DEPARTMENT OF THE INTERIOR

UNITED STATES GEOLOGICAL SURVEY

GEORGE OTIS SMITH, DIRECTOR

BULLETIN 4=78

GEOLOGY AND ORE DEPOSITS NEAR 

LAKE CITY, COLORADO

BY

JOHN DUER IRVING

AND

HOWLAND BANCROFT

WASHINGTON

QX>,VERNMENT PRINTING OFFICE; 

1911

CONTENTS.

Page.

Field work................................................................. 9

Acknowledgments.......................................................... 9

Geography ................................................................ 10

Location and general features.......................................... * 10

Topography........................................................... 11

Official mining districts................................................. 11

Climate................................................................ 12

Timber............................................................... 12

History.................................................................... 12

Production................................................................ .1.4

Mines. ....................... ^........................................... 16

Geology, by Whitman Cross ................................................. 18

San Juan Mountains................................................... 18

General features................................................... 18

The earliest eruptions.............................................. 19

San Juan tuff...................................................... 19

Silverton volcanic series........................................... 20

Picayune volcanic group....'................................... 20

Eureka rhyolite................................................ 20

Burnslatite................................................... 21

Pyroxene andesite.............................................. 21

Henson tuff.................................................... 21

Potosi volcanic series............................................... 21

Hinsdale volcanic series........................................... 22

Lake City district..................................................... 22

General geology.................................................... 22

Silverton volcanic series................................:.......... 24

Picayune volcanic group....................................... 24

Occurrence ............................................... 24

General character......................................... 24

Typical exposures......................................... 25

Eureka rhyolite. ................................................ 26

Burnslatite tuff............................................... 27

Pyroxene andesite........................................... '... 28

Henson tuff.....l............................................. 28

Potosi volcanic series. .................................... ^......... 29

Hinsdale volcanic series........................................... 29

Intrusive rocks.................................................... 30

Rhyolite....................................................... 30

Quartz latite.................................................. 31

Andesite....................................................... 31

Quartz monzonite porphyry..................................... 31

Decomposed porphyry of Deadmaii Gulch........................ 32

3
4 CONTENTS.

Page.

Ore deposits.............................................................. 32

San Juan region....................................................... 32

Geographic continuity ............................................. 32

Genesis of the minerals in the San Juan region....................... 33

Mineralogical similarity............................................ 35

Ore deposits of Lake City district....................................... 37

The lodes.......................................................... 37

General character............................................. 37

Mechanical disintegration....................................... 38

Dimensions.................................................... 39

Terminations.................................................. 41

Strike........................................................ 41

Dip........................................................... 42

Intersections................................................... 42

Faults........................................................ 43

Origin of the lodes.............................................. 43

Distribution of the lodes........................................ 43

Fissure filling and metasomatism ............................... 44

Banding...................................................... 45

Mineralization.................................................... 45

Age ......................................................... 45

Effect of country rock.......................................... 4.6

Kelative abundance of minerals................................ 46

Mineral groups............................................. 46

Tetrahedrite-rhodochrosite group........................... 47

Quartz-galena-sphalerite group.............................. 47

Telluride group............................................ 48

Source of mineralization....................................... 48

Mineralogy........................................................ 51

Primary minerals............................................... 52

Minerals formed at shallow and moderate depths............. 52

Tetrahedrite.......................................... 52

Bismuth compounds................................... 53

Barite................................................. 53

Rhodochrosite................................'......... 53

Hinsdalite............................................. 54

Minerals formed at all depths............................... 55

Pyrite................................................ 55

Galena............................................... 56

Sphalerite (zinc blende) ............................... 57

Chalcopyrite.......................................... 58

Tellurides............................................ 59

Quartz................................................ 60

Dolomite and calcite.................................. 60

Secondary minerals............................................. 60

Oxidation products......................................... 61

Secondary sulphide enrichment minerals..................... 62

Pyrargyrite and proustite.............................. 62

Secondary chalcocite.................................. 63

Covellite.............................................. 64

Bornite................................................ 64

Secondary galena....................................... 64

Gold................................................. 64

Precipitation due to sphalerite.............................. 64
CONTENTS. 5

Ore deposits Continued. Page. 

Ore deposits of Lake City district Continued.

Pay shoots........................................................ 65

Value of the ores.................................................. 66

Summary of ore deposits........................................... 67

Future of the district....................................................... 68

Mining conditions.......................................................... 69

Power................................................................. 69

Labor................................................................ 70

Mining methods........................................................ 70

Extraction of metals.................................................... 71

Detailed descriptions of mines............................................... 72

Capitol City group...................................................... 72

Gallic-Vulcan..................................................... 72

History and production........................................ 72

Development and equipment.................................. 73

Country rock................................................... 73

Veins......................................!................... 73

Ores.......................................................... 74

Excelsior......................................................... 74

History and production........................................ 74

Development.................................................. 75

Country rock.................................................... 75

Veins........................................................ 75

Ores.......................................................... 75

Czar.............................................................. 76

Production and development.................................... 76

Country rock................................................... 76

Veins........................................................... 76

Ores.......................................................... 77

Capitol City........................................................ 77

Yellow Medicine................................................... 78

Lilly............................................................. 79

Chord extension................................................... 79

Woodstock......................................................... 79

Ottawa........................................................... 80

Toby............................................................. 80

Silver Chord....................................................... 80

Czarina............................................................ 80

Lucky Strike tunnel.............................................. 80

Henson Creek mines................................................... 81

Pride of America and Big Casino.................................... 81

Lellie (Red Rover)................................................ 81

Production and development.................................... 82

Country rock................................................... 83

Veins.......................................................... 83

Ores........................................................... 84

Vermont.......................................................... 85

Development and production.................................. 85

Ores.......................................................... 86

Ute and Ulay and Hidden Treasure................................ 87

Development.................................................. 87

Ute and Ulay mine.......................'................. 87

Hidden Treasure mine..................................... 88
6 CONTENTS.

Detailed descriptions of mines Continued. Page. 

Henson Creek mines Continued.

Ute and Ulay and Hidden Treasure Continued.

Country rocks.................................................. 89

Ore bodies.................................................... 90

Veins...................... A.............................. 90

Ute vein................................................... 90

Strike and dip......................................... 90

Movement............................................. 91

Width................................................ 91

Paragenesis............................................... 92

Ores. ..................................................... 92

Character............................................. 92

Value................................................ 93

Distribution of values.................................. 93

Equipment................................................... 94

Hidden Treasure mine..................................... - 94

Ute and Ulay mine........................................ 94

Pelican............................................................ 95

Production and development.................................... 96

Country rock................................................... 96

Veins..........................................................' 96

Ores.......................................................... 97

Missouri Favorite................................................... 98

Production and development.................................... 98

Veins.......................................................... 98

Ores.....:..........................................:.'........ 99

San Cristobal group..................................................... 99

Monte Queen..................................................... 99

Vein .......................................................... 99

Ores.......................................................... 100

Nellie M.......................................................... 101

Lode Star.............................................:........... 101

'Dauphin, Rob Roy, and Sulphuret.................................. 101

Golden Wonder.................................................... 101

Mayflower and Contention claims................................... 102

Production and development.................................... 102

Country rock................................................... 103

Vein .......................................................... 103

Ores.........................,......'...............-...'....... 103

Golden Fleece.................................................... 104

Location and history........................................... 105

Development and production.................................. 106

Country rock and structure..................................... 107

Vein .......................................................... 109

Ores.......................................................... 110

Black Crook ...................................................... Ill

Development.................................................. 112

Country rock................................................. 112

Veins.......................................................... 112

Fault......................................................... 114

Ores........................................................... 114

South Fork of Henson Creek............................................. 116

Moro.>............................................................ 116

Equipment................................................... 116
CONTENTS. 7

'Detailed descriptions of mines Continued. Page. 

South Fork of Henson Creek Continued. 

Moro Continued.

Development................................................... 117

Country rock................................................... 117

Vein .......................................................... 118

Ores.......................................................... 119

Secondary alteration............................................ 121

Hendrison claim................................................... 122

Prospective gold area.................................................. 122

Bibliography............................................................... 122

Index..................................................................... 125

ILLUSTRATIONS.

Page. 

PLATE I. Topographic map showing the location of the more important

mining claims in the southern portion of the Lake City quadrangle. 10

II. A, View of Lake City, Colo.; B, View of north side of Henson Creek.. ' 12

III. Geologic map of the southern portion of the Lake City quadrangle, 

showing the geologic formations and outcrops of the more important 

lodes.......................................................... 18

IV. A, Round top Mountain, Lake City mining region; B, Postglacial

canyon of Henson Creek, showing gorge in Eureka rhyolite ....... 22

V. Plan of the underground workings and outcrop of the Ute and Ulay

and Hidden Treasure ground.................................... 86

VI. View looking south up Lake Fork................................. 102

VII. Plan of the workings of the Golden Fleece.and Black Crook mines... 106

VIII. Plan of underground workings of Black Crook mine................. 112

FIGURE 1. Index map of a portion of Colorado, showing the location of the mining region discussed in this report.............................. 10

2. Curve showing the production of Hinsdale County, Colo., since 1884. 16

3. Relation of erosion to superficial alteration........................ 39

4. Sketch plan of the Ute-Hidden Treasure group of veins, showing

their relations to one another.................................. 42

v 5. Sketch of typical forked-lightning fissure vein..................... 42

6. Hinsdalite from the Golden Fleece mine......................... 54

7. Workings and outcrops of veins of Ocean Wave and Lellie (Red

Rover) mines.................................................. 82

8. Irregularities in the Lellie fissure along the strike................. 83

9. Longitudinal section of the Lellie vein, showing position of rich

upper stopes and inclination of the ore shoot..................... 84

10. Face of Lellie vein, showing irregularities of vein structure........ 84

11. Sketch of the Scotia, Vermont, Ocean Wave, and Wave-of-the-Ocean

group of claims................................................ ' 86

12. Longitudinal section of the Hidden Treasure vein, showing the

stopes and the pitch of the ore shoot............................. 88

13. Galena shattered and infiltrated with quartz, Ute vein............. 93
8 CONTENTS.

Page.

FIGURE 16. Cross section of the Monte Queen vein, showing included rock fragments, strong selvage, and massive vein filling................. 99

17. Plan and longitudinal section of Monte Queen vein, showing ore

shoots ....................................................... 100

18. Occurrence of shoots within shoots, Monte Queen vein........... 100

19. Sketch of Mayflower and Contention claims...................... 103

20. Topographic map of the region around Lake San Cristobal....... 105

21. Sketch of ridge formed by the outcrop of the Golden Fleece vein. 106

22. Longitudinal section of the Golden Fleece vein, showing position of

agglomerate contact and ore shoots............................ 107

23. Outcrop and branches of Golden Fleece vein...................... 110

24. Longitudinal section on plane of Black Crook vein ............... 113

25. Type of fissure in Black Crook (lima) mine....................... 114

26. Sketch showing location of Moro and Hendrison claims............ 117

27. Longitudinal section of the Moro mine, showing depth of anglesite

alteration.................................................... 117

28. Face of Moro tunnel, first level, showing structure of lode........ 118

29. Cross sections of the Moro vein on lines indicated in figure 31.... 119

30. Manner in which Moro vein crosses fissures diagonally on lower level. 119

31. Plan of workings of the Moro mine.............................. 120

32. Ore from the Moro mine, showing certain features of the paragenesis

of the minerals.............................................. 121

33. Face in the Moro tunnel, showing structure of lode ............... 121

INSERT.

Page. 

Primary mineralogy of Lake City district .................................. 46
GEOLOGY AND ORE DEPOSITS NEAR LAKE CITY, COLO.

By JOHN DUER IRVING and HOWLAND BANCROFT.

FIELD WORK.

The field work on which this report is based was begun by the 

United States Geological Survey in the summer of 1904. During

August of that year J. D. Irving spent a month in the district 

examining the properties then accessible and collecting notes and 

specimens for study. In the summer of 1908 new developments in 

the region made another examination expedient, and Howland 

Bancroft was sent to collect additional information and to bring 

Mr. Irving's observations up to date.

The mines have been worked for a long time and in a desultory 

manner and many of them have been abandoned, so that only a small 

part of the ore bodies that have been worked can now be examined. 

The data collected are thus necessarily fragmentary and the writers' 

generalizations are the result of field work done under somewhat 

difficult and unsatisfactory conditions.

This report is written jointly by Mr. Irving and Mr. Bancroft and 

is based both on the original field observations and the later observations and collections. For the chapter on the geology of the region 

the authors are indebted to Whitman Cross, who is also largely 

responsible for the geologic map.

ACKNOWLEDGMENTS.

To the owners and operators of the mines in the Lake City district 

the cordial acknowledgment of the authors is extended for maps of 

workings, statistical data, opportunities to study cost sheets and 

assay results, and unreserved permission to enter and study all accessible underground workings.

The long and eventful history of this camp and the changes of 

personnel in the mining population consequent on the many alternating periods of depression and intense activity have made the collection of accurate historical information very difficult. The history 

of the district (pp. 12-14) has been compiled chiefly from notes furnishc d by Mr. J. J. Abbot, who has been long and intimately associated

9
10 GEOLOGY AND ORE DEPOSITS NEAR LAKE CITY, COLO.

with the region and whose .courteous aid is highly appreciated by the 

writers. These notes would be inserted in full as a section by Mr. 

Abbot if the limitations of space permitted.

GEOGRAPHY.

LOCATION AND GENERAL FEATURES.

The Lake City quadrangle is in southwestern Colorado, between 

longitude 107° 15' and 107° 30' W., and latitude 38° and 38° 15' N., 

adjoining the Our ay quadrangle on the west. (See fig. 1.) It covers 

about 235.7 square miles and contains some of the most rugged

o 20 4o eo so ioo Miles

FIGUEE 1. Index map of a portion of Colorado, showing the location of the mining region discussed in this

report.

mountains in Colorado, the most notable probably being Uncompahgre Peak, which stands 14,306 feet above sea level.

Lake City, a view of which is shown on Plate II (p. 12), is in the 

heart of the San Juan Mountains, in the northern part of Hinsdale 

County, at the junction of Lake Fork, a southern tributary of Gunnison River, and Henson Creek, which flows into Lake Fork from the 

west. The town is 8,663 feet above sea level, nearly the lowest point 

in the mining region here discussed. The ore dfiposits described are 

scattered along Henson Creek, to the west of Lake City, for about 10 

miles and to the south, along Lake Fork and the western shores of 

Lake San Cristobal, for about 3 miles. The main region studied 

embraces an area of about 78 square miles, extending from latitude
U. S. GEOLOGICAL SURVEY 

GEORGE OTIS SMITH, DIRECTOR

I07°30'

BULLETIN 478 PLATE

38* - 

oo' I07°3O'

-

tion by u.s.c.and c.Surveyand j.F. MC Beth.

Surveyed in 1903.

TOPOGRAPHIC MAP OF THE SOUTHERN PORTION OF THE LAKE CITY QUADRANGLE, COLORADO Locations are taken directly from a map £

<-. ! compiled by W. R. Oavey, of Lake City, Colorado 75. i . i ,. i i Showing the approximate locations of patented mining claims

Scale

Park Placet

Golden Mammoth

Golden Wonder

Gold Carbonate

Red Cloud

Belle of St. Louis

Empire

Mountain View

Cora

Sulphuret

Dauphin M. S.

Dauphin

Rob Roy

Lode Star

Golden Pearl

Church Placer

G. ii A. Placer

Nellie M

Crown Mountain

Silver Coin

Mount Morris

Evangeline

M. Ellen

Velveteen

Red Bird

Princeton

Silver Bell

Mammoth

Pride of Colorado

Annie C.

Pelican No. 3

Pelican

Cannon

Benson

Atlanta

Little Chief

Blair

Hunt

Mountain Chief

Pueblo

Cleveland

Fanny Fern

Risorgimento

Alpine

Sequoyah

Cherokee

U. P.

Wye J.

Michigan

Crystal

Hard Tack

Don Quixote

Winner

Hard to Beat

California M. S.

Ulay M. S.

Equator M. S.

Metropole

McCarthy No. 2

McCarthy No. 3

McCombe

McCarthy

Windsor

Otis

Protector

Invincible

Hidden Treasure

Albany

Steele

Leadville

Regulator

Ute

Lightning Striker

California

Yankee Doodle

76.

77.

78.

79.

80.

81.

82.

83.

84.

85.

86.

87.

88.

89

90.

91.

92.

93.

94.

95.

96.

97.

98.

99.

100.

101.

102.

103.

104.

105.

106.

107.

108.

109.

110.

111.

112.

113.

114.

115.

116.

117.

118.

119.

120.

121

122.

123.

124.

125.

126.

127.

128.

129.

130.

131.

132.

133.

134.

135.

136.

137.

138.

139.

140.

141.

142.

143.

144.

145.

146.

147.

148.

149.

Cuter

Free Lance

Ulay

Mayor of Leadville

Maid of Henson

Ulay Extn.

Equator

Mab

Auric

Treasure Hill Spar

Red Rover M.S.

Yellow Jacket

Twin Sisters

Porcupine

Klondyke

Pride of America

Big Casino

Little Casino

Four Aces

Ottumwa

Castle

Burro Cabin

Louise

Jupiter

Syndicate

Finis

Baltimore

Ceres

Saturn

Colorado

Mars

Neptune

Venus

Lellie

Alabama

Ocean Wave

Wave of the Ocean

Meat Auger

Gimlet

Little Hattie

Whitney M. S.

El Norte

El Sud

Alhambra M. S.

Vermont

Delphi M. S.

Scotia

Pearl

Fairview

Empress

Ajax

Ajax M. S.

Silver Chord Extn.

Czar

Czarina

Silver Chord

Broker

Excelsior

Yellow Medicine

Mountain Belle

Capitol City No. 2

Capitol City

Lilly

Ottawa

Keystone State

Paymaster

Capitol Iron Placer

Milford

Julia

Vulcan

Gallic

Ballarat

Burro Cabin M. S.

Iron Placer

5 Kilometers

Contour interval 100 feet. 

is mean sea. 

1911
GEOGRAPHY. 11

38° to 38° 5' N., and from longitude 107° 15' to 107° 30' W. To 

this is added about 3 square miles in the vicinity of Lake San Cristobal and about its shores. The location of these areas is shown in the 

index map forming figure 1 and in detail in Plates I and III and figure 20.

The region may be reached most conveniently through the valley 

of Lake Fork. Before the advent of the railroad a wagon road 

along Lake Fork served as the principal means of access, and the 

active development of the district from 1871 to 1889 was possible 

only under the stimulus of the discovery of rich ores. From other 

directions Lake City is accessible by wagon road from Creede and 

Silverton, and by a steep and rather hazardous trail from Ouray, 

on the west.

A branch of the Denver & Rio Grande Railroad from Lake Junction, 36 miles north of Lake City, now connects the town with the main

narrow-gage line. From Lake City good wagon roads or trails 

lead to the principal mines; supplies are hauled as far as possible by 

teams and are then transferred to pack trains.

TOPOGRAPHY.

The surface of the region is composed principally of igneous rocks, 

which, under the action of streams, glaciers, and atmospheric agencies, 

have been wrought into a topography that is notable for its extreme 

roughness and irregularity. Viewing the country from Uncompahgre 

Peak, one is impressed by the approximate uniformity in the heights 

of the many high peaks of the San Juan Mountains and is led to conclude that these summits represent a formerly existing plateau which 

has been dissected by deep erosion.

The average difference in elevation between the stream beds and 

the ridges separating them is about 2,000 feet, but in some places the 

divide between two forks of the same small stream rises to heights of 

3,000 feet or more above the bottom of the gulch. The lowest altitude in the quadrangle is slightly over 8,000 feet above sea level, 

and the elevation of Uncompahgre Peak, not over 12 miles distant, 

is 14,306 feet.

The region is in general drained toward the north, but the principal 

ruining area is traversed by an eastward-flowing stream called Henson 

Creek, which, in the lower part of its course, runs through a deep, 

picturesque canyon. (See PI. II, p. 12.)

OFFICIAL MINING DISTRICTS.

Hinsdale County is divided into mining districts, which here, as in 

other mining regions, have somewhat indefinite boundaries. As outlined by the legislative act of 1893, this part of Hinsdale County contains two districts, the Galena and the Lake. The Galena district,
12 GEOLOGY AND OKE DEPOSITS NEAR LAKE CITY, COLO'.

named from the presence of considerable quantities of the mineral of 

that name in the earlier exploited ores, extends westward along Henson Creek from Lake City to the Ouray and San Juan County lines. 

The Lake district, so called from its proximity to Lake San Cristobal, 

embraces the north and east portions of Hinsdale County. It 

extends southward from Lake City and westward along the valley 

of Lake Fork, including such prominent mines as the Golden Fleece, 

Black Crook, Isolde, and others in the section known as Burrows

Park.

CLIMATE.

The effect of climate on the mining industry is fully appreciated by 

those who are engaged in mining operations in this region. In winter 

the streams are frozen and most of the mines are forced to use steam 

or 'gasoline engines instead of water power. The extra expense is 

great. Snow is so deep from December to April that operators of 

mines near timber line have to lay in supplies for the winter or cease

work until spring.

TIMBER.

n

The timber in this region is all spruce or aspen, much of it available 

for use in the mines. The laws regarding the use and purchase of 

timber on mining claims, forest reserves, etc., are contained in brief 

in the "Use book" published by the Forest Service of the Department 

of Agriculture.

"Dry rot" of mine timbers is said to be a little more prevalent in 

the mines of the Lake City region than in most of the other mining 

districts in the vicinity. It is possibly due to the use of green timber 

in many of the workings; to insufficient circulation of air; to moisture in the shafts, adits, stopes, etc., sufficient to propagate fungous

growth and not enough water to wash it away; and to the total neglect to use preservatives. The remedies for these evils are selfevident. If a few inexpensive precautions were taken, accidents to 

mine workings would greatly decrease. Circular No. Ill of the 

Forest Service gives a good brief account of methods of prolonging

the life of mine timbers.

HISTORY. 1

The history of the Lake City mining region is one of alternations 

of general depression and of excessive activity which have rendered 

its existence a little more eventful than that of the neighboring towns 

in the San Juan Mountains. These alternations have been due to 

several causes, but chiefly to the extreme richness of a few of the 

ore bodies discovered and the poverty of the rest. The periodical 

discoveries of new ore bodies of promising appearance were immediately followed by great inrushes of all sorts of people, whose presence

1 Based mainly on notes furnished by Mr. J. J. Abbot, some of which are quoted directly.
U. 8. GEOLOGICAL SURVEY BULLETIN 478 PLATE !

A. VIEW OF LAKE CITY, COLO. 

Photograph by Whitman Cross.

B. VIEW OF NORTH SIDE OF HENSON CREEK. 

Photograph by Whitman Cross.
HISTORY. 13

made the country thrive for a time. Similar variant conditions have 

prevailed to a greater or less extent in almost all mining centers, but. 

in few places in Colorado have they been so pronounced as at Lake 

City.

Precious metal was probably first discovered in the Lake City area 

about 1842 by a member of the Fremont party, but no one, not even 

the explorer, has been able to locate the place or even the stream 

from which the. first small amount of gold was panned. On August 

27, 1871, with the discovery of the Ute and Ulay veins by Harry 

Henson, Jorl K. Mullin, Albert Meade, and Charles Godwin, the history of Lake City began. At that time all of the land which is now 

the "San Juan" belonged to the Indians. The reports of mineral 

wealth brought many prospectors into the region, and the red men 

became very much irritated at the frequent encroachments upon 

their domain. Finally, in 1874, to avert open hostilities, a treaty 

was drawn up and ratified by the Senate, whereby a strip of land 60 

miles wide and 75 miles long was ceded to the United States Government by the Ute Indians.

In August, 1874, Hotchkiss (the leader of the expedition that built 

a wagon road from Saguache to Lake City) discovered the rich vein 

now known as the Golden Fleece and named it the "Hotchkiss." 

News of the strike spread rapidly and Lake City soon became a center 

of activity, the county seat being removed from San Juan to Lake 

City, where it has remained. During the same year reduction works 

were erected at Lake City and a third stamp mill was built in the 

Summit mining district.

Development was continued and new discoveries were made almost 

daily. The first boom attained its climax in 1876, coinciding with 

the opening up of Ocean Wave Group and the continued production 

of the Hotchkiss and the Ute and Ulay mines. During the spring 

the erection of a concentrator was begun and ground1 was broken for 

a smelter at the falls just above the city. Soon afterwards the reaction and "lull" so characteristic of the region began.

During the next three years work was continued on the Ute and 

Ulay and the Ocean Wave properties, the Excelsior mine was located 

(April, 1878), and the Crook and Ocean Wave smelters were completed.

The year 1880 marked the beginning of the biggest boom in the 

Lake City region. A great deal of work was done on the Palmetto 

group, which lies just west of the Lake City quadrangle. The St. 

Louis, Capitol, Czar, Silver Chord, Young America, Yellow Medicine, 

Pride of America, Vermont, Red Rover, and many other properties 

near Capitol City were being worked with various results.

Probably the most talked-of find during this period was that of the 

Golden Wonder, in Deadman Gulch, so named from four men who
14 GEOLOGY AND OBE DEPOSITS NEAE LAKE CITY, COLO.

were killed and partly eaten there by their companion, Alfred Packer, 

in the winter of 1874.

This second boom period reached its climax near the close of 1881. 

In that year the Denver & Rio Grande Railroad, which had started 

to build to Lake City, became financially involved and ceased construction. In the fall of 1883 the Ute and Ulay shut down and for 

four years Lake City was practically dead.

In 1887 considerable ore was shipped from the Ulay, Vermont, 

and Yellow Medicine properties. The shipments from the Yellow 

Medicine mine fell off perceptibly in 1888, but the Ulay and Vermont 

continued to ship large quantities of ore. The Gallic was discovered 

during this period and later made a few shipments.

In 1889 the branch railroad was completed and soon afterward very 

rich ore was reported from the Golden Fleece. A single car of petzite 

ore from this mine is said to have yielded $50,000. The extreme 

richness of this ore stimulated mining throughout the region for 

about ten years. The total output of the Golden Fleece mine has 

been $1,400,000.

In 1890 some 20 mines in the Lake City quadrangle were shipping ore. During 1891 the Ute and Ulay alone produced over 

$400,000 and the total production from these mines has been 

$12,000,000.

In the late nineties the mining activity in the region almost reached 

a boom. Much work was done upon other properties in the vicinity 

of the Golden Fleece and some ore was shipped. The Golden Fleece 

Extension, Lake View, Black Crook, Contention, and others were 

operated. In June, 1897, the first ore was extracted by the present owners from the Hidden Treasure mine, as much as 22,000 tons of ore per 

year having been shipped from this property, which still continues to 

produce intermittently. The Czar first became a regular shipper in 

1899, but its active life was short. The crest of the last wave of activity 

was reached during 1899, since which time operations have been more 

or less spasmodic.

PRODUCTION.

Hinsdale County originally included part of what is now Mineral 

County, in which the Creede mining district is located. On March 27, 

1893, the legislature created Mineral County out of parts of Saguache, 

Rio Grande, and Hinsdale counties. For this reason statistics of 

production earlier than 1893 include also the production of Creede, 

which has been deducted in order to determine accurately the output 

of the present Hinsdale County, or practically the mining district here 

discussed. These statistics, except those for a few mines fhaking 

confidential reports, have been compiled from the returns from individual mines as given in the reports of the Director of the Mint, in the 

reports of the State Bureau of Mines of Colorado, and, since 1904,
PEODUCTION. 15

in Mineral Resources of the United States, published by the United 

States Geological Survey.

The following table and figure 2 show the production of the county 

since 1884:

Metallic production of Hinsdale County from 1884 to 1906.

[iFigures derived from United States Mint reports, 1884 to 1896, inclusive; from reports of State Bureau of 

Mines, Colorado, 1897 to 1903; from Mineral Resources of the United States, published by the United 

States Geological Survey, 1904 to 1908.]

Years.

1884..........................

1885..........................

1886..........................

1887..........................

1888..........................

1889..........................

1890..........................

1891..........................

1892..........................

1893..........................

1894..........................

1895..........................

1896. .........................

1897..........................

1898..........................

1899..........................

1900. .........................

1901..........................

1902..........................

1903..........................

1904..........................

1905..........................

1906..........................

1907..........................

1908..........................

Total...................

Gold.

82,500

.2,060

5,214

2,667

1,680

3,577

20,594

 13,529

88,279

95,293

274,421

215,648

168, 171

51,282

38,343

56, 470

76, 148

98,348

16,515

7,692

11,991

24,510

7,520

2,454

1,284,906

Silver.

Fine ounces. 

156; 967

18,586

94,546

110)433

18,673

61,023

186,841

418,422

340, 774

404, 750

466,836

465,598

243, 437

186, 456

155,902

155,485

152, 122

117,177

. 33,139

39,283

54,419

87,940

50, 109

29,498

4,047,416

Copper.

Pounds.

13,545

1,815

40,000

40,950

3,636

20,182

W («)

13,006

8,085

104,038

49, 676

29,180

12,532

8,314

11,263

10,530

84,485

63,261

99, 410

188,698

802,606

Lead.

Pounds.

30,435

657,400

1,495,614 OAA cnn

546,920

5,441, 380

6,225,747

W(°)

3,676,733

6,934,099

3,550,058

9,828,482

10,572,353

9,377,062

7,588,675

6,213,763

459, 462

1,054,421

767,681

753,950

1,204,628

280,465

78,903,828

Zinc.

Pounds.

106,000

175,815

2,085

30,475

23,034

237,409

Total 

value.

8180,317

23,743

128,432

172,586

QQ QAQ

 96,112

442,384

653', 107

354 754

350,286

689,577

725,668

501,822

612,561

600,309

496, 792

428,733

60,910

81,416

94,244

140,543

125,678

54,776

7,577,750

a No figures for lead and copper available.

No production is given for 1885 in the mint report, so the district 

was probably idle in that year. The production prior to 1884 can not 

be definitely determined, but as the Ute and Ulay mine was in active 

operation and the Ocean Wave and others were productive, it is probable that accurate statistics would show a yield nearly, if not quite, 

equal to that given in the table. This is the more likely as the years 

1876 to 1881 marked the greatest boom that Lake City has ever 

experienced.

From these figures the curve in figure 2 showing the production of 

copper, lead, gold, and silver has been constructed. This curve shows 

clearly that the culminating years of the later history of the district 

were 1895 and 1896, in the latter of which the yield was nearly threequarters of a million dollars. It shows the general rise, culmination, and decline of the district, and brings out clearly the alternate 

periods of activity and depression. In 1889 the production was less 

than $35,000, but the advent of the railroad into Lake City that year 

caused a rapid increase, culminating in 1892. In 1893 the financial 

depression, coupled with a gradual decline in the value of silver 

caused a sharp fall, followed by a rapid rise until 1896. The decrease
GEOLOGY AND ORE DEPOSITS NEAR LAKE CITY, COLO.

in 1897 and 1898 was probably due to local conditions. From 1898 the increasingly rapid decline, 

which culminated in 1903, 

represents the rapid exhaustion of the upper portions of the mines, whose 

richness was due to oxidation and secondary enrichment. After 1903 a slight 

revival indicates the attempts to handle lowgrade material. The year 

1908 shows the lowest output since 1885, and it is 

probable that unless the 

discovery of new veins 

should cause new activity 

in this region very little 

further production is to be 

expected.

MINES.

The following is a list of 

the mines which have been 

worked in Galena and Lake 

mining districts and which 

have either yielded some 

ore or have shown evidences of mineralization. 

The arrangement is geographical. .

The production of some 

of these mines, as shown by 

Mint reports, statements 

of owners, the Geological 

Survey's reports entitled 

"Mineral resources of the 

United States," and other 

sources of information, is 

given after the names. 

These figures, serve, to

Thousands of dollars

1881

1882

1883

1884

1885

V 1890

1892

a 1893

§. 1895 5' 

p 

o 1896

gl 1900

I""

 1902 

1 1903

1904

1905

1906

1907 

-1908 

1909 

WiQ;

1

M = 

CD ^

Lsg..

\
PEODUCTIO]$r. 17

.separate in a general way the important productive mines from the 

less productive and from mere prospects.

List of mines in Galena and Lake mining districts. 

Capitol City.

Gallic and Vulcan. Silver Chord Extension.

Woodstock. Silver Chord.

Ottawa. , Czarina.

Toby. Czar.

Lilly. Excelsior ($18,006).

Capitol City ($27,990). Broker.

Yellow Medicine ($40,494). Lucky Strike.

Henson Creek (Main Stream.)

Vermont ($142,207). Cleveland.

Ocean Wave ($26,305). Sacramento.

Wave of the Ocean. Yellow Jacket. '

Lellie (Red Rover). Ute and Ulay (estimated $12,000,000).

Baltimore. Hidden Treasure (estimated $700,000).

Big Casino. U. P.

Little Casino ($420). Pelican.

Pride of America. Missouri Favorite.

Fanny Fern. California.

North Lake Fork (south of Lake City).

Nellie M. lima (Black Crook) ($124,447).

Monte Queen. Belle of the West ($56,302).

Dauphin and Rob Roy. . Contention ($2,332).

Sulphuret and Cora ($3,090). Golden Fleece (from mine records

Golden Wonder. $1,400,000).

Lode Star. Carmi ($580).

Carson. 

[These mines wero not studied.]

Mayflower ($3, 590). Hamilton.

George III ($5,439). St. Jacobs.

Bonanza King ($3,290). Maid of Carson ($27,397).

West Lake Fork. 

[These mines were not studied.]

Isolde. Pelican ($2,084). 

Tobasco. Bon Homme ($2,265). 

Cleveland. Mount King. 

Black Wonder ($162).

South Fork of Henson Creek (south of Capitol City). 

[These mines, except the Moro and Paymaster, were not studied.]

Wyoming ($775). *Bonanza.

Independence ($4,520). *First National Bank.

John Hough ($1,289). *Frank Hough.

Miners' Bank ($2,600). Anchor (probably a little).

Henson Creek ($700). Moro (considerable production).

*Palmetto ($11,206). Paymaster (no data).

Highland Chief.

95249° Bull. 478 11 2
18 GEOLOGY AND ORE. DEPOSITS NEAR LAKE CITY, COLO.

Certain mines indicated in this list were not studied, as they lie 

too far outside of the district examined to warrant field work, and 

they are not further mentioned in this report. Many of them, however, have contributed to the production of Hinsdale County.

Those marked with an asterisk are within the northeastern portion of the Silverton district and have been described by Ransome.1

The observed conditions 300 to 400 feet below the surface lead 

the writers to'believe that only the roots of veins are present in the 

district and that all ore bodies are likely to diminish greatly in value 

in depth. Hence the life of any mine is likely to be brief. The 

change in character of the ore and gangue minerals with depth in 

the Ute and Ulay, Hidden Treasure, Black Crook, and numerous 

others illustrates this point remarkably well.

GEOLOGY.

By WHITMAN CROSS.

The Lake City district is a small part of the volcanic San Juan 

region.. Geologically it is particularly allied to the adjacent portion of the San Cristobal quadrangle on the south, which has been 

recently surveyed, and to the Silverton and Ouray quadrangles on 

the southwest and west, respectively, the geology of which has been 

described in published folios.2 For this reason the geology of the 

San Juan region as a whole will first be briefly discussed, especially 

the important relations of the rock formations that occur in the 

Lake City area. Next the geology of the Lake City district itself

will be described.

SAN JUAN MOUNTAINS.

GENEKAL FEATURES.

The San Juan Mountains consist chiefly of surface volcanic rocks

or of intrusive igneous masses, which now cover an irregular area 

of more than 3,000 square miles. This volcanic area extends from 

San Luis Park on the east to an irregular and abrupt western mountain front in the Telluride quadrangle. On the north the volcanic 

rocks reach out beyond the mountainous district proper, the lower 

lavas capping long low ridges between southerly tributaries of Gunnison River, in some of them extending to the edge of the Black 

Canyon. The southern border of the volcanic district runs from the 

Telluride quadrangle somewhat south of east and a broad arm 

crosses into New Mexico.

It is evident that the lavas once extended far beyond their present 

limits on all sides except the east. Between the San Juan and West

1 Ransome, F. L., A report on the economic geology of the Silverton quadrangle, Colorado: Bull. U. S. 

Geol. Survey No. 182,1901. 

a Silverton folio (No. 120) and Ouray folio (No. 153), Geol. Atlas U. S.
U. S. GEOLOGICAL SURVEY 

GEORGE OTIS SMITH, DIRECTOR BULLETIN 478 PLATE III

107 15'

."'/^ \ / ;J : C Sugar-loaf Rock 

^ '^V^f^T^ IS f .& i

I07'i5'

E.M.Douglas, Geographer in charge. 

Topography by J. F. Me Beth.

Triangulation by U.S.C.and G.Survey,and J.F. Me Beth. 

Surveyed in 1903.

GEOLOGIC MAP OF THE SOUTHERN PORTION OF THE LAKE CITY QUADRANGLE, COLORADO

Scale e25oo

Geology by Whitman Cross, assisted by 

L.H .Woolsey, A.Johannsen, H .Bancroft, 

W.H.Emmons,and G.F.Kay.

Survey completed in I9O9.

5 Kilometers

Contour interval 1OO leet.

SEDIMENTARY ROCKS

QUATERNARY

~\ f~ 

~\ r

Qal

AHuvimii

. Qls I

I____TT_J 

L andslide s

ogi Ths

1911

IGNEOUS ROCKS

TERTIARY

Tp

soils o 

torrential fa

_________

Glacial Minscliile Fotosi 

detritixs volcaidc series volcanic seiies

flava fUn,'S ofrhyoUfe, I 'lava, flovs oFrhyoUte,

! Th i 

Hen son tuff'

Tpa

I'vi'oxeur 

aiid.e,site

Tb ! Te TRY I Trl

U-ITLIIS Kui'eka rtyoHte Picayune iTxti-usive Intmsive Intrusive 

latite tufl' {ia.v«.nsrKs;<xntains vDlcanic group rhyolite and. qiiaz'tz monzo- andesite

(bedflfd.sand.-itoru!, "^^a^^folaLs^ocJf.^ l&nbmcfsaxidfsitv, OUSrtZ lalite nite T3Orr)llVCy

and.are*mitl-,m4unly > uztite,<mdJ rnyGUte. ^- s: S: ~ J

oFlajbite;somefos3ij[ inchaoti^r

Tde

I )CM -i >n i j>osfnl

p( IL'pllVl'V Of

Vein 

with dip indicated
GEOLOGY. 19

Elk mountains, which He north of Gunnison River, there was once a 

continuous covering of volcanic rocks, but these rocks did not necessarily come from a single central source. The Hayden geologic 

map of Colorado is approximately correct in its representation of the 

limits of this volcanic area, but it fails to give any idea of the complexity of the lavas, either as to character or age. The eruptions 

occurred during nearly the whole of Tertiary time, when a great many 

different kinds of lavas were poured out, building up a huge volcanic 

plateau. Eruptive activity was not continuous during the Tertiary 

period, but was broken by long intervals of quiet, during which 

extensive erosion materially changed the topography of the volcanic 

pile.

In the survey of the San Juan region, which now covers more than 

its western half, it has been found desirable to map and to describe 

the rocks of the principal eruptive periods in groups or series rather

than to emphasize the occurrence of special rock varieties, and this 

method will be followed herein.

THE EARLIEST ERUPTIONS.

The commencement of volcanic activity was clearly later than the 

deposition of the Upper Cretaceous coal measures of southwestern 

Colorado, but somewhat earlier than any of the recognized Tertiary 

formations of the region. This is shown by the Animas formation, 

which overlies the coal measures at Durango and which consists 

largely of the pebbles and gravel of andesitic volcanic rocks. These 

beds carry fossil plants and scanty vertebrate remains which prove 

them .to be of the same age as the Denver formation, at the base 

of the Front Range that is, early Eocene or uppermost Cretaceous. 

The source of the volcanic materials of the Animas formation is not 

yet known.

SAN JUAN TUFF.

The Animas formation does not extend into the San Juan Mountains proper, and the lowest or earliest member of the great volcanic 

complex found in the western part of the region is a fragmental 

deposit which has been called the San Juan tuff. It is a more or less 

plainly stratified series of tuffs, breccias, or coarse agglomerates of 

andesitic rocks, in which no fossils have been discovered. No lava 

flows have been found interbedded with the fragmental deposits.

The San Juan tuff has a maximum observed thickness of 3,000 feet 

and forms notable deposits in the Ouray and Telluride quadrangles, 

though it appears in all other surveyed areas on the border of the 

volcanic district. It occurs in typical form in the Cimarron and Blue 

Creek valleys of the Lake City quadrangle.

The source of the andesitic rocks of the San Juan tuff was a mystery 

pxevio.us.to the survey^of the Lake City, quadrangle. It now appears
20 GEOLOGY AND OKE DEPOSITS NEAR LAKE CITY, COLO.

probable that a portion of the older volcanic mass from which those 

tuffs were derived occurs in the valley of Lake Fork a few miles below 

the mouth of Henson Creek. This mass has not yet been described 

and its extent is unknown. Its relations will be described in a forthcoming report on the Lake City quadrangle.

SILVERTON VOLCANIC SERIES.

The group of lavas succeeding the San Juan tuff are known as the 

Silverton volcanic series, as they have their greatest development in 

the Silverton quadrangle. These rocks are of special importance in 

the area treated of in this report. They consist of an alternation of 

andesites, latites, and rhyolites, in both flows and fragmental beds.

PICAYUNE VOLCANIC GROUP.

The earliest of these lavas, first observed in the Silverton quadrangle, is a dark augite andesite occurring in relatively small exposures 

in the Animas Valley and its minor tributary, Picayune Gulch, and 

named in the Silverton folio after the latter locality, the Picayune 

andesite. It is now known that the andesite of Picayune Gulch is 

but one of the rock varieties erupted in x the first part of Silverton 

time and that the complex group of early lavas is most prominent in 

the country between Henson Creek and the head of the Lake Fork 

and in the valleys of these streams. The name Picayune will be 

retained for the group since it is already in use and since the relations 

of these rocks to the overlying rhyolite are well shown in the original 

locality.

The Picayune volcanic group consists largely of andesite of the 

type first observed, but includes also several kinds of more siliceous 

lava. The various elements are so irregularly associated as to make 

it clear that the exposed rocks of the group belong to a central 

volcanic mass made up of surface lava streams, pyroclastic breccia 

and tuff, and intrusive bodies. The massive rocks have in many 

places been shattered and dislocated by volcanic shocks. (See also 

p. 24.)

EUREKA RHYOLITE.

Among the more siliceous varieties of rock in the Picayune group 

is a rhyolitic lava which became more and more abundant until it 

was finally poured out in a thick flow or succession of flows which 

appear to have buried the older complex of Picayune rocks and now 

form a prominent and persistent element of the Silverton volcanic 

series. This rock is called the Eureka rhyolite, from t,he notable 

cliffs of it about Eureka, in the Animas Valley. It may generally 

be effectively described as a flow breccia, for it characteristically 

carries many small fragments of rhyolite and other rocks. Gray or 

pinkish exposures of it are continuous for several miles in the Animas
GEOLOGY. 21

Valley, and appear very typically in the canyon of Henson Creek for 

2 to 3 miles above Lake City.

BURNS LATITE.

The extensive flows of Eureka rhyolite were followed by an eruption 

of several varieties of latite lavas and tuffs more or less in alternation. 

The relations of these lavas are much simpler than those of the Picayune volcanic group and their order of succession is in most places 

plain. Two fine-grained tuffs, especially, are widely distributed in 

the Silverton quadrangle, one below and the other above the principal 

lava flows. This aggregation of flows and tuffs is called the Burns 

latite, from Burns Gulch, a branch of the Animas near Picayune 

Gulch. The rocks of the Burns occurring in the Lake City area are 

all tuffs.

PYROXENE ANDESITE.

The Burns latite is succeeded by dark fine-grained pyroxene 

andesite in a complex of flows and fragmental beds reaching a maximum thickness of nearly 3,000 feet in the central part of the Silverton 

quadrangle. These rocks are closely related to some of the Picayune 

lavas but have distinguishing characters. Massive flows of pyroxene 

andesite of this upper part of the Silverton volcanic series are present 

on the north side of Henson Creek near Capitol City, but they decrease 

in thickness eastward and disappear entirely west of Nellie Creek.

HENSON TUFF.

The uppermost member of the Silverton volcanic series is a greenish 

gray andesitic tuff, named Henson tuff, from its most notable occurrence on North Fork of Henson Creek, in the Ouray quadrangle. Its 

development in the Lake City area is very subordinate.

POTOSI VOLCANIC SERIES.

The long Silverton epoch of eruption was followed by a quiet time, 

during which erosion was very active; and then began another great 

succession of volcanic outbursts, producing lava flows and clastic 

deposits alternately. These lavas appear to have covered a larger area 

than the earlier ones. They are mainly latite and rhyolite, with some 

andesite, all of types different from the preceding ones, and preserved 

in much less altered condition. These rocks are called the Potosi 

volcanic series because of their typical exposure and notable thickness 

and variety in Potosi Peak, Silverton quadrangle.

The Potosi lavas are most widely distributed in the San Juan region. They occur very extensively in the central San Juan Mountains, San Cristobal quadrangle, and extend far down the northern 

slopes toward the Gunnison. They cap certain ridges north of Hen- 

.son Creek and occupy much of the Lake City quadrangle farther 

north. Uncompahgre Peak presents a fine section of Potosi flows.
22 GEOLOGY AND ORE DEPOSITS NEAR LAKE CITY, COLO. 

HINSDALE VOLCANIC SERIES.

The western San Juan region exhibits no lavas more recent than 

those of the Potosi volcanic series, but in portions of the San Cristobal 

and Uncompahgre quadrangles, and presumably in others not yet 

examined, a later succession of eruptions took place, producing a 

series of lavas differing notably from the products of earlier eruptions. 

It is plain that much erosion of the Potosi volcanic series occurred before the extrusion of these later magmas, which, so far as known, 

closed the long sequence of lavas in the San Juan region.

This newly recognized series of lavas ranges from a rhyolite very 

rich in quartz and alkali feldspar but poor in calcic feldspar and in all 

ferromagnesian minerals to a normal olivine plagioclase basalt. Between these two extremes are lavas of several types possessing some 

characteristics distinguishing them from earlier lavas.

No rocks of this recent series have been described in earlier folios 

or reports, and it is proposed to call them the Hinsdale volcanic series 

because of then* important occurrences in Hinsdale County, of which 

Lake City is the county seat. The most extensive deposits of these 

lavas thus far discovered are on the divide between Lake Fork and 

Cebolla Creek, directly east of Lake City. The section exposed is 

nearly' 1,200 feet thick. The lower 800 feet of the series occur within 

the area of the accompanying map on a spur from the divide. Other 

important localities for these rocks are Cannibal Plateau, northeast 

of Lake City; the Continental Divide, between Lake Fork and the 

head of Cebolla Creek; several summits between branches of Clear 

Creek; and the hill north of Lost Lake, the last three being in the San 

Cristobal quadrangle. All localities named are in Hinsdale County.

The Hinsdale is, like the Potosi and Silverton volcanic series, $ set 

of lavas representing one of the major divisions of the San Juan volcanic history rather than a petrographic group. It is too early to 

sharply define its limits.

LAKE CITY DISTRICT. 

GENERAL GEOLOGY.

Nearly all the rocks of the Lake City area (see PL III), belong to the 

Silverton volcanic series, the great intermediate member of the Tertiary volcanic complex. No earlier formation occurs here, and only 

subordinate representatives of the later Potosi and Hinsdale volcanic 

series occur in the district. Intrusive masses are numerous, but 

though these are obviously younger than the rocks which they penetrate their exact age relations are nowhere clear.

The canyon of Henson Creek, which is the most prominent topographic feature of the area, presents an excellent though by no means
U. S. GEOLOGICAL SURVEY

A. ROUNDTOP MOUNTAIN, LAKE CITY MINING REGION, 

Photograph by Whitman Cross.

/;. POST-GLACIAL CANYON OF HENSON CREEK. 

Showing gorge in Eureka rhyolite. Missouri Favorite Mine is in the center.
GEOLOGY. 23

complete section of the prevailingly somber rocks of the Silverton 

series. On its southern side the lowest (oldest) member of the series, 

the Picayune group, predominates, and on its northern side several 

higher (younger) members are well shown. The general northerly 

dip of the lavas and tuffs affords proof that the center of eruption 

during the Silverton epoch of volcanic action was south of the Lake 

City area.

The restrictions of the map prevent representation of the fact that 

the various rocks of the Silverton series do not extend far northward 

beyond Henson Valley nor eastward beyond Lake Fork. This limitation is due to great erosion in the epoch preceding their eruption. 

The San Juan tuff and perhaps earlier massive volcanic rocks once 

existed where the Silverton lavas of Henson Creek now are. By their 

erosion a steep southward-facing slope or cliff was produced near 

the north boundary of the Lake City district. The Potosi rhyolites

and latites cap the divide north of Henson Creek on either side of El 

Paso and Nellie Creek, resting on the uppermost rocks of the Silverton series; they are very prominent in the northern part of the Lake 

City quadrangle, forming plateau-like ridges with a gentle northerly 

dip. They are cut in the valleys of the east fork of the Cimarron, 

Blue Creek, Elk Creek, and other streams, exposing the underlying 

rocks; but these are not at all like the Silverton volcanic rocks of 

Henson Creek, consisting, instead, of a great volcanic breccia or semiconglomerate of rude bedding, which extends west into the Ouray 

quadrangle, where it is shown to be the San Juan tuff, a formation 

entirely older than the Silverton series. These relations of the San 

Juan tuff and the Silverton rocks are not clearly exposed in the Lake 

City quadrangle, but they are exhibited in the Ouray quadrangle and 

have been described and illustrated in the folio dealing with that 

area. The Potosi lavas, therefore, overlap the boundary between the 

San Juan tuff and the Silverton series.

Although the canyon of Henson Creek cuts so deeply into the Silverton volcanic series, it does not actually penetrate below it at any 

point within the Lake City quadrangle. There is, however, evidence 

that granite and very old quartzite rocks lie probably at no great distance beneath the Picayune lavas on Henson Creek.

That granite is one of the foundation rocks is indicated by a small 

exposure of that rock 2 miles southwest of Capitol City in the bed of a 

southerly branch of Henson Creek, which it enters east of the Moro 

mill. This granite is on the north side of a fault of undetermined 

throw and the exposure is but a few yards in diameter. It is but 1£ 

miles from this point south to the large fault block of granite, the great 

part of which lies north of Whitecross, at the head of the Lake Fork.

Quartzite resembling the pre-Cambrian rocks of the Uncompahgre 

Canyon at Ouray occurs in a small exposure, surrounded by volcanic
24 GEOLOGY AND ORE DEPOSITS NEAR LAKE CITY, COLO.

rocks at an elevation of 11,800 feet, a little more than a mile southeast 

of Capitol City. The exposure is insufficient to show whether this 

quartzite is a large block included in the volcanics or a pinnacle of an 

underlying rugged quartzite topography, but it does make it clear 

that rocks other than granite go to make up the prevolcanic complex of 

this vicinity. At several places in the San Cristobal quadrangle 

chaotic breccia masses in the Picayune volcanic group contain fragments of granite and quartzite, some of which are several yards in 

diameter.

SILVEETON VOLCANIC SERIES. 

PICAYUNE VOLCANIC GROUP.

Occurrence. The rocks of the Picayune volcanic group, together 

with intrusive masses, occupy the greater part of the .area between 

Henson Creek and the Lake Fork to the south. They occur connectedly in the Henson Valley from near Capitol City to a point below 

the mouth of Alpine Gulch and in separated areas in Wade Gulch, 

on the slope between Wade and Alpine gulches, and on the west side 

of the Lake Fork opposite Deadman Gulch. The rocks rise higher 

on the south side of Henson Creek than on the north, owing to a general northerly dip of their upper surface, on which the Eureka rhyolite 

rests.

The rocks of the group are prevailingly dark in tone and cause 

somber cliffs in which a rude stratified arrangement of successive 

flows or beds can be recognized in many places. Among the best 

exposures for a study of the Picayune rocks are the steep cliffs at 

several points between El Paso and Modoc gulches, and in Wade 

Gulch near the quadrangle line. There is much landslide and forest 

cover on the south side of Henson Creek, although the rocks are well

exposed in many localities.

General character. The lavas and fragmental rocks here called the 

Picayune volcanic group once formed a great volcano, the center of 

which was situated a few miles south of Henson Creek, in the area 

between that stream and the upper part of Lake Fork. The rocks 

of the group are principally dark andesites, dacites, and quartz 

latites, with a variable amount of light-gray rhyolite. The petrographic distinctness and ths sharp local boundaries of certain masses 

made it at first appear practicable and desirable to distinguish them 

on the map, and much time has been spent trying to do this. But 

with greater knowledge of this old volcano it has become clear that 

a petrographic division of the group can be mapped only at some 

future time, after long and painstaking study and with a topographic 

base of much detail and great accuracy. The lavas, tuffs, and 

breccias of the group are therefore mapped collectively under one 

color, and only the more important and definite intrusive rocks are 

distinguished.
GEOLOGY. 25

The structure of the Picayune mass is most irregular. A large 

part of it is breccia that is, it is made up of angular rock fragments. 

Some breccias are composed almost exclusively of one kind of rock 

and appear to have been made by the shattering of massive rock in 

place. Other breccias are simply chaotic accumulations of several 

different rock types, in large and small fragments. Well-bedded 

deposits of more or less worn, transported material also appear but 

are not continuous enough to express a prevalent structure.

Lava flows alternate with breccias or tuffs in many local sections, 

but these, too, possess little lateral extent. Intrusive masses of 

various shapes and sizes, consisting of rock varieties for the most 

part identical with some of the flows or breccia fragments, are, by 

reason of the prevalent irregularity of all masses, distinguishable 

only with the greatest difficulty and in favorable localities.

No regular succession of magmas of different character has been 

made out. Probably the oldest lavas of the Picayune center were 

andesitic and the later ones chiefly rhyolitic or latitic. Such appears 

to be the general rule, but apparent exceptions are numerous.

The Picayune rocks are more extensively altered than the younger 

lavas. This is quite natural in view of the fragmental character of 

much of the mass and the local extent of even the largest massive 

bodies. These conditions must have been favorable to the free 

circulation of solvent and mineralizing waters.

Typical exposures. The development of the Picayune volcanic 

group in the Henson Valley may be best described by giving details 

of typical localities. One of these is the ridge between Nellie and 

Pole creeks, on the southeast face of which the Picayune rocks are 

exposed for about 1,500 feet, above the mouth of Nellie Creek. A 

well-stratified conglomerate and breccia, forming ledge exposures by 

the roadside at several places between Pole and Modoc creeks, is the 

base of the exposed section. This stratified rock appears at first 

to have nothing to do with the darker volcanic complex about it, 

but it is, in fact, only a phase of the rhyolitic tuffs or conglomerates 

found in local development in many places, at various horizons. 

The conglomerate is overlain by a coarsely stratified breccia, dipping 

25° to 30° N. Adjacent outcrops are similar for the most part but 

differ in relative proportions of rock types and in texture. At about 

200 feet above Henson Creek a brecciated nearly homogeneous rock 

is overlain by a flow, the lower zone of which is marked by fluidal 

structure. This extends for about 100 feet vertically, the dense 

dark rock being almost homogeneous though more or less brecciated. 

At an elevation of 300 feet a finely bedded sandy tuff occurs with a 

flow only 5 to 6 feet thick in its midst. This flow has sharp contacts 

and fluidal border zones. A variable dip reaching 30° N. as a maximum is here distinct. Above these gray tuffs comes another much
26 GEOLOGY AND ORE DEPOSITS NEAR LAKE CITY, COLO.

thicker flow similar to the one in the tuffs. Breccia and irregular 

masses of more basic rocks follow, with gray latite or rhyolite at 

certain horizons, and this alternation continues up to the massive 

Eureka rhyolite flow.

The Picayune rocks east and north of Capitol City deserve particular 

mention, for their relations to the Eureka rhyolite are not fully understood. The heavy coating of glacial debris on North Fork of Henson 

Creek obscures the geology very much, but the Lucky Strike tunnel, 

at Capitol City, penetrates greenish quartz-bearing andesite, quartz 

monzonite porphyry, and rhyolite similar to the Eureka type, the 

whole indicating a complex phase of the Picayune group.

The same rocks and other types known in the Picayune are found 

in Yellowstone Gulch and are encountered in the Gallic tunnel. 

In the latter locality Eureka rhyolite occurs on the slope above the 

tunnel and is the only rock observed along the banks of North Fork 

of Henson Creek, as far as Capitol City. These facts show that an 

arm of the Picayune group rocks extends up North Fork, rising much 

higher on the northeast side.

The rock referred to as quartz monzonite porphyry is no doubt an 

intrusive, identical in composition with the body represented on the 

map as penetrating Eureka rhyolite on the slope west of Capitol City. 

It is not improbable that the coarse quartz monzonite porphyry of 

the Gallic tunnel, Yellowstone Gulch, the Excelsior mine, and the 

Lucky Strike workings, as well as of certain outcrops surrounded by 

glacial material southeast of Capitol City, is of the same age as the 

body in Eureka rhyolite. But the boundaries can not be determined 

and so it can not be separated from the Picayune.

East of Capitol City and north of Henson Creek the line between 

Eureka rhyolite and the Picayune volcanic group has not been accurately determined and hence no definite boundary is shown on the 

map.

Some of the later rhyolite flows of the Picayune epoch were very 

much like the succeeding Eureka rhyolite and they do not seem to 

be so much broken as earlier lavas, so that it is difficult to determine 

whether the rhyolite of some areas south of Henson Creek should be 

referred to the Eureka or not. A massive gray rhyolite on the ridge 

west of Alpine Gulch closely resembles the Eureka, but it dips beneath 

dark andesitic rocks near the mouth of the gulch and is for this 

reason included in the Picayune.

EUREKA RHYOLITE.

The Eureka rhyolite in a succession of flows covers the Picayune 

volcanic group on the north side of Henson Creek and extends up 

the south slopes east of Alpine Gulch and near Capitol City. The 

character of the rock is well shown in the canyon of Henson Creek
GEOLOGY. 27

(PL IV, B) for 2£ miles above Lake City and in the cliffs west of the 

town. It is also present east of the town on the lower slopes.

The Eureka rhyolite is typically a dull ash-gray or green felsitic 

rock with few phenocrysts that exhibits a pronounced fluidal texture 

as seen in exposures a few feet in diameter if not in hand specimens. 

Feldspar and biotit'e crystals give the rock a porphyritic facies, as a 

rule, the groundmass strongly predominating in most places. Inclusions of rock fragments very similar to the Eureka are common in 

most flows and suggest the term flow breccia. These fragments 

are usually but a fraction of an inch in diameter and they are commonly rather flat flakes arranged in bands, emphasizing the fluidal 

structure.

Some of the Eureka rhyolite flows are several hundred feet in 

thickness and their lateral extent is measured by miles. A small

amount of tuff separates some of the flows, but more commonly

these are in direct contact and are so similar that the boundaries are 

often not easily detected.

As has been pointed out (p. 20), the Eureka lavas are practically 

identical in character with some of those in the Picayune group. 

The justification for distinguishing the Eureka as a map unit lies in 

its mass and areal importance. The lava floods of Eureka time 

covered a large part if not all of the complex Picayune volcanic 

group.

BURNS LATITE TUFF.

The Burns latite tuff division of the Silverton volcanic series is 

represented in the valley of Henson Creek only by fine-grained 

sandy tuffs and calcareous beds, which extend northeast from the 

south base of Sunshine Mountain to the ridge west of Nellie Creek 

and beyond the area mapped.. Near Nellie Creek the tuffs rest 

on Eureka rhyolite, in their normal relation, but in El Paso Gulch, 

Empire Mountain, and North Fork of Henson Creek they are separated from the rhyolite by intrusive sheets of pyroxene andesite. 

The tuff band varies greatly in thickness, owing to erosion before it 

was covered by andesite flows; northwest of Yellowstone Gulch it 

wedges out entirely.

In the drainage areas of Modoc, Findley, and Crystal creeks the 

Burns latite tuff is concealed by flows of the Potosi volcanic series, 

but it reappears west of Crystal Peak and occupies a considerable area 

between Slaughterhouse Gulch and Larson Creek. It is, however, 

much obscured by landslide material consisting largely of graygreen Burns tuff, which extends to Lake Fork immediately below 

Lake City.

The tuff reappears east of Lake City, lying on the Eureka rhyolite, 

and continues southward across Deadman Gulch, being interrupted 

by glacial debris and penetrated by several intrusive rocks.
28 GEOLOGY AND ORE DEPOSITS NEAR LAKE CITY, COLO.

The Burns tuffs are mainly fine-grained gray or greenish sandstones, made up chiefly of particles of volcanic rocks. Some beds 

include rock fragments several inches in diameter. Other layers 

are thin laminated shale. Certain layers of some exposures are 

rich in carbonate of lime, and true limestone strata 2 or 3 inches 

thick are locally developed. These calcareous beds are well exposed 

on the flat summit of the ridge east of El Paso Gulch. A few fossil 

leaves have been found in the Burns tuff in the ravine north of North 

Fork of Henson Creek, and fragments of carbonized plant stems are 

common.

PYROXENE ANDESITE.

Dark massive flows of pyroxene andesite normally succeed the 

Burns tuff in the Silverton volcanic series. Such rocks reach a thickness of several thousand feet in the Silverton quadrangle, but they 

do not exceed 800 feet in the valley of North Fork of Henson Creek 

and gradually thin out eastward. They have not been found east of 

Nellie Creek. These andesites occur in flows varying from a few 

feet to more than 100 feet in thickness.

Below the Burns tuff occur nearly identical sheets of rock, which' 

have not been distinguished on the map. In several places it is 

clear that these lower bodies have been intruded, and they no doubt 

belong to the same epoch of eruption a"s the flows above the tuffs. 

In El Paso Gulch and the ridge east of it the evidence of intrusion is 

plain and is expressed in part on the geologic map.

The pyroxene andesites are dark porphyritic rocks, with numerous 

crystals of augite and plagioclase visible to the unaided eye. They 

are massive except in the upper zones of most flows, where a pronounced vesicular texture is commonly developed. Secondary quartz 

and bluish chalcedony are usually found in these vesicles and, as 

they readily weather out of the rock in exposed places, small nodules 

or fragments of them strew the ground in many places near outcrops.

The microscope shows that hypersthene was a former constituent 

of these rocks, its place being now taken by serpentine, chlorite, and 

other alteration products. Quartz and orthoclase are generally 

present in small amount.

HENSON TUFF.

The last member of the Silverton volcanic series is a tuff much 

like the Burns latite tuff. Its greatest development is in the valley 

of North Fork of Henson Creek in the Ouray quadrangle. It lies on 

the pyroxene andesites in the region west of Nellie Creek, but is not 

found east of that stream.

The Henson tuff is made up chiefly of debris of pyroxene andesite, 

but contains particles of other volcanic rocks; locally it contains 

angular fragments of rhyolite, latite, and andesite. There are no
GEOLOGY. 29

calcareous layers in it, like those of the Burns tuff, and no fossil

leaves have been discovered. >

i

POTOSI VOLCANIC SEEIES.

The lavas of the Potosi volcanic series appear in the Lake City 

area only -on the high ridges on either side of Henson Creek and east 

of the Lake Fork. They he on various older formations, in some 

places with unconformity, testifying to much erosion following the 

deposition of the Henson tuff.

North of Yellowstone Gulch the Potosi lavas rest on Henson tuff 

or an intrusive quartz latite sheet, and in Empire Mountain they lie 

on pyroxene andesite and Burns latite tuff. On either side of Crystal 

Creek the Eureka rhyolite is the underlying formation, and east of 

.Alpine Gulch the Potosi lavas come in contact with the Picayune 

rocks.

The Potosi lavas of the region north of Henson Creek are light or 

dark gray quartz latites exhibiting many soda-rich plagioclase feldspar phenoerysts and some of sanidine in a groundmass rich in quartz 

and sanidine. Biotite and augite are original constituents, but are 

generally quite decomposed.

The alteration of Potosi rocks by which they are silicified or kaolinized is extreme in the so-called "Iron beds" northwest of Broken 

Hill. Much of the rock is stained a brilliant red or yellow through 

oxidation of the pyrite which impregnated it at the time of its 

decomposition. Alteration of this type is also exhibited in less degree 

south of Broken Hill.

The Potosi rocks east of Alpine and Wade gulches are quartz latite 

porphyry belonging to a large body which apparently filled a great 

hollow. This rock is characterized by more prominent crystals both 

of plagioclase and sanidine feldspar than are found in the common 

thinner flows north of Henson Creek. The upper parts of Crown 

Mountain and Red Mountain in the San Cristobal quadrangle are 

made up of this same phase of the Potosi quartz latite.

The Potosi lavas east of Lake City are mainly dark pyroxene 

andesite of a type common to the southeast. North of Horse Park 

they are representatives of quartz latite flows beneath the andesites.

HINSDALE VOLCANIC SERIES.

The lavas of the Hinsdale volcanic series overlie the Potosi flows 

east of Horse Park. They belong to the succession of rhyolite, 

basalt, and intermediate rocks forming the upper portions of the 

divide between Lake Fork and Cebolla Creek. The basalts are the 

capping rocks of Cannibal Plateau and are recognized as such in the 

Hayden reports and on the map. These rocks have not as yet been
30 GEOLOGY AND ORE DEPOSITS NEAR LAKE CITY, COLO.

thoroughly examined, and as they are supposed to be more recent than 

the ore deposits of the Lake City region they need no further discussion in this place.

INTRUSIVE BOOKS.

The intrusive rocks of the region are distinguished on the map under 

three colors. These rocks are not intimately related to the ore deposits 

and will be passed over hi this place with but brief mention. Some of 

the types occur hi more important masses in the areas north or south 

of that with which this report deals and will be described in full in forthcoming reports. The various kinds of intrusives may be conveniently 

grouped under the heads of the map legend.

EJiyolite. The most widely distributed type hi this group is a rhyolite which is very abundant south of Henson Creek in bodies of various 

sizes and shapes, cutting the Picayune volcanic group. To the south, 

as far as the Lake Fork, in the San Cristobal quadrangle, this rhyolite 

is very abundant throughout the area of Picayune rocks and makes 

up a large part of some of the highest summits, such as Red Cloud and 

Sunshine peaks. It includes many large blocks of the Picayune lavas, 

a few of which are represented on the accompanying map.

This rhyolite is a grayish porphyry exhibiting phenocrysts or orthoclase, and quartz with a few biotite flakes, in a felsitic groundmass. 

In some places the rock has a strongly marked fluidal texture and in 

others it is massive. Inclusions similar to those in the Eureka rhyolite are abundant in some localities. The groundmass is very fine 

grained in places but is never glassy. A gradation to coarse-grained 

texture takes place in certain masses, so that some of the rock may 

well be called granite porphyry. Masses of Souch texture occur principally in Alpine Gulch, in the San Cristobal quadrangle.

This rhyolite differs markedly from the Eureka rhyolite in the 

constant presence of quartz phenocrysts penetrated by many white 

arms or embayments of the groundmass. It is also more typically a 

rhyolite than is the Eureka, being generally free or nearly so from 

crystals of lime-soda feldspar.

A rhyolite porphyry characterized by numerous phenocrysts of 

smoky quartz and clear sanidine, but almost destitute of any ferromagnesian mineral, occurs in many crosscutting dikes and irregular 

bodies in the drainage areas of Nellie and El Paso creeks and the 

North Fork of Henson Creek. Several small masses of this rock are 

represented on the map. This rhyolite penetrates flows of the Potosi 

volcanic series and is probably much younger than the similar rock 

in the Picayune area, already referred to.

A rhyolite of felsitic type forms the summit of the hill east of Lake 

City, which stands at an elevation of 10,726 feet. It is fine-grained,
GEOLOGY. 31

gray, or pinkish in color, and has a fluidal texture due to the arrangement of spherulitic bands. A smaller mass occurs in the knoll north 

of Deadman Gulch and seems to be intrusive, though surrounded 

largely by glacial gravels.

The intrusive mass west of Crystal Creek opposite Sugarloaf Rock 

is a rhyolite resembling the Eureka rhyolite in many particulars.

Quartz latite. In the hill east of Lake City and in Deadman Gulch 

are several sheets of a fine-grained quartz latite, which cut the Burns 

latite tun0 irregularly. This rock is gray in color, with small crystals 

of plagioclase, sanidine, biotite, and quartz in a subordinate groundmass. The quartz crystals are embayed by tongues of the groundmass, after the fashion of the rhyolite south of Henson Creek, but 

the rock contains much plagioclase, is rich in biotite, and carries a 

little hornblende. It is called quartz latite porphyry.

Another rock of this kind, nearly identical in character with certain 

flows of the Potosi volcanic series, occurs as a sheet or sill injected 

above, below, or within 'the Henson tuff, in the area between North 

Fork of Henson Creek and Nellie Creek. In some places it is 200 to 

300 feet thick. It extends north 2 miles from Broken Hill, reappearing at the head of Cimarron Creek, southwest of Uncompahgre Peak.

This rock is gray, with prominent biotite crystals, and is more 

compact than the usual Potosi flows, but it shows fluidal texture in 

some places and may represent an intrusion during the Potosi epoch 

of a magma which reached the surface elsewhere in the vicinity.

The quartz latite forming the summit of Sugarloaf Rock is a finegrained porphyry different from any of the preceding types. It contains both hornblende and biotite phenocrysts, while quartz is 

restricted to the groundmass.

Andesite. A sheet of dark fine-grained aiidesite cuts obliquely 

across the Burns latite tuff in the face of the hill east of Lake City. 

The rock carries hornblende in abundance, with some augite and 

biotite, all greatly altered. No other mass of this character occurs 

in the area described in this bulletin.

Quartz monzonite porphyry. In the ridge west of Capitol City there 

occurs a branching intrusive body of much more coarsely crystalline 

texture than is exhibited by any other intrusive distinguished on the 

map. It cuts the Eureka rhyolite and is probably more extensive 

than is indicated by the map, for landslide and glacial debris obscure 

its outcrops very greatly.

This rock contains many prominent hexagonal tablets of biotite, 

associated with plagioclase and some quartz phenocrysts. The 

groundmass is rich in orthoclase and quartz of microgranular texture. 

Rock of nearly identical character occurs in the breast of the Gallic 

tunnel, according to Bancroft, and in all probability this mass is 

connected beneath the surface with the body mapped.
32 GEOLOGY AND ORE, DEPOSITS NEAR LAKE CITY. COLO.

Decomposed porphyry of Deadman Gulch. The highly decomposed 

rock occurring in Deadman Gulch and extending into the adjacent 

valley on the south is in part a porphyry with little remaining of its 

original constituents except quartz phenocrysts with penetrating 

arms of the groundmass. This suggests that there may be here 

intrusive bodies of quartz latite or rhyolite porphyry similar to some 

one of the types described, but in a large part of the area the rock is 

so completely silicified or kaolinized that the primary characters have 

wholly disappeared. Since to these obscuring effects of decomposition are added the covering of all but the upper contacts by glacial 

or landslide detritus, it has been impossible to determine the original 

character of the rock or even to decide whether or not more than one 

rock type is represented.

This area of alteration is directly connected with that at the head 

of the great Slumgullion mud flow which dammed the Lake Fork and 

caused Lake San Cristobal. The extreme head of that flow is very 

near the southeast corner of the Lake City quadrangle. The alteration in Deadman Gulch is not quite so thorough as in the Slumgullion 

Basin, but disintegration of the decomposed rock is a common feature 

of prospect dumps in the former area.

The decomposition in question extends upward with diminished 

intensity into the lavas of the Potosi volcanic series, but apparently 

the massive flows of andesite served to confine the decomposing 

waters in some degree and thus promote the alteration of underlying 

rocks.

ORE DEPOSITS.

SAN JTTAN REGION. 

GEOGRAPHIC CONTINUITY.

The Lake City area is not an isolated locality whose general relations may be discussed without reference to those of adjacent regions. 

On the west is the Ouray region; on the southwest the famous and 

productive Silverton and Telluride regions; and still farther southwest are the well-known camp of Rico and the lesser districts of the 

La Plata and Needle Mountains quadrangles. These six mining 

regions together make up the major part of the famous San Juan 

mining region and form one connected mountainous district characterized throughout by extremely rugged topography, a preponderance 

of extrusive and intrusive eruptive rocks, and an extensive and more 

or less closely related mineralization. The Lake City district is 

situated on the northern border of this region and is separated from 

the Creede district to the southeast by a considerable tract of country 

in which no ore bodies of consequence have yet been discovered. 

The veins differ from those of the Telluride, Ouray, and much of the
ORE DEPOSITS. 33

Silverton region in being in an older series of volcanic rocks; the San 

Juan tuff, which is so abundantly mineralized in the latter quadrangles, 

does not outcrop within the mineralized part of the Lake City area. 

The region is geologically continuous, however, with the eastern and 

central portions of the Silverton quadrangle, a great part of the rocks 

there exposed belonging to the same groups as those in the vicinity of 

Lake City. The veins show many close similarities, both physically 

and mineralogically, to those in the adjoining portion of the Silverton 

area; and it is highly probable that they owe their origin to similar 

conditions of mineralization, fissure formation, etc. 1

GENESIS OF MINERALS IN THE SAN JUAN REGION.

It has for some time been recognized that different associations of 

minerals form under different conditions of temperature and pressure. 

Those formed under high temperature and pressure are in extreme 

instances entirely different from those formed under low temperature 

and pressure, and the mineral formation may be regarded as a measure of the vertical depth at which ore formation has occurred; that 

is to say, the earth's crust in any given locality may be divided into 

zones of depth, and within the vertical range of each zone characteristic temperature and pressure may be assumed to have existed. 

The mineral contents of the veins of any region will then express in 

some degree the depth at which the minerals formed. In 1907 Lindgren 2 pointed out the existence of certain zones and set forth the 

minerals characteristic of each of them. In 1908 W. H. Emmons 3 

followed with a paper giving a tentative genetic classification of 

minerals, amplifying the work of Lindgren.

In comparing the different districts of the San Juan Mountains with 

the Lake City district the writers have endeavored, by the use of this 

work of Lindgren and Emmons together with their own additions 

and observations, to classify the minerals constituting the ore deposits 

of the five districts above mentioned into groups, each of which is 

characteristic of a particular zone.4 Six such groups were found to 

exist, as follows: (1) Minerals of the oxidized zone, (2) minerals due 

to secondary sulphide enrichment, (3) minerals formed at moderate 

and shallow depth, (4) contact metamorphic minerals, (5) minerals 

of the deep-vein zone, (6) minerals which may occur in all or most 

zones and are of no diagnostic value.

1 Ransome, F. L., A report on the economic geology of the Silverton quadrangle, Colorado: Bull. 

U. S. Geol. Survey No. 182,1901.

»Lindgren, W. L., The relation of ore-deposition to physical conditions: Congr. geol. Intern., Coinpt. 

rend. 1(X> sess., Mexico, 1906, pp. 701-724,1907; Econ. Geology, vol. 2, No. 2, pp. 105-127,1P07.

»Emmons, W. H., A genetic classification of minerals: Econ. Geology, vol. 3, No. 7, pp. 611-«27, 1908.

«See tables, pp. 34 and 46, compiled to show the comparative mineralogy of the San Juan and the primary 

mineralogy of the Lake City region.

95249° Bull. 478 11; 3
34 GEOLOGY AND ORE DEPOSITS NEAR LAKE CITY, COLO.

The first two groups belong to surficial zones and afford no true 

basis of genetic comparison, as they may be superposed on ajiy series 

of deposits, of whatever origin, which contain sulphides and other 

elements in necessary amount. Differences in them afford comparison only of varying topographic and climatic conditions. As such 

conditions vary but little in the San Juan region, the secondary and 

oxidation products show a striking similarity throughout. The 

third, fourth, and fifth groups furnish a good basis for a comparison 

of the primary minerals. The details of their occurrence (see table 

below) in the various districts of the San Juan region, though accurate 

only within the limits of our present knowledge, yield some significant 

results, which in the writers' opinion, serve to emphasize the close 

relation of the Lake City region and the other areas and to bring out 

such differences as exist.

TABLE 1. Comparative mineralogy of the San Juan region.

1. Minerals of oxi2. Minerals pro3. Minerals of

moderate and

4. Contact metadeep vein zone. .

Lake City.

Kaolinite......

Hematite......

Native silver...

Gold...........

Chalcanthite...

Bornite........

Proustite.......

Hinsdalite.....

Rhodochrosite .

Tetrahedrite...

(Bismuth compounds).

Ouray.

phate.

Native silver...

Gold...........

Rhodochrosite . 

Rhodonite.....

Tetrahedrite...

Tremolite......

Silverton.

Native silver...

Gold (?).......

Rhodochrosite .

Tetrahedrite...

Telluride.

Gold...........

SGricito

Rhodochrosite .

Tetrahedrite . . .

Picotlte........

Garnet. ........

Rico.

Oxidized products not specifically enumerated.

Rhodochrosite.

Tetrahedrite.

Wollastonite

Chlorite.
OEE DEPOSITS. 35

TABLE 1. Comparative mineralogy of the San Juan region Continued.

6. Persistent minerals. ...........

Lake City.

Chalcopyrite...

Sphalerite......

Pyrite.........

Ouray.

Chalcopyrite...

Sphalerite......

Gold...........

Silverton.

Fluorite.. ....

Chalcopyrite...

Sphalerite.:....

Gold...........

Telluride.

PalnltA

Fluorite.......'.

Chalcopyrite . . .

Sphalerite. .....

Gold...........

Pyrite.........

Siderite........

Rico.

PQlnifrt

Chalcopyrite.

Sphalerite.

Pyrite.

In placing the rich silver minerals proustite, pyrargyrite, stephanite, and polybasite in the list of those produced by secondary sulphide 

enrichment the writers have followed mostly ,the results of personal 

observations, but to some extent also the descriptions of Ransome 1 

and Purington.2 Proustite and pyrargyrite are without question of 

secondary origin in the ore deposits of Lake City and Ouray (pp. 

62-63). From Ransome's and Purington's descriptions it seems 

probable that they are secondary in Rico and in Silverton also. 

Stephanite and polybasite are described by Purington and Ransome 

as the last-formed minerals of the veins in which they occur, and in 

the writers' judgment they should also be placed in the secondary 

sulphide column for both the Silverton and Telluride districts.

MINEEALOGICAL SIMILARITY.

Disregarding for the moment the contact metamorphic deposits, 

a general view of the table shows that the veins of the San Juan 

region exhibit a fairly close mineralogical similarity in their most 

common primary constituents. They are characterized chiefly by 

pyrite, argentiferous galena, sphalerite, and tetrahedrite, with a 

gangue composed largely of quartz with subordinate rhodochrosite 

and other carbonates. Little of the argentiferous galena is rich in 

silver in any of these districts unless it is accompanied by tetrahedrite 

or some rich secondary silver mineral. Gold is commonly subordinate in value, to silver, notable exceptions being in the Golden 

Fleece, Camp Bird, and some other mines. Fluorite is rare and 

almost lacking in the Lake City region. Chalcopyrite is almost 

universally present in some part of every vein, but generally in less 

amount than the other minerals. The relative abundance of these 

primary minerals, of course, varies locally and could serve as a basis

1 Ransome, F. L., A report on the economic geology or the Silverton quadrangle, Colorado: Bull. U. S. 

Geol. Survey No. 182, 1901: Ore deposits of the Rico Mountains, Colorado: Twenty-second Ann. Kept. 

U. S. Geol. Survey, pt. 2,1901, pp. 229 et. seq.

2 Purington, C. W., Preliminary report on the mining industries of the Telluride quadrangle, Colorado: 

Eighteenth Ann. Kept. U. S. Geol. Survey, pt. 3,1898, pp. 751 et seq.
36 GEOLOGY AND OKE DEPOSITS NEAR LAKE CITY, COLO.

for partial subdivision, but the differences are either in the minor 

constituents which characterize those minerals now known to be 

secondary (stromeyerite, argentite, etc.), or represent merely local 

preponderances.

In the Lake City and Ouray regions (columns 1 and 2 of Table 1) 

all minerals characteristic of the deeper vein zones are completely 

lacking. In the Rico region, except in certain contact-metamorphic 

deposits, the veins again show a striking want of any minerals characteristic of deep-vein formation. In the Silverton region specularite 

is a not uncommon vein mineral, perhaps indicating an approach to 

a deeper zone of mineralization than is characteristic of the Lake 

City lodes. In the Telluride region the presence of zoisite, spinel, 

picotite, magnetite, biotite, and garnet, associated with the minerals 

which characterize the veins throughout the region, seems to indicate 

formation at greater depths than in the other districts. This is not 

absolutely certain, however, as the exact nature of the deposits of 

these minerals is not stated by Purington.

In both the Rico and Ouray regions contact-metamorphic deposits 

occur where intrusive monzonite intersects or is in close proximity 

to limestone. These deposits are characterized by magnetite, pyrite, 

sphalerite, chalcopyrite, wollastonite, garnet, epidote, specularite, and 

chlorite. Deposits of this type have with little doubt originated 

under conditions of high temperature and great pressures, and they 

are usually regarded as belonging to the deep zone. There seems no 

good reason to believe that in the Ouray region they represent a 

period of ore deposition very widely separated from that of the 

normal lodes and replacements, but they were probably formed long 

enough before the overlying cover of rock had been sufficiently eroded 

and the upper part of the monzonite mass become sufficiently cooled 

to permit the formation of the veins of shallower depth that chiefly 

characterize these districts and in many places intersect the monzonite itself. The added temperature and pressure which these 

contact-metamorphic deposits imply would then have been caused 

by the aggressive entrance of the heated intrusions of monzonite. 

The first effect would be the formation of contact deposits where this 

rock had intersected limestones. The subsequent cooling of the more 

deeply buried mass would have permitted the escape of the veinforming vapors which produced the normal lodes. For these reasons 

the contact-metamorphic occurrences cited seem to the writers to 

have little bearing on the depth of the general ore formation of the 

region, but to have been rather the result of local conditions.

In general, then, the Lake City lodes may be regarded mineralogically as the outer or northeasterly edge of the heavily mineralized 

area of the San Juan. The lodes occur at a slightly older geologic 

horizon than in the other districts and are definitely characterized by
ORE DEPOSITS. 37

formation at moderate depths. The Rico deposits may be considered 

as on the southern periphery and the Ouray veins as on the northern 

periphery of the main mineralized region. In these three districts minerals of comparatively shallow formation alone occur. The ores of 

Silverton and Telluride, on the other hand, may be regarded as having been formed in the heart of the mineralized region where hydrothermal and eruptive activity was most intense, where veins were 

formed under conditions of high temperature and pressure, and where 

deposition occurred under heavier cover of overlying volcanics. In 

these districts a few minerals of the deeper vein zone occur.

ORE DEPOSITS OF LAKE CITY DISTRICT.

THE LODES. 

GENERAL CHARACTER.

The lodes of the Lake City area are fissure veins. In the ordinary 

understanding of the term a fissure vein is a crack or crevice in the 

rock filled with later-introduced vein material. The Lake City lodes 

are only in part of this type. They have also been formed largely by 

replacement and exhibit all stages of the transition from a simple 

filled fissure, whose walls have been comparatively little affected by 

vein-forming solutions, to a zone of sheeting and brecciation where 

most of the mass of vein material has been produced by the alteration 

of the inclosing rock. Both types of mineralization are common in the 

same lode, one prevailing in one part, the other in another. In the 

Golden Wonder lode in Deadman Gulch the fractures are ill defined 

and the replacement has been extensive and irregular. This is perhaps the one deposit in the Lake City district that may be termed a 

characteristic replacement as distinguished from a fissure vein.

Ransome 1 has used the term "lode fissure" for those veins whose 

included mineral has been largely introduced through small, closely 

spaced fractures, from which solutions have replaced the intervening 

rock. The Lake City lodes are in the nature of "lode fissures," but, 

as already stated, so many of them verge toward a simple filled fissure 

that a clean line of division can not as a rule be made. In some 

places, as in the Golden Fleece mine, the vein, although it has a very 

well-defined linear form, consists of a broken zone in which the filling 

of interstices between rock fragments has been the dominant process, 

and replacement has been secondary in spite of the extremely broken 

and shattered character of the zone of mineralization. This vein is 

discussed more fully on pages 104-111.

Included fragments are present in all of the lodes, and many of 

the fragments show a very high degree of alteration, but some have

i Ransome, F. L., A report on the economic geology of the Silverton quadrangle, Colo.: Bull. U. S. 

Geol. Survey No. 182,1901.
38 GEOLOGY AND ORE DEPOSITS NEAR LAKE CITY, COLO.

been simply surrounded by vein material and have undergone little 

alteration from the introduction of mineralizing water.

MECHANICAL DISINTEGRATION.

In a region like that at Lake City, where the land surfaces are precipitous, erosion proceeds with great rapidity and the veins have 

consequently been much dissected. The difference between the 

lowest and highest topographic points (8,758 and 14,306 above sea 

level) within the mineralized region is 5,548 feet. The highest point 

in the outcrop of the several veins examined is 12,800 feet and the 

deepest point that has been reached in mining on any vein is 7,900 

feet. So far as yet determined, therefore, it appears that the veins 

extend over a vertical range of 5,000 feet. The rarity of mineralized 

outcrops above an altitude of 11,000 feet renders it probable that 

their upper limit does not extend much beyond this level. If the 

length of the Ute-Hidden Treasure vein be regarded as an approximate indication of the depth of the fissure (p. 39), we should have a 

presumable lower limit of known fissure formation of 7,400 feet. 1 It 

would therefore appear that the formation of the known Lake City 

fissures has taken place within a vertical range of 5,400 feet and that 

almost the entire range of fissure formation is revealed in one place 

or another by the deep erosion. The mechanical disintegration of 

the lodes has, moreover, proceeded with great rapidity, for slopes are 

steep and frost action through a large part of the year relatively 

intense. Owing to the deep erosion of the country rock in which the 

veins are contained, great lengths of outcrop have been developed.

As a further consequence of the steep and precipitous nature of the 

land surface, the veins show fairly well on slopes. Because of the 

glacial and landslide action, d6bris has accumulated near the stream 

levels and has covered the outcrops there, leaving the veins exposed 

high up on the mountain slopes only. Hence the original discovery 

shafts on a great many of the properties have been sunk at rather 

high elevations and carried down to a depth that would ordinarily 

give the operators an idea of the dip and strike of the lode. The 

intersection of dipping veins with the steep surface, however, leads 

to confusion, so that further exploration is generally made by crosscut. Often these crosscuts are unsuccessful, this being due to the 

fact that after a vein attains any depth in this region it generally 

undergoes a great change in vein filling and suffers a marked decrease 

in values. Hence, if cut at all (and often it is not), its appearance 

is so different that it is seldom recognized as the one that was worked 

four or five hundred feet above. If the vein were stripped for a 

vertical distance of several hundred feet down the slope, and drifts 

run on it, there would be less doubt as to its identity, and as work

1 Irving, J. D., Ore deposits of the Ouray district, Colo.: Bull. U. S. Geol. Survey No. 260,1904, p. 59.
OEE DEPOSITS. 39

progressed the operators might judge whether the work was worth 

continuing. With everything in sight there would be less dead work 

and uncertainty, and the cost of stripping the vein would generally 

be far less than the expense 

of running a long crosscut.

Where veins have been 

sufficiently well disclosed to 

make certain of their" continuation in depth their operation by means of crosscuts 

or drifts has been of distinct 

advantage, as these have 

afforded easy drainage and 

have permitted the development of much stoping 

ground at moderate cost.

The steep slopes have not 

only been of great advantage in exploitation but, in 

view of the nature of the 

oxidation and secondary 

enrichment, have been one 

of the most valuable assets of the district. If the ores several hundred feet below the surface were as good as those near the upper 

levels, this would not be so. As conditions are it is most fortunate, for 

the zone of secondary enrichment is near the surface and nowhere else, 

and the number of linear feet along the veins is much increased by 

the steepness of the slopes. Figure 3 shows the relative zones of 

secondary enrichment for a given horizontal distance in countries 

with steep and gentle topography. In the latter type there is obviously less enrichment for a given horizontal distance on the vein.

DIMENSIONS.

The following table gives the dimensions of those fissures which 

have been most satisfactorily explored:

Dimensions of Lake City lodes.

Gentle slopes 

FIGURE 3. Relation of erosion to superficial alteration.

Lellle...... ..........................................................

Ulay.... .............................................................

Ute-Hidden Treasure. ................................................

Nellie M. .............................................................

Black Crook. .........................................................

Length.

Feet. 

720+

380+

2, 700+

900+

350+

700+

950+

1,965

700+

1,300

2,000

Depth.

Feet. 

700

1,600

1,400+

275+

400+

500+

600+

1,300

700

1,464

500

Width.o

Feet. 

0.5-4

5

4

0.3-4

0.8-2

2

3

1.5-8

1.5

0. 5-10

1.2-3

a These figures represent rough estimates. They cover vein filling only, not altered or replaced parts 

of vein walls.
40 GEOLOGY AND ORE, DEPOSITS NEAR LAKE CITY, COLO.

In this region, as in nearly all mining districts, data regarding the 

dimensions of fissures can be obtained only within the limits of mining operation. Veins are seldom worked to their terminations. 

The plus sign has been used in the table to indicate that the vein 

continues beyond the limit of exploration. Where the plus sign has 

been omitted the work has been continued beyond the point of profitable extraction and has explored the fissure to its apparent termination. The same remarks apply to the depth, although this has been 

more frequently determined definitely than the extension on the 

strike.

In length the Lake City veins average between 1,000 and 1,200 

feet. Exceptionally strong wide lodes, such as the Ute-Hidden 

Treasure vein, Black Crook, and Golden Fleece, extend for nearly 

3,000 feet. The vertical range of the fissures seems to be about 

equal to their explored lengths along the strike. The depths in the 

table given are not the depths of the shafts but the vertical distance 

between the highest point on the outcrop and the deepest part of the 

vein below this point. In a great many mines work has ceased before 

the vein has disappeared, especially where adit tunnels have not 

been run at lower levels to search for the continuation of the vein. 

Among the exceptionally long veins is the Moro-Hendrison, which 

has a length of 2,000 feet, if the correlation of its two parts on either 

side of the small gulch is correct. It probably represents the root of 

a fissure, the greater portion of which has been removed by erosion. 

The Vermont-Ocean Wave-Wave of the Ocean vein is also a vein 

root. The workings on this vein are now practically inaccessible, 

so that the writers were unable to determine whether they are all 

on the same fissure or not, but from the surface outcrops it seems 

very probable that they are. The vein is fairly straight, for the 

curves indicated on the map are in large measure due to the 

effect of topography on the southward dip. If these veins form a 

single continuous fissure, its total length is over 5,000 feet. The 

Vermont tunnel, run from the bottom of Henson Creek to tap the 

vein 1,100 feet below the highest point on the outcrop, has been a 

failure. Admission to this tunnel could not be secured, but it was 

reported that the vein was not discovered in the workings, and it is 

probable that it pinched out above the tunnel level. The Red Rover 

tunnel, which should have intersected this fissure, disclosed no indication of it. The probability that this vein is a fissure whose upper 

portions have been completely eroded and whose roots alone remain 

is strengthened by the extremely rich ores discovered in the upper 

workings and their very rapid impoverishment with depth. A strong 

contrast between primary vein filling, such as occurs in the roots of 

fissures, and secondary enrichment products is, in the writers' opinion,
QBE DEPOSITS. 41

an indisputable proof of the previous existence of a very large vertical 

range of material from which this rich secondary ore can have been 

derived and concentrated. In other words, the greater the contrast 

between the secondary and oxidized ores and the primary ore, the 

nearer is the approach to the point at which the vein may be expected 

to disappear completely.

The widths of the veins in the Lake City region vary between a few 

inches and 20 feet. The average is approximately 18 inches. Many 

veins were wider in their upper portions and grew gradually narrower 

with depth. This was the case in the Lellie, Ulay, Black Crook, 

Golden Fleece, and Vermont. Practically all veins explored by deep 

workings have pinched out almost entirely. Few widths of 20 feet 

are found and these extend for short distances only. That in the 

Hidden Treasure mine was apparently produced by the intersection 

of a branch vein. Widths of 8 and 10 feet are found in a few 

places in the Ute and Black Crook veins and according to report 

in certain portions of the Golden Fleece vein. Pinches and swells 

in the vein occur both in strike and in depth, and it is, indeed, to 

these that the division of ore into shoots is chiefly due. Even the 

Ute vein, which is a singularly uniformly wide fissure throughout its 

length and probably approaches more nearly to the ideal type of fissure vein than any other in the region, is notably irregular and subject 

to many pinches and swells in its extension into the Hidden Treasure 

ground.

TERMINATIONS.

Veins that terminate in depth either narrow into a single small 

nssure, as in the Lellie, Black Crook, and Golden Fleece, or divide 

into a number of stringers which finally disappear entirely. Terminations along the strike usually show a division into many branches 

which finally disappear, as at the southwest extremity of the Ute 

vein. A sufficient number of examples, however, could not be examined to justify any general rule. As all of the upper terminations 

of the fissures are now eroded, their extremities in that direction 

could not be studied.

STRIKE.

Along the strike none of the veins are straight, but twist and turn, 

generally with sharp angles, somewhat in the manner of a flash of 

lightning. This is admirably brought out by the plans of the Pelican and other veins. Some of the veins seem to have formed 

along two intersecting lines of weakness; branch veinlets continue 

along the old direction, though the main vein assumes a new trend. 

(See fig. 5.) A marked conformity of jointing and vein direction 

prevails throughout the district.
42 GEOLOGY AND ORE DEPOSITS NEAR LAKE CITY, COL<3.

Most of the veins in the Lake City area strike in one or the other 

of two general directions, northeast-southwest and northwest-southeast. The richest lodes trend northeast, but this is probably of little 

significance so far as the relation of the ore deposits to the geology is 

concerned. The prominent directions of jointing are approximately 

the same as those of the fissures. The directions correspond in 

general to those prevalent in the Silverton quadrangle, although,

2000 Feet

FIGURE 4. 'Sketch plan of the Ute-Hidden Treasure group of veins, showing their relations to one another.

contrary to natural supposition, the prominent veins in the southwest 

portion of the Lake City quadrangle do not have the same prevailing 

direction as those in the immediately adjoining northeast portion of 

the Silverton, the predominant veins in the former striking northwestsoutheast and, according to Ransome, 1 the predominant veins in the 

latter striking northeast-southwest.

DIP.

Nearly all the lodes have steep dips, ranging from 45° to 90°.

Only one with a 

dip less than 50° is 

known, and that 

one continues for 

only a short disFIGURE 5. Sketch of typical "forked lightning" fissure vein. ta-npA A f P w

veins are practically vertical. The common inclination is between 

60° and 70°. In the Capitol City group of veins the dip is uniformly 

east, but in the other more widely scattered fissures it varies greatly, 

dipping here on one side and there on the other. In depth the dips 

are nearly as irregular. Where there has been much movement this 

feature has also produced differences in width of the veins along the 

dip similar to those which occur along the strike.

INTERSECTIONS.

Intersections of fissures, with different trends undoubtedly take 

place in many veins, but they can seldom be observed. The lima

S MOUTH OF'TUNNEL

i Ransome, F. L., Economic geology of Silverton quadrangle, Colo.: Bull. U. S. Geol. Survey No. 182, 

1901, p. 46.
ORE DEPOSITS. 43

vein, which runs nearly north and south, intersects the Golden Fleece 

vein. The actual intersection can not be observed, but it lies on the 

eastern boundary of the rich ore shoot, which is the most prominent 

feature of the Golden Fleece vein, and with little question had some 

effect in producing this ore body.

FAULTS.

Slickensides are common in the Lake City fissures, but they 

generally indicate movement subsequent to the vein filling. Displacements undoubtedly exist between the two walls of any single 

fissure, and the large quantities of breccia fragments included in most 

of the fissures, the prevalence of pinches and swells in the veins, 

and the selvage clays commonly noted point to some movement 

between vein walls. The extent of this can not be determined, as 

there are no recognizable beds in the alternating complex of volcanics 

to serve as a basis of measurement. It is believed, however, that the 

faulting along fissures has in general been comparatively slight.

Few of the lodes are disturbed by later movement. A definite 

fault was observed in the lima vein which displaces the vein 35 feet, 

and post-mineral faulting was observed in the Gallic ore body.

ORIGIN OF THE LODES.

Too few fissures have been explored in the Lake City country 

to permit any generalization as to their origin. It seems probable 

that they were produced by the same causes that gave rise to 

the fissures in Silverton, Ouray, and Telluride. These causes were 

undoubtedly operative subsequent to the invasion of the volcanic 

series by the monzonite masses, for some of the fissures cut this rock. 

It is believed that the fissures were produced by compressive strains 

due possibly to the gravitative readjustment which accompanied 

recent movements in the region.

In general, the writers believe that there is no evidence for attributing different ages of formation to the lodes which have different 

trends. They are believed to have been formed during a single period 

of fissure formation and to have been mineralized also during a single 

period.

DISTRIBUTION OF THE LODES.

Most of the veins of the Lake City mining district are located on 

the slopes of gulches which drain into Henson Creek. A few are on 

the slope north of the Lake Fork of the Gunnison. Of these two 

localities the former is a part of the Lake City quadrangle, and the 

latter is so near it and of such historic interest that it has been thought 

advisable to incorporate it in the report on this area.

The veins shown on the map (PI. I) are those that have been 

worked, and they were in all probability the most easily discoverable 

in the district. The writers see no geologic reason why the veins
44 GEOLOGY AND OEE DEPOSITS NEAR LAKE CITY, COLO.

should be so segregated as the map indicates, and they are inclined 

to think that others exist which may prove equally valuable if discovered. In other words, the area is one in which local conditions 

have not been the cause of the formation of fissures and the subsequent filling with vein material. The conditions were widespread 

and it is only natural to suppose that the processes which formed 

one vein have been equally active in other parts of the mining 

district proper.

FISSURE FILLING AND METASOMATISM.

Mineral solutions which have penetrated the fissures have deposited gangue and ore minerals in them and have altered the 

adjoining rock. In very few fissures is alteration of the wall rock 

entirely lacking, and in some of them (pp. 113-114) it has been 

so extreme that the entire ore mass in the mine is to be attributed 

to it. In general, however, silicification and sericitizatioh have 

been the predominant types of alteration. These have resulted in 

a very fine-grained dense-black jasperoid material which in places 

extends 4 or 5 feet from the vein filling. Fragments of included 

rock have been especially subjected to this type of alteration 

and are usually spoken of in the mines as black quartz. A later 

alteration of this black material is not uncommon and a light-green 

margin has been developed extending from a fraction of an inch to 6 

inches from the vein filling into the previously altered country rock. 

Many included fragments have 'been completely altered to this 

light-green material, but small cores having the shape of the fragment 

are not uncommonly left in the center. Microscopic study of the 

black material shows that it is composed of very finely divided 

secondary silica and a great abundance of extremely minute particles 

of sericite. The greenish material is generally marked by the coarser 

crystallization of the quartz and a relatively smaller quantity of 

sericite. The original rock is either an andesite breccia or a solid 

andesite with glassy or cryptocrystalline groundmass. Barite, rhodochrosite, sphalerite, galena, and tetrahedrite replacing the wall 

rock beyond the limits of the open spaces have not been observed 

by the writers. Their occurrence, however, as distinct crystals in the 

black silicified fragments shows that they have been deposited either 

as replacements of an already altered country rock or have replaced these fragments previous to their silicification. Pyrite, on 

the other hand, commonly extends into the country rock farther 

than even the silicification and sericitization. It is then well crystallized into minute cubes. Studies of the paragenesis of the ores 

indicate that the pyrite, silica, and sericite represent the earlier 

stages of vein formation and are probably the first results of solutions 

entering the fissures.

BANDING.

Where fissures have been filled with ore minerals or where included plates of country rock have been completely replaced,
OEE DEPOSITS. 45

banded structure is commonly well developed. This is the case in 

the ore from the Hidden Treasure, also in the ore from the new 

shaft of the Ulay mine. The ore in the Ute vein is also roughly 

banded.. No specimen observed, however, shows well-developed comb 

structure throughout the vein. Almost universally one band grades 

into another, making it in many places impossible to determine 

the relative ages of formation. It may be said, however, that 

white crystalline quartz is as a rule the latest mineral deposited. It 

commonly cements shattered galena and sphalerite or chalcopyrite, 

rhodochrosite, and tetrahedrite. It also coats crystals of barite 

which project into cavities. The tetrahedrite in veins belonging 

to the tetrahedrite-rhodochrosite group (see p. 47), is later in 

formation than the galena, as it permeates that mineral in many 

places along cracks and fractures. It is generally closely associated 

with the rhodochrosite, being commonly scattered through the rhodochrosite mass without any regularity. In general, silicification 

and sericitization of the country rock was followed by the deposition 

of vein minerals in the following order: (1) Pyrite in the wall rock 

and in the fissure; (2) rhodochrosite-galena-sphalerite; (3) tetrahedrite; (4) white crystalline quartz; (5) secondary sulphide-enrichment minerals. In many places, however, the sphalerite, galena, 

and rhodochrosite show reversals in the order of their formation, 

and in many it is difficult if not impossible to determine their relative 

ages with any certainty.

MINERALIZATION. 

AGE.

The Veins of the Lake City region cut all flow rocks except the 

Potosi volcanic series and the still later rhyolites and basalts. They 

cut even the monzonite porphyry intrusions, which are believed to 

be of late Eocene age. The vulcan vein cut in the Gallic tunnel 

passes through both monzonite porphyry and andesite, and the 

Chord Extension vein occupies a fissure entirely in monzonite porphyry, both furnishing conclusive evidence that the fissuring has 

taken place since the latest injection of magma. Further exploration in the Lake City district may reveal veins cutting the Potosi 

lavas; in the northern part of the Telluride quadrangle, the veins 

do cut the Potosi and are mineralized therein, though perhaps not so 

frequently as in the lower and older rocks; and some of the Silverton 

lodes cut the Potosi. If the mineralization took place at approximately the same period in these three regions, it is evidently postPotosi; that is, late Miocene or early Pliocene in age. Ransome 

believes that the formation of the veins in the Silverton region 

extended even into the Pliocene. However, there is no way of definitely proving that the veins were formed contemporaneously, and
46 GEOLOGY AND ORE DEPOSITS NEAR LAKE CITY, COLO.

so no fixed age can be given to the period of vein formation and 

mineralization.

Some connection may exist between the fissuring of the region and 

the intrusion of the porphyry; for instance, the fissures may have 

relieved the strains caused by the intrusives. Besides the first 

great period of fissuring there have been at least two subsequent 

periods of displacement. In the Gallic mine there is evidence of a 

primary deposition of ore and gangue minerals, followed by faulting 

and fissuring, with brecciation of the country rock and vein material, 

which was later recemented by a second deposition of quartz carrying 

various ore minerals. A third period of movement is shown by 

the seams of gouge which are present in different parts of the mine. 

The Woodstock prospect in Yellowstone Gulch shows evidences of a 

brecciated vein recemented by a second deposition of quartz. Probably all of the disturbances which have occurred since the original 

veins were formed have been of a minor character.

EFFECT OF COUNTRY ROCK.

The effect of the country rock upon the vein filling has apparently 

been of no marked consequence for the minerals in many of the veins 

vary at places where no change occurs in the wall rock and, on the 

other hand, veins whose mineralogy is the same throughout occur in 

all of the rock formations. The Hidden Treasure mine, located in 

andesite of Picayune volcanic group, has a gangue of rhodochrosite, 

barite, quartz, and fluorite. The Ute, a continuation of the same 

vein, has quartz and barite. The prospects in and around Owl Gulch, 

which are in the same formation as the Ute and Hidden Treasure, have 

mainly quartz. Mines in Eureka rhyolite in Yellowstone Gulch have 

quartz as the predominant vein filling, but the Pelican, in the same 

formation east of Sugarloaf Rock, has barite. Barite is also the 

prevalent gangue mineral in the Missouri Favorite. Evidently the 

nature of the country rock was not the dominant factor in the deposition of the vein minerals.

RELATIVE ABUNDANCE OF MINERALS. 

MINERAL GROUPS.

A preliminary idea of the mineralogy of the Lake City district has 

been given in Table 1 (p. 34), which was compiled to show the mineral 

relations among the districts of the San Juan region. More detailed 

data are given in Table 2 (opposite), in which the relative abundance 

of the minerals in the mines is shown by the size and character of 

the type. The list of minerals has been made as complete as the 

conditions would permit, but it is probable that it would have shown 

much greater variety if all parts of the lodes had been accessible. 

Some errors may also have crept in through inaccurate identification, 

but in general the list is believed to be fairly accurate.
TABLE 2. Primary mineralogy of Lake City district. a

Mines.

Capitol City group:

Henson Creek group:

Lellie.. ............................

Ute.... ............................

North Lake Fork group:

South Fork of Henson Creek:

Persistent minerals.

QUARTZ.....

OTTA'RTy

QUARTZ.....

QUARTZ

QUARTZ.....

QUARTZ.....

QUARTZ.....

QUARTZ.....

QUARTZ.....

QUARTZ.....

QUARTZ.....

QUARTZ.....

QUARTZ.....

QUARTZ.....

QUARTZ.....

SPHALEBITE.......

SPHALERITE.. 

SPHALERITE . . 

SPHALERITE . .

SPHALERITE . . 

SPHALERITE . .

SPHALERITE . .

SPHALERITE..

GALENA.......

GALENA..... 

GALENA..... 

GALENA..... 

GALENA..... 

GALENA..... 

GALENA..... 

GALENA.....

GALENA..... 

GALENA..... 

GALENA.....

GALENA.....

GALENA.....

CATENA

GALENA..... 

GALENA..... 

GALENA..... 

GALENA.....

GALENA.....

GALENA.....

OAT.V.WA

GALENA.....

PYHITE .......

PYRITE .......

Pyrite. ........

PYEITE.......

PYRITE........

PYRITE .......

PYRITE........

PYRITE.......

PYRITE.....

Pyrite. ........

Pyrite........

"PVTMTTP

PYRITE......

Pyrite........

Pyrite........

Chalcopyrite. ....

Chalcopyrite....

Tellurium. .... Tetturides.....

PETZITE....

Apatite.......

Gold..........

Minerals of moderate and shallow depths.

Stibnite. ......

BABITE. ......

Barite... ......

BARITE.....

BARITE..... 

BARITE.....

BARITE.....

BARITE.....

Barite (?).....

BARITE

BARITE.....

BARITE.....

Barite .......

Barite........

Barite........

BARITE..... 

Barite........

Barite .......

RHODOCHROSITE.

RHODOCHROSITE.

RHODOCHROSITE.

JASPEROID (?)..... 

JASPEROID (?).....

JASPEROID..... 

JASPEROID..... 

JASPEROID..... 

JASPEROID.....

JASPEROID........

JASPEROID.....

SERICITE (?).....

SERICITE (?).....

SERICITE (?).....

SERICITE ........

SERICITE (?).....

SERICITE (?).....

SERICITE ........

SERICITE ........

SEKICTTE (?).....

SERICITE ........

SERICITE ........

SERICITE ........ HlNSDALITE ..

Tetrahedrite.

TETRAHEDRITE.

Tetrahedrite.

Tetrahedrite.

TETRAHEDRITE. 

TETRAHEDRITE. 

TETRAHEDRITE.

TETRAHEDRITE. 

TETRAHEDRITE. 

TETRAHEDRITE. 

TETRAHEDRITE. 

TETRAHEDRITE. 

TETRAHEDRITE. 

Tetrahedrite.

TETRAHEDRITE. 

Tetrahedrite. 

Tetrahedrite. 

Tetrahedrite.

Tetrahedrite. 

TETRAHEDRITE. 

TETRAHEDRITE.

Tetrahedrite.

a The relative abundance of the minerals in the mines listed is indicated by differences in the style of type used for the names of the minerals, for example (1, most abundant) SPHALERITE, (2) Sphalerite, (3) SPHALERITE, (4) Sphalerite, (5) Sphalerite. 

95249° Bull. 478 11. (To face page 46.)
ORE DEPOSITS. 47

It is impossible to divide the lodes into groups separated by absolutely sharp and characteristic mineralogical differences. They may, 

however, be divided, according to the relative abundance of their 

component minerals, into three fairly distinct types, which, designated by their most distinctive minerals, are the tetrahedrite-rhodochrosite group, the quartz-galena-sphalerite group, and the telluride 

group. These groups, especially the first two, merge into one another 

at many localities and are without doubt due rather to local 

variations in the nature of solutions than to separate periods, of 

mineralization.

TETRAHEDRITE-RHODOCHROSITE GROUP.

The tetrahedrite-rhodochrosite group of veins comprises those 

whose ores consist of dominant galena and argentiferous tetrahedrite 

with considerable sphalerite and some pyrite in a gangue composed 

chiefly of quartz, rhodochrosite, and barite. The distinctive or 

diagnostic minerals in this group of veins are preponderating tetrahedrite, rhodochrosite, and abundant barite. Pyrite is usually subordinate in quantity. Chalcopyrite is also subordinate. Gold 

values are invariably low and the veins produce chiefly lead and 

silver. Copper is a by-product. Zinc is not generally present in 

paying quantities and unless saved in the mill is objectionable. 

The unenriched primary ore in these veins varies in silver value in 

accordance with the proportion of silver-bearing tetrahedrite which is 

present. The gold seems more closely associated with the pyrite than 

any other mineral. Local increases in chalcopyrite sometimes render 

the copper values important. The mines whose ores fall into this 

class are the following:

Hidden Treasure. 

Missouri Favorite. 

Ute and Ulay. 

Pride of America. 

Casino. 

Lellie.

Ocean Wave.

Wave of the Ocean.

Black Crook.

Belle of the West (?).

Contention.

Silver Chord Extension.

Vermont.

QUARTZ-GALENA-SPHALERITE GROUP.

The veins of the quartz-galena-sphalerite group are characterized 

by dominant galena and sphalerite with usually subordinate chalcopyrite in a quartz gangue. Barite is either absent entirely or very 

subordinate hi quantity. Tetrahedrite is present in many mines, 

but is not prominent. It is, however, sufficiently abundant to yield 

with the argentiferous galena, the rich secondary minerals which 

have enabled the mines to produce silver as their most important 

product. Gold values are a little more important than in veins of 

the tetrahedrite-rhodochrosite type and seem to be associated with 

the larger quantities of pyrite present in the veins of this group.
48 GEOLOGY AND OEE DEPOSITS NEAR LAKE CITY, COLO.

Copper and lead are both important products, and in some mines the 

sphalerite itself is sufficiently abundant to yield profitable returns.

Two or three of the mines of the tetrahedrite-rhodochrosite and 

quartz-galena-sphalerite groups show transitions one toward another. 

The Silver Chord Extension mine, though located in the midst of 

the series of coordinate lodes belonging to the quartz-galena-sphalerite type, shows all of the characteristics of the tetrahedrite series. 

Again, the Ute vein, the most productive vein in the region, shows 

affinities toward the quartz-galena-sphalerite type in the Ute ground, 

but farther north in the Hidden Treasure ground is distinctly a 

member of the tetrahedrite series. In -other mines some shoots show 

affinities toward one group and other shoots in the same vein show 

affinities toward the other group. It is obvious that no sharp line 

of demarcation exists between the two groups, and it is therefore 

probable that they belong to a single period of mineralization and 

were contemporaneous in their origin.

TELLURIDE GROUP.

The telluride group consists of veins containing tellurides disseminated through a fine-grained quartz gangue (Golden Fleece), with 

subordinate galena, sphalerite, pyrite, chalcopyrite, tetrahedrite, 

hinsdalite and barite. If it were not for the tellurides it would be 

impossible to distinguish these veins from those of the normal tetrahedrite group; but as the tellurides are entirely absent in the other 

vein types, they set the former sharply apart. The presence in the 

Golden Fleece of hinsdalite associated closely with tellurides gives 

to this vein a somewhat unique character. Neither the telluride nor 

the hinsdalite are, in the writers' opinion, sufficient to indicate that the 

Golden Fleece vein has an origin different from the other veins or 

belongs to a separate period of mineralization. It rather seems to be 

a variation from the normal type, such as may be frequently encountered in almost any connected area of mineralization. The products 

of the telluride group are both silver and gold. In the Gallic-Vulcan 

mine the silver would probably predominate if the mine were of productive size. In the Golden Fleece the proportion by value of gold 

and silver in the ore was approximately 1:1 (see pp. 110-111), a very 

much higher proportion of gold than is characteristic of any of the 

other mines.

SOURCE OF MINERALIZATION.

It is hardly within the province of a brief paper dealing with a small 

portion of an extensive mineralized region such as the San Juan to 

enter into an extended discussion of the problems connected with 

the origin of the ores. Both Ransome 1 and Purington 2 have disi Bull. U. S. Geol. Survey No. 182,1901, pp. 132-141.

8 Eighteenth Ann. Eept. U. S. Geol. Survey, pt. 3,1898, pp. 819-824.
OEE DEPOSITS. 49

cussed the genesis of the San Juan lodes at considerable length, and 

inasmuch as the Lake City lodes are probably of the same origin a 

further discussion may seem redundant. Nevertheless, since later 

study of genetic problems has led to results applicable to the Lake 

City and the other related San Juan lodes, some suggestive thoughts 

seem worthy of presentation in connection with this question.

The explanations offered to account for the filling of mineral veins 

have of late centered around two opposing hypotheses; the first.holds 

that meteoric waters have dissolved out minute quantities of metallic 

and nonmetallic elements from the country rocks, have descended 

into regions of elevated temperature, become heated, and have risen 

up through fissures and deposited their burden in mineral veins. 

The second holds that the metals and the accompanying elements 

and moisture have been component parts of deep-seated eruptive 

magmas and have, as a final stage of the cooling of the magmas, been 

released, have found their way upward and have been deposited as 

ores in mineral veins. A compromise between the two views has 

often been advocated in the form of a mingling of waters and contained metals derived from both sources.

To the second theory, that of derivation from eruptive rocks, the 

name "magmatic" origin is now generally applied. The older term 

"pneumatolytic" was formerly commonly applied to ores supposed 

to have this derivation, but was used in a much narrower sense, being 

applied only to deposits like the Cornwall tin veins, where minerals 

rich in boron, fluorine, and tin were important constituents, and 

where the veins were distributed in the immediate vicinity of large 

deep-seated masses of intrusive igneous rocks.

In his discussion of the San Juan lodes Ransome considers both of 

these possible modes of origin and dismisses the pnepmatolytic as 

improbable. The following paragraph seems to fairly well epitomize 

his views:

The Silverton lodes, as a whole, possess neither the distribution nor the mineralogical 

characters of those deposits to which, in the light of present knowledge, an essentially 

pneumatolytic origin can be most safely assigned. The known igneous masses had 

certainly solidified and probably had lost much of their heat before the lode fissures 

were formed. It is most probable that the transportation and concentration of the 

Silverton ores was effected chiefly by meteoric waters, which derived their chemicdfl 

and mechanical energy mainly from the heat connected with volcanism and from 

pressure, but possibly in some minor part also from gases and vapors given off at high 

temperatures by solidifying igneous rocks and taken into the deeper meteoric circulation.

There can be no question that the San Juan lodes possess none of 

the characters of pneumatolytic deposits in the older and narrower 

sense of the term either in their mineralogy or in their distribution, 

by which last is probably meant their occurrence as an aureole of 

metalliferous deposits about a deep-seated igneous mass. As stated 

95249° Bull. 478 11 4
50 GEOLOGY AND ORE DEPOSITS NEAR LAKE CITY, COLO.

above, however, such a character is not an essential feature of the 

magmatic origin as now understood.

The minerals formed by any given set of vapors, as the writers 

understand the question, depend on the temperatures and pressures 

under which deposition has occurred; and such temperatures and 

pressures, in their turn, are generally a measure of the distances to 

which the vapors have migrated from the parent magma since their 

emission. In other words, the absence of minerals characteristic of 

pneumatolytic deposits from the San Juan lodes does not signify that 

these lodes were not deposited from magmatic.waters, but simply that 

those waters had migrated to a zone where temperatures and pressures 

were so low that the so-called pneumatolytic minerals could not 

form, because they were unstable compounds under those physical 

conditions.

The comparative mineralogical table (p. 34) shows that in the 

adjoining Telluride region a number of minerals characteristic of high 

temperatures and pressures have actually been deposited; hence in 

that portion of the San Juan region the requisite conditions of temperature and pressure did in some small measure actually obtain. It 

seems, therefore, that the mineralogy of the lodes offers no obstacle 

to this explanation of their derivation from magmatic waters.

The absence of any extensive eruptive" masses, however, from which 

magmatic waters may have had their origin does apparently offer a 

much more serious difficulty.

Ransome's studies in Silverton, like those of the writers in Ouray 

and Lake City, show conclusively that the veins, and hence also the 

contained minerals, cut the monzonites and monzonite porphyries, 

which, aside from the rhyolites and basalts of post-Potosi age (apparently barren of any mineralization), are the latest manifestation of 

eruptive activity in the region. The veins are therefore regarded 

by Ransome as later than the monzonite porphyries and consequently 

as independent of them in their origin. Hence if the minerals are 

derived from an igneous source, that source must be some deep mass 

of later age concerning the presence of which there is no geologic proof.

If the monzonite and monzonite porphyry bodies which cut the 

extrusive volcanics in the Silverton, Ouray, Lake City, and Telluride 

regions, and which are in fact- widely prevalent intrusive rocks 

throughout the entire San Juan region, did not precede the fissure 

formation, they could be regarded with confidence as the igneous 

rock which has had most to do, not only with these ores but with 

the others which are so prevalent throughout this mineralized area. 

This is true because they represent the latest intrusives and because 

they have not escaped to the surface carrying their vapors with them, 

but have cooled at depths and have yielded mineralizing waters as a 

final phase of their consolidation^
ORE DEPOSITS. 51

To the writers the intersection of the upper and first-cooled portions of the monzonite masses by the fissures does not in the least 

preclude the deeper portions of the monzonite magma from consideration as the most probable source of these ores. Monzonite, quartz 

monzonite, granite, and quartz diorite have been so often observed 

by the writers in association with metalliferous ores that their efficiency as a cause seems to them certainly well established. Moreover, as the emission of gases and vapors is the final phase of consolidation, the outer portions must have cooled sufficiently to permit 

fracture and venation before the lower portions could have yielded 

their mineralizers. A close analogue can be seen in this very region 

in the flow' breccias, in which fragments of andesite may be seen 

embedded in andesite. Both fragment and matrix are portions of 

the same magma; the fragment merely represents the outer portion

cooled first and later ruptured by lava movements and then cemented 

by still molten andesite. In like manner with the veins, except that 

here, instead of molten rock and small fragments, emitted vapors and 

widely separated fractures must be considered. Instances of this 

kind are too frequent to need extended comment. In the Black 

Hills of South Dakota the refractory siliceous ores are later in age 

than the phonolite rocks which represent the latest phase of igneous 

activity, but from this alkali-rich magma these ores are almost 

certainly derived.

The potency of the monzonite magma to produce mineral deposits 

is amply attested by the contact deposits that it has produced in the 

limestone masses in Ouray and, as shown by Ransome's description, 

in Rico. Unquestionably these contact deposits with their characteristic minerals are derived from emissions from the magmas in situ. 

The solidification of the main mass of rock and the final emission of 

vapors which migrated upward into the fissures, some of which had 

cut their cooler upper portions, seems to the writers to represent by 

far the most probable sequence of events by which the San Juan 

lodes have been produced.

MINERALOGY.

The mineral species of the Lake City district are either primary or 

secondary. The primary minerals are (1) minerals formed at shallow 

or moderate depths and (2) persistent minerals common to all depths. 

The secondary minerals are (1) minerals due to oxidation processes 

and (2) minerals that result from secondary sulphide enrichment. 

No minerals characteristic of the deeper zones appear in the Lake 

Gty lodes, and (p. 36) it is therefore probable that the latter were 

formed at moderate depths below the surface. In other words, the 

covering of superincumbent rock has been lighter in this region than 

in the adjacent Silverton and Telluride districts.
52 GEOLOGY AND OBE DEPOSITS NEAE LAKE CITY, COLO.

In the following pages the minerals of shallow and moderate depths 

are first considered; then those which may be called persistent minerals. Minerals of surficial origin, .including oxidation products and 

minerals due to secondary enrichment, are taken up last.

PRIMARY MINERALS. 

MINERALS FORMED AT MODERATE AND SHALLOW DEPTHS.

Tetrafiedrite. Tetrahedrite (Cu8Sb2S7 ) is one of the most prevalent 

and, because of its silver content, one of the most important ore minerals in the Lake City country. In many places it is conspicuous in 

the ore, but even where it can be detected with less ease it is very 

important. In greater or less quantity it is present in all mines of 

the district and, in fact, is reported in some quantity in nearly all 

mines of the San Juan region.

Ordinary tetrahedrite of the formula given is usually designated 

"fahlerz" by the Germans, but this type of the mineral does not 

predominate in this Lake City region. The copper is almost everywhere partly replaced by silver and the antimony to some extent by 

arsenic. The following analysis from Genth 1 shows the composition 

of a nonargentiferous tetrahedrite:

Analysis of tetrahedrite.

Sulphur (S)......................'.............................. 25.97

Antimony (Sb)................................................ 25. 51

Arsenic (As)................................................... 3. 22

Copper (Cu)................................................... 37. 68

Iron (Fe)..................................................... .64

Zinc (Zn)...................................................... 7.15

Silver(Ag).................................................... .60

Bismuth (Bi).................................... 1............ .37

Manganese (Mn).............................................. .10

Typical freibergite from Freiberg contains more than 3d per cent 

of silver. The freibergite found in the Lake City quadrangle carries large proportions of silver, much of it running $200 to $300 to 

the ton, and some that is nearly pure reaching even 2,500 ounces to 

the ton. The variety that contains much silver has usually a light 

steel-gray color and is somewhat more greasy in appearance than 

the nonargentiferous variety; also, the streak which in normal 

varieties is gray to black is somewhat reddish in the argentiferous 

types.

The mineral in these lodes is invariably massive, never in crystals, 

is commonly mingled intimately with galena, and, in general, is highly 

argentiferous. The correlative mineral tennantite has not been recognized, and the arsenic is probably not commonly great in amount, 

for almost all the ores yield pyragyrite and not proustite on secondary alteration.

» Genth. F. A., Proc. Am. Philos. Soc., vol. 23,1885, p. 38.
QBE DEPOSITS. 53

Bismuth compounds. The complex sulphur compounds of bismuth 

are reported in considerable quantities in the Monte Queen mine. A 

complete analysis of this mineral is not available, so that its exact 

character is not known. According to the operators it contains high 

percentages of silver, about 20 per cent of bismuth, and considerable 

zinc. It is gray in color, resembling tetrahedrite, but containing 

little or no copper. It seems not unlikely that it results from secondary sulphide enrichment, for it lies close to the oxidized zone and 

is said to carry much higher percentages of silver than most of the 

other ore in the Monte Queen mine. Further study, however, is 

necessary to determine its chemical character and origin.

Barite. Barite (BaS04) is abundant in the gangue of the galenasphalerite veins, especially in those of the variety carrying tetrahedrite, which are developed most characteristically along Henson 

Creek and near Lake San Cristobal, but is less common in those of

the Capitol City type, in which quartz predominates. It is present 

also in much smaller quantity in the telluride veins, where silica 

seems to be the predominant gangue. The barite as a rule is an interlocking network of thin plates whose interstices are filled by fine- 

. grained silica or metallic minerals. This structure discloses but little 

banding and gives a massive appearance to the ore. In many vugs 

it is developed in very beautiful crystals of considerable size and generally perfect transparency. In a few veins it exceeds all other 

minerals in quantity, and when this is the case the ore is of little 

value. The barite is clearly of earlier deposition than the quartz, as 

the latter frequently incrusts crystals that project into central cavities. Barite is very abundant in the Hidden Treasure portion of the 

Ute-Hidden Treasure vein. It offers a strong contrast to the quartz 

in most of the lodes where it is present. Perhaps its commonest association is with the jasperoid or fine-grained quartz described on 

pages 44 and 60.

Rhodochrosite. Rhodochrosite (MnC03 ) occurs in many of the veins 

hi the Lake City region and in some lodes is absent in one portion 

and present in great quantity in another. Thus in the Hidden Treasure mine it makes up the bulk of the vein filling in the northern end of 

the Hidden Treasure ground and is practically absent in the Ute end 

of the same vein. Again, in the Monte Queen mine it is inconspicuous 

in most of the stopes but forms a full 5-foot face of solid mineral in the 

extreme western face of the tunnel. Many of the stopes in the lima 

vein likewise show no evidence of rhodochrosite, though in others it is 

present in large quantities and is notable for its coarsely crystalline 

structure and deep red color.

The majority of the rhodochrosite in all of these veins is contained 

in a very fine-grained aggregate whose individual cleavage faces 

measure not over 1.5 millimeters. When first mined it is generally 

deep pink in color but rapidly bleaches on exposure until it has only
54 GEOLOGY AND ORE DEPOSITS NEAR LAKE CITY, COLO.

a slight pinkish tinge which distinguishes it from dolomite. If the 

exposure be long continued it develops a brownish coating, which 

makes it resemble siderite unless examined on fresh fracture. Rhombohedral crystals of rhodochrosite are common in cavities, in some of 

which they are intergrown with quartz. It is probably one of the 

later minerals deposited. Tetrahedrite is more generally associated 

with rhodochrosite than with any of the other minerals; so much so 

that in milling the crushed ore on the Wilfley tables in the Hidden 

Treasure mill about an inch of rhodochrosite above the line of concentrates and gangue is saved from the tables. This is done because 

the rhodochrosite contains considerable quantities of silver even if 

the included particles of tetrahedrite are too fine for observation.

Hinsdalite. Hinsdalite (2(PbSr)0.3Al2O3 .P2O5 .2S03 .6H20) was first 

collected by E. S. Larsen, to whom belongs the credit of its discovery 

and investigation. Mr. Larsen will soon publish a longer description 

of it elsewhere. It was first found on the dump at the mouth of 

one of the tunnels of the Golden Fleece mine, at an elevation of 

about 9,950 feet, where it is present in considerable amount. It is an

Banded silica

Banded silica withvery fine metallic particles

FIGURE 6. Hinsdalite from the Golden Fleece mine.

original vein mineral associated with quartz and a little pyrite, galenite, tetrahedrite, and barite. It occurs in bands about an inch wide 

or as crystals imbedded in the grayish chalcedonic quartz which f orms 

the matrix of the petzite in the richest ore. Its crystals are not uniformly well defined as to boundaries, but generally form irregular 

bodies ranging from minute particles to masses three-fourths of an 

inch in greatest diameter. The crystals are marked by a very distinct and brilliant cleavage. (See fig. 6.) They are either rhombohedrons, resembling cubes, or pseudohexagonal tablets. If the apparent hexagonal base be taken as the true base, there is a perfect 

basal cleavage, but the cleavage faces are as a rule wavy and striated. 

.The optical data indicate that the mineral is only pseudohexagonal. 

Its hardness is about 5; its luster is vitreous to greasy. The fresh 

mineral is pale greenish, but much of the material is dark gray from 

inclusions. The streak is colorless.

The indices of refraction are somewhat variable, but the values for 

the principal zones are about a = 1.670, (3 1.671, f= 1.688. Sections 

normal to the cleavage show parallel extinction, those parallel
ORE DEPOSITS. 55

to the cleavage are generally hexagonal in outline and show the emergence, of the positive acute bisectrix. They may easpy be taken for 

uniaxial crystals, as the axial angle is small but variable; 2 E is 

usually about 32°. Basal sections are generally divided into six 

radial segments, and the plane of the optic axis in each segment is 

normal to the pseudohexagonal prism edge.

W. T. Schaller furnished the following analysis, which was made 

on fresh light-gray crystals of hinsdalite. They were examined 

microscopically and found to be very pure, but showed a slight zonal 

growth.

PbO.......................................................... 31.75

SrO.......................................................... 3.11

A1203 ........................................................ 26.47

S03 ......................................................... 14.13

. P206 ......................................................... 14.50

H,0.-....... .............................................. 10.25

100. 21

CaO, MgO, Na20, K20, trace. 

D=3.64. 

Formula 2(Pb Sr)0.3Ai203 .P205 .2S03 .6H20.

Hinsdalite is infusible but whitens on heating. It reacts for aluminum when heated with cobalt nitrate and readily yields a button of 

metallic lead. It is insoluble in acids. The water is driven off only 

at a temperature of from about 400° to 600° C.

MINERALS FORMED AT ALL DEPTHS.

Pyrite. Pyrite (FeS2) is present in all lodes of the region and is 

by far the most widely distributed of the metal-bearing minerals. 

It differs in abundance in the different lodes and is generally found 

in greatest amount in the lower and less valuable portions of the 

mines. When associated with galena it is more commonly fine 

grained and shows few crystal faces. It is subordinate in most of the 

ore in many lodes, especially in those which consist chiefly of galena 

and tetrahedrite and those which carry tellurides. When galena is in 

large amount and quartz is the gangue, pyrite is generally insignificant, as in that portion of the Ute vein which contains chiefly argentiferous galena and sphalerite. In the Capitol City series of galenasphalerite-chalcopyrite ores it is, however, relatively abundant and 

in some ores is very conspicuous.

Where not contained in tellurides, gold is apparently more generally 

contained in and associated with pyrite than with any of the other 

minerals. In this respect the Lake City pyrite closely resembles that 

described by Purington from Telluride. In the Contention mine the 

rich silver values contained in the gray copper and its oxidation products contained but little gold, but in the lower levels the vein carried
56 GEOLOGY AND ORE DEPOSITS NEAB LAKE CITY, COLO.

chiefly quartz and pyrite, and in this mixture the gold was commonly 

notable, yielding a much better average than in the more profitable 

silver ores above. Similar conditions were found in the Moro mine.

Pyrite is possibly an exception to the general rule (p. 44) that the 

metallic minerals are not generally present in the country rock, despite 

the fact that silica in many places penetrates to great distances and 

transforms the rock into jasperoid, in which phenocrysts and structures of the original are preserved. In places, as in the lower levels 

of the Contention mine, pyrite replaces the porphyry and occurs as 

disseminated crystals, few of which measure more than one-fourth 

inch and nearly all of which are rather perfect cubes, though generally 

containing pyritohedral striations. Silica and pyrite, singly or 

together, seem to have had a permeating power strikingly lacking in 

the other ingredients of the ore.

Coarsely crystalline pyrite is not common in the Lake City veins, 

nor are large, massive bodies of it seen in any of the veins.

Galena. Galena (PbS) is' absent in few Lake City veins, but its 

amount varies greatly in the different lodes and in the different portions 

of any single lo de. In some mines, as the Ute-Hidden Treasure, it forms 

an extremely abundant and very profitable mineral at one end of the 

lode, and at the other it sinks greatly in amount and is less abundant 

than tetrahedrite. In the lead-zinc-copper group of Capitol City it 

shows the most common association with sphalerite, but in the other 

mines this association is either lacking or is very much less marked. 

When not associated with sphalerite, it is commonly intimately mixed 

with tetrahedrite. The mixture can be detected with the naked eye 

in many specimens, in which the tetrahedrite seems to fill the interstices between shattered fragments of galena (Pride of America, Missouri Favorite, Pelican, and many others). When not apparent to 

the eye, its presence may be detected by polishing the surface of a 

mass of rich silver-bearing galena. Indeed, in the writers' opinion, all 

the high-grade unenriched galena owes its high silver content to tetrahedrite. Little pure galena in the Lake City lodes carries more than 

22 ounces in silver to the ton and much of it carries a good deal less. 

Similar conditions in the Silverton district are recognized by Ransome, who states 1 that the galena there, when free from the richer 

silver minerals, does not contain very much silver.

The authors polished carefully some faces of normal Lake City 

galena carrying about 10 to 15 ounces of silver, but were unable to 

detect any mechanically mixed mineral in it. In this respect the 

Lake City mineral offers a parallel to some described from England by 

Finlayson,2 who found native silver mechanically mixed with much

1 Kansome, F. L., A report on the economic geology of the Silverton quadrangle, Colo.: Bull. U. S. 

Geol. Survey No. 182, 1901, p. 80.

2 Finlayson, A. M., Ore deposition in lead and zinc veins of Great Britain: Quart. Jour. Geol. Soc. London, vol. 66,1910, p. 319.
OEE DEPOSITS. 57

of the silver-bearing galena carrying high values, but could find no 

trace even under higher powers of mechanically mixed minerals in 

galena carrying lower values. His inference seems justified that the 

silver to a certain amount is chemically combined in some manner 

with lead and sulphur, but that when present in very large amount 

it exists as intermingled free silver. The difference in the two cases 

is simply that in the one instance it is native silver and in the other 

argentiferous tetrahedrite. Much of the galena shows complex twinning, due to crushing stress, and this shows admirably in many polished sections. In most of the lodes the galena is rather coarse, but 

much of the finer variety, even down to "steel galena," is also found. 

When associated with sphalerite both are either coarsely crystalline, 

as in the Ute vein, or are extremely fine-grained, as in the Monte 

Queen.

Some interesting practical results follow from the study of the highgrade silver-bearing galena. The Lake City ores offer considerable 

difficulty in milling operations (p. 72), and in the Ute mine especially 

the greatest difficulty was experienced in recovering a reasonably high" 

proportion of silver. The difficulty in saving the silver in the argentiferous galena is without doubt due to the intermixed tetrahedrite, 

for this mineral is so easily slimed that it floats away on top of the 

water, and only canvas tables, of which the writers have seen -none in 

the Lake City region, will save any considerable portion of it. With 

it goes much of the silver, leaving only the chemically combined silver in the galena.

Fully faceted crystals of galena are commonly seen in vugs in the 

Capitol City and other ores, but few of them attain notable size.

Sphalerite (zinc blende). Next to pyrite, zinc blende (ZnS) is the 

most abundant and most universally distributed mineral in the lodes 

of the Lake City region. In practically no mines is it entirely lacking, 

although it is much more abundant in some than in others. Thus in the 

highly zinciferous lodes of the Capitol City region it is generally present 

in such large quantities that the endeavor is now being made to produce a concentrate which will run 29 per cent or more in zinc, and thus 

enable the companies to secure payment for this metal and avoid 

the high penalties charged by the smelters for ores which run between 

10 and 29 per cent in zinc. In much of the gold-bearing telluride 

ore of the Golden Fleece sphalerite is absent and where present is 

extremely subordinate in quantity. The telluride ores in the GallicVulcan mine carry notable amounts of extremely dark-colored 

ferruginous sphalerite. The mineral in this particular mine, as will 

be later explained, has exercised considerable effect on the secondary 

precipitation of gold. In the Capitol City lodes, where sphalerite 

is present in greatest abundance, it is coarsely crystalline and is 

usually light brown to light green and even pure yellow. Less com-
58 GEOLOGY AND QBE DEPOSITS NEAR LAKE CITY, COLO.

monly it has the dark ferruginous character of the iron-bearing 

types known as "Black Jack." All varieties, however, are present 

to some extent in most of the mines of the region. The very fine 

grained, almost massive type is uncommon in the Lake City ores; 

it does occur, however, notably in the Monte Queen mine, in which 

the sphalerite is of unusual interest. It is extremely fine grained, 

approaching the types known from the Friedensville mines in 

Pennsylvania, is very dark in color, and carries high values of silver 

and generally notable percentages of bismuth. It has not been 

possible to determine from the specimens whether the bismuth is 

present as an individual mineral species or is in some manner combined with the zinc. Certain analyses of much of this ore are 

reported to show 20 per cent bismuth. High proportions of bismuth 

are invariably accompanied by increased proportions of silver, and it 

seems probable that the ore includes a mineral (perhaps a variety 

of sphalerite) containing both bismuth and silver in chemical combination. In the Ute vein and the other veins of the district the 

sphalerite is most commonly associated with galena.

In general the sphalerite belongs to one of the earlier periods of 

mineral deposition. This is noticeable in the Ute vein and the Moro 

vein, in both of which the sphalerite is much shattered and penetrated 

by the white quartz which forms a larger portion of the gangue 

material. Where zinc is prominent and yet is not sufficiently 

abundant to be saved it becomes very objectionable and in not a 

few instances has led to the abandonment of workings.

The vertical range of sphalerite seems to be from the lowest workings in decreasing quantities toward the surface. In the Ute mine 

all the veins carry a very large increase in this mineral with depth. 

The Ulay vein, the Ute vein, and the new vein recently opened in the 

west shaft contain large quantities of zinc and show a decrease in 

silver content so great that the ore can not be handled profitably. 

The same is true of some of the Capitol City mines.

Ohalcopyrite. Chalcopyrite (CuFeS2) is especially abundant in veins 

that carry neither the tellurides nor notable quantities of tetrahedrite. In subordinate amounts it is present in all the mines. It 

is always massive, never crystalline, and does not generally carry 

appreciable quantities of either gold or silver. In the Moro mine 

and the related veins near Capitol City it is especially abundant. In 

the Henson Creek mines and those in the vicinity of Lake Fork it is 

subordinate. Where present in large quantities and intimately mingled with sphalerite the separation of the two minerals in milling 

operations has been attended with serious difficulty, the specific 

gravities of the two minerals (sphalerite 3.9-4.2, chalcopyrite 4.1- 

4.3) being so nearly the same that it is extremely difficult to secure 

a clean concentrate. For this reason the Moro mine has installed a
OEE DEPOSITS. 50

Blake-Morscher static electric separator. It is not known whether 

this has proved successful or not.

Chalcopyrite shares with tetrahedrite the copper production of the 

district, but copper is in all of the lodes essentially a by-product. 

Tetrahedrite (gray copper ore), where unaccompanied by silver 

values, is not an important ore in this district, and it is highly improbable that these veins could have been worked for their copper content 

alone.

Tellurides. Tellurides are absent in all except two of the Lake 

City lodes, the Gallic-Vulcan mine and the Golden Fleece mine. 

The Gallic-Vulcan has never been productive and interest in it is 

purely scientific, but the very large proportion of tellurides in the 

Golden Fleece mine gives to the mineral a high relative importance. 

It is noteworthy that in Rico, Telluride, and Ouray tellurium compounds are entirely absent and in Silverton they are present only as 

scientific rarities. Their appearance, therefore, in one or two veins 

in such large quantities and in the midst of other types of minerals 

gives to Lake City a feature which serves to distinguish it from the 

other districts of the San Juan region. Tellurides are also reported 

to occur in the Isolde mine in the Burrows Park region, but these 

statements have not been verified, as that mine is outside of the area 

covered by the present examination.

In the Gallic-Vulcan mines the tellurides occur in small quantities 

distributed through the vugs in the white quartz which constitutes the 

larger portion of the vein material. They range in color all the way 

from lemon yellow through greenish yellow to silver white and steel 

gray. An insufficient amount of pure material was available for 

analyses, so that the individual species can not be definitely stated, 

but from their color and general appearance it is probable that all 

of the varieties calaverite, sylvanite, krennerite, petzite, and hessite 

are present.

In the Golden Fleece mine the prevailing telluride is petzite, an 

iron-gray mineral with a black streak verging toward silver gray. 

In some places it is distributed in irregular bunches, often of considerable size, through a white, dense, granular quartz; it does not 

form regular crystals. Elsewhere it is disseminated in extremely 

fine particles through the chalcedonic quartz, to which it "gives a 

dark-gray color. A great deal of gray copper (tetrahedrite) also 

occurs in the Golden Fleece mine, and when this mineral is in finely 

divided particles in the ore a distinction between it and the telluride 

is difficult. It is significant that the tellurides both in the Golden 

Fleece and in the Gallic-Vulcan mines occur with tetrahedrite and 

other minerals, such as characterize the prevailing lodes in the 

region. These lodes are, therefore, in the writers' opinion, to be 

regarded as local variants of the normal antimonial lead, silver,
60 GEOLOGY AND ORE DEPOSITS NEAR LAKE CITY, COLO.

copper, zinc veins characteristic of this region rather than a separate 

group of telluride lodes of different age and independent origin.

Quartz. Quartz (Si02) is present in the gangue in all the mines 

of the Lake City region and is probably also the most abundant vein mineral in the district. It occurs in two sharply contrasted varieties, both of which are present in greater or lesser 

amount in all of the veins. The first of these is a fine-grained aphanitic variety frequently called jasperoid, which ranges in color from 

almost black, through all shades of gray, to a dense material having 

the appearance of porcelain. A good deal of this jasperoid is banded 

and has apparently resulted from deposition in an open space rather 

than from replacement. Some of it, however, is characterized by 

small irregular cavities lined with minute quartz, crystals (druses); 

this form has almost universally resulted from the silicification of 

the country rock and is a product of replacement rather than of deposition in an open cavity. All of these varieties of jasperoid are 

extremely tough and dense and their true character can not be 

determined without the microscope. Finely divided metallic minerals, such as tellurides and tetrahedrite, frequently give a darker 

color to the fine-grained jasperoid.

The second type of quartz is the ordinary white crystalline variety. 

This is probably the most common type in most of the veins, in the 

majority of which it exhibits well-developed comb structure and is 

the commonest lining of vugs. The white quartz occurs without 

question in more than one generation, but the bulk of it is younger 

than any of the metallic minerals, for it cuts through sphalerite, 

galena, tetrahedrite, pyrite, and even rhodochrosite in places. Veinlets of this white quartz also frequently cement shattered masses of 

the metallic minerals. 

Dolomite and calcite. Dolomite ([Ca, Mg])CO3) and calcite (CaCO3) 

occur very rarely as individual species in the Lake City veins. Calcite 

has been identified by the writers with certainty in only a few 

places; and both these minerals are of such slight importance in the 

district as to be negligible. In this respect the Lake City veins 

differ from those in the Telluride and Silverton districts. It is probable, however, that both calcium and magnesium occur, replacing a 

portion of the manganese in the rho.docrosite, a mineral which is 

very common in these veins, and giving it a light pink color. Both 

calcium and magnesium are present in much of the mixed carbonates 

of the Ouray district, and it is likely that they occur at Lake City 

also.

SECONDARY MINERALS.

Atmospheric agencies have acted on the minerals of the Lake City 

lodes to form oxidation products and secondary sulphide enrichment 

minerals.
ORE DEPOSITS. 61

OXIDATION PRODUCTS.

An extensive discussion as to the character of oxidized products 

formed in the outcropping portions of the Lake City lodes is difficult, 

if not impossible. Few of the outcrops are prominent, many of them 

being covered with landslide material and with different forms of 

rock de"bris, and such workings as have been driven on them are now 

generally abandoned and inaccessible. For this reason the list of 

minerals (p. 34) produced during the processes of oxidation would 

probably be much increased if a more general examination had been 

possible.

In general the oxidized zones of the Lake City ore deposits are not 

deep. Thus in the Moro mine oxidation has penetrated to a depth 

of approximately 100 feet, and on the lima vein, near Lake San Cristobal, to about 200 feet. This lack of depth is due in part to the 

length of the winter season, which, during a large part of the year, 

undoubtedly prevents access of water to the veins. However, in 

'spite of the large preponderance of run-off over infiltration, a great 

deal of water has found its way into the lodes, as is evidenced by the 

extremely rich character of the oxidized ores and the ores produced 

by secondary sulphide enrichment. Probably a very considerable 

part of the eroded portions of the lodes has been carried down in 

solution into the now existing remnants and has enriched them 

enough to make profitable mining possible. With less rapid erosion, 

however, the veins would have been very much richer in then1 upper 

portions than is actually the case.

The minerals produced by oxidation are:

1. Minerals such as the soluble sulphates, chalcanthite, and melanterite, which have been taken into solution and afterwards partly 

crystallized out. These soluble sulphates are rare in the Lake City 

veins, this probably being due to the continued presence of water in 

the veins, which has kept the minerals in solution and prevented 

their crystallization.

2. Minerals formed by the reprecipitation of the dissolved constituents. These are limonite, hematite, basic ferric sulphate, pyrolusite, malachite and azurite in small quantities, anglesite, and cerusite. Cerusite is comparatively uncommon in the Lake City lodes, 

probably on account of the absence of wall rocks containing carbonate of lime. It is, however, present in some quantity in most of the 

lodes. Anglesite, especially in its fine-grained form, is a very common oxidation product of the lead veins. It occurs almost exclusively in the upper 100 feet of the Moro vein. Limonite is by far 

the most abundant of all the minerals produced in this way.

3. Minerals which have been precipitated by the reaction of various 

sulphates on one another. These are native copper and native silver.
62 GEOLOGY AND OKE DEPOSITS NEAR LAKE CITY, COLO.

In the Excelsior mine a mass of native copper weighing 150 pounds was 

found in the oxidized zone, and smaller masses have been found elsewhere, though nowhere in sufficient abundance to be a commercial 

asset. The cepper has probably been produced according to the 

following equation:

CuS04 + 2FeS04 = Cu + Fe2 (S04 ) 3 .

Native silver is also a frequent by-product of oxidation processes, 

having probably been formed in the following manner:

Ag2S04 + 2FeS04 = 2Ag + Fe2 (S04 ) 3 .

It has not been found, so far as the writers have been able to determine, 

below the base of the oxidized ore, but it is distributed in considerable 

quantity among the oxidized minerals. It occurred in the GallicVulcan, Excelsior, Woodstock, Ute, Hidden Treasure, lima, Contention, and Golden Fleece mines, and probably also in many other 

mines concerning whose oxidized ore no data could be secured. 

It is usually in the form of wire silver and has probably had considerable importance in rendering profitable the oxidized ores.

Native gold is not common in the oxidized ores of any except the 

telluride veins, and there only to a minor degree. It is present, 

however, as will be explained later, in the upper part of the zone of 

secondary sulphide enrichment.

SECONDARY SULPHIDE ENRICHMENT MINERALS.

Secondary sulphide enrichment has been the most important of 

all the features that have rendered the Lake City lodes commercially 

profitable. The comparatively low-grade ores which are found on 

the levels at depths below the reach of all secondary action and the 

sharply contrasted and very rich masses of bonanza material in the 

upper levels are the most striking feature of all of the Lake City lodes. 

To the failure to recognize this distinction is in large part due the disappointing results of so much of the expensive development in the 

district. The Vermont tunnel, Red Rover tunnel, and lima tunnel 

(Golden Fleece mine) cost large sums of money and have been 

extremely disappointing.

The minerals produced by secondary alteration are pyrargyrite 

and proustite, chalcocite, covellite, galena, bornite, native gold, and 

probably some argentite.

Pyrargyrite and proustite. The so-called ruby silver ores occurred 

in large quantity hi all of the producing mines, and to their presence 

the major part of the silver production of the region is to be attributed. The two ruby silver minerals are the antimonial sulphide, 

pyrargyrite, Ag3SbS3 (59.8 per cent Ag), and proustite, Ag3AsS3 

(65.5 per cent Ag), the one known as dark ruby silver and the other
D OEE DEPOSITS. 63

as light ruby silver. The antimonial variety seems to have been by 

far the most common hi the ores mined, but the arsenical variety 

undoubtedly occurred, and it is likely that indefinite amounts of 

arsenic replaced the antimony in much of the ore.

Pyrargyrite and proustite are not at present mined to any extent, 

as they have long since been exhausted, leaving only the tetrahedrite 

ores from which they were derived. They occurred either disseminated in crevices and cracks in the sulphide ore, as beautiful crystals 

in vugs, or as irregular bonanza-like masses segregated along cracks 

and fissures through which descending solutions penetrated into 

the unaltered sulphides below. A mass weighing several hundred 

pounds, taken from the Hidden Treasure mine, was exhibited by 

Dr. Hoffman in Lake City. This ore was very abundant, intermingled with the telluride ore above the third level in the Golden 

Fleece and in the adjacent lima mine. It occurred, so far as could 

be learned, in all of the mines at the plane of demarcation between 

sulphides and oxides and, in generally decreasing quantity, to several 

hundred feet below this level. Along cracks and fissures it occurred 

in isolated masses to great depths; for instance, at 1,200 feet in the 

Golden Fleece and at 1,300 feet in the lima. These deep occurrences 

are, however, uncommon and merely indicate the presence of some 

easy line of access for downward-moving solutions.

Ruby silver has probably resulted from the solutions of silver and 

antimony obtained by the decomposition of the .tetrahedrite and 

possibly to some extent also from the argentiferous galena. The 

chemistry of both the solution and reprecipitation of the antimonial 

and arsenical sulphur compounds has not yet been worked out in sufficient detail to permit a statement of the probable steps of the process, but the geological facts show that it has occurred. The proofs 

of the secondary character of the ruby silver are:

1. Its restriction in quantity to the upper levels of the mines.

2. Its invariable occurrence as the latest deposited mineral in the 

veins, either in cracks or crevices in shattered primary ore or as 

crystals in cavities.

3. Its occurrence only in isolated bunches in deeper workings, 

where its origin is probably due to the presence of water channels 

that permit the downward percolation of water from above.

4. Its complete absence from the great mass of deep-seated ore.

It is clearly secondary in all of a large number of specimens of silver ores from the Southwest.

Secondary chalcocite. Chalcocite (Cu2S) in the finely divided sooty 

form is a common constituent of ores high in chalcopyrite and pyrite; 

in some mines, the Moro, for instance, it extends as deep as 500 feet. 

As copper is only a minor ingredient in point of value, this mineral is 

of more scientific than commercial importance.
64 GEOLOGY AND ORE. DEPOSITS NEAR LAKE CITY, COLO.

Covellite. The indigo-blue sulphide of copper, covellite (Cu S), does 

not occur in quantity, but is found in a number of mines as a product 

of secondary sulphide enrichment coating the surfaces of sphalerite. 

The sphalerite at first glance appears to be covellite, as it has the 

luster, color, and general appearance of that mineral. When lightly 

tapped it falls to pieces, but shows no change in its color or luster, and 

only when it is broken up quite small does it exhibit the characteristic 

cleavage and color of sphalerite. It may then be noticed that the 

films of covellite are not more than one thirty-second to one sixtyfourth of an inch thick and have been deposited all through the 

sphalerite. As the covellite is less soluble than sphalerite it is clear 

why the sphalerite has caused the enrichment.

Bornite. Bornite (Cu5FeS4 ) is rarely seen and then only as thin 

films on the surface of chalcopyrite which has been exposed to alteration. In massive form it is absent in these mines.

Secondary galena. Galena (PbS), as a product of secondary enrichment, is uncommon, this being probably due to the fact that oxysalts of lead are so much more insoluble than the corresponding salts of other metals that their transportation from place to 

place goes on in only a minor degree. In many mines which have 

a large content of coarse-grained sphalerite, however, a thin gray 

film of metallic character has been deposited in the cracks of shattered sphalerite. This material occurred especially in the Pelican 

mine. The crystalline form of galena could not be detected under 

the microscope, but from the analogy of this material with some 

from other localities where the cubes were of sufficient size to recognize, it is probable that the mineral is galena. The sphalerite, 

which has been thus enriched, may be broken by the hammer without revealing its true character, as it is so penetrated by lead-lined 

fractures that especial care has to be taken to break a portion of 

the mass that has not previously been shattered. When this is 

done the characteristic cleavage and color of sphalerite at once 

appear.

Gold. In the Gallic-Vulcan mine crystals of sphalerite were 

observed coated with leaves of native gold, the latter mineral having 

apparently been reduced from solution by the zinc sulphide. This 

occurrence, though of no commercial importance, is worthy of special 

note as it has been observed by one of the writers in a number of 

places, notably in the Ibex mine in Leadville, Colo., where metallic 

gold coating crystals of sphalerite was discovered in large quantity 

at about the central part of the sulphide-enrichment zone.

PRECIPITATION DUE TO SPHALERITE.

It is interesting to note that zinc blende in the Lake City veins has 

frequently exerted an extensive effect in re-precipitating downwardmoving sulphates in the form of secondary sulphides. It is not
ORE DEPOSITS. 65

believed that the effect produced by this mineral has been sufficiently considered in most papers on secondary enrichment. Its 

position in the scale of solubilities of the sulphides is of considerable 

interest in this connection. It was until recently believed that the 

series representing the order in which the sulphides of one metal 

would precipitate the sulphides of the other metals was dependent 

on the relative affinities of the several metals for oxygen and sulphur. 

It has been recently shown, however, by Wells,1 and has appeared 

also in studies by one of the writers that the relative solubilities of the 

different sulphides was the determining factor in the precipitation 

of the secondary sulphides. This series of solubilities arranged in 

decreasing order is as follows: Mercury, silver, copper, antimony, 

tin, lead, zinc, nickel, cobalt, iron, arsenic, and manganese. From 

this it appears that, with the exception of pyrite, sphalerite exercises the greatest effect in the production of secondary minerals in 

the Lake City veins, as nickel, cobalt, and arsenic are there absent. 

Chalcocite is probably the only secondary mineral that has not 

been definitely identified in intimate association with zinc blende. 

The ability of sphalerite to precipitate native gold presumably 

from a solution of ferric sulphate and chlorine is also interesting. 

The high silver content of some of the zinc blende encountered in 

the Monte Queen mine and in some other mines may perhaps also 

be explained by the presence of native silver precipitated in like

manner.

PAY SHOOTS.

All of the Lake City lodes are characterized by the lateral segregation of workable ores within certain more or less restricted portions 

of the vein. These restricted portions are usually termed pay shoots, 

as they may be profitably worked, even though the intervening portions are unprofitable. Such localizations of metalliferous minerals 

may be due (1) to the widening of the fissure between two constricted 

portions in which neither ore nor gangue minerals have been deposited 

in any quantity; and (2) to the segregation of metalliferous minerals 

within the vein.

The first type of shoots is the most common appearing in the Monte 

Queen, to some extent in the Hidden Treasure, and in many other 

mines. An interesting feature of the Monte Queen ore body 'was 

the different material in the three known shoots. These are vertical 

and are formed by the swelling of the vein between pinches that 

leave only a few sheeting planes with some stringers of quartz, etc., 

by which the vein may be followed from one shoot to the next. 

In the Monte Queen there are three of these shoots (figs. 17 and 18, 

pp. 100 and 101), with stope lengths measured- along the strike of the 

vein of 50, 75, and 200 feet. Nos. 1 and 3 contain chiefly pyrite

'- Wells, R. C., The fractional precipitation of sulphides: Econ. Geology, vol. 5, No. 1,1910, pp. 1-14. 

95249° Bull. 478 11 5
66 GEOLOGY AND ORE DEPOSITS NEAR LAKE CITY, OOLO.

and some gray copper ore but do not carry profitable values in silver. 

No. 2 consists chiefly of a peculiar rosin-like dark-brown sphalerite, 

mixed with fine steel galena; it averages about 75 ounces of silver to 

the ton and from 1 to 20 per cent bismuth. A fourth shoot, 950 feet 

from the mouth of the. tunnel, carries a massive, fine-grained aggregate 

of rhodochrosite.

Within the limits of the No. 2 shoot additional cross shoots occur 

(fig. 18) which pitch about 15° from the horizontal within the vertical 

shoot along the course of the vein to the southeast. These interior, 

shoots are lenticular in cross section and have a vertical range of 

from 3 to 20 feet, with an intervening barren quartz filling of from 

3 to 12 feet. (See figs. 17 and 18.)

Some of the shoots have great length, as for instance in the Ute 

vein. Here the vein from its southwest end nearly to fthe Hidden 

Treasure line, a distance of 3,000 feet, was of workable width and the 

metallic minerals were distributed with remarkable uniformity throughout its whole length, so that nearly this entire distance constituted a 

shoot. Shoots are reported to have occurred in the Ulay vein, but 

the workings are now inaccessible.

The second type of pay shoot is that in which a segregation of 

valuable minerals within a barren gangue occurs. One in the Golden 

Fleece mine (see fig. 22, p. 107) pitches to the west about 27° and has 

a length along the vein of about 300 feet at the surface but pinches 

down to a point below the third tunnel level. Its pitch is about 

parallel to the trace of the intersection of the lima vein, .which has a 

nearly north and south trend and lies mostly just west of the intersection. It is very probable that this intersection has been the 

determining factor in the origin of the shoot.

In addition to the segregation of the commercially profitable 

minerals the gangue minerals also show a localized distribution.

Thus, in the Monte Queen mine above mentioned, rhodochrosite is 

rare in the first three shoots but is almost the only mineral present in 

the fourth shoot, which shows a total width of 5 feet from wall to 

wall. In the Hidden Treasure, at the northeast end, rhodochrosite 

and barite greatly preponderate, but the former is almost wholly 

absent from the Ute portion of the vein and the latter is present in 

very much smaller amount.

Other details of shoots can not be given, as too few of the mine 

workings are now accessible for their accurate study..

, VALUE OF THE ORES.

The principal product of the Lake City region has been silver, but 

lead, gold, and copper have to some extent contributed to the value 

of the ores. Zinc has had practically no part in the production and 

has been one of the most objectionable components.
ORE DEPOSITS. 67

If divided according to gold and silver content, the veins of the 

region might be classed as silver-bearing veins and gold-bearing veins. 

The tetrahedrite-rhodochrosite group and the quartz-sphalerite-galena 

group would fall together in the silver-bearing class and the telluride 

group in the gold-bearing class. The details of ore values can be 

ascertained only from oral report for many of the mines, because 

many workings have been abandoned and records could not be 

secured. Other workings now ship low-grade ores, whereas those 

mined in early days were of very much higher grade.

In the silver-bearing group the present ores do not average much 

over $6 to $10 a ton and yield a concentrate worth about $40 a ton. 

This includes both the high-grade masses of tetrahedrite scattered 

through the ore and the lower-grade ores that are also a notable 

feature. In the upper levels of many mines the ore has ranged from 

$10 a ton up to $3,000 a ton and even more. Eighty-five shipments

of ore of about 25 tons each from the upper levels of the Vermont 

mine averaged 84.53 ounces silver and 27.96 per cent lead, or approximately $44.80 silver and $12.06 lead, a total gross value of $52.86 

per ton; 63 tons mined in 1894 yielded $79 per ton; and two shipments 

in 1895 and 1896 yielded $22.78 and $22.67 a ton, respectively.

The average of the ore mined in the Hidden Treasure mine in 1898-9 

was from $7 to $9 per ton, yielding $41.67 per ton of concentrates. 

The Black Crook in 1884 produced 1,227 tons of ore valued at 

$124,447, or about $101.39 per ton. All of these rich ores have now 

been exhausted and the ore must be milled. Probably very little of 

the ore runs over $5 to $6 per ton.

' Of the telluride or gold-bearing veins the Golden Fleece alone has 

thus far been a producer. Much of the ore it yielded during its early 

exploitation was of unusually high grade. The following figures, 

kindly furnished by Mr. George W. Pierce, show the grades of ore 

mined and milled:

Precious metals, in ounces per ton, from the Golden Fleece mine.

Class.

1

2

3

4

Gold.

134. 10

6.11

2.00

.40

Silver.

3,077

238

53

15

The values in all the ores vary so widely that it is not possible to 

lay down any rule which will not have as many exceptions as it has 

instances.

SUMMARY OF ORE DEPOSITS.

The lodes of Lake City are fissure veins formed partly through the 

replacement of shattered and sheeted zones in the country rock and
68 GEOLOGY AND ORE. DEPOSITS NEAR LAKE CITY, COLO.

mainly through the filling of open spaces. They average between 

500 and 1,000 feet in length, have a similar vertical range, and an 

average width of 10 inches to 5 feet. They show a wide range of 

strike and dip at steep angles. They consist of three closely related 

mineralogic types. The first contains pyrite, galena, sphalerite, and 

chalcopyrite with subordinate tetrahedrite, in a quartz gangue with 

some barite and rhodochrosite, and yield silver and lead with subordinate copper and little gold. The second contains galena, sphalerite, and tetrahedrite with subordinate chalcopyrite and pyrite, in 

a gangue of quartz, barite, and rhodochrosite, and yield chiefly silver 

and lead. The third contains petzite, tetrahedrite, and minor quantities of other sulphides, in a gangue of fine-grained quartz carrying 

some hinsdalite in places; this type yields silver and gold in proportion 

by value of 1:1 and is characterized by high values hi both gold and 

silver.

The first two groups constitute the bulk of the Lake City lodes, as 

there is but one productive telluride vein. Their ores are low grade 

where unaffected by surficial alteration, the major portion of the 

Lake City production coming from ores enriched by secondary sulphide enrichment that has produced chiefly pyrargyrite as a secondary mineral. Oxidized ores are widely distributed. Lodes are; for 

the most part, separated by considerable areas within which no veins 

have yet been located, the Capitol City group being the only closely 

spaced series of veins exploited.

The Lake City lodes comprise the northeastern portion of the 

mineralized area which includes Rico, Telluride, Silverton, and 

Ouray. The lodes show great similarity to those of these areas, but 

were probably formed under a slightly less cover of overlying rocks.

The lodes are later than all of the rocks exposed in the region 

except the rhyolites and basalts of post-Potosi age and are hence of 

late Miocene or early Pliocene age. They are believed to have been 

derived from the vapors emitted from a magma of monzonite whose 

apophyses as intrusions are scattered through this general region in 

considerable numbers.

FUTURE OF THE DISTRICT.

The Lake City district possibly contains (p. 44) unworked and 

undiscovered veins that are similar in mineralogical character to those 

already developed, and it is on these, combined with the careful 

mining and milling of the ore from the veins already located, that the 

future of the district depends. A quantity of low-grade ore is now 

in sight, associated with which is an enormous amount of zinc blende. 

This ore may perhaps be treated with profit if the proper kind of 

concentrating works are erected, and the zinc may also be sold if 

mechanical means can be successfully used in its separation from 

the commonly associated minerals.
MINING CONDITIONS. 69

As the geology of the region has so little apparent connection with 

the deposition of the ores (p. 46), it is impossible to lay down any rule 

as to the best places to look for new bodies of mineral. The richest 

mines are in the andesite of the Picayune volcanic group, but 

veins found elsewhere in the district have the same general mineralogic content, so that no inference can be drawn from the occurrence 

in this particular andesite.

The fact that some of the veins can be traced on the surface for 

considerable distances would seem to point to the general conclusion 

that the extension of some of the already profitably worked veins may 

be found by a careful study of the topography and the relation of the 

veins to it, taking into consideration their dip and strike. On the 

other hand, as it is rather evident that the district contains mainly 

only the roots of veins, it would probably be more profitable to look 

for new discoveries rather than the extension of those already worked, 

as doubtless the major part of these have been eroded away, leaving 

only their lower parts.

An interesting feature is the date of the location of the properties 

which have proved to be successful producers. Without exception the 

veins which have paid were located in the early days of the mining 

activity. A great many prospects have been abandoned which show 

surface croppings just as promising as those of some of the paying 

properties. Much of the loss that has been sustained in mining in 

this district has arisen from unjustifiably excessive initial expense. 

There have been some startling examples of reckless expenditure in 

the district, which tend to weaken the confidence of the mining 

public and to destroy any chance of obtaining funds for judicious 

exploitation.

MINING CONDITIONS.

POWER.

Until recently a majority of the large mines used coal for the 

generation of power. Lately a few dams have been erected and 

water power utilized for the generation of electricity for the Hidden 

Treasure, Moro, and Lellie mines. The first two take water from 

Henson Creek and the last named from Nellie Creek.

The steep gradient in most of the streams makes it easy to obtain 

the head necessary for hydroelectric installations in a region of limited water supply. An objection, however, to this means of generating power is the low temperature which prevails during the winter 

months, at which time the streams throughout the mining district 

are frozen over. A means of obviating this difficulty is to build a 

dam at such a place that quite a deep body of water may be obtained, 

so that when the surface freezes there will be enough water below the 

crust of ice to furnish the requisite flow. The Hidden Treasure dam 

is said to be 100 feet in height. The natural conditions of the banks
70 GEOLOGY AND ORE DEPOSITS NEAR LAKE CITY, COLO.

of the stream are admirable for such a dam, and a great supply of 

water can be maintained.

The officers of the Moro mine state that sufficient water is available 

to operate the mine during the entire winter, although they think it 

is doubtful whether they can generate enough power to operate both 

mine and mill during the months from December to May.

In all probability it would not be possible to obtain water during 

the winter months from any of the tributaries of Henson Creek, they 

being frozen solid during the cold season.

The large mines using coal for the generation of power have been 

the Ute, Ulay, Golden Fleece, Black Crook, and until 1907 the Moro. 

They have obtained their fuel from Crested Butte, Colo., when possible, and from Somerset, Colo., when the Crested Butte coal was not 

to be had. Run-of-mine coal sold at the time of writing (January, 

1909) at $2.50 to $3 a ton on the cars at the mine, and lump coal at 

$4.50 a ton in carload lots on the cars at Lake City. Run-of-mine 

coal is said by some to be very unsatisfactory, but the lump coal is 

said to be about the.most satisfactory in Colorado for steaming 

purposes.

Gasoline has been used at the Pelican property, but the foundation 

failed to withstand the vibrations of the engine and further use of the 

machine was temporarily abandoned. The company intends, however, to place the engine on a firm foundation and resume its use. 

Gasoline costs 16 cents a gallon in barrel lots on the cars at Pueblo, 

Colo., and that used by the Chicago Tunnel Site Co. is reported to 

have averaged 58° to 65° hydrometer test, each shipment, however, 

showing considerable variation. The Pelican at one time contracted 

with the Lake City power plant to deliver electricity at the mine. 

After having erected the line, however, it was found that the company was unable to furnish enough power to run the mine and the 

scheme was abandoned.

LABOR.

The labor conditions in the Lake City district have been very uniform and the differences between operators and laborers have been 

slight. When there has been great activity in the region it is understood that labor has been easy to procure. The wages paid are 

about the same as elsewhere in the San Juan region, ranging from $3 

to $5 per day, according to the class of work.

MINING METHODS.

The early work on most of the veins was carried on through drifts 

driven on the veins. The adit tunnels run were short and easily 

operated. This was very advantageous during the early stages 

of exploitation, when the deposits were easily accessible. As depth 

was gained, however, long crosscut tunnels became necessary and
MINING CONDITIONS. 71

these have almost invariably proved disappointing. The Vermont 

tunnel, T. C. M. tunnel, Lucky Strike tunnel, Hidden Treasure tunnel, 

and many others have been started, but so far none have had satisfactory results. Most of them have not gone as far as they had 

intended to go at the outset, as the character of the vein encountered 

in depth did not seem to justify the outlay.

No deep vertical shafts are used in the mines, although several 

properties have developed the veins by inclined shafts following the 

general dip of the vein.

The ore is transported from the mines by burros, wagons, or wirerope tramways. The last named are used on the Hidden Treasure, 

Lellie, and Moro properties to connect the mines with the mills located 

several hundred feet below the mine openings and from a quarter to 

three-quarters of a mile distant.

EXTRACTION OP METALS.

From the beginning of active mining operations in the Lake City 

district' there have been smelters and lixiviation plants, which, 

between them, have treated much of the ore from the Lake City district and some from the Silverton district with more or less success. 

Because of the historic interest connected with the early operations 

in the milling and smelting of the ores from this region a few lines 

will be devoted to that subject.

On October 31, 1877, the Ocean Wave smelter turned out its first 

lot of base bullion, about 10,000 pounds. The works were equipped 

with two roasting furnaces and one stack and had a roasting capacity 

of about 15 tons a day. First charcoal and later coke from Trinidad 1 was used for fuel. Crooke's smelter was also in operation at 

this time, although details of its equipment are not at hand. It is 

said to have shipped 300 tons, worth $48,000, during the year 1877.2 

Its slag dump is reported to have been twice reworked with profit. 

The Van Gieson Lixiviation Works were in successful operation at 

an early day and are reported to have had an output of $35,000 in 

silver bars during the fall of the year 1877. 2 The product ranged 

from 850 to 925 in fineness. 1 Other smelters and other lixiviation 

plants existed, but a description of them would be of no real value. 

The only smelter not partly dismantled in the Lake City district in 

1909 was the one under construction by the management of the Lake 

City Mining & Smelting Co. It will have a 100-ton coke furnace, 

40-horsepower boiler, 35-horsepower engine, dynamo, 110 volts 

direct current, blower with 1-pound per square inch pressure, crusher, 

rolls, grinder, and assay office.

i Eng. and Min. Jour., vol. 24,1877, p. 369. 

"Idem, vol. 25,1878, p. 62.
72 GEOLOGY AND OEM DEPOSITS NEAR LAKE CITY, COLO.

The smelters which have received most of the ore from the Lake 

City district have been the Omaha and Grant smelters of Denver, 

Colo., the Eilers plant at Pueblo, Colo., and the Ohio and Colorado 

smelter at Salida, Colo. At times other smelters in the State have 

received consignments from this area, but the majority has gone to 

the above-mentioned plants. The freight charges per ton would 

probably average from $5 to $8 to Salida and Pueblo. The treatment charges plus the cost of mining and shipping will run from 

$10to$15a ton in the Lake City district, so that under existing mining conditions it will hardly pay to work smelting ore running 

under $20 per ton. With concentration, however, a much lower 

grade of ore can be mined and milled with profit. The Hidden 

Treasure, for example, mined and milled $9 ore at a profit. The 

Golden Fleece milled $12 ore, saving 65 per cent of the value, at a 

total cost for mining and milling of probably less than $5 per ton.

On the other hand, the processes employed by some of the mills 

have not proved to be suited to the kind of ore treated, and a large 

part of the valuable metals was carried into the tailings, several tailing dumps having been worked at a fair profit by various means of 

lixiviation. The tetrahedrite, most of which is argentiferous, has a 

specific gravity of only 4.5, and when treated with galena, whose specific gravity is 7.5, it is lost by the same process which saves the 

lead sulphide. Galena is less brittle than tetrahedrite and does not 

slime so readily, so that after the ore is crushed and sent through 

sizers to the tables the galena is easily separated from the rest, and 

the gray copper, being brittle and of rather low specific gravity compared with the commonly associated minerals, is either left in close 

association with the gangue or is largely lost in the slimes.

DETAILED DESCRIPTIONS OF MINES.

CAPITOL CITY GROUP. 

GALLIC-VULCAN.

The Gallic-Vulcan claims are located on the south side of North 

Fork of Henson Creek, at an elevation of 10,300 +. A good wagon 

road from Capitol City, about a mile distant, leads directly to the 

properties. Two patented and six unpatented claims comprise the 

group.

History and production. The Vulcan was discovered in 1883 and 

the Gallic a few years later. The development on the claims has been 

done almost entirely by Benjamin Guionneau and his relatives, who 

have at no time employed large shifts or carried on extensive operations. The development is the result of the work of a few men continued over a long period of years.
DETAILED DESCRIPTIONS OF MINES. 73

The total production of the Gallic and Vulcan mines is small. The 

ore treated has been hand sorted so that no general average of the 

run-of-mine ore can be obtained. The concentrates produced by a 

small mill installed on the ground are said to have contained about 

0.21 ounce gold, 10 ounces silver, 50 per cent lead, and some zinc 

and iron.

Development and equipment. The Vulcan property is developed by 

an adit tunnel driven about 800 feet to cut the Vulcan vein. A vein, 

thought to be the Vulcan, was cut about 600 feet in, but not enough 

work has been done on it to prove its identity. A shallow discovery 

shaft has been sunk.

The Gallic mine has a crosscut about 820 feet long, which cuts two 

veins. The first is about 675 feet in and is possibly a continuation of 

the Vulcan vein; the second is 140 feet farther in. There has been 

about 1,000 feet of drifting and some stoping on the first vein. On 

the second vein 'there is only about 140 feet of work and no stoping.

Most of the ore in the veins has been hand picked. As the 'quartz 

is very sugary, the use of powder is unnecessary.

The equipment of the plant consists of a small concentrating 

building, connected by trestle with the ore house. It contains an old 

boiler, 40-horsepower engine, table, 1-compartment jig, 2-size screen 

trommel, one sizer, one elevator, one set of rolls, one crusher, and a 

small ore bin. From the crusher the ore is raised to a double trommel. 

The ore which does not go through the first screen is sent to a set of 

Cornish rolls and thence back to the screens. The fine material goes 

to the table and the coarse to the jig.

Country rock. The country rock at the Gallic tunnel is mostly 

andesite of Silverton volcanic series, which in places contains quartz 

and hence might be classed as a dacite. At the first vein in the 

Gallic tunnel the country on one side is andesite and on the other 

quartz monzonite porphyry. The vein at one place is in the former 

rock and at others in the latter.

Veins. The fissure in which the vein occurs shows movement both 

prior and subsequent to the introduction of the vein material. Surfaces of galena show striations produced by attrition, much movement 

being noticeable throughout the vein.

The ore shoot is irregular, being wide in some places and almost 

pinching out entirely in others.

In places the vein contains solid masses of galena several inches 

wide, but these are not persistent and no definite idea of the actual 

size of the ore body is obtainable.

The dip of both the Gallic and Vulcan lodes is southwest, the former 

about 60° to 80° and the latter 50°. The strike of both is N. 7° to 

15° W. The trend of the veins is in general rather constant, although 

numerous marked local changes appear in the workings.
74 GEOLOGY AND ORE DEPOSITS NEAR LAKE CITY, COLO.

Ores. The ore comprises galena, sphalerite, pyrite, chalcopyrite, 

gray copper, hessite, sylvanite, native silver, native tellurium, and 

native gold, and the gangue, quartz, barite, calcite, some kaolin, and a 

little fluorite and apatite, the relative abundance being in the order 

named. The first three ore minerals are by far the most abundant, 

and quartz probably composes nine-tenths of the gangue.

The quartz is almost universally sugary and full of cavities, many of 

which are due to the solution of crystals of calcite, barite, or gypsum. 

Within the cavities in the .altered country rock crystals of apatite and 

fluorite occur with pyrite and sphalerite. Both the ore and gangue 

minerals show remarkable crystallization. Some tellurides occur in 

the quartz and a few in thin seams in the country rock near the vein. 

The native gold has been found in association with tellurium and 

sphalerite, in places as a partial coating over these minerals.

The original vein was probably a small one of quartz carrying 

galena, sphalerite, pyrite, and tetrahedrite. Subsequently the vein 

and the country rock in its immediate vicinity suffered severe 

deformation and very thorough brecciation. Next the fragments 

of country rock and vein were cemented by quartz carrying pyrite, 

galena, sphalerite, chalcopyrite, tellurides, free gold, and silver. This 

second deposition of quartz and ore minerals did not completely fill 

the cavities, however, and the resulting vein is spongy and porous 

throughout.

The wall rock has affected the mineralization slightly, if at all. 

The first vein in the Gallic tunnel occurs partly in andesite and partly 

in monzonite porphyry, but neither exerted any noticeable influence 

on the ore deposit.

The depth of oxidation is probably between 400 and 600 feet. Lead 

carbonate has been found in the Vulcan crosscut 400 feet below the 

surface, but none, it is stated, was found in the Gallic workings, 

which are located about 300 feet below the Vulcan.

EXCELSIOR.

The Excelsior mine is owned by Frank Adams and W. B. Owen, 

both of Capitol City", Colo., who work the property themselves. It 

is located on the slope just north of Capitol City, at an elevation of 

10,220 feet, and may easily be reached by wagon road. The ore has 

to be hauled by wagon about 9 miles to Lake City, Colo. The work 

is all done by hand.

History and production. The Excelsior was located in 1878 and 

patented in 1889. The first shipment, made in 1893, consisted of 

two cars, which brought-returns of $65 a ton, averaging 59 ounces 

of silver and 10 to 12 per cent copper. In 1895 and 1896 shipments 

were made of about 200 tons, which averaged $65, running about 

50 to 59 ounces silver, 11 to 15£ per cent copper, and 5 per cent lead.
DETAILED DESCRIPTIONS OP MINES. 75

From 1896 to the present time (October, 1908) from one to five cars 

a year have been shipped.

Development. The workings consist of a crosscut of about 100 

feet to the vein and a drift of 500 feet v along the vein. Some 200 feet 

in on the vein the original discovery shaft connecting the mine with 

the surface is cut. This shaft is no longer in use, the ventilation 

of the mine being accomplished through the Broker, a contiguous 

property whose drifts connect with those of the Excelsior on the 

main level. Above this level considerable work has been done 

in a stope which extends up about 160 feet and is in general 

between 90 and 100 feet long. The material taken out of this stope 

by the Broker and Excelsior companies would amount roughly 

to 64,000 cubic feet. A smaller stope is located just south of the 

main large stope above the first level. Below the main drift is a 

shaft about 106 feet deep, off which short levels have been run, and 

a body of approximately 75 by 30 by 3 feet has been stoped out. 

Practically all of the work was carried on in this mine by overhand 

stoping, the ore and rock being sent down through two mill ways to 

the main level, and then trammed out hi cars, the selected ore going 

direct to the ore bin and the rest being distributed over the dump, 

according to its content of gangue and country, into second and 

third class ore. The country rock broken has been utilized in a 

large measure to fill the stopes.

Country rock. The walls are entirely Eureka rhyolite, which shows 

considerable alteration in the immediate vicinity of the vein and 

is rather highly impregnated with pyrite. That there has been 

movement since the beginning of vein filling is evidenced by the 

inclusion in the vein matter of small pieces of country rock, on either 

side of which ore minerals occur. The vein as a whole, however, 

is tightly frozen to the walls.

Veins. The ore body itself occupies an ordinary fissure and seems 

to be rather regular in size, averaging perhaps 9 inches in width, and 

is fairly continuous throughout the workings. In places it is much 

narrower and elsewhere plays out entirely, leaving only the barren 

vein. The vein dips 60° to 70° N. 80° E. and strikes in a general 

direction of N. 10° to 12° W. In the upper workings the dip is 

more pronounced, approaching the vertical toward the top of the 

upper stope.

Ores. The ore minerals are sphalerite in large quantities, a good 

showing of chalcopyrite (usually occurring with sphalerite) in the 

upper parts of the mine, some galena, a little gray copper, and much 

pyrite. According to the owners, 150 pounds of native copper was 

found 400 feet in on the main level and some native silver was found 

below the level. Native silver is said to become prominent in the 

lower workings, where sphalerite predominates. In the upper work-
76 GEOLOGY AND ORE. DEPOSITS NEAR LAKE CITY, COLO.

ings, the top of which is only about 40 or 50 feet below the surface, 

small quantities of azurite, malachite, and some limonite occur.

Quartz is the only gangue mineral present, the absence of others 

commonly found in the region being notable. On the main level 

sulphate of copper is forming on a small scale.

The ore is sorted in the ore house and shipped as first, second, and 

third class ore direct to the smelters. It is the aim of the operators 

to ship ore containing at least 39 per cent zinc, so that they will 

receive returns for this, as well as the lead, silver, and copper.

CZAR.

The Czar mine is now owned by Julius Seymour, of New York, 

but most of the development on the property was completed 

prior to his ownership. It is located about half a mile from 

Capitol City on the eastern slope of Yellowstone Gulch at an 

elevation of 10,800 feet above sea level and may be reached by wagon 

road. At present (October, 1908) it is not in operation.

Production and development. It is reported that two cars shipped 

to Canon City yielded 22 per cent lead, 26 per cent zinc, and 3 per 

cent copper, 9 to 14 ounces silver, and $3 gold to the ton. A third 

car is said to have averaged 39 per cent zinc, 14 per cent lead, 3 or 4 

per cent copper, and $3 gold to the ton. In 1904 a small car of 

galena averaged 42 per cent lead. As the smelters would not pay for 

both lead and zinc and the sorting of the two ores cost so much it 

was found that the shipments were unprofitable.

The development work on the property consists of two levels 

supposed to be drifts on the same vein, and a shaft connecting the 

upper level with the surface and extending down 120 feet to a junction 

with an upraise of 100 feet from the lower level. Above the upper 

level some stoping has been done, over 7,800 cubic feet of rock and 

vein material having been extracted up to October, 1908; there is 

also a small underhand stope about 10 feet deep and 30 feet long 

just beyond the shaft.

Country rock. The country rock is Eureka rhyolite, which shows 

little or no alteration a very short distance away from the vein and 

in all probability has had slight influence on the ore bodies.

Some faulting was observed in the Czar mine and gouge and a 

small horse of country rock were seen in the breast of the lower level. 

The whole vein has been pretty well shattered.

Veins. The ore body is a fissure vein of pyritic lead-zinc ore. The 

veins comprising it are two in number, one of which is worked in the 

upper level and the other in the lower. Both are small veins, not 

over 2 feet wide in any place; the average "ore course" is not more 

than 3 inches wide, though in places it measures 8 inches and in
DETAILED DESCRIPTIONS OF MINES. 77

others narrows to $ inch. Several small and apparently unimportant 

veins were seen in the breast of the lower level.

Contrary to the general trend in the district, the vein in the 

upper level strikes about 6° NE. and dips from 60° to 80° E. The 

main vein in the lower level has a general northerly strike, with 

approximately the same dip as that in the upper level. However, 

its course is quite irregular and no definite direction can be given 

to it.

Ores. The ore minerals consist of galena thickly interspersed 

with sphalerite, the whole frequently cutting through a thin layer 

of chalcopyrite. Pyrite is a common associate of the quartz, which 

is the only gangue mineral found. Sphalerite and lead sulphide are 

about equally abundant and are very intimately associated. All of 

the ore minerals except the chalcopyrite are fairly well crystallized, 

but the quartz is almost entirely massive. Probably the chalcopyrite 

was deposited first, followed by the sphalerite and the galena, the 

whole being cemented together by quartz and pyrite, which no doubt 

crystallized contemporaneously.

CAPITOL CITY.

The Capitol City mine is located on the west side of Yellowstone 

Gulch at an elevation of 10,600 feet and may be reached by wagon 

road from Capitol City, about a mile distant.

The property has three levels, supposed to be on one vein, which 

probably extend altogether over 1,700 feet. The actual distance 

can not be given with accuracy, as the mine was in poor condition at the time of examination, and the uppermost level "caved," 

so that examination was impossible. Considerable stoping has been 

done in the mine, especially above the lower level. A mill, called 

the Capitol City mill, was operated in connection with this mine. 

It was equipped with a boiler, engine, crusher, rolls, and four jigs. 

In 1900 this mill was torn down.

The Capitol City ore body is in andesite belonging to the Silverton 

volcanic series, which shows considerable alteration along the vein. 

The feldspars are largely changed and the hypersthene crystals are 

almost entirely gone. Some chloritization is noticeable and a great 

deal of pyrite is present in the rock. The rock is a lava flow, as are 

most of the eruptives in the district, and has been more or less disturbed by minor faulting in the vicinity of the vein.

The ore body is similar in many respects to those of the Czar and 

the Excelsior and may be classed with them. The fissure is clearly 

defined and fairly constant in direction. It branches or splits 

up, as shown by the vein in the lower level, which divides after 

going in about 300 feet. The ore body proper varies in width from
78 GEOLOGY AND ORE DEPOSITS NEAR LAKE CITY, COLO.

9 to 12 inches and the vein from 6 inches to 2 feet. The strike of 

the main vein is N. 20° W. and the dip about 80° NE. The western 

branch of the vein, which sphts in the lowest level, is probably the 

one worked in the middle level. It strikes N. 40° W. and dips about 

70° N. 45 E. This branch vein seems more clearly defined and more 

persistent than that in the lowest level.

The minerals found in the veins are sphalerite, galena, pyrite, and 

some chalcopyrite in a gangue composed almost entirely of quartz. 

There are several stages of deposition of the quartz, which is mainly 

in the massive form, though in many places sugary and in some 

showing distinct crystal outlines.

YELLOW MEDICINE.

The Yellow Medicine mine is located in Yellowstone Gulch 10,750 

feet above sea level and may be reached by wagon road from Capitol 

City, about 1$ miles distant.

Previous to 1896 the production, as given by the mint reports, 

amounted to approximately $40,000, the greater part of the value 

coming from silver and about one-eighth from the copper. The 

production before 1892 and after 1896 is unknown, but during 1896 

Crow & Fagan, according to report, shipped 500 tons from the middle 

level. In'1898 the Yellowstone Mining Co. is said to have shipped 

concentrates for about three months. In 1907, under bond and lease, 

O'Brien, Bowles & Bardwell for a time mined and shipped, crude, 15 

tons mill dirt a day to the Moro mill. It is reported that the runs 

through the Moro mill were successful until the price of copper declined. The Moro shipped the results of their treatment as concentrates.

The workings of the mine consist of three levels. Only the upper 

one was accessible at the time of visit; the middle one was caved at 

the entrance, and the lower one half filled with ice for 200 feet, 

beyond which a cave in the roof made further exploration impossible. 

As a consequence the data contained in this report have been obtained 

from the upper level, the ore bins, and the dumps. A mill was 

located just below the lower level and a blacksmith shop on the 

middle level. The mill was built and started to run in 1897. It 

contained a boiler, engine, crusher, 3 sets of rolls, revolving screen 

from each roll, set of revolving screens which went to four Harz jigs, 

and three buddle tables.

The vein occurs at the contact of a monzonite porphyry intrusion 

in a pyroxene andesite flow. The latter is very much altered along 

the contact of the vein and is recognizable only by careful examination.

The ore body occupies a simple fissure. In the upper level it dips 

79° N. 70° E. and strikes N. 13° W.
DETAILED DESCRIPTIONS OF MINES. 79

The minerals found in the vein are galena and sphalerite in large 

quantities (the former predominating), pyrite, and chalcopyrite in a 

gangue of quartz with a very small amount of barite. In places the 

galena is very well crystallized in cubes, but much of it is steel galena 

in large bunches.

LILLY.

The Lilly adit, located at an elevation of about 10,500 feet, was full 

of water at the time of investigation. It is said that ore has been 

shipped to the Capitol City mill for concentration, but the results are 

not definitely known.

CHOED EXTENSION.

The Chord Extension is located at 10,800 feet elevation on the east 

side of Yellowstone Gulch. Development work consists of a shallow 

shaft, a crosscut to the vein, and a drift on the vein. Not much stoping has been done. The vein is in monzonite porphyry and is in few 

places more than 4 inches wide, the ore course varying from I inch 

to 2 inches. The vein dips 75° N. 75° E. and strikes N. 10° W. 

According to report all the ore shipped was taken out when the shaft 

was sunk.

The minerals are tetrahedrite and galena, with some chalcopyrite 

in a gangue of barite, some quartz, and a little fluorite. The vein 

shows inclusions of silicified country (?) and some pure hematite. 

Slickensided surfaces are numerous in the country adjoining the vein, 

but the vein itself seems very tightly frozen to the walls. There 

appears to have been first a deposition of chalcopyrite, tetrahedrite, 

and galena, with a gangue of quartz, followed by movement which disdistorted the vein and a second deposition of minerals in a gangue of 

barite.

WOODSTOCK.

The Woodstock prospect is located in Yellowstone Gulch at an 

elevation of 1 ,100 feet. It is owned by Mr. Whinery, of Lake City, 

who reports that he shipped 200 pounds in 1895 which brought him 

$300; almost all of the value came from gold, which is said to have been 

found native in wire form about 40 feet down the shaft. The developments consist of a shaft 225 feet deep and an adit 75 feet long. 

These are in pyroxene andesite which shows some little mineralization by pyrite a short distance from the vein. The vein itself contains 

brecciated fragments of country rock and is made up of a gangue of 

quartz, with galena, zinc blende, chalcopyrite, and pyrite, in relative 

amounts corresponding to the order mentioned. The vein is tightly 

frozen to the wall and varies from 2 to 6 inches, widening as it descends. 

It dips 70° to 80° N. 70° E, and strikes N. 15° E.
80 GEOLOGY AND OEE. DEPOSITS NEAR LAKE CITY, COLO.

OTTAWA.

The Ottawa prospect is located just above the Woodstock in the 

same country rock. A thin vein of quartz shows some mineralization 

and is supposed to have produced 2 or 3 tons of lead ore, which, according to report, were shipped from the vein near the surface in the summer of 1907. The vein dips N. 73° W. and strikes N. 10° E., and has 

been drifted on for 150 to 200 feet.

TOBY.

The Toby is located a short distance above the Ottawa and has been 

prospected for 150 to 200 feet by a drift on the vein. The vein, which 

is mineralized chiefly by oxidized iron ores, strikes N. 17° W. and 

dips 70° N. 80° E.

SILVER CHORD.

The Silver Chord property is located on the east side of Yellowstone 

Gulch at an elevation of 10,700 feet in country rock similar to that 

of the Czar mine. The' workings consist of a shaft said to be 80 feet 

deep, which, at the time of the investigation, was practically full 

of water. As shown by the inclination of the shaft the vein dips 78° 

S. 60° E. and strikes S. 10° W. From the appearance of the outcrop 

the vein is 6 to 18 inches wide and has an ore course from 1 inch to 

3 inches wide. The gangue is quartz and the ore minerals are galena, 

sphalerite, chalcopyrite, and pyrite, an association common to many 

of the mines and prospects in this gulch. Some ore is reported to 

have been shipped from this property.

CZARINA.

The Czarina is a small prospect in Yellowstone Gulch just west of 

the Czar mine. The shaft on the property is said to have been 25 feet 

deep; rock de"bris, however, has filled one-third of this. A small 

open cut on the vein shows it to contain about 2 inches of quartz with 

no appreciable ore body.

Eastward, across the Czarina property, three small veins outcrop 

with strikes of N. 6° E., N. 10° E., and N. 6° E.

LUCKY STRIKE TUNNEL.

The Lucky Strike adit tunnel, owned by D. M. Jameson, of Capitol 

City, Colo., has been run in hopes of cutting in depth the Excelsior, 

Czar, and other veins worked higher up. The total work done is far 

in excess of that needed to gain the distance desired. In all over 900 

feet of crosscutting has been done to reach a point which could have 

been reached by 600 feet of straight-ahead work. The crosscut 

encountered several veins, but they show little or no mineralization.
HENSON CREEK MINES. 81

They had the following dips and strikes in order, from the entrance 

in: Dip 75° N. 15° W., strike N. 73° E.; dip 83° N. 75° E., strike 

N. 10° W.; dip 70° S. 10° E., strike N. 80° E.; dip 79° S. 65° W., 

strike N. 23° W. The last one was practically at the breast of the 

workings, and the others were approximately one-fourth, two-thirds, 

and three-fourths of the way in.

The workings pass through Eureka rhyolite for 20 feet, pass a 

small dike of very much silicified rhyolite, penetrate 120 feet of Eureka 

rhyolite, cut andesite for a short distance, and pass into monzonite 

porphyry which prevails for about 500 feet. Then the crosscut 

swings sharply to the east and the rock becomes characteristic 

Eureka rhyolite to the breast.

Mr. Jameson has started another crosscut about 250 feet east of 

the present site to intercept the veins of Yellowstone Gulch properties, and at the present writing (1908) this is in 80 feet.

HENSON CHEEK MINES.

The mines of Henson Creek are scattered along Henson Creek 

from a point about three-fourths of a mile west of Lake City as far 

as the narrow canyon just west of Capitol City. They are described 

in order from west to east.

PRIDE OF AMERICA AND BIG CASINO.

A shaft about 60 feet deep has been sunk on a small vein in 

a gulch which heads south from Henson Creek a little west of 

the Red Rover mill. It is 500 feet above the creek bed and about 

10,000 feet above sea level. Two veins are disclosed in this shaft, 

a main vein 2 feet wide dipping 60° S. and striking nearly east 

and a smaller vein striking N. 45° E. Both veins carry galenafreibergite ores, with subordinate sphalerite and but little gangue. 

The galena appears to be the earlier mineral, as it seems to be broken 

with areas of silver-bearing tetrahedrite (freibergite) scattered 

through it. The freibergite is the most valuable mineral and 

carries very high values in silver; the galena, where unmixed with 

other minerals, averages only about 12 ounces or less per ton in 

silver. The assays on this ore showed, according to the owners, 

from 200 to 412 ounces of silver per ton a statement which merits 

belief, as the ore contains a very large quantity of freibergite, which 

in nearly all of these ores is the silver-bearing mineral.

LELLIE (RED ROVER).

The Lellie mine is located on the north side of Henson Creek, 

about 1 mile west of the mouth of Pole Creek, on the steep bluff 

that rises abruptly for 2,500 feet above the bed of the creek. The

95249° Bull. 478 11 6
82 GEOLOGY AND QBE DEPOSITS NEAR LAKE CITY, COLO.

upper and lower workings (fig. 7) are reached by wagon roads, 

connecting with the main road in the bed of Henson Creek. The 

mine is now operated by the Planet Mining & Milling Co.

Production and development. The Lellie has never been a very 

heavy producer. From the upper levels it has produced some ore, 

which, according to the management, was high in grade. The 

mint reports 1 show that in 1899 it was one of the important producers, yielding from the upper stope four cars of ore per week, 

which netted about $800 per car; but as the amount of stoping is 

small and it receives no specific mention in previous or later years, 

its active production seems to have been confined to that year. 

At the time of examination (1904) and since that time it has been

eoo Feet

FIGURE 7. Workings and outcrops of veins of Ocean Wave and Lellie (Red Rover) mines.

only intermittently worked. It was first opened by the upper crosscut in 1897.

The mine is fully equipped with accommodations for miners, 

shops, and a 50-ton concentrating mill, situated next to the main 

,road in the bed of Henson Creek and operated by electricity. Water 

power is furnished to the milt by a 2-foot pipe line 3,700 feet in 

length, with a head of nearly 400 feet.2 A wire-rope tramway 

connects the mine with the mill.

The vein is opened by two crosscut tunnels. The upper, which was 

the first driven, is a short N. 43° W. adit 200 feet long at right angles 

to the strike of the vein; the lower tunnel, which is 500 feet below at 

an elevation of 9,650 feet above sea level and about 260 feet above 

the bed of Henson Creek, is 1,140 feet long and taps the main vein in

i Report of the Director of the Mint for 1899, p. 112. »Kept. State Com. Min. for 1901-2, p. 92.
HENSOET CREEK MINES. 83

a.

its far end. Drifts have been driven northeast on both levels for 

about 700 feet. These two levels are connected by a raise 500 feet 

high (vertical), from which three intermediate levels, separated by 

vertical distances of 120 feet, have been begun. Little drifting, however, has been done on them, as the vein was uniformly low grade and 

narrow. Some crosscutting and exploration on two parallel veins 

lying south of the main vein have apparently been unsatisfactory.

Here, as elsewhere in the district, the stoping near the surface and 

the high grade of the ore there encountered have led to the driving of 

a long (1,140 feet) crosscut for a vein which, when cut, failed to meet 

expectations.

Country rock. The country rocks of the veins belong to the Picayune volcanic group, which consists, as stated by Mr. Cross, of layers 

of volcanic flow breccias, both andesitic and rhyolitic, whose rude 

stratification is well shown in the Red Rover crosscut tunnel, These 

beds vary in dip 

from a comparatively slight northerly inclination to 

one of 45°. For 

the most part they 

are less steep than 

the veins, but they 

seem to have influenced the formation of these to 

some extent. The 

veins steepen up 

in places and run 

parallel to the layers of breccia, giving the impression that they are 

replacements along especially favorable beds. At the far north end 

of the tunnel the sheeting planes of the vein coincide with the stratification of the Picayune volcanic group (which dips 45° N.), making 

recognition of the true character of the vein difficult.

As replacement has for the most part been subordinate to the filling 

of openings, the wall rock seems to have exerted but little effect on 

the deposition of the ore, but until the different rock masses that make 

up the Picayune volcanic group have been carefully platted and 

mapped, the actual relations can not be stated with certainty.

Veins. The Lellie veins are little if at all disturbed by faulting. 

The ore deposits mined are typical fissure veins. Replacement here, 

as elsewhere, has been subordinate, but is more marked than in most 

of the veins of the region. In the upper workings, where for 400 

feet the vein averaged from 1 foot to 4 feet in width, it has fairly 

well-defined walls frozen tightly to the filling material, with little or

FIGURE 8. Irregularities in the Lellie fissure along the strike, o, Plan of 

vein in long drift; 6, plan of vein in short drift; c, plan of small portion of vein, showing irregular branches.
84 GEOLOGY AND OKE DEPOSITS NEAR LAKE CITY, COLO.

no clay selvage present. In the lower workings the vein is much 

more irregular, being generally only 8 to 14 inches wide or being 

broken up into a large number of parallel and intersecting stringers 

separated by irregular sheets of country rock. The vein dips about 

60° NW., but in the bottom level is parallel to the stratification of 

the flow breccia, which dips 45° N. In strike also the vein is 

extremely irregular (fig. 8).

FIGURE 9. Longitudinal section of the Lellie vein, showing position of rich upper stopes and inclination 

of the ore shoot. Elevations given are vertical distances above the lower tunnel level.

In detail the vein shows many angular inclusions of country rock, 

and is for the most part broken up into small irregular stringers, 

with intervening layers of highly altered andesite. It is difficult to

compare the vein in the upper 

workings with that below on 

account of the inaccessible condition of the old abandoned 

upper portions of the mine; 

but it is probable that in this 

mine, as in most others in the 

district, the wide and fairly 

workable veins die out in depth 

into narrow and stringer-like

FIGURE 10. Face of Lellie vein, showing irregularities roots that rarely pay for the

added expense of deeper exploration and operation. 

Ores, The vein fillings consist of quartz, rhodochrosite, barite, 

pyrite, galena, sphalerite, and tetrahedrite, with some chalcopyrite 

in the workings below the first level. The galena, when abundant 

and massive, carries as high as 20 ounces of silver per ton, though it 

often runs below that; but the great bulk of the values lies in the 

argentiferous tetrahedrite, which. is readily distinguishable by its 

greasy appearance. In places it is mixed with the galena and in

of vein structure, a, Country rock with planes of 

sheeting; b, vein filling.
HENSON CREEK MINES. 85

places scattered separately through the gangue. Pronounced banding 

is to be seen here and there.

Some of the ore that carries chalcopyrite runs well in gold, but 

otherwise the gold content is not noteworthy. The high-grade ore 

from the upper levels consisted of an intricate mixture of argentiferous tetrahedrite and galena. The nature of the ore in these levels 

is not known, but it is reported to have carried high values in silver 

and, locally, in gold.

Some of the ore, consisting chiefly of freibergite, averages per ton: 

Silver 200 to 1,000 ounces, value $500 j 1 copper 12 per cent, value 

$33; gold 1.5 ounces, value $30; a total value of $563.

The longitudinal section of the vein (fig. 9) shows that the ore 

occurred in shoots which pitched 30° NE. along the strike of the 

vein. These were separated by barren areas in which the gangue of 

quartz predominated and the metallic minerals were relatively less 

abundant. The shoots had a stope length of about 250 feet. The 

rich ore all occurred in stopes which were near the surface and well 

within the zone of secondary sulphide enrichment. Figure 10 shows 

some irregularities of the vein structure.

VEEMONT.

The Vermont mine is located on the west side of El Paso Creek 

about half a mile north of Henson Creek. It is one of four claims, 

the Scotia, Vermont, Ocean Wave, and Wave-of-the-Ocean, that lie 

end to end in a S. 75° W. direction on what is in all probability the 

same vein (fig. 11).

Development and production. The openings are at the base of 

a high precipitous bluff that forms the west wall of the creek, 

towering upward for 500 feet. A shaft 175 feet deep is reported 

but was not seen. The workings are about 10,000 feet above sea 

and about 500 feet above Henson Creek. A rough wagon road 

leads from the mine down to Henson Creek, where it joins the main 

road to Lake City. The mine is opened by a S: 65° W. tunnel into 

the bluff. The upper workings have been abandoned since 1899 and 

only this drift is now accessible, but the mine has in the past produced 

a considerable tonnage of ore. The high values found in the upper 

workings induced the management to attempt a long adit tunnel 

from Henson Creek to cut the main vein. This was driven in for 

1,500 feet in 1899 at a heavy expense and was then abandoned.

The Vermont is one of the older mines in the Lake City region. 

Work on it has been abandoned since 1906. The production has 

been about as follows:

1 Values figured on price of silver during years when mined and on tonnage shipped.
86 GEOLOGY AND ORE DEPOSITS NEAR LAKE CITY, COLO.

Production of Vermont mine.

[From mint reports.]

1884..................................................... $4,965.00

1887..................................................... 40,436.00

1888..................................................... 62,648.00

1892..................................................... 6,993.00

1895..................................................... 1 182. 24

1896..................................................... ! 119.60

$115,343.84 

j The mine records for the same years show a production of $115,043.84.

Ores. No data are available as to the mineralogical character of 

the ore from the Vermont mine, but as it is of the same general 

vein series as the closely associated veins of the Lellie, Wave-of-theOcean, and Ocean Wave, it undoubtedly consisted chiefly of argentiferous tetrahedrite 

and galena, with 

smaller quantities of 

sphalerite, chalcopyrite, and pyrite. The 

main output of the 

mine has been silver 

and lead. The value 

of the ore from the 

upper workings in 85

shipments of 25 tons

eachranged from 33.9 

to 253.10 ounces of 

silver, and 7.5 to 59 

per cent lead. The 

average silver' and 

lead content for these 

85 shipments was 

84.53 ounces of silver 

and 27.96 per cent 

lead, giving an average value, computed 

on the present market 

prices, of $44.80 silver 

and $12.06 lead, or a 

total average gross value of $56.86 per ton of ore mined. In 1894, 

63 tons mined yielded $4,965, an average of about $79 per ton. Two 

later shipments of ore of 16,078 pounds and 10,504 pounds, in 1895 

and 1896, respectively, yielded an average total value of $22.67 and 

$22.78 per ton each.

i Figures furnished by the company.

FIGURE 11. Sketch of the Scotia, Vermont, Ocean Wave, and 

\ Wave-of-the-Ocean group of claims.
U. S GEOLOGICAL SURVEY BULLETIN 478 PLATE V

100 200 30 400 500 Feet

PLAN OF THE UNDERGROUND WORKINGS OF THE UTE AND ULAY, AND HIDDEN TREASURE MINES; HENSON, COLORADO
HENSON CHEEK MINES. 87 

UTE AND TJLAY AND HIDDEN TREASURE.

The most productive and also the most extensive workings in the 

Lake City region are those of the Ute and Ulay and the Hidden 

Treasure mines. The two, though operated by separate companies, 

are to be regarded as a single unit geologically, inasmuch as they 

are on the same vein or group of veins, and their workings interpenetrate one another. Plate V shows a plan of the underground 

workings and outcrops on the Ute and Ulay and the Hidden 

Treasure ground.

DEVELOPMENT.

UTE AND ULAY MINE.

The workings of the Ute and Ulay mine are located in and adjacent 

to Henson Creek, at the eastern extremity of the town of Henson, a 

settlement which has grown up in consequence of the operation of 

these mines.

Four veins have been extensively worked the Ute vein, the Ulay 

vein, the Annie vein, and an unnamed vein cut in the new shaft. 

The earlier workings of the mine were on the Ulay vein, which crosses 

' the bed of Henson Creek. Two short drifts above the creek on the 

north side enter directly on the outcrop of the vein, but these are not 

extensive, and but little mining has been done on them. The main 

working opening is an inclined shaft dipping northwest. From it 

nine levels have been run. The first three, called third, fourth, and 

fifth levels, are not extensive. The sixth is more extensive, but 

the seventh, eighth, ninth, tenth, and eleventh are the main working 

levels of the mine and from them the large production of the vein 

has been stoped.

All of these workings are in bad repair and the mine is full of water, 

so that no description of the Ulay vein can be given other than that 

furnished by those who have worked in it and operated it.

The workings of the Ute vein interpenetrate those of the Hidden 

Treasure to the northeast. The vein (PI. V) lies about 500 feet northwest of the Ulay and is roughly parallel to it. It is opened only on the 

hill slope northeast of the Ulay shaft and has not been followed 

southwestward across the creek. It is opened by two crosscut 

tunnels to the first and second levels. The fourth level is opened 

by an extremely crooked adit running in from the hillside northeast 

of the Ulay shaft. The lowest level is entered by a long crosscut 

tunnel from a point 70 feet northeast of the Ulay shaft. From the 

most southwesterly point in the mine the workings extend to the 

Hidden Treasure line. Throughout the greater part of this distance 

the ground is stoped, only a few pillars of lean ore being left to support the roof. No stope maps or very reliable information could 

be secured about these workings and statements as to the ores can
88 GEOLOGY AND ORE DEPOSITS NEAE LAKE CITY, COLO.

be based only on inferences drawn from the small amounts of ore 

still remaining.

At the northeastern end of the mine the Ute vein passes into the 

Hidden Treasure ground, the third level of the Ute being continuous 

with the fifth level of the Hidden Treasure.

HIDDEN TREASURE MINE.

The Hidden Treasure property includes the five claims, Hidden 

Treasure, Invincible, Protector, Don Quixote, and Crystal Crown. It

FIGURE 12. Longitudinal section of the Hidden Treasure vein, showing the stopes and the pitch of the

ore shoot.

is equipped with a 100-ton concentrating mill erected in 1898, a waterdriven compressor, a 50-horsepower electric hoist, and a Bleichert 

wire-rope tram, with twenty-five 450 to 500 pound buckets, having 

a capacity of about 12 tons per hour, connecting the shaft with the 

mill.

The shaft was sunk on the vein for 265 feet before it encountered 

ore which paid expenses. The first ore was taken from the mine in 

June, 1897, and from that time until 1908 it has been worked almost 

continuously. During 1897 ore was shipped to the smelters, as the
HENSOF CREEK MINES. 89

concentration plant had not then been erected, but since 1897 the 

bulk of the ore has been milled and concentrates averaging about $40 

a ton have been shipped. Eight levels have been run from the shaft. 

(See fig. 12.) The vein has been stoped almost continuously from 

the fifth level to the surface.

The Ute and Ulay mine has been among, the largest producers of 

silver and lead in Colorado, being reported to have yielded between 

$10,000,000 and $12,000,000 gross. This production takes no account 

of the poorly adapted milling plant in which much of the earlier ore 

was treated and by which it is estimated that a great deal of money 

was lost. The Hidden Treasure mine has produced upward of 

$700,000.

COUNTRY ROCKS.

The country rock in which the ore bodies occur is the Picayune

volcanic group, which carries the largest number of valuable deposits

in the Lake City region. This rock shows a great variety of texture 

and color, so that its identification in the several localities where the 

best-known mines occur .would be impossible without painstaking 

geological labor in tracing it from one locality to another. . Both the 

Ute-Hidden Treasure vein and the Ulay vein lie wholly within this 

rock, although at the northeast end the Hidden Treasure vein closely 

approaches the overlying Eureka rhyolite. In the deeper portions of 

the workings and in the mouth of the long adit tunnel where the rock is 

unaltered by surface agencies it has a dense grayish appearance, almost 

glassy in places. It is characterized by broken brecciated fragments, 

which are of the same nature as the matrix which incloses them and 

which were obviously formed during the flow of the rock as it cooled. 

The congealing crust was broken during the flow and the fragments 

submerged in the still molten portions, giving rise to a breccia in 

which no distinction can be made between matrix and fragments. 

The fragments are of all sizes, varying from almost imperceptible 

irregular flakes to those measuring many inches. The feldspars are 

small, though in places they perceptibly mottle the fresh rock. In 

the vicinity of the Ute vein the rock (see p. 44) has been profoundly 

altered, passing from gray to almost black, and the black giving way 

again, in the immediate contact with the vein filling, to a light green, 

which is chiefly due to the silicification which has accompanied the 

ore deposition.

Small fragments of country rock, when included in the ore, are 

generally entirely altered and no black cores are perceptible, but/ 

large fragments, which alteration has been unable completely to penetrate, consist of a light-greenish shell over a dark blackish core. 

The rock is brittle and rather easily ruptured, so that regular veins 

have formed in it (as in the breccia of the San Juan formation in the
90 GEOLOGY AND ORE DEPOSITS NEAR LAKE CITY, COLO.

Ouray district), whereas in other tougher types of rock, such as the 

coarse even-grained andesites in the vicinity of Capitol City, the veins 

are more discontinuous and constricted. Another consequence of the 

weakness of the rock is the very large number of horses, or fragments of country rock, found in the ore perhaps as striking a feature of these Lake City veins as any observed.

ORE BODIES.

VEINS.

The ore bodies of the Ute and Ulay and the Hidden Treasure mines 

are fissure veins. They are distinctly the result of the filling of open 

fissures and represent only in minor degree a replacement of the wall 

rock. Silicification, as will later be shown, in many places affects 

the walls and included fragments of country rock, but metalliferous 

minerals are confined to the filling material. Four well-defined veins 

have been either partly or extensively explored on the property of 

the Hidden Treasure and Ute and Ulay mines. (See PL V.) In the 

order of their importance they are the Ute, the Ulay, the Annie, and 

an unnamed vein encountered in the new shaft. A small and yet 

undeveloped vein known as the California should also be mentioned. 

An adit tunnel 500 feet in length has been driven to intersect it. 

The Annie, the Ulay, and the new vein were, at the time of the visit, 

entirely inaccessible to examination, so that little can be learned 

concerning them except from the mine maps.

UTE VEIN.

Strike and dip. The Ute and the Ulay are the main veins exposed 

on the property. The Ute has been by far the most productive and 

important of any vein in the district. It has been traced on the surface for a distance of 2,700 feet along the outcrop, from a point

northeast of the Hidden Treasure shaft southwest to a tram house 

just above the mouth of the third level tunnel of the Ute, 1,200 feet 

north of Henson Creek. Beyond these two limits it has not yet been 

traced in either direction.

The vein, as explored in the workings, describes an arc of large 

radius, with the concave side toward the northwest (in the direction 

of dip). At the southwest end the strike is N. 46° E., in the center it 

is N. 37° E., and at the northeast end beyond the Hidden Treasure 

shaft it is N. 19° E. The concavity of the outcrop is increased by a 

shallowing of the dip in the center of the Ute workings. This is brought 

out on PL V, in which the different levels, which may be regarded as 

contours, may be seen to close up at both ends and flare apart toward 

the center of the vein's course.

In detail the strike is irregular, as the vein shows many slight 

deflections in strike as well as in dip, in this respect resembling the
HENSON CREEK MINES. 91

majority of fissure veins. These deflections are rarely large; the 

greatest is that which shows on the third and fourth levels of the Ute 

mine, 325 feet north of the adit tunnel of the second level, where the 

vein diverges 45°, continuing so for 45 feet, and then returns to its 

original direction. In outcrop the course of the vein is much more 

sinuous and diverges to the north from the true strike on account of 

the steep and irregular nature of the topography which it intersects.

Sharp bends occur in the dip also, a fact amply demonstrated in 

the Hidden Treasure shaft, where the skip now descends vertically, 

then moves almost horizontally, and then again goes down at a very 

steep angle. The average dip is between 56° and 60° NW.

Movement. No criteria exist by which to determine definitely how 

much differential movement has occurred between the walls of the 

vein. The variation in width where pinches and swells follow one 

another in the direction of dip and strike indicate that there has been 

movement, but that it has not been excessive. The vein is characterized by considerable brecciated country rock which is included in the 

vein filling, but the brecciation has taken place on a relatively small 

scale. The fragments of wall rock are generally separated from one 

another by considerable distances and no evidences of excessive 

attrition are present. Faulting has not seriously affected the vein. 

A few cross veins are noticeable, but they seem to be of the same age 

as the main fissure. This regular and uninterrupted character has 

done much to facilitate exploration and to make expensive dead work 

unnecessary.

Width. The vein averages about 4 feet in width, but pinches and 

swells after the manner of most fissure veins. The maximum width 

from wall to wall is about 20 feet, the minimum a mere fracture or 

series of fractures with practically no width. The wide places occur (1). 

from the splitting of the vein; and (2) from the movement of the two 

walls past one another, so that two concave surfaces are brought into 

juxtaposition. Such wide places run down to mere fissures at both 

ends, where convex surfaces are in contact; narrow, barren faces 

may be observed in the southwest end of the Ute workings and 

in the northeast end of the Hidden Treasure workings.

Through the Ute mine the vein is well defined between two simple 

walls, but in the Hidden Treasure mine it splits into a number of 

stringers. At the most important of such splits occurred one of the 

widest and most valuable bodies of ore. This split is most noticeable 

on. the fifth level, 45 feet northeast of the shaft. One branch of the vein 

is 10 feet in width, and the'other is 4 feet in width. The main vein 

for 40 feet southwest of the split is 20 feet wide. The junction between these two branches pitches northeast in the plane of the vein, 

so that on the fourth level it is close to the shaft.
92 GEOLOGY AND ORE DEPOSITS NEAR LAKE CITY, COLO.

Another irregularity occurs at the southwest end of the Ute 

workings on the fifth level, where the vein is split into a number of 

parallel stringers of small size. In a short crosscut northwest from 

the adit tunnel these stringers are very clearly shown separated from 

the main vein by spaces of barren but silicified rock; where cut they 

are 40 feet southeast of the mam vein, which here narrows to a 

maximum width of 2£ feet.

PARAGENESIS.

A number of well-defined steps in the formation of the Ute-Hidden 

Treasure ore bodies are evident. The first seems to have been the 

rupture of the country rock with a little but not marked brecciation and but little or no separation of the walls from one another. 

This was followed by the entrance of silicious mineralizing waters, 

intensely altering the country rock into hard, greenish silicified 

material for a short distance from each individual fissure. Later 

movement separated the walls and moved them- slightly past one 

another, producing the pinches and swells and causing some brecciation of the wall rock.

The first period of vein filling then occurred depositing (1) quartz; 

(2) rhodochrosite, tetrahedrite, and galena; and (3) quartz. Later 

movement shattered this vein material and deposited (1) quartz; 

(2) barite with subordinate galena; and (3) quartz.

ORES.

Character. The ore in the Ulay vein can not now be described 

exactly, but it was composed, as nearly as can be learned, of argentiferous galena, with some tetrahedrite, sphalerite, and pyrite, and 

the usual enrichments of ruby silver. From the upper levels considerable native silver is reported to have been taken. In the lowest 

or eleventh level the sphalerite increased in quantity and the silver 

and lead values fell off to such a degree that the mine was abandoned 

and has not been worked for many years. Some idea of the prevailing 

character of the ore may be learned from the production statistics 

for the years 1887 and 1888.

Production of the Ulay vein for 1887-88.

1887.... ..............................................................

1888..........................'........................................

Gold.

81,645

2,500

Silver.

$39,498

84,038

Lead.

819,242

52,800

The absence of copper and the large value of the lead indicate 

that the product was chiefly argentiferous galena and that there was 

less tetrahedrite in the ore than in most of the mines of this region.
HENSON GREEK MINES. 93

The ore in the Ute vein was a mixture of galena, pyrite, and subordinate tetrahedrite in a gangue composed mostly of quartz, with 

subordinate barite and a very small quantity of manganese-bearing 

minerals. In the pillars left in the mine banded ore containing 

chiefly galena and sphalerite was observed. In the breasts of No. 5 

level about 180 feet southeast of the Hidden Treasure shaft the vein 

is 4 feet wide and consists mainly of quartz and barite. Many fragments of country rock, generally altered to a very light greenish 

color, may be seen in the vein.

The sphalerite, galena, and barite of the Ute vein appear to belong 

to the earlier period of mineralization; in all cases where they could 

be clearly observed they are older than the gangue of white quartz in 

which they are embedded. This can be seen from the manner in 

which a great part of the galena is fractured and broken, and the 

interstices filled with white quartz, much of it with well-developed

comb structure perpendicular to the galena fragments. (See fig. 13.)

Value. Small bunches and bonanzas of 

ruby silver in the upper stopes of the 

Hidden Treasure carried high values in 

silver, but the general average of the ore 

extracted from the mine was from $7 to $9 

per ton. Milling operations during 1898 

and 1899 showed that 1 ton of concentrates, worth $41.67, was obtained from 

4.61 tons of crude ore. The cost of operation at the Hidden Treasure, including

freight and smelter charges, Was about FIGURE IS. Galena shattered and

q,. ^ n infiltrated with quartz, Ute vein.

«S4.1Z. a, Quartz; b, sphalerite; c, galena.

Distribution of values. The distribution

of the various minerals in the Ute-Hidden Treasure vein is not uniform. 

From the southwestern extremity of the Ute vein to a point well within 

the lines of the Hidden Treasure property, where the crescent-shaped 

bend in the vein causes it to trend more nearly north, the ore consisted 

of a banded aggregate of argentiferous galena, sphalerite, quartz, and 

barite. Throughout this entire distance tetrahedrite is present in 

small quantities, as is also barite, but rhodochrosite is practically 

absent. If the workings on the vein had been carried no farther than 

the Hidden Treasure line, it would have seemed a remarkably clear 

type of a quartz vein carrying argentiferous galena and sphalerite. 

Beyond the Hidden Treasure line, however, the' barite increases notably in amount and tetrahedrite and rhodochrosite begin to appear in 

the ore; and finally nearly the whole vein consists of rhodochrosite, 

with large quantities of tetrahedrite and barite and small quantities 

of galena. Quartz is present in subordinate amounts. Throughout the long Ute portion of the vein, 3,000 feet in all, the gangue
94 GEOLOGY AND ORE DEPOSITS NEAR LAKE CITY, COLO.

and ore minerals are mingled together with remarkable uniformity, 

so that for nearly the whole of this length the vein is stoped. No 

definite pay shoot can be detected, though low-grade areas of ,small 

dimensions were encountered here and there and the ore in them was 

left standing in the mine. In the Hidden Treasure portion of the vein 

the upper edge of the profitable ore pitches about 15° N., but this 

pitch is due more to a decrease in the size of the fissure than to the 

failure of metalliferous mineral contents. The presence also of the 

branch vein described on page 91 seems to have determined the upper 

edge of this profitable area. Much difference of opinion among those 

who operated these properties exists as to the pitch of the shoots, but 

this arises from the very large area of profitable ore and the consequent difficulty in determining any well-defined shoots. If rhodochrosite and tetrahedrite be regarded as localized from the other minerals 

in the mine, they are clearly restricted to the north end, but so far 

as silver values are concerned there seems to be no regularity about 

the localization.

The ore in the Ulay vein occurred in distinct shoots, two of which 

were found south and one north of the shaft.

EQUIPMENT. 

HIDDEN TREASURE MINE.

The Hidden Treasure mill is connected with the shaft by a Bleichert tramway 3,800 feet in length, with a capacity of 100 tons in 

24 hours. Power is obtained by a 150-horsepower Pelton wheel supplied with water from a dam under a head of 118 feet by a wooden 

pipe line 28 inches in diameter and 1,000 feet in length. The ore 

goes first through a 9 by 15 inch crusher and thence to rolls, one 

set 16 by 24 inches, the other 12 by 20 inches, for finer crushing. 

From here it is sent to a set of trommels, where it is sized, the oversize from the first three trommels being returned to the rolls. The 

two sizes from the last two trommels pass to two sets of jigs. The 

fines are sent to two hydraulic sizers and thence to four Wilfley 

tables, which yield a fair saving. A little of the rhodochrosite is 

saved from the tables, as it contains high values in silver from finelydivided tetrahedrite. The concentrates are not dried. The concentration is 4.6 to 1. Compressed air is supplied to the mine by a 13£- 

inch Leyner duplex compressor of 16-inch stroke, which is operated 

by another 150-horsepower 54-inch Pelton wheel. The hoist is operated by electricity furnished by a 45-kilowatt dynamo, operated by 

steam.

UTE AND ULAY MINE.

The ore from the Ute and Ulay mine was taken to the mill in 

Henson Creek by a wire-rope tram. The mill has a capacity of 90 

to 100 tons a day. The ore goes first to a rock breaker (Blake, 9 by
HENSON CREEK MINES. 95

Rock breaker

i

. Rolls.

Rolls

Rolls

15 inches), and then to three sets of rolls (Allis-Chalmers, 16 by 30 

inches), then through four successive trommels, 36 inches in diameter 

and 7 feet long, which size the crushed ore to 8, 6, 4, and 2£ millimeters. The coarse which passes through the trommels goes to the 

jigs, a double-compartment jig for each trommel. The fines which 

escape from the last trommel pass into two hydraulic sizers, the 

coarse being sent to jigs and the fines going into a third sizer. The 

coarse from this last sizer goes to a jig and the fines run to the buddies, two of which are plain,

16 feet in diameter, and four 

double-deck, 24 feet in diameter. The tailings pass into 

settling tanks where the 

slime is arrested. (See fig.

14.) The Ute ore became 

much higher in sphalerite on 

the fifth level, so that the 

mine no longer paid expenses of operation. In 

this respect it resembles most 

of the other veins of the 

region.

The following statement 

by Rickard 1 will indicate 

the manner in which the 

concentrates are handled:

2 Jigs

1 Jig Buddies

Y

Settling tanks

FIGURE 14. Diagram of treatment at the Ute and Ulay 

mill. After Rickard.

The concentrates are dried and 

mixed by passing through a 

heated revolving cylinder. About 

1$ per cent of moisture is left in 

the concentrates in order to lessen 

the leakage arising from the bad 

flooring of the railroad cars, which 

would be a greater source of loss if 

the concentrates were dry enough 

to run readily. The concentrates 

contain 58 to 61 per cent lead, 13 

to 15 ounces of silver, and 0.05 to 0.06 ounce of gold per ton. They represent 

about 16 per cent in weight of the original ore and an extraction of about 80 per 

cent of the lead and 65 per cent of the silver.

PELICAN.

The Pelican mine is situated in a small dry gulch on the north side 

of Henson Creek about 1£ miles due west of Lake City, at an elevation 

of 9,630 feet above sea level and 875 feet above the bottom of Henson 

Creek. The mine is connected with the main wagon road in Henson

> Rickard, T. A., Across the San Juan Mountains: Eng. and Min. Jour., vol. 76, 1903, pp. 461-462.
96 GEOLOGY AND OBE DEPOSITS NEAR LAKE CITY, COLO.

Creek by a rough second-class road about half a mile long, down the 

north side of the canyon. Power has been furnished by a gasoline 

engine.

Production and, development. The first mention of the Pelican in 

the mint reports occurred in 1891, during which year it is credited 

with a production of $581 in silver. The following year it produced 

$1,503, all silver except $20 in gold.

It is reported that two shipments of about 10 tons each showed 

returns of 0.69 and 0.63 ounce of gold and 165 and 129 ounces of 

silver per ton. To one of these shipments 2.07 per cent .of lead is 

credited.

The workings of this property consist of two shafts, two levels, a 

winze, and several small stopes. The shafts are respectively 75 and 

38 feet deep, the first one connecting the first level with the surface. 

The winze is only 35 feet down from the first level. The first level is 

approximately 450 feet long, and the second (200 feet below the first), 

is about 900 feet long. All the workings except a 400-foot crosscut 

on the second level are on one or another of the veins which form the 

fracture system making up this deposit. The amount of stoping is 

comparatively small. One block, approximately 28 by 38 by 4 feet, 

had (1908) been 'worked at the. shaft on the upper level. Another 

block, approximately 56 by 50 by 2£ feet, had (at the same date) been 

extracted near the breast of the first level.

Country rock. The vein is in Eureka rhyolite, the latter having 

been slightly altered along its contact with the mineralizing agencies. 

Marked disturbances were noted in the country rock between the 

crosscut and the vein worked in the secon.d level.

Veins. In the stope above the lower level the most prominent 

vein is 3 to 4 inches wide, with an ore course varying from one-eighth 

to one-fourth inch in width and is frozen to the walls. It strikes 

N. 10° E. and dips 66° S. 80° E.; the other veins differ somewhat, 

both in dip and in strike.

The ore body is a typical filled fissure. It varies in width from 

about 2 inches to 4 feet at the widest points, with an average of 1 

foot. The dip is fairly uniform, being 70° SE. The vein is formed 

along two series of intersecting fractures, which strike N. 10° E. and 

N. 35° W. No one of these fractures is very long and the mam 

open space extends along one fracture until this becomes narrow, 

and then passes to a fracture of the other strike, to be again taken 

up by a fracture parallel to its first course, and so on. This feature 

is well shown in figure 5 (p. 42). It is probable that similar variations could be observed in dip, but exploration is not yet sufficient 

to disclose them. The fissuring has been accompanied by very 

extensive brecciation, so that the vein is characterized by many 

angular inclusions of country rock, by innumerable branches, and
HENSON CREEK MINES. 97

by other irregularities. (See fig. 15.) In places it is merely a 

sheeted zone which has but little open space for ore deposition.

The structure of the vein filling appears massive on first sight, 

probably on account of the great mass of highly altered rock with 

which the fissure is filled, but on closer examination very fine druses 

are often discernible, either parallel to the walls or following around 

the periphery of included fragments.

Replacement of the country rock has been more extensive in this 

vein than in most of those in the region. Here, as elsewhere, however, it has been chiefly confined to silicification, which has transformed the included rock fragments into hard black flinty silica. 

Barite has also been to some extent introduced into the wall rock, 

and included fragments show a higher degree of replacing action than 

common.

The accompanying sketch shows the brecciated nature of the vein.

Ores. The vein filling consists 

of the following minerals, named 

in the order of deposition: Primary minerals, black dense silica, 

barite, galena, freibergite, barite, 

white quartz, pyrite, and sphalerite ; secondary minerals, pyrargyrite and secondary galena. Silica 

and barite are the most abundant.

A little rhodochrosite also 

occurs in subordinate amount. 

A number of these minerals, 

especially barite and quartz, 

probably appear in more than one generation, but the relative periods 

of deposition can not in all cases be made out with certainty.

The secondary pyrargyrite and secondary galena are without doubt 

connected genetically with oxidation processes. The pyrargyrite occurs 

in later crevices in the ore as well as in defined crystals lying on the 

outer surface of the white quartz druses in open cavities. It has, 

with little question, originated from the reprecipitation of antimonial 

silver solutions derived from the alteration of the freibergite (p. 63). 

It is probable, for this reason, that the ruby silver will not continue 

in depth, or at least will occur only as far as surface solutions could 

gain access along especially favorable channels.

The ores contain many irregular vugs, some of them 8 inches or

more in diameter. Nearly all of them are lined with white quartz,

usually in fine druses. Barite crystals project into many of them,

but all of these are covered with a fine coating of white quartz, show95249° Bull. 478 11 7

FIGURE 15. Face of Pelican drift, showing structure 

of lode.
98 GEOLOGY AND ORE DEPOSITS NEAR LAKE CITY, COLO.

ing that silica was the final phase of the deposition. What is probably 

secondary galena occurs coating the surface of the sphalerite along 

cracks and fractures in the ore. In the hand specimen it may be 

seen merely as a dull lusterless surface, slightly grayish in appearance, 

in sharp contrast to the brilliant luster of the fresh fracture of the 

sphalerite when this mineral is broken, where no crack large enough 

to permit the entry of surface solutions has been available; under the 

microscope, however, it is distinctly coated with some gray mineral. 

In some massive sphalerite the minute galena-coated crevices are so 

numerous that it is nearly impossible to break the ore so as to get a 

perfectly fresh fracture.

MISSOURI FAVORITE.

The Missouri Favorite mine is on an unpatented claim located just 

north of Henson Creek, about three-quarters of a mile west of Lake 

City. The mine is one of the most accessible in the region, being 

near the railroad terminus and a source of supplies.

Production and development. Little is known regarding the history 

of the mine. Mr. Snyder of Lake City has worked the property for a 

number of years and has made two shipments of ore, one of 10 and 

another of 8 tons. The first shipment gave returns of $8 per ton and 

included 800 pounds of sacked ore, which ran $247 per ton. The 

second shipment ran $50 per ton. These are picked lots of ore and 

do not represent the average run of the ore body.

The development on the property consists mainly of drifts. One 

drift runs about 600 feet from the motiih of the adit tunnel along 

the main vein. Some 250 feet iri a stringer, making an angle with the 

main drift of 20° to 30° to the northwest, has been followed for 350 

feet.

Veins. The vein is in Eureka rhyolite, which shows more alteration than is common in the area. In general the localities showing the 

greatest amount of alteration and decomposition appear to have been 

the least prospected, and, indeed, have been left practically unexplored on any extensive scale. The cause for this is not apparent, 

although it may be due to the fact that nearly all of the mining 

operations in the Lake City district have been either in connection 

with placers or on well-defined quartz veins, and the prospector is 

loath to take up a new kind of exploration.

The faulting in the vicinity of this vein is more noticeable than it 

is near many of the mines visited. Most of it seems to have occurred 

on the west side of the vein, where great slickensided surfaces are 

common. Gouge is present in enormous amounts and during wet 

seasons of the year clay and mud fall from the roof in tons. The hanging wall is in several places separated from the footwall by a great
SAN CEISTOBAL GROUP. 99

wide fissure filled with clay and mud. As the portion of the vein 

developed is near the grass roots, much of the clay and mud may be 

due to surficial wash. Toward the west of the main working an 

enormous horse comes in and separates the two walls by 30 or 

40 feet.

From the foregoing it may be inferred that the fissure is irregular 

and shows great variations in size and character. The strike of the 

vein is about N. 50° W., although there are so many variations that 

only an approximate direction can be given. The dip is in general 

about 70° SW. The width varies from a few inches to several feet.

Ores. The ore minerals are galena and tetrahedrite with some 

chalcopyrite and sphalerite. The gangue is composed almost entirely 

of barite with a little quartz. The ores show banding, as is common 

in the ores from this area. The alternate' layers of decomposed rock, 

barite, and ore minerals resemble parts of the Ute-Hidden Treasure

vein.

SAN CRISTOBAL GROUP.

MONTE QUEEN.

The workings of the Monte Queen mine lie due south of Lake 

City, on the west side of Lake Fork, on the eastern slope of the 

mountain, 9,100 feet above sea level and 300 feet above the bed of the 

river. The mine 

is connected with 

the main road 

by a short branch 

road which makes 

it easily accessible.

Vein. The vein 

is opened on its d, c ) a,

FIGURE 10. Cross section of the Monte Queen vein, showing included 

rock fragments, strong selvage, and massive vein filling, o, Unaltered 

country rock; 6, silicifled flow breccia; c, selvage; d, fragments of country 

rock and barren quartz gangue.

outcrop by a tunnel driven S. 73° 

W. for 950 feet. 

The country rock is a grayish stratified breccia evidently formed 

by the fracture of the cooling upper surfaces of successive lava flows 

during their extrusion. Some stoping has been done in the mine, but 

no records of its prc duction or history could be obtained.

The workings are on a fissure vein, produced in greater part by 

the filling of an open crevice and only in minor degree by replacement 

of the country rock. The vein, which departs but little from the 

vertical in its explored portions, is about 3 feet in width. In some 

places it has well-defined walls, locally separated from the country 

rock by strong selvage seams. (See fig. 16.)
100 GEOLOGY AND ORE DEPOSITS NEAR LAKE CITY, COLO.

Ores. The ore minerals are segregated within the barren gangue 

material into vertical shoots which show no appreciable pitch within 

the plane of the vein (see fig. 17). Between the shoots the vein

Barren quartz

Lens of ore

Mam drift /£- 

Plan

FIGURE 17. Plan and longitudinal section of Monte Queen vein, showing ore shoots, a, Tetrahedrite 

and pyrite; b, galena and zinc. 

pinches so that only a few sheeting planes with stringers of quartz, 

etc., are left, by which the vein may be followed from one shoot 

to the next. The shoots have a stope length of 50, 63, and 200 feet, 

respectively. Nos. 1 and 3 contain chiefly pyrite and some gray copper 

ore and do not run very well in silver. No. 2 consists chiefly of a 

peculiar dark-brown, fine-grained, massive, rosin-like sphalerite, 

mixed with fine steel galena and averaging about 75 ounces in silver

and notable percentages of bismuth. 

Some of this ore, 

according to the 

management, ran as 

high as 2,000 ounces 

in silver and contained 20 per cent 

of bismuth. The 

pyritic shoots were 

too low grade to pay. 

A fourth shoot, or 

. . B , u .,..,, 4. « . widening of the vein, FIGURE 18. Occurrence of shoots within shoots, Monte Queen vein. ° '

5 feet in width,

occurs in the breast of the tunnel 950 feet west of the mouth; so far 

as yet explored it contains nothing but massive rhodochrosite.

The metallic minerals in the No. 2 shoot occur in smaller shoots, 

which are separated by vertical intervals of barren quartz and are 

lenticular in both vertical and horizontal section; they pitch slightly 

(15°) along the course of the vein to the southeast. The vertical 

extent of these lenses is from 3 to 20 feet (see fig. 18) and that of 

the barren quartz filling between from 3 to 12 feet. The barren 

portions are filled with included and highly silicified fragments of 

wall rock and the country rock is altered to distances of 4 to 5 feet 

from the vein filling.

TUNNEL

Plpn

Lens of ore

:j[Barren quartz 

I Lens of ore 

Crpss section onA~3
SAN CRISTOBAL GROUP. 101 

NELLIE M.

The workings of the Nellie M. mine are west of those of the Monte 

Queen. The vein is opened by an upper and a lower drift. The upper 

tunnel, which is 510 feet in length, runs S. 53° W. with the vein. 

The lower tunnel is 700 feet in length. The country rock is the 

usual bedded type of andesitic and rhyolitic flow breccia, much 

decomposed, and with very prominent banding. The clip is 65° S. 

The vein, so far as could be learned, has not yielded ore in commercial quantities, but a little sphalerite, chalcopyrite, and some 

silver have been found. A few streaks of metallic mineral could 

be seen here and there along the broken sheeted zone followed by the 

tunnel.

LODE STAR

The Lode Star mine workings consist of a shallow shaft and a few 

short tunnels located on a shear zone from 2 to 300 feet wide. This 

zone has had so little work done on it that its nature can not be 

determined. The mineralized zone is greatly stained with iron 

oxide, is much silicified, and is reported to have yielded somo values 

on assay, but has so far not paid for what exploration has been done.

DAUPHIN, ROB ROY, AND SULPHURET.

On the east side of Lake Fork, about 1| miles south and a little 

east of Lake City, is a great shear zone striking about N. 73° E. On 

one side of this are the workings of the Rob Roy and Dauphin and 

on the other to the southeast are those of the Sulphuret. Sufficient 

work has been done to disclose some gray copper ore, several carloads 

of which have been shipped from the Sulphuret; but the development is insufficient to furnish any' reliable data. It is possible that 

the. Sulphuret may represent the northeast continuation of the Monte 

Queen vein.

GOLDEN WONDER.

The geologic map (PI. Ill) shows an area of silicified rhyolite covering a large part of the southeastern portion of the Lake City quadrangle. Within this area, some 2| miles southeast of Lake City, is 

the Golden Wonder mine. This property is unique in that it is the 

only deposit of those examined by the writers in this area that can be 

classed as a true replacement deposit.

The Golden Wonder claim is on the northern side of Deadman 

Gulch, its side lines extending east and west, approximately parallel 

to the trend of the gulch. A good trail connects the workings with 

the main wagon road to Lake City. Underground examination of 

the Golden Wonder was not possible because of the condition of the
102 GEOLOGY AND ORE DEPOSITS NEAR LAKE CITY, COLO.

workings, but a basis for conclusions as to its deposits was supplied 

by the examination of contiguous and doubtless analogous deposits.

Few authentic data are available in regard to production. Two 

carloads of ore are reported to have been shipped in 1906 which are 

said to have averaged $70 a ton in gold.

The original discovery was made at an elevation of 10,500 feet, at 

which height an adit tunnel is said to have been driven 150 feet east 

into the silicified country rock. Another adit tunnel, started at an 

elevation of 10,375 feet, near the center of the gulch, is said to have 

been driven 850 feet. This crosscut is not a direct one, but is reported 

to twist and turn in a remarkable manner.

The country rock in this vicinity is an altered rhyolite, doubtless 

of intrusive origin. This rock has been greatly changed by silicification and in places by sericitization. Solutions containing pyrite 

have impregnated the surrounding rocks for several miles in all 

directions, and it is probable that in these is to be found the source 

of the gold found in the Golden Wonder workings and elsewhere in 

the vicinity, local concentrations of the gold contained in the pyrite 

having produced the few rich pockets found in the vicinity.

True quartz veins are scarce in the workings examined on contiguous properties, the mineralization appearing to be a simple replacement of the country rock by silica and pyrite. In places, however, 

mineralization, presumably by secondary concentration, has taken 

place along joint planes and fracture zones in the altered rhyolite.

MAYFLOWER AND CONTENTION CLAIMS.

The Contention mine includes the Contention and Mayflower 

claims, which are located about 1,000 feet north of the north end of 

Lake San Cristobal and 3 miles south of Lake City. The claims are

so located that the west end of the Mayflower adjoins the east end of 

the Contention.

Production and development. For short periods during its history 

the mine has produced a considerable amount of silver from its upper 

workings. The ore bodies were small, however, and the mine has 

not at any time been capable of maintaining a heavy output. For 

the four years, 1889 to 1892, the following statistics on the Mayflower 

and Contention are given:

Production of Mayflower and Contention claims, 1889-1892.

1889. ................................................................................

1890. ................................................................................

1891...........................................;.....................................

1892.................................................................................

Total..........................................................................

Grand total ...................................................................

Gold.

$120

63

47

230

$8,

Silver.

8905

1,244

2,456

3,543

8,148

378
U. S. GEOLOGICAL SURVEY

VIEW LOOKING SOUTH UP LAKE FORK.

Lake San Cristobal shows in the distance. Contention Mill is on the right. Ph
SAN CBISTOBAL GROUP. .103

The workings are located on the west side of Lake Fork just above 

the wagon road from Lake City. The tunnel openings by which 

the vein is reached lie on the extreme north end of the Mayflower 

claim, but most of the work is on the Contention claim. (See 

sketch, fig. 19.)

The mine is opened by three tunnels, two on the Mayflower claim 

and one on the Contention. The lower tunnels follow the vein westward into the hill and show low-grade ore. The upper tunnel and 

the workings connected with it are now abandoned but show considerable stoping and indicate that quite a little ore has been removed.

A large mill for treating the ore was erected in 1904. From the 

Gates crushers the ore was sent to rolls, thence to screens and to 

a Huntington mill, thence to classifiers, and after that to Wilfley tables. 

A high-grade concentrate was obtained, and the management claims

to have saved 90 per cent of the gold and 88 per cent of the silver.

Country rock. The country rock 

is the Picayune volcanic group. The 

ore body is a fissure vein with a 

nearly vertical dip, with a slight 

northward tendency, and a somewhat variable trend, averaging approximately S. 60° W. to S. 79° W.

Vein. The vein, which has an 

average width of from 14 inches to 2 

feet, is in places single but not uncommonly splits into stringers along 

the strike. In the lower tunnels it 

is more irregular than in the upper

tunnels and Stopes, from which FIGUHE 19. Sketch of Mayflower and Contenpractically all of the merchantable ion cams. 

ore had been taken at the time of examination in 1904. Pinches and 

swells are numerous, the vein having practically no width between 

stopes. Banding is generally imperfect or absent except in small 

quartz offshoots, where .comb structure is better developed.

Ores. The ore consists of silver-bearing gray copper or freibergite, 

(slightly auriferous), sphalerite, chalcopyrite, and pyrite in a gangue 

of quartz, barite, and rhodochrosite.

In the upper workings the gray copper predominates and often 

makes up the bulk of the ore with a little rhodochrosite, but in the 

lower tunnels pyrite is in greatest abundance and gray copper of 

only secondary importance. Some of the upper ore was extremely 

rich, $60,000 worth of silver having been extracted from a single 

small pocket. Barite and quartz are less abundant in this upper ore.

The ore from the lower tunnels is a massive aggregate of dense, 

fine-grained chalcedonic silica containing innumerable large, open
104 GEOLOGY AND ORE DEPOSITS NEAR LAKE CITY, COLO.

vugs. In this quartz great numbers of thin tabular crystals of barite 

form a network which in many places resembles the feldspars in a 

coarse diabase. Mixed through this quartz-barite gangue is finegrained noncrystalline pyrite, sphalerite, and tetrahedrite, with very 

subordinate galena and chalcopyrite. Open vugs are lined with 

beautiful crystals of barite generally coated with druses of quartz. 

Except that the quartz which coats the barite crystals is the last 

formed, the relative ages of these different minerals can not be definitely determined. In much of the ore secondary pulverulent chalcocite has been deposited as a secondary sulphide on the surface and in 

the cracks of the pyrite crystals. The wall rock has been very much 

altered by the vein solutions and shows a white bleached appearance 

for more than a foot beyond the boundary of the vein matter. This 

bleached rock has been extensively sericitized and is heavily impregnated with cubical pyrite. The gray copper and other metallic 

minerals do not extend beyond the zone of the main vein mass.

The ore occurs in shoots, between which the vein pinches to a narrow sheeted zone, which is slightly replaced by silica and a little 

pyrite, but has afforded no open space for deposition. The upper 

and lower workings were not connected at the time of the investigation, and the manager was of the opinion that they are not on the same 

vein, owing to the greater preponderance of the gray copper in the 

upper workings; in the writers' opinion, however, this difference is 

due simply to the customary gradual falling off in high-grade silver 

minerals with increasing depth.

The gray copper is the most valuable mineral normally found in 

the ore body; in the upper or more oxidized portions of the old 

workings, however, extremely valuable pockets of ore carrying native 

silver are reported to have been found. The gray copper carries

high values in silver, and where massive of ten assays as high as 1,000 

ounces to the ton.- The pyrite in the lower ore carries gold, and a 

test sample of 2,500 pounds is reported to have yielded 0.28 ounce 

,of gold and 11.34 ounces of silver.

GOLDEN FLEECE.

The Golden Fleece mine contains one of the celebrated veins of 

Colorado, and it is much to be regretted that the condition of the 

workings has made an exact and satisfactory examination of the 

mine impossible. A large portion of the upper workings is now 

inaccessible, no faces of ore remain in what few stopes can be observed, 

and the nature of the ore 'from the most productive portion of the 

mine can be determined only from specimens preserved in the offices 

of the company or casually picked up on the old dumps of the mine. 

The description of the mine here given, therefore, leaves much to be
SAN CRISTOBAL GROUP. 105

desired, though it is hoped that it may prove serviceable to those 

who are interested in the property.

Location and history. The upper and productive workings of the 

mine (see PI. VII) are located about 2,600 feet west of the north 

end of Lake San Cristobal, on the easterly slope of a flat-topped, 

mountain 11,800 feet high. The workings are about 10,000 feet 

above sea level and 1,000 feet above the level of the lake. (See 

fig. 20.)

The outcrop of the vein is located in a broad gulch that runs with 

the slope of the hill. It trends about N. 60° E., forming a promiContour interval 100 feet. 

FIGURE 20. Topographic map of the region around Lake San Cristobal.

nent ridge that rises sharply from the broad bottom of the draw to 

a height of 100 to 150 feet with a width of 20 to 30 feet. (See fig. 21.)

The mine is reached by a good wagon road from the lake, and transportation of ore to Lake City has offered no serious difficulties.

The history of the Golden Fleece and Black Crook mines is interesting, and the following extract has been taken direct from an 

article by Rickard: l . 

In 1874 Enos F. Hotchkiss, connected with a Government surveying party which 

was laying out a toll road from Saguache to Lake City, caught sight of the outcrop 

of the Golden Fleece standing conspicuously above the hill-slope, and examined it. 

He located it as the "Hotchkiss" mine and had some assessment work done while

i Rickard, T. A., Across the San Juan Mountains, Eng. & Min. Jour., vol. 76,1903, pp. 307-308.
106 GEOLOGY AND ORE DEPOSITS NEAR LAKE CITY, COLO.

he was engaged in his survey work in the vicinity. As far as known he found no 

ore. A year later, when Hotchldss had abandoned his claim, it was re-located by 

George Wilson and Chris Johnson, under the name of "The Golden Fleece." They 

began what is now known as the No. 1 tunnel, but finding only little stringers of 

rich ore, they ceased work. Others did similar desultory prospecting. 0. P. Posey 

found a very rich bunch of ore in the croppings above the No. 1 tunnel and took out 

several hundred pounds, which were packed to Del Norte and sent thence to the 

Pueblo smelter. Then John J. Crooke took a lease and bond; he also extracted 

about $30,000 from the outcrop above No. 1 tunnel, which had been extended a 

little farther, without result. This was between 1876 and 1878. In 1889 Charles 

Da vis took a lease and bond; he did a good deal of work along the high croppings, 

and finally sunk a shaft 30 feet deep, which struck a body of ore yielding $40,000 

in a very short time. Later in that year, 1889j George W. Pierce bought .the mine

for $50,000 and commenced 

extensive explorations. He 

found out very soon indeed 

that Davis had extracted all 

the ore in sight, and the outlook was not cheerful. All 

the work up to this time had 

been to the north on the supposition that the vein had 

been faulted in that direction . The new owners crosscut south at the No. 2 tunnel, 

which had been previously 

extended a little way, but 

had found nothing. The 

vein was picked up, but 

not much ore was encountered at first. They persisted, however, and within 

a year rich ore was cut on 

No. 2, and it was traced upward until it became easy to 

intercept the same body at 

No. 1. It was discovered 

that the former owners had 

been within 10 feet of the main ore body of the mine, which from that time until 

1897 was very profitable.

Nearly all of the ore of merchantable grade produced was taken 

from the stopes above the third level. A few bunches of high-grade 

ore were found down as far as the main tunnel, where one bunch gave 

the phenomenal assay of 125 ounces gold and 1,255 ounces of silver. 

This was very exceptional, and no ore has been found in quantity 

below tunnel No. 3. ' .

The rich ores of this mine did much to stimulate active prospecting 

in this region,-and it is probable that to it are indirectly due many 

of the other discoveries in the district.

Development and production. The vein is opened by four tunnels. 

Two of these are drifts on the vein and are located on the crest of the

FIQUKE 21. Sketch of ridge formed by the outcrop of the Golden 

Fleece vein. (Not to scale.)
B.WXETIN 478 PLATE VII

KINGS OF THE GOLDEN FLEECE AND BLACK CROOK MINES

1911
SAN CEISTOBAL GROUP. 107

ridge made by the outcrop. Below is a short crosscut tapping the 

vein at a slight angle. In and above these three upper levels are 

located the large stopes from which nearly all of the rich ore of the 

mine was taken at a maximum depth of not more than 400 feet from 

the surface. A shaft connects with the upper level west of the 

mouth. From the lowest of these three levels the vein was for some 

time worked through winzes, but later a long crosscut tunnel was 

driven 1,200 feet below the collar of the shaft. This intersected the 

vein and intermediate levels have been worked by means of it. (See 

fig. 22 and PL VII.)

According to Mr. George W. Pierce the mine produced $1,400,000 

up to 1904.

looo Feet

r Q..".V.-' :\r:-'-:i*-,---x.w.;&--f!

MAIN LOWER ADIT TUNNEL

Volcanic breccia Volcanic tuff Stopes Supposed location Rich tellurof telluride shoots Ide ore

(Foreman) (Foreman)

Mine workings

FIGURE 22. Longitudinal section of the Golden Fleece vein, showing position of agglomerate contact

and ore shoots.

Country rock and structure. The country rock of the Golden Fleece 

consists of a series of plainly stratified flow breccias interbedded with 

-volcanic tuffs and agglomerates. The planes of stratification are 

peculiarly well seen in the weathered rock, which is whitish and 

decomposed into a loose friable clayey material. In the lima workings, north of the Golden Fleece mine, these tuffs and breccias dip 

east, but in the Golden Fleece they are reversed to a strong westerly 

dip of 27°, which prevails through both surface workings and in 

depth.

Above the highest tunnel the fine-bedded tuffs and flow breccias 

give place to a conformable series of extremely, coarse agglomerates
108 GEOLOGY AND ORE DEPOSITS NEAR LAKE CITY, COLO.

containing subangular bowlders embedded in a yellowish tuffaceous 

matrix. Many of these bowlders ara several feet in diameter and constitute most of the rock, the matrix being greatly subordinate. They 

are composed of the same material as the finer tuffs and breccias 

below and in many places show well-marked banding, set at all 

angles according to the position of the bowlder at the time of deposition. This coarse agglomerate, which is very thick, was traced up 

the hill to beyond the upper tunnel, but its total thickness was not 

determined.

The contact of this agglomerate with the underlying beds is conformable, but, as explained below, is probably also a bedding fault. 

The vein throughout all of, the upper workings, where explored, terminates against this contact as a roof and nowhere enters the agglomerate itself. A tunnel was driven across the contact, into, though 

not through, this agglomerate, disclosing neither a different type of 

rock nor any evidence of mineralization.

The abrupt termination of the Golden Fleece vein against this 

plane has been the cause of much expensive exploration and has been 

explained in different ways by different observers. Kickard believes 

that owing to the different physical character of the coarse breccia 

and the underlying tuff the vein broke into minute stringers and 

never penetrated the coarse breccia. His description warrants 

quotation: 1

The outcrop ceases when the vein encounters the coarse breccia; so, also, in the 

underground workings the vein itself comes to an end with a suddenness which is, 

however, only comparative. The contact has been considered a fault; a good deal 

has been said concerning its regularity and clean-cut character. This, however, does 

not, I believe, accord with the facts. The so-called fault is not a break or dislocation 

in the rocks; it merely marks the division between the layers of fine-grained breccia 

and an overlying formation of very coarse breccia. There is no smooth plane or wall 

or defined parting between these two formations, but only a sudden transition, which 

at a distance is more marked than near by. * * * The contact existed before the 

vein was formed. The fracture, followed by the ore, passed easily through the finergrained rock, but ceased abruptly when it met the beds of coarse breccia, because the 

force of fracturing was not only insufficient to overcome the resistance of the harder 

fragments contained in the latter, but it must have been dissipated by the encounter 

with a loose-textured body of rock, much in the way that the power of a diamond drill 

becomes wasted in passing into a shifting mass of loose conglomerate. As a consequence the energy of shattering was diverted along the contact, the vein fracture 

ceased, and the later ore-depositing waters were barred from further advance into the 

coarse breccia, save as a scattering confined to the neighborhood of the contact. At 

the third level the ore body, occurring in the fine-grained country, was notably wider 

immediately at the "contact," and in examining the outcrop of the vein I noticed 

that it wa.. difficult to decide upon the exact line of separation between the two formations, because the mineralization extended from the fine into the coarse breccia so 

as to obscure the divisional plane.

i Op. cit., p. 346.
SAN" CRISTOBAL GROUP. 109

The writers can not agree with Rickard as to the nature of this 

plane. They were unable to note any points at which the ore actually 

entered the coarse breccia, but did, on the contrary, detect fragments of ore material included in the breccia along the line of 

division between the two series. In their opinion, therefore, the line 

of demarkation between the coarse breccia and tuff has been also the 

locus of a bedding fault which has occurred since the vein formation 

and has disturbed the continuity of the vein. Whether exploration 

will reveal the westward extension of the Golden Fleece vein in the 

coarse agglomerate or not can not be said, and it is doubtful if the 

different character of rock would permit its continuation with any 

degree of regularity, but the writers believe that the faulted portion 

exists and may yet be found.

Vein. As far as could be determined from the exposures seen and 

the specimens obtained, the vein of the Golden Fleece mine consisted 

of a mass of very irregular broken country rock with interstices 

filled with dense granular gray and white quartz and fragments 

intensely altered to a hard fine-grained silicious rock impregnated 

with petzite, tetrahedrite, and other minerals. This ore formed 

an irregular zone 8 or 10 feet in width, which from the superior 

hardness imparted to it by mineralization stood out in prominent 

outcrop above the surrounding rock. This outcrop was stained 

brilliant yellow, with here and there a reddish cast, both probably 

due to the presence of oxidized iron minerals and to the kaolinization 

of the clayey material in the tuffs. Some brick-red stains are also 

believed to be due to the presence of tellurous oxide.

The outcrop is now honeycombed by the work of leasers gouging 

around for the many small patches of high-grade ore found near the 

surface. In the upper levels the vein seems to have had no definite 

walls, but to have simply faded out into less broken and imminp.rfl.1- 

ized rock. In the lowermost levels (main tunnel level) it is a narrow but distinct filled fissure with fairly definite walls. The vein 

here could be clearly seen only in the face of the long tunnel, and 

consisted chiefly of light pink rhodochrosite, containing comparatively 

little metallic mineral.

From a wide broken zone at the surface the vein, as stated, narrows down in depth to a fraction of a foot. Between the main or 

adit tunnel level and the third level it could not be seen, and therefore its character could not be determined.

The vein in the lower levels shows the character of most of the 

veins of this region; that is, instead of remaining a single fissure it 

splits into a number of smaller fissures which separate more widely 

in depth and branch out from each other when followed along the 

strike. (See fig. 23.)
110 GEOLOGY AND OKE DEPOSITS NEAB LAKE CITY, COLO.

Ores. The ore from the Golden Fleece mine consisted of petzite, 

pyrite, argentiferous tetrahedrite, galena, hinsdalite,1 and pyrargite in 

a gangue of fine-grained gray and white quartz and some rhodochrosite. 

As the mineral hinsdalite is new, its association with telluride ores is 

interesting. The gray color of the gangue is in places due to the presence of minutely divided grains of petzite.

Of the metallic minerals, petzite is the most important and carried 

the chief gold values of the mine. Galena was scarce and gray copper fairly abundant. The latter mineral offered something of a contrast to its occurrence in other Lake City veins, as it rarely, if ever, 

contained more than $60 worth of silver per ton.

-- £-.^Outcrop Qf.

500 1000 Feet

FIGURE 23. Outcrop and branches of Golden Fleece vein.

The ruby silver came in irregular bunches, some of which are 

reported to have been found 1,200 feet below the surface; but they 

were very much more common in the zone of sulphide enrichment and, 

in the writers' opinion, are clearly of secondary origin. (See pp. 62-63.)

The proportion of gold to silver in the ore may be seen from the 

following record of carload shipments furnished by the management:

Precious metals in ore of the Golden Fleece mine.

Class of 

ore.

1

2

3

4

Gold.

Ounces.

134. 10

6.11

2.0

0.40

Silver.

Ounces.

3,077.0

238.0

53.0

15.0

Ratio by 

weight.

1:23

1:40

1:26

1:37

Ratio by 

value.

2:1

1:1

10:7

1:1

Hinsdalite is a new mineral described more in detail on p. 54.
SAN CEISTOBAL GEOUP. Ill

Apparently the richer ore had a slightly higher proportion of gold, 

but in general the ratio of silver and gold by value may be said to 

have been roughly 1:1.

Most of the rich ore of the Golden Fleece mine was shipped to the smelters, but 

the low-grade mill stuff was treated on the spot. As the values were chiefly contained in telluride minerals (principally petzite, but also some hessite), the treatment, by concentration, presents features of interest. The mill was of latest design, 

erected by Stearns, Roger & Co. It consisted of rolls for crushing, Huntington mills 

for regrinding, Wilfley tables for concentration, and a canvas plant for slimes. No 

use was made of amalgamation. The Huntingtons were provided with screens of 30 

mesh, and experience showed later that 20 mesh would have been better. In treating 18,000 tons having an average assay value of $10.25, half of which was in gold and 

half in silver, the extraction averaged between 45 and 60 per cent; 63 per cent was 

the best result. The concentrates contained 55 to 65 ounces of silver, 1 to 3 ounces 

of gold, and 12 to 18 per cent of lead, in the form of galena. The concentration was 

in the ratio of 12 to I. 1

The ore in the vein (see fig. 23) occurred in a shoot measuring about 

750 feet along the levels. As it was followed down, this shoot narrowed to a point below which only isolated bunches of ore were found. 

Within this shoot a more or less central interior shoot of unusually 

rich telluride ore is reported to have occurred, as indicated by the 

wavy black lines in figure 22. An extremely rich bunch of telluride 

was also found above the first level, west of the shaft, adjacent to the 

contact of the Overlying volcanic agglomerate.

It is notable that this ore shoot occupies nearly the position that 

would be taken by the trace of the intersection of the lima and Golden 

Fleece veins, but as this intersection could not be actually observed 

it is not possible to define its effect on the production of the shoot.

The depth of oxidation as affecting the transformation of tellurides 

into the native metals does not seem to have been great, but as no 

observations could be made in the upper stopes this must remain 

uncertain. Secondary enrichment, though apparently without effect 

on the tellurides, has undoubtedly led to the formation of the rich 

masses and bonanzas of ruby silver found here and there throughout 

the mine, presumably by the solution of the tetrahedrite and its 

later precipitation as the richer mineral pyrargyrite. The fact that 

bunches of this ore were found 1,200 feet below the surface shows that 

the surface water has been able to penetrate along cracks and crevices 

to considerable depth. The ore has without doubt originated chiefly 

from a replacement of the country rock and a subordinate amount of 

actual cavity filling.

BLACK CEOOK.

The Black Crook mine is on the eastern slope of the mountain 

which lies 2,400 feet west of the north end of Lake San Cristobal, 

north of and adjacent to the upper workings of the Golden Fleece.

i Bickard, T. A., op. cit., p. 346.
112 GEOLOGY AND OKE. DEPOSITS NEAR LAKE CITY, COLO.

It is approached from the main wagon road in the valley of Lake 

Fork by a wagon road which winds upward over the hill. The mine 

was operated intermittently for perhaps 12 years until about 1903.

Development. The outcrop of the vein runs along the brow of the 

hill 1,264 feet above Lake San Cristobal, bending westward more than 

the strike, owing to the westerly dip and the curve of the hill. The 

mine is opened by crosscut tunnels. Two of these run slightly north 

of west, tapping the vein near its southern end. The highest, known 

as the Capel crosscut, cuts the vein, which runs S. 30° W., at 150 feet 

below the outcrop at a slight incline. An incline shaft connects this 

crosscut with the lower levels, and through this the mine has been 

worked to a depth of 820 feet. From the upper workings profitable 

stoping has been carried on.

As in the Golden Fleece, Vermont, and many other mines, the difficulty of handling water and the added expense of mining at depth led 

to the driving of a long adit tunnel. Part of the long tunnel of the 

Golden Fleece mine adjoining this property on the south served for 

both mines. From this adit at a point 1,950 feet from the mouth, a 

branch known as the De Camp crosscut was driven, tapping the Black 

Crook vein 1,200 feet below the outcrop. This tunnel was then connected with the upper workings by a raise on the vein. Below this 

tunnel level a winze 100 feet deep was sunk and 240 feet of drifting 

was done. The results obtained by this deep and expensive work 

have been uniformly disappointing in this, as in the other mines of 

the district. The amount of drifting and stoping may be seen from 

the map of the workings (PI. VIII) and the longitudinal section 

(fig. 24).

Country rock. The country rock, in which the lima and Gold King 

veins of the Black Crook mine occur, belongs to the same series of 

bedded flow breccias and tuffs that are found in the Golden Fleece 

mine. The beds dip 15° to 40° E. and the veins intersect them at right 

angles. (See fig. 25.) In the upper levels the tuff is weathered into a 

yellowish-white banded rock whose stratified nature is so well developed as to strongly resemble sandstone. The beds vary from half an 

inch or less to 5 or 6 inches in width. None of the coarse agglomerate 

noticed in the Golden Fleece mine was seen in the Black Crook. 

Interstratified with the layers of tuff are denser though often equally 

(veil banded flow breccias, which when noted in the deeper mine 

workings are greenish or brownish gray hi color and can not easily 

be confused with the tuff. These flow breccias are much more extensively developed on the Golden Fleece tunnel level than in the upper 

workings of the mine.

Veins. The Black Crook mine owes the major part of its production to a single vein known as the lima vein. Other minor veins and 

branches have been somewhat explored, and a little ore has been
U. S. GEOLOGICAL SURVEY BULLETIN 478 PLATE VIII

PLAN OF UNDERGROUND WORKINGS OF BLACK CROOK MINE.

Showing the vein and the manner in which it has been faulted. Vein shown in heavy black, or in heavy dotted black where assumed.
SAN CEISTOBAL GROUP. 113

found along the Black Crook fault, but its amount has been trifling. 

The lima vein strikes nearly north and south; it shows many local 

deviations, and these are often sharply angular, as is the case with 

nearly all the Lake City fissures, but the average direction is remarkably straight.

/ /

II 1

Probably all 

stoped\out

\\A ^ SECOND DRirT

SECOND DRIFT

THIRD DRIFT

A FOURTH DRIFT

THIRD \ '. DRIFT

,'

/

/'

 ' MAIN DRIFT

f

'

1 '\ 

\

\

\

\ ,-, \ MAIN DRIFT

\

k .

1 *

\ o 100 200 300 400 sooFeet 

\ ' ' 

\___________

FIGUBE 24. Longitudinal section on plane of Black Crook vein.

The dip is toward the west. At the surface it was 70°, shallowed 

to 50° and 45°, then steepened again to 58°, which is its inclination 

in the lowest workings, 1,300 feet below the surface.

The vein has numerous branches, most of which make out from

the hanging wall. (See fig. 25.) The foot wall is much more regular

and is frequently separated from the vein filling by a strong layer of

selvage clay; this, however, is not constant. The vein is not a

95249° Bull. 478 11 8
114 GEOLOGY AND ORE DEPOSITS NEAR LAKE CITY, COLO.

simple filled fissure, but rather a series of. sheeting planes, in many 

places brecciated, which have been replaced by ore and gangue 

minerals so as to form what Ransome has termed a lode fissure. 

From one extreme, where all ore shows evidence of formation by 

replacement, to the other, where a narrow and well-defined filled 

fissure occurs with no discernible replacement, this vein furnishes 

examples of nearly all gradations.

The mineralized zone has a width of from 4 to 8 feet through much 

of the mine, but only in the older and more profitable stopes did this 

width pay for extraction, and then only in exceptional cases. The 

pay streak in the ore, where the mineralization had been most intense 

and the filling least confused by waste rock, averaged throughout 

the mine about 18 to 20 inches.

Fault. The lima vein is faulted by a well-defined east-west dip 

fault, called the Black Crook fault on account of its having been first

observed on the Black Crook claim. 

This fault dips 73° W. and has a reverse throw as it offsets the north 

end (the hanging-wall side of the 

fault) of the lima vein about 35 

feet to the west on each successive 

level. The fault is evidently later 

than the vein, as it is mineralized 

only where secondary oxidation and 

enrichment processes have been 

active since surface alteration of 

the vein began.

Ores. The ore of the Black Crook 

consists of sphalerite, galena, a little 

tetrahedrite, pyrite, and very subordinate chalcopyrite with irregular bunches of pyrargyrite in a gangue 

of quartz, barite, and rhodochrosite. The pyrite usually is in small 

amount in the ore, though it frequently impregnates the country rock 

and is then present in well-defined cubical crystals. The most constant mineral is sphalerite, which is but rarely absent in any of the ore 

and in some stopes is so abundant that the term "zinc stope" has 

been applied to them. It is usually of the coarse cleavable variety and 

contains enough iron and impurities to make it rather dark in color. 

An average of 158 samples taken on all levels of the mine showed 3.20 

per cent lead and 15 per cent zinc; this gives a fair idea of the general 

content of the ore in sphalerite and galena. Dark ruby silver, pyrargyrite (Ag3SbS3 ), occurs in bunches through the ore and its relations 

to the other ore clearly prove it to be secondary as it coats cracks 

and fractures in the ore, especially that which runs high in the argenFIGUEE 25. Type of fissure in Black Crook 

(lima) mine.
SAN CEISTOBAL GROUP. 115

tiferous tetrahedrite. Enrichments by pyrargyrite occur in even the 

lowest workings of the mine, 1,300 feet below the outcrop, but their 

number is greatly diminished.

The silver values were contained primarily in the galena and tetrahedrite, chiefly in the latter, but have been redistributed as native 

silver and pyrargyrite by the action of oxidation and secondary 

enrichment. In the oxidized ore of the upper workings a very considerable amount of native silver was found.

Banding is not very well developed, as the ore is chiefly massive, 

irregular, and filled with innumerable horses and fragments of countryrock. Where it is at all well marked it is the result of the replacement 

of sheeted rock rather than of the successive deposition of minerals 

in open space.

A peculiar brownish-green, massive, fine-grained pyrite, locally 

known as "brown iron," was found in most of the upper workings

of the mine, and is said to have run very high in gold. Four specimens of this ore left for only a few weeks in paper trays completely 

corroded the paper by the uncombined sulphuric acid, showing the 

ore to consist of sulphates, sulphuric acid, and pyrite. Probably 

much of this pyrite is secondary and the high values in gold were 

undoubtedly the result of secondary concentration. It does not occur 

below the upper workings of the mine. There is little or no question 

that the workable values of the Black Crook ore have been entirely 

produced by oxidation and secondary enrichment, for the lower 

workings show only primary minerals in small amount and low values. 

All of the rich minerals are of characteristic secondary types, and 

extensive exploration has failed completely to show values that justify 

the continuation of mining operations. The width of many of the 

stopes may also indicate that secondary minerals have been deposited 

not only within the area of the original vein minerals, but also in the 

wall rock, which they may have invaded and replaced in their downward progress, materially increasing the ore masses both in size and 

in richness of contained values.

The paragenesis of the primary minerals, here -as elsewhere, is 

obscure, but the metallic minerals seem to have been among the 

earlier formed, and of these the sphalerite and galena seem older than 

the richer tetrahedrite. The pyrargyrite and native silver are 

unquestionably secondary.

The ore in the mine, even with the aid of the assay plan kindly 

furnished by the management, does not show any well-defined localization. If such localization exists, it has somewhat the position 

shown in figure 24.

To the writers the evidence seems conclusive that further exploration in depth on this vein would fail to reveal any bodies of ore that 

could meet the expense of development.
116 GEOLOGY AND ORE DEPOSITS NEAR LAKE CITY, COLO.

The average value of the ore in the Black Crook mine is difficult 

to determine, as no authentic records of the earlier work could be 

secured. Much of it was undoubtedly high grade, as shown by the 

mint report for 1884. During three months' active production in that 

year the mine yielded 1,277 tons of ore, valued at $124,447, an average of $97.21 per ton. Statements of the superintendent put the 

average yield of this upper ore at 21 ounces silver and 3 ounces gold. 

Much very high-grade ore was undoubtedly included in this average, 

for many small bonanzas and bunches of secondary ruby silver 

yielded from $200 to $600 per ton and in instances gold values ran 

as high as 12 to 15 ounces, but the average seems to be fairly close 

to $100 per ton.

With increase in depth, the value of the ore fell off rapidly, much 

of it averaging not more than $35 per ton in gold and silver. A 

careful sampling recently made shows that the average value of the 

ore now remaining in the mine is much below the bonanza values of 

its early operation.

The values in the ore show no relation to the Black Crook fault, 

as the higher values occur more frequently at a distance from it than 

in its immediate neighborhood. If any connection can be detected 

at all, it is in the direction of impoverishment and not of enrichment.

SOUTH FORK OF HENSON CREEK. 

MORO.

The Moro mine (see fig. 26) is located about 1£ miles in a direction 

S. 60° E. from Capitol City. The mine is operated by the Hanna 

Mining & Milling Co. The openings are on the Moro claim on the 

south side of a small east-west gulch, which heads westward from 

the South Fork of Henson Creek.

Equipment. The Moro is connected with Capitol City by a trail 

about 1£ miles long, over which supplies are brought to the mine. 

Recently a wire-rope tramway was installed, connecting the mine 

openings with the mill in the bed of the South Fork of Henson Creek, 

1,200 feet below the mine and at the mouth of the gulch in which the 

mine is located. The ore was formerly shipped to the smelter, but it 

is now treated in the mill owned and operated by the company. 

The mill has a capacity of 100 tons per 24 hours, and treats not only 

the ores mined in the company's own property, but also undertakes 

custom work from the mines in the neighborhood of Capitol City. 

In 1906 this mill was much enlarged, and now contains rolls, Huntington mills, concentrating tables, slimers, a system of settling 

tanks, and a Blake-Morscher static electric machine for handling the 

zinc concentrates. Power is supplied by the Capitol City Power & 

Electric Co.
SOUTH FOBK OF HENSION CKEEK. 117

Capitol City

Development A fissure vein worked in the mine is opened by three 

tunnels which run into the hill in a direction about S. 15° W., and 

connect with the first, second, and third levels, respectively. (See 

diagram, fig.*27.) 

The first, or uppermost, level opens directly on the vein and 

runs into the hill for 

500 feet; 200 feet 

from the mouth it 

connects with an old 

shaft, by means of 

which the vein was 

first operated. The 

second level has been 

driven 71 feet below 

the first, directly on 

the vein; it runs in to 

the hill for 570 feet. 

The third, or lowest, level is 126 feet below the second. For the first 

75 feet it runs S. 60° W. and cuts through barren rock; it then 

encounters the vein and runs along it for 700 feet. At a point 200 

feet from the breast the third level is connected with the other two 

levels by an inclined raise on the vein. A number of short drifts 

have also been run on branch veins on the third level.

FIGURE 26. Sketch showing location of Moro and Hendrison claims.

FIGURE 27. Longitudinal section of the Moro mine, showing depth of anglesite alteration.

Country rock. The country rock of the region consists of the lower 

members of the Picayune volcanic group of banded flow breccias. 

The banding is caused by the movement of the lava previous to con-
118 GEOLOGY AND ORE DEPOSITS NEAR LAKE CITY, COLO.

solidation. When fresh the flow lines can be seen only indistinctly 

and on close examination, .but when weathered they become very 

prominent and may be seen to be caused by innumerable dark inclusions arranged with their longer axes in the direction of flow. The 

banding is generally horizontal or inclined at a very slight angle. 

The inclusions are usually darker and finer grained than the matrix 

of the rock, and undoubtedly represent the quickly chilled coating 

formed on the surface and later broken and included in the slowly 

moving lava mass. Many of them are markedly chloritized even at 

great distances from the site of mineralization. In some places this 

wall rock shows fewer flow lines, especially in the thicker members, 

and is characterized by well-marked porphyritic texture, caused by 

the presence of numerous small phenocrysts of plagioclase feldspar,. 

The distribution of shoots and vein material in the mine is independent of the banding of the lavas, for there is no tendency toward a 

horizontal variation of mineral material; and it is therefore probable 

that the layers of andesite have had little or no effect on the ore

deposition. Cross mentions (p. 

23) a small exposure of granite 

at the mouth of the gulch near 

the mill, which indicates that 

the Picayune volcanic group is 

nearly cut through here by 

Henson Creek, and it is possible 

that this formation lies less 

than 1,500 feet below the 

lowest level of the mine. 

Vein. The ore deposit is a typical fissure vein well defined and 

with clean walls in the upper levels, but becoming irregular and

stringer-like in the lower levels.

The vein matter in the first level is contained between well-defined 

and quite smooth hanging and foot walls, but contains a great many 

angular fragments of wall rock. Some parallel stringers of quartz 

occur in the wall rock. (See fig. 28.) Locally the vein splits into 

stringers and includes too large quantities of wall rock to permit its 

profitable operation.

On the second level and to a still greater degree on the third level 

the vein is divided into many stringers, some of which make off into 

the foot wall as branches. On the third level the vein is so broken 

up into stringers that it is difficult to follow, and the crosscut 

intended to intersect it was extended far beyond it without recognition. Beyond the crosscut the vein consists of a series of veinlets en 

Echelon running at about 10° to 15° to the general trend of the lode. 

(See fig. 30). The dip of the vein at the surface and on the first and

FIGURE 28. Face of Moro tunnel, first level, showing 

structure of lode, a, County rock; 6, quartz; c, clay 

selvage; d, galena and quartz; e, barlte.
SOUTH FORK OF HENSION CREEK. 119

second levels ils 66° E.,'but this steepens to 78° on the third level. (See 

fig. 29.)

In strike the vein is extremely irregular, as may be seen from the 

plot of ,the workings (fig. 31). Most of the bends are quite angular 

as if caused by the intersections of branching fissures.

This vein is undoubtedly the same as that extensively worked on 

the north side of the gulch. Its total length, as worked on both 

properties, approximates 2,000 feet.

Ores. The ore of this mine when unoxidized consists of galena, 

sphalerite, chalcopyrite, 

pyrite, and tetrahedrite 

in a gangue of white 

glassy crystalline quartz 

with subordinate barite.

The galena is by far the 

most abundant mineral 

and constitutes the chief 

product of the mine. It 

is generally coarse, with 

single cubical cleavage 

masses up to an inch 

across, but in places it has 

the usually fine-grained 

appearance of steel galena. It is everywhere much crushed and often 

shows twinning due to stress. It is also generally characterized by 

curved cleavage faces. Many of the stopes consist of this coarse 

galena, with but little else present, although bunches of sphalerite 

occur here and there through it. The sphalerite varies from almost 

lemcn yellow to nearly black and where present is usually intermixed with the chalcopyrite in the ore, indicating that it was precipitated simultaneously with that mineral. The argentiferous tetrahedrite is 

in far less amount than is common in 

the ores of this region, showing only 

here and there through the ore. The 

metallic minerals of the ore are often 

much shattered and cut by innumerable little veinlets of white glassy quartz, which frequently show a 

very perfect comb structure and form inclosing crusts around the 

shattered fragments. (See fig. 32.) Between the combs of quartz 

are thin bands of a reddish mineral, apparently hematite, which form 

a. delicate tracery that seems to much emphasize the banded nature 

of these crusts. It is stated by the management that where these fine 

reddish crusts are present the ore generally contains notable values 

in gold, and it may be that the increased gold values and reddish

FIGURE 29. Cross sections of the Moro vein on lines indicated 

in figure 31. a, Anglesite In zone of oxidation; 6, primary 

ore; c, fraying out of vein on third level.

FIGURE 30. Manner in which Moro vein 

crosses fissures diagonally on lower level.
120 GEOLOGY AND ORE DEPOSITS NEAR LAKE CITY, COLO.

mineral are both due to secondary precipitation. Vugs of considerable size and in large numbers are thus produced in the ore, and these 

are usually lined with white quartz crystals and some beautiful 

bladed crystals of barite.

The primary ore of the upper level stopes consisted almost wholly 

of galena, which carried an average silver content of 10 to 17 

ounces. The chalcopyrite and sphalerite were most commonly associated with subordinate amounts of galena. The average yield of 

the lower-grade ore from the upper levels is stated to -have been 

10 to 17 ounces silver, 10 to 15 per cent lead, 4.4 per cent copper, and 

6 to 15 per cent zinc, giving a total average value of $30 a ton.

FIGURE 31. Plan of workings of the Moro mine. (See fig. 29 for cross sections.)

This ore carried only very small and usually insignificant quantities 

of gold. The primary ore in the third level shows a marked change,

containing much more chalcopyrite, pyrite, and sphalerite, and 

yielding correspondingly higher gold than the ore from the first and 

second levels. Some of the ore here assayed 0.5 to 3 ounces gold, 10 

to 16 ounces silver, 7 to 30 per cent lead, 7 to 10 per cent zinc, and 

2 to 4 per cent copper.

The primary vein filling is separated, in the upper levels, from the 

hanging and foot walls by a well-defined layer of selvage clay onehalf inch to 3 inches in thickness, making the ore comparatively 

easy to mine.

Except that the quartz is of later origin than the metallic minerals 

the paragenesis can not be clearly made out. It seems probable 

that the barite is the later of the two gangue minerals as it comes 

often in bladelike crystals in cavities. Banding is not well developed 

in the metallic ore of the upper levels as the quartz runs through so 

much of the metallic ore in little veinlets, but a central vug filled
SOUTH FOKK OF HENSION GREEK. 121

FIGURE 32. Ore from the 

Moro mine, showing certain features of the paragenesis of the minerals. 

sp, Sphalerite; eft, chalcopyrite; g, galena; q,

quartz; ft, hematite.

with barite is often present. (See fig. 28.) In the lower levels banding is more prominent (fig. 33).

Secondary alteration. The surface alteration of this vein is extremely interesting. Oxidation has altered the ore to a dense grayishwhite noncrystalline anglesite (PbS04) for about 

200 feet from the surface (see fig. 27); the carbonate, cerusite, is practically unknown in the 

mine. The anglesite in a quartzose gangue, extends in from the surface for 180 to 200 feet. 

The line which separates it from the sulphide ore 

is sharp and follows very closely the contour of 

the hill. As the sulphide zone is approached 

little nuclei of original primary galena may be 

seen in the ore, and the structural arrangement 

of the galena ore is perfectly preserved in the

anglesite.

Below the oxidized anglesite ore considerable enrichment of the ore 

by secondary copper sulphides is manifested by beautiful blue coatings of covellite on the fracture surfaces of the sphalerite. This sphalerite when fresh has a brilliant vitreous 

luster and yellowish-brown color, but 

when broken with a light tap of the 

hammer it falls to pieces along the innumerable fractures which were formed 

prior to the secondary deposition. 

These are so completely coated with 

covellite that it is at first difficult to 

distinguish it from that mineral, but 

when care is taken to break into the 

mineral itself along cleavage planes 

not previously opened its true character 

is apparent.

Considerable black sooty chalcocite is 

also deposited in the ore, but this is confined almost wholly to fractures and 

cavities in the chalcopyrite, while pyrite 

is confined to some surfaces of the 

galena. Some of the sphalerite is also 

covered along fracture planes with a 

gray coating which is believed to be 

galena but which, because of its fine 

grain, is difficult to identify positively 

even under the high powers of the microscope. The minerals indicate 

.that the workings of the mine have not yet penetrated below the 

zone of surface alteration, but already the vein, like others in the

FIGURE 33. Face in -the Moro tunnel, 

showing structure of lode, a, Massive 

galena and quartz, irregularly mingled; 

&, quartz veinlets with well-developed 

comb structure; c, altered country rock 

with veinlets of galena and quartz; <f, 

narrow band of intensely silicifled country rock now altered to aggregate of 

quartz granules; e, blackened silicifled 

country rock; /, darkened and partly 

altered country rock; g, andeslte flow 

breccia.
122 GEOLOGY AND ORE DEPOSITS NEAR LAKE CITY, COLO.

district, shows not only marked impoverishment even in the 500 

feet of vertical distance so far disclosed, but also every indication of 

fraying out and disappearing. It holds no greater promise of profitable deep exploration than do the other veins.

HENDRISON CLAIM.

The Hendrison workings are directly north of the Moro on the opposite side of the gulch. The vein is unquestionably a continuation of 

the Moro and is in every respect similar to it. A tunnel has been run 

on the vein for 400 feet. The ore carries a higher content of zinc than 

that portion of the vein worked in the Moro and is also very much 

more noticeably enriched by pulverulent secondary chalcocite.

PROSPECTIVE GOLD AREA.

Some exploration for gold is being carried on. The Sunshine 

Lode in Larson Creek is said to show assay values of from $1 to 

$10 per ton, but as no shipments have been made, it is not possible 

to say just what value can be placed upon these assays. The lode 

itself does not look very promising, but has not been developed 

enough to disclose its true value. The Golden Crown prospect and 

others in the area are practically undeveloped, and so little can be 

said of them, except that they are very narrow veins of quartz, 

showing few metallic minerals arid these chiefly pyrite. The T. C. 

M. Tunnel is being driven to cut at depth several veins which outcrop 

near Larson Creek, but at present (1908) only reported assays showing total values from $1 to $6 in lead, silver, and gold, can be cited. 

No shipments have been made. The outcrops do not appear to be 

very highly mineralized, although greatly decomposed.

BIBLIOGRAPHY.

There are few publications on the Lake City district. The following bibliography includes practically all of the literature bearing 

directly on the region:

1874 to present. Engineering and Mining Journal, weekly publication. Many

notes, usually from correspondents, on the history, development, production,

etc., of the Lake City mining district. 

1880. Emmons, S. F., Tenth Census, vol. 13, p. 86. Gives a table showing kind

of country rock, ore, and gangue minerals, and dip and strike of veins in eight

mines in Hinsdale County. 

1887. Comstock, T. B., Geology of vein structure of southwestern Colorado. Trans.

Am. Inst. Min. Eng., vol. 15, pp. 218-265. Refers to the Lake City region in

a very casual manner, giving no definite information on it. 

1887, 1888, 1889,. 1890, 1891, 1892. Reports of the Director of the Mint. Contain

statistics of production of individual mines, 1887-1892; also brief notes on the

operations, development, etc., of the various properties.
BIBLIOGRAPHY. 123

1889. Schwarz, T. E., Ore deposits of Bed Mountain, Ouray County, Colo. Trans.

Am. Inst. Min. Eng., vol. 18, p. 140. Mentions the district in connection with

several contiguous Colorado areas. 

1901-2. Report of commissioner of mines, State of Colofado, pp. 93-97. Gives brief

sketch of history, geology, mines, and minerals of Hinsdale County.

1903. Rickard, T. A., Across the San Juan Mountains, pp. 72-77. Contains a description of the Golden Fleece mine, Hinsdale County.

1904. Irving, J. D., Ore deposits in the vicinity of Lake City, Colo. Bull. U. S. 

Geol. Survey No. 260, pp. 78-84. Gives brief account of the mining district 

and a short sketch of the history, geology, and ore deposits.

1880-1908. Mineral Resources of the United States. Contains a few references to 

mines in Hinsdale County, during various periods.

INDEX.

A.

Page. 

Abbott, J. J., work of....................... 9

Acknowledgments to those aiding........... 9

Andesite, distribution and character of...... 31

B.

Banding, cause and effect of:................ 45

Barite, distribution and character of......... 53

Bibliography, of Lake City district........ 122-123

Bismuth compounds, character and occurrence of......................... 53

Black Crook mine,character and location of. 111-116 

country rock of.......................... 112

development of.......................... 112

fault of lima vein at..................... 114

ores and production of................. 114-116

type of fissure in, figure showing......... 114

veins of................................ 112-114

workings of, plates showing............ 106-112

Black Crook vein, longitudinal section on, figure showing..................... 113

Bornite, distribution and character of....... 64

Burns latite tuff, distribution and character

of............................... 27-28

C. 

Calcite, distribution and character of........ 60

Capitol City, mines near, descriptions of..... 72-81

mines near, list of....................... 17

Capitol City mine, development, location, and

ores of........................... 77-78

Carson, mines near, list of................... 17

Chalcopyrite, distribution and character of.. 58-59 

Chord extension, development and minerals

in............................... 79

Climate, character of........................ 12

Contention claim, location of, map showing.. 103

See also Contention mine.

Contention mine, character and location of. 102-104 

country rock at.......................... 103

development and production of........ 102-103

ores of................................. 103-104

vein at.................................. 103

Country rock, effect of, on mineralization.... 46

Covellite, distribution and character of...... 64

Czar mine, character and location of......... 76-77

country rock of.......................... 76

development and production of......... 76

ores of................................... 77

veins of................................. 77

Czarina prospect, location and development

of............................... 80

D.

Page. 

Dauphin workings, ore at................... 101

Deadman Gulch, decomposed porphyry of.. 32 

Decomposed porphyry of Deadman Gulch,

distribution and character of.... 32

Dimensions of lodes, table showing.......... 39

Dip of lodes, direction of.................... 42

Disintegration, mechanical, in lodes, cause

and effect of..................... 38-39

Dolomite, distribution and character of...... 60

E.

Erosion, relation of, to superficial alteration,

figure showing................... 40

Eruptions, in San Juan Mountains, time of.. 19 

Eureka rhyolite, in Lake City district, distribution and character of....... 26-27

in San Juan Mountains, distribution and

character of...................... 20-21

Excelsior mine, character and location of.... 74-76

country rock of.......................... 75

development of.......................... 75

history and production of................ 74-75

ores and veins of........................ 75-76

F.

Faults, effect of, on lodes.................... 43

Field work, character of..................... 9

Fissure filling, effect of...................... 44

Forked-lightning fissure vein, figure showing. 42

G.

Galena, distribution and character of........ 56-57

infiltrated with quartz, figure showing... 93 

Gallic-Vulcan claims, character and location

of............................... 72-74

country rock of.......................... 73

development and equipment of.......... 73

history and production of............... 72-73

ores of................................... 74

veins of................................. 73

Geology, general features of.................. 18-32

Geography, general features of............... 10-12

Gold, precipitation of, by zinc sulphide...... 64

prospecting for.......................... 122

Golden Fleece mine, condition of.......... 104-111

country rock and structure of.......... 107-109

development and production of........ 106-107

location and history of................. 105-106

ores of................................. 110-111

veins of................................. 109

workings of, plate showing.............. 106

125
126 INDEX.

Golden Fleece vein, longitudinal section of,

figure showing................... 107

outcrop and branches of, figure showing. 110

Golden Wonder mine, location, production,

and ore deposits of............. 101-102

H.

Hendrison claim, location of, map showing.. 116 

workings and ores at.................... 122

Henson Creek, plates showing............... 12,22

mines near, descriptions of.............. 81-99

listof............................... 17

Henson tuff, in Lake City district, distribution and character of............ 28-29

in San Juan Mountains, distribution and

character of...................... 21

Hidden Treasure mine, character and location of........................... 86-94

country rock of.......................... 89-90

equipment of............................ 94

ore bodies of............................. 90-94

paragenesis of....................... 92

veins containing..................... 90-92

ores, character of........................ 92-94

production of........................ 92

values of............................ 92-93

Ute vein at, dip and strike of............ 90-91

movement in........................ 91

width of............................. 91-92

workings and outcrops at, plate showing. 8g 

Hidden Treasure vein, longitudinal section of, 

figureshowing.................. 88

Hinsdale County, production of, curve showing.............................. 16

Hinsdale volcanic series, of Lake City district, distribution and character 

of............................... 29-30

of San Juan Mountains, distribution and

character of..................... 22

Hinsdalite, character and analysis of........ 54

from Golden Fleece mine, figure showing. 54 

History of Lake City mining region, general

features of....................... 12-14

I.

lima mine. See Black Crook mine.

Intersection of lodes, example of............ 43

Intrusive rocks, of Lake City district, character, distribution, and subdivisions of......................... 30-32

Labor, cost of............. ............. 70

Lake City,plate showing.................... 12

Lake City district, future prospects of....... 68-69

geology of............................... 22-32

Hinsdale volcanic scries of............... 29-30

index map showing..................... 10

intrusive rocks of........................ 30-32

ore deposits of, general features of........ 37-68

geologic relations of................. 32-37

lodes containing..................... 37-45

mineralization of.................... 45-51

mineralogy of....................... 51-65

pay shoots of, characteristics of...... 65-66

summary of conclusions regarding ., 67-68

Page. 

Lake City district, ores of, value of........... 66-67

See also Lodes, Mineralization, Mineralogy. 

Picayune volcanic group in ............. 24-26

Potosi volcanic series of................. 29

publications on....................... 122-123

Sil verton volcanic series of.............. 24-29

Lake City lodes, dimensions of............. v 39-41

Lake City quadrangle, claims in, map showing.............................. 10

location of............................... 10-11

southern part of, geologic map of........ 18

Lake Fork, plate showing................... 102

Lake San Cristobal region, map showing..... 105

Lellie mine, character and location of........ 81-84

country rock of.......................... 83

development and production of......... 82

ores of................................... 84

veins of................................. 83-84

workings and outcrops of veins of, figure 

showing............................... 82

Lellie vein, face of, figure showing........... 86

irregularities in, figure showing.......... 84

longitudinal section of, figureshowing... 85 

outcrops and workings on, figure showing.............................. 82

Lilly adit, elevation of...................... 79

Lodes, character of.......................... 37-45

dimensions of........................... 39

distribution of.......................... 43-45

dip of................................... 42

faults in................................. 43

intersections of.......................... 43

mechanical disintegration in............ 38-39

origin of................................. 43

strike of................................. 41

terminations of.......................... 41-42

Lode Star mine, workings and minerals of... 101 

Lucky Strike tunnel, development of........ 80-81

M.

Mayflower claim, location of, map showing.. 103 

See also Contention ,mine.

Mechanical disintegration of lodes, cause

and effect of..................... 38-39

Metasomatism, nature of.................... 44

Milling, at Ute and Ulay mill, diagram showing.............................. 95

Mineral groups, characteristics of............ 46-48

quartz-galena-sphalerite group, distribution and character of............. 47-48

telluride group, distribution and character of............................ 48

tetrahedrite-rhodochrosite group, distribution and character of.,......... 47

Mineralization, character of.................. 45-51

comparative abundance of mineral groups

in............................... 46-48

effect of country rock upon.............. 46

source of................................. 48-51

Mineralogy, general features of............... 52-65

of primary minerals..................... 52-60

of secondary minerals.................... 60-65

Minerals,classification of, according to depths. 52-60 

comparative abundance of............... 46-48

groups of . :............................. 46-47
INDEX. 127

Page.

Mines, detailed descriptions of.............. 72-122

productive, list of........................ 16-18

Mining, cost of labor for...................... 70

extraction of values in................... 71-72

generation of power for.................. 69-70

methods of.............................. 70-71

Mining conditions, general features of........ 69-72

Mining districts, official boundaries of........ 11-12

Missouri Favorite mine, character and location of........................... 98-99

development and production of.......... 98

location of, plate showing................ 22

ores of................................... 99

veins of.................................. 98-99

Monte Queen mine, longitudal section of,

figure showing................... 100

ores, veins, and workings at............ 99-100

Monte Queen vein, section showing.......... 99

shoots within shoots at, figure showing.. 101

Moro mine, character and location of....... 116-122

country rock at........................ 117-118

development of.......................... 117

equipment of.......................... 116-117

location of, map showing................ 116

longitudinal section of, figure showing... 117 

ore from, figure showing................. 121

ores of................................. 119-121

secondary alteration at................ 121-122

vein at................................ 118-119

workings of, figure showing.............. 120

Moro tunnel, face of, figure showing......... 118

lode structure in, figure showing......... 121

Moro vein, sections of, figures showing....... 119

N. 

Nellie M. mine, location and ores of........ 100-101

North Lake Fork, mines near, list of......... 17

O.

Ocean Wave group of claims, map showing.. 87 

Ocean Wave mine, workings and outcrops of

.veins of, figure showing.......... 82

Ore deposits, character and distribution of.. 32-68 

geographical continuity of............... 32-33

in Lake City district..................... 37-68

in San Juan Mountains.................. 32-37

Ores, value of................................ 66-67

value of, from Golden Fleece mine....... 67

Ottawa prospect, location and development

of................................ 80

Oxidation products, distribution and characterof............................ 61-62

P.

Pay shoots, types and locations of........... 65-66

Pelican drift, face of, figure showing .......... 97

Pelican mine, character and location of...... 95-98

country rock of.......................... 96

development and production of.......... 96

ores of................................... 97-98

veins of................................. 96-97

Picayune volcanic group, in Lake City district, distribution and character 

of............................... 24-26

in Lake City district, occurrence of....'.. 24

typical exposures of................. 25-26

volcanic source of................... 24-25

in San Juan Mountains, composition of.. 20

Page. 

Potosi volcanic series, of Lake City district,

distribution and character of..... 29

of San Juan Mountains, distribution and

character of..................... 21

Power, generation of, for mining............. 69-70

Precious metals, grades and values of, table

showing......................... 67

Pride of America mine, location and ores of.. 81 

Primary minerals, varieties and characteristics of.......................... 52-60

varieties of, found at all depths.......... 55-60

found near surface................... 52-55

Production of Lake City mining region, statistics of......................... 14-16

Proustite, distribution and character of..... 62-63

Publications, on Lake City district, list of.. 122-123 

Pyrargyrite, distribution and character of.... 62-63

Pyrite, distribution and character of......... 55-56

Pyroxene andesite, in Lake City district, distribution and character of....... 28

in San Juan Mountains, distribution and

character of..................... 21

Q.

Quartz, distribution and character of........ 60

Quartz-galena-sphalerite group, distribution

and character of................. 47-48

Quartz latite, distribution and character of.. 31 

Quartz monzonite porphyry, distribution

and character of................. 31

Red Rover mine. See Lellie mine. 

Rhodochrosite, distribution and character of. 53-54 

Rhyolite and quartz latite, distribution and

character of..................... 30-32

Rob Roy workings, ore at................... 101

Roundtop Mountain, plate showing......... 22

S.

San Cristobal group of mines, descriptions of. 99-116 

San Juan Mountains, geology of............. 18-22

Hinsdale volcanic series of............... 22

ore deposits of, general features of........ 32-37

genesis of............................ 33-35

geographical continuity of........... 32-33

mineralogical similarity of........... 35-37

mineralogy of, table illustrating..... 34-35

Potosi volcanic series of.... 1............ 21

San Juan tuff of......................... 19-20

Silverton volcanic series of............... 20-21

volcanic activity in...................... 19

San Juan tuff, character and thickness of.... 19-20

Scotia group of claims, location of, plate showing.............................. 87

Secondary chalcocite, distribution and character of.......;.................. 63

Secondary galena, distribution and character

of............................... 64

Secondary minerals, distribution and varieties of........................... 60-65

oxidation products among............... 61-62

precipitation of, due to sphalerite........ 64-65

secondary sulphide enrichment of....... 62-64

Secondary sulphide enrichment minerals,

varieties and characteristics of... 62-64
128 INDEX.

Page.

Sllverton volcanic series, of Lake City district, character and subdivisions 

of............................... 24-29

of San Juan Mountains, character and

. subdivisions of.................. 20-21

South Fork of Henson Creek, mines near,

listof.......................... 17

mining development along............ 116-122

Sphalerite, distribution and character of...... 57-58

precipitation due to..................... 64-65

Strike of lodes, direction of.................... 41-42

Sulphides, solubility of, effect of, on precipitation. .......................... 65

solubility of, order of.................... 65

Sulphuret workings, ore at................... 101

Superficial alteration, relation of erosion to,

figureshowing................... 40

T.

Telluride group, distribution and character of. - 48 

Tellurides, distribution and character of...... 59-60

Terminations of lodes, character of........... 41

Tetrahedrite, character and analysis of....... 52

Tetrahsdrite-rhodochrosite group, distribution and character of............. 47

Timber, character of......................... 12

Topography, character of.................... 11

U.

Ute and Ulay mill, treatment at, diagram

showing......................... 95

Ute and Ulay mine, character and location of. 86-95 

country rock of.......................:-.. 89-90

development of.......................... 86-88

equipment of............................ 94-95

Page.

Ute and Ulay mine, ore bodies of, character of. 90-94 

ore bodies of, paragenesis of.......... 92

veins containing..................... 90-92

ores, character of......................... 92-94

production of........................ 92

values of............................. 92-93

Ute vein at, dip and strike of............. 90-91

movement of........................ 91

width of............................. 91-92

workings and outcrops at, plate showing. 86 

Ute-Hidden Treasure veins, figure showing... 42 

Ute vein, character and position of.......... 90-92

dip and strike of......................... 90-91

Galena from, figure showing.............. 93

movement in............................ 91

, width of................................. 91-92

V. 

Values, extraction of......................... 71-72

Vermont group of claims, map showing....... 87

Vermont mine, character and location of...... 85-86

development and production of.......... 85

ores of................................... 86

Volcanic activity, in San Juan Mountains,

time of.......................... 19

W. 

Water power, availability of................. 69-70

Wave-of-the-Ocean group of claims,- map

showing......................... 87

West Lake Fork, mines near, list of........... 17

Woodstock prospect, development and production of....................... 79

Y.

Yellow Medicine mine, location, production,

vein, and workings of............ 78-79

o