K

Reconnaissance for 

Radioactivity in the 

Metal-Mining Districts 

of the San Juan Mountains 

Colorado

GEOLOGICAL SURVEY BULLETIN 1046-O

 --*_-. T»^^

This report concerns work done on behalf 

of the U. S. Atomic Energy Commission 

and is published with the permission of 

the Commission

JAN 291959

Reconnaissance for M>-Om

Radioactivity in the 

Metal-Mining Districts 

of the San Juan Mountains 

Colorado

By C. T. PIERSON, W. F. WEEKS, and F. J. KLEINHAMPL

CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

GEOLOGICAL SURVEY BULLETIN 1046-O

This report concerns work done on behalf 

of the U. S. Atomic Energy Commission 

and is published with the permission of 

the Commission

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1958
UNITED STATES DEPARTMENT OF THE INTERIOR 

FRED A. S EATON, Secretary

GEOLOGICAL SURVEY 

Thomas B. Nolan, Director

The U. S. Geological Survey Library has cataloged this publication as follows:

Pierson, Charles Thomas, 1918-

Keconnaissance for radioactivity in the metal-mining districts of the San Juan Mountains, Colorado, by C. T. Pierson, W. F. Weeks, and F. J. Kleinhampl. Washington, U. S. 

Govt. Print. Off., 1958.

iv, 385-413 p. maps (2 fold, in pocket) tables. 25 cm. (U. S. 

Geological Survey. Bulletin 1046-O. Contributions to the geology of 

uranium)

"Literature cited" : p. 412-413.

1. Radioactivity. 2. Uranium ores San Juan Mountains. i. 

Title. (Series: U. S. Geological Survey. Bulletin 1046-O. Series: 

U. S. Geological Survey. Contributions to the geology of uranium)

622.349

For sale by the Superintendent of Documents, U. S. Government Printing Office 

Washington 25, D. C.
CONTENTS

	Page

Abstract..____________________-- ._________ - 385

Introduction__________-____--___--____-_-__--_----------------_--_ 385

General geology..__ ______________________ _ _ __ 387

Method of testing for radioactivity_________________________________ 388

Results of reconnaissance._________________________________________ 388-

Areas of anomalous radioactivity._________________________ ... 3891

Cochetopa area_________________________ _______________ 38S

CeboUa district..______________________________ 390

Upper Uncompahgre district. ______ _________________________ 390

General geology-__--_-_____-____--_------__----_ ____- 390

Results of reconnaissance___________________---__---_-_- 391

Radioactive localities ____________ _________________ 391

Red Mountain district____________________________________ 394

Introductory statement and general geology-_______ ____ 394

Uranium occurrences___________ ________ __ 399

Bonanza district..____________________ ___________________ 399

General geology and ore deposits. _____ ____________ 399

Uranium occurrences _--_-______--__----_ ___________ 401

Other districts _________________________________ 404

Lower Uncompahgre (Ouray or Paquin) district.__________ 404

Telluride district _________________________ 404

Sneffels district_________-_____-_________--____-_--_-_ 404

Mount Wilson district________________________________ 405

Rico district____________________________________ 405

La Plata district._________________________ 408

Engineer Mountain district________________________ 408

Burrows Park (Whitecross) district-.___________________ 408

Carson Camp district________________________________ 408

Creede district____________________________________ 409

Areas of no anomalous radioactivity____________________________ 409

Silverton area____________________________________________ 409

Summitville-Platoro area_________________________________ 410

Lake City area__________________________________ 410

Other districts___________________________________ 411

Dunton district______________________________________ 411

Ophir district_____________________________________ 411

Needle Mountains area.._______________________________ 411

Spar City district____________________________________ 411

Wanamaker Creek district______________________________ 411

Embargo and Summer Coon districts___________________ 411

Beidell district _________________________ 411

Conclusions.---..--_____________________________________________ 412

Literature cited__________________________________________________ 412
IV CONTENTS

ILLUSTRATIONS

[Plates 43 and 44 are In pocket]

PLATE 43. Generalized geologic map showing areas tested for radioactivity in

the San Juan region, Colorado.

44. Generalized geologic map showing location of radioactivity tests, 

Upper Uncompahgre mining district, Ouray County, Colo.

Page 

FIGUEE 48. Index map* of Colorado showing location of the San Juan

Mountains.___________________________ 386

49. Map showing mines tested for radioactivity, Red Mountain

mining district and vicinity, Ouray and San Juan Counties. 395

50. Map showing mines tested for radioactivity, Bonanza mining

district, Saguache County.__... ______ ______ ___ 400

TABLES

TABUS 1. Localities in the Upper Uncompahgre mining district having 

maximum radioactivity equal to or greater than 3.0 times 

maximum background______ ____ __ ___ _____ 392

2. Mines or mine dumps in the Red Mountain mining district 

having maximum radioactivity equal to or greater than 2.1 

times maximum background________ __ ____ __. 396

3. Mines or mine dumps in the Bonanza mining district having 

maximum radioactivity equal to or greater than 2.1 times 

maximum background___ ______ ______ __ 402

4. Mines or mine dumps in the Telluride, Mount Wilson, Rico, 

La Plata, Engineer Mountain, Burrows Park (Whitecross), 

Carson Camp, and Creede districts having maximum radioactivity equal to or greater than 2.1 times maximum background 406
CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

RECONNAISSANCE FOR RADIOACTIVITY IN THE METALMINING DISTRICTS OF THE SAN JUAN MOUNTAINS, 

COLORADO

By C. T. PIERSON, W. F. WEEKS, and F. J. KLEINHAMPL

ABSTRACT

Thirty-four metal-mining districts in the San Juan Mountains, Colo., were 

investigated during 1951-53 in a reconnaissance for radioactive materials. No 

commercial uranium deposit was found during the reconnaissance, but one deposit 

has since been discovered and developed in the Cochetopa area by private interests. 

Except for the Cochetopa deposit, all the known occurrences of uranium minerals 

are small or of low grade. Additional prospecting, however, might result in the 

discovery of small ore deposits of uranium, or of ores of other metals that contain 

sufficient uranium to be produced as a byproduct.

Samples collected from the Bonanza, Upper Uncompahgre, La Plata, and Red 

Mountain districts contain 2.71, 0.53, 0.40, and 0.35 percent of uranium, respectively; and samples from the Telluride, Lower Uncompahgre, Rico, Engineer 

Mountain, Burrows Park (Whitecross), Carson Camp, and Creede districts eontain smaller though significant amounts of uranium. Radioactivity caused by 

thorium is known in the Cebolla-Powderhorn district and in the Burrows Park 

(Whitecross) district. Radon was largely responsible for the radioactivity measured in the Mount Wilson district.

In the Bonanza district, pitchblende was found on the dump of the caved Whale 

adit, where it is associated with pyrite, galena, chalcopyrite, tetrahedrite, and 

enargite as fracture coatings in silicified andesite of Tertiary age. In the Upper 

Uncompahgre district, pitchblende was found in the Michael Breen mine in a 

narrow vein in the San Juan tuff of Tertiary age and near Bear Creek Falls south 

of Ouray in a shear zone in the slate of the Precambrian Uncompahgre formation. 

In the La Plata district, small amounts of uranium are contained in limonite in 

altered Tertiary diorite from a surface trench on the Tomahawk vein. In the 

Red Mountain district, pitchblende occurs in the pyritic silver-bearing galenasphalerite-chalcopyrite-enargite ores from several chimney and vein deposits of 

Tertiary age. In the Telluride district a uranium-bearing hydrocarbon is found 

in pyritic and silicious galena-sphalerite ore from the footwall of the Montana 

vein in the San Juan tuff of Tertiary age. The small amounts of uranium in the 

other districts occur with base-metal sulfide ores from several geologic environ* 

ments.

INTRODUCTION

A reconnaissance for radioactive minerals in the western part of the 

San Juan Mountains, Colo., (fig. 48) was started by W. S. Burbank 

and C. T. Pierson in 1951 and continued in 1952 by Pierson, W. F.

385
386 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM
EADIOACTIVITY IN METAL-MINING DISTRICTS OF COLORADO 387

Weeks, and F. J. Kleinhampl and in 1953 by Pierson and J. W. 

Hawley. During 1953 a week was spent by Pierson and T. H. W. 

Loomis of the U. S. Atomic Energy Commission in the western part 

of the mountains in reconnaissance and in examination of a pitchblende 

occurrence found by Loomis. The work on which this paper is based 

was done by the U. S. Geological Survey on behalf of the Division of 

Raw Materials of the U. S. Atomic Energy Commission.

Thanks are due V. Robinson of Ouray who accompanied the writers 

on some of the underground work and to the many mine owners and 

operators who gave assistance during studies of their mines, as well as 

access to maps and other data. Theodore Botmelly of the Geological 

Survey provided much data during the microscopic study of the radioactive material.

GENERAL GEOLOGY

The following summary of the general geology and ore deposits of 

the San Juan Mountains has been taken from published reports by 

Burbank and others (1947, p. 396-446) and Cross and Larsen (1935). 

References for the more detailed descriptions of mining districts will 

be given later in this report in the individual sections. Plate 43, reproduced with some modifications from Burbank and others (1947, pi. 

27), shows the general geology of the San Juan Mountains; the mining 

districts or areas examined are shown by numbered rectangles.

The rocks exposed in the area range from Precambrian to Recent 

and consist of the following rock types and units, not all of which are 

differentiated on plate 43. Precambrian rocks consisting of schist, 

gneiss, granite, quartzite, conglomerate, and slate are exposed in the 

deep valley of the Uncompahgre River south of Ouray, along the Lake 

Fork of the Gunnison River southwest of Lake City, in the Needle 

Mountains in the southwestern part of the San Juan Mountains, near 

the Gunnison River, and in the Sangre de Cristo Mountains on the 

north and northeast flanks of the San Juan Mountains. Sedimentary 

rocks of Paleozoic and Mesozoic age are exposed only on the flanks 

of the mountains and in the deeper canyons; locally along the 

margins of the mountains they underlie the volcanic rocks, but in the 

central part of the mountains they were largely removed before the 

volcanic rocks were erupted. Tertiary volcanic rocks, consisting for 

the most part of bedded lavas, tuffs, and breccias, underlie most of 

the higher parts of the San Juan Mountains. The volcanic rocks 

have been divided into the following main units, listed in order of 

decreasing age: The San Juan tuff of Miocene(?) age; the Silverton 

volcanic series of Miocene age; the Beidell latite-andesite and the 

Tracy Creek quartz latite of Miocene (?) age; the Potosi volcanic 

series, also of Miocene age; the Fisher quartz latite of Miocene age; 

and the Hinsdale formation of Pliocene (?) age. Early and late
388 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

Tertiary intrusive rocks, not differentiated on plate 43, consist of 

dikes, sills, stocks, and volcanic pipes. Only the larger areas of 

undifferentiated Tertiary and Quaternary sedimentary rocks and 

alluvium are shown.

The generalized structural features shown on plate 43 consist of highand low-angle faults and monoclinal folds. Areas of cauldron subsidence, near the towns of Silverton and Lake City, are outlined by 

the concentric fault patterns shown on the map. Other structural 

features important in understanding the known uranium occurrences 

will be described in the sections on individual districts.

METHOD OP TESTING FOB RADIOACTIVITY

A scintillation counter was used in most of the districts to locate 

areas of abnormal radioactivity; individual radioactivity readings 

were taken mainly with portable survey meters equipped with 6-inch 

beta-gamma probes, though some readings were made with a scintillation counter. The readings taken at anomalously radioactive 

localities were measured in milliroentgens per hour (mr per hour) 

and are recorded in tables 1, 2, 3, and 4.

For most anomalously radioactive localities, both the maximum 

reading obtained on the most radioactive rock found and the range of 

background readings at that locality are listed in the tables. The 

maximum readings were obtained by repeated tests during which the 

probe was held directly against the rock being tested. All maximum 

readings were made on rocks of hand-specimen size unless the tables 

indicate that a spot reading was taken with the probe held directly 

against a rock exposure. The background readings were obtained by 

holding the probe at waist height for about 1 minute and recording 

the range of readings.

A locality is considered to be anomalously radioactive if the ratio 

of the maximum radioactivity reading to the maximum background 

reading is equal to or greater than an arbitrary figure. The figure 

used was 2.1 for all districts except the Upper Uncompahgre district, 

where a figure of 3.0 was chosen. This exception was made because 

most of the radioactivity readings taken in the Upper Uncompahgre 

district were spot readings, which ordinarily are higher than readings 

made on hand specimens from corresponding outcrops. The radioactivity readings taken hi the other districts were made for the most 

part on samples of hand-specimen size.

RESULTS OP RECONNAISSANCE

Twenty-eight areas embracing about 34 mining districts in the San 

Juan Mountains (pi. 43) have been tested for radioactivity. A few 

of the smaller mining districts, the vanadium-uranium deposits in
RADIOACTIVITY IN METAL-MINING DISTRICTS OF COLORADO 389

sedimentary rocks of Mesozoic age on the west and southwest borders 

of the mountains (Fisher, Haff, and Rominger, 1947; A. L. Bush and 

Leonid Bryner, written communication), and the uranium-bearing 

hydrocarbon deposits in the Placerville area west of Telluride (V. 

R. Wilmarth and R. C. Vickers, written communication) were 

not examined. Results of work in areas 1-7 (pi. 43) have been 

published (Burbank and Pierson, 1953) but are briefly summarized 

here to present a complete picture and to include additional data for 

areas 1, 3, 5, and 6.

Anomalous radioactivity was found in the Cochetopa, Cebolla, 

Upper Uncompahgre, Lower Uncompahgre, Red Mountain, Telluride, 

Sneffels, Mount Wilson, Rico, La Plata, Engineer Mountain, Burrows 

Park (Whitecross), Carson Camp, Creede, and Bonanza districts. 

Uranium is the chief cause of the radioactivity; thorium is important 

only in the Cebolla and Burrows Park (Whitecross) districts; and 

radon is largely responsible for the radioactivity measured in the 

Mount Wilson district. No anomalous radioactivity was found in 

the Silverton, Ophir, Eureka, Animas Forks, Mineral Point, Galena, 

Lake, Spar City, Embargo, Beidell, Summitville, Platoro districts, 

or in several other smaller districts.

Samples were collected that had amounts of uranium, listed in 

the tables, ranging from 0.001 to 2.71 percent; but none of the deposits at the sample localities can be classed as commercial at present 

because of their low grade, small size, or unknown characteristics 

where a sample came from a mine dump at an inaccessible working.

Pitchblende is the main uranium mineral in the Upper Uncompahgre, Red Mountain, and Bonanza districts and probably contains 

the uranium in most of the other districts where the radioactive 

material has not been identified because of fine grain sizes and small 

amounts.

AREAS OF ANOMALOUS RADIOACTIVITY 

COCHETOPA AREA

The results of a brief reconnaissance in the Cochetopa area (pi. 43, 

area 1) in 1951 by Burbank have been published (Burbank and 

Pierson, 1953). Only one minor occurrence of radioactive jaspery 

vein matter was found near the southern limit of the Precambrian 

exposures along Cochetopa Creek. Since the 1951 reconnaissance, 

however, the Thornburg Mining Co., of Grand Junction, Colo., has 

developed a commercial uranium deposit on the Los Ochos claims 

in the Cochetopa area about 12 miles south of U. S. Highway 50 

connecting Gunnison and Salida, Colo.

The geology of the Los Ochos deposit has been described by H. 

S. Stafford and R. C. Derzay (written communication) who found

466773 58 2
390 CONTRIBUTIONS TO THE GEOLOGY OP URANIUM

that the vein follows a major eastward-trending fault that cuts 

steeply across Precambrian granite, schist, and gneiss, as well as 

sedimentary rocks of the Morrison formation of Jurassic age. The 

ore consists of sooty uraninite and secondary uranium minerals which 

are localized where the main fault is intersected by northeastwardtrending cross fractures. The Precambrian rock is the most favorable 

host rock for the ore.

CEBOULA DISTRICT

The thorium-bearing quartz-carbonate-pyrite-sphalerite-galena 

veins in the Precambrian rocks of the Cebolla district (pi. 43, area 2) 

were studied briefly in 1951 by Burbank (Burbank and Pierson, 

1953). Although local samples containing as much as 0.28 percent 

of thorium were obtained, none of the veins studied seemed to be of 

economic value. Olson and Wallace (written communication, 1956) 

later made a detailed study of the thorium and rare-earth minerals 

in the Powderhorn district south of the Cebolla district. Thoriumbearing veins and mineralized shear zones are found in or near alkalic 

igneous rocks. Although selected samples of high-grade material 

contain as much as 4 percent of ThO2, the ThO2 content of the veins 

is generally less than 1 percent and is only 0.05-0.1 percent in many 

of the veins. The age of the thorium deposits is not known more 

closely than pre-Jurassic.

UPPER TOSrCOMPAHGKE DISTRICT

General geology. The generalized geology of the Upper Uncompahgre district (pi. 43, area 3), which lies south of the town of Ouray, 

is shown on plate 44. The geology shown on plate 44 and summarized below has been taken from published reports by Cross and 

Howe (1907), Burbank (1940), and Kelley (1946). The rocks exposed 

in the area, which includes most of the Upper Uncompahgre district, 

comprise steeply dipping quartzites and slates of the Precambrian 

Uncompahgre formation; moderately dipping limestones, shales and 

sandstones of Paleozoic age; and nearly horizontal Telluride conglomerate and San Juan tuff of Tertiary age. Quaternary deposits 

and pre-Tertiary and Tertiary dike rocks are not shown. The 

Uncompahgre formation and the San Juan tuff are of interest to this 

report because they are the host rocks of pitchblende-bearing veins.

The Uncompahgre formation consists of interbedded slate and 

quartzite units, ranging in thickness from 20 to several thousand 

feet, and aggregating about 9,000 feet in exposed thickness. Neither 

the top nor the bottom of the formation is exposed; in the northern 

part of the district the Ouray fault has thrown the Uncompahgre 

formation against the rocks of Paleozoic age, and in the southern 

part of the district the Uncompahgre formation passes beneath the
RADIOACTIVITY IN METAL-MINING DISTRICTS OF COLORADO 391

San Juan tuff. The Uncompahgre formation has been folded into 

a broad anticline trending N. 65° W., with the crest near the Dunmore 

vein. The limbs of the anticline dip between 55°-70°.

The rocks of Paleozoic age, not differentiated on plate 44, consist 

of the Elbert formation and the Ouray limestone of Late Devonian 

age, the Leadville limestone of Mississippian age, and the Molas and 

Hermosa formations of Pennsylvanian age.

The Telluride conglomerate of Oligocene (?) age is chiefly a coarse 

conglomerate containing pebbles and boulders of granite, schist, 

quartzite, porphyritic igneous rocks, and sedimentary rocks of Paleozoic and Mesozoic ages. The overlying San Juan tuff of Miocene (?) 

age, a bedded 1,800- to 3,000-foot thick gray to purplish-gray tuff 

breccia and conglomerate composed of coarse angular andesitic and 

latitic fragments in a tuffaceous matrix, forms the higher parts of 

the steep-walled Uncompahgre River gorge and constitutes an important part of the bedrock of the Upper Uncompahgre district.

The ore deposits of the district occur in the Uncompahgre formation, the rocks of Paleozoic age, and the San Juan tuff. The chief 

deposits in the Uncompahgre formation and in the San Juan tuff are 

fissure veins, which consist mainly of quartz with pyrite, sphalerite, 

galena, chalcopyrite, native gold, argentiferous tetrahedrite, rhodochrosite, and barite. A few veins have ore shoots with tungsten, 

usually huebnerite, and a few others contain sulfobismuthites of lead 

and silver, such as the mineral alaskaite. The ore deposits in the 

rocks of Paleozoic age are found mainly in the Mineral Farm area (pi. 

44) as silver-lead replacement deposits in the upper part of the Leadville limestone.

Results of reconnaissance. Rocks were tested for radioactivity 

along about 16 miles of linear traverse and one-fourth square mile of 

area traverse of the slate and quartzite bands of the Uncompahgre 

formation, and about 5 miles of linear traverse along the Ouray fault. 

Several mines in the Precambrian, Paleozoic, and Tertiary formations 

and about one-fifth square mile of area traverse of the Paleozoic formations in the vicinity of the Ouray hot spring deposit (pi. 44, loc. 1) 

were tested.

Although no uranium deposit of commercial size or grade was found 

in the district, anomalous radioactivity occurs at the hot spring 

deposit (pi. 44, loc. 1) near Ouray, at Bear Creek Falls (pi. 44, Iocs. 2 

and 3), and at the Michael Breen mine (pi. 44, Iocs. 4 and 5). Table 1 

gives data for samples from the anomalously radioactive localities.

Radioactive localities. The radioactivity in calcareous tufa at the 

Ouray hot spring (Burbank and Pierson, 1953), which has been mined 

for manganese and tungsten, is caused mainly by radium and other 

daughter products of uranium. The deposit, just north of the Ouray
TABLE 1. Localities in the Upper Uncompahgre mining district having maximum radioa

background 1

Map 

location

«1 

2 

3 

4

5

Sample

K-43-1 

62-P-20 

62-P-6 

53-P-22

63-P-28

Radioactivity 

(mrper 

hr)>

1.0 

.70 

.35 

20.

.40

Background 

(mr per hr)

0.06 

0.02- .06 

.04- .07 

.02- .04

.01- .03

Equivalent 

uranium 

(percent)

0.11 

.15 

.029

.16

Uranium 

(percent)

* 0.001 

«.099 

.019 

69.53

.14

Sample description

Manganese-stained tufa and manganese ore from 

spring deposit.

Chip sample of highly radioactive slate from the 

near Bear Creek Falls; spot reading 1.30 mr per 

A 2-ft channel sample across a quartz-pyrite-sphale

rhodochrosite vein; from the north face of an 18

ft from portal of adit.

by X-ray analysis) intermixed with about 15 pe

scopically visible galena, native bismuth, c

quartz; from fracture filling in San Juan tun, l

Michael Breen mine, about 245 ft east of ma

crosscut.

Malachite-stained chalcopyrite-tetrahedrite(?)-qu

vein material from outcrop above portal of Mic

mine.

i Chemical, X-ray, and spectrographic analyses by O. Angelo, Q. W. Boyes, Jr., Rene 

Dufour, P. J. Dunton, 8. Furman, R. Q, Havens, A. G. King, W. Mountjoy. W. F. 

Outerbridge, J. N. Rosholt, P. Schuch, and J. Wahlberg, U. 8. Geological Survey.

2 All readings were ma

» Data in part from B

«Disequilibrium caus
RADIOACTIVITY IN METAL-MINING DISTRICTS OF COLORADO 393

fault, rests on rocks of Paleozoic age and is overlain by glacial gravels 

of Pleistocene age. Most of the deposit was tested for radioactivity. 

A sample of tufa from the deposit contains 0.11 percent of equivalent 

uranium but only 0.001 percent of uranium. Spectrographic analysis 

shows relatively large amounts of manganese, silicon, iron, calcium, 

barium, strontium, and tungsten.

Small amounts of uranium, ranging from 0.003 to 0.099 percent, are 

found in the Precambrian rocks at Bear Creek Falls in the quartzite 

wall rock of a quartz-pyrite-sphalerite-galena-rhodochrosite vein, in 

the vein itself (pi. 44, loc. 3), and in a shear zone in slate (pi. 44, loc. 2)* 

The uranium-bearing vein is the easternmost of the two veins shown 

on plate 44; no anomalous radioactivity was found along the other 

vein. The radioactivity of the easternmost vein is confined mainly 

to the pyritized quartzite of the footwall at the north face of an 18- 

foot drift 140 feet from the portal of the northernmost adit; however, 

moderate radioactivity was noted at several places along the outcrop 

of the vein about 50 feet above the adit level. A 2-foot channel 

sample containing 0.029 percent equivalent of uranium and 0.019 

percent of uranium was taken from the north face of the drift; the 

sample included 8 inches of pyritized quartzite from the footwall, 4 

inches of vein material, and 12 inches of quartzite from the hanging 

wall.

The uranium-bearing shear zone crops out near Bear Creek Falls 

(pi. 44, loc. 2). The shear zone is exposed for a length of about 70 

feet, but the total length is at least 125 feet, and may be as much as 

500 feet. The width of the zone ranges from 5 to 15 feet.

Although chip samples of radioactive slate from the zone contain 

as much as 0.099 percent of uranium, the percentages of uranium in 

4 channel samples and 1 chip-channel sample across the strike of the 

zone are generally lower and range from 0.003 to 0.014.

The uranium mineral or minerals in the radioactive samples from 

the Bear Creek Falls area have not been identified. Attempts to 

concentrate the uranium minerals sufficiently for X-ray or other 

studies have not been successful, probably because the initial amounts 

and grain sizes of the uranium minerals have been too small. Examination of the most radioactive specimens of slate under ultraviolet 

light indicates that a mineral fluorescing yellow green, probably a 

secondary uranium mineral, is present on some of the radioactive 

surfaces. Some radioactive surfaces, however, do not contain any 

fluorescent mineral, and the uranium mineral may be pitchblende in 

these samples.

Sample 2 (table 1) was analyzed for Th232 and for radium and other 

daughter products of uranium. No Th232 was detected, and the 

analyses show that the difference between total radioactivity and
394 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

uranium content is caused by radium and other daughter products of 

uranium. Leaching of uranium by supergene processes is the probable cause of this disequilibrium.

Pitchblende hi veins cutting the San Juan tuff was discovered at 

the Michael Breen mine by T. H. W. Loomis and W. A. Hammond 

of the Atomic Energy Commission in 1953 and was studied by T. H. W. 

Loomis, C. T. Pierson, and W. A. Hammond (written communication, 

1953). Two radioactive localities were found: one on level 9 of the 

mine (pL 44, loc. 4), and the other at a hillside outcrop above the 

mine (pi. 44, loc. 5). At the underground locality, pitchblende is 

found in a narrqw vein which strikes N. 15° to 20° W., and dips 85° 

SW. The pitchblende-bearing vein is offset about 4 feet where it 

crosses the main eastward-trending Michael Breen vein.

The pitchblende of locality 4 (pi. 44) is found as a %- to %-inch 

wide seam in a 2- to 3-inch wide quartz-chalcopyrite-pyrite vein. 

The wall rock, in contrast to its usual dark gray, is pink or cream for 

widths up to one-half inch on either side of the vein. The pitchblende 

occurs both hi arborescent and in botryoidal masses and is associated 

with chalcopyrite, pyrite, galena, native bismuth, hematite, malachite, 

and quartz. The pitchblende, at least in part, appears to be earlier 

than the pyrite; age relations to the other minerals are not known.

The uranium content of a 2-inch wide chip-channel sample along 

about 2 feet of dip length of the pitchblende-bearing vein was only 

0.53 percent of uranium because of the spotty distribution of the 

pitchblende which pinches out upward in less than 20 feet and appears 

to occur in lenses along the strike of the vein. Several channel 

samples 2 feet in length that were taken across the fracture by T. H. W. 

Loomis (oral communication, 1953) each contain less than 0.02 

percent of uranium.

The radioactivity noted at the hillside outcrop about 200 feet 

above level 9 of the Michael Breen mine (pi. 44, loc. 5) is hi a narrow 

chalcopyrite-tetrahedrite(?)-quartz-barite vein in San Juan tuff. The 

vein strikes north and dips 80° E. A selected sample from the most 

radioactive part of the 2- to 4-inch wide vein contains 0.14 percent 

of uranium. The radioactive part of the vein has a strike length of 

about 15 feet and a dip length of about 7 feet. This radioactive 

vein is probably distinct from the pitchblende vein of locality 4 (pi. 

44) but is generally parallel to it.

RED MOUNTAIN DISTRICT

Introductory statement and general geology. In 1951 pitchblende (?) 

was found (Burbank and Pierson, 1953) in the Red Mountain district 

(pi. 43, area 5) near Red Mountain pass between Ouray and Silverton. 

Most mine dumps and accessible mines hi the district were examined
RADIOACTIVITY IN METAL-MINING DISTRICTS OF COLORADO 395

for radioactivity in 1952. The radioactivity readings and laboratory 

data are presented together with the previously published information 

(fig. 49, table 2) to give a more complete picture of the uranium

Radioactivity tests by W. S. Burbank a 

C T Pierson. 1951. and C. T. Pierson, 

W F. Weeks and F. J. Klienhampl, 1952 

6000 Feet

EXPLANATION

Adit Adit dump Shaft Shaft dump 

Mine workings or dumps with anomalous radioactivity

Maximum radioactivity equaM>r greater than 2.1 times 

background. Numbers refer to description in table 2

12,222' 

Elevation above sea level, in feet

FIGURE 49. Map showing mines tested for radioactivity, Red Mountain mining district and 

vicinity, Ouray and San Juan Counties.
396 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

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RADIOACTIVITY IN METAL-MINING DISTRICTS OF COLORADO 397

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398 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

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RADIOACTIVITY IN METAL-MINING DISTRICTS OF COLORADO 399

occurrences. The uranium occurrences are at the northwest border 

of the Silverton caldera (Burbank, 1941, p. 148) and are associated 

with chimneylike ore bodies in volcanic breccia pipes, veins, and 

adjacent wall rocks. Many of the deposits have been mined extensively for rich copper-lead-silver ore, and all except one are in the 

Silverton volcanic series of Miocene age. The exception, locality 1 

(fig. 49), is in the underlying San Jaun tuff of Miocene(?) age.

Uranium occurrences. No commercial deposit of uranium was 

found in the Red Mountain district, but specimens from 17 mine 

dumps are anomalously radioactive and locally contain as much as 

0.35 percent of uranium. The sample containing 0.35 percent of uranium is pyritic siliceous galena-enargite(?) ore from a 2-foot wide 

shear zone at the border of a chimne}^ deposit in the Lark mine (fig. 

49, loc. 17). The length and thickness of the shear zone, which 

strikes N. 14° W. and dips 73° SW., are not known.

The ratios of percent uranium to percent of equivalent uranium 

for the 16 analyzed samples from the Red Mountain district range 

from 0.02 (table 2, loc. 8b) to 0.97 (table 2, loc. 17); the average value 

is 0.49. Samples 2, 3b, 8a, 8b, 9, 11, and 14a, all of which have ratios 

lower than the 0.49 average, were analyzed for Th232 and for radium 

and other daughter products of uranium. No Th232 was detected, 

and all the analyses show that the differences between the total radioactivity and the uranium content are caused by radium and other 

daughter products of uranium. As Phair and Levine (1953) have 

shown in their studies of the leaching of pitchblende, the most probable cause for these differences is the leaching of uranium by supergene processes.

In the Red Alountain district the radioactivity is usually associated 

with pyritic base-metal sulfide ore, such as at the Genessee mine 

(table 2, 8a, b, c) and the Carbon Lake mine (14b). In a few places, 

however, as at the Vanderbilt (9) and Carbon Lake (14a) mines, 

pyritized, silicified latite is radioactive.

Sooty pitchblende has been identified as the cause of radioactivity 

in some of the anomalously radioactive locations. In some of the 

other areas the uranium-bearing material has been concentrated somewhat in the laboratory, but none has been obtained in pure enough 

form to permit X-raj^ identification.

BONANZA DISTRICT

General geology and ore deposits. The geology and ore deposits of 

the Bonanza district (pi. 43, area 27), which lies in the northeastern 

part of the San Juan Mountains, have been described by Burbank 

(1932, 1947a). The following general description of the district and 

the base map for figure 50 have been taken from these reports.
400 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

Porphyry Peak 

11,653'

COLORADO 

BELL

ROUND MT

12,041'

^ ^-SHAWMUT 

MINE

x MANITOU MTN

WHALE ADIT 12.137'

,, Hayden Peak 

12,124

Mine working or dump tested 

for radioactivity. Only mines 

tested are shown

Anomalous radioactivity 

Maximum radioactivity equal to 

or greater than 2.1 times maximum background; number 

refers to description in table 3

Datum is mean sea level

Radioactivity test byC. T. Pierson 

Base by U. S. Geological Survey and J. W. Hawley. 1953

FIQUEE 60. Map showing mines tested for radioactivity, Bonanza mining district, 

Saguache County.
RADIOACTIVITY IN METAL-MINING DISTRICTS OF COLORADO 401

Tertiary volcanic rocks cover most of the district and lie on a basement of Precambrian granite, gneiss, and schist, and sedimentary 

rocks of Paleozoic age. The volcanic rocks are chiefly andesite, rhyolite, and latite flows and breccias intruded by many dikes and irregular masses of quartz latite and rhyolite. The volcanic rocks are 

intensely altered locally, and are silicified, pyritized, and altered to 

clay minerals, sericite, and carbonate minerals. Moderate doming of 

the crust may have accompanied the intrusive activity; subsequent 

collapse of the crust resulted in the formation of numerous small tilted 

fault blocks. In general, movements of the faults were downward in 

successive steps toward the central area of subsidence.

All the known metallic ore deposits are veins formed either along 

fault fissures bounding the blocks or in subsidiary tension fissures in 

the walls of large faults.

The ore deposits of the district are chiefly complex base-metal ores 

containing pyrite, sphalerite, galena, chalcopyrite, bornite, enargite, 

tennantite, and st-romeyerite in a gangue of quartz, calcite, rhodochrosite, and barite. Some ores contain a little bismuth which occurs, 

in part, as the mineral cosalite. Quartz veins of relatively high sulfide content containing lead, zinc, copper, silver, and a little gold are 

found chiefly in the northern part of the district; whereas quartzrhodochrosite-fluorite veins, with only minor quantities of sulfides 

valuable mainly for their silver content, are found in the southern 

part of the district.

Uranium occurrences. About 60 percent of the mines or mine 

dumps in the Bonanza district were tested for radioactivity. Figure 

50 shows mines or groups of mines that were investigated. The anomalously radioactive mines are designated in figure 50 by numbers 

which refer to the descriptions in table 3. All the anomalously radioactive localities are concentrated in the north-central part of the district in the vicinity of Rawley Gulch. No anomalous radioactivity 

was detected in the northern or southern parts of the district.

Samples from the radioactive localities have uranium contents 

ranging from 0.033 to 2.71 percent. The highest grade samples came 

from the dump of the caved Whale adit (fig. 50, loc. 3), but significant 

amounts of uranium were found in samples from the Old Rawley mine 

(fig. 50, Iocs. 1 and 2). Lesser though significant amounts of uranium 

were found in samples from the dump of a caved adit south of the 

Whale mine (fig. 50, loc. 5) and from the dump of the Rawley drainage 

tunnel (fig. 50, loc. 6). A few specimens from the dump of the caved 

Whale shaft (fig. 50, loc. 4) showed radioactivity of four times background.

The uranium in samples from the dump of the Whale adit is contained in hard lustrous noncolloform pitchblende which occurs as very
TABLE 3. Mines or mine dumps in the Bonanza mining district having maximum radio

background l

Map 

location

1

2a

2b

2c

3a

3b

Sample

53-P-20

53-P-16

S-2-A

53-P-17

53-P-6

53-P-10

Radioactivity 

(mrperhr)'

0.40

1.00

.10

(spot

reading)

2.00

1.20

15.00

Background 

(mr per hr)

0. 05-0. 09

. 05- . 08

.02- .03

.04- .07

.04- .08

.04-. 08

Equivalent 

uranium 

(percent)

0.27

.75

.62

.064

2.3

Uranium 

(percent)

0.24

3.59

.61

.071

2.71

Sample description

Quartz-barite vein material impregnated 

veinlets of chalcop'yrite, galena, and pyrite

about 730 ft from portal of 200-ft level, Old R

Siliceous chalcopyrite-tetrahedrite-enargite-w

sphalerite-pyrite-bearing ore from chute (to 

about 150 ft south of breast of 500-ft level, 

mine.

Area a few feet square, 35 ft north of main 

level, Old Rawley mine.

Pyritized silicifled andesite(?) from dump of 

mine; probably came from 300-ft level or abo

Sooty pitchblende in vugs in siliceous baritic v

from dump of caved Whale adit.

Galena, tetrahedrite, pyrite, chalcopyrite, an

pitchblende in fine-grained silicified andesite 

of Whale adit. The pitchblende is mainly 

also was observed in a veinlet cutting galen

selvage of a galena veinlet next to silicified a
3c 53-P-15

A-28-A 

53-P-19

53-P-5

.20

.50

.30

. 02- . 05

. 02- . 05

. 03- . 05

.22

.048

44.62

3.055

.033

Hard dark-colored lustrous noncolloform I

blende handpicked from fracture coatings a

in altered andesite from dump of Whale adit

impurities, totalling about 20 percent, w

§

alena, chalcopyrite, pyrite, malachite, 

arite. Pitchblende identified by X-

Coyellite, tetrahedrite, and tennantite w

polished section. 4 

A few specimens from the dump of the caved 

showed minor radioactivity. 

Siliceous vein material from dump of caved 

Pyrite-chalcopyrite-galena-barite vein materi

of caved Eawley drainage tunnel.

1 Chemical, X ray, and spectrograohic analyses by C. Aneelo, G. W. Boyes, Jr., 

N. M. Conkl'n, S. Furman, R. G. Havens, A. G. King, J. Meadows, W. Mountjoy, 

W. F. Outerbridge, J. N. Eosholt, Jr., P. Schuch, and J. Wahlberg, U. S. Geological 

Survey.

2 All readings were 

men size unless noted 

against a rock exposu

3 Disequilibrium ca

« Mineral identifica
404 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

small discrete grains disseminated throughout sulfide vein material or 

as fracture coatings, vug fillings, and late-stage veinlets in limonitestained siliceous vein material or silicified andesitic wall rock. Associated minerals are pyrite, galena, chalcopyrite, tetrahedrite, tennantite, enargite, covellite, quartz, chalcedony, barite, anglesite, hematite, and malachite, and small amounts of an unidentified secondary 

uranium mineral.

The uranium mineral from the other localities probably is also 

pitchblende but is not readily separable for identification.

OTHER DISTRICTS

Lower Uncompahgre (Ouray or Paquiri) district. The geology and 

ore deposits of the Lower Uncompahgre district (pi. 43, area 4), defined to include the mineral deposits of early Tertiary age that are 

chiefly near and north of Ouray in the sedimentary rocks of Paleozoic 

and Mesozoic age, has been described by Burbank (1940). The ores, 

constitute base-metal and precious-metal veins and blanket bodies. 

The results of reconnaissance for radioactive minerals in the Lower 

Uncompahgre district described by Burbank and Pierson (1953) included tests of the Syracuse, Wedge, Bachelor, Sunbeam, J. V. Dexter, 

Calliope, El Mahdi, Pony Express, Slide and Newsboy, Senorita, and 

Black Girl mines or mine dumps.

Slight radioactivity was noted in Jurassic shale from the wall of 

the Pony Express vein in the Pony Express mine north of Ouray. The 

uranium content was only 0.010 percent. Small amounts of radon,, 

ranging from 34 to 910 micromicrocuries per liter of ah- at mine temperature and pressure, were measured by H. Faul (written communication, 1952) of the Geological Survey in the Senorita, Black Girl, 

and Slide and Newsboy mines.

T. H. W. Loomis (oral communication, 1953) of the U. S. Atomic 

Energy Commission made tests in the Lower Uncompahgre district 

in 1953 but found no anomalous radioactivity.

Telluride district. The geology of the Telluride district (pi. 43V 

southern part of area 9) has been described by Burbank (1941). Onlyone mine in the district, the Smuggler Union near the town ol Telluride, was tested for radioactivity. About 20 percent of the accessible 

parts of this mine were checked, and one anomalously radioactive 

locality was found (table 4, loc. 1). At this locality a small area in 

the footwall of the Montana vein contains a viscous uranium-bearing 

hydrocarbon as disseminations and fracture fillings associated with 

galena and pyrite in silicified San Juan tuff. The radioactive zone 

is about 8 feet long and 2 feet wide; the thickness is not known.

Sneffds district. The geology of the Sneffels district (pi. 43, northern part of area 9) has been described by Burbank (1941). Part of
RADIOACTIVITY IN METAL-MINING DISTRICTS OF COLORADO 405

the Campbird mine and several mine dumps, including those of the 

Mountain Top and Keystone mines, were tested for radioactivity. 

Except for several slightly radioactive localities in the Campbird mine, 

no anomalous radioactivity was found. Only about 5 percent of the 

Campbird mine was tested for radioactivity, but 4 small occurrences 

were found at which the maximum radioactivity of "spot readings" 

was about twice maximum background. The radioactive zones, determined by the projection of the occurrences, appear to be about 

parallel to the ore shoots of the Campbird vein.

Mount Wilson district. The geology of the Mount Wilson district 

(pi. 43, area 10) has been described by Varnes (1947a). The main 

mass of the mountains within the district is a stock of Tertiary age, 

which ranges in composition from diorite to monzonite. All the 

mines tested for radioactivity, except the Independence mine, are 

within the stock. The Independence mine is in the Telluride 

conglomerate of Oligocene(?) age. Most of the mines or mine dumps 

in Silver Pick, upper Bilk, and Navajo Basins were tested for radioactivity. Mines in lower Bilk, Elk, Magpie, and several unnamed 

basins were not tested. The maximum radioactivity at any of the 

29 mines tested was only 1.7 times maximum background, except for 

a mine (table 4, loc. 2) in Navajo Basin, where radon was detected.

Rico district. The geology and ore deposits of the Kico district 

(pi. 43, area 12) have been described by Cross and Ransome (1905) 

and by Varnes (1947b). The ore deposits consist of base-metal and 

precious-metal vein and blanket deposits; the main ore zone is the 

Hermosa formation of Pennsylvanian age.

The A. B. G. and C. V. G. mine dumps and the Silver Swan and 

Blaine tunnels were checked for radioactivity by the author and 

T. H. W. Loomis, of the U. S. Atomic Energy Commission. No 

anomalous radioactivity was noted at the C. V. G. or Silver Swan 

mine, but moderately strong radioactivity previously discovered by 

E. N. Harshman (oral communication, 1952) of the Geological Survey 

was noted at the A. B. G. mine, and anomalous radioactivity was 

found in the Blaine tunnel.

A sample of radioactive galena-sphalerite replacement ore in 

siliceous limestone (table 4, loc. 3) from the dump of the A. B. G. mine 

contained 0.013 percent of equivalent uranium and 0.010 percent of 

uranium.

The radioactivity hi the Blaine tunnel (table 4, loc. 4) occurs in a 

20-square-foot area along the Blackhawk vein about 1,750 feet from 

the portal. A sample of radioactive pyrite-quartz vein material 

submitted by T. H. W. Loomis (written communications, 1953) 

contains 0.017 percent equivalent of uranium and 0.009 percent of 

uranium.
406 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

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Vein material containing galena, sphalerite

rhodochroslte from dump of water-filled 

three-fourths of a mile east of old town o

Burrows Park district. The difference be

equivalent uranium and percent uranium 

caused by thorium.

Limonite stained siliceous gouge (?) from d

adit in volcanic rocks of the Silverton series

Carson Pass in the southern part of the 

district.

Anglesite(?) in limonite-stained breccia

rhyolite from a 6-square-ft area in the hang

Amethyst vein, about 815 ft from the p

modore level 3, Creede district. Radioa

not visible.

Spot reading on small area Holy Moses vein

south of crosscut, level 2, Holy Moses 

district. 

Spot reading on a 4-square-ft area in hangin

about 175 ft south of crosscut, Phoenix 

district. 

Barite-quartz-anglesite(?) from vein near 

90-ft level Phoenix mine, Creede district

south of shaft. Zone of radioactivity is p

northward-trending vein and is 2 to 8 in. fro

wall; the approximate strike length of the 

3 to 10 in. wide, is 15 ft. The vertical exten

No uranium mineral visible. 

Spot reading on a 6-square-ft area in the fo

Amethyst vein, 150 ft southeast of crossc

level 5, Creede district.

... 

i Chemical and spectrographic analyses by N. M. Conklin, Rene Dufour, P. J. size unless noted tha

Dunton, S. Furman, R. G. Havens, A. G. King, J. Meadows, P. Schuch, D. Stockwell, a rock exposure, was 

and J. Wahlberg, U. S. Geological Survey. 3 Disequilibrium ca

2 All readings were made in milliroentgens per hour on samples of hand-specimen 
408 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

La Plata district. The La Plata district (Eckel, 1949), (pi. 43, 

area 13), is best known for its gold production, but it also has produced 

silver, lead, copper, and zinc. The chief ore minerals are native gold, 

gold and silver tellurides, galena, chalcopyrite, and sphalerite, which 

occur in quartz-pyrite veins and replacement deposits. Small amounts 

of palladium and platinum are associated with chalcopyrite in one 

deposit.

Only a brief investigation was made in 1953 in the La Plata district 

by the author and T. H. W. Loomis, of the U. S. Atomic Energy 

Commission. A chip sample of highly silicified limonite-stained 

kaolinized diorite was collected from the Tomahawk vein (table 4, 

loc. 5) and found to contain 0.32 percent of equivalent uranium and 

0.40 percent of uranium. However, the highest uranium content of 

7 channels taken across the vein by T. H. W. Loomis (written communication, 1953) was only 0.11 percent

Reconnaissance of part of the Tomahawk vein disclosed several 

localities where readings from 2 to 4 times background were obtained.

Engineer Mountain district. The geology of the Engineer Mountain 

district (pi. 43, area 16) has been described by Kelley (1946). The 

dumps of two mines in this area, the Frank Hough and the Syracuse 

Pride, were tested for radioactivity. No anomalous radioactivity 

was found on the dump of the Frank Hough mine, but a sample of 

siliceous galena-pyrite-sphalerite ore containing 0.051 percent of 

uranium was obtained from the dump of the caved Syracuse Pride 

adit (table 4, loc. 6).

Burrows Park (Whitecross) district. The geology of the Burrows 

Park district (pi. 43, area 19) is discussed in the section on the Lake 

City area (p 410).

The dumps of 3 mines in the Burrows Park district were tested, and 

anomalous radioactivity was found at 2 of them. Both radioactive 

localities are in the volcanic rocks of the Silverton series. The third, 

a nonradioactive locality, is a mine in Precambrian granite.

The radioactivity of 1 of the specimens (table 4, loc. 7) is caused by 

a small amount of uranium, but the radioactivity of the other specimen 

(table 4, loc. 8) is probably caused mainly by 0.1 percent or less 

of thorium shown by spectrographic analysis.

Carson Camp district. The economic geology of the Carson Camp 

district (pi. 43, area 20), south of the Lake City area, has been discussed by Larsen (1911). The ore deposits occur mainly as veins and 

fracture fillings in altered zones in the lavas of the Silverton volcanic 

series near quartz diorite intrusive rocks of late Tertiary age. The 

vein minerals are barite, quartz, enargite, pyrite, marcasite, chalcopyrite, sphalerite, and galena. The chief minerals of economic 

value are silver and some gold and copper.
RADIOACTIVITY IN METAL-MINING DISTRICTS OF COLORADO 409

The dumps of nine mines or prospects, including the Batchelor 

mine, were tested for radioactivity. No anomalous radioactivity was 

found except for a small amount of siliceous limonite-stained gouge (?), 

containing 0.032 percent of equivalent uranium and 0.015 percent 

of uranium, from the dump of a caved adit (table 4, loc. 9) just north 

of Carson Pass in the southern part of the district.

Creede district. The geology and ore deposits of the Creede district 

(fig. 2, area 22), in the central part of the San Juan Mountains, has 

been described by Emmons and Larsen (1923) and Larsen (1929).

The ore deposits of the district consist mainly of veins carrying 

sphalerite, galena, silver, gold, pyrite, chalcopyrite, amethystine 

quartz, barite, and fluorite. The veins occupy faults in rhyolite and 

quartz latite of the Potosi volcanic series of Miocene age. Secondary 

enrichment has been important in the district.

About 20 mines or mine dumps, including the Silver Horde, Magnusson, Alpha, Corsair, Solomon, Emperius, Amethyst, Commodore, 

Holy Moses, Outlet, Phoenix, Colewood, and Equity mines, were 

tested for radioactivity. The locations and descriptions of most of 

these mines are found in the above publications.

Anomalous radioactivity was noted at 5 places (table 4, loc's. 

10-14) in the Commodore, Holy Moses, Amethyst, and Phoenix 

mines. However, the uranium contents of the 2 analyzed samples 

were only 0.055 and 0.020 percent. These were for vein material 

from the Phoenix mine (loc. 13) and altered wall rock of the Amethyst 

vein from the Commodore level 3 (loc. 10).

AREAS OP NO ANOMALOUS RADIOACTIVITY 

8ILVERTON AREA

The geology of the Silverton area and the nearby Arrastra Basin, 

Eureka, Animas Forks, and Mineral Point districts (pi. 43, areas 6, 7, 

and 15) has been described in reports by Cross, Howe, and Ransome 

(1905), Burbank (1933), Burbank (1951), Burbank and others (1947), 

and Kelley (1946). The ore deposits consist mainly of base-and 

precious-metal veins in Tertiary volcanic rocks.

The following mines or mine dumps, most of which are shown or 

described in the above references, were tested, but no anomalous 

radioactivity was detected: In the Silverton area and Arrastra Basin 

district (area 6), the lone Extension claim, Blackhawk tunnel, American tunnel (Gold King), Empire tunnel, Ezra R. mine, A. S. and R. 

tunnel, and Highland Mary mine were investigated. In the Eureka, 

Animas Forks, and Mineral Point districts (area 15), the Columbus 

tunnel, Frisco tunnel, and the Lucky Jack, London, and Bill Young 

mines were tested. The Bandora mine (area 7), 8 miles westward 

from Silverton, showed no anomalous radioactivity.
410 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM 

SUMMITVILLE-FLATORO AREA

The geology and ore deposits of the Platoro, Summitville, Axel], 

Stunner, Gilmore, and Jasper mining districts (pi. 43, area 28) have 

been described by Patton (1917). Most of the mines mentioned 

below are referred to in his report. The districts have chiefly produced gold and silver from quartz-bearing veins in Tertiary volcanic 

rocks of the Conejos quartz latite and the Fisher quartz latite. Radioactivity tests were made in all districts except the Gilmore district, 

but no anomalous radioactivity was found.

In the Summitville district, in the northwestern part of the area, 

15 mines or mine dumps, including the Aztec, Golconda, Bob Tail, 

Esmond, Highland Mary, Winchester, Chandler, Ida, French, Dexter, 

Science, Iowa, Copper Hill, Narrow Gauge, and Reynolds mines were 

tested for radioactivity. The Forest King and Mammoth mine 

dumps were tested in the Platoro district; Wilker's and Glacier mines 

were tested in the Axell district, just east of the Platoro district. 

The Pass-Me-By, Asiatic, Red Mountain No. 1, Louisa, Helper No. 10, 

Apex, and Victor mines were tested in the Stunner district; and the 

Sanger, Guadaloupe, and Miser mines were tested in the Jasper 

district.

CITY AREA

The geology and ore deposits of the Lake City area, including the 

Galena district along Henson Creek (pi. 43, area 17), the lake district 

along the Lake Fork of the Gunnison River (pi. 43, area 18), and the 

Burrows Park (Whitecross) district (pi. 43, area 19), have been 

described by Burbank (1947b). Irving and Bancroft (1911) described 

the geology and ore deposits of the Lake and Galena districts.

Most of the volcanic rocks of the Lake City area belong to thgt 

Silverton volcanic series. The ore deposits are concentrated near the 

border of an oval-shaped down-faulted block or caldera located between 

Henson Creek and the Lake Fork of the Gunnison River, and apparently are controlled by the marginal faults of the caldera. The ore 

deposits consist mainly of quartz-bearing base- and precious-metal 

veins. Silver is particularly important where the veins are enriched 

near the surface. Gold and silver tellurides occur locally. Precambrian granite is exposed along the south side of the caldera and 

on the west near the old town of Whitecross in Burrows Park. A few 

small ore deposits are found in the granite of the Burrows Park district.

The dumps of 11 mines or prospects, including the Ute and Ulay, 

Lucky Strike, and Golden Fleece mines, in the Galena, Lake, and 

Burrows Park districts, were tested for radioactivity. No anomalous 

radioactivity was noted in the Galena or Lake districts; the radioactive specimens from 2 of the 3 dumps tested in the Burrows Park 

district have been described previously.
RADIOACTIVITY IN METAL-MINING DISTRICTS OF COLORADO 411 

OTHER DISTRICTS

Dunton district. The gold and silver deposits of the Dunton district (pi. 43, area 11) are found mainly in Tertiary veins in Mesozoic 

sedimentary rocks. Dumps of the lower adit of the Modern Gold 

Mines Co., and of the main adit of the Free Coinage group were 

investigated and no anomalous radioactivity was found.

Ophir district. The geology of the Ophir district (pi. 43, area 8) has 

been described by Varnes (1947c). Seven mines or mine dumps in 

the district, including the Carbonero, Attica, Badger, Silver Bell, and 

Butterfly, were tested, but no anomalous radioactivity was found.

Needle Mountains area. The Precambrian slates and quartzites 

exposed along an old road east of U. S. Highway 550 in the Needle 

.^Mountains (pi. 43, area 14) were "spot checked" along a 2-mile length 

of the road, but no anomalous radioactivity was detected. However, 

radioactivity has been reported in the Needle Mountains district to 

the south, and additional testing is needed before any conclusions 

can be drawn.

Spar City district. The Spar City district south of Creede (pi. 43, 

area 21) contains sparsely mineralized veins in Fisher quartz latite. 

One mine and two mine dumps were tested, but no anomalous radioactivity was found.

Wanamaker Creek district. The ore deposits of the Wanamaker 

Creek district (pi. 43, area 23), probably mainly valuable for gold and 

silver, occur in pyrite-chalcopyrite-quartz veins hi andesite of the 

Potosi volcanic series, near an intrusive body of Potosi age.

The dumps of eight mines or prospects in the district were checked, 

but no anomalous radioactivity was detected.

Embargo and Summer Coon districts. The Embargo district (pi. 43, 

"area 24), and possibly the Summer Coon district (pi. 43, area 25) in 

the east-central part of the San Juan Mountains, were small producers 

of gold, silver, lead, and copper. In the Embargo district the ore 

deposits occur in fissure veins which cut bedded andesites and quartz 

latite intrusive rocks of late Tertiary age. The vein minerals are 

galena, sphalerite, pyrite, and quartz. No ore minerals were observed 

in the Summer Coon district.

Checks of the dumps of 5 small mines or prospects in the Embargo 

district and of 6 prospects in the Summer Coon district did not disclose 

any anomalous radioactivity.

Beidell district. The ore deposits of the Beidell district (pi. 43, area 

26) consist of gold in limonite-cemented crudely bedded andesite 

breccia of pre-Potosi age; some open pits were dug in a zone of strong 

clay alteration. The dumps of 11 prospects, including a few of the 

cuts in the altered zone, and the face of a large opencut gold mine in
412 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

the andesite breccia were tested, but no anomalous radioactivity was 

found.

The Crystal Hill district just south of the Beidell district was not 

examined.

CONCLUSIONS

A reconnaissance for radioactive minerals in 34 mining districts in 

the San Juan Mountains has disclosed significant though not commercial uranium occurrences hi the Bonanza, Upper Uncompahgre, La 

Plata, Red Mountain, Telluride, Lower Uncompahgre, Rico, Engineer 

Mountain, Burrows Park (Whitecross), Carson Camp, and Creede 

districts. A commercial pitchblende deposit has been developed in 

the Cochetopa area since the reconnaissance. Additional prospecting 

in most of these districts and in the Needle Mountains district migirtr 

disclose some small commercial uranium deposits, although the 

probability does not seem great for the Telluride, Lower Uncompahgre, 

Carson Camp, or Creede districts. Additional reconnaissance in the 

Sneffels, Mount Wilson, Silverton, Eureka, Animas Forks, Mineral 

Point, Poughkeepsie, Summitville, Platoro, Lake, Galena, Dunton, 

Ophir, Spar City, Wanamaker Creek, Embargo, Summer Coon, and 

Beidell districts probably would not be profitable because of the 

generally low level of radioactivity in these districts. Exploration 

in the Bonanza, Upper Uncompahgre, La Plata, and Red Mountain 

districts might result hi finding small amounts of uranium ore, but the 

cost probably would be excessive.

LITERATURE CITED

Burbank, W. S., 1932, Geology and ore deposits of the Bonanza mining district, 

Colorado: U. S. Geol. Survey Prof. Paper 169, 166 p. ^

 1933, Vein systems of the Arrastra Basin and regional geologic structure 

in the Silverton and Telluride quadrangles, Colorado: Colorado Sci. Soc. 

Proc., v. 13, p. 136-214.

 1940, Structural control of ore deposition in the Uncompahgre district, 

Ouray County, Colorado, with suggestions for prospecting: U. S. Geol. 

Survey Bull. 906-E, p. 189-265.

 1941, Structural control of ore deposition in the Red Mountain, Sneffels, 

and Telluride districts of the San Juan Mountains, Colorado: Colorado Sci. 

Soc. Proc., v. 14, p. 141-261.

 1947a, The Bonanza (Kerber Creek) mining district, Saguache County, 

in Mineral resources of Colorado: Colorado Min. Res. Board, p. 443-446.

 1947b, Lake City area, Hinsdale County, in Mineral resources of Colorado: 

Colorado Min. Res. Board, p. 439-443.

1951, The Sunnyside, Ross Basin, and Bonita fault systems and their

associated ore deposits, San Juan County, Colorado: Colorado Sci. Soc. Proc., 

v. 15, p. 285-304.

Burbank, W. S., Eckel, E. B., and Varnes, D. J., 1947, The San Juan region, in 

Mineral resources of Colorado: Colorado Min. Res. Board, p. 396-446.
RADIOACTIVITY IN METAL-MINING DISTRICTS OF COLORADO 413

Burbank, W. S., and Pierson, C. T., 1953, Preliminary results of radiometric

reconnaissance of parts of the northwestern San Juan Mountains, Colorado:

U. S. Geol. Survey Circ. 236, 11 p., 2 pis. 

Cross, C. W., and Howe, Ernest, 1907, Description of Ouray quadrangle

[Colorado]: U. S. Geol. Survey Geol. Atlas, Folio 153. 

Cross, C. W., Howe, Ernest, and Ransome, F. L., 1905, Description of Silverton

quadrangle [Colorado]: U. S. Geol. Survey Geol. Atlas, Folio 120. 

Cross, C. W., and Larsen, E. S., 1935, A brief review of the geology of the San

Juan region of southwestern Colorado: IT. S. Geol. Survey Bull. 843, 138 p. 

Cross, C. W., and Ransome, F. L., 1905, Description of Rico quadrangle

[Colorado]: U. S. Geol. Survey Geol. Atlas, Folio 130. 

Eckel, E. B., 1949, Geology and ore deposits of the La Plata district, Colorado:

U. S. Geol. Survey Prof. Paper 219, 179 p. 

Emmons, W. H., and Larsen, E. S., 1923, Geology and ore deposits of the Creede

district: U. S. Geol. Survey Bull. 718, 198 p. 

TMscher, R. P., Haff, J. C., and Rominger, J. F., 1947, Vanadium deposits near

Placerville, San Miguel County, Colorado: Colorado Sci. Soc. Proc., v. 15,

p. 117-134. 

Irving, J. D., and Bancroft, Howland, 1911, Geology and ore deposits near Lake

City, Colorado: U. S. Geol. Survey Bull. 478, 128 p. 

Kelley, V. C , 1946, Geology, ore deposits, and mines of the Mineral Point, Poughkeepsie, and Upper Uncompahgre districts, Ouray, San Juan, and Hinsdale

Counties, Colorado: Colorado Sci. Soc. Proc., v. 14, p. 289-466. 

Larsen, E. S., 1911, The economic geology of Carson Camp, Hinsdale County,

Colorado: U. S. Geol. Survey Bull. 470 B, pt. 1, p. 22-30.

 1929, Recent mining developments in the Creede district, Colorado: U. S.

Geol. Survey Bull. 811, pt. 1, p. 89-112. 

Patton, H. B., 1917, Geology and ore deposits of the Platoro-Summitville mining

district, Colorado: Colorado Geol. Survey Bull. 13. 

Phair, George, and Levine, Harry, 1953, Notes on the differential leaching of

uranium, radium, and lead from pitchblende in H2SO4 solutions: Econ.

Geol., v. 48, p. 358-369.

Varnes, D. J., 1947a, The San Juan region (Colorado), Mount Wilson district, 

**- San Miguel County, in Mineral resources of Colorado: Colorado Min. Res.

Board, p. 428.

 1947b, The San Juan region (Colorado), Rico mining district, Dolores 

County, in Mineral resources of Colorado: Colorado Min. Res. Board, p. 

414-416.

 1947c, The San Juan region (Colorado), Iron Springs mining district 

(Ophir, Ames), San Miguel County, in Mineral resources of Colorado: Colorado Min. Res. Board, p. 425-427.