches to 2 fee1i in width and are apparently very uniformly mineralized. The ore 

o~ the dumps was iron-stained quartz with 

MINERAL POINT VEIN. mrnor amounts of siderite, some remnants of 

The Mineral Point vein, 300 feet south of the P:yrite, and abundant in1pressions of former pyGold Band tunnel, is opened by a tunnel 180 rite crystals. Some of 1.he sulphide ore carried 

feet long, the first 100 feet of which is crosscut. very small quantities of chalcopyrite but none 

The vein strikes N~ 55° E. and stands nearly of the oxidized ore showed copper c~rbonates. vertical. It is from 1 to 6 inches wide (average The Texas vein, whic:u strikes N. 70° W., is 

about 2 inches). The ore is largely oxidized opened by a shaft 500 feet northeast of Yankee. 

but at the face of the drift shows remnants of The ore on the dump indicated that the vein is 

pyrite and minor ·amounts of galena. Post- at least 10 inches wide and consists of crushed 

mineral slickensided fractures show strire pitch- pyrite-impregnated schist containing som~ ing 80° SE. lenses not over 5 inches wide of quartz and 

SURPRISE VEIN. · coarse pyrite with very Ininor amounts of chalThe Surprise vein is in the head of Peck copyrite. It is said that a little galena was' 

Gulch south of the Alice-Central City road and occasionally found in the ore. The oxidized 

about three-fourths mile southeast of Yankee surface material is said to carry about $50 

Hill. in gold and silver per ton, but the unoxidized 

It is developed by two shafts, an old one on sulphide ore is of low gr;~de. 

the vein, and a relatively new one 50 feet north The Mary Murphy shaft is about 800 feet 

of the vein outcrop. Little work has been done east of the. Texas on the. south side of the 

on the vein for several years, and the workings Alice-Central City road. The shaft is over 40 

are inaccessible. The country rock at the mine feet deep and has about 120 feet of ·drifting on 

is granite gneiss but farther west is Idaho the 40-foot level. The -vein strikes N. 60° E. 

Springs formation. and apparently dips s.teeply north. The ore 

The vein strikes N. 60° E. and apparently in the bins ~as similar to that at. the Texas 

dips steeply north. The ore on the dump con- .shaft. ~ shipment. of ~2 tons of surface ore 

sisted of altered, pyrite-impregnated granite from this property IS said to have had a gross 

gneiss cut by numerous small stringers of white value of $4~ per ton. . 

quartz, coarsely crystalline pyrite, and some The Jennie Jon~s vein, 500 feet north of the 

chalcopyrite. This vein is said to be a continu- Mary Murphy, stnkes abc,ut N. 65° E. and dips 

ation of the Cumberland vein, opened by a 30° to 50° N. It is opened by several shallow 

shaft about three-fourths of a mile southwest. sh~fts, . now full of water. The vein filling, 

FAUST MINE. 

The Faust mine, in Yankee, was idle and inaccessible a:t the time of this survey. The development consists of a shaft 200 feet deep 

without important drifts. The shaft was sunk 

in 1901, and no work has been done on the propwhiCh IS apparently about 30 inches wide; is· 

largely crushed bleached schist with some disseminated pyrite and· is cut by smaU pyritequartz stringers. In one pit an 8-inch streak 

of white quartz with some •::oarse pyrite ~as seen 

on the hanging wall. The surf ace ore is said 

to average about $15 per ton, mainly in gold.~· 
CLEAR CREEK COUNTY. 329 

The Ophir vein, bearing N. 45° E., was 

opened by a tunnel, now caved, and by several 

pits and shallow shafts. The tunnel mouth is 

about 600 feet north of the Texas shaft house. 

The ore· in the bins was entirely iron-stained 

quartz with a little siderite carrying, it is said, 

somQ free gold. . 

The Little Clara and Cap-the-Climax are 

two parallel veins about 150 feet apart, the 

southernmost being ~me-fourth mile north of 

Yankee. They are opened by shallow shafts 

and pits, now largely caved. The Little Clara, 

the southern vein, is 8 to 10 inches wide, and 

the Cap-the-Climax appears to be at least 1 

foot wide. The ore is entirely oxidized and 

sin1ilar to that in the Ophir bins. 

The Barbara vein, one-half mile north of 

Yankee, strikes about N. 70° E. and stands 

nearly vertical. It is opened by a. shaft, said 

to be 80 feet deep with 40 feet of drifting 55 

feet below the collar, and by several near-by 

shallow pits on the vein northeast of the shaft. 

The ore is oxidized to a depth of 40 feet, below 

which the vein consists of fron1 6 inches to 1 

foot of white quartz and pyrite with no chalcopyrite. The sulphide ore is said to be very 

low grade, but some of the surface material 

was rich enough to pay. · 

Three hundred feet south of the Barbara a 

parallel vein of small size and similar mineralization is opened by a few shallow pits. 

NORTH STAR-MANN VEIN·. 

The North Star-Mann vein crosses the divide 

between Peck and Miners gulches about a mile 

east of Yankee Hill on the Central City and 

Alice wagon road. 

The original work on this vein is west of the 

divide on the :Mann ground. It consists of 

·about 500 feet of shallow surface trenching and 

an abandoned shaft said to be over 100 feet 

deep. The North Star shaft is at the head of 

Peck Gulch. It is reported to be 300 feet deep 

with levels at 50, 115, 200, and 300 feet, all 

short except the 115-foot, which is a drift 

tunnel that intersects the shaft about 430 feet 

fr01n the 1nou th and continues westward beyond it for at least 640 feet. There is little 

stoping on the tunnel level. The 50-foot 

level extends 200 feet west of the shaft and 

has been stoped for 170 feet. 

The vein cuts Idaho Springs formation west 

of the divide, a large lens of pegmatite at or 

near the divide, and granite gneiss east of the 

divide near the North Star shaft. Underground, the 50-foot level and all but the west 

200 feet of the 115-foot level, which is in schist, 

are in granite gneiss and pegmatite. The contact. between the schist and gneiss dips mod~rately west. The vein strikes N. 65° W. and 

stands vertical or dips steeply south. It has 

no branches and though strong in all formations is somewhat wider in the granite gneiss 

than in the schist. It varies in width from a 

few inches to a maxin1um of 5 feet with an 

average of about 2 feet. 

The vein consists of crushed silicified waU 

rock which contains more or less disseminated 

pyrite and.is cut by stringers, 4 inches in maximum width, of white quartz, pyrite, and chalcopyrite, or wholly of n1assive pyrite. Siderite 

occurs locally, particularly in druses. Three 

rather well defined ore shoots have been found. 

The easternmost extends from the tunnel 

mouth for 230 feet west along the vein and 

consists of oxidized ore containing remnants of 

pyrite in iron-stained quartz. The second extends westward from the shaft for about 200 

feet. The third is seen in the schist in the last 

80 feet of the 115-foot level. All apparently 

pitch steeply west. 

· A barren fault zone striking N. 60° E. and dipping 54° W. cuts the North Star vein without 

notably displacing it. It is seen on the 50-foot 

level 190 feet west of the shaft and on the 

115-foot level about 250 feet west. A second 

cross fault, also 1.mnlineralized, is seen 500 feet 

west of the shaft on the 115-foot level. It 

strikes N. 20 E. and is vertical. Movmnent 

along the North Star vein has taken place 

subsequent to the fo~n1ation of this fault. 

The unoxidized ore fron1 the North Star vein 

is said to average $8 to $10 a ton in gold, but 

very rich oxidized ore was taken fron1 the 

Mann shaft and surface trenches in the early 

days. The ore was treated in a 10-stamp 

amalgamation and concentration mill near the 

mouth of the tunnel. 

.The present ~wners report that their production is about $16,000 and that the production of 

the_ mine before they acquired it was about 

$100,000. 

LITTLE ELDA VEIN. 

The Little Elda is a north-south vein that 

crops out near the head of Peck Gulch, about 

1! miles east of Yankee Hill. It cuts across 
330 GEOLOGY OF GILPIN, CLEAR CR.EEK, AND BOULDER COUNTIES, COLO. 

the ridge which divides the two parts of Peck 

C:reek and is largely in the Idaho Springs 

formation just west of a. contact with granite 

gneiss. There are two tunnels and a whim 

shaft apparently on this vein, but the size of 

the dumps indicates that the workings, now 

caved, were not extensive. The total width 

of the vein is not known but is at least 8 inches 

in places. Most of the ore on the dump consisted of banded siderite, quartz, pyrite·, and a 

little chalcopyrite; specimens 'from next the 

walls show a thin layer of qu~rtz, a band ·of 

sulphides with some quartz, and a center of 

siderite. The center of the vein i~ not everywhere completely filled, and the druses are 

lined with crystals of siderite one-fourth inch 

in maximum size. 

LEIDENGER TUNNEL. 

The portal of the 'Leidenger tunnel is about 

1 mile southwest of Pecks Flat. The tunnel consists of a 100-foot crosscut and a drift over 1,160 

feet1ong on a vein which strikes N. 60°-68° W. 

and dips steeply north or stands nearly vertical. 

The crosscut portion traverses Idaho Springs 

formation, but the vein drift is entirely in 

granite gneiss. The vein varies from a narrow 

slip to 4 feet in width (average, 8 to 10 inches). 

It corisists largely of crushed granite gneiss 

somewhat silicified and containing a little 

disseminated. pyrite. Numerous small lenses 

of quartz 2 to 3 inches wide (maximum, 2 feet) 

contain pyrite. All the ore is oxidized but 

shows· pyrite casts or remn~nts of that mineral· 

GOLD STANDARD VEIN. 

The Gold Standard ·vein is an east-west 

fracture outcropping on the ridge between the 

two forks at the head of Peck Gulch. So far 

as could be learned the development consists 

of a drift tunnel, now caved, starting near the 

junction of the two forks about half a mile 

west of :f>ecks Flat .. The vein, which cuts 

granite gneiss, shows a quartz-siderite gangue 

carrying dark sphalerite, galena, cl;lalcopyrite, 

and pyrite. Some specimens from the dump 

show a 'little banding, carrying white quartz 

wi~h pyrite next the wall and a central filling 

of siderite, a little quartz, sphalerite, galena, 

and chalcopyrite. Secondary chalcopyrite has 

been deposited along joints as disconnected 

patches o~ small b~ass-yellow crystals. 

LAWSON AND IC~PIRE STATION. 

A number of mines near Lawson and Empire 

station, notably those of Red Elephant Hill and 

Silver Creek, have in the past been among the 

largest silver produce:rs of the region. The 

Joe Reynolds vein a.ppears to have been 

located as early as 1865 but was not actively 

developed until 1877. According to Fossett 1 

the history of active Illining in this part of the 

region dates from the discovery about 1876 

of the Free America vein on Red Elephant· 

Hill by a prospector named D. E. Dulaney. 

Reports of his discovery brought numerous 

prospectors from Georgetown and Central City 

and resulted in the discovery of other veins and 

in the building of the t.own of Lawson. The 

extension of the railroad from Floyd Hill to 

Georgetown in 1877 further stimulated the 

development. of this locality. 

MAUD S. VEIN. 

The Maud S. vein, which crops out on the 

nose of Douglas Mountain, a little over one-

·half mile- southwest of E\mpire station, strikes 

about N. 60 6 E~ and dips 65°-80° NW. It is 

developed at an elevation of about 8,250 feet 

by a tunnel1which is a crosscut for the first 250 

'feet or so and beyond thn.t follows the vein. 

It was accessible for study for about 400 feet 

on the vein. The walls for the fiFSt 300 feet 

are schist of the Idaho E~prings formation but 

beyond that are granite gneiss and some 

granite. 

The vein. varies in width from 4 inches to 5 

feet. Where 5 feet wide it consists 'of granite 

gneiss . traversed by throe veinlets, 2 to 4 

inches in width, which are about half quartz 

and siderite and about hajlf sulphides. Where 

~arrower ~he vein shows similar characters but 

fewer sulphide veinlets. 'I'he study of polished 

specimens of ores under the reflecting microscope shows that they belong to the composite 

type, pyrite of the first mineralization having 

been brecciated and the fractures filled with 

sphalerite, galena, chalcopyrite, quartz, and 

siderite. Subsequent to both mineralizations 

.the ore in the upper parts oJ the vein was again 

fr~ctured and was penekated by solutions 

which deposited secondary chalcopyrite, pearceite, and quartz; Veinlets of one or more of 

these secondary . ~inerals traverse p~in1ary 

1 Fossett, Frank, Colorado, its gold and silver mines, p. 382, 1879. 
I 

CLEAR CREEK COUNTY. 331 

chalcopYJ.·ite, pyrite, sphalerite, and quartz. 

Pearceite also in places metasoma'tically replaces primary quartz. 

No records of the value of the ore or of the 

production are f:l,vailable. 

MARSHALL & RUSSELL TUNNEL. 

T;he portal of the Marshall & Russell tunnel 

is on the north side of Clear Creek at Empire 

station, at an elevation of about 8,250 feet. 

The tunnel, which was about 6,000 feet in 

length at the time of this survey, trends about 

N. 23° W. and is designed to develop at depth 

the veins of the north Empire Creek district. 

Up to the time of this survey no important 

veins had been intersected and no ore shipped. 

The principal veins may be briefly described 

as follows, the letters used corresponding to 

those on figure 67: 

V ~in A. About ·2 inches of light-gray quartz 

carrying a small amount of pyrite and chalcopYJ.·ite. It is 'older than vein B, which intersects it without displacement. 

Vein B. A vein a few inches in width mineralized with siderite, sphalerite, .chalcopyrite, 

and some pyrite and galena. It appears to 

belong to the Lawson type of silver veins. 

Vein C. A small streak of. disseminated ·pyrite and chalcopyrite through altered granite. 

The ore is said to assay $12 per ton in gold and 

copper. 

Vein D. A fracture along which silicification and local development of pyrite has taken 

place through a width of 1 to 2 inches. The 

granite for 1 to 1 t feet on either side is n1ore or 

less altered. " 

Five dikeseut by the tunnel bt?tween 2,000 

and 2,640 feet from the portal are all similar 

and n1ay be classed as bostonite. They are 

fmely crystalline rocks, not notably porphyritic, and under the microscope are seen. to be 

composed almost wholly of anorthoclase laths 

in 1nore or less fluidal arrangement. A little 

original quartz is present, and sericite quartz 

and pyrite are secondarily developed, the latter being most abundant along seams traversing the rocks. 

About 2,700 feet from the portal a single 

dike of unusual appearance shows gray feldspar laths one-fourth inch in maximum· length 

in an aphanitic dark-gray groundmass. Pyrite is very abundantly. developed' in the 

groundmass in irregular masses three-sixteenths 

LEGEND 

1-~-, Porphyry 

dikes 

~ 

Idaho 

~ Sp:in&s format1on 

-~ Barren 

fractures 

0 Veins 

· (Arrows indicate direction of dip) 

quartz monzon1te porphyry 

Dikes all bostonite 

porphyry 

Note: Wall rock is Silver Plume granite unless other- wise indicated 

I 

o 100 200 400 soo feet 

FrGunE 67.-Geolagic plan of :Marshall & Russell tunnel. Surveyed by 

hand compass and pacing. 
332 GEOLOGY OF GILPIN, CLEAR CR.EEK, AND BOULDER. COUN~CIES, .COLO. 

inch or less across and also along minute seams. quartz one-fourth inch in maximum diameter, 

The rock is too much altered for its character many of which show very perfect crystal forms. 

to be certainly determined. The dark color of Less abundant are phenocrysts of pink feldthe groundmass is due to abundant secondary spar one-f?urth inch or less across. The microN 

LEGEND 

Granite gneiss 

~ 

Idaho 

~ Sprin~s 

formation 

5] 

Barren fractures 

52] 

Galena-sphalerite veins 

Arrows indicate direction of dip 

50 100 200 309 Feet 

FIGURE 68.-Geologic plan of Bellevue-Hudson or Rochester tunnel. Surveyed by hand compa;s and pacing. 

biotite in exceedingly small flakes and to magnetite. 

A porphyry dike cut about 4,800 feet from 

the portal shows abundant phenocrysts of 

scope shows the rock to be much altered. 

Both plagioclase and unstriated feldspar are 

present, so that the rock is a quartz monzonite 

porphyry. 
CLEAR CR.EEK COUNTY. 333 

The 7 -foot porphyry dike cut near the face 

of the tunnel is gray in color and contains 

abundant n1agnetite. It is doubtfully classed 

as monzonite. 

BELLEVUE-HUDSON AND ANAMOOSA LODE. 

The Bellevue-Hudson and Anamoosa lode 

apexes on the steep mountain slope forn1ing 

the south wall of Clear Creek valley just 

southeast of Empire station. The first claim 

of this group, the Bellevue, was located in 

1886 and for 10 years after that the mine was 

actively worked. From 1896. until 1907. the 

property re1nained practically idle but since 

1907 has been worked on a small scale by 

lessees. The lode is developed by an upper 

tunnel (from which a shaft has been sunk), by 

anintern1ediate tunnel known as theAnamoosa, 

and by a lower tunnel known as the BellevueI-Iudson or Rochester. which starts near the 

level of the main road from ·Lawson to Georgetown. Together these workings develop the 

lode through a vertical distance of over 1,000 

feet. 

The ·Bellevue-Hudson tunnel begins on the 

south side of Clear Creek near Empire station 

and extends S. 24° E. for about 1,080 feet into 

the mountain.. (See fig. 68.) At 225 feet fron1 

the portal it cuts two veinlets of quartz and 

calcite 1 to 1! inches wide carrying fine galena, 

separated by 1! inches of crushed granite 

gneiss; at 440 feet it cuts a tight vein 1! 

inches wide which shows a little galena and 

. sphalerite; and at 675 feet fron1 the portal it 

cuts a !-inch pyrite stringer. · 

Between 885 and 945 feet it cuts the main 

lode, which here consists of three nearly parallel veins, all of which have been developed to 

some extent by drifts. The southernmost 

vein is about 2! feet in width with 2 inches of 

galena and sphalerite next the hanging wall 

and a slip plane next the footwall, the remainder of the vein ·consisting of crushed 

schist. This vein has been stoped to a height 

of about 30 feet. The northernmost vein, intersected just south of the shaft (fig. 68), is 1 

to 2 inches in width and shows a little galena 

and sphalerite. _The. n1iddle vein is followed 

by a drift for about 200 feet east of the shaft 

but shows little n1ineralization, consisting in 

most places of 3 to 14 inches of crushed and 

decomposed schist. About 155 feet east of 

the tunnel another vein showing 3 to 4 inches 

of gouge comes in from the north or hanging 

wall and is follow'ed by the drift for about 70 

feet. About 230 feet east of the tunnel the 

drift turns north and cuts another and more 

heavily n1ineralized vein, which varies from a 

few inches to 14 inches in width and consists 

of crushed and altered gr~ni te gneiss traversed 

by one or two veinl.ets of galena, sphalerite, 

and pyrite 1 to 3 inches wide. 

The Bellevue tunnel workings are connected · 

by a raise with higher and more extensive 

workings on the vein extending nearly to the 

crest of the hill. The upper portions of the 

vein were worked through an upper tunnel and 

a shaft heading underground also through the 

Anamoosa tunnel, the total vertical extent of 

the workings being about 1,000 feet. The great 

bulk of the ore mined has come from depths of 

less than 500 feet. 

The Bellevue-Hudson vein system belongs to 

the type of silver veins represented by the 

Senator and Millington and the mines of Red 

Elephant Hill and like them appears to owe its 

high silver content mainly to downward sulphide enrichment. Few data could be obtained in regard to the distribution of ore 

values in depth, but the extensiveness of the 

upper workings as compared with those at 

greater depths indicates that the richest ore 

came from depths of less than 500 feet. The 

follow:ing sampling-works assays, selected at 

random from the records of shipments. of 

smelting ore for 1890 and 1891, give an idea of 

metal range in the.upper portions of the lode. 

Sampling-works assays of ore from upper portions of the 

Bellev·ue-Hudson vein system. 

Ore. Gold. Silver.- Lead. 

Netpotmds. Ounces. Ounces. Per cent. 

6,010 ............ 83.00 11.00 

5,506 ............ 193.00 15.00 

670 ............ 565.00 44.00 

1,204 ............ 315.00 37.00 

7,075 ··-········· 244.00 18.00 

11,861 Trace. 268.00 20.45 

1,880 ............. 431.00 52.00 

26,698 ............ 202.85 16. 50 

21,621 ············ 164.50 13.25 

14,826 0.08 25.85 1. 00 

25,596 ············ 338.00 22.50 

33,026' Trace. 208.48 15.90 

23,695 Trace. 161. 65 10.60 

In contrast. to these high silver values 10 

lots of smelting ore shipped by lessees in 1908, 
334 GEOLOGY OF GILPIN, CLEAR CREEK, AND BOULDER COUl~TIES, COLO. 

presumably from the lower levels of the mine, 

showed gold, 0.03 to 0.2 ounce; silver, 12.6 to, 

54.2 ounce's; lead, 4 to'31.6 .per cent; zinc, 3 to 

14 per ce~t. 

'are largely in a ruined and inaccessible condi- \. 

tion and have been stripped of shaft houses and \ 

machinery.· The gr•)ss . prod.u.ction of the 

group is estimated a~ $1,500,000:. 

COMMODORE TUNNJl:L AND REf>. ELE}JHANT. COMMODORE TUNNEL. . 

. GROUP-OF. MINES... . _ .. ThedetailedgeologyoftheCommodoretunnel 

The Com:.;nodore tunnel, which starts at t~e ·and. its connecting drifts beyond a point 2,130 

village of Lawson. and extends'about N~ 40C> W~ . feet from the portal is :3hown in figure 69. Be-

~~~~~~~~~~~~~~~~~--~~~~~~~~~ twoon ~e po~~ and the 

~- ld~tr~~~~~gs 

·§_ 

Galena-sphalerite veins 

E~4 Barren · 

N 

.. ra~~ o...___s...._o_ . ....J10._0 __ __,zo_o ----' 

,, Work inks inac.cessThle 

(Arrows 'indicate direction of dip) 

Note: Wall r~ck ts granite· $neiss except where otlierwise mdicated 

2130 feet to mol,lth of tunnel. ', ', Wall rock is granite gneiss ~ith · ',', 

lenses cif Idaho Springs forma- ','~ 

tion cut by several barren frac- ',~, 

ture planes usually, bearmg WNW. ~ 

ii~nd di ppirig to the north 

FIGURE 69.-Geologic plan of portion of Commodore· tunnel and connecting workitlgs. Surveyed 

b~ hand compass and pacing. 

~-,J~~.O.::.foQ..t P_?~nt the tunnel 

cut:; at 1, 725 feet an unmineralizoo-fracture striking about N. 60° E. and 

dipping 40° NW., along 

whi(~h the· biotite granite 

gneiss is bleached for 2 feet, 

the 'biotite· being altered to 

chlo:rite ;·and ~t 1,910 feet 

a fracture s~riking east and 

dipp:ing 25° N., which carries n<? · metallic minerals 

but EhOWS some calcite and 

along: which the biotite 

granite gneiss is chloritized. 

. At.~O~g_t__the. tunnel 

cuts· the·· St. ·James vein, 

whoso surface portion is 

developed by n. drift tunnel 

about ·400 feet in length, 

now :ii1accessi ble. The 

drifts ·from the Commodore 

tunnei~ are. caved 60 feet 

west nnd -165 feet east of 

the tunnel. . Forty feet east 

of the. tunnel the north fork 

of thel vein consists of ' a' 

~y~jglet_~f_ guartz and 

galena., below . which is a. 

!-inch veinl<~t of siderite. 

. The re.maining 2 feet of the 

vain m:iterial is crushed and 

altered granite gneiss with-· 

out sulphides. Elsewhere 

under Red Elephant Hill (Pl. XXII), is a the vein as exposed in thes13 drifts is practically 

straight crosscut 3,460 feet in length (in 1911). barren.· No stoping has been done. 

It was started in 1900 for the purpose of The following lettering of veins refers to fig .... 

developing ~t- depth th~ veins. of the Tabor, ·ure-'69: 

White, Free America, Boulder Nest, and St. . ·Vein A.· A fracture· zone· along which theJames mine~ on. Red Elephant .·Hill.· These -~a.nite gneiss has been somewhat altered withmines had been acti\rely worked and· had out mineralization. · · · 

yielded rich silver ores through their ·Fhaft -Vein B. A vein which at one place shows 3-

workings from the time of their discovery until to 4 inches of somewhat mushed and altered. 

1889, but have since been idle and at present gra11ite gneiss next the hang:tng wall, succeeded,. 
U. S. GEOLOG ICAL SURVEY PRO~ESSIONAL PAPER 94 PLATE XXII 

LAWSON AND THE MINES OF RED ELEPHANT HILL FROM SOUTH SIDE OF CLEAR CREEK VALLEY NEAR LAWSON. 

Boulder Nest shaft; 2, White shaft; 3, Free American shaft; 4, St. James shaft; 5, Tabor shaft; 6, Commodore tunnel; 7, Commodore power plant. 

Ph otograph by R. B. Morton, 1907. 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 94 PLATE XXIII 

VIEW LOOKING UP SILVER CREEK NEAR LAWSON. 

Dumps on ri ght mark tunnels a nd s haft on Ame rican Siste rs ve in, whose outcrop is indi cated approx imate ly by th e broken line. Large dump to left 

of center is from J o Rey nolds tunn e l. Ph otograph by R. B. Morton. 
CLEAR CREEK COUNTY, 335 

below, by 10 to 11 inches of gray quartz and TABOR VEIN. 

buff-colored siderite carrying galena, pyrite, The-Tabor vein, on Red Elephant Hill, about 

and some sphalerite. In general this vein is not 1,

300 feet southeast .of the Schwartz shaft, 

heavily Inineralized. . is developed by a shaft about 230 feet deep, 

1 

Y ein C. Two inches of g<;mge and no sui- with three levels, and by a tunnel which drains 

P ud~s- . . the mine slightly below the third level of the Ven~ D. A vein that In pl~ces s~ows merely '"l. .ttft. The vein strikes a little south of east, 

1 to 2 lnches of crushed granite gneiss bu~ that )ips north, and shows mineralogic charac;.. 

elsew~1ere broaden~ to ! foot and shows stn~lgers ters similar to those of the other veins of the 

carrytng qua~·tz, siderite, galena, and pyrite. Red Elephant group. The gross production 

A west drift from the tunnel at .2, 730 feet of this mine is said to be about $70 000 

exposes veins of fine-grained siderite and cherty_ ' · 

silica t~u·ough which pyrite is disseminated in. WHITE VEIN'. 

small grains. The White vein, which strikes nearly east, 

BOULDER 'NEST-FREE AMERICA VEIN. dips.50°-75° N., is developed by the Schwartz 

The few details available in regard to the· shaft with 1·3 levels, the lowest of which is conshaft workings in the Boulder Nest-Free nected by. a raise with the .Commodore tunnel 

Ainerica vein are summarized below. workings. What appears to be the White 

vein (vein A, fig. 69) is cut by the Commodore 

tunnel about 2,800 feet from the portal near its 

Vertical Number junction with a northeast-trending lode which ·depth of f 1 

Workings in Boulder Nest-FreP. America vein. 

shaft. 0 leve 8 · may represent the Boulder Nest-Free America. 

Boulder Nest ..................... . Free America .................... . l"ree America Extension .......... . 500 

550 

350 

Near their junction the two veins show numer-

~ ous branches, and the exact relation of any one 

4 of them to the veins developed in the higher 

-------..,..---------!---~--- .workings is uncertain. The characteristics 

A number of other shafts on the lode extend 

to depths of 200 feet or less. The levels range 

from 100 to 1,000 feet in length. There are 

no accurate maps of the workings. 

According to Fossett 1 the Free America 

yielded ore to the value of $100,000 in 1877 and 

$80,000 in 1878. Between the spring of 1877, 

when shipments began, and the end of the year 

the Boulder Nest mine is said to have produced 

ore to the gross value of nearly $110,000. Of 

this ore, 3 91 tons are said to have averaged 3 7 ~ 

ounces of silver. The output in 1878 is reported to have excee.ded $230,000, the silver 

in the ore mined ranging from 30 to 250 ounces. 

Several lots; of smelting or!3 shipped from the 

Boulder Nest mine in the early nineties showed 

the following tnetal content, according to sainpling-works assays: 

Sampling-worl.:s assays of ore from Boulder Nest 1nine. 

Ore. Gold. Silver. 

Net pounds. Ounce. Ounces. 

3, 704 .................... 38.00 

273 .................... 73.00 

171 0. 60 101.00 

198 ..................... 150.00 

4,380 ............... 130.50. 

2,376 ............. 72. 00 

1 Frank Fossett, Colorado, its gold and silver mines, p. 383, 18i9. 

of the White vein are best exhib~ted in the 

thirteenth level of the Schwartz shaft workings, which may be reached through a 135-foot 

raise from the Commodore 'tunnel level. The 

vein there is· a fracture zone varying from 3 

inch~s to 4 feet in·width, which, for much of its 

exposure on the level, follows a contact between 

schist and granite gneiss. In places· the vein 

consists wholly of crushed wall rock, but elsewh~re it shows galena, pyrite, and some chalcopyrite and sphalerite in a gangue of quartz, 

siderite, and barite. The sulphides and their 

gangue form in places sharp-walled veinlets 

but elsewhere grade gradually into altered 

wall rock. Small amounts of gray copper 

inte:r;grown with galena as an original mineral 

are reported from this vein. Some bornite is 

reported from the thirteenth level. 

Although the ore from this level on the 

White vein is in ·general very fresh in appearance it is interesting to record the occurrence 

of crystals of secondary chalcopyrite . and of 

a black brittle sulphide, which is probably 

pearceite. 2 . The mode of occurrence of these 

minerals in vugs indicates that they are prob2 Similar to polybasite but with arsenic instead of antimony. The 

specimens reacted stronf?lY for silver and arsenic and gave a clear copper 

reaction, but did not react for antimony. 
336 GEOLOGY OF GILPIN, CLEAR CREEK, AND BOULDER COUNTrES, COLO. 

ably secondary. It appears, therefore, that 

downward enrichment in silver extends to at 

least the thirteenth level in the Schwartz shaft. 

workings-a vertical depth of about 700 feet. 

The following sampling-works assays ·are of 

ore from the thirteenth level. The high silver 

content of many of the shipments is attributed to downward enrichment. · 

Sampling-works assays of ore from thirteenth level of the 

White vein. 

Ore. Gold. Silver. Lead. Zinc. 

Net lbs. Ounce. Ounces. Per cent. Per cent. 

10,850 0.04 195. 00 20.00 12 

38,900 . 03 111. 50 18.40 12 

28,100 Trace. 64.00 11. 70 7 

21,780 . 02 202.00 25.00 8 

18,800 .......... 188. 10 14.00 9 

27,880 . 05 73. 70 22.30 8 

24,960 . 05 49. 50 24. 00 10 

15,000 .02 108.20 24.80 11 

2,850 . 04 178.00 30.00 6 

5, 750 . 04 126.50 10. 50 4 

LITTLE GIANT VEIN. 

The Little Giant mine is at an altitude of 

about 8,800 feet on the east side of the gulch 

leading north from Lawson. It lies across the 

gulch from the Red Elephant Hill group, 

which it resembles in 1nineral characters. The · 

mine was in operation at the time of this survey, the development consisting of a shaft 270 

feet deep with four levels. Only the two upper 

levels, at 80 and 140 feet, were accessible, the 

lower ones being water filled. Very little 

drifting, however, has been done on the lower 

levels. A short tunnel is being driven eastward 

on the vein on a level with the shaft collar. 

The Little Giant vein strikes from N. 70° E. to 

N. 80° W., and dips about 60° N. As exposed 

on the 140-foot level for about 500 feet east of 

the shaft it consists in most places of sericitized granite gneiss cut by veinlets of quartz 

and siderite, which in some places form an 

intricate network through 2 feet of gneiss. 

The largest of these, 1· inch or so in width, 

locally carry some sulphides. 

At one place in the tunnel a l-inch veinlet 

of galena was bordered by a wall carrying 

disseminated galena. Specimens of _ore from 

the ore bins showed galena and some sphalerite 

in a gangue of quartz and siderite and local 

.barite. The galena of some vugs showed evidence of etching. Oxidation was observed to 

a depth of about 65 feet near the shaft, but 

was 'not observed on the 140-foot level. 

Although no secondary silver n1inerals were 

seen, it is entirely· probable that they occur, 

and that downward en:richment in silver has 

been of much importan,~e. 

PANAMA 'J~UNNEL. 

The Panama tunnel i~~ a little over one-half 

mile northeast of Lawson, at an elevation of 

about 8,800 feet. The geologic features are 

shown in figure 70, to which the vein lettering 

below refers. All of the veins are of the silver 

type common near Lawson. 

LEGE NO 

0 

Bostonite 

porphyry 

Granite ~neiss 

Idaho Sprfn~s formation 

Inaccessible 

workings 

Dip 

so 100 

N 

FIGURE 70.-Geologic plan of Panama tunnel. Surveyed by hand compass and paciitg. 

Vein A. A small vein showing 1! inches of 

sulphides. One assay of o .re from it gives 12 

ounces of silver and 40 per cent of lead. 

Vein B. A fracture zone Hhowing only gouge 

with no sulphides. 

Vein C. A vein that has been stoped west of 

the tunnel to heights as great as 48 feet. The 

portions of the vein exposed show little 

mineral. The value of the ore is said to be 

mainly in silver, which occ·urs native and in 

polybasite. Ore on the dump, said to come 

from this vein, showed· galena, sphalerite, and 

chalcopyrite in a quartz-sid,arite gouge. Several assays average about 120 ounces silver. 
CLEAR CR.EEK ~OUNTY. 337 

Vein D. A vein that shows at the west face 

three subparallel stringers 1 inch or less in 

width of white quartz carrying some siderite 

and a few bunches of galena. The whole vein 

is about 1 foot wide, and the mineralization 

not particularly strong. 

The Panama tunnel is beip.g driven to reach 

a vein known as the No. 2, which has given 

surface assays of $12 to $52 per ton. 

PLATTS VEIN AND PRINCESS OF INDIA TUNNEL. 

The Princess of India tunnel, on the south 

side of South Clear Creek about one-fourth 

mile· southwest of Lawson, is 

in part drift and in part crosscut. (Seefig. 71.) The general 

country rock is granite gneiss, 

in which there are several 

lenses of schist of the Idaho 

. Springs formation. Both 

formations are· cut by porphyry dikes. Near the mouth 

of the tunnel an· east-west 

dike of pyroxene monzonite 

porphyry contains large altered 

feldspar crystals. . Bostonite 

porphyry is exposed in two 

places in the crosscut and also 

near the end of the Platts drift. 

N 

veinlets of dark-gray quartz and barite in which 

there are elongate masses of sulphides up to 2 

inches in width.' Galena and sphalerite are 

the most abundant priinary sulphides, though 

pyrite is present-in all the ore and occasionally 

.a little chalcopyrite is seen. 

· Downward enrichment in silver has played an 

important r6le in this mine, as is shown by the 

occurrence in vugs and small fractures in the 

primary ore of chalcopyrite as a coating of very 

small crystals and of pearceite in black metallic 

crystals. The chalcopyrite is in part later than 

the pearceite, coating it locally.· The occurLEGEND 

uml 

~ Pyroxene monzonite porphyry 

I 

100 

.. Boston1te porphyry 

Granite 11neiss 

Idaho Spr~ngs formation 

Galena- sphalerite veins 

Unmineralized fraCtures 

(Arrows indicate direction of dip) 

0 100 feet 

The ~eins cut by the tunnel are all of the galenasphalerite type. Those in the 

crosscut south of the Platts 

vein are small, and where exposed are not heavily mineralized. The one on which the 

most drifting has been done 

(see fig. 71) has an average 

FIGURE 71.-Geologic plan of Princess of India tunnel, developing the Platts vein. Surveyed 

by hand compass and pacing. 

width of about 4 inches and shows a few fairsized lenses of galena-sphalerite ore with quartz 

and barite as gangue minerals. 

The Platts vein strikes N. 60° W. and dips 

on an average 70° NE. It varies from a tight 

fracture to 14 inches in width. Near the crosscut it splits into ·three branches distributed 

through a width of about 12 feet of altered and 

smnewhat mineralized country rock. The vein 

. sends two feeders into the hanging wall, but 

neither of then1 is strong nor well mineralized. 

The Platt13 vein consists of crushed altered 

country rock, in places barren but elsewhere 

carrying disseminated sulphides and cut by 

44214°--17----22 

_} 

renee of pearceite as a metasomatic replacement 

of quartz and galena has already been described. 

(See pp. 144-145 and figs. 3, 14, and 15.): 

In the Platts drift there are three stopes on 

lenses of ore ·separated by practically barren 

stretches. The longest extends 95 feet along 

the vein and the shortest 30 feet. A drift on 

the Platts vein has also been run from the 170-

foot level of the Murray mine, but this could 

not be entered. 

Sericitization is the principal wall-rock alteration near the vein. 

A second tunnel, several hundred feet above 

the Princess of India tunnel, is crosscut for 60 
338 GEOLOGY OF GILPIN, CLEAR CR.EEK, AND BOULDER COUNTIES, COLO. 

feet and follows the Platts vein for 270 feet. ments ran 45 per. cem~, and copper (wet) in 

The vein, which, as exposed in this tunnel, some as high as 7 per cent. The total prostrikes about N. 55° W. and dips 65° NE., is duction of the property is not known. 

in most places only sparsely mineralized, but 

locally shows sulphide lenses. At the face is a CYMRIC 'l'UNNEL. 

lens 6 inches wide of' very fine "steel" galena The Cymric crosscut tunnel, in the valley of 

associated with some cherty gray quartz. The Silver Creek about three-j:ourths of a mile southbordering· granite gneiss is somewhat altered southeast of Lawson at an elevation of 8,690 

but practically unmineralized. No secondary feet, is about 1,265 feet long and runs S. 11° E. 

silver minerals were observed. The ore when through granite gneiss nnd schist. Near the 

sorted is said to average about $53 a ton. face a 45-foot dike of porphyry, probably bosFew data are available in regard to ore tonite, nearly free from dark-colored minerals, 

values or total production from the Princess strikes a few degrees north of east and dips 

of India tunnel. The ·gold content was low, 55o N. Near the centrnl part of the tunnel 

the principal value being in silver, and, as in three unmineralized frac1iure zones strike eastmost of the veins of this region, the richest northeast. 

ore was apparently at slight depths and owed The Cymric vein, cut 1,155 feet from the por- its high silver content to downward enrichment. . . tal, is an east-west fracture that dips 35°-60°N., 

MURRAY VEIN. and- that has been drifted on west of the 

The .Murray vein, on the south side of South tunnel for 495 feet. In m.ost places it is about 

Clear Creek opposite Lawso11, was inaccessible 4 to 6 inches wide and consists of crushed 

and most of the following information was schist wall rock which is very little mineralobtained from a report by Mr. H. G. Chase. ized. Stopes on two smnll lenses of ore are 

The vein is developed by an old shaft said each 30 feet long and are barren at the backs 

to be 90 feet deep and. by a 275-foot shaft with at heights of 21 and 60 feet above the drift. 

levels at 80, 170, and 265 feet, respectively, The ore from these stopes is crushed wall rock 

580, 550, and 25.7 feet long. and gray-brown cherty silica containing irregA pyroxene monzonite porphyry dike runs ular stringers and bundles <?f fine-grained 

about parallel to the vein and is reported to galena with a little dark sphalerite. Barite 

form the south wall in most of the workings.· occurs exceptionally in the gangue. In some 

The vein strikes' a few degrees north of east of the ore secondary chalcopyrite has been 

and at the surface stands vertical though below deposited along minute fra,ctures. 

the surface it dips · slightly to the north. The Big Horn fracturo, which joins the 

The oxidized surface ore consists of iron- Cymric 395 feet west of the main tunnel, 

stained honeycomb . quartz and crushed and strikes N. 53° W. and dips 40° NE. It has 

altered wall rock, in which a few remnants of been drifted on for 130 fee1~, of which the first 

origina1 galena and pyrite are preserved. The 125 feet is barren, and the last 5 feet contains 

seconda~y minerals are limonit'e, copper car- vein filling to a maximun1 'width of 1 foot. 

bonates, cerusite, and exceptionally polyba- Next the hanging wall at the face there is a 

site. The ore from the upper workings was tight slip plane,· below which is 6 inches of soft 

.richest, and that from the 265-foot level is altered schist and pegm~;,tite, 2 inches. of 

reported. to be low grade. The principal brownish-gray cherty silica, ~11other slip plane, 

values are in silver and are evidently there- 3 inches of fine-grained galena with some cherty 

suit of downward sulphide enrichment. The silica, and 2 inches of chert:v silica. 

silver values above the 80-foot level ranged I · The ore from the small stopes on the Cymric 

from 40 to 285 ounces: -About 108 tons shipped vein is said to have been very rich, its value 

by lessees between 1883 and 1888 showed an being largely in silver and lead. It is probable 

average metal content' of about 0.35 ounce that the rich silver ore haE. been affected by 

gold and 55 <?Unces silver; and 150 tons ship- downward enrichment, but no secondary silver 

ped i:p. 1885-86 an average of about 0.44 ounce minerals were observed. The production of 

gold and 52 ounces silver. Lead in some ship- the mine has been small. 
CLEAR CREEK COUNTY. 339 

<MILLINGTON MINE. 

The Millington mine is about three-fourths of 

a 1nile southwest of Lawson on a steep mountain slope. overlooking the valley of South Clear 

Creek. The workings consist of four drift tunnels whose portals have elevations of approximately 9,225, 9,468, 9,584, and 9,668 feet. 

Observations were confmed to the two lower 

tunnels, the upper tunnels being inaceessible at 

the time of survey. The lowest tunnel will he 

referred to as No. l and the one next above as 

No.2. 

The av.erage. strike· of the Millington vein is 

about N. 45° E. and the dip is nearly vertical. 

No. 1 tunnel is in granite gneiss for about 570 

feet from the point where it first meets the vein, 

and No. 2 tunnel is in the same rock for its 

first 340 feet. Beyond these distances the vein, 

in both tunnels runs nearly parallel to a 2 to 10 

foot porphyry dike, which is probably much 

altered bost.onite porphyry. Though in some 

places forming a single strong fracture the lode 

elsewhere shows a mu.rked tendency to fork, 

especially where associated with the porphyry 

dike. The vein is distinctly later than the porphyry and cuts across it at numerous points. 

Where represented by a single fracture zone the 

width of the vein ranges from 5 i11ches to as 

much as 4 feet. Where it splits into several 

fractures the width may be considerably more. 

A typienl exposure shows 1 inch of iron-stained 

gouge next the hanging wall, followed below by 

7 inches of soft crushed and mineralized granite 

gneiss and by a slip plane on the footwall. 

In addition to the dev~lopment .on the Millington vein son1e mining has been done on a 

cross vein known as the Silver Treasure, which 

strikes about N .. 70° W. and dips at 60°-70° 

NE. This v-ein is cut in No. 2 tunnel about 190 

feet fro1n the portal and has been drifted on for 

about 450 feet. Its material is inore or less 

oxidized on the No. 2 tunnel level, but shows 

ren1nants of originnl quartz and fine-grained 

galena at several points. Oxidized ore from 

this vein has yielded a large content of native 

silver. and horn silver. 

Very little ore was seen in place in the workings on the Millington vein, but specimens fron1 

the dump and ore bins showed remnants of 

galena, sphalerite, and pyrite in a matrix of 

limonite, some azurite, and other oxidation 

products. The richer ore, which is· reported to 

·Occur principally in hunches or pockets, undouhtedlx owes its high silver content to downwnrd enrichment. 

The following assajTS selected from a large 

number of sa1npling-works returns give some 

idea of the range in the metal content of the 

sme1ting ore: 

Year. Ore. Gold. Silver. I Lead. Remarks. 

-----

Net lbs. Oz. Oz. P. ct. 

-1893 .. 25,430 0.07 39.60 3.50 Lowest return. 18~3 .. 5,652 . 75 195.25 12. 70 Unusual1y high 

in gold. 

1896 .. 53,656 . 09 277.00 7.50 Large shipment. 

1899 .. 164 . 28 1,266. 70 12.00 Parti.cularly 

1899 .. 312 .17 

high grade. 

658.25 14.40 High in silver. 

1902 .. 3,980 .10 45.40 17. 20 High in lead. 

In general the gold content of the ore is below 0.1 ounce, even in lots carrying several 

hundred ounces of silver. 

. The gross production of the property is said . 

to have been about .$50,000. 

AMERICAN SISTERS VEIN. 

The American Sisters vein outcrops about 

three-fourths of a mile south of Lawson, where 

its position is marked by conspicuous dumps 

on the hill west of the settlement of Silver 

Creek. (See Pl. XXIII.) The vein is developed by a succession of drift tunnels along the 

slope of the mountain and by a shaft at the 

base. Plans of the workings were not available, and the development can not be described 

in detail, but it is known to be very extensive. 

The only portion of the workings that could be 

entered was the tunnel just above the lower 

shaft, which was studied for about 740· feet, 

the vein being stoped out for practically all of 

this distance. 

The vein as shown in this tunnel strikes N. 

50°-75° E. and dips 65°'-70° NW. The roof of 

this tunnel is timbered except in a few places 

where the vein appears practically barren and 

no ore was seen in place. 

Specimens from differant dumps showe~ original galena, sphalerite, chalcopyrite, pyrite, 

quartz, and siderite. Many small vugs lined 

with crystals, mostly of clear quartz, less com-. 

.monly of siderite, and exeeptionally of galena 

and sphalerite were noted. Little 'Of the galena 

seen was coarse, and much of it was exceptionally fine grained. Some of the sphalerite was 

of the resin variety. One specimen found 
340 GEOLOGY OF GILPIN, CLEAR CREEK, AND BOULDER COUNTIES, COLO. 

shows banding formed by an alteration of narrow layers of siderite and wider layers of galena, 

but such a niode of occurrence appears rare in 

this mine, as well as in the district as a whole. 

Some small veinlets are mainly siderite with a 

little galena and a few are wholly siderite. 

Many specimens of disseminated ore are very 

rich in sulphides, and this type of ore is said to 

. have formed an important part of the output 

Although no sweeping conclusions can be 

drawn from only two analyses these results 

suggest that primary sphalerite may be very 

important as a silver caiTier. 

Assays of primary ore from American Sisters vein. 

No. Gold. Silver. Copper 

(wet) . ~ead. .Zinc. 

------------------1·---

\ of the mine. One specimen of this type shows Ounces. Pe1' cent. Per cent. Per cent. 

· \ granite gneiss trav..ersed by a ~etwor~ of narrow ~::::::: ~~:~~: ~: ~~ 0

: ~~ ~ ~: ~g 1 stringers of galena, cha.Jcopyl'lte, pyrite, q~artz, 1 and siderite the rock between the strmgers I ' 

: containing abundant disseminated grains of 

sulphides. Under the microscope the rock between the sulphide veinlets is seen to be granite 

gneiss, in which the feldspars are crowded 

with sericite flakes and in which a carbon.ate, 

Sampling-~orks record~ of 18lots of smelting 

ore from the American E\isters mine, shipped 

from 1893 to 1898, incluBive, show gold 0.08 

to 0.4 ounce, silver 33.5 to 367.2 ounces, lead 

2 to 14.50 per C(:;nt, zinc .6 .. rto 13 per cent 

probably siderite, is abundant in irregular gran- JO REYNOLDS ,VEIN. 

ular aggregates. Pyrite is abundant in irregu- The ·Jo Reynolds vein,· which outcrops on 

· lar grains.most of which are partly rimmed and the west side of Silver Creek a short distance 

in some cases wholly inclosed by sphalerite. south of the American Sist€,rs vein, is developed 

Little of the latter mineral is present except in by two tunnels, by a shaft which connects the 

association with pyrite, but it is uncertain two tunnel levels but does not extend to the 

whether it has replaced the pyrite or befm de- surface, an,d by two shallow shafts. None of 

posited around it. Galena is sparsely scat- the worl9ngs, however, were acces~ible at the 

tered. through the rock in minute grains· but is time of this survey. 

much subordinate to both pyrite and sphalerite. The 1,1ppe~ or Daily tunnel has its portal in 

Downward sulphide enrichment has been an the upper part of the settlement of Silver 

important factor in this vein and to it is prob- Creek at an elevation of about 9,000 feet. 

ably due the bonanzas. Specimens found on The lower or Elida tunnel, driven in 1900 to 

the dumps show small secondary crystals of 1903, has its portal on the west side of Silver 

proustite and pearceite developed ·On fractures Creek at an elevation of about 8,500 feet and 

and in vugs in the primary ore. A specimen is connected by a tramway 3,500 feet long with 

belonging to Mr. P.R. Stanhope shows granite a 40-ton mill on Clear Creek. Most of the· ore 

gneiss carrying abundant primary dissemi- has been obtained from ni:r..e ·.levels, ranging 

nated galena and chalcopyrite and cut ·by from 200 to 1,500 feet in length, between the 

fractures along which secondary pearceite 0) two tunnels. Three. veins have been worked 

and chalcopyrite have been deposited. An- on the upper levels but only OI{e below the 

other specimen from a private collection shows fourth level. The average strike of the main 

a vug lined with large quartz crystals, on which vein is N. 65° E. and the dip 70° NW. 

some pearceite0) had later been deposited and The Jo Reynolds claim was located in 1865 

had in turn been coated in places by an irreg- but it was not until the compl,3tion of the Tail 

ular intergrowth of pearceite and chalcopyrite road in 1877 tha't any important amount of 

Phenomena of replacement in the silver enrich- mining was done. From 1877 to 1907 the 

ment of this vein have already been described property .was worked almost continuously. 

on page 146. The vein is similar in mineral 1

characters to 

In order to determine the probable source of the neighboring American Sisters vein. The 

the silver in the secondary silver minerals two primary metallic ~inerals are galena, sphaler 

samples of fresh primary ore were collected ite, pyrite, chalcopyrite, and gray copper; ~nd 

and were assayed with the results given below the secondary minerals polybt:1site, pearcmte 

No. 1 was almost wholly fine-grained galena, proustite, argentite (original~)·' native silver 

No.2 was m~inly sphalerite with a little galena chalcopyrite, and galena. 

,. 
CLEAR CR.EEK COUNTY. 341. 

Scattered flakes of native silve~ in talclike 

material are reported to occur as low as the 

ninth level. 

Like the other veins of the Lawson silver 

district the Jo Reynolds vein appears to owe 

its richness n1ainly to downward enrichment, 

the ore values showir1g a gradual decrease in 

depth. The records of the ore shipped are 

unusually complete. There are no records of 

any very rich ore betw.een the surface and a 

~epth of 50 feet. The gold content is everywhere low and fairly constt;tnt, being generally between 0.05 and 0.15 ounce~ rarely as 

much as 0.25 ounce. The silver content in all 

shipments, classified according to source in the 

mine, is as follows: 

· TURKEY GULCH. 

ROCKFORD TUNNEL. 

The Rockford tunnel starts in Turkey Gulch, 

on the south side of Clear Cre.ek,. a. short d.is:-

tance west of its juncti~n with· Fall River, and 

extends S. 30° E. undor Trail Creek and, into 

the hill beyond, its t~~tal.l~ngth being about 

2,000 feet. The tunnel is mainly in the Idaho. 

Springs formation, but the last 120 feet are in 

granite gneiss. It cuts a 2-:-foot dike of porphyry at 70 feet from the portal and a 20-foot 

one at 1,220 feet. Both are bostonite, and the. 

larger dike is probably identical with the one· 

shoWI.l on the ~ap near. the crest ·of the ridge. 

separating Turkey Gulch from Trail Creek. 

The tunnel cuts two. unimportant ~nd un-· 

Silver content of ore from the Jo Reynolds veins. d l eve oped veins at 180 . and 1,390 feet. At. 

Daily ·tunnel level. .Some shipments as low as 20, but few 950 feet it intersects the Megalona vein and 'at 

less than 50 and one as high as f h 

1,208 ounces. Ounces. 1,830 eet t. e Donaldson-Champion Dirt vein,. 

First level................................. 75 to 310 both of whiCh have been developed by ex tenSecond level............................... 42 to 262 sive workings. ~ 

Third level. ............. ~. . . . . . . . . . . . . . . . . . 36 to 245 The apex of the Megalona. vein is on t:he 

Third and fourth levels ..................... 34.50 to 311 south slope of tl~e ridge between Trail Creek 

Fourth level west of shaft................... 52 to 171 and· Turkey Gulch. It strikes about N. 60o 

Fifth level. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 to 241 

Sixth level................................. 31 to 153 E., at about right angles to the trend' of the 

Seventh level.............................. 28 to 357 tunnel, and dips 15° to 45° NW. (average about 

Eighth level............................... 28 to 279 30°). On the Rockford tunnel level it has not 

In general, the silver content slightly de- been developed to the east of the tunnel, but 

creases with depth, the highest being found to the west has been drifted on for over 2,400 

above the third level. A single small block of feet, throughout which distance the wall rocks 

ore in this part of the mine yielded $80,000 in are schists of the Idaho Springs formation and . 

ore running 800 to 1,000 ounces in silver. The some pegmatite. At 250 feet west of the tunnel 

average content of -the ores below the third the vein cuts sharply through a dike of por-· 

level is said to be ·about gold 0.1 ounce, silver ·phyry (probably bostonite), and is therefore· 

100 ounces, lead 10 per cent, zinc 12 per cent. the younger. In general the vein lies about. 

As compared with these high silver values, parallel to the foliation of the schist, is strongly 

which are due t6 enrichment, the precious- defined, and in places is heavily mineralized. 

metal content of the primary ore appears to be In some portions 'it shows only 3 to 4 inches of 

very low. A sample of "steel" galena from sheared and some~hat silicified schist carrying· 

the Elida tunnel level, which appeared to carry scattered small grains of pyrite, but in other 

no secondary minerals, showed,, according to portions it shows a foot of coarse pyrite; in one 

Mr. R. B. Morton, 73 per cent of lead and 14 place it shows 3 feet of light-gray quartz and. 

ounces of silver. very- coarse pyrite mingled in nearly equat 

Previous to 1904 the ore extracted was sent amounts, some of .the pyrite crystals being 2 

dir~ct to the smelter, but from 1904 to 1907 the inches in diameter. The heav:ily mineralized 

company operated a mill on Clear Creek, be- portions of the vein form an ore shoot "about 

tween Dumont and Lawson, which concen- 600 feet long, whose center is about 1,450 feet 

trated the lower grade material. In 1907, 267 west of the tunnel, at a point where a raise 

tons of smelting ore and 414 tons of concen- and a winze have been excavated. This ore 

trates were shipped. shoot has been stoped for most of its length, 

The total gross production of the property and is the only portion of the· vein which has 

is placed at about $1,462,500. been worked. At the end of the drift the vein 
.342 GEOLOGY OF GILPIN,' CLEAR CREEK, AND BOULDER COUNTIES, COLO. 

is cut off by a fault zone striking nearly north The upper workin~~ in the Donaldsonand south. Champion Dirt vein have been fully des,cribed 

The ore consists almost wh<;>lly of pyrite, with by Spurr.1 According to him the 50-foot)evel 

only small amounts of chalcopyrite. Sampling- below the Centurion tunnel yielded a small. 

works assays of two fairly representative pocket of ore, mainly ga1ena and chalcopyrite,. 

_shipments, weighing 11.39 and 9.52 tqns, show, with subordinate pyrite, "gray copper," and. 

respectively, gold 1.~ and silver 6.24 ounces, an iron-bearing carbonate. Throughout most 

and gold 0.34 ounce and silver 1.16 ounces; of the vein, however, tho ore is almost excluboth assays show a trace of copper. sively pyrite with .a quartz gangue. 

The average content. of over 2,000 tons Sampling-works· assay~ of 12 shipments of 

shipped in '1910 was gold 0.427 ounce, silver smelting ore;. obtained from this vein through 

0.769 ounce, _copper practically negligible (in the Rockford tunnel, show gold, 0.32 to 3.16 

no shipment'exceeding 0.4 per cent). ounces; silver, 0.69 to 12.4 ounces; ~opper 

1 Drifts on the Donaldson-Champion Dirt vein (wet), a trace to 2.92 per cent. · 

and its bran~hes extend about 140 feet east The average value of the qre sp.ipped from 

and over 2,000 feet west ·of the Rockford tun-· the Donaldson vein through the Rockford tunnel. The vein, which in general is nearly par- nel in 19iO and 1911 was as follows: · 

allel to the Megalona, dips 25°-35° N. (average 

- Average value of ore shipped from Dor~:aldson vein, 191D-1J. about 30°). The strike is very variable, shifting from nearly east-west to about N. 50° E. 

. 'From. a point- 850 fe~t. west ·of the Roc:Kford 

tunnel the drift is largely in granite gneiss for 

, 650 feet. and in schist of the Idaho Springs formatio:q. and pegmatite for 500 feet more (to the 

fa~~),;··: It cuts a dike of much-altered porphyry, · 

probably· bostonite, at about 1,450 feet from 

the· tunb.el. · · 

As exposed near the tunnel the vein consists 

of 5 inches of nearly solid pyrite between tight, 

sharp walls carrying some disseminated pyrite. 

Near the raise leading to the upper or shaft 

workings the ve·jn is 2 feet wi4e-between pegmatite walls. Next the hanging wall is a 5-

inch band of gray quartz' and pyrite in _about 

equal amounts~ and next the footwall a 3-inch 

band of nearly solid pyrite; cross stringers connect the two. The wall rock contains very 

little disseminated pyrite. About 1,100 feet 

west of the tunnel short branch drifts on which 

some stoping has been.· done follow branches of 

the vein, which, like the main vein, dip 25°-

1350 N. Beyond ·a point 1,500 feet from the tunnel the mineralization is weak, and the last 150 

feet of the drift appears to be off the vein. Most 

of the stoping has been done between the branch 

drifts .mentioned above and the raise leading to 

the upper workings; that is, between 675 and 

1,100 feet west of the tunnel. 

The Centurion shaft has been connected with 

the Rockford tunnel workings on the Donaldson vein, and a raise from the.Centurion tunnel 

Ore. Gold. Silver. Copper 

(wet). 

Net tons. Ounces .. ·ounces: Per cent. 

1910 ....... -- ........... 0.618() 1.·567 0. 335 

1911. ........ 1,000 1. 1091) 3.200 1.189 

The highest percentage of copper in the 1~10 

shipments was 0.646 per cent and in the 191~ 

shipments 3.858 per cent. 

SPRING GULCH. 

SILVER KING VEIN. 

The Silver King vein, exposed on the west 

side of Spring Gulch about a mile: north of its 

junction with South Clear Creek, is developed 

by two drift tunnels, the lower of which (see 

fig. 72) is accessible to 960 feet, where it is 

blocked by a cave. From this tunnel a 1,750-

foot ·raise on the vein. connects with the upper 

tunnel,. which is short and was not visited. 

The wall rocks are Idaho Springs formation 

injected by varying amounts of grani~e pegmatite. 

The vein strikes N. · 7 5° E\. on the average 

and dips 40°-70° N., the avorage for the first 

700 feet being ·65 ° N. and for the remainder of 

the tunnel about 43°· N. It varies from 1 to 4 

feet in width with an averago of about 2 feet, 

and has two prominent branches running into 

the foot or south wall. 

1 Economic geology of the G;eorgetown quadrangle, Colo.: U.S. Geol. 

connects with the Champion Dirt tunnel. survey Prof. Paper 63, pp. 336-340, 1908. 
CLEAR CR.EEK COUNTY. 343 

The vein consists of crushed altered wall rock 

and gray quartz containing abundant galena 

and sphalerite and some ch~copyrite and 

pyrite; galena is very much in excess of sphalerite. In n1ost places ore of this sort is cut by 

numerous stringers of solid sulphides up to 8 

inches in width. 

Postmineral movement along the general 

, course of the vein has produced a fine breccia 

of wall rock, quartz, and ore, only partly cemented by buff cherty silica and siderite, and 

may have produced a rough banding noted exceptionally in the sulphidt;} seams. Near the 

center of the tunnel the vein is displaced by an 

unmineralized fault that strikes N. 16° E. and 

dips 68° · W. A secorid north-south fracture 

about 900 feet from the mouth is mineralized 

in the same manner as the main vein. PostN 

0 50 100 200 300 F'eet 

bearmg N.17° E., which has beendriv.en for over 

510feet, at which distance it is blocked by a cave. 

The country rock is schist of the Idaho Springs 

formation intruded by granite peg~atite. 

The veins cut in the part of the tunnel open 

for inspection are only fe~bly mineralized. A 

minor fracture, 230 feet from the portal, strikes 

N. 75° W. and dips 45° N. and shows 5 inches 

of unmineralized crushed schist below an inch of 

gouge. A second fracture, 290 feet from the. 

portal, stri.kes.N. 42° W. and dips 60° NE. and 

shows 2 feet of crushed pegmatite that carries 

a little disseminated pyrite. A fracture zone at 

390 feet strikes N. 83° W. and dips 50° N. and 

has been drifted in for 50 feet east of the tunnel 

and beyond a cave for 90 feet west. A winze, 

now: full of water, is sunk from the west drift. 

This fracture zone, which is about 1 foot wide 

LEGEND 

EJ 0 

Galena-sphalerite Barren veins fractures 

~ 

~ 

(Arrows mdic.ate 

direction of dip) 

Inaccessible 

workings 

Note: Wall rock IS Idaho Springs format1on 

with some pegmatite lenses 

FIGURE 72.-Geologic plan of Silver King twmel, in Spring Gulch. Surveyed by hand compass and pacing. 

mineral fracturing has taken place along this 

vein but has not offset the main vein. J 

The sorted ore, consisting of massive galena 

and chalcopyrite, such as is seen in the bins, 

is said to carry from 35 to 100 ounces of silver, 

12 to 35 per qent lead, .and 5 to 10 per cent 

copper per ton. The high silver content of 

some of the ore is probably the result of downward enrichment, although no secondary silver 

minerals were visible at the time of this survey. 

FmEMEN AND CONDUCTORS TUNNEL. 

The Firemen and Conductors tunnel is at an 

elevation of 8,500 ·feet on the north side of 

Spring Gulch about 1! miles northwest of its 

junction with South Clear Creek. A small 

stamp mill is near by; The tunnel is a crosscut 

and has gouge on both walls, carries a little 

disseminated pyrite both in the crushed rock 

which fills the fracture zone and in the walls 

for short distances from it. Some very small 

seams of quartz with pyrite were noted in the 

hanging wall of the west drift cutting across the 

schistosity. 

PIONEER TUNNEL. 

The Pioneer tunnel, a little over· a ffii.le north 

of Dumont on the divide between Spring Gulch 

and Mill Creek, was idle· and. inaccessible at the 

time of this survey, but is said to be about 1,000 

feet in length. A winze extending 170 feet 

below the timnel and several raises to the surface develop the vein. The. ore was hauled for 

treatment to a 30-stamp mill at Dumont owned 

by the company. 
344 GEOLOGY OF GILPIN,. CLEAR CREEK, AND BOULDER COUN'IIES, COLO. 

AL:MmA TUNNEL. 

The Almira tunnel, 1! miles north-northwest 

of·Dumont on the divide between Spring Gulch 

and Mill Creek, was inacc·essible at the time of 

this suryey. It trends nearly south and is 

about 350 feet long, with seve.ral short branch 

drifts.· 

GOLD CHEST TUNNEL. 

The Gold Chest group of claims, on the ridge 

between Fall River and the head of Spring 

Gulch, is opened by several shallow pits on a 

series of nearly parallel fissures that strike 

north-northeast and dip vertical or steeply west. 

The or·e in all these pits is iron-stained quartz. 

A crosscut tunnel to intersect these veins has 

been started from the ~outh wall of Fall River 

valley, about half a mile west of Hamlin Gulch 

at an elevation of 8,500 feet., The· tunnel was 

not entered, but the dump indicates that it can 

not be of great length. It cuts only schist of 

the Idaho Springs formation. A small amount 

of ore on the dump has a quartz-calcite-siderite 

gangue and carries galena and sphalerite with 

some pyrite and chalcopyrite. 

DUMONT AND VICINITY. 

BLUE RIDGE AND SENATOR MINE. 

The Blue Ridge and Senator mine 1s about 1 

mile squthwest of D'umont on the nose of a 

ridge overlooking Clear Creek, at an elevation 

of approximately 9,000 feet. The workings 

accessible at the time of this survey (see fig. 73) 

develop two veins, a northeastward-t:r:ending 

vein known as the Senlittor and a smaller northwestward-trending branching lode, known as 

the Blue Ridge. No large amount of stoping 

has been done on the Blue Ridge vein from the 

Middle West tunnel level, but stopes from the 

Upper West tunnel, locally 4! feet in width, 

extend for about 100 feet on either side of the 

raise. The Senator• vein has been extensively 

stoped for much of its length. 

In the Middle West tunnel the Blue Ridge 

vein is first exposed about 27Q feet from the 

portal, and it forks about 565 feet from the 

portal. None of the exposures show heavy 

mineralization and in most places the vein is 

practically barren. Near where it is first cut 

it shows merely a slip plane, with 3 inches of 

gouge next the hanging wall, and 2 feet of somewhat silicified ·granite gneiss. At. another 

place it consists of 15 inches of gray flinty~ 

looking·quartz apparently barren of sulphides. 

In a stope about 400 feet from the portal the 

vein is 1! feet wide, the lower half· being gouge 

and the upper half decc•mposed granite gneiss 

traversed by a l-inch stringer of white quartz 

and by a few narrow v-einlets of galena and 

sphalerite. 

The Senator is the principal vein of the mine. 

On the middle tunnel lev-el it cuts through the 

Blue Ridge vein, and th9 latter has not been 

found ·beyond this crossing. For the northern 

700 feet or so of its e~posure in the mine workings, the Senator ·vein is nearly parallel to a 

wide dike of bostonite p01~phyry. The vein is 

later than the dike,· follows either or both dike 

walls and finally leaves it enti~ely. North of 

the place where it crosses the Blue Ridge vein 

the Senator vein so far aB explored is in the 

porphyry dike and is practically barren. 

A smaller dike 1 to 5 feet wide of nonporphyritic bostonite runs nearly parallel . to the 

larger porphyritic dike ~nd. is ,exposed at five 

points in the mine workings. This dike has 

been traced on the surface for over a mile east 

of this mine. (See Pl. I, in pocket.) At a 

point in the lower east tunnel 140 feet southwest of the main shaft it is intrusive ih the 

bostonite porphyry. The nonporphyritic bostonite ·is mineralized locally tmd 'at one place is 

cut through by the Senator vein. The vein 

formation is therefore later than both bostonite 

and bostonite porphyry. 

In general abundant gouge· gives evidence at 

many points of extensive moyement along the 

Senator vein and makes heavy timbering necessary. The most heavily mineralized portion is 

in the southwest part of .the n1ine from 350 to 

1,200 feet southwest of the 1nain shaft. On 

account of the softness of the vein and the 

heavy timbering used the ore can be studied at 

only a few points, the best exposures being near 

the new. raise about 675 feet southwest of the 

main shaft. This raise, which at the time of 

survey was up 115 feet, is being driven in the 

hope of reaching an ore shoot that on the higher 

levels carried rich ores. At this raise on the 

tunnel level the vein is 18 to !~0 inches wide, 

with gouge-covered slip planes on each wall, 

bounding crushed granite gneiss traversed by a 

single sulphide lens 2 inches in maximum 

width and extending ~ feet horizontally. At 

the top of the raise the vein consists of 4 to 8 

feet of more or less fractured granite gneiss 
CLEAR CREEK COUNTY. 345 

traversed by several slickensided slip· planes I are wholly quartz and sulphides in the center but 

and by sulphide veirilets which have been more which grade gradually into the ~ranite gneiss. 

LEGEND 

Bostonite 

(Not porphyritic.) 

Granite gneiss 

~~~~~;~r~~gs 

~ 

~ 

. 

. Galena-sphalerite 

veins 

6j· 

Unmineralized 

fractures 

Arrows indicate d i,rection of dip 

R, Raise 

W, Winze· 

C, Chute 

N 

0 50 100 200 300 400 Feet 

FIGURE 73.-Geologfc plan of portions of the Blue Ridge and Senator mine. 

or less crushed. Sulphides occur not only in 

the regular veinlets but in irregular masses 

(probably metasomatic replacements)~ which 

The Blue Ridge vein, as stated, is in 

places barren or only feebly. mineralized. 

few places narrow veinlets of galena 

most 

In a 

and 
' 346 GEOLOGY OF GILPIN, CLEAR CREEK, AND BOULDER COUNTIES, COLO. 

sphalerite were noted. The mineralization of parts of the vmnB where enrichment in silver 

the Senator vein is also of the galena:-sphalerite or in, gold has ta:k:en place. Most of the un 

type, the ore minerals being' sphalerite and altered primary ore appears to carry only 

galena. with a little local chalcopyrite and small amounts of the precious metals, as shown 

pyrite in a gangue of quartz and calcite. Some by the two followjng assays of heavy sulphide 

barite is locally present. ore free from seco:rrdary silver minerals. Both 

The ores exposed in the middle and lower assays were made for the Survey from samples 

tunnels are in general unoxidized, oxidized collected from thE, Senator vein by Mr. Basore being o?served only in the upper tunnel, tin-No. 1 from 115 feet above the tunnel level 

where remnants of galena and sphalerite occur in· the· raise, 675 feet sout_hwest of the shaft, 

in a porous iron-stained matrix in which small and No.2 from a p·oint near the tunnel level. 

acicular crystals of cerusite are abundant. 

Specimens of ore from the Senator vein Assays of unenriched silver ores from the Senator vein. 

taken from the bins at the Middle West tunnel 

are of especial interest because they· show the 

importance of downward sulphide enrichment 

in the mineralization of the vein. Small crysGold. ) 

Ounce. 

0.03 

• OS 

Silver. 

-

Ounces. 

7.17 

3. 10 

Copper 

(wet). Lead. Zinc. 

Per ct. Per ct. Per ct. 

0.20 76.50 1.20 ........... 51.00 . ........ tals of proustite (rubJisilver) and of polybasite 1 No.1. ...... 

are developed along fracture s-eams in the No. 2 · · · · · · · 

original ore and upon crystals of quartz in ____ _!__ __ __!_ ___ ....!...__ __ __!_ __ __!_ __ 

vugs. Mostly they are associated with sec- A shipment of 2~li tons of smelting ore from 

ondary chalcopyrite in aggregates or coatings the raise above roferred to ~howed gold 0.08 

of minute crystals and in less degree with ounce, silver 47.5 ounces, lead 22.9 per cent. 

seconda~y galena. · Part of the chalcopyrite This ore oame from depths of about 500 to 

-is later than the secondary silver minerals, for 600 feet vertically below the surface, and it is 

in places it coats them. probable from the considerable silver content 

' . -Microscopic study of polished sections. of ore that it has suffered some enrichment. Secfrom the Senator vein shows that the secondary ondary silver minerals were noted by the 

silver minerals are not confined to fractures in writer in ore from a depth of about 600 feet 

the original ore but also occur, as in a number m another part of the Senator vein. The 

of other silver veins, in the solid ore as metaso- very rich silver oro thus far obtained in the 

· matic replaceruents of the primary minerals~ mine has come from vertical depths not 

(See :fig. 14, p. 144.) It is believed that galena greater than 450 feet, and the evidence at 

originally occupied the entire space· between hand indicates that. silvero enrichment extends 

the sphalerite and the galena shown in this to a depth as gretLt as 600 feet only where 

figure and that the polybasite has developed local fracturing has rendered the vein unusuby metasomatic replacement of the galena. ally pervious to descending solutions. The 

Secondary chalcopyrite is also present, partly most promising field for exploration would 

deposited contemporaneously with the poly- appear to lie on the Senator vein above the 

basite and pa~tly later, replacing the polybasite lower and possibly above the middle tunnel. 

along fractures, as shown in the :figure. It is As in most of the mines of this district, in 

significant that in the enriehed ores of this which downward enrichment has been a 

vein, as in those from other silver veins, the prominent factor, the precious-metal content 

galena has undergone replacement while the is exceedingly irregular. The few assays availsphalerite ~as been wholly immune. This is a able show that sonte oxidized ore from near 

reversal of the relations characteristic of the the surface carried Beveral ounces of gold and 

oxidized zone and is attributed (see p. 142) to only a few ounces of silver. On the other 

the neutral or alltaline nature of the waters hand, two shipment:;; of ore from stopes in the 

which deposited the secondary silver minerals. upper tunnel on the Blue Ridge vein are 

The ore of the Blue Ridge and Senator veins reported to have g:iven gold 1.6 ounces and 

is . probably of workable grade only in those silve~ 3 ourices, and gold 2.55 ounces and silver 

1 :Carkgray,metallic; reactsforsilver,arsenic,antimony,andslightly 6·ounces .. It appears, therefore, that gold has, 

for copper. as usual, been concentrated near the surface, 
CLEAR CREEK COUNTY. 347 

and that silver has been leached and redeposited at greater depths, enriching ore which 

succeeds the leached and oxidized ore. This 

enriched ore, which extends locally to depths 

'of about 600 feet, has constituted the main 

resource of the mine. · Its gold content is 

generally between a trace and· 0.2 ounce, but 

its silver content generally exceeds 50 ounce~, 

and in many shipments ·exceeds 100. ounces, 

varying with the abundance of the secondary 

silver minerals, polybasite and proustite. The. 

following sampling-works ass·ays of shipmE:mts 

from the Senator vein from 1891 to 1893 give 

some idea of the metal content of thi3 class of 

ore: 

Sampling-'Works assays of ore from Senator vein, 1891-1893. 

~I Gold. Silver .. Lead. Zinc~ 

Net 

po1tnds. Ounce. Ouncls. P. ct. P. ct. 

4,000 0. 10 45.50 10. 15 9.50 

2,344 Trace. 49. 50 14.50 7.00 

860 Trace. 91.50 34.00 5.00 

3, 704 Trace. 45.50 ........ 10.00 

3,109 Trace. 57.00 22.00 11.00 

Below the zone of enrichment occurs the 

unaltered primary ore, whose content in precious metals appears in general to be low, as 

shown by the assays on page 346. 

The gross production of the property is said 

to have been about $250,000. 

OHIO CREEK TUNNELS. 

Two tunnels belonging to the Ohio Creek 

Gold Mining Co. are in Ohio Gulch about a 

mile southwest of Dumont, at elevations of 

8,250 and 8,400 feet. The country rock in tlw 

vicinity is granite gneiss, inclosing several 

smoll detached masses of schist of the Idaho 

Springs formation. 

The lower tunnel, after trending N. 80° W. 

for 60 feet between schist walls, cuts a vein 

striking N. 25° E. and follows it southwestward 

for more than 100 feet to a door which prevented further examination. This vein, which 

dips· 60° W., cutting schist of the Idaho Springs 

formation, consists of gouge and crushed rock 

in n1ost places about 3 inches wide. A small 

amount of ore on the dump showed white 

quartz, siderite, and a little rather fine grained 

pyrite. 

The upper tunnel is a crosscut 160 feet long 

that bears N. 17° W. and has intersected two 

veins. The first vein, which bears N. 32° E. 

and dips 35° NW., is cut ~100 feet from the 

portal and has been followed for 20 feet east 

to where there is a raise to the surface and for 

100 feet west to where progress is blocked by 

a cave. This vein has schist walls that in 

most places show only crushed rock and an 

in~h or so of gouge next the hanging woll but 

that near the caye show a few l-inch stringers 

of pyrite and calcite adjacent to the fracture. 

The second vein is cut by this tunnel 160 

feet from the portal. It strike~ N. 22° E. 

and dips 55°-60° NW. Its west drift, which 

is over 300 feet long (the first 110 feet being in 

schist and the remainder in granite g~eiss) cuts 

a 30-foot east-west bostonite ( ~) dike 250 feet 

from the tunnel. This vein varies from onehalf inch to 10 inches in width and is almost entirely crushed wall rock with very little mineral. 

At. 120 feet west of the tunnel the vein splits, 

and at 200 feet the footwall streak goes out of 

the drift. The hanging-wall streak continues 

along the drift to the porphyry dike but does 

not go through it. · 

No data were' available as to the value of 

the ore or the production, but the production 

has evidently been small. 

4-C TUNNEL. 

The 4-C tunnel, on the north side of Clear 

Creek, about three-fourths of a mile west of Dumont, was not in operation at the time of this 

survey. The priiicipal geologic features are 

shown iri figure 74~ to which the lettering of 

veins used below refers. 

Vein A: About one-half inch of gray quartz 

and pyrite bordered by 6 inches of crushed wall 

rock. 

Vein B: A vein showing, at the west face, 1 

inch of gray quartz. carrying pyrite and 1 inch 

of crushed schist. 1 

Vein C: A vein showing a ma..ximum .of 4 

inches of gray quartz carrying a little pyrite. 

Vein D: A vein showing, on the east of the 

tunnel, about 1 foot of altered granite gneiss 

with a few small lenses and pockets of pyrite. 

West of the tunnel the mineralization is very 

weak. The porphyry occurring near this vein 

is too altered for precise identification but is 

probably monzonite. 
\. 

348 GEOLOGY OF GILPIN, CLEAR CREEK, AND BOULDE~ COTJ~TIES, COLO. 

' No stoping of importance has been done on 

any of the veins cut by this tunnel, and no data 

as to the value of the ore are available. 

LEGEND 

~~~;~/, ')I -IGranite g~eiss 

~· Idaho Springs formation 

EJ 

Pyritic ve·,ns 

0 

Unmineralized · fractures 

Arrows indicate 

direction of dip 

100 50 0 roo Feet 

FIGURE 74.-Geologic plan of 4-C tunnel. 

SILENT FRmND VEIN. 

N 

The Silent Friend vein, on the south side of 

the valley ·of Clear Creek, about one-half mile 

south of the village of Dumont, is developed by 

two tUn.nels vertically about 172. feet apart. 

(See fig. 7·5.) 

The Silent Friend vein strikes about N. 45° 

W. and dips 35°-65° NE. The wall racks are 

schist of the Idaho Springs formation and altered bosto:r;Iite 0) porphyry, carrying more or 

less disseminated p}rrite. ·The vein, which cuts 

sharply through the porphyry, than which it is 

distinctly younger, is a strong fracture zone following in general the northeast side of the dike, 

though in places cutting it and in places leaving 

it entirely. The lower tunnel shows a notable 

forking of the vein between 570 and 800 feet 

from the portal, but this is not apparent in the 

upper tunnel. The vein is offset slightly at 

several points by faults trending northeast and 

is offset for over 20 :feet by a mineralized fracture known as th.e Fault vein, which strikes 

nearly north and dips 35 °-40° W. 

Throughout ·most of its exposed portion the 

Silent Friend vein co:rrsists of 2 inches to 3 feet 

9f wall rock traversed by numerous subparallel 

Lower eunnel 

N 

Note: Vertical distance between 

tunnels about 17Z feE:t 

LEGEND 

a 

Pyr:itic 

vems 

ESJ Unmineralized fractures 

r;[J 

in=~~e 

(Arrow:~ indicate di~ection of djp) 

R, Raise 

W, Winze 

Note: Wall rock is Idaho Sprin8s 

formation except where 

porphyry is shown 

±' 

o.___,so_-'-roo ___ z_._oo...,...-_-Jaoo Feet ~ 

FIGURE 75.-Geologic plans of workingn of Silent Friend mine. Platted 

from hand compass ao.d pacing surveys. 

fractures and carrying disseminated pyrite. In· 

its more heavily mineralized parts it carries also 

distinct veinlets or irregular lenses of pyrite in 

crystals one-half inch in 1naximum size or of 

pyrite and gray quartz, ranging in width from 

less than an inch to 3 inc he:', arid in one place to 

1 foot. 

The nortl;l.east fork of the vein in the lower 

tunnel (A, fig. 75) lies between schistwalls and 

is known as the Arrowhead vein. The southwest fork, which may·be considered the Silent 

Friend vein proper, follows i~he contact between 
CLEAR CR.EEK COUNTY. 349 

schist and a porphyry dike. The, mineraliza- Few data were obtained concerning · the 

tion in the two forks is of similar character. value of the ore from the Silent Friend workAbout 600 feet from the portal of the upper ings, but over 6 tons showed, according to 

tuilnel (B, fig. 75) the main vein cuts through sampling-works assays, 0.08 to 0.2 ounce of 

a porphyry dike and is joined by a branch vein gold and 2.1· to 62.9 ounces of silver. The . 

which follows the southwest wall of the dike. higher silver values were in ore from slight 

The Fault vein is cut in the lower tunnel depths' and are probably ·attributable to 

480 feet from the portal and in the upper downward enrichment. The largest and richtunnel 440 feet fron1 the portal. It is a zone est bodies of ore have been found in the Silent 

of fractured and decomposed schist and Friend vein near. its .intersection with the 

porphyry fto1n 3 to 4 feet. in width, along Fault vein, and it is significant that these ore 

which the Silent Friend vein has been offset bodies show not only pyritic ore bu.t also ore 

for a horizontal distance of over 20 feet. of the galena-sphalerite type. The free gold 

Most exposures of the Fault vein show no occurring in quartz was probably of primary. 

mineral, but a short crosscut following it in rather than of secondary origin. 

the lower tunnel shows 10 inches of gray According to Mr. Philip Stanhope one sample 

quartz and pyrite in bands parallel to the of ore from the Silent Friend vein just above 

general trend of the vein. Some of the pyrite its junction with the Fault vein assayed gold 

has been crushed by postmineral movement 10· ounces, ·silver 65 ounces, and copper 15 per 

along the vein, and breccia and gouge have cent; and ore from the Silent Friend vein just 

been produced in many places. below the Fault vein carried from 1.5 to 7.5 

A third vein known. as. the Hecla is exposed ounces of gold. . 

for the first 440 feet of the lower tunnel. The gross production is said to have been 

Throughout most of this distance this vein about $22,000; 

EARL OF. RENT MINE. 

shows only gouge or barren gray quartz, but ·· 1 

about 300 feet fron1 the portal several veinlets of 

quart~ and pyrite up to half an inch wide are 

seen. The vein has no commercial importance. 

The Earl of Kent vein, on the south side of 

South Clear Creek opposite Dumont, is close 

to the valley bottom and is in consequence 

largely covered by slide. It is developed by 

four crosscut tunnels-the Puzzler, New,. 

Lower Kent, and Upper Kent, named from 

west to east. The Puzzler i.n,clined shaft, 275 

feet deep, starts from the Puzzler tunnel. 

That there has been much movement 

subsequent to mineralization along the Silent 

Friend and Fault veins is shown by the presence of gouge and breccia and by crushing 

of the ore. 

The predon1inan t n1ineraliza tion of all of the 

veins 'of this mine belongs to the pyritic type, 

much of the ore consisting of a heavy dissemination of pyrite in schist, though in the 

more heavily mineralized portions veins of 

nearly solid pyrite are present. In a few 

places, however, as in the Silent Friend vein, 

near its intersection with the Fault vein, ore 

of the galena-sphalerite type is also present. 

In addition to its predon1inant sulphide, this ore 

carries chalcopyrite, pyrite, tennantite, and a 

little sphalerite in a quartz and calcite gangu~. 

Specimens fron1 the ore bins show the galena 

ore cutting the pyritic ore in irregular stringers.· 

.A pocket of rich ore containing free gold in 

white quartz was found in the Silent FrienCl 

vein in the lower tunnel about 40 feet beyond 

(below) its junction with the Fault vein. 

The Puzzler tunnel, 245 feet long, cuts the 

Earl of Ken.t vein 120 feet from. the portal. 

A drift easterly on the vein was followed for 

290 feet to a point, wh~re the workings are 

caved. 

The New cross'cut, 4 70 feet long, cuts the 

Earl of Kent vein 370 feet from the portal and 

develops it by drifts that extend 80 feet west 

and 370 feet east. The Lower Kent tunnel is 

260 feet long to the Kent vein with a 100-foot 

east drift' and 160-foot west drift. The Upper 

Kent tunnel is 490 feet long and cuts the vein 

180 feet from the mouth. A drift to the ~est· 

is 150 feet long. 

The predominant wall rocks in all the workings are schists of the Idaho Springs formation · 

with rather abundant small lenses of granite 
350 GEOLOGY OF GILPIN, CLEAR CREEK, AND BOULDER COUNTIES, COLO. 

pegmatite. In the New crosscut the Kent 

vein, where first intersected, has a porphyry 

footwall, which continues along the south wall 

of the west drift but is not exposed elsewhere. 

The v·~in is evidently younger than the 

porphyry, into which it sends two. small 

stringers and which has been very much 

altered and impregnated. with pyrite. The 

porphyry is probably bostonite, though it is 

so much altered that definite determination is 

not possible. The same variety is exposed in 

:the Silent Friend 1nine. 

The Earl of Kent vein strikes on the average 

about N. 55° W. and dips 15°-45° NE. Slight 

variations of dip where the vein is relatively 

flat produce large variations in the trend of 

the drifts, as, for example, at the Puzzler shaft 

where the drift turns through at least 50°. 

The vein has few branches. It varies from 

one-half inch to 4 feet in width with an average 

of about 10 inches and consists of altered, 

somewhat crushed wall rock that carries more 

or less abundant disseminated pyrite and is 

cut by narrow. vein lets of pyrite and gray 

quartz one-eighth to 1 inch wide. In .a few 

places a very m~or amount of chalcopyrite is 

present with the pyrite, and at one place a 

few small crystals of galena were seen associated with dark-gray quartz. 

The tunnels intersect a number of fractures 

whose strike parallels the Kent vein and 

whose mineralization is similar but whose dip 

is steeper. They also intersect a northeastsouthwest series of barren fractures, one of 

which near the face of the east drift of the New 

crosscut strikes N. ·50° E. and dips at 32° W., 

and has displaced the east side of the Kent 

vein 6 feet.. The New crosscut south of the 

Kent vein follows a fault' that dips 68° W., 

cutting both the porphyry and the vein arid 

displacing the vein 8 feet. Postmineral movement along the Kent vein has developed in 

most places a small amount <?f gouge on one or 

both walls. 

There has been some stoping from the shaft 

levels a~d the Lower Kent tunnel. From this 

material, which is said to average about $10 a 

ton there has been a reported production of ' . $12,000, including a small amount of smelting 

ore valued at $25 per ton. About 85 per cent 

of the valuable metal is gold and the other 15 

per cent silver. · 

BIG :DIPPER VEIN. 

The _Big Dipper vein is _about one-fourth 

mile south of South Clear Creek, opposite ~he 

east end of the town of Dumont. It is opened 

by a 150-foot cros~1cut to the vein and by a 

110-foot drift eastward on the vein. A shaft 

near the crosscut {lXtends 50 feet below the 

tunnel level. The country rock is schist of 

the Idaho Springs formation, with some pegmatite lenses .. 

The vein strikes N. 76° W. and dips 40° N. 

It varies from 8 to 18 inches in width (average 

about 10 inches). The vein material is largely 

crushed wall rock with abundant disseminated 

pyrite, but in most places carries a 1! or 2 inch 

veinlet of ·quartz and. coarse -pyrite next the 

hanging wall and ~1as one-half inch to 1 t 

inches of gouge on each wall. 

A fault that cuts o:ff the Big Dipper vein 110 

feet east of the crosscut strikes N. 32° E. a:rid 

dips 77° NW. It is unmineralized, but contains 6 to 12 inches of crushed schist and shows 

a slickensided hanging wall with strire about 

parallel to the dip. This fault also cuts but 

does not displace a yery slightly mineralized 

north-south fracture dipping 80° W. A little 

drifting beyond the :main fault has failed to. 

expose the vein,· though a crosscut 20 feet 

south and 10 feet eas~ of the place where the 

Big Dipper vein . was lost cuts a small frac-· 

ture plane, which strikes N. 85° W. and dips 

48° N. If this is the ·~ontinuation of the vein, 

the displacement has been about 25 feet, the 

east side of the fault having moved southwest. 

A little stoping has been done west of the 

shaft for 40 feet along the- vein, but no data. 

concerning the value of the ore were available. 

SYNDICJ..TE MINE. 

The Syndicate workings, on the south side 

o{Clear Creek valley a short distance southeast 

of Du~ont, include four drift tunnels-two 

lower ones, on a ·west•em hillslope, known as. 

the Western Syndicate workings and two 

higher ones, on the eaBtem slope of the same, 

hill known as the Et;>Stem . Syndicate work-· ' . ings. The exact corre:~pondence of the vems. 

developed in the eastern and western workings. 

has not been determined, and they will there--

fore be separately described. 

The Eastern Syndica.te workings consist of 

two tunnels at an elevation of appro~mately 
OLEAR CREEK COUNTY. 351 

8,700 feet, the portal of the upper being about 

75 feet above and 150 feet southwest of the 

portal of the lower. The upper is about 250 

feet long and is entirely on the vein. The 

lower, which alone was carefully. studied, is 

about 450 feet long and follows a well-defined 

vein that strikes generally nearly east-west and 

dips 35°-40° N. In general this vein, is not a 

fissure filling but is made up of fractured and 

altered schist and pegmatite, in places barren 

but elsewhere carrying abundant pyrite as a 

replacement of the wall rock near a number of 

subparallel fracture planes. Silication has locally replaced the schist with white and gray 

quartz in the more pyritic portions. The vein 

varies fron1 2 to 5 feet in width.· Although . ~. ! 

0 50 100 200 Feet 

to several feet,. in ·one place to 5! feet. For 

the last 250 feet of the main drift it shows only 

sparse mineralization but becomes well mineral-

.ized west of its junction with two branches 

(A, fig. 76). The br~ch exposed in the short 1 

crosscut 560 feet from the portal is 14 inches'\. 

wide and consists of a granular association of 

quartz and pyr,ite, the latter being most abundant in the 6 inches. next the footwall. The 

branch 450 feet from the portal is unimportant. The short crosscut to the south 425 

feet· from the portal-exposes two nearly parallel veins having several seams of gray quartz 

and pyrite as much as an inch across, bordered by several inches of wall rock carrying 

disseminated pyrite. These veins are replaceETI 

Pyritic 

veins 

LEGEND 

[::=i:] (Arrows indicate [___J directionofdip) 

Barren 

fractures 

Note: Wall rockls schist of Idaho Sprin~s formation 

R1 Raise 

w, Winze 

FIGURE 76.-Ge:>Joglc pbn of upper Western Syndicate tunnel. 

mainly a replacement vein, it consists in one 

place of network of small quartz-pyrite stringers traversing pegmatite for a width of 1! feet. 

About 350 feet from the portal a vein striking N. 20° E. and dipping 75°-80° W. is cut 

and has been followed by a branch drift for 

about 130 feet. Though barren in most 

places t~s vein shows locally 1! inches of gray 

quartz carrying a little pyrite. The lower 

and upper tunnels are connected by a raise. 

The upper tunnel of the western workings 

starts in the small gulch due south of Dumont. 

(See fig. 76.) The wall rock is entirely schist 

of the Idaho Springs formation. As exposed 

in this tunnel the Syndicate is a branching 

vein in places barren and elsewhere heavily 

mineralized. Although in most places less 

than 6 inches in width the vein locally widens 

ments of the wall rock rather than fillings of 

open fractures. 

About 300 feet from the portal the Syndicate 

vein obtains its greatest exposed width of 

about 5! feet, its detailed character heing as 

follows: 

Section of Syndicate vein about 300 feet from portal of uppe:r 

western tunnel. 

Hanging wall. . Ft. in. 

Pegmatite, traversed by ill-defined stringers of 

quartz and pyrite and carrying some disseminated pyrite. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 

Pegmatite, carrying only a little pyrite along small 

fractures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 3 

Silica, cherty, nearly barren ............... ~...... 1 

Pegmatite, with sparsely disseminated pyrite...... 5 

Pegmatite, carrying abundant disseminated pyrite. 2 0 

Rock, crushed and altered, with very little pyrite.. 1 · 0 

Footwall. 

5 0 
352 GEOLOGY OF GILPIN, CLEAR CREEK, AND BOULD:em COUNTIES, COLO. 

The vein, as exposed in the lower w.estern 

tunnel, is similar to that in the upper tunnel, 

except that it sends off no important branches. 

About 650 fe·et from the portal the vein is 4 

feet wide ·and shows next the hanging wall a 

slip plane with little gouge, the remainder of 

the vein consisting of pegmatite traversed by 

obscurely bounded veinlets of quartz and py-

-rite. Pyrite is disseminated throughout the 

pegmatite,· but becomes more and more abundant as the veinlets are approached. Some of 

the pyrite crystals are one-half inch across. A 

few small vugs in the veinlets are lined with 

crystals of quartz and pyrite. 

Assays from various parts of the mine, taken 

from a report on the property by Mr. George 

Collins, show that the gold content usually lies 

between 0.1 and 0.5 ounce, though occasionally reaching 1 or· even 1.5 ounces .. No progressive change in the gold content with depth 

after the oxidized zone has been passed can be 

traced. The silver content in ~the western 

.workings is usually between 1 and 4 ounces 

but is occasionally as great as 6 ounces. In the 

shallower workings of the Eastern Syndicate 

silver occasionally runs as high as 40 ounces 

and may be t,he result of enrichment by descending surlace waters. The richer bodies of 

ore appear to be very irregular and are more 

like pockets than persistent and well-defined 

shoots. 

The gross production of the property is said 

to be about $16,000. 

FREELAND TUNNEL. 

The Freeland tunnel, which begins on the 

south side of South Clear Creek, about half a 

mile east of, Du.mont, is a crosscut, bearing 

S. 12° E. and extending south for a little over 

a mile. It was driven ·to devel9p the Freeland 

and other veins at the head of Turkey Creek 

near the town of Freeland. A cave about 

5,210 feet from the portal bars access to the 

principal veins. 

The country rock is largely schist of the 

Idaho Springs formation for the first 3,600 feet 

from the mouth and beyond 3,600 feet is granite gneiss with l~nses of schist and pegmatite. 

(See fig. 77.) Dikes of several varjeties are 

cut by the tunnel. The 20-foot bostonite 

porphyry dike, cut_ 2,745 feet from the portal, 

. contains disseminated pyrite throughout and 

zoo 

J l 

LEGEND 

l:j:~-~{~03 Granite gneiss 

Idaho 

D. 

Barren fracture 

G 

Pyritic vein 

Arrows indicate direction of dip 

o zoo 400 Feet 

N 

.\ 

FIGURE 77 .-Geologic plan of Freeland tunnel. Surveyed by compass 

and pacing . 
CLEAR CREEK COUNTY. 353 

carries mi its footwall 1 inch of gray quartz 

and pyi·ite which in places follows the contact 

and elsewhere lies in the schist ~bout a foot 

below the contact. A dike of basalt porphyry 

4 feet in width, cut 3,185 .feet from the mouth 

of the tunnel is amygdaloidal, the amygdules 

being calcite. A dike of bostonite, cut 3,475 

feet frmn the 1nouth, is .tr~versed in all directions by s1nall sean1s of pyrite. A 20-foot dike 

of ;much altered porphyry (probably n1onzonite porphyry), cut 4,200 feet frmn the portal, 

contains abundant dissen1inated pyrite. The 

adjacent granite gneiss is also n1ineralized for 

a few feet fron1 the contn,ct. 

Nun1erous fractures are cut by the tunnel 

and several of thmn are 1nineralized. The 

nun1bers in the following descriptions correspond to those in figtlre 77. 

1. A vein striking N. 79° E. and dipping 

45° N., in general parallel to the schist.foliation. 

At its widest part it is 1! feet wide, the lower 

half consisting of gray quartz containing some 

pyrite and the upper half of a' post1nineral 

breccia of schist frag1nents. At one place it 

carries a 1!-inch veinlet of solid pyrite. 

· '2. A 1 to 4 inch sharp-walled vein of gray 

quartz carrying pyrite. 

3. A 1!-inch stringer of dark-gray quartz 

and pyrite, separated frmn the hanging wall 

by one-half inch of gouge. 

4. A one-fourth to 1 inch tigl~t stringer of 

gray quartz and pyrite. 

5. A zone 4 inches to 2 feet wide of crushed 

wall rock so1newhat in1pregnated with p~rite. 

Son1e of the crushing is later than the mineral-. 

ization. This is supposedly the Syndicate. 

vein. Two parallel fractures lie 4 and 6 feet 

above this vein. 

6. A flat branching vein of gray quartz and 

pyrite that runs about parallel to the line of 

the tu1mel. At its widest it shows 4 inches of 

gray quartz carrying pyrite. 

7. '1.\,ro intersecting fractures-a 5-foot 

northwest to southeast zone traversed by 

nun1erous stringers of quartz and pyrite and a 

· narrow northeast to southwest zone containing 

crushed quartz and pyrite. 

8. Two v,eins which strike parallel but dip 

town,rd each other. The northern vejn is 4 

:inches wide and is a breccia of pyritiferous 

quartz cetnented by quartz. The south vein 

is 2 to 3 inches wide and consists of irregular 

44214°-17-23 

stringers of white. and gray quartz and pyrite. 

The country rock bet,veen these veins is altered 

and contains fine-grained disseminated pyrite . 

. 9. A one-fourth to · 1 inch veinlet of gray 

quartz containing pyrite. 

10. A fracture, zone along which the country 

rock is altered and contains abundant disseminated pyrite. A one-fourth to '4 inch veinlet 

contains ·onl}7 clear quartz. 

11. A sharp-walled vein, three-fourths inch 

to 2 inches ~n width, of white and gray quartz, 

with pyrite irregularly distributed throughout 

and with some small vugs in its central part. 

12. A white and gray quartz vein 2 to 7 

inches· wide, which carries pyrite and in places 

consists of nearly pur~ pyrite in stringers 1 t 

inches in maximum. width. 

13. A fracture about 3 inches wide, ·containing 11 inches of decomposed schist next the 

footwall, one-half inch of siderite and pyrite 

and 1 inch of altered schist containing disseminated pyrite. 

None of the veins described have been worked 

from the tunnel, but it is repO'rted that the 

Freeland ve~n, beyond the cave in the tunnel, 

has been drifted on to some extent. 

The unmineralized fracture zones vary in 

width, reaching a maximuin of several feet. 

One of them, 4,340 feet from the mouth of the 

tunnel, is a 2-foot zone of brecciated schis.t and 

pegmatite, well cemented by finely crushed 

wall rock. 

I 

So far as known· there has been little production from the Freeland tum10l. 

GILPIN ·AND CLEAR CREEK 1'UNNEL. 

The Gilpin and Clear Creek tunnel, on the 

north side of South Clear Creek about onefomth nrile east of D:umont, is a crosscut driven \ 

N. 10° W. for 870 feet to develop a large group of 

clain1s in the ridge between Spring Gulch and 

Clear Creek. The country rock throughout the 

tunnel is schist of the Idaho Springs formation. 

Seven veins have been cut by the tlinnel, 

though practically no· drifting has been ·done 

on any of them. The first, exposed 220 feet 

in from the mouth, strikes N. 50° W. and dips 

40° NE. It consists of one-half to 1 inch of 

altered schist that carries gray quartz and a 

little pyrite. 

Three veins are cut 260 feet from the n1outh 

of the tunnel. The first of these veins strikes 

I . 

I 
354 GEOLOGY OF GILPIN, CLEAR CREEK, AND BOULDER COUNTIES, COLO. 

N. 75° W. and dips 8.5° N. and consists of 4 to 8 

inches of altered wall rock containing disseminated pyrite and trafl:sversed by a l-inch 

stringer of quartz and pyrite. This vein is 

cut off by a flat vein, 2 to 4 inches wide, ~triking N. 55° W. and dipping 30° N. and consisting 

of gray quar~z with pyrite. The third vein, 

consisting of about 1 inch of quartz ancl pyrite, 

strikes N. 75° W. and dips 80° N. The wall 

rock between this vein and the flat vein is more 

or less altered and contains disseminated pyrite 

near the cros_sing. 

A -~-inch stringer of quartz and pyrite, 340 

feet from the mouth of the tunnel, strik~s N. 

75° W. and dips 80° S. A vein 605 feet from 

the portal strikes N. 70° W. and dips 40° N. 

and is developed by short drifts east and west. 

The vein is about 2 feet wide, consisting of 

crushed, somewhat silicified schist and pegmatite containing disseminated pyrite. In the 

east drift a 2-inch stringer of quartz contains 

galen.a, sphalerite, pyrite, and chalcopyrite, 

with some barite as a gangue mineral just below 

the hanging wall. In the west drift the vein 

is represented by four fracture3, with the intervening schist more or less 'altered and pyrit.ized. 

The pyrite here is· coarse grained, cubes half 

an inch on a side being common. At the face 

of the tunnel there is a 1-inch veinlet of gray 

quartz earry.ing pyrite and chalcopyrite; it 

strikes N. 73° W. and dips 55° N. 

No ore has been mined from this tunnel except a small amount taken from the drifts on 

the vein 605 feet from the portal. 

A concentration and amalgamation mill on 

the south side of Clear Creek a short distance 

west of the mouth of the tunnel is part of the 

mine property. 

SUNSHINE MINE. 

The Sunshine tunn~l,' on the north side of 

Clear Creek valley immediately northeast of 

the village of Dumont,- is about 200 feet in 

length and develops a single vein striking about 

N. 60° E. and dipping· about 70° NW. The 

wall rock is schist of the Idaho Springs formation. The vein shows a maximum width of 

about 3 inches and consists of gouge and of 

gray quartz carrying pyrite. Locally the vein 

has been reopened and some veinlets of siderite 

deposited. A specimen from the dump shows 

a small veinlet of quartz, chalcopyrite, and 

galena traversing the pyritic ore. · 

The Sunshine shaft, 30 feet deep, near the 

mouth of the tunnel, is on another vein which 

strikes N. 75° W. and dips about 40° N. The 

ore on the shaft dump is largely quartz and 

pyrite with somt:r later siderite and a little 

secondary specult,rite. 

A composite sa.mple including both milling 

and smelting ore from the tunnel vein is said 

to have assayed gold 0.64 ounce and silver 

5.4 ounces. 

· Other assays are reported as follows: 

Assays of ort from the Sunshine mine. 

Gold. Silver. Copper 

(wet). 

Ounces. Ounces. Per cent. 

3.24 15.00 ................... l. 60 11.40 3.20 

2.40 17.60 :-········-"'"' 3. 10 '18.13 ................. 3.40 22.80 7. 10 

Practically no ore has as yet been shipped. 

AL:BRO VEIN. 

The Albro vein on the north side of Clear 

Creek about one-half mile northeast of Dumont is developed 'by several shafts and drift 

tunnels, most of whi.ch have long been idle and 

are inaccessible. At the time of this survey 

mining was in prog:r~ss through . a shaft 185 

feet deep with short levels at 70, 150, and 1,75 

feet. The general strike of the vein is nearly 

east and west and the dip 30°-50° N. One of · 

the best exposures i:; in a stope near the east 

end of the 150-foot lt;)Vel, where the vein has a 

width of 3 feet, consi'sting, next the hanging 

wall, of 6 inches of silicified ·schist and pegmatite carrying much disseminated pyrite, suceeeded below by It feet of much less altered 

schist carrying only t.mall amounts of disseminated pyrite but trav-ersed by a few small sulphide v~inlets, and by 8 inches of schist and 

pegmatite carrying very abundant disseminations of pyrite, galena, sphalerite, and chalco- . 

pyrite. In most plaees on the 150-foot level 

the vein is 8 inches to 1 foot in width and consists of altered schist nnd pegmat_it~ which carries disseminated pyri.te and is cut locally by 

veins of solid sulphides. One vein, 3 inches 

wide, cousists almost wholly of sphalerite and 

ehalcopyrite. Some of the pyrite of the vein 

is extremely fine grained. The ore now being 
CLEAR CREEK COUNTY. 355 

mined fro1n the Albro vmn, although smne- of the schist wall rock (Idaho Springs fonnawhat si1nilar mineralogically to that of , the tion). 

Lawson group of silver mines, differs frmn it. The vein consists of fractured and altered 

by containing more chalcopyrite and more gold. country rock containing more or less dissmniIn general it is more comparable with that ob- nated pyrite. .The hanging wall. is marked 

tained farther east frmn such veins as the tl;lroughout by one-half to 1 inch· of gouge and 

Gladstone, near Idaho Springs, and the To- generally by a slip plane, 16· inches to 5 feet 

peka, near Russell Gulch. Smelting ore from below the hanging wall, that limits the nlinera stope above the 150-foot level is said to have a.lization on the other side. The better ore is 

run as high as 2! <?r 3 ounces in gold. Silver near the hanging-wall slip and averages 10 

averaged 12 to 14 ounces (maximun1 25 ounces) inches in width. In this part of the vein numancl copper 7 to 8 'per cent. erous stringers of white quartz and siderite lt 

'fen lots of smelting or~ shipped in 1909 and inches in maximum width .carry pyrite and a 

aggregating about 160 tons showed, according little chalcopyrite and locally a little galena. 

to sampling-works assays, gold 0.39 to 1.02 These stringers show a narrow band of comb 

(average 0.·6~) ounces, silver. 7.6 to 21 (aver- quartz on either wall. 

age 10.09) ounces, copper (wet) 3 to 10.2 (aver- The winze is sunk where a fracture strikes 

age 4.45) per' cent. . N. 35° E. across the n1ain vein oil a pocket of 

Similar assays for 202! tons of smelting ore ore about 10 feet across. 

shipped in 1908 give gold, 0.48 to 2;77 (aver- The ore from the Golden flop~ vein is said 

age ·0,.54) ounces, silver 2.5 to 13 (average 5.65) to carry about $18 in gold and· a very little 

·ounces, copper (wet) 2.4 to 17 per cent. silver, which, however, is somewhat augmented 

The total gross production of the property where the ore carries galena. 

is said to be about $5.00,000. CINCINNATI VEIN. 

DUMONT GROUP OF PYRITIC VEINS. The Cincinnati vein, on the south side of 

A group of pyritic veins striking a little north Mill Creek 1 ~ niiles northwest· of Dun1ont, is 

of west and dipping 40°-60° N. apex on the developed by a drift tunnel' that in 1911 was 

ridge between Spring Gulch and Clear Creek, caved near the mouth. The country .rock· is 

about three-fourths of a n1ile northeast of granite gneiss. The ore on the dump was 

Dun1ont. They have been developed by several altered wall rock containing disseminated pyrite 

shallow shafts, all of which are now idle. The and cut by stringers of quartz and siderite 

ore on the clmnp showed coarse pyrite and gray which carried pyrite and, more rarely, sphalquartz in irregular associn,tion. erite, galena, pyrite, and chalcopyrite. Son1e 

CARTER TUNNEL. of the ore was brecciated and recemented by 

buff-colored cherty silica or by finely ground The portal of the Carter tunnel, in the north country rock. ' 

side of Clear Creek, about three-fourths mile The smelting ore is said to carry $15 to $20 

west of its junction with Fall River, was closed in gold and silver (the gold being by far the 

at the time of survey. The wall rock on the· most important) and, rarely, 2! per cent of 

dmnp was mainly schist frmn the Idaho Springs copper. The. lead a,nd zinc are very low. 

formation, and the ore was pyrite in a white The vein is said to have produced $2,000 to 

quartz gangue. A few vugs lined with quartz $3,000 worth of ore, 1nost of which was taken 

crystals were noted. out in 1905. 

MILL CREEK. 

GOLDEN. HOPE VEIN. 

The Golden I-Iope vein, on the north side of. 

Mill Creek about 1i miles northwest of Dunlont, is developed by a drift tunnel 320 feet 

long and a winze that was filled with water in 

1911. The vein strikes N. 60° E., dips at 

35°-65° NW., and about parallel to the foliation 

KEITH TUNNEL. 

The Keith tunnel: on the north side of 

Mill Creek 1! miles northwest of Du1nont, is a 

northward-trending crosscut 690 feet long, that 

intersects five fractures. The country rock is 

largely schist with lenses of pegmatite but near 

the face of the crosscut is granite ·gneiss. _ · 

At 90 feet the tunnel cuts a 2-inch barren 

fracture that strikes N. 74° E. and dips 54° N. 
356 GEOLOGY OF GILPIN, CLEAR CREEK, AND BOULDER COUNTIES, COLO. 

Between 300 and 430 feet it follows a westward- At the tirne of this survey all the machinery 

dipping barren fracture, and at 440 feet it cuts on the property was being removed. The 

· an 8-inch fracture containing unmineralized 

crushed rock that strikes N. 45° E. and dips 

37° NW. A drift follows the "fracture northeast for 80 feet; at 610 feet a 2-foot zone' of 

crushed schist and pegmatite is cut and has 

been drifted on for 50 feet west of the tunnel. 

Jt strikes N; 80° W., is vertical, and is unmineralized. The Keith vein cut 650 feet fro1n 

the tunnel1nouth, strikes about east and west, 

and dips on an average 50° N. It consists of 

about 1 foot of crushed wall rock somewhat 

silicified and altered and carrying scattered 

crystals of pyrite. 

GREAT NORTHERN VEIN. 

The great Northern vein is exposed on the 

north side of Mill Creek, just west of its first 

·branch, about 2 1niles northwest of Dumont. 

It is opened. by a drift tunnel 1,200 feet long 

and by an old, apparently abandoned tunnel 

about 30 feet below the present workings. 

The country rock is granite gneiss, cut by a 

12-foot quartz-bearing monzonite porphyry 

.dike striking N. 85° 'E. The vein follows the 

north side of the dike and commonly stands 

nearly vertical though in some places it dips 

very steeply south. In most places it is a 

barren fracture 1 inch to 3 feet wide filled with 

gouge and crushed granite gneiss. In' the last 

200 feet of the tunnel some white quartz 

partly fills small anastomosing fractures between the walls. Where the filling is not complete the druses are in places coated with a 

thin layer of small yelloWish calcite crystals. 

About 100. feet from the face of the drift a 

streak of fine-grained galena and· sphalerite 

· 1 inch wide and 15 feet long occurs near the 

center of the silicified vein filling. 

As far as could be learned there has been no 

·production fro1n and almo~t no stoping on this 

vmn. 

TRAIL CREEK AND AREA: BETWEEN IDAHO 

SPRINGS AND FALL RIVER. 

MIAMI TUNNEL. 

The Miami tunnel (see fig. 78), which starts 

in Dry Gulch near Idaho Springs at an elevation of about 7,900 feet, has been idle for some 

MooB"h>'Y 

Pyritic vein 

D 

Composite vein 

EJ Barren fracture 

(Arrows indicate direction o)f dop") 

Note: Wall rock is Idaho Springs 

formation except wher·~ 

otherwise indicated 

100.___,__----'----1-'-00 __ _!JO Feet LAGG£0 

time and is in fact sup plan ted by the Big Five FIGURE 78.-Geologic plan or Miami tunnel. 

tunnel, which cuts the same veins at greater ·principal veins cut are as follows, the letters 

depth and offers better transportation facilities. referring to those in figure 78. 
CLEAR CREEK COUNTY. 357 

A. Two to three inches of crushed schist 

carrying a little disseminated pyrite. 

B. A small pyritic 'vein showing 2 inches of 

white quartz and pyrite. Fractm·ing along the 

vein subsequent to mineralization has locally 

produced 6 inches of crushed rock and vein 

material. The vein is undeveloped .. 

. 0. A zone of fractured schist and pegmatite 

14 inches in maximum width. It is only faintly 

mineralized, the wall rock in places carrying 

a little disseminated pyrite. A number . of 

branch fractures enter the walls and toward the 

face of the west drift the vein becomes very 

weak One !-inch tight stringer of galena and 

sphalerite was observed. 

D. A con1posite vein, which, about 50 feet 

east of the tunnel, is 7 inches wide, comprising 

~ inches pyrite and gray quartz and (next the 

hanging wall) 1 inch galena and sphalerite in a 

gray quartz matrix. ~rhe contact of the two is 

sharp and regular. The galena-blende veinlet 

has locally been cut by small stringers of cherty 

silica. · 

E. A mineralization along fractures about 

parallel to the foliation of the schist walls. At 

the west face the vein shows a 3-:inch hanging 

wall streak of highly silicified schist carrying 

disse~inated pp:ite. A similar streak 6 inches 

• wide occurs 3 feet below. In places the vein 

narrows to 1 inch of quartz and pyrite. 

F. A small tight vein of solid galena, sphalerite, and pyrite 1 to 1! inches wide. A nearly 

vertical dike of bostonite porphyry showing a 

very fine groundmass in which only scattered 

feldspar phenocrysts occur lies just north of 

this vein. 

G. A l-inch veinlet of quartz and pyrite and 

some dis.seminated pyrite in the bordering wall 

rock. 

Ii. A fracture zone 4 to 6 inches wide, locally 

showing a little disseminated pyrit.e. 

I. A tight vein of quartz and pyrite 1 to 1! 

inchea wide. 

The Edgar. vein is cut by the tu.nnel a short 

distance beyond the cave. 

BIG FIVE OR CENTRAL TUNNEL. 

The Big· Five tunnel starts ne~r the road 

bridge across Clear Creek at the west end of the 

town of Idaho Springs and runs due north. 

The tramway from the tunnel continues eastward along the south side of Clear Creek to the 

1nills near the mouth of Chicago Creek, where 

much of the ore is treated. In 1911 the tunnel 

had been driven 8,975 feet, and had cut four 

veins belonging. to the Big Five Co. and several belonging to others, as shown on Plate 

XXI, B (in pocket). 

The tunnel cuts mostly schist of the Idaho 

Springs formation but also intersects m.any 

small lenses of granite pegmatite, 1 of granite 

gneiss, and 12 porphyry dikes, 9 of which are 

of monzonite porphyry and 3 of bostonite. 

Most of the dikes are more or less altered and 

mineralized. The second dike from the portal 

(10 feet south of the Edith S. lateral) is bostonite porphyr·y, 6 feet wide. The fourth dike 

is a monzonite porphyry, 5 feet wide, that occurs 130 feet south of the Edgar vein. lt is 

much altered and, carries disseminated pyrite 

and pyrite coatings along joint planes. 

The larger veins cut by the tunnel have also 

been developed through other workings and 

are descr~bed elsewhere. :Minor veins cut by 

the tunnel are described below. 

· The first vein of ·any consequence; cut 1,150 

feet from the mouth of the tunnel, strikes N. 

75° E. and dips 85° N. It consists of 2 feet 

of crushed ·silicified schist carrying disseminated pyrite, and is separq.ted from the footwall by one-half inch of gouge and from the 

hanging wall by a tight slip plane. 

The Edith S. vein is cut 1,240 feet fron1 the 

portal and has been drifted on for 450 feet east 

from the ·tunnel. The vein strikes about N. 

78° E. and dips 75°-80° :N., cutting schist, peg ... 

matite, and bostonite porphyry. The 6-foot 

dike of porphyry near by is cut by the vei1i 140 

feet east of the tunnel and from there on forms 

the hanging wall. The vein varies from 2 

inches to 1 foot in width but averages less than 

6 inches. It consists of crushed, som~what 

silicified schist that contains in a few places 

abundant disseminated pyrite and in some 

places narrow stringers of gray quartz that 

carry pyrite and locally galena. On the whole 

the vein so fo.r as developed is not wellinineralized, the ore being said to run $5 to $18 a 

ton in gold, with SOUle narrOW stringers that 

are reported to assay as n1uch as $20 gold a 

ton. 

A 4 to 8 inch vein of crushed schist carrying 

abundant disse.minated pyrite, cut 2,405· ·feet 

from the portal, strikes N. 57° E. and dips 58° 

NW. The vein 1naterial, which is all1nore or 

less iron stained, is separated from tlie hang~g 

wall by one-fourth inch and from the footwall·by one-half inch of g'ouge. 
358 GEOLOGY OF GILPIN, CLEAR. ·cREEK, AND BOULDER COUNTIES, COLO. 

Fifteen feet beyond the vein last described a The Hudson vein,. cut 6,445 feet from the 

4~inch quartz vein carries pyrite and chalco- portal, has been op•:med by short drifts both 

pyrite. Above the quartz there are 2 inches of east and west. It ~trikes N. 65° E. and dips 

crushed schist and one-half inch of gouge lies about 65° NNW., cutting schist of the Idaho 

next the footwall. Springs formation. It consists of 6 to 12 

The Edgar vein is cut 2,510: feet from the inches of crushed and silicified wall rock that 

mouth of the tunnel, and short drifts are run, carries mor~ or less abundant disseminated 

both ways on it. (See p. 360.) pyrite and is cut by small stringers of quartz, 

An 18-inch zone of crushed altered schist, galena, and dark sphalerite. 

100 feet north of the Edgar, carries throughout The Good for N1)thing and Great Center 

a small amount of disseminated pyrite. veins intersect without displacement 7,000 

The Jenny Lind vein is 3,690 feet from the feet from the mouth of the tunnel. The Great 

portal. A drift east on this vein could oe Center vein, strikes K. 47° W. and dips 65° NE. 

entered for only 250 feet, though it is said to be It consists of 2 to 10 inches of crushed schist · 

625 feet long. The Jenny Lind vein strikes, in which there are a ::ew short, narrow stringers 

N. 71° E. and dips 32°-52° N. (average about of quartz and pyrite. The Good for Nothing 

45°). A: fracture striking N. 21° E. and dip- vein strikes N. 70° IG. and dips 60° NNW. It 

ping 63° W., intersected 200 feet eas~ of the varies from a tight slip to 6 inches in widtli 

tunnel, is probably the Jenny Lind No .. 1 vein. and .consists in its wider portions of white 

·The Jenny Lind vein is bent northward by quartz with rather abundant pyrite in coarse 

this fracture and dips 85° W. As far as seen crystals. 

neither of these veins is strongly mineralized, The Ken.tuck vein is cut by the tunnel about 

both consist1ng of crushed wall rock in which 7,320 feet from the portal, and short drifts ~ast 

minor amounts of pyrite are disseminated. and west have been driven on it. The vein 

The Jenny Lind No. 1 measures. 20 inches to strikes N. 78° E. and dips 55° NNW. It con4-:fe~t;.between walls and is said' to average sists of 4 to 12 inches of silicified schist that carabout 0.2 ounce gold and 2 to 6 ounces silver ries disseminated pyrite and is cut by a one-half 

a ton. . to 2 inch stringer of galena and dark sphalerite . 

. The Shafter vein is cut by the Big Five This stringer is gene:rally frozen to the hanging 

tunnel 4,250 feet from the ·portal. (See pp. wall, but in some places occupies the center of 

360-361.) · · the vein. · There has been· very ·little post-

. At 40 feet north of the Shafter a 4 to 6 inch mineral movement· along the vein,· but in one 

quartz-pyrite v~in strikes N. 66° E. and dips place a tight slip separates the lead-zinc ore 

83° NNW. · It has tight slip .planes along both from pyritic material. 

walls. The Lake vein is developed by short drifts 

At 730 feet north of the Shafter vein an that leave the tunnel at 8,345 feet. (See pp. 

east-west zone of crushed schist about 2 feet 284-285.) 

wide carries a little disseminated pyrite. One- The Belman vein :[s cut by the Big Five tunfourth inch of gouge is ;next the footwall of nel8,905 feet from the mouth. In 191llessees 

this vein, and a 2-inch open watercourse is were working both east and west from the 

next the hanging· wall. crosscut. (See pp. ~~83-284.) 

The Strong vein, cut by the Big Five tunnel The Big Five tunnel is 8 by 8 feet in cross sec5,660 feet from the mouth, is developed by a tion for its first 1,850 feet, beyond which it is of 

lateral that is caved 50 feet west from the single-track width, with the exception of 

tunnel. The vein strikes N. 75° E. and dips switching room. at ~.everal points. Driving is 

75°-85° N. The small part of it exposed shows done by air drills, and ventilation beyond the 

only a very slight pyritic mineralization. It Shafter vein is maintained by fans and air pipe. 

varies from 7 inches to 1 foot in width and The power house, offices, etc., are near the 

consists of crushed silicified . schist carrying tunnel mouth. 

· sparingly disseminated pyrite. The ore is 

separated from the hanging wall a~d the foot- MAYFLC,WER TUNNEL. 

wall by narrow seams of gouge. Neither the The Mayflower tu.nnel, on the south side of 

value of this ore nor the production from the Clear Creek about 1! miles west of the central 

vein could be learned. pa:r;t of the town o:f Idaho Springs, has been 
CLEAR CREEK .00UNTY. 359 

described in detail by Spurr and Garrey.t The has been done below the· tunnel level. The 

vein is evidently of the composite type. Spurr wor~ngs are all in schist of the Idaho Springs 

and Garrey regarded the pyritic mineralization formation. 

as later than the galena-sphalerite mineraliza- The average strike of the vein in the tunnel 

tion. This is the ~everse of the relationship is about N. 60° E. and the average dip 70° 

observed in most of the composite veins of the NW. This or a c,losely parallel vein is tracedistrict, but as the workings were inaccessible able northeastward into continuity with the 

at the time of this survey the w'riter had no Edgar vein. The 1nineralization is in the main 

opportunity of checking their conclusion. pyritic but locally galena-blende ore is prOlninent~ A typical exposure of the pyritic portion CROCKET VEIN. about 280 feet northeast of the shaft showed, 

The Crocket vein is developed by a tunnel frozen to the hanging wall, 6 inches of gray 

on the north side of Clear Creek near the n1outh quartz containing scattered quartz crystals 

of I-Iukill Gulch and by a shaft on the hillslope below which came 3 inches of schist lll:Ore or 

above at an elevation of about 7,800 feet. ·less impregnated with pyrite and, next the footThe tunnel is about 550 feet long, 1nostly on wall, a bn,nd of nearly solid pyrite one-half to 

the vein, which strikes about N. 50° E. and 1 inch wide. Ore from the shaft shows double 

dips 55°-60° NE. The wall rock is mainly mineralization, portions of the vein consisting 

schist of the Idaho Springs formation, but in almost exclusively of pyrite, chalcopyrite, and 

places is 1nonzonite porphyry. f'he vein cuts gray quartz and other portions consisting of 

through the porphyry in one place, and the galena and sphalerite with subordinate pyrite. 

distribution of the porphyry underground and The presence in one specimen of a band of 

on the surface shows that it is a dike nearly con1b quartz separating the two types of ore 

parallel to theocourse of the vein. In general, shows that they were not formed contempothe vein is a zone of fractured rock hnpreg- raneo'usly. ' 

nated with pyrite and varies from a few inches Few data are available in regard to the value 

to 2! feet in width. Where the vein cuts of 'the ore. According to sampling-works 

through the porphyry it becomes a single assay.:; quoted by the con1pany six lots of smelttight fracture filled with quartz and fine pyrite. ing_ ore, aggregating about 1.8 tons, shipped in 

.In one pln,ce a tight veinlet one-half inch to 1! 1911, showed 1.08 to 2.84 ounces of gold and 

inches wide shows galena, sphalerite, and 11 to 24 ounces of silver. 

pyrite. . As·the property has been actively developed 

Sn,Jnpling-works assays of 14 lots of sn1elting only for a short tin1e the gross production is 

ore shipped between 1891 and 1902 show gold s1nall. 

0.4 to 1.8 ounces, silver 13.2 to 88 ounces, copper 

(wet) 2.1 to 8.5 per cent, zinc 8 per cent or less, 

silica 21 to, 52 per cent. The notable feature 

of the assays is their high copper content, which 

is nor1nally 3 to 7 per cent. 

CENTENNIAL-TWO XINGS VEIN. 

The Centennial-Two Kings vein outcrops on 

the west side of I-Iukill Gulch and is developed 

by the Centennial tunnel and Two Kings shaft, 

about one-fourth 1nile above the mouth of the 

gulch. The' tunnel starts as a crosscut running 

nearly north, intersects the vein 7 5 feet from the 

portal, . and. continues 115 . feet beyond. A 

drift on the vein 330 feet long connects with 

the tunnel and also with the shaft. · No work 

t "Economic geology or the Georgetown quadrangle, Colo.: U.S. Geol. 

Survey Pror. Po per 63, pp. 365-366, 1908. 

U. S. TUNNEL. 

The U. S. crosscut tunnel, starting on the 

west side of Hukill Gulch at an elevation of 

8,050 feet, is 600 feet long and bears N. 26° W. 

The country rock is schist of the Idaho Springs 

formation, cut by three monzonite porphyry 

dikes, one of which is 8 feet wide and 140 feet 

from the portal, another 10 feet wide and 350 

feet from the portal, and tho third, 3 feet wide 

and 550 feet from the portal. Three fracture 

planes, cut in the central pn.rt of the tunnel, are 

all nearly parallel to the schistm;ity, which 

strikes N. 80° to 85° E. and dips 60°-70° N. 

All of them are practioally barren gouge-:fill,ed 

fissures, carrying in most places a little disseminated pyrite. At one place 2 inches of 

quartz carrying a minor amount of pyrite was 

seen frozen to the hanging wall. 
360 GEOLOGY OF GILPIN, CLEAR CREEK, AND BOULDER COUNTIES, COLO. 

EDGAR VEIN. 1 per· ton.· The high E:ilver content in the upper 

levels was probably the result of downward 

The Edgar vein, which cuts across Hukill enrichment. 

Gulch at an elevation of a"Qout 8,125 feet, is in The gross producti.on is not known. 

alignment with and may be the. eastward continuation of the Centennial-Two Kings vein. SHAI'TER VEIN. 

The developments near 'the head of Hukill The Shafter vein runs northwestward' across 

Gulch include four drift tUilli.els and three the middle portion of Hukill Gulch, about half 

shafts, the lowest of which reaches 250 feet a mile nor~h of its junction with South. Clear 

below the lowest tunnel level. Most of these Creek. It is developed by the Shafter' Fairworkings were inaceessible because of caving. mont, and Summit shafts, by the Adit and 

The vein is also cut by the Big Five tunnel, but Waterbury drift tunnels, and· by the Anon and 

the laterals there are caved 130 feet from the Shafter crosscut tunnels. On the Shafter 

tunnel. ground there are SfLid to be 10,425 feet of 

The wall rock is mostly schist of the Idaho drifts on the vein. The Shafter shaft is 893 

Springs formation, but is· monzonite porphyry feet deep on the dip of the vein and connects 

at one place in the Hukill Gulch workings. by a lateral, which follows the ':"ein, with the 

The Edgar vei.ri strikes N. 65° E. on the aver- Big Five tunnel (4,250 feet from the portal). 

age and dips 70°-85° NW. It consists of The ;Fairmont shaft is 464 feet deep and is 

crushed wall rook, slightly silicified, from a few connected with the first, second, and third 

inches to 3 feet in width, containing more or levels of the Shafter. 

less abundantly disseminated pyrite. .In the The vein between the Shafter and Fairmont 

tunnels subparallel stringers of galena and sphal- shafts has been largely stoped out· to the severite traverse the vein where it cuts the mon- enth level, and east of the Shafter shaft it has 

zonite porphyry, and the porphyry between· been ext~nsively stoped fo.r 300 to 400 feet to 

these veinlets contains abundant disseminated widths of 2 to 7 feet. On account of the open pyrite and some sphalerite and galena. Though character of some of these stopes many of the 

no galena and sphalerite were observed in the levels can be entered for short distances only, 

short lel).gth of this vein exposed in the Big and those that are ac(~essible contain only s1nall 

Five laterals, their presence. at this depth is pillars or relatively barren stretches of ,vein 

shown by the following assays: that have not been mined. 

Assays of ore from Edgar vein in the Big Five t'unnellateral. 

Gold. Silver. Lead. Zinc. 

Ounces. Ounces. Per cent. Per cent. 

0.51 39. 50 17.00 10 . 48 67. 20 26. 50 15. 

Sampling-works assays of 176 tons of smelting ore sold from 1898 to 1909, inclusive, show 

an average content of gold 0.6 ·ounce and 

silver 16.07 ounces per ton. In these lots copper·was from less than 1.5 to 6.5 per cent, lead 

59 per cent or less, and zinc 16 per cent or less. 

According to Raymond/ ore obtained in the 

early seventies carried much. more silver than 

any now obtained, first-class ore averaging 0.5 

ounce gold and 80 ounces silver and seldom 

less than 45 to 50 per cent of lead. Some lots 

of ore carried as much as 165 ou11ces of silver 

1 Statistics of mines and mining in the States and Territories west of 

the Rocky Mount!liins, 1871, p. 350, 1873. 

The wall rock is schist of the Idaho Springs 

formation injected by granite pegmatite. A 

35-foot dike of monzonite porphyry that runs 

about parallel to' the Yein and 200 feet south of 

it is shown both in the Anon and the Big Fiv·e 

tunnels but is obscured on the surface by the 

extensive dumps. 

The Shafter vein strikes from N. 40°-:60° E., 

the average bearing of the drifts being about 

N. 47° E. In some places the vein dips as low 

as 65° NW., and in others it stands vertical~ but 

in general it dips 78°-:30° NW. This strike and 

·dip are nearly parallel to the foliation of the 

schist wall rock. The vein varies from. a few 

inches to 10 feet in width, though most of the 

stopes, carried the full width of the vein, are 

from 2 to 4 feet wide. The vein consists of 

crushed . silicified schist and pegmatite with 

abundant disseminated pyrite, cut by stringers 

of white quartz and pyrite with a little local 

light-colored chalcopyrite. These stringers are 

in general 2 to 5 inches wide, though in some 
CLEAR CR.EEK COUNTY. 361 

places they attain a width of 2 feet. On the feet from the portal, but in the distance acseventh level the stopes were originally 6 feet cessible it exposes two northeast-striking veins. 

wide, but in 1911 it was found that the hanging -These veins. are nearly parallel and show sharpwn.ll was mineralized for at least 10 feet beyond walled stringers of pyritiferous quartz, 4 inches 

what was originally considered the vein. The in ma.ximum width, bordered by more or less 

same conditions have since been found on the silicified schist cut by ~ery minute ore stringers. 

third level near the Fairmont sha.ft. 

BULLION KING MINE. Later veinlets of chalcopyrite, galena, sphalerite, and a little tennantite have been formed The following account of the Bullion King 

in openings in th~ dominantly pyritic Shafter n1ine is quoted from the report of Spurr and 

vein, particularly west of the Shafter shaft and Garrey. 1 

above the fifth level. Few of these veinlets The Bullion IGng mine is located at an elevation of over 

exceed 2 inches in width, and most of them are 8,400 feet near the top of the north slope of the ridge sepaless than 1 inch~ They apparently favor the rating Clear Creek from Spring Gulch, about 1,700 feet 

hanging wall of the vein, and in s

9me places are south 20° west of the ore house of the Stanley mine. An 

underground study of this mine was not made, as the 

frozen to it and separated from the pyritic ore openings to the mine were closed and the owners were not 

by a narrow seam of gouge. In other places the to be found. * * * 

later minerals .are found in veinlets cutting the The vein seems to have a general north 55°. east trend. 

pyritic ore or forming a rna trix arom~d fragments It is probably a branch of the Little Mattie-Newton system 

of pyrite and quartz. Polished sections show of veins and joins the vein along the porphyry dike, which 

is located farther southwest. It is probably also the same reln.tions similar to those noted in ore from the vein as is developed in the Mayflower mine to the northSpecie Payment vein. (See figs. 9 and 10, p. east. 

113.) Above the fifth level fractures in the chal- The low-grade ore found on the mine dump contains 

copyrite are coated with secondary chalcocite. gal~na, pyrite, and black sphalerite, and occurs as small 

The lead. and zinc sulphides are most abundant seams running through granite and pegmatite or as a cementing material inclosing angular fragments of the same above the second level, though they are present rocks. A few small specks of tetrahedrite or polybasite 

in the ore from a stope above the Big Five were also found associated with the galena. 

tunnel on the eighth or lateral level. These Considerable ore is reported to have been obtained from 

narrow stringers constitute the richest ore in the Bullion King workings. 

the mine; a !-inch streak in a stope 550 feet Sampling-works assays of three lots of smeltwest of the shaft on the third level is said to ing ore shipped from the BUllion King mine in 

carry as high as 17 ounces of gold per ton. 1902-3 a.re as follows: · 

According to sampling-works assays the 

average content of 1,428 tons of smelting ore 

shipped in 1909 and 1910 wa.s gold, 1.14 ounces, 

and silYer, 5.75 ounces. The copper content. in 

Inany shipn1ents was less than 1.5 per cent, but 

in many others was 3 to·4 per cent, and in some 

6.9 per cent. Most of the shipn1ents do not 

sho'v lead or zinc in commercial amounts. 

Where lea~ is present .it is accompanied by 

unusually high silver values. Sampling-works 

assays of 243 tons of smelting ore from the 

Shafter vein .within the limits of the Refuge 

clain1, shipped in 1908-1910, show gold, 1.33 

ounces; silYer, 1.63 ounces; copper, usually 

below 1.5 per cent, and no lead and zinc. 

SUMMIT TUNNEL. 

The Sumn1it tunnel, on the west side of 

I-Iukill Gulch, ·at an elevation of 8,350 feet, 

forms appa.rently the continuation of the 

, Refuge-Shafter lode. The tunnel is caved 150 

Sampling-works assays of ore from Bullion King mine, · 1902-3. 

·CopOre. Gold. Silver. per Lead. Zinc. Silica. Iron. 

(wet). 

Netlbs. Oz: Oz. P. 'ct: P. ct. P. ct. P. ct. P. ct. 

8, 864 0. 08 32. 40 4. GO 33. 20 12 ........... . . 18, 266 . 22 25. 30 2. 50 13. 70 ................. . 31, 732 . 18 18. 80 2. 80 21. 50 12 40 "4 

STANLEY MINE. 

The Stanley mine is in tl~e valley of South 

Clear Creek just west of Idaho Springs. Its 

history, development, and geologic featm·es 

have been described at length by Spurr and 

Garrey, 2 and the portions of the mine accessible 

for study at the time of the writer's visit 

1 Economic geology of the Georgetown quadrangle, Colo.: U. S. Geol. 

Survey Prof. Paper 63, pp. 304-305, 1908. 

. 2ldem,pp.341-349. 
362 GEOLOGY OF GILPIN, CLEAR CREEK, AND BOULDER COUNTIES, COLO. 

revealed no significant facts not presented by 

these writers. The most significant geologic 

feature of the mine is the occurrence at several 

places of biotite-latite porphyry which is not 

only younger than bostonite porphyry but 

younger than the mine~alization as well, as 

conclusively shown by Spurr and Garrey. · In 

only one other mine in the quadrangle (the 

Blue Bird mine, near Nederland) was porphyry 

younger than .the mineralization noted. The 

writer observed the latite porphyry in contact 

with bostonite porphyry on the third level of 

the main shaft workings, but the mutual age 

relations at that place were obscure. 

The following sampling-works assays of 

smelting ore shipped in 1910 give some idea of 

the ore mined in recent years : 

Sampling-works assays of ore from Stanley mine, 1910. 

Ore. Gold. Silver. Copper: Lead. Zinc. 

Net lbs. Ounces. Ounces. Per cent. Per cent. Per cent. 

5,450 0.40 18.60 .................. .............. ................ 12, 700 .18 2.00 .................. .............. ................ 3,770 1.31 14.20 ............... ............. ............ 25, 150 . 42 '6. 70 ............... .......... ............. 35,070 . 94 13.00 2.9 12.0 3.0 

8,610 1. 24 7.20 ............. ............. .............. 20,840 . 62 11. 70 1.4 11.2 4. 6 

26,210 1. 06 21.70 2.4 18.6 5.0 

23,620 . 31 9.00 1.3 6.2 5.0 

24, 750 .18 7.00 ................ 3.0 .............. 6,390 . 77 24. 90 ............. 43.5 .. ............ 

7,520 . 91 10. 70 3.8 ................. ............... 

26,730 1. 00 19:'80 2. 1 29.6 7.0 

2,230 2.00 30.00 ........... ................. .............. 21,130 1.46 19.50 1. 2 ................. ............. 39,160 . 75 19.80 2.4 ................. ............... 26,660 1. 23 18.50 1.5 2. 5 ............. 37,840 1.28 25.20 3.5 ................. .............. 

The average content of the sn1elting ore 

shipped m 1910 was gold 0.85 ounce, silver 

15.3 ounces, copper 0.70 per cent, and lead 1.4 

per cent. 

The total gross production is said to have 

been about $3,650,000. 

SALISBURY VEIN. 

The Salisbury vein and the development on 

it have been described by Spurr and Garrey 1 

and need not be repeated in this report. In 

1911 some work was being done by lessees 

above the tunnel level' in stopes where small 

s.tringers of gale~a-sphalerite ore clearly cut 

the original pyritic vein. 

According to sampling-works assays the 

av:erage metallic content of 140 tons shipped 

1 Op. cit. p. 354. 

from 1908-1910 was gold 0.84 ounce and silver 

8.91 ounces. The percentage of copper in 

most shipments was too small to be paid for, 

but occasionally r13ached 11 per cent; several 

shipments showed 2 to 3! per cent. Lead is 

occasionally present to the extent of 4 to 23 

per cent. Zinc is usually not determined, but 

one assay showed D per cent. The percentage 

of silica in seven shipments ranged from 40 to 

70 per cent. 

CARDIGAN VEIN. 

The Cardigan vein, in Cardigan Gulch ·about 

a mile west of Idaho Springs,. is developed by 

three drift tunnels at different elevations on 

the mountain side t:md by a connecting shaft. 

Most of the workings are inaccessible, but the 

following description of the vein is given by 

Spurr and Garrey: 2 

Near the shaft on the lower level, where two nearly _ 

parallel leads were noted, the vein consists of leads of 

crushed gneiss and clay 2 inches to 1! feet in width. In 

places these leads contain;~d vein quartz and pyrite. The 

general trend of the vein, .:ts seen from the mine maps, was 

abo:ut N. 60° E. and the dip about 40° NW . 

The most abundant ore on the dump consisted of pyrite and chalcopyrite in a n1atrix 

of quartz and some ealcite. Thin coatings of 

secondary chalcocite occurred along fractures 

in the chalcopyrite. So1ne galena and sphalerite lined vugs in the pyritic vein or 'for~ed 

small stringers in rather sharp contact with 

the pyritic ore. The mineralization plainly 

'belongs to the composite type. 

Excellent exposures of typical hostonite 

porphyry occur near t:1.is vein. 

Sampling-works ass.~ys of six shipments of 

ore in 1898 and 190H show gold 0.7 ·to 2.9 

ounces, silver 6.6 to 2'l.25 ounces, copper 1 to 

5.5 per cent, silica 36 to 58 per cent. A lot 

of 560 pounds shipped in 1898 sampled ·gold 

5 ounces, silver 51 owtces, copper .4 per cent, 

silica 36 per cent.· 

ENGLAND MINE. 

The following data -on the England mine is 

in part from the ·report of Spurr and Garrey.9 

The England mine con~ists simply of a tunpel 

whose portal is at an elevation of 8,550 feet a 

little more than a mile due west of Idaho 

Springs. The wall rocks of the vein consist 

wholly of granite gneiss and pegn1atite, but 

2 Idem, p. 353. a Idem, pp. 352-353 and fig. 134. 
CLEAR'CREEK COUNTY •.. 363 

two dikes of bostonite porphyry outcrop a. pyrite a.nd chalcopyrite, arid is. traversed by a 

short distance to the east. · more or less definite band of galena and sphalerTho strike of tho vein, which is developed by a drift ap- ite 1! inches wide. A specimen from an ore 

:proximately 400 feet in length, is abo~tt S. 60° W., and its bin showed a small amount of bornito inti-

-dip is about 45° to 50° NW. The vein .is not an especially 1nately intergrown-with galena. Postmineral 

.strong one, being formed of a series of connected minor movement along the vein has in places crushed 

:fractures. Locally, the vein consists of a series of string- h l -ers of quartz, here and there showing comb structure, in t ega ena and chalcopyrite to an aggregate of 

:gno.iss; elsewhere it consists of gray quartz containing a very fine grains of luster much duller than the 

few angular fragments of wall rock, and showing some normal. 

little replacement by mineral. .The vein is only slightly As at many other mines in the district, the, 

mineralized, but in places carries a little ore consisting of geologic evidence suggests two mineralizations. 

:galena, .pyrite, quartz, and both brown and resin zinc Film 

blonde. s of native copper have been deposited py 

GLADSTONE VEIN. mine waters along seams in some of the ore, 

The Gladstone vein is developed by a tunnel 

:and shaft on'the south side of Clear Creek, near 

the mouth of-Cardigan Gulch, about a mile west 

-of Idaho Springs. The tunnel, which is about 

-630 feet long, is entirely in Idaho Springs 

formation. and pegmatite. The following description is quoted from Spurr and Garrey: 1 

The main vein strikes about N. 65° E. and' dips from 60° 

'to 70° NW. The vein consists of a quartz lead, ranging 

'from 2 inches to over a foot in width, which locally .is 

·made up solely of quartz with a little pyrite, though else-

·where it is composed of quartz, pyrite, galena, and brown 

iSphalerite. 

About 370 feet frmn the mouth of the tunnel 

·the main vein is joined from the west by a clay lead sev-

·cral inches wide, which runs in contact with the vein for 

:about 50 feet and then crosses it and disappears in the 

footwa.ll. .. 

Since Spurr's description was written devel-

()pnlent has been carried below -the tunnel 

level by a winze 85 feet deep and 100 feet fron1 

~the tunnel portal, and by a shaft sunk to an 

.equal depth just outside the portal. A. second 

1evel about 75 feet below the tunnel level connects the new sP,aft with the old winze, and 

·extends 155 feet beyond, making its tota.l 

length 265 feet. Much stoping has been done 

between the two levels. 

· As exposed in the stopes and the second 

1evel the vein lies approxima:tely parallel to the 

planes of foliation of. the schists. At one 

place the vein is 2 inches wide and is frozen to 

'the walls. It consists of pyrite, chalcopyrite, 

:gray copper, and some galena in a gangue com-

:posed of white quartz and some calcite. At 

.another plaee the vein shows 7 inches of fractured schist next the footwall, succeeded by 

'2 to 4 inches of gray to white quartz carrying 

1 Op. cit., p. 353. 

but otherwise no evidence of downward enrichment was seen. 

About 320 feet from the portal a crosscut to 

the west cuts a vein at 45 feet from the Gladstone vein and another at 70 feet. The vein 

cut at 45 feet strikes N. 60° E., dips 70° W., 

and may be a branch of the Gladstone. It 

shows 1 to 2 inches of gray quartz and pyrite 

frozen to the walls. The vein cut at 70 feet 

strikes N. 30° E. and dips 35° W. It shows 

3 to 4 inches of somewhat crushed schist next 

the hanging wall, followed by 2 inches of some-

'what vuggy white quartz carrying pyrite. 

Neither of these veins has been worked to any 

important extent. 

Smelting ore shipped in 1908 contained gold 

1.25 to 1.65 ounces and silver 5 to 14 ounces; 

that shipped in 1911 contained gold 0.5 ounce 

to 8.82 (mostly 2 to 3) ounces, and silver 6 tq 50 

(mostly 10 to 20)' ounces. Copper in the 1911 

shipments rangedfrom 1 to·11 per cent, though· 

2'to 5 per cent was more common . 

DONNA J'UANITA VEIN. 

The small Donna Juanita vein, about 300 

feet n·orthwest of the Gladstone vein, strikes 

N. 65° E.' and dips 40° NW. It is developed 

by a small tunnel 250 feet long that was inaccessible at the time of this survey. 

READY CASH .VEIN. 

The Ready Cash vein is developed by a shaft 

36 feet deep about 175 feet northwest from the 

mouth of the Gladstone tunnel. A dr~ft 50 

feet long extends southwest from the shaft 

along the vein, which strikes N. 60° to 65 ° E. 

The footwall streak dips 45° NW. and consists 

of 6 to 10 inches of silicified schist impregnated 

in various degrees with pyrite. Al:\1 irregularly 
•. I 

3S4 GEOLOGY OF GILPIN, CLEAR CREEK," AND BOULDER COUNTIES, COLO. 

bounded band one-half to 1 t inches wide is a 

·black powdery aggregate apparently of crushed 

sulphides. The footwall vein is said to run 

about $8 per ton. The hanging-wall streak, 

which lies about 6 feet above and about parallel to the footwall streak, consists of 10 inches 

of more or less silicified schist, carrying dis,. 

seminated pyrite and cut by veinlets of white 

quartz and pyrite three-fourths inch in maximum width and by others of galena, sphalerite, 

chalcopyrit.e, and pyrite one-half inch in maximum width. The hanging-wall streak is said 

to have an average value of about $28 a ton. 

A. MAUDE MUNROE VEIN. 

The A. Maude Munroe vein is developed by a 

drift tunnel about 400 feet long, with portal on 

the north side of Clear · Creek about threefourths mile west of Idaho Springs .. The vein, 

which is of the pyritic variety, was not studied 

underground. The following sampling-works 

assays of lots of smelting ore and concentrates 

shipped between 1891 and 1898 give some idea 

of the ore. 

Sampling-works assays of ore from A. J;Jaude Munroe vein. 

Ore. Gold. Silver. Copper Silica. (wet) . 

------

Net lbs. Ounces. Ounces. Per ct. Per ct. 

{ 5,584 1.08 13.50 ......... ......... 

2,982 . 90 22. 00 ........... 23 

Smelting ore .... 230 .40 17.00 ........... 65 

1,720 2.65 24.00 ............. ........... 

7,500 . 42 6.00 2. 65 61 

Concentrates .... { 4,732 . 95 19. 30 ............ 13 

2,924 . 55 2.50 ........ 18 

LOST VEIN. 

The Lost vein outcrops on the south side of 

the ridge between South Clear Creek and 

Georgia Gulch. It is developed by a 690-foot 

drift tunnel, which starts 300 feet ~ast of 

Georgia Gulch below the wagon road on the 

north side of Clear Creek. A crosscut 440 feet 

from the mouth extends 80 feet south to a second vein, .which has been fo~owed 150 feet. 

The country rock is· Idaho Springs formation. 

The Lost vein strikes about N. 75° E. and 

dips 60° N. near the mouth of the tunnel and 

65° N. in the last few hundred feet of it. The 

vein at the end of the crosscut strikes N. 4 7° 

E. and dips 70° NW. Both veins have small 

branches near the ends of the drifts. Both 

are small fracture:;, the Lost vein being nowhere 'over 8 inches (commonly about 2 inches) 

and the other vein .2 to 5 inches wide. 

The mineralization of the two veins is similar: A small stringer of quartz with son1e pyrite is more or less eontinuous throughout the 

main vein, usually next the footwall. On 

either side of the quartz, though more often in 

the hanging wall, the schist is somewhat 

crushed, bleached, and sparsely impregnated 

with pyrite. In the south vein the quartz is 

absent, but the crushed schist is somewhat 

·mineralized. 

No stoping has been done on either vein. 

One small lot of ore shipped in 1910 shows 0.2· 

ounce gold and 3.2 ounces silver, amounting to 

less than $6 per ton. 

LITTLE SD: TUNNEL. 

The Little Six tunnel, on the east side of 

Georgia Gulch about three-eighths mile north 

of Sovth Clear Creek at an elevation of 8,050· 

feet, trends generally southeast for 425 feet to 

where a cave blocks further advance. Its extent beyond the cave is not known. At 320 

feet from the mo'\lth a drin runs east-northeast 

for 360 feet. The rock exposed in all the 

workings is schist of the Idaho Springs formation, ih some places highly injected by granite· 

pegmatite. The mouth of the tunnel is in a 

dike of monzonite porphyry, which runs north. 

and is not elsewhere exposed . 

The northwest-southeast part of the workings follows a barren tight fracture which in 

many parts is traced with difficulty and is nowhere wider than half an inch. The drift at. 

320 feet is on a 2 to 10 inch fracture that 

strikes N. 72° E. ~nd dips about 70° ·N. In 

its wider portions it is filled with barren crushed 

schist, in places sparsely i1npregnated with. 

pyrite and in its narrow portions by gouge that 

is locally mineralized. 

WYANDOTTE TUN.tmL. 

The Wyandotte tunnel is on the east side of 

Georgia Gulch three-eighths of a n1ile north of 

South Clear Creek. A crosscut tunnel140 feet 

long intersects two veins. A drift N. 45° E. 

on the Lilly vein is 900 feet long and another on 

the Gold Dust vein runs N. 75-8'/ 0 E. and is 680· 

feet long. The country rock throughout is. 
·CLEAR ~REEK COUNTY. 365 

Idaho Springs formation in son1e places intruded py n1uch granite pegn1atite. 

'fhe Lilly vein dips 65 ° N. and is not well 

1ninernlized except for 130 feet near its junction 

with the Gold Dust vein. In n1ost places it 

consists of 1 inch to 4 inches of barren gouge or 

crushed wall rock impregn·ated with pyrite. 

Near the junction the vein broadens to 14 or 18 

inches with 2 to 4 inches of white quartz and 

coarse pyrite below the hanging-wall slip. The 

remninder of the filling is crushed, somewhat 

silicified schist carrying dissen1inated pyrite. 

The Gold Dust vein for 410 feet frmn the 

tunnel is a· small barren fracture dippi~g 

·60°-70° N. and comn1only ~ontaining 2 to 3 

inches of crushed schist between walls that are 

bleached and in places silicified for 1! to 2 

inches.. In a few places a little pyrite is disseminated in the vein filling and at one place 

a l-inch stringer of white quartz and coarse 

pyrite was noted: 

There has been a little stoping on the Lilly 

vein for 130 feet northeast of the junction and 

on the Gold Dust for 50 feet. Sampling-works 

assays of several lots of smelting ore s~iipped 

fron1 the Wyandotte tunb.el are as follows: 

SamJJl•irtg-'works assays of o~e from the Wyandotte tunnel 

Da.te. Ore. Gold. 

Net lbs. Ounces. 

2, 058 1.85 

6.392 2.93 

1891-1808 ... 14,538 3. 20 

8,984 2. 67 

8.'270 2. 60 

1901. ....... { 5;368 :r.. 21 

5, 702 :r.. 49 

Silver. \ 

Ounces. 

7.00 

10.00 

11.50 

10. 20 

17.00 

7. 70 

6.60 

Copper Silica. (wet). 

Percent. Percent. ............... .............. 

4.90 25 

7. 65 23 

5.50 19 

11.50 22 

5.40 28 

4.75 30 

Shipments made in 1908 and l909 were cmnLINCOLN AND SOUTH LINCOLN VEINS. 

The Lincoln and South Lincoln veins, on the 

south side of Clear Creek about a mile west of 

Idaho Springs, have been described by Spurr 

and Garrey, 2 and as there had been no important' developments since their survey the 

nlines were not reexamined. 

Sampling-works assays of smelting ore 

shipped from 1888 to 1902, inclusive·, show that 

the metal content of the ore is very variable. 

SantJJling-works assays of ore from the Lincoln, and South ·· Lincoln veins. 

CopOre Gold. Silver. per Lead. Zinc. S.ilica. 

(wet). 

Net lbs. Ounces. Ounces. P. ct. P_.ct. P. ct. P. ct. 

1,058 0. 35 40.00 ...... 10 22 ....... 

7,454 5.90 13.40 4. 70 ............ ........... 

9,376 ]. 24 3.22 ......... .......... ........... 12.0 

13,320 1. 68 3.70 ......... ........ ......... 37.0 

8,414 l. 49 4.40 3.20 ....... ....... 32.5 

The vem 1s apparently of the composite 

type, certain portions being largely pyritic and 

other po~·tions carrying abundant gttlena and 

sphalerite. 

ORO-MORNING STAR VEIN. 

The Oro-Mon1ing Star vein crosses the ridge 

between Oro and Georgia gulches and is developed by two shafts, the Oro near the bank of 

Clear Creek and the .Morning Star in Georgia 

Gulch at an elevation of about 8,350 feet. 

Two tunnels have been driven, the longest of 

which, the Syracuse tunnel, connects with the· 

:Morning Star shaft. The wori?ngs were 1\ot 

entered. The follo~ving are sampling-:works 

assays of a few lots of smelting ore shipped 

between 1891 and 1894: 

partttively low grade, the gold ranging frmn Sampling-works assays of smelting ore front the Oro-Morn- . ing Star vein. · 0.16 to 0.4 ounqe and the silver frmn 0.5 ounce 

to 2 ounces. In 1911 the tu1u1el was being re-

·oponecl after several, years of idlenes~. 

JOSEPHINE AND BARBER & ELLIOTT VEINS. 

The Josephine and Barber & Elliott veins on 

the south side of Clear Creek about a u1ile west 

of Idaho Springs were not visited during this 

:sm·vey. They were studied by Spurr and 

Garrey 1 to whose report the reader is referred 

1 Op. cit., pp. 356-358. 

Ore. Gold. Silver. 

Net lbs. Ounces. Ounces. 

12,450 1. 50 24.00 

16,350 1.30 22. 50 

5,718 0.60 13.00 

7,435 1.45 24.50 

Copper 

(wet). 

l?er cent. 

1.00 

1.50 ..... · .......... 

2.00 

Silver. 

Per cent. 

48 

43 ............ 

................ 

The ore is apparently of the· pyritic type. 

2 Op. cit., pp. 354-356. 
366 GEOLOGY OF GILPIN, CLEAR CREEK, AND BOULDER COUNTIES, COLO. 

METROPOLITAN TUNNEL. c?ntact between pc:~gmatite and porphyry conThe Metropolitan crosscut tunnel starts at s1sts of quartz and pyrite and sends off narrow 

an elevation of about 7,750 feet near the branchesintobotht,hepegmatiteandporphyry. 

mouth of Trail Creek and runs S. 23o W. for Some of the pyriti·~ veinlets show small vucrs 

about 2,600 feet, S. 45° E. for 180 feet, and lined with crystals of quartz and pyrite. At 

S. 28° W. for 330 feet to the face. The tunnel several points in the, drifts on this vein a 1-foot 

is headed for the Metropolitan vein, which unmineralized friction breccia is exposed. 

crops out in Spring Gulch,l and ,in. October, Metasomatic alte.rations along the Hoosac. 

1911, was said to extend to within 1,100 feet vein were studied in. two thin sections. The 

of the Metropolitan shaft: first showed· mineralized granite-pegmatite in 

The wall rock of the tunnel is schist of the which the principal changes were the developIdaho Springs formation and a few small ment of sericite and pyrite. The original minmasses· of granite gneiss. A dike of altered erals of the pegmat.ite appear to have been 

porphyry, probably hostonite, is cut at 250 feet q_uartz, orthoclase, rrmscovite,_ and a little piafrom the portal and another dike, of bostonite g10clase. Sericite is largely confined to the 

porphyry, at 2,020 feet. The northernmost feldspars, where it is usually most abundant in 

dike could not be found on the surface, although ~ands par.allel to the deavages. Pyrite may be 

a special search for it was made.. Inclosed either by feldspar or quartz crystals or 

The only vein of importance cut by the may lie between the:rn in grains, most of which. 

tunnel enters from the east wall about 7 50 are irregular and inclose small masses of quartz, 

feet from the portal and passes into the west and ~ericite, but a few of which show crystal _ 

wall870 feet from the portal. It strikes about ol!tlines. Calcite is d·~veloped sparingly in ag--

N. 20° E. and dips 35° W. As exposed in the gregates of minute grli>ins. 

tunnel the vein shows 2 to 3 inches of gray ~e second thin ~ection studied was of bos--

quartz c~rrying abundant pyrite and bounded tm~Ite · _po~hyry .a~ja~~ent to the veins. Theon One Or both sides by several inches of gouge., ~ock COnSISted O~Igina.\ly Of anorthocl.ase lathsIt has not been worked. Ore from this vein ~n so~e~hat fluidal a.rrangementl With some 

found on the dump showed some, chalcopyrite Interstitial quart~ .. The. metasomatism has notand sphalerite and a little galena in addition to been severe. Sericite bas been developed in t~e 

the pyrite. · feldspar, aggregates of minute carbonate grains. 

HOOSAC TUNNEL. are moderately numerous, and there are a few 

. The fioosac tunnel, which was started about 

1908 on the north side of Clear Creek, a little· 

east of its confluence with Fall River, develops 

the Rising Sun, Martha Perks, and Hoosac 

veins. (See fig. 79.) 

The Hoosac vein is a somewhat irregular zone 

of fracturing and mineralization with general 

east and west trend. In places it follows the 

contact between monzonite porphyry and peg-

'matite but elsewhere intersects both these 

rocks. In places the mineralization consists 

only of a dissemination of pyrite in fine grains 

in pegmatite and porphyry, evidently a result 

of met~somatic replacement by mineralizing 

solutions penetrating along minute fractures 

'and working out into the wall rock. In other 

parts the mineralization assumes the form of 

·well-defined veinlets bounded by altered wall 

rock carrying disseminated pyrite. At the 

east face of the drift a vein 3 inches wide at the 

1 U. S. Geol. Survey Prof. Paper 63, p. 35~, 1908. 

sm_all grains of pyrite . 

The Martha Per~ Yein, as exposed in· the, 

east drift, cuts solely granite gneiss, but in thewest drift it follows for :wme distance the south 

side of a monzonite porphyry dike and at two 

places cuts through the porphyry. The mineralization is entirely pyritic. The vein ranges. 

from 3 to 6 inches in width and is formed for the· 

inost part by r~placemert of the wall rock along· 

a zone of fracturing. About 215 feet east of the· 

tunnel the Martha Perks fracture abuts againsta mineralized fault. The mineralization, which 

is continuous with that of the Martha Perksvein, shows that the fault' is not entirely postmineral, although it may have undergone some· 

movement subsequent to mineralization. The. 

vein shows 3 to 6 feet of more or less silicified 

granite gneiss traversed hy small seams of pyrite and carrying more or less fine disseminated 

pjrite.· Several fracture planes parallel to thetrend of the vein and showing slickensides but, 

little gouge are commonly present. 
CLEAR CR.EEK COUNTY. 

The Rising Sun vein, which is followed by the schist now thoroughly consolidated. In places 

I-Ioosac tunnel for about 570 feet from the por- the vein shows 5 to 8 inches of white quartz untal, is con1n1only 3 to 8 inches in width. At its mi"'{ed with sulphides. The vein is later than 

ea.sternn1ost exposure the. vein proper is 6 the dike of ·bostonite porphyry, cut about 320 

inches wide and consists mostly of pyrite irreg- 'feet from the .portal, for stringers of pyrite 

uln.rly associated with son1e gray and white traverse the porphyry. The Rising Sun vein is 

LEGEND 

Monzonite porphyry 

Granite gneiss 

Idaho Springs 

-

formation 

EJ 

Pyritic veins 

I~ I 

Barren fractures 

(Arrows indicate 

direction of dip) 

N 

100 0 100 200 300 Feet 

FIGURE 79.-Geologic plan of Hoosac tmmel. Surveyed by pacing and hand compas3. 

quartz gangue. Below the vein the granite 

gneiss for 4 to 5 feet carries a little disseminated pyTite and is traversed by sn1all stringers of pyTite. Above the vein an unmineralized 

stre_ak lt feet wide is apparently composed of 

fragn1ents of pegmatite in a matrix of ground 

the only one on which any important amount 

of stoping has been done. 

The production of the I-Ioosac tunnel has 

been small and few details were available. 

.. 

INDEX. 

Page. Page. 

Aclmowlodgments to those aiding................................ 20 Bangor mine, features of .............. , . . . . . . . . • . . . • . . . . . . . • • . . . . 256 

A. 

Aduddoll mine, features of ......................... 102,269-272,304-305 Banta Hill, mines on............................................. 280 

geologic plan of ............................................... , 305 Barbara vein, features of......................................... 329 

After Suppor-Sioopy Hollow vein, features of ............... 102,226-227 Barber & Elliott vein, location of................................. 365 

Albro vein, features of ..............•... · ................ 112, 143> 354-355 Barnes mine, features of •... · .................................... 109,243 

Algor-I(nnsas vein, features of.................................... 229 ores of ..•. ················ .................................. 151,243 

All co, glaciation ncar ................................... .'... . . . . . . 59 plan of··········· •...................... ,. . . . . . . . . . . . . . . . . . . . . 243 

minos ncar ................................................. 319-326 Basalt porphyry, dike of......................................... 54 

Allee mine, alteration in ................................... .' 108-109,324 Bastin, E. S.: 

alteration in, plato showing................................... 97 on geography and geology •....•.............•.•............. 19-152 

features of .............................................. 106,323-326 work of...................................................... 20 

minorolization in ....................................... 98, 106,325 Bastin, E. S., and Palmer, Chase, on precipitation of gold . . . . . . . 139 

figure showing........................................... 98 on precipitation of silver ................................ 141 149 150 

placer mining at ................ : ........................... 120;325 Bastin, E. S., and Hill, J. M., on mines ofthe district ......... .' 177:a67 

workings of, figure showing................................... 324 Bastin, E. S., Henderson, C. W., and Hill, J. M., on ore treatment 

Alluvium, description or......................................... 60 ·· labor, royalties, etc ................................. isa i7o 

distribution of, plates showing.......................... In pocket. Bates Hill, mines on and near .................................. ~227 gold in ................................................. ·.· ... 60, 120 Bates mine, gold from ........................................... ·. 119 

Almaden mine, features oL .................................... 315-317 Baxter mine, features of.......................................... 232 

orcs of .......................................... 143-144,147,316-317 Beaver Creek, mines near ...................................... 192-193 

Almira tunnel, developments in.................................. 344 Becky Sharp mine, features of.................................... 254 

Alps IIJll, mines on ................................ 237-238, 244, 245, 247 Belcher mine, ores of ........................................... 242-243 

Alps mine, features of ........... ·.·............................... 244 ores of, assays of .............. ·.·.............................. 242 

pltchblondo in .................. : .......................... 123,244 pitchblende in ............................................. 123, 242 

Alsdorf, P.R., on Calhoun vein ................................ 245,246 Belden tunnel, features of ...................................... 208-210 

Alteration. See Wall rock, alteration of. geologic plan of............................................... 209 

Alton tunnel, dikes in ....................................... 51, 185-186 Bellevue-Hudson and Anamoosa lode, features of .............. 333-334 

features of .................................................. 185-187 Bellevue Mountain, mines on ..... .' ............................ 285-288 

geologic plan of............................................... 186 Bellevue tunnel, features or. ............................... 112,333-334 

Amalgamation, practice of ..................................... 154-155 Bellman vein, character or....................................... 110 

A. Mnudo Monroe vein, features of............................... 364 Bell vein, features of .....•....................................... · 300 

American City, minos near .....••........................... , .. 203-205 Belman ve~, features of ... · ........................ 281,283-284,304,358 

American Sisters vein, features of ..•........................... 339-340 Belmont vem, ores of ................ ,............................ 228 

ores of .................................. 111,119,144, 146, 150, 339-340 Berry vein, features of............................................ 309 

American Smelting & Refining Co., sampling by................. 164 Bezant mine, features of.......................................... 248 

American vein, features of ...................................... 102,321 Bibliography····................................................. 22 

Annmoosa lode. See Bellevue-Hudson and Anamoosa lode. Big Dipper vein, features of....................................... 350 

Anchor Gulch, mines of......................... . . . . . . . . . . . . . . . . . 320 Big Five tunnel, alteration in....... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107 

-Anchor mine, features of ................................... 106,274-275 alteration in, figure showing.................................. 108 

Andesite, dikes of ................................................ 50-51 . ~:;:~ op~-~i ::::::.·::.·:.·::.·.·_-_-_-_:.".".".":.·:::.·::.·.·.·.·.·.·.·.·. 1In07,p305ck:7-3e58t. 1 

Annaborg, Saxony, pltchblondo'at.. .. .. .. ... .. ... .. ............. 122 

Aimlo H. voiil, features of........................................ 205 Biotite-sillimanite schist, character of.. ........... ·............... 27 

Annie tunnel, features of......................................... 204 Black Canyon, mines in.......................................... 190 

Anything vein, features of ............................. :.......... 189 Blackhawk, mines near ........................................ 225-228 

Apex, mines near .................... ·. .. . . . . .. . . . . . . . . . . . . . 190,200-205 Blackhawk smelter, charges at ................................. .162-163 

Apoxlnw,orlginof .......... ~.................................... 68 historyof ................... : ............................... 154161 

Argo mill, methods at .......................................... 156, w2 Black Hills vein, features of .................... :................. '191 

Argo tunnel, features of ........................................ 303-306 • YBlaternick tunnel, features of..................................... 190 

mouth of, view of ......................................... ·... 222 Blazing Star vein, ores of......................................... 316 

orcs or ........... .' .......................................... 113 304 Blue Belle ve~, features of ..................................... 281-282 

Argo vein, features or ....................................... 109,~261 Blue Bird mine, dips in ......................................... 94,185 

Arrastres, usc of ......................................... ·......... . 153 features of .................................................. 101,185 

Arsenic, occurrence or. ...................... :.................... 99 Blue Ridge and Senator mine, features of ....................... 344-347 

See also Enargitc. geologic plan of.. .................................. ~.......... 345 

Aumlin, founding of.. ............................................ 67-68 Blue Ridge v~in, ores of ................................ ia9, 344, 345-~6 A urn Verde vein, features of ................................. :.... 319 Bobtail Hill, mines on and near ................................ 223-228 

Aurora mine, features of.. .............................. 109,137,259,200 Bobtail tunnel, features ~f .............................. : ....... 119,225 

orcs of .................•.......................... : .... 139-140 2GO plans of, plates showmg ..................... , ....... 224; in pocket. 

· n. ' ~~!:::·t=:t~:~::·~i.".":::::::::::::::::::::::::::::::::::: ~= · 

Bald Eaglo vein, orcs of.......................................... 285 Bonnie Briar mine, features of .................................. 318-319 

Bald Mountain, mines or......................................... 178 Boomerang Gulch, mines in ................................ 294,301-302 

rocks of. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . • . . . . . . . 42 Bornite, occurrence of .................................... , . . . . 126, 127 

silver veins of .............................................. 178-181 Boson-Plume vein, character of......................... . . . . . . . . . . 276 

l3all, S. H., on Carboniferous sand_stone ......................... 37,133 Boss tunnel, features of.. ......................................... • 318 

on Idaho Springs formation ............................ 27, 28, 29,31 Boston and Idaho tunnel, ores in................................. 181 

on igneous intrusion ............................ ·.............. 62 Bostonite, analysis of............................................. 53 

on Tertiary gravels...... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60 character of. ..... -:-. . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . .. . . . 52 

on 'l'ertiary intrusive rocks ................................... 38,39 description of ................................................ 52-53 

44214°-17--24 369 
370 INDEX. 

Page. 

Bostonite. distribution of........................................ 52 

origin of... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5~54 

photomicrograph of ............................ : . . . . . . . . . . . . . 52 

Boulder County, mines of. ..................................... 177-189 

Boulder County Hill, ores of. .................................. 182-185 

Boulder County mine, dikes in ........................... 51,52,182-183 

features of ..•.............................................. 182-184 

ores of .•........•....................................... 143,183-184 

view of. •............................... : . . . . . . . . . . . . . . . . . 96 

wall rock of, alteration of. ... , ............................... 52, 111 

Boulder Nest vein, features of.................................... 335 

. Boulder Park, mines near........................................ . 191 

Bourbon vein, features oL... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 310 

Breed mill, equipment of......................................... 156 

Bride vein, features of..... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 302 

Brooklyn mine, features of. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 223-224 

Buckeye mine, features of. ....................... ·... . . . . . . . . . . . . . 191 

Buell mine, gold from ......................................... ~-- 119 

Bull Hill, mine on............................................... 326 

Bullion King mine, features of.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . · 361 

Bullion tunnel, features oL ................. . : ... ... .' .......... 202-203 

Btirr House mine, features of.:.. . . . . . . . . . . . . . . . . . . . . . . ... . . . . . . . . . 280 

Burchard, H. C., on Alice mine placers ....... ·"· .......... .-...... 120 

Burroughs vein, features of.. ............. : ................ ~- 97,229-230 

gold from. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119 

Buttermilk Gulch, mines of ................................ 297,30Q-301 

c. 

Caledonia vein, features of................... . . . . . . . . . . . . . . . . . . . . . 207 

Calhoun mine, features of. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 245 

ore from ............................................... 124,246-247 

figure showing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124 

pitchblende from ............................................ 124,247 

California milling, type of. ........................... :.: ....... 154-155 

California-Gardner-Hidden Treasure lode, features of. 97,102,137,233-234 

California vein, features of ....................................... 95,306 

Cap the Climax vein, character of. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 329 

Carbonates, effect of, on silver precipitation .... , ....... 14Q-141, 142,152 

Carboniferous sandstone, occurrence and character of............. 37 

g:~:= ~::,h;C:;:so:f·.-~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~~ ~ ~-~:: :::: :~:: _ ~62-:: Cardinal, mines near .............. .". . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 184 · 

Cardinalose, analysis of • • . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 

. description of................................................ · 47 

Cari~::rl~~a~~~:_~f-·:::::::::: ::::::::::::::::::::::::::::::::::: . !! 

Caribou, history of. ..................................... · _.. . . . . . . . 177 

iron or~s near ....................................... 99,101,129-130 

. photomicrographs of ................. •.................... 52 

mines near ........................................ '.~: ...... 177-184 

monozorutic rocks near ............................ ~ ....... 42-49,98 

chemical relations of diagram showing. . . . . . . . . . . . . . . . . . . 49 

views of.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 

silver at •...... : ............................... :. . . . . . . . . . . . . . 177 

view of .................................. : . . . . . . . . . . . . . . . . . . . . 136 

Caribou Hill, mines on ......................................... 179-181 

silver veins of. ............................................. 178-181 

Caribou mine, features oL ... ; ........................ --.- ...... 179-180 

history of. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177 

wall rock of ............................................ , . . . . . 46 

Carlman mill, methods at........................................ 156 

Carnotite, production oL ....................................... _. 121 

Carr vein, features of. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109, 227 

g:~:: =e~ fe~~:~s ~r~:::::: ::::::::::::::::::::::::::::::::: ·m.:~ geologic plan of. ....................................... :. . . . . . 295 

tellurium in .......................................... : ..... 114, 299 

Casto vein, features of... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 208 

Centennial-Two Kings vein, features of........................... 359 

ores of. .................................... ·. . . . . . . . . . . . . . . . . 113, 359 

Central City, claims near ....................................... 222-228 

claims near, hst of... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69-82 

map showing .............................•... Pl. V,inpocket. 

description of................................................ 25 

dips near ................................. :·................... 94 

ores .near, content of. .......................... :.............. 110 

vicinity of, claim map of.. ........................ Pl. V, in pocket. 

geologic map of ............................. PI. III, in pocket. 

Page. 

Central City quadrangle, climate of............................... 24 

drainage of. ... · . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 

economic geology of. .................................. 16-18,67-152 

geography of. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-22 

geologic history of. ..................... ·. . . . . . . . . . . . . . . . . . . . . . 63-66 

geologic map of. ........................................ In pocket. 

geology of. ........ : ....................................... 16,26-62 

location and area of. ..................................... : . .. 19-20 

map of. ............................ · .............. Pl. II, in pocket. 

map, geologic, of ............................ · ...... PI. I, in pocket. 

mines in ... .' ............................................... 177-367 

distribution of. ........................................... 93-94 

lists of. ................................................... 69,92 

mining in .................................................. 153-175 

history of. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67-69 

oresof. ••... : ................................................ 105-175 

See also Gold-silver ore>; Uranium ores; Tungsten ores; 

Copper ores; Iron oros; Ores. 

production in .............................................. 171-175. 

settlement in................................................ 25 

topography of. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 

vegetation of. ................................................ 24-25 

Central Hill, mines on ............... -· .......................... 222-223 

Ceratgyrite, precipitation of...................................... 141 

Chalcocite, gold and silver in..................................... 116 

occurrence of. .............................................. ·.. 127 

Chalcopyrite, occurrence of ................................. 105, 126, 127 

gold and silver in ........................................... 116,119 

Champion Dirt mine, ores of. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 342 

Champion-Trio mine, features. of. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 288 

Champion vein (Rollinsville area) .. features of.................... 193 

Champion veins (Alice area), features of......................... 321 

Chapman, Pearson, work of...................................... 20 

Charcoal Charlie vein, features of. .......... -................. ·- 20Q-201 I 

Chase Gulch, mines on ....... ~ ............................... ~. 208-212 

Chase mine, features 6C: .....•..•................... 102,109, 136, 275-276 

geologic plan of...... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 275 

Chemung-Belmont mine, features of.............................. 228 

Chesapeake tunnel, features of. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 321 

Chicago Creek, gold on, d.lscovery o:' .............................. 67-68 

placers on......... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120 

Chieftain vein, features of. ..................................... 195-196 

Chlorination, use of.............................................. 156 

Chlorine, occurrence of............. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141 

silverand .. , ................................................. 141 

Cincinnati vein, features of....... . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 355 

Claims, maps of ................................. Pis. V, VIII, in pocket. 

maps of, finding lists for..................................... 69 

Clarissa mille, features of ................................. · ....... 281-282 

geologic plan of. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 282 

Clay County vein, features of..................................... 228 

Clear Creek, glaciation on .... ~ ................. :. . . . . . . . . . . . . . . . . 59 

gold on....................................................... 120 

gravels on ............................................. 57,58,59,120 

mines on ........................................... 331-334,341-359 

Clear Creek County, metal productiou of ................. _._ .... 172-173 

mines of. .................................... · .............. 281-366 

Clear Creek tunnel. See Gilpin and Clear Creek tunnel. 

Clifford vein, features of.. ...................................... 317, 318 

Climate, character of. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 · 

Climax mine, features of. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 232-233 

Cobalt, occurrence of. ... :......................................... 49 

Cobalt-silver ores, pitchblende in ............. ~ ................. 122-123 

Creur d'Alene mine, features of... . . . . . . . . . . . . . . . . . . . . . . . . . . . 96, 103, 221 

Collins, G. E., on gold and silver in on' minerals ............... 116-119 

Colorado, index map of........................................... 19 

map of, showing metal distributior........................... 93 

metalliferous districts in...................................... 13 

map showing ...................................... ~..... 93 

mining in, early history of ....•............................... 67-69 

Colorado & Southern Ry., freight rates on ...................... 169-170 

Colorado Mountain, mines on .................................. 190, 204 

Colorado tunnel, features of ....................... :. . . . . . . . . . . . . . 198 

Columb.ia tunnel, features of ................................... :. 232 

Columbus vein, features of .......•.......................... ~..... 254 

Commercial Union tunnel, features of. . . ...................... ·. . 98, 326 

Commodore tunnel, features of .................................. 334-335 

geologic plan of................................................ 334 

Compeer vein, character of. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 305 
INDEX. 371 

Page. 

Compensation vein, ohamctor of .. ,............................... 305 

Composite ores, c~amctor of ................................. 16,112-113 

distribution of ................ .' ........................ ~..... 116 

micrographs of ................................... : : . ..... :. . . 113· 

plates showing .................................... : ..... ':·. . . . 96 

tenor of.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114 

Comstock mlno, description of.. ............................... : 180-181 

Concentrating or~, definition of ..................••......... :....... 154 

Concontmtlon, pmctico of ...................................... 154, 155 

Concreto mine, features of •..•..... ·.:.·: •..• :.: ..... : ...•. 95,112,214-216 

Conductors tunnel. See Fireman an~ Conductors tunnel. 

Conglomomtos, metamorphosed, character of..................... 29 

Cooke, H. C., on silver salts ........ ::·.: ...... :................... 14.0 

Cook mlno, ores of ...................... .'........................ 139 

Coon 'l'mll Crook, minos on ................................. 185-187,189 

Copper, ourlchment of ......... L ..................• 138, 150-151,152,262 

occurrence of.......... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hi, 105 

production of ........... · ............................... .' ... 173-175 

Copper ores, character of ........................................ 17, 126 

distribution of. ...................... ·........................ 99 

enrichment of ........................................... 18, 129, 138 

magmatic segregation of ..................... .' ........... 98,126-129 

minerals of ................. ~ ........................... 100, 126, 127 

occurronco of, mode of ...................................... 126-128 

origin of .................................................... 128-129 

smelting of, charges for....................................... 163 

Cornwall, England, pitchblende at ................... :........... 123 

Corydon mine, features of ................. : .................... "109, 222 

Crawford, R. D., Goorgo, R. D., o.nd, on tungsten orcs ......... 126,132 

Cretaceous time, ovonts in ....•••.............................. 21, 64-65 

Crockot vein, features of ....••••........ : ......................... · 359 

Cross, Whitman, on Denver fJrmation .............. .'............ 39 

Cross Lode tunnel, orcs in........................................ 181 

Crown Point and Virginia mine, features cf.. . . . . . . . . . . . . . . . . . . . . 281 

Crystal tunnel, features of .................................. 112,298-299 

geologic plan of............................................... 299 

Cumborh:md Gulch, mines on. : . ....................... 318-319, 326-327 

Cumberland mine, features of .............•........ .'............. 325 

Custom mills, methods of ................... L , •••••••••••••••• 155-156 

requirements of.............................................. 155 

Cyanide process, uso of ........................................... · 156 

Cyclops voln, ores of ........................... ~ ............. -:-:.. 211 

Cymric tunnel, foatures'of . .'...................................... 338 

D. 

Dakota Hill, minos on.. . . . • . . . . . . . . . . . . . . . . . • . . . . . . . . . . . . . . . . . . . 200 

Danube voln, ores of ...........................•. ;............... 299 

Dnrdanoll No. 2vein, character of ....................... ,; .. ·..... 171 

orosof ............••................................ 147,149,178,179 

See also Up to Date mine. · 

D6brls shoots, description of...................................... 60 

distribution of, plato showing ........................... In pocket. 

goldin ....................••....... , ........................ 60,120 

Decatur vein, character or .............................. :......... 276 

Do Lcssops tunnel, features or.. ............................ ~..... 290 

Delight vein, ores of ........................................... ·''. 210 

Delmonico vein, features of ......... .' .. ·........................... 244 

Dolondoso, analysis of............................................ 43 

description of ................ : . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 

Denblgh voln, features of......................................... 312 

Denver, founding or ............................................ ·.. ·67 

Donvor & Salt LakeR. R., freight rates on ....... .'............... 170 

Depth, relation of, to oro value ................................. 137-138 

Diamond Blll claims, features of................................. 195 

Dlkos, ago of..................................................... 49 

copper ln ............................... : ....... , ........... 126-128 

geologic relations of ....................................... ,.. 128 

occurrence and character of ........................... 49-52,127-128 

Diorite, dikes of ..........................................•....... 51-52 

Donaldson-Champion-Dirt vein, features of. .................... 109,342 

Donna Juanita vein, development on.. . . • • . . . . . . . . . . . . . . . . . . . . . . 363 

Douglas Mountain, mines on ..................... .' ............. 330-331 

Dover tunnel, features of ....................................... 306-307 

geologic plan of............................................... 307 

Dminago, description of. ............. :........................... 24 

Druid mine, features of ................................. 102,104,272-274 

Dry Gulch, mines in ........................................... 356-357 

Dual minomlization. See Mineralization; Composite ores. 

Page. 

Dubuque mine, features of. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . • 308 

Dumont, mines ncar .......................................•... 344-356 

Dumont group, character of...................................... 355 

Dyke vein, ores of ........................ :....................... 306 

E. 

Eagle Bird mine, vein of......................................... 182: 

Earl o(Kent mine, features of ............ · ............••........ 349-35() 

Early Bird tunnel, features of.................................... 191 

East Lake tunnel, features of..................................... 28S 

East N otaway mine, features of .. · .............................. 264-265- v 

geologic plan of............................................... 265-

tellurium in ............................................ 114, 115, 265-

veins in ............................. : ............. ; ..... 95, 102, 2fl4-

Economic geology, details of .... ·' .............................. 67-175· 

outline of .................................................... 16-IS. 

See also Mining. 

Edgardine vein, features of....................................... 303-

Edgar vein, features of ...................................... ~ .. 358,360 

Edith S. vein, ores of.. .............................. ,............ 357 

Egyptian mine, features of·.· ........... • .................... 112,151,239 

planof....................................................... 239 

Eldora, glaciation near.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59 

intrusion near, view or....................................... 53 

mines near ................................................. 187-189 

tellurium in ............................................ 115, 116 

outwash plain near, view of ................ •.................. 53 

Eldorose, analysis of. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 

description of. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 

Elida tunnel, ores of.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119 

Elizabeth vein, features of ............................. •. 102,217-218,300 

Elk Creek, mines on ...................................... ; .... 203-204 

Elkhorn Gulch, prospects near ................................. 279-280 

Ellery vein, features of........................................... 208 

Emmons, S. F., work of .... .' ...................................... 13-14 

Empire, glaciation near,.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .•. . . . . . . 59 

mines near ....................... ·. . . . . . . . . . . . . . . . . . . . . . . . . • 330-334 

Enargitc, occurrence of ........ -:-:.-: ..•............... 99,105,110,115,133 

Engardine vein, features of....................................... 303 

England, pitchblende in. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123 

England mine, features of ............................ ~ ......... 362-363 

Enrichment, depth of ........................................... 137-138 

limitspf .•...•.•............................ .-: ................ 17-18 

ores affected by ••................................. · ......... 138-15Z 

processes of .•••..•......................................... 137-138 

studycf ....••............................ , ........... ~...... 14 

See also Gold; Silver; Copper; etc. 

Enterprise vein (Eldora area) features of......................... 188 

ores of ....................................................... 115, ISS 

Enterprise vein (Yankee area), character of .. :. . . . . . . . . . . . . . . . . . . 321 

Erzgebirge, Germany, pitchblende in .......................... 121-123 

Eureka vein (Gilpin Eureka mine), features of ...... :............ 213 

·Eureka vein (Up to Date mine), features or .................... 178-179 

Europe, pitchblende in ......................................... 121-123 j 

Evergreen mine, dikes in ............ ' ................ = ......... 126-128 

dikes in, breccia of............................................ 127 

petrology of. ........................................... 127-128 

photomicrograph of ......... '............................. 124 

:;~:;:u~~t-·::::::::::::::::::::::::::::::::::::::::::::::·1~~::' geology in .................................................. 126-128 

mineralization in ............................... : . . . . . . . . . . . 126, 129 

ores or •••...•.•........................ 17, 98, 99,101,126-129,151,202 

F. 

Fairhaven vein, features of....................................... 193 

Fairmont tunnel, featqres of.. ............... .' .................. 282-283 

geologic plan of...... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 283 

Fall River, mine!! on. ..•..... · .................. 120,306-3~9;344,366-367 

Fannie vein, ores of ............................ ':.. . . . . . . . . . . . . . . . 211 

Faults. deposits along ......................•..................... 62,64·· 

origin of. •................................ ·.................... 62 

Faulting, complexity of.......................................... 95 

~~~:r::~~ ~~i~ti~~~ ~f:::::: ::: :::: :: ::::: : :::: :::::: ::: ·. ~~·. ~~· :~~ wall rock and, relations of ................................ 95-96, 103 

Faust mine, development at. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 328 

Federal mine, features of......................................... ~51 
372 .INDEX. 

Page. 

:Ferberite, occurrence of........................................... 126 

:Fifty Gold Mines Co.'s claims, features of. .................. 10!l, 225-226 

Firemen and Conductors tunnel, features of ....... :. . . . . . . . . . . . . 343 

:Fish vein, features of............................................. 204 

.Fisk vein, features or............................................. 225 

Flat vein, features of •.......................................... 270-271 

Fluorite, occurrence or. ........ ~ .. ~ .................... 105-106,114,115 

:Foliation, character of. •.......... ~ ............................... 47,61 

development of ........... ~ ... · ........ ~ .................... 15-16,61 

See also Schistosity. 

Four-C tunnel, geologic plan of.................................. 347 

veins of ........................................ ; ............ 346-347 

Fourth ofJuly vein, features of................................... 230 

ores;:~t~·~h~~~~~~ ~: ::::::::::::: ~:::: ::::::::::::::::::: -~1~,~~ Foxhall tunnel, features or........................................ 299 

geologic plan or .......................... ~ ..... '. . . . . . . . . . . . . . 295 

:Fracturing. See Faulting. 

Franklin vein, features or. ............ : ................ 110,112,292-294 

..Free America vein, features or.................................... 335 

Freedom vein, features of........................................ 211 

Free Gold vein, features of ...................................... 199-200 

Freelandose, analysis of.......................................... 56 

descripti~n of ................................................ 56-57 

Freeland tunnel, features of. ................................... 352-353 

geologic plan of ..•...................................... :. . . . . 352 

Freeman Gulch, mines near •••.............................. 0 •• 200-201 

Freight, rates of •................................. : ............. 169-170 

Freighters Friend mine, workings of .•.......................... 290, 291 

·Frontenac mine, features of ................. 96,102,156,269-272,304-308 

geologic plans of .•.......................................... 269,305 

Front Range, peneplain of .... : .................................. 21,23 

peneplain of, views of........................................ 20 

topography of .. ~............................................. 22 

G. 

Gabbros, analyses of............................................. 43 

description of ................................................ 45-46 

Galena, etching of. .........•................................... 136-137 

etchingof,plateshowing..................................... 136 

gold and silver in.. . • . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119 

Galena-sphalerite ores, character of............................... 16 

character of, variations in.................................... 132 

-definition of.................................................. 110 

distribution of. ............... ·...... .. .. .. .. .. .. .. .. .. .. .. . . . 116 

enrichment of ...................................... 138, 141-143, 152 

See also Ruby silver; Native silver. 

goldin....................................................... 16 

metalsin..................................................... 112 

minerals in ................................................. 100, 110 

gold and silver in ............. : ......................... 116-119 

paragenesis of.. . . . .. .. . . .. .. . . .. . . .. . . .. . . . . . . .. . . .. . . . . . 110 

porphyries and, rel.ations of................................... 101 

silv::~;~i~~f:: :::::::::::::::::::::::::::::::::: ::·::::. ~~·- ~42-:~~ structuJ;e of ................................................ 110-111 

plates showing ........................................... 96,97 

tenor of...................................................... 112 

texture or. ................................................. 110-111 

wall rock and, relations of .............................. 103,111-112 

Gamble Gulch, features of. •.................................... 195-198 

gold in, discovery of.......................................... 68 

placers in. . .. . .. .. .. .. .. .. . . .. . .. . .. . .. .... .. . . . . .. . .. . . . .. .. . 120 

Gardner lode, features of .................................... 97, 234, 237 

ores of •................................................. 102,234, 237 

Garrey,G. H. See Spurr and Garrey. 

--~::~l:!t:~~:~:~~!~:~~~-f::::::::::::::::::: :.::::::: :·:::::::::::: ~~~ Gem mine (Alps HilD. features of................................ 245 

Gem mine (Seaton Mountain), features of .................. 290-292,297 

ores of. ......................................... 116, 119, 291-292,297 

tellurium in ................................................. 114, 291 

Geography. description of: ....................................... 24-25 

Geologic history.outline of ....................................... 63-65 

Geologic maps, Central City quadrangle .............. ·• Pl. I. in pocket. 

Central City vicinity ............................ Pl. III, in pocket. 

Idaho Springs vicinity ........................... Pl. VI, in pocket. 

Geology ,economic. See Economic geoloby, · 

Page. 

Geology, account of. ................................... : . .. 15-16,26-62 

maps showing •.. : .......................... Pis. III, VI, in pocket·. 

George, R. D., and Crawford, R. D., on tungsten ores .......... 126,132 

Georgia Gulch, mines on ....................................... 364-365 

German mine, features of.. ..................................... 240-243 

pitchblende ore in ....................................... : .. 241-243 

figures showing .......................................... 97, 124 

Germany, pitchblende in ....................................... 121-123 

Gettysburgh vein (Gilpin area), features of....................... 200 

Gettysburgh vein (Russell Gulclt), features of .... '................ 258 

Gilpin, mines near. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 200 

Gilpin and Clear Creek tunnel, fe:ltures of ...................... 353-354 

Gilpin County., metal production of ............................ 174-175 

mines of... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 190-280 // 

Gilpin Eureka mine, features of ................................ 213-214.,.(' 

Gilpin Tramway, freight rates on................................. 169 ~ 

Gilson Gulch, gravels in........................................... 57 

mines in ....................................... 288-290, 292-294,303 

rhodochrosite in... .. .. . .. .. . .. .. . .. . .. .. . .. .. . . . .. .. .. . .. 110 

Glacial deposits, description of. ............... : .................. 58-60 

See also Glaciation. 

Glaciation, age of ...... · .......... 0. • • • • • • • • • • • • • • • •.• • .. • • • • • • .. • • • 60 

effects of. ................................................. : .. 21-22 

erosion during... . .. .. . .. .. . . . . . . .. .. . .. . .. . .. . .. .. .. .. . . .. . . . 58 

occurrence of ................................................. 57-60 

Gladstone vein (Idaho Springs), features of. .................... 143,363 

Gladstone vein (Russell Gulch), features of.. ................ 95,109,259 

Gloria Mundi vein, ores of. ..................................... 307-308 

Gneisses, description of.. ......................................... 27-32 

Gneissic structure. See Foliation. 

Golconda mine, features of ..... · ........ : . ...................... 315-316 

Gold,enrichmentin ..................................... 17,138-140,152 

.fineness of ................................................. .' 119-120 

occurrence of, in ore minerals ......................... 116-117,119-138 

precipitation of ..................................... .' ..... :... 139 

production of ............................................... 172-175 

saving of, percentage of....................................... 155 

solution of .................................................. 138-139 

Gold Anchor mine, features of...... . .. . . .. .. .. . .. . .. .. .. .. . . .. .. . 321 

Gold Band vein, features of ........................... ;.......... 427 

Gold Ohest tunnel, features of....... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 344 

Gold Collar mine, alteration in................................... 111 

features of .................................. :................. 214 

vein in ...................................................... 96, 214 

Gold Dirt mine, features of.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119, 197 

Gold Dirt vein, features of........................................ 197 

Golden, smelting at.............................................. 162 

Golden Cloud mine, features of ................... , ............. 250-251 

Golden Eagle_yein, features of........ . . . . . . . . . . . . . . . . . . . . . . . . . . . . 228 

Golden Flint vein, features of. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 200 

Golden Hope vein, features of.................................... 355 

Golden Rod mine (Gilson Gulch), features of..................... 303 

Golden Rod mine (Silver Creek), features of...................... 206 

Golden Sun tunnel, features of ................................. 191-192 

g~ologic plan of................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . 192 

Golden Treasure-Slaughter House vein, branching of.. . . . . . . 95, 214-215 

Gold King mine, features of .............................. · ... 143, 18-i-185 • 

Gold placers, importance of .............................. 57, 98, ios, 120 

Gold Queen vein, features of. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 194 

Gold Reserve group, features of ............................. ·. . . . . 326 

Gold Reserve vein, features of. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . • . 204 

Gold-silver ores, character of. .............. · .... ; ... :. 16-17,105,138,154 

classification of. .................... · . .-. . . . . . . . . . . . . . . . . . . . . . . . 105 

concentration of, by weathering ..................... ' ...... ~. 138 

depth of, range of. .... ·.· ......... · .... · ............... ·~........ 134 · 

distribution of.. .................................. -....... 99,115-116 

enrichment of.. .................................... :. 1-7-18,138-140 

minerals of. ............................................ .' ...... o 100 

gold and sih·er in ............ , ...................... ; ... 116-119 · ·. 

payment for ...................... : ....................... · .. 164-168 

porphyril;)s and, relations of. ................. : .......... · .... •. 101 

wall rock and, relations of. ........ .' ... · ......... 103, 107-i09, 111-112 

See also Pyritic ores; Galena-sphalerite ores; Composite o~es; 

Telluride ores; Silver ores; ·Gold. 

Gold Standard vein (Apex area), rea turns of...................... 202 

Gold Standard vein (Yankee area), featnres or. .......... ; ........ · 330. 

Gold tunnel. See H-ill and Gold tunnel. 

Good for Nothing vein, character of.............................. 358 
INDEX. 373 

Page. 

Gmnd Army vein, features of ........................... 95,216-218,306 

Grand Island district. See Caribou. 

Granito gneiss, ago or. ............................. ,. . . . . . . . . . . . . . . 15, 32 

dofulltion or ............................... ·...... . . . . . . . . . . . . . 30 

distribution or.... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 

lithology of... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 

origin or. ........................................... ; ......... 31-32 

sphalerite In, plato showing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96 

structure or. .............................................. 3G-31,61 

Gmnlto pegmatite, age of. ........................................ 15,35 

chnmcter or ......... :. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 

doflnltlon of. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 

derivation or................................................. 35 

distribution of. ............................................... 33-34 

!~~~~~~~~~ ~~·- ~~~~~ ~~~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~: ~: ~ ~ ~ ~ ~ ~ ~. 34-35, :~ viowsof. ...................................................... 21,53 

Gmnlto porphyry, ago or......................................... 54 

character and distribution of................................. 54 

Grasshopper voln, features of..................................... 255 

Gravels, ago or................................................... 15 

goldin .................................................... 57,60,98 

See also 'l'ortiary gravels; Ploistocono grovels. 

Groat Con tor vein, character of................................... 358 

Groat Northern mine, orcs of ................................... 182,356 

G rogory, J. H., gold discovered by. . . .. .. .. .. . .. .. .. . .. . . .. .. .. . . 68 

Gregory Gulch, minos in ....................................... 226-227. 

Gregory Hill, minos on ......................................... 224-227 

Jnlnos on, view or. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 223 

Gregory vein, features of ....................................... 225-226 

gold from.................................................... 119 

tollurimn in ................................................ 114,226 

Gulch mine, features of. ........................................ 265-266. 

Gunnell-Orand Army mine, features of ...................... 95,216-218 

Gunnell vein, features or. ...................... 102,119-12G,216-218,306 

H. 

Hague, J. D., on Burroughs vein .............................. 229-230 

on Tlllnols mine ............................................ ·.. 239 

H!\U and HBlf vein, features or................................... 304 

HBilmlno, fonturos or. ............................. ,............. 256 

Hamlin Gulch, minos on......................................... 318 

Hmnptonmlno, fcBturos or.. ..... · .................. ·.............. 279 L 

HBrsh vein, features of........................................... 248 

IlBttlo vein, character or.......................................... 306 . 

Hayseed vein, features of ............................... 112, 136,211-212 

galena In ................................ ~ .................. 136,212 

·platoshowing............................... ........ ..... 136 

wall rock or. ........................................... .'..... ,111 

Hazeltine vein, features of ...................................... 268-269 

Boola mine, chamutor of.. ....... ~ ..... ~........................... 349 

vein or. ...................... ~ . .. . . . . .. .. . . . . . . . . .. .. . . . . . . . 97, 349 

Holen tmmol, features of......................................... 311 

Henderson, C. ,V., on production of mines ..................... 171-175 

workof...................................................... 20 

Sec also Bastin, Henderson, and Hill. · 

Doss, 1<'. L., aid of................................................ 121 

Hicl~: ~~1 ~l~~~~~i~e ss~~~:::::::::::::::::::::::::::::::::::::::::: ~~! Bidden Treasure-~~lifornia-Oardner lode, features of. 97, 132, 137,233-234 

geologic plan of..: ... .'. .. .. . . . . .. .. .. . . . . . . . . . . . . . . . . . . . . . . . . . 233 

Hid don Tr\lasuro vein, character or ............................ 102,322 

Bill, J. M.,. work or............................................... 20 

See also J3astln, Henderson, nnd Hill; Bastin and Hill. 

Eill,N.l~.,smolterof. .......................................... 154,161 

smeltor of. See also Blackhawk smelter. 

Bill and Gold tunnel, features of................................. 190 

Blllhouse-Columbus vein, fo!\turos of ........................... 2ii7-258 

Blllmlno, reaturos.or.. ... ~................... .... . . . . . . .. . . . . . . . . . 280 

History, geologic, outline of. ......... : .... : ...................... G3-65 

History, mining, outline of.. ..................................... 67-69 

. :Hollister, 0. J., on Gold Dirt vein ............... :................ 197 

· FIOJ'iloold, definition of ............... :........................... 32 

B.omestako vein, fo!\turos of. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136, 264-265 

telluride oro ln............................................... 102 

Hoosac tunnel, features of. ..................................... 366-367 

geologic plan, of..~ ....................... ·'-.................... 367 

Page. 

Hornblende gabbro, description of.. .............................. 45-46 

Hornblende monzonite porphyry, dikes of. ....................... 49-50 

Hornblende schist and gneiss, character or..... . . . . . . . . . . . . . . . . . . . 28 

veinof....................................................... ·53 

Homblendite, analysis of... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 

description of. .. :............................................ 46 

occurrence and character of.. ................................. 32-33 

Hubemockcr vein, features of.................................... 204 

Hubert mine, branding of. ...................................... 95,220, 

breccia in ............................................ 97-98,101,220 

figure showing .......................... : . . . . . . . . . . . . . . . . . 97 

features of.. ................... ~ ........................ 112,218-221 

ores of, view of .......................... : .......... : ........ 96,220 

workings of, figures showing ................................ 219,220 

Hudson-Burr tunnel, ores of...................................... 294 

Hudson lode. See Bellevue-Hudson and Anamoos:llodo. 

Hudson Reduction Co.; mill of................................... 155 

Hudson vein, features of ........ :. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112,358 

Hukill Gulch, mines on ........................................ 359-361 

I. 

Idaho Mountain, gold ores of. .................................. 181-182 

Idaho Springs, claims ncar ..................................... 356-367 

claims near, list of.. . .. . . . .. . . . .. .. . .. . .. .. . . . . .. . . .. .. . .. . .. . 82-92: 

map showing.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . ri. VIII, in pocket. 

descriptiCin of. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25-

dipsnear..................................................... ·.94 

.discovery of. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67 

gravels at.................................................... 51 

vicinity of, map of.. ........................... n. VII, in pocket. 

map, geologic, or ........................... Pl. VI, in pocket. 

Idaho Springs formation, age of. .......................... , ...... 15,30 

character of. ................................................. 15,23 

deposition of. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63 

distribution of................................................ 26 

erosion of.... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 

fracturing in ................................................. 95-96 

injection gneiss in, view of.................................... 21 

intrusions in. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 

tlth~~~~so~~~::::::::::: ~:::::::: :': ~:::::::::::::::::::::::: :·: 21•: 

origin of.. . . . .. .. . . .. .. . .. . . . .. . . . .. .. . .. . . . . . . . . . . .. .. . . . . .. . 29-3()1 

schists in, views of. .......................................... 21,53-

structure of. . . .. . .. . .. . .. . .. . .. .. . .. . . . . . . . . . . . . . . . . . . . .. . 26-29,61 / 

Idaho mine, ore from, assay of.. ................................ 147,177 . 

Idaho Mountain, mines on ................................. 181-182,184: 

Idaho tunnel (Caribou).· See Boston and Idaho tunnel. 

Idaho tunnel (Seaton Mountain), altcmtion in.................... 108: 

features or. ................................................. 301-302: 

geologic plan of... . .. . .. . .. . . .. . . .. .. . . . . . . . . . . .. . .. . .. . . . . .. . 302' 

Ida May tunnel, features of....................................... 317 

Igneous rocks, intrusion or. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . M 

occurrence and chamcter of ..... ~ ............................. 30,62 

See also Intrusive rocks. 

Illinois-Kansas vein, ore or....................................... 229• 

Illinois mine, features ol. ....................................... 239-24QJ 

Illinois vein, ore of. ................... ·........................... 205 

Ingram vein, features of. ....................................... 201-202 

Injection gneiss, character of ................................ :. . . . 29 

view or....................................................... 21 

Intrusive rocks, age of.. ...................................... 15, 21,133-

intrusion of. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11) 

See also Tertiary intrusive rocks. 

Iron Duke mine, fea.turos of. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 256-

Iron mine, features of. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 254-255-

Iron ores, character of...... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16, 17, 48, 129 

dis~ribution of.. .......... : ............................... 17, 99,129 

~~~:a~~-~~~~~~~~~~~~~~~~~~:~:~:~:~::~::: ::: ~:::::: ~: ~: :: :: ~. ~00, ~~~ photomicrographs of. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48, 5Z 

titanium in................................................... 130 

effects or. ................................. .'.: ........... 17,130 

Iroquois vein, features of... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 279 

Irving, J. ~··on parage!ilesis of ores............................... 132 

Ivanhoe vern! f?atures of.. ............................. 112,136,237-238 

ore brecCia 1n.... .. .. . . . .. . . .. . . . . . . . .. .. . . .. • •. . .. .. . . . . .. . 136,237 • 

plate showing .............. ~....... . . . . . . . . . . . . . . . . . . . . . . 97 
·'374 INDEX. 

J. Page: 

:.Jack Pot tunnel, features of .................................... 143,184 

Jackson, G. A., gold discovered by ....... ~........................ 67 

:.Japan vein, character of:......................................... 305 

J'asper tunnel, features of......................................... 189 

Jefferson-Calhoun vein, features of.. ............................ 245-247 

ores of. ................................................. 124,246-247 

figure showing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124 

pitchblende ore in ........................................... 124,247 

wor.kings on, plan of ............. ,............................ 247 

Jennie Jones vein, features of..................................... 328 

.Jennings, E. P., analyses by ... ;................................. 43 

on ti taniferous iron 9res ....... :. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 

Jenny Lind Gulch, mines in ............. ,~;., .................. ; 190-192 

Jenny Lind vein, features of ......•............ , .......... ,........ 358 

Joaquimsthal, Bohe~a,;~itchblende.~t ...... ~................... 122 

Johanngeorgenstadt, Saxony, pitchblende at..................... 122 

John L. Emerson vein, features of.. ............................. 95,309 

,,Johnson prospect, features of. ...... ·'· .............. ,.·............. 207 

Johnson tunnel, features of....................................... 192 

Jointing, character of............................................. 62 

.Jo)~eynolds mill, character of.. ......... ·.~ ......... : ....... ,...... 156 

. !o.~eynolds vein, features of ...............• ,, ...........•.... 147,340-341 

• ··:{~~i~:;~i;\\::: \:::::\::: ij i! ::~:, •c::~;,~],i~'.! OO, ~· K. ,·, .• 

~ ., f~ I} 

·Kansas-Burroughs group, veins of. ................. :.:, .. 97,2~!!:-:~0,236 

··Kansas vein, features of ......................... .' ....... 97, :1,1~;~28-229 

.. Keith tunnel, features of. .................................. ·.~; -~::355-356 

Kent County vein, features of. ................................. ,, .• ,, p9, 238 

. ·~en tuck vein, features of ....................................... ,, 358 

:Kent vein, features of. ........... _ ................. _ ...... ·.; ... , .. 349-350 

. Kinda vein, features of .............. · ......................... ;," 310 

. King Bee mine, features of ....... :............................... 305 

. Kingston, mines near. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 205 

Kirk vein, features of.. ......................................... 244-245 

pitchblende in ............................ , ................ 123, 244 

Kithil, K. L. See Moore and Kithil. 

·Klondike vein, features of ...... _ J. • • • • • • • • • • • • • • • • • • • • • • • • • 110, 249-250 

Knickerbocker tunnel, features of ............... : . ....... _ . . . . . . . 311 

Xoh-I-Noor tunnel, dump of ............. : ................... _... 189 

Xokomo mine, features of. ........... , ....... : ............. 102, 150,274 . 

L. 

:Labor, conditions of.............................................. 168 

·.La Crosse tunnel, features of. ..................... ~ ......... ;_ ... 234-235 

·:Lake Gulch, mines in ..................... · ................. 228,264-265 

:Lake tunnel, plan of..... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 284 

Lake vein (Big Five tunnel), character of. ..................... 107,358 

character of, figure showing.................................. 108 

development on..... . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 358 

Lake vein (Virginia Canyon), features of ....................... 284-285 

, Lakes, artificial, construction of. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 

Lalla vein, features of ................... ·. . . . . . . . . . . . . . . . . . . . . . . 322-323 

Last Chance veii:t, character of. ............................. :. . . . . 322 

· Latite, age of..................................................... 57 

analysis of. ................................................... · 56 

character and distribution of. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56 

Laurvikose, analysis of.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 

description of. ................ : . . . . . . . . . .. . . . . . . . . . . .. . . . . .. . 55-56 

Lawson, glaciation near .................................... _ . . . . . 59 

mines near ............................................. 330,334-341 

view of. ........ , ......................................... _ . . . 334 

Lead, enrichment of. ...................................... ·. 138, 151, 152 

production of ........................................... _ .. 172-17ti 

~~~;~;y~:=~~~-f~~~~:: :::::::::: ::': ::::::::::: :~:: ::::::::: ~:t~~~ Leavenworth Gulch, mines on .. _ ........................... 245,248, 258 

Leidenger tunnel, features of. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 330 

Lime-silicate rocks, character of ................... ·. . . . . . . . . . . . . . . 28-29 . 

Lincoln vein, ores of. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 365 

Lindgren, Waldemar, on Mogul tunnel . . . . .. . . . .. .. . . .. .. . . . . .. . 188 

on telluride ores.... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115, 187-188 

Page. 

Literature, list of.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 

Little Annie mine, ores of... .. . . .. .. . . .. . .. . .. .. . .. . .. . .. . . . . .. .. 113 

Little Blanche tunnel, featur·~s of. .. _............................. 319 

Little Clara vein, character o~: ............. _. _ .... _. . . . . . . . . . . . . . . 329 

Little ~Ida vein, features of .... _ ........... _ ....... _ .. _ ........ 329-330 

Little Giant vein, features of ............................... 137-138,336 

Little Jimmie vein; features of. ................................. 186-187 

Little Mary vein, features of. ....... _ ....... _ ......... _. _ ....... _ . 323 

Little Six tunnel, features of ........... _ .... _ ....... _..... ... . . . . . 364 

Livingston mine, features of. ............. __ ...... _ ......... _..... 251 

Lombard mine, features of ........................... : . ........ 326-327 

Lond.on vein, features of.. .................... _ ....... _ .......... _ . 205 

Lone Star vein, features of ............... _ ....... _ ....... _....... 193 

Lost vein, features of. .......... _ ................... _ ....... __ .. _ . 364 

Lotus mine, features of. ....... _ ~. _ ......... ~ ............. __ .. . . 256-257 

geologic plan of. ......................... _ .................. _. 256 

Lucania t~el, features of ............................. _......... 309 

Lucky group, features of ......................... _ . . . . . . . . . . . . . . . 313 

Lump Gulch, mine in .......... _ ......... __ ........ __ .. . . . . . . . . . . 200 

Lutz yein, features of...... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 258 

M . 

Mackey vein, features of. ............... .'.. . . . . . . . . . . . . . . . . . . . . . 203-204 

plan of ............................................. ~.. . . . . . . . 203 

Macon tunnel. See Sherman-Macon tunnel. 

.... Magdalena vein, feat~res of.. .......................... _. . . . . . . . . . 311 

; ~~pna, ore segregations from ......................... _ . . . . . . . . . 98, 1.00 

~Maine Hamlet mine, feature~ of. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 222 

- .·:·!"eins in ................................. ,.................... 222 

figure showing ........... _ .. . . . . . . . . .. . . . . .. . .. . .. .. .. . . . 222 

'Mammoth Bill, mines on an•l near ............. _,_ .............. 223-226 

,, . View of....................................................... 222 

) ;Mammoth vein, features of.. ............................. 95, 97, 223,306 

' · · ~~~~~~~~!; ~i~~- ~i ~:: ~:: ~::::::: ~::::::::::::::::::::::. ~~~~ ~~ • ;~~ Mandolina vein, features of. ..... ::.. . . . . . . . . . . . . . . . . . . . . . . . . . . . 310-311 

Manhattan tunnel, features of.................................... 318 

Mann vein, features or ..................... '....................... 329 

Maps, claim, Central City vic:inity ...................... Pl. V, in pocket . 

Idaho Springs vicinity .................... · ..... Pl. VIII, :n pocket . 

Maps, geologic, Central City quadrangle ...... _ ........ Pl. I, in pocket. 

Central City vicinity ....... · ......... _ ........... Pl. III, in pocket. 

Idaho Springs vicinity .......................... Pl. VI, in pocket. 

Maps, topographic, Central City quadran~;le .......... Pl. II, in pocket. 

Central City vicinity ............................ Pl. IV, in pocket. 

Idaho Springs vicinity ......................... Pl. VII, in pockst. 

Mareau vein, features of.. ................................. : ..... 19()....200 

Marshall & Russell tunnel, fclatures of .......................... 331-333 

geologic plans of.. .......... , ............................... 331,332 

veins in ................................................ , . . . . 113, 331 

Mars vein, features of. ...... ,.................................... 255 

Martha Perks vein, features of................................... 366 

Maryland Mountain, mines on ................................. 211-212 

Mary Murphy vein, features of .................................. _ 328 

Maud S. mine, features of. ................................ _ .... 330-331 

ore from ........................................ 113, 145-146,330-331 

figure showing........................................... 145 

Mayflower tunnel (Alice area), features of. . . . . . . . . . . . . . . . . . . . . . . . 320 

geologic plan of.......... .. .. .. .. .. . . . . .. .. . . . . . . .. . . . . . . .. . . . 320 

Mayflower tunnel (Idaho Springs), features of .................. 358-359 

Megolona vein, ores of. ...................................... 109,341-342 

Melett vein, features of.. . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193 

Melrose tunnel, features of.. .................................... 190-191 

Merry Monarch tunnel, features of.. ........ .'..................... 318 

Mesozoic time, events in. . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64 

Metalliferous districts, belt of, trend of. .......................... 13, 93 

distribution of.. .............................. , ............ 13, 93-94 

investigation of............................................... 13 

Meteor tunnel, features of.. .. . .. .. .. .. .. . . .. . . . . . . . . .. . .. . .. . . . . . 204 

Meteor vein, features of ............................. .' ........... 319-320 

Metropolitan tunnel (Idaho Springs), features of.................. 366 

wall rock in ....... ___ ........... _............................ 111 

Metropolitan tunnel (Sea toll Mountain), ores of.................. 294 

Miami tunnel, features of. .......................... : ........... 356-357 

geologic plan of ............................................. ·.. 356 

Michigan Hill, mines on .............. .' ........... :............... 201 

Middle Boulder Creek, glaCif}.tion on.............................. 59 

glaciation on, view of. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53 
INDEX. 375 

Page. 

Mlll Crook, minos on ................................... 343-344,355-356 

ntOI'l\ino on................................................... 59 

Milling, charges for ................................... -~......... 163 

history of .................................................. 153-156 

procossos of. ........................................ _. . . . . . . . . . 177 

M:lllington mino, foaturos of. ......................... .'........... 339 

M:lllionalro voin, foaturos or ..................................... 311-312 

:Mills, oquipmont of. ........................................... 156-161 

list of ...................................................... 157-161 

typos of. ........................................... ·.......... 154 

M1norallzation, dual form of. ........................... 102, 112-114,125 

dual form of, plato showing................................... 96 

relation or, to wall rock ................................. 101-102,104 

variations in ...................................... ~ ........ 101-102 

See also particular ore typos. 

Mineralizing solutions, composition of .......................... 134-135 

M:inornl Mountain, mines on ......... · ......................... ·.·.. ~89 

Mlnomlogy, description or.. ..................................... 99-100 

M1nornl Point vein, features of................................... 328 

Minerals, etching of. ........................................... 136-137 

list of. ..................................................... 106-107 

paragenesis or ..................... · ..... i . . . . . . . . . . . . . . . . . . . . . 100 

Minor's law, adoption of.......................................... 68 

'1\finos, lists of. ................................................... 69-92 

location or, maps showing ..... Pis. II, IV, v, vn,ynr, in pocket. 

Mining, history of. ................................... .-.. . . . . . . . . . 67-69 

Mining camps, distribution of. ................................... 93-94 

fOLUldlng of ....... ~ ........................................... 67-69 

Mino waters, q uallty or.. .. ,...................................... 142 

Minnesota voln, oros of........................................... 257 

Missouri Gulch, minos in......................................... 207 

Missouri mlno, features of.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 258 

Missouri vein, foaturos of. ............. : ...... :................... 237 

Mitch oil mino, ores oL........................................... 243 

pitchblende ln ............................................. 123,243 

Mogul tunnol, fouturos of......................................... 188 

Mohawk voin, fonturos of ............ .' .............. ·.............. 313 

Molybdonito, occurronco of....................................... 106 

Mona voin, foaturos of.. .............................. : ......... 285-286 

Montana Hill, minos on ........................................ 204-205 

Montl\lla Hill tunnel, features of . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 205 

Mont D'Oro ttmnol, features of................................... 210 

Monzonite porphyry, dlkes of ............................ 49-50,126-128 

dlkos of, copper in .......................................... 126-128 

See Quartz monzonite. 

Moon 0 ulrJt, foaturos of ........................................ 194-197 

Moon voin. See Sun and Moon voin. 

1\f.oor, D.l!~., work or ........................ ·..................... 20 

Mooro, R. B., 1\lld IGthil, K. L., on Kirk vein.................... 244 

on pitchblondo production ................................. 242-243 

Mooso mino, foaturos of........ .. .. .. . .. .. .. .. .. .. .. . .. . .. . . . . . . 110, 280 

Mooso voin, features or.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 205 

Moraines, occurronce of.... . .. . . . .. .. . .. . . . . . .. . . . . . . .. . . . . .. .. .. . 59 

Morning Star voin (Argo tmmol), ores of. ................ :....... 304 

Morning Star voin (Georgia Gulch). See Oro-Morning Star vein. 

Morris mlno, features of. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 266 

Morrison, l~oo, work or........................................... 20 

Mountain Cltiof mino, features of ................... ·.............. 200 

Mou.ntttin Monarch tunnel, feati.ues or. ......................... 195-196 

geologic plan or. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195 

MUllor, H., on pitchblondo ..................................... 121-122 

Murray vein, features of.......................................... 338 

Mystic Boll vein, fonturos or ................................... 196-197 

N. 

Nl\llcy r~oo voin, features of...................................... 202 

Nashville ntino, foaturos of. ........... :.......................... 251 

National mine, foaturos of. ..................................... 107,237 

section of.... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 237 

vol.ttof. ..................... ~ ............................... 97,237 

Native silver, onrichmont by ................................... 147,149 

Nodorland, dlkos noar ............................................ 49-52 

glaciation noar ............................................... 59-60 

1ninos ncar ................................................. 184-187 

vi ow noar... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53 

Nevada Oulcl1, minos in ............................... 221-222, 23(}-232 

Nevada Hill, minos on ......................................... 218-222 

Novadavillo, mines nour ........................ 221-222,229-230,233,234 

Pag<>, 

New Century vein, ores of ..................................... .'.. 210 

Newfoundland mine, featuresin ................................ 221-222 

Nowhquse tunnel. See Argo tunnel. 

Next President mine, features of................................. 224 

Niagara vein, ores of. . . . .. . . .. .. .. .. .. .. .. . . .. .. .. .. . . . .. . . . .. . .. 257 

Nigger Hill, !nines on............................................ 208 

Ninety-Four tunnel, features of.. ................................ 321-322 

geologic plan of. .......................... ·. . . . . . . . . . .. . . . . .. . 322 

Nishihara, a. S., on neutralization of sulphuric acid.............. 142 

No Name vein, features of........................................ 181 

North Clear Creek, gold on, discovery of.......................... 68 

ill.ines on ....................... .' ....................... 201-202, 205 

placers on ................................................ :... 120 

North mine, vein of. ......................... : . . .. .. . .. . .. . . . . . . . 245 

North Star-Mann vein, features of................................ 329 

N otaway vein, featuies of. ..................................... 264-265 

Nugget, mines near. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 203 

0. 

Officer tunnel, features of ............................ :. . . . . . . . . . . 195 

Ohio Creek tunnels, features of................................... 347 

OhloOulch,Jninesin ..................... , ...................... 347 

Ohio vein, ores of. .......... :. .. . .. . .. . .. . .. .. . . . . . . .. . . . . . . .. .. . 328 

0. K. mine, features of. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109, 223 

Old Kentucky !nine, features of.................................. 207 

Old Town mine, featmes of ............................. 95,107,252-254 

workings of.................................................. 252 

Olivine monzonite, description of................................ 44 

O'Neil vein, featmes of.. ................................... 109,224-225 

Ophir vein, features of............................................. 329 

Ore deposits, character of........................................ 16 

classification of. .............. .' ............................... 94-98 

faulting and, relations of. ................................ 62, 65, 136 

mineral composition of....................................... 102 

Jnineralization of.. ......................................... 101-102 

relation of, to wall rock ................................. 101..:102 

See also Mines; Veins; Stockworks. · 

Oregon Hill, mines on .......................................... 205-206 

Ores, alteration in .............................................. 136-152 

breccia of, plate showing ...................... ·............... 97 

deposition of. ........................................... 17,131-132 

temperatme and pressme during ....................... 133-134 

depth and, relations or ..................................... 137-138 

distribution or, geographic................................... 99 

enrichment of ...... ~ ......................................... 17-18 

processes of. ........................................... 136-138 · 

See also Gold ores; Silver ores; Copper ores. 

faulting and fracturing in.· ............................... 62, 65, 136 

plate showing .......................... : . . . . . . . . . . . . . . . . . 97 

formation of, depth of ...................................... 133-134 

pressure and temperature of. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134 

genesis of. ...................................... 106-107, l10, 131-135 

intrusive rocks and, relations of. .................. ·.· ........ 17,131 

Jnilling of .......... ~ ....................................... 153-156 

Jnills for, list of. ........................................ ~57-161 

mineral composition of ...................................... 99-100 

minerals of, etching of .............. ~ ....................... 136-137 

, ct9hing of, plate showing................................. 136 

payment for, by sampling works ........................... 164-168 

porphyries and, relations of ................................. 17,101 

post mineral alteration ...................................... 136-152 

production of. .................................. : .......... 171-175 

:~~~~~ :r~-- ~: :::::::: :·::::::::::::::::::::::::::::. ~53~~5~. ~~~=~: tenor or, relation to depth .................................. 137-138 

texture of. .. . . . . . . . .. . . . .. . . . .. .. . . . .. .. . .. . .. .. . . .. . . . . . . . . . 98-99 

plates showing ....................................... 96, 97, 124 

thermal solutions and ...................................... 131-133 

treatment of ......... , .............. : ...................... 153-168 

history of. ............................................. 153-1E4 

Oro-Morning Star vein, ores of................................... 365 

Outwash deposits, character of ................................... 58-60 

viewof....................................................... 53 

Owatonna vein, featmes of. ........... ' ................ 102, n2, 288-289 

Oxidation zone, copper enriChment in ...................... 137-138,150 

gold enrichment in ......................................... 138,140 

silver enrichment in ........................................ 140-141 
376 INDEX. 

P. Page. 

Packard Gulch, mines in ................................ i. . . . . . . . 224 

mines in, view of.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 223 

Paleozoic time, events in ......................................... 63-64 

Palmer, Chase, and Bastin, E. S., on precipitation of gold........ 139 

on precipitation of silver ............................... 141, 149-150 

Panama tU.I).nel, features of ....................... , ............. 336-337 

geologic plan of. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 336 

Patch. See The Patch. 

Pearce, Richard, process Invention by ............ , ............ 161-162 

on pitchblende ........................ ; . . . . . . . . . . . . . . . . . . . . . . 123 

Pearceite, occurrence of. ....................................... 144-145 

occurrence of, figures showing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144, 145 

Pearce mine, features of... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 266 

Pease-Kansas vein, features of.................................... 238 

Peck Gulch, mines on and near. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 330 

Pegmatite, intrusions of.......................................... 34 

intrusions of, plate showing.................................. 53 

See also Granite pegmatite. 

Peneplain, development of .................................... 21, 23,65 

views of...................................................... 20 

Pennsylvania tunnel, features of ............................... 312-313 

Penobscot tunnel, features of. .................................. 196-197 

geologic plan of.............................................. 196 

Perigo, mines near ............................................. 197-200 

Perigo mine, features of ................................ 109,119,198-199 

tunnels of, plans of ......................................... 198,199 

Pettibone mine, features of... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136, 205-206 

Pewabic mine, features of. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 256 

pitchblende in............................................... 123 

production of. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 255 

Pewabic Mountain, dips on ...................................... 94-95 

mines on.: ......................................... 2S2-284,288-289 

Philadelphia tunnel, features of ............................ 306,307-308 

geologic plan of. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 307 

Philips tunnel, features of........................................ 313 

Phillips Gulch, mines in ....................................... 309-310 

Phoenix, mines near ........................................... 192-193 

Phoenix-Burroughs vein, features of. .......................... 236-237 

Physiography, history of ......................................... 21-22 

Pile Hill, mines on ........................................... :. 204,205 

Pine Cone tunnel, features of..................................... 207 

Pine Creek, mines on . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 202-203 

Pine Grove mine, features of. .............................. 112, 143, 184 

Pine Shade vein, features of. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 298 

Pioneer tunnel (North Clear Creek), features of................... 201 

Pioneer tunnel (Moon Gulch), features of......................... 194 

Pioneer tunnel (Spring Gulch), features of....................... 343 

Pitchblende, mineral associations of ............................ 121-125 

occurrence of. ................................... 1i,105,121-124,132 

ores of. ................................................ 241-243,245 

plate showing .......................................... 124,125 

production of .......................................... 242-243 

pyritic ores, relation to ........... :....................... 125 

views of. ................................................ 97,124 

See also Uranium .. 

Pittsburg mine, features of ................................. 109,261-262 

geologic plans of.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 261 

ores of. ................................................ 100,151,262 

Placers, gold, occurrence of.. .......................... 59, GO, 98, 105, 120 

Plateau vein, features of. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 204 

Platts vein, features of ......................................... 337-338 

Pleasant Valley, mines in and near ............................. 279-280 

Pleistocene gravels, description of. ...................... '......... 60 

Polar Star tunnel, features of..................................... 317 

Pomerose, analysis of. ........... ·................................ 43 

description of. ............................. ' . . . . . . . . . . . . . . . . . 4 7 

Population, distribution of ....................... :............... 25 

"Porphyries.'' See Tertiary intrusive rocks. 

Powers vein, features of. ....................................... 103, 279 

Pre-Cambrian rocks, occurrence and character of ........... 15, 20,26-37 

Pre-Cambrian time, events in ........................... -.-...... · 63 

Precipitation, records of.......................................... 24 

Princess Alice vein, features of. ........................... -.... 109,323 

Princess of India tunnel, alteration in. . . . . . . . . . . . . . . . . . . . . . . . . . . . 111 

features of... . . . . .. . . . . . . . . . . .. . . . . . . . . . . . . .. .. . . . . . . . . . . . . . 337-338 

ore from ............................................... 144,337,338 

figure showing........................................... 144 

. Page. 

Prize mine, features of ...•..................................... 221,306 

ores of. ............................................... ; . . . . 139, 224 

Process mania, history of ....................................... 153-154 

Prompt Pay mine, featur,!s of.................................... 247 

Prosser Gulch, mines in. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 213-218 

Puritan vein, features of. ...................................... 109,320 

Putnam, B. T., on iron ores...................................... 129 

Puzzler tunnel, development in.................................. 349 

Pyrite, crystal forms of.... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99, 106 

gold and silver in . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116 

Pyritic ores, character of .................................... 16,105-110 

copper in ............................................ 16,105,150-151 

definition of ................................... : . . . . . . . . . . . . . . 105 

distribution of ...................................... : ......... , 115 

enrichment of. ........ · .............. · ............... 138,139-140,151 

goldin....................................................... 16 

metals in ................................................... 109-110 

minerals of ................................................. 105-106 

gold and silver in ....................................... 116-119 

paragenesis of .......................................... 106-107 

pitchblende in. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125 

silver in ................................................. 16,142-143 

structure of. . . . .. .. .. .. . . .. . .. . .. .. . .. . . . . . . . . .. . . .. . . .. . .. . . 107 

plate showing..... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96 

telluride ores and, relations of .............................. 106,277 

tenor of ......................................... , .......... 109-110 

texture of. . . . .. . .. . . . .. .. . . . . . . . . . . . . . . . . . . . .. . . . . . . .. . . .. .. . 107 

variation in . .. .. . .. . . .. . . . . . .. . . . . .. .. . . . . .. . . .. . . . . . .. .. . . . . 132 

wall rocks of, alteration in .............. : ................... 107-109 

Q. 

Quartz, deposition of. . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136 

Quartz-biotite schist, analysis of.................................. 27 

character of. . .. . .. . . . . . .. . . .. . .. . . . . . . . . . .. . .. . .. .. . .. . . . . .. . . . 27 

Quartz diorite, age of . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15, 33 

character of. ................................................. 32-33 

definition of.......... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 

distribution of..... . . .. .. . . . . .. . . . . .. . .. . .. . .. . . .. . . . . . .. . . .. . 32 

origin of.. . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 

structure of ..................................... ~ . . . . . . . . . . . . 33, 61 

Quartz gneiss, description of.. .................................... 27-28 

Quartz Hill, mines on .......................................... 228-250 

pitchblende at ..................................... 121, 123-124, 132 

plate showing ........................................ :. . . 124 

uranium at .......................................... 99, 121, 123-124 

Quartz Hill tunnel, featur1lS of.. ................................ 230-232 

geologic plan of...... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 231 

Quartz Hill mine, features of..................................... 248 

Quartz monzonite, analysEs of.................................... 43 

character of. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15, 39-41 

distribution of..... . .. . . . . . . . .. . .. . . . . .. . .. . .. . . . . . . .. . . . . . . . . 39 

felsic types of...... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42, 44 

analyses of. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 

mafic types of.... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44-46 

analyses of............................................... 43 

magmatic differentiation in ............................... 42,48-49 

types of... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42-49 

ultramafic-magnetite, rich types of. . . . . . . . . . . . . . . . . . . . . . . . . . . 46-48 . 

analyses of ...... .'. . . . . . . . . . .. . .. . . . . .. . . . . . . . . . . . . . . .. . . . 43 

Quaternary deposits, chancter of.. .............................. 15,57 

gold in... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60, 98 

See also Glacial deposi1;s; Debris; Talus; Alluvium. 

Quaternary time, events iit....................................... 65 

Queen vein, features of........................................... 303 

Quindaro tunnel, featll!es of...... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 194 

R. 

Radium, occurrence of. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 

Railroads, lines of................................................ 25 

lines of, early construction of ................................. 68-69 

Ralls County mine, featurEs of ................................. 238-239 

Ransome, F. L., preface b:r ...................................... 13-14 

Raymond, R. W., on Boulder County vein . . . . . . . . . . . . . . . . . . . . . . 183 

on leasing system. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 168 

on process mania ............ .' .............................. 153-154 

on silver veins ............................................. 139, 143 

on smelter charges...... . .. .. . .. . .. .. .. .. .. . . . . . .. . .. .. . . .. . . . 163 
INDEX. 377 

Page. 

Roady Cash vein, features of ................................... 363-364 

. Rod l~lophant group, mines or. ................................. 334-336 

Rod Elephant Hill, minos on ............................... 330,334-336 

minos on, view of. ............................ :.............. 334 

Reform vein, features of.......................................... 200 nouor, description of............................................. 23 

Replacement, character of ...................................... 103-104 

relation or, to wall rock....................................... 104 

Rhodorick Dhu vein, merging of................................. 97 

H.hodochrosito, occurrence of... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110 

Richardson vein, features of. ................................ .'.... 255 

Rickard, Forbes, aid of........................................... 121 

on German mine orcs......................................... 242 

Rickard, '1'. A., on Enterprise mine ..................... ,........ 188 

on stamp mill types.......................................... 154 

on telluride oro ........................... , ................ :.. 115 

Rising Sun vein, character of.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 367 

H.ittor, E. A., on Evergreen copper mine ....... , ............... 126,128 

Robert Emmet mine, features of................................. 212 

Rockford mine, features of. . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . 109, 250 

Rockford tunnel, featureS of .................................... 341-342 

Rocky Mountains, southern, geologic history of................... 21 

geology of ....................... ~. . . . . . . . . . . . . . . . . . . . . . . . . . . . 20-:!2 

structure of ......................... ·. . . . . . . . . . . . . . . . . . . . . . . . . 20 

Rocky Mountain Terror mine, features of....... . . . . . . . . . . . . . . . . . . 251 

Rogers, A. F., on copper ores ................................ :.... 127 

Rollinsville, minos near ........................................ 192-197 

Rooks County mine, features of. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 190 

ores or.... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99, 106, 190 

Royalties, system of ............................................ 168-169 

Royal vein, ores or............................................... 257 

Ruby silver, enrichment by .................................... 143-146 

enrichment by, figures showing ............................ 144,145 

Russell, W. G., gold discovered by............................... 68 

Russell Gulch, mines in ..................................... 68, 25(}-266 

placers on.................................................... 120 

Russell tunnel. See Marshall and Russell tunnel. 

Husson vein, features of.......................................... 251 

s. 

St. James vein, character of...................................... 334 

St. Louis mine, features of.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120, 181 

St. Marys Lake, minos near .......................... : ......... 319-320 

Salisbury vein, ores or............................................ 362 

Sampling works, development of. .............................. 163-164 

payment by ................................................ 16·1-168 

San Juan mine, features or. ............................ 101, 10!l, 234-236 

mineralization on ....................................... 97, 101, 236 

plans or. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 234 

San Juan Matmtains, mine waters of. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142 

Santa ]:~e vein, features of ...................................... 112, 290 

Saratoga mine, features or .............................. 109, 267-268,305 

Saturation, limits of ............... :.............................. 137 

Saxony, pitchblende in ......................................... 122-123 

Scandia mine, features or........................................ 243 

Scandill vein, features or.......................................... 189 

Schistosity, plato showing......................................... 21 

See also Foliation. 

Schists, description of ............................................ 26-28 

Schnooborg, Saxony, pitchblende at ............................ 122-123 

Schultz Wonder mine, features or... .. .. .. . .. .. .. .. .. .. .. .. . . . . . . 201 

Seabird tunnel, features of........................................ 195 

Seaman ttmnol, features or. ........................... :.......... 318 

Searle vein, ores· or ............................................. 273-274 

Seaton Gulch, mines of........................................... 299 

Seaton mlno, features of ......................... 95, 110, 112, 294-297,304 

geologic plan of. ................ ·:............................. 295 

Seaton Mountain, mines on .................................... 290-300 

Seaton-Pine Shade vein, features of . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 298 

Senator vein, features of.. ...................................... 344-347 

oro fron1 ............................................... 145,346-347 

figure sl1owing ............................ '............... 145 

Seriate, definition of............................................. 32 

Seven-Forty tunnel, features of.................................. · 316 

Shafter vein, features of .................................... 358, 36(}-361 

Shaft vein, orcs of ........ .'....................................... 265 

Sherman-Macon tmmel, features of............................... 205 

Sherman vein, features of. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 181 

SherwoOd Creek. See Boulder County Hill. Page . 

Shoshonose, analYses of... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 

dos::ription of .................... , ............................ 44, 46 

Siebenthal, C. E., on solution of galena........................... 137 

Silent Friend mine, features of. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 348-349 

geologic plans of.............................................. 348 

Silver, carbonates or. ...................................... 14(}-141, 142 

chlorine and ......... :....................................... 141 

enrichment of .................................. 14(}-150, 152,317,337 

depth and distribution of .......................... 146-147, 152 

typos or. ........ : .................................. 142, 152, 317 

relations of. ........................................ 149-150 

See also Pyritic ores; Galena-sphalerite ores. 

fineness or: ................................................. 119-120 

occurrence of, in oro minerals ........................... 116,118-119 

precipitn.tion of ........................................ 116, 141-150 

price of, chart showing ................ :...................... 148 

prOduction of. ............................................. 172-175 

saving of, percentage of .................................... :. 155 

solution of ................................................. 14(}-141 

sulphate of................................................... 140 

See also Silver ores: Gold-silver ores. 

Silver Age Gulch, minos in....................................... 294 

Silver Age tunnel, features of., ........................... :. -112,292-293 

· geologic plan of .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. . . .. . .. . . . 292 

Silver Creek, mines on ..................... 205-207,319,321-323,330,:l3S 

view on...................................................... 335 

Silver Dollar vein, features of ........ : . ........................ 278-279 

Silv(Jr Hill, mines on............................................. 211 

Silver King vein, features or. .................................. 342-343 

geologic plan of. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 343 

Silver minerals, character of .................................... 99,140 

Silver ores, discovery of.......................................... 68 

enrichment in ........................................ 17-18,140-150 

im poverislmlen t of ............................ :. . . . . . . . . . . . 146-14 7 

nulling of. . . . . .. .. . . .. . .. .. . .. .. . . . . .. . . . .. . .. .. .. . . .. . . .. . . . 156 

payn1ent for ................................................ 164-168 

smelting or, charges for....................................... 163 ' 

tenor or .................................................... 146-147 

See also Gold-silver ores; Silver; Ruby silveri Native silver; rearcite; etc. 

Silver plume granite, age of. ..................................... 15,37 

character of .................................................. 35-36 

definition of ...................................... :. . . . . • . . . . 35 

distribution of.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 

structure of. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36-37, 61 

Silver veins, character of. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138, 139 

surficial gold enrichment in. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139 

· Singewald, J. T.,jr., on iron ores ............................... 129-130 

Skipper vein, features of ............. ·............................ 198 

Slaughter House vein, branching of ......................... 95,214,215 

Sleepy Hollow vein, features of ............................ 102,226-227 

Slide vein, features of. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 258 

Smelters, construction of ............................. · .......... 153, 161 

Smelting, charges for .... : ........................... , .......... 162,163 

history of .......................................... 153-154,161-162 

Smelting oro, definition of. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154 

Smuggler vein, features of. ...................................... 194-195 

Snowden vein, features or ...................................... 206-207 

Solutio~s, thermal. See Thcnnal solutions. 

South Boulder Creek, mines on ................................ 190-194 

South Clear Creek, mines on ................... 337,341,349-353,361,364 

South Lincoln vein, ores of. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 365 

South Willis Gulch, mines in and ncar ..................... 266,268-278 

mines in and near, enargitc and fluorite in. . . . . . . . . . . . . 105, 115, 132 

Specie Payment vein, features of. . . . . . . . . . . . . . . . . . . . . . . . . . . 1J6, 286-288. 

geologic plan of. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 288 

orcs of. ................................................ 109,113,286 

figures showing. : . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113 

Spencer Mountain, mines on. . .. .. .. . . . .. .. .. .. .. . .. .. .. .. .. .. .. . 188 

Sphalerite, gold and silver in ......................... ~............ 119 

veinlets or, plate showing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96 

Sphalerite ores. See Galena·sphalerite ores. 

Spring Gulch (to Clear Creek), mines on ............... 232,237,240,259 

Spring Guich '<fo South Clear Creek), mines in ......... 315,342-344,355 

Spur Daisy group, features of. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 208 

Spurr, J. E., on distribution of oro deposits...................... 13 

on relation of ores to porphyry. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101 
378 INDEX. 

. . . Page. 

Spurr, J. E., and Garrey, d.:H., on Bullion: King mine ...... :.... 361 

on Tertiary gravels .... · .......................... · .......... ·.. 57 

on Tertiary intrusive rocks ............................... 38, 55,93 

Stamp mills, use of. ................ ." .......................... 153-161 

Standard tunnel, features of. ................................. I. 313-315 

geologic plan of. ......... , . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 314 

Stanley mine, features of ........................ : .......... 101,361-362 · 

Steiger, George, analyses by:. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 

Stewart Gulch, mines in ........................... : ........... 206-207 

Stewart vein, features of. .......................... : ........ ~.... 207 

Stockwork, definition of. .................................... :. . . 96 

occurrence and character of. ................. , . . . . . . . . . . . . . . . 96-98 

view of. .................................... ········'······... 96 

Stonewall vein, ores of. ........................................ 321-322 

Stratigraphy, description of .......................... : ........... 26-61 

Strong vein, features of.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . 358 

Structure, character of ........................... : . . . . . . . . . 15-16,61-62 

Structure, dynamic, character of .............................. 15-16,61 

SulpWde zone, copper enichmernt in ........................... 15D-151 

gold enrichment in ..................................... 138,139-:-140 

silver enrichment in ....................................... 141-150 

• See also Enrichment; Gold; Silver; Copper. 

Summary of results ........... : .................................. 15-18 

Summit prospect, features of..~.................................. 189 

Summit tunnel, veins in......................................... 361 

Sun and 111oon ,·ein,"features of. ............................... 102-289 

Sunshine mine, features of. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 354 

Surprise vein, features of. ............................ '. . . . . . . . . . . . 328 

Swansea smelter, history of. .................................. :.. 161 

Swathmore mine, features of. .................................. 188-189 

Swiss tunnel, features of. ........ :. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 196 

Syenite porphyry, age of. ........................................ 5[)-56 

character and distribution of ................................. 54-55 

Syndicate mine, features of. ............................... 107,350-352 

geologic plan of. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 351 

T. 

Tabor vein, features of. ..................... :.................... 335 

Talus, occurrence and character of ........................... : . . . 61 

Telluride ores, character of. .................................. 16-17,114 

· goldin ... ." .................................................. 17,119 

minerals in ............................................ 100,114-115 

paragenesis of............................................ 11·1 

oxidation of. ........... ~ ..................... ." ........... , . . . 139 

porphyries and, relations of. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101 

pyritic ores and, relations of. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106, 277 

treat1nont of. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 156 

veins of, width of ........................................... 95, 264 

wall rocks and, relations of................................... 103 

Temperature, character of. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 

Tennantite, gold and silver in .............••............. · ..... 116, 119 

Terrace gravels, description of.................................... 60 

Tertiary gravels, description of. ........................ ,......... 57 

gold in ....................................................... 57,98 

occurrence of. ............................... ·. . . . . . . . . . . . . . . . . 15, 57 

Tertiary intrusive rocks, age of. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38,39 

character of ........... : . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15,37-57 

occurrence of ................................................. 37-38 

ores and, relations of. ....................................... 17,101 

Tertiary time, events in .................... : .................. 21,64-65 

peneplain in.···.·········································· 21,23,65 

views of.................................................. 20 

Texas vein, ores of. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 328 

The Patch, features of .................................... 96-97,233-237 

view at...................................................... 96 

Thermal solutions, compo3ition of. .......................... 17,134-135 

composition of, changes in................................... 133 

regional variation in ................................... 131-132 

deposition by ............................................... 17,131 

metamorphism by. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63 

Thomas tunnel, features of....................................... 318 

Thompson, Lawr~nce, on Caribou Inine ........................ 179-180 

Till deposits, character of. ....................................... 58,59 

distribution of, map showing ........................... In pocket. 

Tim ~)cr, character of. ........ ".. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-25 

Titaniferous iron ores. See Iron ores. . Page. 

Togo vein, features of ............................. ~.:............ 2~ · 

Topeka mine, alteration in ......................... ; .... ,........ 111 

features of. ....................................... .' ..... 143,248-250 

geologic plan of. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 249 

ore of. ................................................. 143,249-250 

plate showing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97 

Topography, description of. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22, 23-24 

Total Eclipse vein, character of ........................ ~ . . . . . . . . . 299 

Trachytoid texture, occurreace of................................ 53 

plate showing................................................ 52 

Trail Creek, mine on.............................................. 366 

Transportation, mean~ of ..... , . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 

Treasure Vault mine, featur•lS of. .............................. 30D-301 

tellurium in ........................ · ........................ 114,301 

Trio mine. See Champion-'l~rio mine.' 

Tropic tunnel, features of ....................................... 297-298 

geologic plan of................................................ 297 

Tropic vein, fractures of ........ ·1· ..................... 297-298,303-304 

Tunnels, location of, maps showing ......... Pis. II ,'IV, VII, in pocket. 

See also particular tunnel1. 

Tungsten ores, character of ... · .......... .' ........................ 17,126 

· distribution of .......................................... 99, 126, 132 

enrichment of................................................ 138 

minerals of... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99, 132 

occurrences of... . .. .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . 16, 126 

production of. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126 

relation of, to other ores .. ·. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132 

Turkey Gulch, mines in ........................................ 341-342 

Tweedy, Frank, work of.......................................... 20 

Twelve-foot vein, features of. .. . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . .. . 195-196 

Two Brothers tunnel, features of................................. 285 

Two-Forty vein, fe'atures of. ............................... 109,266-267 

Two Kings vein, ores of... .. . . . . . . . . .. .. . . . . . . . .. .. . . . .. .. . . . . . 113, 359 

u. 

Unexpected vein, features of ................... :.................. 228 

United Gold tunnel, features of................................... 308 

geologic plan of........... . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 308 

U. P.R. mine, features of.. .................................... 309-:-310 

Up to Date tunnel, features or .............................. 111,178-179 

geologic plan of............................................... 178 

ores of. ................. · ................................ 147,149, 179 

wall rock of ..... : ....................................... 46, 111, 179 

Uraninite, occurrence of.. ....................................... 17,121 

paragenesis of. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132 

plates sho\ving. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125 

production of. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121 

Uranium ores, character of. .............................. 16, 17, 105, 132 

distribution of............................................... 99 

enrichment of... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138, 151 

Ininerals of.. . . . . . . .. .. . . . . . . . . .. .. .. . . .. .. . . . . .. . . . . . . . . . . . .. 99 

'occurrence of. ........................................... 99,121-124 

porphyries and, selections of.. ......................... :. .. . . . 101 

production of. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121 

relation to gold-silver min•}ralization ....................... 105, 125 

U.S. tunnel,featuresof. ...... _................................... 359 

V. 

Vasa vein, features of........ . . .. . . . . . .. . .. . .. .. . . .. . .. . .. .. . . .. . 224 

Vegetation, character of ..... ·. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-25 

Veins, branching of. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95 

brancWng of, figure showing.................................. 96 

depth of. ............................... , .. .. . . . . . . . . . . . . . . .. . 95 

. distribution and character of ................................. 9·1-96 

faulting and, relations of.. ..................................... 62,65 

location of, maps sho\ving ......... : ... Pis. II, IV, VII, in pocket. 

wall rock and, relations of ................................ 95-96,103 

See also particular veins. ' 

Victoria vein, features of. ........... ·............................. 200 

Virginia Canyon, mines on ......................... 281-286,288,298-306 

schist in, view of.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 

Virginia mine, features of......................................... 281 

Vogt, J. H., on titaniferous iron orcs.............................. 48 

Volcanism, occurrence of......................................... 65 
•• 

IN.DEX. 379 

w.. Page. 

Wngos, rntos or................................................... 169 

Wall rock, nltorotlon or.. ....................... 102-104,107-109,111,112 

nltorotion of, pinto showing................................... 97 

fnultillJ{ and, rotations or .................................. 95, 96,103 

rotation or, to miner-alization ............................ 101-102,104 

to veins ................................... 95-96,103,107-109,111-112 

Wur Drutco mine, feutures of ................................... 276-277 

ores or.. ........................................ 103,114-115,276-277 

tellurium in ........................................ 114-115,276-277 

Wnr Eagle mine, feuturcs or. ....... :............................. 198 

Wushington tunnel, features of................................... 313 

'Vushington vein, feutures or. ................................. :.. 224 

Watauga vein, features of. ...................................... 95,252 

Water supply, development of. ............................. .-.... 153 

''\'nter table, depth or .......................................... 137-138 

Wellington No.6 vein, features of................................ 305 

West Notuwuy mine, features of ................................ 263-264 

geologic plans of... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 263 

White vein, features of ..................................... 144,335-336 

Whiting mi.no, features of........................................ · 218 

Wigwum mine, description of.................................... ISO 

Willis Gulch, minos in ....................... ~ ......... 267-268,277-279 

Windsor Castle vein, churocter or ........................... 95,112,284 

Page. 

Winnebago Hill, mines oo ... : ...... : ........•.................. 208-211 

Wisconsin glacial stage, deposits of ................................ 59-60 

Wood mine, features or.. .... .' .................................. 244-245 

ores of ..................................... .'.................. 245 

fi.gu.i-es showing ......................................... 123,124 

pitchblende in ......... : ................................ 123-124,245 

plate showing... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124 

Woodpecker Gulch, mines in .............. .' .................... 313-318 

Woodpecker mill, nature of...................................... 153 

Wyandotte tunnel, fe~turcs of ................................. "364-365 

Wyomed tunnel, features of. ............................... .'..... 318 

geologic plan of ...... ·......................................... 318 

Y. 

Yankee, mines ncar ................................ 319,321-323,326-330 

Yankee Centellllial veLl, character of. ............... ·: ......... 321,322 

Yankee Htll, mines on and neJ.r ................................ 327-329 

York Gulch, mines in ...................................... 31D-313,317 

z. 

Zinc, enrichment of ........................................ 138,151,152 

production of..... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172-175 

Zinc orcs, payment fo:- ........................................• 165-168 

treatment of. ..................•...•. ·•.•.........•••.•••.••..• 162 

0 

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