UNITED STATES DEPARTMENT OP THE INTERIOR 

Harold L. Ickes, Secretary

GEOLOGICAL SURVEY 

W. C. Mendenhall, Director

Professional Paper 178

GEOLOGY AND ORE DEPOSITS

OF THE

MONTEZUMA QUADRANGLE, COLORADO

BY 

T. S. LOVERING

Prepared in cooperation with the

STATE OF COLORADO, COLORADO METAL MINING FUND

COLORADO MINING ASSOCIATION, AND GEOLOGICAL

SURVEY BOARD OF COLORADO

UNITED STATES

GOVERNMENT PRINTING OFFICE 

WASHINGTON : 1935

For sale by the Superintendent of Documents, Washington, D. C. ------- Price $1.25

CONTENTS

Abstract._ ________________________________________

Introduction ______________________________________

Field work and acknowledgments. ______ i_ _______

Location and population________________________

Topography and drainage--____________----___-_

Climate and vegetation_________________________

Industries, power, and transportation____________

Bibliography ____________________________ ______

Descriptive geology_________-___________-------_-__

Algonkian (?) formations. ______________________

Idaho Springs formation.___________________

Swandyke hornblende gneiss.______-__-_--__

Algonkian system..____________________________

Quartz monzonite gneiss.___________________

Granite gneiss._____-__-______-_____-___--_

Quart/diorite and associated hornblendite___ 

Pikes Peak granite.________________________

Silver Plume granite.______________________

Pegmatites.. _--_-__--_-__--_--_-----_-----

Sedimentary formations________________________

Carboniferous system (Pennsylvanian(?) and 

Permian series)___________________ _!______

Maroon formation _____________________

Jurassic system (Upper Jurassic series) _______

Morrison formation ____________________

Cretaceous system (Upper Cretaceous series) _. 

Dakota quartzite.____________----_-_-_

Benton shale__________________________

Niobrara limestone...__________-_-__-_-

Pierre shale.__________________________

Quaternary deposits and topographic evolutionEocene land surface..___________________

Late Tertiary land surface._____________

Early Pleistocene t6pography___-________

Early Pleistocene deposits.______________

Late Pleistocene topography ____________

Late Pleistocene (Wisconsin) deposits....

Recent topography.____________________

Recent deposits..______________________

Cretaceous (?) and Tertiary igneous rocks_--_-___- 

General features_________ ________.-..______

Established relations of the intrusives._______

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Descriptive geology Continued.

Cretaceous (?) and Tertiary igneous rocks Contd. 

Correlation ________________________________

Petrographic descriptions ___________________

Differentiation.. ___________________________

Rock alteration____________________________

Hypogene alteration..__________________

Weathering. __________________________

Structure. ________________________________________

Regional structure.____________________________

Local structure-___-___________--_-_______-----

Pre-Cambrian structure _____________________

Laramide structure----__-________-__-------

Williams Range thrust fault.________--__

Structural relations of the Montezuma 

stock_______________________________

Transverse faults and fractures of the 

mineral belt.________________________

Intrusive relations of dikes and small

masses __ __________________

Geologic history ____________________________

Economic geology..--___-_____-____________.

Mineralogy. ____________________________

Minerals occurring in the quadrangle. 

Minerals of the ore deposits_________.

Paragenesis ____-___--____________..

Ore deposits____________________________

Contact-metamorphic deposits ________

Stockworks________________________

Veins______________________________

Types and distribution._________

Possible centers of mineralization. 

Mineral associations.____________

Relation of ore to depth. ________

Enrichment. ___________________

Dimensions of ore shoots.._.____.

Vertical range of ore deposition... 

Localization of ore._____________

Suggestions for prospecting._..______.

Future of the district.___________________

History of mining_______________________

The mines_________________________________

Index.____________________________________

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ILLUSTRATIONS

Page 

PLATE 1. Airplane view looking south westward up

Leavenworth Creek____.________________ 6

2. Airplane view looking southward toward

Loveland Pass___________________________ 6

3. Geologic map of Montezuma quadrangle-_ In pocket

4. Structure sections of Montezuma quad- 

! rangle______--____________-_-______ In pocket

5. Geologic map of the Front Range___________ 6

6. A, Idaho Springs formation on east side of 

Grays Peak; B, Photomicrograph of quartzbiotite-sillimanite schist from northeast 

slope of Grays Peak_____________________ ' 6

7. A, Typical exposure of Swandyke hornblende 

gneiss near head of St. Johns Gulch; B, 

Anticlinal dome of Dakota .quartzite cut 

through by the Snake River; C, View looking east at Ruby Gulch from Lenawee 

Mountain._____________________________ 7

8. A, View looking east up the Snake River from 

conical shale hill 1 mile west of Montezuma 

quadrangle; B, View looking south from 

south end of Teller Mountain near pashier 

mine __________________________________ 22

9. Erosion surf aces of Montezuma quadrangle. In pocket 

' 10. A, Glacial lake at head of Smelter Gulch; B,

Rock glacier at head of Stevens Gulch_____ 22

11. A, Pho'tomicrograph of Silver Plume granite 

from Santa Fe Mountain; B, Photomicrograph of augite diorite from east slope of 

Bear Mountain.________________________ 30

12. A, Photomicrograph of hornblende diorite near 

mouth of the Middle Fork of the Swan River; 

B, Photomicrograph of rhyolite porphyry 

from dike on wagon road west of Argentine 

Pass; C, Photomicrograph of granite porphyry from dike in Horseshoe Basin_______ 30

13. A, Photomicrograph of ore from level 3, Santiago mine; B, Photomicrograph of zinc ore 

100 feet above main tunnel level, Stevens 

mine____________--_-_----------------_ 54

14. 'A, Photomicrograph of ore from dump of Star 

"of "the West no. 2 mine, Teller Mountain; B, 

Photomicrograph of silver ore from Lower 

'" Jerry tutinel____---___------_----_---__- 55

15. Topographic map of Montezuma quadrangle

showing mine locations/.____________ In pocket

16. Silver Wave mine, Collier Mountain, level 5__ 62

17. Pl&n and longitudinal section of Bell mine__ 70

18. Silver Wing and Spelter King tunnels________ 70

19. Bullion mine.__________-_____---_______ 70

20. Buster tunnel, near Silver Plume Mountain_ 70

21. Plan and vertical projection of Cashier and

Champion mines._______________________ 70

22. Chatauque mine, main (lower) adit, 1929____ 70

23. Fisherman vein, on the Snake River; Congress 

mine, Ruby Mountain; and Star of the West 

no. 2 mine, Teller Mountain..______ ______ 78

Page 

PLATE 24. Hunkidori mine, Grizzly Gulch, and Missouri

mine, Hall Valley.______________________ 78

25. Plan and section of Ida Belle mine, Jones

Gulch.________________________ 78

26. Jerry and Equity adits____________________ 78

27. Josephine mine, Kelso Mountain..._________ 78

28. More Work tunnel, Glacier Mountain, and

Kelso mine, Kelso Mountain _____________ 86

29. Mohawk mine, Teller Mountain____________ 86

30. Morgan mine, adits 1, 2, and 3______-_--__- 86

31. New York tunnel, 1929--__--__________.__ 86

32. Old Timer mine, Glacier Mountain, and Rainbow mine, Keystone Gulch. ______________ 86

33. Level F and part of level C, Pennsylvania

mine, Decatur Mountain________________ 86

34. Peruvian mine, Ruby Mountain ____________ 94

35. Lower level, Sts. John mine, Glacier Mountain............ _______________________ 102

36. Levels 3 and 5, Santiago mine, McClellan

Mountain__________________________ 102

37. Upper and lower adits, Silver King mine,

Glacier Mountain_________.____________ 102

38. Detail of south end of main drift and plan of

level 14, Stevens mine, Stevens Gulch_____ 110

39. Toledo tunnel, Montezuma-___.!___________ 110

40. Workings on Whale and Brilliant mines, Halls

Gulch_________________________ 110

FIGURE 1. Index map showing location of the Montezuma and neighboring quadrangles. _____ 2

2. Sketch showing glacial trenching of Flattop

peneplain ____________________________ 3

3. Correlation of sections measured from

Boreas Pass to Keystone._____________ 18

4. Correlation of sections measured at Palmer

ranch and Keystone._________________ 19

5. Major structural. features of the Montezuma quadrangle. ____________________ 46

6. Center of vein in stope on vein 5, Sts. John

mine._______________________________ 58

7. Section along raise in Bell mine, level 6____ 63

8. Longitudinal section of Baker mine, 1869. _ 69

9. Cross section along line of Britannic tunnel. 70

10. Mineralization of broken ground in premineralfault zone.___________________ 72

11. Vein following S-shaped fracture cleavage

of premineral reverse fault, Bell mine___ 72

12. Chatauque vein, west stope looking east__ 77

13. Grand Trunk adit, Geneva Gulch. _______ 79

14. Hannibal vein, lower adit--_-_______-___- 81

15. Diagrammatic section of Ida Belle stope.. 83

16. General relations of Santiago, Commonwealth, Independence, Tobin, and Paymaster workings and geology of Waldorf 

tunnel. _____________________________ 84

17. St. Elmo, Glacier Mountain, 1929_____ 87

18. Occurrence of ore in Missouri mine, 10 feet

above level 5__-_-----_---___------__ 88

IV
CONTENTS

F.IGU.UK 19. Relations of "low grade" (galena)'ore seam 

to "high grade" (bismuth) ore seam, 

level 5, Missouri mine---______--__-__-

20. Occurrence of ore in "roll" in Missouri

21. Stope map of north vein o'f Pennsylvania 

mine, 1902______...____.________.._.

22. Quail mine, Morgan Gulch._____________

23. .Rothschild tunnel, Cooper Mountain, 1929_

24. Looking north at vein 5, 750 feet north of 

main cross cut, Sts. John mine________-

Putro

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FIGURE 25. Stope map of vein 5, Sts. John mine_._____ 103

26. Stope map of Santiago mine, looking west. 105

27. Sketch map of stopes in Silver King mine,

August 1929, looking north, _.___._._._ 107

28. Approximate shape of ore shoots on Silver

Wave vein, looking southeast._________ 108

29. Approximate relations of stopes along main

tunnel level, Stevens mine.____________ 110

30. Workings on Wild Irishman vein, Glacier

__----_-----___-_________ 115

INSERT

Tentative correlation of Cretaceous (?) and Eocene porphyries in several districts in the northeastern part of the mineral 

belt of Colorado, with special reference to the Front Range-_--_-___-__-_-_--_-____-__--_-_____----_-__._-________

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ABSTRACT

Pre-Cambrian rocks cover most of the Montezuma quadrangle, but Mesozoic sediments are present in the southwestern 

part, and Tertiary intrusive rocks occur in a belt running from 

the southwest corner to the northeast corner. The Idaho 

Springs formation, the oldest in the quadrangle, covers most of 

the eastern half and is present along the western border. 

Quartz-biotite schist and gneiss containing sillimanite are the 

most abundant rocks in the formation, but quartz gneiss or 

quartz schist, lime silicate rocks, and garnetiferous schist are 

locally abundant. At some places ellipsoidal masses of quartz 

and sillimanite a few inches in diameter are distributed with 

remarkable regularity in the planes of schistosity. They are 

interpreted as the knots developed during the metamorphism 

of the schist rather than the mashing of an original conglomerate. 

In places granitic intrusions have converted the schist into an 

injection gneiss. The rocks were originally shaly sediments 

containing small sandy and calcareous lenses, and the planes of 

schistosity are nearly everywhere parallel to the original bedding 

planes. 'Isoclinal folds are common. The regional structure, 

though modified by the nearby granitic masses, shows a north 

to northeast trend.

The gneisses and schists in the west half of the quadrangle 

have been termed the Swandyke hornblende gneiss. They are 

probably metamorphosed quartz diorite sills or lavas of similar 

composition intercalated in or overlying the upper part of the 

Idaho Springs formation. The Swandyke gneiss, like the Idaho 

Springs formation, is changed to injection gneiss wherever 

pegmatitic or aplitic seams are abundant.

Although a large mass of quartz monzonite gneiss occurs to 

the east, there are only a few small masses of it in the Montezuma quadrangle. It is intrusive into the Idaho Springs formation and is believed to be somewhat later than the Swandyke 

gneiss. Like the earlier formations it shows the effect of granulation and recrystallization. Its contacts with the Idaho 

Springs formation are commonly parallel to the schistosity. 

Assimilation was locally important in determining its composition. It is probable that much of the early injection along 

the foliation planes of the schist was accomplished by this 

quartz monzonite magma.

Granite gneiss occurs in only a few isolated masses in the 

Montezuma quadrangle. The small bodies are lenticular, but 

the contact of large bodies with schists and gneisses is irregular. 

In places the granite gneiss forms sills directly related to zones 

of injection gneiss in the earlier schists and gneisses. Its predominant facies is a gneis,sic aplite or fine-grained gneissic 

silicic granite. Granulation of the quartz and feldspars in the 

granite gneiss is much less prominent than in the earlier rocks. 

' Dikes and small irregular masses of Algonkian age ranging in 

composition from hornblendite through diorite and quartz 

diorite to a nearly pure anorthosite occur in a few places. The 

central parts of the larger irregular masses of diorite and quartz 

diorite are usually massive and have a faint orthogneissic character, but the edges generally show a banded structure and 

some evidence of mashing. The quartz diorite is closely related 

to the early dioritic facies of the Pikes Peake granite.

The Pikes Peak granite is found only in the southeastern part 

of the Montezuma quadrangle but extends at least 80 miles 

southward. Quartz monzonite border facies are found in 

irregular masses at :the edge of the main batholith. The two

grade into each other at many places and were not mapped 

separately.

The Silver Plume granite crops out extensively in the north 

half of the quadrangle, and many isolated masses are found in 

the south half. At many places it probably followed fault 

lines and fracture zones.

Pegmatite and aplite intrude all the above-mentioned preCambrian rocks. Their structural relations indicate that their 

intrusion extended over a long period. They were probably 

intruded at intervals from a time shortly after the formation 

of the Swandyke gneiss to the end of the consolidation of the 

Silver Plume granite.

The Maroon formation (Pennsylvania!! (?) and Permian), 

consisting of micaceous grit, shale, sandstone, and conglomerate, 

probably about 50Q feet thick, crops out a short distance outside 

of the quadrangle. The Morrison formation (Upper Jurassic) 

comprises about 350 feet of sandstone and variegated shale. 

The Dakota quartzite (Upper Cretaceous) ranges in thickness 

from 20 to 227 feet. It generally comprises a thick basal gray 

quartzite, a middle member of thin-bedded quartzite and black 

to gray shale, and an upper bed of quartzite from 20 to 50 feet 

thick. It is unconformably overlain by about 350 feet of 

black Benton shale, above which lies a dark-colored petroliferous 

limestone that may belong wholly or in part to the Benton. 

This limestone is succeeded by the limy shales of the Niobrara, 

which is about 370 feet thick and is overlain by somber-colored 

Pierre shale, which is about 4,000 feet thick near Keystone.

The Flattop peneplain of the Rocky Mountain National 

Park, which developed and was much dissected before the formation of the pre-Oligocene Medicine Bow peneplain, has been 

traced south through the Fraser quadrangle into the Montezuma 

quadrangle. It is a smooth, irregular surface and forms the tops 

of the mountains in the southern part of the quadrangle at an 

altitude of about 12,000 feet. The Rocky Mountain peneplain 

of the east side of the Front Range is imperfectly developed in 

the southwestern part of the quadrangle. This surface lies 

between 10,000 and 11,000 feet above sea level.

Early Pleistocene glaciation was widespread. Remnants of 

valleys cut at this time are found as much as 1,500 feet above the 

floors of the present valleys in the high country near the Continental Divide. The deposits comprise early morainic material 

and high terrace gravel. Much of the material of these deposits is more deeply weathered than that of the later moraine 

and outwash gravel.

The present topography was largely carved in the .Wisconsin 

glacial stage of late Pleistocene time, and the most conspicuous 

features are due to ice work. Since Wisconsin time erosion has 

changed the topography but little.

All the post-Cambrian igneous rocks of the Montezuma 

quadrangle probably belong to one period of intrusion. They 

occur in a zone called the "porphyry belt," which is coextensive 

with a belt of mineralization and extends southwestward across 

the Front Range from Boulder to Breckenridge. These rocks 

are younger than the folding and faulting, which probably 

occurred during the Laramide revolution, but are older than the 

Flattop peneplain and were therefore intruded about the beginning of basal Eocene time. They are mostly porphyries and 

range from calcic to silicic in composition but the bulk of them 

are intermediate between diorite and quartz monzonite. In

VII
VIII MONTEZTJMA QUADRANGLE, COLORADO

general the calcic types are early and the silicic types late. A 

study of the Front Range and other parts of Colorado suggests 

that the igneous and related structural history of the Front 

Range during the early Eocene is essentially as follows:

1. Intrusion in early Denver time (basal Eocene) of sills and 

dikes of felsite.

2. Uplift of the Front Range accompanied by intrusion and 

extrusion throughout middle Denver time of calcic andesite 

and potassic basalt.

3. Culmination of Laramide revolution, characterized by 

strong folding, thrust faulting, and tear faulting at the end of 

Denver time, accompanied by the intrusion of granite-diorite 

magma.

4 Minor faulting followed by intrusion of dikes and sills 

of medium-grained porphyritic quartz monzonite.

5. Faulting accompanying and preceding the batholithic 

invasion of coarse-grained porphyritic quartz monzonite.

6. Minor faulting and intrusion of dikes of porphyritic sodic 

quartz monzonite.

7. Intrusion of dikes of sodic rhyolite and sodic granite 

porphyry.

8. Intrusion of granite and rhyolite porphyry.

9. Intrusion of alkali syenite, trachyte, and bostonite.

10. Minor faulting and the formation of gold, silver, lead, 

zinc, and copper ores.

11. Intrusion of felsite dikes and pipes of rhyolite agglomerate.

12. Development of Flattop peneplain.

The quartz monzonite porphyries of group 5, which are represented by the large stocks at Montezuma and in the southwestern part of the quadrangle and by small stocks and dikes 

elsewhere, have many times the volume of all other early 

Tertiary intrusive rocks of the Front Range. The Montezuma 

stock cuts the Williams Range thrust fault, which was formed 

during the Laramide revolution (the third stage listed above). 

Most of the porphyritic quartz monzonite dikes are slightly 

altered, and the uniformity of the alteration suggests that it was 

endomorphic. This type of alteration becomes more and more 

noticeable in the later silicic rocks.

A comparison of published analyses and age relations of the 

Tertiary intrusive rocks of the Front Range suggests.an orderly 

succession of differentiates from a deep-seated magma. Three 

types of magmatic differentiation are indicated. The earliest 

type started with an initially dioritic magma and resulted in 

calcic and ultracalcic rock. The second type also started with a 

dioritic magma but gave rise successively to monzonite, quartz 

monzonite, granite, and alaskite. The third type, splitting from 

the quartz monzonite differentiate, resulted in alkalic rocks 

such as bostonite, alkalic syenite, and alkalic trachyte. The 

second type of magma, became progressively more hydrous, and 

the third type became progressively drier.

The regional structure of the pre-Cambrian rocks is much 

obscured by complex local folds. Most of the schist southeast 

of the mineral belt dips north or northeast, but close to the 

Pikes Peak granite it is folded into irregular anticlines and 

Bynclines. Northeast of the mineral belt a northward-trending anticline extends from Georgetown into Estes Park, and a 

syncline runs north-northeastward from a point near Breckenridge to Fraser.

The northward-trending Front Range is made up in large part 

of northwesterly folds having an echelon arrangement. These 

folds are commonly overturned toward the west and at many 

places are broken by reverse faults. Thrust faults occur on 

both borders of the range; the largest, known as the Williams 

Range thrust fault, crosses the southwest quarter of the Montezuma quadrangle. At its southeast end it passes into an oyerturned fold.

A narrow belt of fractures follows a. sinuous northeasterly 

course from Breckenridge to Boulder and passes through the 

western border of the range where the Williams Range thrust

fault breaks from the overturned fold. In this belt nearly all 

the Tertiary igneous activity and mineralization of the central 

part of the range has been localized. The veins in this belt 

commonly occupy faults and fissures that strike from northeast 

to east, but a few northwesterly veins have been found. So far 

as known, in all the eastward-trending mineralized faults in the 

west half of the range the north wall has moved east almost 

horizontally. More vertical than horizontal movement is 

commonly shown in the northeasterly faults, and both reverse 

and normal faults are common. Most of the northwesterly 

faults dip northeast and are reverse faults.

The horizontal movement of the easterly faults suggests 

shearing related to the breaking of the overturned fold where 

it passes into the thrust fault. The eastward movement of the 

north walls of the shear faults in the block overlying the thrust 

fault suggests drag of an inactive block by an actively moving 

footwall block. It seems probable, therefore, that the Williams 

Range thrust fault is an underthrust.

The minerals of economic importance in the Montezuma 

quadrangle include gold, silver, sulphides of lead, zinc, silver, 

arsenic, antimony, copper, and bismuth, and their supergene 

alteration products. The earliest minerals deposited by the 

ore solutions were sericite, quartz, and pyrite, and the wall 

rocks near the principal veins are largely altered to these 

minerals. Sericite is confined to the wall rock, but quartz 

and pyrite are abundant both as fissure fillings and as disseminations in the walls. Locally calcite and manganosiderite 

were deposited shortly afterward. Chalcopyrite, locally associated with gold, was deposited in the next stage of mineralization and is in places contemporaneous with early sphalerite. 

In most places galena and sphalerite are essentially contemporaneous and are later than chalcopyrite. Tennantite and tetrahedrite are in part contemporaneous with sphalerite and galena. 

After the deposition of gray copper, ankeritic gangue minerals 

containing some iron and manganese were formed in many of 

the veins. The ankerite stage ended the mineralization of many 

veins, but some were reopened and invaded by silver-bearing 

solutions which deposited quartz, argentite, native silver, silver 

sulphantimonides and sulpharsenides, and some galena. Bismuth minerals in a quartz gangue were probably formed at 

about this time.

The ore deposits are classed as contact-metamorphic deposits, stockworks, and mesothermal veins. Contact-metamorphic deposits, not economically important, occur near the 

west end of the Montezuma stock and in the Cretaceous sediments in the southwest corner of the quadrangle. The host 

rock is Cretaceous shale, and the invading rock a coarse-grained 

monzonite porphyry.

Stockworks are found only in the southwestern part of the 

quadrangle. They are shattered masses of quartz monzonite 

porphyry, some of which are crowded with fragments of the 

Cretaceous sediments. The complexly fractured rocks are 

strongly sericitized and contain sporadic seams and masses of 

ore. Sphalerite, pyrite, galena, gold, silver, and bismuth are 

irregularly distributed in the primary ores. Enrichment was 

an important factor in making the early work on these deposits 

profitable. They are much richer in gold near the surface 

than below the zone of oxidation.

The veins were formed at moderate depth, pressure, and 

temperature. Most of them strike northeast or east-northeast and dip northwest, but a few dip steeply southeast. The 

most productive veins strike between N. 15° E. and N. 35° E. 

Lead-zinc-silver veins consisting chiefly of galena, sphalerite, 

pyrite, and quartz are common in the northeast quarter of the 

quadrangle. On Mount McClellan veins of this general type 

carry barite and fluorite. In the south half of the quadrangle 

tetrahedrite is much more common than farther north, but 

galena, sphalerite, and pyrite are the most abundant ore minerals. Barite is abundant in a southeastward-trending branch
ABSTRACT IX

of the mineral belt, running from Glacier Mountain to Hall 

Valley. In the southeast quarter of the quadrangle veins carrying bismuth and silver minerals are common, and these minerals are associated with chalcopyrite in a quartz gangue. A 

few veins occur in the hanging-wall block of the Williams 

Range thrust fault north of the North Fork of the Swan River, 

though this area is underlain by underthrust Cretaceous shales. 

The veins in the southern part of the Montezuma stock consist 

chiefly of sphalerite and pyrite and contain moderate amounts 

of galena in a quartz-ankerite gangue. Farther north in the 

stock small veins containing rich silver ores occur.

The distribution of the less common ore minerals suggests 

that certain mineral associations are characteristic of distinct 

types of ore. In many of the ores gold and silver are associated 

with chalcopyrite, and silver is commonly associated with tetrahedrite and tennantite. The lighter-colored gray copper ores 

contain more silver than the dark-colored gray copper. Ores 

containing chalcopyrite and no gray copper commonly have a 

quartz or ankerite gangue, but the gangue of veins containing 

gray copper generally contains barite. The most abundant 

silver minerals,' miargyrite, pyrargyrite, proustite, and stromeyerite, are commonly associated with manganiferous ankerite 

or rhodochrosite gangue. The bismuth-silver minerals, emplectite and schapbachite, are associated with quartz, pyrite, 

and chalcopyrite. Veins of massive pyrite or pyrite and 

quartz contain very little gold in the primary ores, but close 

to the surface they may have a high gold content due to 

enrichment.

Galena is commonly most abundant in the upper part of a 

vein. The copper content generally increases slightly with 

depth, and chalcopyrite usually becomes relatively more abundant than gray copper in the lower levels. The silver content 

of the ores shows little relation to the depth from the surface in 

the veins in the pre-Cambrian area. In Glacier Mountain, however, the ores are generally richer in silver in the lower part 

of the ore shoots than in the upper part. Most of the silver is 

believed to be primary, but enrichment has affected many veins. 

Rich secondary gold and silver ores bottom at much shallower 

depth in the pre-Cambrian rocks than in the later sedimentary 

rocks in the western part of the quadrangle. In the veins that

crop out on the Flattop peneplain rich gold ore was found only 

to a depth of 25 feet, where it changed abruptly into low-grade 

pyrite. In the ores that crop out on the Rocky Mountain 

peneplain rich secondary gold and silver continue to much 

greater depth.

The largest ore shoots range from 600 to 1,100 feet in length 

and have a vertical extent of 400 to 850 feet. The vertical 

range of ore deposition was at least 2,000 feet and probably more 

than 3,000 feet. However, it seems probable that the bottoms 

of the larger ore shoots indicate the bottoms of the local zones 

in which commercial bodies of ore were deposited nearby.

Hard, strong rocks such as pegmatite, granite, porphyry, and 

gneiss are the common walls of persistent ore shoots. Softer, 

more plastic rocks such as mica and hornblende schists rarely 

form the walls of extensive ore shoots. Ore shoots commonly 

occur at the intersections of veins, near the junction of branching 

veins, and where marked changes in the dip or strike occur. 

These changes can usually be correlated with open spaces 

caused by the movement of the irregular walls of the fault. In 

a fissure whose walls move horizontally a change in course will 

either allow the walls to pull apart or cause them to rub tightly 

together. Ore occurs where they pull apart. Similarly ore 

tends to occur in the steeper parts of premineral normal faults 

and in the flatter parts of premineral reverse faults. In areas 

of schist or gneiss ore shoots are more common where the vein 

breaks across the schistosity than where it is parallel. Veins 

having pyritized and silicified wall rock, recording many periods 

of brecciation, are more likely to have been open while metalliferous minerals were being deposited than veins that do not 

have these characteristics.

Reserves of high-grade ore are small, but there are many 

veins that might yield small but profitable amounts of ore if 

mined by lessees. Some of the baritic lead-zinc ores might be 

profitably concentrated in a flotation mill. Moderately large 

bodies of low-grade auriferous disseminated zinc-lead ores, 

unprofitable to the present time, occur in the stockworks 

near Tiger. The ore occurrences in the Ida Belle and Rainbow 

mines indicate the possibility of finding ore bodies in the brecciated zone of the Williams Range thrust fault where it is crossed 

by mineralized fissures.
GEOLOGY AND ORE DEPOSITS OF THE MONTEZUMA QUADRANGLE, COLORADO

By T. S. LOVERING

INTRODUCTION

FIELD WORK AND ACKNOWLEDGMENTS

The surface geology of the Montezuma quadrangle 

was mapped during the summers of 1926, 1927, and 

1928, and the underground work was done chiefly in 

the fall of 1926 and the summer of 1929. The writer 

was assisted by L. B. Graft in most of the work, but 

for short periods in 1927 and 1928 Mart Barclay and 

H. W. Putnam acted as assistants.

Many of the mines in the quadrangle have been idle 

for years, and several of them were inaccessible, but 

the writer was allowed access to all mines open at the 

times of his visits except the Koyal Tiger, and he 

wishes to express his appreciation of the courtesy of the 

many mine operators who facilitated this work.

Mr. C. W. Henderson, of the United States Bureau 

of Mines, contributed much helpful information on the 

mines; the production figures since 1904 are taken 

directly from his records, and most of the earlier production figures come from sources suggested by him. 

Mr. Percy Barbour, of Georgetown, kindly gave the 

writer access to his collection of mine maps, and many 

of those used as base maps for the geology of the mines 

are copied from his tracings. Dr. M. N. Short contributed much to the study of the ore minerals.

LOCATION AND POPULATION

As shown in figure 1, the Montezuma quadrangle is 

in the heart of the Colorado Front Range, about 40 

miles west of Denver. It lies between parallels 39°30' 

and 39°45' and meridians 105°45' and 106° and includes an area of about 230 square miles. The Continental Divide follows a sinuous northerly course 

through the quadrangle and is a natural boundary 

between counties of the eastern and western slopes. 

East of the Continental Divide the central and northern 

parts of the quadrangle are in Clear Creek County 

and the southern part is in Park County. West of the 

divide the northern part is in Grand County and the 

central and southern parts are in Summit County. 

The southwestern part of the quadrangle includes some 

of the Breckenridge district, which was studied by

i Ransomo, F. L., Geology and ore deposits of the Brockenridgo district, Colo.: 

U.S. Gool. Survey Prof. Paper 75, 1911.

 Levering, T. S., Geology and oro deposits of the Brockenridge mining district, 

Oolo.: U.S. Gool. Survey Prof. Paper 170,1034.

Ransome in 1909 : and by the writer in 1928 ; 2 the 

central portion was mapped by Patton and students1 of 

the Colorado School of Mines in 1908.3 Adjoining the 

quadrangle to the east is the Georgetown quadrangle, 

whose geology and ore deposits were mapped and 

studied in 1904.4 Part of the Central City quadrangle 

lying immediately northeast of the Montezuma quadrangle has been mapped and studied by Bastin and Hill.5

The Colorado & Southern Railway's narrow-gage 

line, which serves the country between Denver and 

Leadville, has a short spur from Dillon east to Keystone. This hamlet is on the Snake River about a 

mile east of the western boundary of the quadrangle 

and is dependent on a small lumber mill for its existence. In 1929 no post office or station was maintained 

there, although it was the only shipping point for the 

lumber and ore found in the Snake River drainage basin.

Montezuma, an incorporated town, is on the Snake 

River about 8 miles east of Keystone and very near the 

center of the quadrangle, to which it has given its 

name. Montezuma has a post office and general store, 

and daily stage service to Dillon is maintained throughout the year. According to the 1920 census Montezuma 

had a population of 69; in 1930 the population was 38. 

Mining is the chief industry of the region near the 

town.

Tiger, about the size of Montezuma, is on the Swan 

River 2}£ miles northeast of the southwest corner of the 

quadrangle. It is supported almost wholly by the 

activities of the Royal Tiger Mining Co. Its nearest 

shipping point is Braddocks Switch, about 4 miles west 

of the town.

Montezuma, Tiger, and Keystone are the only 

inhabited towns or hamlets in the Montezuma quadrangle. Swandyke, on the Middle Fork of the Swan 

River, is a small "ghost town", and only two or three 

empty buildings remain at Graymont, on Clear Creek. 

Silver Plume at the end of the Clear Creek branch of 

the Colorado & Southern Railway .is only a mile east 

of the quadrangle and is the shipping point for the ores 

from the Clear Creek drainage basin.

8 Patton, H. B., Tha Monteiuma mining district, Oolo.: Colorado Qeol. Survey 

First Kept., pp. 112-144, 1909.

4 Spurr, J. E., Garrey, G. H., and Ball, S. H., Economic geology of the Georgetown quadrangle, Colo.: U.S. Geol. Survey Prof. Paper 63, 1908.

« Bastin, E. S., and Hill, J. M., Economic geology of Gilpin County and adjacent 

parts of Clear Creek and Boulder Counties, Colo.: U.S. Gool. Survey Prof. Paper 

94,1017.
MONTEZUMA QUADKANGLB, COLOEADO

TOPOGRAPHY AND DRAINAGE

The Montezuma quadrangle (see pis. 1, 2) lies on 

and near the Continental Divide, and as shown on 

plate 3, it contains much high, rugged country. The 

altitude ranges from 9,100 feet a short distance west of 

Keystone to 14,274 feet at the summit of Grays Peak, 

5 miles northeast of Montezuma. Most of the valleys 

have been severely glaciated in recent geologic time

narrow and at many places rise to impassable knifelike 

divides.

The Continental Divide includes the highest and 

most rugged peaks in the region. In this quadrangle 

it is in general above 12,000 feet in altitude and passes 

through many peaks higher than 13,000 feet, including Grays Peak (altitude 14,274 feet), the highest 

peak in the Front Range and one of the highest in 

Colorado.

106'

20 Miles

FIG ORE 1. Index map showing location of the Montezuma and neighboring quadrangles. 1, Montezuma quadrangle; 2, Breckenridge district (Prof. Paper 75); 3, Tenmile 

district (Folio 48); 4, Leadville district (Prof. Paper 148); 5, Mosquito Range (Mon. 12); 6, South Park coal field (Bull. 381-C); 7, Georgetown quadrangle (Prof. Paper 

63); 8, Gilpin County and vicinity (Prof. Paper 94); 9, Boulder district (Bull. 265); 10, Aspen district (Mon. 31); 11, Red Cliff district (Colorado Geol. Survey Bull. 

30);- 12, Ward region (Colorado Geol. Survey Bull. 21); 13, Boulder tungsten area (Colorado Geol. Survey, 1st Rept.); 14,Tarryall district (Colorado Geol. Survey 

Bull. 31); 15, Alma district (Colorado Geol. Survey Bull. 3); 16, part of Breckenridge district (Prof. Paper 176).

and are broad and U-shaped. Steep-walled cirques are 

common at altitudes above 11,500 feet, and where the 

preglacial surface has been preserved they contrast 

strongly with the smooth topography of the old upland in which they were carved. (See fig. 2.) Remnants of the elevated tilted plateau are present only 

in the southwestern and eastern parts of the quadrangle; throughout the central part the ridges are

High spurs from the Continental Divide separate 

the major streams. As shown on plate 3, the valleys 

of the largest streams, such as the Snake River on the 

western slope and Clear Creek on the eastern slope, 

trend nearly east and west. North and south tributaries to these major streams have cut deep valleys 

into the high spurs from the Continental Divide and 

given the country its rugged, broken character.
Most of the northeast quarter of the quadrangle 

is drained by Clear Creek and its tributaries, and the 

southeastern part is drained by Geneva Creek, which 

discharges into the North Fork of the Platte Kiver 

about 5 .miles southeast of the quadrangle. The 

drainage basin of the Snake River occupies about a 

third of the region mapped and includes most of the 

central-western part of the quadrangle. The extreme 

southwestern part is drained by the Swan River, and 

the northwestern part is drained by Straight Creek 

and the South Fork of the Williams River. Large 

parts of these streams lie between 9,200 and 11,000 

feet above sea level, and the interstream divides commonly rise from 1,200 to 2,000 feet above 

them.

Many beautiful glacial lakes spangle the high 

country, marking places where the glaciers of 

the ice age dug deeply and unevenly into the 

bedrock near the heads of the streams. At 

lower altitudes, usually less than 11,000 feet, 

many large ponds have been formed in 

the valleys through the activity of beavers, 

which are especially numerous on the western slope.

CLIMATE AND VEGETATION

No recent record of temperature and precipitation is available for any point in the 

Montezuma quadrangle, but at Dillon, 4 miles 

west of Keystone, at an altitude of about 8,800 

feet, the mean annual temperature is 33.4° F. 

and the mean annual precipitation is 18.31 

inches. In the high country east of Dillon, 

however, the average temperature is less and the 

precipitation is more. A clipping from a paper published in 1873 states that the snowfall at Sts. John 

that winter was an even 100 feet, that the ground 

was covered to an average depth of 9 feet, and that 

4 feet of snow had to be cut through in June in order 

to open the road from Sts. John to Montezuma. Snow 

remains on the higher peaks throughout the year, and 

even in the lowest valleys deep drifts linger on northward-facing slopes until the later part of June. Most 

of the quadrangle is bare during July, August, September, and part of October. Heavy snows usually 

mantle the range late in October or early in November, 

and frequent storms during December, January, 

February, and the early part of March bury the region 

beneath several feet of snow. Storms are common in 

summer but generally occur more frequently in May, 

early June, late July, and August than in the other 

months of summer and fall.

About half of the quadrangle is above timber line, 

which ranges from 10,500 to 12,000 feet but is generally close to 11,700 feet. Below timber line forests 

of pine and spruce cover most of the mountain slopes, 

but thick groves of aspen are common in some places

and usually mark the sites of old forest fires. The 

most abundant conifers are the lodgepole pine (Pinus 

murrayana) and the Engelmann spruce (Picea engelmanni), but in dry localities in the lower parts of the 

region some yellow pine (Pinus ponderosa) and 

Douglas spruce (Pseudotsuga mucronata) .are found. 

The balsam or alpine fir (Abies lasiocarpa) is a common 

associate of the lodgepole pine and is most abundant 

below an altitude of 11,000 feet. The limber pine 

(Pinus flexilis), on the other hand, is seldom found 

much below timber line. In wet marshy places and 

along streams dense growths of alders and willows 

occur, made up chiefly of the mountain alder (Alnus

Glacier 

Mtn.

FIGURE 2. Sketch showing glacial trenching of Flattop peneplain. From southern spur of 

Lenawee Mountain, looking south-southwest.

tenuifolia) and the subalpine willow (Salix glaucops). 

Grasses and sedges are common in parklike open 

spaces near streams and in moist zones above timber 

line.

Temperature, in degrees Fahrenheit, at Montezuma, Colo., 1884 

[As reported by the Montezuma Mill Run]

Week ending 

Jan. 5------__--______-

Jan. 12 _ ______ __^___

Jan. 19.. ______________

Jan. 26 _ ______ _ ....

Feb. 2_.______________

Feb. 9__ ______________

Feb. 16. .__.________._

Feb. 23_______.____.__

Mar. !___ _______ ____

Mar. 8-_-_____-__-_.__

Mar. 15_________._____

Mar. 22. __ ______ __

Mar. 29. _-----______-.

Apr. 5 _ ______________

Apr. 12... ____________

Apr. 19__. .__--______.

Apr. 26..... _ _ ______

May 3______-______ __

May 10__ __ _____ ____

May 17__. ___-.__.___.

May 24_____ _________

Mav 31_. _._.-..___.-.

Highest

28

24

37

41

46

38

38

40

44

42

42

57

62

65

71

55

60

60

69

69

63

85

Lowest

-15

-17

-17

-14

-2

3

-24

-6

-6

3

-9

6

-3

4

8

11

6

6

14

14

15

22

Average 

maximum

13

20

26

25

28

30

25

25

27

27

30

43

41

44

45

46

51

51

58

58

57

59

Average 

minimum

-3

2

-7

-6

5

8

-9

9

7

17

6

10

10

13

13

16

18

18

19

19

27

25
MONTEZUMA QtJAbilAJiGLE, COLORADO

Temperature, in degrees Fahrenheit, at Montezuma, Colo., 

1 884 Continued

Week endingJune 7______ _____ __

June 14_______ _______

June 21____ _ ________

June 28________ ______

July 5.. ._._.. __.___..

July 12_. _____________

July 19... _____________

Aug. 2. _______________

Aug. 9___ _ __________

Aug. 16____. __________

Aug. 23_____ __ ______

Aug. 30__ ______ ____

Sept. 6________________

Sept. 13_ _________ _

Sept. 20_______________

Sept. 27_______________

Oct. 4.________________

Oct. 11_. ______________

Oct. 18--____.________

Oct. 25____.___________

Nov. 1__ _ _ _ _ _ __

Nov. 8__ ____ __ __ _

Nov. 15 _ ____ _ . __

Nov. 22. ____ _ _ __

Nov. 29--_____._______

Dec. 6________________

Dec. 13_ __ ___________

Dec. 20________ ______

Dec. 27____. __________

Highest

64 

92 

72 

72 

72 

72 

72 

72 

76 

63 

63 

76 

76 

74 

68 

63 

62 

62 

62 

59 

59 

45 

45 

33 

31 

31 

26 

35 

35

Lowest

28 

30 

30 

30 

30 

30 

30 

30 

30 

30 

30 

31 

31 

14 

18 

18 

18 

18 

18 

11 

3 

8 

8

_ g

-2 

-2 

-8 

5 

5

Average 

maximum

69 

69 

67 

67 

67 

67 

67 

63 

60 

56 

56 

58 

58 

53 

57 

54 

54 

54 

54 

44 

34 

34 

34 

22 

21 

21 

21 

26 

26

Average 

minimum

35 

35 

35 

35 

35 

35 

35 

35 

35 

32 

32 

32 

32 

28 '30 

30 

30 

30 

30 

23 

13 

13 

13 

11 

9 

9 

5 

9 

9

Mean annual temperature, 31.5°.

INDUSTRIES, POWER, AND TRANSPORTATION

Most of the population is supported by the mining 

industry. There are a few ranches in the western 

part of the quadrangle on Soda Creek and the Snake 

River, and small sawmills were operating on the North 

Fork of the Swan River, on Clear Creek, at Tiger, 

.and at Keystone in 1926-29. Many large bands of 

sheep graze above timber line in July, August, and 

September.

No attempt has been made to develop the water 

power of the region. The volume of the streams within 

the quadrangle is too small to warrant the construction of large hydroelectric plants, and as electric 

power is easily obtainable from the 100,000-volt 

transmission line passing through the quadrangle by 

way of the Snake River, Argentine Pass, and Leavenworth Creek, it is doubtful whether small power units 

would be economically justified.

The narrow-gage line of the Colorado & Southern 

Railway from Denver to Leadville by way of Grant, 

Breckenridge, and Dillon carries all products shipped 

from the western and southern parts of the region. 

The northeast quarter of the quadrangle is served by 

the Colorado & Southern narrow-gage line that extends 

from Denver to Silver Plume and by an autobus line 

that maintains year-round service. The comparatively light snowfall a few miles east of the Continental 

Divide permits automobile service in winter as well 

as summer, but on the western slope the roads are 

usually closed to cars from November to April, and 

during these months all freight is moved to and from

the railroad by horses, burros, or men. The Denver 

& Salt Lake Railroad (Moffat road), a standard-gage 

line, passes through Kremmling, 35 miles northwest 

of Dillon, and if the Colorado & Southern Railway 

Co. is permitted to abandon its Denver-Leadville 

narrow-gage line, Kremmling would be the nearest 

shipping point available throughout the year to the 

western part of the region.

The main roads in the region are kept in good condition, and most of the secondary roads can be traversed 

by automobiles, though with difficulty. The secondary roads crossing the Continental Divide have not 

been repaired in many years and are so badly washed 

out that it is doubtful if wagons could be hauled over 

them in their present condition. Many of the mines 

high above the valley floors are accessible only by 

trails, and supplies and ore are moved by pack trains.

A State highway over Loveland Pass was completed 

in 1933 and places Montezuma within 60 miles of 

Denver by road, less than half the former distance, 

making the whole quadrangle much more accessible 

than it was when this survey was made. Most of 

the road passes in the adjoining regions are closed from 

late in November to late May or early June, and 

Loveland Pass remains closed a somewha't longer time. 

It is probable that the western slope will always 

remain comparatively isolated during the winter.

BIBLIOGRAPHY

Aside from brief references to the region in statistical reports such as Mineral Resources, very little 

has been written about the area included in the 

Montezuma quadrangle. The references given below 

include practically all the literature dealing specifically 

with any part of the quadrangle and also includes some 

reports on the adjoining regions.

Anonymous, Brief notices of some recently described minerals. Am. Jour. Sci.,' 3d ser., vol. 22, pp. 490-491, 1881. 

Describes ilesite, (Mn,Fe,Zn)S04.4H2O, a new mineral from 

Hall Valley.

Bastin, E. S., and Hill, J. M., Economic geology of Gilpin 

County and adjacent parts of Clear Creek and Boulder Counties, Colo.: U.S. Geol. Survey Prof. Paper 94, 1917. Gives the 

geology of the north-central part of the Front Range mineral 

belt.

Bechler, G. R., Geographical report on Middle and South 

Parks, Colo., and adjacent region: U.S. Geol. and Geog. 

Survey Terr. Ninth Ann. Rept., for 1875, pp. 371-440, 1877.

Burchard, H. C. [and others], Report of the Director of the 

Mint, calendar years 1880 to 1928. These reports give the 

production of many individual mines in the Montezuma 

quadrangle.

Callbreath, J. F., Jr., The mineral resources of Summit 

County, Colo.: Mineral Reporter, vol. 40, pp. 342-345, 370- 

371, 1899. Lists the principal mines in Summit County and 

gives location, development, and an estimate of their production 

prior to 1899.

Chauvenet, Regis, The iron resources of Colorado: Am. Inst. 

Min. Eng. Trans., vol. 18, p. 268, 1890. Describes briefly the 

bog-iron ore in Handcart Gulch and Hall Valley and gives an 

analysis of the ore.
Colorado State Bureau of Mines, reports and bulletins, 1897 

to 1929. Give statistics and general information on mining in 

the State.

Corregan, R. A., and Lingane, D. F., Colorado mining directory, 1883, Denver, Colorado Mining Directory Co. Lists 

almost all mines in the State by counties, giving a brief summary 

of their ore, production, development, and organization. Has 

been found fairly reliable and not unduly optimistic.

Emmons, S. F., Geological sketch of the Rocky Mountain 

division: Tenth Census, vol. 13, pp. 60-104, 1885. Features of 

the geology and mineralogy of several mines in Colorado, by 

counties. Mentions Geneva and Hall Valley mines.

Fosset, Frank, Colorado, a historical, descriptive, and statistical work on the Rocky Mountain gold and silver mining regions, 

pp. 419-420, Denver, Daily Tribune Printing House, 1877. 

Brief history and features of a few veins in the Hall Valley, 

Geneva, and Montezuma districts.

Hague, J. D., Mining industry in Colorado: U.S. Geol. Expl. 

40th Par. Rept., vol. 3, pp. 617-624, 1870. Describes the newly 

discovered Snake River (Montezuma) district and gives information on the geology of the Comstock vein (Sts. John) in the 

upper workings.

Henderson, C. W., annual chapters on production of gold, 

silver, copper, lead, and zinc in Colorado, in Mineral Resources 

of the'United States, 19*08-31.

 Mining in Colorado: U.S. Geol. Survey Prof. Paper 

138, 1926. Gives the history of raining in Colorado and presents 

many details of production and development for individual 

mines.

Hillebrand, W. F., On an interesting variety of lollingite and 

other minerals: Am. Jour. Sci., 3d ser., vol. 27, pp. 355-357, 

1884. Gives description and analysis of a new bismuth mineral 

(later named cuprobismutite) from Hall Valley.

Jernegen, J. L., Jr., The Whale lode of Park County, Colo.: 

Am. Inst. Min. Eng. Trans., vol. 3, pp. 342-356, 1875. Gives 

detailed description of the Whale vein, Hall Valley.

 Notes on a metallurgical campaign at Hall Valley, 

Colo.: Am. Inst. Min. Eng. Trans., vol. 5, pp. 56-575, 1877. 

Notes on the character of the Hall Valley and Geneva Gulch 

ores; describes the smelter in Hall Valley and tells why it was 

unsuccessful.

Lee, W. T., Relation of the Cretaceous formations to the 

Rocky Mountains in Colorado and New Mexico: U.S. Geol. 

Survey Prof.- Paper 95, pp. 27-58, 1915. Gives reasons for 

believing that the Dakota formation once completely covered 

the site of the Front Range, which he believed was a geosyncline 

throughout Cretaceous time.

 Peneplains of the Front Range and Rocky Mountain 

National Park, Colo.: U.S. Geol. Survey Bull. 730, pp. 1-17, 

1923. Describes the Flattop and Rocky Mountain peneplains 

and tentatively assigns them to the mid-Tertiary and late 

Tertiary respectively.

 Correlation of geologic formations of east-central 

Colorado, central Wyoming, and southern Montana: U.S. 

Geol. Survey Prof. Paper 149, 1927. Description and correlation of the Pennsylvanian, Permian, Triassic, Jurassic, Lower 

Cretaceous, and some of the Upper Cretaceous beds bordering 

the Front Range.

Levering, T. S., Geologic history of the Front Range, Colo.: 

Colorado Sci. Soc. Proc., vol. 12, pp. 59-111, 1929.

 Localization of ore in the schists and gneisses of the 

mineral belt of the Front Range, Colo.: Colorado Sci. Soc. 

Proc., vol. 12, pp. 234-268, 1930.

 Geology and ore deposits of the Breckenridge mining 

district, Colo.: U.S. Geol. Survey Prof. Paper 176, 1934.

 See also Van Tuyl, F. M., and Levering, T. S. 

Marvine, A. R., The metamorphic crystalline rocks of the 

mountains: U.S. Geol. and Geog. Survey Terr. 7th Ann. Rept.,

for 1873, pp. 137-153, 1874. Gives one of the best accounts of 

the pre-Cambrian core of the Front Range that has been 

written.

Mineral Resources of the United States, 1882-1931, U.S. 

Geol. Survey, 1882-1923; U.S. Bur. Mines, 1924-31. Gives 

statistics of production for counties and many details of the 

mining in various districts for each year. (See Henderson, C. W.)

Mineral Industry, vols. 1-29, 1892-1920. Gives statistics 

and details of mining for each year.

Patton, H. B., The Montezuma mining district of Summit 

County, Colo.: Colorado Geol. Survey 1st Rept., pp. 105-144, 

1909. General features of the geology and mines of an area of 

22 square miles, including most of the Montezuma or Snake 

River district and parts of the Hall Valley and Geneva districts. 

Contains geologic and topographic map of the area studied, 

scale 1: 18,000.

Ransome, F. L., Geology and ore deposits of the Breckenridge 

district, Colo.: U.S. Geol. Survey Prof. Paper 75,1911. Includes 

the southwestern part of the Montezuma quadrangle.

Raymond, R. W., Statistics of mines and mining in the 

States and Territories west of the Rocky Mountains, 1869-75. 

Many local details of production.

Ritter, E. A., The Montezuma mining district, Colo.: Eng. 

and Min. Jour., vol. 85, pp. 241-244, 1908; Mines and Minerals, 

vol. 28, pp. 501-504, 1908. Gives map of the principal veins of 

the region and brief description of several mines near Monte^ 

zuma.

Spurr, J. E., Garrey, G. H., and Ball, S. H., Economic geology 

of the Georgetown quadrangle, Colo.: U.S. Geol. Survey Prof. 

Paper 63, 1908. Gives the geology of the quadrangle bordering 

the Montezuma quadrangle on the east.

Van Horn, F. A., Occurrence of proustite and argentite at the 

California mine, near Montezuma, Colo.: Geol. Soc. America 

Bull., vol. 19, pp. 93-98, 1908. Gives brief description of the 

mine and assays of ore and describes the occurrence of a small 

shoot of rich silver ore.

 A new occurrence of proustite and argentite: Am. 

Jour. Sci., 4th ser., vol. 25, pp. 507-508, 1908. Similar to 

reference above but less detailed.

Van Tuyl, F. M., and Lovering, T. S., A contribution to the 

Cenozoic history of the Front Range [abstract]: Geol. Soc. 

America Bull., vol. 43, p. 170, 1932. Correlate and date many 

Tertiary and Pleistocene erosion surfaces.

Widmar, R. J. A., Dill, R. G., and others, The Montezuma 

district: Mining Investor, vol. 49, pp. 155-170, 1907. A series of 

optimistic reports on the mines near Montezuma.

DESCRIPTIVE GEOLOGY

Pre-Cambrian granites, gneisses, and schists cover 

most of the Montezuma quadrangle. Mesozoic sediments are present in the southwestern part, and Tertiary intrusive rocks occur in a belt running from the 

southwest corner to the northeast corner. The preCambrian rocks are similar to those studied by Ball 

in the Georgetown quadrangle and can be easily correlated with them; additional work south of the Georgetown quadrangle has enabled the writer to trace the 

fRosalie granite 6 of Ball into the Pikes Peak granite 

of Cross, and as the formation names of Cross in the 

Cripple Creek region have priority over those of Ball,

«A dagger (t) preceding a geologic name indicates that the name has been abandoned or rejected for use in classification in publications of the U.S. Geological 

Survey. Quotation marks, formerly used to indicate abandoned or rejected names, 

are now used only in the ordinary sense.
6 MONTEZTJMA QJJADIt ANGLE, COLORADO

the term "Pikes Peak granite" is used in this report 

instead of "jRosalie granite." The | Archean quartz 

monzonite mapped as a separate unit by Ball is 

almost indistinguishable from the Pikes Peak granite 

in most of its occurrences in the Montezuma quadrangle and has not been separated as a distinct formation by the writer. The Mesozoic sediments bordering the pre-Cambrian mass on the west have been 

studied in detail for the first time in this region, and 

the stratigraphy of the Upper Jurassic and Upper 

Cretaceous given on pages 16-22 is characteristic of 

these sediments from Como to Kremmling.

ALGONKIAN (?) FORMATIONS 

IDAHO SPRINGS FORMATION

DISTRIBUTION

The Idaho Springs formation covers most of the east 

half of the quadrangle south of Clear Creek and is 

present along the western border north of the Snake 

River. The details of its occurrence and structure are 

shown in plates 3 and 4. It is the predominant 

schistose rock of the Front Range and is widely distributed in the region east and north of the Montezuma 

quadrangle, as shown in plate 5.

The schist in most of the quadrangle is closely folded 

and trends north. In the central part of the region 

the folds are moderately open and the strikes of the 

schistosity are less easily correlated because of the 

many subsidiary wrinkles imposed upon the folds. In 

the west-central part the axes of the folds strike northwest, but in the east-central part an east-west anticline is present. (See fig. 5.) In the southeast corner 

of the quadrangle the schistosity veers from southwest to south and finally to southeast as it is followed 

southward. This curving reflects the influence of the 

great east-west syncline whose axis is parallel to the 

valley of the North Fork of the Platte River a few 

miles southeast of the quadrangle.

AGE

The Idaho Springs formation is older than the Pikes 

Peak granite, which is older than the Cambrian quartzites of the Pikes Peak region and is believed to have 

been intruded in early middle Algonkian time. These 

pre-Cambrian rocks, as well as most of the other 

metamorphic and granitic rocks of the Front Range, 

have been referred to the Archean by some previous 

writers. Although the possibility that the Idaho 

Springs formation may be Archean must be admitted, 

a comparison of the geologic history of the region with 

that of the Lake Superior country strongly suggests 

that it belongs to the early Algonkian. 7 It is here 

tentatively classified as Algonkian (?).

' Lovering, T. S., Geologic history of the Front Range, Colo.: Colorado Sci. Soc. 

Proe., vol. 12, pp. 73-74,1929.

1ITHOIOGY

Megascopic features. The metamorphism of the 

Idaho Springs formation has developed many lithologic varieties, ranging from almost monomineralic 

schists to highly complex gneisses. The abundance 

of intrusive pegmatite varies greatly, but lit-par-lit 

injections and crosscutting seams and dikes of aplite 

and pegmatite are nearly everywhere present.

Quartz-biotite schist and gneiss are most common 

and grade into each other. The quartz-biotite schist 

is a moderately dense, gray rock, which presents a 

"pepper and salt" appearance on fresh fracture. It 

is made up of fine-grained quartz and biotite in nearly 

equal proportions with some accessory magnetite. 

The quartz-biotite gneiss is commonly a greenish-gray 

rock banded with black seams 1 to 3 centimeters 

wide, spaced from 2 to 15 centimeters apart. It is 

made up chiefly of quartz, microcline, plagioclase 

(oligoclase), and biotite, with some magnetite and 

sillimanite and rarely some hornblende. The black 

seams in the gneiss are largely biotite. All possible 

gradations between quartz-biotite schist and quartzbiotite gneiss can be found. These rocks are well 

shown in the region near Grays Peak and Argentine 

Pass. (See pi. 6, A.) Facies of the quartz-biotite 

gneiss and schist rich in sillimanite or muscovite or 

both are common throughout the formation.

Quartz "gneiss" and quartz schist make up only a 

small part of the Idaho Springs formation but are 

common in certain localities. The quartz "gneiss" is 

.a gray to brown rock in which over 90 percent is quartz. 

It ranges from a dense fine-grained rock to a mediumgrained granular gneiss resembling very siliceous 

granite gneiss. Hornblende and biotite are the chief 

accessory minerals. Very little feldspar is present, 

and the propriety of calling the rock a gneiss is questionable; its gneissic appearance and the fact that similar rocks have been described as quartz gneisses in 

nearby regions 8 have led the writer to use this term. 

Quartz gneiss is found on the top of the high eastern 

spur of Argentine Peak directly north of Silver Dollar 

Lake and can be traced east and northeast from this 

point to Sugar Loaf Mountain, in the Georgetown 

quadrangle, where it was noted by Ball. The largest 

bed of quartz schist is in the southern part of the 

Montezuma quadrangle a short distance east of the 

contact of the Idaho Springs formation and the 

Swandyke hornblende gneiss. The quartz schist probably has a maximum thickness of about 1,500 feet and 

is lenticular. However, this belt of siliceous schist 

can be traced north from Red Cone for several miles. 

The quartz schist ranges from a quartz-sericite schist 

to a schistose quartzite containing a small amount of 

mica and a little feldspar. It consists chiefly of

»Ball, S. H., op. cit. (Prof. Paper 63), p. 41. Bastin, E. S., op. cit. (Prof. Paper 

94), pp. 27-28.
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 178 PLATE 1

AIRPLANE VIEW LOOKING SOUTHWESTWARD UP LEAVENWORTH CHEEK. 

Courtesy of Geological Society of America.
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 178 PLATE 2

AIRPLANE VIKW LOOKING SOUTHWARD TOWARD LOVELAND PASS. 

Courtesy of Geological Survey of America.

Independence Mtn. 

Georgia
U.S. GEOLOGICAL SURVEY

106' 105° 30'

PROFESSIONAL PAPER 178 PLATE 5 

105'

L^l i_U + :^^^»Z/2222^ \" . * ~ k

EXPLANATION

Dike

Late Cretaceous and Tertiary 

intrusive and extrusive rocks

Cenozoic sedimentary rocks

Strike and dip of schistosity

39 39

IOG IO530

20 Miles

IO5

GEOLOGIC MAP OF THE FRONT RANGE,

Faults
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 178 PLATE 6

A. IDAHO SPRINGS FORMATION ON EAST SIDE OF GRAYS PEAK. 

Shows sill-like seams of aplitc and pegmalile parallel to the nearly horizontal schistosity and cross-breaking branch seams.

B. PHOTOMICROGRAPH OF QUARTZ-BIOTITE-SILLIMANITE SCHIST FROM NORTHEAST SLOPE OF GRAYS PEAK. 

Showing pronounced schistose texture. Crossed nicols. s, Sillimanite; q, quartz; b, biotite.
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 178 PLATK 7

A. TYPICAL EXPOSURE OF SWANDYKE HORNBLENDE GNEISS NEAR HEAD OF ST. JOHNS GULCH.

The gneissic struclure of the dark-gray hornblende gneiss is accentuated by the parallel and crosscutting light-gray seams of pegmatite and aplite. The dip of the

formation is uearly horizontal at this outcrop, which is near the crest of an anticline.

B. ANTICLINAL DOME OF DAKOTA QUARTZITE (Kd) CUT THROUGH BY THE SNAKE RIVER. 

Kp, Pierre shale; Kn, Niobrara limestone; Jm, Morrison formation; Ais, Idaho Springs formation.

C. VIEW LOOKING EAST AT RUBY GULCH FROM LENAWEE MOUNTAIN. 

The steepness of the right-hand side of the gulch was caused by glacial scour where the course of the former glacier swung from southwest to west.
ALGONKIAN (?) FORMATIONS

strongly sheared white quartz, in which most of the 

grains are between 0.2 and 1.3 centimeters in length. 

The weathered surfaces of some facies rich in sericite 

and feldspar simulate the blotched chalky appearance 

of altered porphyry, for which the quartz schist is 

sometimes mistaken.

Lime-silicate rocks, including hornblende-diopside 

gneiss, quartz-magnetite gneiss, and massive rocks 

composed of epidote, garnet, calcite, lime silicates, and 

quartz, are common in the Georgetown quadrangle 

but almost lacking in the Montezuma quadrangle. 

The lime-silicate rocks probably resulted from the 

regional and igneous metamorphism of limy sediments 

and are invariably close to granite stocks. A small 

mass of the epidote rock was observed on the northwest side of the valley of the North Fork of the Snake 

River about half a mile from its junction with the 

Snake.

Quartz-biotite-garnet schist is very common in the 

southwestern part of the quadrangle in the narrow 

strip of the Idaho Springs formation between the west 

edge of the Swandyke gneiss and the Cretaceous .sediments. It is a strongly foliated rock composed chiefly 

of moderately coarse grained biotite, medium-grained 

garnet, quartz, and microcline, with some muscovite 

and magnetite. It weathers readily to crumbling reddish-brown fragments and tends to form smooth slopes. 

It is well exposed on the precipitous banks of the 

Middle Fork of the Swan River, however, and forms 

much of Tenderfoot Hill, northwest of Keystone.

Injection gneiss is abundant at many places. PreCambrian aplites, pegmatites, and granites are so intimately injected into the schists everywhere that it is 

almost impossible to find any mass of schist 25 feet 

thick that is not seamed by one or more of the granitic 

rocks. In many places the seams of aplite and pegmatite lying parallel to the schistosity make up most of 

the rock, and the thin partings of schist that separate 

the intrusive seams give the rock the appearance of a 

granite gneiss. Although its composition is actually 

that of granite gneiss, it is more properly called injection gneiss, as it was formed by the injection of granitic 

magma into the schists. In extreme cases the schist 

has been so thoroughly permeated by the intrusive 

that only the shadowy outlines of its structure are 

preserved as biotite-rich layers. Gradations are common from simple schist through injection gneiss to 

granitic intrusives containing almost completely assimilated masses of schist. Injection gneiss is most frequently found bordering large masses of pegmatite, 

aplite, or granite, and the genetic relation of the gneiss 

is apparent.

The relations of the schists near a small stock of Pikes 

Peak granite in Bruno Gulch are unusually clear. The 

quartz-biotite-sillimanite schist of the region is greatly 

changed for a distance of several hundred feet from

the border of the granite stock. As the granite is 

approached, the normal quartz-biotite-sillimanite schist 

gradually gives way to a finely layered injection gneiss 

made up of alternating layers of biotite and quartzmicrocline aplites. The next change observed is the 

segregation of some of the quartz and microcline into 

knots about 1.5 centimeters long scattered sparingly 

through the rock. Toward the granite mass these 

knots become more and more conspicuous; most of 

them are sharply angular, after the habit of orthoclase or microcline, and many of them consist of welldefined individual crystals containing small amounts 

of included quartz. Close to the granite contact these 

metacrysts are so abundant that the rock strongly 

resembles a coarse-grained granite gneiss, and indeed 

it is shown on the map of the Georgetown quadrangle 

as a granite gneiss. The aplites instrumental in forming the injection gneiss are very quartzose and contain 

only small amounts of feldspar. The seams parallel to 

the schistosity are cut by cross-breaking dikes and 

seams of white siliceous aplite and pegmatite of similar 

appearance. These intrusives are distinctly earlier 

than the metacrysts, many of which are associated 

with thin seams of pink aplite and pegmatite. Pink 

coarse-grained pegmatite consisting of orthoclase, 

microcline, quartz, biotite, and some muscovite is the 

latest rock in this locality. The areal relations indicate that the various pegmatites and aplites were 

derived from a common source.and were given off at 

various stages in the consolidation of the Pikes Peak 

granite.

"Ellipsoidal masses" and "pebble-bearing gneiss" 

are the terms under which Ball and Spurr 9 respectively 

describe facies of the Idaho Springs formation that 

somewhat resemble a metamorphosed conglomerate. 

In the Montezuma quadrangle grayish-white ellipsoidal 

or discoidal masses occur in the schists at several places. 

The masses are commonly from 1 to 3 centimeters long 

and about 0.5 centimeter thick. They consist largely 

of medium-grained quartz and always carry a small 

amount of sillimanite or fibrolite, but feldspar is rare. 

The masses usually occur in bands from 1 to 10 feet 

thick, and both the bands and the discoidal masses are 

parallel to the schistosity. These masses are distributed with remarkable regularity in the plane of schistosity, arid the evenness of their spacing, usually from 

1 to 3 inches apart, suggests the development of a 

knotted schist through severe metamorphism rather 

than the mashing of an original conglomerate. The 

quartz-fibrolite knots are much more closely spaced 

across the schistosity than parallel to it and may be 

separated from overlying or underlying masses by a 

mere film of schist. In some places the masses are 

drawn out to long, narrow elliptical bodies that swell 

and pinch; in other places the smooth elliptical shape

» Spurr, J. E., Garrey, G. H., and Ball, S. H., op. cit. (Prof. Paper 63), pp. 41,177.

71880-35-
8 MONTEZUMA QUADRANGLE, COLORADO

of river pebbles is simulated. Here and there the 

ellipsoidal or discoidal masses are connected by thin 

veinlike seams of quartz, and the masses appear to be 

genetically related to such veins. The schistosity 

curves around the masses, and in some places they are 

crossed by fractures standing at a high angle to the 

schistosity. The knotted schists are widely distributed 

in the Montezuma and Georgetown quadrangles but 

were not noted by Bastin 10 in the Central City quadrangle. They are most abundant near the large intrusive masses of pre-Cambrian granite and are rare in 

the region a few miles away from the mass of fRosalie 

granite and quartz monzonite (see Pikes Peak granite, 

pp. 12-13) in the Georgetown quadrangle. The knotted schists in the Montezuma quadrangle occur chiefly 

near its eastern border and can be seen at many places 

near the heads of West Geneva and Leavenworth 

Creeks. It is worthy of note that the region in which 

the knotted schists or "metamorphosed conglomerates" occur abundantly coincides with that in which 

the most highly aluminous pegmatites were found. 

Tourmaline-bearing pegmatites are commonly associated with the knotted schists, and many of them 

carry garnet, sillimanite, or corundum. The writer 

believes that most of the ellipsoidal and discoidal 

masses in the schists are the result of extreme metamorphism attended by the migration of siliceous and 

aluminous material, in part magmatic and in part derived from the schist itself. No facies of the Idaho 

Springs formation that can be safely interpreted as a 

metamorphosed conglomerate has been observed in 

the-Montezuma quadrangle.

Microscopic features. A microscopic study of the 

Idaho Springs formation shows that the schistosity is 

developed chiefly through the parallelism of sillimanite 

and biotite crystals. The general elongation of quartz 

and feldspar in the direction of the schistosity is also 

an important factor, but the schistose structure becomes more and more clearly defined as the proportion 

of sillimanite or biotite becomes greater.

The most common minerals in the schists, named 

in the order of their abundance, are quartz, biotite, 

orthoclase, oligoclase, and sillimanite. Locally hornblende, magnetite, garnet, muscovite, sericite, tourmaline, and epidote (much of it near clinozoisite in 

composition) become prominent, and some of them, 

such as magnetite and sericite, are nearly everywhere present, though usually in small amounts. 

Zircon, titanite, apatite, and rutile are common accessory minerals.

Quartz occurs in granulated, sheared, and interlocking crystals showing wavy extinction. The size 

of the grains usually ranges from 0.1 to 2.0 millimeter, 

but in exceptional occurrences quartz crystals may 

reach a length of 1.0 centimeter. The quartz found 

in the schists near the western border of the quad10 Bastin, E. S., op. cit. (Prof. Paper 94), p. 29.

rangle contains few fluid inclusions, but the quartz in 

the schists near the eastern border are crowded with 

hairlike lines of liquid and gas inclusions. In some of 

the liquid inclusions minute cubes of salt that exhibit 

Brownian movement can be seen.

Biotite occurs in bladelike crystals, many of which 

are much frayed at the ends. Some green biotite has 

been found, but most of that present is the brown 

variety. In a few places the biotite contains radioactive inclusions surrounded by pleochroic halos. 

Most of the biotite is fresh, but some crystals are 

partly altered to chlorite, magnetite, and sericite. (See 

pi. 6,5.)

Sillimanite occurs chiefly in laminae made up of 

rods parallel to the direction of schistosity but is 

common also in confused masses intergrown with 

other minerals. It is in places sparsely disseminated 

throughout layers consisting, largely of quartz, feldspar, or mica and has apparently developed by replacement. As sillimanite was formed both through 

regional metamorphism and through contact metamorphism, it is not surprising to find some sillimanite 

that has replaced other minerals. Although needles 

of sillimanite penetrate all the other essential minerals 

of the schist, it has more commonly replaced biotite 

and muscovite than quartz or feldspar. Mediumgrained muscovite is common in the sericitic quartz 

schists, and large crystals occur in many of the sillimanite schists. Sagenitic rutile and skeletal ilmenite 

crystals were observed in some of the muscovite, but 

most of it is free from inclusions. In many of the 

slides biotite and muscovite are contemporaneous, but 

a little muscovite is apparently secondary to the 

biotite. Orthoclase is the predominant feldspar and is 

in places micropegmatitically intergrown with quartz. 

The chief plagioclase found in the schists is an albiteoligoclase. Microcline and andesine occur rarely. 

Locally the feldspars show wavy extinction, and this is 

most pronounced in the strong gneissic rocks. Sericite is common as a fine-grained matrix in the quartz 

schists and as an alteration product of the feldspars in 

the feldspathic schists and gneisses.

STRUCTURE AND ORIGIN

During the study of the Idaho Springs formation in 

the Montezuma quadrangle the writer reached the 

conclusion that the schistosity is nearly everywhere 

parallel to the bedding planes of the original sediments. J. T. Stark and F. F. Barnes, working in the 

schists of the Sawatch Range, to the west, and M. F. 

Boos, studying the pre-Cambrian of the Rocky Mountain National Park, to the north, informed the writer 

that they had reached a similar conclusion. It is 

well known, however, that planes of schistosity may not 

be parallel to bedding planes, and for this reason 

little attention was given to the structure of the schist 

in earlier studies of the region.
ALGONKIAN (?) FORMATIONS 9

Some observers have recently found that lit-par-lit 

injection of sediments usually converts them into 

schists and gneisses whose schistosity is parallel to 

the bedding planes of the original sediments. 11 As 

there is reason to believe that most of the schistosity of 

the Idaho Springs formation was developed during a 

period of batholithic invasion and that lit-par-lit 

injection occurred on a large scale, the writer has given 

special attention to the detailed structure of the schist 

and has found that schistosity coincides with bedding 

throughout the quadrangle. The cause of this coincidence is discussed in the following paragraphs.

The main processes active in the formation of schist, 

according to Leith, 1 '1 are granulation, recrystallization, rotation of grains through differential movement 

of adjacent layers, gliding on crystallographic planes, 

slicing, and coarse fracturing. These processes result 

in a mineral aggregation whose dimensional arrangement is nearly parallel, and schistose or flow cleavage 

is a cleavage parallel to the long and short or the long 

and intermediate dimensions of the mineral grains.

Recrystallization is commonly the result of solution 

and deposition almost in place, and it becomes more 

and more active and rapid as moisture and heat 

increase. The other processes all result from some form 

of shearing and can be ascribed to differential pressure. 

Although, differential pressure is commonly the chief 

factor in the formation of schists, the texture and 

coarseness of grain are largely dependent on the conditions of temperature and moisture. The physical 

and chemical properties of the rock, the original arrangement of minerals, and the length of time involved 

are also important factors.

In the absence of heat and moisture, differential pressure does not readily cause the formation of large 

bodies of schist. Sediments may be intensely crumpled with no appreciable rotation of the mineral grains 

and .without recrystallization, and, as a consequence, 

flow cleavage is lacking in many strongly folded beds, 

if a long-continued differential pressure should act on 

sediments after they were closely folded, tending to 

elongate them in one direction, and to shorten them in 

another, flow cleavage would slowly develop parallel to 

the direction of elongation, even in the absence of heat 

and moisture as important contributing factors. 

The cleavage of roofing slate has evidently been developed in this way. The direction of elongation is 

essentially that of the flow lines in a viscous body 

deformed by differential pressure. Recrystallization 

takes place, and the new crystals grow in the direction 

of relief of pressure. The crystals are minute in slates, 

but if heat and moisture increase, recrystallization 

becomes more active, larger crystals grow, and a 

phyllite or even a schist develops. Many forms of flow 

cleavage, including slaty cleavage, are clearly inde-

" lloss, C. P., and Butlor, B. S., personal communication.

" Loith, C. 1C., Koclc clonvngo: U.S. Geol. Survey Bull. 239, pp. 05-70, 1905.

pendent of bedding, and if the final result is a schist, 

schistosity is also independent of bedding, although in 

most places there will be a general parallelism between 

bedding and foliation in the limbs of folds. This 

parallelism reflects the tendency of limbs of folds to be 

perpendicular to regional compression in closely folded 

sediments. Where slaty cleavage has been imposed on 

closely folded sediments, the cleavage is generally the 

same over wide areas and is rarely contorted and closely 

folded itself. The slate belt of Pennsylvania affords a 

good example of metamorphism of this type.

During, strong folding there is a varied differential 

movement between competent and incompetent beds. 

If deformation takes place at moderately high temperatures and pressures in the presence of moisture, 

schist may develop without any intermediate stage 

of slaty cleavage. Recrystallization takes place in the 

direction of greatest relief, which coincides with the 

flow lines of the material. During simple folding the 

beds have differential movement on the limbs but show 

no movement relative to one another on the crests of 

folds. As the folds become isoclinal with vertical axes, 

the flow of material from the thinning limbs to the 

swelling crests may be considerable, and the flow lines 

in the crests will on the whole be nearly parallel to the 

axes of the folds. If, however, the crests, instead of 

rising vertically, move sideways, forming overturns and 

fan-shaped folds, they will pass into material formerly 

on the limbs of the folds. The flow lines of the deformed material would then be complex but should be 

roughly parallel to the bedding of the contorted sediments. The countless minor folds and contortions in 

the Montezuma quadrangle indicate much flowage, and 

the fact that the elongate minerals follow the minor 

crumplings without being granulated suggests their 

development during the. period of flowage. The 

development of schistosity under such conditions is 

essentially a dynamic process, in contrast to slaty 

cleavage and schistosity, which develop under much 

more static conditions.

Bedding planes themselves are original cleavage surfaces or partings, and the original minerals of a sediment tend to have a marked dimensional arrangement 

parallel to them. This arrangement would be increased 

by shearing along the bedding planes, and under favorable conditions of heat and moisture, recrystallization 

and crystal growth would take place quickly and would 

rapidly accentuate the original rock cleavage. Differential, movement would be at a maximum in interlayered plastic and brittle beds. The injection of countless 

thin seams of water-rich magma along the bedding 

planes (lit-par-lit injection), would raise the temperature, increase the moisture content, and produce layers 

differing greatly in plasticity from the original sediments. Such conditions would be ideal for the rapid 

,development of schistosity parallel to the bedding of 

a crumpling mass of sediments.
10 MONTEZUMA QUADRANGLE, COLORADO

The contorted appearance of the Idaho Springs 

formation (pi. 6, A) and the abundance of lit-par-lit 

injections suggest that such conditions were present 

during its development. In this formation there is 

a concordance between the occurrence of certain 

recognizable sedimentary zones and the planes of 

schistosity, and the structure of the schist as interpreted 

from the dips and strikes of the schistosity is inferred 

to represent approximately the structure of the ancient 

sediments.

SWANDYKE HORNBLENDE GNEISS

Distribution and name. The Swandyke hornblende 

gneiss, which overlies the Idaho Springs formation, is 

the chief metamorphic rock in the west half of the 

quadrangle. It was called the "hornblende gneiss" 

by Patton, 13 who studied the Montezuma district in 

1908. The studies of the writer in the Montezuma 

quadrangle and the regions to the north and south have 

shown that the formation is very extensive on the west 

side of the Front Range and should be recognized by a 

distinctive formation name. It is typically developed 

in the southern part of the Montezuma quadrangle, 

near the "ghost town" of Swandyke, on the Middle 

Fork of the Swan River, and it is proposed to recognize 

this region as the type locality of the formation. Accordingly the "hornblende gneiss" of Patton is here 

named the "Swandyke hornblende gneiss."

Structure. The general strike of the Swandyke 

gneiss and of its schistosity is north to northwest, and 

its general structure is isoclinal, as shown in plate 4, 

section D-D'. In the southern part of the quadrangle 

its prevailing dip is to the east or northeast through 

most of the large syncline that the gneiss occupies, but 

its eastern contact with the Idaho Springs formation 

dips west at an average of about 70°. In the central 

part of the quadrangle, a few miles south of the Snake 

River, the gneiss has been thrown into a series of anticlines and synclines that trend from north to northeast. Owing to its position in a southward-plunging 

syncline the gneiss thins rapidly north of the Snake 

River and disappears a short distance north of the 

South Fork of the Williams River. It reappears a 

short distance to the northwest, and about 3 miles 

north of the Montezuma quadrangle it enters the west 

side of the Fraser quadrangle, where it crops out in a 

wide belt running northeast nearly to Fraser.

Lithology. The Swandyke gneiss consists of hornblendic gneisses and schists with some interlayered 

quartz schists, all intimately injected by pegmatite, 

aplite, granite, and granite gneiss. These granitic 

rocks make up almost 50 percent of the main area in 

which the formation is exposed. Where the intrusions 

are abundant the schists and gneisses are commonly 

so contorted that it is impossible to observe any relation to a regional structure. Where the intrusions are*

i 3 Patton, H. B., The Montezuma district in Summit County, Colo.: Colorado 

Oeol. Survey 1st Kept., for 1908, pp. 123-124, 1909.

less abundant, however, the direction of schistosity 

is remarkably uniform over large areas.

The most common variety of the Swandyke gneiss, 

well exposed in the type locality, is a medium-grained 

greenish-gray hornblende gneiss. It is banded parallel 

to the schistosity, owing to a slight segregation of 

feldspar and hornblende in alternate bands, but both 

minerals are abundant throughout the rock. On 

fresh fracture the gneiss has a conspicuous pepper and 

salt appearance, caused by the dark-colored hornblende 

crystals lying in a groundmass of gray plagioclase. 

)n Glacier Mountain and in Keystone Gulch the hornblende gneiss grades into a diorite gneiss containing 

biotite as the chief ferromagnesian mineral. In a few 

places the hornblende gneiss passes into a dense chloritized greenstone.

The schists are of secondary abundance and are 

usually interlayered with the hornblende gneiss in 

lenticular masses from 5 to 100 feet thick and rarely 

more than a few hundred yards in length. Quartz 

schists and feldspathic quartz-biotite schist are more 

common than hornblende schist, but in some places 

layers of nearly pure hornblende schist occur. Garnet 

is rather common in both the hornblende and 

the biotite schist. No muscovite, sillimanite, or 

chlorite schists have been observed in the Swandyke 

gneiss.

On joint surfaces the gneiss weathers a dark green, 

but where the formation is exposed on cliffs the color 

is commonly a dull earthy brown or a dull grayish 

green. Against this background the intrusive pegmatites, aplites, and granites stand out as light-buff or 

pinkish seams and masses, which cut the darkercolored schists and gneisses into irregular blocks of 

greatly varying.size.

Injection gneiss is developed in the schist facies of 

the Swandyke gneiss wherever pegmatitic or aplitic 

intrusives are abundant. The massive hornblende 

gneiss is a less favorable host rock for the thin lit-parlit intrusions that produce injection gneiss, but in 

many places thin sills are so abundant that the rock 

must be classed as injection gneiss. In plate 7, A, 

typical exposures of the Swandyke gneiss are shown.

Hornblende and andesine are the chief minerals of 

the Swandyke gneiss and together make up over 90 

percent of most of the dark bands in the formation. 

The schistosity is parallel to alternating bands of 

hornblende-rich and feldspar-rich seams; the long axis 

of the hornblende crystals and the cleavage are generally parallel to the plane of schistosity, but most of 

the feldspars have random orientations. The plagioclase and hornblende crystals commonly range from 

0.2 to 0.4 centimeter in length. Some quartz is 

usually present in the dark bands, and it may make up 

a third of the rock in the light-colored bands. As 

hornblende and andesine decrease biotite and microcline usually increase. Where microcline is abundant 

the plagioclase is generally albite-oligoclase. Apa-
ALGONKIAN SYSTEM 11

tite, magnetite or ilmenite, titanite, zircon, and some 

pyrite are common accessory minerals.

Origin. The petrology of the formation indicates 

that it is a metamorphosed igneous rock intermediate 

between gabbro and diorite in composition. The 

Swan dyke gneiss is essentially conformable with the 

enclosing Idaho Springs formation. In most places 

( /lie contact between the two formations is gradational, 

but just south of the Montezuma quadrangle the base 

of the Swandyke hornblende gneiss is marked by a 

persistent bed of banded magnetite jasper. At most 

places a very coarse-textured garnet-epidote rock lies 

between the jasper and the hornblende gneiss. Schistose quartzite or "quartz gneiss' 5 is interbedded with 

the .lior.nble.nde gneiss a few miles .s'outhwest of Hall 

Valley, and some of the hornblende gneiss nearby 

weathers with a patterned surface suggesting the fragniental structure of a schistose volcanic breccia. The 

jasper and quartz gneiss are clearly of sedimentary 

origin, and it is believed that the intervening layers of 

born blende gneiss were originally surface flows of andcsitic composition. The areal relations shown on 

plate 3 suggest a thick series of lavas whose lower members were contemporaneous with the upper beds of 

the Idaho Springs formation.

Distinct intrusive relations were not found in the 

Montezuma quadrangle, but half a mile southeast of 

Whale Peak, just south of the mapped area, a dike of 

biotite-ho.mb.le.nde schist cuts quartz gneiss that is intcrbcddcd with, hornblende gneiss. The dike cuts the 

quartz gneiss at a marked angle to the gneissic structure, but the schistosity of the dike is parallel to its 

own walls. The dike was probably formed in the same 

general period of volcanic activity as the andesitic lavas 

that make up the bulk of the Swandyke hornblende 

gneiss. According to Ball 14 hornblende gneiss cuts 

the Idaho Springs formation at some places in the 

Georgetown quadrangle, but the dikes of hornblende 

gneiss observed in the Montezuma quadrangle are 

gneissic facies of the quartz diorite, which was nearly 

contemporaneous with the Pikes Peak granite. Intrusive hornblende gneiss was also found in the schists 

of the Central City quadrangle by Bastin, 15 who 

mapped them as Archean quartz diorite; he found no 

hornblende gneiss that was earlier than granite gneiss. 

Granite gneiss is clearly later than the Swandyke gneiss 

in the Montezuma quadrangle, and it seems probable 

that some of the intrusive relations of the hornblende 

gneiss noted by Ball belong to dikes originating long 

after the Swandyke gneiss.

ALGONKIAN SYSTEM 

QUARTZ MONKONIT13 GNEISS

Distribution and structure. The quartz monzonite 

gneiss is not abundant in the Montezuma quadrangle,

'« Ball, S. H., op. cit. (Prof. Paper 03), p. 45.

"« Bastin, E. S., op. cit. (Prof. Paper 94), pp. 32-33.

although some large bodies occur in the Georgetown 

quadrangle and one of them extends a short distance 

into the Montezuma quadrangle south of Leavenworth 

Creek. A poorly exposed mass of quartz monzonite 

gneiss intrudes the Swandyke gneiss on Keystone 

Mountain. A small mass of the quartz monzonite 

gneiss is exposed on the Loveland Pass road about \% 

miles north-northwest of the pass. It is intrusive into 

the Idaho Springs formation and probably also into 

the Swandyke gneiss. It grades into the Swandyke 

imperceptibly in most places, however, and can be 

distinguished only by the appearance of bio tite and 

disappearance of hornblende, although it is commonly 

more massive than the hornblende gneiss. Where it 

intrudes the Idaho Springs formation remote from the 

Swandyke gneiss, its contacts are parallel to the schistosity of the schists, and it shows intense penetration 

of the schist through lit-par-lit injection. It is probable that much of the early lit-par-lit injection of the 

schists, so instrumental in their metamorphism, was 

accomplished by this quartz monzonite magma.

Lithology. The quartz monzonite gneiss is a moderately dark gray medium to coarse grained gneiss 

which is locally porphyritic. The most abundant 

minerals are smoky quartz, andesine or calcic oligoclase, biotite, rnicrocline, orthoclase, and hornblende. 

Megascopic crystals of magnetite, pyrite, and titanite 

are visible in many places, and most thin sections show 

zircon and apatite as additional microscopic accessory 

minerals. Much of the feldspar and quartz shows 

marked granulation and some recrystallization. The 

minerals are alined parallel to the gneissic structure, 

which is marked by alternating layers rich and poor in 

biotite. In many places schist inclusions are abundant. 

Their schistosity is always parallel to that of the gneiss, 

and streamers of biotite extend out from many of the 

inclusions into the enclosing rock, where they gradually 

fade out and are indistinguishable from the biotite-rich 

layers not obviously related to schist inclusions. Most 

of the inclusions have been intensely injected by the 

quartz monzonite magma, and in some places only a 

shadow of the former inclusion is left. It is apparent 

that assimilation was locally an important factor in 

determining the composition of the quartz monzonite 

gneiss.

GRANITE GNEISS

Distribution and structure. Granite gneiss is abundant in the Georgetown quadrangle, but only a. few 

masses have been found in the Montezuma quadrangle. 

It occurs in the region between the North and Middle 

Forks of the Swan River, on the ridge between Keystone Gulch and Soda Creek, and on Bear Mountain. 

The granite gneiss nearly everywhere follows the 

schistosity of the enclosing schists or gneisses, but in 

some places it cuts across the schistose structure. 

Small masses are lenticular or sill-like in form, but the, 

contact of large bodies that have broken through schists
12 MONTEZUMA QUADRANGLE, COLORADO

is very serrate and irregular, and innumerable 

apophyses feather out along the schistosity of the 

country rock. In some places it forms sills that are 

directly related to the formation of injection gneiss. 

The contact between the granite gneiss and the Swandyke hornblende gneiss is usually gradational, the 

granite gneiss passing into injection gneiss and this in 

turn into hornblende gneiss.

. Lithology. The granite gneiss comprises metamorphosed granite, aplite, and pegmatite, but gneissic 

aplite or fine-grained gneissic granite is the predominant rock. Most of it is a light-gray even-grained rock 

consisting largely of quartz and feldspar. Mica is 

rarely prominent, but biotite is usually present in small 

amounts, although in some of the formation the chief 

dark-colored mineral is magnetite. Locally muscovite 

occurs in large crystals, and facies containing garnet 

are common. The granite gneiss is more siliceous than 

the later granites and pegmatites and on fresh fracture 

has a sugary appearance. When examined with a hand 

lens the quartz grains are seen to be slightly granulated, a condition not found in the orthogneissic facies 

of the later granitic rocks.

The microscope shows that the quartz has been subjected to strain but has not been so extremely crushed 

and recrystallized as the quartz in the older formations. 

There is little tendency for the quartz or feldspar to 

occur in bands, and the texture is essentially granitoid. 

The biotite and muscovite, however, are parallel to the 

gneissic structure and occur in short strings of frayed 

and shredded crystals. Orthoclase and microcline are 

both common but rarely exceed quartz. Oligoclase is 

present in most of the formation and locally it is the 

only feldspar. Sodic granite gneiss of this type occurs 

on the northeast spur of Bear Mountain. Apatite, 

magnetite, and zircon are always present in' small 

amounts, and here and there clear crystals of garnet can 

be seen.

The gneissic structure is due to the parallelism of the 

mica, the slight granulation of the quartz and feldspars, 

and the original parallel orientation of feldspars and 

quartz which occurs in some places. The structure is 

most prominent on the outer borders of granite gneiss 

bodies, and complete recrystallization is found only 

here.

QUARTZ DIORITE AND HORNBLENmTE

Distribution and structure. The Algonkian quartz 

diorites and associated hornblendites are very sparsely 

distributed in the Montezuma quadrangle, although 

moderately abundant in the Central City and Georgetown quadrangles, where they were mapped as "Archean quartz diorite." It is now believed that the 

quartz diorites are of Algonkian age (see p. 11), and 

they are so classified in this report. Dikes and small 

irregular masses cut the Idaho Springs formation northwest of Silver Plume, near Argentine Pass and Mount

Edwards, and in the southern part of the quadrangle 

near the head of Sawmill Gulch.

Lithology. Most of the Algonkian quartz diorite is a 

dark-colored medium or coarse-grained rock having a 

mottled black and white appearance. As it ranges in 

composition from a hornblendite through diorite and 

quartz diorite to a nearly pure aiiorthosite, its color 

ranges from greenish' black to light gray. The darker 

facies of the formation commonly occur in dikes or near 

the borders of small stocks and usually have a welldeveloped gneissic structure. In some places, as in the 

dikes northwest of Silver Plume, they have been converted into hornblende schist. The central parts of 

the irregular masses of diorite and quartz diorite are 

usually massive or have a faint orthogneissic character, 

but the edges generally show a banded structure and 

some evidence of mashing. Although great variations 

in composition occur, most of the formation is a calcic 

quartz diorite resembling a coarse-grained gabbro, and 

as some augite is almost invariably present, many parts 

of the formation poor in quartz might properly be called 

gabbro.

Plagioclase (generally labradorite), hornblende, biotite, and quartz are the essential minerals, and in some 

places orthoclase or augite becomes an abundant constituent of the rock. Ilmenite, apatite, magnetite, 

titanite, and pyrite are common accessory minerals, 

and rutile and zircon are locally present. In the gneissic facies the biotite is alined parallel to the schistose 

structure, the hornblende, plagioclase, and quartz are 

slightly segregated in bands, and the quartz and some 

of the feldspars show a pronounced wavy extinction.

According to Ball 1G the quartz diorite grades into 

the so-called |"Archean quartz monzonite" (Pikes 

Peak granite) near St. Marys Lake but cuts it in other 

places. He accordingly favors the hypothesis that 

both rocks are differentiation products from the same 

magma but that the quartz diorite separated after 

most of the magma had solidified as quartz monzonite. 

Bastin, 17 on the other hand, states that'the relations ol 

the granite gneiss and the quartz diorite suggest that 

the two rocks are of nearly the same age and may have 

come from a common source. As indicated on pages 

13 and 49, the writer believes that the granite gneiss, 

quartz diorite, quartz monzonite, and Pikes Peak or 

fRosalie granite belong to the same general period of 

magmatic invasion and that there is comparatively 

little difference in the age of the different rocks, although the granite gneiss is probably slightly older 

than the others;

PIKES PEAK GRANITE

Distribution and structure. The Pikes Peak granite 

is found only in the southeastern part of the Monteis Ball, S. H., op. cit., p. 56. 

'» Bastin, E. S., op. cit., p. 33,
ALGONKIAN SYSTEM 13

zuma quadrangle but occupies a little more than half 

of the Georgetown quadrangle, where it has been 

mapped as fRosalie granite and fArchean quartz 

monzonite. It extends southward at least 80 miles to 

the southern border of the Pikes Peak quadrangle, 

forming a belt of granite/from. 10 to 30 miles wide. 

The contact of this batholith with the enclosing schists 

and gneisses is moderately smooth and reguhir, and 

few stocklike protrusions are found in the region bordering the large mass. Near the north end of the 

batholith, however, some isolated masses of Pikes 

Peak granite occur a short distance away from the 

main body. Dikes of typical Pikes Peak granite .are 

very rare, although at many places the granite grades 

into pegmatites that pass into dikes. When the border is examined in detail, however, many pegmatitic 

tongues can be found extending into the surrounding 

schists, and. partly assimilated inclusions of the older 

rocks are very abundant in the monzonitic border 

facies.

Lithology. The typical Pikes Peak granite is a 

coarse-grained granular pink rock, consisting largely 

of microcline and quartz. Porphyritic masses have 

been found in a few places and pegmatitic facies are 

common. Near the borders of the large masses an 

orthogneissic facies usually occurs, differing slightly in 

composition from the central granite. As the border 

of the granite is nearly everywhere parallel to the 

schistosity of the enclosing formations, the movement 

of the magma developed flow structure, which for long 

distances almost coincides in strike and dip with the 

nearby schists. This border facies is a gray, moderately coa,rse grained, slightly porphyritic rock, usually, 

containing abundant biotite.

The typical pink Pikes Peak granite contrasts 

strongly with much of the gray, slightly gneissic quartz 

monzonite border facies, and Ball mapped them as 

separate formations; but complete gradations from 

one rock into the other can be found at many places 

between Summit Lake, in the Georgetown quadrangle, 

and Bruno Gulch, in the southeastern part of the 

M.ontczuma quadrangle. The orthogneissic structure 

of the quartz monzonite border facies is caused by 

the flow structure of the feldspars and biotite and to 

a less extent by the parallelism of the numerous imperfectly assimilated schist inclusions. The chief 

difference in composition between the two rocks lies 

in the relative abundance of biotite and oligoclase. 

With a decrease in these minerals and an increase in 

microcline, the quartz monzonite assumes the pink 

color of the typical Pikes Peak granite, and where 

the flow structure is not evident the two rocks are 

indistinguishable. The perfect gradation from one type 

of rock to the other shows that they are genetically 

related and that part of the Pikes Peak granite and 

part of the quartz monzonite are contemporaneous. 

The regional relations indicate that the quartz monzonite is a border facies of the Pikes Peak batholith 

and is slightly earlier than the bulk of the granite. 

Although both rocks are coarsely granular, the quartz 

monzonite is liner grained than the granite. The 

feldspars in the quartz monzonite commonly range 

from 0.5 to 2 centimeters in length and those in the 

typical Pikes "Peak granite usually range from 1 to 5 

centimeters in length.

Under the microscope the Pikes Peak granite is 

found to be an uneven-grained, coarsely granitoid rock 

consisting chiefly of microcline, quartz, orthoclase, 

oligoclase, and biotite. Much of the microcline is 

microperthitic, and microcline, orthoclase, and oligoclase contain abundant inclusions of blood-red hematite. Quartz rarely shows any evidence of granulation 

and occurs both as xenomorphic crystals and as micropegmatitic intergrowths with feldspar and biotite. 

Hematite inclusions are much less abundant in the 

quartz than in the feldspars. Biotite commonly occurs 

in interstitial subhedral blades, arid the bent, ragged 

crystals common in the older rocks are absent. Where 

hornblende is present, it occurs as individual columns 

or as intergrowths with biotite. It is most abundant 

in the monzonitic border facies of the granite. Magnetite, apatite, and zircon are the-most plentiful accessory minerals, but locally titanite, allanite, and pyrite 

were also found. Muscovite is rare.

Age. Samarskite from Devils Head, 37 miles eastsoutheast of the Montezuma quadrangle, probably 

occurring in miarolitic cavities in the Pikes Peak granite, has been analyzed and the lead, uranium, and 

thorium determined with considerable precision. The 

lead-uranium ratio indicates that the age of the mineral 

is approximately 1,025,000,000 years. This age corresponds to early middle Algonkian time. 18 The Pikes 

Peak granite is definitely older than the Silver Plume 

granite, which cuts it at many places. It is believed to 

have formed near the middle of a batholithic C37cle that 

commenced with the intrusion of the quartz monzonite gneiss and ended with the intrusion of the finergrained facies of the Silver Plume granite.

SILVER PLUME GRANITE

Distribution and structure. The Silver Plume granite 

crops out extensively in the north half of the quadrangle, covering a rudely triangular area whose apex is 

at Keystone and whose base extends along the northern 

boundary from a point 2 miles east of the northwest 

corner to a point 1 }{ miles west of the northeast corner. 

This mass is part of a small batholith that extends several miles north into the Fraser quadrangle. In the 

eastern part of the Montezuma quadrangle a narrow 

southwestward-trending body of granite stretches from 

Silver Plume to Mount Edwards, and isolated masses 

occur at several places, chiefly in the southeast quarter 

of the quadrangle.

is Holmes, Arthur, The age of the earth: Nat. Research Council Bull. 80, pp. 338, 

438-441, 1931.
14 MONTEZUMA QUADRANGLE, COLORADO

The Silver Plume granite has sharp straight contacts 

with the older rocks at many places and probably followed fault lines and fracture zones more commonly 

than the older intrusive rocks. Inclusions of schist are 

common in the batholithic mass, and where they are 

abundant the schistosity is usually concordant in the 

different masses. It is probable that both roof pendants and xenoliths are present and that overhead 

stoping was an important factor in the invasion of the 

granite, although probably less important than in the 

development of the Pikes Peak batholith. 19 Dikes of 

Silver Plume granite are rare, as the narrower masses 

are usually the pegmatitic facies discussed on page 15. 

In general, the granite occurs as a batholithic mass, 

small stocklike masses or irregular tongues from the 

batholith.

The type locality of the Silver Plume granite is only 

a mile east of the Montezuma quadrangle, and large 

masses of the rock extend across the border. Thus the 

correlation of the granite in the Montezuma quadrangle 

with the Silver Plume granite can be made with certainty. The Santa Fe and Bear Mountain granites of 

Patton 20 are both correlated with the Silver Plume 

granite by the writer.

 Lithology. Most of the Silver Plume granite is a 

pinkish-gray medium-grained, slightly porphyritic biotite granite. A conspicuous feature of the granite is the 

general parallelism of the subhedral to euhedral feldspar 

crystals. As there is no granulation except in shear 

zones, the alinement of the feldspars is a primary structure due to movement in the magma after the formation 

of crystals. This flow structure is very pronounced 

near the borders of moderately large stocks, where the 

granite is commonly porphyritic; here lathlike phenocrysts from 1 to 3 centimeters in length give this facies 

a striking appearance the "corn rock" of the miners. 

The size of the crystals in the large masses of the granite, however, generally ranges from 0.25 to 1 centimeter. The parallel' arrangement is confined almost 

entirely to the feldspars, and biotite and muscovite 

rarely show any parallelism. In Geneva Gulch, and a 

few other localities, however, small masses of Silver 

Plume granite have a pronounced orthogneissic structure developed through the alinement of both biotite 

and feldspars.

Differences in color caused by changing proportions 

of the minerals make some facies appear to be different 

formations, but gradations can be found between the 

normal Silver Plume granite and these variants. 

Some of the granite contains no mica except muscovite, 

and in the northern part of the quadrangle, near 

Hassell Lake, widespread chloritization has given a 

large mass of this muscovite granite a strong greenish 

cast. In some places hornblende is abundant, and 

with an increase in the amount' of oligoclase present 

the granite becomes dark colored and has a dioritic

i» Ball, S. H., op. cit., p. 52.

so Patton, H. B., op. cit., pp. 126-128.

appearance, but this facies is rare. The Bear Mountain granite of Patton differs from his Santa Fe granite 

in being coarser-grained and containing biotite but no 

muscovite, whereas his Santa Fe granite carries both 

muscovite and biotite. (See pi. 11, A.) A calcic porphyritic differentiate grades into the granite in some 

places and cuts it at others. This rock was found 

only in a few places in the northern part of the 

quadrangle.

Orthoclase and microcline together usually make up 

more than half of the Silver Plume granite, quartz from 

15 to 30 percent, and oligoclase about 15 percent. 

The amount of biotite and muscovite varies greatly. 

Only a few specimens were found in which mica made 

up as much as 20 percent of the rock. Blood-red 

inclusions of hematite such as those observed in the 

Pikes Peak granite are very rare in the Silver Plume 

granite, but a few orange-red laths were found in the 

early, coarse-grained border phases of the large stocks. 

Orthoclase and microcline usually occur in subhedral 

crystals from 2 to 5 millimeters in length and contain 

inclusions of quartz and oligoclase. Both oligoclase 

and quartz generally show much smaller grain size 

than the potash feldspars, although at some places 

large crystals of oligoclase are abundant.. Micrographic intergrowths of quartz and the feldspars occur 

at the borders of some of the large feldspar crystals. 

Biotite is generally a late mineral and occurs in small 

interstitial flakes between the feldspa.r. Muscovite 

is usually present in larger crystals than biotite where 

both minerals are found in the same rock. The usual 

chloritic and sericitic alteration products of the essential minerals are present in most of the slides studied. 

Apatite, zircon, magnetite, and rarely rutile and titanite are accessory minerals.

PEGMATITES

Distribution and structure. Pegmatite is abundant 

in the Idaho Springs formation, in the Swandyke 

gneiss, and near the borders of stocks and batholiths 

of Pikes Peak granite and Silver Plume granite. Small 

irregular masses and short dikes of pegmatite are common in the interior of the batholith in the northern 

part of the quadrangle, but much more pegmatite 

occurs near its edge than near the center. The general 

distribution of the larger pegmatite masses is shown 

on plate 3, but because of the irregularity of outline 

of many of them and the occurrence of much pegmatite 

as a labyrinthine network of innumerable closely 

spaced seams and dikes surrounding irregular fragments of schist and gneiss, an accurate picture of the 

pegmatites cannot be given on a map, and much 

generalization is necessary.

The bulk of the pegmatite and aplite is interlayered 

with the schists and gneisses of the Idaho Springs 

formation and the Swandyke gneiss and occurs in 

seams whose width ranges from less than an inch to 

several feet. These seams have many branches which
ALGONKIAN SYSTEM 15

cut irregularly across the schistosity of the enclosing 

rock, and both the seams and their branches are cut 

by many dikes and irregular masses of later pegmatite. 

(See pi. 7.) The contact of the sill-like masses of 

pegmatite with the schists and gneisses is sharp at 

some places but is indefinite at others, where the walls 

have been partly assimilated or replaced by the pegmatite magma. Most of the pegmatite dikes are less 

than 10 feet wide and persist for less than a thousand 

feet, but a few are as long as half a mile. The pegmatites that occur in granite areas have sharp contacts 

with the enclosing rock at most places, but gradational 

contacts are not uncommon. Individual masses of 

pegmatite cut cleanly across the granite in some places 

and merge with it in others.

The structural relations of the pegmatites to themselves and to other rocks indicate that their intrusion 

took place through a long period. Ball 21 recognized 

four different periods of pegmatite formation an 

early period contemporaneous in a general way with 

the intrusion of the Swandyke hornblende gneiss, 

when pegmatites formed in greatest abundance; a 

second period broadly contemporaneous with the 

intrusion of the p're-Cambrian quartz diorite; a third 

period contemporaneous with the final solidification of 

the Silver Plume granite; and a fourth period of intrusion later than any of the others. The structural 

relations observed by the writer indicate that aplites 

and pegmatites were intruded after the formation of the 

Swandyke gneiss but before the intrusion of any 

other rock, that much of the granite gneiss is pegmatitic, that the pegmatites associated with the border 

facies of the Pikes Peak granite (the so-called " Archean 

quartz monzohite" of Ball), with the main mass of the 

Pikes Peak granite, and with the Silver Plume granite 

are in part contemporaneous and in part later than 

these granites.

Lithology. Microcline is the predominant mineral 

of the pegmatites, but sodic plagioclase and quartz 

are also abundant. Biotite, muscovite, and magnetite 

are common but generally form only a small part of 

the total mass. The mineralogy of the pegmatites of 

different ages is not distinctive enough to permit 

mapping them separately, and all have been shown by 

one symbol on the geologic map. Certain characteristics are worthy of note, however.

The early aplite and pegmatite seams that inject the 

Idaho Springs formation and the Swandyke gneiss consist chiefly of quartz and oligoclase, or quartz and microcline. Many lenticular masses of pegmatitic quartz 

several feet wide and a few rods long occur in the 

Idaho Springs formation. They are probably contemporaneous with the early lit-par-lit pegmatite and 

aplite injections and are believed to be related to the 

magma that formed the Algonkian quartz monzonite 

gneiss. The pegmatites associated with the Pikes

«' Ball, S. H., op. cit, pp. 00, 01.

Peak granite and its monzonitic border facies contain 

a variety of minerals. Oligoclase, microcline, quartz, 

biotite, muscovite, and magnetite are abundant, and 

orthoclase, tourmaline, garnet, allanite, epidote, corundum, sillimanite, scapolite, and hornblende occur 

locally. Not all the minerals of this second group 

have been found in the Montezuma quadrangle, but 

the few that were not observed have been reported by 

Ball 22 from localities nearby in the Georgetown 

quadrangle. Oligoclase is more common than potash 

feldspar in the pegmatites related to the monzonitic 

border facies of the Pikes Peak granite batholith, and 

the reverse is true of the later pegmatites, which were 

approximately contemporaneous with the Pikes Peak 

granite itself. In the southeastern part of the quadrangle, near Kirby and Smelter Gulches, pegmatites 

that are probably related to the nearby stocks of Pikes 

Peak granite but may be related to small masses of 

Silver Plume granite contain tourmaline, garnet, 

sillimanite, and muscovite in addition to the ubiquitous 

quartz and microcline. Black tourmaline crystals as 

much as 2 inches in diameter and 4}£ inches long are 

locally abundant in the pegmatites, and finer-grained 

tourmaline is common in the surrounding schists. 

Tourmaline is one of the earliest minerals of the 

pegmatites and the latest mineral of the schists. 

Microcline, which is later than the tourmaline, is 

earlier than quartz but much less abundant. Muscovite, in separate crystals and intergrown with 

sillimanite, is probably in part contemporaneous with 

quartz and in part later. Garnet is definitely later 

than quartz in many places but may be earlier than 

quartz at others. Sillimanite occurs in rosettes and 

fibrous mats between crystals of quartz, tourmaline, 

and- orthoclase. Many crystals of tourmaline and 

orthoclase are partly replaced by sillimanite, which is 

evidently one of the latest minerals of the pegmatite. 

Some of the bladed sillimanite crystals are as much as 

half an inch long. Magnetite is locally abundant in 

the pegmatites of this part of the quadrangle, and on 

the ridge north of Kirby Gulch some dikes contain 

about 20 percent of it. Both quartz and orthoclase 

are earlier than the magnetite.

The pegmatites associated with the Silver Plume 

granite are generally simpler in their mineralogy than 

those associated with the rocks of the Pikes Peak 

granite batholith. Microcline is more abundant than 

quartz in these later pegmatites and is generally early. 

Biotite is present in nearly all the pegmatites that cut 

the Silver Plume granite, and magnetite is common. 

Many of these late pegmatites are banded, having a 

central seam of quartz and biotite bordered by massive 

pink feldspar.

Although there are many exceptions to the rule, 

the broad generalization that the mineralogy of the 

pegmatites is directly related to the character of the

22 Ball, S. H., op. cit., p. 62.
16 MONTEZUMA QUADRANGLE, COLORADO

country rock, first made by Ball,23 has been substantiated by the writer's work in the Montezuma quadrangle.

Most of the pegmatites have biotite but little or 

no muscovite where they cut granite masses and contain muscovite but no biotite where their walls are 

schist. The tourmaline-sillimanite pegmatites occur in 

quartz-sillimanite-tourmaline schists. In the Georgetown quadrangle 24 pegmatites containing allanite are 

restricted to the monzonitic border facies of the Pikes 

Peak granite, which contains allanite as an original 

constituent. The pegmatites found in the hornblende 

gneisses and schists of the Swandyke gneiss contain 

much biotite and some hornblende but rarely contain 

primary muscovite. Where a persistent dike of pegmatite crosses the contact of such dissimilar rocks as 

granite and quartz-sillimanite schist, the mineralogic 

relations noted above are generally well shown, and 

the dike that contains biotite within the granite mass 

contains both biotite and muscovite near the schist 

contact and has muscovite but no biotite a few hundred feet away from the granite.

SEDIMENTARY FORMATIONS

The unmetamorphosed sedimentary rocks of the 

Montezuma quadrangle are all post-Cambrian and 

occur in the southwest quarter. Rocks of Paleozoic 

and Mesozoic age probably have a maximum thickness of 5,300 feet near Keystone. The Paleozoic rocks 

do not crop out within the quadrangle but underlie 

the later rocks not far below the surface where the 

Snake River crosses the western boundary. The 

sediments have been described in another report,25 

where some of the details of the stratigraphy near 

Breckenridge are more fully discussed than in the 

present paper. Most of the sediments lie in the 

northeastern part of the Breckenridge district, which 

was mapped by Ransome and Bastin in 1908,26 and 

the writer has used their map with but few changes. 

In the Breckenridge district the sediments are so 

intricately cut by intrusive rocks that the stratigraphy is obscure, but along the Snake River west 

of Keystone the rocks are less disturbed, and a satisfactory section is exposed.

CARBONIFEROUS SYSTEM (PENNSYI/VANIAN (?) AND 

PERMIAN SERIES)

MAROON FORMATION

Although the Maroon formation does not crop out 

within the Montezuma quadrangle it is exposed less 

than a mile to the west along the Snake River and 

from 1 to 2 miles bevond the southwest corner on

» Ball, S. H., op. cit, p. 64.

24 Idem, p. 62.

" Lovering, T. S., Geology and ore deposits of the Breckenridge mining district, 

Colo.: U.S. Oeol. Survey Prof. Paper 176, pp. 4-14, 1934.

2» Ransome, F. L., The geology and ore deposits of the Breckenridge district, 

r,olo.: U.S. Qeol. Survey Prof. Paper 75, pi. 1,1911.

Gibson Hill and along the Blue River. Its easterly 

dip implies that it extends beneath the western part 

of the quadrangle. South of the quadrangle, however, it thins rapidly eastward and is overlapped by 

the Morrison, and probably this structural condition 

continues beneath the quadrangle, as.suggested in 

sections B-B' and C-C', plate 4.

The exposures along the Snake River comprise 

about 100 feet of red and green micaceous shales overlain by the nonmicaceous beds of the Morrison formation. The base is not exposed. On Gibson Hill the 

formation is about 700 feet thick and includes a great 

variety of beds that change in character within short 

distances. At the Owl tunnel, on Gibson Hill, where 

the contact with the pre-Cambrian is shown, thick 

beds of bouldery conglomerate alternate with black 

shale in the basal part; near the Sultana mine, a mile 

northwest of the Owl tunnel, the basal bed is a gray 

grit 2 feet thick and is overlain by a thick bed of 

bright-red micaceous sandy shale. The Maroon formation has received considerable study by the writer 

during his 6 years of work in the Front Range and 

other parts of Colorado and the regional relations of 

the formation are discussed elsewhere. 27

JURASSIC SYSTEM (UPPER JURASSIC SERIES)

MORRISON FORMATION

The Morrison formation, like the Maroon, is exposed 

west and south of the Montezuma quadrangle. It also 

thins out eastward and is overlapped by the Dakota 

quartzite, but it is believed to underlie the western 

part of the quadrangle, as shown in sections B-B' and 

C-C', plate 4. It consists of nonmicaceous variegated 

shales and light-colored sandstones that have a nrnximum thickness of 350 feet west of the quadrangle. 

These beds overlap the, Maroon and are separated 

from it by an erosional unconformity whose irregularities are of small size. Their contact with the Dakota 

quartzite is abrupt in some places, but in others it is 

marked by a gradational zone of alternating quartzites 

and shales as much as 20 feet in aggregate thickness. 

For a detailed description the reader is referred to the 

writer's paper on the Breckenridge district. 28

CRETACEOUS SYSTEM (UPPER CRETACEOUS SERIES)

DAKOTA QUARTZITE

Distribution and stratigraphic relations. The Dakota 

is a.persistent formation in Colorado. In the Montezuma quadrangle it consists chiefly of quartzite, being 

composed of a massive basal quartzite, a thin-bedded 

shaly quartzite, and a medium-bedded quartzite. The 

formation ranges, from 20 to 225 feet in thickness. It 

is essentially parallel to the underlying Morrison forma27 Lovering, T. S., and Johnson, J. H., Meaning of unconformities in stratigraphy 

of central Colorado: Am. Assoc. Petroleum Geologists Bull., vol. 17, pp. 353-374, 

1933.

28 Lovering, T, S., op. cit. (Prof. Paper 176),
SEDIMENTAKY FORMATIONS 17

tion and the overlying Ben ton shale, but it overlaps 

the Morrisori and rests upon pre-Cambrian rocks in 

the southwestern part of the Montezuma quadrangle 

neax the Swan River. The formation is 200 feet thick 

at Boreas Pass, 6 miles south of the southwest corner 

of the quadrangle, but thins rapidly as it is followed 

northeast. In Georgia Pass, 2% miles south of the 

quadrangle and 4 miles north-northeast of Boreas 

Pass, the Dakota quartzite if present is only 20 feet 

thick and is represented by a bed of quartzite and 

conglomerate that has its sedimentary contact with 

the Swandyke hornblende gneiss well exposed.

The thinning and successive overlap of the Maroon, 

Morrison, and Dakota formations eastward in the 

Breckenridge region has been interpreted by Ransome 20 and by the writer 30 as reflecting the gradual 

submergence of a highland that occupied much the 

same area as the present Front Range. It seems 

probable that the Dakota quartzite was not deposited 

in the region a short distance northeast of Georgia 

Pass, and it is possible that the thin quartzite found 

in the pass is stratigraphically higher than the upper 

Dakota beds farther west and should properly be 

classed, as the basal member of the Benton shale. 

Detailed studies have not been made in this region, 

however.

Lithology. The Dakota quartzite exposed on the 

east slope of the Swan River Valley (see pi. 3). is estimated to be between 20 and 50 feet thick and probably 

consists of only a single massive bed. Farther west, 

near the southwestern boundary of the quadrangle, 

the formation has three distinct members and is from 

100 to 160 feet thick. There is no place in the quadrangle where a section of the formation can be measured, however, and the thickness must be inferred from 

information gathered outside. The Dakota is about 

225 feet thick in the Snake River section 1)4 miles 

west of the quadrangle; about 100 feet thick on Prospect Hill, a mile southwest of the quadrangle; 175 

feet thick at Rocky Point, 3 miles south of the quadrangle; and, as stated above, not more than 20 feet 

thick at Georgia Pass.

In the region southwest of the quadrangle the 

Dakota commonly comprises an upper and lower 

quartzite separated by a carbonaceous shale. The 

shale member disappears farther east, however, and 

only a single massive layer of quartzite is present. 

The three members are well exposed and easily distinguishable at Rocky Point, south of Breckenridge. 

They are well exposed in the Snake River section, but 

only one member can be recognized on Prospect Hill 

and in the region farther east.

Where three members are present the lowest is 

predominantly massive light-gray quartzite and ranges

« Runsomo, F. L., op. cit. (Prof. Paper 75), p. 182. 

5° Covering, T. S., op. cH. (Prof. Paper 176), p. 8,

in thickness from 75 to 120 feet. Gritty or conglomeratic beds are commonly found near the base, and a 

few thin beds of gray or rarely black shale are nearly 

everywhere present in the basal part of the formation. 

These shale beds are not persistent, however, and individual beds may thin and disappear in short distances. The middle member is the most Available in 

lithology. It contains more shale than any other part 

of the formation, but the individual shale beds are 

lenticular, and the thickness of the member ranges 

from 5 to 96 feet but in most places is less than 60 feet. 

Both black and gray shales are common, and the thinbedded quartzite layers of this member are more 

commonly dark-colored or black than those in other 

parts of the formation. The upper member comprises 

massive and thin-bedded light-colored quartzite, separated by shale partings, and ranges in thickness from 

10 to 30 feet. For more details of lithology the reader 

is referred to the writer's report on the Breckenridge 

district. 31 The lithology of the Snake River section 

given below is characteristic of the region, but the 

thickness of the middle member is much greater than 

that found to the east and south.

Section of the Dakota quartzile l}/-i miles west of Keystone

Feet

Benton shale: Black shale with a thin basal conglomerate 

containing pebbles half an inch to 2 inches in diameter of 

chert, quartzite, micaceous red sandstone, schist, and 

granite ____________________________________________ 1

Dakota quartzite:

Upper member: ;.

Medium-bedded gray quartzite-____.1____.____ 10 

Thin-bedded gray quartzite-__-__-___-^. ___..__ 5 

Massive light-gray quartzite_____-._-_-________ 32

Middle member:

Black shale._____._-___-_-_-__-.___-____-_._ 13

Massive gray quartzite_^-___----_--_--------- 1

Thin-bedded shale and quartzite-__-_l-___--.__ 3 

Massive quartzite_-_----_--_---__--i-_------- 25

Interbcdded black shale and thin- to, mediumbedded light- and dark-gray quartzite_-_--___ 50

Lower member:

Massive gray aandy quartzite---___-___-_-.___- 16 

Hard massive gray quartzite, conglomeratic at 

base___-_--______-__--_-_- -------------- 69

224 

Morrison formation: Fissile gray-green shales____J_______ 10

Topographic expression. The Dakota quartzite is 

the only prominent cliff-forming sedimentary rock in 

or near the Montezuma quadrangle. Nearly everywhere that the formation has a thickness of more than 

50 feet it crops out in steep, cliffy slopes. As the hard, 

resistant quartzite is overlain by soft shales, erosion 

tends to remove the overlying formations from the 

Dakota, leaving it as a bare hill whose surface is 

essentially a dip slope. The anticlinal structure of the

s> Lovering, T. S., op. cit. (Prof, Paper 176).
18 MONTEZUMA QUADRANGLE, COLORADO

Dakota between Keystone and Dillon is clearly expressed in the topography, as shown in plate 7, B. 

Where the formation is thin, it rarely crops out in a 

cliiT, as the thick black shales that overlie it readily 

disintegrate and bury its outcrop with slope wash. In 

such places the presence of the formation is betrayed 

by numerous scattered blocks of quartzite a short 

distance below.

Correlation. No fossils that could be identified have 

been found in the Dakota near the Montezuma 

quadrangle, although fragmentary plant remains are 

abundant near the base and in the carbonaceous shales 

of the middle member at many places.

The distinctive lithology of the formation, however, 

and its presence immediately below beds of definite 

Benton age show that it must be correlated with the

Morrisonat

 ,. . . Rocky Point Morrisonat .. r...." 

Boreas Pass

Kd

Jm

Cm

\

,---

' '&':±*-

Covered

litpif

jjgjjZfegg

' . .',

; ' . ;

-=7:;.-:.-.-.r=:

v (ac 

\ F 

\ Kb

\ 

\

\

\ 

\

\ 

\

\

\

Om

Boreas 

:ording 

?ansome

n

 ^ijtg ti: r-'V-jn

 J.y .'.'.'

quartzite at the base of the Benton shale suggest a 

transition.

The Benton shale persists beneath the Niobrara 

formation throughout the southwestern part of the 

Montezuma quadrangle, as shown in the structure 

sections of plate 4. Some sliced masses of Benton 

shale occur near the Williams Kange thrust fault a 

short distance north of Tiger but have not been separated from the Niobrara limestone on the geologic map.

Lithology. In the Montezuma quadrangle the Benton shale is about 350 feet thick, but good sections are 

rare. Although poorly exposed, it can be measured 

with fair accuracy on the north side of the Snake River 

a mile west of the western boundary of the quadrangle. 

The basal conglomerate, containing pebbles of all the 

older formations, is easily found at the top of the

\ Rocky Point

Vertical scale

200 Feet

Kb * Benton shale 

Kd - Dakota quartzite 

Jm -Morrison formation 

Cm - Maroon formation

f IGUBE 3. Correlation of sections measured from Boreas Pass to Keystone.

Dakota formation of central and eastern Colorado. 

It is the most persistent and easily recognized formation in the State, and its regional correlation is shown 

in figure 3.

BENTOIT SHAIB

Distribution and stratigraphic relations. The black 

Benton shale is commonly from 300 to 400 feet thick, 

and in central Colorado it overlies the Dakota quartzite everywhere that it has not been removed by erosion. It crops out in a northward-trending belt a 

short distance west of the Montezuma quadrangle. Its 

contact with the underlying Dakota quartzite is 

marked locally by a bed of conglomerate from 6 to 18 

inches thick, but it is conformable with the overlying 

Niobrara limestone. The contact with the Dakota is 

generally sharp, but in some places in the extreme 

southwestern part of the quadrangle a few thin beds of

Dakota quartzite, and the limestone that marks the 

upper limit of the formation crops out in a low ridge a 

short distance northeast, but the beds between these 

exposures are concealed. The lithology of the Benton 

is best studied in the railroad cut just northeast of 

Rocky Point, about 3J£ miles south of the southwest 

corner of the quadrangle. At this locality the lower 

300 feet of the Benton shale is exposed, by far the 

thickest visible outcrop in the region, and though disturbed by intrusions of quartz monzonite porphyry 

and locally overturned, its general character can be 

determined. The upper part of the Benton can be 

seen in the railroad cut on Nigger Hill at the north 

end of the railroad trestle crossing Illinois Gulch, about 

0.8 mile north of Rocky Point.

In this region the lower part of the Benton is commonly black fissile shale from 30 to 50 feet thick, but
SEDIMENTARY FORMATIONS 19

in some places a layer of gray shale from 5 to 15 feet 

thick intervenes between the Dakota quartzite and the 

black shale. Locally a few thin beds of quartzite are 

present near the base of the formation. Between the 

lower black shale and a horizon about 250 feet above 

the base the shale, though dark, has a marked grayish 

cast, ranging from dark gray to grayish black, and is 

moderately fissile. Thin-bedded black shales and 

limestone alternate for about 35 feet above the grayishblack shales and are overlain by about 50 feet of black 

fissile shale. Capping the fissile black shale is a bed 

of shaly limestone about 25 feet thick. It is a fetid 

black limestone, probably in part the equivalent of the 

t Niobenton sand of the oil-well drillers of North Park. 

It seems to include the top of the Benton shale and the 

base of the Niobrara formation, for Niobrara fossils 

have been obtained near Breckenridge from the shales 

at the top of the limestone, which itself yields typical 

Benton forms. In the Snake River section Niobrara 

fossils were found in the top of a limestone whose base 

is black, fetid, and unfossiliferous and is 370 feet above 

the Dakota quartzite. The lower part of this limestone is believed to belong to the Benton shale. The 

general character of the Benton and its relation to the 

other formations are shown in figure 4.

Topographic expression. The Benton shale is generally marked by a smooth depression between an 

escarpment of Dakota quartzite and the low ridge of 

dark-colored limestone that marks the base of the 

Niobrara formation.

Correlation. Benton fossils have not been collected 

in the Snake River section. In the top of the formation at the railroad trestle in Illinois Gulch, near 

Breckenridge, Inoceramus fragilis Hall and Meek and 

Prionocyclus wyomingensis Meek were found by the 

writer and identified by J. B. Reeside, Jr. According 

to Reeside, these forms are typical of the upper 

Benton, (Carlile fauna). Ransome 32 collected Ostrea 

lugubris Conrad, Inoceramus fragilis Hall and Meek, 

and Scaphites warreni Meek and Hay den in a thin 

dark fetid limestone 500 feet north of Rocky Point. 

They were regarded as upper Benton forms by T. W. 

Stanton, who identified them. .In the Tarryall district, 10 miles south of the Montezuma quadrangle, 

Muilonberg 33 found the forms listed above and in 

addition obtained specimens of Inoceramus labiatus 

Schlotheim, Inoceramus dimidius White, and Trigonarca depressa White.

The Benton shale was first mapped as a separate 

unit in the region near the Montezuma quadrangle 

during the restudy of the Breckenridge district in 

1928, although its presence was recognized earlier by 

Ransome and by Muilenberg. Benton fossils have 

been found at many localities west of the Front Range,

SJ Knnsomo, F. L., op. cit., p. 41.

" Miiilonbcrg, O. A., Geology of the Tarryall district, Park County, Colo.: 

Colorado Gool. Survey Bull. 31, p. 27,1925.

and it is now evident that the Benton shale is persistent for long distances to the north, west, and south of 

Breckenridge, but it has been comparatively little

Palmer Ranch

Covere

Kp-Pierre shale 

Kn-Niobrara formation 

Kb-Benton shale 

Kd-Dakpta quartzite

Kn

Kb I

Vertical scale sooFeet

FIGURE 4. Correlation of sections measured at Palmer ranch and Keystone.

studied in this region. Spurr 34 found 350 feet of black 

calcareous shale of Benton age underlying the Nios< Spurr, J. E., Geology of the Aspen mining district, Colo.: U.S. Geol. Survey 

Mon. 31, p. 41, 1898.
20

brara limestone at Aspen, 50 miles west of Breckenridge. Eldridge 35 found 150 to 300 feet of black shale 

and interbedded fetid limestone of Benton age in the 

Crested Butte quadrangle, 60 miles southwest of the 

Breckenridge district. The Benton fauna found in 

the Tanyall district by Muilenberg was in black 

bituminous shale and fetid limestone overlying the 

Dakota quartzite.

Henderson 36 assigns a thickness of 300 to 400 feet to 

the Benton in the Rabbit Ears district and in the 

vicinity of Kremmling. According to drill records the 

Benton is 550 feet thick in North Park, near Walden, 

but Beekly gives the thickness as ranging from 100 

to 200 feet and probably averaging about 165 feet. 37 

In North Park the Benton shale consists of three 

distinct members- a lower black shale, an intermediate 

gray limy shale, and an upper sandy shale.

The correlation of the Benton shale in several 

districts in central Colorado is shown in plate 3 of 

Professional Paper 176.

NIOBRARA LIMESTONE

Distribution and stratigraphic illations. The Niobrara limestone is about 350 feet thick and comprises 

the dark-colored shaly limestones and limy shales that 

overlie the Benton shale. It is present beneath the 

Pierre shale throughout the southwestern part of the 

quadrangle and crops out a short distance west of the 

western boundary on the north side of the Snake 

River. Broken masses of the formation occur at 

several places along the west side of the Williams 

Range thrust fault and at the mouth of Summit Gulch. 

Other outcrops of the Niobrara formation may be 

present in the part of the quadrangle that is covered by 

the northwest quarter of the Breckenridge geologic 

map, as most of tin's area was not remapped by the 

present writer, and Ransome did not separate the Niobrara from the Pierre and Benton formations. The 

Niobrara is conformable with the overlying Pierre 

shale and the underlying Benton shale, and its upper 

and lower limits are not sharply marked.

Lithology. The Niobrara formation, so far as the 

writer knows, is not well exposed in any accessible 

locality near the Montezuma quadrangle, but information gathered in the Breckenridge district indicates 

its general character. Its base is commonly a graj^ 

limestone from 10 to 30 feet thick that rests upon the 

thin brown fetid uppermost limestone of the Benton 

shale, but locally the lowermost beds are calcareous 

shales. The formation is rather uniform for 250 feet 

above the base and is chiefly greenish-gray limy shale 

but contains some interbedded clay shale and sandy

as Eldridge, G. H., U.S. Geol. Survey Geol. Atlas, Anthracite-Crested Butte 

folio (no. 9), p. 6, 1894.

38 Henderson, Junius, Reconnaissance of the geology of the Rabbit Ears region, 

Routt, Grand, and Jackson Counties, Colo.: Colorado Geol. Survey Bull. 5, p. 31, 

1913.

s? Beekly, A. L., Geology and coal resources of North Park, Colo.: U.S. Geol. 

Survey Bull. 596, p. 35,1915.

shale. The upper 50 feet of the formation is made up 

of thin-bedded black limy shale and thin-bedded limestone containing abundant lenses and veinlets of 

secondary white calcite. Near the Snake River a 

persistent Ostrea-beening limestone about 1 foot 

thick occurs 285 feet above the base. The general 

character of the formation is shown in the columnar 

section in figure 4.

Topographic expression. The basal limestone commonly forms a low ridge that rises 15 to 25 feet above 

the floor of somber-colored shales adjoining it. The 

calcareous member at the top of the formation seldom 

weathers in relief, but its presence is usually indicated 

by abundant fragments of secondary calcite at the 

surface.

Correlation. The Niobrara formation was known to 

occur in central Colorado, in the region near the 

Montezuma quadrangle, but prior to the restudy of 

the Breckenridge district it had not been separated 

from the Pierre and Benton shales. It is conspicuous 

near Kremmling, 40 miles northwest of Dillon, and 

was reported from that locality by Henderson 38 in 

1913. A Niobrara fauna was found in the Tarryall 

district by Muilenberg, 39 but he did not separate the 

formation from the other Upper Cretaceous shales.

Ransome found imperfectly preserved specimens of 

Inoceramus dejormis in the basal limy beds of the 

Niobrara 1,500 feet southeast of the summit of Little 

Mountain, close to a railroad cut. The following 

fauna was collected by the writer from the basal limestone of the Niobrara formation on the north side of 

the Snake River \% miles west of Keystone and was 

identified by J. B. Reeside, Jr.:

Inoceramus aff. I. subquadratus Schluter. 

Ostrea aff. O. congesta Conrad. 

Baculites sp. 

Globigerina sp.

Inoceramus deformis Meek was found by the writer 

in a dark limestone near the Williams Range thrust 

fault in the southern part of sec. 1.3, T. 6 S., R. 77 W.

In the Snake River section, three-quarters of a mile 

west of the western boundary of the Montezuma 

quadrangle, the calc.areous beds definitely belonging 

to the Niobrara formation are 350 feet thick. The 

somber-colored clay shales overlying these beds contain very few limy layers and are poor in fossils. 

Fragments of Plypsydon, Ostrea, and Baculites were 

found in a thin limy layer 125 feet above the calcareous beds of undoubted Niobrara age, but as the species 

could not be determined it is impossible to state the 

age of this layer definitely. The lithology is more 

characteristic of the Pierre than the Niobrara, and the 

writer believes that the top of the calcareous beds 350 

feet above the Benton shale coincides with the top of 

the Niobrara formation.

as Henderson, Junius, op. cit., pp. 31-32. 

39 Muilenberg, G. A., op. cit., p. 28.
SEDIMENTARY FORMATIONS 21

In the Anthracite-Crested Butte area the rocks 

called "Niobrara limestone" consist of a limestone bed 

about 30 feet thick overlain by about 150 feet of calcareous gray shale. At Aspen these rocks are said 

to be about 100 feet thick and to grade upward into 

shales of Montana age without any perceptible break. 

In North Park, according to Beekly,40 the average 

thickness of the Niobrara formation is about 800 feet. 

Well records later confirmed this estimate. The 

formation in this region, as well as in the country to the 

south, is made up of a basal thin-bedded limestone 

overlain by interbedded calcareous and clay shales, 

locally capped by a thin limy sandstone.

The correlation of the Niobrara formation in several 

districts in central Colorado is shown in plate 3 of 

Professional Paper 176.

PIERRE SHAIE

Distribution and stratigraphic relations. The thick 

somber-colored shales of Montana age that lie above 

the Niobrara formation in the Montezuma quadrangle 

and the nearby region are identified with the Pierre 

shale of eastern Colorado. They border the preCambrian rocks in the southwestern part of the 

quadrangle. At the junction of the North Fork of the 

Snake River with the main stream, a considerable area 

of silicified Pierre shale is exposed in a "window" in 

the warped surface of the Williams Range thrust fault. 

A short distance to the south a similar "window" 

occurs in Jones Gulch. The structural relations at 

these places are shown in plate 4, sections B-B' 

and C-C'.

The contact of the Pierre and Niobrara is identified 

as the top of the calcareous sediments of the lower 

part of the Cretaceous section, but no unconformity 

was observed. The upper limit of the Pierre shale in 

the Montezuma quadrangle is marked by the irregular 

sin-face of the Williams Range, thrust fault, which has 

brought pre-Cambrian rocks onto the upper Pierre. 

In South Park the marine shale of Montana age is 

conformably overlain by an unfossiliferous coal-bearing 

formation that Washburne 41 designated "Laramie." 

Although abundant coaly fragments are present in the 

uppermost beds of the Pierre shale in Middle Park, 

the sandstones directly below the Eocene Middle 

Park formation contain marine fossils and are of Pierre 

age. 42 In the regions where a younger Cretaceous 

formation is present, it rests conformably on the Pierre 

shale.

Lithology. The Pierre shale is about 4,000 feet thick 

in the Montezurna quadrangle, and its original thickness was much greater. In the Snake River section, 

which was measured a short distance north of the Snake 

River near Keystone, the Pierre is 3,975 feet thick, and

<° Bookly, A. L., op. cit., p. 39.

41 Woshburue, C.W., The South Park coal field, Colo.: U.S. Oeol. Survey Bull. 

381, p. 309, 1910.

42 Lovcring, T. S., The Orauby anticline, Grand County, Colo.: U.S. Geol. Survey 

Bull. 822, p. 72, 1930.

the upper limit is the Williams Range thrust fault. 

Twenty miles northwest of Keystone, about 4,800 feet 

of Pierre lies beneath the Williams Range thrust fault. 

Sections made at these places are shown in figure 4.

The formation is predominantly dark olive-brown 

shale but contains a few thin beds of limy sandstone. 

It is well exposed on the Snake River west of Keystone 

and at many places on the Blue River between Dillon 

and Kremmling. The thin-bedded black or dark olivebrown clay shale that makes up the lower 1,850 feet 

of the formation contains very few fossils and no 

persistent beds distinguishable through differences in 

color or lithology. Above the thick lower shale there 

are several moderately persistent beds of sandy or 

shaly fossiliferous limestone. As shown in plate 8, A, 

these beds are from 10 to 50 feet thick and commonly 

crop out in low ridges or cliffs. Three, four, or five of 

these limy beds commonly occur within a few hundred 

feet, interbedded with shale of the same appearance 

as that found below. Another thick shale member lies 

above the shaly limestones and is overlain by a persistent sandstone at a horizon about 3,800 feet above 

the Niobrara. This sandstone is very close to the 

thrust fault in the region near Keystone, but farther 

northwest a shale member about 650 feet thick is found 

above it and is capped by a bed of white sandstone 

about 100 feet thick. Further details of the lithology 

are given in the following sections measured at Keystone and at the Palmer ranch, 20 miles to the northwest.

Section of Cretaceous formations on north side of Snake River near

Keystone

Algonkian (?) schist, in fault contact with Pierre shale. 

Montana group (Upper Cretaceous):

Pierre shale: Feet 

Black fissile shale_________________________. 20

Black sandy shale_________.________________ 10

Greenish-gray limy sandstone.______________ 25

% Dark gray sandstone.______________________ 15

Interbedded shaly gray sandstone and shale. __ 30 

Black and dark olive-brown shale.___________ 1, 400

Greenish-gray sandy shale._________________ 200

Thin-bedded fossiliferous limy brownish-gray 

sandstone, ridge-forming member.________

Fissile gray limy .s,hale____-___--________-__

*Hard sandy and limy shale 43 _ __.!_-______--.-

Black or dark olive-brown and dark-brown clay

shales, in part fissile______ ________________ 1, 850

Slightly limy brown shale containing fossil fragments, interbedded with blue-black noncalcareous shale.__________________________

Blue-black fissile clav shale__-___--________.

10

115

3,975

Colorado group:

Niobrara limestone:

Blue-gray limy shale containing abundant secondary calcite ___________________________ 30

Fissile blue-black limy shale containing several 

beds of coarse gray limestone 1 to 2 inches 

thick____.______________________ 30

43 Probably equivalent to bed marked * in the Palmer ranch section.
22 MONTEZUMA QUADRANGLE, COLORADO

Section of Cretaceous formations on north side of Snake River near 

Keystone Continued

Colorado group Continued.

Niobrara limestone Continued.

Fissile gray limy shale separated from overlying Feet 

bed by 3-inch layer of white calcite. _______ 40

Shale, largely covered._____________________ .240

Dark grayish-black thick-bedded dense fossiliferous limestone-__________'_______________ 10

Benton shale: = 

Thin-bedded bluish-gray limestone grading 

downward into purplish limy shale.________

Covered, but mostly black shale with bed of

350

30

conglomerate 10 inches thick at base_______ . 340

Dakota quartzite: Massive and medium-bedded finegrained gray quartzite-___________________________

370

47

Section of Cretaceous shales exposed above Palmer ranch, on 

northeast side of Blue River about 20 miles northwest of Dillon

Pre-Cambrian gneiss thrust over Cretaceous rocks. 

Pierre shale: Feet 

Dark-gray limy sandstone--.________-__---_-__.__ 100

Massive soft white sandstone.----------_________ .25

Dark sandy shale__---__-_______---_-----_____- 25

Black fissile shale_____________-_____-_____-__-_ 400

Dark-gray limestone.__________________________ 2

Black fissile shale_______________-____--________ 200

Fissile gray shale._____________________________ 118

Medium-bedded fossiliferous cross-bedded lightbrown sandstone._ ___________________________ 50

Dark-colored shale containing a few thin limy layers

near base.__________________________________ 1, 100

Thin-bedded brown sandy limestones with thin shale

partings-_ _______^___-_--_____--------__--__ 25

Dark-gray shale_______________________________ 225

Medium-bedded gray limy shale.__-_-__-_-______ 10

Dark-gray shale.___-____-_____-____-_---__---_ 10

Thin-bedded, slightly oolitic limy sandstone.______ 10

Thin-bedded grayish-brown limestone ____________ 10

Medium-bedded light-brown limestone (cliif-forming)______________________________________,_ 15

Grayish-black limy shale._-_________-___________ 15

Medium-bedded brown shaly limestone, a cliffforming member.____________________________ 10

Black shale.__________________________________ 150

Thin-bedded limestone and dark-gray limy shale. _ 125 

Medium-bedded light-brown sandy limestone..____ 10

Fissile grayish-black shale.--____--_--___________ 180 .

* Thin-bedded gray sandy limestone, cliff-forming

member, with shale partings 44 .--__---_________ 20

Fissile grayish-black shale with a few %-inch layers

of limestone at the base_-__-__-_-________'_____ 1, 160

3,995

Topographic expression. The soft shales of the 

Pierre weather into broad valleys and smooth slopes. 

(See pi. 7, B.) The hard pre-Cambrian rocks that lie 

on top of the Pierre shale in Tenderfoot Hill, just north 

of Ke37stone, and in the ridge east of Soda Creek 

protect the shale from erosion, but even on their

" Probably equivalent to bed marked * in the Snake River section.

moderately steep slopes outcrops of shale are rare. 

The shaly limestones near the middle of the formation 

form low ridges and cliffs a short distance west of 

Keystone. These ridges and the subdued topography 

characteristic of the associated shales are shown in 

plate 8, A.

Correlation. The following table lists the fossils 

found by the writer in making the sections shown 

above and gives the distance above the Niobrara 

formation at which they were collected. The fossils 

were identified by J. B. Reeside, Jr.

Keystone section: Feet 

Mactra aff. M. nitidula Meek and Hayden._______ 2, 200

Inoceramus barabirii Morton____________________ 2, 200

Baculites ovatus Say___________________________ 2, 200

Clionasp. _-__-_---____-___-_-_---_-_-__---___ 2, 300

Inoceramus sagensis Owen___________ 2,200, 2,300, 3,930

Baculites ovatus Say var. haresi Reeside__---_____ 2, 600

Palmer ranch section:

Ostrea aff. O. larva Lamarck______.____.________ 4, 650

Inoceramus aff. I. barabini Morton_______________ 3, 800

Pteria linguaeformis Evans and Shumard.________ 3, 800

Protocardia subquadrata Evans and Shumard_____ 3, 800

Dentalium gracile Evans and Shuinard___________ 3, 800

Baculites ovatus Say______________________ 2,250, 2,800

Baculites compressus Say (?)____,____ 2,250, 2,800, 3,800

Inoceramus sagensis Owen ______________________ 2, 250

2,800, 3,800, 4,650, 4,800 

Vanikoro sp.__________________________________ 1, 750

Fish scale.__________________._____._..__ 1, 750

According to Reeside the fossils listed above are all 

of Pierre age, and even those from the highest beds 

are characteristic Pierre forms. Until detailed work 

is done in the region between Dillon and North Park 

it seems unsafe to attempt to subdivide the Pierre into 

the units used farther north, although it is probable 

that the Steele shale and the Mesaverde formation are 

present and will eventually be separated. The correlation of the Pierre in several districts in central 

Colorado is shown in plate 3 of Professional Paper 176.

QUATERNARY DEPOSITS AND TOPOGRAPHIC EVOLUTION

Much of the present topography of the Moritezuma 

quadrangle and the surrounding country was developed 

in Quaternary time, but remnants of earlier land surfaces are preserved in some places. Two Tertiary and 

three Quaternary erosion cycles are evident, but no 

deposits corresponding to the Tertiary cycles have 

been recognized nearby. For convenience of treatment, the different topographic stages and the deposits 

formed during them will be discussed together.

Eocene land surface. By the end of Eocene time a 

well-developed peneplain had formed in the northern 

part of the Front Range,45 where it bevels the upturned 

Cretaceous sediments at the edge of the mountains 

and is cut by channels containing Oligocene sediments. 

In the Livermore and Home quadrangles, just south

45 Lovering, T. S., Geologic history of the Front Range, Colo.: Colorado Sci. 

Soc. Proc., vol. 12, p. 108, 1929.
U.S. GEOLOGICAL SURVEY PRO

A. VIEW LOOKING EAST UP THE SNAKE RIVER FROM THE CONICAL SHALE HILL 1 MILE WEST OF THE MONTEZUMA QUA

The bluffs on the north side of the river are formed by calcareous layers in the Pierre shale. The low hill in the right middle distance is part of the terminal moraine west of Keyst

middle distance is made by the outwash gravel from the Wisconsin glacier.

B. VIEW LOOKING SOUTH FROM THE SOUTH END OF TELLER MOUNTAIN NEAR THE CASHIER MINE.

Glacial trenching of the Flattop peneplain is well shown.
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 178 PLATE 10

A. GLACIAL LAKE AT HEAD OF SMELTER GULCH, VIEWED FROM MOUNT LEWIS.

B. ROCK GLACIER AT HEAD OF STEVENS GULCH.
SEDIMENTARY FORMATIONS 23

of the Colorado-Wyoming boundary, this Eocene 

peneplain, which can be correlated with the nearby Medicine Bow peneplain,46 can be traced southward into the Rocky Mountain National Park, where 

it forms a conspicuous bench nearly 1,000 feet below 

the well-known "Flattop" peneplain, described by 

Lee. 47

The Flattop peneplain, probably developed during 

early Eocene time, is .conspicuous in the high mountains south of the park and has been traced through 

the Fraser quadrangle into the Montezuma quadrangle 

by the writer. (See pi. 9.) It is not a horizontal surface nor even an inclined plane. At the edges of the 

mountains it approaches a tilted plane in its configuration, but near the center of the Front Range uplift, in 

the Montezuma and Georgetown quadrangles, it is a 

smooth but irregular surface (see pi. 8, B, arid fig. 2) 

and may be described as a mature hilly upland. In 

places this upland surface has been modified to a 

marked extent by Miocene and Pliocene erosion, and 

in such places it is difficult to define sharply the essentially Eocene land surface:

The late Pleistocene glaciers trenched parts of the 

Flattop peneplain deeply and produced conspicuous 

topographic contrasts, as shown in plate 8, B. The 

smooth, gently sloping surfaces that form the mountain 

tops in the southwestern part of the quadrangle stand 

above steep-walled cirques and precipitous slopes tha.t 

drop abruptly into U-shaped valle37s whose floors are 

from 500 to 1,500 feet below, and remnants of the old 

upland in the northeastern part of the quadrangle are 

as much as 3,000 feet above the floors of the glacial 

valleys.

Basal Eocene beds occur in South Park, but no 

deposits of later Eocene age are known in or near the 

quadrangle.

Late Tertiary land surface. On the east side of the 

Front Range, in the Georgetown and Denver Mountain Parks quadrangles, a maturely dissected surface 

lying at an altitude of 7,500 to 8,500 feet forms the 

edge of the mountains. This surface was described by 

Lee 48 as the Rocky Mountain peneplain. It probably 

developed during Oligocene, Miocene, and Pliocene 

time and represents the gradual encroachment of a 

piedmont plain toward the central highland. In most 

places the much older Medicine Bow peneplain has not 

been separated from the Rocky Mountain peneplain, 

although the two are easily distinguished on the east 

side of the Front Range west of Boulder and near 

Nederland. As the Medicine Bow surface was first 

recognized in that locality during the writer's study 

of the tungsten deposits, after the field work in the

M Van Tuyl, F. M., and Lovoring, T. S., A contribution to the physiographic 

history of the Front Range, Colo.: Ocol. Soc. America Bull., vol. 43, p. 172, 1932.

" Loo, AV. T., Peneplains of the Front Kongo and Rocky Mountain National 

Park, Colo.: U.S. Geol. Survey Bull. 730, p. 4,1923.

18 .Idem, p. 5.

Montezuma quadrangle had been completed, no attempt is made in the following discussion to differentiate the two surfaces. The Rocky Mountain peneplain 

is not well developed on the west side of the Front 

Range, but a maturely dissected late Tertiary land 

surface that is well preserved in the Breckenridge 

district is here correlated with it. Much of the Rocky 

Mountain peneplain lies between 10,000 and 11,000 

feet above sea level in the southwestern part of the 

Montezuma quadrangle and is conspicuous in the hilltops west of Browns Gulch. As shown in plate 9, it 

can be recognized in the hills bordering the North Fork 

of the Swan River where its altitude is in general a 

little inore than 11,000 feet. On both sides of this 

stream, about a mile north of Garibaldi Gulch, the 

relation of the Rocky Mountain peneplain to the Flattop peneplain is well shown. The younger surface is 

from 400 to 600 feet below the Flattop peneplain and 

is separated from it by a moderately steep slope. 

Farther north it is difficult to distinguish the effects 

of early Pleistocene erosion from those of the late 

Tertiary.

No deposits corresponding to the Rocky Mountain 

peneplain erosion cycle are known near the Montezuma 

quadrangle unless parts of the high-basin debris sheets 

are of this age.

. Early Pleistocene topography. Early Pleistocene 

glaciation was widespread in the Front Range, and 

remnants of the topography carved during this glacial 

stage can be seen in many places, although later 

glaciation has destroyed or modified most of the features belonging to this early stage. Many of the highlevel cirques that form hanging basins tributary to 

deeply cut valleys, as well as the upper basins in 

compound cirques at the heads of glacial valleys, were 

formed in the early glacial stage which the writer has 

correlated with the early Pleistocene (Kansan?) 

glaciation of the plains.49 Remnants of the valleys 

cut in early Pleistocene time are preserved as rock 

shelves as much as 1,200 feet above the floors of the 

present valleys. (See pi. 9.) Such rock benches are 

found at lower and lower levels as they are followed 

downstream toward the lower limit of early Pleistocene 

glaciation, and near the terminal moraines of this stage 

they may be within 100 feet of the present valley 

bottoms. The moraine-covered terrace 500 feet above 

the Snake River at Keystone is believed to be the floor 

of the valley carved by early Pleistocene glaciers. The 

writer has correlated the 160-foot terrace at Idaho 

Springs with the post-Kansan or Yarmouth interglacial stage,50 although Ball 51 has dismissed the

< 8 Lovering, T. S., Geologic history of the Front Range, Colo.: Colorado Sci. 

Soc. Proc., vol. 12, pp. 104-105, 1929.

so Alden, W. C., and Stebinger, Eugene, Pre-Wisconsin drift in the region of Glacier National Park, Montana: Geol. Soc. America Bull., vol. 24, p. 569,1913. Alden, 

W. C., Physiographic development of the northern Great Plains: Idem, vol. 35, 

p. 405, 1924.

«' Ball, S. H., op. cit. (Prof. Paper 63), p. 84.

71880 35 3
24 MONTEZUMA QUADRANGLE, COLORADO

possibility that this terrace is Pleistocene, because 

Clear Creek has cut a canyon in bedrock 600 feet wide 

and 160 feet deep since its formation. Ball believed 

that the great size of the canyon proved that the 

terrace was preglacial. Work by Alden in the northern 

Great Plains and in Glacier National Park, however, 

has shown that interglacial erosion in Pleistocene time 

deepened the major stream valleys 1,000 feet or more. 

Capps 52 estimated that Wisconsin glaciation deepened 

certain stream valleys from 200 to 800 feet in the 

Leadville quadrangle, just southwest of the Montezuma quadrangle. It thus seems that the writer's 

correlation of the high terraces and rock benches on 

Clear Creek with the early Pleistocene glacial stage is 

in accord with the probable amount of erosion that has 

occurred. The altitude of the rock benches on the 

north side of Clear Creek a few miles west of Silver 

Plume suggests that the bottom of the Clear Creek 

Valley in early Pleistocene time was about 1,200 feet 

above the present valley floor, and this is the deepest 

post-Kansan trenching noted in the quadrangle.

The mature topography of the late Tertiary mountainous upland was characterized by wide, gently sloping valleys, and most of the early glaciers must have 

been broad but relatively thin. The work of such 

glaciers would be greater at the sides than at the bottom 

and would result in forming wide U-shaped valleys 

that were little deeper than the original stream-cut 

valleys. Stream cutting in the succeeding interglacial 

stage probably carved moderately deep, steep-sided 

valleys and gorges in the bottoms of these broad glacial 

valleys.

Early Pleistocene deposits. Most of the material 

deposited by the Kansan (?) glaciers has been removed 

by later erosion, but remnants of the early till occur 

well above the present valley bottoms in several places 

and are shown on plate 3. Much of this early morainic 

material is more weathered than the later till and is 

commonly covered by a heavy growth of pine. The 

till is made up of unsorted boulders of Tertiary intrusives and pre-Cambrian rocks in a matrix of brownishyellow sand and sandy clay. The boulders show a 

great range in size, and some erratics of Montezuma 

quartz monzonite on the north bank of the Snake River 

near Keystone are 10 feet in diameter.

The high-terrace gravel deposits of the Breckenridge 

district were laid down by the glacier-fed streams of the 

early Pleistocene glacial stage and by the streams of the 

succeeding interglacial stage. In the Montezuma 

quadrangle this formation is only meagerly represented 

and is confined to the drainage basin of the Swan 

River. The bedrock floor on which the high terrace 

gravel was deposited is everywhere above the level of 

the present streams, but its altitude is variable. As 

shown on plate 3, the high terrace gravel in this quadrangle is only 50 to 150 feet above the streams; a few

82 Capps, S. R., Pleistocene geology of the Leadville quadrangle, Colo.: U.S. Qeol. 

Survey Bull. 386, p. 12, 1909.

miles farther west, however, in the valley of the Blue 

River, these deposits are as much as 650 feet above the 

valley floor and cover large areas. They are made up of 

well-rounded boulders and pebbles and contain little 

fine sand or clay. Most of the boulders are less than 

12 inches in diameter, but some are as much as 30 

inches. In the region west of the quadrangle quartzite, porphyry, granite, and schist are the most common 

rocks present in the high-terrace gravel, but micaceous 

red grits, red shales, and black shales also occur. 

Within the quadrangle the micaceous red grits and 

shales were not observed in these deposits. Many of 

the boulders are deeply weathered and can be readily 

broken up with a hammer.

Late Pleistocene topography. Much of the present 

topography was carved in the Wisconsin glacial stage, 

and the most conspicuous features are due to glacial 

cutting, although moraines and valley trains are 

abundant. The line of perpetual snow in Wisconsin 

time was probably near an altitude of 11,000 feet in the 

Montezuma quadrangle, and valleys heading at lower 

levels were unglaciated. Frey Gulch, Keystone Gulch, 

and Soda Creek, in the western part of the quadrangle, 

are valleys of this type and lack the glacial features so 

common in most of the other valleys of the region.

Cirques are one of the most striking features of 

glacial sculpture and are abundant in the high country 

near the Continental Divide. They are steep-walled 

rock basins at the heads of streams and were formed 

by the plucking and abrasion of the ice near the source 

of former glaciers, where valley deepening from glacial 

erosion was at a maximum. Compound cirques are 

common, and the higher cirques in such places are 

probably relics of early Pleistocene glaciation. The 

headward erosion of cirques on opposite sides of a 

ridge may result in impassable knife-edged divides, 

and many examples of this type of erosion can be 

found in the quadrangle. The uneven rock floors of 

the cirques have been filled by lakes in many places. 

From the summit of Grays Peak, Argentine Peak, or 

Mount Lewis many of these glacial lakes can be seen 

gleaming like emeralds at the base of sheer iron-gray 

cliffs. The tarn arid cirque at the head of Smelter 

Gulch are shown in plate 10, A. Although most of 

the lakes are caused by the uneven surface excavated 

by the glaciers, some of them fill depressions in the 

ground moraine. Swamps are more common than 

lakes in the deposits left by the retreating glaciers.

Hanging valleys and U-shaped valleys, typical of 

glacial erosion, are characteristic of the high country, 

and many features of ice erosion are well illustrated in 

the quadrangle. The effect of a marked change in the 

course of a glacial valley 011 the action of the glacier 

is well shown in Ruby Gulch, about 3 miles northeast 

of Montezuma, and is illustrated in plate 7, C. As 

the movement of the glacier was changed from south 

to due west the southeast and south side of the gulch 

bore the brunt of the work of redirecting the mass of
25

moving ice, and the wall of the gulch was hewn almost 

vertical while the opposite slope of the valley was little 

affected. The rasplike action of boulders embedded 

in the moving glaciers smoothed, striated, and channeled the bedrock on the floors and sides of many 

valleys. Glacial striae are uncommon on the valley 

walls, but tliere are many places on the valley floors 

where they are fresh and well preserved. They can 

be easily distinguished on the smoothly polished 

hummocks of bedrock, as at the head of St. Johns 

Creek.

Late Pleistocene (Wisconsin) deposits. Most of the 

valleys a,re occupied by thin, discontinuous bodies of 

alluvium, Wisconsin till, and valley-train gravel. The 

till includes terminal moraines, lateral moraines, 

recessional moraines, ground moraines, and medial 

moraines, but these have not been distinguished by 

separate conventions on plate 3. The poorly sorted 

material that makes up the drift is little weathered 

and shows a great range in size and shapes. Subangular boulders as much as 20 feet in diameter are 

intermingled with small pebbles, sandy clay, and small 

boulders. The till is known to be more than 100 feet 

thick in some places, but drill records in the till 

deposits nea,r Breckenridge suggest that locally its 

thickness is as much as 150 feet.

The coarse gravel of the valley train was deposited 

by the streams issuing from the foot of the glaciers, 

and in many places its superposition on the till marks 

the later part of the glacial stage, when the glaciers 

were retreating toward the snowy cirques. Glaciofluviatile deposits of this sort are most widespread on 

the Snake River between Keystone and Cold Spring. 

They consist chiefly of moderately well-rounded 

cobbles, small pebbles, and sand, but small boulders 

are rather common. The pebbles and boulders are 

fresh, and ii.nweath.ered, in contrast to those found in 

the high terrace gravel.

Recent topography.- Since the retreat of the Wisconsin glaciers erosion has modified the topography 

but little. Canyons from 10 to 30 feet deep have 

been, cut in the bottoms of some of the large glacial 

valleys; landslides, rock glaciers, and talus streams 

have been active in some places; small alluvial fans 

have formed at the mouths of tributary streams in 

certain valleys; and many small lakes have been 

formed by beaver darns in the poorly drained ground 

moraines below 11,500 feet.

Recent deposits. Thin strips of alluvium border the 

streams at many places and are commonly covered 

with a dense growth of Arctic willow. Swampy lake 

beds, in part of late Wisconsin age, occur in the 

poorly drained hollows of some ground moraines, 

notably in Geneva Gulch just east of the quadrangle. 

Small alluvial fans composed of moderately fine pebbly 

gravel and coarse sand have formed at the mouths of 

several side gulches that enter the Snake River

between Keystone and Soda Spring. Landslides are 

abundant along the oversteepened sides of the glaciated 

valleys. The largest landslide is on the north slope of 

Decatur Mountain a short distance east of the Pennsylvania mine. The rasping attack of the glacier as 

it swung west from the Horseshoe Basin to the main 

course of Peru Creek was chiefly absorbed by the 

north shoulder of Decatur Mountain and probably 

resulted in greatly oversteepening it, and when the 

supporting pressure of the ice was removed, a large 

mass of the mountain slumped into the valley. 

Smaller landslides occur at many other places in the 

quadrangle and are shown on plate 3. Slowly moving 

masses of angular rock fragments, generally termed 

rock glaciers, are forming at the foot of steep ridges in 

several places. They are most common in the southeastern part of the quadrangle, and the largest and 

most striking one occurs at the head of Handcart 

Gulch. The brilliantly colored slopes of Red Cone are 

covered with small angular fragments of the pyritized 

bedrock, which are constantly feeding the slowly 

spreading accumulation at the base. The rock 

glacier at the head of Stevens Gulch is shown in 

plate 10, B.

Pyritized Slope wash in Handcart and Geneva 

Gulches and near the head of the Snake River has been 

the source of local deposits of bog iron ore. As ground 

water passes over the oxidizing pyrite it becomes rich 

in iron sulphate, which soon hydrolyzes and forms 

limonite. The limonite cements the slope wash and 

ground moraines of the valleys to a depth of 20 feet 

or more at some places. Most of the limonite contains 

so much extraneous material that it is almost valueless as an iron ore, although it was used as a flux by 

the Hall Valley and Geneva Gulch smelters in the 

seventies. The distribution of the ^bog iron ore is 

shown on plate 3. An analysis of some of the material. 

in Handcart Gulch used by the Hah1 Valley smelter 

in 1875 showed Si02 7.18 percent, Fe203 67.55 percent, 

P205 1.82 percent, CaO 1.22 percent, H20 and organic 

matter 22.37 percent.53

The high basins that have been little affected by 

glaciation have been filled to depths of as much as 100 

feet by the gradual downward creep of slope wash from 

the surrounding hills. Although this process is still 

going on, most of the material accumulated in Pleistocene time. These high-basin debris sheets are made 

up of unsorted, angular, more or less weathered fragments, embedded in sand and sandy clay. The slopes 

of the unglaciated valleys that head below 11,500 feet 

are covered with slope wash very similar to the highbasin debris sheets. The valley bottoms contain some 

material ranging in appearance from that characteristic of the high terrace gravel to that indistinguishable 

from the gravel of the late Wisconsin valley trains.

68 Chauvenet, Regis, The iron resources of Colorado: Am. Inst. Min. Eng. Trana. 

vol. 18, p. 268, 1890.
26 MONTEZUMA QUADRANGLE, COLORADO

CRETACEOUS (?) AND TERTIARY IGNEOUS ROCKS 

GENERAL FEATURES

As the true relations of the igneous rocks of the 

Montezuma quadrangle and their places in geologic 

history, can be appreciated only after a study of the 

entire Front Range province, the following pages are 

devoted to a general regional discussion, with paragraphs on the local rocks interposed at appropriate 

places.

Post-Cambrian igneous rocks are common in the 

Montezuma quadrangle and, as shown on plate 5, 

they are part of a belt of porphyries that is coextensive 

with a belt of mineralization. The late intrusive 

rocks of the Front Range are found chiefly in a narrow 

zone extending southwestward from Boulder to 

Breckenridge. West of Breckenridge the porphyry 

belt widens toward the southwest and continues across 

the State to the San Juan mining region. Ball 54 was 

one of the first to summarize the occurrences of porphyry in Colorado and, with Spurr and Garrey, 55 to 

point out that mineralization and intrusive activity 

are localized in this northeastward-trending belt. 

These porphyries were intruded in late Cretaceous (?) 

and early Tertiary (Eocene) time.

The porphyries have many features in common. 

Although they show a great range in texture and in 

mode of occurrence, they are nearly all siliceous or 

intermediate igneous rocks. Certain types, such as 

the Lincoln porphyry of the Leadville and Alma 

districts, are generally found in cross-breaking bodies; 

others, such as the monzonite of Bald Mountain, in the 

Breckenridge district, are more commonly found as 

sills. Certain porphyries have such distinctive features that they are easily recognized as one rock formation in widely^ separated regions. The Lincoln 

porphyry, for example, has been correlated with similar 

appearing rocks in districts 60 miles from the type 

locality on Mount Lincoln, Park County.56 Attempts 

to correlate other porphyries have been less convincing: 

thus Ball 57 has correlated an alaskite porphyry, one 

of the latest intrusives of the Georgetown quadrangle, 

with the earliest of the porphyries of the Leadville 

district, the White porphyry. Although Crawford 

does not specifically correlate porphyries other than 

the Lincoln porphyry, he gives a general summary of 

his interpretation of the igneous history of central 

Colorado. This summary is in general accord with the 

conclusions of most geologists who have worked in this 

region and is as follows: (1) Intrusion of porphyries 

from great depth; (2) large-scale folding and faulting; 

(3) intrusion of quartz diorite in small bodies throughout a wide region; (4) batholithic invasion of quartz

« Ball, S. H., op. cit. (Prof. Paper 63), pp. 67-71. 

" Spurr, J. E., and Garrey, G. H., idem, p. 107.

85 Crawford, R. D., A contribution to the igneous geology of central Colorado: 

Am. Jour. Sci., 5th ser., vol. 7, pp. 365-388, 1924. 

« Ball, S. H., op. cit., p. 70.

monzonite; (5) minor faulting; (6) deposition of 

minerals emanated from the quartz monzonite magma; 

(7) a second intrusion of porphyries; (8) more faulting. 

As the result of additional study throughout a great 

part of the Front Range and in other parts of Colorado, 

a slightly more detailed and definite age sequence can 

now be given.

In order that the reader may have clearly in mind the 

igneous and structural sequence that should be established in the next few pages, the conclusions are summarized before the general discussion. The postCambrian igneous and related structural history of the 

Front Range is believed to be essentially as follows: 

(1) Intrusion in early Denver time (lowest Eocene) 

of sills and dikes of silicic felsites, notably the White 

porphyry of Leadville and the felsites of the Ward 

district; (2) gradual vertical uplift of the Front Range 

region, accompanied by the intrusion and extrusion 

throughout early and middle Denver time of calcic 

andesites and potassic basalts such as the interbedded 

basalts of Table Mountain, near Golden; the Valmont 

dike, east of Boulder; and the gabbro, diabase, and 

ultrabasic dikes of the Boulder, Central City, and 

Georgetown quadrangles; (3) strong folding and 

thrust faulting at the end of Denver time, preceded 

and accompanied by the intrusion of monzonitic 

magma, locally dioritic or granodioritic in composition, 

such as the Johnson Gulch porphyry of Leadville, the 

diorite of the Buckskin Gulch stock of the Alma district, the diorite and monzonite porphyries of Breckenridge, the dacite of the Georgetown quadrangle, and 

the hornblende and biotite diorites of the Central City 

quadrangle; (4) minor faulting followed by the intrusion of dikes and sills of porphyritic quartz monzonite 

such as the Evans Gulch porphyry of Leadville, the 

quartz monzonite porphyry (intermediate type) of 

Breckenridge, and the Elk Mountain porphyry of 

the Tenmile district; (5) faulting preceding and 

accompanying the wide-spread invasion of coarsegrained porphyritic quartz monzonite, mostly in 

stocks and dikes and rarely in sills, represented by the 

Lincoln porphyry, the Princeton quartz monzonite of 

Crawford, the Montezuma quartz monzonite, and the 

quartz monzonite porphyries of the Georgetown quadrangle; (6) minor faulting and the intrusion of dikes 

of porphyritic sodic quartz monzonite such as the 

alaskitic quartz monzonite porphyry of the Georgetown quadrangle and the porphyritic Brainerd quartz 

monzonite of the Ward district; (7) the intrusion of 

dikes of sodic rhyolite and porphyritic sodic granite 

such as the aslaskite of the Georgetown quadrangle 

and the porphyritic Modoc quartz monzonite of the 

Ward district; (8) the intrusion of porphyritic granite 

and rhyolite such as those of the Georgetown and 

Montezuma quadrangles; (9) the intrusion of alkaline 

syenites and trachytes such as the alkali syenite and 

the bostonites of the Georgetown and Central City
CRETACEOUS (?) AND TEETIARY IGNEOUS ROCKS 27

quadrangles and the trachyte of Sunset, in the Ward 

district; (10) minor faulting and the formation of goldsilver-load-zinc-copper ores throughout the mineral 

belt of Colorado: 58 (11) the intrusion of felsites and 

related rocks, such as the rhyolite agglomerate of 

Leadville, the biotite latite of the Georgetown quadrangle and the biotite andesite of the Bluebird mine, 

near Nederland; (12) cutting of partial peneplain by 

the end of Fort Union time (the Flattop peneplain); 

(13) minor uplift in early Wasatch time and widespread peneplanation during remainder of Eocene 

time (formation of Medicine Bow peneplain); 59 (14) 

marked vertical uplift at end of Eocene time, accompanied by faulting; (15) denudation throughout Oligocene time; (16) volcanic activity throughout the Miocene in the San Juan region and periodically in the 

southern and north-central parts of the Front Range, 

locally accompanied by the formation of important 

ore deposits; (17) denudation and minor volcanism 

during the Pliocene; (18) faulting and regional uplift 

in early Pleistocene time, followed by strong erosion.

The igneous activity that commenced early in 

Denver time and continued through that epoch well 

into the lower Eocene is not as readily subdivided into 

separate stages as the summary given above might 

lead one to believe. As many writers have already 

pointed out, the porphyritic intrusives are all intimately related to one another and are probably differentiation products of one deep underlying magma. In 

the long period of time that the magma was active its 

slowly changing composition was manifested in the 

changing composition of successive intrusions. Definite age relations established by one type of intrusive 

cutting another have been recorded for most of the 

groups given in the foregoing summary, but only in a 

few widely separated localities. The trend of differentiation has been well shown at some places, and it is 

noteworthy that this evidence indicates the same sequence as the age relations found in distant parts of 

the mineral belt. There seems to be good reason to 

believe that petrographic similarity, where not obscured by alteration, all'ords an important and moderately trustworthy basis for correlation, but it is used 

only to supplement the method of comparing definitely 

established rock sequences.

ESTABLISHED RELATIONS OF THE INTRUSIVES

The earliest record of intrusive activity is found in 

the lower part of the Denver formation, at about 600 

feet above the Laramie formation. Pebbles of lightcolored silicic felsites carrying sparse phenocrysts of 

augite are abundant in the lower beds on South Table

M Burbanlc, W. S., Revision of geologic structure and stratigraphy in the Ouray 

district of Colorado and its hearing on ore deposition: Colorado Sci. Soc. Proc., vol. 

12. pp. 213-232, 1030.

»' Van Tuyl, F. M., and Lovcring, T. S., A contribution to the physiographic 

history of the Colorado Front Range [abstract]: Geol. Soc. America Bull., vol. 43, 

p. 170, 1032.

Mountain.60 The andesite pebbles in the higher parts 

of the Denver formation are distinctly less silicic and 

more calcic than those found lower down. Thus, a few 

hundred feet higher in the section pebbles of the lightcolored andesites are followed by dark-colored varieties 

low in magnesia, which are typical of most of the eruptive material found both in the pebbles and in the interbedded lavas. Still more calcic andesites are reported 

from a horizon about 1,400 feet above the base on Green 

Mountain, where Cross 61 found a dense pyroxene andesite containing both augite and hypersthene; this is 

said to be the lowest observed occurrence of the highly 

magnesian variety indicated by hypersthene. Interbedded lavas occur in the Denver formation above the 

horizon of the light-colored andesite pebbles. The 

analyses given in the table on pages 36-37 show that 

the basalts are characterized by moderately low silica 

and high alumina, ferrous iron, magnesium oxide, and 

calcium oxide.

In the Ward district, a few miles northwest of 

Boulder, mica dacite and felsite are probably earlier 

than a diabase dike, which in turn is older than quartz 

monzonite.62 In the Central City quadrangle biotite 

and hornblende andesites are older than biotite and 

hornblende diorites.63 In the Montezuma quadrangle 

augite diorite is earlier than monzonite and porphyritic 

quartz monzonite. In the Leadville district the 

White porphyry, a silicic felsite porphyry, is older than 

all the other post-Cambrian intrusives.64 The analyses 

of the White porphyry of Leadville and the much 

altered felsite porphyry of the Ward district (nos. 55- 

57, p. 37) show considerable differences in the composition of these two rocks, which so far as known are the 

oldest porphyritic rocks in their respective districts. 

The presence of silicic andesite pebbles in the lowest 

part of the Denver formation indicates that more acidic 

rocks preceded the normal and calcic andesites which 

supplied most of the early sediment to the formation. 

As the earliest of the porphyritic rocks in the Ward 

district agree in composition and sequence with the 

earliest eruptive material in the Denver sediments, 

they are believed to be of Denver age. Although the 

White porphyry of Leadville is more silicic than the 

early felsites of the Denver formation, it is grouped with 

them because it is the earliest porphyry of the district 

and is earlier than the post-Denver folding and faulting 

of the Laramide revolution. The age relations and the 

similarity in composition of the intrusive augite diorite 

and diabase of the Front Range to the calcic augite

60 Cross, Whitman, Geology of the Denver Basin: U.S. Geol. Survey Mon. 27, 

pp. 161-171,1896.

8i Idem, p. 178.

a" Worcester, P. G., The geology of the Ward region, Boulder County, Colo.: 

Colorado Geol. Survey Bull. 21, p. 46,1920.

03 Bastin, E. S., Economic geology of Gilpin County and adjacent parts of Clear 

Creek and Boulder Counties, Colo.: U.S. Geol.-Survey Prof. Paper 94, p. 52, 1917.

 < Emrnons, S. F., irving, J. D., and Loughlin, G. F., Geology and ore deposits of 

the Leadville miniug district, Colo.: U.S. Geol. Survey Prof. Paper 148, pp. 51-52, 

1927. Crawford, R. D., A contribution to the igneous geology of central Colorado; 

Am. Jour. Sci., 5th ser., vol. 7, p. 371, 1924,
28 MONTEZUMA QUADRANGLE, COLORADO

andesite pebbles and the interbedded basalts of the 

Denver formation (nos. 44-54, p. 37) suggest that they 

may be correlated.

The relation of the early diorites and diabases to the 

rocks of the granodiorite group is shown at few places. 

In the main tungsten area of Boulder County diabase 

is clearly older than a calcic dacite.65 As the dacite 

consists chiefly of andesine, orthoclase, biotite, hornblende, and augite with, interstitial quartz that Crawford believes to be largely secondary, the rock belongs 

to the early monzonitic rocks which are included in 

the granodiorite group for purposes of correlation. 

As pointed out above, the calcic diorites are earlier 

than the porphyritic quartz monzonite near Montezuma also. It is worthy of note that in the Middle 

Park formation, whose lower part is equivalent to the 

Denver formation, the first pebbles of quartz monzonite porphyry noted by the writer were far up in the 

section, nearly 5,000 feet above the base, but in the 

lower beds andesitic material was abundant. The 

evidence, though meager, seems sufficient to place the 

calcic andesite and diabase groups as definitely older 

than the granodiorite and the quartz monzonite groups.

At Breckenridge monzonite and orthoclase-bearing 

diorite grade into each other and may be considered 

typical of the monzonite group. They are older than' 

the quartz monzonite porphyry of this district.66 

Diorite of the same type is older than the Lincoln 

porphyry (quartz monzonite) of the Leadville, Alma, 

and Tenmile districts.67 In the region from Breckenridge to Como the rocks of the monzonite group were 

intruded in large masses along the axis of a regional 

fold that developed during the Laramide revolution. 

The rocks are involved in much of the faulting that 

accompanied this orogeny, but some faulting and 

folding had taken place before their intrusion. Their 

age is probably later than that of the Denver formation 

of the type locality, but they may be contemporaneous 

with the upper part of the Middle Park formation. 

If the Laramide revolution is regarded as marking the 

end of the Cretaceous period, the granodiorite rocks 

should be called the latest Cretaceous rocks in the 

Front Range, but if, on the other hand, the Denver 

formation is an early Tertiary (Eocene) formation, as 

it is at present classed by the United States Geological Survey, the monzonite as well as all other postCambrian intrusive rocks of the Front Range were 

formed in the Tertiary period.

In the Breckenridge district the moderately porphyritic quartz monzonite classed by Ransome as the 

"quartz monzonite porphyry (intermediate type)" is

88 George, R. D., and Crawford, LI. D., The main tungsten area of Boulder County 

Colo.: Colorado Geol. Survey 1st Rept., pp. 23, 28-30, 1908.

60 Ransome, F. L., Geology and ore deposits of the Breckenridge district, Colo.: 

U.S. Geol. Survey Prof. Paper 75, p. 71, 1911. Lovering, T. S., Geology and ore 

deposits of the Breckenridge mining district, Colo.: U.S. Geol. Survey Prof. Paper 

176, p. 16, 1934.

87 Crawford, R. D., op. cit., p. 371. Emmons, S. F., U.S. Geol. Survey Geol. 

Atlas, Tenmile district folio (no. 48), structure-section sheets, 1898.

clearly earlier than the Lincoln porphyry.68 Recent 

work in the Mosquito Range south of the Leadville 

district shows that a porphyritic quartz monzonite 

similar in appearance to the intermediate quartz 

monzonite porphyry of Breckenridge cuts a rock 

that strongly resembles the monzonite porphyry 

of Breckenridge.69 These relations as well as 

the intermediate texture and composition indicate that the moderately porphyritic quartz monzonites, such as the Elk Mountain porphyry of the 

Tenmile district and the intermediate quartz monzonite porphyry of the Breckenridge district, are older 

than the Lincoln porphyry and younger than the rocks 

of the monzonite group.

In the preceding paragraphs examples have been 

given to show that the coarsely porphyritic qiiartz 

monzonite porphyries, typified by the Lincoln porphyry, are clearly younger than the White porphyry 

of Leadville, the granodiorite, and the intermediate 

quartz monzonite porphyries, and that rocks of similar 

composition to the Lincoln porphyry but of different 

texture cut basic diorite and diabase. Near Montezuma the large stock of coarsely porphyritic quartz 

monzonite cuts the Williams Range underthrust 

fault,70 which was formed during the Laramide revolution, and this stock is older than the Flattop peneplain, 

which is believed to be of early Eocene age. 71 Near 

Silver Plume quartz monzonite porphyry of finer texture but similar composition is cut by granite porphyry and alaskite porphyry. 72 In the Leadville 

district it is cut by rhyolite dikes,73 and in the Tenmile 

district it is earlier than the rhyelites.74 In the Alma 

district the Lincoln porphyry is earlier than a felsite 

dike 75 and a "late white porphyry" 76 that is probably 

equivalent to a rhyolite or sodic quartz monzonite in 

composition. The Lincoln porphyry is cut by veins 

in many districts, but the sediments that it invades in 

the Montezuma quadrangle show contact metamorpbism. It is evidently older than the main period of 

ore deposition throughout the mineral belt but is nevertheless genetically related to the mineralization. It is 

probably early Eocene.

Throughout the mineral belt there are many dikes 

whose composition is intermediate between that of the 

quartz monzonite porphyry group typified by the Lincoln porphyry and that of the granite and rhyolite

83 Lovering, T. S., op. cit., p. 16.

8« Behre, C. H., Jr., unpublished report.

70 Lovering, T. S., The Williams thrust fault: Geol. Soc. America Bull., vol. 

39, p. 173, 1928.

71 Lovering, T. S., Geologic history of the Front Range, Colo.: Colorado Sci. 

Soc. Proc., vol. 12, p. 99, 1929.

72 Spurr, J. E., and Garrey, G. H., op. cit. (Prof. Paper 63), p. 133.

73 Emmons, S. F., Geology and mining industry of Leadville, Colo.: U.S. Geol. 

Survey Mon. 12, pp. 198, 350, 1886. Behre, C. H., Jr., Revision of structure and 

stratigraphy in the Mosquito Range and Leadville district, Colo.: Colorado Sci. 

Soc. Proc., vol. 12, p. 43, 1929.

74 Emmons, S. F., U.S. Qeol. Survey Geol. Atlas, Tenmile district folio (no. 48), 

p. 3, 1898.

" Crawford, R. D., op. cit., p. 371.

76 Singewald, Q. D., Preliminary report on the geology of Mount Lincoln and the 

Russian mine, Park County, Colo.: Colorado Sci. Soc. Proc., vol. 12, p. 396, 1930.
CRETACEOUS (?) AND TERTIARY IGNEOUS ROCKS 29

group. In the Georgetown quadrangle sodic quartz 

monzonite, according to Ball,77 is in part contemporaneous but mos,tly earlier than granite aplite. Porphyritic sodic granite, the granite porphyry of Ball, is 

younger than porphyritic quartz monzonite at Silver 

Plume 78 and is earlier than the ores. Porphyritic 

sodic granite is also later than the Lincoln porphyry 

type of quartz monzonite in the Montezuma stock. 

These structural relations place the sodic rocks intermediate in time between the quartz monzonite and the 

granite aplite. Though they bear a close relation to 

the aplite, they are also intermediate in composition 

between those two rocks and are therefore in keeping 

with a progressive differentiation into more and more 

salic facies.

For the purposes of description this intermediate 

series has been subdivided into the group of sodic 

quartz monzonites and the group of sodic granites. 

Although the age of this series is known, the relative 

ages of the two groups have not been established by 

structural evidence. The sodic quartz monzonite 

group, however, because of its composition, is thought 

to be an earlier differentiate of the quartz monzonite 

magma a,nd is provisionally regarded as earlier than 

the sodic granite group.

Dikes and small stocks of porphyritic granite and 

rhyolite are found throughout the mineral belt of 

Colorado. Granite porphyry and alaskite porphyry of 

this group are later than quartz monzonite porphyry 

near Silver Plume and earlier than ore. 79 In the 

Tenniile district the rhyolites of McNulty Gulch and of 

Chalk Mountain are later than diorite and Lincoln 

porphyry and earlier than the silver ores of the Grand 

Union or Silver Bowl mine.80 Bodies of granite aplite 

occur in the Montezuma quartz monzonite stock, and 

although they nearly everywhere cut across it with 

cleanly defined contacts, there are some places where 

the two rocks grade into each other. In these places 

the granite is probably a local salic derivative of the 

stock itself and indicates the general course of differentiation of the quartz monzonite magma.

A group of moderately silicic alkalic rocks is found in 

the Front Range east of the Continental Divide but 

is unknown in the major part of the Colorado mineral 

belt between the Georgetown quadrangle and the San 

Juan, region. These rocks are 'characterized by their 

high percentage of alkalies, soda and potash together 

always making up more than .10 percent of the fresh 

rock, and by moderately high alumina, which always 

constitutes more than 16 percent. As shown in the 

analyses of group 9 (p. 36), they have many other 

characteristics in common. Near Idaho Springs bostonite is cut by "biotite latite" that is also later than

" Ball, S. H., op. cit. (Prof. Paper 63), p. 74. 

'3 Spurr, J. 13., and Garroy, O. H., idem, p. 133. 

« Mem, p. 135.

so Emmons, S. F., U.S. Geol. Survey Geol. Atlas, Tenmile district folio (no. 48), 

pp. 3, 4, 1808.

the ores of that district. 81 The bostonites on the other 

hand, are earlier than both the lead-zinc and the 

pyritic gold ores of the Central City quadrangle. 82 

Spurr believed that the alkalic syenite of the Georgetown quadrangle was the youngest Tertiary intrusive 

in that district, because of the fresh appearance of the 

rock, because hot springs were found at the edge of a 

small stock of the syenite near Idaho Springs, and 

because it was not associated with ore deposits. 83 

However, many of the older rocks have a fresh appearance where they are not cut by veins; the hot spring 

in the Dyke vein, on the Argo tunnel level, is several 

miles from the nearest alkali syenite known; and 

finally the alkali syenite is less than half a mile from 

some veins. As only two masses of the alkali syenite 

are known a small stock and a short dike close by 

its lack of direct association with veins is not a strong 

reason for regarding it as a postmineral intrusive. Its 

location in the heart of a region where bostonite and 

bostonite porphyry dikes are abundant and the marked 

similarity in the peculiarly distinctive composition of 

the two rocks suggest strongly that they came from 

the same magmatic source in the same intrusive epoch. 

The writer believes that the bostonite and the alkali 

syenite are both premineral. The relations of the bostonites to the ores and to the biotite latite are all that 

are on record. However, the writer has found that 

bostonite cuts monzonite porphyry on Nigger Hill, at 

the western edge of Central City. The monzonite 

porphyry follows a northeast fissure that has been offset 

by the northwesterly fault followed by the bostonite 

porphyry, the northeastern segment of the monzonite 

porphyry moving about 60 feet northwest of the southwestern segment. The bostonite porphyry is very 

fresh in spite of its premineral age, but the monzonite 

porphyry is much, altered. The bostonites are thus 

definitely later than the monzonite porphyries and 

earlier than the ores of the Central City district.

In the Rosita Hills district, 110 miles south of Idaho 

Springs, Cross established the order of eruptions for 

the Rosita volcano.84 The successive changes in 

chemical composition indicated by the rocks in that 

district are very close to those indicated by the rocks 

of the porphyry belt that crosses the Montezuma quadrangle. The earliest eruptive rocks', the Rosita and 

Bunker andesites, were of intermediate composition 

and were followed successively by more calcic diorite, 

a more silicic dacite, a still more silicic rhyolite, an 

alkalic andesite, and finally a trachyte. None of these 

rocks have the characteristic high alumina and combined alkalies found in the rocks of the alkalic group 

of the porphyry belt, but some of the andesite that 

followed the rhyolites contains as much as 10.32 per-

" Spurr, J. E., and Qarrey, Q. H., op. cit., p. 344.

82 Bastin, E. S., op. cit. (Prof. Paper 94), p. 101.

83 Spurr, J. E., and Garrey, Q. H., op. cit., p. 135.

s« Cross, Whitman, Geology of Silver Cliff and the Rosita Hills, Oolo.: U,R, 

Geol. Survey 17th Ann. Eept., pt. 2, p. 326, 1890.
30 MONTEZUMA QUADRANGLE, COLORADO

cent of combined alkali and 18.40 percent of alumina. 

The trachyte, latest of the eruptive rocks of the Rosita 

volcano, is still higher in both alkalies and alumina. 

The magmatic sequence in this region is clearly parallel 

to that established in the porphyry belt and is believed 

by Cross to be of Eocene age. As alkalic rocks are 

later than rocks of the granite and rhyolite group at 

Rosita and later than monzonite porphyry at Central 

City, it seems probable that rocks of group 9 are the 

latest premineral intrusives in the porphyry belt.

Postmineral igneous rocks are rare in the Front 

Range. Bastin 85 found a dike of fine-grained gray 

biotite andesite that was later than the ore of the Blue 

Bird mine, near Nederland. Spurr and Garrey 86 

found a fine-grained biotite latite dike that was later 

that the ore of the Stanley mine, near Idaho Springs. 

Loughlin 87 describes pipes of rhyolite agglomerate 

that are definitely later than the ores in Leadville. 

All are similar in composition. The biotite latite of 

the Georgetown quadrangle has a glassy groundmass 

whose index of refraction is between 1.49 and 1.50; 

this indicates a glass of rhyolitic composition.88 As 

the groundmass makes up the largest part of the rock, 

it should be classed as a rhyolite rather than a latite. 

No detailed description of the andesite of the Bluebird 

mine is on record, but its general description suggests 

a rock similar to the biotite latite of the Georgetown 

quadrangle. The few rocks that are definitely postmineral are probably close to rhyolites in composition. 

The analysis of the biotite latite given on page 36 

(no. 1) indicates a moderately calcic member of the 

granite family. All these rocks are older than the 

Rocky Mountain peneplain, which was developed in 

Miocene and Pliocene time.

CORRELATION

It is beyond the scope of the present report to make 

a detailed comparison of all published rock descriptions that bear on the intrusives of the porphyry belt. 

As most of the petrographic descriptions had to be 

studied in preparing the classification adopted in this 

report, a tentative correlation of the porphyries in 

some of the mining districts of the Colorado mineral 

belt has been prepared and is given in the accompanying table. The table on pages 36-37 compares most of 

the published analyses of intrusives from the porphyry 

belt together with some from Cripple Creek and the 

Rosita Hills.

PETROQRAPHIC DESCRIPTIONS

In the foregoing pages reasons are given for classifying the intrusive rocks of the porphyry belt into several 

groups in which, rocks of similar composition and age

ss Bastin, E. S., op. cit, p. 101.

so Spurr, J. E., and Oarrey, Q. H., op. cit., p. 135.

87 Loughlin, O. F., Geology and ore deposits of the Leadville mining district, Colo.: 

U.S. Geol. Survey Prof. Paper 148, p. 59, 1927.

88 George, W. D., The relation of the physical properties of natural glasses to their 

chemical composition: Jour. Geology, vol. 32, p. 368, 1924.

are considered. All groups are not present in the 

Montezuma quadrangle, but a brief description of the 

salient features of each group is given ,here, in order 

that the information may be placed on record. The 

groups are listed below in the order of age, the youngest 

at the top. The ores are also listed in order to show 

their position in the sequence.

11. Late silicic intrusives.

10. Ores.

9. Alkalic group.

8. Granite and rhyolite group.

7. Sodic granite group.

6. Sodic quartz monzonite group.

5. Quartz monzonite group.

4. Intermediate quartz monzonite porphyry group.

3. Monzonite group; includes diorite and granodiorite.

2. Gabbro group; includes peridotites, gabbros, calcic diorites, 

and andesites.

1. Early felsite group; includes rhyolites, dacites, latites, and 

silicic andesites.

The ages of these groups can be summarized as 

follows: Groups 1 and 2 are of Denver age, later than 

the Upper Cretaceous Laramie formation and older 

than the Laramide revolution; groups 3 to 9 are older 

than the mineralization of the porphyry belt and are 

probably all of early Eocene age; group 11 is postmineral and pre-Miocene.

GROUP i

There are 110 early felsites in the Montezuma quadrangle. In other parts of the Front Range rocks of 

this group are light-colored fine-grained porphyries and 

in. most places are much altered. Phenocrysts make 

up less than one third of the rocks and are commonly 

15 percent or less. They range from 1 to 5 millimeters 

in length but are usually about 2 millimeters. Small 

gray laths of plagioclase, near andesine in composition, 

are the most abundant phenocrysts, but quartz, biotite, 

and hornblende are common. In the highly altered 

state characteristic of this group, biotite is usually 

altered to inuscovite or sericite. The groundmass 

may be partly glassy but is more commonly a very 

fine, even-grained aggregate of feldspar and quartz. 

Both orthoclase and plagioclase are usually present 

in the groundmass, and rarely a little biotite is 

found. Sericite and calcite are abundant alteration 

products. Zircon, magnetite, and pyrite are common 

accessory minerals, but allanite and titanite, so common in the later rocks, do not occur in the felsites, so 

far as known. Many of the quartz phenocrysts have 

a border of fine-grained quartz drawn from the groundmass, which is optically continuous with the quartz 

of the phenocryst. Further descriptions of the rocks 

of this group are given in the reports of Loughlin,89 

Bastin,90 Crawford, 91 and Worcester.92

89 Loughlm, G. F., op. cit., pp. 43-46.

80 Bastin, E. S., op. cit., pp. 50-51.

81 George, R. D., and Crawford, R. D., op. cit., pp. 24-26.

82 Worcester, P. G., op. cit., pp. 29, 43, 44.
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 178 PLATE 11

A. PHOTOMICROGRAPH OF SILVER PLUME GRANITE FROM SANTA FE MOUNTAIN. 

The minute cracks in Ihe quarlz (q) indicate slight strain. Crossed nicols. mg, Magnetite; me, microcline; ms, mnscovite; b, biolite; ol, oligoclase.

B. PHOTOMICROGRAPH OF AUGITE DIORITE FROM EAST SLOPE OF BEAR MOUNTAIN. 

Showing typical network of andesine laths (striped crystals) intergrown with augite (stippled appearance). Black rods of ilmenilc abundanl. Crossed nicols.
PLATE 12 

PHOTOMICROGRAPHS OF ROCKS FROM THE MONTEZUMA QUADRANGLE

A. Hornblende diorite near mouth of Middle-Fork of Swan River. Augite core (a) surrounded by hornblende (h), which in turn

is surrounded by rim of biotite (b), indicating reaction of augite with magma of changing composition. 

73. Rhyolite porphyry from dike one-tenth mile north of bench mark 11,905, on wagon road west of Argentine Pass. The phenocrysts of quartz have an optically continuous border of quartz in the fine-grained rnicrogranular groundmass of quartz and

orthoclase which surrounds them. Crossed nicols. 

C. Granite porphyry from dike in Horseshoe Basin near foot of trail to Argentine Pass. Micrographic intergrowth of quartz and

orthoclase in groundmass; nearly euhedral quartz phenocrysts. Crossed nicols.
tl.S. GEOLOGICAL SURVEY PROFE

PHOTOMICROGRAPHS OF ROCKS FROM THE MONTEZUMA QUADRANGLE.
Tentative correlation of Cretaceous (?) and Eocene porphyries in several districts in the northeastern part of the mineral belt of Colorado, with special reference to the Front Range

Vertical uplift at end of 

Eocene

Early Wasatch uplift

Gradual development of 

Flattop peneplain

Culmination of Laramide 

revolution

Early Eocene (Denver) uplift

Porphyy group 

(this 

report)

13

12

11

10

9

8

7

6

5

4

3

2

1

Ward district

(Medicine Bow peneplain)

Ore

Trachyte at Sunset

Modoc quartz monzonite

Brainerd quartz monzonite

Mount Alto quartz monzonite

Mica dacite porphyry, 

quartz latite porphyry, 

and White Raven 

quartz monzonite

Monzonite, latite, diorite, 

and andesite porphyries

Diabase and olivine basalt

Felsite

Nederland district

Ore

Hornblende and biotite 

andesites

Latite, dacite, and basalt 

porphyries

Pyroxenite 

Gabbro

Felsite

Central City quadrangle

Andesite at Bluebird mine

Ore

Bostonite

Quartz monzonite of 

Apex mine

Quartz monzonite

Caribou stock differentiates 

Monzonite 

Hornblende and biotite 

diorites

Gabbro

Hornblende and biotite 

andesites

Georgetown quadrangle

Biotite latite

Ore

Alkali syenite 

Bostonite

Rhyolite 

Granite porphyry

Alaskite 

Dacite

Alaskitic quartz monzonite

Quartz monzonite porphyry

Montezuma quadrangle

Ore

Rhyolite and granite 

porphyritic

Porphyritic sodic quartz 

monzonite

Montezuma quartz monzonite

Diorite

Augite diorite

Breckenridge district

Ore

Quartz monzonite porphyry

Intermediate quartz monzonite porphyry

Monzonite 

Diorite

Leadville district and adjoining 

region

Rhyolite agglomerate

Ore

Rhyolite and "late White 

porphyry"

Lincoln [quartz monzonite] porphyry

Evans Gulch [quartz monzonite] porphyry

Johnson Gulch porphyry 

Diorite of the Buckskin 

Gulch stock in Alma 

district

Mount Zion porphyry 

White porphyry

71886 35. (Face p. 30.)
CRETACEOUS (?) AND TERTIARY IGNEOUS ROCKS 31

GROUP 2

The rocks of group 2 vary greatly in texture but are 

more commonly granular than porphyritic and are 

generally very uneven grained. Rocks of this group 

are characterized by abundant plagioclase, generally 

ranging in composition from calcic aridesine to labradorite, but in some places bytownite occurs. Orthoclase is rarely found, augite is common, hornblende 

and biotite vary greatly in abundance but are usually 

present, and olivine occurs in the more ferromagnesian 

rocks of the group. Magnetite and apatite are abundant accessory minerals, and titanite is not uncommon.

In the Montezuma quadrangle augite diorite occurs 

at many places in the form of small irregular masses 

and in dikes. Unlike the other late intrusive masses, 

it is irregularly distributed throughout the quadrangle, 

as shown on plate 3. The augite diorite is generally 

a fresh medium-grained dark-colored rock having a 

slightly greenish cast. Its texture ranges from finely 

porphyritic to unevenly granular, but the largest crystals are rarely more than 4 millimeters long. The rock 

weathers to a uniform rusty brown (after prolonged 

exposure), but in the early stages of weathering the 

plagioclase phenocrysts stand out as numerous small 

cJi.alky-g.ray laths that contrast strongly with the 

brownisli groimdmass.

The microscope shows that in the augite diorites 

andesine and augite are the essential minerals and usually are found in the proportion of 3 to 1. The andesine ranges from Ab55An45 to Ab6oAn40 and occurs in 

moderately fresh appearing laths that reach a maximum 

length of about 2 millimeters. In the porplryritic 

varieties the average size of the andesine phenocrysts 

is about 1 millimeter and of the augite phenocrysts 

about 0.8 millimeter; the crystals in the groundmass 

have a considerable range in size, but the andesine 

laths average about 0.15 millimeter and the augite 

crystals about 0.10 millimeter in length. The granular 

augite diorites differ from the porphyries in showing a 

continuous variation in the size of the grains; although 

most of the crystals lie between 0.10 and 1.0millimeter, 

crystals of any length between 0.01 and 2.0 millimeters 

can usually be found. In the porphyries the proportion of augite to andesine is about the same in the phenocrysts as in the groundmass, but the phenocrysts are 

usually fresh, whereas nearly half of the augite originally present in the groundmass is altered to fibrous 

green hornblende. The andesine commonly shows 

some alteration, to fibrous mica, probably paragonite 

but is in the main almost unaltered. Titaniferous 

magnetite is abundant, both as an original constituent 

and as an alteration product of the augite, and may 

make up as much as 15 percent of the rock. Titanite 

occurs as an accessory mineral and as an alteration 

product of titaniferous magnetite. Rims of titanite 

surrounding titaniferous magnetite are common in some 

specimens. The augite commonly occurs in subhedral

simple crystals which are interstitial between the andesine laths, but in some places it poikilitically incloses the andesine. The network of andesine laths 

typical of the augite diorite is shown in plate 11, 13.

GROUP 3

The monzonite group includes rocks belonging to the 

diorite, monzonite, and granodiorite families. No 

coarsely porphyritic rocks have been found in this 

group. Most of the rocks are fine-grained porphyritic 

rocks near granodiorite in composition, but both 

granular and porphyritic rocks of medium grain are 

not uncommon. The granular rocks are usually more 

calcic than the porphyritic rocks and more commonly 

occur as cross-breaking bodies. The phenocrysts may 

make up as little as 20 percent of the rock and are 

commonly from 1.5 to 3 millimeters in length. Plagioclase, biotite, and hornblende are the common phenocrysts, but rarely apatite or quartz also occur as 

phenocrysts. The plagioclase is generally labradorite, 

but andesine is not uncommon. The groundmass is 

chiefly an intergrowth of labradorite or andesine laths 

with a small amount of interstitial quartz and orthoclase, but some ferromagnesian mineral is usually 

present also. Apatite is always an abundant accessory 

mineral, magnetite is common, zircon and allanite are 

frequently found, but titanite is rare. Distinctive 

features of this group of rocks are the even texture, the 

lack of ortlioclase phenocrysts, the rarity of quartz 

phenocrysts except in the dacites,' the abundance of 

gray plagioclase laths about 2 millimeters in length, 

and the presence of interstitial quartz and orthoclase 

in the groundmass.

Representatives of the monzonite group in the 

Montezuma quadrangle include several dikes, which 

are most numerous in the southwest quarter of the 

quadrangle. A stock about half a mile in diameter 

occurs at the mouth of the Middle Fork of the Swan 

River, just south of the quadrangle. Most of the rocks 

belonging to this group would be classed in the field 

as porphyritic hornblende diorite or hornblende 

monzonite. They are dark gray and medium to fine 

grained, and the phenocrysts nowhere exceed 5 millimeters in diameter and are nearly everywhere less than 

3 millimeters. Hornblende or augite, less commonly 

biotite, is usually the most conspicuous phenocryst 

and is associated with smaller but more abundant 

laths of gray plagioclase. Quartz and orthoclase are 

not present as phenocrysts. The rocks of this group 

are generally very fresh and differ markedly in this 

respect from the granite porphyries.

Under the microscope the diorite and monzonite 

porphyries show subhedral and euhedral phenocrysts 

of plagioclase, hornblende, augite, or biotite, in a 

matrix consisting chiefly of moderately fine grained 

plagioclase, orthoclase, and quartz. The plagioclase 

is commonly andesine, but labradorite is sometimes
32 MONTEZUMA QUADKANGLE, COLORADO

found. The plagioclase phenocrysts are about 2 

millimeters in diameter. The ferromagnesian phenocrysts occur in a variety of ways. The most common 

of these minerals is hornblende, but it is usually associated with some biotite and augite. In the diorite 

at the mouth of the Middle Fork of the Swan River 

some crystals of the hornblende show a central core of 

augite, and nearly all the hornblende crystals are 

surrounded by a rim of brown biotite. (See pi. 12, A.) 

The crystal orientation of augite, hornblende, and 

.biotite is the same, and it is probable that the different 

minerals represent reaction zones developed during 

the final stages of crystallization in the dioritic magma 

and suggest the type of differentiation described by 

Bowen. 93 A short distance farther west, rocks of this 

group have hornblende phenocrysts partly replaced 

by aggregates of small augite or diallage crystals, 

and in some of the dikes on Collier Mountain east of 

Montezuma hornblende is lacking, and augite phenocrysts as well as some biotite are abundant.

The groundmass forms about 60 to 80 percent of the 

rock and is also illustrated in plate 12, A. It consists 

of network of andesine or labradorite laths in a matrix 

of quartz and orthoclase. Nearly all the quartz is 

interstitial, but rarely some crystals enclose plagioclase 

laths. The orthoclase occurs in larger grains and 

poikilitically encloses both plagioclase and apatite 

crystals. Apatite, magnetite, zircon, and titanite 

are common accessory minerals.

GROUP 4

The intermediate quartz monzonite porphyry occurs 

in the southwestern part of the quadrangle as sills and 

dikes cutting the Cretaceous shales. It is a moderately light colored gray rock, profusely speckled with 

small black crystals of hornblende or biotite, or both. 

Quartz crystals are always visible in the hand specimen 

and range from 1 to 15 millimeters in diameter but 

are commonly between 1.5 and 2 millimeters. The 

gray laths of oligoclase or andesine, which are abundant, are usually between 0.5 and 2 millimeters in 

length. Superficially the rock resembles the granodiorites, but the presence of the quartz phenocrysts 

is a distinctive feature that permits its ready identification in the field.

Under the microscope the quartz phenocrysts are 

seen to be strongly corroded and are commonly surrounded by a thin rim of fine-grained quartz drawn 

from the groundmass. The rim is optically continuous 

with the quartz of the phenocryst. The plagioclase 

occurs in individual subhedral crystals and in aggregates of three or more. The abundant biotite or 

hornblende occurs in subhedral or euhedral crystals, 

containing inclusions of apatite and rarely zircon. 

The groundmass is a microgranular mosaic of quartz

°s Bowen, N. L., The evolution of the igneous rocks, pp. 60-62, Princeton Univ. 

Press, 1928.

and orthoclase crystals in nearly equal proportions. 

Magnetite is the most abundant accessory mineral, but 

zircon and titanite are not uncommon.

GROUP 5

The porphyritic quartz monzoiiite correlated with 

the Lincoln porphyry of the Leadville district has many 

times the volume of all other Tertiary intrusive rocks. 

It occurs in a variety of forms, but the presence of 

prominent orthoclase phenocrysts, more abundant but 

smaller plagioclase laths, quartz, and some ferromagnesian mineral, all of megascopic size, generally 

suffices to distinguish it from other intrusives. Although porphyritic quartz monzonite occurs in dikes 

throughout the porphyry belt, by far the largest masses 

are found in stocks.

One stock and part of another occur in the Montezuma quadrangle. The stock at Montezuma lies in 

the center of the quadrangle and has a surface area of 

16% square miles. The other stock is in the southwestern part of the quadrangle and extends beyond its 

borders. It is much smaller but more irregular than 

the Montezuma stock, and it is impossible to .distinguish the cross-breaking mass from sills in many 

places, but the entire area in which quartz monzonite 

porphyry occurs is slightly less than 12 square miles. 

In addition to these two large masses, a few small crossbreaking bodies of irregular shape deserve mention. 

On Torreys Peak a very irregular body of pinkish-gray 

medium-grained and porphyritic rock crops out 

through an area of about 27 acres. It is similar to 

the Montezuma quartz mouzonite in every way except 

in the size of grain. A slightly larger stock of coarsegrained quartz monzonite porphyry forms a peak, rising 

to an altitude of 12,500 feet, a quarter of a mile west of 

Webster Pass. Irregular cross-breaking and sill-like 

bodies of quartz monzonite porphyry aJso occur near 

the head of West Geneva Creek. Aside from these 

occurrences the porphyritic quartz rnonzonites are 

found as dikes that range in length from about 100 

feet to slightly more than a mile.

Great differences in texture are found in the rocks of 

the quartz- monzonite group, but no felsitic rocks 

belonging in this class occur in the Montezuma quadrangle. In the large stocks most of the quartz monzonite porphyry is coarsely porphyritic, and even dikes 

in which a. felsitic groundmass makes up most of the 

rock show conspicuous quartz and orthoclase crystals 

from 5 to 12 millimeters in length. In a few places 

in the Montezuma stock complete gradations from the 

coarsely porphyritic rock into fine-grained porphyry 

have been found.

As the rock of the Montezuma stock typifies the 

coarse-grained varieties of the quartz monzonite group 

and forms the largest single body of late intrusive rock 

in the Front Range, it will be described in more detail
CRETACEOUS (?) AND TERTIARY IGNEOUS ROCKS 33

than the other porphyries. Patton 94 refers to the 

rock as the Montezuma "granite", but as orthoclase 

and andesine occur in about equal proportions (or 

within the arbitrary limits set for monzonite) it is 

more appropriately called the Montezuma quartz 

monzouite.

The Montezuma quartz monzonite is a beautiful 

stone: at a little distance it appears a dappled pinkish 

gray, and when studied more closely the abundant large 

flesh-colored crystals of orthoclase are found to stand 

in pleasing contrast to the finer-grained gray matrix, 

mottled with small black biotite crystals. Most of 

the conspicuous orthoclase occurs in crystals from 15 

to 20 millimeters in length, but in some places the 

crystals are much larger, and a few reach a length of 

50 millimeters. Smoky quartz and the abundant 

gray or grayish-green plagioclase commonly occur in 

crystals ranging from 3 to 5 millimeters in length. 

Hexagonal crystals or "books" of biotite about 2.5 

millimeters in diameter are plentiful, and the euhedral 

shape of this mica is characteristic of its occurrence in 

the quartz monzonite.

Because of the handsome appearance of the rock, its 

use as a building stone has been suggested. Unfortunately, most of the rock is much jointed, and it 

might be difficult to find a place where dimension blocks 

of satisfactory size could be quarried. In most places 

three or four systems of joints cut the quartz monzonite into rhombic blocks. The jointing appears so 

regular and is so conspicuous that dips and strikes were 

recorded at many places, but the results showed that 

the trend of both minor and major joints varied greatly 

in different parts of the stock. This lack of concordance suggests that the prominent jointing is not the 

reaction of the stock to regional compression but is 

more probably in part the result of forces transmitted 

through the deeper portions of the solidifying magma 

and in part the result of slow cooling. The pronounced horizontal sheeting found on Lenawee 

Mountain is confined to the mountain top.

Under the microscope the coarse-grained granitoid 

quartz monzonite is found to contain as its essential 

minerals quartz, orthoclase, andesine, and biotite and 

to have accessory magnetite, titanite, apatite, zircon, 

and allanite. Andesine occurs in subhedral laths, 

which range in composition from Ab67An33 to Ab53An47 

in the thin sections examined. Andesine makes up 

from 30 to 40 percent of the rock, and is earlier than 

quartz, orthoclase, or biotite. Quartz is earlier than 

some of the orthoclase, but in places it is in micropegmatitic iritergrowth with orthoclase and is evidently 

contemporaneous. From 20 to 30 percent of most 

sections is quartz, which is anhedral, shows a great 

range in size, and contains many minute fluid inclusions. 

Orthoclase makes up from 25 to 35 percent of the thin 

sections studied, but the large crystals that are so

»« Pntton, H. B., op. cit, p. 125.

prominent in an outcrop of the quartz monzonite were 

avoided in selecting material for. microscopic work. 

As the large crystals make up about 10 percent of the 

rock, the total orthoclase content is correspondingly 

greater than that observed under the microscope. 

Most of the orthoclase is anhedral and fresh. The 

brown biotite, which forms about 10 percent of the 

rock, is subhedral and contains inclusions of apatite, 

magnetite, and zircon. It is more or less altered to 

chlorite and epidote.

Although most of the Montezuma stock is coarsely 

porphyritic, some small bodies of finer-grained rock 

occur. Patton mapped these finer-grained porphyries 

as separate formations, but the writer has included 

them with the typical coarse-grained Montezuma 

quartz monzonite because the contact between the two 

types is nearly everywhere gradational and because 

their composition is the same. In some places the contact is moderately sharp, but even in those places the 

finer-grained facies shows a coarsening of grain near 

the contact. The finer-grained rock probably represents the intrusion of magma late in the quartz 

monzonite epoch of differentiation. It consists of gray 

and pink feldspar phenocrysts less than 10 millimeters 

in diameter and small crystals of quartz and biotite, 

set in a fine or medium grained grayish-green groundmass. Commonly orthoclase makes up 25 percent of 

the phenocrysts and about 35 percent of the groundmass. Nearly all the orthoclase phenocrysts are 

twinned after the carlsbad law. The plagioclase 

phenocrysts are smaller than the orthoclase but are 

much more abundant and make up a decidedly larger 

percentage of the phenocrysts. Most of the plagioclase is andesine, ranging from Ab55 An45 to Ab85 An35 , 

but many of the crystals are surrounded by a more 

sodic border, and locally no andesine is present and the 

only plagioclase is oligoclase. The quartz phenocrysts are anhedral, commonly occur in aggregates, 

contain many lines of minute bubbles and fluid inclusions, and rarely show slightly embayed outlines suggesting the beginning of magma tic resorption. The 

phenocrysts of biotite are either subhedral or euhedral 

and contain many small inclusions of apatite and in 

some crystals inclusions of zircon., titanite, or magnetite.

The groundmass is composed chiefly of a xenomorphic mosaic of quartz and orthoclase crystals which 

poikilitically enclose small plagioclase laths. The 

plagioclase ranges in composition from andesine to 

albite-oligoclase, but most of it is sodic andesine. 

Biotite is moderately abundant in the groundmass, and 

locally titanite is common; both minerals poikilitically 

enclose andesine. The accessory minerals, named in 

the order of their abundance, are apatite, magnetite, 

titanite, zircon, and allanite.

Although orthoclase, plagioclase, and quartz are 

usually fresh, the biotite is in general partly or wholly
34 MONTEZUMA QUADRANGLE, COLORADO

altered. Its most abundant alteration product is 

chlorite, with which some epidote is usually associated; 

less commonly rutile and leucoxene appear among its 

decomposition products. Where the plagioclase has 

been altered some distance from veins, carbonate was 

more commonly formed than sericite (or paragonite), 

but close to veins sericite is abundant.

The porphyritic quartz monzonite stock in the southwestern part of the quadrangle is very similar in its 

general features to the Montezuma stock. It differs 

markedly in the number of inclusions of older rock 

which it carries, however. In the Montezuma stock a 

few small schist fragments were found, but the stock 

as a whole is remarkably free from inclusions of older 

rock. The stock near Tiger is in places so full of fragments of the formations into which it was intruded 

that it is best described as an intrusion breccia. Inclusions of quartzite are very abundant and range 

from some that measure less than an inch to xenoliths 

many yards in diameter. Inclusions of silicified shale 

and silicified limestone are moderately abundant, and 

schist is not uncommon. In the regions where the 

quartz monzonite is relatively free from country-rock 

fragments it is commonly finer-grained and more 

porphyritic than the Montezuma quartz monzonite. 

Under the microscope it shows the same minerals and 

the same general relations. The quartz phenocrysts 

are more corroded and have thin borders of quartz 

drawn from the groundmass added to them in optical 

continuity. Orthoclase and quartz are more abundant 

in the groundmass than in the phenocrysts and are 

micropoikilitic in their relation to the andesine or 

oligoclase microlites.

The coarsely porphyritic and coarse-grained quartz 

monzonite of the stocks weathers a pinkish gray or light 

rusty brown. The large orthoclase crystals remain 

lighter-colored than the groundmass and weather in 

relief except where the rock has been hydro thermally 

altered. The light-colored, slightly protruding orthoclase crystals give the weathered surface a knobby 

appearance that is distinctive and easily recognized.

The porphyritic quartz monzonite dikes* range in 

color from dark pinkish gray to moderately light 

greenish gray and in texture from coarsely to finely 

porphyritic. No felsitic rocks belonging in this group 

have been found in the quadrangle. In most of the 

dikes the phenocrysts range from 3 to 10 millimeters in 

length, but rarely crystals of orthoclase 25 millimeters 

in diameter can be found. Orthoclase and plagioclase 

are abundant as phenocrysts, quartz is always present 

but is usually inconspicuous, and biotite and rarely 

hornblende also occur as megascopic crystals. The 

groundmass makes up 25 to 75 percent of the rock.

Under the microscope the relation of the dike rocks 

to the Montezuma quartz monzonite is more apparent 

than in the hand specimen. In most of the dikes over 

half of the phenocrysts are plagioclase, ranging in

composition from andesine to oligoclase, and many 

of the crystals are strongly zonal. From 20 to 35 

percent of the phenocrysts are orthoclase, commonly 

twinned after the carlsbad law, and most of the remaining crystals of megascopic size are quartz. The 

quartz is rarely subhedral, more commonly showing 

embayed outlines indicating magmatic resorption. In 

the sodic varieties, such as the oligoclase-quartz monzonite porphyries, the corroded quartz crystals generally show added rims of fine-grained quartz in the 

groundmass, which are optically continuous with the 

phenocrysts. The rims are locally present in a groundmass that is microgranular but are much wider and 

more prominent in a micropoikilitic groundmass. 

Biotite and hornblende are not abundant and are more 

or less altered to chlorite, epidote, sericite, and magnetite.

The groundmass consists chiefly of quartz and 

orthoclase, but small amounts of plagioclase, generally 

near albite-oligoclase in composition, are usually 

present. The proportion of orthoclase to quartz 

varies greatly, but rocks having a groundmass in 

which the two minerals are nearly equal are the most 

common. The texture of the groundmass is generally 

microgranular, but micropoikilitic texture is not uncommon, and rarely the quartz and orthoclase are 

micrographically intergrown. Apatite is the most 

abundant accessory mineral, but magnetite, zircon, 

and titanite are also found. The Cretaceous shales in 

the valley of Soda Creek, near the west edge of the 

quadrangle, are intruded by sills of quartz monzonite 

porphyry which have a glassy groundmass, but all 

dikes and sills in the pre-Cambrian rocks of the quadrangle are entirely crystalline.

Most of the porphyritic quartz monzonite dikes are 

moderately altered. The feldspars are sericitized, 

and the ferromagnesian minerals are heavily cliloritized. The uniformity of the alteration over wide 

areas suggests that it was endomorphic and occurred 

shortly after consolidation, induced by hot solutions 

emanating from the dikes themselves during cooling. 

To use a homely simile, the dike rocks were cooked in 

their own juices. This type of alteration is more and 

more noticeable in the later silicic rocks.

GROUP 6

The sodic quartz monzonite differs from the rocks 

of group 5 in being much less silicic and more sodic. 

Quartz is confined to the groundmass, and the plagioclase is either albite or albite-oligoclase. In color the 

rocks of this group range from dark gray to moderately 

light greenish gray, and in texture from very finely 

porphyritic felsites to porphyries having abundant 

phenocrysts as much as 5 millimeters in length. Most 

of the phenocrysts are light greenish-gray tabular 

crystals of albite. Orthoclase phenocrysts are not 

uncommon but are nowhere abundant. Hornblende
CRETACEOUS (?) AND TERTIARY IGNEOUS ROCKS 35

or biotite is present in most of the dikes but not everywhere in megascopic crystals.

The ground mass is much darker than most of the 

phenocrysts and is darker in the medium-grained porphyries than in the felsitic varieties. Its chief minerals, named in the order of abundance, are albite, 

orthoclase, and quartz. The proportions of the minerals vary greatly, but quartz nowhere forms more 

than 25 percent of the groundmass, and orthoclase 

commonly ranges between 20 and 50 percent. Many 

small flakes of chlorite occur in the groundmass and 

probably indicate the former presence of fine-grained 

biotite or hornblende. Apatite is so abundant in the 

groundmass of many of the rocks that it should be 

classed as an essential rather than as an accessory 

mineral. Where albite is very abundant, the groundmass commonly has a micro tr achy tic texture, but 

where orthoclase is abundant the albite microlites are 

poikilitically included in the much larger orthoclase 

crystals. The groundmass of some of the felsites is 

so finely microgranular that it suggests a devitrified 

glass.

Most of the sodic quartz monzonite porphyries show 

marked alteration. The feldspar phenocrysts are 

sericitized, the minute flakes of mica following crystallographic directions. The phenocrysts of hornblende or biotite are commonly replaced completely 

by carbonate, epidote, and pleochroic green chlorite.

In the Montezuma quadrangle the sodic quartz 

monzonite porphyries occur in short dikes, none of 

which are more than a few hundred yards in length, 

and are found only in the northeast half of the quadrangle.

GROUP 7

Rocks of the sodic granite group are light gray but 

generally have a buff or brownish tint. The rocks 

are porphyritic, and their groundmass is fine grained 

but is distinctly granular in appearance, even to the 

naked eye. All of the sodic granite porphyries carry 

abundant quartz. In most of them the quartz is 

prominent in both grouudmass and phenocrysts, but 

in some rocks it is largely confined to the groundmass. 

The latter type can be distinguished from the sodic 

quartz monzonites by the dominance of orthoclase 

over albite in the phenocrysts. Dark-colored minerals 

are not common and are in general greatly altered.

Dikes of the sodic granite porphyry group are 

abundant in the porphyry belt northeast of the 

Montezuma stock. Most of them are light-colored 

felsites and fine-grained porphyries, but close to the 

Montezuma stock there are some dikes that have 

abundant quartz and orthoclase phenocrysts from 5 to 

10 millimeters in diameter.

Under the microscope the essential minerals are 

found to be quartz and albite or albite-oligoclase. 

The proportions of orthoclase and quartz vary widely, 

but albite or sodic oligoclase generally makes up from

10 to 20 percent of the slide. In some specimens 

quartz phenocrysts greatly predominate over orthoclase, and the groundmass may be 80 percent quartz; 

in others orthoclase is much more abundant than 

quartz in both groundmass and phenocrysts. Both 

corroded quartz and euhedral quartz may be present 

in a thin section. The boundary of the quartz phenocrysts is usually sharp, but in the more silicic varieties 

or those having a groundmass of micropoikilitic quartz 

and orthoclase, the quartz phenocrysts have an optically continuous border of fine-grained quartz in the 

groundmass. Orthoclase phenocrysts are subhedral 

and commonly occur as carlsbad twins. Some orthoclase is perthitically intergrown with albite. Many 

phenocrysts of a-lbite and sodic oligoclase show broad 

twinning bands, unusual in such sodic plagioclase. 

Biotite, where present, is generally partly altered to 

chlorite. Muscovite crystals 0.5 millimeter in diameter 

are not uncommon, but as they are invariably intergrown with magnetite, they may be secondary. The 

groundmass is usually a microgranular mass of quartz, 

orthoclase, and albite. Micropegmatitic and microperthitic intergrowths of the minerals .in the groundmass are common, and in some specimens the plagioclase microlites are micropoikilitically enclosed in the 

minute anhedral orthoclase crystals.

Fresh specimens are rare. In all the sections examined the feldspars were sericitized, and isolated 

aggregates of unoriented muscovite crystals about 0.1 

millimeter in length occur in them. Epidote and 

chlorite are common alteration products of the biotite.

Zircon and apatite are the most common accessory 

minerals.

GROUP 8

Granite and rhyolite porphyries (pi. 12, B, C] are 

abundant in the porphyry belt from the Montezuma 

stock northeast to Jamestown. They are lightcolored silicic rocks, finely porphyritic or dense and 

felsitic. Dark-colored minerals are generally lacking, 

and wherever phenocrysts are present quartz is prominent and in many places is the only mineral large 

enough to be seen without the aid of the microscope. 

Orthoclase is moderately abundant in the phenocrysts 

of some dikes, and muscovite is sparingly present in 

many specimens. In most places the diameter of the 

phenocrysts is from 1 to 2 millimeters, but some quartz 

crystals are 4 millimeters in length. The microscope 

shows that quartz phenocrysts having optically continuous borders of fine-grained quartz in the groundmass are present in most of the rocks. The outlines 

of these crystals are always irregular and show magmatic resorption prior to the addition of the finegrained rims. The feldspar phenocrysts are seldom 

fresh; orthoclase is sericitized, and the rare plagioclase 

is altered to sericite, carbonate, and quartz. The 

muscovite is probably secondary, as it is streaked and 

intergrown with finergrained decomposition products.
36 MONTEZTJMA QUADRANGLE, COLORADO

The phenocrysts nowhere exceed 25 percent of the 

rock and usually make up less than 10 percent. Quartz 

is the chief mineral of the groundmass and is generally 

twice as abundant as orthoclase. These minerals 

usually form a microgranular mosaic, but in some of 

the dense, aphanitic varieties the groundmass is an 

indefinite mixture of quartz and orthoclase clouded 

with innumerable minute bubbles and opaque inclusions. Sericite and zoisite are commonly disseminated through the groundmass in moderate 

amounts. Apatite and rarely zircon are present in 

small amounts.

The rocks of this group in the Georgetown quadrangle, were mapped by Ball 95 as granite and rhyolite 

porphyries, and he correlated them-with the white 

porphyries of Leadville because of the megascopic 

muscovite that is common to both. As indicated 

earlier, the writer does not believe that the composition 

or the age relations justify this correlation.

GROUP 9

Rocks of group 9 have not been found in the Montezuma quadrangle, but they are abundant in the adjacent Georgetown and Central City quadrangles. 

Some of the rocks of group 9 are almost granitoid, 

but most of them are porphyritic felsites, haying a 

marked trachytic texture. Most of the rocks of this 

group have a pinkish or purplish tint and where unweathered are generally a light pinkish gray. AnorM Ball, S. H., op. cit. (Prof. Paper 63), pp. 75, 76.

thoclase and orthoclase greatly predominate over the 

other minerals present and in many places together 

amount to over 95 percent of the rock. Locally 

aegirite-augite is abundant, or had been abundant 

prior to alteration, garnet and titanite are present, 

and oligoclase is common. Quartz, apatite, magnetite, 

zircon, and fluorite, and rarely biotite occur as accessory minerals. The groundmass of the porphyritic 

varieties is composed of orthoclase and anorthoclase 

laths, which have a trachytic arrangement where the 

phenocrysts are not abundant but have a microgranular 

texture in the rocks having more phenocrysts than 

groundmass. Rocks of group 9 occur as small stocks 

in a few places, but most of them were intruded as 

dikes, some of which persist for miles.

GROUP 10

Ores; see pages 59-64.

GROUP 11

Rocks of group 11 have not been found in the Montezuma quadrangle. Most of them are glassy rocks that 

are slightly porphyritic, but in some the groundmass is 

finely crystalline. The felsitic varieties are light 

gray; the glassy rocks range from light gray to dark 

.greenish gray. Orthoclase, biotite, and albite or oligoclase are the most abundant phenocrysts, though 

quartz crystals are not uncommon. Microlites of 

labradorite are generally present in the glassy groundmass, but as the glass has an index less than 1.50, it 

is much more silicic than these microlites would suggest. The rocks of group 11 occur as dikes and pipes.

Analyses of intrusive rocks of central Colorado, chiefly from the mineral belt

11. Late silicic intrusive group

No.

1. ..........

Si02

60.44

A12 03

14.98

FeaOs

1.57

FeO

0.43

MgO

0.18

CaO

2.47

Na2 0

1.12

K2 O

3.32

H2 0

4.06

HsO4.60

Ti02

0.20

P2 05

0.11

MnO

0.13

Inel.

f CO2 0.67

1 b . UZ

Sum

JlOO. 42

Specific 

gravity Reference °

P.P. 63, p. 134.

Ha. Comparative group of late (Miocene) alkalic rocks

2.. .........

3.--. --

4...........

58.05

59.38

54.34

58.78

57.64

17.66

19.47

19.23

20.03

19.10

3.51

1.60

3.19

1.87

2.54

1.65

1.19

2.11

.49

1.38

1.55

.36

1.28

.16

.84

4.48

1.96

4.53

.83

2.95

5.80

7.80

6.38

9.36

7.33

4.06

5.83

5.14

5.50

5.13

0.87

.69

1.17

1.57

1.09

0.35

.11

.14

.31

.23

0.91

.58

1.09

.29

.72

0.40

.08

.27

.03

.20

0.13

.15

.08

.09

ZrO 0. 02

ZrO .10

ZrO .07

ZrO .17

.09 99.33

Do.

Do.

Do.

9. Alkalic group

7 -- -'--

8.-.... -

10. 

60.30

07.41

64.82

05.41

63.49

58.94

03.40

18.12

16.21

17.71

18.78

18.40

17.19

17.73

2.45

.85

1.95

.94

2.44

2.63

1.88

1.25

1.14

.44

.72

1.09

1.98

1.10

0.28

.15

.22

.16

.06

1.52

.50

3.89

.14

1.03

1.58

2.30

4.45

2.23

5.83

3.95

4.37

5.91

5.70

4.20

4.99

5.01

7.19

6.09

 5.41

4.62

3.90

5.37

0.77

.88

1.17

1.38

1.04

4.53

1.63

0.75

.67

.71

0.55

.16

.20

.27

.24

0.25

.05

.05

.06

0.12

.16

.10

.10

.10

.12

( ZrO 0. 01

\ BaO . 20 

ZrO .11

CO2 .56

} 99. 90

99.65

99.84

100. 29

99.90

99.94

99.95

2.58

2.621

2.69

2.65

P.P. 63, p. 134.

Do.

Do.

Do.

8. Granite and rhyolite group

12....... 

10

14..........

15- 

16- .

74.45

75.07

75.39

73.11

75.20

74.64

14.72

12.15

13.65

13.16

12.96

13.33

1.62

.38

.62

.37

.60

0.56

n.d.

.18

.23

.27

.25

0.37

.14

.15

.19

.12

.19

0.83

.86

.51

.54

.29

.61

3.97

4.12

1.84

2.85

2.02

2.96

4.53

4.57

6.81

5.10

8.38

5.88

0.66

1.34

1.13

4.05

.58

1.55

Trace

0.01

Trace

0.28

. .05

.14

.03

.13

100.38

99.92

100. 18

99.99

100.22

100. 14

M. 12, p. 589.

P.P. 99, p. 969.

A.R. 17, 2, p. 324.

Do.

Do.

See footnotes, p. 37.
CRETACEOUS (?) AND TERTIARY IGNEOUS ROCKS 

Analyses of intrusive rocks of central Colorado, chiefly from the mineral belt Continued

G. Sodic quartz monzonite group

37

No.

.18... .....

SiO2

07.0!

05.04

00. 47

AlaCh

18. 03

10.00

J7.01

FeaOj

0.00

.00

.03

FoO

0.72

1.74

1.23

MgO

0.84

1.02

.93

CaO

3.99

2.87

Na2 0

4.42

3.85

4. 13

K8 O

3.53

4.50

H2 0

0.91

1.13

1.02

H2 0~ TiOa PtOt

0.10 .'23

.17

MnO

0.09

.05

Incl. Sum

100. 40

100. 20

99.84

Specific 

gravity

2.072

Reference °

B. 148, p. 170. Do."

5. Quartz monzonite group

.10..... __ ..

20...........

21.. .........

99

23.... 

24...........

25 . 

20...........

27.... 

28-... -

00.45

08.00

05.51

07.04

08. 14

07. 53

05. 38

00.07

08.34

00.87

15.84

10. 21

17.01

14.75

15.29

15.40

17.54

10.72

10.90

10. 27

2.50

1.07

.81

.35

2.18

2.14

2.79

2.54

.44

1.73

1.43

1.57

2.79

LOG

2.42

1.72

1 01

.72

1.02

1.72

1.21

1.05

.90

.94

.20

.16

1.51

1.70

1.47

1.94

1.11

2.90

2.01

3.16

3.98

3.03

3.24

2.90

2.88

3.03

3.12

3.09

3.92

3.29

3. 82

3.40

3.59

3.24

3.82

3.77

3.67

3.25

3.58

2.89

3.88

4.07

4.07

3.80

2.98

3.10

2.49

3.50

0.84

.92

1.78

.19

.39

.55

.89

1.32

J.05

1.12

.90

0.13

.40

.23

.20

.28

.13

.05

.20

0.10

1.30

.30

.41

.50

.40

.30

.40

.48

0.30

.21

.13

.20

.17

.01

.10

0.09

.09

.27

.12

.10

.26

.15

C02 1.35

.31

100. 09

100.32

100. 15

99.76

99.65

99.03

99.58

99.40

99.99

100. 00

2.07

2.04

2.066

M. 12, p. 332.6

B. 148, p. 176.

Do.

P. P. 75, p. 45.

Do.

Do."

Do.

Do.

4. Intermediate quartz monzonite porphyry group

20.... 

30...........

31...........

33.... 

34.... 

35...........

67. 29

68. 10

08.01

04.28

03. 25

07.20

05.04

15. 78

14.97

14.27

16.99

16.16

14.95

.17.49

15.80

1.80

2.78

.90

a 59

2.60

5. 19

2.52

2.63

1.97

1.10

.23

9 fi4

2.44

2.80

1.60

0.72

1.10

.67

1. .13

1.62

2.39

2.27

1.41

2.36

3.04

.60

3.95

2.99

.30

5.08

2.02

3.77

3.40

1.90

3.78

3.54

4.00

3.31

3.40

3.55

2.93

7.15

3.26

.89

i in

3.30

2.10

1.28

.43

.25

1.85

2.13

.66

1.24

1.12

.07

.63

.08

.47

0.07

.41

.49

.50

.70

.36

0.28

.16

.16

.32

.30

.24

0.21

.09

.02

.14

.36

.16

COa 0.40

.06

100. 10

100.11

100. 49

100. 38

100. 02

97.45

99.58

99.24

2. 730

2.43

A. R. 14, p. 227.

M. 12, p. 332.

P. P. 148, p 49."

P. P. 75, p. 58.

P. P. 148, p. 51.

Colo. Sci. Soc.,3, p. 357.*

3. Monzonite group

37.. .

38..........

39. , ........ 

40.. . .......

dO

57.35

55.44

50.62

04.81 

03. 04

57. 55

53.60

68.43

1C. 29

14. 95

.10. 74

15.73 

18.05

15.52

17. 0.1

16.33

3. 15

4.37

4.94

1.08 

2.14

2.08

4.06

3.29

4.36

5.18

3.27

2. 91 

1.80

2.48

4.81

3.54

2.4t

3.58

4.08

2.82 

1.01

1.37

3.54

2.69

5.00

0.12

7.39

4.22 

3.30

5.85

5.73

5.48

4.50

4.44

3.50

3.98 

3.65

4.90

3.42

4.06

3.39

2.83

1.97

1.43 

4.73

2.95

2.08

2.77

0.70

.84

.92

.02 

1.07

2.15

2.58

1.27

0.15

.15

1.15

.11

.22

1.07

1.22

.08 

.43

.24

.74

0.07

.49

.23 

.18

.83

.30

0.12

.22

.15

.08 

.40

.87

.31

COa 1.15

COa 1.08

COS 3.57

COj .84

.95

100. 55

100. 44

100. 73

100. 61

100. 21

100. 05

100. 36

2. 703

2.827

2.768

2.740 

2.568

Do.

M. 12, p. 589.

B. 148, p. 173. 

Colo. Sci. Soc., 6 p. 181.

Colo. Q.S.,31,p.45.'

2. Gabbro group, ultrabasic subgroup (b)

43

44. .. .......

45.. . .......

44.93

39.22

22.24

35.40

18.32

4.93

11.78

11.08

8.70

18. 12

4.74

10.52

21.09

6.00

3.35

10.11

0.47

3.01

25.00

9.09

1.41

19.20

10.19

10.27

2.12

2.51

3.29

2.04

0.58

.68

3.64

1.63

Trace

.21

5.63

1.95

'

2.92

3.49

.36

2.26

.61

.61

COa 1.24

C02 8.79

3.34

100.54

99.20

99.62

100. 16

2.73

2. Gabbro group, calcic subgroup (a)

47. .. .......

48....- 

40.. . .......

50

61. ... ......

52..........

54. ...... ...

48.93

59. 29

59.20

52.59

40.69

48.25

57. 01

53. 80

50.47

53. 25

20.99

21.27

23 62

17.01

16. 73

18.41

20.13

18.73

19.34

2.02

3.33

.30

3.81

2.04

3.99

3.69

3.57

4.19

3.06

9.36

1.04

.57

5.18

6.19

6.28

2.36

2.63

4.92

4.28

4.39

1.12

.31

4.11

5.73

5.77

2.34

2.26

3.48

3.28

8.03

5.25

7.24

8.24

8.32

4.29

5.60

8.82

6.80

3.00

3.30

4.94

2.94

2.99

3.24

4.05

5.20

4.02

3.93

1.80

3.00

4.78

3.83

3.90

4.08

3.72

4.49

3.50

3.68

1.18

1.63

.74

1.24

.91

1.72

2.20

.90

.58

1.24

0.84

.85

.89

.27

.43

.51

.63

0.15

.23

.14

.81

.08

.42

.50

.10

.39

0.31

.21

.13

.21

.29

.11

.18

Cl 0.05

100. 22

99.70

99.88

99.96

99.86

100. 00

100. 12

3.027

2.590

2.83

2.099

2.708

B. 228, p. 187.

Do.

M. 27, p. 300.

A. R. 17, 2, p. 321.

A. R. 17, 2, p. 324.

Do.

1. Early fclsite group

fiS.. ........

57.... 

70.74

73. 50

63. 85

09.30

14.08

14. 87

15.44

15.00

0.69

.95

3.14

1.59

0.58

.42

1.66

.89

0.28

.29

J. 16

.58

4.12

2.14

4.18

3.48

2.29

3.46

1. 19

2. 31

2.59

3.50

.08

2.08

2.09

.00

7.45

3.48

0.00

.03

.05 .71

100. 47

99.53

2.08 P. P. 148, p. 45.

« M, U.S. Geological Survey monograph; P.P., U.S. Geological Survey professional paper; A.R., U.S. Geological Survey annual report; Colo. G.S., bulletin of the 

Colorado Geological Survey; Colo. Sci. Soc., proceedings of Colorado Scientific Society; B, U.S. Geological Survey bulletin. 

6 Analysis of doubtful value because of altered condition of rock.
38 MONTEZUMA QUADRANGLE, COLORADO

Descriptions of the rocks represented by the numbered analyses in the accompanying table are given 

below. They have been abstracted from the references given in the table, and none are the result of 

petrographic work done by the writer.

1. Biotite latite, Chicago Creek near Idaho Springs. The 

groundmass greatly predominates over the phenocrysts and in 

general is aphanitic. Small phenocrysts of biotite and feldspars are numerous and equally abundant. The minerals 

found as phenocrysts, in the order of their abundance, are orthoclase, biotite, plagioclase, and rarely brown hornblende.

2. Latite-phonolite, Cripple Creek (Anaconda mine). Ranges 

in color from dark gray to black and is finely holocrystalline. 

It is porphyritic and contains prismatic phenocrysts of pyroxene 

and feldspar 2 centimeters or less in diameter. The feldspar 

phenocrysts predominate and are chiefly albite or albite-oligoclase. Orthoclase is common and ranges in size from 0.05 to 

over 1.0 centimeter. Pyroxenes are moderately abundant. 

Hornblende, biotite, and apatite are always present and in some 

places are prominent. Sodalite, noselite, and analcite are generally present and in many places are abundant. The groundmass is compact and dark and locally contains inclusions of 

hornblende syenite.

3. Latite-phonolite, Cripple Creek (Bull Cliff). Same as 

no. 2.

4. Syenite, Cripple Creek (Longfellow mine). Light gray 

and finely-granular. Orthoclase, albite, oligoclase, and aegiriteaugite are the principal constituents, but orthoclase is by far 

the most abundant. Much of the pyroxene is surrounded by a 

zone of greenish-brown hornblende, but hornblende also occurs 

alone. Sodalite is present in rather large grains, and more or 

less decomposed nosean occurs in small quantities. Analcite is 

plentiful in irregular grains and is associated with the feldspars. 

Extremely minute needles of stilbite (?) penetrate the analcite 

grains. Biotite, apatite, titanite, and magnetite are common 

accessory minerals.

5. Phonolite, Cripple Creek. A fresh phonolite from dark 

gray to greenish. The texture ranges from dense, microcrystalline to porphyritic, but phenocrysts are scarce. Flow 

structure is almost always present. Most of the phenocrysts 

are clear glassy feldspar. The groundmass is largely made up 

of microlites of soda orthoclase. Nepheline makes a large 

percentage of the rock and sodalite, noselite (and haiiynite?) are 

common. Analcite, aegirite, and aegirite-augite are present in 

varying amounts in different places. The aegirite is most 

abundant and in many places is alone. A blue amphibole is 

present and is generally associated with aegirite.

6. Alkali syenite, Idaho Springs. The texture ranges from 

one in which the groundmass equals the phenocrysts to a holocrystalline texture. The groundmass is composed chiefly of 

anorthoclase and orthoclase, but rarely quartz is also present. 

The phenocrysts are chiefly orthoclase, anorthoclase, pyroxene, 

and brownish-black garnets; they include also a little titanite. 

Fluorite is present in the groundmass, and oligoclase is not 

uncommon.

7. Bostonite, Idaho Springs. A light pinkish-gray felsitic to 

porphyritic rock. The phenocrysts are commonly small but in 

some places reach a diameter of 1 inch. The groundmass has a 

trachytoid texture. The phenocrysts are chiefly alkali feldspars and plagioclase; pyroxene pseudomorphs are common. 

Between the lathlike anorthoclase crystals of the groundmass 

are equidimensional wedge-shaped masses of orthoclase and 

quartz, which have solidified after the crystals of anorthoclase.

8. Trachyte, Sunset. Contains about 25 percent phenocrysts. The texture of the groundmass ranges from microgranular to glassy. The phenocrysts consist chiefly of orthoclase (sanidine) and oligoclase. Small crystals of apatite, titanite, and octahedrite occur but are not abundant. Small 

. amounts of magnetite, limonite, biotite, zircon, and augite (?) 

are sometimes found in the groundmass and rarely as phenocrysts. The groundmass consists largely of orthoclase microlites in a glassy base, but it is decomposed, and its composition 

and structure are difficult to ascertain.

9. Trachyte, Rosita Hills. Occurs in dikes and surface flows. 

The dikes vary greatly in physical appearance and range from 

true trachytes to a dark dense porphyry. The phenocrysts are 

predominantly sanidine crystals, usually less than 1 centimeter 

in length, but oligoclase is also abundant. Biotite is present 

though not plentiful. The groundmass, which greatly predominates over the phenocrysts, is ash-gray. It consists largely 

of fine granular orthoclase, with very subordinate quartz and 

pla,gioclase. Apatite and .zircon are also present in small 

amounts.

10. Andesite (dike), Pringle andesite, Rosita Hills. The 

Pringle andesite occurs in both surface flows and dikes. The 

chemical composition is the same, although the dike rock is 

darker, is finer grained, and has a larger percentage of groundmass than the surface flows. The rock is a dark-gray porphyry. 

Phenocrysts of oligoclase and andesine are more common than 

orthoclase, although the orthoclase is one of the characteristic 

minerals of the rock. Biotite is more plentiful tha,n augite, but 

neither is abundant. Hornblende is' rarely present. The 

groundmass is a coarse-grained mixture of feldspar microliths, 

augite, and magnetite, and in some places it contains a subordinate amount of quartz.

11. Andesite (flow), Rosita Hills. Same as no. 10 except 

that it is a surface flow instead of a dike.

12. Rhyolite, northwest point of Chalk Mountain, Leadville. 

Contains sanidine, plagioclase, and quartz in abundance and a 

little biotite and magnetite.

13. Nevadite, Summit County, probably from the Tenmile 

district. The rock is a grayish-white felsite porphyry, containing quartz and glassy white feldspar in moderately large phenocrysts. Some hornblende and albite phenocrysts are also 

present. The groundmass is a very fine grained intergrowth 

consisting chiefly of albite, sanidine, anorthoclase, and quartz 

but contains a small amount of mica and hornblende. An 

analysis of the white glassy feldspars gave the following results: 

Si02 , 65.49 percent; A12O3 , 18.74; Fe2 03 , trace; CaO, 0.39; 

 K2O, 9.45; Na2O, 3.53; loss on ignition, 1.30; total, 98.90.

14. Rhyolite, Rosita Hills. The texture of the rhyolites is 

variable. The rock is generally porphyritic and contains rather 

large crystals of orthoclase in the granular groundmass. The 

phenocrysts are commonly quartz and two feldspars. The 

groundmass is made up of a rather coarse intergrowth of quartz 

and orthoclase.

15. Pitchstone, Rosita Hills. The pitchstone in this locality 

is variable in texture, and the color may be red, yellow, green, 

brown, or black. Small phenocrysts of feldspar are sometimes 

present. The pitchstone is related to the rhyolites and except 

for the large proportion of glass present, its mineral composition 

will probably approximate that of the rhyolites.

16. Rhyolite, Rosita Hills (Round Mountain). Similar to 

no. 14.

17. Diorite porphyry, Tenmile district (Copper Mountain). 

Contains oligoclase, hornblende, and biotite phenocrysts in a 

groundmass of quartz, orthoclase, plagioclase, and magnetite. 

Zircon, sphene, and apatite are accessory minerals. Small 

amounts of secondary chlorite and epidote are present.

18. Granite porphyry, Jefferson tunnel, Tenmile district. 

Contains orthoclase, oligoclase, quartz, and biotite phenocrysts 

in a groundmass of quartz and orthoclase. Magnetite, apatite, 

zircon, and allanite are accessory minerals. Chlorite, calcite, 

and magnetite are present in small amounts as decomposition 

products of biotite.
CRETACEOUS (?) AND TERTIARY IGNEOUS ROCKS

19. Lincoln porphyry, summit of Lincoln Mountain, Leadville quadrangle. A coarse-grained porphyritic rock containing phenocrysts of quartz, orthoclase, plagioclase, and biotite in 

a groundmass of plagioclase, orthoclase, and quartz. The 

amount of plagioclase in the groundmass is rather small, but 

most of the phenocrysts are plagioclase near andesine in composition. The orthoclase phenocrysts are large, some reaching 

a length of 2 inches.

20. Granite porphyry, McNulty Gulch, Tenmile district. 

Contains phenocrysts of orthoclase, oligoclase, andesine, quartz, 

biotite, and altered hornblende in a groundmass of quartz, 

orthoclase, and magnetite. Accessory minerals are titanite, 

allanite, apatite, and zircon. A small amount of secondary 

chlorite is present.

21. Granite porphyry, Jefferson tunnel, Tenmile district. 

Similar to no. 18.

22. Quartz monzonite, Monarch-Tomiche district. The 

feldspars are the most abundant minerals of the quartz monzonite, and as a rule plagioclase predominates over orthoclase. 

Quartz is invariably present but nowhere in great quantity and 

usually occurs in small crystals. Hornblende and biotite are 

usually associated in about equal -amounts. Titanite is a 

prominent accessory mineral, and apatite, zircon, and magnetite are usually present. The plagioclase is poikilitic in many 

. places and encloses biotite and hornblende.

23. Quartz monzonite porphyry, Browns Gulch, Breckenridge. Has rather large and conspicuous phenocrysts and a 

rather fine, even-grained groundmass. There are several large 

phenocrysts of orthoclase, but the plagioclase (andesine) phenocrysts are much more abundant. Quartz phenocrysts are 

plentiful, biotite is common, and hornblende is rare. The 

groundmass is composed almost entirely of quartz and orthoclase. Allanite is common and occurs in rather large crystals.

24. Quartz monzonite porphyry, Browns Gulch, Breckenridge. 

district. Similar to no. 23.

25. Quartz monzonite porphyry, near Halfway, Tarryall district. Moderately porphyritic, finely granular, light to dark 

gray. Contains orthoclase, andesine-oligoclase, biotite, quartz, 

and hornblende phenocrysts in a matrix consisting chiefly of 

quartz and orthoclase. -Apatite, titanite, allanite, and zircon 

are accessory minerals. Plagioclase phenocrysts are more 

abundant than orthoclase and in some places poikilitically 

enclose both biotite and quartz.

26. Quartz monzonite porphyry, north of Halfway, Tarryall 

district. Similar to no. 25.

27. Quartz monzonite porphyry, Little French Creek, Tarryall district. Similar to no. 25.

28. Quartz monzonite porphyry, Mineral Ranch Hill, Tarryall district. Similar to no. 25.

29. Quartz porphyrite, Sugar Loaf Mountain, Tenmile district. The phenocrysts are chiefly plagioclase, biotite, and 

quartz; the evenly granular groundmass is principally quartz 

and orthoclase.

30. Gray porphyry, Onota shaft, Johnson Gulch, near Leadville. The mineral composition is almost the same as that of 

the Lincoln porphyry (no. 19). It is holocrystalline and has 

large phenocrysts. The porphyry is usually somewhat altered, 

although it appears quite fresh. Large crystals of orthoclase 

and small and numerous crystals of plagioclase and biotite are 

the rule. The groundmass has the same minerals as the Lincoln 

porphyry, although it is not quite so coarse-grained.

31. Gray porphyry (Johnson Gulch porphyry), Leadville. 

The color ranges from greenish gray to dark gray. Its essential 

minerals are orthoclase, plagioclase, quartz, biotite, and horn-' 

blende; the accessories are magnetite, apatite, titanite,' and 

allanite. The phenocrysts are plagioclase, a few large ortho.- 

clase crystals, quartz, biotite, and hornblende. The ground71880 35 4

mass in the lighter varieties consists chiefly of quartz, alkalic 

feldspar, and subordinate and variable amounts of plagioclase. 

The porphyry is usually much altered, and sericite and chlorite 

are invariably present; pyrite, epidote, calcite, and siderite (?) 

are common, and some secondary quartz occurs. Calcite is 

more abundant in the darker varieties.

32. Quartz monzonite porphyry, Mount Guyot, Breckenridge. 

Almost equigranular, with little distinction between groundmass and phenocrysts. Plagioclase is the most abundant 

mineral and is between andesine and labradorite in composition. Orthoclase probably predominates over quartz. Biotite 

is plentiful, and in places some hornblende is intergrown with it. 

Titanite, apatite, and magnetite are accessory minerals.

33. Evans Gulch porphyry, Evans Gulch, Leadville. An 

even, fine-grained porphyritic rock which has from 25 to 30 

percent of oligoclase-andesine. Quartz and orthoclase are 

generally associated in the groundmass. A small amount of 

albite is also reported. The biotite has been altered to chlorite, 

and small grains of magnetite are closely associated with the 

quartz and orthoclase. Apatite and zircon are accessories.

34. Quartz porphyry, Flagstaff Hill, Boulder. Contains 

moderately large crystals of quartz, feldspars, and biotite in a 

felsitic groundmass. The feldspars have been badly altered, 

but it is believed that they were originally sanidine. Quartz is 

abundant. It is difficult to ascertain the composition of the 

groundmass because of its decomposed condition, but probably 

its original minerals were quartz and feldspar (orthoclase or 

sanidine).

35. Quartz monzonite of Silverheels, head of Little French 

Creek, Tarryall district. A greenish-gray, moderately fine 

grained porphyritic rock containing abundant hornblende and 

labradorite-andesine phenocrysts as well as a few inconspicuous 

phenocrysts of biotite and quartz. The fine-grained groundmass consists of quartz, orthoclase, and hornblende.

36. Diorite p'orphyry, Wellington mine, Breckenridge. Has a 

seriate fabric, and the phenocrysts are rather small. The 

largest phenocrysts present are hornblende and are accompanied 

by plagioclase, pale augite or diopside, hypersthene, biotite, 

magnetite, and apatite. The predominating mineral of the 

groundmass is labradorite, but quartz and orthoclase are present, and hypersthene is common. Biotite is rare and occurs in 

very small flakes. Accessory zircon and magnetite are present.

37. Diorite porphyry, Wellington mine, Breckenridge. 

Essentially the same as no. 36 except for minor alteration. 

The hornblende has apparently been altered to biotite, and 

some secondary calcite is present.

38. Porphyrite, Buckskin Gulch, Park County. Darkcolored and fine-grained. Contains abundant unevenly sized 

hornblende, much plagioclase, and a little biotite. The groundmass is essentially quartz and orthoclase (?). Magnetite and a 

little apatite are present.

39. Biotite porphyry, North Mosquito Amphitheater, 

Mosquito Range. Similar to no. 38 except that it contains no 

hornblende and much biotite. Plagioclase, orthoclase, quartz, 

biotite, magnetite, apatite, and zircon are present. Small 

amounts of secondary calcite, chlorite, and pyrite are also 

present.

40. Andesite, Sugarloaf Mountain, Boulder County. Brownish gray with a ratio, of about 33 percent phenosrysts to 67 

percent groundmass. The feldspar phenocrysts are the most 

abundant and form about 20 percent of the rock. The composition and proportion of the different phenocrystic minerals is as 

follows: Orthoclase and sanidine about 13 percent, plagioclase 

7 percent, pyroxene 5 percent, biotite 3 percent, hornblende 2 

percent, and magnetite 3 percent. Apatite and titanite are 

present in very small amounts. The extremely fine grained 

groundmass is essentially feldspar.
40

41. Mica andesite, West Sugarloaf Mountain, Boulder 

County. About one-third of this rock is made up of phenocrysts, and the remainder is a microcrystalline groundmass. 

About 54 percent of the phenocrysts are sanidine, about 21 

percent labradorite, 7J4 percent biotite, 4)4 percent magnetite, 

and 0.6 percent titanite. Apatite is present in small quantities. 

Secondary calcite is abundant, and kaolin (?) and secondary 

quartz occur in small amounts. The groundmass is largely 

feldspar but includes considerable magnetite and some limonite.

42. Diorite porphyry, Boreas Pass, Tarryall district. Medium fine grained, dark gray, porphyritic; contains abundant 

small phenocrysts of plagioclase and biotite. Hornblende is 

also conspicuous but is less abundant than the other two 

minerals. The groundmass is holocrystalline and consists 

chiefly of plagioclase. Some orthoclase may be present, and 

quartz and apatite are noted as accessory minerals.

43. Basalt, Alum Hill, Boulder County. A dark-colored 

porphyry, containing moderately large crystals of augite and 

plagioclase in a glassy groundmass. About 49 percent of the 

rock is augite, 32 percent is plagioclase, 16 per cent is titaniferous 

magnetite, 1.6 percent is haiiyne, and 1.6 percent is tridymite.

44. Basalt, Alum Hill, Boulder County. A fine-grained 

greenish-gray rock. The groundmass is a glass and is the matrix 

of small crystals of plagioclase, augite, some hematite, and a 

little calcite. No magnesite, titaniferous iron ore, quartz, or 

apatite were seen.

45. Olivinite, 2 miles southwest of Boulder, Boulder County. 

Dark gray to purplish. Serpentine nodules are abundant and 

show a clear resemblance to the original crystalline olivine 

which they replace. Well-crystallized magnetite is very abundant. Titanite occurs in rather coarse nodules and apparently 

is not present in the groundmass. The specimen selected for 

analysis contained a minimum of titanite. Garnet is sparingly 

present in the form of pyrope; most of it is fresh, but some of 

it is slightly decomposed. Calcite is apparently'primary; some 

of it is cryptocrystalline, but some occurs as phenocrysts. 

Both light and dark micas occur meagerly. A mineral that 

strongly resembles zeolite was also noted:

46. Diabase, east of Sugarloaf Mountain, Boulder County. 

Contains labradorite, orthoclase, augite, and magnetite, with 

small amounts of hornblende, biotite, apatite, and secondary 

chlorite.

47. Augite andesite, pebbles in Denver formation, Table 

Mountain, Golden. Contains a few augite and andesine 

phenocrysts in a granular groundmass of' oligoclase, orthoclase, 

quartz (?), and some augite and magnetite.

48. Augite andesite, pebbles in Denver formation, Table 

Mountain, Golden. Contains andesine phenocrysts, but 

megascopic augite and biotite, though present, are rare. The 

groundmass is made up of plagioclase, augite, magnetite; and 

minor accessories. Ptilolite was also observed.

49. Basalt, Table Mountain, Golden; a flow interbedded in 

upper part of Denver formation. This basalt is a dense black 

rock which has many augite and olivine crystals in a dark, dense 

groundmass. Plagioclase phenocrysts are present though not 

conspicuous to the unaided eye. The groundmass consists 

chiefly of plagioclase microlites with orthoclase (?) grains between them. Augite, magnetite, and apatite are a1 so present, 

and biotite is sometimes found.

50. Augite-mica syenite, North Fork of Turkey Creek, 

Jefferson County. Dark-colored and coarse-grained near the 

center of the mass. The predominant mineral is orthoclase, 

but biotite and augite are common in about equal amounts. 

The augite has many inclusions of apatite, magnetite, and biotite.

The dark-brown biotite contains many inclusions of magnetite. 

Apatite is very abundant and locally includes some augite. 

Magnetite is sparingly present, and quartz is found only in small 

quantities in the finer-grained varieties of the rock.

51. Valmont dolerite dike, 3 miles east of Boulder, Boulder 

County. Dark greenish gray and slightly porphyritic. The 

greater part of the rock is made up of plagioclase, but crystals 

of augite and olivine are also abundant. Orthoclase and biotite 

are common, and biotite is moderately abundant. Magnetite 

and apatite are accessory minerals.

52. Bunker andesite, Rosita Hills. A dark porphyritic 

holocrystalline rock of compact texture in which the groundmass exceeds the phenocrysts. The chief minerals of the 

phenocrysts, named in the order of abundance, are feldspars, 

augite, biotite, and hornblende. The groundmass is made up 

of feldspars, augite, magnetite, and quartz. Magnetite and 

apatite occur in small phenocrystic grains.

53. Augite diorite, Rosita Hills. Chiefly labradorite, augite, 

biotite, and small amounts of olivine. Most of the rock is 

granular, although locally it is somewhat porphyritic. In the 

specimen analyzed there was some orthoclase, and where orthoclase is present there is a tendency for hornblende to develop 

at the expense of augite and biotite.

54. Augite diorite, Rosita Hills. Essentially the same as 

no. 53 except that it lacks the orthoclase and has a greater 

amount of olivine.

55. White porphyry (muscovite granite porphyry), quarry in 

California Gulch, southwest base of Iron Hill, Leadville. 

The White porphyry is usually creamy white or light gray. 

It is felsitic but contains a few small, thinly scattered phenocrysts of feldspar and quartz and a few small scales of muscovite 

and biotite. The feldspar is andesine, and iron oxide and hexagonal crystals of muscovite are occasionally found. The 

muscovite was regarded as secondary by S. F. Emmons, but 

Loughlin reports small clusters of muscovite that appear both 

earlier and later than the quartz, which is believed to be primary. 

The groundmass is microgranular and consists essentially of oligoclase, orthoclase, and quartz. The oligoclase and orthoclase 

are about equal in quantity. The quartz is abundant and interstitial among the feldspars. Minute grains of zircon and rutile 

are rather common, but magnetite and apatite are very scarce.

56. White (Zion) porphyry, Little Harry shaft, Prospect 

Mountain, Leadville. The essential minerals are plagioclase, 

orthoclase, and quartz. Orthoclase slightly predominates over 

plagioclase. Many muscovite leaves are present and contain 

small crystals of rutile or stout crystals of anatase (?). Zircon 

is abundant and some biotite is present; magnetite and apatite 

are very rare.

57. Felsite dike (porphyrite), Niwot mine, Ward district. A 

light greenish-gray, very fine grained, slightly porphyritic rock 

in which most of the primary minerals have been greatly 

altered. Small feldspar phenocrysts and a few chloritized or 

micaceous needles are visible in the .hand specimen. Most of 

the feldspars were originally plagioclase, but some are not banded 

and may have been orthoclase. The rock as a whole seems 

to be an aggregate of kaolinlike minerals, with much secondary 

quartz. Titanite (?), chlorite, leucoxene (?), rutile (?), mica (?), 

and actinolite (?), may be present, but the abundant fine-grained 

silica has greatly altered the original and early secondary minerals. Some pyrite is also present. The specimens analyzed 

appeared fairly fresh but were obtained close to the Niwot vein, 

300 feet below the surface. The analysis indicates much 

hydration and removal of alkalies, and the CaO is abnormally 

high.
CRETACEOUS (?) AND TERTIARY IGNEOUS R 

Summary of averages of analyses, showing approximate composition of the different groups

41

Si02 ---. __ ---

A12 03 . . --------

Fe2 03- ---------

FeO-----_-_-_.

MgO... -------

CaO--_ __ ---.

Na2 0_--------

K2 0.__-------

H2 0 +- -.---- -.

H2 0-..-------

Ti02 --------

P2 0s

MnO.---------

C02 --------

ZrO --------

Sum_____

Epoch 3

lla

57. 64 

19. 10 

2. 54 

1.38 

.84 

2. 95 

7. 33 

5. 13 

1.09 

.23 

. 72 

.20 

.09

. 09

b 99. 44

11

66. 44 

14.98 

1.57 

.43 

. 18 

2.47 

1. 12 

3.32 

4.06 

4.60 

.20 

. 11 

. 13 

.67

100. 40

Epoch 2

9

63.40 

17. 73 

1.88 

1. 10 

. 50 

2. 23 

4. 99 

5. 37 

1.63 

.71 

.24 

.06 

. 12

99. 95

8

74. 64 

13. 33 

.60 

. 25 

. 19 

. 61 

2.96 

5. 88 

1. 55

. 13

100. 14

7°

70. 55 

15. 17 

.61 

.74 

. 56 

1.97 

3. 55 

5.02 

1.28

. 10 

.09 

.38

100. 02

6

66.47 

17.01 

.63 

1. 23 

.93 

3. 43 

4. 13 

4.05 

1. 02

. 17 

.05

. 77

99.89

5

66.87 

16. 27 

1.73 

1. 72 

1. 11 

3.09 

3.58 

3. 50 

.90 

.20 

.48 

. 16 

. 15 

.31

100. 06

4

65.94 

15. 80 

2. 63 

1. 60 

1.41 

2. 62 

3. 40 

3. 30 

1. 24 

.47 

.36 

.24 

. 16 

.06

99. 24

3

58.43 

16. 33 

3.29 

3. 54 

2. 69 

5. 48 

4. 06 

2. 77 

1. 27 

. 22 

. 74 

.30 

. 31 

.95

100. 36

Epoch 1

2

35! 46 

11. 68 

10. 52 

10. 11 

9. 69 

10. 27 

2. 64 

1. 63 

1.95

2. 26 

. 61

.334

 100. 16

53. 25 

19. 34 

3.06 

4. 28 

3. 28 

6.86 

3. 93 

3. 68 

1. 24

.63 

. 39 

. 18

100. 12

1

69.36 

15.00 

1. 59 

. 89 

.58 

3. 48 

2. 31 

2. 08 

3. 48

.05 

. 71

99. 53

Calculated as intermediate between groups 6 and 8. 6 Late alkaline subgroup. ' Ultrabasic subgroup.

The succession of intrusions in the Front Range 

porphyry belt suggests their derivation from a common 

magma whose composition was gradually changing 

during the intrusive period. The course of rock 

differentiation can be traced rather clearly and can be 

divided into three epochs (1) an early epoch marked 

by ferromagnesian differentiates; (2) a middle epoch 

marked by moderately to highly silicic differentiates; 

(3) a late epoch marked by alkalic differentiates.

The earliest rocks (groups 1 and 2) suggest an 

unusual type of differentiation the change from an 

intermediate to a ferromagnesian magma. On the east 

side of the Front Range tins early stage started with 

a magma whose composition was that of a moderately 

silicic diorite, but the succession of early intrusives 

indicates that it gradually grew much more ferromagnesian and locally became highly ferromagnesian. 

These early intrusions, unlike the later ones, were 

widespread in the Front Range and were not concentrated in the mineral belt.

After a period of rest a second epoch of differentiation commenced. The early intrusives of the second 

epoch (group 3) had the composition of diorites, but 

the successive intrusions show that the magma became 

steadily more and more silicic. It had successively 

the composition of a diorite, monzonite, quartz monzonite, sodic quartz monzonite, sodic granite, granite, 

and alaskite. A great upward migration of magma 

occurred during the quartz monzonite stage, and the 

later differentiates represent a comparatively small 

amount of the material from the magmatic reservoir, 

and their composition suggests filter-pressed residuum

from the partly consolidated quartz monzonite. 

Although most of the residual magma progressively 

changed until it .finally had the composition of an 

alaskite, a part of it or perhaps a deeper magma 

became more and more sodic. The rocks that formed 

in the early stage of sodic (alkaline) differentiation are 

contemporaneous with the granite porphyries of the 

diorite-alaskite epoch.

During the later part of the second epoch of differentiation the composition of the magma changed from 

albite-oligoclase-quartz monzonite (group 6) to alkali 

syenite (group 9). The end of the second epoch of 

differentiation overlapped the beginning of the third, 

and the alkalic series that characterized the third 

epoch apparently represents a late branch of the 

diorite to granite differentiation.

Some of the details of differentiation are clear and 

are worthy of consideration. The usual changes in 

the feldspars occurred. Labradorite, andesine, oligoclase, and albite appear-successively in later and later 

rocks. Quartz and orthoclase are inconspicuous in the 

early rocks of the second epoch but increase in abundance in later rocks. They are confined to the groundmass in the diorites and first appear as abundant 

phenocrysts in the quartz monzonite porphyry. By a 

gradual decrease in the other constituents the rock 

series move toward alaskite. In the alkalic stage, 

however, quartz decreases while orthoclase continues 

to increase. In the sodic differentiates oligoclase 

changed to albite and still later, through the addition of potash, to anorthoclase.

The ferromagnesian minerals have an interesting 

history. The augite of the early diorites changed to
42

hornblende in most places, and the hornblende in turn 

to biotite. Local reversals of order occurred from 

time to time, and in some places hornblende became 

Unstable after its formation and changed into augite 

again. Hornblende is the characteristic ferromagnesian mineral of the diorite and early monzonite, and 

biotite is characteristic of the quartz monzonites and 

granite porphyries. However, in some of the albiteoligoclase-quartz monzonite porphyries and sodic 

granite rocks, hornblende is abundant again. In the 

more sodic differentiates augite is the chief ferromagnesian mineral. It would seem that the changing 

conditions of equilibrium were such that the f erromagnesian constituents crystallized successively as augite, 

hornblende, biotite, hornblende, and augite.

In the section on rock alteration the gradual increase 

of water during the differentiation of the diorite magma 

is traced. Apparently the water was concentrated in 

the granite differentiate while the alkaline differentiate 

became relatively dry.

ROCK ALTERATION

HYPOGENE ALTERATION

In general, alteration has been more widespread in 

the later intrusive rocks than in the older ones. As 

the later intrusives preceded the ores by only a short 

interval, there was probably a marked tendency for 

them and the ore solutions to follow the same channels, 

whereas the older intrusives may have followed fractures that by the time of ore formation had become 

tightly sealed. Thus a more frequent occurrence of 

zones of alteration may be expected in the late than 

in the early intrusives. Hydro thermal alteration was 

not confined to the period of ore formation, however, 

as the metamorphism of the country rock surrounding 

the porphyritic Montezuma quartz monzonite stock 

shows that appreciable alteration accompanied its intrusion. As its intrusion was separated from the ore 

stage by an interval during which alaskite and alkali 

syenite magmas were formed and intruded, it is probable 

that rock alteration began feebly in an early stage of 

the diorite and granite period of differentiation and continued with growing power until it culminated shortly 

before ores commenced to form. Much of the rock 

alteration was not related to channels of mineralization, and the evenness of its effects indicates deuteric 

or endomorphic changes.

Some late albite-quartz monzonite porphyry intruded 

at the edge of the Montezuma stock shows an unusual 

type of alteration. The albite phenocrysts are partly 

replaced along their borders and cleavages by a more 

calcic feldspar. The alteration was probably effected 

by calcic emanations from the partly cooled mass of 

quartz monzonite in the adjacent stock.

The endomorphic as well as the exomorphic changes 

were made chiefly by watery solutions at high temperatures. The increase of alteration marks the gradual

accumulation of water and other volatile constituents 

of the magma as it became more and more silicic and 

potassic. If a water-rich magma were intruded into a 

pervious fissure, the volatile constituents would move 

into regions of lower pressure as the molten rock solidified, finding avenues of escape through the shattered or 

porous material in the fissure zone. If a water-rich 

magma were intruded into a tightly sealed opening, 

the volatile material would be trapped with the solidifying rock. Thus, where the volatile fluids could 

escape little deuteric alteration of the porphyry would 

occur, although, if a similar porphyry nearby had cooled 

in contact with the fluids squeezed out during crystallization, it would show pronounced endomorphic changes 

The most thorough deuteric alteration occurred in the 

rocks of the granite group, and, although the rocks of the 

alkalic groups are greatly altered along channels of 

mineralization, they show little alteration in other 

places. It would thus appear that water was segregated with the granite magma during differentiation 

and that the alkalic fraction was relatively dry. This 

supposition is substantiated by the occurrence of 

biotite in the granitic rocks and augite in the alkalic 

rocks, minerals characteristic of relatively wet and 

relatively dry magmas respectively.

Aside from the lack of relation to channels of mineralization, deuteric alteration 96 is commonly marked by 

coarser-grained secondary minerals than those formed 

by local hydrothermal alteration, but in many places, 

especially where the alteration has been intense, the 

two types are indistinguishable. Where deuteric 

alteration was feeble, sericite or fine-grained muscovite has replaced the feldspars, chiefly plagioclase, 

and chlorite has replaced the ferromagnesian minerals. 

Where the alteration was more intense, the muscovite 

and sericite are not confined to the feldspars but also 

appear in the ferromagnesian minerals, which contain 

more or less chlorite, quartz, epidote, leucoxene, 

magnetite, rutile, and zoisite. In some places carbonate is apparently contemporaneous with this suite 

of alteration products, but in most places it is later.

As in many places local hydrothermal alteration 

affected rocks that had already undergone deuteric 

alteration and, furthermore, as the hot solutions were 

not only changing but probably fluctuating in composition, pressure, and temperature, the sequence of 

alteration products is not everywhere the same. 

There is nevertheless a fairly definite paragenesis of the 

alteration minerals. Although sericite and chlorite 

probably formed in the cooler parts of the contactmetamorphic zone at the same time as the typical 

contact minerals were developing closer to the stock, 

in general such minerals as garnet, tremolite, hematite, 

magnetite, and epidote are the earliest products of 

exomorphic alteration. Sericitization was active from

98 "Deuteric" is used in the sense originally given to the term by Sederholm 

(Comm. geol. Finlande Bull. 48, p. 142,1916), for alteration produced during the later 

stages of the consolidation of a magma.
CKETACEOUS (?) AND TERTIARY IGNEOUS ROCKS 43

the time of the intrusion of the Montezuma stock till 

the period of ore formation. During the earl}7- part 

of this period, and at later stages in places where 

alteration was not intense, chlorite and epidote 

actively replaced ferromagnesian minerals. During 

the later part of the period of serialization, or locally 

at an earlier stage in regions where early alteration was 

intense, fine-grained quartz partly or completely 

replaced the ferromagnesian minerals and the feldspars. 

Locally sid.er.ite or ankerite was introduced into the 

country rocks during the solidification of the quartz 

monzonite porphyry stocks and reacted with magnetite 

to form pyrite. Sulphur was not given off in large 

quantities until near the end of the period of sericitination. Then the bulk of the pyrite was precipitated 

in the veins or replaced the wall rock. During the 

vein-forming period silicification was the dominant 

type of alteration, but in some places the wall rocks 

were replaced to a minor degree by ankerite and impure 

siderite. Most of these carbonates formed near the 

end of the period of mineralization. The latest effect 

of hydrothermal solutions in veins was the introduction of calcite and fine-grained quartz. In many 

porphyries the calcic feldspars were replaced by calcite 

and fine-grained quartz, both of which are later than 

the sericitization of the rock. The absence of clay 

minerals and iron stains indicates that this alteration 

was not due to weathering and suggests that it also 

occurred late in the period of waning hydrothermal 

activity.

WEATHERING

During weathering the feldspars are converted to 

carbonates and clay minerals, while the ferromagnesian 

minerals are gradually changed into limonite, carbonates, and clay. If the rocks are already somewhat 

altered, weathering is more rapid, and the ferromagnesian minerals disappear much more rapidly than the 

feldspars. Where aJl the minerals were fresh before 

reaching the zone of weathering, some of the dark 

minerals, such as biotite, are as resistant to weathering as plagioclase. In the coarse-grained porphyritic 

quartz monzonites that have been hydro thermally 

altered, the large, slightly altered orthoclase phenocrysts commonly weather more rapidly than the 

silicified and sericitized plagioclase minerals, especially 

if they are exposed to slightly acid solutions, and the 

porphyry becomes pitted on the weathered surface by 

the removal, of the large phenocrysts. Quartz phenocrysts are everywhere more resistant to weathering 

than the other constituents of the porphyries. Where 

previously unaltered rocks are exposed at the surface, 

the plagioclase usually weathers more rapidly than the 

other minerals, and the phenocrysts of orthoclase and 

quartz both weather in relief.

In most places in the pre-Cambrian complex there is 

little difference between the dike rocks and the country 

rocks in their resistance to erosion or weathering, but

in some of the softer members of the Idaho Springs 

formation and the Swandyke gneiss the dikes weather 

in relief. In the sediments west of the pre-Cambrian 

rocks the porphyries are generally much more resistant 

to erosion than their country rock and stand up in 

ridges or hills above the softer shales and grits.

Owing to the abundance of pyrite and other sulphides, the outcrops of veins are commonly less resistant to both weathering and erosion than their country 

rock, and their surface form is usually a linear depression. The acidity of the soil above pyritic bodies is 

unfavorable to the growth of many plants, especially 

aspen and willow, and in a thicket of these trees and 

shrubs the outcrop of a vein is marked by stunted 

growth, or, if the soil is thin, by a narrow barren strip 

of ground.

STRUCTURE

REGIONAL STRUCTURE

The Front Range is an elongate dome extending 

north from Canon City, Colo., into Wyoming. In 

the broad pre-Cambrian area exposed in this uplift the 

most obvious structural features are those developed 

in pre-Cambrian time, but the effects of the much 

later Laramie orogeny, so apparent in the bordering 

Paleozoic and Mesozoic sediments, can also' be recognized within the metamorphic complex. The preCambrian rocks that make up most of the Front 

Range are chiefly granites and schists. The regional 

pre-Cambrian structure has already been described by 

the writer,97 and only the general features will be considered here. A large mass of granite, the Pikes Peak 

granite batholith, extends north from Canon City to 

Georgetown, a distance of about 90 miles. North of 

the Pikes Peak batholith several smaller batholiths of 

granite intrude into the schist between Georgetown 

and Laramie, Wyo., but schist is as abundant as 

granite. Although the regional structure of the schist 

is comparatively simple, the minor folds and crenulations are complex. Most of the schist southeast of the 

mineral belt dips north or northeast, but close to the 

Pikes Peak granite it is folded into irregular synclines 

and anticlines. Northwest of the mineral belt a 

northward-trending anticline extends from Georgetown into Estes Park, and a syncline runs northnortheastward from the vicinity of Breckenridge to 

Fraser. Within the mineralized belt the schists are 

folded into a series of sharp synclines and anticlines, 

most of which trend from east to northeast.

Nearly all the post-Cambrian events that affected 

the structure occurred in late Cretaceous and earliest 

Eocene time. They included strong folding accompanied by thrust faulting and related tear faulting; 

several stages of minor faulting preceding, accompanying, and following the intrusion of quartz monzonite

" Lovering, T. S., The Front Range mineral belt: Colorado Sci, Soc. Proc., vol. 

12, pp. 233-268, 1930.
44 MONTEZUMA QUADRANGLE, COLORADO

porphyry stocks and dikes; vein formation; and minor 

postmineral faulting.

Although the Front Range uplift has a distinctly 

north-south regional trend, it is made up in large part 

of northwesterly folds arranged en e'chelon. These 

folds and their associated faults are the earliest effects 

of the Laramide revolution. Where deformation was 

not severe, these northwesterly flexures are open 

asymmetric folds, but where the mountain-building 

forces were stronger, the folds are overturned toward 

the southwest and in many places are broken by reverse faults, downthrown to the west. In the Montezuma quadrangle the west edge of the Front Range 

coincides with a broken fold of this type. Thrust 

faults have been found on both borders of the range, 

but, as shown on plate 5, the largest one known at 

present breaks this western fold and is known as the 

Williams Range thrust fault. It has been traced from 

the Breckenridge district for 50 miles northwestward 

to Muddy Butte, a short distance beyond Kremmling. 

Farther northwest it is hidden under Tertiary sediments, and its extreme northern limit is unknown. At 

its southeast end it passes into an overturned fold that 

continues southeastward into South Park where it is 

hidden beneath Pleistocene gravel. This fault, as will 

be shown presently, is interpreted as an underthrust.

A narrow zone of irregularly spaced but well-alined 

porphyry stocks trends N. 40° E. across the Front 

Range from Breckenridge to Jamestown. Nearly all 

the dikes, sills, and mineral deposits except the Miocene 

ores of Cripple Creek are concentrated in the region 

just southeast of the zone of stocks in a northeastwardtrending "mineral belt" ranging from 3 to 12 miles in 

width. Although persistent northwesterly faults extend across the mineral belt and for long distances 

both northwest and southeast of it, easterly and northeasterly fractures, which include most of the vein fissures, are abundant only in the mineral belt. This 

belt passes diagonally across the Montezuma quadrangle. The northeasterly course of the zone of stocks 

and the mineral belt of the Front Range is shown on 

plate 5. The veins in the mineral belt commonly 

occupy faults and fissures that strike from northeast 

to east, but some northwesterly veins have been found. 

The eastward-trending mineralized faults in the west 

half of the range show a marked uniformity in the direction of their displacements. So far as known, in all 

faults of this system the northern walls have moved 

east almost horizontally. The northeasterly faults 

commonly show less horizontal than vertical movement, and both reverse and normal faults are common 

south of the Montezuma stock. As indicated above, 

the northwesterly faults are commonly reverse faults 

that dip northeast. The mineral belt comes to the 

west edge of the range in the Montezuma quadrangle 

at the place where an overturned fold breaks and passes 

into the Williams Range thrust fault, and it seems 

clear that these structural features are related.

The easterly faults of the mineral belt show the 

presence of widespread horizontal shearing forces, and 

the Williams Range thrust fault, which dips eastnortheast at a low angle, also records the presence of a 

regional stress that was nearly horizontal. Both types 

of fracturing are thought to have been the result of a 

regional compression, for when the overturned fold 

broke into the thrust fault near Tiger the movement 

of the fracturing rock masses was greater than in the 

adjacent folding layers, and strong tearing stresses 

developed between the areas of thrusting and folding. 

Thus as one part of the overturned fold broke loose 

and moved along the thrust fault past the less active 

part of the fold a transverse shear zone marked by tear 

faults was formed.

The terms "overthrust" and "underthrust" have 

been used to indicate which block was believed to be 

active. In most places, no field evidence has been 

given that would indicate that one block was more 

active than the other, and the use of either "underthrust" or "overthrust" as descriptive terms depended 

largely on the theories of the user. Where the side of 

a thrust-fault block ends against a tear fault it may be 

possible to determine whether the upper block was 

more active than the lower block. If the lower block 

has been pushed actively under an inert upper block, 

the movement along the tear fault will not be the same 

as it would be if the upper block had moved actively 

over a nearly inert lower block. Points on the active 

side of the tear fault will be carried past the inactive, 

or fold, side parallel to the dip of the thrust fault. If 

the upper block moves over an inert lower block, 

points on the thrust-fault side of the tear fault will 

move up the dip of the thrust fault relative to the 

fold side of the tear fault, whereas if the lower block 

moves beneath an inert upper block, points on the active side of the tear fault will move down the dip of the 

thrust fault. Drag of the inert block by the active 

block would cause the same relative movement in the 

tear faults bordering both the active and the inert 

blocks of the thrust fault. As the direction of movement of the tear faults in the mineral belt shows that 

the north side of each fault moved east while the fold 

south of the Williams Range thrust fault was overturning to the west, and as this fold is deflected slightly 

eastward where it adjoins the tear-fault zone, it is 

probable that the lower block of the thrust fault was 

more active than the upper block, and thus that the 

Williams Range thrust fault can, with some assurance, 

be called an underthrust.97a

Overfolding toward the southwest accompanied by 

either overthrusting or underthrusting has been common in Colorado northwest of a line extending from 

Boulder southwest to Gunnison, a line that nearly 

coincides with the center of the Colorado mineral belt. 

In a wide zone southeast of this line, persistent steep

" Levering, T. S., Field evidence to distinguish overthrusUog from underthrusting: Jour. Geology, vol. 40, pp. 660-863,1932.
STRUCTtTRE 45

northerly faults, down thrown oil the west, are common, but thrust faults are not found. The southern 

limit of this zone trends nearly west from the north 

end of the Wet Mountains to the north end of the San 

Juan Mountains. Farther south overfolding and 

overthrusting toward the northeast a direction opposite to that of the overfolding northwest of the 

mineral belt have been common.08 Thus, in the 

Front Range, the mineral and porphyry belts mark the 

northwestern limit of a transition zone between opposite types of deformation. The broad regional 

structure, as well as the more local relation of the mineral belt to the Williams Range thrust fault, indicates 

northeast-southwest shearing stresses concentrated in 

this belt during the Laramide revolution, in early 

Eocene time.

As the Montezuma quadrangle is on the western 

border of the Front Range uplift, where the mineral 

belt intersects the Williams Range thrust fault, the 

local structure described below is an excellent sample 

of the regional geology.

LOCAL STRUCTURE

The major structural elements of the Montezuma 

quadrangle are shown in figure 5. The metamorphic 

rocks are greatly broken and intruded by pre-Cambrian 

granites and Tertiary porphyries, but the axes of the 

chief folds of the schist have been shown. The 

Williams Range thrust fault is present in the southwestern part of the quadrangle and passes into an 

overturned fold near the southern boundary. The 

fault plane is domed up at the western edge of the 

large stock of quartz monzonite porphyry near the 

center of the quadrangle, and a "window" has been 

cut through the gneiss of the hanging wall by the 

Snake River and Jones Creek, exposing the underthrust 

Cretaceous shales.

The mineral belt runs diagonally across the quadrangle from southwest to northeast and, as in other 

parts of the Front Range, coincides with a belt of 

porphyries. These major features and the associated 

structure will be discussed in detail below.

PRE-CAMBRIAN STRUCTURE

Much of the pre-Cambrian granite in the Montezuma quadrangle shows flow structure, especially near 

the contacts with the schists or gneisses. The parallelism of the tabular feldspars and biotite crystals 

indicates the direction of movement in the granite 

masses during their emplacement and is well developed 

in the Silver Plume granite masses and in the small 

outlying stocks and bosses of Pikes Peak granite in 

the southeastern part of the quadrangle. The direction of the flow lines was not systematically studied, 

as time was lacking for the detailed work that would 

be required, but several observations were made and

«s Oral Information from W. S. Burbapk and JS, N, Gpddard,

are recorded on plate 3. In most places the flow lines 

are parallel to the schistosity of the enclosing schists 

or gneisses, suggesting the intrusion of the granite in 

sill-like masses, but cross-breaking contacts between 

granite and schist are common, and here the flow lines 

are parallel to these contacts in the adjacent granite. 

In the large mass of Silver Plume granite in the north 

half of the quadrangle many of the small bodies of 

schist, and most of the larger bodies, show such marked 

concordance in the direction of the schistosity that it 

seems probable that they are roof pendants; on the 

other hand, the small isolated bodies of schist that 

show no relation to the regional structure are probably 

xenoliths that had been stoped from the overlying 

batholithic cover and were trapped by the solidifying magma. The direction of foliation of the schist 

masses is shown oh plate 3, and the random orientations 

of the schist inclusions contrast so markedly with the 

regularity of strike in the roof pendants that they can 

be easily distinguished.

The general structure of the schists is shown in the 

cross sections on plate 4. The Swandyke gneiss marks 

the center of a syncline which is about 5 miles wide 

near the southern boundary of the quadrangle. Several minor folds occur on the sides of the major syncline, and complex crenulations of small magnitude 

are present everywhere. The axis of the major syncline runs north through the western part of the 

Montezuma quadrangle and swings northeast soon 

after entering the Fraser quadrangle. To the east of 

the syncline the general dip of the schists is toward 

the west, but several minor anticlines and synclines 

have been recognized and are shown on figure 5 and 

in the cross sections on plate 4. The direction of the 

schistosity is indicated by short lines on plate 3, 

where many flexures are shown that are not of sufficient importance to be described here. The larger 

features are also indicated by this convention and the 

approximate course of schist beds can be ascertained 

by studying the direction of the lines.

The most pronounced structural feature in the 

schist in the east half of the quadrangle is the westwardplunging anticline at the head of West Geneva Creek. 

Although it is not plainly shown in the cross sections, 

the abundant measurements of dip and strike and the 

swing of the lines of schistosity on plate 3 clearly 

indicate its position and structure. It differs from 

the northeastward-trending anticlines and synclines 

north of it in being a comparatively open fold. Dips 

of 20° to 40° are common in it, whereas farther north 

in the schist area northeast of Grays Peak the schistosity is generally steep and the folds are almost 

isoclinal.

As stated elsewhere," the progressive increase in the 

degree of metamorphism of the schists as the large

««Lovering, T. S., Geologic history of the Front Range, Colo.: Colorado Sci. 

Soc. Proc., vol. 12, pp. 67-71, 1929.
46 MONTEZUMA QUADRANGLE, COLORADO

pre-Cambrian granite masses of the Front Range are 

approached suggests that the schistosity was developed 

during the period of pre-Cambrian batholithic invaLocally the structure of the schists appears related to 

this large granite mass, and in the Georgetown quadrangle the schistosity swings around the nose of the

EXPLANATION

R.77W. R.76W. R.75W.

FIGUKE 5. Major structural features of the Montezuma quadrangle.

sion. The crumpling of the sediments, which were 

metamorphosed into schists and gneisses, was caused 

by regional forces that were active before and during 

the formation of the Pikes Peak granite bathohth.

bathohth approximately parallel to the contact of the 

two rocks. In that region it dips at low angles away 

from the granite on the east and north but becomes 

steep along the west and southwest sides and in many
STRUCTURE 47

places shows no parallelism to the granite contact. 

It is probable that much of the present structure of 

the schist was developed before the intrusion of the 

granite and was locally modified by the intrusion.

JjARAMEDE STRUCTURE

Williams Range tlwust fault. The" Williams Range 

thrust fault enters the Montezuma quadrangle about 

a mile northwest of Keystone and follows a southsouthwesterly course to the North Fork of the Swan 

River, where it turns due south and passes into an 

overturned fold. The schist and gneiss that crop out 

above the fault generally supply a moderately thick 

cover of slope wash that creeps over the soft Cretaceous shales underlying the fault and effectually concoals the contact of the two formations. The contact 

of the sediments and metamorphic rocks was seen at 

only one place along the western boundary of the preCa,mbrian mass. Near the head of Soda Creek, where 

the fault crosses the east line of sec. 3, T. 6 S., R. 77 W., 

some prospect holes were driven into the brecciated 

fault zone, and about 30 feet of it is exposed. The 

lowest part of the outcrop is sandy and moderately 

fine grained and grades up into a breccia that near the 

top contains angular fragments of granite and pegmatite as much as 5 inches in length. Hematite and 

green copper stain are abundant in cross fractures. 

A very prominent sheeting is present that strikes due 

east, dips 25°-30° N., and is probably parallel to the 

fault plane in this locality. Slickensides dipping 46° 

N. 70° E. were observed, but the grooves and heavy 

striations, which are very prominent, dip due east at 

50°. The shales nearby dip 24° NNE. In most 

places the sediments west of the fault dip east or eastnortheast at 20° to 30° and show no change in dip as 

the fault is approached. Locally, however, the shale 

is much disturbed, and in the irrigation ditch 0.4 

mile north of Keystone the Pierre dips 50°-90° E.

Farther south the geology, which is described below, 

indicates that an overturned fold south of the Middle 

Fork of the Swan River becomes more and more 

broken toward the north and passes into the thrust 

fault near Tiger. Although. pre-Cambrian rocks rest 

only on the Pierre from the place where the fault 

enters the quadrangle, near Keystone, south to a 

point about a mile north, of Tiger, they abut against 

fragments of the Niobrara and Dakota formations at 

several places farther south, as shown on plate 3. On 

the south bank of the Middle Fork of the Swan River 

about a quarter of a mile east of its mouth a nearly 

vertical thin bed of Dakota quartzite lies between 

schist and a mass of intrusive hornblende diorite, but 

the contacts are covered. Farther south both the 

Benton shale and the Dakota quartzite lie between the 

diorite and the pre-Cambrian rocks, and at Georgia 

Pass, 2V2 miles south of the quadrangle, the sedimentary 

contact of the Dakota quartzite and the pre-Cambrian

schist is clearly exposed. It is overturned and dips 

about 65° E.

The eastward continuation of the Williams Range 

thrust fault for at least 4 miles from its main outcrop 

at Keystone is shown by a "window" that adjoins the 

Montezuma stock. Just west of the stock hard, slaty 

shale crops out for about a mile on the lower slopes of 

the western spur of Porcupine Peak, near the junction 

of Snake River and its north fork, 1% miles east of 

Keystone. Poorly preserved casts of Tnoceramus show 

that the rock is Upper Cretaceous, and its lithology indicates that it is the Pierre shale. It is overlain by 

the Swandyke gneiss from 200 to 700 feet above the 

valley floor, and the two formations are separated by 

an indurated fault breccia about 30 feet thick. The 

fault surface is very irregular but dips in a general 

northerly direction as shown in plates 3 and 4. South 

of this exposure of the fault, on the northwest spur of 

Independence Mountain, shale is found at much higher 

altitudes, and the fault crosses the spur about 2,300 

feet above the valley of the Snake River. Keystone 

Gulch is the western limit of the southern mass of shale 

and almost certainly follows a strong fault. The fault 

contact descends rapidly as it is followed south from 

the crest of the Independence Mountain spur, and the 

shale passes from sight beneath the overlying gneiss in 

the bottom of Jones Gulch 1.8 miles from its mouth.

Structural relations of the Montezuma stock. A wedge 

of the Montezuma quartz monzonite stock projects 

west into the shale in the valley of the Snake River, 

and, as shown on plate 3, the thrust fault is cut oft' 

abruptly by the stock a short distance east of meridian 

105°55', on both the north and south sides of the 

wedge. The shale dips away from the quartz monzonite at 10° to 50°, showing that the wedge is near the 

axis of a domal uplift. It is uncertain whether the difference in altitude of the thrust-fault surface on the 

two sides of the wedge is due chiefly to faulting or to 

doming, but the straightness of the north edge of the 

quartz monzonite suggests that it followed a transverse 

fault. It is known that the doming of the thrust fault 

was accompanied by faulting along Jones Gulch, and 

it seems probable that the dome was also broken by an 

eastward-trending system of faults either before or 

accompanying the intrusion of the stock.

The contact of the Montezuma stock and the schists 

is nearly straight for distances of several miles in some 

places. On the northern and southeastern sides of the 

stock the straight-line contacts generally trend N. 70° 

E., suggesting a preporphyry system of fractures having this trend. It is probable that they represent fractures related to the tear or transverse shear faults of 

the mineral belt. In most places the contact of the 

quartz monzonite and the metamorphic rocks is steep, 

but on the eastern border of the stock the contact dips 

45° E. down the southwest spur of Grays Peak, through 

an observed vertical'distance of 1,200 feet. The schist
48 MONTEZUMA QUADRANGLE, COLORADO

nearby is badly crumpled and may have been crowded 

by the intrusion of the stock, but in most places the' 

Intrusive rock breaks cleanly across the schistoeity of 

the country rock, and there is no indication that the 

structure of the schist affected the shape of the stock. 

The upward bulge of the Williams Range thrust fault 

at the west end of the stock suggests that the quartz 

monzonite was intruded near the center of a local 

east ward-trending anticline, and the primary linear and 

platy structure of the intrusive and the position of the 

aplite seams indicate that it was moving upward and 

N. 80° E. at an angle of about 25° to the horizontal in 

this locality.

The stock is strongly jointed but has few persistent 

faults or fissures. As it was intruded after the region 

had been through the period of stress when the Williams 

Range thrust fault was formed, it was probably subjected to much milder fracturing stresses than the 

country rock nearby.

The region northwest of the stock contains almost 

no dikes of porphyry, but the region southeast, of it 

has many dikes and small irregular masses of porphyry. 

As pointed out in the discussion of regional geology, 

this is a relation that exists throughout the porphyry 

belt of the Front Range; the large stocks of porphyry 

all occur northwest of the belt of porphyry dikes, which 

is also the belt where veins are abundant. This relation 

suggests the presence of subjacent magmatic chambers 

southeast of the zone of stocks and their absence to the 

northwest. These chambers were probably the source 

of the solutions that mineralized the fractures of the 

mineral belt. The regional position of the Montezuma 

stock in the northeastward-trending zone of stocks 

suggests that its intrusion was dependent chiefly on 

regional shearing stresses between provinces of different 

types of deformation, rather than on the presence of 

the thrust fault which it cuts.

Transverse faults and fractures of the mineral belt. 

The distribution of the veins and dikes of the mineral 

belt that extends diagonally across the quadrangle is 

shown on plate 3. In the northeastern part of the 

quadrangle they are concentrated in a narrow northeasterly belt extending from Kelso Mountain to 

Brown Gulch. South of Kelso Mountain the belt is 

slightly broader, probably averaging about 2 miles 

wide, and runs almost due south to the head of West 

Geneva Creek, where it swings southwest and widens 

greatly. In this part of the quadrangle it would not be 

recognized as a distinct northeastward-trending belt if 

it were not considered part of a regional feature. (See 

pi. 5.)

West and south of the head of West Geneva Creek 

scattered veins occur in many places, but the largest 

veins are still concentrated in narrow belts. Near 

Montezuma the best-known and most productive 

veins, which on the whole have northeasterly trends, 

occur in a strip about a mile wide that runs nearly due

west from the head of West Geneva Creek to Glacier 

Mountain, Where" it swings sharply south-southeast 

through Teller Mountain into Hall Valley. The scarcity of veins west of Glacier Mountain is attributed to 

the fact that the pre-Cambrian in that area terminates 

downward against the underthrust plastic, impervious 

Pierre shale, which was an effective barrier to rising 

ore-forming solutions. The northwestward-trending 

belt of northeastward-trending veins in the Hall Valley 

area is probably related to the fault at the east side of 

South Park, with which it alines and with which the 

prominent regional north-northwest faults correspond 

in movement.

It is difficult to obtain information about the movement of faults in the schists and gneisses, as definite 

horizons are not usually recognized, but in some of 

the veins and faults the direction of movement was 

found. Of the many criteria that have been suggested 

for determining the direction of movement of fault 

walls, 1 the writer has found that the only trustworthy 

ones are displacement of recognizable horizons, drag of 

adjacent layers of schist, interior faulting within a fault 

zone, curved tension cracks, S-shaped compression 

fractures in the fault material indicating the relative 

movements of the two walls, and grooves and furrows 

cut into hard walls and believed to be parallel to the 

direction of strongest movement. These criteria have 

been used to determine the direction of movement in 

faults of the Montezuma quadrangle..

The premineral faults in the northeastern part of 

the quadrangle, near Silver Plume, commonly trend 

east-northeast, and in the Gold Belt tunnel the north 

wall of the chief vein fissure apparently moved down 

and east. A few miles to the southwest most of the 

veins strike north-northeast, and in the Stevens mine 

the west wall of the vein fissure apparently moved 

down and north at an angle of about 60°. Most of the 

veins in the mineral belt farther south also strike northnortheast or northeast, but a few trend east or northwest. In the Pennsylvania vein, about 5 miles south 

of the Stevens mine, the available data, though not 

conclusive, suggest that the northwest wall of the fissure moved up and northeast at an angle of about 30°. 

Near Montezuma the Bell-Meteor Wing vein, the Bullion vein, the Chatauque vein, and the Sts. John or 

Comstock vein follow reverse faults that dip northwest, and the Silver King follows a normal fault that 

dips southeast, its southeast wall moving down to the 

northeast at an angle of about 70°. Thus in the premineral faults near Montezuma for which the movement could be ascertained the up thrown wall was consistently on the north and the angle of movement was 

moderately steep. This movement was probably expressed by step faulting related to the formation of the 

east-west anticline associated with the Montezuma

i Willis, Bailey, and Willis, Eobin, Geologic structure, pp. 132-145, New York, 

McGraw-Hill Book Co., 1929.
GEOLOGIC HISTORY 49

quartz rnonzonite. The Ida Belle fissure, on the east 

slope of Jones Gulch, strikes nearly due east and cuts 

the Williams Range thrust fault. Its north wall 

moved down to the east at a low angle. If the movement on these faults is representative of the region 

near them, it seems probable that they were formed in 

response to a regional shearing stress, modified later by 

local vertical stresses attending the intrusion of the 

Montezuma quartz monzonite stock.

Postmineral faults are not common in this quadrangle, but several were observed in Glacier Mountain, 

south of Montezuma. Most of them have a northerly 

strike and an easterly dip and are normal faults. 

Movement along these faults may be as much as 350 

feet. (See pp. 85, 102.)

The veins in the southeastward-trending branch of 

the mineral belt that runs through the Hall Valley 

area are in transverse relation to a fault zone that is 

parallel to the schistosity of the Swandyke gneiss in 

this region and strikes north-northwest. The displacement on the three north-northwest faults in this 

zone (shown as one fault on pi. 3) is not uniformly in 

the same direction, but on two of the three faults for 

which the direction was ascertained the movement 

was very much greater than on the third, and in these 

two the west wall moved down and to the south. The 

veins that are related to the fault zone strike northeast, 

but the direction of movement of their walls is not 

known with certainty, although the occurrence of ore 

in the flatter parts of the Missouri vein suggests 

that it is a reverse fault in which the northwest wall 

moved up.

Intrusive relations of dikes and small masses. With 

the exception, of the Montezuma quartz monzonite 

stock and the quartz monzonite mass in the southwestern part of the quadrangle, all the Tertiary 

intrusives occur in relatively small masses. Most of 

the intrusives north of West Geneva Creek are dikes, 

but southwest of this stream small irregular-shaped 

masses are common. The longest dikes in the quadrangle are less than a mile long, and most of them are 

less than half a mile commonly less than 1,000 feet. 

The short length of the dikes in the Montezuma 

quadrangle contrasts strongly with the great length of 

those found in the northeastern part of the mineral 

belt, where Bastin and others have mapped many 

dikes several miles long. These long dikes strike 

northwest, and, as already pointed out, fractures 

trending northwest are probably related to Echelon 

folding and are much more persistent than northeastward-trending fractures. Nearly all the dikes in the 

Montezuma quadrangle strike from east to northeast, 

and apparently all the porphyry was intruded along 

comparatively nonpersistent fissures. Many of the 

intrusives are parallel to the schistosity of the enclosing 

schists and gneisses, but because of the steep dip of 

most of these rocks, the intrusives are regarded asdikes rather than sills. At the head of West Geneva 

Creek, however, sill-like offshoots from the irregular 

mass of monzonite porphyry on Revenue Mountain 

were intruded between layers of the gently dipping 

schists not far from the crest of the westward-trending 

pre-Cambrian anticline described on page 45. In the 

shale area west of the Williams Range thrust fault 

sills are more common than dikes, as may be seen in 

structure section D-D', plate 4. Most of the dikes that 

are not parallel to the schistosity strike either east or 

northeast and are nearly vertical. In some places, as 

in the Burke tunnel, a mile south of Montezuma, 

porphyry masses are exposed underground that do not 

crop out at the surface. In other places a dike that 

dies out along its strike is succeeded by small masses 

of porphyry in line with it, which are probably upward 

projections from a continuous mass that at depth 

follows the same fracture zone as the exposed dike. 

Similar relations were noted in the adjoining Georgetown quadrangle by Ball,2 who concluded that dikes 

were probably more abundant at depth than at the 

surface.

GEOLOGIC HISTORY

During pre-Cambrian time, probably early in the 

" Algonkian,3 a thick series of sandy shales was laid down 

on an unknown basement. After the deposition of 

these sediments, and in part during the later stages 

of their accumulation, large masses of basaltic and 

andesitic lavas were extruded. The sediments and the 

lavas were strongly folded and metamorphosed into 

schists and gneisses at the beginning of a great period 

of batholithic invasion, which followed the period of 

extrusion.

The earliest rocks of the batholithic period were 

intruded while the crumpling sediments were being 

gradually metamorphosed, and at the depth at which 

these events occurred the heat and emanations from 

these intrusives were instrumental in changing the 

sediments into schists and gneisses. Small masses of 

monzonite, granite, aplite, pegmatite, and quartz 

diorite were intruded in many places. Most of the 

early magmas were very fluid and searched out and 

followed bedding-plane fractures. This lit-par-lit injection of the sediments was widespread but was most 

intense in the regions later intruded by the granite 

batholiths. Continued diastrophism and injection 

accompanied the invasion of a very large mass of 

granite magma, and many of the earlier intrusives were 

converted into gneisses during its slow formation. The 

Pikes Peak granite batholith, which formed at this 

time (about a billion years ago), is the largest known in 

the Front Range, and the intrusive activity as well as 

the metamorphic processes waned markedly after its 

formation.

» Ball, S. H., op. cit. (Prof. Paper 63), p. 72.

3 Lovering, T. S., Geologic history of the Front Range, Colo.: Colorado Sci. 

Proc., vol. 12, pp. 73-74. 1929.
50 MONTEZUMA QUADRANGLE, COLORADO

After the Pikes Peak granite had solidified, another 

epoch of granite invasion occurred. The later preCambrian granites and their associated pegmatites of 

this epoch were intruded at many places in the Front 

Range. The Silver Plume granite, the Cripple Creek 

granite, the Longs Peak granite, and the Mount 

Olympus granite belong to this epoch and represent 

the latest pre-Cambrian intrusive activity in the 

Front Range. It is uncertain whether they belong 

to the last stage of the batholithic invasion of the 

Pikes Peak granite or to a much later period.

The formation of the late granites was probably accompanied by uplift and was certainly followed by a 

long period of erosion. By the end of Algonkian 

time the earlier mountains had been worn down to 

nearly featureless plains on each side of a slightly 

higher tract of land, which existed along the site of 

the present Front Range. This early Front Range 

highland has remained a positive topographic area 

ever since and has supplied sediments to the surrounding region many times. The Front Range highland 

was separated by a broad basin from a similar high 

area stretching northwest and southeast of the present 

site of Creede. . Sediments of the early Paleozoic 

systems are not present in the Montezuma quadrangle, 

but Cambrian, Ordovician, Devonian, and Mississippian sediments were deposited in the basin west of 

the Front Range highland, a short distance away. 

Oscillations of the earth's surface resulted in successive 

invasions and withdrawals of the sea from the lowlands 

during these periods, but it is improbable that any of 

these seas covered the Front Range highland. The 

areas occupied by the sea in each period were much 

the same, but in general each marine invasion was a 

little more widespread than the one before.

There is little in the character of the Cambrian, 

Ordovician, Devonian, and Mississipian sediments to 

indicate proximity to a rugged land surface, but there 

is clear evidence of the rejuvenation of erosive agents 

in the Pennsylvanian. Elsewhere in the Front Range 

there is evidence of minor warping between these 

periods,4 but apparently no uplift of magnitude occurred 

until late Mississippian or early Pennsylvanian time, 

when the Front Range highland was elevated and the 

adjoining areas were depressed. Thick continental 

and interstratified marine delta deposits were formed 

in these troughs during Pennsylvanian and Permian 

time. The eastern shore line of the Pennsylvanian 

sea probably passed through the Breckenridge district 

very close to the southwest corner of the Montezuma 

quadrangle, and the Permian sediments overlapped it 

and extended a few miles farther east onto the preCambrian rocks.

Little erosion or diastrophism occurred in this region 

at the end of the Permian or during the Triassic period, 

and no sediments of Triassic age are known nearby.

< Levering, T. S., op. cit, pp. 75-81.

During the later part of the Jurassic period thin marine 

sediments were deposited along the northern borders 

of the Front Range, and some sediments of this age 

have been reported not far from the Montezuma quad' 

rangle. Neither erosion nor deposition, however, 

was notably active at this time. Still later in Jurassic 

time the Front Ra nge highland was reduced to a series 

of low hills rising from broad, nearly featureless piedmont plains teeming with large swamp-loving reptiles. 

The fresh-water sediments of the Morrison formation 

were laid down on these plains but did not cover the 

hills. The Lower Cretaceous sea is not represented in 

the area.

The Upper Cretaceous sea advanced over the slowly 

sinking highland and deposited the Dakota sands and 

shales, but the central part did not subside as rapidly 

as the margins, and, as in Pennsylvanian and Permian 

time, a much thicker series of sediments formed along 

the edge than over the center. The maximum subsidence probably occurred about the middle of the Pierre 

epoch, and uplift began soon after subsidence ceased. 

Before the end of Pierre time the central part of the 

Front Range highland was pushed above the level of 

the sea, and the recently deposited shales were exposed 

to erosion. They were reworked into the upper part 

of the marine Cretaceous, and the Dakota sandstone 

was also exposed and reworked at many places and 

was probably the source of much of the sandy material 

found in the upper part of the Pierre shale and in the 

Fox Hills sandstone. During the succeeding Laramie 

epoch the pre-Cambrian core was exposed and was 

contributing feldspathic sediments to this formation. 

Before the end of the Laramie the central part of the 

Front Range highland was elevated well above the 

surrounding plains. This elevation was probably due 

to a gentle arching of the whole Front Range highland, 

forecasting the violent mountain-making movements 

that occurred early in Eocene time, soon after the 

Denver epoch. Increasingly rapid uplift and marked 

volcanic activity followed the Laramie and ushered in 

the Denver epoch. At this time acidic felsites and 

gabbro were intruded at many places in the Front 

Range, and the gabbro dikes found scattered through 

the Montezuma quadrangle are believed to be of 

Denver age. At the same time that the highland was 

being arched, the border lands were being down-warped, 

and sometime after the end of the Denver epoch a 

great mass of the earlier sediments was thrust eastnortheastward under the pre-Cambrian rocks in the 

western part of the Montezuma quadrangle. This 

folding was accompanied and followed by intrusive activity. Sills and dikes of diorite and monzonite 

porphyries were succeeded by dikes and stocks of 

quartz monzonite porphyry, which in turn were 

followed by dikes of more acidic rocks such as the granite and sodic quartz monzonite porphyries. Emana- 

'tions from the underlying magma formed many metal-
MINERALOGY 51

Jiferous veins, probably under a moderate cover of preCambrian rocks and Tertiary lavas.

The rejuvenation of the streams that accompanied 

the mountain building at the end of the Denver epoch 

caused rapid erosion, and it is probable that the volcanic rocks that covered the pre-Cambrian core of the 

range during most of the Denver epoch were removed _ 

over large areas before Wasatch time, developing an 

imperfect peneplain called the "Flattop" peneplain. 

Renewed uplift, probably in early Wasatch time, 

rejuvenated the streams, and by the end of the Eocene 

erosion had cut a broad bench, known as the "Medicine 

Bow" peneplain, about 1,000 feet below the level of the 

Flattop peneplain. Both surfaces were locally halted 

at some of the places where the little-folded pre-Dakota 

peneplain was reexposed. It is probable that many of 

the conspicuously level surfaces of the Flattop peneplain are a,lso remnants of the earlier erosion surface 

over which the Upper Cretaceous sea advanced at the 

beginning of Dakota time and which was slowly uncovered by Eocene erosion. Some of the ore deposits 

in the Montezuma quadrangle may have been within 

reach of ground water since the early part of the Eocene 

epoch.

Minor uplift and erosion occurred during Oligocene 

time but had little effect on the topography near the 

Montezuma quadrangle. A much greater uplift 

marked the Miocene, and in many places in the Front 

Range there was volcanic activity at that time. The 

rejuvenated streams commenced carving a new erosion 

surface on the flanks of the range but cut a plain farther 

back on the east side than on the west side. This surface, known as the "Rocky Mountain peneplain", is 

poorly developed in the Montezuma quadrangle but

can be recognized at many places. During lower and 

middle Pliocene time this peneplain continued to 

develop on the flanks of the higher mountains, while 

they themselves were carved into a mature mountainous upland. Little erosion occurred in the upper 

Pliocene, when for the first time since the Triassic, 

the region was visited by an arid climate. Although 

unimportant in its effect on the sculpturing of the 

mountains, this aridity was probably economically 

important in aiding the enrichment of the ores.

A broad regional uplift raised the Front Range at the 

beginning of the Quaternary period, and some of the 

postmineral faults observed in the quadrangle may 

have been formed at this time. The uplift started a 

period of vigorous erosion that has lasted to the 

present. Two major glacial stages followed the uplift, 

and it is probable that a less extensive glaciation 

occurred during the interval between them. A great 

amount of erosion took place in some of the large 

valleys after the first glaciation, and some of them were 

deepened as much as 1,200 feet by later stream and 

glacial erosion. The last glaciers have disappeared in 

comparatively recent time, and little erosion has been 

effected by the streams since.

ECONOMIC GEOLOGY

MINERALOGY 

MINERALS OCCURRING IN THE QUADRANGLE

All the minerals that are known to occur in the Montezuma quadrangle are listed in the table below, and 

the mode of occurrence of each mineral is indicated. 

Additional information is given for many of the minerals on pages 53-58.

Minerals in the Monlezuma quadrangle

Mineral

Allanite, Caa [A1.0H](Al,FeJ Ce 1 La,Di)2[Si04 ]3- ---

Amphibole, CaMg;)(Si03)4------------------------- ----

Ankerite, (Ca,Mg,Fe)C03 __ _ ------ _ ___________________

Apatite, (Ca,F)Ca4P3 Oi 2 _--__ _ --- __ ------ _ ._._______.

Augite, CaMgSi 2 00 with (Mg.Fe) (Al.FeJO.Sia -.-. ------

Azurite, 2CuC03 .Cu(OH)a_ ____ -_ - - 

Barite, BaS04 ---. _________ ._.--__ __ _ _ ._ _ -----

Beegerite, 6PbS.Bi2S3 - ______ ----- ____________ ___

Biotite, (Hl K)a(Mg> Fe) a A] 2SiOsOi2__.. .- --------

Bismuthinite, Bi2S3 _ ______________________________________

Bismutite, Bi 2 03 .C02 .H2 0---_ ____ _... _____ .---.__-_

Bromyrite, AgBr_ ________________________________________

Calcite, CaC03 _ _ -____ __ _-_.--_ _ __ __ __ ___ _______

Calamine, H2 (Zu2 0)SiO., __ _ _ 

Cerusite, PbC03 _--__ _____ __ __-__.-_ _ __ _ _ _ _

Chalcanthite, CuS04 .5H2 0___--__---____ _______ --__-__--

Chalcedony, SiOs------ _--_-__--_-_-_____________________

Ifypogene

Regional 

metainorphism

X 

X 

X

X

Igneous 

rocks

X 

X' X

X

X

X

Contact 

metamorphisra

X

X

,

High-temperature 

deposits

Moderatetemperature 

deposits

X

X

X 

X

X 

X

X

X

Supergene

Sulphide 

zone

?

X 

X

Oxidized 

zone

X

?

X

xxxxxxx
MONTEZUMA QUADRANGLE, COLORADO

Minerals in the Monlezuma quadrangle Continued

Mineral

Chalcopyrite, CuFeS2 - ___-_--_-__-------_--_- ----- ____

Chlorite____-______-_-__-____________-_____ ______ ______

Chrysocolla, CuSi03 .2H2 0_- _ _.___.._ _ ___ __ __ __ _

Clay____-__-____-___-_-_-____"--__-_----_--___--__-_--_ 

Clinozoisite __ __-_______-__-___-__--_-_____---___ ______

Covellite, CuS_______. _ __._______-. ___ _______________

Cuprobismutite, 3Cu2S,4Bi2S3---- _ -------- ____________ -

Diopside, CaMg(SiO3 ) 2 ___ --- -_- ---------- ___ _______

Dolomite, CaMg(C03)2__ ______ --- - _____ --- __

Epidote, H2 0.4CaO.3(Al3Fe) 2 O3 .6Si02--------_-------------

Epsomite, MgSO4 + 7H2 0___ ____ _ _____________

Fibrolite ____________________________ ___________________

Fluorite _ ________ _ ________________ _______________

Freibergite, 4(Cu2S,Ag2S) 3 .Sb2 S __ _ ____ ._ _ ._ ____ _-

Galena, PbS __ ___ _ __ __ _ __ _____________ _ __ _

Garnet, 3R"O.R" ' 2 03 .3SiO2 (whenR" = Ca,Mg,Fe,Mn; R" ' = 

Al,Fe(Mn),Cr,Ti) _____._________-_--_-___.__.________-_

Goethite, Fe2 03 .3H2 O___ _______ _______________________

Gold, Au____ ____________ _ _____ _ _ __ _-

Goslarite, ZnS04 .7H2 0_. _____ ______ ._ ____________

Graphite, C____________ _ _ ____ _____ ______ __________

Gypsum, CaS04 + 2H2 0 ____ __________ _ ___ ____ _

Hornblende, Ca(Mg,Fe) 2 (SiO3 ) 2 ____ _ _ _ _ ____ J ________

Hypersthene, (Mg,Fe)Si03 -____ _____ ______ _____ __ -_.

Ilesite, (Fe,Mn,Zn)SO4 .4H2O--_- ____ _ . ___ __________

Ilmenite, FeTiO3 -------___-__ _ _ _________ ______ _ _

Jarosite, K2O.3Fe2 03 .4SO3 .6H2 O _ __ _ _____ __ _ _

Kaolin, 2H2O.Al2O3 .2Si02 -_----__---_-------_----_--_---_-

Labradorite (see plagioclase) _ _______________ __ _____ ___

Leucoxene ______________ _ ____________ ________ _______

Limonite, 2Fe2 03 .3H2O_____- __________________ ___

Magnetite, Fe3 O4 _ ____ ___________ __________ __

Malachite, CuC03 .Au(OH) 2 ________ ______ _ _____ ___

Manganosiderite, (Fe,Mn,Mg)CO3 ___ __ _ __________ _ _ Marmatite, (Zn3Fe)S______ _.______ _-__---___ __ _-__

Melanterite, FeS04 .7H2 O __ _ ___ __ _ _______________

Miargerite, Ag2 S.Sb2S3 __ ______________ __ ___________

Microcline, KAlSi3 08 _ ----------- __ ______________ _____

Molybdenite, MoSo _ _ ____ _ _ _ ______ _ _ _________

Orthoclase, KAlSi3 08 _ ________ __ _ _____ _______ ____

Paragonite, NaH2Al3 (Si04 ) 3 ___-___-------_----__ _ _-_.__.

Pearcite, Ag9AsS6 _ _________ __________-_-_-________-___-

Perovskite, CaTi03 -_-____-____-___-----_---_______-___---

Plagioclase, x (NaAlSi3Os) .y (CaAl2Si2 Os) -----_-----_-__-_--_

Psilomelane, H4 MnOs__ _ __________________________________

Pyrargyrite, Ag3SbS3 _-_--_______---_----__--- ____

Pyrite, FeS2 ---_--__--____________----_______-_______--._

Pyrolusite, MnO2 ._ _____________________________________

Quartz, SiO2 _____-_____________. ______ _____________ ___

Roscoelite, vanadium mica______________________«_____ ___

Rutile, Ti02 __ _ ___ ___ ___ __ _______ .. _____ ___

Schapbachite, PbS.Ag2 S.Bi2 S3 .___ __ _ _______________

Sericite, KHjAMSiOOs -- -- ------ « 

Siderite, FeC03 _ _ _______ ___ _____ ___________ ___ _

Native silver, Ag _ ___ ____________ _______ ____________

Smithsonite, ZnC03 _____._________-____--___________-_---

Sphalerite, ZnS__--_-______ _______________________ _____

Stephanite, Ag5SbS4 _ _ ____^________-_____ ______________

Stromeyerite, CuAgS_ ___________ _________ _______________

Sulphur, S ______________________________ ______________

Tetrahedrite, Cu8Sb2S7 ___ ----- _ - ----- ___ ___ _

Titanite, CaTiSi05 or CaO.Ti02 .Si02 __ _ ______ ____ ___

Tourmaline (black) _ _ ___________________________________

Hypogene

Regional 

metamorphism

.

X

X

X

X

X

X 

X

X

X

X.

X

X 

X 

X

X 

X

X

X

X

X

Igneous 

rocks

?

X 

X 

X

X

X

X

X

X 

X 

X

X 

X

X

X

?

X 

X

Contact 

metamorphism

X

X

X

X

X

X

X

X

X

X

High-temperature 

deposits

X

X

X

X

X

?

X

X

X

X

X

X

Moderatetemperature 

deposits

? 

X 

X

X

X

X 

X 

X 

X

X 

X 

X

X

X

X

X 

X

X

X

X 

X

X

X 

X

X 

X 

X 

X 

X 

X 

X

X

X 

X 

X

X 

X

Supergene

Sulphide 

zone

X 

X

X

X

?

X

X

X 

X

X

?

?

?

X

X

?

Oxidized 

zone

X 

X

X

X

X 

X 

X

X

X

X 

X

X 

X

X

X

X

X 

X

X

X
MINERALOGY

Minerals in the Montezuma quadrangle Continued

53

Mineral

Treinolite, CaMg3 (Si03) 4 - ___ --- _ -- _ ---- _ - ____ -

Turgite, 2Fe2 03 .H2 0_ ___ ._..........___ _ ----- _ - ....

Wad, mixtures of oxides, chiefly of manganese, with water____

Wolframite (Fe,Mn)W04 __ ----_____-____---------._---_-

Zircon, ZrSi04 __-_-__-_...-.---------------_--__--._._---

Zoisite, HCa2Al3 (Si04)3 __ ____.___.__-_-_-___-_.-__-______

Hypogene

Regional 

metamorphism

X

X 

X

Igneous 

rocks

X

Contact 

metamorphism

X

High-temperature 

deposits

Moderatetemperature 

deposits

X

X

Supergene

Sulphide 

zone

Oxidized 

zone

X 

X

MINERALS OF THE ORE DEPOSITS

Alabandite. Alabandite has been found in the Queen of the 

West mine at the head of Peru Creek, a short distance northnorthwest of Argentine Pass. 5 It occurred in a vein from 1 to 

6 inches wide, and small amounts of dolomite, pyrite, and rhodochrosite were associated with it. The rhodochrosite occurred 

in small crystals lining vugs in the alabandite. The mineral 

had perfect cubic cleavage and strongly resembled galena except 

in color and the readiness with which it tarnished when exposed 

to the air. A single crystal showed the cube and tetragonal 

trisoctahedron.

Ankerile. Ankerite is a common gangue mineral in many 

of the galena-sphalerite veins. Much of it contains manganese 

and weathers black at the surface. Carbonates of calcium, 

iron, magnesium, and manganese form an isomorphous 

series, and although the pure carbonates containing only one 

base are sometimes found, in most places the gangue is an ankerite containing several base-forming elements. Iron is an 

abundant constituent of most of the ankerite, and much of the 

carbonate could be properly called an impure siderite. The 

ankerite is light pinkish brown and occurs in compact crystalline aggregates which show curved cleavage faces. Much of 

the ankerite is later than the sulphides and encrusts them or 

lines vugs in the ore. In many places late ankerite occurs in 

veinlets ramifying through the sulphides in branching masses. 

In some veins the ankerite becomes more abundant near the bottom of an ore shoot and may be earlier than the ore minerals. 

The porphyries near lead-zinc veins are partly replaced by ankerite, and in some places noteworthy amounts of ankerite have 

been introduced into the walls of the veins.

Argentile. Argentite is reported from many veins and has 

been observed in some of the silver ores in the north end of 

Glacier Mountain. Here it is closely associated with galena, 

miargyrite, and pyrargyrite, all of which seem contemporaneous. 

It is found in a gangue of manganiferous ankerite. Argentite 

is not a common silver mineral in the ores of the Montezuma 

quadrangle, however.

Arsenopyrile. Arsenopyrite was observed in the barren 

quartz between the two ore shoots cut by the fifth level of the 

Silver AVave mine. It seemed to be contemporaneous with the 

quartz and with a small amount of pyrite, and all are believed 

to be earlier than the main period of sulphide mineralization. 

The arsenopyrite occurred in small irregular grains disseminated 

through the quartz.

Azurite. Azurite is an uncommon secondary copper mineral 

found near the surface of some of the cupriferous lead-zinc ore 

bodies. It usually occurs in thin coatings on the free surfaces 

of fractured country rock, and not in contact with other ore 

minerals.

Barite. Barite is an abundant gangue mineral of the leadzinc ores, especially those that contain gray copper. Some 

barite is found as a late mineral in the veins, but most of the

« Smith, W. B., Mineral notes: Colorado Sci. Soc. Proc., vol. 2, p. 168, 1887.

barite is earlier than the sulphides or contemporaneous with 

them. Large bladed crystals of barite are conspicuous in the 

veins of Glacier Mountain, Teller Mountain, and Hall Valley, 

and some barite is also found in the veins on Revenue Mountain, 

on the east slope of Collier Mountain, and on the east slope of 

McClellan Mountain, where it is associated with fluorite. 

In most of the veins it is unevenly distributed and may occur 

as solid masses completely filling the vein or in a loose opentextured mass with many other minerals. Quartz is almost 

universally associated with barite, in part contemporaneous 

and in part later. Handsome specimens of coarse barite encrusted with quartz, sphalerite, and galena are found at the 

Sts. John mine, although at this place barite was deposited 

almost throughout the period of sulphide mineralization. Late 

barite, which may be supergene, is reported by Ransome 0 and 

Spurr 7 from veins near the Montezuma quadrangle, but none 

was observed by the writer. Some barite occurs in the Montezuma quartz monzonite porphyry remote from known veins 

and is comparatively late, but as it is interstitial between 

quartz and orthoclase, it is believed to be an accessory igneous 

mineral.

Beegerite. Beegerite was first described in 1881 by Koenig, 8 

who used material from the Baltic lode, Revenue Mountain, 

near the head of West Geneva Creek. The beegerite occurred 

in small well-defined isometric crystals and as a massive lightgray mineral intergrown with quartz. Its specific gravity 

was 7.273. It contained no silver, although it was probably 

associated with silver minerals, as the Baltic vein produced silver 

ore. The analyses of four samples of the beegerite from this 

vein are given below.

Bi __ -_ -_ 

Cu...... ........................

Pb.. ...... _ . ____ -. . .

S................................

20.59

64.59

15.71

100.89

1.70

64.07

14.23

64.60 63.66

Bismite. Bismite is found in the oxidized zone of bismuthsilver ores, where its bright color makes it conspicuous and has 

caused it to be called the "canary-yellow" by the miners. 

The principal occurrence known is at the Missouri mine, in Hall 

Valley, where it formed a noteworthy part of the ore for many 

years. It was related to a fault that permitted deep circulation 

of ground water and occurred to a depth of 200 feet from the 

present glaciated surface of the valley. It was associated with 

bismutite and a little malachite. The primary bismuth minerals oxidized more readily than chalcopyrite, however, and 

bismutite and bismite were found in ores containing chalcopyrite 

that looked fresh and unaltered, although no bismuthinite nor 

emplectite was present. They had probably been completely 

oxidized.

 Eansome, F. L., op. cit. (Prof. Paper 75), p. 91.

i Spurr, J. E., op. cit. (Prof. Paper 63), pp. 257-263.

s Koenig, O. A., Beegerite, a new mineral: Am. Chein. Jour., vol. 2, p. 379,1881.
MONTEZUMA QUADRANGLE, COLORADO

Bismuthinite. The primary bismuth mineral bismuthinite 

occurs in the bismuth-silver veins in the south half of the 

quadrangle. It is associated with quartz, pyrite, chalcopyrite, 

and the silver bismuthides emplectite and schapbachite. It is 

generally found in fine-grained shining lead-gray specks disseminated through quartz, in which small grains of pyrite are 

moderately abundant.

Bismutite. Bismutite, the white secondary oxide of bismuth, 

occurs in the oxidized parts of bismuth-silver veins, and its 

general relations are those of bismite.

Calamine. Calamine is not common in the ores of the 

Montezuma quadrangle but has been observed near the surface 

in a few veins. It occurs in thin white or colorless crystals in 

open spaces in oxidized ore. Some of the crystals are chiselshaped, and others are so thin that they resemble short pieces 

of glass .thread. The calamine is commonly associated with 

brown iron oxides and is found in small vugs in zinc ore which 

has been partly replaced by smithsonite. It is always a product 

of weathering.

Calcite. Calcite is most common'in late supergene veinlets 

that cut the ores not far from the surface. It is also found in 

late hypogene veinlets or in well-formed crystals in vugs. It. 

is not abundant, however, and much of the material that 

resembles calcite is pale ankerite. The ground waters of the 

region are heavily charged with carbon dioxide and dissolve a 

large amount of calcium carbonate, which is deposited as a 

smooth crust where the waters are tapped by underground 

openings.

Bromyrite. Bromyrite is reported from the oxidized zone of 

some of the rich silver veins, such as the Baker mine, but none 

was observed by the writer.

Brown iron oxides. Hydrous oxides of iron are most abundant 

in the bog iron ores of West Geneva Creek, Handcart Gulch, 

Hall Valley, and the Snake River. These ores consist chiefly of 

the brown and yellow hydrous oxides, limonite and goethite, but 

some of the red hydrous oxide, turgite, is also present. Turgite 

is more common as a stain on the outcrops of veins than in 

the bog iron, however, and is associated with limonite and 

goethite in the oxidized parts of veins. An analysis of the bog 

iron ores is given on page 25.

Cerusite. Cerusite is the common secondary lead mineral of 

the veins and is found near the surface. It is generally associated with galena at the outcrops of the veins, as the ore is 

rarely so thoroughly oxidized that all the galena is gone. In 

many ores the galena is apparently altering directly to cerusite 

without an intermediate border of anglesite being present. It is 

difficult, however, to give a plausible reaction by which the 

sulphide could be converted directly into carbonate, and it is 

probable that the galena oxidized to sulphate, which was so 

readily converted into carbonate that little or none of it remains. 

Cerusite occurs in small open spaces in the veins to a depth of at 

least 200 feet and is commonly found in well-formed crystals 

from 2 to 10 millimeters long.

Chalcanthite. Chalcanthite has been reported from the upper 

parts of several of the cupriferous lead-zinc veins of the quadrangle and is said to have been very abundant in the upper part 

of the Pennsylvania mine. It is not uncommon on the sides 

of drifts beneath old stopes in moderately dry mines. Wellcrystallized Chalcanthite forms coatings from 0.1 to 2 centimeters thick on the walls of the fifth level of the Silver Wave 

mine.

Chalcedony. Chalcedony is rare in the Montezuma quadrangle. Extremely fine grained quartz, probably in part 

chalcedonic, is found in some of the thoroughly silicified dikes 

in the northeastern part of the porphyry belt, and some of the 

silicified shale near the large stocks of quartz monzonite porphyry is probably replaced by chalcedony. None has been 

observed in the veins of the quadrangle.

Chalcocite. Chalcocite is not abundant but has been observed in many ores close to the surface. It has replaced both 

chalcopyrite and galena, and in every eccurrence studied it is 

clearly supergene. It probably was a common mineral in the 

enriched surface ores that were eagerly sought and mined 50 

years ago. The typical relations of chalcocite to galena and 

chalcopyrite are shown in plate 13, A.

Chalcopyrite. Chalcopyrite is the most abundant copper 

mineral found in the Montezuma quadrangle. It is present as 

minute blebs and blades in nearly all the sphalerite. (See pi. 

13, B.) It also occurs as distinct masses which vein and 

replace pyrite. Most of the chalcopyrite is massive and rarely 

shows crystal faces, but in some of the veins, such as the 

Waldorf, it is found in well-crystallized tetragonal sphenoids in 

open vuggy ore. Two or more generations of chalcopyrite are 

present in many veins. Much of the early chalcopyrite is 

earlier than galena and sphalerite, but some seems to be contemporaneous. This early chalcopyrite is medium- or coarsegrained (pi. 14, A), and in many polished specimens it shows 

twinning bands in polarized light. The later chalcopyrite is 

fine-grained and untwinned. Small flakes of gold are sometimes found in the early chalcopyrite but are not invariably 

associated with it.

Chrysocolla. Chrysocolla is not common but is sometimes 

found in the upper parts of veins associated with limonite.

Copper. Native copper has been reported from many of the 

veins in the district but has not been observed by the writer in 

any of the ores. Near the southern breast of the drift on level 

F in the Pennsylvania mine, however, acid mine waters were 

attacking iron rails in 1929 and replacing them with spongy 

native copper. (See p. 93.) An- interesting occurrence is 

reported from Handcart Gulch, where copper is said to have 

been washed out of the boggy alluvium bordering the stream 

by placer miners, who believed it to be a "red gold." Its 

occurrence here is probably explained by the reducing action 

of organic matter in the boggy alluvium. The water of the 

creek contains a large amount of iron sulphate, and it is probable that a small amount of copper is .also carried in solution. 

The occurrence and geologic setting are similar to those of the 

bog copper ores of Cooke, Mont., which have been studied by 

the writer. 9

Covellile. Covellite is rare in the veins of the Montezuma 

quadrangle but is found with chalcocite in some of the cupriferous lead-zinc veins. Like the chalcocite, it occurs in small 

veinlets cutting and replacing both galena and chalcopyrite.

Cuprobismutite and emplectite. Cuprobismutite is found 

in the rich bismuth-silver veins in the southern part of the 

quadrangle. It occurs massive, disseminated through the 

pyritized quartz of the veins, and in shining steel-gray needle- 

'like crystals projecting into open spaces in the quartz with 

which it is always associated. Three analyses of Cuprobismutite 

made by Hillebrand 10 in 1883 and one of emplectite are given 

below.

Bi_.-_____________.____________._

Ag. ... .... cu.-._._____.:_:_:._.._::__.._..

Ph.... . . ..... ..... .__...«

Fe. _ -.-.-...-.. ... i 

Zn... _ . _ ....................

S .-_-.-._ _._______.__.._ -

Cuprobismutite

1

60.80 

.89 

15.96

2.13 

.10 

"19. 94

99.82

2

63.42 

4.09 

12.65

.59 

.07 

"18. 83

99.65

3

62.51 

9.89 

6.68 

2.74 

.10 

.07 

17.90

99.89

Emplectite

- 62. 16

18.72

18.83

99. 71

° Calculated by Hillebrand.

» Lovering, T. S., The organic precipitation of metallic copper: U.S. Oeol. Survey 

Bull. 795, pp. 45-52, 1923; The New World or Cook City mining district, Park 

County, Mont.: U.S. Geol. Survey Bull. 811, pp. 85, 86, 1929.

10 Hillebrand, W. F., On an interesting variety of lollingite and other minerals: 

Colorado Sci. Soc. Proc., vol. 1, pp. 53-55, 1884.
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 178 PLATE 13

A. PHOTOMICROGRAPH OK ORE KROM LEVEL 3, SANTIAGO MINE. 

From gob 800 feet from portal. Illustrates the common relations of chalcocilc (c), galena (g), and chalcopyrilc (cli). p, Pyrile; q, quartz.

B. PHOTOMICROGRAPH OF ZINC ORE 100 FEET ABOVE MAIN TUNNEL LEVEL, STEVENS MINE.

Showing intergrowth of chalcopyrite (white) and sphalerite (light gray).
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 178 PLATE 14

A. PHOTOMICROGRAPH OF ORE FROM DUMP OF STAR OF THE WEST NO. 2 MINE, TELLER MOUNTAIN. 

Graphic intcrgrowth of quartz (dark gray) and chalcopyritc (light gray). The quartz is replacing the chalcopyrite but is earlier than galena.

B. PHOTOMICROGRAPH OF SILVER ORE FROM LOWER JERRY TUNNEL. 

From vein trending N. 30° E., 320 feet from the portal. Miargyrite (m) replacing twinned pyrargyrite (p). Crossed nicols.
MINERALOGY 55

As a small amount of admixed chalcopyrite and sphalerite 

was present in the material analyzed, in spite of very careful 

sorting, the iron present was calculated as chalcopyrite and 

the zinc as sphalerite by Hillebrand, who then calculated the 

formula of the cuprobismutite from the first three analyses. 

It is 3RS,4Bi2S3, where R represents Pb and the double atoms 

Ag2 and Cu2. He concluded that "the needles are a pure 

sulphobismuthite of copper, and that in the more compact 

portions of the massive ore silver replaces a portion of the 

copper, while in some cases a further replacement of copper by 

lead takes place." The material for analysis 1 came from the 

Missouri mine, Hall Valley, and occurred as slender, deeply 

striated needles in open spaces in the ore, where it was associated with chalcopyrite and wolframite in a quartz gangue. 

Its specific gravity is about 6.31. The material for analysis 2 

also came from the Missouri mine and was a dark bluish gray 

substance without distinct crystal form, intergrown with 

quartz and a small amount of chalcopyrite. The material for 

analysis 3 came from Hall Valley and is doubtfully referred to 

the Missouri mine. It is similar in appearance to the material 

used in analysis 2, except that no chalcopyrite could be seen in 

it. Its specific gravity was approximately 6.68. As the 

material was not examined in polished section, it is possible 

that the compact material was an intergrowth of argentite, 

chalcopyrite, galena, and cuprobismutite or bismuthinite, 

similar to the intergrowths of bismuthinite, galena, and argentite that Loughlin u found in the Leadville district. The 

cuprobismutite is very similar in composition to emplectite, 

and the material gathered in the Missouri mine is the only 

known occurrence of cuprobismutite. Short believes that the 

two minerals are identical. 12 An .-analysis of emplectite from 

Tannonbaum, taken from Dana's "System of mineralogy", is 

given for comparison in the table.

Dolomite. Pure dolomite is not common in this quadrangle, 

although the impure forms which have been considered under 

ankerite are abundant. Dolomite occurs in well-formed saddleshaped crystals in vugs in some of the veins, and in most places 

it was formed after the sulphide mineralization was complete.

Enargite. Enargite was not observed by the writer but is 

reported to have been present in some of the ores found in the 

Missouri mine in the early eighties. 13 It occurred as small 

blades in a quartz gangue and was associated with tetrahedrite, 

chalcopyrite, and a bismuth mineral.

Epidote. Epidote is a common constituent of altered rocks 

in the Montezuma quadrangle. It has been formed by contact 

metamorphism in calcareous sediments near quartz monzonite 

porphyry stocks and is a common microscopic constituent of the 

altered porphyries. (See pp. 42-43, 59.)

Epsomite. Epsomite is a common mineral in moderately dry 

mines that have been abandoned for several years. It occurs 

in thick incrustations on the sides of drifts, generally beneath 

stopes in veins having an ankerite gangue. It forms in needlelike crystals which are commonly perpendicular or at a high 

angle to the walls. The crystals are white, and some reach a 

length of an inch. Epsomite is associated with goslarite in 

most places.

Fluorite. Fluorite is a rare gangue mineral except on McClellan Mountain, where it is moderately abundant, and is associated with barite and ankerite.

Freibergite. Freibergite was found about 1,200 feet below 

the surface in a vein striking north-northeast in the Toledo 

tunnel. It is probably contemporaneous with a late generation 

of chalcopyrite, and both minerals are distinctly later than

'i Loughlin, O. F., op. cit. (Prof. Paper 148), pp. 170-171.

11 Short, M. N., Microscopic determination of the ore minerals: U.S. Qeol. Survey 

Bull. 825, p. 104, 1931.

13 Cross, Whitman, A list of specially noteworthy minerals of Colorado: Colorado 

Bci. Soc. Proc., vol. 1, p. 137, 1884.

71880 35 5

galena and sphalerite. The vein has a quartz-ankerite gangue. 

The freibergite and chalcopyrite are regarded as primary.

Galena. Galena most commonly occurs in medium-grained 

anhedral masses but in some places well-shaped crystals are 

abundant. Rarely do individual crystals measure more than 

a centimeter in diameter, but in some veins coarse cube galena 

as much as 5 centimeters across has been found. The wellshaped crystals always occur in open-textured ore and generally 

line vugs, and in many places they are associated with good 

crystals of sphalerite, chalcopyrite, and ankerite. Most of the 

galena in the quadrangle is intergrown with other sulphide 

minerals, but in some places moderately large masses occur that 

are nearly free from the other base-metal sulphides. Galena 

is generally associated with sphalerite, pyrite, and a small 

amount of chalcopyrite. In many places it is later than these 

minerals and cuts them in veinlets, but a large part of the galena 

was contemporaneous with sphalerite and chalcopyrite, though 

later than much of the pyrite. Galena is common in the 

oxidized zone and is present at the outcrops of many veins. 

Nodules of galena surrounded by cerusite are always found in 

the oxidized zone of the lead veins, and galena also occurs with 

the cerusite as a loose, open-textured, sandy mass. The galena 

found in the Montezuma quadrangle is believed to be primary.

The silver content of the galena is variable, and, contrary to 

the widespread belief that high-grade galena ore is good silver 

ore, the nearly pure sulphide generally contains less than 20 

ounces of silver to the ton. Some late galena is intergrown with 

silver minerals but is not much more abundant than the silver 

minerals themselves.

Steel galena has been formed by postmineral movement along 

some veins, notably the Pennsylvania vein.

Garnet. A brown garnet is abundant in the contact-metamorphosed sediments near the quartz monzonite porphyry 

stocks, and a red garnet occurs in the schists of the Idaho 

Springs formation. The brown garnet is probably the ironcalcium garnet, andradite, and occurs in granular masses associated with epidote and fine-grained quartz.

Goethite. See Brown iron oxides.

Gold. Crystalline gold was common in the upper part of 

the stockworks in the southwestern part of the quadrangle 

and in the oxidized portion of the veins on Wise Mountain. 

Several million dollars' worth of gold has been won from the 

valley of the Swan River by dredging, hydraulicking, and 

sluicing. Many of the lead-silver-zinc veins farther northeast 

contain moderate amounts of gold, but visible free gold is rare. 

In most of these veins the gold is associated with chalcopyrite 

and occurs as small grains in chalcopyrite that was formed later 

than pyrite and is nearly contemporaneous with galena and 

sphalerite. Some rich oxidized gold ore is reported to occur in 

the Star of the West mine, on Teller Mountain, but like the ore 

on Wise Mountain, the vein did not prove profitable far below 

the outcrop. Primary gold is a constituent of most of the bismuth-silver ores, where it is probably related to the moderately 

abundant chalcopyrite.

Goslarite. Goslarite is formed by the leaching of zinc ores 

after they have been opened by mine workings and has the same 

mode of occurrence as epsomite.

Graphite. Fine-grained flakes of graphite are abundant in 

the contact-metamorphosed shales at the west end of the 

porphyritic Montezuma quartz monzonite stock but can be 

seen only with a microscope.

Gray copper. Tetrahedrite and tennantite cannot be distinguished in the field, and both are abundant. They have not 

been found together by the writer, though it is probable that 

both are present in some ores. The tetrahedrite is generally 

later than the coarse-grained early chalcopyrite and is commonly later than sphalerite and galena, although in some specimens it appears to be contemporaneous witli them. It is
56 MONTEZTJMA QUADRANGLE, COLORADO

earlier than the fine grained late chalcopyrite and is also earlier 

than covellite and chalcocite. All the tennantite observed was 

definitely a late sulphide. The relations of the tetrahedrite 

suggest that it was formed slightly earlier in the period of mineralization than tennantite. Gray copper is most commonly 

found in the quartz-barite ores, where it occurs in small irregular 

masses that are later than the barite and quartz. These ores 

usually contain silver, some of which is probably present in the 

molecules of the gray copper minerals. Apparently pure specimens of dark-colored gray copper from Hall Valley are said to 

assay 100 ounces of silver to the ton, but assays of light-colored 

gray copper from the head of West Geneva Creek are reported 

to show much more silver.

Gypsum. Gypsum is a secondary mineral that is formed by 

the action on calcareous rocks of sulphuric acid from decaying 

pyrite. It occurs in fractures in the black Cretaceous shales 

near pyritic ores.

Hematite. Hematite occurs in contact-metamorphosed sediments near the quartz monzonite porphyry stock in the southwestern part of the quadrangle. It is associated with garnet, 

epidote, fine-grained quartz, magnetite, and some tremolite, 

pyrite, and chalcopyrite.

llesite. Ilesite was first found in Hall Valley, where it 

occurred as an efflorescence on the outcrop of the McDonnell 

vein, and in the oxidized parts of other veins very close to the 

surface. The material when fresh, according to Cross, 14 is a 

light transparent green and resembles melanterite, but after it 

has been exposed to the light and air for some time it loses some 

of its contained water and becomes white. Its specific gravity 

is 2.16, and its formula as calculated by lies is FeSO4.ZnS04. 

5MnSO4.28H2 0, but Cross suggests that the material analyzed 

had probably lost some water and would need several molecules 

of water added to the formula given above if it were to correspond to the mineral as found in nature.

Jarosite. Jarosite has been found in the oxidized ores west 

of Tiger, in the southwestern part of the quadrangle, but is not 

common. It is a fine-grained yellowish-brown mineral having a 

silky luster that distinguishes it from the limonite and jaspery 

quartz with which it is associated.

Kaolin and the clay minerals. Kaolin and the other-clays are 

not common gangue minerals, and wherever found their relations to the surface and to the other vein minerals indicate that 

they are supergene. Clay minerals are common in the fault 

gouges and in the upper parts of veins where the wall rocks 

have been attacked by surface water containing acids from the 

decaying sulphides. Some of the clayey filling of the veins 

close to the surface carried silver and gold in notable amounts. 

It is always more or less stained with limonite and ranges from 

a cream-color to deep reddish brown.

Limonite. See Brown iron oxides.

Magnetite. Magnetite is a common accessory constituent of 

all the intrusive rocks of the quadrangle and is locally abundant 

in coarse-grained aggregates in some of the pegmatites of the 

southeast quarter. It also occurs in the contact-metamorphic 

ores in the southwestern part of the quadrangle, where it is 

associated with garnet, epidote, fine-grained quartz, tremolite, 

and hematite.

Malachite. Malachite is conspicuous but not abundant in 

the upper parts of the cupriferous lodes. It occurs chiefly as 

thin crusts on the outcrops of the veins and to a less extent in 

small veinlets cutting the oxidized ore.

Manganosiderite. Manganosiderite is locally abundant in 

the mines on Glacier Mountain. It is found in the lower levels 

of the Wild Irishman vein and apparently gives way to quartz 

and barite in the upper levels. Galena is the chief sulphide 

associated with it, -but both sphalerite and pyrite are also present.

14 Cross, Whitman, A list of specially noteworthy minerals of Colorado: Colorado 

Sci. Soc. Proc., vol. 1, pp. 140-141, 1885.

Marmatite. The dark iron-bearing zinc sulphide, marmatite, 

is abundant in the mines in the Breckenridge district a mile 

south of the southwestern part of the quadrangle. It also 

occurs in many of the veins in the quadrangle, but most of the 

zinc is moderately light colored sphalerite. The marmatite is 

associated with pyrite, galena, and chalcopyrite. It occurs in 

medium-grained masses which are later than the pyrite and 

either contemporaneous or earlier than the galena. Chalcopyrite is intergrown with the marmatite in small blebs and 

blades, as .shown in plate 13, B. The grains of marmatite do 

not have crystal faces except where they project into open 

spaces in the ore. Most of the grains are less than 3 millimeters 

in diameter and are generally smaller than the pyrite and galena 

with which they are associated.

Melanterite.-^-Melanterite is not uncommon in old drifts in 

moderately dry mines, where it forms by evaporation of the 

sulphate waters that descend through the vein. It forms lightgreen crusts and stalactites beneath old stopes in the sulphide 

zone. None has been observed at the surface, but it probably 

occurs in the oxidized portion of many veins.

Miargyrite. Miargyrite is one of the most abundant silver 

minerals in the quadrangle. It is everywhere associated with 

pyrargyrite, with which it is intergrown. It is present in most 

but not all of the ruby-silver ores. Miargyrite, like the 

other ruby-silver minerals, is later than most of the pyrite, 

galena, and sphalerite but is contemporaneous with a late 

generation of galena and chalcopyrite. A typical intergrowth 

of miargyrite arid pyrargyrite is shown in plate 14, B. 

Manganifefous ankerito is generally associated with the rubysilver minerals.

Molybdenite. Molybdenite is rare but was observed in a 

quartz vein on the crest of Glacier Mountain a few hundred 

feet east of the Tiger vein. It has also been found in small 

sporadic masses in the Montezuma quartz monzonite stock, 

apparently unrelated to definite veins.

Pearcite. Pearcite was found in the ore on the dump of the 

Star of the West No. 2, on the west side of Teller Mountain. 

It occurs as small blebs scattered through galena. Quartz and 

tennantite, replacing chalcopyrite, are associated with the 

galena and pearcite. The minerals are probably primary.

Proustite. Proustite is a common mineral of the ruby-silver 

ores but is less abundant than pyrargyrite and miargyrite. 

It is generally associated and contemporaneous with pyrargyrite, 

argentite, and late quartz. It is later than siderite and the 

bulk of the galena and sphalerite. Van Horn 15 describes an 

interesting occurrence of proustite in the Bell mine, near 

Montezuma, where all these relations could be ascertained. 

Argentite and proustite were found for 30 feet along the strike 

of the vein and for 25 feet along its dip. The vein was about 

21 inches wide, and bands of different minerals were symmetrically arranged about a central seam of contemporaneous 

argentite, pyrargyrite, proustite, and quartz. These minerals 

were flanked by layers of siderite (manganiferous ankerite?), 

and the siderite by layers of mixed galena and sphalerite. This 

vein structure shows the same relations of the base-metal 

sulphides, the carbonate gangue minerals, and the rich silver 

minerals as those found in a study of the relations of the various 

minerals in thin section and polished section. Sphalerite and 

galena are clearly earlier than the ankerite, and the ankerite is 

earlier than the silver minerals.

Psilomelane. See Wad.

Pyrargyrite. Pyrargyrite is a common silver mineral and is 

present in most of the ruby-silver ores. It is almost everywhere 

intergrown with miargyrite, forming mutual boundary structures at the edges of small grains. An example of this intergrowth is shown in plate 14, B. The ruby-silver ores are genis Van Horn, F. R., Occurrence of proustite and argentite at the California mine 

near Montezuma, Colo.: Qeol. Soc. America Bull., vol. 19, pp. 93-98, 1908.
MINERALOGY 57

Orally intergrown with quartz, late galena, and chalcopyrite in 

dark fine-grained masses.

Pyrite. Pyrite is the most abundant sulphide mineral in the 

Montezuma quadrangle. It occurs disseminated through 

altered porphyries and the country rocks of the veins; it is 

present in the contact-metamorphic deposits near the large 

stocks; it is abundant in the sericitized rocks of the stockworks in 

the southwestern part of the quadrangle; and it is the most 

common mineral of the veins. Unlike galena and sphalerite, 

most of the pyrite occurs in grains showmg distinct crystal 

outlines, although massive pyrite is not uncommon. It is 

present in most of the veins but is not uniformly distributed 

through them, and some bodies of galena and sphalerite ore 

are almost free from it. In other veins, such as those near 

Swandyke, quartz and pyrite are almost the only minerals 

tl»at can be seen. Most of the pyrite is earlier than the other 

sulphides, but a small amount of late pyrite is present in many 

places. It is certain that most of the pyrite is primary, but some 

of the late pyrite may have been formed by descending ground 

water. The pyrite of the Montezuma quadrangle is rarely 

auriferous unless chalcopyrite is also present, and the general 

effect of pyrite is to lower the grade of an ore.

Most of the pyrite has been formed by the introduction of 

both iron and sulphur, but it is probable that much of the pyrite 

disseminated through the porphyries of the region has formed 

at the expense of the original magnetite and the ferromagnesian 

minerals of the rock, by the introduction of sulphur alone.

Pyrolusite. See Wad.

Quartz. Quartz is the most abundant gangue mineral of the 

ore deposits. Near the west end of the Montezuma quartz 

nionzonite stock a great mass of the Pierre shale has been 

silicificd and now consists of very fine grained dark quartz and 

a meager sprinkling of contact-metamorphic minerals. In 

some places clear crystals of quartz, occur in openings in the 

hornstone and are evidently later than the first intense silicification. The early quartz of the veins, however, is moderately 

coarse grained and is cut in many places by a later generation of 

fine-grained quartz which was contemporaneous with the deposition of the sulphides. Fine-grained veinlets later than the 

ore minerals are present in most of the ores (pi. 14, A), and some 

of them may be supergene. Much of the hypogene quartz 

contains many minute fluid and solid inclusions, but the abundance of these inclusions varies greatly in different veins and 

even in different parts of the same vein. The quartz most 

commonly occurs as interlocking anhedral or subhedral grains 

having poorly formed crystal faces, though in some of the ores 

most commonly those containing barite a large amount of 

clear, glassy quartz is present in prismatic crystals from 2 to 8 

millimeters in diameter. Most of the vein quartz is free from 

strain effects, but some in the Sts. John mine shows an unusual 

border having strain shadows but grading into a clear central 

grain core. These strain effects probably are the result of 

movement of the vein walls during mineralization.

Although the amount of silicification in the contact-metamorphosed shales is impressive and quartz is the most abundant 

gangue mineral of the ore deposits, many of the veins consist 

largely of sulphides and contain very little gangue. Quartz is 

relatively more abundant in the low-grade pyritic veins and in 

the quartz-barite veins than in the other deposits.

Rhodochrosite. Pure rhodochrosite is rare, but some of the 

ankerite contains so much manganese that it may be called 

impure rhodochrosite. Moderately pure rhodochrosite occurs 

in coarse-grained masses several inche's thick in the Jerry tunnel, 

at the north end of Glacier Mountain. It is associated with 

pyrargyrite, miargyrite, and argentite but is earlier. Rhodochrosite is reported to be present in the Queen of the West 

mine, near the head of Peru Creek, where it occurs in vugs 

iu alabandite.

Schapbachite. Schapbachite may be present in the bismuth 

ores found in the Grand Trunk and nearby veins, at the head 

of West Geneva Creek, as an analysis of the ore is reported to 

be very nearly that of schapbachite. (See p. 79.) None of the 

bismuth ores from this part of the quadrangle have been seen 

by the writer, however, and the reported occurrence could not 

be verified.

Sericite. Sericite is abundant in the walls of most of the 

veins and is intergrown with the quartz of many veins. It is 

also abundant in some gouges, where it may be due to the brecciation of sericitized wall rocks or to the sericitization of a clay 

gouge. Sericite is an early mineral and was formed at about the 

same time as the early quartz. Where sericite is abundant 

it is generally related to channels of mineralization, but in 

many rocks, especially porphyries, scanty sericite is found 

some distance from any known occurrence of ore.

Siderite. Siderite, like the other simple carbonates, is rare, 

although iron-rich ankerite is very common. As the iron content of the ankerite increases it grades through impure 

siderite into siderite. Most of the sideritic gangues contain 

some manganese and weather black when exposed on the 

dumps of the mine for a few years. Siderite is generally later 

than the sulphides, but in some places it is contemporaneous 

with them; it occurs in well-formed crystals and in open-textured granular masses in the veins. Some of the wall rock may 

be replaced by siderite, but most of the carbonate that has replaced the wall rocks is ankerite.

Silver. Native silver is moderately abundant in the rich 

silver ores found near Montezuma, but if native silver has been 

found in other parts of the quadrangle the writer has not learned 

of it. In many of the mines on Glacier Mountain wire silver 

occurs in vugs and is scattered through moderately open textured galena-sphalerite ore that is cut by thin crustified veinlets 

of pink manganiferous ankerite. Wires of silver from 1 to 4 

millimeters long occur on the galena, sphalerite, and ankerite. 

In some places the wires are scattered sparingly through the ore, 

and in others they occur in compact nests.

Smithsonite. Thin brownish crusts of smithsonite are sometimes found in the open vuggy ore of the oxidized zone, 

but secondary zinc minerals are rare in the Montezuma 

quadrangle. 

Sphalerite. Sphalerite is a common mineral in almost all 

the ore deposits in the quadrangle and is the most abundant 

sulphide in many of the ores. It generally occurs in mediumgrained masses intergrown with pyrite and galena. It rarely 

shows good crystal forms unless it occurs in vuggy ore, but opentextured ores are not uncommon in the quartz-barite veins and 

in the leaner parts of other veins. Most of the sphalerite in the 

mines near Montezuma is moderately light colored, and some of 

it is a clear amber-yellow. This light-colored sphalerite is later 

than the early pyrite and quartz and in most places is contemporaneous with galena or slightly later. Like the other sulphides 

it is generally earlier than the carbonate gangue with which it is 

associated in many places. It is everywhere earlier than the 

silver minerals. In the northeastern part of the quadrangle 

dark-colored sphalerite is more common than the light-colored 

variety and has the same relations to the other minerals. In 

some masses of dark-colored sphalerite there are small amounts 

of light-colored sphalerite that appear to be later than .the dark 

variety. There is no reason for believing that the abundant 

light-colored sphalerite near Montezuma is later than the dark 

sphalerite found on McClellan Mountain, however, and the 

difference in color is probably due to a local difference in the iron 

content of the ore solutions during mineralization. In many 

places in the southwestern part of the quadrangle dark-colored 

sphalerite is associated with gold ores, but in the region northeast of the stockworks such an association is rare and probably 

fortuitous where it is found.
58 MONTEZUMA QUADRANGLE, COLORADO

Stephanite. Stephanite is found in some of the ruby-silver 

ores near Montezuma but is rare in the ores examined by the 

writer. Stephanite or "brittle silver" is frequently mentioned 

in mining reports published before 1900, but its identification 

is not known to have been carefully made, and doubt exists 

regarding the identity of the mineral called brittle silver by the 

miners.

Stromeyerite. Stromeyerite is reported to be the chief mineral 

in the rich silver veins on Lenawee Mountain, near the center 

of the Montezuma quartz monzonite stock. An.analysis of 

some ore from the Winning Card vein (see p. 114), quoted by 

the Montezuma Mill Run, shows a larger proportion of copper 

to silver than is present in Stromeyerite, but it is probable that 

the ore contained more than one sulphide, and some unobserved 

chalcopyrite may have increased the total copper content of 

the specimen analyzed. In the Santiago mine Stromeyerite 

is present in sphalerite-chalcopyrite ore on the fifth level. It is 

contemporaneous with a small amount of late galena and quartz, 

the three minerals occurring in small veinlets that cut early 

chalcopyrite; all are believed to be hypogene.

Sulphur. Sulphur is sometimes found in the oxidized zone 

of lead-zinc deposits, where it commonly occurs mixed with 

earthy masses of cerusite and anglesite.

NW.

FIGURE 6. Center of vein in slope on vein 5, Sts. John mine, 700 feet from main 

crosscut, level 6.

Tennantite. See Gray copper.

Tetrahedrite. See Gray copper.

Twr0$e, See Brown iron oxides.

Wad, The outcrops of many veins are blackened by a 

mixture of manganese oxides. Both pyrolusite and psilomelane 

have been seen, and it is probable that other oxides are also 

present. These oxides form fine-grained intergrowths and occur 

in moderately hard mammillary crusts close to the surface and 

commonly result from the oxidation of manganiferous ankerite 

or manganosiderite. Much of the secondary manganese occurs 

as a soft black sooty coat that covers the outcrop of the manganiferous veins. This is typical wad and consists of an indefinite 

mixture of the secondary oxides of manganese and other material.

Wolframite. Wolframite was identified by Cross in the 

bismuth ores of the Missouri mine, in Hall Valley, where it 

made up as much as 2 percent of the ores. It occurred in small 

crystals intergrown with quartz and cuprobismutite.

PARAGENESIS

Although mineralization may not have taken place 

throughout the quadrangle at precisely the same time, 

a study of ores from many different deposits suggests 

that all were approximately contemporaneous and 

had very similar sources. The veins as a group show 

an orderly sequence of events, though all the events

may not be recorded in a particular deposit. The relations of the minerals show that the ores were not 

injected into the veins but were deposited from solutions that moved upward through the most easily 

available channels for a considerable length of time.

Sericite, quartz, and pyrite are the earliest minerals 

directly related to the ore solutions. Some of the 

quartz and sericite formed almost in place by molecular 

rearrangement of the original constituents of the rocks, 

and much of the fine-grained early pyrite resulted from 

the addition of sulphur to the iron already present in 

magnetite or some ferromagnesian mineral, such as 

hornblende. Near major channels of mineralization, 

however, solutions rich in iron, silica, potash, and sulphur attacked the wall rocks and added these elements. 

In such places the sericite and quartz are in part 

earlier than the pyrite and in part contemporaneous. 

The sericite is largely confined to the walls, but quartz 

and pyrite occur both as fissure fillings and disseminated in the walls. This epoch of mineralization was 

followed by an interval during which movement occurred along many veins, resulting in brecciation of the 

quartz and pyrite. At about this time calcite and 

manganosiderite were deposited in small amounts in 

a few places. During the next stage of mineralization 

moderately coarse grained chalcopyrite was deposited 

in many veins, and at some places gold is associated 

with it. Much of this chalcopyrite is twinned, whereas 

the later chalcopyrite is finer-grained and untwinned. 

A little sphalerite is contemporaneous with the early 

chalcopyrite, but most of it is later. A large part of 

the galena is contemporaneous with sphalerite, but 

some of it is later. It is probable that galena began to 

form in notable amounts about the time that the deposition of the early chalcopyrite ceased, and that it 

continued to be precipitated for some time after nearly 

all the sphalerite had been deposited. There was little 

movement during the chalcopyrite, galena, and sphalerite stages, but locally readjustment took place along 

the veins. The gray-copper minerals, tennantite and 

tetrahedrite, may have been contemporaneous with 

sphalerite and galena locally, but most of the gray 

copper was precipitated during and after the galena 

stage. Barite is essentially contemporaneous with 

galena and sphalerite, but its epoch of deposition was 

probably shorter than theirs. In a few places sphalerite and galena are earlier than barite, in many places 

they are later, but in most places they are probably 

contemporaneous. (See fig. 6.) A small amount of 

quartz was crystallized with the base-metal sulphides, 

chiefly at the end of the chalcopyrite stage. It is 

present in small amounts in most veins.

After the deposition of the bulk of the sphalerite, 

galena, chalcopyrite, and gray copper, ankeritic gangue 

minerals were deposited. Most of them contain 

much iron and some manganese. In many places the 

ankerite stage ended the period of mineralization, but
ORE DEPOSITS 59

locally veins were reopened and silver-bearing solutions deposited small amounts of galena, quartz, 

argontite, native silver, and the silver sulphantimonides and sulpharsenides, such as proustite, pyrargyrite, 

miai'gyrite, stephanite, freibergite, stromeyerite, and 

polybasite. It is probable that bismuth and silver 

minerals formed in a quartz gangue in the south half 

of the quadrangle at about this time, but their exact 

relations to the galena-sphalerite mineralization are in 

doubt. They may be contemporaneous with the late 

stage of quartz, which commonly followed ankerite in 

the galena-sphalerite veins, but they may be much 

earlier. Fine-grained late chalcopyrite is present in 

most of the veins, but whether it is primary or secondary is uncertain. It is later than the other primary 

sulphides but is earlier than covellite and chalcocite. 

Briefly summarized, the general order of deposition 

of the minerals is as follows: (1) Sericite, quartz, 

pyrite, calcite, manganosiderite; (2) chalcopyrite; 

(3) quartz, sphalerite; (4) barite, galena, sphalerite; 

(5) galena, gray copper; (6) ankerite, dolomite; (7) 

galena, quartz, argentite, silver, rriiargyrite, stromeyerite, pyrargyrite, freibergite, polybasite, proustite, 

stephanite, pearcite; (7?) quartz, bismuthinite, cuprobismuthinite, emplectite, schapbachite, beegerite, argon tite; (8) chalcopyrite; (9) covellite, chalcocite.

ORE DEPOSITS

The distribution of the veins of the Montezuma 

quadrangle is shown on plate 3. (See also pi. 15.) 

The relation of the veins to the mineral belt of the 

Front Range is considered briefly on pages 44 and 48, 

and the general features of the mineral belt have been 

considered elsewhere. 10 Lead-zinc-silver ores are much 

more abundant than ores of other types, but some gold 

ore occurs in the southwestern part of the quadrangle, 

and some bismuth ore is found in a narrow'belt extending north from Hall Valley to the head of West Geneva 

Creek. Most of the ore deposits are fissure fillings, 

and few ore bodies of economic importance have been 

formed by replacement. Many of the veins have a 

shallow enriched zone at the surface, but most of the 

ore now present is primary and was deposited from hot 

magmatic solutions during early Eocene time.

The ore deposits are classified according to their 

origin and mode of occurrence as contact-metamorphic 

deposits, stockworks, and veins.

CONTACT-METAMORPHIC DEPOSITS

A contact-metamorphic deposit is a high-temperature replacement deposit close to the edge of an intrusive to which it is genetically related. No deposits 

of this type in the Montezuma quadrangle are commercially important. Contact-metamorphic deposits 

occur in the southwestern part of the quadrangle be18 Lovoring, T. S., Localization of ore in the schists and gneisses of the mineral 

bolt of tho Front Range, Colp.; CpJprp<Jp Spi, Spc, Prpc., vol. 12, pp. 234-268, 1930 ,

tween Browns Gulch and Summit Gulch, and also near 

the west end of the Montezuma quartz monzonite 

stock. In both places high-temperature minerals 

have replaced Upper Cretaceous shale, of Pierre age. 

'In the southwestern part of the quadrangle the most 

abundant contact-metamorphic minerals are epidote 

and brown garnet, but dark-green amphibole, pyrite, 

chalcopyrite, and magnetite are also present. The 

shale that is most thoroughly replaced consists of a 

moderately coarse grained aggregate of the brown 

garnet-epidote-amphibole rock, and the less altered 

formation nearby is commonly a hard, cherty green 

shale. Near the Montezuma quartz monzonite stock 

large masses of the Pierre shale have been silicified, and 

in much of this hornfels fine-grained garnet and pyrite 

are visible. Layers consisting largely of mediumgrained brown garnet but containing small amounts of 

pyrite, chalcedonic quartz, tremolite, and sericite 

were observed a short distance below the Williams 

Range thrust fault about 0.1 mile north of Cold 

Spring. Epidote is locally abundant but is much less 

common than in the southwestern part of the quadrangle. Several prospect pits and tunnels have been 

put into this metamorphosed shale, and some ore has 

been found in thin veins, but no ore of contact-metamorphic origin was observed here.

STOCKWORKS

Stockworks are found only in the southwestern part 

of the quadrangle, in the region studied by Ransome. 17 

According to him, the stockworks are thoroughly 

fissured rocks, generally quartz monzonite, in which the 

ore occurs in minute veins and thin, discontinuous 

seams and not in well-defined lodes. The only deposits 

of this type in the Montezuma quadrangle are in the 

Cashier, I. X. L., and Hamilton mines. In 1929 they 

were being exploited by the Royal Tiger Mining Co. 

Although the writer was not allowed to study these 

mines or go underground in them, a considerable 

amount of information has been gathered from various 

reports and from a study of the region nearby, and it is 

believed of sufficient interest to be included in this 

report.

The I. X. L. stockwork, near Tiger, is typical of this 

group. It is a shattered mass of quartz monzonite 

porphyry crowded with fragments of the Upper Cretaceous sediments, of which Dakota quartzite is by faith e most abundant. Complexly interlacing and crossing fractures cut the porphyry and included fragments 

and served as channels for hydro thermal solutions. 

The rocks are strongly sericitized and contain sporadic 

seams and masses of ore. Sphalerite is the most abundant ore mineral and occurs chiefly in irregular-shaped 

masses less than an inch in diameter sparsely scattered 

through the bleached porphyry and quartzite. Thin 

veinlets of pyrite, chalcopyrite, and sphalerite were

" Ransoine,' F. L., op. cit, pp. 143-157,

ORE DEPOSITS 61

The veins near Clear Creek, in the northeastern part 

of the quadrangle, are probably related to the center of 

mineralization near Silver Plume, a short distance east 

of the quadrangle.

Mineral associations. Galena, sphalerite, pyrite, 

and quartz are found in nearly all the ore deposits of 

the Montezuma quadrangle and are much more abundant than the other minerals. The variations of the 

less abundant minerals, however, give certain ores a 

distinctive appearance that suggests their inclusion in 

groups by themselves. Copper minerals are the most 

abundant of the .minor constituents of the ores and 

occur in most of the veins of the quadrangle. Copper 

is usually present in negligible amounts, but in some 

places it contributes materially to the value of the ore. 

In addition to the value of the copper itself, the common association of gold and silver with chalcopyrite 

and of silver with tetrahedrite and tennantite makes 

the presence of these minerals especially welcome to 

the miners. The gray-copper minerals examined by 

the writer contain comparatively small amounts of 

combined silver, however, and most of the silver in 

these ores occurs as separate minerals, usually a silver 

sulphantimonide or silver sulpharsenide. The lightcolored gray copper contains more silver than the darkcolored gray copper, pure specimens of which are reported to assay only 100 ounces of silver to the ton. 

Copper-bearing veins containing chalcopyrite and little 

or no gray copper commonly have a quartz or ankerite 

gangue; the gangue of veins in which tetrahedrite or 

tennantite is abundant generally consists largely of 

quartz and barite with moderate amounts of manganiferous ankerite. Galena-sphalerite ores containing 

barite and gray copper, which are abundant in Hall 

Valley, Teller Mountain, and Glacier Mountain and 

on the eastern slope of McClellan Mountain, have 

heretofore been regarded unfavorably because of the 

difficulty of separating barite from them. Such ores 

can now be treated successfully by flotation, however. 

The galena-sphalerite ores containing chalcopyrite and 

having a quartz-ankerite gangue are common from the 

south end of McClellan Mountain southwest to Glacier 

Mountain and include most of the veins that have 

been successfully exploited in the past.

The most abundant silver minerals are miargyrite, 

pyrargyrite, proustite, and stromeyerite and are commonly associated with a manganiferous ankerite or 

rhodochrosite gangue. Some silver veins, such as 

those of the American Eagle and Winning Card mines, 

in the Montezuma quartz monzonite stock, contained 

little galena and sphalerite and consisted essentially of 

stromeyerite and gray copper in a quartz gangue. In 

the lead-zinc veins on Glacier Mountain, a short distance south of the stock, native silver, pyrargyrite, 

proustite, miargyrite, and argentite are the most common silver minerals, although locally freibergite, polybasite, stephanite, and pearcite- occur. The silver

minerals are later than the bulk of the lead-zinc-iron 

minerals and are not disseminated evenly through the 

galena-sphalerite ores with which they are associated. 

They are usually concentrated in rich shoots, whose 

occurrence is independent of the amount or kind of the 

earlier base-metal sulphides in the vein.

All the bismuth-silver veins found on the southeast 

or east side of the mineral belt contain silver and gold. 

Generally the silver is chemically combined with bismuth in emplectite or schapbachite. The moderately 

common occurrence of galena-sphalerite ores in the 

bismuth-silver veins toay be fortuitous, as bismuthsilver ore shoots occur alone in many places and were 

apparently formed at a different time from the leadzinc ores. Quartz, pyrite, and chalcopyrite are 

usually found in the bismuth-silver ores, less commonly 

tetrahedrite and galena, and very rarely barite and 

ankerite.

Veins of massive pyrite, or pyrite and quartz, occur 

on Wise Mountain, in the southern part of the quadrangle. Some of these veins carried rich gold ore at 

the surface, but none of them are known to contain 

commercial ore more than 25 feet below their outcrop. 

The gold and silver content of the massive unoxidized 

pyrite is reported to be uniformly less than $3 a ton. 

(See p. 75.)

The gold ores near Tiger are briefly discussed on 

pages 59-60.

Relation of ore to depth. In most of the lead-zinc 

veins sphalerite and pyrite increase with depth. The 

bottom of an ore shoot may be marked by an abrupt 

change into pyrite and quartz or the appearance of 

barren ankerite that completely fills the vein. Galena 

is commonly much more abundant in the upper part of 

a vein than in the lower part, but it is a persistent 

mineral and occurs throughout many ore shoots. In 

the veins containing notable amounts of copper the 

copper content generally increases slightly with depth. 

Where both chalcopyrite and gray copper are present, 

chalcopyrite usually becomes relatively more abundant 

in the lower levels and gray copper decreases. In 

most of the veins, however, the amount of copper is 

small, and there is little relation between depth and 

the copper content or minerals of the ore. The silver 

content of the ores does not seem to be related to 

depth from the surface nor to distance from the 

bottom of the lead-zinc ore shoots, although in Glacier 

Mountain the ores are generally richer in silver in the 

lower part of the ore shoots than in the upper part. 

In the Bell mine, on the east slope of the mountain, 

ruby silver occurs at an altitude of 11,600 feet, about 

130 feet below the surface, but farther northeast on 

the same vein ruby silver and native silver occur at an 

altitude of about 10,500 feet, about 300 feet below the 

surface. On the west side of the mountain ore containing ruby silver and native silver was found at an 

altitude of about 10,900 feet, 700 feet below the surface,
62 MONTEZUMA QUADRANGLE, COLORADO

and low-grade unoxidized galena and sphalerite containing sporadic streaks of gray copper extended from 

the surface to this rich shoot of silver ore. The history 

of the Stevens mine, on McClellan Mountain, suggests 

that the upper part of the ore shoot was richer in 

silver than the ore now exposed on the lower levels, 

and that the silver content of the ore gradually decreased with depth. In some of the veins nearby, 

'.lowever, rich silver ore was found near the surface but 

".hanged abruptly into lower-grade ore from 100 to 200 

feet below the outcrop. It is probable that most of 

the silver ore now known in the quadrangle is not 

:elated to the surface. The conclusion that most of 

the silver ore is primary is supported by field evidence 

and by the relations of the ore minerals found during 

their microscopic study. (See pp. 53-58.)

Enrichment. The writer has recently discussed at 

some length 18 tlje problems of enrichment of the ores 

in a supplemental report on the Breckenridge district. 

Part of that district is included in the Montezuma 

q uadrangle, and the conclusions reached are applicable 

to the region treated in the present report. It will be 

unnecessary to repeat the evidence given in the report 

oh the Breckenridge district, and only the general 

conclusions are given below.

The relations of rich gold ore to postmineral beddingplane faults on Farncomb Hill clearly show that these 

pockets are secondary. In many veins in the Montezuma quadrangle the surface ores carry rich secondary 

gold and silver minerals, but these ores bottom at much 

shallower depths in the pre-Cambrian rocks than they 

do in the later sedimentary rocks in the western part 

of the quadrangle. It is improbable that noteworthy 

enrichment has extended more than 100 feet below the 

surface in any of the veins in the gneisses and schists 

in the quadrangle, although in a few places silver 

enrichment may extend to a depth of as much as 300 

feet. No secondary galena or sphalerite has been 

recognized in the mines studied, and if present they 

make up an inconspicuous amount of the total leadzinc ore.

Surface enrichment of the ores has been extensive 

only where the present surface coincides closely with 

that of the Flattop peneplain or the Rocky Mountain 

peneplain. In some veins that crop out on the Flattop 

peneplain or only slightly below it, such as those on 

Wise Mountain, in the southern part of the quadrangle, 

rich gold ore was limited to a depth of 25 feet from the 

surface, below which the ore turned abruptly into very 

low grade pyrite. In ores that crop out on the early 

Pleistocene surfaces, such as the stockworks in the 

extreme, southwestern part of the quadrangle, rich 

secondary gold ore was found at the surface and gradually passed downward into much lower grade sulphide 

ore. The enrichment of the veins in the rugged parts

is Lovering, T. S., Geology and ore deposits of the Breckenridge mining district, 

Colo.: U.S. Oeol. Survey Prof. Paper 176, pp. 28-32,1934,

of the mineral belt that have been subjected to late 

(Wisconsin) glaciation is insignificant, although there 

is commonly a shallow zone at the surface where the 

vein contains some secondary ore richer in gold and 

silver than the primary ore a short distance below.

Dimensions of ore shdots. The largest individual ore 

shoots range from 600 to 1,100 feet in strike length and 

are known to have a vertical extent of 400 to 850 feet. 

In some of the mines the ore shoots have a greater 

strike length than vertical extent, but in other mines 

these relations are reversed. The ore shoot of the 

Stevens mine was about 600 feet long and 850 feet or 

more deep. The ore shoot of the Santiago mine was 

followed for 1,100 feet along the strike and exploited 

to a depth of 700 feet. The ore shoot of the Pennsylvania mine was about 800 feet long and 400 feet deep. 

In the Sts. John mine the Oomstock ore shoot probably 

had a maximum strike length of 1,300 feet, and the ore 

has been mined to a depth of 700 feet, but the bottom 

of the shoot is not known to be reached by the deepest 

level. Several ore shoots occur in some of the largest 

and most continuous veins, and some of these veins 

have been productive for over a mile in length. The 

ore shoots are not related to the present surface, 

although most of those that are known crop out. 

Several of the small ore bodies near Montezuma 

occurred in blind shoots and were discovered during 

underground exploration.

Vertical range of ore deposition. Although the 

greatest known vertical range of ore in a single shoot 

is only 850 feet, the vertical range of ore deposition 

was certainly much greater. The galena-sphalerite 

ore of the Pilot vein, near the mouth of Jones Gulch, 

occurs at an altitude of about 9,500 feet, and similar 

ore in the Ida Belle vein, less than a mile to the south, 

occurs at an altitude of about 11,600 feet. As the 

Pilot vein is at the contact of the Montezuma quartz 

monzonite stock, it might be expected that both temperature and pressure were greater than at the Ida 

Belle vein, which is about 2,000 feet from the contact. 

The ore in the Pilot vein, however, shows no evidence 

of higher temperatures or pressures and is very similar 

in appearance and mineralogy to that in the Ida Belle. 

Sphalerite ore occurs in the bottom of the valley of 

the Snake River near Montezuma at an altitude of 

10,000 feet in the Fisherman vein, and galena-sphalerite ore is found at about 10,350 feet in the Jumbo, 

Waterloo, New York, and other veins. Le'ss than a 

mile south of Montezuma galena ores occur in the 

Cooley and other lodes near the top of Glacier Mountain at an altitude of about 12,000 feet; about \% miles 

southeast of the town galena ore was found in the Silver 

Wave vein, at the crest of the range, in the saddle 

between Sullivan Mountain and Santa Fe Peak, at 

12,850 feet. Ore was mined from the Blanche vein, 

in the valley bottom directly below the Silver Wave, 

at about 11,250 feet. The ores from the Silver Wave
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 178 PLATE 16

inze 104' deep, bottom out of ore 

70'sub level,in ore ro'SW. 20'HE.of winze

Stoped above and below

^-I0"quartz and arsenopyrite

12 vein 

SZnS s 

l"BaS04(dis.) 

6 fine quartz

7JVuggy quartz vein 

"quartz, l"CuFeS2

 Ore-bearing portion of vein on 

level 6

 - - Ore-bearing portion of vein on 

level 5

Sphalerite

Vein 12" wide; Tquartz 

and pyrite

EXPLANATION

Barren fissure, fault, or vein less than 

1 inch wide

Strike and dip 

Strike and vertical dip 

Strike of schistosity 

ZnS, sphalerite 

CuFeSo, chalcopyrite 

CuSO4, copper sulphate

BaS04(dis.), barite disseminated 

Timbered drift

PLAN OF SILVER WAVE MINE, COLLIER MOUNTAIN, LEVELS

5 AND 6 (A), AND OF LOWER TUNNEL, LUCKY BALDWIN

MINE, COLLIER MOUNTAIN (B)
ORE DEPOSITS 63

and. the Blanche are similar and consist chiefly of 

galena, sphalerite, pyrite, and chalcopyrite. In this 

region the evidence shows that the ore minerals were 

deposited through a vertical range of at least 2,000 

feet and suggests that they extend through a vertical 

range of 3,000 feet or more. There is little doubt 

that many undiscovered blind ore shoots exist in the 

district, although it is questionable whether they can 

be discovered and mined cheaply enough to justify 

exploration for them.

The vertical range of the ore in the mineral belt a 

mile east of the Montezuma quadrangle, near Silver 

Plume, is known to be 2,500 feet. Many of the ore 

shoots there had a depth of over 1,200 feet, and a few 

contained ore through a vertical range of 1,800 feet. 

On McClellan Mountain, near the Stevens and Santiago mines, ore has been found at various places from 

an altitude of about 11,500 feet to about 13,000 feet.

In considering the observed vertical range of ore in 

the Montezuma quadrangle it is difficult to appraise 

the importance of the fact that, with few exceptions, 

all the ore bodies have been discovered because they 

cropped out at the surface. In the mineral belt the 

difference in altitude between the valley bottoms and 

the ridges above them is commonly less than 2,000 

feet; and as only a few ore shoots are more than 500 

feet deep, it is evident that the observed vertical range 

of ore could hardly be more than 2,500 feet under the 

most favorable circumstances and that it would generally be less. However, the most productive veins 

are concentrated in several small areas in the mineral 

belt, and in some of these localities similar changes in 

the ore are found at approximately equal altitudes, 

suggesting vertical zones of ore deposition; in other 

places the changes of ore with depth show zonal relations to certain centers of intrusion. These facts suggest that the bottoms of the larger ore shoots indicate 

the bottom of the zone in which important masses of 

ore were deposited nearby.

Localization oj ore. As the ores of the veins are 

fissure fillings, the localization of the ore.is related to 

the physical character of the wall rocks, the irregularities of the vein, and the position of the vein in the 

mineral belt. The chemical composition of the walls 

of a vein has little influence on the localization of ores 

in the Montezuma quadrangle. The reaction of the 

rocks to the regional stresses of early Tertiary time 

determined the size and shape of the openings along 

the faults that later became veins. Qn their journey 

from the magma to the surface the ore solutions had 

to take the easiest possible route, and thus the most 

open fractures would generally serve as the conduits 

for the largest amount of metallizing fluid.

Hard, brittle rocks, such as pegmatite, granite, 

porphyry, and gneiss, are the common wall rocks of the 

persistent ore shoots, and soft, plastic rocks, such as 

mica and hornblende schists, seldom form the walls.

The intersection of two fractures was more likely to 

be open than either fracture at a distance from the 

crossing, and the well-known localization .of ore shoots 

at the intersections of veins or near the junctions of 

branching veins indicates that the solutions found an 

easy way to the surface along such openings. The 

occurrence of ore where there are marked changes in 

the dip or strike can usually be correlated with an 

ancient open space caused by the movement of the 

irregular walls of the fault. If the north wall of an 

eastward-trending .vein has a large horizontal compoSE.

3dlevel

Character ofvefa 

unknown

4th level

NW.

^"galena 

l-4'sphalerite

Ore occurs where fissure 

has been opened by 

movement as indicated, 

northwest side going up

25.

6th level [ 

o

 Tight, nearly 

barren

ICfgalena

T/ghtnear/y 

barren

25 Feet

FIGURE 7. Section along raise in Bell mine, level 6, on south branch of main drift, 

930 feet from portal; raise 175 feet from main drift.

nent of movement toward the east, the vein should 

tighten where it swings northeast and open where itbends southeast, and ore shoots are most likely to 

occur in the eastward- or southeastward-trending segments. The occurrence of the ore shoots in .the Bell 

vein suggests that to such a structural history may 

be ascribed in part the localization of the ore. (See 

p. 72 and pi. 17.) If the horizontal component of 

movement was small, ore tends to occur in the steeper 

parts of a vein that follows a premineral normal fault 

and in the flatter parts of a vein that follows a premineral reverse fault. The cross section of the Bell
64 MONTEZUMA QUADRANGLE, COLORADO

vein shown in figure 7 illustrates the relation of change 

in dip to ore occurrence in a vein filling a premineral 

reverse fault.

In the complex pre-Cambrian mass many different 

lands of rock may be traversed by one fissure. The 

schistosity of the metamorphic rocks may be crossed 

by the fissure at a large angle in some places and trend 

parallel to it in others. A fault cutting a strong rock 

tends to open well-defined fissures, which usually narrow on passing into a weaker rock. If the fault 

trends parallel to the schistosity of the wall rock, it 

commonly loses its identity as a single fracture, and 

the movement is distributed over several parallel or 

interlacing slips, forming a sheeted zone. Unless the 

direction of the vein or the schistosity changes, such 

a sheeted zone is not likely to contain good ore in 

schist, although it may be productive in gneissic and 

granitic rocks. This relation is illustrated at the 

Silver Wave mine, near Montezuma, shown in plate 

16. The schistosity there is parallel to the vein in 

some places and crosses it at an angle in others. The 

ore shoots occur where the vein breaks across the 

schistosity of the wall rock.

The relation of fissuririg to kind of wall rock becomes 

increasingly important with increasing depth. Close 

to the surface, open fissures may be common even in 

poorly consolidated clays and sands, but with increasing depth the fractures in such materials become tight, 

although open fissures may be abundant in stronger 

rocks much farther below the surface. Similarly, in 

the region under consideration, open fissures do not 

persist to as great depths in the relatively weak schists 

as in the stronger gneisses and intrusive rocks. Accordingly, in any one district profitably worked veins 

in schist are likely to be more numerous at high than 

at low altitudes. For these reasons, it seems.advisable 

to confine deep explorations to the stronger rocks. 

SUGGESTIONS FOR PROSPECTING

The occurrence of ore shoots reflects the presence of 

fissures that were open at the time of mineralization 

and within reach of mineralizing fluids. As the ores 

were formed by emanations from the deep parts of the 

porphyry masses, ore deposits should not be expected 

to occur far from the places where porphyry is moderately abundant. Search for new veins should be confined to the porphyry belt (see pi. 3) and should be concentrated in the areas where earlier prospecting has 

shown that productive veins exist. The structure and 

bedrock of the region determined the size and continuity of the openings followed by the rising ore solutions, and persistent veins should be sought in hard, 

brittle rocks such as granites and gneisses; conversely, 

shale, biotite schist, or other weak rocks are unfavorable to the occurrence of strong veins. As the quartz 

monzonite porphyry stocks were intruded after much 

of the regional folding and faulting had been accomplished, they are less thoroughly fractured than the

rocks nearby, and persistent veins are rare in them. 

Minor fractures in a stock, however, may be the weak 

continuations of reopened major fissures in the country 

rock nearby. In many places, as at the Quail mine, it 

would be well to follow ore-bearing veins from a stock 

into the enclosing rock, if the distance is not too great, 

in the hope that the vein would be stronger in the older 

rocks. However, if the invaded rock is an exceptionally weak rock, the vein is more likely to narrow than 

to widen where it leaves the stock.

In considering any vein that has been partly explored, great attention should be given to the structure 

of the region nearby, in the hope of finding some of 

the conditions favorable to the localization of ore that 

have been discussed on pages 63-64. The vein 

material may also yield valuable indications of probable 

changes in mineral content if considered with reference 

to the mineral associations characteristic of certain 

types of ores. (See pp. 58, 61.)

If many periods of brecciation are shown in an apparently barren but strong vein, the chance of finding 

an ore shoot somewhere in it is much better than in a 

barren vein which apparently was never reopened after 

the barren filling was deposited; thus a study of the 

paragenesis of the gangue and the ore may be very 

significant.

Alteration of wall rock, as shown on pages 42-43 

has been effected by solutions that were active before, 

during, and after ore deposition. The early alteration 

has little relation to ore channels, as is shown by the 

widespread formation of chlorite and epidote in the 

porphyry belt. Garnet, magnetite, hematite, and finegrained quartz have formed early in the period of 

mineralization near some of the large quartz monzonite porphyry stocks that are closely related to centers of mineralization. Sericitization preceded and 

accompanied ore deposition and is strongest in gold 

districts. It was commonly related to mineralization 

channels, though not necessarily to ore shoots. Pyritization and silicification of the wall rocks also preceded and accompanied ore deposition. Small amounts 

of carbonates were formed through a long period of 

time, but most of the carbonate gangue is later than 

the galena-sphalerite ore stage. The replacement of 

wall rocks by siderite and ankerite was very common 

near strong lead-zinc-silver veins but rare near gold 

veins. Post-ore carbonates (generally calcite) are not 

commonly related to channels of mineralization and 

are abundant constituents of only a few altered rocks. 

Alteration to clay minerals took place after ore deposition. Rocks slightly replaced by any of the abovenamed minerals can be found throughout the mineral 

belt, but strong or complete replacement by sericite, 

ankerite, pyrite, or quartz generally indicates proximity to a channel of ore deposition.

Geophysical methods of prospecting may show the 

presence of additional ore shoots in a productive vein. 

As the structural conditions are decidedly adverse to
HISTORY OF MINING 65

the use of the seismic methods, and as the topography 

and small size of the ore bodies make it impossible to 

use the torsion balance or pendulum apparatus, and 

as the abundance of magnetite in the country rock 

would, give misleading results with a magnetometer, 

the electrical methods are the only ones that offer 

much hope of success. 19

FUTURE OF THE DISTRICT

With the exception of the placer gold found in the 

valley of the Swan River, in the southwestern part of 

the quadrangle, most of the production of Summit, 

Park, and Clear Creek Counties has come from mines 

outside of the Montezuma quadrangle, and that of the 

quadrangle has come largely from a few productive 

veins. About 15 mines have produced more than 

1,000 tons of ore, but most Of the mines described on 

pages 68-116 have produced much less. Although the 

low production figures are in part due to the small 

size of most of the ore shoots thus far explored, many 

veins have proved unprofitable because of the high cost 

of transportation and mining or the lack of successful 

ore treatment by adequate mills. The reserves of 

high-grade shipping ore are small, but there are many 

veins that will yield comparatively small but profitable 

amounts if mined by lessees. There are probably no 

veins in the quadrangle rich enough to repay investors 

in a heavily capitalized stock company.

It is probable that several veins contain sufficient ore 

of milling grade to warrant their exploitation. Some of 

the quartz-barite-lead-zinc ores, although previously 

exploited at a loss when treated in a gravity separation 

mill, could be profitably concentrated in a flotation 

mill, as proved by the successful operation of the WLale 

flotation mill. There may be some bodies of milling 

ore in or near McClellan Mountain that are sufficiently 

extensive to justify consideration, although the deep 

snow of the long winters in this region and the difficulties of avoiding mill-tailing contamination of the 

streams are factors which must be considered in addition to the grade of ore and the cost of transportation 

and milling. Much of the ore in the veins of the 

Montezuma quadrangle has a comparatively -low 

proportion of gangue. Although this is very favorable 

to mining and permits quick and easy hand sorting of 

the high-grade ore, the scarcity of extensive bodies of 

gangue containing disseminated sulphides suggests 

tliat much of the ore that may be milled in the future 

will be the mixed sulphide ores that are almost valueless as mined but may be separated by differential 

flotation. Most of the few flotation mills that have 

been built to treat the ores of the Montezuma quadrangle are of the same design and have been notably 

unsuccessful, although tests on these ores in the standard types of flotation units, such as those in the experi10 Holland, C. A., Geophysical methods of prospecting: Colorado School of Mines 

Quart., vol. 24, pp. 1-103,1929.

mental mill of the Colorado School of Mines, have been 

entirely successful.

The most notable occurrences of low-grade ores are 

the auriferous disseminated zinc-lead ores foimd in the 

stockworks west of Tiger. The average grade of these 

ores is low, however, and they have not been commercially successful. As they must be mined by underground methods and crushed to small size before treatment at the mill, it is impossible to exploit them as 

cheaply as the low-grade "porphyry coppers" with 

which they are supposed to be comparable. Thus far 

the cost of producing a pound of ore from the lowgrade disseminated ores near Tiger has been more than 

its selling value. Until the cost of mining and milling 

can be materially decreased, or until the price of lead, 

zinc, silver, and bismuth becomes higher than it was 

from 1915 to 1930, there is little reason for believing 

that the low-grade disseminated gold-silver-zinc-leadbismuth ores of the stockworks can be profitably 

worked.

HISTORY OF MINING

The first wave of prospectors that rushed through 

the east side of the Front Range in 1859 and 1860 was 

intent on the discovery of gold, and only gold. Most 

of the early production came from placers, and it was 

not until the rich oxidized gold ore of the lodes near 

Central City had been mined for some time that 

silver was reported in them. As silver became of more 

and more economic importance as a part of these gold 

ores, prospectors began to hunt for argentiferous lodes. 

In 1863 a prospector named Coley left Empire and 

went south to Kenosha Pass, thence northwest to 

Georgia Pass, and up the North Fork of the Swan 

River to Glacier Mountain, where in the spring of 

1864 he found the first silver lode to be discovered in 

Colorado. On his return to Empire he mentioned his 

discovery, and in September of that year a party of 

three men set out from Empire with the avowed purpose of finding silver in the high mountains between 

them and Breckenridge. According to Hollister, 20

Early in September 1864, Gov. R. W. Steele, James Huff, 

and Robert Layton started out of Empire in search of silver, 

"which", says Governor Steele, "we supposed to exist in and 

around the range near the heads of the southwestern branches of 

Clear Creek, where the same interlock with the heads of the 

Snakes." Two or three days found them in camp on Huff 

Gulch, where the Argentine cabins now stand. Next morning 

Huff went directly up the long eastern slope of McClellan 

Mountain, Steele and Layton going up Huff Gulch to the right, 

and all intending to meet on the summit somewhere, and if they 

should find nothing, seek a pass through on to the Snakes. It 

happened that Huff passed over the "cropping" of what was 

afterward called the "Belmont lode", which occurs well up 

on the ridge and is scattered over a considerable area. He 

picked some of it up, and upon exhibiting it to his comrades, they 

all agreed that it was silver ore or blossom and that they need 

go no further. Opening the ground slightly, they got a few 

pounds from the vein in place, took it to Central City, and had

M Hollister, 0. J., The mines of Colorado, pp. 252-253, Springfield, Mass., 1867.
66 MONTEZUMA QUADRANGLE, COLORADO

it assayed, with results varying from $200 to $500 per 

ton. * * * Next year there was a rush to the spot. A district 

embracing the sources of the south fork of South Clear Creek 

and the north branch of North Platte was laid out and called 

"Argentine." The lodes generally assayed high in silver, and 

during the succeeding (last) winter, several eastern and some 

home companies were organized rather for the purpose of 

prospecting and acquiring property by discovery than for 

working the mines for their profits.

The discovery of silver in the Argentine district 

caused widespread prospecting in the region nearby and 

led to the discovery of the highly productive deposits 

at Silver Plume and Georgetown, as well as those on 

McClellan Mountain and Kelso Mountain and those 

in the Snake River drainage basin, to the west. The 

Baker and Belmont were the most important mines 

opened in the Argentine district at this time and were 

worked successfully for many years. Furnaces were 

built at Graymont and Georgetown to treat their 

ores, and after a few years of discouragement the 

developments of these two mines encouraged a second 

rush to the district in 1869 and 1870. The Stevens 

vein was probably found in 1869 and commenced a 

long period of productivity in spite of the high cost of 

transportation. The completion of a railroad to Graymont in 1885 further stimulated mining in the Argentine district, but the panic of 1893 caused silver mining 

to become almost dormant throughout the quadrangle. However, the mines on McClellan Mountain 

were again producing a moderate amount of ore by 

1900, and for several years they shipped ore over a 

narrow-gage railroad that had been built from Silver 

Plume to the top of McClellan Mountain, primarily as a scenic route for tourists. This railroad was 

abandoned when autoinobiles became. common, and 

little mining has been carried on here since.

After the first intensive search for silver ore in 1865 

comparatively little was done in the western part of 

the Argentine district until 1879, when two settlements, Chihuahua and Decatur, were made in the 

valley of Peru Creek, a few miles northeast of Montezuma. In 1882 Chihuahua, at the mouth of Chihuahua Gulch, had 54 buildings and was the home of many 

prospectors who were exploring veins in Cooper 

Mountain, Brittle Silver Mountain, and Morgan 

Peak. The lack of important discoveries in the next 

few years discouragecl the men, however, and after the 

town was destroyed by a forest fire in 1889 it was 

never rebuilt. Decatur, about a mile east of Chihuahua, is in the path of snowslides from Ruby Mountain, 

and in 1930 only two houses were intact, but the piles 

of crushed and broken lumber marking the former 

location of buildings suggested that the town may have 

been as large as Chihuahua. During the eighties a 

small furnace was built here and some ore from the 

mines in the Horseshoe Basin was treated. It was 

closed about 1889, and since that time the town has 

been almost abandoned. The Pennsylvania mine, 

directly south of Decatur, has been one of the most

productive in the quadrangle. The vein was discovered in 1879, and the mine reached the zenith of 

its production about 1803 and was one of the few 

properties that were steadily operated during the lean 

years that followed the panic of 1893. The mines in 

the Horseshoe Basin have never been operated continuously for more than a few years at a time, but 

intermittent work at different mines has resulted in 

some activity in this region every few years since 

1865.

Although the first silver ore discovered in Colorado 

was found on Glacier Mountain early in 1864, no 

further prospecting was done there until 1865, when 

the Argentine rush carried a wave of eager prospectors 

into this region. The Comstock and many other 

veins were found, and in the next few years mills and 

smelters were erected for'treating the ores. The long 

haul necessary to take the ore to Denver or Blackhawk 

induced the mining companies to build a toll road up 

the Snake River to Webster Pass and down Handcart 

Gulch and Hall Valley to the North Fork of the 

Platte River. For many years this road was the chief 

freight route from Denver to the Snake River mining 

district. In 1869 a toll road was built from Georgetown to Montezuma by way of Argentine Pass, and a 

few years later another toll road was completed over 

Loveland Pass. The latter road was abandoned 

about 1883. All these roads were supported by 

charges against wagons and stock using them. The 

tolls ranged from 5 cents a head for loose stock or 

pack trains to $1 for a team and wagon. About 1883 

the counties bought the Argentine Pass toll road for a 

public highway, but little money was spent on its 

upkeep, and it was soon impassable for teams and 

wagons. The completion of a railroad to Dillon in 

1883 simplified the problem of transportation greatly, 

and most of the freighting since has been done on the 

valley road between Dillon and Montezuma.

The first settlement at Montezuma was made in 

1865, and the town has been continuously occupied 

ever since. It was incorporated in the fall of 1881 and 

was the center of much activity during the next few 

years. According to the first issue of its local newspaper, the Montezuma Mill Run, June 24, 1882,

We now have two commodious hotels the Summit House, 

by L. C. Preston, and the Rocky Mountain House, by J. R. 

Newman; several restaurants and boarding houses; three stores; 

three saloons; two blacksmiths; one shoemaker; and mechanics 

in abundance. * * *

Montezuma claims the first discovery of silver in Colorado. 

As early as 1863 a prospector by the name of Coley living in 

Empire, near Georgetown, made prospecting trips over Kenosha 

Pass and then over Georgia Pass; up the North Swan, over the 

pass at the head of Bear Creek, and on Glacier Mountain made

the discovery 

*****

of silver.

The lode from which he took the first silver is now the property of the Sts. John or Boston Silver Mining Co. The crude 

furnace in which he smelted the ore is still to be seen on Glacier 

Mountain, within 1,000 feet of the Sts. John property.
HISTORY OF MINING 67

The first lode discovered after Coley * * * was called 

the Harrisburg, now the Little Annie. It was discovered and 

located by W. P. Pollock, John Christian, and Pratt. 

The ore cropped out of the ground, and the vein could be traced 

by its outcroppings for 500 or 600 feet.

Shortly after the location of the Harrisburg, prospecting 

became general, and in rapid succession other lodes were located. 

In 1865 Eel. Guibor came to the camp, built his cabin where 

the Sts. John now is, and prospected Glacier Mountain, located 

the Potosi and an extension of the Coley lode; later the Herman 

and Bell lodes. John T. Lynch and Pratt discovered the Tiger 

and Tiger Extension lodes in 1865. In 1866 J. T. Lynch discovered the Sukey lode, now the Silver King. He organized a 

silver-mining company, and they built the Sukey mill to treat 

the ore. They worked the property until 1869, lost the vein or 

ran off from it, and then abandoned the property altogether. 

In 1.866-67 prospecting was energetically carried on. "Doc." 

King and Captain Short organized the first mining company and 

put up a mill in 1867. The Bell was discovered in 1866 by 

William Bell, and about that time the Chatauqua was discovered 

by H. M. Teller and G. H. Bull. The Sts. John property was 

discovered by John Cullom and bought by the Boston Silver 

Mining Co., who began work in 1867; erected their mills later. 

In 1868 Captain Ware took charge of the works, and now there 

is no more completely developed mine in the State. The work 

clone by Captain Ware shows that a master hand directed it.

The first gray copper discovered was in the Coley Extension, 

and the first ruby was found in the Potosi in 1867.

The Silver Wing was discovered in 1867 by W. P. Pollock, 

George Link, Mike Dowd, and Charles Breese. The property 

was bought by the St. Lawrence Silver Mining Co. They 

erected a substantial mill and tried to reduce the ore by chlorination by Ayers' improvement on the Stedefelt furnace. It did 

not prove a success, and the work was abandoned.

The Woodchuck, Walker, and other lodes were discovered in 

1869 and 1870.

The mines spoken of thus far are on Glacier Mountain and 

* * * are those discovered before 1870. Since then there 

have been discovered the Centennial Buckeye, Alabama, Old 

Timer, Eureka, St. Joe, Harrison, Silver Prince, Silver Princess, 

Zula King, Wild Irishman, Lady Green, Mendenhall, Lily, 

Bonanza King, Silver Ledge, and Silver Ware.

On Collier Mountain the first lode discovered was the Cooper, 

then the Old Settler by Joe Duffield in 1865, then the Lancaster 

by Bob Espey. * * * The Hannibal, Waterman, Washington, and Morgan Avere discovered afterward. Besides these 

there are scores of other properties that will undoubtedly prove 

to be valuable when developed.

On Teller Mountain, immediately south of town, are to be 

found the Cashier, Star of the West, Star of the West No. 2, 

Iowa, Radical, and other properties. The Cashier is probably 

one of the best-paying mines in the county, if not in the State. 

The Star of the West, owned by J. Harvat, of Georgetown, is 

very prominent for its richness; assays as high as 22,000 ounces 

in silver and 70 ounces gold per ton have been obtained from the 

ore taken from it. The Star of the West No. 2 bids fair to rival 

the original in richness.

On Independence Mountain, west of Bear Mountain, is the 

Great Republic, discovered by Jonas Conwell and Joe 

McKinney, * * * [also the] DOHI Pedro, discovered by 

0. Milner. The Hunki Dori was discovered in 1880 by Penry, 

Murphy, Dougherty, and Keogh. The Ida Bell was discovered in 1880. Besides these there are other valuable properties on the same mountain.

The Erickson mine and other good properties are at the head 

of Keystone Gulch and near the head of Bear Creek.

Several veins were discovered near Montezuma in 

the eighties and small lots of ore were taken from many 

of them. Mining waned steadily after 1888, however, 

and since that time most of the activity has been due to 

the sporadic exploitation of various properties by stock 

companies. Some mines the Sts. John, Bell, and afew others produced ore continuously for several 

years at a time, but most of them did not. Further 

details of the mining history in this district can be 

found in the descriptions of the individual'mines (pp. 

68-116).

About 1871 baritic lead-silver ores were found in 

Hall Valley and at the head of West Geneva Creek and 

almost immediately were acquired or leased by a 

British syndicate, the Hall Valley Silver-Lead Mining 

& Smelting Co., Ltd. Halltown 'was built in Hall 

Valley about half a mile south of the quadrangle, and 

soon elaborate equipment was installed for treating 

the ores. Three Piltz blast furnaces were erected but 

were unsuccessful because of the high percentage of 

barite in the ores. In 1874 and 1875 a reverberatory 

furnace 64 feet long and a wet concentrator were installed, to dress the ore and roast it before smelting. 

Because of its high specific gravity, the barite could 

not be separated from the sulphides in the mill, and 

the whole enterprise was abandoned. 21 Remnants of 

the wooden tram, 4 miles long, that connected Halltown with the mines at the head of the valley can still 

be seen, but Halltown itself has been obliterated. 

After the failure of the English company the mines 

were operated individually by private owners or by 

lessees, and some ore has been shipped almost every 

year since. Severlal unsuccessful attempts were made 

to concentrate the baritic ores by gravity mills prior to 

1917, when a flotation mill was built that successfully 

separated the barite from the sulphides. This mill 

was shut down in 1921 and has not been operated since. 

Aside from the concentrates produced by this mill (see 

p. 114) practically all the ore shipped from the valley 

has been highrgrade silver ore that was sorted by 

hand. No large-scale operations have been carried on 

in Hall Valley since 1876, but several of the mines, 

chiefly the Whale and Missouri, have produced considerable ore. The baritic veins in Revenue Mountain, near the head of West Geneva Creek, supplied 

some of the ore so disastrous to the Halltown smelters, 

but nevertheless, after the failure of the English company, a smelter was built at the mouth of Smelter 

Gulch to treat this baritic ore. The smelter was operated in 1880 and 1881 but had difficulty in obtaining 

ore sufficiently low in barite to smelt successfully and 

was soon abandoned.

The auriferous gravel of the Swan River Basin, in 

the southwestern part of the quadrangle, was discovered

21 Jernegen, J. L., Jr., The Whale lode of Park County, Colo.: Am. Inst. Min. 

Eng. Trans., vol. 3, pp. 352, 356, 1875; Notes on a metallurgical campaign in Hall 

Valley, Colo.: Idem, vol. 6, pp. 560-575, 1877.
68 MONTEZUMA QUADBANGLE, COLOBADO

in 1859 or 1860, and the gulches draining into the 

main valley were soon yielding much placer gold. The 

deeper gravel of the main valley was not successfully 

worked till after 1905, when dredging emerged from a 

7-year period of experiment and failure into one of 

steady and profitable production. The thin but 

extraordinarily rich gold veins of Farncomb Hill, about 

a mile south of Brewery Hill and just south of the 

quadrangle, were discovered about 1879 or 1880, and 

a few years later the stockworks west of Tiger were 

found. The latter deposits were producing oxidized 

gold ore before 1890 and were profitably mined until 

after 1900. As they were followed deeper and the 

low-grade primary ore became more and more abundant, it was found increasingly difficult to work them 

at a profit. These properties were acquired about 

1912 by the Royal Tiger Mines Co., and since then 

much time and money have been spent in an effort to 

prove that the low-grade ores were of commercial 

grade.

THE MINES

Of the many veins discovered in the Montezuma 

quadrangle before 1891, during the years when silver 

was worth more than $1 an ounce, some yielded little 

or no ore, while others yielded more than 100,000 tons. 

Most of the mines have long been inactive, however, 

and only a very few were accessible when the writer 

studied the region. Nearly all the veins, large and 

small, have been the subject of optimistic prospectuses 

as enthusiastic promoters strove to capitalize both fact 

and legend. Some of the veins justify further exploration, but the size of the ore bodies mined in the past 

and the opportunities for finding rich bonanzas or 

large and profitable bodies of milling ore in the immediate future are commonly overestimated. Many 

veins whose total production is less than 5 tons have 

been the nominal object "of exploitation of stock companies capitalized for $500,000 or more. The writer 

has searched the files of the local papers the Montezuma Mill Run, the Georgetown Miner, and the 

Georgetown Courier for mining news of the region 

and has supplemented this information by much 

gathered from men who have been resident in the 

quadrangle for 40 to 50 years. Some material is also 

quoted from the reports by R. W. Raymond on mining 

in the States and Territories west of the Rocky 

Mountains, and from the reports of H. C. Burchard, 

Director of the Mint. As noted in the text, manuscript reports by examining engineers have also been 

used for a few mines to supplement other information. 

It seems worth while to have these data set down, even 

though some of the veins described are small and unimportant. Many of them have been the basis for 

highly speculative and overcapitalized stock companies, and it is hoped that the information in the following pages will help the mining investor as well as 

the mine operator.

ADDER

The Adder vein is on the northern slope of Glacier Mountain, 

about half a mile southwest of Montezuma. It was opened 

in the eighties but had no recorded production until 1919, when 

5 tons of lead-silver ore was shipped by Todd & Hatton. As 

shown below, the mine has been intermittently productive 

since that time. Two adits aggregating about 300 feet and a 

shaft about 20 feet deep were made before 1890, and in 1919 the 

shaft was deepened 15 feet, and a short drift was turned on the 

vein. In the next few years the shaft was deepened to 85 feet 

and another level turned. In 1929 about 100 feet of drifts 

were reported in the shaft workings, but .the mine was inaccessible.

The country rock of the vein is the Swandyke gneiss, which 

strikes N. 30° E. The vein is said to run N. 45° E. and to be 

nearly vertical. The ore is from 4 to 12 inches thick, according 

to the Colorado Mining Directory for 1S83, and consists of 

quartz, galena, and silver minerals.

Production of Adder vein

1Q1Q

1923.. .......... .____- 

Ore (sbort 

tons)

5 

8 

23

Gold (fine 

ounces)

0.10

Silver 

(fine 

ounces)

258 

542 

1,192

Lead, wet 

assay 

(pounds)

899 

1,417 

7,290

No production in 1901-18, 1920-22, 1925-28.

AITOONA

The Altoona vein is on the west slope of Glacier Mountain 

near the Wild Irishman mine and is opened by a few shallow 

shafts and short adits, at an altitude of about 11,500 feet. It 

was located in 1881 and produced a small amount of silverbearing gray copper and galena ore during the eighties. The 

vein strikes northeast and carries from 4 to 8 inches of galena 

and gray copper in a quartz gangue. According to the Colorado 

Mining Directory its total production prior to 1883 was 20 tons, 

but during the next few years it probably produced about 10 

tons more.

AMERICAN EAGLE (ELIZA JANE)

The American Eagle vein, or, as it is locally known, the Eliza 

Jane, is on the crest of Lenawee Mountain, 1% miles north of 

Montezuma, at an altitude of about 12,500 feet. It is opened 

on the northwest slope of the valley of the stream that empties 

into Snake River near U.S.L.M. Adrian, and is a short distance 

southwest of the Winning Card mine. It was located in 1880 

and produced some very rich silver ore in the next few years. 

In 1881 4 tons of "gray copper ore" was shipped that netted 

$500 a ton, and during 1882 and 1883 the mine was working 

but its production is not recorded, although the Georgetown 

Courier for October 1, 1883, notes that this mine "shipped over 

3 tons of first-class ore in the last 2 weeks." In 1884, 2 carloads 

(about 27 tons) netted the lessees $9,000; in 1885, 20 tons netted 

$6,000, and in 1886 3 tons of unknown value was shipped. There 

was no production during 1887 and 1888, and the mine is not 

listed later. Silver was the only metal in the ore for which 

the lessees received pay. The total production of the mine was 

probably about 85 tons of ore averaging about 350 ounces of 

silver to the ton. Little Is known of the vein except that the 

character and occurrence of the ore were very similar to those 

of the Winning Card, which is described on pages 1.14-116. The 

ore seam was from 1 to 6 inches wide and contained galena, gray 

copper, quartz, and a silver mineral that was probably stromeyerite. " ATLANTIC

The Atlantic vein is on the west slope of Collier Mountain, 

about a mile east-southeast of Montezuma. It lies between
THE MINES 69

altitudes of 12,000 and 12,500 feet. It was located in 1873 and 

yielded about 50 tons of silver-bearing galena ore before 1883, 

but very little has been shipped from it since that date. The 

total production is probably about 75 tons. The Atlantic is 

said to be a quart/- vein from 4 to IS inches wide and contains 

galena locally. The shipping ore assayed about 60 percent 

of lead and from 50 to 100 ounces of silver to the ton. The vein 

trends northeast toward the Sarsefield mine, a short distance 

away, and may be the southwestern continuation of the Sarse- 

(ield vein.

BAKER

The Baker lode is on the east slope of Kelso Mountain, 6^ 

miles northeast of Monte/uma, west of the Stevens mine, at an 

altitude of about 12,000 feet. No work has been done on it 

since about 1885, but the mine wias one of the most productive 

in the Argentine and Silver Plume mining districts in the 

seventies. The lode was discovered in 1865, during the rush 

caused by the discovery of silver in this region late in 1864. In 

spite of the desertion of the district in 1867, 1868, and 1869, the 

Baker was developed steadily, and during the winter of 1869-70 

communication was maintained with Bakersville (Graymont) 

without difficulty, and a team and sled was able to make frequent trips between the town and the mine. The use of teams 

instead of pack trains reduced the cost of transportation about 

$3 a ton. In 1869 the Baker Co. completed its reduction works 

at Bakersville, and in 1870 two shoots of good ore were opened, 

and for a short time the reduction works smelted from 15 to '65 

tons a month. In July 1871 the Bakersville smelter was completely destroyed by fire. This was at the height of its activity, 

and production fell off immediately. The Baker was listed by 

Raymond as one of the chief mines worked during 1873, but 

little ore was shipped after 1874, and the mine was idle during 

the later seventies. Some work was carried on in the early 

eighties by the British Queen Mining Co., but no production is 

recorded for this time. According to the Georgetown Miner for 

January 19, 1871, the total bullion produced in 1870 was $27,- 

567.97, or about 21,321 ounces of silver. In January 1872 the 

total bullion produced in the past year was reported to be 

$4,509, or about 3,4.87 ounces of silver, incomplete records for 

1874 indicate that over 1,000- ounces of silver was produced in 

that year.

According to Hollister,22 the two principal veins, called the 

north and south crevices, strike N. 72° E. and N. 60° E. and 

dip 65° and 85° N.

"They are traced and disclosed by many prospecting pits, 

showing bodies of uncommonly rich ores, varying in width from 

20 inches to 20 feet. The crevices consist of sulphuret and 

bromide of silver and argentiferous galena, all these ores being 

more or less interspersed within the vein matter of quartz and 

feldspar. Samples of ore taken from these crevices yielded by 

. assay as high as $800 to $2,000 per ton. At the junction of the 

north and south crevices a tunnel has been commenced which 

shows a large body of ore 7 feet in width. * * * Samples 

of all the different tunnels and surface pits, pulverized, and 

equal weights of each mixed together. This' average ore 

yielded by assay gold $6.11, silver $69 $75.11 per ton of 2,000 

pounds. * * * Two tons of the ore, unselected, undressed, 

and without roasting, was smelted last winter, yielding 25 

pounds of silver, coin value $422.90, and 1,500 pounds of lead, 

at 10 cents a pound, $150. 'About 3 miles above the right fork 

and 2,000 feet up from the creek occur the John Brown, United 

States Coin, and Mammouth Lodes, parallel and within 50 feet 

of each other, standing above the surface, the Mammouth 

assaying $60 a ton for 30 inches, the Coin $200 a ton for 18 

inches in width, and the Brown $350 for 16 inches. Some ore 

from the Brown has been smelted rthey are all argentiferous

« Hollister, 0. J., Mines of Colorado, p. 200, Springfield, Mass., 1867.

galeria and the lead riches, of which the yield is nearly one-half 

the weight of the dressed ore, assays about $1,000 per ton."

In 1869, according to King, 23 the Baker was one of the most 

thoroughly developed properties in the region, but the amount 

of ore found had been disappointing. The width of the vein 

averaged about 3 feet and locally was as much as 15 feet, but 

the ore seam was not continuous. The ore consisted of galena, 

sphalerite, and silver minerals and occurred in pockets and 

chimneys. The chief gangue mineral was quartz, but fluorite 

was abundant in all but the uppermost of the three levels.

In 1871, according to Raymond,

"The Baker * * * opened to a depth of 320 feet; 

worked by three adits, 187, 212, and 420 feet long, all connected 

by a shaft, extending to a depth of 168 feet below the third 

level. The mine is in good ore above the first level. The 

ground between the first and second levels is entirely worked 

out, and between the second and third levels nearly so. Though 

nine-tenths of all the ore found in the lode was on the footwall, 

the deep shaft has been sunk on the hanging wall, and no ore 

was found beyond a depth of 60 feet. This summer a crosscut 

was started toward the footwall, which, at a distance of 10 feet 

from the hanging wall, struck a vein of solid ore 2% inches in 

width and assaying $650 per ton. Here again, as in all instances 

where true fissure veins have been sunk upon to greater depth, 

it has been proven that the ore continues downward, though of

FIGURE 8. Longitudinal section of Baker mine, 1869.

course varying in richness as well as thickness, and sometimes 

pinching up entirely for some distance. In the stope above the 

first level there is a vein of ore, varying from 2 to 10 inches, 

yielding ore of $200 (mill assay). The stope between the second 

and third carries from 1 to 6 inches of $130 mill ore. Below the 

third level no ore has been taken out except in sinking the shaft. 

The driving of levels preparatory to taking out ore was just 

contemplated when the company's mill was destroyed by fire. 

This accident stopped operations for a considerable period. 

Next year a deep tunnel, gaining over 400 feet below the third 

level, is to be started to facilitate cheap working."

In 1883 the mine was developed by four levels, all connected 

by a 200-foot shaft. A partial section of the workings taken 

from Raymond's report for 1869 is shown in figure 8.

The country rock of the mine is Silver Plume granite, quartzbiotite schist, and injection gneiss cut by many dikes of granite 

and rhyolite porphyry. The average width of the Baker vein 

is said to be about 16 inches, and the ore a short distance below 

the surface consisted of stephanite, silver-bearing galena, and 

chalcopyrite in a quartz gangue.

BALTIC AND REVENUE

The Baltic and Revenue veins are opened by the Britannic 

tunnel, on the southwest slope of Revenue Mountain at the 

head of West Geneva Creek, 3 miles east of Montezuma. There 

are several other workings on the veins of this group, including 

a shaft on the Revenue vein that has its collar on the Continental

» King, Clarence, U.S. Qeol. Expl. 40th Par. Kept., vol. 3, pp. 599-560, 1870.
70 MONTEZUMA QUADRANGLE, COLORADO

Divide at an altitude of about 12,600 feet. The altitude of the 

Britannic portal is about 12,125 feet.

The property is accessible from Grant, about 11 miles to the 

southeast. A good automobile road runs as far as the foot of 

Kirby Gulch, 7 miles from Grant, and is passable for cars for 2 

miles more, and a wagon road continues to a point within half 

a mile of the Britannic tunnel, which is on the main trail from 

West Geneva Creek to Cinnamon Gulch.

The Baltic and Revenue veins, discovered in 1872, were 

famous in the seventies, and the ruins of a smelter erected to 

smelt their ores in 1879 can still be seen at the foot of Smelter 

Gulch. Some of the ore produced by the veins was sent to the 

Hall Valley smelter in 1873-75, at the time the mines in Hall 

Valley were being exploited by the Hall Valley Silver-Lead 

Mining & Smelting Co., Ltd. In his report for 1874 Raymond 

says: "It has been opened for about 400 feet and to a depth of 

about 65 feet and carries a very regular seam of galena and 

gray copper, averaging about $120 per ton in silver:" After 

the failure of the Hall Valley enterprise the mines in the valley 

of West Geneva Creek produced almost nothing until 1880, but 

during this time the Britannic adit was driven, and drifts were 

turned from it on many of the veins that were cut. In 1881 the

SW.

tained an average dip of 45° for the remaining 75 feet of the 

winze shown in the cross section in figure 9. The vein below 

the 250-foot sublevel is said to consist largely of barite with 

moderate amounts of chalcopyrite and dark-colored sphalerite 

but has small amounts of quartz, galena, and gray copper. 

The vein was followed 600 feet west from the Britannic adit, 

and the ore shoot continued for about 500 feet of this distance 

and was stoped as much as 150 feet above the tunnel level, 

according to James Kimberly. East of the winze the ore became 

very pyritic, and little work was done in that direction. The 

ore pinched so markedly above the Britannic level that the ore 

shoot may properly be considered a blind one, although the 

vein itself crops out. The shoot is said to have had a pronounced pitch to the northeast, but the amount of pitch could 

not be given. According to the Georgetown Miner for August 

16, 1879, the Baltic vein had 8 inches of solid gray copper ore 

on the tunnel level, and the winze showed 12 inches of yellow 

copper (chalcopyrite) and galena ore. The stope on the Revenue vein 100 feet above the tunnel showed 14 inches of pyrite, 

galena, yellow copper, and gray copper ore.

The Revenue vein strikes about N. 55° E. and dips about 75° 

NW. The Britannic tunnel cuts it about 200 feet beyond the

NE1.

FIGURE 9. Cross section along line of Britannic tunnel, looking northwest.

Geneva mining district is credited with a production of $30,000, 

and in the next year with $7,000; most of this was probably 

produced from the Revenue and Baltic group of veins. The 

district as a whole is not mentioned again, but in 1887-91 the 

Baltic is listed as a producer and is given credit for a production 

of $1,300 in gold and $69,132.93 coin value in silver, a total of 

$70,432.93. The production records during the nineties were 

very poor for all the mines in Colorado, so that it is not surprising that no further production is recorded for the Baltic, 

although miners in the district state that some ore was mined. 

Six carloads are said to have been shipped from the Baltic in 

1898, and two carloads more in 1902. Because of the long haul 

to the railroad, all ore shipped from this region has had a tenor 

of $50 or more to the ton. Except for two small shipments 

from the Revenue vein, no ore is known to have been shipped 

from this group since 1902.

The Baltic vein strikes northeast and dips 45° to-75° NW. 

The steep dips occur in the upper part of the vein, and as it 

was followed downward from the Britannic tunnel level the 

dip changed from 65° to 55° and maintained this angle for 

nearly 200 feet, below which it flattened still more and mainBaltic vein and is connected to the surface by a shaft 455 feet 

deep. The vein is somewhat narrower than the Baltic and 

averages about 6 inches in width. It contained a higher proportion of gray copper than the Baltic, and near the surface 

it had a high percentage of galena. The silver content of the 

ores of the Baltic and Revenue group increased with the content of gray copper. The gold content, which was locally high, 

increased with the content of chalcopyrite. The country rock 

of the veins is largely injection gneiss and quartz-sillimanitebiotite schist, striking northeast and dipping at an average 

angle of about 55° N W. Small dikes of monzonite and quartz 

monzonite porphyry are common on the surface and were probably found underground in some of the workings. . The veins 

appear to be essentially parallel to the schistosity, and the cause 

of the localization of the ore shoots is not known.

Emmons 24 notes that a specimen of ore from the Baltic mine 

was "ore and gangue, pyrite, chalcopyrite, blende, fahlerz 

(gray copper), and a little galena in siliceous gangue; occasional 

pink calcite crystals."

« Emmons, S. F., Tenth Census, vol. 1, pp. 77,188.
U. S. GEOLOGICAL SURVEY

sw. 

A

Eastern /im/t of 

e unknown

PROFESSIONAL PAPER 178 PLATE 17

NE.

-* *-

EXPLANATION

Barren fissure, fault, or vein less than 

1 inch wide

Barren fissure, fault, or vein from 1 to 

12 inches wide

Barren fault or vein more than 12

inches wide 

Slightly mineralized vein more than

12 inches wide

Mineralized vein with 1 to 12 inches

of ore 

Mineralized vein with more than 12

inches of ore

Strike of schistosity 

PbS, galena 

ZnS, sphalerite 

MnCOs, rhodochrosite

AD/T A/O.6 

EL. O.'o

SECTION AND PROJECTION 

Points cut by line /4-/4'shown in solid black

PLAN AND LONGITUDINAL SECTION OF BELL MINE, SOUTH OF MONTEZUMA
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 178 PLATE 18

Z4"2nS breccia in 

pink ankerite matrix 

Rufcy and wire 

l6"breccia;ZnS in 

ankerite matrix

I0"gougy sheeted zone 

" ~eS2 veinlet

DETAIL AT LINE A~A 

o

6"2nS 

(some ruby A

IO"ZnS ore

*-x. 3"ZnS 

(^also some

I2"bettvee 

wa/ls

EXPLANATION

Barren fissure, fault, or vein less than 

1 inch wide

 -- Course of vein in Spelter King adit 

Chiefly sphalerite in vein

 Chiefly pyrite and quartz in vein

Chiefly ankerite in vein

+ ~70 ° 

~~*~-~ Strike and dip

\\V\\ Strike of schistosity 

PbS, galena 

ZnS, sphalerite

pyrite 

Agf, silver 

Slick, slickensides

PLAN OF SILVER WING AND SPELTER KING TUNNELS,

GLACIER MOUNTAIN
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 178 PLATE 19

PLAN

2 "PbS 

/ J ss° / / '2'Vein

j a / .8Cu and qtz.

/ , , YELLOWJACKET VEIN

' I ' 1.1 1 L.

EXPLANATION

 Barren fissure, fault, or vein less than 

1 inch wide

 Barren fissure, fault, or vein from 1 to 

12 inches wide

 X x Barren fault or vein more than 12 

inches wide

 Slightly mineralized vein less than 1 

inch wide

 x x Slightly mineralized vein more than 

12 inches wide

 X X Fissure zone more than 12 inches

wide carrying from 1 to 12 inches 

of ore (red dots) or more than 12 

inches (red crosses)

4fO a

"""*- Strike and dip

^<^ Strike and vertical dip 

/////// Strike of schistosity 

Pb, lead ore 

PbS, galena 

Cu, copper sulphides 

Fe, iron sulphide 

qtz, quartz

SECTION

100i i i

300 FEET

a, Pb generally between Cu and hanging wall. Winze 185' deep, all reported in ore, average 3" wide b, 1 foot 

quartz, very vuggy and carrying CuFeSs sphenoids, c. Pocket of ore ff long and barren streaks 2CF. d, Sheeted 

zone, It'-ff, narrow Pb and Cu veins.

PLAN AND SECTION OF BULLION MINE, NEAR MONTEZUMA
U. S, GEOLOGICAL SURVEY PROFESSIONAL PAPER 178 PLATE 20

\, \\ \

EXPLANATION

Barren fissure, fault, or vein less than 

1 inch wide

Barren fissure, fault, or vein from 1 to 

12 inches wide

Barren fault or vein more than 12 

inches wide

Vein or fissure carrying from 1 to 12 

inches of gangue and sulphide

Relative proportion of sulphide 

(solid) and gangue minerals 

in ore

Strike and dip 

Strike and vertical dip 

\\\ 0\ Strike of schistosity

Downthrown side of fault

PLAN OF BUSTER TUNNEL, NEAR SILVER PLUME MTN.
U.S. GEOLOGICAL SURVEY

PROFESSIONAL PAPER 178 PLATE 21

//Crosscut to 

Ready Pay lode

N O- 2 or //Cashier lode

No.4//lode

2/0-FT. LEVEL

r3 f60-FT. LEVEL

100-FT. LEVEL 

WINZE

ENGINE 

HOUSE

FILLED ADIT

DISCOVERY ^ LEVEL ON 

SHAFT ^ READY PAY

PORTAL OF 

UPPER TUNNEL

End of Champ/on tunnel 

Crosscut to Ready Pay vein

\ To mouth of'tunnel 400'

Portal of lower 

or Cashier tunnel Tunnel level on Cashier vein

50-FT. LEVEL

100-FT LEVEL

160-FT. LEVEL

_____ _ _ ___ _ _ _ _ __ _____ _ _ PprtaJ of_Cha_mpioji tunnel

Tunnel level on Ready Pay /ode

Auo. /884

810-FT LEVEL

100 0

I I I I I I I. I I I I... 100

I ......

300 Feet

PLAN AND VERTICAL PROJECTION OF CASHIER AND CHAMPION MINES.
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 178 PLATE 22

2 strong walls 6'apart; PbS 

on hanging wall and footwall 

streak. VeinlZ"to30" 

Z"to8"seams PbS; also 

breccia or rubble cemented 

by quartz,ankerite,and PbS. 

Some gray copper

8'gouge and breccia

100" strongly 

sheeted zone

Sloped abov

Many branching stringers 

of quartz, ankerite,and Fe S? disseminated through 

waif rock 15' from vein

- Dacite , , 

c--^' porphyry

Biotite gneiss

24'gouge and 

ateredrock V zo Striations on wall strike N. and S 

roughness and drag suggest 

a reverse fault

6"gouge 

Hornblende gneiss

24"gougy sheeted zone

EXPLANATION

Barren fissure, fault, or vein less than 

1 inch wide

Barren fissure, fault, or vein from 1 to 

12 inches wide

Slightly mineralized vein less than 1 

inch wide

Slightly mineralized vein from 1 to 

12 inches wide

Slightly mineralized vein more than 

12 inches wide

Vein with galena ore more than 12 

inches wide

Strike and dip 

Strike of schistosity 

PbS, galena 

FeS2 , pyrite 

Timbered drift

50 100 Feet

-Hornblende gneiss

PLAN OF MAIN (LOWER) ADIT, CHATAUQUE MINE, GLACIER MOUNTAIN, 1929
THE MINES 71

The incomplete production figures given below are all that 

have been found.

Production of Baltic and Revenue veins

Baltic: 

1887-., . -.

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

1880 

1800.... ...... ...

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

Revenue: »

.1878.............

1880.............

1881 

1887-89. ..

1011.. ..

1919 

1927..... 

Ore (short 

tons)

(V)

(Y)

CO

CO

(?)

1

45

52

43

30

2

14

4

Gold (fine 

 ounces)

02.89

1.31

CO.C2

54.02

.08

 .30

Silver 

(fine 

ounces)

10, 459

9,158

10, 378

10,003

8,018

41

6, 266

17, 825

12, 055

328

960

300

Lead, 

wet assay 

(pounds)

673

569

2,398

1,635

Copper, 

wet assay 

(pounds)

5,063

21, 057

13, 345

98

2,443

703

< No record available for 1877, 1879, 1883-86, 1890-1900; no production in 1901-10, 

1012-18, 1920-26, 1928.

BEII, METEOR, AND WING

The California, Sunburst, Meteor, and Wing claims, on 

Glacier Mountain, are on the lode commonly known as the Bell 

vein. The original discovery was made by William Bell on 

the California claim in .1.866, and the ground was taken up as the 

Bc.ll East and the Bell West. These claims were not patented, 

but the portions of the vein which they covered were steadily 

worked until about .1893. The ground was relocated in 1897 

by John and Frank Burke, who patented the claims in 1899 as 

the California and the Sunburst. The Silver Wing claim was 

located about 1870, and the original claim was 3,000 feet long 

and 50 feet wide. This claim, as surveyed, failed to keep the 

apex of the vein between its side lines for more than 300 feet 

from the discovery shaft, and the Burkes located the Meteor 

claim on the ground between the California and the place 

where the vein crossed the side lines of the Silver Wing claim, 

thus gaining control of the apex for nearly 4,500 feet.

The California and Sunburst claims were sold to the Cleveland Mine Development Co. in 1902. Work was carried on 

until the summer of 1903, and mixed lead-zinc ore was found on 

the no. 6 tunnel level. Work was then discontinued, and little 

or no work was done until 1925.

In 1924 H. B. McGowan, of New York City, obtained a lease 

and bond on the Sunburst, California, Meteor, and Silver Wing 

claims. He obtained the services of G. H. Short (formerly 

associated with George Graham Rice as manager of the Idaho 

Copper Co.) in driving a crosscut adit, which was expected to 

tap the vein under the Meteor claim. The adit failed to reach 

its objective and is said to have caved within a few months of 

the time that work was discontinued. It was inaccessible at 

the time of the writer's first visit to the district, in the fall of 

1926,

, McGowan defaulted a payment in May 1925 and lost his 

lease. In the later part of the summer Short bought the 

California and Sunburst claims from the Cleveland Mine 

Development Co. and organized the Bell Silver Mining Co. 

in Salt Lake City. The property was worked by Short and his 

associates from September 1925 until December 1926, and lessees 

operated it during the winter of 1927-28.

The Silver Wing adit was advanced about 250 feet by Short 

in .1924, at the time that this property was under lease to McGowan, and at the same time a raise was made in ore, but little 

stoping was done. No other work has been done in this adit 

since that time (1924-29).

The chief workings of the Bell mine are above 11,600 feet on 

the east side of Glacier Mountain, about a mile south of Montezuma. As shown in plate 17, there are about 3,000 feet of drifts 

and crosscuts in six adits and a short sublevel. The lowest

71880 35 6

adit, no. 6; has its portal a short distance above the ore house 

at the terminus of the wagon road that leads to the Bolivar mill, 

half a mile south of Montezuma.

The vein trends northeast, and the general dip is about 65° 

NW. The surface of the vein is flexuous, and its course varies 

from N. 30° E. to N. 70° E. in some places, but in most of the 

workings it is not far from N. 40° E. The inclination of the 

vein is more irregular than its course, commonly ranging from 

40° to 80°, but in places it is vertical and may even dip steeply 

southeast. The vein everywhere cuts across the schistosity 

of the Swandyke gneiss, which is the prevailing country rock. 

A small body of granite is cut near the entrance of the lowest 

adit, but hornblende and biotite gneiss seamed with pegmatite 

make up the wall rocks of the vein in the rest of the accessible 

parts of the mine. The gneiss strikes nearly due north and 

dips 50°-75° E. About 480 feet from the portal of adit 6 

the Bell vein is cut by a normal fault striking N. 10° E. and 

dipping steeply west. The fault zone is about 3 inches wide 

and has offset the vein about 5 feet. Another normal fault 

striking in the same direction but dipping east offsets the vein 

a few feet about 600 feet from the portal. A short distance 

beyond this fault the drift swings west on a sheeted water-bearing fault zone about 24 inches wide, which contains a seam of 

gouge 6 inches wide. This fault dips 55° N. and apparently 

moved the southwestern part of the Bell vein about 15 feet 

east. This fault is also recognized on level 4, where its displacement is only about 10 feet. The vein is apparently terminated on level 4 by a northerly fault dipping 70° E. and marked 

by a seam of gouge 3 inches thick. The plan of the upper levels, 

now inaccessible, suggests that this fault occurs in them also 

and that the vein was not found west of it. If this fault is 

normal, like the other faults having a similar strike, the Bell 

vein should be found by turning north after passing through the 

fault, but exploration has not been carried out in that direction. 

A few small northwesterly normal faults, later than the northerly 

faults, have been mapped but do not persist from one level to 

another.

The ore seam of the Bell vein ranges from 3 to 24 inches in 

width but is commonly from 4 to 12 inches. Except where the 

vein dips southeast, the ore streak is remarkably free from gangue 

and consists chiefly of light-colored sphalerite and galena. 

(See fig. 10.) Sphalerite strongly predominates in the northeast half of the workings, but galena is more abundant than 

sphalerite in the southwest half. This change in the character 

of the ore is apparently unrelated to depth and is a lateral rather 

than a vertical change. Gray copper is uncommon, but a 

small lens occurred in the vein on level 6. Very little gold has 

been found, but the vein is noted for its rich silver shoots. 

The most common silver-bearing minerals observed are pyrargyrite and miargyrite, or dark ruby silver, but argentite and 

proustite are not uncommon. Wire silver is said to occur 

sparingly, but none was seen by the writer. The ruby silver 

occurs in lenticular masses in the center of the vein and is 

abundant in some places for distances of 20 to 30 feet along the 

drifts. The largest mass of which there is an authentic record 

was described by Van Horn.25 (See p. 56.)

In most of the vein the ore occurs in a single seam, but in 

some places where premineralization movement developed 

many strong branching gougy seams and slips between the 

main walls of the vein, or where small parallel or branching 

fissures occur near the main premineral fault, several sulphide 

veins may follow the strongest of the premineral fractures. 

In some parts of the vein the introduction of the sulphides into 

the broken ground resulted in irregular masses of ore, which 

themselves have the misleading appearance of being badly 

faulted, as is illustrated in figure 10. The ore shoots are lentic25 Van Horn, F. R., Occurrence of proustite and argentite at the California mine 

near Montezuma, Colo.: Oeol. Soc. America Bull., vol. 19, pp. 93-93, 1903.
72 MONTEZUMA QUADRANGLE, COLORADO

ular and are related to the changes in dip and direction of the 

vein. A steep dip or a strike near N. 30° E. is distinctly unfavorable for the occurrence of ore shoots, and conversely a

SE. NW.

SE.

FIGURE 10. Mineralization of broken ground in premineral fault zone. Apparent 

postmineral fault (upper left) is seen to be premineral (upper right).

gentle dip or a strike close to N. 45° E. is usually found where 

ore shoots occur. The cross section of the raise near the breast 

of adit 6, where the vein dips at more than 60°, coincides with a change in the course from N. 35° E. to N. 

55° E., but the junction of the vein with other premineral fissures may have had some effect on the 

richness of the ore.

About 100 feet from the portal of adit 4 a vuggy 

quartz vein 12 inches wide was found that contains 

a small amount of galena and sphalerite. The vein 

strikes N. 70° E. and dips 30° N.; this dip and strike 

if maintained would cause it to intersect the Bell vein 

on level 6 about 650 feet from the portal, where a rich 

pocket of ruby silver was found. At this place a 

sheeted zone in the footwall of the Bell vein strikes N. 

70° E. and dips 35° N., suggesting that the vein found 

in adit 4 was a factor in localizing ore at its junction 

with the Bell vein. The intersection of a strong gougy 

 fissure striking N. 75° E. and dipping 55° N. with the 

Bell vein in the southwestern part of level 6 apparently had no effect on the localization of ore, although 

the strike and dip of the fault indicate that it is probably a continuation of the Wild Irishman vein zone. 

Although the fault is later than the Bell fissure, the 

relations are not clear enough to allow a decision as 

to whether the fault is later than the ore in the Bell 

vein. It is possible that this fault and the Bell vein fissure 

are both premineral. The S-shaped fractures in the Bell vein 

shown in figure 11 suggest that the ore was. deposited in a 

reverse fault.

The Silver Wing or Wing adit and the Spelter King adit, half 

a mile northeast of the Bell mine, close to the Bolivar mill, are 

shown in plate 18. The Wing adit, 135 feet above the Spelter 

King, is about 700 feet long. Several ore shoots have been 

found in this adit; the first, 170 feet long, and the second, 60 

feet long, have been stoped, but little ore had been taken from 

the other shoots in 1928, and the character of the ore was well 

shown.

The country rock is a biotite gneiss of the Swandyke gneiss, 

and its prevailing strike is about N. 25° E. It dips steeply 

east near the portal of the adit, but in the southwestern half 

of the workings it dips steeply west. Although the vein strikes 

parallel to the gneiss for short distances, it everywhere cuts 

across the schistosity because of its much gentler dip. The 

general course of the vein in the Wing and Spelter King adits is 

N. 50° E., and its average dip is about 65° NW. Although it is 

well defined and the miners followed it without much difficulty, 

it branches, splits into closely spaced parallel fissures, pinches 

into a tight, narrow seam of quartz and pyrite in some places, 

and swells into a sulphide vein 24 inches wide in others. In 

the first two ore shoots most of the ore left is massive lightcolored sphalerite, carrying a small amount of galena, but a 

shipment made from the Wing in 1907 consisted of 36 tons of 

galena ore containing 35 percent of lead and 23^ ounces of 

silver to the ton. Shipments from the Spelter King indicate 

that the zinc ore carries only about 15 ounces of silver to the 

ton. However, some rich pockets of ruby silver and native 

silver were found in a few places, usually at the beginning or 

end of an ore shoot and close to the intersection of a branching 

fissure. About 525 feet from the portal of the Wing adit some 

high-grade silver ore was seen by the writer. As indicated in 

plate 18, some movement occurred in this part of the vein 

after the deposition of the sphalerite, which occurs as a breccia 

about 24 inches wide, cemented by manganiferous ankerite. 

The cementation is not complete, and the vein is moderately 

open and vuggy in this place, and many of the vugs contain 

abundant wire silver, which was apparently one of the latest 

minerals.

The ore solutions did not find a single gaping fissure during 

the formation of the Bell vein, but rather a northeastwardtrending fissure zone through which the ease of travel was much

FIGURE n. -Vein following S-shaped fracture cleavage of prefnineral reverse fault 80 feet beyond 

second winze on level C, Bell mine. Rh, Rhodochrosite.

greater in some directions than in others. As shown in figure 

11, reverse faulting caused the formation of this fissure zone. 

Movement of the hanging wall upward over the footwall 

tended to create an opening wherever the dip of the walls
THE MINES 73

flattened, and thus it is not surprising that in general the solutions found the more gently dipping parts of the vein more open 

and accessible than the steeply dipping parts. The dip of the 

vein in the Spelter King adit is steeper than in the Wing, and 

the localization of ore seems directly related to the occurrence 

of cross fissures.

The study of the Bell vein brings out the discontinuous character of the ore shoots common in the veins of the Montezuma 

quadrangle. The occurrence of many shoots separated by 

weakly mineralized or barren places on the vein is evident from 

the maps, and it is probable that several ore shoots similar to 

those already worked exist between the Wing adit and the Bell 

mine.

The available production figures are given below, but they are 

fragmentary and incomplete prior to 1902.

Production from Bell and California groups

Prior to and including 

1882".......... .---.

Iftft'* a

1884 «... . ------

1885"......-. ........

1 QQft a

i 007

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

1880..... -.--..--- -

toon

1891. -

1920....... - - .

1027.. .: 

1028. 

Ore 

(short 

tons)

1,000 

300

40 

00 

155

" 125 

"100 

(?) 

(?) 

(?) 

281 

760 

31 

37

Gold 

(fine 

ounces)

3. 45 

10. 00 

.30 

.38

Silver 

(fine 

ounces)

25, 000 

7, 500

1,000 

2,250 

3,875 

3,831

1, 408 

I, 342 

2, 941 

1,253 

3,220 

12, 640 

610 

040

Lead, 

wet assay 

(pounds)

900, 000 

270, 000 

36, 000 

81, 000 

139, 000

85, 765 

83, 428 

187, 550 

40, 900 

159, 772 

439, 957 

34, 005 

37, 802

Copper, 

wet assay 

(pounds)

527 

3,312

Zinc 

(pounds)

176, 249 

441, 668

» Estimated,

No record available for 1892-1900; no production in 1901-24.

BELMONT (QUS BELMONT, JOHNSON)

The Gus Belmont was the first recorded lode in Colorado, 

although it was discovered several years after mining became 

active in the Central City district. It is close to the crest of 

McClellan Mountain, a few hundred yards northwest of the 

Santiago mine and G^ miles northeast of Montezuma. The 

mine is well above timber line and lies at an altitude of about 

13,000 feet. Rumors of the existence of silver-bearing lodes in 

this region, caused by the discovery of silver on Glacier Mountain, south of Montezuma, early in the summer of 1864, led to 

systematic prospecting for silver in September of the same year. 

Gov. R. W. Steele, James Huff, and Robert Layton left Empire 

in search of silver and on September 14 discovered the outcrop 

of the Belmont vein, from which they took several pounds of 

ore that averaged $827.48 a ton in gold and silver, chiefly 

silver. The next year there was a rush to the region, and many 

other veins were discovered. After a year of only moderate 

success most of the prospectors deserted the district, but both 

the Belmont and the Baker mines worked steadily through this 

period of depression. In 1870 their developments encouraged 

a second rush to the district, and nearly all the known veins in 

the Argentine district were discovered before the end of the 

following year. A small custom stamp mill, driven by water 

power, was built on Leaven worth Creek, about 3 miles southeast 

of the Belmont vein, and operated intermittently for many 

years. Although known as the International mill and built to 

treat the ores of both the International and the Belmont lodes, 

most of the ore put through the stamps in the years from 1870 

to 1872 was bought from the Belmont. According to the 

Georgetown Miner for November 10, 1870, 11% tons of ore 

from the Belmont yielded $113 at the coinage value of silver, 

and in February 1871 this paper noted that the "Belmont was 

in a large body of ore running $694 a ton." In his report for

1873 Raymond noted that "this, one of the principal mines of 

the district, worked during the year."

The Belmont was not patented under its original name, and 

there has long been a dispute over the exact location of the original Gus Belmont lode. An excerpt from the Georgetown Courier 

for April 3, 1884, definitely indicates that it was relocated as 

the Johnson: "The Johnson * * * has been leased and 

will commence work as soon as snow melts and the building 

is repaired. This is an excellent piece of property and produced 

a great deal of fine ore when worked as the Belmont." The 

same paper on February 19, 1885, noted that the Johnson had 

from 2 to 3 inches of ore on the lower level, which was sorted 

into two grades of ore. The first-class ore ran 200 ounces of 

silver to the ton, and the second-class ore 100 ounces. Some 

ore from 1 to 6 inches wide was reported as present in the upper 

levels. The property was worked steadily by lessees until 1893 

and produced a few tons of ore running from 100 to 200 ounces 

of silver to the ton. The vein had not been worked for many 

years when visited by the writer in 1927 and was inaccessible. 

The lode probably strikes northeast and is near the southeast 

side of a small stock of Silver Plume granite, but so far as known 

is lies entirely within the granite.

According to the Colorado Mining Directory the mine had 

produced prior to 1883 $300,000 from "galena and sulphurets 

in a quartz gangue", which assayed, when sorted, from 50 to 200 

ounces of silver to the ton. In 1883, according to the same 

authority, it was developed by 4 tunnels aggregating 976 feet 

and by 2 shafts aggregating 163 feet.

BLANCHE

The Blanche vein is on the southwest slope of Collier Mountain, a short distance north of the Silver Wave mine, and lies 

between 11,000 and 12,250 feet above sea level. It was located 

in 1874 and yielded some ore during the eighties but has not 

been worked since 1890. The known production has been 3 

carloads (about 40 tons) in 1883, averaging $50 a ton; 30 tons 

in 1885, netting $1,950; and an unknown amount in 1888, 

netting $544.23 in lead and silver. The mine was worked 

during 1884 and produced about 40 tons of ore; it is not listed 

as a producer in 1886 or 1887 by the Montezuma Mill Run and 

was probably idle during those years. Its total production is 

about 125 tons of lead-silver ore, averaging'about 35 ounces-of 

silver to the ton and 35 percent of lead. It was opened by two 

adits aggregating about 400 feet and a shaft 85 feet deep. The 

shipping ore was 14 inches wide and contained quartz, gray 

copper, galena, and sphalerite. The vein where exposed in,the 

lower workings, a quarter of a mile north of the wagon road to 

Webster Pass, strikes N. 57° E. and dips 58° NW. Here it is 

about 2 feet wide and contains abundant quartz and a seam of 

sulphide 3 inches thick. Galena is slightly more abundant 

than either chalcopyrite or sphalerite, which are present in 

nearly equal amounts. The vein swings northeast a few 

hundred feet from the lower adit and strikes N. 35° E. as far 

up the slopes of Collier Mountain as it has been traced. The 

available figures for production are as follows:

Production from Blanche vein

ISS^. ........................................

\SM............... ..........................

\S^5... ......................................

\S8&. ........................................

Ore (short 

tons)

40

40

30

(?)

Silver (fine 

ounces)

1,400

1,400

1,050

190

Lead, wet 

assay 

(pounds)

28,000

28,000

21, 000

No record available for 1886-87.

BOND

The Bond is a small prospect in Warden Gulch about threequarters of a mile south of Peru Creek. The vein contained
74 MONTEZUMA QUADRANGLE,COLORADO

about 3 inches of gold and silver bearing quartz, and in 1882 a 

small amount of ore was sold to the Chihuahua mill.

BRITTIE SILVER

The Brittle Silver group, which includes the Boston, Brittle 

Silver, Little Nell, Peary, and White Sparrow claims, is on the 

north slope of Brittle Silver Mountain, slightly below an altitude of 12,000 feet, about half a mile south of Peru Creek. The 

country rock in this region is the Montezuma quartz monzonite. 

The veins are from 3 to 15 inches wide and contain galena, 

gray copper, "brittle silver" (stephahite), and a small amount 

of gold. The ore is said to average about 100 ounces of silver 

to the ton, but the only known statement as to the production of 

the property, a carload of about 14 tons in 1885, does not include 

the value of the ore. There was no production in 1887 and 1888, 

and although there was some in 1889 the figures were confidential 

and were not published.

BUDA

The Buda is on the south slope of Cooper Mountain, about 

2 /2 J miles northeast of Montezuma, well above timber line, at an 

altitude of about 12,000 feet. It is developed by a shaft about 

25 feet deep and an adit said to be about 300 feet long. It was 

located in 1880 but produced nothing until 1886. In that year 

8 tons of silver-lead ore was shipped, and in the next 3 years 

about the same amount was produced each year, but only the 

figures for the value are on record; these are given below. The 

ore came from a narrow vein 3 to 6 inches wide, containing 

quartz, pyrite, sphalerite, galena, and some silver and gold.

Production of Buda mine 

[Estimate by Montezuma Mill Kuni

1886.. 

1887 

1888. 

1889... . ..

Ore (short 

tons)

8

(?)

(?)

(?)

Gold

$0.80

.97

Silver

$273

359

127

Lead

8,111

BUENA VISTA

The Buena Vista is on the south slope of the high western 

spur of Collier Mountain, about 1,000 feet northwest of the 

Sarsefield mine and a mile east of Montezuma. The adit by 

which the mine is developed is at an altitude of about 12,000 

feet. In 1889 it produced an unrecorded amount (probably 

about 6 tons) of lead-silver ore, valued at $1,077.82; no other 

record is available. It did not produce prior to 1887 but is 

locally credited with an output of about 35 tons during the 

late eighties. The tonnage of ore in 1889 is not given but was 

probably about 6 tons. The vein trends east-northeast and has 

a narrow quartz-galena seam.

BULLION

The Bullion mine is on Collier Mountain, about a mile southeast of Montezuma, at an altitude of about 11,800 feet, 1,400 

feet above the Snake River. It has an aerial tramway connecting the main level of the mine with a wagon road in the 

valley bottom, but the cables were dismantled in 1928, and in 

1929 the only method of reaching the mine or moving supplies 

to it was over a steep trail.

The Bullion vein was discovered by the Tyler brothers about 

1870, and the Yellowjacket vein, from which nearly all the production of the mine has come, was discovered shortly afterward. 

The two claims were sold to Colonel Williams, who slowly 

developed the mine in the eighties and nineties and sold ore to 

the local smelters. Unfortunately little record of the amount 

could be found, but in 1882 2 tons of galena and gray copper ore 

was sold to local smelters for $290 a ton. The Mayhem Investment Co. bought the Bullion mine from Williams about 1900

and entered on an extensive development program. Several 

thousand tons of ore was produced in 1902-3 after the construction of the Bullion tram. About 1903 some money was 

obtained from the Jackling interests to finance a tunnel starting 

near the foot of the tram to tap the Yellowjacket and other 

nearby veins at depth. No work was done on the proposed 

adit, and in 1904 the loan was foreclosed and the Bullion mine 

became one of the assets of the Florence smelter. When the 

Cripple Creek Short Line and the Florence smelter were sold 

to the Golden Cycle Co., the Bullion mine became the property 

of that corporation, which still owned it in 1933. In 1907 H. B. 

Clifford became interested in the mine and shipped 200 tons of 

ore to various mills for treatment, in order to obtain information 

on the best method of beneficiation before erecting a mill near 

the mine. The operations were stopped during the panic of 

1907 and were not again resumed by Clifford. A carload of ore 

was shipped by a lessee, Charles Dunn, in 1926, but so far as 

known no other work was done in the interval between 1907 and 

1929.

The underground workings of the mine are shown on plate 19. 

The main adit was driven on the Bullion vein and a cross drift 

turned on the Yellowjacket vein about 150 feet from the portal. 

A winze was sunk 40 feet on the Bullion vein, but no sublevels 

were turned. On the Yellowjacket vein a winze 185 feet deep 

connects the cross drift with sublevels 45 and 100 feet below it. 

As shown on plate 19, much of the ground above the first sublevel lias been stoped. A small underground hoist serves the 

winze but is probably inadequate to lift rock economically from 

the bottom of the present winze. The bottom of the winze is 

dry, but the air in it would not support combustion, and the 

present writer was unable to examine the lower workings of the 

mine.

The country rock of the region consists of quartz-biotite schist 

and quartz-biotite-sillimani'e schist, which trend N. 35° E. and 

dip about 65° SE. The Bullion vein strikes parallel to the schist 

and dips parallel to it south of the Yellowjacket vein but becomes vertical and then dips steeply to the west a short distance 

north of the Yellowjacket. For most of its length the Bullion 

vein is a barren sheeted zone about 12 inches wide, containing a 

2-inch seam of gouge; about 230 feet from the portal, however, 

a thin seam of galena is visible for about 50 feet, beyond which 

the vein again becomes barren. The winze on the galena ore 

apparently failed to find encouraging ore below the adit, and no 

further work was done on the Bullion vein.

The Yellowjacket vein strikes about N. 75° W. and dips 

about 65° N. in its productive portion; it dips very steeply to the 

north or south in the nearly barren segment exposed in the first 

100 feet east of the Bullion drift. The Bullion vein faults the 

Yellowjacket vein and displaces the western segment about 10 

feet north of the eastern segment. Two faults parallel to the 

Bullion and with similar displacements cut the Yellowjacket 

vein 20 and 100 feet east of the Bullion drift. West of the third 

fault the Yellowjacket vein is about 6 inches wide and contains 

only a few short, narrow lenses of vuggy quartz incrusted and 

intergrown with pyrite. East of the third fault the vein, which 

is much wider but largely quartz, bends to the southeast. 

Thin seams of galena appear in the walls of the drift about 60 

feet beyond the fault and gradually converge to a junction with 

the main quartz vein near a small eastward-trending quartzbarite vein 100 feet east of the fault. Beyond this place the 

vein resumes its normal course and widens to 24 inches of 

siliceous lead-copper ore. As shown on plate 19, this ore shoot 

is about 240 feet long, and much of it has been stoped. The 

ore shoot extends to the surface but is much shorter at the outcrop than in the main drift. The shoot is stoped 100 feet below 

the level, and the bottom of the winze is reported to be in ore. 

The vertical dimensions of the ore shoot undoubtedly exceed 

the horizontal dimensions somewhat. East of the ore shoot the 

vein has been followed for 150 feet and consists largely of vuggy
THE MINES 75

quartz, carrying short, narrow lenses of galena or chalcopyrite 

separated by barren stretches 20 to 30 feet long.

In the ore shoot the main vein is a persistent seam of quartz 

from 15 to 30 inches wide, carrying abundant chalcopyrite and 

locally containing small amounts of bismuth and a high silver 

content. A seam of galena which, according to observation and 

report, generally lies between the copper-bearing quartz and 

the hanging wall of the vein, is said to be much more variable 

in width than the copper ore, pinching to a width of 1 inch in 

some places and swelling to a maximum of 20 inches in others. 

The galena is nearly free from sphalerite in all the ore seen.

The occurrence of the ore shoot in the Yellowjacket vein, 

which cuts across the schistosity of the country rock, and the 

weakness of the mineralization in the Bullion, which is essentially parallel to the foliation of the schist, are in harmony with 

occurrences of ore in other veins nearby. It is probable that 

further exploration of the Yellowjacket vein would prove the 

existence of other ore shoots similar to that exposed in this 

mine.

The production record of the Bullion so far as it is known is 

given below. It is incomplete but probably gives the bulk of the 

production, as comparatively little ore is reported to have been 

sold before 1900.

Production of Bullion mine

1881. ..........................

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

1SSO... ._____.._._.._........_.

18S7...........................

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

1920...........................

Ore

(short 

tons)

2

4

10

10

200

30

Gold 

(fine 

ounces)

0.70

Silver 

(fine 

ounces)

224

4,500

749

Lead, 

wet assay 

(pounds)

141, 176

1,393

Copper, 

wet assay 

(pounds)

3,996

No record available for 1882 and 1889-1900; no production in 1883-84, 1SS8, 1901-6, 

1UOS-25, 1927-28.

BUSTER

The Buster tunnel is in the northeastern part of the quadrangle, on the north side of Clear Creek about 2 miles west of 

Silver Plume. The main tunnel is at an altitude of about 0,800 

feet and is connected with the main highway by a short wagon 

road. As shown on plate 20, there are two short adits above the 

the main tunnel, but the Avriter did not visit them. The Buster 

tunnel has been driven N. 14° W. for about 1,100 feet, and two 

drifts have been turned from it, one to the east and one to the 

west. The tunnel is in Silver Plume granite for the first 200 

feet, but the rest of it, as well as all the west drift, is in schist 

and gneiss of the Idaho Springs formation. Several fissures 

and faults trending east or northeast were cut, but none were 

mineralized in the schist. The east drift enters granite about 

200 feet from the main tunnel, and the fissure which it follows 

splits into several branches a short distance farther east. Two 

of these branches strike.nearly east and dip steeply south and 

are mineralized. A few mine cars of ore is reported to have 

been found at the crotch where these branches left the northeastward-trending master fissure, but the veins where seen by 

the writer were less than 3 inches wide and consisted chiefly of 

quartz. Thin seams of galena were present in the quartz and 

in places widened to half an inch.

CABLE

The Cable mine is on the northeast slope of Glacier Mountain 

a few hundred feet northwest of the King tram and about a 

quarter of a mile south of Montezuma. It was located in 1881, 

patented in 1882, and active!}' developed through two adits in 

the next few years. It was a regular shipper in 1882-85, producing a total of about 100 tons of ore. The vein is said to be 

from 5 to 8 inches wide and to contain quartz, galena, and some

gray copper. It strikes northeast and is essentially parallel to 

the schistosity of the hornblende gneiss of the Swandyke gneiss, 

which is the country rock.

CARRIE

The Carrie mine is on Wise Mountain 'between the North 

and Middle Forks of the Swan River, at the head of Garibaldi 

Gulch. In 1929 the workings were inaccessible, and the buildings were in poor repair. The mine is said to have produced a 

moderate tonnage of gold ore prior to 1900, and a trial run of 1 

ton of ore in 1905 netted 2 ounces of gold and 10 ounces of 

silver. At that time the mine workings included a tunnel 900 

feet long, a 90-foot shaft, and 3,000 feet of drifts. The mill and 

the portal of the tunnel are near timber line at an altitude of 

about 11,750 feet. According to C. M. Snyder, who worked in 

many of the mines near Swandyke before 1900, the Carrie, in 

common with several other veins on the top of Wise Mountain, 

contained rich gold ore in the shallow oxidized zone close to the 

surface, but profitable mining ceased at a depth of about 25 

feet. The heavy pyrite found below this depth carries almost 

no lead, copper, or zinc, and the value of gold and silver as 

recorded in several assays was between $2 and $4 to the ton.

The rich surface showings of the Carrie, Blackhawk, and 

De Soto encouraged the Carrie Mining Co. to drive its lower 

adit to prove the veins at depth. Thomas Griffith was employed as superintendent in the late nineties, and after crosscutting many strong but very low grade pyritic veins, and 

drifting on some of them to points known to be directly below 

rich surface ore, he recommended the closing of the mine. 

Work was accordingly discontinued-in 1902, and almost no 

work has been done since.

The Carrie and the other veins on Wise Mountain strike 

a little north of east and are almost vertical. The country 

rock consists of granite gneiss and quartz monzouite porphyry, 

both of which are impregnated with pyrite. The top of Wise 

Mountain is only slightly below the general level of the early 

Eocene Flattop peneplain, and the free gold found in the shallow 

oxidized zone on the top of this mountain is probably the result 

of enrichment. No similar concentration of gold was found in 

the pyritic lodes exposed on the glaciated flanks of the mountain.

CASHIER (CHAMPION)

The Cashier mine is on the southeastern slope of Teller 

Mountain, V/i miles due west of Webster Pass and 3 miles 

south of Montezuma. It is opened by four adits between 

altitudes of 12,000 and 12,450 feet, where the vein cuts the 

crest of Teller Mountain. In 1929 most of the workings were 

inaccessible. The Cashier vein was discovered in the early 

seventies by Dickson Southworth, who worked the mine until 

about 1880. In spite of its isolated position, the rich silver ore 

enabled Southworth to make a profit from his small-scale 

operations, and during his tenure of the property 54 shipments were made by pack train to the smelters at Blackhawk. 

The records were preserved in a report made by G. K. Sabin, 

who was subsequently in charge of the property, and are given 

on page 76. Southworth shipped in all 108 tons 312 pounds 

of ore, assaying over 200 ounces of silver to the ton, which 

netted him $20,736.16, or $192 a ton after the smelting charges 

of about $25 had been deducted. The Cashier & Champion 

Mining Co., incorporated in Colorado in 1882, with Sabin as 

superintendent, developed the property extensively in the 

next 10 years. The ore was moved by pack train to the head 

of Hall Valley, about a mile south of the mine, and hauled by 

wagons from that point to the railroad at Webster, 7 miles 

away. The cheaper transportation enabled Sabin to ship 

lower-grade ore than Southworth, and in the report referred 

to above, which unfortunately is not dated, he states that 

under his management the property had then produced 710
76 MONTEZUMA QUADRANGLE, COLORADO

tons 1,927 pounds of ore, yielding $63,349.83, giving an average price of $89.10 a ton after deducting the smelter charges 

of about $25 a ton. According to the Colorado Mining Directory for 1883, the Cashier shipped 320 tons in 1881 and 250 

tons in the first 8 months of 1882. The same authority states 

that the Cashier & Champion Mining Co. was organized by 

the New York & Colorado Mining Syndicate Co. (incorporated 

in Colorado in 1880), whose avowed object was the purchase 

of mines and prospects and their development for sale and for 

the organization of new companies under its control. After 

the mine had been opened up in the early eighties and the 

veins exposed sufficiently to indicate the nature and probable 

extent of the ore, production is said to have stopped, and 

Munson 26 lists the mine as a nonproducer in 1887. Production was resumed about 1889, however, and in 1890, 1891, 

and 1892, according to men who were freighting ore from the 

mine at that time, the Cashier was a shipper. An estimate 

of 300 to 400 tons of ore during this period of production was 

made by one of these men. This figure is probably approximately right, as in 1889 Munson 27 records a total production 

of $4,688.68; as the ore commonly averaged about $90 a ton, 

about 52 tons, or one-quarter of the estimated production, 

would have been produced that year. No production is known 

from the Cashier after 1892. The exact amount of underground 

development work is unknown, but, as shown in plate 21, it 

is more than 2,000 feet and includes a 230-foot winze on the 

lower, adit.

The country rock of the Cashier vein is the Swandyke 

gneiss, which strikes about N. 25° W. and dips 70° W. The 

vein breaks across the schistosity of the gneiss and strikes 

northeast and is said to dip steeply northwest. The ore is 

reported to be from 2 to 24 inches wide and to average about 

12 inches. It consists of galena and gray copper in a quartz 

gangue containing some barite. According to the Monte- 

/Aima Mill Run for March 10, 1883, the lower and main adit 

starts on the vein in the Champion claim and follows it through 

the Champion end lines into the Cashier claim, 300 feet from 

the portal. At the end lines there is a crosscut 100 feet long 

to the Ready Pay vein, which contains some galena and gray 

copper in a quartz gangue. At 200 feet beyond the crosscut 

there is an inclined winze on the Cashier vein that follows it 

to a depth of 230 feet below the level. The ore was continuous to the 100-foot level, where a short crosscut to the southwest had 3 feet of massive barite in the breast. At 70 feet 

southwest of the winze on the 160-foot level the breast of the 

drift was in good ore, and the 230-foot level was also in good 

ore. The ore was continuous from the top to the bottom of 

the winze, according to Mr. Oliver, the editor of the Mill Run, 

and ranged from 10 to 36 inches in width, with an average of 

about 20 inches. It consisted chiefly of gray copper, quartz, 

and barite.

According to a report by E. N. Riotte in 1882, the lower 

adit goes into the hill almost at right angles to the vein and 

strikes it 80 feet from the portal "and then turns and runs in 

on the vein. The vein here is small and poor but becomes 

enriched very soon without widening, and much ore was taken 

out above the tunnel. This pay shoot lasted for 40 feet or 

more and then pinched out, apparently leading southward and 

downward. After passing a barren zone of 20 or 30 feet, the 

vein again becomes rich and. widens, and the top of a new pay 

shoot was struck. This shoot did not reach the upper level 

and was not of great extent in that direction. To prospect it 

a winze was sunk near its commencement, and another 80

26 Munson, J. C., Report of the Director of the Mint upon the precious metals 

in the United States during the calendar year 1887, p, 159,1888, 

" Idem for 1889, p. 153,

feet therefrom the first one to a depth of 50 feet and the 

second to a depth of 100 feet They were connected by a 

drift from the bottom of the first winze. All along these 

openings the vein is very rich, widening in places to 18 inches 

of the richest and 4 feet of the average ore."

According to a manuscript report by L. B. Carpenter dated 

1900, the Cashier lower adit goes west into the hill and cuts the 

vein 20 feet from the entrance. The adit was caved 200 feet 

from the portal at the time of his visit, however. An 18-inch 

seam of lead ore was found 40 feet from the portal of the tunnel 

and was thought to be a "sort of feeder to the main vein." The 

Comstock tunnel, 140 feet below the Cashier lower tunnel, was 

open for its entire length of 500 feet. "At a point 300 feat from 

the mouth it encountered the Cashier vein, and a small stope 

was started, which shows a streak of about 2 feet of good-looking 

lead ore. * * * In another place ore is showing in a crosscut to the north, 400 feet from the mouth. This streak is small, 

however, and would not pay to prospect."

Incomplete production figures for the Cashier and' Champion 

are given below.

Production of Cashier and Champion claims

Cashier: 

1876.. .....................

1877 .......... ..........

1878.....................

1879............ . .......

1880 «. . .-...

1881 «.. . ......

1882 « _ . 

1883..-.........-.- .....

1889.-.-..-----...--..-.-.

1892. -.. 

Champion: 

1876 

1880-82 (see Cashier). 

1886:

1888. 

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

1891 

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

Ore 

(short 

tons)

3

57

35

17

28

311

372

150

(?)

(?)

(')

20

10

(?)

(?)

(?)

(?)

Gold 

(fine 

ounces)

126. 75

19.35

32.12

Silver 

(fine 

ounces)

557 

11, 686

6,321

< 5, 767

<>31, 361

»35, 730

1, 599. 89

6, 614

14

20, 352

5,364

10, 001

Lead, 

wet assay 

(pounds)

68

Copper, 

wet assay 

(pounds)

9 nsfi

5 032

2

CCQ

b OQ 77K

0 Includes Champion.

6 Estimated by comparison with production in 1878.

c Less than half a ton.

Cashier, no record available for 1884, 1888, 1890-91; no production in 1885-87. 

Champion, no record available for 1877-79, 1883-85, 1887; no production in 1890.

CHATAUQUE

The Chatauque mine is on the east slope of Glacier Mountain, 

about V/2 miles south of Montezuma. Its lower workings are 

about 400 feet above Deer Creek, at an altitude of about 11,000 

feet. Several buildings in poor repair are clustered around -the 

portal of the lower adit, at the end of a fair wagon road to 

Montezuma. Most of the production of the mine came from 

two upper adits about 400 (?) feet above the lower workings.

The vein was discovered by Giol Ball and H. M. Teller in 

1866. In 1879 the mine was acquired by the Montezuma Silver 

Mining Co., which held it for many years. By 1870, according 

to Raymond, 100 tons of silver ore averaging 363 ounces to a 

ton had been extracted. According to Frank and William 

Burke, a small amount of ore was stoped and shipped by. them 

as lessees in 1883. In 1884 and 1885 a moderate tonnage of ore 

was shipped, according to J. R. Southerland, who worked in the 

mine during those years. A record of the production from 1887 

to 1892 is given below. The Chatauque is said to have produced 

little or nothing in the next 10 years, and no production is 

known from 1902 to 1929.
THE MINES 77

Production of Chatauque mine

187(1

\SSA. ....................................

IS8-I. ................... ...... ..... 

l^.. ...................................

1QQ7

IS8S. .......................... ...... .

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

1891. 

Oro 

(short 

tons)

100 

7,r) 

28 

10 "15

sCO

(V)

Gold 

(fine 

ounces)

.110.00 

-1. 52

Silver 

(flno 

ounces)

188 

10, 368 

202 

390

Lead, 

wet assay 

(pounds)

9,381 

390, 726

28,522

NW.

« .Estimated.

No record available for 1886 and ISSd.

The accessible part of the lower workings is shown In plate 22. 

The main adit extends IS). 29° W. for 1,130 feet from the portal 

and intersects the Chatauque vein at a distance of 790 feet. 

The western drift on the vein is 175 feet long and was still accessible in 1929, but the eastern drift, said to be 400 feet long, 

was caved a few feet east of the main adit.

The country rock is chiefly the biotite gneiss facies of the 

Swandyke gneiss, but thick layers of pegmatite and hornblende gneiss are common in the first few hundred feet of 

the adit. The schistosity strikes from north to N. 30° E. 

nnd dips 70°-90° W.; the prevailing strike is N. 10° E., and 

the average clip is about 80° W. A dike of dacite porphyry 

about 30 feet wide, parallel to the foliation of the gneiss, is 

cut by the main adit about 75 feet south of the vein, which 

it intersects east of the accessible part of the drift. The 

Chatauque vein strikes from IS!. 80° E. to due east and dips 

40°' -50° N. It is a strongly sheeted or brecciated /one from 

2 to 10 feet wide, and the drag of the gneiss shown in plate 

22 suggests that it is a premineral reverse, fault. The ore is 

chiefly galena, but small amounts of gray copper and sphalerite were seen. As illustrated in figure 12, the galena 

occurs in branching veins and stringers, or as a breccia 

cemented by pink manganiferous ankerite and quart/. In 

the two ore shoots exposed in the west drift the gray copper, which is the silver-bearing mineral of the mine, was 

confined to the brecciated type of ore. In the westernmost 

ore shoot the brecciated ore is about 25 inches wide and 

appears to grade into the branching seams of galena illustrated in figure 12. Interminerali/ation movement on the vein 

was probably carried partly by the ore shoot and partly by the 

barren slips in the sheeted zone; and the ore solutions were more 

active in the open brecciated parts of the vein than in the tight 

scams of the sheeted /one. The Chatauque is a strong vein and 

breaks across the foliation of the country rock, but the exposures 

of the vein were too small at the time of the writer's visit to 

serve as an indication of the strength of its mineralization.

According to the Montezuma Mill Run, the chief workings 

in 1883 consisted of a shaft, an adit 173 feet vertically below 

the collar of the shaft, and the lower tunnel, which was 1,000 

feet long at that time. The upper adit tapped the vein through 

a crosscut 150 feet long and followed the vein for over 100 feet. 

The ore shipped in the next few years came from stopes above 

the upper adit. The lower'tunnel was supposed to be short 

of the Chatauque vein and was driven 130 feet farther in 1885 

in an effort to reach the vein. The Mill Run states that a 

strong vein was cut at 725 feet and was supposed to be the 

Franklin vein. There was a "fine streak of mineral in the breast 

.of the west drift, but it is not solid." The breast of the northcast drift did not impress the editor of the paper so favorably. 

Both breasts were about 35 feet from the main crosscut tunnel 

at the time of his vis.it,

CHRYSOLITE

The Chrysolite vein is in Warden Gulch, about 2 miles east 

of Montezuma. It was discovered about 1884 and produced 

about 15 tons of galena ore, carrying 15 ounces of silver to the 

ton, in 1887 and 1888. The vein is said to have a maximum 

width of 24 inches, but it could not be seen at the time of the 

writer's visit.

CLARION

The Clarion vein is on the west slope of Collier Mountain, 

about 2 miles southeast of Montezuma, between the Bullion 

and Silver Wave mines, at an altitude of about 12,200 feet. It 

was located by William Howell in 1880 and slowly developed in 

the eighties and nineties. A small amount of ore was produced 

during this time, chiefly from a chimneylike shoot about 40 

feet long discovered in 1884. Most of the production was made 

prior to 1893 and is shown below. This ore was chiefly galena 

but contained a small amount of gray copper and assayed from

FIGURK 12. Chatauque vein, west stope, looking east. Footwall streak.

40 to 100 ounces of silver to the ton. The mine probably produced nothing in 1892-1901, but a shoot of lead ore was found 

in driving an adit in 1902, and about 25 tons of ore was produced 

from the drift. As shown below, the ore taken from this shoot 

carried much gold, averaging about 30 ounces to the ton. The 

Clarion was worked intermittently until 1918 but has been idle 

for the last 10 years.

Production of Clarion mine

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

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

1888. 

1889 

.1890.. 

1906. .-

1910.. ................... ......

1916. 

1917... 

Ore 

(short 

tons) .

2 

12 »5 

"50 

(?) 

(?) 

41 

7 

11 

6 

18 

15

Gold 

(fine 

ounces)

1.20

1.00 

12.30 

.84 

3.00 

5.13 

1.06 

.63

Silver 

(fine 

ounces)

316

321 

569 

2, 449 

385 

863 

487 

523 

413

Lead, 

wet assay 

(pounds)

5,232

4,574 

8,166 

25, 427 

3,592 

6,028 

3,934 

5,368 

11,011

Copper, 

wet assay 

(pounds)

149 

223

868 

812

0 Estimated.

No record available for 1891-1900; no production in 1901-2, 1904-5, 1907-9, 1912-15, 1918-28, - - - , if 1
78 MONTEZUMA QUADRANGLE, COLORADO

COLEY (COAIY)

The Coley is noteworthy as the first silver-bearing vein to be 

discovered in the State of Colorado. It is on Glacier Mountain at an altitude of about 11,800 feet, a little less than a mile 

south of Montezuma. The vein was discovered by a Mr. 

Coley in July 1864, but little work was done in the district 

until the following year. It was chiefly valuable for the interest in the silver-bearing lodes that it excited. In the mint 

report for 1883 Burchard states that the mine had yielded but 

a very small amount of bullion and had been worked little save 

by open cuts along the surface. A carload of silver-lead ore 

was shipped from the claim in November 1883, but the value 

of the ore is unknown. No other record of production has been 

found. The vein strikes northeast and is in the Swandyke 

gneiss.

COMMONWEALTH

[See Santiago and Waldorf] 

CONGRESS

The Congress mine is on the north side of Peru Creek at an 

altitude of about 11,500 feet, about 3% miles east-northeast of 

Montezuma. The mine is opened by two adits about 75 feet 

apart vertically and is connected to a wagon road by a steep 

wooden tram. The lower level is more extensive than the 

upper level and is shown in plate 23. The known production of 

the property is small and has come from small rich pockets of 

lead-silver-gold ore. According to the Georgetown Courier for 

November 29, 1888, the vein was 3 feet wide in some places, 

and the mine shipped 2 cars of ore running $350 a ton in 1888 

and had some ore assaying 700 ounces of silver and 5 ounces of 

gold to the ton. The available production figures follow.

Production of Congress mine

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

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

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

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

1892...............- .......

1922..........................

1923............. ...........

Ore 

(short 

tons)

(?)

(?)

(?)

(?)

(?)

88

3

Gold 

(fine 

ounces)

1.26

1 80

Silver 

(fine 

ounces)

207

726

516

1,051

62

Lead, 

wet assay 

(pounds)

i one

18, 540

3,345

2,484

1 3Q*}

Copper, 

wet assay 

(pounds)

86

No record available for 1893-1900; no production in 1901-21, 1924-28.

As shown on plate 23, the vein strikes N. 20° E. and dips 50° 

W. It is from 2 to 30 inches wide, and for much of its length 

it consists of vuggy seams of quartz and py'rite cutting bleached 

quartz monzonite. In places it carries vuggy masses of galena, 

which contain considerable silver and gold, but unfortunately 

the ore bodies are lenticular along both dip and strike. The 

vein is very close to the contact of the quartz monzonite stock 

with the schists, and the course of the vein would carry it out 

of the granite in a short distance. The mine workings are 

entirely within the quartz monzonite stock, and though it is 

improbable that the vein carries good ore far into the schist, 

there is a distinct possibility that ore may be found in the vein 

where it crosses the contact of the two rocks.

COPENHAGEN

The Copenhagen vein is on the west slope of Independence 

Mountain, about 2% miles west of Montezuma, at an altitude 

of about 11,500 feet. It is about 800 feet south of the Ida 

Belle mine and is accessible by the same trail and road. It was 

discovered by Hans Brandt in 1886, and by 1888 he had driven 

four adits on the vein aggregating about 800 feet. In 1887 6 

tons of ore was shipped, netting $297 in silver and $3 in gold. 

The property is listed as a nonproducer in 1888 and is not again

mentioned in the statistical reports of the State. According to 

the Montezuma Mill Run there was in 1887 a maximum width 

of 14 inches of massive galena ore in the mine, and in 1888 it 

notes that 4 inches of good ore had been found in most of the 

lower level.

The vein strikes nearly due east and is vertical. The adits 

have long been caved, but the ore on the dumps indicates that 

the vein was from 1 to 12 inches wide and consisted of galena, 

sphalerite, and quartz. The greatest width of solid galena 

observed was 3 inches. The vein is parallel to the Ida Belle and 

like it cuts Swandyke gneiss that has been thrust-faulted onto 

black Upper Cretaceous shale, which crops out conspicuously 

on the lower slopes of the mountain. The general relations are 

shown in the cross sections of .the Ida Belle mine in figure 15. 

As the best ore.in the Ida Belle was found where the vertical 

vein crossed the brecciated contact of the Cretaceous shale and 

the overthrust Swandyke gneiss, it is probable that the best 

ore in the Copenhagen would be found in a similar structural 

setting. The dip of the overthrust fault carries the contact of 

the shale and the overlying hornblende gneiss downhill south of 

the Ida Belle mine, and the lowest adit on the Copenhagen vein 

is about 250 feet above the place where the contact of the shale 

and the gneiss comes to the surface. However, as the overthrust fault dips southwest in this region, the lower adit would 

cut the fault if continued far enough east. No shale was found 

on any of the dumps, and it is evident that the fault was never 

reached by the old workings.

DELAWARE

The Delaware, Delaware Extension, and Sunrise claims are 

on the north slope of Decatur Mountain near the mouth of Cinnamon Gulch, about 3 miles east of Montezuma. The Delaware vein was discovered in 1879 by William Mendenhall and 

J. F. Sypher, and development was started the same year. By 

1883 about 800 tons of ore had been shipped, and the underground workings included an adit about 400 feet long and a 

shaft 165 feet deep, from which three levels had been turned, 

aggregating about 400 feet. Unfortunately the mine was in a 

district where no reports on production were maintained, and 

the amount of ore removed is unknown. It is said to have been 

a steady producer in the eighties, but is not mentioned by 

Munson in his reports for these years. In July 1884 it was 

producing 3 wagonloads of ore a day (probably about 8 tons). 

It was not mentioned by the local paper of Montezuma during 

the next few years, but it is safe to say that the total production 

exceeded 1,000 tons. The vein was several feet wide and con- 

.tained from 6 to 36 inches of galena, gray copper, and chalcopyrite in a quartz gangue, assaying in shipments from 25 to 600 

ounces of silver to the ton. The Delaware vein is the southwestern extension of the Pennsylvania vein, and the reader 

; is referred to the description of that vein on pages 93-95 for a 

discussion of the general geology.

DON PEDRO

The Don Pedro is on the east slope of Independence Mountain, a few hundred feet south of the Hunkidori mine and about 

2 miles west of Montezuma. It was discovered in 1874 by 

Smith, John Lynch, and Joseph Love but was little worked 

until 1880. Most of its development was the work of Oliver 

Milner and Joseph McKinney from 1880 to 1887, and no 

record of production for later years has been found. It was 

opened by four adits along the vein, of which the lowest was 

about 200 feet long. The vein strikes northeast and dips about 

50° NW. The ore streak was from 6 to 12 inches wide and 

contained galena and gray copper in a quartz gangue. The 

inaccessibility of the deposit discouraged development, as most 

of the ore required concentrating before it could be profitably, 

shipped. Only carefully sorted ore was loaded on the mule
U. S. GEOLOGICAL SURVEY

PROFESSIONAL PAPER 178 PLATE 23

2nS-FeS2

Ore in bottom

1'bet.walis

;:

7S" ^&r 6" ZnS ^?<?

4"ZnS-FeS2

A

t'8"ZnS-FeSz ore 2'6"bet.walls 

J\ 4" ZnS ore at top

Vertical grooves on wall

i oo oo Feet

2"ZnS ore

Knife-blade seam 

PbS andankerite

Stopedabove

Fissure 2"between 

walls, barren

!2"fissure stoped above 

15' Pyrite seams, vuggy 

quartz, some galena

B

Good ore

100 Feet

15" vein 

0.9 quartz 

0.1 Pb and Cu

lOOFeet

C

EXPLANATION

Barren fissure, fault, or vein from 1 to 

12 inches wide

Mineralized vein more than 12 inches 

wide

Galena vein less than 1 inch wide 

Galena vein from 1 to 12 inches wide 

Sphalerite vein less than 1 inch wide

Sphalerite vein from 1 to 12 inches 

wide

Sphalerite vein more than 12 inches 

wide

Pyritic vein from 1 to 12 inches wide

Strike and dip

Pb, lead ore

PbS, galena

ZnS, sphalerite

Cu, copper sulphides

FeSa, pyrite

Timbered drift

PLANS OF FISHERMAN VEIN, ON SNAKE RIVER (A); CONGRESS MINE, 

RUBY MOUNTAIN (S); AND STAR OF THE WEST No. 2 MINE,

TELLER MOUNTAIN (C)
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 178 PLATE 24

Z"- 12" iron-stained 

sheeted zone

a"sheeted zone

^ 4 sheeted zone k anker-lte \ iron stained 

3" FeS, a/id quartz 

T'PbS

EXPLANATION

Barren fissure, fault, or vein less than 

1 inch wide

Barren fissure, fault, or vein from 1 to 

12 inches wide

Barren fault or vein more than 12 

inches wide

Mineralized vein

Mineralized vein with many barren

stretches alternating with lenses

of ore

Galena ore 

Strike and dip 

Strike and vertical dip 

Strike of schistosity 

Downthrown side of fault 

Grooves and sllckensides 

Sheeted zone 

Timbered drift

PbS, galena

FeCu, iron and copper

pyrite 

Mn, manganese 

Bi. bismuth

'Broken 

rock

NO. S L£V£L ° JvN^. 

EL. 11,600' >

PLANS OF HUNKIDORI MINE, GRIZZLY GULCH (A), AND 

MISSOURI MINE, HALL VALLEY (B)
U. S. GEOLOGICAL SURVEY PROFESSION

EXPLANATION

Barren fissure, fault, or vein less than 

1 inch wide

Barren fissure, fault, or vein from 1 to 

12 inches wide

Barren fault or vein more than 12 

inches wide

Slightly mineralized vein from 1 to 

12 inches wide

Slightly mineralized vein more than 

12 inches wide

Mineralized vein with 1 to 12 inches 

of ore

Mineralized vein with more than 12

inches of ore 

Strike and dip

Striations

TU'MZ&TrfjjP*^

Hornblende gneiss and interlayered

^(JaniS WilUar"±-- -~~~~~ ~ 

_^ ---~~~~ Black shale

ff?S\

granite gneiss 

INTERMEDIATE L£V£L jr

thrysl__ - ^^ 

(Pier-re ?)

 ^Off.

\ H Thicl< 4 . ,B\acK| ^-~i; \x . \ fault .» * ishaie'lllllmi^ -,\\ , brec»c ' a 2^ySsc!Mr=

PLAN AND SECTION OF IDA BELLE MINE, JONES GULCH
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 178 PLATE 26 

ROAD - i .

Barren fissure, fault, or vein less than 

1 inch wide

Barren fissure, fault, or vein from 1 to 

12 inches wide

Barren fault or vein more than 12

inches wide 

Slightly mineralized vein from 1 to

12 inches wide

 Mineralized vein from 1 to 12 inches 

wide

 xxx Fissure zone more than 12 inches

wide carrying from 1 to 12 inches 

of ore (red dots) or more than 12 

inches (red crosses)

~--iZf 0 Strike and dip

///// Strike of schistosity

 -£_ Downthrown side of fault

 i- Relative movement of walls 

~* (horizontal component) 

Pb, lead ore

Cu, copper sulphides 

Rh, rhodochrosite 

COs, carbonate

Ruby silver, Rh,Pb

Hornblende gneiss

Evening Star vein

Morning Star vein

50 0

' I I I I I______L

NO.5 TUNNEL 

EL. IO.450'

Rh,Pb, Ruby silver/^T^arren g°uge

Tight 40°

2"gouge,3'sheeted zone

70'

, NO. 3 TUNNEL 

Z-EL. II.O23'

30'slip,60'shif

Open

2-4'PbandRh

Hornblende 

gneiss

NO. 2 TUNNEL 

EL. 11.12 3'

200 Feet i

Hornblende

/ /gneiss

PLANS OF JERRY AND EQUITY ADITS, MONTEZUMA
U.S. GEOLOGICAL SURVEY PUOFKSS1ONAL PAPER 178 PLATE 27

UPPEK JOSEPHINE TUNNEL

£1.10,8 9 3

=&. -Ill- tope NEW RAISE 2"to4"ore MIDDLE JOSEPHINE TUNNEL

("ore m bottom 2"ore 'J in bottom .- 2ore Tl 2"to4"ore

2*ore

u

2"to4"ore in bottom

', 2 ore 11 CROSSCUT

WINZE

U U IUJ LOWER JOSEPHINE TUNNEL

£1.10,651'

SECTION

PLAN 

JOSEPHINE MINE, KELSO MOUNTAIN.
THE MINES 79

train and taken to Keystone, the nearest shipping point. In 

September 18S2, according to the local paper, "the last shipment of 30 sacks was 4,060 pounds and ran 72 ounces per ton 

in silver and assayed 62 percent lead." The total production 

of the mine during the eighties was probably about 50 tons.

ERICKSON

The Eriokson is 3 miles southwest of Montezunia, on the 

southwest slope of Keystone Mountain, at an altitude of about 

12,000 feet. It was discovered by ,T. B. Erickson in July 1880 

and was worked from 1884 to 1888. During this time a shaft 

125 feet deep and an adit reported to be about 250 feet long were 

driven on the vein. In 1885 20 tons of lead ore netted the 

owners $600, and in 1886 37 tons of unknown value was shipped. 

This is probably the total production of the property. The 

vein strikes N. 45° E. and is nearly vertical. Most of the ore 

produced came from stopes above the 125-foot level of the shaft, 

but the ground was so heavy that the stopes became dangerous, 

large masses of ore and waste caving daily with little^ warning, 

and in 1888 work in them was abandoned. The ore in these 

upper workings was largely galena and reached a maximum 

width of 18 inches; in the adit, some distance lower on the vein, 

the ore seam was much narrower and contained as much zinc 

blende as galena. The galena ore is reported to assay about 25 

ounces in silver to the ton. The country rock of the region is 

the Swandyke gneiss, which strikes from north to northeast 

and is nearly vertical but dips steeply to the west in many 

places. The vein is on the line of tear faulting that formed when 

the Williams Range underthrust broke the overturned fold a 

short distance north of Tiger. (See p. 44.)

FISHERMAN

The Fisherman workings are about half a mile north-northwest of Montexuma, at an altitude of 10,040 feet, a few hundred 

feet south of the high bridge on the main road from Montezuma 

to Keystone. The vein was discovered in the late eighties, but 

no production is recorded until 1905, and miners are agreed that 

it produced less than 150 tons before 1900. Its total production 

does not exceed 300 tons and is probably somewhat less. 

Sphalerite is the chief mineral in the vein, but galena is locally 

abundant. The vein is entirely in Montezuma quartz monzonite and strikes N. 45°-65° E. Its average dip is nearly 

vertical, but steep northwest and southeast dips are common. 

As shown in plate 23, the ore occurs in lenticular swellings in 

the vein, and the best shoot exposed is at the place where the 

course of the vein changes from N. 63° E. to N. 45° E. and the 

vein dips 75° SE. As shown in plate 23, however, the ore 

pinches very abruptly a short distance above the drift but is 

20 inches wide at the top of the drift. Very little gangue is 

present in the ore, but a few fragments of partly replaced 

inonzonite were observed in a wide seam of sphalerite. The 

minerals present, named in the general order of abundance, are 

dark-colored sphalerite, pyrite, galena, quartz, and arsenopyrite. Galena is distinctly later than the pyrite and sphalerite, and the sphalerite is also earlier than most of the quartz. 

The character of the ore is shown by. the available production 

figures, as follows:

Production of Fisherman mine

.Prior to 1900..... ..........

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

1900....-......... ..........

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

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

Ore

(short 

tous)

« 100-150 

20 

27 

"21 

3

Gold 

(fine 

ounces)

3. 62 

. 1.11 

1.74

Silver 

(fins 

ounces)

1,300 

1,012 

279 

45

Lead, 

wet 

assay 

(pounds)

14, 118 

34, 944 

13, 176 

2,941

Zinc 

(pounds)

14, 202 

5,250

 Estimated. 

6 lloprosonts concentrates from 100 tons of milling ore. 

No production in 1901-4, 1909-28.

GLENDALE, GRAND TRUNK, TREASURE VAULT, AND ISRAEL WILLIAMS

The group of claims comprising the Glendale, Grand Trunk, 

Treasure Vault, and Israel Williams crosses the crest of the high 

spur from Collier Mountain that leads to Silver Mountain, and 

it laps down into the valley of West Geneva Creek on the south 

and into Warden Gulch on the north. The claims are about 2 

miles east of Montezuma and lie between 12,000 and 12,750 

feet above sea level. They have been explored by openings in 

both West Geneva Valley and Warden Gulch, but their production has been small. The Glendale produced 5 tons of ore in 

1887; 3 tons in 1SSS, which netted $438 for the silver; and an 

unknown amount in 1889, which brought $96.97 for the silver. 

The Israel Williams produced 50 sacks (about 2 tons) of silver 

ore in 1885 and a small amount of ore in 1886 and 1888. The 

Treasure Vault, according to Raymond's report for 1874, 

"contains bismuth-silver ores and at the time of its discovery 

created considerable excitement. Several other veins of the 

same character have been found, and it is now known that there 

is a well-defined belt of lodes carrying ores of this metal at the 

head of Geneva Gulch. They have a uniform course nearly 

north and south, crossing the others, and give every indication 

of more recent formation. As yet they have produced but 

little beyond specimens, but their location and the poverty of 

their owners will easily account for that. During the last

I f-6' quartz" 

'If and pyrite

'

N 

A

Idaho Springs 

 formation. 

/ (quartz and- 

' biotite schist)

FIGURE 13. Grand Trunk adit, Geneva Gulch.

summer about 1,500 pounds of slide found on the slope below the 

Hidden Treasure, and supposed to have come from it, were 

taken to Georgetown and sold at the rate of $400 per ton. The 

ore has been examined and approaches in its analysis very nearly 

that of the mineral schapbachite."

No production is recorded for the Treasure Vault claim, 

which adjoins the Glendale and is on the same vein, although 

the Georgetown Courier for November 11, 1883, states that 

"the Buffalo lode, extension of the Glendale, mill run gave, 

first class, 495 ounces; second class, 445 ounces; third class, 

112.8 ounces; and fourth class, 43.2 ounces silver per ton. 

* * * The run netted over $900 clear. * * * |The 

vein has] a solid pay streak of 8 inches." According to the 

Colorado Mining Directory for 1883, this vein had ore from 10 

to 40 inches wide, which carried quartz, galena, gray copper, and 

bismuth, and from 25 to 2,500 ounces in silver to the ton.

The Grand Trunk adit is at the head of West Geneva Creek, 

at an altitude of 12,000 feet. A sketch map of the tunnel is 

shown in figure 13. Although the adit is rough!}' parallel to the 

Grand Trunk claim, no vein was observed in the adit having 

a course approaching that of the claim. A vein striking N. 

40° E. and dipping 80° SE. is cut about 400 feet from the portal, 

and another vein striking N. 10° E. and dipping 55° W. is 

cut about 200 feet farther north. The first vein is from 2 to 12 

inches wide and is chiefly quartz, but pyrite is abundant. The
80 MONTEZUMA QUADRANGLE, COLORADO

second vein is from 1 to 6 inches wide and is of the same 

general character as the first. The country rock of the mine 

comprises Silver Plume granite and schist and injection gneiss 

of the Idaho Springs formation, which strikes about N. 10° E. 

and dips about 55° W. There are small stopes on the veins, 

and about 2 tons of ore has been sacked and was on the dump 

in 1928. This ore was open and vuggy and consisted of galena, 

light-colored sphalerite, and barite.'

GOLD BELT AND HA MILL

The Gold Belt and Hamill tunnels are in the northeastern 

part of the quadrangle on the south side of Clear Creek, about 

2 miles west of Silver Plume. As shown on plate 3, the Gold 

Belt has an altitude of about 9,625 feet, and the Hamill/ a 

short distance southeast of it, about 9,800 feet. Both are 

easily accessible by automobile from Silver Plume. The mines 

were not working in 1928 and 1929, and the writer was able 

to make only a cursory examination of one of them, the Gold 

Belt. It is developed by a tunnel about 3,000 feet long, which 

runs south-southeastward into the base of Ganley Peak. 

Several carloads of ore was found in a vein cut by the tunnel 

1,600 feet from the portal. This vein strikes N. 80° E. and 

dips 80° S. In places the south wall swings away from the 

north wall until it strikes about N. 70° W., and in such places 

there is a wide zone of crushed rock. Slickensides dip about 

70° E., and the drag of the schist walls indicates that the south 

wall has moved upward. There was no indication of ore in 

the vein on the tunnel level, but a raise tapped the bottom of 

the ore shoot a short distance above. The vein is chiefly in 

schist and gneiss of the Idaho Springs formation, but locally 

it cuts Silver Plume granite, and this rock made the walls of 

the ore shoot.

A quartz monzonite porphyry dike was cut by the main tunnel 

about 3,000 feet from the portal, and drifts were turned northeast and southwest along its contact with the granite, which 

there forms the country rock. The contact was feebly mineralized, and one small pocket of ore was found that contained a 

few thousand pounds of lead and zinc sulphide.

The available production figures follow.

Production of Gold Belt and Hamill tunnels

Hamill tunnel: 

1924 ... . 

1QOK

1928 

Ore 

(short 

tons)

« 336

439

7

Gold 

(fine 

ounces)

0.40

Silver 

(fine 

ounces)

32, 160

36, 972

1,034

Lead, 

wet 

assay 

(pounds)

25, 386

31, 075

953

Zinc 

(pounds)

68,247

2,640

Dry smelting ore

Mary Etta group (includes Gold 

Belt, Mary Etta, Silver Plume 

tunnel, and others):

1902

1911

1Q-1O

1913. 

1Q1d

1919 

1920 

 moo

1Q9**

2

2

8

22

33

5

1

43

683

7.00

2.79

.12

.37

.16

358

183

1,353

2,137

2,172

242

174

1,215

47,749

404

1,796

3,022

74

61

57,077

° Includes 14 tons of concentrates containing 0.40 ounce of gold, 4,894 ounces of 

silver, and 3,528 pounds of lead. Concentrates were produced from 30 tons of milling ore.

No production in 1901-23,1926-27,

Production of Gold Belt and Hamill tunnels Continued 

Lead smelting ore

1912.... ._ _ __ ......... .

1913. .

1914.........----.--.....-...... .

1921 (Gold Belt)...----... . ...

1923 .

1928 

Ore 

(short 

tons)

6

88

3

92

16

Gold 

(fine 

ounces)

0.02

.09

.23

Silver 

(flue 

ounces)

1,844

789

8,866

542

10 C\QA

1,074

Lead, 

wet 

assay 

(pounds)

1,240

1,563

2?, 481

582

1ft fV?Q

1,145

2 d1^

ZiiiC 

(pounds)

7 2§8

Zinc smelting ore

1915 ....... ........ 27 1,590 99 9fi

Mary Etta group: 

1914..,..... .................

1923.......... _ .

Concentrates 

(short 

tons)

4

26

Gold 

(fine 

ounces)

0.74

Silver 

(fine 

ounces)

117

1,763

Lead, 

wet 

assay 

(pounds)

364

2,350

Zinc 

(pounds)

Lead concentrates

1914

1921...... ...................... ....

1922 - . .

1923....... .........................

1925 (probably from Silvery

48

5

39

99

20

4.05

.82

.87

7.52

.97

c 4QQ

362

1,158

3,280

12, 383

1,045

1,595

1,215

4,G04

15,287

4,372 10, 082

Zinc

1923... .... ............... ........

208

58

6,952

998

10, 960

4,380

178,115

46, 630

Lead-zinc

1914.. 3 213 571 2,556

Ore to concentrating mills from Mary Etta group

Short tons

1914....--..--...--.---.-..-----. »2,040 

1920 "40

1921..-.-:.........---..---.---,- &20

1922.

1923.

1925.

Short tons 

.:... M95 

..... «615 

..... "108

Lead-zinc ore. 

»Dry silver ore.

HANCOCK

The Hancock is on the northeast slope of Glacier Mountain, 

close to the crest, at an altitude of about 11,700 feet, about 

half a mile southwest of Montezuma. The vein was discovered 

about 1881 but is not mentioned as a producer by the local 

paper. The workings were inaccessible in 1929. The vein 

strikes about N. 30° E. and is reported to carry galena in a

quartz gangue.

HANNIBAL

The Hannibal vein is on the west slope of Collier Mountain 

and is exposed in adits and open cuts between altitudes of 

10,750 and 11,540 feet. The lower adit is a mile south-southeast of Montezuma and can be reached by automobile over 

the secondary road that continues south from the foot of the 

Bullion tramway. The vein was discovered in 1880, and an
THE MINES 81

adit was driven near timber line for a distance of 330 feet 

before the end of 1883. There is a small stope in this adit 

not far from the portal, and it is probable that some ore was 

shipped from this place in the early eighties, but no production 

is recorded. The lower adit has been driven by Thomas 

Sharpc since 1906, but no ore had been obtained from it up to 

the end of 1929. The total production of the property probably 

does not exceed 25 tons.

A map of the lower adit is shown in figure 14. At 220 feet 

southeast of the portal a branch drift turns to the east, but it 

was bulkheadecl in 1929 and could not be examined. The 

main drift continues southeast to the Hannibal vein, which is 

cut 280 feet from the portal. The country rock of the entire 

adit is quartz schist of the Idaho Springs formation, which 

strikes northwest and dips about 50° SW. The vein strikes 

about N. 88° E. and dips about 85° N. The vein in the breast 

of the lower adit in 1929 was from 6 to 8 inches wide and consisted chiefly of quartz seamed with pyrite, but a few thin 

veinlets of manganiferous ankerite from 6 to 12 inches long 

cut the quartz and pyrite. A few grains of galena were also 

found. Seams of massive pyrite from one-eighth to 1 inch in 

thickness are abundant in the wall rock near the vein. 

In the upper workings the vein contains from 1 to 7 

inches of galena, but very little work has been done, 

and it is difficult to estimate the extent of the ore. 

However, the vein can be traced easily for half a mile 

and as it cuts across the formation and is essentially 

parallel to the Yellowjacket vein of the Bullion mine, 

it probably also contains some workable chimneys of 

ore. Additional prospecting should be done on the 

vein near its intersection with other veins.

Production of Harrison mine

188»................. ....................

1884... ........ ................ .._-.._ 

18S7 - - . 

1889.. ........ - - 

1890...-. .-- .............. .

1918..... ... _ 

Ore (short 

tons)

50 

15 

4 

(?)

(?) 2

Silver 

(fine 

ounces)

3,000

395 

1,570 

5,146 

23

Lead, wet 

assay 

(pounds)

2,944 

13, 905 

41,778 

1,434

Copper, 

wet assay 

(pounds)

8

No record available for 1885-86, 1891-1900; no production in 1888, 1901-17, 1919-28. 

HERMAN

The Herman vein is on the west slope of Glacier Mountain 

near the head of St. Johns, Creek, at an altitude of about 11,700 

feet, 2 miles southwest of Montezuma. It was located in 1875, 

patented in 1881, and developed during the early eighties but 

has not been worked since 1890. It is listed as a "heavy 

shipper" by the local paper in 1882 and 1883. It shipped in 

1884 and 1885 but was a nonproducer in 1886-88 and is not 

again mentioned in the reports examined by the writer. Its

\\\

HARRISON

The Harrison vein is on the west slope of Glacier 

Mountain at an altitude of about 11,200 feet, half a 

mile southwest of Montezuma. The vein was discovered in the early seventies, but little work was 

done on it until 1883. From that year until 1890 

the vein was worked and produced a moderate amount 

of lead-silver ore. According to Burchard's report 

for .1883, "The Harrison, the property of the Gem 

City Mining Co., on the eastern slope of Glacier 

Mountain, that has been idle so long on account of 

litigation, has finally settled all dispute and is now one of the 

big producers of this section. The developments * * * are 

two tunnels * * * on the vein * * * and three open 

cuts * * * and the discovery shaft, * * * aggregating 200 feet. Ore is shown in all the workings and improves 

with depth * * * being gray copper and galena which 

averages about 60 ounces of silver per ton."

These workings are on the west side of Glacier Mountain 

and were inaccessible at the time of the writer's visit. One adit 

on the steep northeastern face of the mountain was open in 

1927, but no ore was found in it. The tight barren fissure that 

was followed southwest from the portal split into two barren 

seams in a short distance. Both branches were explored for 

about 100 feet, but no ore was found in either branch.

According to James Southerland, the Harrison produced most 

of its ore in 1888 to 1890, and all of it'came from the shaft 

sunk on the west slope of the mountain some distance above 

the adit described above. The ore was nearly solid galena, 

but some quartz and barite were present. The vein in the 

shaft strikes northeast and clips steeply northwest. The 

known production, of the mine is given below.

Quartz schist 

(containing a few 

seams ofqtsartzdiotite schist) a\)' Pyrite and quart* 

T offset

3~6 crushed zone

Pyntic vein from 1 to 12 inches wide

Strike and dip

Barren fissure, fault, or vein from 1 to 

12 inches wide

Strike of schistosity

FIGURE 14. Hannibal vein, lower adit.

total production is probably about 115 tons of lead-silver ore, 

worth at the time pf prqduction about $85 a ton. According 

to the Colorado Mine Directory for 1883, the Herman vein 

was 5 feet wide and had a "pay streak 20 inches wide"; the 

ore contained galena, gray copper, ruby silver, silver glance, 

and quartz, assaying abput 18 "percent of lead and from 75 to 

200 ounces to the ton in silver. ' In Raymond's report for 1883 

he notes that the Herman had been shipping some ore and 

that the "crevice is about 6 feet wide, and all the crevice matter 

pays for shipment, the average grade being between 60 and 

70 ounces silver per ton. This is probably the largest ore 

body in the district, and with development will probably be 

one of the largest producers."

The vein is parallel to the Wild Irishman and about 100 feet 

south of that vein. The country rock is the Swandyke gneiss, 

which strikes N. 359 E. and dips 70° E.

HUNKIDORI

The Hunkidori mine is on the east slope of Independence 

Mountain, in Grizzly Gulch, 1^ miles due west of Montezuma, 

at an altitude of about 11,200 feet. The vein was discovered 

in July 1880 by Messrs. Penry, Dougherty, Murphy, and
82 MONTEZUMA QUADRANGLE, COLORADO

Keogh. The first work was done about 1,500 feet southwest 

of the present adit portal, at an altitude of about 11,550 feet. 

This adit was driven 110 feet but had to be abandoned because 

of the constant caving of the roof. Another adit was driven 

660 feet farther northeast at a lower level, and most of the ore 

shipped from the mine came from this adit. In 1882 the Montezumfi, Mill Run reported that this adit had been driven 280 

feet and that "the first mineral in this level was struck at a distance of 84 feet from its mouth and continues to improve steadily for 40 feet, where a fault occurs in the crevice, and a crosscut 

was driven 15 feet south, which exposed a vein which was drifted 

on for 72 feet. This vein shows mineral the greater part of 

this distance, and in the breast of the drift the pay streak is 

2 inches wide in the top and 12 inches wide in the bottom. The 

breast of the main drift is not in pay at present, but the crevice 

matter is rapidly improving, and there is no doubt but that 

another body of mineral will soon be struck. In the ore house 

there are about 75 tons of very clean, fine-looking mineral. 

No stoping worth speaking of has been done."

The lowest adit, in which, all the recent work has been done, 

was started in 1882. There are no maps of the upper levels, but 

the lower workings and the geology of the mine are shown in 

plate 24. The Hunkidori commenced shipping small lots of 

ore by pack train in 1882 and has been intermittently productive 

since that time. According to the Colorado Mine Directory for 

1883 the vein of the Hunkidori at that time was 22 inches 

wide and contained galena, gray copper, and quartz, and the 

sorted ore averaged 40 percent of lead and 157 ounces to the 

ton in silvjer.

I Production of Hunkidori mine

\

1882.. .........I.................

1883.. .............. .............

1885 

18S6--.,....-..--.-- __ -...----.

1889. 

1890.-... -

1911. - .- . ----------

Ore (short 

tons)

£0

10

10

1

(?) 

2

Gold (Hue 

ounces)

0.11

Silver (fine 

ounces)

471

67

Lead, wet

assay 

(pounds)

11,367

No record available for 1884, 1891-1910,1912-28; no production in 1887-88.

The country rock of the lower workings is Montezuma quartz 

monzonite, but the vein crosses into hornblende gneiss a short 

distance southwest of them. Most of the ore produced by the 

property probably was mined near the contact of the monzonite 

and the gneiss and was between gneiss walls. As shown on 

plate 24, there are two distinct fr& cture systems in the monzonite, 

both of which are mineralized. The principal vein is the Hunkidori, which strikes N. 57° E. and dips 85°-90° S. In its barren 

parts it is an iron-stained sheeted zone from 2 to 12 inches wide; 

where it carries ore the vein consists of quartz, manganiferous 

ankerite, pyrite, galena, and a small amount of zinc blende 

and ranges in width from 10 to 30 inches. There are several 

other fissures in the mine, most of which strike northwest. 

Most of them are iron-stained, some of them carry pyrite, some 

carry both pyrite and galena, and in one of them a seam of 

barite and galena .6 inches wide was seen. Little gouge is 

present on any of the fissures; instead, there is A strongly sheeted 

structure or a zone of slightly crushed and altered rock. At the 

breast of the adit in 1928 the vein showed evidence of repeated 

movements during the period of mineralization. Darkcolored quartz containing abundant pyrite disseminated through 

it had been brecciated and cemented by pink manganiferous 

ankerite. Seams of light-colored quartz apparently contemporaneous with the galena that is disseminated through it 

follow the wall of the vein, but the relation of the quartz to the 

other minerals was not evident.

The vein appears much stronger and better mineralized as 

it is followed southwest; the occurrence of the productive ore 

body in the upper level close to the contact of the monzonite and 

the Swandyke gneiss suggests that the ore in the lower adit 

will be found to improve as the drift is pushed southwestward 

to the contact of these two formations.

IDA BELLE

The Ida Belle vein is on the west slope of Independence 

Mountain about 3 miles west-northwest of Montezuma, at an 

altitude of about 11,450 feet. A steep road, which is passable 

with difficulty for most automobiles, leads from the DillonMontezuma highway 2 miles east of Keystone to the lower cabins 

of the Ida Belle in Jones Gulch, at an.altitude of about 10,250 

feet. The mine workings are connected with the lower cabin 

by a steep trail, and supplies and ore are packed by burros or 

horses over this trail. A very good trail also leads from the 

lower cabins directly down Jones Gulch to the Dillon-Montezuma highway, and a trail from the mine to Montezuma runs 

along the north slope of Independence Mountain past the 

Hunkidori mine.

The Ida Belle vein was discovered in 1880 and developed by 

three adits in the next few years. The mine shipped steadily 

during most of the eighties but never in large amounts. It is 

not credited with any production between 1889 and 1916 and 

was undoubtedly idle during most of that time. The known 

production is given below.

The upper adit was not accessible in 1928, and only the two 

lower adits are shown on plate 25. Both adits are about 440 

feet long. A winze 125 feet deep, 165 feet from the portal of 

the upper adit, connects it with the lower adit. An intermediate 

level 50 feet below the upper drift has been driven 110 feet 

east from the winze. As shown in the longitudinal section in 

plate 25, some small stopes have been made above the lower and 

upper workings, but in 1929 very little ore had been removed 

between the two levels. Most of the upper adit is on the Ida 

Belle vein, which strikes about N. 80° E. and dips 65°-90° N. 

.but averages about 85°. The lower adit in part follows the 

vein and in part follows a barren fissure a few feet south of the 

main vein.

Production of Ida Belle mine

1883 . ------

1884 

1887. 

1888 - 

1916. . .-.-. -----

1917 

1922--..........--..

1923 

1924... ___-..-. .

1928.... --------

Ore 

(short 

tons)

50

50

°30

(?)

11

37

29

*30

8

28

Gold 

(fine 

ounces)

3.39

.56

5.16

.70

10.37

4.70

4.40

Silver 

(fine 

ounces)

739

223

588

385

340

114

366

Lead, 

wet assay 

(pounds)

33, 353

11, 275

23, 610

13,823

18, 930

19, 069

Copper, 

wet assay 

(pounds)

45

82

47

Zinc 

(pounds)

6,565

4, 338

4,338

o Estimated.

i> Includes 22 tons of lead ore, containing 6.30 ounces of gold, 340 ounces of silver, and 

16,850 pounds of lead.

No record available for 1885-86,1889-1900; no production in 1901-15,1918-21,1925-27.

The most prominent geologic feature of the mine is the 

Williams Range thrust fault, which separates the pre-Cambrian 

gneiss and the Upper Cretaceous shale. This fault, as shown 

on page 47, has a horizontal component of movement of at 

least 4 miles. Its regional relations are indicated in cross 

section C-C', plate 4. The fault breccia is from 40 to 70 feet 

thick in the Ida Belle mine and dips 5°-40° W., averaging about 

16°. The Ida Belle fissure offsets the thrust fault, and the 

contact of the shale with the overlying brecciated gneiss is 

accordingly found from 5 to 40 feet farther east on the north 

side of the vein than on the south side, §J tokens, ides and
THE MINES 83

grooves on the walls of the vein in the upper adit dip 10° E. 

and suggest that most of the displacement was horizontal. 

The movement along the Ida Belle fissure formed a gougy, 

sheeted zone from 2 to 6 inches wide in the shale, a crushed and 

sheeted zone from 24 to 60 inches wide in the breccia, and a 

fissured zone from 12 to 45 inches wide in the overlying gneiss. 

The mineralization of this vein, as would be expected, was 

strongest in the thrust-fault breccia and weakest in the shale. 

The ore observed in the thrust-fault breccia close to the contact 

of the shale was much better than that 50 feet above and was 

'commonly about 24 inches thick. Both galena and zinc blende 

are present, and there is'little waste in the ore close to the 

contact. The character of the ore 50 feet above the shale and 

breccia contact is shown in figure 15. Most of the ore between 

the shale walls is pyritic, but some galena ore occurred in places 

close to the contact of the thrust-fault breccia. Although it is 

possible that other ore bodies are present in the baked shale east 

of the present workings, the geology of the region suggests that 

the best ore will probably be found close to the contact of the 

shale and the overlying breccia and will pitch about 15° or

20° W.

INDEPENDENCE

The Independence vein is on the southeast slope of McClellan 

Mountain, a few hundred feet northwest of the Santiago mine 

and about QY< miles northeast of Montezuma, at an altitude of about 12,300 feet. The workings were inaccessible in 1927. The date of the discovery of the vein is 

not known, but in 1877 it was located as the Independence 

and subsequently patented under that name. According 

to the Colorado Mining Directory for 1883 the Independence had produced about $300,000 prior to that year, 

and it is known to have been productive from 1883 to 1890.

The amount of development work is indicated by 

Burchard's report for 1883, as follows:

"The Independence has been one of the best-paying 

mines in this locality and is developed by a main tunnel 

710 feet in length, having a depth of 400 feet at the 

breast. On this tunnel are four shafts 35 to 80 feet in 

depth. In one shaft, at a depth of 60 feet, is a drift 100 

feet west, showing in a streak of mineral 4 to 8 inches of 

galena, which mills 70 ounces of silver per ton. The bestpaying ore just now comes from a stope about 125 feet 

from the tunnel mouth and 60 feet above it, now under lease to 

J. B. Johnson. At 440 feet is a pay streak from 6 to 12 inches 

wide that mills from 216 to 316 ounces of silver per ton. *Four 

liundred feet from the mouth of the tunnel is a winze connecting 

the main level with the next level, 110 feet above. In this 

level the streak is from 3 to 5 inches, milling about 80 ounces 

per ton."

The vein is mentioned frequently by the Georgetown Courier 

in the eighties, and the comments suggest that it was one of the 

best shippers in the East Argentine district during that period. 

Shipments of 1 to 12 tons at a time are often mentioned, and 

the average tenor of the ore was apparently well above $100 a 

ton. Silver was the chief valuable constituent, but in some 

places the gold content was also noteworthy.

The vein has been worked several times since 1890, but very 

little is known of these later operations. As shown in figure 16, 

the vein has been cut several liundred feet below its outcrop 

by drifts from the Tobin and Waldorf adits. According to 

A. A. Atkins, formerly general manager of the Imperial Mines 

Co., no ore was found in the vein where it was cut on the Waldorf 

tunnel level at an altitude of about 11,650 feet, although ore 

had been mined from it on the Tobin tunnel level, about 300 

feet above.

The vein strikes northeast and dips about 80° NW. The 

vein is in Silver Plume granite and is a sheeted zone from 4 to 

12 inches wide carrying galena, pyrite, and a small amount of 

sphalerite in a quartz gangue. The ore shipped in the eighties 

assayed from 70 to 300 ounces of silver and from a quarter of an 

ounce to ?>% ounces of gold to the ton. If the mine has produced since 1904, the figures of production are probably included 

in those of the Waldorf group.

IOWA

The Iowa is on the north slope of Teller Mountain, about 

2^ miles south of Montezuma. It was discovered in 1880 and 

developed by several shallow shafts. It is credited with a production of 50 tons in 1883 by the Colorado Mines Directory, 

and in 1885, according to the Montezuma Mill Run, it shipped 

10 tons of ore, which netted $500. No other production is 

recorded for the property. The shipping ore is said to have 

come from, a vein 17 inches wide carrying galena in a quartz 

gangue and assayed, when sorted, 50 percent of lead and 25 

ounces of silver to the ton.

JERRY, EQUITY, DENVER, AND CELTIC

The Jerry tunnel is on the northeast face of Glacier Mountain, 

about a quarter of a mile southwest of Montezuma, at an altiFIGURE 15. Diagrammatic section of Ida Belle stope.

tude of about 10,450 feet, and the Equity adit is about 265 feet 

above it. These tunnels were started in the eighties to cut the 

Mark Twain Extension at depth, but most of the development 

work was done by the Jerry Mining Co. and the Washington Gold 

Quartz Mining Co. in 1922 to 1925. As shown on plate 26, 

the only vein that was stoped to any extent was the eastwardtrending vein cut by the Equity adit, although a few carloads 

of ore was shipped from the northeasterly vein found in the 

lower workings. The production of the property is given 

below.

Production of Jerry, Equity, Denver, and Celtic veins

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

1908 (Jerry group ?)_._.__ 

1918.. 

1919.. 

1921. 

1923 (Denver and Celtic). 

1924 (Denver and Celtic) . 

1925 (Denver and Celtic).

Ore 

(short 

tons)

3 

3 

4 

2 

14 

11 

51 

40 

16 

32

Gold 

(fine 

ounces)

0.08 

.03 

.34 

.20 

1.50 

.80

1.40

Silver 

(fine 

ounces)

171 

744 

278 

154 

467 

351 

1,239 

1, 190 

92 

1,207

Lead, 

wet 

assay 

(pounds)

2,935 

2,007 

1,533 

719 

2,078 

3,334 

18, 599 

12, 000 

807 

10,869

Copper, 

wet 

assay 

(pounds)

28 

31

Zinc 

(pounds)

406

283

1,620
84 MONTEZUMA QUADRANGLE, COLORADO

copper stam^^r U^£&r\te T/ «&» J A s *jts&zC'K an,dp,yrlte * , vA6

rite and coP>^^£ '/-% C . - ,V^ ' ^

^'f//^

Fissure less than one 

inch wide

Fissure or vein one 

to 12 inches wide

Fissure or vein 12 inches 

or more

FIGURE 16. General relations of Santiago, Commonwealth, Independence, Tobin, and Paymaster workings and geology of

Waldorf tunnel.
THE MINES 85

Production of Jerry, Equity, Denver, and Celtic veins Continued

1923 (Denver and

Celtic). -

1024 (Denver and 

Celtic).. .. ......

Ore to

concentrating 

mills 

(short

tons)

637

(?)

Concentrates 

produced 

(short

tons)

55

83

Gold 

(fine 

ounces)

2.38

.88

Silver 

(fine 

ounces)

2,271

1,159

Lead, 

wet 

assay 

(pounds)

30, 678

12, 202

Copper, 

wet 

assay 

(pounds)

236

Zinc 

(pounds)

11,968

40, 879

No production in 1901-2, 1905-7, 1909-17, 1922, 1926-28.

The country rock of the mine is hornblende gneiss and pegmatite of the Swandyke gneiss. The gneiss strikes about N. 

1.5° E. and dips steeply east. On the lower level a barren fault 

parallel to the schistosity of the gneiss was followed by the adit. 

About 320 feet from the portal a thin northeasterly vein is cut 

by this fault and is displaced about 15 feet, the eastern segment 

moving north. The vein is largely rhodochrosite from 1 to 4 

inches wide, but some galena and sphalerite are also present. 

Locally ruby silver can be seen, and a rich pocket of silver ore is 

said to have occurred near the intersection of the vein and the 

fault. About 100 feet from the portal of the upper level a fault 

was cut which is parallel to the one on the lower -level and is 

probably part of the same fault zone. It was followed south 

to the Denver and Celtic "veins", from which most of the ore 

shipped from the Jerry mine was produced. As shown on the 

map, the two veins are faulted portions of one eastward-trending 

vein that has been cut by the northerly fault, the eastern segment moving north of the western segment. The horizontal 

slip between the displaced segments is about 30 feet, but the 

shift between the undisturbed parts of the vein beyond the 

influence of the fault is nearly 60 feet. The dip and strike of 

the western part of the vein west of the fault would make it 

crop out near the center line of the Denver claim, and the dip 

and strike of the eastern segment of the vein would throw its 

outcrop close to the center line of the Celtic claim. In the 

Jerry workings this vein was from 6 inches to 2 feet wide and 

consisted largely of galena and rhodochrosite; sphalerite and 

quartz were also common, and ruby silver occurred locally.

JOSEPHINE

The Josephine mine is on the north slope of Kelso Mountain, 

about 7 miles north-northeast of Montezuma and 5 miles by 

road from Silver Plume. As shown on plate 27, the vein is 

opened by three adits at altitudes of 10,893, 10,801, and 10,651 

feet. These adits have been driven southward into the mountain 320, 1,090, and 960 feet respectively but were inaccessible 

at the time of the writer's visit. The Josephine vein was located 

in 1876, and the upper and intermediate adits were driven 60 

and 120 feet before 1883, but most of the development work 

has been done since 1900. The mine probably produced little 

before 1905, but as shown in the production table below, it has 

been an intermittent producer of lead-silver ore since that year.

The Josephine vein strikes about N. 12° E. and dips about 

67° W. The country rock includes Silver Plume granite and 

schists and gneisses of the Idaho Springs formation. According 

to 0. B. Wilmarth, the main vein is well defined and was easily 

traced past the junctions of several minor branch veins and 

cross veins. The vein filling in the barren stretches between 

ore shoots is reported to be chiefly quartz, but the ore is remarkably clean and free from gangue. The average width of the 

ore in the stopes is said to be about 1 foot, although its width 

ranges from 1 to 30 inches. Galena is the chief ore mineral, 

and some sphalerite, pyrite, and chalcopyrite are also present.

Production of Josephine mine

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

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

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

1909.....................

1910. - - -..

1911...-..-.------.-...--.

1912................ ......

1913. ..--.-----........

1914.,. ................

1915...--....--....--....

1917------.-..-.....--..

1919.... .-..--.......

1926 (Josephine group,

Ore 

(short 

tons)

43 

25 

28 

249 

246 

175 

162 

410 

476 

120 

107 

7

11

Gold 

(fine 

ounces)

35.02 

1.98 

17.28 

33.94 

14.49 

30.27 

40.51 

29. 57 

15.49 

7.61 

1.28

.62

Silver 

(fine 

ounces)

1,721 

376 

336 

3,034 

3,227 

2,219 

2,889 

5,509 

4,391 

1,385 

1,743 

82

127

Lead, 

wet 

assay 

(pounds)

4,376 

28, 835 

26, 359 

371, 205 

256, 332 

251, 295 

196, 747 

514, 496 

325, 997 

112,080 

139, 785 

8,390

14, 905

Copper, 

wet 

assay 

(pounds)

722

1,830 

2,001 

565

Zinc 

(pounds)

9,861

13, 643

549

No record available for 1889-1900; no production in 1901-5, 1916, 1918, 1920-25, 

1927-28.

JUMBO

The Jumbo mine is on the north slope of Morgan Peak, about 

1 mile east-northeast of Montezuma. It is developed by three 

adits two short ones several hundred feet above Peru Creek 

and a much longer, lower adit at an altitude of about 10,320 

feet a short distance above the wagon road in the valley bottom. 

The property was discovered in the late eighties and is said to 

have shipped about 100 tons of lead- ore in 1888 and about 25 

tons in 1900. This ore was found in the upper adits, and in 

1905 some work was done on them, but the ore exposed contained 

too much zinc to allow shipping without concentration. The 

upper adits were then abandoned, and the lower adit was driven 

during 1906-9. In 1914 the property was taken over by the 

Philadelphia Mining Co. and was operated in conjunction 

with its Toledo mill, about halfway between the mine and Montezuma. During 1914 and the next 4 years 6,798 tons of ore was 

produced and all but 38 tons was milled. Most of it can be 

credited to the Jumbo, although a small amount was obtained 

from other sources. The lower adit is said to extend almost due 

south into Morgan Peak for about 1,100 feet. The ore obtained 

from this level was chiefly zinc blende but contained a small 

amount of galena. The vein averaged about 6 inches in thickness, but in some places reached 1 foot. Most of the ore came 

from a single stopo, which is said to be about 300 feet long and 

about 100 feet high. The ore exposed on the dump is massive 

sphalerite with a little pyrite between quartz walls. Some 

galena is present but is not abundant. The ore in the upper 

adits contained a notable proportion of galena, and the sphalerite present was very loose-textured and light-colored. Copper 

minerals are not conspicuous in the ore, but some tetrahedrite 

and chalcopyrite are microscopically, intergrown with the darkcolored sphalerite from the lower adit. The country rock of 

the entire mine is Montezuma quartz monzonite.

The following are incomplete figures on the Jumbo mine and 

the Philadelphia group:

Production of Philadelphia Mining Co.

llncludes Waterloo, Philadelphia, Little Jumbo, Collier Mountain group, Rosengarten tunnel, and Colorado-Toledo]

1915 (see also milling ore)..

Ore 

(short 

tons)

24 

14

Gold 

(fine) 

ounces)

0.89 

1.23

Silver 

(fine 

ounces)

260 

137

Lead, 

wet 

assay 

(pounds)

9,468 

3,154

Copper, 

wet 

assay 

(pounds)

328 

411

Zinc 

(pounds)

11,699 

9, 598
86 MONTEZUMA QUADRANGLE, COLORADO

Production of Philadelphia Mining Co. Continued

1914.............

19J5.. ...........

1916... ..........

Ore to 

concentrating 

mills 

(short 

tons)

150 

500

5,658 

490

Concentrates 

produced 

(short 

tons)

64 

162 

13 

943 

27 

20

Gold 

(fine 

ounces)

2.06 

7.71 

.88 

35.46 

.81 

1.55

Silver 

(fine 

ounces)

632 

1, 332 

138 

7,065 

113 

269

Lead, 

wet 

assay 

(pounds)

20, 768 

43, 513 

8,162 

193, 878 

1,346 

3,150

Copper, 

wet 

assay 

(pounds)

486 

830

2,802 

108 

182

Zinc 

(pounds)

32,683 

74,000

444, 094

No production in 1901-13, 1919-28.

KELSO

The Kelso mine is on the north slope of Kelso Mountain at 

an altitude of 10,800 feet, about 6% miles north-northeast of 

Montezuma. The early history of the property is not known, 

but in 1926-29 it was worked by the Kelso National Mining 

Co., of Georgetown. At the time of the writer's visit no ore 

had been produced, but several tons of silver-lead ore was 

shipped in 1927 and 1928. As shown in plate 28, the country 

rock of the mine is schist and injection gneiss.

The ore occurs in northwestward-trending veins and is much 

better where the walls of the veins are gneiss than where they 

are schist. Although the workings expose many fissures and 

faults striking from north-northeast to east, the only ore seen 

by the writer was in fissures belonging to a branching vein 

system striking N. 10°-40° W. Some of the north-northeast 

faults are younger than the northwest veins. The ore was 

from 1 to 8 inches wide and contained chiefly galena and pyrite 

and minor amounts of light-colored sphalerite in a quartz and 

ankerite gangue. The upper tunnels were not accessible at the 

time of the writer's visit, but the veins which they followed are 

probably the same as those exposed in the southeastern drifts 

of the lower tunnel workings, the southern drift following the 

Kelso vein, and the drift 75 feet to the northeast following the 

National vein. As these two veins dip toward each other they 

probably join about 150 feet below the level, and an ore shoot 

may occur at this junction. No ore shoot was found where 

the National vein branched from the North Kelso on the tunnel 

level, however, but at this place, as shown on the map, the two 

veins were in schist, which is a less favorable wall rock than the 

gneiss.

Production of Kelso mine

1920.... ......... ......

1925. 

1926 (Kelso National) 

Ore 

(short 

tons)

2

6

43

15 

32

Gold 

(fine 

ounces)

0.24

.32

8.42

7.60 

8.80

Silver 

(fine 

ounces)

15

41

521

210 

626

Lead, 

wet 

assay 

(pounds)

2,090

3,720

47, 844

17, 414 

46, 032

Zinc 

(pounds)

1,612 

1,931

No production in 1901-19, 1922-24, 1928.

KITTY OWSIEY

The Kitty Owsley vein is on the east slope of McClellan 

Mountain, about 1% miles north of the Waldorf mine and 7% 

miles northeast of Montezuma. The portal of the lower tunnel 

has an altitude of about 11,850 feet. The mine was inaccessible 

in 1927, and little is known of its history. The vein is said to 

be parallel to the Kitty Owsley claim and if so strikes about 

N. 20° E. The ore on the dump is chiefly brecciated sphalerite 

in a quartz-barite gangue and came from a vein at least 7 inches 

wide in places. The country rock is Silver Plume granite, but 

the strike of the vein would carry it into the Idaho Springs

formation a few hundred yards north of the tunnel, 

production figures follow.

Production of Kitty Owsley mine

Incomplete

1912. .................... ..

1913 

1917 

1918 

1921 

1907 

1913. 

Ore 

(short 

tons)

49 

23 

6 

36 

1

Ore to 

concentrating 

mills 

(short 

tons)

(?) 

39

Gold 

(fine 

ounces)

6.28 

2.06 

1.47 

3.21 

.11

Concentrates 

produced 

(short 

tons)

427 

15

Gold 

(fine 

ounces)

68.31 

.88

Silver 

(fine 

ounces)

272 

163 

129

788 

18

Silver 

(fine 

ounces)

3,032 

172

Lead, 

wet 

assay 

(pounds)

27, 528 

12, 661 

6,141 

29, 725 

616

Lead, 

wet 

assay 

(pounds)

106, 503 

730

Copper, 

wet 

assay 

(pounds)

72

Copper, 

wet 

assay 

(pounds)

88

Zinc 

(pounds)

28, 115 

11,430

Zinc 

(pounds)

245, 000 

12, 608

No production in 1901-6, 1908-11, 1914-16, 1919-20, 1922-28. 

LANCASTER

The Lancaster vein is on the southwestern spur of Tiptop 

Peak, about half a mile east of Montezuma, and was developed 

by three adits at altitudes of about 11,400 to 11,700 feet. The 

property has long been idle, but it produced a small amount of 

ore in the eighties. It is credited by the Colorado Mine Directory 

with a total production of 210 tons prior to 1883 and produced 

1 ton of ore in 1886 and $185.11 in lead ore in 1888. No other 

production for the mine is on record. In 1883 the three adits 

were 165, 260, and 15 feet long, and little work has been done 

since that time. The vein strikes nearly due east and is entirely 

in the Montezuma quartz monzonite. It is reported to be a 

fissured zone about 4 feet wide, containing a vein of galena 

about 5 inches thick. The ore, when sorted, assayed 55 percent 

of lead and 34 ounces of silver to the ton.

The occurrence of the ore was probably similar to that of the 

Morgan mine, a few hundred feet south of the Lancaster, described on pages 90-91.

LUCKY BALDWIN

The Lucky Baldwin claim is immediately southwest of the 

Silver Wave claim (see p. 108) and is probably on the extension 

of the Silver Wave vein. It has two adits on it at altitudes of 

12,000 and 12,060 feet. The upper adit was not accessible in 

1929, but both adits are driven northeast to the end line of the 

claim, and the lower one was examined and is shown on plate 16. 

It is 425 feet long and follows the vein for 310 feet of this distance. The country rock of the vein comprises Idaho Springsformation and Silver Plume granite; both quartz schist and 

quartz-biotite-muscovite schist are present and strike about 

N. 10° E, and dip steeply west. The vein strikes northeast and 

dips steeply northwest or southeast. It was first cut about 

110 feet from the portal in quartz schist and is thin and 

poorly defined until it passes into Silver Plume granite, -160 

feet from the portal. The vein gradually widens in the next 30 

feet, and there is a stope about 25 feet high and 30 feet long 

200 feet from the portal. There are no other stopes on this 

drift, but the vein is well marked and is from 6 to 12 inches wide. 

Most of the vein is quartz, however, and the chief sulphide is 

pyrite; some chalcopyrite occurs, and in places the walls of the 

drift are copper-stained. Small amounts of galena and sphalerite were noted in the drift, and some lead-zinc ore was found 

on the dump.

MAID OF ORLEANS

The Maid of Orleans vein is on the southeastern spur of 

Lenawee Mountain, and the chief workings are at the foot of 

the mountain, in the valley of Peru Creek about 1% miles north-
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 178 PLATE 28

Oo OOOOOO

EXPLANATION

Barren fissure, fault, or vein less than 

1 inch wide

Barren fissure, fault, or vein from 1 to 

12 inches wide

Barren fault or vein more than 12 

inches wide

Mineralized vein with less than 1 

inch of sulphide

Mineralized vein with 1 to 12 inches 

of sulphide

Mineralized vein with more than 12 

inches of sulphide

Approximate position of vein in 

upper adit

Granite gneiss and injection gneiss

Strike and dip of bedding

Strike of schistosity

Downthrown side of fault

PbS, galena

ZnS, sphalerite

FeS2, pyrite

BaS04 (dis.), barite disseminated

Timbered drift

Slick, slickensides

PLANS OF MORE WORK TUNNEL, GLACIER MOUNTAIN (A) 

AND KELSO MINE, KELSO MOUNTAIN (B)
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 178 PLATE 29

E/.J1,5OO

Thrown gouge, 

Hanging walK<4^"decomP°sed gneiss

300 Feet

EXPLANATION

Barren fissure, fault, or vein from 1 to 

12 inches wide

Barren fault or vein more than 12 

inches wide

Slightly mineralized vein more than 

12 inches wide

Vein more than 12 inches wide with 

galena ore

"~~~*^ Strike and dip

PLAN OF MOHAWK MINE, TELLER MOUNTAIN
U. S. GEOLOGICAL SURVEY PROFES

"vuggy Zn and Fe S2

6"FeS2 l"-9"Mn. ankerite.

FeS2 and ZnS 

5"Mn. ankerite

iz"gouge;thin crushed seams of 

FeS2 , ZnS,and PbS in gouge

N/ ,

-3"Fe stained sheeted zone

8'sneeted zoi

X

Mn02- A/o ffo/d in MnOf or gouge when panned, FeS? abundant

ADIT No.3

Barren fissure, fault, or vein less than 

1 Inch wide

Barren fissure, fault, or vein from 1 to 

12 inches wide

Barren fault or vein more than 12 

inches wide

Mineralized vein with less than 1 

inch of sulphide

I5"sheeted zone 7"FeS2 and a 

little PbS

'6"Fe and Mn stained gouge some crushed

EXPLANATION

- Mineralized vein with 1 to 12 inches 

of sulphide

Mineralized vein with more than 12 

inches of sulphide

Fissure zone more than 12 inches 

wide carrying from 1 to 12 inches 

of sulphide

Strike and dip

PbS, 

ZnS, 

Fe, i

FeS2

Mn, 

MnO

MnCO

PLAN OF MORGAN MINE, MONTEZUMA

(Relative position of adits not shown)
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 178 PLATE 31

75°

300 Feet

Barren fissure, fault, or vein less than 

1 inch wide

Barren fissure, fault, or vein from 1 to 

12 inches wide

Barren fault or vein more than 12 

inches wide

Mineralized vein from 1 to 12 inches 

wide

EXPLANATION

 * x Mineralized vein more than 12 inches

wide

A A Composition of ore, 25 percent represented by a triangle, 33X percent represented by a square 

blue, galena; yellow, sphalerite; 

red, pyrite

B Barren of galena-sphalerite ore

Relative proportion of sulphide 

(solid) and gangue minerals 

In ore

Strike and dip 

Strike and vertical dip 

PbS, galena 

ZnS, sphalerite 

pyrite

PLAN OF NEW YORK TUNNEL, MONTEZUMA, 1929
U. S. GEOLOGICAL SURVEY

24 sheeted zone 

with two 2"veins 

of ankente,quartz/' 

and PbS

150 Feet

| [Cabin

PROFESSIONAL PAPER 178 PLATE 32

EXPLANATION

Barren fissure, fault, or vein less than 

1 inch wide

Barren fissure, fault, or vein from 1 to 

12 inches wide

Barren fault or vein more than 12 

inches wide

Mineralized vein from 1 to 12 inches 

wide

Mineralized vein more than 12 inches 

wide

Vein with galena and ankerite from 

1 to 12 inches wide

Vein with galena ore more than 12 

inches wide

Strike and dip 

Strike of schistosity 

Downthrown side of fault 

Pb, lead 

PbS, galena 

Timbered drift

400 Feet

PLANS OF OLD TIMER MINE, GLACIER MOUNTAIN (A), AND 

RAINBOW MINE, KEYSTONE GULCH (B)
U. S. GEOLOGICAL SURVEY

PROFESSIONAL PAPER 178 PLATE 33

Silicified 

pyritized 

quartz - 

biotite schist

OHIO OR*F"LE.VEL

£L. II,QS7 9O'

EXPLANATION

I 7S°

Barren fissure, fault, or vein

Mineralized vein

Vein with galena ore

Pyritized and silicified wall rock

Strike and dip

Strike and vertical dip

Strike of schistosity

Strike of gneissic structure

PbS, galena

Cu, copper sulphides

Fe, iron

FeSa, pyrite

Mn, manganese 

CaCOa, calcium carbonate 

SiOz, quartz 

Timbered drift

-. - ' S6 '. 36"FeS 2 andjaspery 

FeandCaC03 quartz, brecciated - _ 

precipitate and re cemented by 

r white, vuggy crystalme r~" 

quartz

Looking at southwesc wall 

of small crosscut at split on 

"F" level showing ore occurence

200 Feet

WINZE

Delaware vein

Quartz monzonite 

porphyry

SUR NO 13686A ANNABEL MILL- S/TE

SUK. NO. 13686 A COLUMBINE

PLAN OF LEVEL F AND PART OF LEVEL G OF PENNSYLVANIA MINE, DECATUR MOUNTAIN
THE MINES 87

east of Montezuma. The shaft by which the mine was worked is 

on the north side of the creek at an altitude of about 10,300 feet, 

but it was full of water at the time of the writer's visit. The 

vein was discovered in 1882 and worked during the eighties, but 

no production has been made since' 1888, so far as is known. 

Several carloads of ore were shipped in 1885, about 2 tons of 

ore in 1887, and about 13 tons of ore in 18SS; the total production 

of the mine was probably about 50 tons of silver ore worth about 

$60 a ton. According to the Colorado Mining Directory for 1883 

the Maid of Orleans vein was "a fissure varying in width and 

containing pockets of galena, copper pyrites, and sulphurets, 

assaying from 50 to 150 ounces silver per ton." The ore on the 

dump in 1929 was pyritic quartz containing a small amount of 

sphalerite and apparently came from a vein about 6 or 8 

inches wide.

Production of Maid of Orleans mine

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

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

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

Ore (short 

tons)

35

(?)

(?)

Gold (flue 

ounces)

0.28

3.23

Silver (fine 

ounces)

64

223

Lead, wet 

assay 

(pounds)

1,221

7,589

No record available for 1886, 1889-1900; no production in 1901-28. 

MARK TWAIN AND ST. ELMO

The Mark Twain and St. Elmo claims are on the northwest 

slope of Glacier Mountain and are developed by several adits 

and a shaft 225 feet deep, whose collar is a short distance west 

of the crest of the mountain, at an altitude of about 11,400 feet. 

The lower adit, called the St. Elmo tunnel, has its portal on the 

west slope of the mountain about 500 feet below the collar of the 

shaft and may be reached from Montezuma over a wagon road 

that leaves the St. Johns Creek road about half a mile west of the 

town. The Mark Twain vein and the St. Elmo tunnel site were 

located in 1881, and work was begun on both at once. The tunnel 

was driven 550 feet and cut the Mark Twain and St. Elmo 

veins; the St. Elmo vein was followed northeast and southwest 

for an aggregate distance of about 500 feet. Stopes from 45 to 

60 feet high and about 40 feet long are said to be present in these 

drifts, but, as shown in figure 17, little of the property was 

accessible in 1929. In sinking the shaft on the vein, ore was 

saved and shipped, and several hundred feet of drifts were 

driven from it, but little stoping Avas done, and the property 

remained idle from about 1892 until 1918, when the St. Elmo 

tunnel was rehabilitated by the St. Elmo Mining Co. A crosscut from the main tunnel was driven and is said to cut the Mark 

Twain vein 266 feet from the portal. The mine shipped ore in 

1881, 1882, 1883, 1884, 1887, and 1889, but produced nothing in 

1885, 1886, and 1888. According to Burchard's report for 1883,

"The Mark Twain is now developed with capacity for working 150 men in the stopes, but on account of the railroad not 

supplying sufficient number of cars only about 14 men have been 

employed. The developments consist of a crosscut tunnel 400 

feet long, cutting the Mark Twain and St. Elmo veins. On the 

Mark Twain lode is a shaft 205 feet deep and an aggregate of 

630 feet in levels. The pay streak averages 8 inches wide of 

galena and gray copper, carrying about 140 ounces of silver per 

ton. The workings are supplied with T-rails, ventilators, etc. 

Charles Buckland is manager. The Mark Twain extension has 

been worked during the year."

There is no record of production since 1890. The Mark Twain 

vein strikes northeast and dips steeply to the northwest in the 

tipper part of the shaft, where the shipping ore was found. At 

50 feet above the bottom of the shaft the vein bends and dips 

southeast at a steep angle.

Production of Mark Twain and St. Elmo mines

1882..........................................

1883-....... ...............................

1883 (Cable and Mark Twain Extension).....

1884 (Cable and Mark Twain).... .. _..

1885 (Cable and Mark Twain). _ ...... _ ..

1887 (St. Elmo).... ......... ...... ........

Ore (short 

tons)

50

30

40

10

50

10

Silver (fine 

ounces)

431

Lead, wet 

assay 

(pounds)

2,311

No record available for 1886, 1888-1900; no production in 1901-28. 

MISSOURI

The Missouri mine is near the head of Hall Valley, about 

4 miles south of Montezuma and half a mile south of the Whale 

mine, at an altitude of about 12,100 feet. The substantial 

cabins of the mine can be reached by automobile from Webster, 

9 miles to the southeast, although in 1928 the road was very 

steep in places and more suitable for wagons than trucks or cars.

100 100 Feet

FIGURE 17. St. Elrno tunnel, Glacier Mountain, 1929.

The Missouri lode was discovered in the late seventies and 

developed by several adits and a few shallow shafts. Burchard 

in 1882 says:

"The Missouri is one of the prominent mines in Halls Gulch. 

The developments consist of shafts and about 500 feet of tunnels 

upon the vein. The fissure is 30 feet wide, as proven by a crosscut run from the level when in about 240 feet. The ore streak 

is from 6 inches to 3 feet wide and runs in bismuth, silver, gray 

copper, copper pyrites, and iron. The ore also carried gold, 

running from a trace up to 11% ounces. Mill runs at Argo gave 

from 150 to 219 ounces of silver per ton, with 0.6 ounce in gold 

and, 10 percent copper."

In his report for the next year Burchard says:

"This mine has an established reputation as a producer, 

having shipped considerable ore up to the past season. Developments consist of a shaft and about 600 feet of tunnels on the 

vein. The fissure is from 20 to 25 feet wide, pay streak from 

4y2 to 22 inches wide; average value of ore 125 ounces silver, 

and carried as high as 10 ounces gold. This ore carries silver, 

gold, copper, iron pyrites, and bismuth, also gray copper; but 

very little lead in this ore, which is rather strange, as every 

mine in the camp carries lead to a great extent."

In 1884 there was much activity in Hall Valley, and the 

Monte'zuma Mill Run in that year noted that the Missouri

71886-35 7
88 MONTEZUMA QUADRANGLE, COLORADO

mine was furnishing 5 tons of .concentrating ore daily to the 

Quincy Milling & Reduction Works. In 1887 the paper noted 

that the Hall Valley smelter was unsuccessful and that there 

was little activity in the gulch. There is no record of any 

activity at the Missouri between 1887 and 1920, when C. M. 

Snyder took over the property. The known production of the 

mine is given below.

Production of Missouri mine

1920.. .............. ......

1921......................

1922_____. ............ ....

1923. .....................

1924. .....................

1925. ............... ......

1926..--...-...--.-.. _ ..

1927..-. ... ........ ...

1928........ ..............

Ore 

(short 

tons)

65 

15 

13 

73 

23 

55 

2 

23 

27

Gold 

(fine 

ounces)

0.40 

7.69 

11.80 

54.81 

5.90 

50.39 

17.66 

47.60 

2.42

Silver 

(fine 

ounces)

2,051 

744 

1,838 

9,176 

1,127 

5,973 

444 

1,887 

912

Lead, 

wet 

assay 

(pounds)

1,802

491 

3,056 

1,596 

3,570 

162 

915 

14, 611

Copper, 

wet 

assay 

(pounds)

7,221 

1,498 

540 

5,979 

3,192 

5, 396 

169 

2,333 

2,620

Zinc 

(pounds)

906

692

412 

2,917

No production in 1901-19.

FIGURE 18. Occurrence of ore in Missouri mine, 10 feet above level 5.

In 1928 the mine was developed by three accessible adits at 

altitudes of 11,600, 11,628, and 11,710 feet. As shown on 

plate 24, there are about 2,100 feet of drifts on the three levels 

and 150 feet of winzes. Most of the work from 1923 to 1928 

was done below the upper adit, locally known as tunnel 3, and 

the bulk of the production has come from the vein opened by 

adit 5.

The country rock of the mine is hornblende and injection 

gneiss of the Swandyke gneiss. The schistosity strikes about 

N. 25° W. in most of the mine and dips 65°-85° E. The gneiss

is cut by several strong bedding-plane faults that are later than 

the vein fissures, although not certainly later than the vein, 

fillings. The strongest of these northwesterly faults was found 

110 feet.from the portal of adit 4 and is probably the same as 

the fault found 120 feet from the portal of adit 3. No veins 

have been found that cross this fault. The Laclede vein, on 

the west side of the fault, bends to the north as it approaches 

the fault; on level 4, 350 feet from the portal, a westwarddipping vein flattens notably as it goes into the fault from the 

east; the northwestward-dipping Missouri vein ends abruptly 

to the west at the fault, but no drag was observed; the Leftwick 

vein was not found on level 4 until after the fault had been 

passed, but beyond it was followed with little difficulty for 400 

feet. Grooves and striations on the walls in adits 3 and 4 are 

consistent and dip 45°-50° SE. Although the data are incomplete, it is believed that the east wall of the fault moved downward and southeast past the west wall, but the amount of displacement is not known. The only ore shoot that justified 

stoping on the Leftwick vein in the 400-foot drift on level 4 was 

found close to its junction with the northwesterly fault. The 

mineralization of the Missouri vein was weak where it was first 

cut by adit 5 but became stronger and stronger toward the 

fault, and the best ore occurs within 100 feet of the fault. 

Small masses of ore have been found in many other veins in 

the mine, but all of them are close to the northwesterly fault. 

These facts suggest that the northwesterly fault was an ore 

channel and was instrumental in localizing ore shoots in the 

veins which it intersects.

The Missouri mine is the only one in the Montezuma quadrangle where the occurrence of bismuth ore could be satisfactorily studied. The Missouri vein contains lead and bismuth 

ore, but the bismuth is generally distinct from the lead. The 

Missouri vein strikes N. 20°-50° E. and dips about 45° NW., 

although locally steeper and flatter dips occur. As shown in 

figure 18, the lode is a wide sheeted zone and carries ore chiefly 

on the footwall. On level 4 the ore shoot extends from the 

main northwesterly fault to a point about 140 feet northeast, 

where the workings broke into hillside wash. On level 3 the 

ore shoot was barren gouge for the first 15 feet northeast of the 

fault, but farther northeast the ore was continuous to the surface. The ore close to the fault was highly oxidized, and the 

raise from level 4 to level 3 at the southwest edge of the ore 

shoot close to the fault is known as the "Canary-Yellow raise" 

because of the brilliantly colored oxide of bismuth that was 

abundant here. The ore rapidly graded into sulphides northeast of the fault, and there was little evidence of oxidation even 

at the surface. Near the fault, however, white and yellow 

oxides of bismuth are conspicuous as far down as the ore shoot 

was explored in 1928. The occurrence of the oxidized ore so 

close to the bottom of a heavily glaciated valley suggests deep 

oxidation in preglacial time. Remants of an ancient land surface, the Eocene Flattop peneplain, are well preserved in the 

summits of the mountains bordering Hall Valley on the west 

and north. Reconstruction of this ancient peneplain over the 

valley suggests that the surface may have been as much as 700 

feet above level 4, but it is probable that Hall Valley had been 

cut a few hundred feet below the peneplain before the end of 

Tertiary time. Oxidation along favorable channels may have 

reached a depth of several hundred feet in late preglacial time, 

and the acceleration of deep ground-water circulation caused by 

glacial trenching during Pleistocene time may have been one 

cause in effecting the oxidation of the ore.

 The sulphide ore occurs in two well-defined seams known as 

the high-grade or footwall streak and the low-grade or hangingwall streak. There is everywhere a thin seam of gouge between 

the high-grade ore and the solid rock wall; the low-grade 

streak is separated from the underlying high-grade streak by 1 

to 40 inches of gouge or highly altered sheeted rock and vein
THE MINES 89

matter. The thickness of the footwall ore seam ranges from 

that of a knife blade to a maximum of 12 inches but is generally 

between half an inch and 5 inches, averaging about 3 inches; 

the thickness of the low-grade seam ranges from 6 to 36 inches 

and is usually about 15 inches. Where unoxidized the chief 

minerals of the high-grade streak are clear, fine-grained quartz, 

"bismuth-silver", and bismuthinite, but locally chalcopyrite 

and galena are present. (See p. 54 for .an analysis of the mineral called "bismuth-silver.") Wherever chalcopyrite is present 

in the footwall seam it is said to be always below the bismuthbearing quartz and to lie on a thin seam of gray talcky gouge. 

Bismuth is almost wholly confined to the footwall streak, but 

some bismuth was found in the hanging-wall ore above the third 

level. Here the copper content of the hanging-wall streak decreased as the bismuth content increased. The chief minerals 

of the hanging-wall streak are quartz, pyrite, chalcopyrite, and 

a dark-colored gray copper. Locally galena is abundant, 

reaching a thickness of 24 inches in some places (fig. 19); barite 

also occurs locally and usually is associated with galena. Near 

the main northwesterly fault the high-grade 'streak was completely oxidized to the white and yellow oxides of bismuth, but 

the hanging-wall streak, though heavily stained with malachite, 

contained fresh chalcopyrite. Chalcopyrite is more abundant 

on the upper levels than on the lower levels, and the darkcolored gray copper is more abundant between levels 4 and 5 

than elsewhere in the mine. Ore rich in chalcopyrite contains 

more gold and silver than the gray copper and lead ores. Pure 

galena assays about 18 ounces of silver to the ton, and the darkgray copper assays about 100 ounces. The high-grade ore 

commonly contains from 5 to 10 percent of bismuth, 1 to 8 

ounces of gold and 100 to 1,200 ounces of silver to the ton, and 

a few percent of copper. The analysis of two shipments of

FIOUIIK 19. Relations of "low grade" (galena) ore seam to "high grade " (bismuth) 

ore seam, level 5, Missouri mine.

high-grade ore showed (a) 22 percent of bismuth, 3.80 ounces of 

gold and 280 ounces of silver to the ton, and 3 percent of copper; (b) 10 percent of bismuth, 8 ounces of gold and 260 ounces 

of silver to the ton, and 3 percent of copper.

An interesting, structural feature was associated with the 

richest pocket of bismuth ore in the mine. About halfway 

between levels 3 and 4 and 30 feet northeast of the main 

northwesterly fault the Missouri vein becomes much steeper,

and at the place where it again flattens to its normal dip there is 

a large wrinkle in the footwall, as illustrated in figure 20. The 

ore decreased to a thin, nearly barren seam as the vein steepened 

and disappeared near the crest of the hump caused by the 

wrinkle in the wall; on the other side of the hump, however, the trough contained a mass of very high grade bismuth sulphide ore about 5 feet long, 4 feet wide, and 12 

inches thick in the center. The axis of the trough pitches

FIGURE 20. Occurrence of ore in "roll" in Missouri mine.

about 30° NE., away from the main northwesterly fault. The 

thinning and disappearance of the ore where the dip steepened 

and the occurrence of a rich pocket where the vein flattened 

strongly suggest that the Missouri vein occupies a premineral 

reverse fault. On level 5, as shown in figure 19, the occurrence 

of the thickest mass of solid galena in the low-grade streak is 

coincident with a marked flattening of the ore seam.

Little could be seen of the ore occurrence in the other veins of 

the mine, and most of the information obtained is recorded on 

plate 24. The ore in the Leftwick vein was chiefly galena, 

gray copper, and chalcopyrite in a quartz-barite gangue. The 

width of the ore ranged from 3 to 24 inches and was commonly 

about 6 inches. Some ruby and native silver are 

reported from the upper levels. The total development on this vein is unknown, but in 1883 

there were six adits on the vein aggregating 2,000 

feet.

High-grade bismuth ore is said to have been shipped from 

the northward-trending vein opened by the southern workings 

of level 3. This drift, like most of the others in the mine, is 

very wet, and aside from a heavy copper stain in the walls of the 

drift near the old stopes little could be seen. According to the 

miner who worked this part of the mine in the eighties, the vein 

in the breast was chiefly barren gouge, but at the raise 90 feet 

north the vein carried 12 inches of good ore, which pinched to a 

seam of gouge a short distance farther north but widened to pay 

ore in 20 feet and continued as such for 100 feet. Most of this 

ore shoot has been stoped above the level, but it is reported that 

the large amount of water present compelled the miners to 

abandon the winze near the center of the ore shoot before any 

ore had been taken out below the level. The ore is said to be 

very similar to that in the Missouri vein farther north, consisting 

of a vein of low-grade ore against the hanging wall and one of 

high-grade ore on the footwall.
MONTEZUMA QUADRANGLE, COLORADO

MOHAWK

The Mohawk mine is on the northwest slope of Teller Mountain at an altitude of about 11,500 feet, about 2 miles south of 

Montezuma. There is no road to the mine, and the ore must 

be packed over a trail to the Chatauque mine road on Deer 

Creek, which it joins 1% miles from Montezuma. The vein 

was discovered in 1880 by John Sundragger and was a steady 

but small shipper during most of the eighties. The known 

production of the property is given below.

The mine has two accessible adits, as shown on plate 29. 

The portal of the lower adit is about 175 feet below the upper 

adit, and all the production has come from the upper level. 

The country rock of the district is the Swandyke gneiss, which 

strikes about N. 30° W. and dips 50° SW. The Mohawk vein 

strikes slightly north of west and dips steeply to the north. 

It is a fissured zone from 1 to 5 feet wide and contains from 4 to 

24 inches of quartz and galena. The lead ore occurs in chimneys separated by nearly barren masses of quartz. The ore 

shoot being worked in 1928 was about 70 feet long and had been 

proved to a depth of 30 feet below the level. The ore carries 

little silver and no copper, a shipment of 37 tons averaging 

about 9 ounces of silver to the ton and 42 percent of lead.

Production of Mohawk mine

No record available for 1885, 1890-1900: no production in 1901-24, 1926-28. 

MORE WORK

The More Work vein is on the west side of Glacier Mountain 

1 mile south-southwest of Montezuma, and is only 500 feet 

north of the main adit of the Sts. John mine. The property 

is developed chiefly through an adit whose portal has an altitude 

of about 11,050 feet. Some stoping has been done on this 

lev.el, and about 50 tons of ore is known to have been shipped. 

The history of the mine was not ascertained. As shown in 

plate 28, the vein strikes N. 60°-80° E. and dips about 70° N. 

The country rock is hornblende gneiss of the Swandyke gneiss; 

it strikes east-northeast to west-northwest and dips 35°-70° E. 

The unstoped portions of the vein are from 5 to 12 inches wide. 

Barite is the most abundant mineral in the vein, but galena 

and sphalerite together make up more than half of the vein 

in many places. Quartz is also common. The branching 

character of the vein, shown in plate 28, makes its course difficult to foretell in advance of development work. The vein will 

probably be cut off a short distance east of the 1929 breast by 

the northerly fault, which terminates the Comstock vein 

(no. 5 vein) of the Sts. John mine a few hundred feet south. As 

this is a normal fault, the eastern continuation of the More 

Work vein is some distance south of the western segment.

Production of More Work mine

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

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

1917. ...............

1919. 

Ore 

(short 

tons)

(?)

4

70

3

Gold 

(fine 

ounces)

1.25

.10

Silver 

(fine 

ounces)

23

40

401

27

Lead, wet 

assay 

(pounds)

1,738

5,647

14, 952

3,034

Copper, 

wet assay 

(pounds)

rtfiO

Zinc 

pounds)

47, 689

1882.. ............. ........ ......

1883-- 

1884. __. 

1886 

1887. 

1888 

1889 

1925. _________ . -.-.

. Ore 

(short 

tons)

10

45

45

58

(?)

(?)

(?)

37

Gold 

(fine 

ounces)

0.60

Silver (fine' 

ounces)

144

110

537

339

Lead, wet 

assay 

(pounds)

9,004

12,388

55, 619

31, 202

WIO. .........................

1917. 

1919

Ore 

(short 

tons)

5 

35 

10

Gold 

(fine 

ounces)

0.17

Silver 

(fine 

ounces)

194 

700 

303

Lead, wet 

assay 

(pounds)

2,913 

7,765 

462

Zinc 

(pounds)

21, 645

No production in 1901-9, 1911-16, 1918, 1920-28.

MORGAN

The Morgan mine is on the south slope of Tiptop Peak, 

about half a mile east of Montezuma. It is developed by three 

adits between altitudes of 10,975 and 11,205 feet and is reached 

by a steep wagon road from the town. The mine was worked 

in the eighties, but only a small amount of ore was shipped. 

It has produced a few carloads of ore intermittently since 1900 

but has never been worked for many years at a time.

Production of Morgan mine

No record available for 1890-1900; no production in 1902-16, 1918, 1920-28.

The Morgan mine is typical of many small mines in the 

Montezuma quartz monzonite and is therefore discussed in 

some detail as representing a type. The underground workings, 

aggregating about 1,800 feet, and the geology are shown in 

plate 30. The country rock of the entire property is the Montezuma quartz monzonite. The lowest adit contains no stopes, 

and no ore was observed in it. The drifts follow strong gougy 

fissures, which are heavily stained with manganese dioxide near 

the surface. A short distance underground the fissure filling is a 

light-colored talcky gouge, which is more or less stained with 

limonite. This gouge was reported to have a high gold content, 

but the writer found none, although he panned several pounds 

of it. The heavy residue at the end of the operation proved to 

be crushed pyrite, and no doubt it is this mineral that has given 

the iron-stained appearance to the gouge. As shown in plate 

30, the main fissure, striking about N. 80° E. and dipping 55° 

N., cuts and displaces a fissure that strikes N. 55° E. and dips 

65° NW. The movement indicates that the main fissure is a 

normal fault.

The intermediate adit has been driven close to the mine 

buildings, which include a boarding house, smithy, and compressor house. The adit cuts three fissures which are almost 

parallel and strike about N. 60° E. and dip 62°-70° N. The 

first fissure, 80 feet from the portal, is a barren iron-stained 

sheeted zone about 3 inches wide. The second fissure, 180 feet 

farther in, is marked by 2 feet of altered sheeted rock, 6 to 12 

inches of gouge, and 2 to 4 inches of sulphides, most of which 

are badly crushed. A drift follows this vein 40 feet, and a seam 

of crushed pyrite from 2 to 3 inches wide persists throughout 

this distance. A seam of severely crushed zinc blende from 

half an inch to 2 inches thick is also present most of the distance, 

but the galena occurs sporadically in a few crushed lenticular 

masses 1 to 2 inches wide and 2 to 5 feet long. The third 

fissure contains a sulphide vein from 4 to 15 inches wide under 

a hanging wall of gouge from 1 to 8 inches wide. As shown in 

plate 30, the sulphide vein turns out of the drift away from 

the gouge seam 10 feet southwest and 100 feet northeast of the 

main crosscut. It is probable that postmineral movement 

developed the gouge, and that the movement was only locally 

confined to the vein. Manganiferous ankerite is about as 

abundant as the sulphides in the vein. The ankerite occurs as 

solid seams from half an inch to 5 inches thick, parallel to 

the sulphide. The sulphide is predominantly pyrite, but lightcolored sphalerite is also abundant. Sporadic bunches of galena 

were observed, but none were large enough to be stoped.

The upper adit has produced all the ore that has been 

shipped. The veins that have been stoped are nearly parallel
THE MINES 91

and strike N. 75°~80° E. and dip 60°-SO° N. In some places 

they send off northeastward-trending branches, and in others 

they are crossed by small veins that strike N. 35°-55° E. 

Stoping ore commonly occurs at the intersections of cross veins 

or where a branch vein forks from the main easterly veins. 

In the widest vein cut by the adit, however, a chimney of ore 

that extended to the surface is not related to the intersection of 

fractures on this level. This vein consists chiefly of quartz 

and pyrite, but sphalerite is also abundant, and lenticular 

bunches of galena are common. The ore is from 2 to 28 inches 

wide. The next vein, about 120 feet farther north, is much 

flatter and varies greatly along both the dip and strike. In 

the exposed part of the vein the chief mineral is manganiferous 

ankerite about 6 inches wide. Thin layers of pyrite and 

sphalerite occur in the ankerite, generally in crustified layers. 

The vein at the breast of the adit in 1929 was chiefly quartz 

and pyrite but carried abundant sphalerite at its intersection 

with a cross vein about 20 feet east. This vein is about 8 inches 

wide and is open and vuggy in many places. Very little 

ankerite was observed in it.

NEW YORK AND AILADINS LAMP

The New York mine is on the southeast edge of Montezuma 

at an altitude of about 10,350 feet. Several veins have been 

cut by the New York tunnel, the largest of which are the New 

York and the Alladins Lamp. The Alladins Lamp was discovered in 1882 by Oliver Milner, and some ore from it was 

shipped in 1888 and 1926, as shown below. No production has 

been recorded from the New York vein, and little is known of 

its history.

Production from Alladins Lamp vein

:188S....~ .....................

1920 ........................

Ore 

(short 

tons)

(?)

25

Gold 

(fine 

ounces)

0.86

Silver 

(fine 

ounces)

67

115

Copper 

wet assay 

(pounds)

762

9,164

Zinc 

(pounds)

6,839

No record available for 1889-1900; no production in 1901-25, 1927-28.

The underground workings are shown in plate 31. The 

country rock of the mine is Montezuma quartz monzonite, 

and it is cut by northeasterly and easterly mineralized fissures 

and northerly barren fractures. The northerly fractures are 

nearly vertical and are later than the mineralized fissures, but 

the displacements of the faults are small, and many of them do 

not persist along their strike for more than a few hundred feet. 

The New York vein is the best-mineralized vein in the mine 

and has been followed for about 900 feet. It strikes northeast 

and dips about 70° NW. In some places it is barren, but for 

most of its length it carries sphalerite, galena, and pyrite in a 

quartz-ankerite gangue. The ore seam is generally from 4 to 

10 inches wide, but in the main shoot, about 1,000 feet from the 

portal of the tunnel, the vein is from 10 to 36 inches wide for a 

distance of about 300 feet. No stoping had been done here in 

1929, but a raise 60 feet high showed the ore to be 24 inches 

wide for this distance above the drift. Channel samples taken 

at many places on this ore shoot are said to average about 35 

percent in combined lead and zinc. The lead and zinc are 

nearly equal in most samples, but in some of them one metal is 

as much as five times as abundant as the other. The ore in the 

Alladins Lamp vein is from 3 to 6 inches wide and is similar to 

the ore in the New York vein. Most of it carries about 10 

.ounces of silver to the ton, but assays of 20 ounces have been 

obtained from some places.

The ore in the New York vein is the largest and most continuous body of ore which the writer has seen in the Montezuma quartz monzonite. It contains so much zinc and iron

that it could not be shipped unless these constituents were 

separated from the lead, and in 1929 there were no successful 

flotation mills near Montezuma. The ore shoots are not 

found at the junction of fractures, as in the Morgan mine, but 

on the contrary the ore becomes poorer in most places where 

two fractures intersect. A strong, well-mineralized fissure 

commonly splits and branches at its junction with another 

vein, and both become nearly barren. It is probable that the 

stresses that produced most of these premineral fractures in 

the Montezuma quartz monzonite were relieved by many 

small fractures where major fissures crossed. The lack of 

mineralization at the junctions would thus be explained by 

the poorer channel for circulation afforded in these parts of 

the veins. The lack of continuity of the veins and the branching character of the fractures are shown in plate 31.

OLD SETTLER AND WATERLOO

The Old Settler vein is on the east slope of Collier Mountain 

directly east of Montezuma, and the western part of the vein, 

known as the "Waterloo", has its lower dump within the limits 

of the town site. The Old Settler was discovered by Joseph 

DufReld in 1865 and worked intermittently through the seventies- and eighties. Raymond's report for 1870 states that the 

Old Settler was developed by a tunnel 260 feet long and that 

the ore streak, which assayed from 20 to 100 ounces of silver 

to the ton, was 2 feet wide and contained galena, sphalerite, 

gray copper, and pyrite. There is no recorded production from 

the property, but it is said to have shipped a small amount in 

the seventies. The vein is well exposed in a small cut on the 

Waterloo claim, a short distance east of Montezuma, but the 

workings were inaccessible in 1929. The vein strikes N. 60°- 

65° E. and dips steeply to the north. Where it is exposed it 

is about 12 inches wide and consists predominantly of galena, 

sphalerite, and pyrite in a quartz gangue. The sulphides are 

much more abundant than the quartz; galena and sphalerite 

are present in about equal amounts and are more abundant 

than the pyrite.

OLD TIMER

The Old Timer lode is on the northeast slope of Glacier 

Mountain, about half a mile south of Monte/uma. The chief 

adit is at an altitude of about 10,600 feet, a few hundred feet 

south of the Silver King tram. The Old Timer was discovered 

in 18Sl«by Messrs. Benight and Robbins. Several years earlier 

the St. Lawrence Mining Co. had driven a tunnel 300 feet on a 

barren vein parallel to the Old Timer and only about 15 feet 

away. This old drift was used by Benight and Robbins, wh'c 

drove crosscuts from it to their vein. Two other adits were 

driven on the vein, and a few carloads of lead-silver ore were 

shipped in the next few years. The known'production of the 

mine is given below.

In 1882 the local paper noted that the lower level was 100 

feet long and carried a wide quartz vein streaked with galena, 

and that in the upper adit, then about 70 feet long, 12 inches of 

nearly solid galena had appeared in the breast. The galena 

carried a small amount of wire silver in some places. According to the Colorado Mining Directory for 1883, the 'ore when 

sorted assayed from 100 to 225 ounces'of silver to the ton and 

about 30 percent of lead. Little work has been done on the 

property since the eighties, and its total production has been 

small.

The country rock of the vein is the Swandyke gneiss, which 

strikes N. 20° E. and dips about 75° E. The vein strikes northnortheast and dips about 70° NW. As shown in plate 32, only 

one short stope has been made on the vein. At the ends of the 

stope the vein has 6 inches of galena and manganiferous 

ankerite, but the ore on the dump suggests a vein from 6 to 10 

inches thick consisting chiefly of galena and quartz, The
92 MONTEZTJMA QUADRANGLE, COLORADO

galena is disseminated through the quartz and is associated with 

a moderate amount of light-brown sphalerite. A little pyrite 

is present but seems confined to the wall rock. Barite and 

manganosiderite are present in many of the specimens lying on 

the dump and appear earlier than the sulphides and quartz.

Production of Old Timer mine

1881... 

1882....... ........... .................... .

1883 

1887-........... ................. ..........

Ore 

(short 

tons)

5

15

5

(?)

Silver 

(fine 

ounces)

80

Lead, wet 

assay 

(pounds)

5, 362

No record available for 1884-86,1889-1900; no production in 1888,1901-28. 

ORPHAN BOY

The Orphan Boy is on the east slope of Morgan Peak near the 

head of Warden Gulch, about a mile east of Montezuma. It is 

developed by three adits between altitudes of 11,800 and 12,100 

feet. The vein was discovered before 1875, but the exact date 

is not known. It was worked intermittently from 1875 to 1890, 

but little work has been done on the property since then. .The 

mine produced 45 tons of ore in 1881, 100 tons in 1887, and an 

unknown amount that yielded 378 ounces of silver and 1,894 

pounds of lead in 1889. According to the Colorado Mining 

Directory for 1883, the Orphan Boy was developed at that time 

by a drift 150 feet long and a crosscut tunnel 125 feet long. 

The ore was reported to be galena in a quartz gangue, assaying 

when sorted from 10 to 40 ounces of silver to the ton and about 

35 percent of lead. The vein was said to be from 10 to 30 inches 

wide.

PAYMASTER

The Paymaster mine is in Horseshoe Basin a quarter of a mile 

north of Falls Gulch and about 4}i miles northeast of Montezuma. The shaft is at an altitude of 12,050 feet and was partly 

filled with water in 1929; the adit has an altitude of 11,725 feet 

and was inaccessible when the writer visited it. The Paymaster vein was discovered in the late sixties, and its ore is 

briefly mentioned by Raymond in his report for 1870. The 

activity of the Argentine district in 1870, caused by the developments on the Baker and Belmont veins, encouraged prospecting 

in Horseshoe Basin, and some work was done on the Paymaster 

at that time, but it was not until 1879, when the claim was 

relocated, that active development was undertaken. In the 

next few years an 80-foot shaft was sunk on the vein, and a few 

hundred feet of drifts were driven. A three-story mill was completed in 1882 and was joined to the mine by a tramline 1,300 

feet long. The Paymaster, Silver Ball, and Seven-thirty claims, 

all on the same vein, were patented in 1881.

The recorded production of the mine is small. Some galena 

ore was shipped to Frisco in 1882 but probably not more than 10 

tons. In 1883, according to the Montezuma Mill Run, the 

mine was having development work done, but no mention of 

shipments was made. According to the same authority it was 

active in 1884, 1885, and 1886 and shipped some ore in 1886, 

probably about 30 tons.

Production of Paymaster mine

1882.. ....................

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

1917 ...... ...... 

1Q99

Ore 

(short 

tons)

10 

30 

12 

23

Gold 

(fine 

ounces)

(?) 

(?) 

0.54 

1.40

Silver 

(fine 

ounces)

(?) 

(?) 

153 

200

Lead, 

wet 

assay 

(pounds)

(?) 

(?) 

10, 403 

4,375

Copper, 

wet 

assay 

(pounds)

(?) 

(?) 

74

Zinc 

(pounds)

(?) 

(?)

No record available for 1893-1900, 1918-21; no production in 1883-85, 1887-92, 

1901-16, 1923-28.

As shown above, the mine is credited with two shipments 

since 1902. This ore probably came from the Paymaster shaft, 

where the vein is reported to have had seams of quartz and galena about 10 inches in aggregate thickness in a sheeted zone 

about 4 feet wide. The ore on the dump near the shaft indicated 

that the vein was at least 10 inches wide. It consisted largely 

of coarse-grained vuggy quartz, barite, and galena, but manganosiderite and light-colored sphalerite were common. Pyrite 

was confined to the wall rocks. The ore milled in the eighties, 

according to the Colorado Mining Directory, assayed about 34 

percent of lead and 30 ounces of silver to the ton. The vein is 

nearly parallel to the schistosity of the enclosing Idaho Springs 

formation, which is almost vertical and strikes north-northeast. 

The country rock is injection gneiss and quartz-biotite-sillimanite schist.

The paragenesis of the ore on the dump shows that silicification and pyritization of the wall rocks occurred early and was 

followed by the formation of manganosiderite in the vein; 

barite was deposited later and was followed by galena, sphalerite, 

and quartz. A large amount of quartz is later than all the other 

minerals.

PENNSYLVANIA

The Pennsylvania mine is on the northwest slope of Decatur 

Mountain, about a quarter of a mile south of Peru Creek and 3 

miles east-northeast of Montezuma. It has been one of the 

most productive mines in the quadrangle and has a large mill 

run by electric power and several smaller buildings for living 

quarters and offices. The mine is easily accessible by automobile over a good wagon road, which has few steep grades. The 

mill and the mine buildings are at an altitude of about 10,900 

feet and are connected with the two main openings of the mine 

by short aerial'tram lines.

The vein was discovered by J. M. Hall in 1879 and slowly 

but steadily developed by him and his associates during the 

next decade. Almost no ore was shipped until about 1887, 

but from this year until 1893 the production of the mine 'increased steadily from a few carloads to nearly 7,000 tons a 

year; from 1894 to 1907 the mine was active, but production 

gradually fell off, and in 1908 no ore was shipped. The production has been intermittent since 1909 and has fluctuated 

greatly; thus over 12,000 tons of ore was treated in 1911, less 

than 50 tons the next year, and about 3,000 tons in 1913. Early 

in' 1892 the mine was leased by the original owners, J. M. Hall, 

R. S. Morison, B. A. Hopkins, C. N. Foster, and J. H. Husted, 

to the Decatur Mining Syndicate, Ltd., an English organization, 

which operated the property during the peak of its production 

but disposed of it in 1895 to the Pennsylvania Mines Co., which 

held it for several years. The ore sold prior to 1894 was sorted 

by hand and shipped directly to the smelters, but in 1895 a 

mill was completed, and almost all the ore sold since that time 

has been concentrated in the mill, which has been revamped 

several times. In 1902 the Ohio Mines Co. bought the property 

and drove the lowest level on the vein, known as the Ohio or 

F level. The mine again changed hands in 1905 and was held 

by the New Pennsylvania Mines Co. until 1918; it was then 

taken over by the Liberty Mining & Reduction Co. and operated by that company until 1927, when the company was reorganized as the Consolidated Pennsylvania Mining Co.

The mine is opened by six levels, known as A, B, C, D, E, 

and F. Level A is the highest and is 30 feet above level B but 

is not connected with it. Both are adits but have long been 

caved. Level C, 130 feet below level B, is opened by an adit 

whose portal is at an altitude of 11,290 feet and is connected 

to the mill by an aerial tram. It was the level through which 

the mine was operated for many years, and a winze sunk on the 

vein from this level was used for opening levels D and E, 50 

and 130 feet below level C. Level F was opened by another 

adit and is about 100 feet below level E, its portal having an
THE MINES 93

altitude of 11,058 feet. The geology and the plan of the accessible workings are shown in plate 33.

The Pennsylvania vein strikes N. 20°-35° E. and averages 

about N. 30° E. It dips steeply to the west in most places 

but locally overturns and dips about 80° E. The vein is chiefly 

in schistose rocks a few hundred feet east of the Montezurna 

quartz monzonite stock. (See pi. 3.) The most common rocks 

on the lowest level of the vein are quartz schist, quartz-biotite 

schist, injection gneiss, and granite gneiss. Locally thin dikes 

of Silver Plume granite are present, and a dike of quartz 

inoiizonite is cut near the breast of the southwestern split of 

the vein. (See pi. 33.) On level C the prevailing wall rocks 

are granite gneiss and injection gneiss, but Silver Plume granite, 

quartz monzonite porphyry, and quartz-biotite schist are cut 

by the crosscut on this level. The wall rock of the vein has been 

markedly silicified and pyritized for a distance of 30 feet west 

of the vein, but east of the vein the silicification was less intense, 

although pyrite is abundant 20 feet away.

Only a part of level C was accessible at the time of the writer's 

visit. The vein has been stoped for over 800 feet on this level, 

and the stopes are from 6 to 14 feet wide, the largest stopes being 

at the place where the vein divides into the "east and west 

splits." As shown in plate 33, these two branches diverge at 

an angle of about 25° until they are nearly 50 feet apart and then 

resume the general course of the main vein, continuing parallel 

as far as they have been explored. .

About 180 feet northeast of the "split" and a short distance 

north of the point where the level C crosscut intersects the vein 

a pillar of ore has been left. This ore is probably of lower 

grade than much of that taken from the stope but is instructive 

as illustrating its general mode of occurrence. The vein here is 

about 12 feet wide and is a strongly sheeted zone in granite 

gneiss. Between the walls of the sheeted zone numerous veins 

of galena, pyrite, chalcopyrite, and quartz seam the altered 

gneiss. Most of the minor veins are parallel to the walls, but 

several of them follow an irregular diagonal course across the 

sheeted zone. Galena is the most abundant mineral in the veins 

and occurs in seams from 1 to 12 inches wide; about 30 inches 

of the sheeted zone is galena, S inches pyrite, and 2 inches 

chalcopyrite. The relations of the veinlets clearly show that 

quartz, pyrite, and chalcopyrite are earlier than galena and that 

a small amount of dolomite formed later than the galena. 

According to the miners some of the best ore at the "split" 

was 14 feet wide, contained less than 2 feet of waste, and carried 

very little pyrite. Argentiferous gray-copper ore was much 

more abundant near the surface than in the lower workings, 

and according to the Georgetown Courier for September 11, 

1890, when the vein was first opened large quantities of copper 

sulphate were found.

Level F follows the vein 1,800 feet south of the level F crosscut, and here, almost vertically below the "split" in level C, 

the vein branches. The west branch, which has been followed 

300 feet farther, is apparently the main vein and shows little 

change from the course followed by tlie vein to this point. The 

east branch has been followed about 200 feet. The walls of the 

vein and its branches have been intensely silicified and pyritized 

throughout the level. The vein is smaller on this level than it 

is on level C, and the ore is commonly lean, pyritic, and thin, 

but in a few places some good lead ore occurs and stoping has 

been done. A few feet north of the crosscut a winze was sunk 

to an unknown depth in 1902, and according to Thomas Sharpe, 

who worked in the mine in that year, the vein carried only 

pyrite and quartz as far as the winze was sunk, and no drifts 

were turned from it. The vein is said to maintain its westerly 

dip to the bottom of this winze. About 350 feet south of the 

crosscut the first shoot of lead ore occurred in the vein on level 

F, although small amounts of galena were sparsely distributed 

in the pyritic quartz of the vein in.many places north of this

place. The ore shoot was about 12 inches wide and 50 feet 

long and, unlike the others seen, dipped steeply to the east. A 

short distance farther south the vein resumed its normal dip 

and again became pyritic. At 70 feet south of this ore body 

another galena ore shoot was found. The vein here was from 3 

to 5 feet wide and had 12 to 30 inches of galena ore for a distance of about 100 feet along the drift. At the south end of the 

ore shoot a winze was sunk 75 feet. The winze was full of water 

at the time of the writer's visit, but the vein is said to have 

galena ore in it as far as the winze was sunk; the maximum 

width of lead ore in the winze is reported to be about 24 inches, 

but little stoping was done below the level. Apparently the 

amount of galena was not large enough to pay the cost of 

pumping the heavy flow of water found in the winze. At 220 

feet south of the winze a short galena ore shoot was found, and 

a raise has been put up on the vein. At the level of the drift 

the vein dips 73° W.; 30 feet above it the vein becomes vertical; 

and 70 feet above the level it overturns and dips 85° E. The 

galena ore 30 feet above the drift is distributed through about 

24 inches of broken sheeted rock, but 70 feet above the drift it 

pinches to 4 inches in width. Little ore was exposed between 

this ore body and the place where the vein branches. Here a 

short crosscut toward the west exposes a sheeted zone about 7 

feet wide containing many veins and stringers of galena, which 

aggregate about 12 inches in width. Very little ore is exposed 

in the west branch, however, until a point about 140 feet farther 

south is reached; here an ore shoot containing both lead and 

copper was found, and some stoping has been done. This 

shoot is about 80 feet long on level F but is somewhat longer a 

short distance above it. Although the drift was less than a 

year old at the time of the writer's visit, the water from the vein 

carried so much copper that deposits of metallic copper half an 

inch thick and from 3 to 7 feet long were formed in many places 

on the iron rails under the stope. The east branch contains 

very little galena but is heavily seamed with pyrite; this part 

of the vein is from 12 to 48 inches wide and in places carries as 

much as 15 inches of pyrite.

Small veins striking parallel to the Pennsylvania vein occur 

east of it on both levels C and F. The Ouray vein is cut 225 

feet east of the Pennsylvania vein on level C. It strikes N. 

30° E., dips 80° W., and carries 2 inches of galena ore. On 

level F a narrow vein locally stained with copper, iron, and 

manganese is cut about 75 feet east of the Pennsylvania vein. 

It has been followed about 200 feet north and south of the main 

crosscut but without encouraging results. About 100 feet 

farther east another small vein carrying calcite and pyrite was 

found. No other veins were discovered in this crosscut. The 

breast is about 400 feet east of the main vein, and there is a 

heavy flow of water issuing from it.

No conclusive evidence has been found regarding the direction 

of the premineral movement on the Pennsylvania fissure. 

Grooves and striations on the wall of the vein dip about 30° 

SW.; the occurrence of galena in diagonal fractures such as 

those shown in plate 33 suggests gash veins in a reverse 

fault; and the marked thinning of the northeastern ore shoot 

on level F where the vein steepened and overturned toward 

the east suggests the closing of an irregular open fissure 'by 

reverse faulting. The meager evidence available indicates that 

the west wall moved upward to the northeast relative to the 

east wall.

As shown on plate 3, the Pennsylvania vein is nearly parallel 

to the schistosity of the enclosing schist and gnefss. In the 

Central City and Idaho Springs districts deep exploration has 

shown that the most productive veins either cut across the 

schistosity of the country rock or have walls of granite gneiss, 

porphyry, or pegmatite. 28 In many veins in those districts the

13 Lovering, T. S., Localization of ore in the schists and gneisses of the mineral 

belt of the Front Kange, Colo.: Colorado Sci. Soc. Proc., vol. 12, pp. 234-268, 1930.
ME.

E\ \CROSSCUT NO.5 LEVEL EAST

50 100 Feet Sloped previous to Stoped Octobe

October 1,1895 to January 1,1

FIGURE 21. Stope map of north vein of Pennsylvania mine, 1902.
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 178 PLATE 34

jocation of 

porphyry dike on No.6 level

SW. cor..sec.l6,T.5S.,R.75W.

5OO 1,000 Feet

PERUVIAN MINE, RUBY MOUNTAIN.
THE MINES 95

occurrence of ore shoots is definitely related to the occurrence of 

layers of granite gneiss in the Idaho Springs formation, and an 

apparently barren vein becomes productive on passing into 

granite gneiss, or a productive vein becomes barren on passing 

into schist. In the Montezuma district ore shoots are most 

commonly found in veins where the schistosity of the enclosing 

rock makes a decided angle with the vein, or at the intersection 

of two veins. The large body of ore found in the Pennsylvania 

vein occurs where it branches and in that part of the vein which 

has walls of granite gneiss. The split in the vein occurs very 

close to the south end of the granite gneiss wedge and suggests 

the weakening of the vein as it passes from the competent gneiss 

into the incompetent schists. The strain, which was relieved in 

the granite gneiss by strong fracturing confined to a narrow 

sheeted zone, may have been distributed over a much wider 

space in the weaker schists; as a result the vein may weaken 

and branch as it is followed into the schist. Although there is 

little likelihood of finding an ore body in the schist comparable 

to that in the gneiss, it is probable that chimneys or good ore 

can be found at the "splits" in the vein and in other favorable 

places. The extension of the Pennsylvania vein to the southwest has been traced in the Delaware, Delaware Extension, and 

Sunrise claims, but little ore has been produced here except from 

the Delaware. The workings on the Delaware have long been 

inaccessible, but their production and history are discussed on 

page 78.

The known and estimated production of the Pennsylvania 

group is shown below.

Production of Pennsylvania group

1885........-. -- 

1QQ/1

1887.. 

1889 (Ohio) 

1800° 

1801 < -.- . 

IQOO a

1893". 

181)0" -

1807".. 

1808 

.1809". 

1900". 

1001- 

1002 (Ohio) 

1903.. -

1904. 

1905 . 

1900.. 

1007. . 

1009. 

1012.. 

1018.. - 

1919.. 

1920.. 

1021. 

1922... - --

1023.. .* 

Ore to 

concentrating 

mills 

(short 

tons)

1911. .- 12,488

1913 3,094

1920............ 1,023

1921.... 8,000

1027 . 1,400

1928 .-- 1,391

Ore (short 

tons)

45

68

30

(?)

4, 670. 418

3, 299. 577

1)52. 726

.1,672.087

1,129.515

120

5,941

2,430

1,284

1, 000

35

58

31

45

37

117

33

30

79

112

Concentrates 

produced 

(short 

tons)

1,167

1,719

476

134

920

171

100

Gold 

(fine 

ounces)

467. 04

91.28

95. 27

160. 30

85. 25

90.04

112.05

7.50

594. 10

121.50

38.70

50.02

38.98

7.40

4.70

4.28

7.84

3.64

4.70

7.80

7.80

Gold 

(fine 

ounces)

160. 46

268. 62

61. 08

12.60

154. 62

8.80

12.00

Silver 

(flue 

ounces)

g

16,681

74, 915

88, 538

49 478

40,414

63, 895

41,996

54, 104

3, 600

29, 705

12, 150

24, 504

3,000

3,500

1,088

851

795

1,399

6,024

1,639

1,647

3,239

7,986

Silver 

(fine 

ounces)

28, 320

46, 434

8,989

4,351

33, 728

7,003

4,200

Lead, 

wet 

assay 

(pounds)

2,086

567, 847

1,048,616

321, 599

484, 330

318,331

410,098

50, 471

594, 100

486, COO

85, 106

200, 000

9,796

6,523

9,677

17,289

38, 496

9,390

5,022

32, 233

30, 575

Lead, 

wet 

assay 

(pounds)

193, 421

288, 107

71, 556

31,653

215,860

38,281

38, 000

Copper, 

wet 

assay 

(pounds)

485

795

264

2,275

826

755

2,415

Copper, 

wet 

assay 

(pounds)

17, 390

20, 115

3,489

2,795

16, 088

4,644

2,000

Zinc 

(pounds)

486, 000

200, 000

10, 789

Zinc 

(pounds)

206, 280

13, 000

" Content estimated from tonnage, gross value, and average lead, gold, and silver 

content of ore.

No record available for 1888.

PERUVIAN AND SHOE BASIN

The Peruvian vein and Shoe Basin veins are on the eastern 

slope of 'Ruby Mountain, about 4 miles northeast of Montezuma, at altitudes of about 11,800 and 11,500 feet. They were 

originally opened by shafts on the veins, but in 1911 a long adit 

wf.s driven that cuts both veins at an altitude of about 11,120 

feet. The portal of this adit is on Peru Creek at benchmark 

11,099, on the wagon road from Montezuma to Argentine Pass. 

It is accessible by automobile and marks the eastern limit of 

such transportation.

The Peruvian vein was discovered in 1874 and was moderately 

active from that time until 1893. During this period its most 

productive year was probably 1891; the Georgetown Courier 

for August 29, 1891, reports that "it has averaged 65 tons a 

month this year; ore from 49 to 63 ounces of silver per ton and 

from 7 to 20 percent lead." Little work was done after 1893 

until the Shoe Basin tunnel was driven by the Shoe Basin 

Mines Co. in 1914. As shown below, about 400 tons of ore 

was shipped in 1914 and 1915. No work has been done on the 

property since that time, and in 1929 the workings were inaccessible, and the information given below had to be obtained from 

various reports on the mine, which were kindly made available. 

Little is known of the history of the Shoe Basin vein; it is said 

to have been worked in the seventies through a shaft 300 feet 

deep, but the mine is not mentioned by any of the reports of 

that time. In 1928 the workings were inaccessible.

Production of Peruvian mine

1881.. 

1888 

1890. 

1914 (Shoe Basin and

1915 (Shoe Basin and

Ore 

(short 

tons)

100 

(?) 

(?) 

f 15 

\ -40

14

Gold 

(fine 

ounces)

0.98 

.14

Silver 

(fine 

ounces)

2,348 

8,445 

471 

1,257

109

Lead, 

wet 

assay 

(pounds)

55, 271 

40, 895 

8,609 

25, 997

10, 405

Copper, 

wet 

assay 

(pounds)

143 

308

Zinc 

(pounds)

2,280 

4,104

« Concentrates produced from 370 tons of ore.

No record available for 1876-80, 1882-84, 1886-87, 1889, 1892-1900; no production in 

1885, 1901-13, 1916-28.

The Shoe Basin adit and the underground workings of the Peruvian mine are shown in plate 34. Prior to 1914 the Peruvian 

vein was worked by a shaft 450 feet deep from which five 

levels were turned and by an upper level reached through a 

crosscut adit 395 feet long. The Shoe Basin adit cuts the 

Peruvian vein on the sixth level about 1,400 feet southwest 

of the bottom of the shaft and has been continued 1,100 feet 

northwest of the shaft as a crosscut to the Shoe Basin vein. 

The long drift on the vein is said to have been caved in 1920, a 

short distance north of the main crosscut from the portal and 

a short distance south of the shaft. The vein followed by this 

caved drift is known as the "Tunnel vein" and is connected by a 

crosscut to the Shaft vein, which is 30 feet west of it and about 

10 feet east of the shaft. The Shaft vein apparently branches 

from the Tunnel vein about 150 feet north of the shaft and 

rejoins it about 180 feet south of the shaft. The southern 

junction dips about 60° S., and the northern junction dips 

about 40° S. between the fifth and sixth levels, but its inclination in the shallower workings is not known. The Tunnel vein 

strikes N. 32° E. and dips 84°-90° W. The Shaft vein trends 

nearly parallel to the Tunnel vein and dips steeply toward it.

Most of the ore mined was found above the fourth level close 

to the southern junction of the Shaft and Tunnel veins. There 

is little stoping north of the shaft except on the first and second 

levels. The upper level has been caved for a long time, but
96 MONTEZUMA QUADRANGLE, COLORADO

according to men who were in the mine about 1915, the second 

level has several stopes in the first 170 feet north of the shaft. 

Some stoping has been done on the Shaft vein in the first 70 

feet north of the shaft on the third level, but almost no ore has 

been taken from the veins north of. the shaft on the lower 

levels. The ore shoots in the Shaft vein are separated by lowgrade or barren stretches of quartz, but little gouge is present, 

whereas the Tunnel vein is said to have many wide gouge 

seams between the ore shoots. The ore close to the surface is 

said to contain gray copper, galena, zinc blende, pyrite, and 

from 10 to 50 ounces of silver to the ton. The shipping ore 

was about 20 inches wide, but the vein averaged nearly 6 feet 

between walls and widened to about 14 feet at the junctions. 

Below the fourth level the ore is said to carry more zinc than 

it does in the higher levels, although galena is still the most 

abundant sulphide.

The ore on the dump of the Shoe Basin tunnel was of two 

kinds a thoroughly silicified gneiss containing disseminated 

sulphides, and a fissure filling consisting of quartz, barite, dolomite, and sulphides. Galena was abundant and occurred in 

medium-sized grains disseminated through the vein quartz, 

barite, and sihcified gneiss. The barite was abundant in some 

specimens and lacking in others. Pyrite and brown sphalerite 

were common; some gray copper was present and was associated 

with dolomite, but both were rare. The ore on the dump of 

the Peruvian shaft was chiefly galena and sphalerite in a 

quartz-barite gangue, but gray copper was moderately abundant. The earliest mineralization introduced pyrite and quartz 

and was followed by barite, which in turn was earlier than 

sphalerite and galena. The ore on the dump of the Shoe Basin 

workings was very similar in appearance to the Peruvian ore 

and must have come from a vein at least 10 inches wide.

The Peruvian vein is nearly parallel to the schistosity of the 

enclosing Idaho Springs formation. A dike of monzonite 

porphyry exposed on the surface near the shaft strikes about 

N. 45° E. and is probably the dike found on the sixth level, 

about 100 feet south of the shaft. The dike is reported to make 

an angle of about 30° with the vein at its intersection, very 

close to the reported junction of the Shaft vein and the Tunnel 

vein. This intersection coincides with the largest stopes found 

below the fourth level. On the surface the dike of quartz 

monzonite porphyry west of the vein intersects it at the shaft; 

this suggests that the Peruvian vein occupies a fault whose 

east side moved south, but unfortunately the dip of the porphyry dike is unknown, and the displacement of the fault 

cannot be accurately given.

POTOSI

The Potosi vein is on the west slope of Glacier Mountain at an altitude of about 11,400 feet, about 1 mile 

southwest of Montezuma and a few hundred yards southeast 

of the Sts. John mill. It was discovered by Edward Guibor 

in June 1865, but little work was done on the vein at the surface, 

although the Sts. John mine developed it at depth by the main 

crosscut tunnel. Raymond notes that the Potosi was worked 

and shipped ore in 1875, but no other production is on record. 

The shipment was probably small, as the Colorado Mining 

Directory in 1883 states that the total developments consist of 

three drifts 25, 28, and 16 feet long. The vein was reported 

to have two pay streaks 4 and 6 inches wide, and the ore was 

said to be galena and some ruby silver in a quartz gangue, 

assaying 150 ounces of silver to the ton when sorted.

QUAIL

The Quail mine is on the west slope of Collier Mountain 

near the head of the south fork of Morgan Gulch, at an altitude 

of about 12,000 feet, 1 mile due east of Montezuma. A steep

1907---....-.... . - ...

1918------.---.--.. . ....--.

1919 --.- -......-...-..

Ore

(short

tons)

37

70

26

Gold

(fine

ounces)

0.30

.30

Silver

(fine

ounces)

741

728

372

Lead, wet

assay

(pounds)

AH 0^9

70, 380

94 01 fi

Copper,

wet assay

(pounds)

qo

206

wagon road leads from the town to the mine, but in 1929 it was 

in such poor repair that it was not passable for automobiles. 

As shown in figure 22, the chief workings are two adits, each 

of which follows the vein for about 400 feet. Close to its breast 

the lower adit is connected with the upper adit by a raise about 

210 feet high, and a short intermediate level turns from the 

raise about 130 feet up. According to James Southerland, of 

Montezuma, the Quail vein was discovered by Philip Bianchi 

in the nineties, and some lead ore was shipped by him from the 

upper tunnel. Most of the work was carried on by Mr. Southerland or under his direction, and after the company's operations 

stopped in 1916, he leased the mine for several years. He 

states that 100 to 120 tons of galena ore was shipped each 

year in 1914, 1915, and 1916, seven 25-ton carloads in 1917 

and 1918, and one carload in 1919. The ore sold direct to 

the smelter is shown below.

Production of Quail mine

No production in 1901-0, 1908-14, 1920-28.

The Quail vein is of especial interest because it goes from 

the Montezuma quartz monzonite stock southwest into the 

enclosing Idaho Springs formation. It strikes about N. 40° W. 

and is nearly vertical. The ore found in the mine since 1914 

has come from two ore shoots, one in the quartz monzonite 

stock and the other in the schist at the contact of the two 

rocks. The top of the first shoot was cut in the upper level 

and extended only a few feet above the bottom of the drift, 

and the vein a short distance away was a tight, barren fissure, 

containing only a very thin seam of quartz. The shoot had a 

maximum .strike length of about 50 feet on the intermediate 

level and bottomed about halfway between the lower level and 

the intermediate level. The best ore in the shoot was nearly 

pure galena, about 1% feet wide The second ore shoot was 

approximately triangular in shape, and only the lower tip of 

the triangle entered the upper drift, where it was cut 30 feet 

southeast of the top of the first shoot. The contact of the 

quartz monzonite and the schist was the northwestern limit of 

the ore and is said to pitch steeply south. The general pitch 

of the ore shoot is northwest, and it had a pitch length of about 

35 feet and a maximum strike length of about 30 feet. The 

ore ranged from 3 to 16 inches in width, and about 100 tons of 

ore was shipped from this stope. The vein on the lower level 

was chiefly quartz and contained very little shipping ore, 

although locally pyrite and sphalerite were abundant. The vein 

is said to range from 3 inches to 3 feet in width on this level.

The occurrence of the two shoots at the contact of the stock 

and the schist, one above the other, suggests that other shoots 

might be found at greater depth similarly related to this contact, but the size of the shoots does not warrant extensive 

exploration for them.

QUEEN OF THE WEST

The Queen of the West vein is on the steep east side of Horseshoe Basin, 1,200 feet northwest of Argentine Pass and about 

5J4 miles northeast of Montezuma. The vein was explored at 

several places by short adits between altitudes of about 12,500 

and 13,000 feet, but it was inaccessible in 1928, when the writer 

visited it. It strikes N. 70° E. and cuts quartz-biotite schists 

of the Idaho Springs formation. The occurrence of alabaiidite 

in the Queen of the West; makes it unique, as no other vein in.
THE MINES 97

H a
98 MONTEZUMA QUADRANGLE, COLORADO

the region is known to have this mineral. Smith 29 describes 

the occurrence as follows:

"The society is indebted to Mr. J. S. Randall, of Georgetown, for several massive specimens of alabandite, a considerable quantity of which was found last fall in a small vein 1 to 6 

inches wide, encountered in sinking a shaft on the Queen of the 

West mine, near Snake River in Summit County. These specimens have a distinct cubic cleavage and resemble ordinary 

massive galena except in color, which is nearer a steel-gray on 

a surface freshly fractured but which soon tarnishes to a dull 

brown or iron-black. Among specimens recently shown me by 

Mr. Randall is one containing a single distinct crystal, about 

6 millimeters square, embedded in the massive material. The 

forms exhibited are the cube and the tetragonal trisoctahedr'on. 

Unfortunately, but one perfect corner of the. crystal is shown, 

and it is impossible to tell whether there is a tetrahedral development or not. The associated minerals are small" crystals of 

rhodochrosite in cavities of the alabandite probably resulting 

from the decomposition of the latter small dolomite crystals 

and a few small pyrites. Mr. L. G. Eakins tested the mineral 

qualitatively and found it to be a manganese sulphide."

RADICAL

The Radical mine is on the western spur from Teller Mountain, known as Radical Hill, about 2^ miles south of Montezuma. The vein was discovered in the seventies, but the exact 

date is not known; J. B. Briggs, probably the discoverer, sold 

some ore to the Sts. John smelter in 1875, but no other shipment 

in the seventies is on record. The mine was idle in 1880, 1881, 

and 1882 but was worked from 1883 to 1888. As shown below, 

the production during these years was not large. The mine is 

reported to have been idle during the nineties and is known to 

have been nonproductive since 1900. It was inaccessible in 

1929. According to miners who have worked in the Radical, 

the ore streak was about 6 inches wide and consisted of galena 

in a quartz gangue. Unlike most of the .veins nearby, no 

barite was associated with the quartz and galena. According 

to the Montezuma Mill Run the ore was from 8 to 16 inches 

wide in 1883.

Production of Radical mine

IQQ'J

1884 .. - .:- -

1 Sfift

Ore (short 

tons)

2

10

10

(?)

Silver (fine 

ounces)

49

75

Lead, wet 

assay 

(pounds)

2,533

9, 148

No record available for 1876-82, 1885-87, 1889-1900; no production in 1901-28. 

RAINBOW

The Rainbow.mine is on the west slope of Keystone Mountain, 5 miles due west of Montezuma, at an altitude of about 

10,250 feet. A good wagon road turns up Keystone Gulch 

three-quarters of a mile east of Keystone and runs past a trail 

to the mine, about \Yz miles south. The trail rises 600 feet in 

the half mile to the mine and is too narrow for automobiles. 

Little is known of .the mine's early history. It shipped about 

five carloads of ore in 1-916 and 1917, but there is no other recorded production. The amount of lead and silver in these shipments is given below.

Production of Rainbow mine

1916 

1917. 

Ore 

(short 

tons)

31 

37

Gold 

(fine 

ounces)

2.39 

1.43

Silver 

(fine 

ounces).

1,141 

749

Lead, 

wet assay 

(pounds)

 795

Copper, 

wet assay 

(pounds)

58 

12

No production in 1901-15, 1918-28.

3» Smith, W. B., Alabandite from Summit County, Colo.: Colorado Sci. Soc. 

Proc., vol. 2, p. 158, 1887.

As shown on plate 32, the chief opening is the lower adit, 

which has about 1,100 feet of drifts. "Two shorter adits, 225 

and 300 feet above, expose the vein at'higher levels.

The country rock of the mine-is, hornblende-biotite gneiss of 

the .Swandyke gneiss. .It strikes N. 10°-35° W. and dips 

40°-55° E. The vein-strikes N. 80° E.-and dips 55°-65° N. 

In the uppermost adit the vein is a sheeted zone about 15 feet 

wide and contains 1" to -3 feet of -thoroughly oxidized lead ore, 

but it. was exposed only for a distance of 25 feet in 1928. In 

the intermediate adit the vein is cut off by a mineralized fault 

80 feet east of the portal;- a shoot of galena ore 12 inches wide 

and 40 feet long occurs in the vein just west of the fault, but 

the vein is barren between the shoot and the portal. The fault 

strikes N. 30° E. y dips 70° E., and is about 24 inches wide. 

It hats been followed north for 60 feet, but the eastern continuation of-the vein has not been found. If the fault is normal, 

as its~steep dip suggests, the vein will be south instead of north 

of the fault; a projection of the vein from the uppermost adit 

indicates that it should be about 20 feet south of the western 

segment at the fault. In the lower adit the vein is barren 

where it is first cut," 350 feet from the portal, and the first ore 

shoot occurs 3,20 feet farther east. The vein is from 3 to 15 

inches wide in this interval but is sparsely mineralized. No 

faults were observed-'cutting it, but the vein jogs over several 

feet at a place in line with a small fault disclosed in a branch 

drift 140 feet away. It is probable that this sharp bend reflects 

the movement that caused the fault. The vein branches in a 

few places, as shown on- plate 32, but these divisions do not 

correspond to the location of the ore shoots. The first ore 

shoot is about N. 30° E. of the ore shoot on the intermediate 

level and is close to the place where the mineralized fault noted 

there should appear on the lower level. It was not observed, 

however, and if present is much less prominent than on the 

intermediate level. At 60 feet northeast of the ore shoot a 

strong vein was found striking N. 85° E. and dipping 60° N. 

As shown in plate 32, it is probably a branch of the vein followed by the drift west of this place and should intersect the 

main vein a few feet beyond the breast of the drift. An ore 

shoot occurs at the breast, and a small stope has been made. 

This ore shoot is directly down the dip of the vein from the oxidized ore in the uppermost adit and may be part of the same 

shoot.

As shown in cross section C C', plate 4, the hornblende gneiss 

country rock of the mine is underlain by Upper Crel-aceous 

shale, over which it has been carried by the Williams Range 

thrust fault. In the Ida Belle mine, described on pages 82-83, 

the best ore occurred where the vein cut the thrust-fault breccia 

at the contact of the shale and the gneiss. A similar relation 

might be found where the Rainbow lode cuts the underlying 

shale, but the depth to the contact may make it impracticable 

to mine such ore economically. If the thrust fault maintained 

its normal dip of about 30° from its outcrop on the east slope 

of Soda Creek, it would be about 4,500 feet below the lower 

level of the Rainbow mine. There is a strong fault in the valley 

of Jones Gulch, half a mile west of the Ida Belle mine, striking 

N. 10°-25° W., having a displacement known to be more than 

2,500 feet, and the east side of the fault has risen relative to the 

west side. Keystone Gulch is parallel to Jones Gulch, and the 

' Rainbow mine is on the east slope of the valley. It is a structural 

valley and is thought to follow a fault similar to the one that 

'produced Jones Gulch, but there is no way of determining the 

displacement on this fault except by geophysical methods or by 

diamond drilling. Resistivity measurements, made by J. H. 

Wilson during the writer's study of the geology of the proposed 

Blue River water-diversion tunnel, verified the presence of a 

strong fault zone along the valley but indicated that the 

Cretaceous shales were probably at a depth of more than 1,000 

feet below the valley bottom, half a mile south of the Rainbow 

mine. The depth to the shale makes it unprofitable to explore
THE 99

for a body of ore at the place where the Rainbow lode intersects 

the thrust fault.

RED JACKET

The Heel Jacket claim is on the northeast slope of Teller 

Mountain, about 1% miles southeast of Montezuma. The deposit was discovered about 1885 and yielded 10 tons of ore the 

next year. No other recorded production has been found for 

the mine, but according to John Sundragger, who has owned 

and worked the nearby Mohawk mine for 45 years, about three 

carloads of ore were shipped in 1894 and 1895. The ore was 

chiefly galena and carried a little silver.

ROBERTA (MARLIN)

The Roberta tunnel is on the west side of St. Johns Creek, 

about half a mile west of Montezuma. The tunnel runs 

N. 80° W. into the Swandyke gneiss of Bear Mountain and was 

about GOO feet long in 1927. A 6-inch vein of galena, quartz, 

and oxidized pyrite was found about 60 feet from the portal. 

It strikes northeast and dips 35° NW. At 300 feet from the 

portal a normal fault is exposed that strikes N. 55° W. and dips 

75° SW. The zone of gougy crushed rock is about 5 inches 

wide. A vein of ankeritc about 4 inches wide was found 500 feet 

from the portal; it strikes northeast and dips 65° SE. The 

property has not shipped any ore, so far as known.

ROCHESTER QUEEN (ARRASTRE QUEEN) .

The Rochester Queen or Arrastre Queen, as it was later known, 

is on the North Fork of the Swan River 3 miles from its mouth 

and about 3% miles southwest of Montezuma. It was discovered by Daniel Patrick about 1880, and in 1883 it was developed by a 75-foot shaft, 325 feet of drifts, a tunnel 100 feet 

long, and a 75-foot winze. The town of Rexford sprang up a 

few hundred yards below the mine chiefly because of the extensive work carried on at thC'Rochester Queen. A mill was built 

and connected with the portal of the mine by a wooden tram 

.line, and ore was milled for many years. According to Burchard the mine produced $5,000 worth of ore a month for 3 

months in 1881, and shipments were sent to the Argo smelter 

in 1881 and 1882, but no work was done in 1883. The ore contained iron, copper, galena, and some honeycombed gold-bearing 

quartz. According to the Colorado Mining Directory for 1883, 

the Rochester Queen had produced 500 tons of gold-silver ore 

prior to that year. The veins were said to be fissures from 6 to 

10 inches wide containing decomposed iron-stained porphyry 

and quartz and had a fair tenor in both silver and gold, assaying 

when sorted about $50 a ton in these two metals. The mine 

was inaccessible in 1929, and the town of Rexford had long been 

abandoned. According to C. M. Snyder, of Hall Valley, the 

tunnel at Rexford was visited by him in 1918 and was in very 

poor repair at that time. The workings did not follow any welldefined vein but explored several narrow fissures in the strongly 

fractured gneiss and porphyry. The soft decomposed rock in 

the fissures carried only half an ounce of gold to the ton, according to Mr. Snyder, but samples of the hard wall rock next to 

these fissures assayed from $20 to $40 a ton, chiefly in gold. 

The gold content was erratic, however, and could be discovered 

only by assaying. As shown on plate 3, the country rock of1 

the mine comprises biotite diorite porphyry and hornblende 

gneiss that have broken away from the cliffs above and slid to 

their present place since the last retreat of the glacier which 

formerly occupied the valley. It is probable that the channel 

was oversteepened by the action of the ice and that large landslides resulted when the glacier melted. The gold ore found 

near Rexford was probably formed by the enrichment of lowgrade pyritic ore similar to that found in the Carrie mine nearby. 

Its occurrence in the valley bottom is accidental, as it is a rock 

mass which was at a much higher level during the progress of 

gold and silver enrichment.

ROTHSCHILD (MINEROU)

The Rothschild tunnel has been driven 4,600 feet northwest 

under Cooper Mountain and has its portal 200 feet above Peru 

Creek, about half a mile northwest of the mouth of Cinnamon 

Gulch. It is 3 miles east-northeast of Montezuma arid is easily 

accessible by automobile over a good wagon road. The tunnel 

was driven with the object of exploring the veins of Cooper 

Mountain at depth and providing a transportation tunnel for 

them. Since the work of driving the tunnel stopped little has 

been done except for a small amount of stoping on some of the 

veins opened during the main work on the tunnel. The known 

production of the property has been small, although some ore 

was produced from the shallow upper adits and would increase 

the figures given below if the amount were known.

Probably the most productive veins on Cooper Mountain are 

the Tariff and the Rothschild. They were discovered in 1873 

by W. T. Lewis, and after a moderate amount of development 

work and the shipment of some rich silver ore, the claims were 

sold in 1878. Exploration of the veins was continued by the 

new owners during 1879 and 1880. In 1883 the property was 

still idle and according to the Colorado Mining Directory was 

owned by W. T. Lewis. It is credited with a total production 

of $20,000 in 1883, and the ore is reported to have assayed from 

20 to 35 percent of lead and 100 to 500 ounces of silver to the 

ton when sorted. The ore was from 3 to 36 inches wide and 

consisted of galena, gray and yellow copper, and some ruby silver, in a quartz gangue. The production came from the Tariff 

East and Rothschild claims.

The property was idle during the eighties and most of the 

nineties but became active again about 1899. In May 1900 the 

main crosscut tunnel was started, and by 1906 it had been 

driven its present length. It has been operated intermittently 

since 1907,. and some good silver ore has been shipped by various 

lessees. As shown in figure 23, the tunnel is entirely in the 

Montezuma quartz monzonite. The veins are thin, but 

lenticular swellings in them occur in places and carry workable 

bodies of ore, consisting of galena, sphalerite, pyrite, and some 

ruby silver in a quartz gangue. The known production of the 

property is shown below.

Production from Rothschild tunnel

1901..-- . 

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

1907 

1922...................

1923. ...... ...... ......

Ore 

(short 

tons)

2, 500-5, 000 

10 

300 

20 

78 

24

Gold 

(fine 

ounces)

12.50

1.80 

.50

Silver 

(fine 

ounces)

1,875 

7,500 

4,000 

3,544 

1,190

Lead, 

wet 

assay 

(pounds)

v 58,824 

4,240 

9,565 

4,630

Copper, 

wet 

assay 

(pounds)

7,143

13

Zinc 

(pounds)

47, 000

No record available for 1879-80, 1883-86, 1889-1900; no production in 1881-82, 

1887-88, 1902-5, 1908-21, 1924-28.

ROYAL TIGER

The Royal Tiger Mines Co. controls a large amount of 

property in the southwestern part of the quadrangle and in the 

Breckenridge district, south and southwest of the quadrangle. 

Up to 1930 little ore had been produced, although several 

properties were explored for many years and considerable sums 

of money had been spent on the mill at Tiger.. John Traylor, 

the general manager, stated that he expected to solve the 

difficulties of successfully milling the low-grade ores of the stockworks west of Tiger and hoped ultimately to raise enough money 

to build a 5,000-ton mill for exploitation on a large scale. As 

the writer was denied the opportunity of studying any of the 

mines controlled by the Royal Tiger Mines Co., he was unable 

to learn what the developments since Ransome's visit in 1909
100 MONTEZUMA QUADRANGLE, COLORADO

had disclosed. Many of the properties of the company, 

particularly the Cashier and I. X. L., were studied by Ransome, 

and the reader is referred to his report for details concerning their 

geology and history. 30 The geologic setting of the deposits and 

the general character of their ore has been summarized on pages 

59-60.

STS. JOHN

The Sts. John mine is the oldest producing mine in the 

Montezuma district and is one of the oldest silver mines in 

Colorado. It is on the west slope of Glacier Mountain about a 

mile southwest of Montezuma. The mill and the chief mine 

buildings are at an altitude of about 10,800 feet and are at the 

end of a wagon road that leads from Montezuma to the mine. 

The road is passable for automobiles but has some very steep 

grades a short distance southwest of the town.

The Comstock lode of the Sts. John mine was discovered ic 

1865, and work was started on the vein at once. The Bostor 

Silver Mining Association was organized in 1866 and opened the 

vein by two adits close to the outcrop of the vein. According tc

in the mill, and, according to a mining paper, in July 1875 the 

ore treated by the company from the upper levels had averaged 

40 ounces of silver to the ton.

In 1875 the mine was worked by the Boston Silver Co. but 

with the same officers as before. The mill was thrown open 

for custom ore and consumed nearly all the ore produced in the 

Montezuma district that year. The ore receipts of the Boston 

Silver Co. for 1875-78 are extant and indicate that less than 50 

tons of ore was purchased in a year. By the later part of 1875 

the lowest adit had reached a length of 1,075 feet and had cut 

nine veins, but the Comstock lode was not recognized. Good 

ore was found on vein 5, and a drift was driven north to prepare 

for stoping. At the end of the year the company had about 800 

tons of ore on hand, three-quarters of which was dressing ore and 

was to be concentrated in its mill and smelted into pig lead. 

The mine was active during 1876, 1877, and 1878 and bought 

ore from the surrounding mines and treated its own ore, most of 

which came from vein 5 north of the main adit. The mine 

was taken over by the Boston Mining Co. in 1878 and operated 

intermittently by it for many years. There is no record of the

Knife seam of 

, FeS2 and quartz Hand seam fegouge 

 4o\ V Discontinuous seam

C-----I,. ^ + ^ , . v \j s^v ^ , ^-^ao° " v ^v 1- ' v

l-i Barren " is -SV- 

\ 3"gouge 1 1 "to 3"of gouge Fe S2 streak on\V 70 

withFeS? ' both walls XX"7 

3J£-4 apart v

PbS in quartz, 

no gouge, very

v ^T v ^2\ x'XJK1^6"

r- 7 ' P- / ,, Nis^S5

Zn;FeS2 ,and quartz, 

l"widey no.gouge

Montezuma quartz rnonzonite

2^tol"xnSstreak very hara^C5 * ' ' 0^w* 

-^wideXankerite, quartz 1 quartz ahd 

specks of 

CuFe Sa., little 

iron, JA gouge, 

no Znb or PbS; 

vertical slicken sides

Continued 

from above-

'.Barren v ^ ^ .Barren ,Montezuma guartz rnonzonite

FeS2 searr>; 

little quartz

Stoped 

above 40'

PbS and anker-1,1 \ 

ite, no gouge

70°

0

i i i

500 Feet

FIGURE 23. Rothschild tunnel, Cooper Mountain, 1929.

Anker ite, 

quartz 

"

King, 31 who visited the mine in 1869, the upper adit was from 

60 to 100 feet below the surface, and the second adit was 70 feet 

lower. Some Scotch hearths had been built, and base bullion 

carrying from 100 to 170 ounces of silver to the ton and valued at 

$3,500 had been produced. At this time complex ore carrying 

zinc and copper assaying from $100 to $200 a ton was not 

worked. In 1870, according to Raymond, the lower adit was 

150 feet long and connected with a drift on the vein 425 feet long. 

A winze 75 feet deep connected this level with a sublevel about 

200 feet long, and a raise 70 feet high joined it to the upper adit 

level. About 3,000 tons of ore worth from $40 to $400 a ton was 

piled at the mouth of the tunnel ready for the reduction works. 

This ore was not satisfactorily smelted by the furnaces, and the 

mine had much the same difficulty with barite as the Hall 

Valley smelter had a few years later. Mining was almost 

suspended in 1871, and a 50-ton concentration mill was started. 

It was not finished until late in 1872, and only a few tons of ore 

was treated. The long adit cutting the vein about 700 feet 

below the outcrop was started in this year and was driven 

steadily ahead until about 1878. During the next 2 years no 

ore was stoped, but the ore on the dump was probably dressed

30 Ransome, F. L., The geology and ore deposits of the Breckenridge district, 

Colo.: U.S. Geol. Survey Prof. Paper 75, pp. 148-150,1911. 

« King, Clarence, U.S. Geol. Expl. 40th Par. Rept, vol. 3, pp. 617-624,1870.

production for the years from 1871 to 1880, but the mine had 

been inactive for several years in 1882, when the Montezuma 

Mill Run commenced publication. Some ore, probably less 

than 50 tons, was shipped to the Sissapo sampler at Montezuma 

during 1882, but 1,000 tons was said to be stored at the mine. 

The mine was idle in 1883. In 1884 operations were resumed, 

and ore was shipped during the later part of that year as well as 

in 1885, 1886, and 1887. Only a small force worked at the 

mine in 1887, and operations were suspended during the winter 

of 1887-88. Work was resumed with a small force in 1888, but 

there was no production in that year or the next. In 1889 

shipments were again resumed, and the mine was operated 

steadily for several years. In 1890 the mine was worked by the 

Boston Mining Co. under the management of T. E. Schwartz, 

and a moderate and steady production was maintained until the 

panic of 1893, when the company suspended operations. Ore 

was mined intermittently until 1899 by lessees, however, and 

according to a report by Mr. Schwartz about 3,000 tons of ore 

was shipped in 1890-99 and commonly assayed from 30 to 35 

percent of lead and 40 to 45 ounces of silver to the ton. No 

mining was done between 1900 and 1913, though several small 

shipments of ore sorted from the dump were made by various 

lessees. In 1910 the mine was bought by the St. John Mines 

Co., Ltd., which operated it from 1913 to 1916. It was bought
THE MINES 101

by the Montezuma Silver-Lead Mines Co., Ltd., in 1917 and 

operated by that company in 1917-18. A small production was 

maintained in 1919, 1.920, and 1921 by lessees of this company, 

but in 1923 the property reverted to the St. John Mines Co., 

Ltd., which still owned it in 1929.

Most of the ore above the main tunnel level had been removed before the writer's visit to the mine, but some early 

accounts of the property describe the ore found in the upper 

levels. The country rock is hornblende gneiss and pegmatite 

of the Swandyke gneiss. The gneiss strikes from northeast to 

north and dips 50°-90° E.; the prevailing strike is slightly east 

of north, and the prevailing dip is about 75° E. Most of the 

ore has been obtained from the Comstock vein, which is more 

commonly known as vein 5. It strikes northeast, dips steeply 

northwest, and crosses vein 7, which strikes north of east and 

dips about 55° N. Vein 7 contains much more barite than the 

Comstock vein and has been exploited to only a moderate degree because of failure to mill the ore satisfactorily.

According to Clarence King, the ore exposed in the Comstock 

vein in 1869, less than 160 feet below the surface, was argentiferous galena, two or three kinds of zinc blende, a little 

argentiferous gray copper, and ruby silver, in a gangue of barite, 

quartz and siderite. The vein filling was from 1 to 8 feet wide 

and averaged about 3 feet; it was separated from the walls by a 

thin seam of gouge. The pay streak was from 6 to 12 inches 

wide and occurred on either the hanging-wall or footwall side 

of the vein. "The continuity of the pay seam * * * is 

one of the notable features of this lode." In his report for 1870 

Raymond says:

"The vein of the Comstock stands nearly perpendicular and 

varies in size. At one point it spread out to 8 feet, and at 

another it contracted to a few feet, but it preserved a general 

width of 4 or 5 feet. At the point of greatest width there was a 

stratum of compact ore 2 feet thick upon the hanging wall; the 

same upon the footwall; while ore was disseminated through the 

intervening mass of feldspathic gangue. In the different works 

disclosing the vein the solid ore ranged from 4 inches to 2 feet 

thick, and I should judge it fairly averaged 18 inches. The 

galena was massive and formed perhaps one-third of the ore. 

Zinc blende and iron and copper pyrites occur also abundantly, 

and in the deepest works silver glance and brittle silver are not 

uncommon. Handsome crystals of heavy spar are of frequent 

occurrence."

In 1875 the main crosscut tunnel 700 feet below the outcrop 

of the vein had been driven 1,100 feet and had cut nine veins. 

Nos. 1, 2, 3, 4, 6, and 9 contained iron pyrites in a quartz 

gangue; nos. 5 and 8 had zinc blende and galena in a quartz 

gangue; no. 7 had barite, zinc blende, galena, and a little pyrite. 

llaymond says:

"While at the intersection of the tunnel with no. 5 only 

galena, blende, and a little iron pyrites were found, containing, 

when solid, 60 to 70 ounces of silver per ton, the vein carried 

beyond a point 75 feet from the entrance northward, besides 

the minerals named, rich silver ores such as ruby silver, stephanite, polybasite, and tetrahedrite in considerable quantity, so 

that the average value of the ore was more than doubled. The 

south drift on no. 5 * * * lias since been driven to the 

intersection with no. 7, 140 feet from the tunnel. In this drift 

only one pocket of ruby silver, stephanite, and fahlore [gray 

copper] was found. The drift on no. 7 north of the tunnel was 

in soft ground * * * carrying no ore. The south drift 

was in about 200 feet and showed ore (zinc blende and galena in 

barite) for almost the whole distance, the vein being on the 

average from 4 to 5 feet wide, and the ore streak varying from 

1 to 3 feet. * * * About 130 feet from the entrance the 

drift encountered a horizontal fault of about 8 feet (the vein 

being thrown to the east), and 12 feet farther a second fault 

of 6 feet in the same direction. Between the two the vein 

carried very good galena. About 6 feet beyond the second fault

the galena became very solid and contained much native silver, 

which continued for a distance of 30 feet. The ore in no. 7 at 

the intersection with the tunnel contained in solid galena from 

48 to 50 ounces of silver; at the farther end of the drift, where 

the native silver was visible, it contained from 100 to 500 

ounces, and in ordinary galena from 70 to 80 ounces. * * * 

[From the north no. 5] extraordinarily rich silver ores are now 

being extracted, carrying, however, very little galena. * * * 

On no. 7 one raise now 120 feet high has been made. * * * 

There are three stopes opened on no. 7, two of which produce 

ore."

The Comstock vein has been followed over 800 feet northeast of the main crosscut tunnel and 1,100 feet southwest of it 

and has been stoped for much of its length. The northern ore 

shoot was almost continuous from the main tunnel to a place 

about 750 feet northeast, where the vein is cut by a strong 

northward-trending fault. The drift is caved a short distance 

beyond and could not be examined in 1927, but it is reported 

that no ore was found farther north. The rich silver ore was

NW. SE.

FIGURE 24. Looking north at vein 5, 750 feet north of main crosscut, Sts. John 

mine. Vein in wide premineral fault but aSected by later movement along the 

fissure, o, Pyrite; 6, galena; c, sphalerite; d, ankerite; e, strongly sheeted altered 

granite; /, slightly fractured gneiss.

mined out in the seventies, but some of the leaner ore near the 

fault was seen, and its mode of occurrence is illustrated in figures 

6 and 24. The vein becomes poorer and poorer as it turns into 

the fault zone and is nearly barren for the last 50 feet in which 

it is exposed. The decrease in mineralization coincides with 

an increase in the amount of gouge. Quartz, pyrite, and barite 

predominate as the fault zone is approached, and galena and 

sphalerite gradually increase as the vein is followed away from 

it. At 50 feet from the fault the vein contains about 10 inches 

of gangue and 8 inches of ore, and 50 feet farther away the vein 

carries 10 inches of gangue and 18 inches of ore. Here the 

gangue is chiefly barite but contains moderate amounts of 

rhodochrosite and a small amount of quartz. The ore consists 

of galena and sphalerite in nearly equal amounts. No gray 

copper was seen, and the silver-bearing minerals were probably 

found in the southwestern part of this ore shoot.

The Comstock vein splits a short distance southwest of the 

main tunnel, where two overlapping parallel northeasterly 

fissures about 80 feet apart are connected by a northerly 

bedding-plane fracture. The vein, which had been following 

the western fissure, continues southwest on the eastern fissure. 

It is barren on the lower level near the junction of the northerly
102 MONTEZUMA QUADRANGLE, COLORADO

and northeasterly fissures, and no ore was observed for 120 feet 

south of the junction. Southwest of this place the vein has 

been stoped almost continuously for 850 feet. At some places, 

however, pillars of lean ore have been left, and in them the vein 

filling is about 6 inches wide and is chiefly quartz with a moderate amount of barite and galena. In the productive part the 

vein dips 55°-60° NW., but steeper dips were observed in the 

leaner pillars that came down to the level of the drift. In a 

stope 150 feet northeast of the breast the vein has a dip of 65° 

in the first 60 feet but flattens to 51° for the next 50 feet. The 

ore is from 4 to 6 inches wide in the first 60 feet and from 6 to 

12 inches wide in the next 50 feet. The ore in this stope is 

chiefly galena, but a thin seam of rhodochrosite, quartz, and 

barite is commonly present; moderate amounts of sphalerite 

are associated with the galena, and locally small amounts of 

argentiferous gray copper occur. Where the vein flattens in 

the stope a strong gougy fissure goes into the hanging wall, 

continuing the steep dip of the vein up to this point. A small 

normal fault dipping steeply eastward displaces the vein about 

24 inches 105 feet above the drift; as shown in the cross section .in plate 35, it is undoubtedly the same fault that was 

followed south from its intersection with the vein on the lower 

level, 270 feet northeast of the breast. The presence of gouge 

and steel galena in the Comstock vein indicates postmineral 

movement along the vein, and the bedding-plane fault just 

described probably carried some of the movement, which was 

in places taken up by the vein 'fissure.

The Comstock vein has a general dip of 55°-60° for almost 

its entire length on the main tunnel level, and this dip if maintained would cause it to crop out where the Tiger vein is exposed 

on the surface. About 70 feet above the second level, 150 

feet above the main tunnel level, the vein steepens and becomes 

nearly vertical, dipping 75°-80° NW. This dip is maintained 

for at least 50 feet more, but the workings of the mine were 

inaccessible above this place in 1929. However, according to a 

report quoted earlier, the vein is nearly vertical in the upper 

levels, and it is probable that the average dip from the outcrop 

of the Comstock vein to a line about 150 feet above the main 

tunnel level is between 75° and 80°. The Tiger vein at its outcrop dips 60° NW., and it should join the Comstock vein near 

the main tunnel level or be cut by the main crosscut a short 

distance east of the Comstock vein if its dip steepened. The 

Tiger vein has not been recognized in the Sts. John workings by 

anyone who has studied the mine. Although the change in 

dip of the Comstock vein 150 feet above the main tunnel level 

suggests that the Tiger vein may come in from the footwall side 

and join the Comstock vein at this place, it is unlikely that such 

a junction would be unrecognized along 1,300 feet of stopes. 

However, the dip and strike of the two veins are almost parallel, 

the character of the ore and gangue is very similar, the Tiger 

at its outcrop is as wide as the Comstock, it can be traced on the 

surface as great a distance as the Comstock, and probably it 

persists to as great a depth as the Comstock. The strong 

northerly fault that terminates the Comstock on the main 

tunnel level dips 75° E. in the caved part of the drift, according 

to miners who worked in that part of the mine. It is strong 

and readily recognized where it is cut by the main crosscut 

tunnel, 1,000 feet to the south, and there it dips 65° E. Sshaped fractures in the fault indicate that its hanging wall moved 

downward. Nearly all the other northerly faults in the mine 

dip east, and on all those in which the direction of movement 

was ascertained the displacement is normal; it is very probable, 

therefore, that this fault, which is the strongest of the northerly 

faults observed in the mine, is also a normal fault. As it 

definitely limits the Comstock vein, it probably terminates the 

Tiger vein also, and the writer believes that the Tiger vein is 

the downthrown continuation of the Comstock vein. The 

intersection of the vein with the fault would pitch about 50° 

N., and the dip slip would be about 350 feet. It is noteworthy

that the stope map of the Comstock vein indicates that the 

northwest termination of the ore pitched less than 50° N. If 

the Tiger vein is broken by this fault it should end against it 

about 750 feet above the main tunnel level at a point vertically 

above the crosscut tunnel, and the intersection of the vein and 

the fault should be found on the tunnel level about 700 feet 

north of the main crosscut.

About 170 feet south of the main tunnel on the lower level 

the Comstock vein crosses vein no. 7. The Comstock fissure is 

barren at this place but is clearly later than vein no. 7. The 

intersection of the two veins is not exposed on the next level, 

but on level 3, about 175 feet above the lower level, the junction is easily studied. Here the Comstock vein consists of 

about 3 inches of barite, quartz, and galena and cuts across 

vein no. 7 without a break, although there is a small vertical 

fault almost at the junction which displaces the veins about 5 

inches. Vein no. 7 is from 12 to 36 inches wide for most of its 

length and consists chiefly of barite containing moderate 

amounts of quartz, sphalerite, and galena. It strikes a little 

north of east and dips 48°-60° N., averaging about 55°. The 

drift following vein no. 7 on the main tunnel level east of the 

Comstock vein has long been caved, and no map of it was available, but according to a report quoted earlier some very good 

lead-silver ore was found a short distance east of the junction. 

Much of the ore has been stoped east of the junction above the 

second level, but little work has been done above the third level. 

At the top of the stopes, west of the junction of the two veins, 

about 70 feet above the second level, the vein is about 12 inches 

wide and contains comparatively little barite. It is largely 

rhodochrosite, with moderate amounts of galena, sphalerite, 

and quartz. The vein is barren and tight at the west end of the 

drift on the main tunnel level and is barren a short distance 

east of the place where it is cut by the main crosscut tunnel. 

The length of the ore shoot, including the short barren interval 

at the junction of the veins on this level, is about 650 feet. 

The upper limit of the ore shoot is not exposed on the upper 

levels, but the vein is much poorer at the west end of the drift on 

the second level than it is directly below, in the drift on the main 

tunnel level. The vein has not been exploited close to the surface, and nothing is known of the character of the ore above the 

third level.

The drag in the gneiss next to the Comstock vein, shown on 

the first level about 70 feet south of the junction of the two 

veins, indicates that the vein follows a premineral reverse fault. 

The direction of movement on vein no. 5 is unknown. The 

widening of the ore where the Comstock vein flattens is in 

harmony with the supposition that the vein occupies a reverse 

fault. Some of the ore on the lower level in the Comstock vein 

is reported to have been 4 feet wide, and the width of some stopes 

suggests that the report is correct. Above the second level, 

however, all the accessible stopes indicate that the ore was less 

than 2 feet wide in most places, but the report of Clarence King 

indicates that it was much wider in some places near the surface. 

The stope maps (see fig. 25) indicate that the vein was poorer 

above the third level than below this level, and it is possible 

that the ore body found near the surface was localized by the 

northerly fault that terminates the vein.

An interesting feature of the mine is the presence of richer 

silver ore on the lowest level than was found on the upper levels. 

According to the available records, the ore less than 150 feet 

from the surface was chiefly galena with moderate amounts of 

sphalerite, a little tetrahedrite, and rarely some polybasite. 

The ore coming from the mine, when the workings had been 

deepened 75 feet more, is reported as chiefly galena, but sphalerite, pyrite, and chalcopyrite were also abundant, and argentite and brtttle silver were not uncommon. There is no record 

of the kind of ore found between the upper levels and the rich 

silver ore found at the main tunnel level, but here proustite, 

polybasite, stephanite, and argentiferous tetrahedrite were
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 178 PLATE 35

Hornblende gneiss

EXPLANATION

Barren fissure, fault, or vein less than 

1 inch wide

Barren fissure, fault, or vein from 1 to 

12 inches wide

Barren fault or vein more than 12 

inches wide

Mineralized vein; width as noted

Mineralized vein more than 12 inches 

wide

6 gouge 

I2"between walls

Pyritic vein from 1 to 12 inches wide

Sphalerite vein from 1 to 12 inches 

wide

Galena vein from 1 to 12 inches wide 

Galena vein more than 12 inches wide

Galena-sphalerite-barite vein more

than 12 inches wide 

Strike and dip 

Strike and vertical dip 

Strike of schistosity 

Downthrown side of normal fault 

PbS, galena

) I // , ,

( Broken / ' I \ '

TBT--- . 

ZnS, sphalerite 

Rh, rhodochrosite 

Ba, barite

qtz, quartz 

Timbered drift

Vein e 10'Vein matter m breast I8- 20, hard, some Zn, 

much ankente , ,, e\o

PLAN OF LOWER LEVEL OF STS. JOHN MINE, GLACIER MOUNTAIN
U. S. GEOLOGICAL SURVEY

NO. 3 LEVEL

PROFESSI

5 ft. vein 

(breccia fillirn

l'6"qtz. H 

\ and FeSz://, , . Vein filling .////J>

.75 PbS \~~^lffl$ 

.1 FeSz ^ ^fff/i^ 

.ICuFesJ , 7lW7^

 °5 ZnS J 6 S^f

WINZE T^j/Y-X *9

(.75 PbS 

\.10 CuFeSz

'8 ft. vein (sUiciffed brecciaJ

2-5 ft.vein 

Ca\/ec/

Caved

MO. S L£V£L

(.05 CuFeS2 I .10 PbS 

 S.IO FeS2 

.75 ZnS

3OO

I I

o

I 1 1

3OO 

EXPLANATION

- « Barren fissure, fault, or vein from 1 to 

12 inches wide

-* * Barren fault or vein more than 12 

inches wide

- Mineralized vein from 1 to 12 inches 

wide

 x x Mineralized vein more than 12 inches 

wide

 .r'.y.'V.Y.-.: Pyritized and silicified wall rock 

1 7a Strike and dip

PbS, gale

ZnS, spha

CuFeSo, c

pyri

PLANS OF LEVELS 3 AND 5 OF THE SANTIAGO MINE, McCLELLAN M
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 178 PLATE 37

N

Injection gneiss

8"quartz,ankerite,and 

pyrite in the back

8"quartz,ankerite, 

and pyrite '

 '

24"sheeted zone, 

3'gouge

/ // T/ 2 "quartz / // and pyr

100 Feet

2 grooves on 

/ / walls

/ ' / / 

Fissured zone 

3"to I2"wide

. ,

/ / /

Barren sheeted 

zone48"wide LOWER ADIT

1OO IOO Feet

EXPLANATION

Barren fissure, fault, or vein less than 

1 inch wide

Barren fissure, fault, or vein from 1 to 

12 inches wide

-x x Barren fault or vein more than 12 

inches wide

 Pyrite vein less than 1 inch wide

- Pyrite vein from I to 12 inches wide 

Pyrite vein more than 12 inches wide

Fissure zone more than 12 inches 

wide carrying from 1 to 12 inches 

of pyrite

Galena vein from 1 to 12 inches wide 

Strike and dip 

////// Strike of schistosity

Downthrown side of normal fault 

Relative movement of walls

(horizontal component) 

PbS, galena 

ZnS, sphalerite 

Mn02, manganese oxide 

qtz, quartz 

Timbered drift 

Slick, slickensides

PLANS OF UPPER AND LOWER ADITS, SILVER KING MINE,

GLACIER MOUNTAIN
NORTH

MAIN TUNNEL /sf / LEVEL

FIGUEE 25. Stope map of vein 5, Sts. John mine.
104 MONTEZUMA QUADRANGLE, COLORADO

abundant in ore that carried only a small amount of galena. 

The ore south of this shoot was chiefly galena with little sphalerite and a small amount of tetrahedrite. In vein no. 7 northeast of the junction of the main tunnel level, native silver was 

found in ore that was chiefly galena. This rich silver ore did 

not continue above the next level, however, and probably 

changed into a mixed sphalerite-galena ore in a quartz-barite 

gangue. The ores on the main tunnel level show no oxidation 

or evidence of enrichment, and few veins in this region are 

appreciably oxidized more than 50 feet below the surface. It is 

very unlikely that the silver ore shoots in the Sts. John mine are: 

related in any way to the action of surface waters.

The available production figures of the Sts. John mine are 

shown below.

Production of Sts. John mine

1870, August to December 

1882 

iasd

1885 

1886 

1887 

1890 

1891'. -

1892.. 

1893^99. iQHft

1901... - 

1904 

1916 (Tiger extension) ....

1918 (old Comstock

1Q1Q

1920. 

1922 (old Comstock

1924... . 

1Q9Q

1910 

1911.. ----------

1914 

1916 (Tiger extension and others) 

1917. -------

1918 (Old Comstock dump).... 

1926.-. 

1927. 

Ore 

(short 

tons)

50 

25 

200 

35 

94 

44 

805 

628 

1,523 

80 

1 

5 

181 

23 

3 

17

27 

67 

29

21 

93 

94 

13

Ore to 

concentrating 

mills 

(short 

tons)

330 

2,730 

7,400 

50

530 

1,200

1,120 

3,000 

4,000

Gold 

(fine 

ounces)

0.99

 .10 

2.11

 .20

.20 

.40

.30

Concentrates 

produced 

(short 

tons)

33 

273 

74 

12

53 

137

112 

200 

340

Gold 

(fine 

ounces)

1.13 

.36

1.09 

1.42

; .55 1 : i. 20

'. .30

Silver 

(fine 

ounces)

3,354 

1,650 

32,274 

24, 773

2,936 

138 

125 

6,842 

1/088 

683 

720

1,045 

2,952 

857

407 

1,615 

2,174 

411

Silver 

(fine 

ounces)

482 

8,086 

2,754

1, 586 

3,259

3,405 

4,987 

2,239

Lead, 

wet 

assay 

(pounds)

-29, 720

23, 174 

39, 785 

1,293,307 

607, 518

79, 200

4,000 

110, 234 

13, 138 

629 

12,528

4,814 

34, 914 

23, 852

13,273 

97, 462 

101, 874 

11, 694

Lead, 

wet 

assay 

(pounds)

21, 455 

241, 621 

79, 176

32, 279 

53, 176

83,092 

76, 424 

58, 015

Copper, 

wet 

assay 

(pounds)

327 

78 

47 

70

251 

175 

22

22

Copper, 

wet 

assay 

(pounds)

174 

493

108 

114 

23

Zinc 

(pounds)

9,600

1

Zinc 

(pounds)

17 ,j 000

T

7, 200-

i

I

122, 378 

226, 632

« Base bullion. . ( 

No record available for 1871-75, 1877-80; no production in 1876, 1881,1883, 1888-89, 

1902-3, 1905-9, 1912, 1921, 1925. ;

SANTIAGO-COMMOJNWEALTH-CENTENNIAL

The Santiago mine is on the southeast slope of McClellan 

Mountain, at an altitude of about 12,OQP feet. It is about half 

a mile northwest of the Waldprf tunnel and 6% miles northeast 

of Montezuma. The vein is opened by five tunnels and an 

underground shaft 300 feet deep on level 5. At the time of the 

writer's visit tunnels 3 and 5; were partly accessible, and they 

are shown on plate 36. The mine can be reached by automobile 

from Georgetown, although the road was in poor condition in 

1927 and had many steep grades. The lower tunnel is connected by an aerial tram with the Waldorf mill, 450 feet below 

and half a mile southeast.

The Santiago mine is on the southern part of a vein that has 

been productive for nearly a mile in length and 800 feet in 

depth. The Santiago ore shoot is about 1,100 feet long and

has been explored to a depth of about 700 feet below its top. 

As shown in figure 26, the top of the ore shoot is well below the 

surface, and, though some ore along the north side cropped out 

in the steep-walled glacial cirque where the mine is situated, the 

ore is virtually in a "blind" shoot.

Little is known of the history of the mine, but unlike most of 

the veins nearby, the Santiago has yielded the bulk of its production since 1900, and the figures given below probably give a 

fair approximation of the entire output.

Production of Santiago mine

1901. .

1903-. .

1905 

1906 

1908 

1909 

1913 

1916.. 

1917.. 

1918 

1927 .

.Dry ore: 

1902. 

1904 

1917 

1919 

Copper ore: 

1910., --.

1911. -..

1914. 

1915.. 

1916...--.-.

1917. -.

1918... .

1919. -

1920 j.

1923.. -.

1924.. 

Lead -copper ore: 

1912 

1915 

1916 

1917 

1918 

Commonwealth: 

1888

1889 - - 

1890.... .

1907 .. 

1918-- -

Ore to 

concentrating 

mills 

(short 

tons)

1,050 

5

Ore

(short 

tons)

300 

40 

1,037 

715 

1,253 

1,200 

944 

60 

68 

67 

23

175 

494 

17 

2

1.-871 

2, 713 

731 

20 

825 

30 

54 

213 

', 85 

42 

17

1,577 

1,070 

113 

439 

21

ffl

(?)

Concentrates 

produced 

(short 

tons)

279 

2

Gold 

(fine 

ounces)

292.62 

20.00 

528.74 

202.30 

645. 18 

799. 00 

561. 24 

15.89 

81.07 

10.60 

11.28

90.00 

230. 87 

8.18 

.03

2, 288. 32 

1,961.15 

896. 93 

42.80 

950. 76 

9.35 

30.30 

206.63 

97.20 

30. 15 

16.00

802. 41 

1, 226. 65 

100. 80 

439. 02 

9.90

.73 

2.33 

44.00

Gold 

(fine 

ounces)

209.66 

1.77

Silver 

(fine 

ounces)

9,627 

1,200 

22, 086 

11, 785 

25, 419 

32, 000 

10, 833 

707 

1,084 

506 

383

7,189 

7,660 

155 

135

40, 801 

36, 452 

12, 504 

717 

23, 323 

221 

954 

4,209 

2,746 

837 

328

26, 507 

15, 266 

2,944 

9,529 

405

527 

1,873 

9,765

Silver 

(fine 

ounces)

5,668 

34

Lead, 

wet 

assay 

(pounds)

61, 924 

5,176 

202, 028 

120, 826 

162, 372 

356, 322 

223, 455 

24, 976 

30,585 

33, 124 

10, 675

717 

157

12, 395 

9,832 

18, 657,

66, 199 

1,037 

4,447 

13, 427 

8,266 

4,002 

1,633

578, 650 

53, 668 

27, 596 

52, 826 

5,102

15, 247 

51, 215 

241, 549

Lead, 

wet 

assay 

(pounds)

4,728 

2,917

Copper, 

wet 

assay 

(pounds)

16, 044

44, 361 

81, 067 

41, 988

4,405 

434 

896

2,831 

784

205, 821 

187, 920 

73, 185 

3,864

116,671 

2,143 

5,278 

39, 025 

19, 796 

5,668 

2,024

105, 153 

96, 157 

16, 233 

57, 801 

1,358

Copper, 

wet . 

assay 

(pounds)

15, 421

Zinc 

(pounds)

26, 644 

56, 020

1,893

2,136

Zinc 

(pounds)

No record available for 1891-1900; no production in 1928.

The vein is a fissured zone that strikes N. 15°-35° E. and 

dips 70°-85° W. It is from 3 to 8 feet wide on the third level 

and from 2 to 5 feet wide on the fifth level, where the writer 

saw it, but neither level was open to the breast. In the widest 

parts of the vein on the third level the filling is coarsely brecciated granite which has been strongly silicified and pyritized. 

This silicification and pyritization was earlier than the leadzinc-copper metallization and does not indicate the presence of 

pay ore; the lead-silver-gold tenor was so low in a place where 

the pyritic silicified breccia was 8 feet wide that no stoping was 

done. The ore on the third level and above it is chiefly galena 

containing moderate amounts of chalcopyrite; but pyrite is 

usually present in small quantities, and sphalerite is common, 

though it rarely makes up more than 5 percent of the ore. 

On the fifth level sphalerite is the most abundant sulphide in 

those parts of the vein that remain unstoped; galena and pyrite 

are present in nearly equal amounts but are much less abundant 

than the sphalerite; chalcopyrite is common but is less abundant 

than on the third level. Altho.ugh some of the gangue on the
THE MINES 105

third level is manganlferous ankerite, quartz greatly predominates over the carbonate, but on the fifth level the relative 

proportions of the two gangue minerals are reversed, and the 

ankerite is much more abundant than the quartz. In most 

places where the ankerite is wide the ore is thin. The sixth 

and seventh levels were not accessible at the time of the writer's 

visit, but according to a miner who had worked in the lowest 

level the mineralization was not as strong there as it was on 

the upper levels, and sphalerite and pyrite were the predominant 

sulphides, although galena and chalcopyrite were locally abundant. The gold content on the lower levels was reported to be

MC CLELLAN MTN.

the vein is also opened at about 11,650 feet by the Waldorf or 

Wilcox tunnel. The relation of the tunnels and the general 

geology are shown in figure 16. Where the Commonwealth 

vein is cut by the Waldorf tunnel it strikes N. 25° E., dips 

about 70° SE., and carries small amounts of lead, zinc, and iron 

sulphides. About 300 feet northeast of the crosscut tunnel the 

vein swings north and strikes N. 12° E. and dips steeply to the 

northwest. Here the ore is of much better grade and was 

stoped, although the extent of the stoping is not known. The 

ore in this part of the vein is chiefly galena carrying moderate 

amounts of sphalerite and some pyrite. Some of the ore left

&£* ^>110W$»*1§ w& $Z^$m Jk^ "i^'V'X'y' s/4vM%7$Mn 7^^ ^f '"^Sc'ST-STx ?~J*~*~".'^~/\~

Ore of shipping grade Low-grade ore 

(Probably stoped 

before 1930)

Stope

100 300 Feet WILCOX TUNNEL LEV£L

FIGURE 20. Stope map of Santiago mine, looking west. (From map by F. Ricci.)

directly related to the presence of light-colored sphalerite, or 

"rosin jack."

About a quarter of a mile north of the Santiago mine a few 

dilapidated buildings cluster about the caved entrance to the 

Commonwealth tunnel. This part of the Santiago-Commonwealth-Centennial vein was worked in the seventies and 

eighties, but little is known about the production or the developments prior to 1900. The Georgetown Courier for December 

6, 1888, reports a shipment of 4 to 5 tons of ore, which ran 68 

ounces of silver to the ton and 61 percent of lead, and the 

same paper mentions the mine again in 1889 and 1890. The 

altitude of the Commonwealth tunnel is about 12,000 feet, but

is from 3 to 5 inches wide and contains very little gangue. The 

vein becomes barren about 1,000 feet north of the crosscut tunnel, and when the writer visited it in 1926 the drift .was caved 

a short distance beyond. According to A. A. Atkins, who 

had charge of the Waldorf tunnel when the last work was done 

prior to 1926, the Commonwealth vein was followed about 800 

feet farther, but no ore shoots were found. This barren segr 

ment of the vein is on the Centennial claim, but little work has 

been done at the surface in this ground, and some ore may be 

present. The wall rock of the vein is Silver Plume granite, 

Idaho Springs schist, and granite gneiss, and, as shown on 

plate 3, the schist becomes increasingly abundant to the north.
106 MONTEZUMA QUADRANGLE, COLORADO

SARSEFIELD

The Sarsefield mine is on the west slope of Collier Mountain, 

about 1% miles east-southeast of Montezuma. It is opened 

by three adits at altitudes of 12,270, 12,390, and 12,445 feet, 

and the upper adit is connected to the surface by an air shaft. 

The mine was originally located in the seventies as the Waterman and was relocated about 1881 as the Sarsefield. It was 

owned and worked by Cunningham & Taylor from 1883 to 

1888, and several carloads of ore were shipped during those 

years. Only a small amount of ore is known to have come from 

the first adit, which was driven before 1883; the second adit 

was driven in 1885, and most of the production made in the 

eighties came after its completion. The mine was idle during 

most of the nineties, but in 1898 the lower adit was driven 

120 feet below the second adit. All the workings of the Sarsefield were inaccessible at the time of the writer's visit, and most 

of the information regarding the mine has been obtained from 

James Southerland, who had charge of driving the lower adit.

The ore obtained from the upper workings occurred in a single 

vertical ore shoot, which cropped out on the shoulder of the 

mountain. The richest part of this shoot was nearly pure 

galena ore 3 feet wide. The lower adit was driven east 200 feet 

to the vein, which was followed to the northeast for about 

400 feet. The vein dips 80° SE., and its course in the upper 

levels is N. 43° E., but in the lower adit the vein strikes N. 32° 

E. where it was first tapped by the crosscut. About 100 feet 

northeast of the crosscut the vein swings northeast and follows 

the same course that it maintained in the upper levels. The 

vein is about 6 feet wide, but the ore streak is commonly less 

than 15 inches thick. The best ore shoot found on this level 

occurred about 70 feet from the crosscut and continued 80 

feet along the drift. At the northeast edge of the shoot a 

winze was sunk 82 feet and is reported to have passed through 

the ore shoot at 50 feet. A short drift was driven northeast 

from the bottom of the winze, and the ore shoot was stoped to 

the surface. It maintained its pitch of about 40° toward the 

northeast throughout this distance. The ore was nearly free 

from gangue and was from 24 to 36 inches wide. It was chiefly 

galena and light-colored sphalerite but contained small amounts 

of pyrite, gray copper, barite, and quartz. Most of the ore 

shipped assayed about 45 percent of lead and 72 ounces of 

silver to the ton. The ore above the lower adit level contained 

about 14 percent of zinc, but the ore from the bottom of the 

winze carried a little more than 20 percent of zinc. The silver 

content is said to have been much higher close to the surface 

than at the adit level.

A vertical ore shoot was found about 100 feet northeast of 

the shoot just described. This second shoot was about 40 

feet long, and the ore in the drift was only 4 inches wide. A 

short distance above the drift, however, it widened to 12 inches, 

and ore of this width was stop'ed upward for about 50 feet, to a 

point where it pinched to a seam only an inch in width. The 

shoot was not followed farther, but from its position in the mine 

it seems probable that this ore is in the lower part of the chimney 

exploited in the upper level. The ore was of better grade than 

that in the first shoot and is said to have been almost pure 

galena.

The country rock of the mine is the Idaho Springs formation, 

which strikes about N. 30° E. and dips 80°-90° W. Several 

small masses of fine-grained sodic rhyolite porphyry crop out 

near the mine, and it is probable that some porphyry was cut 

by the mine workings. The southwest ore shoot occurred 

where the vein changed its course, and the vertical shoot was 

found where the vein was cutting across the schistosity of the 

enclosing quartz-biotite-sillimanite schist.

The production of the mine is given below. 

Production of Sarsefield mine

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

1885.... ._..-_._..__..._. ......

1886......-......... .......

1888 

1899 

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

1905 

1906 

1907 

Ore 

(short 

tons)

13 

35 

26 

(?) 

198 

75 

10 

35 

9

Gold 

(fine 

ounces)

5.36

.77

Silver 

(One 

ounces)

1,824 

16, 121 

4,008 

396 

1,362 

466

Lead, 

wet 

assay 

(pounds)

11, 435 

185, 856 

64, 602 

10,107 

28, 790 

 6, 333

Zinc 

(pounds)

65, 125 

17, 012 

3,334 

12,844 

4,018

No record^available for 1889-98; no production in 1887, 1901-4, 1908-29.

SIIL

The Sill vein is at the head of West Geneva Creek, on the 

east slope of Collier Mountain, 2 miles east of Montezuma, 

at an altitude of about 11,700 feet. It is at the end of a wagon 

road leading up West Geneva Creek from Grant, about 12 

miles to the southeast, but the last 3 miles of the road was in 

poor condition in 1928. The mine is said to have shipped 

about 10 tons of gold ore in the nineties and about the same 

amount of lead ore in 1909, but no record of the shipments 

has been found. The vein is from 12 to 24 inches wide and 

strikes N. 38° E., parallel to the schistosity of the quartzbiotite-sillimanite schist, which is the country rock of the 

region. The ore consists chiefly of well-crystallized pyrite 

and quartz, but both light and dark sphalerite are present in 

the ore left on the dump. The pyrite is earlier than the sphalerite, and the sphalerite is earlier than the coarse-grained quartz. 

The shipping ore is said to occur in pockets which contained 

appreciable amounts of gold.

SILVER CORD (RAINBOW)

The Silver Cord claim is 150 feet wide and 1,500 feet long 

and is an early patent on the Silver Wave vein northeast of 

the Silver Wave claim. The Rainbow claim, covering the 

same portion of the vein, was patented later and is 300 feet 

wide and 1,500 feet long. It lies on the east slope of the Continental Divide, on the west side of West Geneva Creek, and 

has been opened by three adits. The portals of these adits 

were locked at the time of the writer's visit in 1928, and he 

did not examine them. The upper adit is at an altitude of 

about 12,950 feet, the intermediate adit at 12,850 feet, and the 

lower adit at about 12,500 feet. According to the owner, 

James Southerland, an ore shoot was found in the upper adit 

100 feet from the portal and a second one 15 feet from the 

breast, which at that time was at the end line between the 

Silver Cord and Silver Wave claims. The first shoot was 

about 30 feet long and 12 inches wide and consisted chiefly ©f 

galena assaying about 20 ounces of silver to the ton. This 

shoot was also found on the second level and has about the 

same dimensions and character as on the first level; it is said 

to pinch at the bottom of the drift, and no effort was made to 

explore it below the level. The second ore shoot was largely 

mined through the Silver Wave workings and was part of the 

shoot shown at the northeast end of adit 1 in figure 28. The 

first ore shoot is almost over the long stope on level 5 of the 

Silver Wave and is probably part of the same ore channel. 

The vein has the same strike in the Silver Cord claim as it 

does on the Silver Wave claim and dips 74° NW. near the 

upper adit. No information was obtained on the lower adit. 

The known production of the Silver Cord consists of 70 ounces
THE MINES 107

of silver and 953 pounds of copper in 1888 and 700 ounces of 

silver and 23,082 pounds of copper from 20 tons of ore in 1902.

SILVER KING

The Silver King mine is on the east slope of Glacier Mountain, about 200 yards northwest of the Bolivar mill and half 

a mile south of Montezuma. The lode was discovered by 

J. T. Lynch in 1866 and was called the Sukey until 1880, 

when it was relocated as the Silver King. According to 

Raymond's report for 1870 the Sukey was developed by two 

adits and a 40-foot discovery shaft. The shaft was 180 feet 

above the upper adit, which was 96 feet long, and 330 feet 

above the lower adit, which was 260 feet long. The vein was 

reported to be from 4 to 6 feet wide and to have an ore seam 

from 20 to 36 inches wide. Most of the ore was worth between 

$35 and $40 a ton. At this time the mining company owned 

a 5-stamp mill, a roasting furnace, and two amalgamating pans. 

In 1873 this plant treated 70 tons of 

ore that averaged 60 ounces of silver 

to the ton; the cost of reduction was 

$23 a ton. The mine was not operated again until 1875, when the 

mill made a short but unsuccessful 

run on some of the lower-grade ore 

of the mine. Some high-grade ore 

was shipped that summer, but the 

amount is not known. The mine 

was operated more successfully in 

the next 5 years, however, and a 

dividend of $50,000 was paid in 1881. 

In 1882 the mine was developed by 

three drifts, 155, 460, and 600 feet 

long, with connecting winzes aggregating 170 feet, according to the 

Colorado Mining Directory. The 

ore was from 8 to SO inches wide 

and consisted of galena, gray copper, 

ruby silver, and native silver in a 

quartz gangue, and sorted ore 

assayed 55 percent of lead and from 

50 to 100 ounces of silver to the ton. 

The mine produced about 5 tons of 

ore a day for some time and treated it 

in a 10-stamp mill before shipping. 

In the summer of 1883 the old Sukey 

mill was remodeled by the Silver King Mining Co., and in 

November the mill started operating on ore bought from the 

Radical and Chatauque mines. The mill did not run all winter, 

however, and it burned down early in the summer of 1884 

and has never been rebuilt. A small amount of ore from the 

Silver King was concentrated in the mill before it burned, but 

no more ore was shipped until 1886. The mine was steadily 

operated, however, and the drifts were extended-in the search 

for new ore bodies. In 1886 a carload of ore was shipped 

which netted the company $90 a ton. As shown in the table 

below, a small amount of ore was shipped the following year, 

but the mine was not worked in 1888-91. In 1892 it shipped 

15 carloads of ore, but it was again closed in 1893 and was not 

reopened until about 1899. In this year and in 19.01 a small 

amount of ore was shipped. The Silver King was again 

operated in 1909 by the Silver Princess Mining Co., and during 

the next 3 years a few carloads of ore were treated at this 

company's mill in Montezuma. The exact amount of ore 

milled is unknown, as the mill was using ore from the Chatauque, Silver Wave, and Silver King mines, but the best 

estimates available have been used in prorating the ore treated 

at the mill in 1909-12, and the production figures given are 

probably fairly close to the actual output of the various

mines. No work has been done on the Silver King since 

1912.

As shown on plate 37, the vein strikes N. 35°-60° E. and 

dips 65°-88° SE. On the upper level the vein everywhere 

cuts across the schistosity, which strikes about N. 25° E. and 

dips steeply to both east and west. On the lower level the 

vein in some places turns and runs parallel to the schistosity 

for short distances before resuming its general trend of N. 

60° E., and on this level there are many branching veins parallel to the bedding planes of the enclosing gneiss. In short, 

the vein is much less definite on the lowest level than it is in 

the upper level and has the appearance of a vein that is splitting or "horsetailing" and will disappear at no great depth. 

Little ore was found in that part of the lowest level which was 

accessible at the time of the writer's visit, but, as shown on 

figure 27, the lower part of the ore shoot opened by the upper 

level was found and stoped.

E.

Caved

Caved

FIGURE 27. Sketch map of slopes in Silver King mine, August 1929, looking north.

The direction of movement of the premineral fault occupied 

by the Silver King vein can be given with some confidence. 

The walls are deeply grooved on both the upper and lower levels, 

and the grooves pitch 57°-68° NE.; S-shaped fractures in the 

barren fissured zone east of the ore shoot indicate that the hanging wall moved downward and eastward, and thus it may be 

assumed that the Silver King vein occupies a normal fault in 

which there was a small horizontal component of movement, 

the hanging wall moving downward and northeastward at an 

angle of about 63°. Movement in this direction would tend 

to create open spaces wherever the vein swung from a N. 60° 

E. course to one which was more northeasterly. The ore shoots 

on the upper level and those in the accessible part of the lower 

level occur where the vein swings to a northeasterly course. 

On the lower Jevel mineralization followed the intersection of 

the vein and a premineral fault striking parallel to the gneiss, 

but the quartz, pyrite, and ankerite vein filling was of too low 

grade to stope. A small ore shoot was also formed at the junction of the vein and a branching fissure and is said to have 

contained some ruby silver a short distance above the level.

The ore in the accessible part of the lower level consisted 

chiefly of quartz, pyrite, and ankerite, with a small amount of 

galena and sphalerite sparsely distributed through the other
108 MONTEZUMA QUADRANGLE, COLORADO

minerals. On the upper level galena was slightly more abundant 

than sphalerite, and the two sulphides were about equal to the 

quartz gangue; small amounts of pyrite and chalcopyrite were 

present also, and near the end of the ore shoots manganiferous 

ankerite was abundant and is said to have been associated with 

some ruby silver.

The following are the available figures of production:

Production of Silver King mine

1883. . ...

1886. - 

1887. 

1892. _ 

1904. ___ . 

1909. . 

1910.. 

1912. _ ..................

1928- - 

Ore

(short 

tons)

25 

10 

7 

203 

5 

80 

10 

39 

1

Gold 

(fine 

ounces)

72; 94 

11.00 

1.60 

.68 

1.57

Silver 

(fine 

ounces)

379 

7,923 

103 

460 

210 

602 

181

Lead, 

wet 

assay 

(pounds)

144, 099-

15, 500 

12, 222 

16, 138

487

Copper, 

wet 

assay 

(pounds)

83 

58 V 315

Zinc 

(pounds)

40, 122

No record available for 1871-74, 1876-80, 1882, 1884-85, 1889-91, 1893-1900; no production in 1870, 1875, 1881, 1888, 1901-3, 1905-8, 1911, 1913-27.

The Silver Wave vein was discovered about 1882 and was 

actively developed in the next few years. The mine commenced production in 1885 and continued to 1890; it was probably idle most of the time from 1890 to 1905, when the Silver 

Wave Mining Co. began to develop it. The mine has been an 

intermittent producer since that time, and for a while, about 

1909^ was operated by the Silver Princess Mining Co. The 

upper adits have long been inaccessible, but no. 5 and part of 

no. 6 were 'open in 1929. According to the Montezuma Mill 

Run, in 1885 the upper adit reached ore after following the 

vein 60 feet through a barren stretch. Adit 2 started in ore 

running 160 ounces of silver to the ton, and good ore, averaging 

12 inches in width and reaching a maximum of 36 inches, continued for about 60 feet, when a barren space was found. 

Adit 3 found no ore until it came under the shoot discovered at 

the portal of adit 2, and 78 feet of this adit out of a total of 300 

feet was in ore. Most of adit 4 was in ore, although much of 

it showed only in the bottom of the drift; 200 feet of the 225 feet 

driven was called ore, and at that time (1885) a stope 165 feet 

long was well started on ore that averaged about 9 inches in 

width. Level 5 was 116 feet on the lode, which carried quartz

S/LV£fl WAVE LEVEL /

FIGURE 28. Approximate shape of ore shoots on Silver Wave vein, looking southeast.

SILVER PRINCE

The Silver Prince mine is on the west slope of Glacier Mountain at an altitude of about 11,300 feet, about 2 miles south of 

Montezuma. It is probably the western continuation of the 

Wild Irishman vein, but the development work on the two 

claims is not enough to establish the continuity. The vein was 

located in 1881 by E. L. Doyle and yielded some ore in the next 

few years. According to the Colorado Mining Directory the 

ore was from 6 to 20 inches wide and consisted of gray copper 

and galena in a quartz gangue. The known production has 

consisted of 3 tons of ore in 1882, 45 tons in 1884, and 37 tons in 

1885.

SILVER WAVE

The Silver Wave vein is in the small gulch between Santa Fe 

Peak and Sullivan Mountain, on the west slope of the Continental Divide, about 2 miles southeast of Montezuma. The 

vein has many workings on it, but the chief production has come 

from the Silver Wave mine, developed by six adits spaced about 

65 feet apart vertically, at altitudes of 12,987, 12,920, 12,855, 

12,790, 12,725 and 12,657 feet. The lowest adit, no. 6, is at the 

terminal of a long aerial tramway, which connects the mine 

with the wagon road 1,650 feet below in the valley of the Snake 

River, about a mile south of Montezuma. There are several 

buildings near the portal of adit 6, but both they and the 

tramway were in poor repair when the writer visited the mine 

in 1929.

streaked with "mineral." In 1886 adit 2 was 300 feet long, and 

260 feet of the drift was reported to expose shipping ore. According to James Southerland, the best ore was found on level 4 

in two strong shoots which were about 50 feet apart and not 

far from the portal of the adit. The ore in the first shoot did 

not continue down to level 5 but was stoped to the surface about 

level 4. The second shoot was also stoped to the surface and 

is reported to have been in some places largely fine-grained 

galena 34 inches wide. Little information was found concerning the other ore shoots above level 5. The data gathered from 

many sources, including an early stope map, have been graphically summarized in figure 28.

As shown on plate 16, the country rock of the mine is largely 

quartz schist of the Idaho Springs formation, which strikes N. 

25° W. to N. 55° E. but is nearly north and south in most of the 

workings. The schist dips west or northwest at 45° to 75° 

and in some places is parallel to the vein, which strikes N. 27°- 

50° E. and dips steeply northwest throughout most of its length. 

A small mass of Silver Plume granite is cut 130 feet from the 

portal of adit 5 and is also present on adit 6 vertically below. 

Some small masses of monzonite porphyry were found near the 

vein on the surface, but none was observed underground. 

Although small amounts of ore occur in the vein under the first 

shoot of level 4, and the walls of the drift are in places incrusted 

with copper sulphate 1 inch thick, the first ore body of commercial size was found about 310 feet from the portal. As the 

drift was driven in the footwall of the vein for about 80 feet
THE 109

before the ore was cut, the ore shoot was entered near its northeast end and a drift was driven back southwest for 50 feet, to a 

point where the ore abruptly pinched to a thin, unprofitable 

quartz seam. This ore shoot is about 70 feet long on level 5 

and is reported to have about the same length on level 6, but 

the drift was caved 10 feet beyond the southwestern limit of 

the shoot on the lower level, and the distance could not be 

measured.. According to Jack Ryan, who was a lessee in 1917, 

the ore shoot was followed below level 6 by a winze 104 feet 

deep, but the ore pinched suddenly about 5 feet from the 

bottom. The writer was able to descend this winze only about 

15 feet because of the thick coating of ice on the ladders; at this 

place the vein was well exposed, however, and contained 22 

inches of sulphide ore. Over half of the ore was zinc blende, 

but chalcopyrite and pyrite were abundant, some galena was 

present, and in the siliceous walls of the main sulphide seam 

arsenopyrite was common. Here the vein strikes N. 35° E. 

and dips 85° NW. For about 150 feet northeast of this ore shoot 

on level 5 the vein is chiefly fine-grained quartz 6 to 8 inches 

wide and contains many ramifying veinlets of arsenopyrite. 

It is open and vuggy in many places, and late barite is common 

in the vugs, but little galena, sphalerite, or other sulphides 

were seen. At the end of this barren stretch an ore shoot 190 

feet long was found and is stoped both above and below the 

level and was undoubtedly reached by level 6. The breast of 

the drift is 50 feet beyond the stope, and here the vein is 12 

inches wide and consists of nearly equal parts of light-colored 

sphalerite and fine-grained quartz, but a moderate amount of 

barite occurs disseminated through the other minerals.

The Silver Wave vein is a mineralized sheeted zone whose 

individual fissures branch and intertwine or gather together in a 

single strong fissure. In many parts of the barren stretches the 

vein is followed -with great difficulty because of the common 

occurrence of diverging fracture planes. The ore shoots 

studied all widen abruptly from narrow seams of ore to commercial bodies .12 to 24 inches wide within a distance of 5 or 

10 feet and, of course, pinch as abruptly into lean unprofitable 

streaks. According to Mr. Ryan, the lower termination of the 

second ore shoot was as abrupt as its lateral termination. 

There was little evidence on level 5 of the presence overhead of 

the first ore shoot of level 4. The schistosity of the wall rock is 

in some places parallel to the vein and in other places makes a 

decided angle to it; the vein is nearly barren on level 5 wherever it 

is parallel to the schist, and ore occurs wherever the vein is 

decidedly cross-breaking. The termination of an ore shoot 

sketched in plate 16 illustrates the character of the fissuring in 

the vein as well as the rapid change in width of the sulphide ore. 

It is difficult to estimate the depth to which a given ore shoot 

will extend, but the chimneylike longitudinal section suggests 

that the vertical extent is generally greater than the horizontal 

extent. The ore in the upper levels was largely galena and 

contained moderate amounts of gray copper, and the ore on the 

lower levels was chiefly sphalerite and chalcopyrite. The 

known production is given below.

Production of Silver Wave mine

Production of Silver Wave mine Continued

1 Lead concentrates: 

1913............

1914. _ . _ ....

1915............

1916............

1917............

1922............

, Zinc concentrates: 

1913............

1914............

1915............

1916............

1917............

Ore to 

concentrating 

mills 

(short 

, tons) 

«!

171 

75 

1,560 

3,231 

(?) 

(?)

Concentrates 

produced 

(short 

tons)

24 

32 

72 

305 

4 

20

49 

40 

100 

54 

5

Gold 

(fine 

ounces)

2.15

9.16 

15.47 

.25 

.50

7.00

.06

Silver 

(fine 

ounces)

1,243 

915 

2,875 

10, 769 

130 

549

1,330

3,320 

2,081 

148

Lead, 

wet 

assay 

(pounds)

37, 825 

29,876 

79, 464 

304, 252 

3,511 

3,704

9,214 

479

Copper, 

wet 

assay 

(pounds)

1,147 

6,581 

74 

421

212

Zinc 

(pounds)

' 43,040 

30, 923 

74,000 

36, 856 

3,734

1885

1880

1QQ7

1888

1889

1800

1010

1011

1012

1913 

1014 

1016 

1917

soo also milling oro).__... 

SQO also milling ore).. .... 

soo also milling oro) ..

Ore 

(short 

tons)

70

908

75

(?)

?)

(?)

22

30

291

310 

143 

18

net

Gold 

(fine 

ounces)

23.18

32.20

2.67

4.35

19.66

26.67 

5.47 

1.66

1

QQ

Silver 

(fine 

ounces)

5, 715

2,497

447

3,857

746

983

8,714

7,367 

4,041

588

eon

Lead, 

wet assay 

(pounds)

 153,253

9,796

24, 101

11,319

13, 309

91,672

93, 155 

100, 580 

18,580

Copper, ' wet assay i 

(pounds) ;

4,011

1,962 

10,074

7,323 

3,491 

308

No record available for 1891-1900; no production in 1901-8,1918-21,1923-28; production in 1909 probably included with that of Silver King mine, as both that mine and 

the Silver Wave were then being operated by the Silver Princess Mining Co, 

(See pp. 107-108.)

STAR OF THE WEST

The Star of the West mine is on the west slope of Teller 

Mountain, about 2% miles south of Montezuma, at an altitude 

of about 11,800 feet. The vein was discovered in 1874, and 

according to the Montezuma Mill Run, the lower level in 1882 

comprised a crosscut 218 feet long and a drift on the vein 200 

feet long. The vein was reported to be "a soft light-colored 

gangue matter" 30 feeb wide. The middle level was driven 

225 feet on the lode, which carried from 1 to 6 feet of paying ore. 

The upper level was 60 feet long on the vein, and the ore seam 

was about 1 foot wide and contained high-grade gold and silver 

ore. Free gold, gray copper, chalcopyrite, bismuth, and 

galena were found, and high assays were reported. There is 

little recorded production for the "mine prior to 1886, but some 

ore is known to have been shipped in 1875 and 1882, and ore is 

said to have been shipped about 1898. The tonnage was never 

large, and the total production was probably less than 50 tons. 

The ore shipped in 1887 averaged 5 ounces of gold and 40 ounces 

of silver to the ton. The mine was inaccessible in 1929.

STAR OF THE WEST NO. 2

The Star of the West no. 2 is about a quarter of a mile west 

of the Star of the West and a few hundred feet below it. The 

lode was located in 1880 by Oliver Milner and was developed 

by two adits. No production is vecorded for the propertj7 . 

The vein in places is said to have carried from 10 to 15 inches of 

quartz, galena, and gray copper and assayed from half an ounce 

to 1 ounce of gold and 75 to 125 ounces of silver to the ton and 

40 percent of lead. The geology of the lower adit of this 

prospect is shown in plate 23.

STEVENS

The Stevens mine is in Stevens Gulch, about 6% miles nortiieast of Montezuma, at an altitude of about 11,400 feet. It 

can be reached by automobile from Silver Plume, 7 miles distant 

by road. In 1927 the roads were in poor condition and had so 

many steep grades that supplies were hauled to the mine by 

wagons.

The Stevens mine has been one of the most productive in the 

Montezuma quadrangle, although its output has been small 

since 1910. The lode was discovered in the late sixties, but the 

exact date is unknown. The mine is mentioned by the Georgetown papers much more frequently than any other in the quadrangle and apparently was a steady producer from 1870 until 

1893 and has been intermittently productive since that time. 

The total production is not accurately known, but the figures 

given below indicate the tenor of the ore. and suggest the general 

order of magnitude of the tonnage that has been produced.
110 MONTEZUMA QUADRANGLE, COLORADO

The record of the mine's early shipments suggests that the 

surface ore was not exceptionally rich but carried considerable 

lead and silver. The Georgetown Miner for October 13, 1870, 

reports that the Crescent Silver Mining Co., operating the 

Stevens mine, had produced 40 tons of ore which yielded $200 

a ton simply in drifting on the vein. Raymond's report for 

1872 says:

"The Stevens lode has been constantly and profitably 

worked during the year, yielding an average of 30 tons per 

month of good ore, averaging 150 ounces of silver per ton, with 

a high percentage of lead. This lode is owned by a company 

who are conducting their operations with economy and ability."

The Georgetown Miner for February 12, 1876, reports that 

20 men were working at the Stevens and that the mine was 

producing ore assaying from 80 to 100 ounces of silver to the

for almost 400 feet, although on the level 100 feet higher, ore 

was stoped continuously for 350 feet of this distance. Where 

the ore comes down to the main tunnel level at the south end 

of the shoot, it continues about 120 feet along the drift. A few 

small pockets of ore have been found south of this shoot, but the 

mineralization spread along branching fractures, and the ore 

bodies are small. Plate 38 shows the mineralization of the 

branching and intersecting fissures in the southern part of the 

mine. On the level 100 feet above the main tunnel level, where 

extensive stopes overlie barren vein matter in the lower level, 

the ore left on the walls of the stopes, in the pillars, and in the 

gob is invariably much higher in lead than the ore found on the 

main tunnel level. Much of the ore seen in the upper level was 

essentially clean galena, although some sphalerite and chalcopyrite were found in the bottom of the drift near the north end of

the shoot. In the main level

N.

High-grade

galena ore

2/2 "PbS

S.

? 

Nearl>j barren fqtz+MnCOj),

6"ZnS ore

Stoped area

100

FIGUKE 29. Approximate relations of stopes along main tunnel level, Stevens mine. Sketched by T. S. Levering.

ton and averaging about 65 percent of lead. Ten years later 

the tenor of the ore being shipped was somewhat poorer, a 10- 

ton mill run on September 16, 1886, assaying 1.1 ounces of gold 

and 44 ounces of silver to the ton and 47 percent of lead. During 

1888 several hundred tons of ore was shipped, averaging about 1.1 

ounces of gold and 26 ounces of silver to the ton and 50 percent 

of lead. In 1891 seven carloads of ore averaged 0.1 ounce of 

gold and 24 ounces of silver to the ton and 66 percent of lead. 

A gradual decrease of silver with depth is indicated.

The mine was opened by several adits and by winzes sunk 

from some of the levels. Most of the portals of the upper levels 

have been obliterated by snowslides or caving, and it is impossible to tell how many tunnels were driven. The main tunnel 

level is known as the fourteenth level, and the next tunnel level 

above was called the ninth level and is supposed to be about 300 

feet above the main level, suggesting that the levels were 

numbered every 10 fathoms in depth. At the tirhe of the writer's 

visit the main tunnel level and part of the next level above it 

were accessible. Two winzes have been sunk from the main 

tunnel level and are reported to be 80 feet deep and to be con-. 

nected by a drift. They were filled with water in 1927, however, and this information could not be verified by observation.

As shown on plate 38, the ore occurs in branching fissures 

whose general trend is slightly west of north and whose general 

dip is 60°-75° E. Most of the ore found on the main tunnel 

level contains more sphalerite than galena and has a moderate 

amount of pyrite and manganiferous ankerite. Ore of this 

character, 4 to 10 inches wide, occurs in a shoot about 200 feet 

long just south of the main tunnel where it cuts the vein. As 

shown in figure 29, no more ore is found in the vein on this level

1870........... ........

1070

1Rft7

1888..- 

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

1SQ9

Ore

(short 

tons)

40

9flfl

(?)

(?)

Gold 

(fine 

ounces)

54.12

91.91

103. 34

Silver 

(fine 

ounces)

25, 000

12, 947

21, 135

17, 890

42, 666

Lead, 

wet 

assay 

(pounds)

200, 000

390, 698

857, 653

811, 106

2,601,203

Copper, 

wet 

assay 

(pounds)

Zinc 

(pounds)

mam

directly beneath the stopes the 

vein consisted of a narrow vein 

of quartz and pyrite or a wide 

seam of manganiferous ankerite. 

Beneath the stopes the walls of 

the drift on the main tunnel 

level were covered with a white 

coating of limy carbonate, which 

was stained brilliant green in 

some places and partly covered 

with jet-black deposits in otherplaces, no doubt reflecting the 

leaching of lime, copper, and 

manganese by water descending 

over the broken ore in the stopes 

above. Where this ore shoot is 

exposed on the-main tunnel level 

the southern part of it contains 

more galena than the northern 

part, and the galena seems to

rest on much more zinciferous material pitching southward at

a low angle. This is shown in figure 29.

Available production figures for the Stevens mine are given

below.

Production of Stevens mine

300 Feet

No record available for 1872, 1877-80, 1884, 1893-98; unknown production in 1871, 

1874-76, 1883, 1885-86, 1890-91, 1899-1900; no production in 1881-82, 1901, 1921-28; 

for 1902-20 see Waldorf group, p. 112.

TIGER, TIGER EXTENSION, ST. CIOUD, AND WINDSOR

The Tiger and Tiger Extension claims are on the crest of 

Glacier Mountain, about a mile southwest of Montezuma, and 

are developed by several shafts. The deepest shaft is about 

100 feet deep, and its collar is at an altitude of 11,775 feet. 

The property can be reached by a steep trail that leads up the 

west slope of the mountain from the Sts. John mine. It was 

discovered before 1870, and ore was sold to the Sts. John 

smelter prior to 1880. The mine is not mentioned as an active 

property by the Montezuma Mill Run until 1885. The shipments are shown in the table below, The mine has been 

inactive since 1890.
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 178 PLATE 38

8ore(.8ZnS,B5PbS 

I'gangue 

-Stoped above

50 Feet

IOO'ABOVE 

MAW LEVEL

300 Feet

Z"gangue

EXPLANATION

Barren fissure, fault, or vein less than 

1 inch wide

Barren fissure, fault, or vein from 1 to 

12 inches wide

Barren fault or vein more than 12 

inches wide

Vein with sulphides from 1 to 12 

inches wide

Vein with sulphides more than 12 

inches wide

- -x -x-- Vein with sulphides more than 12 

inches wide on upper level

Strike and dip 

Strike of schistosity 

Downthrown side of fault 

PbS, galena 

ZnS, sphalerite 

CuFeS2, chalcopyrite 

Rh, rhodochrosite

PLAN OF LEVEL 14, STEVENS MINE, STEVENS GULCH (A), 

AND DETAIL OF SOUTH END OF MAIN DRIFT (B)
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 178 PLATE 39

i r 6ore-$£. 1 ./7 - ,/ > 7 7 v > v " 65'M7ZnS 7ov "/ r '

l2VeWw{2PbS 70y,,/ , k 

7 " ' ^^^W^S2 / 24^reccia » Ore entirely FeS 2 

^^^^^ ^§^r\ Vor^^^g^'

^ r V50"breccia

- v v '"7*;^^$'^ T "

" " / Montezuma quartz monzonite 

/"

,a I-/LJ

EXPLANATION

Barren fissure, fault, or vein from 1 to 

12 inches wide

Barren fault or vein more than 12 

inches wide

- Mineralized vein from 1 to 12 inches 

wide

Relative proportion of sulphide 

(solid) and gangue minerals 

in ore

Downthrown side of fault

PbS, galena

ZnS, sphalerite

FeS2, pyrite

Rh, rhodochrosite

Mineralized vein more than 12 inches 

wide

Strike and dip

PLAN OF TOLEDO TUNNEL, MONTEZUMA
U.S. GEOLOGICAL SURVEY

PROFESSIONAL PAPEU 178 PLATE 41)

CONTINENTAL DIVIDE 

of 

 

MOUNTAIN~

,£1.307' 

?_ BRILLIANT 2

LANE TUNNEL 

o £f. O'

SECTION 

Assuming the average dip of 60

WORKINGS ON WHALE AND BRILLIANT MINES, HALLS GULCH.
THE MINES

Production from Tiger and Tiger Extension claims

Tiger: 

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

^887.... ..................................

Tiger Extension: 

J889......... ....... ....... ...............

KW........ ..............................

Ore (short 

tons)

6 

(?)

(?) 

(?)

Silver (fine 

ounces)

304

537 

1,602

Lead, wet 

assay 

(pounds)

13, 252 

28,418

Tlpor: No record available for 1886, 1880-1001; no production in 1888. Tiger 

Extension: No record available for 1801-1900; no production in 1901-0; for 1910-28 

see Sts. John.

In 1870 Raymond reported that the Tiger had a shaft 20 

feet deep on a vein that was 6 feet wide and contained two pay 

streaks. The ore next to the north wall was chiefly galena 

assaying about lOO ounces of silver to the ton and was 10 

inches wide. The ore next to the south wall was 6 inches wide 

and assayed from 1,000 to 2,500 ounces of silver to the ton. 

The vein matter between the two ore streaks assayed from 16 

to 30 ounces of silver to the ton. In 1883, however, according 

to the Colorado Mining Directory, the ore assayed about 55 

percent of lead and 100 to 150 ounces of silver to the ton and 

contained galena, gray copper, and "chlorides" in a quartz 

gangue. The ore on the dump of the mine in 1929 contained 

both galena and sphalerite in a quartz-barite gangue, and the 

vein from which the ore was broken must have been at least 

9 inches wide.

The vein strikes N. 4.0° 13. and dips 60°-80° NW. The 

Sts. John tunnel, 700 feet below, was driven 1,000 feet east 

of its vein in search of the Tiger vein but without success. 

The dip of the Tiger vein would carry it through the Sts. John 

tunnel very close to the place where vein 5 of that mine 

was found. It is probable either that vein 5 is an upfaulted 

part of the Tiger vein, or that the Tiger vein runs into vein 5 

above the lower Sts. John tunnel.

TOIEDO

The Toledo tunnel and the Toledo mill are on the east side 

of the Snake River Valley, about a quarter of a mile north of 

Montezuma, at an, altitude of about 10,300 feet. The wagon 

road from Montezuma to Chihuahua and Decatur runs past 

the portal of the tunnel, which is just across the road from the 

mill. Neither the mine nor the mill has been operated since 

1915. Most of the ore treated by the Toledo mill came from 

the Jumbo mine (see p. 85), but some of the ore was taken 

from the Toledo tunnel and other properties. As shown on 

plate 39, the tunnel is about 3,150 feet long and runs eastnortheast into the lower part of Tiptop Peak. It is entirely 

in the Montezuma quartz monzonite, most of which is very 

fresh and unaltered. A few small pyritic veins-were cut that 

trend a little more northeasterly than the tunnel, but the 

drifts that follow these veins have no stopes, and the ore was 

N probably of low grade. Near the breast of the tunnel, 2,800 

and 2,900 feet from the portal, two veins striking northnortheast were cut, and both contain lead-silver ore. The 

veins are 3 to 13 inches'wide and contain pyrite, galena, sphalerite, and some freibergite. At 3,000 feet from the mouth of 

the tunnel a strong eastward-trending brecciated fault zone 

was found. Like the other eastward-striking fractures, it is 

pyritic but does not contain appreciable amounts of the lead, 

zinc, or silver sulphides.

TIDIER

The Vidler tunnel is in Mount Edwards, a short distance north 

of Argentine Pass and about 5 miles east-northeast of Montezuma. It was originally intended to be a railroad tunnel and 

to serve a proposed narrow-gage railroad extending from Silver 

Plume to Dillon. Work was started on the tunnel in 1901, 

and for a time headings were driven from both the east and the 

west portals. The west portal was abandoned after the face 

had been carried about 700 feet, but in spite of repeated changes 

in ownership and reorganizations, the eastern section of the 

tunnel was gradually advanced until in 1911 it had a length of 

5,118 feet. No work is known to have been done since that 

time, however, and the breasts of the east and west sections 

are reported to be separated by about 1,700 feet. The altitude 

of both portals is about 11,650 feet. The east half of the tunnel 

trends S. 7G°47' W., and the west half N. 58° 17' E. The tunnel 

was not accessible at any time during the writer's visits, but 

some information was found in reports by G. W. Schneider, 

J. W. Astley, and -Herbert Strickland, quoted in a prospectus 

of the Argentine Tunnel Railway Co. The eastern section of 

the tunnel is reported to cut veins at distances of 227, 248, 

265, 330, 380-, 500, 885, 1,956, and 2,175 feet from the portal. 

Most of the veins were small and contained only quartz and 

pyrite, but three carried lead-zinc ore. Galena and sphalerite 

containing 12 ounces or less of silver to the ton and very little 

gold were found in the veins cut at 227, 265, and 885 feet, but 

only the last vein, known as the Flossie or Red Light, was 

strong enough to encourage much development. This vein 

strikes about N. 33° E. and dips about 85° NW. It carried 

galena and sphalerite in a quartz gangue, and the ore-beating 

part of the vein ranged from 1 to 18 inches in width, averaging 

about 6 inches. Some ore was stoped in this vein both north 

and south of the main crosscut tunnel. No production figures 

have been found, but the property has never been an important 

producer.

WAIDORF, PAYMASTER, AND COMMONWEALTH

The Waldorf mine is near the head of Leavenworth Creek, 

6}^ miles east-northeast of Montezuma, at an altitude of about 

11,600 feet. It can be reached by automobile from Georgetown, 6 miles northeast of the mine, but the wagon road has 

many steep grades and was in poor condition in the summers 

of 1926-29. There were several buildings at the mine in a fair 

state of repair, including boarding houses and a 50-ton mill. 

The Wilcox tunnel, whose portal is close to the mill, goes northwest into McClellah Mountain about 4,000 feet. It was driven 

primarily to cut the Commonwealth vein, which is described 

on page 105. As shown in figure 16, the tunnel cuts many veins, 

but as most of them are pyritic and carry little gold or silver, 

few of them have been explored. Most of the tunnel is in schist 

or injection gneiss, which strikes north or east-northeast and is 

nearly vertical. Silver Plume granite is found near the portal 

and in the last 1,000 feet of the tunnel. About 1,600 feet from 

the portal a dike of rhyolite porphyry was found that strikes 

northeast and dips about 40° NW. No ore was associated with 

the dike where it is cut by the tunnel.

Near the breast Of the tunnel the vein locally known as the 

Paymaster was cut about 350 feet below the upper Paymaster 

or Commonwealth tunnel. This vein strikes northwest and'dips 

steeply southwest. It was nearly barren on the Wilcox tunnel 

level but contained some gold-bearing chalcopyrite ore a short 

distance above the tunnel. The walls of the drift were heavily 

coated witn copper-stained deposits of lime at the time of the 

writer's visit, but no good exposures of the vein were seen.
112 MONTEZUMA QUADRANGLE, COLORADO

Incomplete production figures for the Waldorf, Paymaster, 

and Commonwealth group are given below.

Production of Waldorf, Paymaster, and Commonwealth group

Paymaster: 

1882.................

1887.. . 

1DQQ

1QQQ

1890- 

1892.. . 

Dry ore

Waldorf group: 

1907 (Tobin, Stevens, 

and Argentine) 

1908.. 

1910- 

1913 (Commonwealth)

1915 (probably Waldorf and Tobin) ....

Copper ore

1Q1Q

1914

1915 (probably Waldorf and Tobin). 

1Q17

Lead ore

Waldorf group: 

1902.. .... ------------

1903- 

1909.. 

1910. 

1911 (Common1911 (Paymaster) .....

1912 (Common1913 (M U) - -

1914 (Paymaster) ..... 

1915 (probably Waldorf and Tobin) 

1918.. 

1919 (Centennial and

1921 (Waldorf) 

Gold-silver-copper ore 

1915 (probably Waldorf

1916.. 

1917.. 

1920 (Centennial, StevDry gold-silver ore 

1915 (probably Waldorf

Lead-zinc concentrates

Waldorf group: 

1904- 

1905 (Stevens)-.---.

1906. 

1910. 

1913 (Stevens) ........

Lead concentrates

1907 (Tobin, Argentine, 

and Stevens)... _ .....

1908.. 

1909.. . 

1910.. 

1913 (M U) 

1914 (Waldorf)..... .......

1915 (Waldorf and Tobin). 

1916. 

1917..... . .. ..

1920 (Centennial, Stevens, Waldorf)...- .......

Ore

(short 

tons)

5 

(?)

(?) 

(?) 

(?) 

(?)

896 

200 

231 

582 

17 

7

70

41 

132

30 

43

200 

100 

68 

123 

4

19 

20 

101

31 

10 

4

185 

58 

16

18 

10

219 

336 

46

97 

78

Concentrates 

(short 

tons)

197 

133 

225 

15 

9

99 

150 

236 

84 

3 

19 

228 

205 

489

14

Gold 

(fine 

ounces)

18.09 

57.97 

19.00 

28.14

277. 76 

23.19 

66.01 

224. 66 

18.78 

.42

34.72

19.32 

150. 31

29.94 

29.90

30.00 

21.77 

 15. 36 

27.01 

1.61

2.79 

2.99 

20.09

6.06 

1.96 

.60

, 52.66 

28.33 

4.40

4.10 

1.35

340. 03 

331. 77 

56.91

29.56 

50.67

Gold 

(fine 

ounces)

36.00 

169. 31 

278. 45 

4.95 

2.50

143. 05 

58.52 

98.47 

41.22 

1.11 

7.16 

91.00 

116. 22 

211.43

6.62

Silver 

(fine 

ounces)

1,555 

3,992 

13, 679 

3,197 

4,496 

36,882

25, 240 

6,124 

3,531 

13, 360 

278 

58

1,834

551 

2,571

1,406 

1,268

12,000 

6,553 

625 

4,805 

63

343 

452 

1,815

588 

125 

103

3,285 

1,249 

320

384 

566

9,765 

12, 126 

2,684

1,964 

1,633

Silver 

(fine 

ounces)

3,180 

9,934 

30,988 

553 

108

6,536 

1,586 

3,525 

1,307 

68 

136 

4,757 

4,255 

9,421

222

Lead, 

wet assay 

(pounds)

68, 691 

177, 248 

595, 584 

133, 562

481, 686

6,292 

1,880

16, 183

672

580 

8,880

4,968

97, 087 

28,821 

40, 802 

16, 446 

6,038

12, 422 

14, 016 

55, 837

19, 793 

1,274 

4,255

150, 387 

24,233 

16, 206

11, 792 

2,120

89, 158 

58, 271 

7,542

70, 198 

2,127

Lead, 

wet 

assay 

[pounds)

156, 949 

200, 251 

459, 527 

2,133 

4,128

259, 190 

77, 491 

81,412 

55, 369 

3,164 

2,406 

81,701 

60, 695 

210, 566

2,994

Copper, 

wet assay 

(pounds)

1,560

30, 757

699

2,859 

12,288

8,719 

7,149

1,874 

692

565

2,699 

4,799 

407

328

48, 795 

63, 549 

11,209

5,597 

 1,463

Copper, 

wet 

assay 

(pounds)

14, 456 

305

1,206 

6,866 

1,846

577 

9,000 

11, 378 

19,466

332

Zinc 

(pounds)

241

505 

1,170 

3,390

2,413

2,180

245

Zinc 

(pounds)

63, 709 

50, 966 

302, 000 

10, 118 

 3, 682

Production of Waldorf, Paymaster, and Commonwealth groupContinued

Copper concentrates

Lead-copper concentrates 

1915 (probably Waldorf

1919 (Waldorf) ..... ....

Concentrates 

(short 

tons)

537

123 

52

Waldorf group: 

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

1905 (Stevens).'- ---.

1906. .

1907 (Argentine, Tobin,

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

1909..... ...............

1910 .... ... .... 

Gold 

(fine 

ounces)

455. 69

95.12 

29.47

Ore to 

concentrating 

mills 

(short 

tons)

1,180 

800 

1, 348

595 

900 

1,071 

2,100

Silver 

(fine 

ounces)

6,365

. 2,708 

798

Lead, 

wet assay 

(pounds)

31,650 

6,566

Copper, 

wet assay 

(pounds)

27, 620

11, 677 

3,164

Waldorf gro 

1913 (M 

1914 (W 

1915 (W 

1916

up Continued. 

U and Stevons).- 

aldorf). .... ...

aldorf and Tobin).

1917

1919 (W 

1920 (V 

nial, S

aldorf).... ........

raldorf, CentenZinc 

(pounds)

5,600

Ore to 

concentrating 

mills 

(short 

tons)

36 

180 

3,184 

1,435 

2,690 

520

100

No record available for 1883-86.

WASHINGTON

The Washington vein is on the northeast slope of Collier 

Mountain at the head of the south fork of Morgan Gulch, at 

an altitude of about 12,500 feet. It is about 1% miles due east 

of Montezuma and can be reached by way of the trail from the 

town to Warden Gulch. The vein was discovered by Isaac 

Ware in 1873 and was worked intermittently during the seventies 

and eighties. As shown below, it produced a few carloads of 

lead ore in 1886 and 1887. No work is known to have been 

done on the property, and the workings had long been inaccessible in 1929. According to the Colorado Mining Directory 

for 1883, the ore was from 10 to 18 inches wide and consisted of 

"yellow and gray copper and sulphides in quartz" and assayed 

20 percent of copper and 100 to 200 ounces of silver to the ton. 

At that time it was developed by a drift 175 feet long and was 

credited with a total production of 50 tons.

The vein strikes N. 20° W. and cuts across the schistosity 

o'f the Idaho Springs formation, which is the country rock of 

the vein and strikes about N. 20° E. and dips 60°-70° E.

The only available record of production is given below.

Production of Washington mine

1876 - ..................................

1878... ..................................... .

1886 - - -.. .

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

Ore (short 

tons)

1

1

18

15

Silver (fine 

ounces)

64

86

Lead, wet 

assay 

(pounds)

910

No record available for 1877, 1879-85.

WAUKEEGAN

The Waukeegan vein is on the west slope of Collier Mountain 

about V/z miles southeast of Montezuma and is developed by 

three adits at altitudes of 12,350, 12,380, and 12,470 feet.. It is 

about 1,500 feet above the valley of the Snake River and is 

accessible only by a steep trail, which leads past the Bullion 

mine. The vein was discovered about 1880, and a small amount 

of lead ore was shipped in 1885 and 1889. No work is known
THE MINES 113

to have been done on the vein since 1890. The country rock 

is the Idaho Springs formation, which strikes northeast and is 

essentially parallel to the vein.

WHALE

The Whale mine is at the head of Hall Valley, about 3% 

miles south of Montezuma, and is opened .by seven adits between 

altitudes of 12,100 and 12,530 feet. As shown in plate 40, the 

levels are from 25 to 110 feet apart vertically. The mine is at 

the end of the wagon road leading from Webster up Hall Valley, 

but in 1929 the road was not passable to automobiles a mile 

south of the mine.

The Whale vein was discovered in 1869, and the mine was 

the chief one of the Hall Valley Silver-Lead Mining & Smelting 

Co., Ltd., at the time that company made an unsuccessful 

attempt to mine and smelt the silver-bearing barite ore of this 

region. In 1873 the development of the Whale was pushed by 

this company while it was erecting several blast furnaces 3 miles 

down the valley and laying a wooden tramway from the mine 

to the smelter. According to Raymond's report for 1873,

"The Whale lode is opened by three tunnels run in along the 

vein and by a fourth adit, which runs across the country rock 

from the foot of the mountain and will strike the vein at a 

distance of 800 feet. The latter is intended as the principal 

working tunnel. It was in 125 feet at the end of the year; 225 

feet vertically above it is level no. 1, which was 166 feet long; 

60 feet higher up is level no. 2, 85 feet long at the end of the 

year; and 70 feet still higher is level no. 3, which had reached a 

length of 122 feet. The faces of all the levels stand in ore. -A 

sample of 20 tons of average ore from the mine assayed 120 

ounces of silver per ton."

After the unsuccessful attempt to smelt the refractory barite 

ore in 1876, the English company failed, and the Whale was 

idle until 1883. At this time the Comet Consolidated Mining 

Co. obtained the mine and operated it for several years. Burchard's report for 1882 says:

"The Whale has about 2,000 feet of development on the vein 

in the four levels, with a pay streak from 8 inches to 2 feet in 

thickness and continuous. The ore is gray copper and galena, 

the first-class milling 250 ounces in silver, and second-class 100 

ounces, with an average of over 30 percent lead. At least 5,000 

tons of concentrating ore are dumped at the mouths of the 

different levels."

In 1883 Burchard reported:

"The Whale mine has four levels on the vein, aggregate 

development about 3,300 feet; * * * only a small force 

of men employed, averaging nine, partly in development and 

partly in extraction of ore; ore, argentiferous galena, with gray 

and yellow copper; average assay, 375 ounces of silver pers ton 

and 20 percent lead; average width of pay ore, 10 inches; 

* * * total weight shipped, 232J/£ tons; gross value of 

production, $24,515.85."

The mine was acquired by C. C. Welch, of Golden, about 

1888 but was involved in litigation for several years afterVard. 

The title to the property was finally cleared about 1894, and 

Mr. Welch still retains the chief interest in the mine. Except 

for a little work in 1890 the property was idle from 1888 to 

1898, when the mine was reopened by C. E. Street. As shown 

in the table below, the mine has been intermittently active 

since that time, but it was inaccessible in 1929 and had been 

idle for many years. A mill was built for gravity concentration of the ores in 1874 and was unsuccessful in separating the 

sulphides from the barite gangue; another gravity concentration mill was installed later but is said to have been unsatisfactory also. A flotation mill was erected about 1917 and made 

a good concentrate, separating the ore cleanly from the barite 

gangue.

The country rock of the mine is hornblende gneiss of the 

Swandyke gneiss and strikes about N. 15° W. and dips about 

80° W. Some dacite porphyry dikes were found on the surface 

near the trace of a strong north-northwest fault; similar porphyry is said to cut and fault the vein underground, but the 

vein is not certainly recognized east of the porphyry. The vein 

strikes N. 75° E. and dips 45°-60° N., averaging about 57°. 

A good description of the v.ein as it appeared in 1873 was given 

by Jerhegen 32 and is summarized below. On the surface of the 

mountain the vein crops out in a depression and is evidently 

less resistant to weathering than the surrounding gneiss. The 

walls of the vein were from 5 to 10 feet apart, but the pay ore 

ranged from less than an inch to 36 inches in thickness. Between 

the ore and the walls of the vein the rock was light-colored, 

altered, and impregnated with pyrite; in many places the ore 

seam was separated from the altered rock by a thin seam of 

gouge. The ore seam swells and pinches markedly and has a 

banded appearance in the thinner parts and a "porphyritic" 

appearance in the wider parts, where the abundant white - 

barite encloses irregular lumps of galena and gray copper. The 

ore also contains quartz, brown dolomite, and chalcopyrite, 

but pyrite is almost wholly confined to the altered rocks on each 

side of the central ore seam. Near the surface malachite, azurite, 

and copper sulphate occurred. Barite was almost the only 

gangue mineral where the ore vein was wide, but where it became 

narrow quartz and dolomite appeared, barite becoming much 

less abundant or disappearing entirely, especially if the vein 

carried no ore. In some places the vein splits and encloses a 

horse of country rock, and short spur veins are not uncommon. The spurs are parallel to the schistosity of the gneiss 

and are not persistent.

"As regards the distribution of the metalliferous minerals 

within the vein, it seems to be more or less influenced by the 

nature of the country rock, gangue, and width of the crevice. 

Where the crevice is wide the gangue is soft and decomposed 

and at the same time strongly impregnated with iron pyrites, 

and the metalliferous minerals seem to be present in much 

greater proportion. Where the vein is pinched the wall rocks 

are unconformable, hard, and of a less decomposed nature, 

light-greenish or black mica forming one of the vein's principal 

constituents; it is deficient in iron pyrites and at the same time 

contains numerous little stringers of grayish quartz. The gray 

copper oftentimes seems to be present in proportionately larger 

quantities in the narrower parts of the vein; or, more strictly 

speaking, the relative proportion of gray copper to galena is 

greater than in the wider portions of the vein. Where barite 

occurs in large crystals, the metalliferous minerals are much 

more scattered and less frequent. Where the vein throws off 

spurs or divides in making a horse, it is almost always poorer. 

It is probable that in further exploitation the ore will be found 

chiefly confined to zones, or chimneys, as already the first, 

second, and third levels have been drifted through considerable 

ground on the vein that has proved quite barren of ore, though 

the crevice has always remained well defined."

According to miners who have worked in the Whale, the ore 

seam in the lowest workings was of about the same width as in 

the upper workings. Chalcopyrite is said to be a little more 

abundant in the lowest workings than it is in the upper tunnels.

As shown in plate 40, the stope length of the ore is much 

shorter near the surface than on the lower levels, but no exploration was made beyond the place where the vein pinched and 

became barren on the upper levels. Two or three persistent ore 

shoots from 50 to 150 feet long, separated by lean narrow 

stretches of the vein, were found northeast of the main ore 

shoot on the fourth and fifth levels. Very little work was done

a* Jernegen, J. L., Jr., The Whale lode of Park County, Colo.: Am. Inst. Min. 

Eng. Trans., vol. 3, pp. 352-356,1875.
114 MONTEZUMA QUADRANGLE, COLORADO

at the southwest end of the main shoot on any of the levels, 

according to miners, and plate 40 corroborates this information. 

The occurrence of the ore close to the strong northwesterly 

fault shown on plate 3 is very similar to the occurrence of ore in 

the Leftwick and Missouri veins, a short distance south. The 

same northwesterly fault is associated with the localization of 

ore shoots in the three veins and probably traces the course of 

a deep-lying channel of mineralization.

Incomplete production figures for the Whale are given below.

Production of Whale mine

1877... ........ ...................

1878 

1879 

1880 

1881 

1882- 

1883..-.--.-- ...... ...... ...

1884 . 

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

1887... ... 

1888 

1890 

1916 

1917... ....... __ . ..-... .-

1922 (Whale, Lane, and Leftwick). 

1928 

Brilliant claim (upper adits on 

Whale vein): 

1899 

1900 .-. __ ..... - 

1903 

1904 

1918.. 

1919..- 

1920 (Whale, Lane and

1921 (Whale, Lane and

Ore 

(short 

tons)

99^

16 2 

3 

2 

10 

232H

26 

54 

41

28 2 

12 

20 

5

83 

7 2

Gold 

(fine 

ounces)

9.09

.20 

.10

Ore to concentons) tons)

910 91 

2, 290 229

800 71 

2, 655 164

Silver 

(fine 

ounces)

1,324 

252 

1,842 

210 

199 

842 

13, 000 

3,001 

1,050 

3,087 

2,271 

758 

430 

1,040 

363 

666 

234

7,318 

3,888 

282 

2,161

Gold Silver 

(fine (fine 

ounces) ounces)

.... . 4,310

0.19 12,608 

.-.- .. 4,466

.. .... 11,646

Lead, 

wet assay 

(pounds)

3,665 

1, 548 

2,108 

1,631 

1,919 

' 4,482 

74, 500 

14, 012 

6,410 

22, 755 

23, 100 

5,428 

3,305 

2,988 

2,820 

6,024 

1,184

28,463 

29, 035 

4,835 

25, 192

Lead, 

wet. assay 

(pounds)

47, 506 

82, 762

48, 254 

94, 827

Copper, 

wet 

assay 

(pounds)

154

25 

6,550

456 

500 

756 

324 

127 

1,021 

188 

590 

99

Copper, 

wet assay 

(pounds)

1, 915 

6,383

1,917 

1,941

No record available for 1886, 1889, 1891-98; DO production in 1901-2, 1905-15, 

1923-27.

WHITE SWAN

The White Swan vein is in the valley of the Middle Fork of the 

Swan River about three-quarters of a mile east of Swandyke and 

about 5 miles south of Montezuma. The workings are at an 

altitude of about 11,250 feet and are at the end of a secondary 

road that follows the stream down to the Swan River, where it 

joins another wagon road that leads to Tiger. The vein strikes 

N. 85° E. and dips 85° N. The principal opening is an adit, 

which follows the vein east for a few hundred feet. As the 

portal is only a short distance from the stream and the adit is 

almost parallel to the course of the valley, depth is gained very 

slowly, and the breast is only a short distance below the surface. 

A sheeted zone about 12 inches wide contains galena, pyrite, 

sphalerite, and ankerite veins whose aggregate width is commonly about 4 inches. Striations on the walls of the vein dip 

about 10° W., and the south wall moved west. The country 

rock of the vein is hornblende gneiss.of the Swandyke gneiss, 

and it strikes about N. 20° W. and dips steeply west.

No ore is known to have been shipped from the White Swan.

WILD IRISHMAN

The Wild Irishman mine is on the west slope of Glacier 

Mountain near the head of St. Johns Creek, about \% miles 

southwest of Montezuma. The vein was discovered about 1880 

and was rapidly developed in the next few years. The mine 

was a steady shipper from 1883 to 1886 but has no recorded 

production from that year until 1901, when it shipped several 

carloads of ore; some ore was shipped the following year, but 

little has been produced since that time. A small concentrating 

mill was built at the mine in 1884 but was unsuccessful in 

separating the barite from the sulphides and was soon abandoned.

The mine was inaccessible in 1929, but the underground 

workings are shown in figure 30, and the vein was studied on 

the surface by the writer. The lower adit has an altitude of 

about 11,400 feet, and the ore on its dump indicates that here 

the vein consists largely of manganosiderite carrying moderate 

amounts of galena. At 350 feet above the lower adit manganosiderite is rare, and the gangue is chiefly fine-grained quartz and 

small amounts of coarse-grained barite. Galena is moderately 

abundant, and pyrite and sphalerite are rare. Much of the 

galena is disseminated through the quartz in scattered individual 

grains and in thin veinlets, but some seams occur that are-as 

much as 3 inches wide. Most of the vein material is very vuggy 

and open-textured, and in places the vein is apparently a mineralized fault breccia at least 8 inches wide. The country rock 

of the region is hornblende gneiss of the Swandyke gneiss and 

strikes about N. 30° E. and dips about 75° E. The vein 

strikes N. 75° E. and dips steeply to the north. The early 

accounts of the mine in the Montezuma Mill Run, as well as 

the stope map shown in figure 30, indicate that the ore occurred 

in nearly vertical shoots or chimneys from 40 to 100 feet long 

separated by barren stretches along the vein. The presence of 

barite in the ore made it difficult to use before the days of the 

flotation mill but should present little difficulty to the modern 

ore-dressing plant.

The following are incomplete production records: 

Production of Wild Irishman mine

1SS3. .....................

1884.. . 

TQQC

1886.. 

1901.. 

1902...--.. . 

1907.. 

1913.- 

Ore 

(short 

tons)

30

35

48

56

28

35

113

Gold 

(fine 

ounces)

Silver (fine' 

ounces)

5,726

1,960

1,269

1,392

Lead, 

wet 

assay 

(pounds)

26, 353

29, 652

115, 736

Copper, 

wet 

assay 

(pounds)

45

Zinc 

(pounds)

No record available for 1887-1900; no production in 1903-6,1908-12, 1914-28. 

WINNING CARD

The Winning Card mine is on the south slope of Lenawee 

Mountain at an altitude of about 12,500 feet, at the head of the 

valley of the small stream that empties into the Sna'ke River 

at U.S.L.M. Adrian. It is about 2 l/i miles north of Montezuma 

and is reached by a Forest Service trail, which passes over the 

crest of Lenawee Mountain a short distance west of the mine. 

The vein was discovered in 1882 by Isaac Filger, and in 1885 

rich silver ore containing stromeyerite was found in it. As 

shown in the table below, several tons of high-grade ore was
FIGURE 30. Workings on Wild Irishman vein, Glacier Mountain.
116 MONTEZUMA QUADRANGLE, COLORADO

shipped in the next few years. According to the Montezuma 

Mill Run, a 50-foot shaft was sunk in 1885 where the original 

crosscut adit cut the vein, 30 feet from the portal. No ore 

was found east of the shaft at its top or bottom. In the main 

drift the ore was said to range from 2 to 6 inches in thickness 

and to average about 5 inches. This ore seam was nearly continuous for 130 feet. In 1886 the main drift had been extended 

to a length of 170 feet east of the winze and the vein was reported 

as being from 1 to 3 inches wide. At the bottom of the winze 

the vein was followed 90 feet east, but very little ore was found. 

The drift west from the bottom- of the winze followed a thin 

seam of quartz and stromeyerite for 60 feet. The ore in this 

drift was from 1 to 3 inches thick but increased slightly in thickness as it was stoped upward toward the main level. An 

analysis of the ore from the lower drift, by Robert Newman, of 

Georgetown, indicated that the sulphide contained 36 percent 

of copper and 40 percent of silver.

According to James Southerland, who leased the Winning 

Card in 1886, the vein strikes northwest and is vertical. The 

main ore body was about 30 feet long and about 100 feet from 

top to bottom. It was from 2 to 6 inches wide in most places

and consisted of nearly pure stromeyerite but had a small 

amount of quartz gangue. The ore shoot was vertical and 

nearly in the center of the Montezuma quartz monzonite stock. 

Partial production records are given below.

Production of Winning Card mine

lf&5.... ......................................

\9&Q... ................................... ....

19&1...... ....................................

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

Ore (short 

tons)

«25

7

1

(?)

Silver (fine 

ounces)

1,915

201

Copper, 

wet assay 

(pounds)

761

° Value, $25,090.

No production in 1884,1888.

YORKSHIRE

The Yorkshire mine is on the north slope of Glacier Mountain 

about a quarter of a mile west of Montezuma. The vein was 

discovered about 1880 and yielded 20 tons of ore in 1885 and 

18.86. No other work has been done on the property, so far as 

known, and it was inaccessible in 1929.
INDEX

Abstract of report.._____________ ... vn-ix 

Acknowledgments for aid___................................. .... 1

Adder volu, workings on and production of. .. 68

Algonklan (?) foraiatious, occurrence and character of... 6-11 

Algouklau system, occurrence and character of rocks of. .... .. .. 11-16

A'lgonkiau time, events of....._______-- . .- 49-50

Mladius Lamp vein, production of..____-. . .............. 91

Alluvium, occurrence and character of.___. . ..... 25 

Alteration, hypogono, features of.... . 42-43

Altoona vein, workings on and production of . 68 

American Eagle vein, workings on and production of. . - 68 

Anticline, pro-Cambrian, features of.___... ...-.... - 45 

Archoan quartz mon/.onito, correlation of_...- .-.. -- 6,13 

Argentine claim, production of._______ - 112 

Arrastro'Quoou mine, workings and production of.. . 99 

Atlantic vein, production of,__________...... .. 69

B

Baker lode, workings on and production of.... ...... ........ 69

Baltic vein, production of___._____..__._.__... 71

workings on__________............ .... ............ 69-70

Boar Mountain granite, correlation of..._ . . . . . 14 

Boll group of claims, production of........... . . .. 73

Boll mine, plan and longitudinal section of................. pi. 17

Boll vein, workings on______................................... .. 71-73

Belmont lode, workings on and production of... . . 73 

Bonton shale, correlation of________...... . 19-20

distribution and stratigraphic relations of. .. ......... 18

fOSSilS Of.................................. ........ ---- 19

lithologyof..............................---.. -.-.---. - 18-19

section of._________________......... ..... 22

thickness of.______________...___.......... 20

topographic expression of________ 19 

Bibliography________________. . 4-5 

Blanche vein, workings on and production of. 73 

Bond prospect, production of , 73-74 

Boston claim, production of_________.. 74 

Brilliant mine, workings of........__................... . ............. pi. 40

Britannic tunnel, features of________ 69-70 

Brittle Silver group of claims, production of... .. . -- 74 

Buda mine, workings and production of_.... ... -. 74

Buoua Vista mine, workings and production of ......... . 74

Bullion mine, production of.___ ... 75

workings of...._____________ . 74-75, pi. 19

Burchard, H. 0., quoted.....-....--........... ... - -- .- 81,83,87,113

Buster tunnel, features of._________....__ . 75, pi. 20

Cable claim, production of.________ . 87 

Cable mine, features of..__________ . . 75 

California claim, history of._._:____. . 71 

California group of claims, productipn of._ ...... 73

Cambrian time, events of._______.... ... .... .. . 50

Carboniferous system, occurrence and character of beds of. ..... 16

Carrie mine, workings of...:____________ .... ...... 75

Cashier mine, production of_______. 76

view from Teller Mountain near____ pi. 8

workings of. .1____________.. .. .. 75-76, pi. 21 

Celtic vein, general features of__________.______________ 85

production of________________...____...______.___ 83,85 

Centennial claim, general features of______.. .._____...___ 105

production of.________________________________ 112 

Champion mine, production of_______________________... 76

workings of ._____________________.__________ 76, pi. 21 

Ghatauquo mine, main (lower) adit of____________________. pi. 22

production of_______________. ________________ 77

workings of____________________________________ 76-77 

Chrysolite vein, production of... -.. . . - - - _.......... 77

Clarion mine, workings and production of... ........_________ 77

Climate, features of.___________..__.______..______ 3-4

Coaly vein. See Coley vein.

Coley vein, production of_________ ... .........____ 78

Collier Mountain group, production of..... .. 85-86

Colorado-Toledo claim, production of.______.. .-..._ 85-86 

Commonwealth claim, production of.._____......... .....--- 112

Commonwealth tunnel, features of..___...... ... .... Ill

Commonwealth vein, production of........._ . 104

workings on. 105 

Comstock vein of Sts. John mine, general features of. . . ... 101-102 

Congress mine, production of 78

workings of.________________________-_________ 78, pi. 23 

Contact-metamorphic deposits, occurrence of. . 59 

Copenhagen, general features and production of................ ... .. 78

Cretaceous formations, features of............--------- ...... .... 16-22

sections of__._ ....... __....._. --_. -.-*.. _ . 21-22

Cretaceous tune, events of . ...-. . . 50-51

D

Dakota quartzite, anticlinal dome of, cut through by Snake River pi. 7 

correlation of______ ...... 18

distribution and stratigraphic relations of .. ... 16-17 

lithologyof-. . 17 

section of_________ .... . 17 

topographic expression of __ . . . 17-18 

Delaware Extension claim, general features of. .... .. 78

Delaware vein, general features and production of.... . .... 78

Denver time, events of........ ........................... 50-51

igneous activity during .... ... ... ... 26,27

Denver vein, general features of... ..... ..... ... ._ . 85

production of..._____ . -_____ 83,85

Devonian time, events of 50 

Dikes and small masses, intrusive relations of.. .. . 49 

Diorite, augite, photomicrograph of.___ ... pi. 11

hornblende, photomicrograph of_... pi. 12

quartz, distribution, structure, and lithology of. 12

Don Pedro vein, general features and production of 78-79

Drainage, features of...__.... . 3

E

Eliza Jane vein. See American Eagle vein.

Enrichment of ores, occurrence of 62 

Eocene land surface, features of. 22-23 

Eocene time, events of. . '. .. . 51 

Equity adit, general features of.. . 83

workings on________..._.. .... .. -... pi. 26

Erlckson vein, general features and production of. 79 

Erosion surfaces of Montezuma quadrangle.. pi. 9 (in pocket)

Faults, transverse, of the mineral belt... . 48-49

Felsite group, petrographic descriptions of rocks of ._....--._._... 30,40

Field work_________________..___.......__..._____ 1

Fisherman mine, production of . .. . .. .. 79

workings of._______________________________ 79, pi. 23

Flattop peneplain, features of.___ - ._._......__.....______ 23

Front Range, post-Cambrian igneous and related structural history of__ 26-27

structure of__________.___________.....___... 43-45

G

Gabbro group, petrographic descriptions of rocks of ... . 31,40 

Geologic history____________________________________ 49-51 

Geologic map of Front Range..._____________________.__ pi. 5 

Geologic map of Montezuma quandrangle______..____ pi. 3 (in pocket) 

Glendale claim, general features and production of.. ... .......... 79

Gneiss, features of._____________________________ 6-8,10-12

granite, distribution and structure of.._____. . .____ 11-12 

lithologyof_______________________________ 12

quartz monzonite, distribution, structure, and lithology of._....___ 11 

Gold Belt tunnel, general features and production of____....__.___ 80 

Grand Trunk claim, general features and production of._._._______ 79 

Granite a.nd rhyolite group, petrographic descriptions of rocks of.____ 35-36,38 

Granite group, sodic, petrographic descriptions of rocks of. _________ 35,38 

Granite porphyry, photomicrograph of..___________________ pi. 12 

Gus Belmont lode. See Belmont lode.

117
118 INDEX

H Page 

Ham ill tunnel, general features and production of....._.__.__.- -- 80

Hancock vein, general features of. ... ...- . -- 80 

Hannibal vein, general features of...___-.__-.-._____..------- .. 80-81

Harrison vein, workings on and production of...--..- -.. 81 

Herman vein, general features of._____ .____-._--.__-_----.-.--- 81

Hollister, O. J., quoted._______ --_-_.__-_-_----_-..--_--.- - 65-66,69

Hoodoo mine, production of___ ._-_--__------__-.___ 86

Hornblendite, distribution, structure, and lithology of__._.____.. 12 

Hunkidori mine, production of_ ------- ...__--..-. .-.-.. 82

workings of______...____ _....-. .. -- 81-82, pi. 24

Ida Belle mine, plan and section of...-_______________ pi. 25 

workings and production of_ --------------------------- 82-83

Idaho Springs formation, distribution and age of____-..__------ -- 6

lithology of____-----_____.__ 6-S

structure and origin of-_______________-__--------- 8-10

view of, on east side of Grays Peak____________-...-_._ pi. 6 

Igneous history of the region, summary of..._____.___..-.---.-----. 26-27

Igneous rocks, Cretaceous (?) and Tertiary, correlation of.____.__--- 30

Cretaceous (?) and Tertiary, established relations of__.___... 27-30

general features of.___ . _.________----- 26-27

petrographic descriptions of..--. ----... 30-43

pre-Cambrian, occurrence and character of...--.___-------------. 6-16

Independence vein, workings on and production of-i-...__--------------- 83

Industries in the area_________._______.--.----.._----------- 4

Intrusions, differentiation of..._..__.____------------------------- 41-42

Intrusive rocks, chemical analyses of..._________.--...--.--....-. 36-37,41

Intrusive rocks, late silicic, petrographic descriptions of...___._----- 36,38

Iowa vein, general features and production of__.-__..._.-_---------- 83

Israel Williams claim, production of.___________._____.-._.-.- 79 

I. X. L. stockwork, features of_______-.-.-_.-.-._.-..------.---- 59-60

Jerry mine, photomicrograph of ore from..____...__._..-__------- pi. 14

production of._______________..______--------------- 83,85

workings on_____________________________. __ 83,85, pi. 26 

Johnson lode. See Belmont lode.

Josephine mine, general features and production of.._________ ... 85-86

workings of _____________________.__ - __ - __ - pi. 27

Jumbo mine, general features and production of._.... ..- ...-- 85-86

Jurassic system, occurrence and character of beds of.._...-.- ---- 16

Jurassic time, events of____________________________-- 50

K

Kelso mine, production of ___________________________- 86

workings of-____________________________. ______ 86, pi. 28

Kelso National mine, production of.____________.__.__... 86

Kitty Owsley mine, general features and production of..---.-... ---. 86

Lancaster vein, workings on and production of......_____1_.--_ 86

Laramie epoch, events of._____________.__.__-..___... 50

Leavenworth Creek, airplane view looking up__________..____-. pi. 1

Lincoln porphyry, correlation of.__________________--____-- 26

Little Jumbo claim, production of_____________-.-..__-..__.--- 85-86

Little Nell claim, production of____________...__-__-__---- 74

Location of the area._______..__________..__------------ 1

Loveland Pass, airplane view looking toward.------------------------------- pi. 2

Lucky Baldwin claim, workings on___-.__-.__-_-_-_------.--.--_-..-- 86,

M

Maid of Orleans mine, general features and production of_.----.-.-.------ 86-87

Mark Twain claim, workings on and production of._-.---.--.------------- 87

Mark Twain Extension mine, production of____-.-_------------------ 87

Marliu claim. See Roberta tunnel.

Maroon formation, occurrence and character of.... ---... -.. 16

Mary Etta group, production of.______________-______-__-- 80 

Medicine Bow peneplain, relations of, to Rocky Mountain peneplain_-... 23 

Meteor claim, history of.___________..__....__-.....-.--_... -71

Mineralization, possible centers of..._____._____.-__---__---- 60-61

Minerals, lists of....__________________..__-.__.-.-__-. 51-58

paragenesis of..._________________._._______.__. 58-59 

Minerou property. See Rothschild tunnel.

Mines, descriptions of._______________.________-..___ 68-116 

map showing locations of-_______.._..__......---- pi. 15 (in pocket)

Mining, history of_____________.__.___________._____ 65-68 

outlook for future...____________________.--.___.. 65

Mississippian time, events of__________ ________ ______ _ - 50

Missouri mine, general features of._______________________'.-- 87-88 

occurrence of bismuth ore in________________________- 88-89 

production of_______________________________.. 88 

workings of__________._____ ____________. ____- pi. 24

Page 

Mohawk mine, production of._____--....-.-.-.__..__..__......... 90

workings of.________________________._____ 90, pi. 29 

Montezuma stock, structural relations of.._____________.____.. 47-48 

Monzonite group, petrographic descriptions of rocks of.________ 31-32,39-40 

More Work mine, production of.__________.______._____._ 90

workings of._____.____________.________.___ 90, pi. 28 

Morgan mine, adits 1, 2, and 3...______________.__._____ pi. 30

workings and production of-.-...-_.__.__----..-.-----.-.__..-. 90-91

Morrison formation, occurrence and character of..--...__._...---..------ 16

Mount Kelso mine, production of...__.._.__..__....____....... 86

M U claim, production of-. _______________________ 112

N

National mine, production of--.... -...._____-..._.__.... ..... 86 

New York mine, production of...__--.-._-----------__-...-.__.... 91

workings of-_____________-._._____..-._------- 91, pi. 31

Niobrara limestone, correlation of..___..__._____................. 20-21

distribution, stratigraphic relations, fossils, lithology, and topographic

expression of- .. -... ........ ..... 20

. section of - . . 21-22

O

Old Settler vein, workings on and production of-__------------------------ 91

Old Timer mine, production of.._.______...__.._._-----.--... 92

workings of.____________________-_________----- 01-92, pi.32

Oligocene time, events of--.. ..--..-. ^...................... 52

Ordovician time, events of-....------- .........--.--..---.......--..... 51

Ore, enrichment of........ -.-----_-- ----_----.- ..---------... .. 60

localization of.-.-...---.-----------------.------------------.----------- 63-62

photomicrographs of --. --......-..-.--..-....-..--.--- pis. 13,14

relation of, to depth...-_.-- ... --------- -------- ___ _ 61-64

Ore, vertical range of deposition of.-.-. .-- -..-----.---...-.---------. 62-62

Ore deposits, features of..._-__.....~..................................... 59-63

minerals of.________-_----.-_------------------..-.-.-------- 53-55

Ore shoots, dimensions of___---- ------..--.--------------..- -.-..... 68

Orphan Boy vein, workings on and production of-.-----.-------.----.-.--.- 92

Paymaster mine, workings and production of. -... ..-. .. 

Paymaster vein, general features of ,.. .--. . ....

production of._____-. --------_.__ ..

Peary claim, production of.... .. ....... _ ......

Pegmatites, distribution and structure of ----------__------------

lithology of______ -.---._..._...........

Pennsylvania group, production of.... .. -------------__ ..

Pennsylvania mine, level F and part of level C in..--.-.-----.... ....

workings of- ___ --------- 

Pennsylvanian time, events of. .... .. ...

Permian time, events of.. ------- 

Peruvian mine, production of.. -.. ---.... -

workings of_____.. - .. ------------- 95-96,

Philadelphia claim, production of.-----.---.....-- . 

Philadelphia Mining Co., production of...- --.. --.. ----

Pierre shale, distribution and stratigraphic relations of------------ ------

lithology of..- ... -...

sections of_______ . 

topographic expression, correlation, and fossils of -------- . ---.

Pikes Peak granite, distribution and structure of..:----. -.-.-.---------.

lithology and age of... -- .-.-.. --------

Pleistocene deposits, early, occurrence and character of------------ -------

late, occurrence and character of . ----------------. --..

Pleistocene topography, early... ........ .

late--.-----.-._------- ... . ... .----...-

Pliocene time, events of..._________________...............

Population of the area...-. -- 

Potosi vein, workings on and production of- ..- . ..................

Power, sources of-----.-... . .-.-.--._..-------.----.---

Prospecting, suggestions for. . . ... ....-.

92

111

112

74

14-15

15-16 

95

pi. 33

92-94

50

50

95

pi. 34 

85-86 

85-86

21

21-22 

21,22

22

12-13 

33

24

25

23-24

24-25

51

1

96

4

64-65

Q

Quail mine, workings and production of__---------- -------- 96,97

Quartz monzonite group, petrographic descriptions of rocks of. 32-34,39 

sodic, petrographic descriptions of rocks of . 34-35,38 

Quartz monzonite porphyry group, intermediate, petrographic descriptions

ofrooksof 32,39

Quaternary deposits, occurrence and character of. . 24-25 

Quaternary time, events of. . -- ------ 51

Queen of the West vein, general features of------ -- -------- 96

R

Radical mine, general features and production of....-..- . 98 

Rainbow claim, development work on____.________.. .. 106
INDEX 119

Page 

Rainbow mine, production of.. ........^__.......... ....... 98

workings of.................................-............... ---- 98-99, pi.32

Raymond, R. W., quoted.......................................... 69,101,110,113

Recent deposits, occurrence mid character of_.............'......-.....-... 25

.Rod Jacket claim, production of..-...---....-----.-------------.------------- 99

Roosido, J. !.»., Jr., fossils iclontinocl by.......................... ... 19,20,22

.Revenue vein, production of...-....-......-....-...-......-.-...--- ----- 71

workings on............................................................. 69-70

Rhyolito porphyry, photomicrograph of............ ....................... pi. 12

Roberta tunnel, development of..........-..-.-------.----------------------- 99

Rochester Queen mine, workings and production of-......--------.--------- 99

Rocky Mountain peneplain, general features of-........-.--....--.---------- 23

Rosalie granite. See Pikes Peak granite.

Rosongarton group, production of................--..-.-......-.-------- 85-80

Rothschild tunnel, general features and production of.........--...-......-- 99

Royal '.rigor Minos Co., general features of property of..................... 99-100

Ruby Gulch, view looking oast at......................................... pi. 7

St. Cloud claim. Sec Tiger claim.

St. .Elmo claim, workings on and production of...-...--......----------.---- 87

Sts. John mine, general features of . ..... . ----- ---- 100-104

lower level of..----.-------------..----------------------------- ------ pi. 35

production of..___......___.__................. ----- 104

Samarskito, determination of ago of Pikes Peak granite by lead-uranium ratio

Of-.-.-...-.-.---.--..- -------------------------------- 13

Santa Fo granite, correlation of.--...-..........-.---------------...---.---.- 14

Santiago mine, levels 3 and 5 of__.........-.........-.....-- ............ pi. 36

photomicrograph of oro from__..._............. ...--. ......... pi. 13

workings and production of__....._...........__...... ----- 104-105

Sarseflold mine, workings and production.of...... - - - -- 106

Schist, minerals of..........-... . _______.....__.... ... . 8

processes of formation of...._.._______... - 9

quarte-blotlto, features of.....________._ . ...... 6-8

ciuartz-biotito-sillinianito, photomicrograph of................. pi. 6

Sedimentary formations, age and occurrence of.... ..... ... ... 16

Seven-thirty claim. See Paymaster mine.

Shoo Basin vein, workings on and production of.. . 95-96

Sill mine, general features of.______....... . ......... ... 106

Silver Ball claim. Sec Paymaster mine.

Silver Cord claim, workings on and production of.... .... ....... 106-107

Silver King mine, general features of..._._..__. . .--- 107-108 

production of.___........................................ ....----- 108

upper and lower adits of......................................... -----. pi. 37

Silver oro, photomicrograph of._.......____.... - - ... pi. 14

Silver Plunio granite, distribution and structure of....... 13-14

llthologyof.............-.... -.......-- . .- 14

photomicrograph of..................._ . - pi. 11

Silver Plume tunnel, production of........_____-_ . . SO

Silver Prince mine, general features and production of... .... ... 108 

Silver Wave mine, level 5 of-.....................----...-.-.-.- ... pi. 10

production of.___.______....___........ 109

worklngsof . --------------- - ----- 108-109

Silver Wing claim, history of..._.___..___ - 71

Silver Wing tunnel............................. .------- -- pi. 18

Smelter Gulch, glacial lake at head of__ ..... pi. 10

Smith, W. B., quoted.................................. .. - 98

Snake River, view looking oast up_...................... . _ .. pi. 8

Spelter King tunnel.._...._.______........ .... - pi. 18

Stanton, T. W., fossils identified by................. - -- 19

Star of the West mine, general features and production of.................... 109

Star of the West no. 2 mine, general features of--.-- 109

map of..._.............................___ pi. 23

photomicrograph of oro from dump of....__.... . - pi. 14

Slovens claim, production of..._ ------ ........... 112

Page 

Stevons Gulch, rock glacier at head of... ............i.,..,................ pi. 10

Stevens mine, general features of.-.--..---------.- ..-.- ...._........ 109-110

photomicrograph of ore from......................................_... pi. 13

production of.... - - -._ _.__. ..__________... 110

workings of __ . ... . .. _ ___ pi. 38

Stockworks, occurrence of...-........ ..-. ........_..................... 59-60

Structure, Laramide, features of ---- _.......... 47-49

pre-Cambrian................................................__.... 43,45-47

regional..________.________........_____._....__..._ 43-45

sections showing-.. ... . -.. ................_..... pi. 4 (in pocket)

Sunburst claim, features of..------.--.-...-.-...-.. ............_........ 71

Sunrise claim, general features of..--.... ..................._...... . 78

Swandyke hornblende gneiss, distribution, name, structure, and lithology of.. 10-11 

origin of.. ----.-.---.-----------.- ... .......... .... ...... 11

typical exposure of...-..---------..--.----.-.----.- .__.............. pi. 7

T 

Tariff vein, production of-..-._.........._....................____. 99

Tertiary land surface, late, features of...__...___...__._______ 23 

Tiger claim, production of................................................... Ill

workings on_.--..._ .. _ ._ ___............ 110,111

Tiger Extension claim, production of_ . ..__....._......__.._.. Ill

Timber, distribution of_._.------.-.----.-.-...___-.-------...__.. 3

Tobin claim, production of.-.. ........................................... 112

Toledo tunnel, general features of._------------_.__............. ill, pi. 39

Topographic map of Montezuma quadrangle.-,--.---._---..-. pi. 15 (in pocket) 

Topography, evolution of.__..__...__... .. _____.......____.. 22-25

features of. . - - . ... 

Recent._...........................

Transportation, features of... __........

Treasure Vault claim, general features of. 

Triassic time, events of- .-- .. ..

2

25

4

79

50

V

Veins, general features of _-----..... . _..__ ....... 60-64

mineral associations in__.. . ......._.............. 61

types and distribution of..---------- ........._....... '. 60

Vidler tunnel, general features of..__------.-.-...._............... 111

W 

Waldorf mine, general features of_______.__._________..... Ill

production of...---.--.....__ ---- __._.............._..... 112

Washington vein, general features and production of.____-_ -- _... 112 

Waterloo claim, general features of............ ................... ... 91

production of._____.__-...._.______.____.__....__... 85-86

Waukeegan vein, general features and production of...__.._..-----... 112-113

Weathering, effects of..._-_._____.____.__......_____ 43

Whale mine, general features of._..--..-.- _.___................ 113-114

production of_... .._._. ___-------__-.....----_....... 114

workings of._____.........................___..........-.----__ pi. 40

White porphyry, correlation of ____...........................___.. 26

White Sparrow claim, production of-___._________.________. 74 

White Swan vein, general features of...........____.....__... ..... 114

Wild Irishman mine, general features and production of.._ -- 114-115

Williams Range thrust fault, features of_......__.................... 44-45,47

Windsor claim. See Tiger claim.

Wing adit, features of.......__..__-.-....__..........__...__.... 72

Wing claim, history of-__-....__...__................._..-__.... 71

Winning Card mine, general features of.___._________._.___ 114,116

production of._________._____..._.___..._________ 116 

Wisconsin deposits, occurrence and character of....__......._...-....-. 25

Y 

Yellowjacket vein, features of._-------___..-.___..........__.... 74-75

Yorkshire mine, general features and production of...---.._......_.._- 116

Z 

Zinc ore, photomicrograph of._........__--------__.._.___... pi. 13

o

71886 30 !>