Bulletin No 254 Sfirifls / A) Economic Geology, 49 Bulletin no. &A benes | ^ Descriptive Geologyj 61

DEPARTMENT OF THE INTERIOR 

UNITED STATES GEOLOGICAL SURVEY

CHARLES D. WALCOTT, DIRECTOR

REPORT OF PROGRESS

GEOLOGICAL RESURVEY OF THE CRIPPLE 

CREEK DISTRICT, COLORADO

BY

WALDEMAR LINDGREN AND FREDERICK LESLIE RANSOME

WASHINGTON

GOVERNMENT PRINTING OFFICE

1904

CONTENTS.

Page.

Letter of transmittal...................................................... 5

Introduction............................................................. 7

Production ......_........_._..... ...:......................_...._....... 8

Mining and metallurgy ................................................... 9

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

General geology. ............................................'.......^...... 11

First geological survey of the district ................................... 11

Modifications of earlier results ......................................... 12

Economic geology ................ '........................................ 14

Earlier work........................_.----...--..-.--................ 14

Extent of productive territory......................................... 14

Underground development............................................ 15

Brief review of the mines............................................. 15

Character of the ores ................................................... 20

Structural 'characteristics of the deposits .............................. 22

Types of.deposits..................................................... 22

Depth of oxidized zone ............................................... 26

Eelations of ore bodies to depth....................................... 26

Underground water ....................................................... 31

Subterranean gases....................................................... 32

Future of the district..................................................... 33

Index .............................i..................................... 35

'.LETTER OF TRANSMITTAL.

DEPARTMENT OF THE INTERIOR, 

UNITED STATES GEOLOGICAL SURVEY,

Washington, D. C. , November 3, 1904-

SIR: I have the honor to transmit herewith the manuscript of a preliminary report on a "Resurvey of the Cripple Creek district of Colorado," by Messrs. Waldemar Lindgren and F. L. Ransome, under my 

general supervision.

Although only ten years had elapsed since a careful study of the 

geology of this district was made by Messrs. Cross and Penrose, the' 

people of Colorado had been so strongly impressed with the economic 

importance of a scientific examination of the ground opened by mining 

operations during that period, that they urgently requested this resurvey and have materially assisted in its execution.

The present report, made in advance of the final laboratory examinations, is a summary .of those facts that bear upon the economic 

development of the region and are of immediate importance to the 

miners. 1 therefore request that it be published with the least.possible dela}^, that its results may be promptly available to all interested 

in the region.

Very respectfully,

S. F. EMMONS,

Geologist in Charge Section of Metalliferous Deposits. 

Hon. CHARLES D. WALCOTT,

Director United States Geological Survey.

REPORT OF PROGRESS IS THE GEOLOGICAL RESURVEY 

OF THE CRIPPLE CREEK DISTRICT, COLORADO.

By WALDEMAR LINDGREN and FREDERICK LESLIE KANSOME.

INTBOPTTCTIOlSr.

The Cripple Creek gold deposits were discovered in 1891. Shortly 

afterwards, in 1894, an examination of the new district was undertaken 

by the United States Geological Survey, Mr. Whitman Cross having 

charge of geology and petrography and Mr. R. A. F. Penrose, jr., 

undertaking the examination of the mines. Their report, accompanied 

by a geological map, was published in the Sixteenth Annual Report of 

the Geological Survey, Part II, pages 1-207, and has for the last ten 

years served as a useful and accurate geological guide .to mining 

. operations.

With the astonishingly rapid development of the Cripple Creek 

mines the opportunities for geological study multiplied, revealing 

great complexity of vein phenomena and stimulating a desire for further investigation, particularly with a view of obtaining some evidence 

as to the persistence of the veins in depth. This desire found expression in a request by citizens of Colorado for a reexamination of the 

district by the United States Geological Survey and in an offer of 

cooperation, whereby the cost would be equally divided between the 

State of Colorado and the National Survey. The necessary amount 

having been subscribed in Cripple Creek, Colorado Springs, and Denver, the State contribution was put in the hands of Mr. John Wellington Finch, State geologist of Colorado, and by him disbursed. The 

cordial thanks of the geologists in charge of the work are due to Mr. 

Finch for his heart}^ and efficient cooperation.

The reexamination began with a thorough revision of the topographic 

map of Cripple Creek by Mr. R. T. Evans, Mr. E. M. Douglas in 

charge. This involved a great deal of painstaking workj nearly every 

prospect hole being located, as well as all shafts and tunnels. The 

new map is on the scale of 1:19,495, or about 2£ inches to the mile, 

and includes practically the same area as the old map, a small strip 

only being added on the western side, so that the total area mapped is 

about 40 square miles. The small developments outside of this area
8 EESUEVEY OF CRIPPLE CREEK DISTRICT. [BULL. 264.

did not seem to justify further extension of the boundaries. Contours 

are 50 feet apart, and a numbered list of 324 mines is given on the 

margin of the sheet. A line of accurate levels was run to Cripple 

Creek from Colorado Springs, thus settling the conflicting data of the 

different railroads.

The geological and mining work was undertaken jointly by the 

authors of this preliminary report. The examination began in June, 

1903, and, with some interruptions, due to various causes, the field 

work was concluded in April, 1904. Practically every accessible mine 

in the district was examined in greater or less detail. Mr. L. C. Graton served as assistant throughout this time, actively participating in 

all branches of the work. Messrs. A. M. Rock and J. Bruce also 

rendered very efficient aid as draftsmen.

PRODUCTION.

Though situated close to the centers of population in Colorado and 

in an easily accessible region, the gold deposits of Cripple Creek were 

not discovered until 1891. To a great extent the lateness of the discovery was due to the extremely inconspicuous character of the vein 

croppings and to the equally inconspicuous appearance of the darkbrown, powdery gold set free by the oxidation of tellurides. As soon 

as the true character of the veins was ascertained the development of 

the district proceeded rapidly. In 1894, when the first survey was 

made, the production was a little less than $3,000,000, but the next 

year this amount was more than doubled, and in 1900 the maximum 

production of a little over $18,000,000 was attained. In 1901 and 

1902 the production declined slowly, and dropped the next year to 

$13,000,000. The sudden decrease in 1903 was to some extent brought, 

about by the impoverishment of several mines, but the labor troubles 

of that year had also much to do with it. From August, 1903, to 

the summer of 1904 many mines experienced more or less difficulty 

from this cause. It is probable, however, that the output for the 

current year will show a considerable increase over that of 1903.
LINDGREN ANDl 

KANSOME. . J

Production of the Cripple Creek district according to the reports of the Director of the Mint.®

Year.

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

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

1893.1............

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

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

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

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

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

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

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

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

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

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

Total.......

Gold.

$449

583, 010

2, 010, 367

2, 908, 702

6, 879, 137

7, 512, 911

- 10, 139, 709

13, 507, 244

15, 658, 254

18, 073, 539

17,261,579

16, 912, 783

12, 967, 338

124, 415, 022

Silver.

Fine ounces.

5, 019

25, 900

70, 448

60, 864

57, 297

68, 195

82, 520

80, 166

90, 884

62, 690

42, 210

646, 193

The total dividends can not be ascertained on account of the many 

individuals and small companies operating in the district. The dividends of the larger companies, it is stated, amounted to $32,752,000 to 

the end of 1903. In that year it is reported that $1,716,000 was paid 

by fourteen mines, Portland, Strong, and Stratton's Independence 

leading, with $360,000, $300,000, and $250,000, respectively.

MINING AND METALLURGY.

At the present time there are about 300. mines in the district, though 

many of these are idle and others are consolidated into larger properties. The number of shafts 1,000 feet or more in depth is about 22; 

of these the Lillie is the deepest, having attained 1,500 feet. Comparatively few of the mines are pumping, the district being drained by 

tunnels, as will be described in a following paragraph. The motive 

power for hoisting is ordinarily steam, electric power being used only 

in smaller shafts. The mining methods employed present few features 

of particular interest. The width stoped ranges from 3 to 50 feet or 

more. The stopes are sometimes filled, but are of ten left open after 

the broken rock between levels has been drawn off. Operations are 

facilitated by the great hardness of the rock, stopes 200 feet or more 

in .height sometimes standing for years. To an annual production of 

$18,000,000 (1900) corresponded a maximum output of about 600,000 

tons. The ores are not adapted to concentrating by ordinary means.

a The figures given in the Mint reports are considerably lower than those usually quoted in mining 

journals and popular descriptions of the district.
10 RESUEVEY OF CRIPPLE CREEK DISTRICT. [BULL.254.

Hand sorting and washing-, the latter in order to separate the fines, are 

the methods employed. More care is now taken than formerly, but 

at many places there is still room for improvement.

The district contains many large mines operated by strong companies, but the system of leasing to individuals and small companies, with 

royalty charges of 15 to 25 per cent of the net output, remains a 

conspicuous feature. At the present time the mines of the northwestern and northeastern parts of the district are only slightly productive. Among the formerly highly productive mines in this section 

may be mentioned the Victor, Isabella, Wild Horse, Damon, Logan, 

Orpha May, Pharmacist, C. 0. D., Gold King, and Anchoria-Leland. 

The southwest quarter of the district contains the active and important El Paso, Mary McKinney, and Elkton mines, but the maximum 

output during the last few years has come from the southeastern portion, within which are the Portland, Gold Coin, Ajax, Strong, Golden 

Cycle, Vindicator, and Last Dollar mines. The Portland mine has for 

some time been the heaviest producer in tonnage as well as in value. 

Its output is from 60,000 to 90,000 tons per annum. In 1903 this 

mine produced $2,600,000.

The metallurgical history of the camp is interesting. Beginning 

with local amalgamating mills, the .practice soon changed to local 

chloririation and cyanide plants. It was soon found, however, that 

better situations would be found in the valleys, and at present a very 

large part of the tonnage is shipped to chlorination and cyanide works 

at Colorado City and Florence. About a sixth of the output, comprising the higher grade ores, is sent to smelting works at Denver 

or Pueblo. A still smaller amount is treated in a local chlorination 

plant near Victor. While in former years the practice leaned more 

toward the cyanide process, the bulk of the ore is now treated in large 

chlorination mills with automatic roasters and revolving barrels. .It 

has always been found necessary to roast all except the completely 

oxidized ores. At the present time there are in the district two small 

mills in which the cyanide process is used without previous roasting, 

and which are thus enabled to work ores containing as little as $5 a 

ton in gold. The extent of these low-grade ores is not yet fully 

demonstrated. Regarding the value .of the ore, see page 21.

Treatment charges at the mills fluctuate somewhat, but usually range 

from $7 to $13 a ton, according to the tenor of the ore; in the early 

part of 1904 the prices were reduced, it is reported, and ranged from 

$5.50 to $10 per ton. Recently they have again been increased. On the 

whole the mining and milling expenses are very high at Cripple Creek 

compared with those of other localities western Australia, for example, where similar ores and conditions prevail. Few of the large 

mines seem to have reduced total expenses below $16 per ton.
LINRDAGNSOME.ND] TOPOGRAPHY AND GENERAL GEOLOGY. 11

TOPOGRAPHY.

The mines are situated in a group of bare, rounded hills forming 

part of the high plateau extending south westward from Pikes Peak, and 

are only about 10 miles distant from that prominent landmark. The 

elevations range from 9,000 to nearly 11,000 feet above sea, the highest 

point in the district being Trachyte Mountain (10,863 feet). Bull 

Hill and Bull Cliff are but slightly lower. The drainage is chiefly 

southward toward the Arkansas River. The district contains two 

important towns. Cripple Creek is situated on the northwest side of 

the producing area, while Victor, 3 miles distant, lies on the southwest edge of the same area. Two railroads connect the district with 

Colorado Springs, the Colorado Midland circling around the. north 

side of Pikes Peak, while the Short Line descends to the valley along 

the picturesque eastern slope of the same mountain. The Florence and

Cripple Creek Railroad runs southward to Florence in the Arkansas 

Valley. An excellent system of electric-car lines connects the towns 

with all the important mines.

GENERAL GEOLOGY.

FIRST GEOLOGICAL SURVEY OF THE DISTRICT.

When Mr. Whitman Cross made his careful study of the geology of 

the Cripple Creek district, ten ye&rs ago, mining had barely begun 

and the various hills were not, as now, perforated by deep underground workings. That his work has in general stood the test of 

subsequent ^underground exploration and continues to be highly 

regarded in the district is convincing proof of its high quality. Later 

workers, however they may modify or amplify his results, should 

acknowledge their debt to the pioneer who first deciphered the 

history of this volcanic district. The account of general geology, as 

given by Cross, may be very briefly summarized as follows:

The Cripple Creek hills lie near the eastern border of an elevated 

and much dissected plateau which slopes gently westward for 40 

miles, from the southern end of the Colorado Range, dominated by 

Pikes Peak, to the relatively low hills connecting the Mosquito and 

Sangre de Cristo ranges. The prevailing rocks of this plateau are 

granites, gneisses, and schists. The granites inclose masses of Algonkian quartzite and are therefore post-Archean. But they are older 

than the only Cambrian sediments known in Colorado, and on the 

Cripple Creek map have been indicated as Algonkian. During 

Tertiary time volcanic eruptions broke through these ancient rocks at 

several points and piled tuffs, breccias, and lavas upon the uneven 

surface of the plateau. The eruptive rocks of the Cripple Creek 

district are the products of one of the smaller isolated volcanic centers
12 KESUEVEY OF CEIPPLE CREEK DISTRICT. [BOLL. 254.

of this period, a center characterized by the eruption of phonolite, 

which does not occur elsewhere in this general region.

The most voluminous products of the Cripple Creek volcano now 

preserved are tuffs and breccias. They occupy a rudely elliptical 

area in the center of the district, about 5 miles long in a northwestsoutheast direction and about 3 miles wide. According to Cross these 

breccias and tuffs rest in part upon an earlier flow of andeslte, but 

mainly upon an unevenly eroded surface of the granites and schists, 

although along the southwest edge of the area the contact was found 

to be so steep as "to support the idea that the central vent or vents of 

the volcano were adjacent to this line." The breccia is much indurated 

and altered, but was thought by Cross to consist mainly of andesitic 

fragments, although it was recognized that fragments of phonolite are 

locally abundant. The most characteristic massive rock of the Cripple 

Creek volcano is phonolite, which was erupted at several periods and 

more abundantly than any other type. It occurs as dikes and masses, 

not only in the breccia but in the surrounding granitic rocks.

The general succession of igneous rocks, according to Cross, is as 

follows: The earliest rocks were andesites containing some orthoclase. 

Then came a series of allied phonolitic rocks, rich in alkalies and moderately rich in silica, together with some andesites. Among them are 

trachytic phonolite, nepheline-syenite, syenite-porphyry, phonolite, 

mica-andesite, and pyroxene-andesite. Phonolite was erupted at several periods. The nepheline-syenite he considered as probably younger 

than the trachytic phonolite. At the close were intruded a small number of narrow dikes of basic rocks, the so-called basalts, which contrast 

very markedly with the phonolite. .,,

MODIFICATIONS OF EARLIER RESULTS.

In the course of the present investigation the geology of the 

district has been entirely remapped upon the carefully revised topographic base. The granites, gneisses, and schists have been differentiated and outlined in greater detail than was practicable in the earlier 

investigation. The oldest rocks in the district are muscovite- and 

fibrolite-schists. These are closely associated with the fine-grained 

granitic gneisses such as underlie most of the town of Cripple Creek. 

This gneiss, in the earlier report, was mapped partly as schist and 

partly as granite. Both gneiss and schist are cut by a reddish granite 

which occupies a considerable area extending from Anaconda westward beyond the limits of the area studied. This granite is well 

exposed along Cripple Creek in the vicinity of Mound.

A second type of granite distinguished and mapped is the coarsely 

porphyritic rock referred to by Cross as the Pikes Peak type of granite. 

This rock occupies over half of the district and is the prevailing type
] ^ GENEBAL GEOLOGY. 13

along the northern, eastern, and southern borders of tut; area. It is 

well exposed on Squaw Mountain and is the granite of the El Paso, 

Elkton, Ajax, Portland, Independence, and Gold Coin mines. Of 

these two kinds of granite the Cripple Creek variety is probably the 

younger. The Cripple Creek granite, the gneiss, and the schist 

together form a wedge-shaped area projecting into the Pikes Peak 

granite from the west. The center of volcanic disturbance practically 

coincides with the point of this wedge.

The present investigation indicates some necessary modifications of 

the earlier report in the way of stronger emphasis on the intimate 

genetic relationship of the rocks. The "phonolite," "nephelinesyenite," "trachytic phonolite," "syenite-porphyry," and "andesites" 

of Cross are all very closely related and have been found to be in most 

cases connected by intermediate types. They are clearly all slightly

divergent eruptive facies of one general niagraa characterized chemically \>y containing from 9 to 15 per cent of potash and soda, the soda 

being always somewhat higher than the potash, particularly when the 

comparison is made by molecular ratios. None of the massive rocks 

can properly be called andesite, and although it can not be affirmed 

that andesitic fragments are entirely absent from the usually much 

altered volcanic breccia, the term "andesitic breccia" does not seem 

applicable to this formation as a whole. It would be more accurate to 

describe it as a phonolitic breccia, although in places it consists chiefly 

of particles of the older rocks through which the Tertiary eruptives 

broke.

None of the massive rocks erupted from the Cripple Creek volcanic 

center and now preserved in the district show any evidence of having 

been surface flows. They are for the most part intrusive porphyries, 

ranging in texture, however, from the granular so-called nephelinesyenite near the town of Independence to the nearly aphanitic phonolite of the smaller dikes and sheets. Most of them will come under 

the designations phonolite, trachytic phonolite, trachydolerite, and 

alkali-syenite. The extensive underground workings show that the 

"nepheline-syenite" does not cut the "trachytic phonolite," but that 

the tSvo rocks represent textural and, to some extent, mineralogical 

facies of the same mass, while the trachytic phonolite in turn may pass 

into phonolite. The trachytic phonolite is in some instances cut by 

dikes of phonolite, showing, as Cross has already pointed out, that the 

-phonolitic intrusions were not all synchronous.

While it is undoubtedly true that much of the breccia in the northeastern part of the volcanic area rests upon a very uneven surface of 

granite, gneiss, and schist, the results of field work during the last 

season, favored by deep workings not in existence when the district 

was originally surveyed, have emphasized the fact that the breccia 

lying southwest of a general northwest-southeast line drawn through
14 EESUEVEY OF OEIPPLE CEEEK DISTEICT. [BULL. 254.

Big Bull Mountain and Gold Hill occupies a chasm of profound depth 

in the fundamental rocks of the region. From the Conundrum mine 

on the western slope of Gold Hill to Stratton's Independence mine on 

the south slope of Battle Mountain the contact plunges steeply down, 

with dips ranging in general from 70° to vertical. In some instances 

the granite walls of this chasm actually overhang the breccia. It is 

probable that this entire southwest contact represents a part of the 

wall of the great pit formed by the volcanic explosions that produced 

the breccia. It is further probable that an arm or branch of this 

volcanic abyss, now filled with breccia and intrusive rocks, extends 

northeastward past Bull Cliif and the town of Altman.

ECONOMIC GEOLOGY.

EARLIER WORK.

To the excellent work of Mr. E. A. F. Penrose, jr., apply statements 

similar to those made in the discussion of the purely geological branch 

of the subject. Few shafts had then attained a depth of 400 feet, and 

most of the exposures were masked by surface oxidation. It would 

be surprising, in view of the facilities created by the later development of hundreds of mines, if a subsequent investigation should not 

bring out some slight modifications of earlier results.

EXTENT OF PRODUCTIVE TERRITORY.

There is nothing in the history of the district since 1894 warranting 

any extension of the bounds of the productive territory as then known. 

Now, as then, a circle of 3 miles radius described from the summit of 

Gold Hill would include all deposits of known or prospective value, 

while the really important mines would be embraced by a circle of about 

half that radius, with its center near the summit of Raven Hill. That 

scattered deposits of greater or less value may be found in outlying 

portions of the district is by no means improbable. But the close 

dependence of the typical Cripple Creek ores upon the main volcanic 

center, and the consequent remarkable compactness of the gold-bearing 

area, are features highly characteristic of the district and are likely 

always to remain so.

The greater part of the ore has undoubtedly come from the central 

area of breccia, particularly from that part of this area in which the 

breccia extends to great depth. Very productive ore bodies have 

been found, however, in the granitic rocks, usually within 1,000 feet 

of the steep contact limiting the breccia on the southwest. The important Beacon Hill mines, with ore bodies nearly three-quarters of a 

mile from this contact, are exceptional, and are probably genetically 

connected with the intrusive mass of phonolite. forming the core of 

the hill. .
ECONOMIC GEOLOGY. 15

UNDERGROUND DEVELOPMENT.

At the time of the earlier survey the deepest shafts, those of the 

Moose, Pharmacist, and Anna Lee mines, were down only about 400 

feet, while few of the other mines were over 200 feet in depth. Many 

subsequently prominent mines were then mere prospects or had not 

been located.

The deepest shaft at present is the Lillie, which is over 1,500 feet 

deep, although the Stratton's Independence shaft, 1,400 feet deep, has 

the lowest sump in the district. The American Eagle shaft is nearly 

as deep as the Lillie, while there are about twenty other shafts over 

1,000 feet in depth, and at least 100 shafts deeper than the deepest 

workings existing in 1894. As regards absolute elevations, the Gold 

Hill shafts are scarcely down to a level of 9,000 feet above sea; the 

Elkton, El Paso, and Lillie shafts descend to 8,750 feet; Stratton's 

Independence reaches the lowest level at 8,450 feet; while the Gold 

Coin shaft, at 8,550 feet, is of interest from the fact that the deepest 

ore shoot in the district is now being stoped f rom its twelfth level.

The amount of drifting and crosscutting accomplished since the 

earlier survey is more than commensurate with the increased number 

and depth of the shafts, and the district is further intersected in various directions and at different levels by two long tunnels run for 

drainage purposes and by a dozen or more extensive adits, many of 

which have their portals in the granitic, rocks and extend well into the 

central part of the breccia area.

BRIEF REVIEW OF THE MINES.

The productive district, as stated above, is practically covered by the 

area of a circle 3£ miles in diameter. The center of this circle would be 

located halfway between Raven Hill and Bull Hill, and the towns of 

Cripple Creek, Victor, and Cameron would be situated on its periphery. 

A very few mines notably the Galena and the Fluorine and many 

prospects lie outside of this area.

The culminating points of the district are found in a ridge of high 

and bare hills that extends in a northwest-southeast direction and 

divides the waters flowing into Cripple Creek and Wilson Creek on the 

southwest from those joining Spring Creek and Grassy Creek on the 

north. From northwest to southeast the following hills mark this 

divide: Mineral Hill, Carbonate Hill, and Tenderfoot Hill, north 

or northeast of Cripple Creek; Globe Hill, Ironclad Hill, and Bull 

Hill, the latter being near the center of the district and equidistant 

from Cripple Creek and Victor; the ridge is continued by Bull Cliff 

and Big Bull Mountain, the latter, really outside of the productive 

area, being the highest point in this dividing range of hills. Its elevation is 10,826 feet. Three long spurs project to the southwest from
16 RESURVEY OF CRIPPLE CREEK DISTRICT. [BULL. 254.

the dividing range separating the deep trenches of Cripple Creek, 

Squaw Gulch, Arequa Gulch, and Wilson Creek; the first, called Gold 

Hill, rises directly east of Cripple Creek; the second is Raven Hill, 

being continued to the southwest by the lower spur of Guyot and 

Beacon hills; the third is Battle Mountain, continued by the almost 

equally high salient of Squaw Mountain.

The important mines are situated in this region of sharply accentuated topography. As has been several times emphasized, the volcanic 

area practically coincides with the hills and ridges just described and 

is surrounded on all sides by granitic rocks.

Globe and Ironclad hills and Gold and Raven hills consist chiefly of 

heavy masses of breccia, and were, scenes of great activity during the 

early years of the district. Near Poverty Gulch, just northeast of 

Cripple Creek, is the Abe Lincoln, not a large mine, but still actively 

worked with satisfactory results. Higher up are the Gold King, with 

dividend records of $150,000, and the C. O. D., with a reported production of $600,000 and dividends of $150,000. Both were idle in 1904 

and have attained their eighth or ninth levels.

On the summit of Globe Hill'are the Stratton properties of Plymouth Rock and Globe mines, in which extensive low-grade mineralization without many sharply defined veins seems to be .the rule. 

Adjoining is the property of the Homestake Company, including the 

Ironclad mine, where direct cyaniding of oxidized surface ores is now 

carried on in a mill erected on, the property.

Gold Hill is crowned by the Anchoria-Leland mine, with a production of over $1,000,000 and dividends of $198,000. The shaft is 1,100 

feet deep. The adjoining Moon-Anchor has paid dividends of $261,000, 

and the Half Moon (Matoa G. M. Go.) has a gross production of $650,000 

to its credit, but is reported to have paid only a small amount in dividends. None of these mines is being worked at present, except on a 

small scale by lessees.

On the western slope is the Midget mine, actively worked at present, 

with a depth of 800 feet, a total production of $662,000, and dividends 

of $195,000. The Conundrum, in the same vicinity, is likewise worked 

with good results to a depth of 600 feet. The Midget, like the mines 

described above, follows a vein in breccia, while the Conundrum is mining on a "basalt" dike in granite, close to the contact of the breccia.

In the deep gulch between Gold Hill and Raven Hill are situated 

the Anaconda, Doctor-Jack Pot, and Mary McKinney mines, all working on sheeted zones forming lodes in the breccia. The Anaconda produced about $1,000,000, chiefly from upper levels, and is now idle. 

The Mary McKinney is one of the most successful mines worked at 

present in the district. Its depth is 600 feet. The Doctor-Jack Pot 

has $4,000,000 to its credit and likewise a handsome dividend record.
LINDGREN ANBT , _ MTTNTtfC} 1 7 

RANSOME. J 1MA M1IN.IW3. 1 <

The shaft is only YOO feet deep, water having until now prohibited 

deeper sinking.

The breccia-granite contact is found on Guyot Hill a short distance 

south of the Mary McKinney. The extreme spur of Raven Hill, 

called Beacon Hill, is formed of an intrusion of phonolite in granite, 

and about this outlying volcanic center cluster a group of veins of 

great production and promise. On the eastern side of the hill are 

located the Prince Albert, Gold Dollar, and others, not active producers at present, while on the western side lie the El Paso, C. K. 

& N., and Old Gold mines, with their narrow but extremely rich fissure veins in granite, now activety and successfully worked.

A great number of smaller mines have been worked on veins cutting the breccia of Raven Hill. The famous Elkton mine is situated in 

the deep hollow between Raven Hill and Battle Mountain. It has been 

working on an exceptionally long vein, partly contained in breccia, 

partly in granite, and generally following a "basalt" dike. The production approaches $6,000,000, and the depth .attained is about 900 feet, 

excessive water having formed a serious obstacle to deeper sinking. 

Dividends amount to $1,200,000. The Moose mine, situated higher 

up on the slope of Raven Hill, had a good ore shoot, from which 

$500,000 was obtained.

Continuing northwest, we soon attain the summit of Bull Hill, which 

affords a magnificent panorama, not only of the whole camp, but of 

a large part of the State of Colorado. Toward the east, and 5,000 feet 

lower, spread the great plains at the foot of the Rocky Mountains; 

westward the Sangre de Cristo, Collegiate, and Mosquito ranges a 

snowy and jagged line of ramparts define the distant horizon.

A multitude of small mines occupy the southwestern slope of Bull 

Hill. On the northwestern side an area of brecciated granite appears 

among the volcanic rocks, and in this formation is situated the Wild 

Horse mine. This lode, which has been.worked to a depth of 1,250 

feet, has produced over $1,000,000, but is now operated only by 

lessees. A number of smaller producers may be found on the northern slope, toward Cameron, among them the Damon, Jerry Johnson, 

W. P. H., and Pinnacle.

Those who have followed this description on a map will have noticed 

that the mines are chiefly situated on the periphery of a circular area, 

the central part of which, comprising the upper part of Squaw Gulch, 

has thus far yielded very little. Few strong veins have been met 

with in this part of the breccia, but, on the other hand, the developments in depth are not extensive.

On the east and southeast side of Bull Hill begins that most important belt of lodes which extends southward to Victor and includes the 

richest group of producers in the camp. A characteristic feature of

Bull. 254 05 2
18 RESURVEY OF CRIPPLE CREEK DISTRICT, [BULL. 254.

this belt is the intrusion into the breccia of thick masses of trachytic 

phonolite and syenitic rocks.

With few exceptions the veins of this belt strike north-northwest. 

We may begin the description with the system of linked veins, 3,000 

feet long, covered by the Isabella and Victor mines. The last-named 

mine, on the southern end of the system, is situated just below the 

western slope of Bull Cliff. It has been worked to a depth of over 

1,000 feet, has produced about $2,200,000, and has paid dividends 

amounting to $1.150,000. The Isabella has attained a depth of 1,127 

feet, produced $3,200,000, and paid dividends of $600,000. Both mines 

lost their pay shoot in depth.

The small but rich cross veins of the Empire State, Burns, 

Pharmacist, and Zenobia connect this vein system with that of the 

Stratton mines on Bull Hill. South 'of the Burns begins the great 

Vindicator vein system, traced southeasterly for a mile through the 

Findley, Hull City, Vindicator, Lillie, and Golden Cycle mines. The 

Hull City and the Lillie have each produced over $1,000,000, the Vindicator and Golden Cycle over $2,000,000 each, all with corresponding dividend records. The Lillie is deepest, having attained 1,500 feet. 

Next in depth is the Vindicator, 1,200 feet. All of them, except the 

Lillie, are still actively worked. In the whole system water has been 

and is still a source of trouble. The deepest mine evidently drains 

all the others in this vicinity.

The Stratton properties on Bull Hill, with the Logan, Orpha May, 

and Pikes Peak veins, on which maximum depths of 1,200 and 1,500 

feet have been attained, are now worked only to a slight extent, 

whereas in the early days of'the'camp they were highly productive.

This vein system is continued southward in the Last Dollar mine, 

now working at a depth of 1,270 feet. .The production exceeds 

$1,000,000. South of the Last Dollar the veins enter the Modoc 

ground, a mine worked for a long time and with gratifying success. 

The Blue Bird, an old-time producer, is situated a short distance west 

of the Last Dollar.

South of the Modoc is the Battle Mountain vein system, crossing 

from the granite into the breccia, with general northerly or northnorthwesterly directions, and distinguished by heavy production 

and ore bodies of imposing size. None of the veins are of great 

length, and the whole system extends scarcely a mile along the strike 

of the veins. The veins can not be directly connected with others 

already described, though, in its general trend, the system heads 

toward the Dexter, Blue Bird, and Moose veins.

Beginning on the southwestern side, we first come to the Gold Coin 

mine, the veins of which are in granite; one of them is successfully 

worked at present at a depth of 1,200 feet. The total production 

approaches $6,000,000; the dividends paid exceed $1,000,000. North
LINDGREN A 

KANSOMEf'D ] THE MINES. . ' 19

of the Gold Coin.is the Ajax, working partly in veins, partly in large, 

irregular ore bodies in the granite. The total production is very considerable. The depth attained is 1,200 feet.

Between this and the Portland vein system, almost within the town 

of Victor, are the Granite, Dillon, and Dead Pine veins. They are 

worked at present at depths of from 800 to 1,000 feet.

The Portland vein system begins on the south at the Strong mine, 

now worked at a maximum depth of 900 feet, on a vein in granite 

that'follows a "basalt" dike, which is in places accompanied by a 

phonolite dike. The mine is an unusually regular and profitable 

producer, the total dividends since 1892 amounting to $2,500,000.

The veins of Stratton's Independence run about parallel to those of 

the Strong, a few hundred feet eastward. They extend from the 

granite into the breccia, following for some distance a phonolite dike. 

The production of this mine amounts to over $11,000,000, with a dividend record of -$4,000;000 since 1899. At present the company is 

leasing the various levels to tributers. From the two properties last 

described the vein systems .continue into the Portland mine, but in 

the northern part of that great property are replaced by another and 

still richer aggregate of veins, the Captain system. The Portland is, 

beyond question, the most prominent mine of the Cripple Creek district. Its total production from 1894 to the end of 1903 amounted to 

$18,000,000, derived from 466,000 tons of ore (both in round figures), 

from which $4,600,000 has been paid in dividends, the remainder going 

to acquirement of territory, extensive milling and mining plants, and 

operating expenses.

Outside mining pro2)erties. The area outside of the principal volcanic area contains very few productive properties, but it is by no 

means barren. A great deal of money has been spent here, usually 

with unsatisfactory results. Although there are man}^ properties of 

merit and although much honest effort has been made in this part of 

the district, it has long been the favorite camping ground of concerns 

more or less lacking in stability.

The granite hills west and south of the city of Cripple Creek contain few prospects; phonolite dikes occur in places, but usually show 

little value. Along Gold Run and Arequa Gulch prospects with a little 

ore have been found, down to the junction with Cripple Creek,.and 

even at isolated places below this locality. Grouse Mountain, with its 

phonolite cap, shows many prospects from which occasional good assays 

have been obtained, but neither here nor On Straub and Brind mountains has anything of permanent value been developed thus far. It is 

claimed that ore bodies of low grade, containing a few dollars per ton, 

exist.

 The breccia caps of Mineral, Carbonate, and Tenderfoot hills are 

dotted with prospect dumps, and even shafts several hundred feet
20 RESURVEY OF CRIPPLE CREEK DISTRICT. [BULL. 254.

deep. Nothing of permanent value is recorded from Mineral Hill, 

though fairly productive placers have been worked at its southwestern 

base, almost in the town of Cripple Creek.

On Carbonate Hill the Elkhorn has been a small producer; on Tenderfoot Hill the Friday, Hoosier, Black Diamond, and Mollie Kathleen 

contribute their parts to the production. Two miles north-northwest of 

Cripple Creek is the Galena mine, the vein of which follows, for a part 

of its course, a phonolite dike in granite and has a small output to its 

credit. About the same distance north of the city is the small volcanic 

center of Copper and Tttiyolite mountains. At the former the Fluorine 

mine has produced $160,000, and low-grade ore is now being cyanided. 

Prospects are found on Rhyolite Mountain, and in fact all over the flat 

granite country between it and Trachyte Mountain. The Lincoln mine, 

near Gillette, and several other prospects farther south, along a belt 

of phonolite dikes, have produced a little ore. It is claimed that there 

are low-grade veins on both sides of Bernard Creek, northwest of 

Gillette, in a region of granite with occasional dikes and masses of 

phonolite. Trachyte Mountain, southeast of Gillette, is covered by 

phonolite, and a little ore is occasionally found in veins at its southern 

foot. Some work has also been done on Cow Mountain, about 4 miles 

northeast of Bull Hill.

The eastern margin of the central volcanic area, east of Victor Pass 

and extending southward across Big Bull-Mountain to Blind Mountain, 

has thus far failed to produce anything of importance, though well 

covered by prospects. A survey of these outlying parts of the district 

serves to emphasize strongly the remarkable concentration of deposits 

within the narrow limits of the central volcanic area.

CHARACTER OF THE ORES.

The characteristic feature of the Cripple Creek ores is the occurrence 

of the gold in combination with tellurium, chiefly as calaverite, but 

partly also as the more argentiferous sylvanite, a and probably to a 

minor extent as other gold, silver, and lead tellurides. The tellurides 

are frequently associated with auriferous and highly argentiferous 

tetrahedrite, with molybdenite, and occasionally with stibnite. While 

these minerals have not yet been closely studied, preliminary examination indicates that their contents in gold are due to an intimate mechanical mixture of tellurides. Pyrite, while widely disseminated through 

the country rock and of common occurrence in the fissures, is rarely 

sufficiently auriferous "to constitute ore. Such of the pyritic ores as 

have been tested reveal the presence of tellurium', indicating that the 

ore is a mixture of pyrite and gold-silver tellurides. Galena and

a Calaverite (AuAg) Tea: tellurium, 57.4 per cent; gold, 39.5 per cent; silver, 3.1 per cent. Sylvanitc 

(AuAg) Tea: tellurium, 62.1 per cent; gold, 24.5 per cent; silver, 13.4 per cent.
HNDCBEN AND"1 

EANSOME. ] CHARACTER OF THE ORES. . 21

sphalerite occur in small quantities in many of the mines, but rarely 

contain enough.of the precious .metals to form ore. Native gold 

appears to be absent from the telluride ores, except as it may be set 

free by the oxidation of these tellurides.

The usual gangue minerals of the ores are quartz, fluorite, and dolomite. Roscoelite and rhodochrosite are also found in places. Celestite, 

or sulphate of strontium, while never present in large amount, frequently occurs as little acicular ciystals in the quartz vugs of, the lodes. 

Calcite occurs interstitially in much of the breccia near the ore bodies, 

but is rarely found in distinct crystalline form with the ore minerals. 

Secondary potassium feldspar is common in the ores; it is especialty 

abundant in the ores inclosed in granite, particularly those in the 

Pikes Peak type. 'This feldspar has the composition of orthoclase or 

microcline, and is formed by the recrystallization of the original 

potassic feldspar contained in the rocks. In the granitic ores of the

Stratton's Independence, Portland, Ajax, and Elkton mines, this secondary feldspar is the principal gangue mineral.

Oxidized ores, while still worked in many properties, are of relatively less importance than when Penrose described the district. 

They contain the characteristic dull gold, often in pseudomorphous 

skeletons, resulting from -the oxidation of the tellurides, associated 

with tellurite (tellurium dioxide), emmonsite or durdenite (both 

hydrated ferric tellurites), and probably other oxidized compounds of 

tellurium and iron. These minerals occur in association with kaolin, 

alunite, and ferruginous clays. The deep workings of the present 

day show that kaolin is always connected with oxidation, and is not a 

product of the original mineralization of the district, as was supposed 

by Penrose.

The Cripple Creek ores, as a rule, contain very little silver, the 

average proportion being about 1 ounce of silver to 10 ounces of gold. 

In the Portland and Stratton's Independence mines the proportion is 

very much less, the silver from the Portland in 1901 amounting to 

only 2.4 ounces for each 100 ounces of gold. In the Blue Bird, 

Doctor-Jack Pot, Conundrum, Pointer, and other mines containing 

notable amounts of tetrahedrite or galena, the proportion of silver 

rises considerably above the average.

The average value of the Cripple Creek ores lies probably between 

$30 and $40 per ton. In some of the larger mines the average value 

sinks to about $25 per ton. From a lower economic limit of about 

$12 per ton the values of individual shipments swing through a wide 

range up to ores carrying $3,000 or $4,000, or even $8,000, per ton. 

Occasional!}' smaller amounts one or two tons have yielded as much 

as $50,000 per ton.
22 RESURVEY OF CRIPPLE CREEK DISTRICT. [BULL. 264. 

STRUCTURAL CHARACTER OF DEPOSITS.

With few exceptions the ore bodies, of whatever shape, are causally 

connected with fissures, and most of them constitute fissure veins of 

various types. The fissure system of the district appears to radiate 

from a point near the northern limit of the volcanic area. In the 

eastern part the prevailing directions are northwest or north-northwest, 

gradually changing to a northerly strike in the southern portion and 

to predominant north-northeast or northeast courses in the western 

side of the district.

Individual veins are rarely over half a mile in length, but linkedvein systems often extend for a mile in the same direction. The dip 

is generally very steep. The movement along these fissure planes 

appears in all cases to have been very slight. The fissures charged 

with ore are sometimes simple veins with one fracture plane; much 

more commonly, however, they are composite veins or lodes which 

consist of several .closely spaced and frequently linked fissures, all 

more or less ore bearing. A better expression for this structural type 

as it appears in Cripple Creek is the term "sheeted zone."

TYPES OF DEPOSITS.

The most important types of auriferous ore bodies occurring in the 

district are:

1. Tabular in form and strictly following simple fissures or sheeted 

zones. A subtype comprises lodes in which the sheeted zone follows 

"basalt" or phonolite dikes.

2. Irregular bodies adjacent to fissures and formed by replacement 

and recrystallization of the country rock usually granite. 

These types are not always sharply distinct, but may be connected

by deposits of intermediate character.

All the ore bodies, of whatever type, exhibit certain common features 

which serve to distinguish the deposits of Cripple Creek from those 

of most other mining districts. In the first place, the actual openings 

in the rocks available for the deposition of ore are, as a rule, remarkably narrow. In the second place, the amount of material carried in 

the mineralizing solutions and deposited as gangue and ore minerals 

was comparatively small. In consequence of these two conditions, the 

district contains no such massive veins, solidly filled with quartz or 

other vein minerals, as are characteristic of the San Juan region in 

Colorado or the Mother Lode region in California. Even the small 

fissures of the Cripple Creek district are rarely completely filled, but 

exhibit a characteristic open or vuggy structure. Where the fractures 

are of unusual width, or where the i ;>cks are extensive!}7 shattered, as 

in the Midget and Moose mines, the small volume of available vein 

matter is particularly noticeable. The walls of such fractures and the
] TYPES OP DEPOSITS. 23

fragments of the shattered rock are usually merely coated with a thin 

deposit of quartz, fluorite, and other minerals. As the rich tellurides 

were usually among the minerals, last to form, and are particularly 

abundant on the walls of the vugs, it is probable that had quartz, fluorite, or other gangue minerals been more abundantly deposited the 

ores would have been of much lower grade.

Sheeted veins. The mineralized sheeted zones constitute the most 

characteristic deposits of the district and occur in practically all the 

rocks, although particularly common in breccia. They consist of a 

varying number of narrow,^approximately parallel fissures, together 

composing a sheeted zone that may range from a fraction of a foot to 

50 or 60 feet in width. Such uncommonly wide zones of fissuring, 

however, can usually be resolved into two or more sheeted zones lying 

so close together that the whole constitutes for practical purposes a 

single ore body, as in the Captain vein system of the Portland mine. 

Usually the sheeted zones are from 2 to 10 feet in width. In other 

cases the fissures may be very numerous, the rock for a foot or more 

in width being divided into thin parallel slabs, while on each side of 

this medial portion the fissures become farther and farther apart as 

the lode grades into the normal country rock of the vicinity. In still 

other cases there may be two main fissures, 3 or 4 feet apart, accompanied by more or less irregular fracturing of the intervening and 

adjacent rock. As a rule the fissures are mere cracks, showing no 

brecciation, slickensiding, or other evidence of tangential movement 

of the walls. Usually the tellurides are exclusively confined to the 

narrow fissures and cracks, and do not, in this type of deposit, in any 

sense constitute a replacement of the country rock. The rocks in, the 

vicinity of the fissures are partly replaced by dolomite, pyrite, and 

a little fluorite; the telluride ores, however, do not "share this propensity, but coat the open fissures, associated with a little quartz and 

fluorite. Eeplacement by tellurides does occur in two other types of 

deposits, to be described later; but as regards the simple veins and 

sheeted zones, it will be necessary to modify the results of Penrose by 

restricting the metasomatic r61e of the tellurides. In the oxidized 

parts of the veins, such as were almost exclusivel}7 available for observation when Penrose visited the district, these relations can seldom be 

clearly ascertained, and would easily lead one to overemphasize replacement as a feature of vein formation. The fissures are not, in general, 

planes of faulting. Appreciable movement has undoubtedly occurred 

in some instances, but the displacement probably rarely exceeded 1 or 

2 feet.

Although found most abundantly in the breccia or trachytic phonolite, sheeted zones and single fissures are often well developed in the 

granite, as in the El Paso, C. K. & N., and Gold Coin mines. While in 

some of these lodes the ore minerals are as plainly confined to the lis-
24 RESURVEY OF CRIPPLE CREEK DISTRICT. [BULL. 254.

sures as in the breccia, in other cases the ore to some extent permeates 

the granite alongside the fissure, this constituting a deposit intermediate in nature between types 1 and 2. They also frequently follow 

phonolite dikes, the general tendency of these dikes to develop a platy 

parting parallel to their walls being particularly favorable to the production of a well-defined sheeted zone when the direction of fissuring happens to coincide with that of the dike.

The metasomatic alteration accompanying these sheeted zones is surprisingly slight, and consists of a partial replacement of the breccia, 

phonolite, trachytic phonolite, or "basalt" by dolomite and p}n-ite 

accompanied by a small amount of sericite and a little secondary potash 

feldspar. But even in the most altered rock the newly formed minerals rarely form more than a small percentage of the rock mass. The 

alteration in granite exhibits a somewhat different phase, described in 

a subsequent paragraph.

Not all the sheeted zones carry ore, nor is the ore of a productive 

sheeted zone necessarily coextensive with the fissuring. The ore occurs 

in pay shoots up to 2,000 feet in length and 1,000 feet in depth, but 

usually very much smaller than is indicated by these limits. The 

boundary between the ore and the barren portions of the lode can be 

determined, as a rule, only by assays. No single factor that can 

account for the localization of the ore in these pay shoots has been 

discovered. In some mines the pay shoots occur where the lode is 

intersected by cross fissures; in other mines no such relation exists. 

In some mines ore occurs where the fissures pass through phonolite 

dikes; in other mines the lode, elsewhere productive, becomes barren 

when it enters phonolite; while in still others the presence of the 

phonolite has had no apparent influence upon ore deposition. It 

thus appears that the occurrence of two or more favorable factors is 

necessary to determine the position of a pay shoot in a lode. The 

discovery of these factors is one of the unsolved problems connected 

with the Cripple Creek district.

Replacement deposits in granite. The replacement deposits in 

granite all occur in close proximity to the contact with the breccia, 

and are well developed in the Elkton (Thompson), Ajax, Independence, 

and Portland mines. Although these bodies of ore are related to fissures and occur particularly where several fissures intersect, or where 

they meet a dike, the ore is not confined to the actual fractures. The 

rock in the vicinity of these fissures is often extensively altered. The 

change from altered to unaltered rock, while never perfectly sharp, is 

often fairly abrupt and may take place within a distance of a few feet. 

The most obvious characteristic of the metamorphosed rock is a porous 

texture and a change of the reddish color of the normal granite to 

grajdsh or greenish tints. Closer examination shows that, while the 

porphyritic aggregates of pink microcline, so prominent in the Pikes
)] TYPES OF DEPOSITS. 25

Peak type of granite, may remain unaltered, the rest of the rock, consisting originally of microcline, oligoclase, quartz, and biotite, may be 

completely recrystallized as a porous, vuggy aggregate of secondary 

orthoclase (valencianite), quartz, fluorite, pyrite, calaverite or sylvanite, 

and, in exceptional cases, sphalerite and galena. The ore minerals are 

partly inclosed in the other secondary minerals, but occur most abundantly with little projecting crystals of fluorite, quartz, and valencianite 

on the walls of the irregular pores so characteristic of the altered rock. 

The biotite of the original granite yields most readily to alteration, and, 

in rock otherwise almost entirely unaltered, may be changed to an 

aggregate of fluorite, quartz, and ore minerals. Some of the ore of 

the Ajax mine exhibits well this initial stage of alteration. With further alteration the original quartz and oligoclase of the granite are 

attacked. The quartz, originally in large homogeneous and irregular 

grains, recrystallizes as aggregates. Secondary orthoclase or valencianite forms often in clear, sharply idiomorphic crystals, which either 

project into open cavities or form aggregates with the secondary quartz. 

In many cases, however, the secondary valencianite results from the 

recrystallizationof the older microcline practically in place. The two 

generations are sometimes distinguishable by the greater clearness and 

more or less idiomorphic form of the younger mineral and the absence 

of the characteristic microcline twinning. But it is often impossible 

to determine the line between feldspar which, from its association with 

quartz and fluorite, is clearly secondary and the original microcline of 

the granite. Occasionally a little calcite may be detected in the 

altered granite, but this is rare. The original apatite and zircon of 

the granite are not, so far as observed, affected by the alteration 

described.

While the replacement deposits in granite are important because of 

their size and the readiness with which the ore may be mined free 

from waste, the ore itself is usually of lower grade than that formed 

in the fissures of the sheeted zones.

Mineralized " basalt" dikes. The ore bodies formed by the mineralization of basic dikes are in some ways closely related to the sheeted zones 

already described. Like the phonolite dikes, the "basalt" exhibits 

a pronounced tendency to split into thin sheets parallel with the dike 

walls. Normally, the minute fissures so formed are filled with veinlets 

of calcite and contain no ore. When, however, a zone of fissuring 

coincides with the dike* the latter may be traversed by veinlets of 

quartz and fluorite carrying sylvanite or calaverite, while the body of 

the dike may be impregnated with pyrite. Such ore differs from that 

of the usual sheeted zones in breccia or phonolite in that the tellurides 

are not so clearly confined to the actual fissures, but appear to some 

extent to permeate the rock with the pyrite. The richest portion of 

the ore, ho.wever, undoubtedly occurs in the small veinlets in the dike,
26 BESURVEY OF CRIPPLE CREEK DISTRICT. [BULL. 254.

and usually near one or both walls where the fissuring is best developed. The occurrence of rich ore bodies in basic dikes in the Portland (Anna Lee), Moose, Elkton, Conundrum, Pinto, and other mines 

has tended to exaggerate the importance of these dikes in general, 

and some have even supposed a genetic relation to exist between 

them and the mineralization of the district. 05 . Such an hypothesis, 

however, loses sight of the vast amount of profitless work that has 

been expended in the district in driving on the usually unproductive basaltic dikes, and the very small proportion of the known ore 

bodies that can be shown to have any connection whatever with these 

intrusions. That the basaltic dikes are not alwa}7 s readily mineralized 

even when accompanied by fissuring is shown in the interesting case 

of the Strong mine, where the ore occurs as mineralized granite on 

each side of the dike, while the latter is barren.

DEPTH OF OXIDIZED ZONE.

At a few points, as in the Abe Lincoln and El Paso mines, tellurides 

are found almost at the surface. It is much more common, however, 

to find an upper zone, from 200 to -400 feet deep, in which free gold 

prevails and which gradually changes to the zone of pure telluride 

ores. As may be expected from the varying surface form and conditions of drainage, there is great range in the depth attained by oxidation. Partial oxidation extends in many mines to a depth of over 

1,000 feet, especially along the often more or less open fissures. In 

the Wild Horse mine the zone of complete oxidation reaches a depth 

of 1,100 feet and then suddenly ends. In the Isabella mine partial 

oxidation attained at least 1,200 feet, and the same applies to the Gold 

Coin mine in Victor, although telluride ores prevail at that depth as 

well as in many levels above. The question is chiefly one of depth of 

ground water and of facilities for circulation of oxygen. Further 

data bearing upon this problem may be found on page 31.

RELATIONS OF ORE BODIES TO DEPTH.

It is well known that the payable ores in auriferous lodes are rarely 

equally distributed in the lode, but form tabular bodies of more or less 

regular outline. The projections of these ore bodies on the plane of 

the lode often appear as elongated areas with greater vertical than 

horizontal extent. The ore bodies or shoots of Cripple Creek show 

great similarity to those of other gold-bearing veins; their limit in 

depth is usually as well defined as their extent in a horizontal direction.

Of sixty pay shoots of Cripple Creek mines plotted together for

"Stevens, E. A., Basaltic zones as guides to ore deposits in the Cripple Creek district: Trails. Am. 

lust. Min. Eng., vol. 33,1903, p. C86.
] RELATIONS OF ORE BODIES TO DEPTH. ' 27

purposes of coDiparison, over thirty extended from the surface to a 

depth of less than 500 feet. The maximum individual production of 

these is less than $1,000,000. Near six of these ore bodies further 

exploration developed new shoots below the old ones, but usually of 

smaller extent. In practically air thirty cases the development work 

had been carried down a few hundred feet below the last ore of the 

surface shoot. The form of these smaller shoots is often equidimensional; in a few cases the horizontal extent is greater than the vertical, or the shoot is wholly irregular; in many cases the shoot pitches 

steeply northward on the plane of the vein and the ratio of vertical to 

horizontal extent is 2:1 or 3 :1. .

In eight of the sixty cases the shoot extended from the surface to a 

depth of 1,000 feet, or a little more, and ended. Further development 

to about 1,500 feet failed to find new shoots of any importance, though 

small pockets were often discovered. In six of these eight cases the 

ratio of vertical to horizontal extent varies from 3:1 to 5:1, and 

the shoots usually pitch northward at angles of 60° to nearly 90° from 

the horizontal. In the remaining two cases the shoots have about the 

same horizontal as vertical extent. The maximum horizontal length 

is 1,300 feet, while 400 is much more common. In two of the sixty 

cases the pay shoot is 1,500 to 2,000 feet long, maximum depths of 

600 and 1,000 feet having been attained and the bottom level being still 

in ore. In thirteen of the sixty cases the shoot began over 200 feet 

below the surface; in eight of these the bottom of the shoot has been 

reached, while in five the lowest level is still in ore. Steeply dipping, 

irregular elongated forms prevail. Many of this group of thirteen 

represent veins parallel and close to those on which pay shoots outcropping at the surface were found.

These statements will give an idea of the form of the shoots. Of 

course, in the case of shoots reaching the surface, a certain part has 

probably been removed by erosion. Judging from the shoots which 

distinctly began below the surface, the normal form of the ore bodies 

is elongated, vertical, or pitching sharply northward, the ratio of vertical to horizontal extension varying from li:l to 5:1. Some of 

these shoots are, however, of about equal dimensions, vertically and 

horizontally, while in a few the horizontal dimension is the greater.

Of the known ore bodies, as few exceed 1,000 feet in length, so 

very few exceed 1,000 feet in depth or extend more than 1,000 feet 

from the surface. Speaking broadly, explorations below that limit have 

not proved very satisfactory. Drawing the lines a little closer, it may 

be said that in proportion to the amount of exploration the upper 700 

or 800 feet have yielded more than the interval from that limit to the 

lowest levels reached about 1,500 feet. It must not be overlooked, 

however, that four or five mines still have good ore bodies at a depth
28 RESURVEY OF CRIPPLE CREEK DISTRICT. [BULL. 254.

of 1,200 to 1,400 feet from the surface. The developments of the 

next year or two will probably give a safer basis for generalization.

Roughly speaking, the above-mentioned distribution holds good for 

any elevation within the district. In other words, the principal productive zone everywhere occupies the space from the surface down 

to about 1,000 feet below it, and its lower limit thus forms a curved 

surface approximately parallel to the surface of the ground.

It is probable that the minimum depth of rock removed from the 

district by erosion amounts-to 1,000 feet in the central part and to 

400 or 500 feet about the periphery. The.shape and number of the 

ore bodies formerly existing in this eroded zone can be only conjectured. It is probable that the veins were formed shortly after the 

close of igneous activity, while the volcano yet possessed a much - 

greater height than at present. The absence of hot waters and the 

depth of oxidation attained indicate that vein formation at Cripple 

Creek is by no means a recent phenomenon.

The general features of the vertical distribution of the known ore 

bodies recorded above have of late years received more or less recognition, and there has been a decided tendency to attribute them to a 

process of secondary enrichment effected by waters moving generally 

downward from the surface. It has been supposed a that such waters 

have carried down a part of the auriferous contents of those portions 

of the lodes now removed by erosion and have enriched originally lean 

pyritic ores by the secondary deposition of gold and silver tellurides 

and argentiferous tetrahedrite, with associated gangue minerals.

It is clear that the hypothesis in question is suggested by the distribution of known pay shoots. The question arises, How far does 

the distribution of known pay shoots represent the distribution of all 

the pay shoots in the district? In other words, How far has exploration been impartial in revealing ore bodies near the surface and at 

depths greater than 1,000 feet?

It requires but little examination to make clear the fact that ore 

bodies within 1,000 feet of the surface are far more likely to be discovered than those at greater depth. While shafts have been sunk for a 

few hundred feet without any indication of ore and have ultimately 

been developed into productive mines, such a procedure is considered 

bold prospecting, and few well-informed mining men would seriously 

contemplate sinking a shaft over 1,000 feet in depth solely on the 

expectation of finding possible ore bodies below that depth. Most of 

the large mines in the district have started upon some indication of ore 

near the surface and have grown by the subsequent discovery of other 

lodes and ore bodies in the course of their underground development. 

As few individual ore bodies persist for more than 1,000 feet in depth, by

a Bancroft, Geo. J., Eng. and Min. Jour., vol. 74,1902, pp. 752-753, and vol. 75,1903, pp. 111-112. 

Finch, J. Wi, Proc. Colorado Sci. Soc., vol. 7,1904, pp. 193-252.
] RELATIONS OF ORE BODIES TO DEPTH. 29

far the greater part of the underground prospecting is at less depths, 

there being usually little inducement to go deeper, unless, as in the 

case of the Gold Coin and Portland mines, lodes are discovered in 

which the ore, beginning several hundred feet below the surface, 

extends deeper than the pay shoot upon which the mine was originally opened. Thus deep prospecting is usually confined to the 

vicinity of the larger and more persistent pay shoots which have been 

followed down from near the surface. Underground water has also 

proved a most serious obstacle to deep prospecting, few properties 

being able to develop below tlie 1,000-foot zone unless there is abundant and high-grade ore in sight. '

It may thus be concluded, without necessarily advocating promiscuous exploration below the 1,000-foot zone, that any ore bodies existing below that depth are far less likely to be discovered than those 

above, where from the surface to depths of several hundred feet the

rocks of the district are riddled with shafts, drifts, crosscuts, and 

adits. It is exceedingly difficult, however, to determine, even approximately, the relative importance of this factor in the problem. 

It is probably safe to assume that the chances of discovering a given 

ore body within the 1,000-foot zone are at least ten times those of discovering an ore body below that zone, and the ratio may be very much 

greater. It is probably true that there was originally more ore within 

the 1,000-foot zone than there is in a corresponding zone below, but 

this disparity is not necessarily anything like so great as is indicated 

by the vertical distribution of known pay shoots.

Another important line of inquiry bearing upon the relations of the 

ore bodies to depth is concerned with the question of the relative size 

and abundance of the fissures near the surface and at greater depth. It 

has been shown that all the ore bodies are intimately connected with 

fissures. If such fissures are generally smaller and less abundant 

below the 1,000-foot zone than th&y are within it, obviously there is 

introduced a factor which diminishes the supposed importance of secondary enrichment by affording an anterior and physical explanation 

for the decrease of ore with increase of depth.

Detailed examination of practically all the accessible mines in the 

Cripple Creek district has led to the conclusion that the fissures, which 

ordinarily are narrow and often appear as mere cracks, .do become less 

abundant and less conspicuous as greater depth is attained. No mine 

exhibits this feature better than the Stratton's Independence, in which 

the very complex systems of productive fissures on the fifth and higher 

levels contrast most strikingly with the few, insignificant, and unproductive fractures visible on the fourteenth level. In less degree the 

same feature is shown in many others of the deep mines, but the rule 

is 'not without some very marked exceptions.
30 RESURVEY OF- CRIPPLE CREEK DISTRICT. [BULL.264.

The dependence of the ore zone on the surface would then merely 

express the depth to which fissuring extended in a conical volcanic 

mountain. 

We have thus two factors of importance to account for the scarcity 

of ore shoots below the 1,000-foot level first, difficulties of development and exploration, and second, the disappearance of fissures in 

depth. They do not seem to be sufficient, however, and it is believed 

that a third factor, as yet undiscovered, exists, and that it is related to 

the chemistry of the actual ore deposition. '

In those districts where so-called secondary sulphide enrichment is 

known to have taken place the ore minerals exhibit in general an 

orderly sequence, both in relative abundance and in kind, from those 

characteristic of the most highly enriched ore near the zone of oxidation to those constituting the original, lean, and unaltered ore. The 

secondary minerals produced are such as caii result from rearrangement and concentration of elements present in different combinations 

in the primary ores. At certain points within this range of alteration 

it is possible to detect direct mineralogical evidence of the change of 

one mineral to another, effected by solutions moving downward from 

the zone of oxidation. In most cases the secondarily enriched ores 

bear a recognizable relation to the lower limit of oxidation.

Careful study of the Cripple Creek ore deposits has failed to discover 

that the hypothesis of secondary enrichment is supported by crucial 

evidence of the kind just indicated. . The minerals are not arranged 

in any discoverable definite sequence, nor does the present investigation find much to support the view that the rich telluride ores, as a 

rule, pass with increasing depth into low-grade pyritic ores. Frequently such ore as occurs below a depth of 1,000 feet is precisely the 

same in character as ore found within 100 feet of the surface. Tetrahedrite, which has been regarded by some, without definite proof, as a 

secondary mineral, occurs sporadically throughout the district and at 

all depths reached by present workings. The richest ore does not 

uniformly occur immediately below the oxidized ore. There is, in 

fact, little indication of enrichment in the oxidized zone such as is so 

often found in gold-quartz veins of the normal type. Frequently the 

fresh telluride ore is extremely rich, and high-grade pockets occur 

impartially in oxidized and fresh portions of the veins. Neither 

would it be correct to say that there is a gradual decrease in the value 

of ore in depth. It is quantity, not value, which decreases.

While it is certain that pyrite, and possibly other minerals, has 

formed at more than one period during the mineralization of the district, and while it is equally clear that in general the rich tellurides 

were the last of the ore minerals to be deposited, there is apparently 

no evidence that any one of these minerals has been formed by enriching solutions at the expense of primary minerals. So far as definite
] UNDERGROUND WATER. 31

'conclusion is warranted in an investigation as yet incomplete, it 

appears that the unoxidized ore deposits of the Cripple Creek district 

represent the product of one general period of mineralization and that 

they have not been appreciably modified by secondary enrichment 

during the subsequent erosion of the region.

UNDERGROUND WATER.

The conditions of underground waters are interesting and somewhat 

unusual. A dry climate and a heavy percentage of run-off minimize 

the annual additions to the underground supply. Nevertheless, the 

ground-water level is not unusually deep, and large quantities of water 

are encountered in all the mines below that level. The original water 

surface of the district in the volcanic rocks stood at elevations of 9,400 

to 9,700 feet, or 100 to 600 feet below the surface of the ground. At

 first pumping was commenced by individual mines, but it was soon 

found that the radius of drainage had unusual length that is, that one 

mine would drain others situated at a distance. Drainage tunnels were 

then undertaken, and the Chicago and Cripple Creek, the Ophelia, the 

Standard, and lately the El Paso tunnels were driven, each of which 

practically accomplished the drainage of a large part of the district 

almost down to its own level, thus showing that the ground water is 

limited in quantity and is more of the nature of a local reservoir than 

a "subterranean sea."

The plug of volcanic rocks which fills the throat of the old volcano 

is rudely circular, with a diameter of 3 miles. This mass is extremely 

porous, and is, moreover, cut in many directions by partly filled fissures 

and sheeted zones, so that water can circulate within it with comparative freedom in several directions. It retains this character down to 

the greatest depth yet reached. On the other hand, the surrounding 

granite is relatively impermeable and is less traversed by open fissures. 

No doubt it contains ground water down to a.depth of 2,000 feet or 

more, but in very much smaller quantity, and the circulation of this 

water must be extremely slow. This is clearly shown by the fact that 

the water in the breccia is not drained by Cripple Creek and Arequa 

Gulch below the level of the points where they leave the volcanic area. 

Thus the volcanic plug resembles a water-soaked sponge inserted in a 

hole cut in an impermeable substance. The drainage of the mines is 

therebj7 greatly facilitated, as it is not necessary to extend the tapping 

tunnels to each mine.

The El Paso tunnel, completed in the winter of 1903-4, has an elevation of 8,790 feet at the portal. Within a short time it effectually 

drained not only the Beacon Hill mines but also the Gold Hill mines, 

and its influence extended even to the Last Dollar and the Elkton 

mines. But the foregoing statement in relation to draining the dis-
32 EESUEVEY OF CEIPPLE CEEEK DISTEICT. [BULL.254.

e>

trict must be so modified as to exclude a certain part on the eastern 

side, comprising the mines about Independence on the east side of Bull 

Hill and those on Battle Mountain and in the town of Yictor, in which 

the effect of the El Paso tunnel is slight. The Findley, Hull City, 

Vindicator, and Golden Cycle mines about the town of Independence 

seem to occupy a separate drainage basin, probably divided from the 

main area by masses of relatively impermeable rock.

The Portland, Stratton's Independence, and the other mines near 

Victor occupy another drainage basin. Of these the Gold Coin and 

the Stratton's Independence have shafts below the level of the El Paso 

tunnel, and their piamps have probably drained the surrounding territory to a considerable extent. -The influence of the drainage tunnel 

on the Portland mine is a question upon which opinions differ.

The subject of the drainage of the Cripple Creek mines has been 

actively studied in late years, and valuable contributions to the subject 

have been made by Mr. Victor G. Hills and others, who have shown 

that the water can be tapped, without prohibitive expense, down to an 

elevation of 7,500 .feet, or 1,300 feet below the El Paso tunnel; for 

this depth a tunnel 3^ miles long would be needed. On account of the 

great porosity of the rocks it is not probable that the next thousand 

feet below the El Paso tunnel level will show any great diminution in 

the amount of water stored in the rocks.

SUBTERRANEAN GASES.

During the earlier years of Cripple Creek no unusual amount of 

mine gases was observed, but, as the shafts and workings deepened, 

several properties began to experience much annoyance and even 

serious interference with work, often in spite of vigorous measures 

for ventilation. These gases appear to issue chiefly from the breccia,

especially where it is of porous and loose texture, but they.sometimes 

flow from partly open vein fissures in such quantity that a light held 

up to the fissures is immediately extinguished. Thus far the mines 

on Battle Mountain and those of the Golden Cycle, Vindicator, and 

Isabella groups have suffered no inconvenience, but most of the mines 

west of this line .have had more or less trouble with this subtle and 

insidious enemy. At least one mine has been forced to close down 

entirely, and several others are often obliged to abandon work for 

days. Sometimes the amount of gas issuing is small, and ordinary 

ventilation will carry it away; again it may issue in large volumes 

and practically fill the mine for some time. In other mines the gas 

persistently hangs at certain places, forming barriers which can be 

passed only with difficulty. The outflow of gas is unquestionably 

related to barometric fluctuations, though it is usually locally reported
] SUBTEEEANEAN GASES. 33

to be influenced by the direction of the wind. The investigations

 concerning this subject are not }^et concluded. It may be said, however, that a sudden lowering of the barometer seems to be the most 

important factor. Upon such a fall the gas issues in great volumes, 

but decreases when the barometer remains steadily low for several

 days. The gas is often very heavy, filling lower parts of drifts and 

Avinzea like water, and cases are reported in which it has actually been 

- bailed from a shaft. Its temperature is somewhat higher than that 

prevailing in the mine under normal conditions.

It has practical!}7 no smell or taste, but small quantities of it easily 

produce effects of suffocation. Miners working in places where this 

gas is mixed with the air soon experience various forms of physical 

distress, and several fatal accidents have been caused by men entering 

drifts and winzes filled with it.

The characteristics of the gas seemed to point to carbon dioxide, 

and it is generally so termed. Preliminary determinations of carbon 

dioxide by a portable apparatus yielded percentages which seemed far 

too small in comparison with the effects of the gas examined, and led 

.to the belief that some other substance was present. Samples were 

then collected and analyzed. The analyses showed the gas to be a 

mixture of nitrogen with about 20 per cent carbon dioxide and a small 

.amount of oxygen.

The occurrence of these exhalations over a large part of the orebearing area is of much, interest. They certainly increase in quantity 

with depth, and it is to be feared that in some cases they may seriously 

affect mining operations. The evil has proved very difficult to cope 

with. Ventilation alone has rarely proved efficient, and the only 

practicable remedial measures appear to be cementation of drifts at 

particularly bad places and working the mine under air lock at a pressure slightly exceeding the normal.

The origin of these gases can not reasonably be sought in any such 

explanation as the oxidizing of sulphides and accompaaying absorption 

of oxygen. We believe that they represent the last exhalations from 

the throat of the extinct Cripple Creek volcano.

FUTURE OF THE DISTRICT.

To predict the future jdeld of any mining district is no easy task; 

the conditions under which most ores are deposited are as yet too 

imperfectly understood, and the deposits themselves are usually too 

erratic in form and distribution, to give certitude to such predictions, 

even when these are based upon a careful stud}' of the history and 

present condition of a district. Nevertheless, it is part of the dut}r of 

the geologists who have officially investigated the Cripple Creek district to interpret to the best of their ability the bearing of ascertained 

Bull. 254 05 3
34 EESUEVEY OF CBIPPLE CKEEK DISTEIGT. [BULL. 254.

facts upon future mining development. For such a forecast of the 

future moderate probability is all that can be claimed.

As has been pointed out in the preceding pages, the largest known 

ore bodies of the district are apparantly confined within a zone which 

extends from the surface to a depth of 1,000 feet. In general, explorations below that depth have been much less satisfactory, as regards 

quantity of ore, than explorations above. It is certainly true that 

some large ore bodies as yet show no sign of depletion in depth, and 

that some good pay shoots have been found at a depth of 1,400 to 

1,500 feet. On the other hand, the number of ore shoots that have 

been exhausted with increase in depth is considerable.

It is probable that the ore bodies, known or unknown, occurring 

below the 1,000-foot zone are neither so large nor so abundant as 

those nearer the surface. The discovery and exploitation of these 

deeper ore bodies is, moreover, beset with increasing difficulties, chief 

among which is the problem of dealing with the underground water. 

For these reasons it is unlikely that the zone between the 1,000-foot 

and 2,000-foot levels will yield as much as the zone between the surface and the 1,000-foot level, but the possibility is not denied that 

soire strong fissures may carry payable ore to far greater depths than 

those yet attained.

As regards the zone above the 1,000-foot or 1,500-foot level, it is 

well to bear in mind that it still contains much ore, both as parts of 

known ore shoots and as yet undiscovered ore bodies. It js certain 

that many of these undeveloped ore bodies will be mined in the near 

future and that this zone will contribute the most important part of 

the production.

It is probable that the production of the district, while exhibiting 

fluctuations, will on the whole slowly decline. New ore bodies will 

undoubtedly be discovered from time to time, and individual mines 

may be as profitable in the future as they have .been in the past, or 

even more profitable. An increased output may be expected to 

follow each successful step in deep drainage. But existing conditions 

indicate that if the maximum production of $18^000,000, in 1900, is to 

be surpassed the increase will be due to the ore bodies encountered in 

the upper zone.
INDEX.

Abe Lincoln mine, location of ............. 1C

Ajax mine, depth of..0...................... 19

Anaconda mine, production of............. 16

Anchoria-Leland mine, production and

depth of........................ 16

Bancroft, G. J., on down ward-moving

waters.......................... 28

Basalt dikes, ore in......................... 25-26

Battle Mountain vein system, mines on.... 18

Beacon Hill, mines on...................... 17

Breccia, occurrence and character of... 12,13-14 

Bruce, J., work of .......................... 8

Bull Hill, mines on......................... 17

Calaverite, composition of.................. 20

 Calcite, occurrence of...................... 21

 Carbonate Hill, prospects on............... 20

Celestite, occurrence of.................... 21

 Chlorination process, use of................ 10

Conundrum mine, depth of................ 16

Cripple Creek granite, occurrence of....... 13

 Cross, Whitman, work of................... 7,11

Cyanide process, use of..................... . 10

Dainon mine, location of................... 17

Dikes, mineralized basalt, description of.. 25-26 

Doctor-Jack Pot mine, production and

depth of........................ 16

Dolomite, occurrence of.................... 21

Douglas, E. M., work of.................... 7

El Paso shaft, depth of..................... 15

JElkton mine, production and depth of..... 37

Elkton shaft, depth of...................... 15

Evans, R. T., work of ...................... 7

, Feldspar, occurrence of.................... 21

Einch, J. W., acknowledgments to......... 7

Finch, J. W., on downward-moving waters. 28 

Fissures, character of....................... 22

See also Veins. 

Fluorine mine, production of.............. 20

Fluorite, occurrence of..................... 21

Galena, occurrence of...................... 20

 Gangue minerals, description of ........... 21

Gases, subterranean, discussion of......... 32-33

Globe Hill, mines on ....................... 1C

Gold, discovery of, date of ................. 7,8

production of........................... S-!>

See also Ores. 

Gold Coin mine, production of............. 18

Gold Coin shaft, depth of................... 15,19

Gold Hill, mines on ........................ 10

 Gold King mine, production of............. 10

 Golden Cycle mine, production of.......... IS

Page/

Granite, occurrence and character of..-. 11,12-13 

replacement deposits in ................ 24-25

Graton, L. C., work of...................... 8

Half Moon mine, production of............ 16

Hills, V. G., work of........................ 32

Hull City mine, production of.............. 18

Igneous rocks, occurrence and character of. 11-14 

Independence mine, production of ........ 19

Independence shaft, depth of.............. 15

Isabella mine, oxidation in, depth of...... 26

production and depth of................ 18

Jerry Johnson mine, location of............ 17

Last Dollar mine, production and depth of. 18 

Lillie mine, production of.................. 18

Lillie shaft, depth of..................... 9,15,18

Map, topographic, revision of.............. 7-8

Mary McKinney mine, depth of........... 16

Metallurgy and mining, discussion of...... 9-10

Midget mine, production and depth of..... 16

Mineralized basalt dikes, description of.... 25-26

Minerals, description of.................... 20-21

Mines, area including ...................... 14

description of .......................... 15-20

methods of working.................... 9

Mining and metallurgy, discussion of...... 9-10

Moon-Anchor mine, production of......... 10

Moose mine, production of................. 17

Rock, A. M., work of....................... 8

Ore bodies, relation of, to depth............ 20-31

structure of............................. 22

,types of.1............................... 22-20

Ores, character of.......................... 20-21

treatment of............................ 10

Oxidized ores, occurrence and character of. 21 

Oxidized zone, depth of.................... 26

Penrosc, R. A. F., jr., work of.............. 7,14

Phonolite, occurrence of................... 12

Pikes Peak granite, occurrence of.......... 12

Pinnacle mine, location of................. 17

Portland mine, production of.............. 10,19

Portland vein system, mines on............ 19

Poverty Gulch, mines near..........:...... 16

Production of gold, table showing ......... 9

Productive area, extent of.................. 14

Pyrite, occurrence of....................... 20

Quartz, occurrence of......................... 21

Raven Hill, mines on....................... 17

Replacement deposits in granite, description of.......................... 24-25

Rhodochrosite. occurrence of.............. £1

Roscoelite, occurrence of................... 21

35
INDEX.

Page.

Shafts, depth of ............................ 15

Sheeted veins, description of........... '.... 23

Silver, occurrence of, in ores ............... 21

production of........................... 9

Sphalerite, occurrence of................... 21

Stevens, E. A., on basalt dikes ............. 26

Strong mine, production and depth of...... . 19

Structure of ore bodies, description of...... 22

Sylvanite, composition of.................. 20

Tellurides, occurrence of................... 20

Topographic map, revision of.............. 7-8

Topography, description of................. 11

Tuff and breccias, occurrence and character

Of............................... 12

Page. 

Underground development, extent of.'..... 15

Underground water, discussion of.......... 31-32

Veins, sheeted, description of.............. 23

Victor mine, production and depth of ..... 18

Vindicator mine, production and depth of. 18 

Vindicator vein system, mines of.......... 18

Volcanic rocks, occurrence and character of 11-14 

W. P. H. mine, location of.................. 17

Water, underground, discussion of......... 31-32

Wild Horse mine, oxidation in, depth of... 2& 

production of........................... IT

o