Carnotite-bearing 

Sandstone in Cedar

Canyon, Slim Buttes

Harding County

South Dakota

GEOLOGICAL SURVEY BULLETIN 1009-1

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

CARNOTITE-BEARING SANDSTONE IN CEDAR CANYON, 

SLIM BUTTES, HARDING COUNTY, SOUTH DAKOTA

BY JAMES R. GILL AND GEORGE W. MOORE

Carnotite-bearing sandstone and claystone have been found in the Chadron 

formation of the White River group of Oligocene age in the southern part of the 

Slim Buttes area, Harding County, S. Dak. The carnotite is an efflorescent 

yellow coating on lenticular silicified sandstone. Locally, the mineralized sandstone contains 0.23 percent uranium. The uranium and vanadium ions are 

believed to have been derived from the overlying mildly radioactive tuffaceous 

rocks of the Arikaree formation of Miocene age. Analyses of water from 26 

springs issuing from the Chadron and Arikaree formations along the margins of 

Slim Buttes show uranium contents of as much as 200 parts per billion. Meteoric 

water percolating through tuffaceous rocks is thought to have brought uranium 

and other ions into environments in the Chadron formation that were physically 

and chemically favorable for the deposition of carnotite.

INTRODUCTION

Carnotite was found on March 15, 1953, in Cedar Canyon in the 

southern part of the Slim Buttes area in the NE^NEX sec. 8, T. 16 

N., R. 8 E., Harding County, S. Dak. Carnotite has been found 

since in the Chadron formation at two other places in the Slim Buttes 

region, and the known area of the carnotite deposits in Cedar Canyon 

has increased.

A geologic and topographic map (pi. 10) shows the stratigraphic 

and topographic relations of the mineralized sandstone to the underlying and overlying rocks. The map, made by planetable and 

alidade, covers an area of 1,550 by 1,870 feet at a scale of 1:2400. A 

second geologic map (pi. 11) was prepared at a scale of 1:31,680 to 

show the relation of the geologic features of the Cedar Canyon area 

to similar features in adjacent areas. Other carnotite localities are 

shown on this map, which may also serve as a guide for future investigations in the southern part of the Slim Buttes area.

This investigation was undertaken on behalf of the Division of 

Raw Materials of the Atomic Energy Commission as a part of a 

program conducted in search for and appraisal of uranium-bearing 

carbonaceous rocks in the Rocky Mountain region.

Many geologists have contributed to knowledge about the Slim 

Buttes area. The lignite resources have been investigated by

249
250 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

Winchester, Hares, Lloyd, and Parks (1916), the structural geology 

in relation to oil and gas by Toepelman (1923), and the general 

geolog}7 by Baker (1952). The origin of uraniferous lignites has been 

discussed in written communications by N. M. Denson and others 

(1950), E. P. Beroni and H. L. Bauer, Jr. (1952), and H. D. Zeller 

(1952).

The writers received assistance from Roy C. Kepferle, Murray 

Levish, and Robert E. Melin during the fieldwork and the preparation 

of this report. James D. Bump of the South Dakota School of 

Mines visited the area and helped to correlate the Oligocene rocks 

with the rocks of the White River badlands in Pen.ningto.ii and 

Washabaugh Counties about 150 miles southeast of the Slim Buttes.

The writers appreciate the many courtesies extended by local 

ranchers, particularly William and Esther Warn men. Vernon 

Wammen provided great assistance by helping the authors to obtain 

oblique aerial photographs of the Cedar Canyon caraotite deposit.

LOCATION AND ACCESSIBILITY OF AREA

The Slim Buttes area lies within the Custer National Forest in the 

southeast part of Harding County, S. Dak. It is about 30 miles 

southeast of the town of Buffalo and" about 60 miles north of the 

town of Newell, the nearest rail shipping point. The mapped area 

covers parts of Tps. 16 and 17 N., Rs. 7, 8, and 9 E.

A well-graded county road crosses the area and connects State 

Highway 8, about 11 miles north of the area, with U. S. Highway 

212 at Newell. The parts of the area not accessible by this county 

road can be reached by dirt ranch roads and Forest Service trails.

The Slim Buttes form a rugged and imposing topographic feature 

in contrast to the surrounding gently rolling plains. Steep cliffs, 

which form the margins of the Slim Buttes, are as high as 250 feet 

and are broken at several places by V-shaped canyons. Steep-walled 

gullies and landslide blocks make travel along the base of the cliffs 

difficult. Along the base of the cliffs springs are common, but 

perennial streams are absent.

STRATIGRAPHY

The rocks exposed in the southern part of the Slim Buttes area 

range in age from Late Cretaceous to Recent. All the rocks are 

continental in origin, but conditions of sedimentation ranged from 

those favoring the deposition of lignite to those favoring the accumulation of volcanic ash. The sequence of sedimentation has been broken 

by at least two major periods of erosion, which are shown by two 

unconformities: one at the base of the rocks of Oligocene age and the 

other at the base of the rocks of Miocene age.
CARNOTITE-BEARING SANDSTONE IN CEDAR CANYON, S. DAK. 251 

UPPER CRETACEOUS ROCKS

HEM, CREEK FORMATION

The oldest rocks exposed in the mapped area of the southern part 

of the Slim Buttes are those which have'been assigned to the Hell 

Creek formation. The Hell Creek formation is Late Cretaceous in 

age and is composed of continental sediments that are about 400 feet 

thick. Along the North Fork Moreau River, 17 miles south of the 

mapped area, the Hell Creek formation rests on the marine Fox 

Hills formation, also of Cretaceous age.

The Hell Creek formation in the mapped area consists largely of 

medium-grained greenish-gray friable sandstone and dark-gray 

sandy ben to nitic shale. Thin beds and concretions of mediumgrained sandstone cemented by siderite are generally abundant. 

The siderite is commonly weathered to limonite on the surface, and 

in fresh exposures it is brownish black. Loglike dark-yellowishbrown calcareous concretions as much as 10 feet long occur in the 

friable sandstone. Thin lenticular beds of lignite occur in the upper 

part of the formation.

The contact between the Hell Creek formation and the overlying 

Ludlow member of the Fort Union formation is not obvious in the 

area. The units were distinguished by earlier workers (Winchester, 

Hares, Lloyd, and Parks, 1916, p. 19) on the basis of the lithologic 

change from the somber-colored rocks of the Hell Creek formation 

to the yellowish-brown rocks of the Fort Union formation. In the 

southern part of the Slim Buttes area this criterion is difficult to 

apply because the two lithologic types alternate for a vertical distance of 100 feet or more. In this report the contact has been placed 

at the base of the lowest persistent lignite bed (Brown, 1952). In 

most of the area this lignite bed lies below a resistant dark-yellowishbrown sandstone bed.

TERTIARY ROCKS 

FORT UNION FORMATION

The Ludlow member of the Fort Union formation of Paleocene age 

conformably overlies the Hell Creek formation and is separated from 

it by a transitional zone. The Ludlow member is composed largely 

of poorly cemented yellowish-brown very fine grained sandstone 

interbedded with carbonaceous shale and lignite. Moderately well 

indurated, medium-grained sandstone is found also.

In the mapped area the Ludlow member of the Fort Union formation ranges in thickness from a featheredgc to about 100 feet. Exposures of this formation to the north of the mapped area indicate that 

it was originally more than 300 feet thick and was conformably 

overlain by at least 300 feet of sandstone and shale of the Tongue
252 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

River member. Erosion preceding deposition of the White River 

group has truncated the northeastward-dipping Fort Union formation, resulting in the thinning of the formation in the mapped area 

and, locally, in its complete removal.

Lignite has been mined from the Ludlow member of the Fort 

Union formation at several localities within the Slim Buttes. The 

discovery that some of the beds in the southern part^of Slim Buttes 

contain uranium was made in 1950 (N. M. Densori and others, written 

communication). However, no uranium minerals are apparent in 

the lignite, and the uranium is thought to be retained as a metalloorganic constituent (I: A. Breger and Maurice Deul, written communication, 1952).

WHITE RIVER GROUP

The White River group of Oligocene age unconformably overlies 

both the Fort Union and Hell Creek formations. The White River 

group consists of the Chadron and Brule formations.

The Chadron formation is the basal formation and is the only 

part of the group generally present throughout most of the mapped 

area. Pre-Arikaree erosion has removed the overlying Brule formation in many areas. The lower part of the Chadron formation consists of medium-yellow to dark-yellowish-orange sandstone and 

siltstone, and in some localities contains much material reworked 

from the Fort Union and Hell Creek formations. At a, few places 

the formation contains beds of detrital lignite, as much as 6 inches 

thick, derived and reworked from the underlying Ludlow member of 

the Fort Union formation. The upper part of the Chadron formation is composed mainly of white fine- to coarse-grained pebbly sandstone, and light-olive-gray bentonite. Tuffaceous sandstone and 

opalized clay are present locally. Where the reworked material is 

absent, the white sandstone of the upper part of the Chadron formation rests on older rocks.

The Brule formation is exposed at only three localities within the 

mapped area at the north end of Flat Top Butte, chiefly in sees. 29 

and 30, T. 17 N., R. 9 E., west of Square Top Butte in sec. 31, T. 17 

N., R. 8 E., and along the south face of Slim Buttes in sec. 14, T. 16 

N., R. 8 E. In all of these areas the Brule formation is preserved 

in landslide blocks which were dropped before the deposition of the 

Arikaree formation. The contact between the Brule and the Chadron 

formations is exposed at the north end of Flat Top Butte. The authors 

followed a practice that originated in the Big Badlands area where 

the classic White River exposures are found. The practice is to place 

the contact at the top of a fresh-water limestone bed which separates 

the uppermost bentonite bed of the Chadron formation from the 

orange-pink sandy claystone and tuffaceous sandstones of the Brule
CARNOTITE-BEARING SANDSTONE IN CEDAR CANYON, S. DAK. 253

formation (Bump, 1951). The Brule formation is composed of tiiinbedded to massive sandy claystone and tuffaceous sandstone, which 

are well indurated and contrast sharply with the poorly cemented 

sandstone and bentonitic clay of the Chadron formation. (See fig. 40.)

FLAT TOP BUTTE

SEifi sec. 30, 

T.I7N., R.9E.

FINGER BUTTE

SW/4 sec. 35, 

T.I7N..R.8E.

CEDAR CANYON

NEis. sec. 8, 

T. 16 N., R.8E.

ANTELOPE CREEK

SEfc sec. 12, 

T..I6N., R.8E

I I I

I I I

I I I

I I I 

I I I

FIGURE 40. Stratigraphic sections of rocks exposed in the southern part of Slim Buttes. 

Harding County, S. Dak.

In some areas the White River group is absent and the Arikaree 

formation rests directly on the older rocks. This condition occurs in 

sees. 11 and 14, T. 16 N., R. 8 E. Before the deposition of the White 

River group, resistant sandstone beds in the Ludlow member of the 

Fort Union formation and Hell Creek formation formed hills having

3<I3704 55 2
254 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

as much as 100 feet of relief. Only a thin mantle of Chadron was 

deposited on these hills, and subsequent pre-Arikaree erosion removed 

this mantle to expose some of these ancient hills.

Rocks of the White River group contain, on the average, about 

0.0010 percent uranium.

ARIKAREE FORMATION

The Arikaree formation of Miocene age unconformably overlies 

the rocks of the White River group. No diagnostic fossils have been 

found in this unit in northwestern South Dakota, and the correlation 

with the Arikaree formation of Miocene age in southwestern South 

Dakota and southeastern Montana is made on the basis of lithologic 

similarities. A beaver of late Miocene age from the Arikaree formation 

has been described by Wood (1945) from rocks in southeastern Montana; these rocks are lithologically similar and correlate with those in 

the Slim Buttes.

The Arikaree formation is resistant to erosion and is the rock unit 

that causes the tops of the Slim Buttes to stand more than 500 feet 

higher than the surrounding plains. The formation is composed 

mainly of yellowish-gray very fine grained tuffaceous sandstone and 

is more than 250 feet thick. The basal 50 feet contains much material 

reworked from the White River group and is thin bedded in comparison 

with the more massive upper part. Locally, one or more beds of conglomerate occur at or near the base of the Arikaree formation.. These 

beds of conglomerate consist of claystone pebbles and cobbles averaging 2 inches in diameter. Most of the pebbles and cobbles have been 

derived from the Brule formation. Very coarse sand and pebbles from 

the Chadron formation are also incorporated into the ,basal part of 

the Arikaree formation.

Rocks of the Arikaree formation contain on the average about 

0.0015 percent uranium. It is thought that the uranium is in the 

volcanic material of which the formation is largely composed.

QUATERNARY DEPOSITS 

v TERRACE DEPOSITS

Deposits of probable Pleistocene age occur as alluvial fans that 

extend from the bases of the cliffs and as terraces along many of the 

stream valleys. Many of these deposits resemble the White River 

formation from which they are derived. The terrace deposits have 

flat upper surfaces, and recent erosion has cut into these surfaces at 

many places leaving the deposits as isolated "tables." These deposits 

were not mapped separately.
CARNOTITE-BEARING SANDSTONE IN CEDAR CANYON, S. DAK. 255 

LANDSLIDE MATERIAL

Landsliding was extensive around the periphery of Slim Buttes 

during Pleistocene and early Recent time. Blocks and masses of 

Arikaree material containing some White River and older rocks extend 

at some places more than three-quarters of a mile from the cliff faces. 

In some places coherent blocks, as much as half a mile long, have moved 

as a single unit; but commonly the landslide material is made up of 

smaller blocks and rubble. On the south and west sides of Slim 

Buttes the landslide material obscures the contacts between the older

rocks for long distances.

STRUCTURE

In the southern part of the Slim Buttes the main structure of the 

Fort Union and Hell Creek formations is a homocline that dips to the 

northeast, generally less than 1°. This uniform structure is modified 

locally by minor undulations.

The rocks of the Chadron and Arikaree formations reflect little 

of the underlying rock structure because of the unconformity at the 

base of the Chadron formation. The Chadron and Arikaree formations 

are preserved in a gentle syncline, whose axis follows approximately 

the topographic crest of the Slim Buttes. On the west side of the area 

this axis is nearly north and south, and it curves to the southeast at 

the east end of the Slim Buttes.

. No faults .have been, recognized, in the southern part, of the. Slim 

Buttes area. Pre-Arikaree landslide blocks are bounded by fractures 

that resemble faults, but there is no surface displacement in the area 

that reflects tectonic activity.

After the deposition of the White River group and before the deposition of the Arikaree formation, there were many landslides in the 

Slim Buttes area. Enormous blocks, some of which have remained 

intact, slipped down as much as 200 feet. The interpretation of these 

landslide blocks puzzled early workers who thought them to be fault 

blocks (Todd, 1895, p. 303) and later to be a result of crossbedding 

(Winchester, 1913). Toepelman (1923) first recognized that they were 

blocks which had slipped into steep-walled canyons cut into the White 

River and Lucllow sediments. One block is exposed at the north end 

of Flat Top Butte where tilted White River material lies more than 

50 feet below the contact of the White River group and the Lucllow 

member of the Fort Union formation. A thin lignite bed in the 

Ludlow member can be recognized on both sides of the block in the 

undisturbed nearly horizontal rocks behind the landslide block. 

Only in these dropped blocks can the Brule formation be found in 

the Slim Buttes area. The age of the sliding is probably Miocene as 

fossils of late Oligocene (Whitneyan age of MacDonald,. 1951) have 

been collected from the landslide blocks.
256 CONTRIBUTIONS TO THE 'GEOLOGY OF URANIUM 

CARNOTITE DEPOSITS

Carnotite occurs near the top of the Chadron formation at the 

head of Cedar Canyon (pi. 10). It is in inclined thin lenticular beds 

of silicified fine-grained tuffaceous sandstone and in thin beds of 

sancty claystone which are truncated by sandstone and conglomerate 

of the basal part of the Arikaree formation. The mineral carnotite 

was identified by A. J. Gude 3d by X-ray diffraction methods.

The carnotite-bearing unit of interbedded fine-grained tuffaceous 

sandstone and sandy claystone is as much as 9 feet thick. Lenses 

of sandstone ranging from 0.5 to 2.5 feet in thickness are separated 

by beds of claystone ranging from 0.1 to 1.5 feet in thickness. The 

lenses of sandstone contain disseminated carnotite, and small amounts 

of carnotite are found also in the adjacent claj^stone. Some carnotite 

is present throughout the 9-foot unit, but the principal mineralization 

has been in the upper 4 feet. The carnotite occurs through a distance 

of about 300 feet along the outcrop. The greatest concentration of 

carnotite is in thin coatings on fracture surfaces in the sandstone, and 

lesser amounts are disseminated throughout the sandstone. Carnotite is present also as a thin coating around sand grains in the sandy 

clay adjacent to the sandstone.

The Chadron formation at the Cedar Canyon carnotite deposit 

consists of light-gray to j^ello wish-gray fine to very fine grained 

sandstone, siltstone, and yellowish-gray and grayish-olive bentonite. 

The rocks of the Chadron formation are unconformably overlain by 

rocks of the Arikaree formation composed of medium- to coarsegrained yellowish-gray sandstone which locally contains pebbles and 

cobbles, and by very fine grained light- to yellowish-gray tuffaceous 

sandstone. The following partial section of the Arikaree and Chadron 

formations was measured in Cedar Canyon at locality 2 (pi. 10).

Thickness 

Arikaree formation: (feet)

Conglomerate, pebble to cobble, yellowish-gray, weathers darkyellowish-orange, lenticular, poorly indurated. Pebbles and cobbles are limy yellowish-gray claystone typical of the Brule formation. Waterworn bone fragments reworked from the White River 

group are numerous_______________________________________ 2. 0+

Sandstone, very fine grained, light-gray, tuffaceous, forms cliff ______ 15. 0

Conglomerate, as above, well indurated______________--___-_--._ 2. 6

Sandstone, medium- to coarse-grained, yellowish-gray; contains a 

few claystone pebbles______-_---___--____-__--_---_----__--_ 3. 1

Sandstone, medium to very coarse grained, conglomeratic. The clay 

matrix contains many light-olive-gray subangular to rounded claystone fragments. At some places the sandstone contains thin 

lenses of well-indurated coarse-grained sandstone less than 4 inches 

thick___________________________-__---___--___---- 3. 1

Total thickness measured of the Arikaree formation_________ 25. 8
CARNOTITE-BEARING SANDSTONE IN CEDAR CANYON, S. DAK. 257

Thckness

Chadron formation: (feet) 

Sandstone, very fine grained, light-gray, silicified; has carnotite coating on sand grains____----.---------------------_--.--.-..--- 0. 2

Claystone, sandy, light-gray, soft.-..______________-._._........__ .1

Sandstone, as above; contains no visible car notite. _-__---....-,..-_ 1. 2

Claystone, as above__-_______---_----_--...---.-.--.....-_---.- 1. 2

Sandstone, as above; with carnotite_.. ........................... .7

Claystone, as above.____________________-_._--_-._.....---_-..-.- . 1

Sandstone, as above; contains no visible carnotite...-.-..-..-__.. .5 

Claystone, as above--.--..--.----.---.-.-.-..---..-....-.---.- .5

Sandstone, as above; with carnotite-_...-_--._..-.-_.....-..----- .6

Claystone, as above... _______ _-________- -_._---.-,--..-.....-- 1.0

Sandstone, as above';" contains no visible carnotite- _..-_.-._._.-.. .7 

Sandstone, as above, less silicified, poorly indurated, contains carnotite -_-____-_._.-______.______-___ 7 _--___-__------_----.-.. . 6

Sandstone, very fine grained, light-gray, eilicified; has carnotite coating on sand grains._____________'_______________-_--______--_ . 9

Claystone, as above_-_----_-__--_-.-- T ------------------------ . 5

Sandstone, fine-grained, pale.-rplive; contains many pebbles of very

sandy pale-olive claystone derived from underlying units.__.-_.. 3. 3 

Sandstone, very fine grained, pale-olive streaked with dark-yelloworange, poorly indurated. Contains a few pebbles of very sandy 

claystone eroded from underlying unit___._-______._-._______--_ . 6

Bentonite, sandy, pale-olive with a few dark-yellow-orange streaks.- 2. 1 

Sandstone, very fine grained, clayey, very light gray, weathers in

fluted columns _ ________________________-________________-'__ 8. 0-f

Total thickness measured of the Chadron formation...________ 22. 8

Base of section in ditch north side of road.

Figure 41, an aerial view of Cedar Canyon, illustrates the general 

topography of the area; and figure 42 shows the stratigraphic relationship of the carnotite-bearing sandstone in the Chadron formation to 

the overlying Arikaree formation. The geologic map of the Cedar 

Canyon area (pi. 10) indicates the areal extent and relation of the 

various formations to the area of mineralization in the Chadron formation. Much of the Chadron and Ludlow outcrop is obscured by 

talus an.dY .R,ecent landslide blocks. Where possible, the attitude of 

the landslide blocks has been indicated on the map (pi. 10) because 

the block directly south of the outcrop of mineralized sandstone also 

contains carnotite.

The mineralized area in this landslide block has a lateral extent of 

about 100 feet and is as much as 0.8 foot thick.

Analyses of six samples from the Cedar Canyon carnotite deposit 

are listed in table 1.
258 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

FIGURE 41. Aerial view of Cedar Canyon, Arrow indicates outcrop of mineralized sandstone.

FIOUEE 42. Stratigraphic relationship of the earnotite-bearing sandstone in the Chudron formation to the 

overlying Arikaree formation in Cedar Canyon, Slim Buttes area, South Dakota.
CARNOTITE-BEARING SANDSTONE IN CEDAR CANYON, S. DAK. 259 

TABLE 1. Analyses of samples collected from the Cedar Canyon carnotite deposit

Locality no. 

pi. 10

1

2

3

4

5

6

7

Serial 

no.

92321

92322

87613

87612

92323

92324

92324a

eU 

(percent)

0. 036

 14

. 13

. . 055

.091

.018

.063

u

(percent)

0. 037

. 10

.23

.080

. 19 .

.001

.086

Description

Claystone, sandy, yellowish-gray; contains no

visible carnotite. 1-foot channel sample.

Claystone, sandy, yellowish-gray; has carnotite coating on sand grains. 0.3-foot

channel sample.

Sandstone, fine-grained, light-gray, silicified;

carnotite is concentrated on fracture surfaces. Selected grab sample.

Sandstone, fine-grained, light-gray, silicified;

contains disseminated carnotite. Grab

.'" sample.

Sandstone, fine-grained, light-gray, silicified;

has carnotite disseminated throughout.

Grab sample.

Sandstone, very fine grained, light-gray, silicified; contains no visible carnotite. Grab

sample.

Sandstone, fine-grained, light-gray, silicified;

contains disseminated carnotite. Grab

sample.

A grab sample of carnotite-bearing sandstone (loc. 7) collected 

from the landslide block, about 300 feet south of the mineralized 

outcrop, contains 0.086 percent uranium. The mineralized sandstone 

in this landslide block is similar to that exposed in the outcrop.

Carnotite has been found at two other localities in the southern 

part of the Slim Buttes, and abnormal radioactivity readings have 

been obtained at the contact of the White River group and the 

Arikaree formation throughout the Slim Buttes.

There is a large landslide block at locality 8, in the SW^ sec. 9, 

T. 16 N., R. 8E. In the Chadron formation, found hi the block, 

carnotite coats quartz granules in sandstone and sand grains disseminated in bentonitic clay. Carnotite can be seen in about only 

5 feet of outcrop, because of poor exposures in the area. A grab 

sample of clay, in which there are carnotite-coated sand grains, 

contains 0.025 percent uranium.

On the south side of Square Top Butte, at locality 9 in the SW% 

sec. 29, T. 17 N., R. 8 E., carnotite is found as fracture-surface 

coatings in the basal 0.2 foot of a 1.0 foot opalized clay bed. This 

opalized clay occurs in the Chadron formation, 19 feet below the 

contact of the Chadron formation and the Arikaree formation, and is 

overlain and underlain, by beds of bentonite. Laterally, this opalized 

clay grades into nonopalized bentonite. Small amounts of carnotite 

are present for about 100 feet along the outcrop.
260 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

ORIGIN

The Arikaree formation and formations of the White River group 

exposed in the Slim Buttes contain large quantities of volcanic glass 

and altered volcanic material, including bentonite. In the southern 

part of the Slim Buttes about 250 feet of very fine grained tuffaceous 

sandstone is present in the Arikaree formation, and an unknown 

thickness has been removed by erosion. Throughout the Slim Buttes 

area springs issue from the base of the Arikaree formation, and, at a 

few places, from the upper few feet of the Chadron formation. These 

springs result from a water table perched on impervious bentonite and 

bentonitic sandstone in the upper part of the Chadron formation. 

Water samples from these springs contain much more uranium than 

water samples collected from wells and springs in the underlying 

Fort Union and Hell Creek formations. Water from Summit Spring 

(sec. 5, T. 16 N., R. 8 E.), issuing from the base of tne Arikaree formation, contains 51 parts per billion of uranium; and water from Pnillips 

Spring (sec. 34, T. 17 N., R. 8 E.), which* fl'ows also from the fyase of 

the Arikaree formation, contains 170 parts per billion. Water from 

Section 17 Spring (sec. 17, T. 16 N., R. 9 E.), which issues from the 

Hell Creek formation, contains only 1 part per billion of uranium. 

Thirty-four analyses of water from springs and wells within the mapped 

area (pi. 11 and table 2) show the contrast in uranium content between water in the Arikaree and Chadron formations and water in 

the underlying formations. ^

The water from Summit Spring contains 0.42 gram per liter of 

residue. The residue from 48 liters (12.6 gal) of water from this 

spring was analyzed chemically and spectrographically. These 

analyses are tabulated in tables 3 and 4.

Chemical analyses of tuffaceous sandstone from the Arikaree 

formation indicate that the rock contains about 0.0015 percent uranium. No vanadium analyses were made, but Davidson (written 

communication, 1953) reports an average vanadium content of 0.05 

percent for 16 samples from the White River group and Arikaree 

formation in eastern Wyoming.

It is postulated that the uranium, vanadium, silicon, and other 

elements found concentrated in the Cedar Canyon area as carnotite 

and silicified sandstone were leached, by moving ground water, from 

the weakly radioactive volcanic material present in the Arikaree 

formation. These elements were deposited then in sandstone and 

claystone along the base of the perched water table, near the top of 

White River group.
CARNOTITE-BEARING SANDSTONE IN CEDAR CANYON, S. DAK. 261

TABLE 2. Analyses of water samples collected from wells and springs in the southern 

part of Slim Butles, Harding County, S. Dak.

Road Draw no. 1 Spring.. _____

Rabbit Creek Spring, _______ __

Thybo well -_--_---_ ___

Unnamed spring ____ ________

Red Tank Spring______ ____ __

Unnamed spring. ___________ _

Do____--__-_________.___

Do_ 

Do____---___-_---__-_--_

Do__-__.-_. _____________

Thybo Spring___-.-____. ______

Deer Draw Spring. __ __________

Fish Spring_________ ______ _

Unnamed spring _____________

Do 

Do . 

Do_--_-___-_- ---___-.___

Hines Spring. _ ________ _____

Section 17 Spring____________ _ Wolf Spring.... ____________ _

Unnamed spring. ___ ____.-_ _

Sec.

?5

25

?5

36

?,6

?fl

30

31

32

32

34

32

9,

?,

3

3

4

5

5

6

8

9

10

10

13

13

14

14

?4

17

19

?0

31

32

Locatio

T. (N.)

17

17

17

17

17

17

17

17

17

17

17

17

16

16

16

16

16

16

16

16

16

16

16

16

16

16

16

16

16

16

16

16

16

16

11

R. (E.)

7

7

7

7

8

8

8

8

8

8

8

9

8

8

8

8

8

8

8

8

8

8

8

8

8

8

8

8

8

9

9

9

9

9

U content

billion)

30

22

46

39

5

2

40

27

41

2

. 170.

5

14

200

14

32

10

51

12

20

15

56

66

38

24

13

13

46

11

1

13

2

4

5

Do.

Do.

Arikaree.

Hell Creek. . Do.

Chadron.

Do.

Do.

Fort Union.

Fort Union.

Chadron.

Arikaree.

Do.

Do.

Do

Do.

Do.

Chadron.

Do.

Do.

Do.

Do.

Do.

Do.

Fort Union.

Hell Creek.

Arikaree.

Chadron.

Fort Union.

Do.

TABLE 3. Chemical analyses of metals in the residue from 48 liters (12.6 gal) of

water from Summit Spring

[Sample serial No. D-86659. Analysts: H. E. Crowe, W. Mountjoy, and P. Schuch]

Element

Vanadium _______________________--__-__----___-.__

Uranium __________________________________________

Nickel __ _---____-___-_-_-__-____-_-__----- -_.___

Copper. ________-__-_____--_____-_---_-__---______-

Lead____-__-_____ _____-_-________--__-_--_---_-_-_

Molybdenum ______________________________________

Cobalt- . 

Element in 

residue 

(percent)

0.070

.010

.0010

.0008

.0006

.0002

.0001

Element in 

water (parts 

per billion)

290

42

4.2

3.6

2.5

.8

.4
262

TABLE 4. Semi-quantitative spectroyraphic analyses of the residue from J+8 liters 

(18.6 gal) of water from Summit Spring

[Sample serial No. D-86659, spectrographic plate No. 11-720. Analyst: A. T. Myers]

Element '

Iron..-- __ _ ____ __

Calcium. ___^ _ _ _ _

Percent

x +

X

Element

Zirconium ________ _

Barium ________ __

Percent

OOX 

ooox

1 Looked for but not detected, as the amount present was below the threshold amount of the element: 

Ae, As, Au, Be, Bi, Cd, Ce, Co, Dy, Er, Ga, Od, Ge, Hf, Hg, In, Ir, La, Li. Mo, Nb, Nd, Ni, Os, P, Pb, 

Pd, Pt, Re, Rh, Ru, Sb, Sc, Sn, Sm, Ta, Th, Tl, Te, U, W, Y, Yb, and Zn.

The mechanism for the localization of carnotite in the Cedar 

Canyon area is not clearly evident, but probably slight irregularities 

on the pre-Arikaree surface, and, therefore on the base of the perched 

water table, might exert some structural influence on the deposition 

of carnotite by controlling the flow of ground water. In most of the 

southern part of the Slim Buttes the base of the perched water table 

coincides with the top of the uppermost bentonite bed in the Chadron 

formation. However, at the Cedar Canyon carnotite deposit, this 

bentonite bed has been removed by pre-Arikaree erosion; and tuffaceous sandstone of the Arikaree formation directly overlies sandstone and sandy clays of the Chadron formation. Differences in 

porosity and permeability of the individual layers, caused by alternating fluviatile sandstone and sandy clay, might have formed a 

restricted channel for ground-water migration beneath the normal 

perched water-table horizon. Conditions in this zone have been 

favorable for the deposition of carnotite, although the specific physical 

and chemical factors which have made this a good host rock have not 

been determined.

The uranium content of some of the samples from the carnotite 

deposit is out of balance with the equivalent uranium. Equivalent 

uranium is a measure of the radioactivity of uranium and its decay 

products. When uranium is in equilibrium with its daughter products 

the equivalent uranium value equals the percent of uranium. It 

requires about 600,000 years for uranium to reach equilibrium with 

its daughter products (Kovarik, 1931, p. 11). Deposits that are 

out of balance are either younger than 600,000 years or leaching of 

one or more elements has taken place.

The uranium in samples 3, 4, and 5, table 1, is in excess of the 

equivalent uranium, but sample 6 is strongly out of balance in favor 

of equivalent uranium. These facts suggest that there has been recent
CARNOTITE-BEARING SANDSTONE IN CEDAR CANYON, S. DAK. 263

movement and reconcentration of material within the deposit, probably as a result of weathering. Perhaps some of the uranium in 

highly uraniferous spring water is being derived from undiscovered 

concentrations of uranium much like the deposit at Cedar Canyon.

SUGGESTIONS FOR PROSPECTING

In the southern part of the Slim Buttes occurrences of carnotite are 

found in sandstone and clay in the upper few feet of the Chadron 

formation, where it is unconformably overlain by the Arikaree formation. In areas where pre-Arikaree slumping has taken place and the 

Arikaree formation unconformably overlies the Brule formation, 

abnormally high radioactivity readings are commonly obtained at the 

contact of these two formations. One such anomaly was recorded 

at the contact between the Arikaree and Brule formations in the 

NE#SE#NWtf Sec. 31, T. 17 N., R. 8 E.

Thirty-four analyses of water from springs and wells for uranium 

are shown on plate 11 and in table 2. Waters from the Arikaree and 

Chadron formations contain a much greater amount of uranium than 

waters from the Fort Union and Hell Creek formations. The uranium 

content of water from springs in the Arikaree and Chadron formations 

has a considerable range. These ranges in content may be due in 

part to differences in rates of water flow, as springs of low flow generally contain more uranium than springs of high flow. A uranium 

content of 10 to 20 parts per billion in water is representative for 

springs issuing from the Arikaree and Chadron formations in the 

Slim Buttes. A uranium content of 30 or more parts per billion is 

abnormally high and may indicate the concentration of uranium 

minerals nearby.

Particular attention should be given to the areas around the 

following springs:

Uranium

content 

(parts per

billion) Location

Unnamed spring........ 200 NE^SW^ sec. 2, T. 16 N., R. 8 E.

Phillips Spring......... 170 NW^SEJ^ sec. 34, T. 17 N., R. 8 E.

Antelope Spring........ 66 SWJ^NEJ^ sec. 10, T. 16 N., R. 8 E.

Unnamed spring........ 56 NE^SW^ sec. 9, T. 16 N., R. 8 E.

Summit Spring......... 51 SEJ^SE^ sec. 5, T..16., R. 8 E.

Unnamed spring..._____ 46 NWMSW^ sec. 14, T. 16 N., R. 8 E.

J. B. Spring............ 46 SW^SEM sec. 25, T. 17 N., R. 7 E.

Guard Station Spring... 41 SWJ^SW^ sec. 32, T. 17 N., R. 8 E.

Unnamed spring........ 40 SWMSEJ4 sec. 30, T. 17 N., R. 8 E.

Rabbit Creek Spring.... 39 SE^SE^ sec. 36, T. 17 N., R. 7 E.

Rock Spring........... 38 NE^SEM sec. 10, T. 16 N., R. 8 E.

Other favorable areas for the concentration of uranium minerals 

may be found where the rocks are folded into synclines or where there
264 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

are sandstone channel deposits. Commonly, silicification of the rocks 

has accompanied carnotite mineralization. Prospecting should not 

be restricted to the Arikaree, Brule, and Chadron formations but 

should include also an investigation of the sandstone beds of the Fort 

Union and Hell Creek formations, particularly where they are unconformably overlain by the Arikaree formation and by the White 

River group.

The recent discovery of uranium-bearing sandstone in the Chadron 

formation in the White River badlands, Pennington County, S. Dak. 

(G. W. Moore and Murray Levish, written communication, 1954), 

suggests that other areas where the Arikaree formation and the White 

River group are present should be prospected. These units, or their 

equivalents, crop out in parts of North and South Dakota, Wyoming, 

Montana, Colorado, Nebraska, and adjacent States.

LITERATURE CITED

Baker, C. L., 1952, Geology of Harding County: S. Dak. Geol. Survey Kept.

Inv. 68. 

Brown, R. W., 1952, Tertiary strata in eastern Montana and western North

and South Dakota: Billings Geol. Soc. Guidebook, 3d ann. field conference,

p. 89-92. 

Bump, J. D., 1951, The White River badlands of South Dakota: Soc. of Vertebrate

Paleontology. Guidebook for a field conference (5th), p. 35-46. 

Kovarik, A. F., 1931, Calculating the age of minerals from radioactivity data and

principals: Natl. Research Council Bull. 80, p. 73-123. 

MacDonald, J. R., 1951, Additions to the Whitneyan fauna of South Dakota:

Jour. Paleontology, v. 25, no. 3, p. 257. 

Todd, J. E., 1895, Recent geological work in South Dakota: Am. Geologist, v. 16,

p. 303. 

Toepelman, W. C., 1923, The possibilities of oil in eastern Harding County, S.

Dak.: S. Dak. Geol. and Nat. History Survey Circ. 12.

Winchester, D. E., 1913, Crossbedding in the White River formation of northwestern South Dakota: Jour. Geology, v. 21, p. 550-556. 

Winchester, D. E., Hares, C. J., Lloyd, E. R., and Parks, E. N., 1916, The lignite

field of northwestern South Dakota: U. S. Geol. Survey Bull. 627. 

Wood, H. E. 2d, 1945, Late Miocene beaver from southeastern Montana: Am.

Mus. Novitates 1299.

U. S. GOVERNMENT PRINTING OFFICE: 1955