Uranium Deposits in 

Fall River County 

»South Dakota

GEOLOGICAL SURVEY BULLETIN 1009-G

; This report concerns work done on behalf 

of the U. S. Atomic Energy Commission 

and is published with the permission 

of the Commission

A CONTRIBUTION TO THE GEOLOGY OF URANIUM

URANIUM DEPOSITS IN FALL RIVER COUNTY, 

SOUTH DAKOTA

By HENRY BELL and W. E. BALES

ABSTRACT

In 1951 uranium deposits containing carnotite were discovered in the southern 

Black Hills near Edgemont, Fall River County, S. Dak. Many carnotite deposits 

haye; since been found in sandstones in the Inyan Kara group of Early Cretaceous 

age, and uranium-bearing material has been discovered in the Minnelusa sandstone of Pennsylvanian age and the Deadwood formation of Cambrian age in the 

southern Black Hills. Ore has been produced only from the Inyan Kara group, 

mostly within an area of about 30 square miles along the southwest flank of the 

Black Hills uplift between Dewey and Hot Springs, in Custer and Fall River 

Counties. In addition, occurrences of uranium in other parts of the Black Hills 

and the surrounding area are known or reported in sedimentary, igneous, and 

metamorphic rocks of pre-Cambrian to Tertiary age.

The lowermost and uppermost formations of the Inyan Kara group the Lakota 

and Fall River sandstones contain the productive uranium deposits. These 

terrestrial formations are composed predominantly of massive sandstone lenses 

with thin units of thinly bedded sandstone and mudstone, but locally they contain abundant mudstone and thinly bedded sandstone. The massive sandstone 

lenses commonly overlap and truncate underlying lenses. Iron stain, carbonaceous material, thin seams of gypsum, ripple marks, concretions, and fossil roots 

are common in the mudstone and thinly bedded portions of these formations.

Some high-angle normal faults of small displacement are found in the area 

containing the largest number of uranium occurrences in the Inyan Kara group. 

Although no ore deposits seen were cut by faults, high-angle fractures parallel to 

and at right angles to the faults contain carnotite for short distances.

The productive uranium deposits are most common where the Lakota and 

Fall River sandstones locally contain a large proportion of mudstone and thinly 

bedded sandstone. Other deposits are in the massive sandstone lenses of .the 

Lakota sandstone and in the thin units between the lenses.

Although carnotite is the most conspicuous and important mineral in most 

deposits, corvusite is an important constituent of some deposits. Other uranium 

minerals in the deposits are tyuyamunite, rauvite, and autunite. Ore produced 

in 1952 from the Fall River and Lakota sandstones contained about 0.2 percent 

of UaOs and 0.6 percent of VzOj. In general, deposits in the Fall River and 

Lakota sandstones contain about the same percentage of U3 08, but the deposits 

in the Fall River sandstone appear to have a higher percentage of vanadium. 

The grade of individual deposits, however, is highly variable. Most deposits 

are small, but a few have yielded as much as a thousand tons of ore.

211
212 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

INTRODUCTION

The first discovery of carnotite in South Dakota was in Craven 

<Canyon, 8 miles north of Edgemont, Fall River County, .S. Dak. 

(fig. 32), in June 1951 (Page and Redden, 1952). Additional discoveries have since extended the area of known occurrences. All 

the known commercial uranium deposits in the southern Black Hills 

&re in the Inyan Kara group of Early Cretaceous age (fig. 33).

Several hundred lode claims have been staked for uranium in Fall 

Biver County, mostly in the Harney National Forest, although 

numerous discoveries have been made on privately owned ground.

FIQTJKK 32. Index map of South Dakota showing the location of Craven Canyon area, Fall River

County.

JN"ot all claims are known to contain occurrences of radioactive material, and only a few contain uranium deposits of ore grade.

]VEost of the ore produced, from the area was shipped by railroad to

mills in Colorado until December 1952 when an ore-buying s^ion

Was established at Edgemont by the Atomic Energy Commission. 

Shipping points on the Chicago, Burlington & Quincy Railroad, 

Which passes through Edgemont, are easily accessible by dirt roads

and United States Highway No. 18-85A. Mining lias been done

with shovels and wheelbarrows in open pits and short adits. Bulldozers and front-end loading machines have been used to remove soil

cover, expose ore deposits, and load the mined material on trucks.

The first comprehensive geologic work in the area was^done by N. H. 

Darton and others of the U. S. Geological Survey between 1898 and
FIGURE 33. Map showing outcrop pattern of formations of the Inyan Kara group, and distribution of urani
214 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

1925 (Darton, 1904, 1902; Darton and Smith, 1904; Darton and 

Paige, 1925), and subsequently many other geologic studies have been 

made for special purposes. In 1951 the U. S. Geological Survey 

(Page and Redden, 1952) and the Atomic Energy Commission 

described * the first uranium deposits discovered. Later these agencies contributed to the knowledge of the district through geologic 

mapping, core drilling, and radioactivity reconnaissance using airborne equipment and equipment mounted on automobiles.

During 1952, the writers, assisted by J. D. Ryan and R. B. Taylor, 

made detailed geologic and topographic maps of two areas, at a scale 

of 1:1,200, one in Craven Canyon and one in Red Canyon (pis. 3 

and 4). Preliminary mapping of an area including the areas mapped 

in detail was completed at a scale of 1:24,000 (pi. 5). Many prospects 

and mines were studied and mapped. These geologic investigations 

have been directed toward the development of criteria for the recognition of ground .favorable for the occurrence of uranium deposits.

The writers wish to express their thanks to the many prospectors, 

mining companies, and private property holders who, without exception, cooperated and gave freely of their time, assistance, and 

information. The work of the Geological Survey was carried out in 

behalf of the Division of Raw Materials, Atomic Energy Commission, 

and the writers wish to thank Howard Stafford and his associates of 

Hot Springs, S. Dak., for their material assistance and for access to 

data collected in their studies.

REGIONAL SETTING

The pre-Cambrian, Paleozoic, and Mesozoic rocks of the Black 

Hills area were uplifted in Laramide time into a domal structure

about 60 miles wide and 120 mile8 long trending northwest, Subsequent erosion exposed a central crystalline core around which the 

sedimentary rocks now form a plateau, hogbacks, and cuestas.

The oldest sedimentary rooks lie on the pre-Cambrian core, anct

outward from the center of the uplift the sedimentary rocks are

progressively younger. In trie southern Black Hills tnese formations

are, in ascending order: the Deadwood formation of Cambrian age; the

Englewood and Pahasapa limestones of Mississippian age, the Minnelusa sandstone of Pennsylvanian age, the Opeche formation and

nVEinnekalita limestone of ]?errciia.rL( ?) age, ttie Spearfisli formation of

Triassic(?) age, the Nuggetf?) sandstone, Gypsum Springs formation,

Sundance formation, Unkpapa sandstone, and Morrison formation of

Jurassic age, and the Lakota sandstone, Minnewaste limestone,

Fuson shale, and Fall River sandstone of Early Cretaceous age.

i Baker, K. E., Smith, L. E., and Rapaport, Irving, 1952, Carnotite deposits near Edgemont,'South 

Dakota: U. S. Atomic Energy Commission, Div. of Raw Materials, RMO-881.
URANIUM DEPOSITS, FALL RIVER COUNTY, S. DAK. 215

Some of the characteristics of the formations from the Cambrian to 

Lower Cretaceous are summarized in the stratigraphic chart (p. 216- 

217). Upper Cretaceous and Tertiary rocks are extensively exposed 

over wide areas adjacent to the Black Hills uplift. Some of these 

rocks include tuff and volcanic debris that contain small amounts of 

uranium. 2

From 5 to 10 miles east of Red Canyon and Craven Canyon in the 

southern Black Hills, two north-trending flexures are superimposed 

on the main domal structure. Within the area mapped, however, the 

Cretaceous rocks strike nearly east and dip from 1° to 2^° to the 

south. Faults with large displacements are not common in the 

southern Black Hills, but the pre-Cambrian rocks contain northeasttrending zones of structural weakness. The more competent sedimentary beds are highly jointed. Several high-angle northeast-trending 

faults of small displacement have been found in the area mapped. 

Most faults in the map area have a displacement of 10 to 20 feet, but 

one fault has a displacement of as much as 75 feet. Most of the 

faults are in the Craven Canyon area where uranium occurrences are 

most numerous, but none of the faults mapped cut a uranium deposit. 

In Craven Canyon more than 200 fractures in the Lakota sandstone 

were measured. These have dominant strikes of N. 11° W. and N. 

75° E. and dip at high angles. The strike of these fractures is approximately parallel to or at right angles to the trend of the faults mapped. 

Some fractures near uranium deposits are filled with calcite, but none 

are radioactive. In the Red Canyon area a poorly exposed fracture 

zone contains traces of yellow uranium minerals.

The most conspicuous topographic feature of the southern Black 

Hills is the broad valley eroded in soft red shales between the older 

and harder Paleozoic rocks lying on the crystalline core of the Black 

Hills and the Cretaceous sandstones that form prominent hogbacks 

and cuestas around the margin of the uplift. Remnants of Tertiary 

sedimentary rocks in this valley and isolated gravel deposits on the 

plateau and encircling hogbacks indicate that the entire Black Hills 

area may have been covered by Tertiary rocks.

Uranium occurrences in the Black Hills area are known or reported 

in pre-Cambrian, Cambrian, Pennsylvanian, Cretaceous, and Tertiary 

rocks. In the northern Black Hills, autunite has been identified in 

the Deadwood formation (Vickers, 1953) and in Tertiary monzoiiite 

intrusives. Uraniferous fluorite veins have been found in both intrusive and sedimentary rocks of the Bear Lodge Mountains near 

Sundance, Wyo. A highly radioactive breccia has been reported from 

a fault zone in metamorphic rocks of pre-Cambrian age near Keystone

»Denson, N. M., Bachman, Q. 0., and Zeller, H. D., 1950, Summary of new information on uraniferous 

lignites in the Dakotas: U. 8. Oeol. Survey Trace Elements Memo Eept. 175.

839289 55 2
216 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

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218 CONTRIBUTIONS TO, THE, GEOLOGY OF URANIUM

in the central Black Hills. South and west of the Black Hills near 

Lusk, Wyo., uranophane and other secondary uranium minerals have 

been found in sulfide veins cutting pre-Cambrian and Cambrian rocks 

(Wilmarth and Johnson, 1954). Uranophane and carnotite-type minerals also t occur in sandstones of Tertiary age near Pumpkin Buttes, 

Wyo. (Love, 1952). Some uranium-bearing material in the InyaiV 

Kara group has been mined near Carlile, Wyo., and other deposits 

are being explored near Aladdin, Wyo. North of the Black Hills 

there are uranium-bearing lignites at Slim Buttes and other nearby 

areas. 3

URANIUM-BEARING FORMATIONS

In the southern Black Hills the Inyan Kara group contains the only 

productive uranium deposits, but the Deadwood formation and the 

Minnelusa sandstone also contain uranium-bearing material.

The Deadwood formation, in<somesplaces where it is a coarse-grained 

iron-atained quartzite, contains uranium-bearing material.

The Minnelusa sandstone contains uranium-bearing black shale, 

sandstone, and limestone in Hot Brook Canyon, north of the town 

of Hot Springs (fig. 33). Here red and gray sandstone, limestone, 

and shale, some thin coaly shale, and thin dark-gray petroliferous 

siltstone are exposed in the upper part of the formation.

The Inyan Kara rocks are extremely variable terrestrial deposits. 

The uppermost formation of this group is the Fall River sandstone. 

This formation is predominantly a. massive, crossbedded sandstone, 

from 60 to 125 feet thick, containing thin lenses of gray muds'tone! 

In the area between Craven Canyon and Coal Canyon, however, the 

Fall River sandstone is chiefly interbedded mudstones and thin lenses

of crossbedded sandstone. These thin lenses of sandstone are only 

25 feet thick in places. Where these lenses thicken they tend to 

become massive and crossbedded, with large, thick concave cross

strata. Where the lenses are thin they are thinly bedded or laminated

and there are commonly abundant macerated carbonized plant remains on the bedding surfaces. Within the sandstone there are zones

of angular charcoal fragments. Fossil roots, worm tubes, ripple

marks, and concretions of calcite, pyrite, and limonite are common 

where the formation is chiefly interbedded; mudstone and sandstone.

Iron stain is prominent particularly where the sandstone lenses are 

very thinly bedded and plant remains are abundant. Pyrite is common in drill cores'a"s'"Me^graMed di^semina't'ed criyistals and as noffules

in carbonaceous layers. Thin layers of gypsum and films of jarosite

are common in the mudstone.

> Beroni, E. P., and Bauer, H. L., Jr., 1962, BeconnaiuanM for tmniforens lignites in North Dak«ta, 

South Dakota, Montana, and Wyoming: U. 8. Oeol. Surrey Tract Blnntnts IDT. Rept. 191.
URANIUM DEPOSITS, FALL RIVER COUNTY, S. DAK. 219

The lowe&t formation of the Inyan Kara group is the Lakota sandstone. It is a thick-bedded white to pale-brown sandstone with 

some gray mudstone, carbonaceous shale, and thin coal seams. 

Massive lenses of crossbedded sandstone are well exposed in the 

bottom of Craven Canyon. These lenses are as much as 70 feet 

thick. Some of the lenses are conglomeratic in the lower parts, and 

the thin lenses may be coarse-grained throughout. The lenses overlap and truncate the underlying lenses. Parallel banding of manganese stain in the massive sandstone has been found in some places 

adjacent to thinly laminated units. In Craven Canyon, a lens of 

carbonaceous shale, parts of which weather into paper-thin laminations, thickens from less than an inch to as much as 30 feet within a 

distance of a mile and a half. The thicker parts of this bed contain 

coal reportedly of bituminous grade (Stone, 1912). In the Red 

Canyon area, the Lakota sandstone has been divided into three units: 

an upper unit composed chiefly of mudstones with some thin lenticular 

sandstone; a middle unit of cliff-forming fine- to medium-grained 

crossbedded sandstone with some mudstone; and a lower unit of thin 

mudstone and sandstone. Plate 6 shows these units as mapped; 

however, it seems unlikely that these divisions can be distinguished 

in other areas. Plate 4 shows sandstone lenses and mudstone in the 

two upper units of this division. The MinneWasfee limestone and the 

Fuson shale of the Inyan Kara group do not contain commercial 

uranium deposits.

ORE DEPOSITS

DISTRIBUTION

Fall River County uranium deposits have been found in the Fall 

River and Lakota sandstones in the area between Dewey and a point 

in Chilson Canyon about 3 miles east of United States Highway No. 

18-85A. The deposits have been found in both the Fall River and 

Lakota sandstones in the Craven and Red Canyon area (pi. 5), but 

in the area west of Craven Canyon they have been found mostly in 

the Fall River sandstone. In Chilson Canyon the deposits are mostly 

in the Lakota sandstone southeast of United States Highway No. 

18-85A. Some uranium-bearing black shale and limestone have 

been found in the Minnelusa sandstone at good exposures in Hot 

Brook Canyon about 2 miles north of Hot Springs.

SIZE AND SHAPE

The uranium- and vanadium-bearing material in the Inyan Kara 

group occurs as small impregnations in sandstone and mudstone. 

Little is known of the size and shape of these deposits. One of the 

large uranium and vanadium deposits has been mined for a length
220 .CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

White, friable, bleached 

sandstone

;::?&Sv

rown 

son

iro 

dsto

n-s 

ne

EXPLANATION

Dark uranium-vanadium 

minerals; contains 

corvusite

Yellowish-brown sandstone;

Light-brown, laminated sandstone; 

abundant carbon

Light-brown and dark-gray 

sandstone and siltstone; 

abundant carbon

Foot

FIGURE 34. Cross section of a pod of ore minerals in the Fall River sandstone.

of 170 feet and a width of 50 feet. This deposit has produced over 

1,000 tons of ore, and several others are nearly as large. In Craven

Canyon, exposures of carnotite in the Lakota sandstone are as much

as 60 feet long and range from a few inches to a few feet thick. t>ome

of the numerous smaller exposures in this area have been tested, but 

none has produced more than 150 tons of ore.

Most ore deposits are essentially parallel to the bedding, but a few

cut across the bedding. Most ore deposits have gradational boundaries, but some in the Fall River sandstone have sharp boundaries.

A small deposit at one locality in the Fall River sandstone is roughly 

elliptical, or pod-shaped, in cross section; the long diameter measures

about 1 foot, 7 inches and. the snort diameter, 1 foot 2 inches (fig. 34).

The length of this pod is unknown.

In the Lakota sandstone small fractures cutting ore deposits are 

filled with high-grade yellow uranium minerals for a vertical extent 

of as much as 12 feet.
URANIUM DEPOSITS, FALL RIVER COUNTY, S. DAK. 221

In Hot Brook Canyon where the upper part of the Minnelusa sandstone is well exposed there are outcrops of radioactive shale as much 

as 1,000 feet long. Most of the radioactive beds are less than 1 foot 

thick, although one is more than 3 feet thick.

MINERALOGY

Carnotite, Ki(U02) 2 (VO4) 2 -3H20, and its calcium analog tyuyarnunite, Ca(U02)2(V04) 2 -nH20, are the most conspicuous and important 

ore minerals in the Inyan Kara group. A black mineral that has an 

X-ray pattern identical with corvusite, V204-6V205-xH20, has been 

found, and other dark uranium and vanadium minerals, as yet unidentified may also be present. Some hand specimens contain sparsely 

disseminated carnotite, abundant stain resembling limonite, and as 

much as 5 percent V205 . X-ray studies indicate that the brown 

stain is not limonite but may be a uranium and vanadium mineral, 

perhaps rauvite, CaO-2U03 -5V:O5 -16H2O. These ore minerals coat 

sand grains and fill the interstices of sandstone. Yellow uranium 

minerals also stain sandstone in thin irregular concentric bands and 

halos around deposits and fractures in the Lakota sandstone, fill 

joints, and coat the surfaces of fractures. This material has been 

identified at a few places as tyuyamunite. It often contains more 

uranium by chemical assay than equivalent uranium by radiometric 

analysis. Other minerals of sparse occurrence are autunite, 

Ca(U02) 2 (P04) 2 -10-12H20, and hewettite, CaO-3V205 -9H20. Various states of hydration of these minerals are known, and metahewettite and metatyuyamunite have been identified from these deposits. 

It is very difficult to distinguish between carnotite, tyuyamunite, 

and metatyuyamunite in the field. These minerals will be referred 

to as carnotite, therefore, unless they'have been identified in the 

laboratory. A grass-green stain similar to that found by prospectors 

on the Colorado Plateau occurs as long streaks or splotches on the 

surface of rocks.

Pink sandstone is commonly associated with the ore deposits. 

The color, probably caused by small amounts of hematite, is abundant near deposits containing dark uranium and vanadium minerals. 

This pink stain may be analogous to the hematite commonly found 

with pitchblende veins in Canada (Lang, 1952, p. 25-27) and perhaps 

to the hematite noted by Gruner (1952, p. 16) in experiments in 

synthesizing of pitchblende. Also white bleached sandstone is commonly associated with dark uranium and vanadium minerals (figs. 

34 and 35). ..;-..- ... 

Some yellow uranium minerals and an unidentified green radioactive 

mineral have been found in coaly shale and limestone of the Minnelusa sandstone, but radioactive shales are much more extensive than
222 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

EXPLANATION

Sandstone, white, bleached, thinly bedded, 

contains carbonaceous material

Sandstone, pink, thinly bedded, contains 

carbonaceous material

Sandstone, mineralized, crosshatching shows higher grade 

material with well defined boundaries, other boundaries 

less well defined: contains carbonaceous material. Dark 

uranium and vanadium minerals predominate

Mudstone, brownish- and yellowish-gray, 

contains carbonaceous matertai

5 Feet 

II___1

Approximate scale

Flora* 38. Sketch showing relationship of white and pink S81ldst<fflfl tO mineralized TOCfe JD 8 deposit

In the Fall River sandstone.
URANIUM DEPOSITS, FALL RIVER COUNTY, S. DAK. 223

the megascopic yellow and green minerals. These deposits may 

contain uranium-bearing material similar to that in other radioactivfe 

lignites and black shales. i

During 1952, ore produced from deposits in the Inyan Kara group 

averaged 0.22 percent U308 and 0.6 percent V205 ; a ratio of about 

3 parts V205 to 1 part U308 . Although nearly the same tonnage 

was produced from the Fall River and Lakota sandstones, the ratio 

of V2O5 to U308 in ore from the Fall River sandstone was 4 to 1, 

whereas the ratio of V205 to U3O8 in ore from the Lakota sandstone 

was 2 to 1. The ratio of V205 to U308 in individual deposits, however, 

is highly variable and some deposits in the Lakota sandstone have a 

grade and ratio about equal to deposits in the Fall River sandstone. 

Within any one deposit the ore minerals are unevenly distributed. 

The grade of any sample, therefore, is not necessarily representative 

of the grade of the mine face or the deposit.

Although the mine workings are not extensive, it appears that 

in some deposits carnotite is more abundant near the outcrop, and 

dark uranium and vanadium minerals predominate a few feet below 

the surface. Ore having a grade of about 0.4 percent U308 and 1.4 

percent V205 has been produced from deposits consisting chiefly 

of dark uranium and vanadium minerals. Some ore deposits in the 

Lakota sandstone contain only carnotite with some high-grade fracture 

fillings and concentric irregular banding of yellow minerals. Ore 

produced from these deposits commonly has a grade of about 0.3 

percent U,08 and 0.2 percent V206.

LOCALIZATION OP DEPOSITS

Most of the ore deposits in the Inyan Kara group seem to be 

localized in or near thinly bedded sandstone. West of Craven 

Canyon, deposits in the Fall River sandstone are chiefly in the mudstone and thinly bedded sandstone facies of the formation. The 

deposits seem to be associated with the sides and bottoms of sandstone 

lenses where the lenses are very thinly bedded or laminated and where 

there are concentrations of iron stain and plant fragments (fig. 36).

The deposits in the Lakota sandstone in Craven Canyon are in 

thinly laminated sandstone and mudstone beds, and in massive 

sandstone lenses directly above and below such beds (pi. 7). Small 

fractures in the massive sandstone lenses are filled and coated with 

carnotite. These deposits appear to be most common where the 

..sandstone lenses thin or are truncated by an overlying lens.

In other places deposits in the Lakota sandstone seem to be localized where this formation is proportionally high in thinly bedded 

sandstones and mudstones.
224 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

. Silty sondston* with" fossil rootss

!lThickly bedded,massive sandstone* 

Prominent bedding planes £|

EMud stone;

EXPLANATION

FIGURE 36. Generalized section of part of a sandstone lens in the Fall River sandstone.

ORIGIN

The origin of the uranium deposits in Fall River County, S. Dak., 

is unknown. However, the uranium and vanadium apparently was 

deposited by ground waters in two different environments. Ore 

deposits containing dark uranium and vanadium minerals and the 

concretionary type of deposit illustrated by figure 34 occur in an 

environment of thinly bedded sandstone and mudstone. The sandstone and mudstone contain thin seams of gypsum, pyritized plant 

material, and various types of concretions. Ore deposits containing 

dark uranium and vanadium minerals in this environment seem to 

be older than deposits containing only carnotite.

Deposits containing only carnotite occur in an environment of 

thinly laminated sandstone, mudstone, and massive sandstone lenses 

(pi. 7). A relatively recent period of mineralization is suggested 

for these deposits by two factors: uranium in excess of the equilibrium 

state in the yellow uranium minerals found in fractures hi the massive 

Lakota sandstones, and the presence of bands of the uranium and 

iron minerals parallel to fractures and plant remains, suggesting 

that these minerals were introduced by ground-water solutions after 

lithification and subsequent fracturing of the host rocks.

The localization of many of the uranium deposits near the edges 

of truncated sandstone lenses and in or near units of interbedded 

sandstone and mudstone possibly indicates that the mineral-bearing 

solutions were trapped by the overlying sandstone lenses or by the

less permeable mudstones and subsequently precipitated their mineral 

content.

SUGGESTIONS FOR PROSPECTING

The most favorable areas for.prospecting in the Inyan Kara group

of formations seem..to be vtrtere. tHe Fall River and Lakota. sa,n.d.stones

are thinly bedded and contain large amounts of mudstone; abundant 

iron stain, and carbonized plant remains. Pink sandstone may be 

a helpful guide in finding ore deposits.
URANIUM DEPOSITS, FALL RIVER COUNTY, S. DAK. 225

Results of geologic mapping suggest that in the area west of Craven 

Canyon the Fall River sandstone is favorable for prospecting, whereas 

in the area east of Red Canyon the Lakota sandstone seems to be 

favorable. Between Craven and Red Canyons the Fall River and 

Lakota sandstones both consist of massive sandstone lenses with 

minor amounts of mudstone. This area, therefore, is considered 

less favorable than the areas to the east and west. Plate 5 shows the 

two areas considered to be favorable for finding large uranium and 

vanadium deposits.

DESCRIPTION OF SELECTED AREAS 

AREA BETWEEN CRAVEN CANYON AND COAL CANYON

The area between Craven Canyon and Coal Canyon contains uranium and vanadium deposits in the Fall River sandstone. This 

area, the western part of plate 5, is only partly mapped geologically; 

however, the mapping completed indicates the ore deposits are near 

the base of the Fall River sandstone where this formation is predominantly mudstones and thin sandstones. At the Coal Canyon 

claim (pi. 5, no. 1) the uranium is in thinly bedded sandstone at 

the base and apparently at the side of a sandstone lens. This lens 

is well exposed on the south side of a west-trending ridge that is about 

250 feet wide. The lens thickens within a distance of 150 feet from 

12 feet on the west to 23 feet at the eastern exposures. This lens 

extends southward as far as the Coal Canyon No. 14 claim (pi. 5, no. 2) 

and perhaps farther. The poor exposures and the thin lenticular 

character of the sandstones have made it nearly impossible to correlate definitely the mineralized sandstone at the Coal Canyon claim 

with the ore-bearing sandstones at the Get Me Rich No. 1 claim 

(pi. 5, no. 4), the Ridgerunner No. 3 claim (pi. 5, no. 3), or the 

Virginia C. No. 2 claim (pi. 5, no. 5). However, the ore deposits 

on all these claims are in thinly bedded sandstone that is overlain and 

underlain by brownish- and greenish-gray sandy mudstone containing some thin sandstone beds, carbon, films of jarosite, and thin 

seams of gypsum. The carbonaceous material that is associated 

with ore deposits is abundant as macerated plant fragments on bedding 

planes and as fragments of charcoal as much as one-fourth inch in 

diameter. On the Coal Canyon claim, a bed 4 feet thick of very fine 

grained silty sandstone contains abundant fossil roots.

The sandstones containing the ore deposits are highly fractured. 

Some closely spaced fractures are filled with calcite near the ore 

deposits on the Coal Canyon claim. Some poorly exposed highangle northeast-trending normal faults are near the ore deposit on 

the Trail Fraction claim (pi. 5, no. 6). The displacement along these 

faults ranges from less than a foot to 10 or 20 feet, but one fault
226 CONTRIBUTIONS TO THE GEOLOGY 0F URANIUM

southeast of the ore deposit on the Trail Fraction claim has a displacement of as much as 75 feet.

The uranium and vanadium deposits in the area between Coal 

Canyon and Craven Canyon contain predominantly carnotite, tyuyamunite, and metatyuyamunite, but in some deposits a large percentage of the ore consists of the dark uranium and vanadium minerals 

corvusite and rauvite. The ore minerals are parallel to bedding planes 

in sandstone, but at some places they cut sharply across the bedding. 

Some streaks of ore have gradational boundaries, but others have 

distinct boundaries. Areas of bleached white friable sandstone and 

yellowish-brown and pink iron stain (fig. 35) adjoin concentrations 

of high-grade ore. On the south side of the Coal Canyon claim is a 

small distinctive pod of ore (fig. 34). In the center of this pod is a 

bleached white friable medium- to fine-grained sandstone surrounded 

by high-grade dark uranium and vanadium minerals and light-brown 

and pink iron stain. Selected samples of the dark ore-grade material 

assay 0.62 percent equivalent uranium, 1.05 percent uranium, and 

7.7 percent V206 .

Most of the deposits in the area between Coal Canyon and Craven 

Canyon have been mined by opencut methods, but the Coal Canyon 

claim has been mined by an adit with side drifts. Several of the 

deposits produced over a hundred tons of ore in 1952, and one 

deposit produced over a thousand tons. In November 1952 the 

largest deposit had been exposed for about 170 feet and had been 

mined for a maximum width of about 50 feet. The thickness of ore 

at some places was 4 feet. The grade of the ore produced in 1952 

from deposits in the area between Coal Canyon and Craven Canyon 

was 0.22 percent U3O8 and 0.8 percent V2OS , a ratio of about 4 parts 

V2O6 to 1 part UjO8 . The grade of ore within individual deposits and 

from one deposit to another is highly variable. Those deposits that 

have a large percentage of dark uranium and vanadium minerals 

in the ore may have a ratio of V205 to U308 of as much as 7 to 1, 

whereas ore from deposits containing mostly carnotite may have 

a ratio of V2O6 to U3O8 of 1.5 to 1. Deposits within 3 or 4 feet of

the surface suck as tne deposit on tne Trail Fraction claim seem to

contain mostly carnotite, whereas deeper deposits seem to contain

larger proportions of dark uranium and vanadium minerals.

CRAVEN CANYON

The uranium deposits in Craven Canyon are in the Lakota sandstone. The outcrops of the Morrison formation and the Lakota 

sandstone in part of Craven Can3Ton are shown in plate 3. A mudstone lens, a carbonaceous shale lens, and seven individual sandstone 

lenses within the Lakota sandstone have been mapped (pi. 7). The
URANIUM DEPOSITS, FALL RIVER COUNTY, S. DAK. 227

 sandstone lenses are as much as 70 feet thick but overlap and truncate 

underlying lenses. Between the thick lenses of massive sandstone 

are units consisting of alternating thinly bedded sandstone and 

mudstone. These units are as much as 4 feet thick but commonly 

are much thinner. The thinly bedded alternating sandstone and mudstone between the sandstone lenses are represented in plate 7 by the 

lines separating individual sandstone lenses. These units contain 

macerated carbonized plant remains, light-brown and pink iron stain, 

and uranium deposits. Halos and thin concentric irregular bands of 

yellow uranium minerals in the massive sandstone lenses surround 

deposits in the thinly bedded units. These halos and bands are 

particularly common where fractures in the massive sandstone lenses 

cut deposits in the thinly bedded units. These fractures may be 

filled with uranium minerals for a vertical extent of as much as 12 

feet. Fractures in the Lakota sandstone are common in Craven 

Canyon; more than 200 were measured in the area of plate 3. These 

fractures have dominant strikes of N. 11° W. and N. 76° E. and dip 

at high angles. The strike of these fractures is approximately parallel 

to, or at right angles to, the strike of normal faults.

The higher grade carnotite deposits in Craven Canyon are in the 

thinly bedded units consisting of sandstone and mudstone, and the 

lower grade deposits are in the massive sandstone lenses directly 

above and below. Many of the deposits seem to be more abundant 

ha places where a massive sandstone lens thins or is truncated by an 

overlapping lens. In plate 7, sandstone lenses II and III are truncated by lens IV. The trace of the intersection ot the erosion surface 

and the east edge of lens III trends about N. 15° W. Most of the 

deposits in the thinly bedded units between these sandstone lenses 

are within 300 feet of the line along which the lens is truncated. At 

one place within sandstone lens IV, plate 7, uranium-bearing material 

has been found where there is no continuous erosional diastem but 

only a discontinuous thin layer of thinly bedded sandstone. However, the uranium-bearing material is low grade and the deposits 

appear to be small. Most ore deposits within the thinly bedded 

units are essentially parallel to the bedding but a few cut across the 

bedding.

Deposits in the thinly bedded units contain carnotite, but the halos, 

concentric irregular bands, and fracture fillings contain tyuyamunite. 

The tyuyamunite commonly contains more uranium than equivalent 

uranium. No dark, uranium and vanadium minerals have been found 

in the deposits in Craven Canyon.

There are numerous exposures of mineralized sandstone in Craven 

Canyon (pi. 3), but few have been mined. One is as much as 60 feet 

long and ranges from a few inches to several feet thick. Deposits on
228 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

the Flora, Gertrude, Imogene, Dagmar, Clarabelle, and Clarabelle No. 

4 claims (pi. 5, nos. 7-10) have been tested by opencut methods or 

by short adits. The untested deposits on the Pictograph claim (pi. 

5, no. 11) in Craven Canyon are similar in character to and probably 

are similar in size and grade to the deposits that have been mined. 

The deposits tested on the Dagmar and Imogene claims were found 

to extend only a few feet beyond the outcrop, although one deposit 

has produced over 100 tons of ore. The grade of this ore in 1952 was 

0.32 percent UsOg and 0.2 percent V205 . Some of the mineral deposits 

in this area have been described by Page and Redden (1952).

BED CANYON

The uranium deposits in the Red Canyon area are in the Lakota 

sandstone. This formation in Red Canyon has been divided into 

three units: an upper unit composed chiefly of mudstone with some 

thin lenticular sandstone, a middle unit of cliff-forming fine- to 

medium-grained crossbedded sandstone with some mudstone; and a 

lower unit of thin mudstone and sandstone (pi. 6). Plate 4 shows 

several sandstone lenses and thick units of mudstone in the two upper 

units of this division ha part of the Red Canyon area. Most of the 

uranium deposits are in the cliff-forming crossbedded sandstone unit 

(pi. 6), but the largest deposit, on the Hot Point No. 3 claim, is in 

thinly bedded sandstone. This thinly bedded sandstone is cross 

laminated, contains seams of sandy mudstone, carbonized plant material, and fragments of charcoal, and has a light-brown and pink iron 

stain. Detailed geologic mapping suggests that in this area the 

Lakota sandstone contains more mudstone in proportion to sandstone 

than in Craven CanyOn, and that the proportion of mudstone increases 

to the east. The sandstones in this area are fractured, and a poorly

exposed fracture zone contains traces of carnotite.

Although ore from the Hot Point No. 3 mine contains dark uTanilim

and vanadium minerals, carnotite is the most important ore mineral.

The ratio of V2O6 to U3O8 is about 1 to 1. Most of the ore contains

Only CarnOtite finely disseminated in sandstone, but some ore is light 

brown with small splotches and streaks of corvusite, and some is white 

to r>ale gray with a few nodules of corvusite surrounded by carnotite".

80me Or6 maV alSO COntain raUVlte. Small fragments of oKareoal,

carbon on bedding planes, and some gypSUUl are found 111 tuG OI*G,

The distinctive pink iron stain commonly associated with ore deposits

is very abundant in the barren sandstone near ore in the Hot Point

No. 3 mine.

Less than a hundred tons of ore has been produced from the Hot 

Point No. 3 mine. Most of this ore came from a stope 30 feet long, 

15 feet wide, and about 3 feet high parallel to the bedding. Talus
URANIUM 'DEPOSITS, FALL RIVER COUNTY, s.' DAK. 229

blocks of high-grade ore containing only carnotite have been mined 

at the discovery pit on the Hot Point No. 1 claim. Also on the Hot 

Point No. 1 claim, some carnotite in several thin layers in a finegrained poorly cemented sandstone has been mined from a small 

opencut. Near this opencut, soil containing small fragments of carnotite-bearing sandstone was high enough in grade to be shipped as ore. 

Although the Hot Point No. 3 mine has produced only a little 

ore, it is a significant mine because of the presence of corvusite in 

thinly bedded sandstone. About a mile and a half to the east where 

the Lakota sandstone is proportionately high in thinly bedded sandstone and mudstone, several large deposits have produced ore averaging about 0.19 percent U3O8 and 0.4 percent V205 and containing 

a high percentageiof dark uranium and vanadium minerals. The ore 

from these deposits' is similar in character to ore from deposits in the 

Fall River sandstone that contain dark uranium and vanadium minerals. This suggests that similar environments in the Lakota 

sandstone and Fall River sandstone were favorable for the deposition 

of the richer deposits containing dark uranium and vanadium minerals.

HOT BROOK CANYON

The Minnelusa sandstone in Hot Brook Canyon contains uraniumbearing material outcropping in sees. 10 and 15, T. 7 S., R. 5 E. 

Black Hills meridian, about 2 miles north of Hot Springs (figs 33 and 

37). The upper part of the Minnelusa sandstone, the Opeche formation, and the Minnekahta limestone are exposed in Hot Brook Canyon. 

These formations are folded into a north-trending anticline that is 

cut by Hot Brook Canyon. The upper part of the Minnelusa sandstone in this area consists of red and gray sandstone, limestone and 

shale, some thin coaly shale, and thin dark-gray petroliferous siltstone.

Some yellow uranium minerals and an unidentified greenish radioactive mineral have been found in coaly shales and in limestone in 

the Minnelusa sandstone, but radioactive shales are much more 

extensive than the megascopic yellow and green radioactive minerals. A radioactive shale exposed in a north-trending cliff face for 

about 1,000 feet in sees. 10 and 15 (fig. 37) is black to green, generally 

nonfissile, and contains thin lenses of petroliferous siltstone. This 

shale ranges from 2.4 to 4.4 feet in thickness, averages approximately 

3 feet thick, and contains at one locality 0.012 percent equivalent 

uranium, 0.009 percent uranium, and 0.66 percent V205 . Three 

radioactive coaly shale beds are exposed along the railroad cut in 

the southwest quarter of sec. 10, and two radioactive coaly shale 

beds are exposed in an east-trending cliff in the north-central part 

of sec. 15. Thin black fissile shale beds overlie and underlie a limestone bed at one locality and overlie a calcareous sandstone at another
230 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

R.5 t. 

(Block Hills Meridian)

EXPLANATION

Outcrops of radioactive material, 

dashed where approximate

1000 4000 feet

Contour interval 100 feet 

Datum is mean sea level

Topography based on Minnekahta NE

quadrangle, 7 */z minute series, 1951

FlOUM 3?. Map of part of Hot Brook Canyon, Fall River County, S. Dak., showing outcrops of radioactive material.

locality about 2,500 feet distant. These two black fissile shale beds 

are exposed on the flanks of the anticline; they have not been traced 

from one locality to the other, but they may be correlative. A 

composite sample of these two black shales at each locality contained 

0.036 and 0.046 percent equivalent uranium, 0.021. and 0.069 percent 

uranium, and less than 0.1 percent V205 . The following table gives,
URANIUM DEPOSITS, FALL RIVER COUNTY, S. DAK. 231

the assay results from samples of various radioactive beds in Hot 

Brook Canyon.

Assays of various radioactive beds in the Minnelusa.sandstone, Hot Brook Canyon^ 

Fall River County, S. Dak.

Sample

no.

1.. ....... ...

V.. ........ ..

3............

4............

6.... .....

6.. .. ........

7 ».... .._ .

*».-. . 

Thickness

(ft)

1.3

3.3

.6

.7 (')

1.4'

<1.0

<1.0

eTJi

0.017

.012

.029

.018

.52

.012

.036

.046

Percent

U

0.007

.009

.027

.011

.69

.006

.024

.069

V3 0s

0.46

.66

.36

.50

.36

< !

< !

<.l

Shale, coaly.

mineral.

Shale, black, fissile.

1 Equivalent uranium.

* Grab sample.

« Samples 7 and 8 may be from the same beds; composite sample.

LITERATURE CITED

Darton, N. H., 1902, Description of the Oelrichs quadrangle, South Dakota- 

. Nebraska: U. S. Geol. Survey Geol. Atlas, folio 85.

 1904, Description of the Newcastle quadrangle, Wyoming-South Dakota: 

U. S. Geol Survey Geol. Atlas, folio 107.

 and Paige, Sidney, 1925, Description of the Central Black Hills quadrangle, 

South Dakota: U. S. Geol. Survey Geol. Atlas, folio 219.

 and Smith, W. S. T., 1904, Description of the Edgemont quadrangle,

South Dakota-Nebraska: U. S. Geol. Survey Geol. Atlas, folio 108. 

Gruner, J. W., 1952, New data of syntheses of uranium minerals; Part I, Annual

Report for July 1, 1951 to June 30, 1952: U. S. Atomic Energy Commission, Tech. Inf. Service, RMO-983, p. 16. 

Lang, A. H., 1952, Canadian deposits of uranium and thorium (interim account):

Geol. Survey of Canada, Econ. Geology Series no. 16. 

Love, J; D., 1952, Preliminary report on uranium deposits in the Pumpkin Buttes

area, Powder River Basin, Wyoming: U. S. Geol. Survey Circ. 176. 

Page, L. R., and Redden, J. A., 1952, The carnotite propsects of the Craven

Canyon area, Fall River County, South Dakota: U. S. Geol. Survey Circ.

175. 

Stone, R. W., 1912, Coal near the Black Hills, Wyoming-South Dakota: U. S.

Geol. Survey Bull. 499, p. 10. 

Vickers, R. C., 1953, An occurrence of autunite, Lawrence County, South Dakota:

U. S. Geol. Survey Circ. 286. 

Wilmarth, V. R., and Johnson, D. H., 1954, Uranophane at Silver Cliff mine near

Lusk, Wyoming: U. S. Geol. Survey Bull. 1009-A.

INDEX

Page

Autunite............................... 211,215,221

Carnotite ~.. 211-212,218,220-221,223-224,226-229

Claims. See names of claims.

Clarabclle claim.............................. 228

Clarabelle No. 4 claim.-...-.-........-...._ 228

Coal Canyon. See Craven Canyon.

Coal Canyon No. 14 claim........-.--.....- 225-226

Corvusite.......................... 211,221,226,228

Craven Canyon, area between Coal Canyon

and............................ 225-226

mode of occurrence of uranium... ___ 227-228 

uranium deposits....................... 226-228

Dagmar claim.________________ 228

Deadwood formation, age__-...___.._ 214

uranium occurrences.._.......... 211,215,218

Fall Eiver sandstone, character__..__. 218 

size of deposits..___._____._____ 220 

uranium content....__________ 211,223 

uranium occurrences ______ 219,224-226

Faults. See Structural features.

Flora claim......................_______ 228

Folds. See Structural features.

Fuson shale.....__.____.-._____ 219

Gertrude claim............................... 228

Get Me Rich No. 1 claim..................... 225

Harney National Forest.-...___.--_..--_._... 212

Hewettite.-....-..---...-...............-.... 221

Hot Brook Canyon, formations exposed.._ 229

uranium deposits.___.__._.__ 229-230

Hot Point No. 1 claim........................ 229

Hot Point No. 3 claim...................... 228-229

Hot Point No. 3 mine.......--..-....-.-.-. 228-229

Imogene claim___.._..."_..___. 228 

Introduction................................. 212

Inyan Kara group, age..... .._..._.. 214

character.--.__.--....-._._.___ 216

origin of deposits...._.__._.___ 224

uranium content...____._____ 221,223 

See also Fall River sandstone, Fuson shale, 

Lakota sandstone, and Minnewaste limestone.

Lakota sandstone, character....._.......... 219

division of in Graven Canyon....... _ 226-227

division of in Red Canyon.............. 219,228

Page

Lakota sandstone Continued

size of deposits..._____._........... 220

uranium content...___._..._ 211,221,223 

uranium occurrences.. __..... 219-220,225-229

Literature cited..._______.............. 231

Metahewettite..___.__.___......._ 221

Motatyuyaminite._...__._........... 221, 226

Mines. See names of mines.

Mining methods........................ 212,226,228

Minnelusa sandstone, age.................._ 214

size of deposits______.....^...___ 221

uranium content_____..........._ 229-231

uranium occurrences... _......... 218,229-231

Minnewaste limestone______...._..... 219

Previous work.____________........ 212-213

Rauvite................................ 211,226,228

Red Canyon, ore production............_ 228-229

uranium deposits..______...._.. 228-229

Regional geologic setting___...._. 214-215,218

Ridgerunner No. 3 claim...__.............. 225

Stafford, H., assistance acknowledged.... __ 214

Stratigraphic chart________.......... 216-217

Structural features.....___........... 211,214-215

Trail Fraction claim.._______......... 225-226

Tyuyaminito... .... .......... 211,221,226-227

Uraniferous fluorite____................. 215

Uranium-bearing rocks, Cambrian age....._ 218 

Cambrian age. See also Deadwood

formation.

Cretaceous age. See Inyan Kara group. 

Pre-Cambrian ago______--____ 215,218 

Pennsylvanian age. See Minnelusa sandstone. 

Tertiary age__..___...-.....--.--__ 215

U raniuin minerals. See names of minerals.

Uranium occurrences, age of rocks

containing.._................. 215,218

distribution of deposits__............ 219

favorable prospecting areas_..... 224-225

localization of deposits____ . .... 223

See also particular formations.

Uranophane.__ .. .. 218

Vanadium minerals. See names of minerals. 

Virginia C. No. 2 claim....................... 225

o

233