GEOLOGICAL SURVEY CIRCULAR 215

URANIUM IN THE 

METAUMINING DISTRICTS 

OF COLORADO
UNITED STATES DEPARTMENT OF THE INTERIOR 

Douglas McKay, Secretary

GEOLOGICAL SURVEY 

W. E. Wrather, Director

GEOLOGICAL SURVEY CIRCULAR 215

URANIUM IN THE METAL-MINING DISTRICTS 

OF COLORADO

By R. U. King, B. F. Leonard, F. B. Moore, and C. T. Pierson

This report concerns work done on 

behalf of the U. S. Atomic Energy 

Commission and is published with 

the permission of the Commission

Washington, D. C., 1953

Free on application to the Geological Survey, Washington 25, D. C.
URANIUM IN THE METAL-MINING DISTRICTS OF COLORADO

By R. U. King, B. F. Leonard, F. B. Moore, and C. T. Pierson

CONTENTS

Abstract......................

Introduction.'..................

Distribution of uranium deposits. 

Geology and mineralogy ........

Page

1

1

2

3

Guides for prospecting, 

References ...........

Unpublished reports...

Page 

4

ILLUSTRATIONS

Plate 1. Index map showing the distribution of uranium deposits in Colorado. 

Figure 1. Relation of pitchblende deposits to bostonite dikes in the

Front Range mineral belt, Colorado ..........................

2. Relation of pitchblende deposits to mineral zoning in the

Central City district, Colorado .............................

Page

Inside back cover 

5

TABLE

Table 1. Uranium deposits in Colorado shown on plate 1 ...

Page 

7

ABSTRACT

Many varieties of abnormally radioactive rocks 

and ores have been found in Colorado as a result of 

more than eight years of geologic studies by the 

U. S. Geological Survey, but only a small proportion 

of these contain uranium in sufficient quantities to be 

of possible commercial interest.

The most favorable ground in Colorado for 

uranium ore deposits, exclusive of the Colorado Plateaus, 

is the central mineral belt. Here potentially important uranium deposits occur in metalliferous veins in 

pre-Cambrian igneous and metamorphic rocks, usually 

in association with Tertiary intrusive rocks. The 

deposits also occur in Paleozoic, Mesozoic, and 

Tertiary rocks that surround the pre-Cambrian core 

of the Rocky Mountains.

Uranium deposits of eight types occur in 

Colorado: (1) disseminations in sedimentary rocks, 

(2) veins, (3) replacement deposits, (4) volcanic 

breccia pipes, (5) disseminations in igneous and 

metamorphic rocks, (6) pegmatites, (7) radioactive 

inclusions in rhyolite, and (8) hot-spring deposits. 

Disseminated carnotite-like minerals in sedimentary 

rocks constitute the important uranium deposits in the 

Colorado Plateaus; vein deposits are the most important 

in the metal-mining districts.

Pitchblende is the most common urajiium mineral 

in the vein deposits. In Colorado pitchblende has been

found in six kinds of veins: (1) pyritic gold, (2) lead-zincsilver, (3) fluorite, (4) telluride, (5) pyrite-siderite, 

and (6) polymineralic-hydrocarbon veins.

Detailed studies have shown that several geologic guides are useful in prospecting for new deposits. 

They include (1) stratigraphic position, (2) mineral 

associations, (3) sedimentary structure, (4) rock 

alteration, and (5) regional zoning. In addition the 

following relations may be useful: (1) uranium deposits 

are commonly associated with post-Cretaceous 

volcanism; (2) uranium is commonly found in metalmining districts that have produced gold, silver, lead, 

and copper; (3) accumulations of radon and helium are 

theoretically related to deposits of uranium; (4) many 

uranium deposits are associated with bostonite dikes; 

(5) uranium deposits seem to occupy a definite place 

in some types of hypogene zonal patterns; and (6) the 

purple variety of fluorite and the smoky variety of 

quartz are believed to be related to radioactivity.

INTRODUCTION

Since 1944 the U. S. Geological Survey has been 

engaged in the study of uranium deposits in Colorado, 

first on behalf of the Manhattan Engineer District, 

and later on behalf of the Division of Raw Materials 

of the U. S. Atomic Energy Commission. The effort 

has been primarily in the Colorado Plateaus in the 

southwestern part of the state (Fischer, 1949), and 

secondarily in the metal-mining districts of central
Colorado (Staff of Reconnaissance Group, U. S. Geol. 

Survey, 1951). But the search for uranium has been 

made in every county west of Denver, and even in a 

few places in eastern Colorado.

Early field work consisted chiefly of radiometric 

reconnaissance of localities known or reported to 

contain radioactive materials. Current work includes 

radiometric reconnaissance, sampling, search for 

favorable geologic criteria, and geologic mapping, 

followed by detailed geologic studies of the favorable 

localities or districts.

This paper summarizes the results of the field 

studies of the Survey's reconnaissance group and 

outlines some geologic criteria that may be useful 

in guiding the search for uranium ore. The writers 

wish to acknowledge the cooperation of the mining 

companies and individuals who materially aided the 

program by reporting radioactive localities and by 

submitting samples of radioactive rocks and ores.

The writers wish to thank the following Survey 

geologists for information not specifically credited 

to them in the text: J. W. Adams, A. J. Gude, 3d, 

and E. P. Beroni (Nigger Shaft area, Ralston Creek 

district); J. W. Adams and F. B. Moore (thorium 

deposits in Gunnison County); E. P. Beroni and 

F. A. McKeown (scattered deposits in northwestern 

Colorado); Henry Faul, W. E. Bales, J. E. Harrison, 

and B. F. Leonard (radon and radioactivity in mines 

of the,Idaho Springs and Lawson areas); Henry Faul 

and A. Y. Sakakura (radon in some natural gases); 

E. N. Hinrichs, D. M. Sheridan, and F. B. Moore 

(pitchblende in gold-telluride veins near Hessie, 

Boulder County); G. E. Manger (porosity and permeability of radon- and helium-producing horizons); 

H. T. Schassberger, George Phair, and 

K. O. Shimamoto (radioactive inclusions in 

Chalk Mountain rhyolite porphyry); P. K. Sims and 

George Phair (Copper King deposit); Q. D. Singewald 

and C. T. Pierson (St. Kevin, Leadville, and Alma 

districts); and V. R. Wilmarth and D. H. Johnson 

(Jamestown district). Special acknowledgment is due 

L. R. Page for his contributions to this report.

DISTRIBUTION OF URANIUM DEPOSITS

The main source of uranium ore in Colorado is 

in the Colorado Plateaus area (pi. 1) in the southwestern part of the state (Fischer, 1950). Ore also 

has been mined, although in small quantities, in such 

widely scattered places as the La Veta Pass area, 

Huerfano County; the Skull Creek area, Moffat County; 

the Brush Creek area, Eagle County; the Prairie Divide 

area, Larimer County (Granger and King, 1951); the 

Quartz Hill area, Gilpin County (King, 1950b; 

Armstrong, 1952; Moore and Butler, 1952); the 

Lawson-Dumont area; Clear Creek County (King and 

Granger, 1950; King, 1951; Harrison, 1952; Harrison 

and Leonard, 1952); the Caribou area, Boulder County 

(Ridland, 1950, King, 1950a; Wright, 1951; Moore and 

Cavender, 1952); near Garo in Park County (Gott, 1951); 

and the Ralston Creek area, Jefferson County 

(Berthoud, 1875; Gott, 1950; McKeown andGude, 1951). 

Localities where uranium minerals are known to occur 

are shown on plate 1. At present, more than 100 deposits in Colorado are known to contain radioactive 

materials.

Excluding the Colorado Plateaus, the metalmining districts of the central mineral belt of 

Colorado (pi. 1) have been considered to be potentially 

the most important uraniferous areas. Discoveries of 

radioactive deposits in 1951 by the Geological Survey 

in the Alma, Leadville, and St. Kevin districts 

(Pierson and others, 1952), and in the upper and lower 

Uncompahgre and Red Mountain districts in the 

San Juan Mountains (Burbank and Pierson, 1953), lend 

some support to this view. However, recent discoveries 

of pitchblende outside the central mineral belt suggest 

that uranium is not confined to those districts from 

which metal production was high.

In the central mineral belt, the potentially important deposits of uranium are in metalliferous veins 

that cut pre-Cambrian igneous and metamorphic rocks, 

commonly in association with Tertiary intrusive rocks 

(Alsdorf, 1916; Bastin, 1916; Bastin and Hill, 1917; 

Phair, 1952). Within and fringing the central mineral 

belt, uranium deposits occur also in Paleozoic and 

Mesozoic sedimentary rocks (Berthoud, 1875; 

Gott, 1950; Gott, 1951; Mckeown and Gude, 1951; 

Burbank and Pierson, 1953). The uranium generally 

occurs as pitchblende in the Lawson-Dumont (King and 

Granger, 1950; King, 1951; Harrison, 1952; Harrison 

and Leonard, 1952), Central City (King, 1950b; 

Armstrong, 1952; Moore and Butler, 1952), 

Ralston Creek, and Caribou-Grand Island (King, 1950a; 

Ridland, 1950; Wright, 1951; Moore and Cavender, 1952) 

districts in the Front Range. About 300 tons of highgrade uranium ore has been produced in these districts, 

most of which was mined between 1872 and 1919 from 

deposits on Quartz Hill in the Central City district 

(Moore and Kithil, 1913).

In the Prairie Divide area, Larimer County 

(Granger and King, 1951), a pitchblende-bearing ore 

is being mined from a vein that cuts a deposit of 

skarn and sulfide minerals in granite. The importance 

of the area is not yet known because little prospecting 

has been done in this part of the state.

In several areas of late Paleozoic and 

Mesozoic sedimentary rocks in Colorado, conditions favor the occurrence of uranium deposits 

of both the carnotite type (Fischer and Hilpert, 

1952; Fischer, Stokes, and Smith, 1944; 

Webber, 1947), such as those found on the 

Colorado Plateaus, and the vein type. The 

country from La Veta Pass, Huerfano County, 

northward to South Park (Gott, 1951) and 

eastward to Colorado Springs (Beroni and 

King, 1950) contains a number of small carnotite 

deposits in Pennsylvanian, Permian, and 

Jurassic sandstones, and further search may 

uncover larger and richer deposits. The 

Placerville district, San Miguel County, well known 

for its roscoelite ores in the Entrada sandstone 

(Fischer, Haff, and Rominger, 1947), also contains 

veins with uraniferous hydrocarbons and sulfides 

that cut the sedimentary rocks below the Entrada sandstone (Hess, 1913; Wilmarth, 1951). In the Skull Creek 

area, Moffat County, small cupriferous carnotite 

deposits occur in sandstones of Mesozoic age. In the 

Ralston Creek area, Jefferson County (Berthoud, 1875; 

Gott, 1950; McKeown and Gude, 1951), carnotite has 

been found in silicified coal and sandstone of the 

Laramie formation of Cretaceous age.
Uranium-bearing pegmatites are common in 

such places as Quartz Creek, Trout Creek Pass, and 

Crystal Mountain (Hanley and others, 1950; Page, 1950). 

The uranium occurs in complex silicates and oxides, 

commonly in association'with rare-earth and 

thorium minerals. None of the Colorado or other 

domestic pegmatites have been found to contain 

sufficient quantities of uranium minerals to warrant 

mining for the uranium content alone. It is possible, 

however, that small quantities of uranium may be 

recovered from these deposits as byproducts of 

mining for other pegmatite minerals.

In connection with the search for uranium, 

several new deposits of thorium have been found in 

Colorado. In 1950 the Geological Survey investigated 

thorium-bearing veins in a large area of granitic 

rocks in the Wet Mountains, Fremont and Park Counties 

(Dellwig and Gott, 1951). Similar deposits have been 

found in Gunnison County.

GEOLOGY AND MINERALOGY

The known uranium deposits of Colorado may be 

classified into eight types: (1) disseminations in 

sedimentary rocks, (2) veins, (3) replacement 

deposits, (4) mineralized volcanic breccia pipes,

(5) disseminations in igneous and metamorphic rocks,

(6) pegmatities, (7) radioactive inclusions in 

Tertiary rhyolite, and (8) hot-spring deposits. Of 

these, only the first two disseminations in sedimentary rocks, and veins have so far proved to be 

commercially important.

Disseminations of uranium minerals in sedimentary rocks appear to be of secondary origin. By 

far the most important deposits of this type are the 

carnotite ores of the Colorado Plateaus that are found 

in the Salt Wash -sandstone member of the Morrison 

formation. These have been adequately described by 

Fischer (1950) and others. These deposits are 

characterized by fine-grained, disseminated uranium 

minerals associated with vanadium in or near beds rich 

in clay pellets and planV remains. Stream channels 

apparently played an important role in localizing the 

deposits, but the origin of the carnotite is not well 

understood.

The roscoelite ores in the Entrada sandstone of 

the Placerville district (Fischer, Haff, and 

Rominger, 1947), the carnotite ores of the Morrison 

formation in the Meeker area (Webber, 1947), and 

the cupriferous uranium ores in sandstone of 

Mesozoic age in the Skull Creek area are similar 

in structure and mineralogy to the carnotite ores of 

the Colorado Plateaus. The deposits in the La VetaPass 

area also are similar in structure and habit, but they 

contain mainly volborthite rather than carnotite.

The deposit near Garo (Gott, 1951) is in sandstones of the Maroon formation of Pennsylvanian(?) 

and Permian age; it contains carnotite associated 

with volborthite, secondary copper sulfides, and 

carbonates. The absence of plant remains and other 

carbonaceous material is noteworthy. This blankettype deposit is in porous white sandstone beds near 

small cross faults. Such a deposit might be the 

oxidized upper part of a pitchblende-sulfide ore 

body.

The carnotite at the Old Leyden coal mine in 

the Ralston Creek area, Jefferson County 

(Berthoud, 1875; Gott, 1950; McKeown and Gude, 1951\is 

associated with silicified, veined, and brecciated 

coal and sandstone of the Laramie formation. The 

deposit is thought to be related to hydrothermal 

activity of post-Cretaceous age. Carnotite at the 

Mike Doyle prospect, southwest of Colorado Springs 

(Beroni and King, 1950), occurs as fracture fillings 

as well as disseminations in sandstone of the 

Morrison formation.

Uranium in veins chiefly in the mineral 

pitchblende is the source of most of the- world's 

supply. In Colorado, pitchblende has been found in 

six types of veins: (1) pyritic gold, (2) lead-zincsilver, (3) fluorite, (4) gold-telluride, (5) pyritesiderite, and (6) polymineralic -hydrocarbon veins. 

Most of these are in granite or metamorphic rock of 

pre-Cambrian age, but a few are in monzonite of 

post-Cretaceous age or in late Paleozoic and 

Mesozoic sedimentary rocks. The time of the uranium 

deposition-is thought to be Tertiary.

The pyritic gold veins contain pitchblende in 

hard, irregular, lenticular masses or pods as much 

as 1 foot thick and 10 feet in diameter. Streaks of 

soft, sooty pitchblende usually cut and surround these 

hard masses. Pyrite, galena, and sphalerite are 

commonly associated with pitchblende in these 

deposits, but galena and sphalerite may be absent. 

Chalcopyrite is present in some deposits but 

generally is not abundant. Fine-grained, dense quartz 

is the common gangue. The pitchblende -bearing rock 

commonly forms an irregular ore shoot within the 

main shoot of the gold ore. At Central City, however, 

the miners found that the pitchblende -bearing parts 

of the vein had a low gold content (Alsdorf, 1916). 

Hand-cobbed shipping ore from these deposits 

contained as much as 70 percent

The occurrence of pitchblende in lead-zinc-silver 

veins is similar to that in the pyritic gold veins. 

Pods of hard pitchblende, with accompanying sooty 

pitchblende, form shoots in parts of the main sulfide 

ore bodies. In addition to galena, sphalerite, and 

silver minerals, some pyrite and Chalcopyrite are 

present. Quartz and carbonates comprise the 

gangue (Bastin and Hill, 1917; King, 1950a; 

Ridland, 1950; Wright, 1951; Moore and Ca vender, 

1952). At the two better-known occurrences 

of this type, the Caribou (King, 1950a; Ridland, 1950; 

Wright, 1951; Moore and Cavender, 1952) and the 

Jo Reynolds (Bastin and Hill, 1917; King, 1951; 

Harrison and Leonard, 1952) mines, the known 

pitchblende occurs at depths of about 900 to 1, 050 feet 

below the surface; in contrast, the pitchblende in the 

pyritic gold veins at Central City (King, 1950b; 

King and others, 1952) occurs at depths of 40 to 

400 feet.

Fluorite veins, such as the deposits at 

Jamestown (Beroni and others, 1950; Goddard, 1946; 

Goddard, 1947; Phair and Onoda, 1950; Phair and 

Shimamoto, 1952; Wilmarth and others, 1952) contain uraninite and uranothorite as finely disseminated 

grains in fluorite associated with pyrite, galena, 

sphalerite, and, rarely, Chalcopyrite.
Pitchblende has been tentatively identified in sooty 

material on quartz that lines vugs and fractures in goldtelluride veins nearHessie, west of Nederland, Boulder 

County.

A pyrite -siderite vein deposit at Prairie Divide 

(Granger and King, 1951) contains pitchblende in a vein 

that cuts or borders a massive copper-zinc sulfidebody. 

The sulfides pyrite, chalcopyrite, sphalerite, and 

pyrrhotite are believed to have beenformed by a much 

earlier, probably pre-Cambrian, period of ore deposition.

Polymineralic-hydrocarbon veins in the Placerville 

district contain galena, sphalerite, erythrite, tetrahedrite, 

molybdite, chalcocite, azurite, and malachite in a gangue 

of calcite andbarite. The uranium is in a solid hydrocarbon, 

perhaps thucholite, that forms rounded to irregular masses 

as much as 6 inches across in the veins andadjacent 

limestone (Wilmarth, 1951).

Black uranium minerals have been reported from 

several metalliferous replacement deposits in Colorado. 

Virtually nothing is known about such occurrences of uranium.

Pitchblende associated with lead-silver-copper ores, 

in volcanic breccia pipes occurs in the Red Mountain mining 

district (BurbankandPierson, 1953); however, the mine 

workings in the uranium-bearing pipes are inaccessible, 

and the amount of pitchblende present is not known.

Disseminations of uranium minerals in igneous and 

metamorphic rocks, such as in the San Juan region (Burbank 

and Pierson, 1953), and near Steamboat Springs, are generally too low in grade to be commercially important. 

Scattered samples containing as much as 0. 05 percent 

uranium have been obtained from slates in the San Juan region 

(Burbank and Pierson, 1953), but the average grade is lower.

Inclusions of an earlier phase of the Chalk Mountain rhyolite porphyry intrusive near Climax contain small amounts 

of beta-uranophane andpitchblende(?). This occurrence, 

found by the Geological Survey in 1949, appears to be unique.

In the San Juan region (Burbank and Pierson, 1953) 

and near Steamboat Springs, pre-Pleistocene springdeposited tufa has been found to contain uranium, but the 

deposits are small and low in grade.

Secondary uranium minerals are quantitatively 

unimportant in the pitchblende-bearing veins of Colorado, 

and they are rarely abundant enough to serve as a guide 

to primary ore.

GUIDES FOR PROSPECTING

Prospecting for uranium deposits by looking for 

uranium minerals in outcrops or float is practicable in 

areas containing deposits of the carnotite type, but we 

do not know of a single natural exposure containing 

pitchblende in the Front Range. The only surface indications of the pitchblende deposits are scattered flakes of 

green or yellow secondary uranium minerals, such as 

torberniteandautunite, or radioactive gossan. Leached 

outcrops and dumps in which no uranium minerals can 

now be seen may be radioactive, however, from residual 

radium or other radioactive decay products. Consequently, 

the examination of outcrops, dumps, and mine workings, 

using a Geiger counter or other radioactivity-detecting 

apparatus, is a first step in prospecting for uranium in 

vein deposits.

A radiation detector, though the most useful single 

aid in prospecting f or uranium deposits, is only a tool. 

Its use maybe supplemented by geochemical techniques, 

such as sampling vegetation (Cannon, 1951a, 1951b) 4

and mine and spring waters for uranium, and sampling 

mine air for radon. Such tools and techniques, however, 

attain their maximum effectiveness only when they are 

applied in areas which seem to be most favorable, geologically, for the occurrence of uranium deposits.

Stratigraphic position, mineral associations, plant 

remains, favorable sedimentary structures, rock alteration, 

geochemical studies of vegetation, and broad regional 

zoning have beensuccessfulguides in the search for carnotite ore on the Colorado Plateaus (Fischer, 1950; 

Weir, 1952). So far, however, systematic prospecting 

for pitchblende has been difficult, perhaps chiefly because 

of the smaller size of the target and the greater complexity 

of the geologic environment of pitchblende deposits. On 

the basis of preliminary data, we suggest that the following 

geologic relationships might be useful in the search for 

uranium outside the Colorado Plateaus: (1) uranium 

tends to occur in areas of post-Cretaceous igneous 

activity (Kaiser and Page, 1952;Phair, 1952; Waters and 

Granger, 1952); (2) uranium commonly is found in or near 

metal-mining districts that have produced gold, silver, 

lead, and copper; (3) accumulations of helium and radon 

are theoretically related to uranium; and (4) the darkcolored variety of fluorite and the smoky variety of 

quartz in some instances are believed to be 

related to radioactive minerals. One may expect the 

utility of these general guides to vary widely, depending 

on local geologic conditions.

If the uranium deposits in the western United States 

are plotted on the geologic map (Kaiser and Page, 1952), 

many of the occurrences in veins and sandstones appear 

to have a relatively close spatial relation to postCretaceous volcanic and intrusive rocks. Therefore,, 

we believe that the areas subjected to igneous activity 

in post-Cretaceous time are more favorable for prospecting 

than those that contain only the older igneous rocks.

From a tabulation of the metal production of western 

mining districts, it was noted that uranium was most 

commonly present in those districts from which gold, 

silver, lead, and copper had been produced.

For more than three years the Geological Survey has 

been studying the relation of helium-rich gases, particularly 

those containing radon, to the enclosing rocks (Faul and 

others, 1951; Hill, 1950;McNeal, 1950). Bothheliumand 

radon are decay products of uranium. Uraniferous hydrocarbons recently were found in well cuttings from a heliumbearing gas well outside of Colorado. The presence of 

these hydrocarbons has provided a clue to the possible 

source of the helium and radon found in the natural gas. 

This suggests that prospecting in such helium-rich areas 

of Colorado as the Model dome,in Las Animas County, and 

North Park, Jackson County, might be rewarding.

Dark-purple to black varieties of fluorite and black 

or smoky quartz have been noted in many radioactive deposits 

throughout the United States. These color variations in 

fluorite and quartz'have been used with some success as a 

guide in locating the radioactive parts of the deposits.

In addition to these general guides to uraniferous areas, 

the following may be useful in finding pitchblende deposits: 

(1) the occurrence of bostonite dikes (Alsdorf, 1916;Bastin, 

1916; Bastinand Hill, 1917; King and others, 1952;Phair, 

1952), and (2) the zonal pattern of hypogene mineral deposits 

(Leonard,. 1952).

In the Front Range, slightly uraniferous intrusive 

trachytes of Tertiary age, locally termed "bostonites" 

(SpurrandGarrey, 1908; Bastinand Hill, 1917;Lovering 

andGoddard, 1950), occur as dikes and small masses in 

areas known to contain pitchblende-bearing veins (fig. 1).
JAMESTOWN

Bostonite stocks

CARIBOU

EXPLANATION

e

Pitchblende deposit 

Bostonite dike

CENTRAL CITY

_5 MILES

Geology after Levering and Goddard, 1939

Figure 1. Relation of pitchblende deposits to bostonite dikes in the Front Range mineral belt, Colorado.

5
The bostonite dikes are only one member of a complex 

series of Tertiary igneous rocks occurring in a-zone 

that trends diagonally across Colorado. In part, this 

zone coincides roughly with the Front Range mineral 

belt,whichincludes many of the Tertiary mineral deposits 

of Colorado. In the principal pitchblende-bearing 

areas of the Front Range, pitchblende deposits and 

bostonite dikes are closely associated (Alsdorf, 1916; 

Bastin, 1916; King and others, 1952; Phair, 1952). 

Whether the spatial relationship has genetic significance, 

we do not know; but the association does provide a 

possible guide to areas where pitchblende may occur.

Recently, preliminary studies have been made on 

the relation of uranium deposits to zoning in the metalmining districts of the Front Range (Leonard, 1952). 

In the Central City district, for example, a small 

central area containing enargite-fluorite veins is

surrounded successively by (a) an area containing 

pyritic gold veins; (b) an intermediate or transitional 

zone containing veins bearing gold, silver, copper, 

zinc, and lead; and (c) a rather wide zone containing 

silver-lead-zinc veins (Collins, 1903; Bastin and Hill, 

1917; Goddard, 1947; Lovering and Goddard, 1950). 

(See fig. 2.) All the known pitchblende deposits are 

in the transitional zone (b) (Leonard, 1952). Most of 

them are on the west side of the district, but at least 

one small uranium prospect is on the east side. Three 

other pitchblende deposits, found since figure 2 was 

prepared, are also in the transitional zone. The 

distinctive position of the pitchblende deposits in this 

zonal pattern suggests that the transitional zone 

(b) in the Central City district, and perhaps in other 

districts having the same zonal pattern, is especially 

favorable for the occurrence of pitchblende (Leonard, 

1952).

I05°35' 105° 30'

Vein systems from Levering 

and

J08*SO'

i[11 M(j 1 n 1 11 rl 

Gold telluride veins

Silver- lead veins

Pyritic gold veins

EXPLANATION

Enargite-fluorite veins

Pitchblende veins

X 

Pitchblende prospect

Area favorable for pitchblende deposits 

(based on intermediate zone)

?

Position or continuation of areas favorable 

for pitchblende deposits is uncertain

2 Mites 

J

Figure 2. -Relation of pitchblende deposits to mineral zoning in the Central City district, Colorado.
Other districts near Central City show zones of 

silver-lead-zinc deposits about a central area of 

pyritic gold deposits, though enargite-fluorite veins 

are usually lacking (Lovering and Goddard, 1950). 

Among these districts are Georgetown-Silver Plume, 

Empire, Lawson-Idaho Springs, Alice-Yankee Hill, 

Caribou-Grand Island, and Ward-Sunset. Several 

others, such as Breckenridge, Montezuma, 

Michigan Hill, and Jamestown, show similar relations 

differing in scale, complexity, or dominant type of 

mineralization. In these districts, the central area is 

not so sharply defined as it is at Central City; the 

central area with its surrounding zones is likely to be 

irregular, the pattern complicated by the presence of 

more than one central area of pyritic gold deposits. 

Nevertheless', the pitchblende deposits at Caribou, 

Lawson, Michigan Hill, and Jamestpwn seem to fit a 

variant of the pattern of hypogene zoning.

The recent discovery of pitchblende withcopper-, 

lead-, and silver-bearing volcanic breccia pipes 

of the San Juan region (Burbank and Pierson, 1953) 

has focused attention on a type of ore 

deposit not previously investigated for uranium. 

Guides for selecting favorable volcanic breccia pipes 

"have not yet been recognized.

Many mining districts of the central 

mineral belt have not yet been systematically 

prospected for uranium deposits. Districts 

that have produced gold, silver, lead, and 

copper remain favorable places to look 

for uranium. Where appropriate geologic guides 

can be recognized and applied, every effort 

should be made to test their usefulness.

Table 1. Uranium deposits in Colorado shown on plate 1,

Map 

no.

1 

2

1>

4

6

7 

8

9

10

11

12 

13

14 

15 

16 

17

18 

19

20 

21 

22 

23

24

25 

26 

27 

28 

29

Name or locality

Prairie Divide 

Rusty Gold-Cerite 

Springdale 

Gold Hill 

Copper Rock 

Eldora 

Leyden 

Pall River 

Central City 

Golden Gate 

Canyon.

Bellevue -Hudson 

Jo Reynolds 

Spring GulchAlps Mountain.

Georgetown 

Steamboat SpringsBrush Creek 

Rifle 

OkCLuL_L UI^t?K- - 

Climax 

County

Larimer - 

Boulder -

 do -

 do 

. do 

Jefferson 

 do 

Clear Creek- -

Gllpin 

Jefferson 

Clear Creek 

 do 

 do 

 do 

 do 

Routt 

 do 

 do 

Garfield 

Rio Blanco 

Moffat 

Type

Vein 

Pegmatite 

Vein 

Vein 

Disseminated 

Vein 

 do 

 do 

DisseminatedVein 

 do -

 do 

 do 

Shear- zones 

and veins. 

 do 

Di s semina te d -

Spring 

 do 

Disseminated -

 doDisseminated 

Rock

Granite -

Granite , 

schist. 

Granodlorlte -

dnVil at- _ ___ 

Granite , 

schist. 

Silicified coal, 

sandstone . 

Schist, 

pegmatite.

Gneiss -

Schist, 

gneiss.

 do -

Schist- -

 do -

Granite , 

gneiss. 

Schist, 

gneiss.

Schist -

 do -

 do -

 do - 

 do -

Radioactive 

minerals

Pitchblende . 

Cerite , uraninite .

Uraninite , 

torbernite, 

uranothorlte . 

Radium-radon . 

Pitchblende . 

Unknown 

Pitchblende . 

Do. 

Do.

Carnotite .

Pitchblende, second 

ary uranium miner 

als, thucholite(? 

Pitchblende . 

Do.

Do. 

Do. 

Uranophane ( ? ) . 

Pitchblende(?), 

tor-ber-nite . 

Unknown .

Radium-radon ( ? ) .

Radium(?) . 

Autunite . 

Radium-radon . 

Uranium - 

radium-radon ( ? ) .

Carnotite(?). 

Carnotite . 

Do. 

Do. 

Pitchblende (?). 

Torbernite, 

monazite,

brannerite(?).
Table 1. Uranium deposits in Colorado shown on plate 1 Continued

MaP 

no.

30 

31

32 

33

34

35 

36 

37

38

39 

40 

41 

42

43 

44

45

46

47 

48 

49 

50 

51

Name or locality

Chalk Mountain - 

St. Kevin -

Garo -

Trout Creek Pass -

Duff lelds -

Mike Doyle -

Bull Domingo -

Roslta-Haputa - 

Mclntlre -

Cebolla -

Lower Uncompahgre -

Upper Uncompahgre -

Ouray -

County

_ _ c\n _ _ __ _

 do 

 d.0 

 do 

_ rtn - --

Ona f'o Y»

_ /q 0 _ _

Costllla 

 do 

San Mlguel 

Ouray 

 do 

 do 

Type

Inclusions 

Disseminated, 

fracture 

coatings, 

vein.

Vein, replace - 

ment(?).

Vein 

Vein 

 do 

 do 

 do 

 do 

Spring 

Volcanic 

breccia pipe, 

vein.

Rock

Rhyolite 

porphyry. 

Granite, 

s'chist.

<^Vtn 1 f - -

Granite, limestone 

shale.

Sandstone 

Granite 

Granite -

Sandstone, 

shale. 

Granite -

Schist, gneiss -

 do 

Schist and 

aplite . 

Ultrabasic and 

alkaline intrusive rocks . 

Sandstone, limestone .

Tnfn _____ ____ _ 

Rhyolite, 

latite.

Radioactive 

minerals

Beta-uranophane , 

pitchblende (?). 

Metatorbernite , 

torbernite, 

florencite.

Pitchblende(?). 

Pitchblende, 

secondary uranium 

minerals. 

Carnotite, volborthite . 

Euxenite . 

Unknown . 

Kasolite, 

pitchblende(?). 

Carnotite.

Pitchblende . 

Unknown . 

Thorite . 

Secondary uraniumvanadium minerals. 

Carnotite . 

Unknown .

Thorite .

Pitchblende, 

thucholite(?). 

Pltchblende(?). 

Radium, uranium. 

Pltchblende(?). 

Radium. 

Pitchblende(?).

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Phair, George, and Onoda, Kiyoko, 1950, 

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INT.-OOP. SEC., WASH., D.C. J9«77

10
GEOLOGICAL SURVEY CIRCULAR 215 PLATE 1

FRONT

1 LARIMER

JEFF£RSON UDENVER

Ve\ns(wcluding adjacent replacement todies)

COLORADO

MESA

Disseminations in sedimentary racks

PLATEAUS

I D E LTA

Numbers designate deposits listed in table I. 

Numbers 41 and 45 designate deposits that 

are dominantly thorium-bearing

3l HUERFANO

%

a ^

COSTILLA> S

ARCHULETA

INDEX MAP SHOWING DISTRIBUTION OF URANIUM DEPOSITS IN COLORADO, 

GENERALLY EXCLUSIVE OF THE COLORADO PLATEAU