1C. 352

GEOLOGICAL SURVEY CIRCULAR 352

PRELIMINARY REPORT ON URANIUM 

IN THE GAS HILLS AREA, FREMONT 

AND NATRONA COUNTIES 

WYOMING

This report concerns work done on 

behalf of the U. S. Atomic Energy 

Commission and is published with 

the permission of the Commission.
UNITED STATES DEPARTMENT OF THE INTERIOR 

Douglas McKay, Secretary

GEOLOGICAL SURVEY 

W. E. Wrather, Director

GEOLOGICAL SURVEY CIRCULAR 352

PRELIMINARY REPORT ON URANIUM IN THE GAS HILLS AREA 

FREMONTAND NATRONA COUNTIES, WYOMING

By J. D. Love

This report concerns work done on 

behalf of the U. 8. Atomic Energy 

Commission and is published with 

the permission of the Commission.

Washington, D. C., 1954

Free on application to the Geological Survey, Walhington 25, D. C.
R.89 W. 

Tida 

p u 

(?

L

R. 91 W. R. 90 W. R. 89 W. 

Geology from published and unpublished maps by J. D. Love, J. L. Weitz, F. B. Van Houten, and C.J. Hares

I 5 Miles

I

Figure 1. Geologic map of Gas Hills area, central Wyoming.
PRELIMINARY REPORT ON URANIUM IN THE GAS HILLS AREA 

FREMONT AND NATRONA COUNTIES, WYOMING

By J. D. Love

CONTENTS 

Page

Abstract...................................... 1

Introduction................................... 1

Geography.................................... 2

Geology....................................... 2

Stratigraphy .................................. 2

Uranium occurrences.......................... 4

Page

Uranium occurrences Continued

Description of localities.................. 4

Origin of uranium in the Gas Hills area......... 9

Possibility of industrial health hazard .......... 10

Selected references .......................... 10

Unpublished reports .......................... 11

ILLUSTRATIONS

Page

Figure 1. Geologic map of Gas Hills area, central Wyoming.............................................. ii

2. Uraniferous sandstone in Wind River formation at locality 5..................................... 7

3. Wind River formation at locality 7 ............................................................ 8

Table

TABLES

Page

1. Analyses of samples........................................................................ 6

2. Analyses of water.......................................................................... 10

ABSTRACT

Uranium minerals have been discovered in the 

Wind River formation of early Eocene age, in strata 

of middle and late Eocene age, and in the Thermopolis 

shale of Early Cretaceous age in the Gas Hills area of 

central Wyoming. Localities of uranium mineralization were found independently by prospectors and by 

geologists of the U. S. Geological Survey. Geologists 

of the Atomic Energy Commission have made evaluation studies of many of the occurrences in the area as 

well as reconnaissance that led to new discoveries.

The uranium is concentrated in clayey and conglomeratic sandstone and in carbonaceous shale. Several selected samples of sandstones in the Wind River 

formation, taken for mineral determination, contain 

more than 10 percent uranium. The highest analysis 

of a channel sample is 6.72 percent uranium from a 

1-foot section of conglomeratic sandstone in the Wind 

River formation. The highest analysis of a carbonaceous shale in this formation is 0.062 percent uranium. 

A sample of sandstone from the sequence of middle and 

late Eocene age contained 0.078 percent uranium. A 

sample from the Thermopolis shale directly overlain 

by the Wind River formation contained 0.041 percent 

uranium.

Several uranium minerals are present. The dominant one is meta-autunite, Ca(UO2 ) 2(PO4)2» 2|-6iH2O, 

a pale greenish-yellow highly fluorescent mineral. In , 

some samples, arsenic appears to be more abundant 

than phosphorus and the mineral may be uranospinite, 

Ca(UO2) 2 {AsO4 )2 8-12H2O. A greenish-yellow nonfluorescent mineral is present in several localities. 

X-ray studies indicate that it is a calcium uranyl phosphate, possibly a new mineral.

The writer believes that the source of the uranium may have been tuff in the White River formation 

(Oligocene) or younger Tertiary rocks that once overlay this portion of the Wind River Basin. The available evidence suggests that the uranium was carried 

downward and laterally along sandstone aquifers in the 

middle Eocene sequence and Wind River formation and 

was concentrated in favorable host rocks.

INTRODUCTION

The Gas Hills area is located in eastern Fremont 

and western Natrona Counties, central Wyoming (fig. 1). 

A reconnaissance examination of some of the rocks in 

the area was made with a Geiger counter in 1951 while a 

Geological Survey field party was engaged in oil and gas
investigations there. A water sample (no. 1, table 2) 

was collected for analysis by the Oak Ridge laboratory of the Atomic Energy Commission. The 

water sample and the rocks showed small amounts 

of uranium. Data obtained on the geologic occurrence of uranium during 1952 and 1953 in the 

Pumpkin Buttes (Love, 1952) and Miller Hill (Love, 1953) 

areas suggested that the Gas Hills area warranted 

a detailed scintillation counter survey. This survey was begun on September 27, 1953, Abnormally high background radiation was noted throughout many square miles and rock samples were 

collected for analysis from several of the localities shown in figure 1. However, the writer was 

unaware at that time that Mr. Neil McNeice, of 

Riverton, Wyo., had already discovered radioactive sandstone in sec. 22, T. 33 N., R. 90 W. 

(loc. 7) on September 9, 1953. Early in October, 

Mr. McNeice informed geologists of the Atomic 

Energy Commission of the location of his discovery claim and they began detailed studies of the 

uranium deposits in the area. N. M. Denson and 

the writer likewise examined and sampled many 

of the localities in October.

This discovery received widespread publicity 

which resulted in an intensive search for uranium 

throughout the general region and several hundred 

claims were staked in the Gas Hills area. The 

Atomic Energy Commission is continuing evaluation studies of occurrences in the area and is 

assisting in the physical exploration and development of individual deposits. The Geological Survey is making further studies of the relation of 

uranium occurrences to geologic features.

C. C. Towle, chief, Denver Exploration Branch 

of the Atomic Energy Commission, read the manuscript and contributed valuable suggestions. L. F. Rader 

and his associates made the chemical and radiometric analyses. Mrs. Alice D. Weeks and L. B. Riley 

identified the uranium minerals. The reconnaissance examination of the Gas Hills area was 

made on behalf of the Division of Raw Materials 

of the U. S. Atomic Energy Commission.

Stratigraphic and structural studies of the 

Wind River Basin, including the Gas Hills, have 

been in progress by the U. S. Geological Survey 

since 1944, as part of a regional oil and gas 

investigations program. The results of many of 

these studies have been published and are listed 

in the selected bibliography. The Gas Hills area 

is included in published topographic maps, scale, 

1:24,000, of the Puddle Springs, Coyote Springs, 

Gas Hills, and Ervay Basin SW quadrangles, 

7. 5-minute series, with 20-foot contour interval.

GEOGRAPHY

The Gas Hills area lies along the southern 

margin of the Wind River Basin. The hills to 

which the name is applied are steep hogbacks of 

Mesozoic rocks on the north and west flanks of 

the Dutton Basin anticline which projects northward from the Beaver Divide. The Beaver. Divide 

escarpment marks the southern boundary of the 

area and trends generally east. The steep north

face rises 300 to 800 feet above the Wind -River 

Basin to the north. The lip of the escarpment 

is essentially the drainage divide between northward-flowing tributaries of the Wind River having 

high gradients and southward-flowing tributaries of 

the Sweetwater River having low gradients.

Although the Gas Hills area has no towns 

and no improved roads most of the area is 

accessible by car. Moneta is the nearest post 

office, 25 miles to the north on U. S. Highway 20. The nearest railroad station is at 

Lysite, on the Chicago, Burlington, and Quincy 

Railroad, 34 miles to the north. The area has 

no permanent residents. Sheep and cattle ranching is the only industry. Vegetation is sparse 

and bedrock is moderately well exposed.

GEOLOGY

The Gas Hills are hogbacks of steeply dipping 

Mowry shale and of sandstone in the Cloverly formation on the north and west flanks of the Dutton Basin 

anticline. This anticline branches off the Granite 

Mountains to the south and plunges northwestward 

into the Wind River Basin. Folding occurred near 

the close of Paleocene time and erosion developed 

the present topography on the pre-Eocene rocks. 

The overlying Wind River formation and the succeeding younger Tertiary strata were then deposited until the structural basin between the 

Granite Mountains to the south and Owl Creek 

Mountains to the north was filled with nearly horizontal Eocene, Oligocene, Miocene, and possibly Pliocene 

rocks, at least to the level of the present crest of the 

Beaver Divide escarpment. Pliocene and Pleistocene 

uplift started the present erosion cycle, and as the 

face of the Beaver Divide escarpment moved southward, 

the Gas Hills and other areas of older resistant folded 

rocks along the south margin of the Wind River Basin 

were exhumed. Remnants of lower and middle Eocene 

rocks are present in steep pre-Eocene valleys between the hogbacks of Mesozoic rocks. These valleys 

extend generally south and probably continue for some 

distance beneath the Tertiary strata that form the 

Beaver DMde. This relationship may have a bearing 

on the orientation and distribution of uranium deposits, 

and is discussed in more detail in the description of 

individual deposits. About 10 miles southeast of the 

Gas Hills, in and south of the Rattlesnake Hills is a 

volcanic field of middle and late Eocene age, the rocks 

of which were intruded through pre-Cambrian, Paleozoic, and Mesozoic rocks. These vents furnished much 

of the volcanic debris in the middle and upper Eocene 

rocks in the Gas Hills area.

STRATIGRAPHY

Detailed descriptions and thicknesses of the rock 

units in the Gas Hills area are summarized below:

Alluvium: Gravel, sand, and clay derived from Tertiary 

rocks along the Beaver Divide escarpment and deposited along stream "bottoms.

Landslide debris: Claystone and sandstone masses of 

Eocene and Oligocene rocks that nave "broken loose 

and moved north down the slopes of the Beaver 

Divide.
Miocene rocks: Sandstone, gray and white, soft, tuffaceous; containing lenses of conglomerate near the 

base and pumicite in the upper part. Thickness 

ranges from a feather edge to 100 feet.

White River formation (Oligocene): Tuff, light-gray, 

limy, biotitic, vitric, and tuffaceous mudstone. 

Basal bed is 50 feet thick. The upper 200 to 

300 feet is grayish-orange to yellowish-gray sandy 

mudstone with some layers of gray vitric tuff and 

thin lenses of conglomerate. South of Coyote 

Spring, this sequence is, in part, soft plastic 

tuffaceous variegated claystone. The formation in 

the Gas Hills area is of Chadron age. The thickness ranges from a feather edge to more than 

It-50 feet.

Upper and middle Eocene volcanic rocks: Dacite, lightgray to dark-gray; hornblende latite, sodic 

trachyte, andesite, and alkalic rocks. They are 

intruded through pre-Cambrian, Paleozoic, and 

Mesozoic rocks in the Rattlesnake Hills and furnished boulders and ash that are incorporated in 

the upper and middle Eocene sedimentary sequence. 

The volcanic rocks are overlain by Oligocene and 

Miocene strata.

Upper and middle Eocene sedimentary rocks: Six units 

are recognizable along the Beaver Divide escarpment. (Van Houten, F. B., personal communication.)

6. Conglomerate, volcanic, very coarse grained, 

more than li-O feet thick. Crops out in a 

massive ledge at the top of the formation and 

forms the lip of the Beaver Divide escarpment 

at some places.

5. Sandstone, dark-yellowish-gray, tuffaceous; 

and volcanic conglomerate consisting chiefly 

of andesite porphyry. Uraniferous sandstone 

at locality 9 is believed to be a northward 

extension of this unit.

It-. Tuff, biotitic; lapilli tuff, and cobbles of 

volcanic rocks. Bed is 1*5 feet thick.

3. Sandstone, tuffaceous; sandy mudstone, and conglomerate containing pebbles and cobbles of 

sodic trachyte pumice, tuff, and lava. Bed is 

90 feet thick. Giant boulders of pre-Cambrian 

gneiss and granite are present in lower 25 feet 

of the unit.

2. Mudstone, soft; and arkosic sandstone containing very little tuffaceous debris. The uppermost bed is a dredge-forming arkose and conglomerate containing pebbles of sodic trachyte 

lava.

1. Mudstone, green to olive, ledge-forming; contains a thin bed of acidic tuff that probably 

records the initial volcanic outburst in the 

Rattlesnake Hills volcanic field. Thickness 

at base is 25-30 feet.

Middle and lower Eocene rocks: For a distance of 5 miles 

or more north of the Beaver Divide and east of the 

Gas Hills, the Wind River formation is overlain by 

rocks of middle Eocene age. The formations look 

very much alike and have not as yet been mapped 

separately. Both sequences contain yellow soft 

sandstone, lenses of ferruginous brown sandstone, 

and conglomerate. The chief lithologic difference 

is that conglomerate in the middle Eocene sequence 

contains abundant boulders of andesite derived from 

the Rattlesnake Hills, whereas the conglomerate in 

the Wind River formation contains no locally derived volcanic rock fragments. The sequence ranges 

in thickness from a feather edge to more than 

200 feet.

Wind River formation (lower Eocene): This is an extremely variable sequence of rocks that was deposited on a rugged topography cut in folded and 

eroded Paleozoic and Mesozoic rocks. In the northwestern part of the area the basal strata are 

brightly variegated claystones and clayey sandstones. In the southeastern part of the area the 

basal beds are yellow to gray arkosic sandstone 

and granitic conglomerate. Higher in the sequence 

are lenticular sandstones, some of which are highly 

ferruginous. The sandstones contain many of the 

uranium deposits in this area. Thin carbonaceous 

shales and coals likewise contain some concentrations of uranium. The formation ranges in thickness from a feather edge to more than -300 feet.

Cody shale (Upper Cretaceous): Shale, gray, soft; sandy 

in the upper part. The Cody shale is more than 

3,000 feet thick and underlies extensive areas of 

the Wind River formation north and west of the Gas 

Hills. Because of its low dips, extent, and impermeability, the Cody shale was of major significance 

in confining some of the ground water containing uranium within the overlying Wind River formation.

Frontier formation (Upper Cretaceous): Sandstone,

chiefly gray, soft, lenticular; interbedded with 

gray to black soft shale. White tuff and bentonite 

beds mark base of formation, which is about 580 feet 

thick.

Mowry and Thermopolis shales (Lower Cretaceous): The

Mowry shale is dark-gray hard siliceous; containing 

abundant fish scales; weathers silvery gray and 

crops out in ridges forming the outer portion of the 

Gas Hills. The shale is about It-70 feet thick and is 

underlain by the Thermopolis shale containing the 

Muddy sandstone member at the top. The Muddy sandstone member is 32 feet thick and consists of gray 

fine-grained sandstone and siltstone interbedded 

with black shale. It IB underlain by 150 feet of 

soft black fissile shale. This shale contains one 

of the uranium deposits in this area.

Cleverly and Morrison formations (Lower Cretaceous and 

Upper Jurassic): Sandstone, chiefly ferruginous, 

80 feet thick; and conglomerate which forms the 

highest inner ridges of the Gas Hills, 200 feet 

thick. The middle and lower part of the sequence 

is interbedded variegated claystone and sandstone.

Jurassic rocks: Sundance formation, sandstone, gray

and green shale; 2^0 feet thick; underlain by gray 

and white Nugget sandstone, 170 feet thick.

Chugwater formation (Triassic): Only the upper part of 

this formation is exposed. The Popo Agie member 

at the top is 300 feet thick and consists of red 

shale, red sandstone and siltstone, and thin sparse 

limestone pellet conglomerates. It is underlain 

by the Alcova limestone member, a gray thin-bedded 

hard limestone 5 feet thick. The underlying 

Red Peak member is a red sandstone, siltstone, and 

shale sequence about 700 feet thick.

Phosphoria formation (Permian): Dolomite, interbedded,| 

cherty and red shale containing thin anhydrite beds. 

This formation is about 325 feet thick.

Tensleep sandstone and Amsden formation (Pennsylvania^): 

Tensleep sandstone, white, hard, fine-grained, 

about 200 feet thick; underlain by the Amsden 

formation, consisting of about 200 feet of red and 

green shale, cherty dolomite, and a basal ferruginous 

sandstone about 60 feet thick.

Madison limestone (Mississippian): Limestone, blue-gray, 

massive to thick-bedded, cherty; containing some 

dolomite near the base. This formation is 300 feet 

thick.
Cambrian rocks: Sandstone, chiefly arkosic red and 

brown in the lower half; green and gray sandy 

and silty shale, and sparse thin limestones in 

the upper half. Thickness is about 800 feet.

Pre-Cambrian rocks: Granite, chiefly red and brown, 

granite gneiss, and black schist cut by quartz 

pegmatite dikes.

URANIUM OCCURRENCES

The purpose of this report is to present 

geologic data on several types of uranium deposits in the Gas Hills area rather than to give 

the complete description of each locality where 

radioactivity or uranium minerals occur. Therefore, some localities are described that are of 

geologic significance but in which there is no 

commercial-grade uranium ore, whereas other 

localities where rocks contain more than 0.1 percent uranium are omitted because the geologic 

setting is similar to that of one already described 

in this report. The Atomic Energy Commission 

has been actively engaged in physical exploration 

throughout the area, beginning in October, 1953, 

with the objective of evaluating tonnage and grade 

of many of the deposits. Therefore, the Geological Survey has made no attempt to estimate tonnage and grade in any locality in the Gas Hills 

area.

Uranium occurs in the Thermopolis shale of 

Early Cretaceous age, in the Wind River formation, and in middle Eocene rocks. Occurrences 

of uranium minerals are most abundant in soft 

sandstones in the Wind River formation. One conspicuous feature of the area is the background of 

radioactivity. It is commonly more than twice as 

high on outcrops of the Wind River formation and 

middle Eocene rocks than on adjacent outcrops of the 

Cody shale.

Description of localities

Locality 1 (SWjSEJsec. 24, T. 33N.. R. 91 W). - 

The site of this locality is a water well at the 

Puddle Springs ranch, and is reported to be 

80 feet deep. The water issues from an arkosic 

sandstone in the lower part of the Wind River 

formation, A water sample obtained by hand 

pumping contained 0.012 ppm uranium.

Locality 2 (C SWJ sec. 32. T. 33N.. R. 90 W). - 

A radioactive carbonaceous shale is the site of 

locality 2. It is stratigraphically above the uraniferous sandstone beds at localities 3, 4, and 5. 

Locality 2 is considered significant because (a) it 

is one of many stratigraphic zones in which uranium occurs in the Wind River formation, and 

(b) it shows how much uranium is present in carbonaceous rocks where they are overlain by a 

soft porous sandstone. By comparison, another 

carbonaceous shale, north of locality 1, is overlain and underlain by variegated claystone and 

contains very little radioactivity. A preliminary 

reconnaissance section including the carbonaceous 

shale at locality 2, from top to bottom, is shown 

in the following section:

Unit 

no.

Thickness 

(feet)

20

Lithologic character

6 Sandstone, pale green, arkosic, coarsegrained, finely conglomeratic in upper 

10 feet; 1 3-foot granite boulder present but average size is less than 

2 inches; no volcanic rock fragments 

observed; most fragments are of gray 

granite.

5 Shale, dark brown, carbonaceous, contains .5 

O.OJ1 percent equivalent uranium and 

0.021 percent uranium; contains flattened 

plant and tree fragments; forms top of 

ledge.

k Shale, black, coaly, interbedded with thin 1.5 

coal partings.

3 Shale, brown and gray, carbonaceous, platy; 2.2 

contains leaf impressions.

2 Claystone, pale green, plastic, soft. 5

1 Sandstone, pale brownish green, soft, 15 

coarse-grained, interbedded with arkose 

and fine-grained conglomerate with small 

black chert and granite pebbles.

In the general vicinity of this locality there 

are many places of higher radioactivity, and 

uranium minerals occur in some of them, chiefly 

in sandstone, above and below the carbonaceous 

shale. Although this shale is of no commercial 

value, carbonaceous shales with readily detectable uranium content probably can be useful 

guides in locating areas of possible uranium 

deposits. These shales are conspicuous and 

can be easily checked. Where such shales are 

underlain or overlain by porous sandstones, if 

any uranium is in the vicinity, some of it will 

probably be concentrated in the carbonaceous 

shale.

Locality 3 (SWiSEiSWi- sec. 1. T. 32 N.. 

R. 91 W). Meta-autunite is disseminated in 

sandstone of the Wind River formation at locality 3. The relationship of the uraniferous 

sandstone to overlying and underlying rocks 

of the Wind River formation can be observed. 

Localities 3, 4, and 5 are stratigraphically 

lower than locality 2. The rocks at locality 3 

dip about 1° SW. The stratigraphic section 

shown below was measured on the west-facing 

slope just west of the uraniferous deposit. Unit 

1 is at the base of the section.

Unit 

no.

Lithologic character

Sandstone, pale green, clayey, in lower 

5 feet, grading up to ledge-forming 

coarse-grained gray sandstone, and 

then to granite boulder conglomerate. 

The top of the unit is the top of the 

knob just west of the uranium locality. 

The uranium is concentrated in a pale 

green and brown clayey sandstone about 

7 feet above the base of the unit where 

readings are locally 2.5 mr/hr. A 

trench sample of 1 foot of beds contains 0.13 percent equivalent uranium 

and 0.050 percent uranium. Overlying 

strata of the Wind River formation are 

eroded away so there is no way to 

determine the total thickness of the 

formation here.

Thickness 

(feet)
Unit 

no.

Thickness 

(feet) Lithologic character

Sandstone, dark brown, hard, forming 1 

ledge, lenticular; appears at slightly 

different levels in outcrops to northeast and southwest; locally gives readings of 1.5 mr/hr.

Sandstone, pale green, interbedded with 18 

conglomerate of granite fragments, very 

soft; sandstone is very coarse grained 

but has a greenish clay matrix in part; 

roundstones are chiefly of gray granite 

as much as 6 inches in diameter but 

averaging 1 to 2 inches.

Sandstone and conglomerate, greenish- 10 

brown; matrix is so soft it is almost 

unlithified; rock fragments are chiefly 

gray granite; gives readings of 0.2 to 

0.25 mr/hr.

Conglomerate and sandstone, gray to brown, 6 

forming ledges; middle part is a mass 

of boulders as much as 2 feet in diameter jumbled together; almost all are 

coarse grained gray granite but some are 

black chert from Paleozoic rocks; sandstone is coarse grained and lentiular; gives readings of 0.1 to 

0.15 mr/hr.

Sandstone, pale greenish brown, soft, 66 

with clay matrix, interbedded with 

brownish-green plastic claystone in 

which are many sand grains, in lower 

half of unit; upper half is largely very 

coarse grained greenish-brown soft 

arkosic sandstone.

Sandstone, gray, hard, lenticular; forms 0-12 

ledges that appear intermittently 

in outcrops to south at this same 

position; very coarse grained and pebbly; 

most pebbles are of granite as much as 

1 inch in diameter but commonly less 

than 1/10 inch; gives reading of 

0.06 mr/hr.

Sandstone, greenish gray, coarse-grained; 22 

with clay matrix; less clayey toward 

top; gives readings of 0.06 to 

0.07 mr/hr.

Claystone, "brownish green, soft, plastic, 1? 

very sandy; grades up to coarse-grained 

arkosic sandstone with a clay matrix; 

in upper 5 feet and particularly at top 

are abundant groups of aragonite crystals 

as much as 2 feet in diameter; gives 

reading of 0.05 mr/hr.

Total thickness of measured part of Wind 187-199 

* River formation.

The underlying rocks are not exposed but the base of 

the section probably is not more than 50 to 75 feet 

above the contact with Cody shale.

The area within 50 feet of the spot sampled 

for analysis (fig. 2) is markedly radioactive. To 

the northwest, where the section was measured, 

the radioactivity appears to extend through a stratigraphic interval of 7 feet of sandstone, but at the spot

sampled, a trench only 1 foot, deep was dug. This 

trench sample contained 0.13 per cent equivalent uranium and 0.050 percent uranium (table 1). The bright 

greenish-yellow highly fluorescent mineral at this 

locality is meta-autunite which is disseminated through 

the soft sandstone and in places is concentrated in small 

green pods.

Locality 4 (NE4-NEiNWi sec. 12. T. 32 N.. 

R. 91 W). This locality yielded some of the highest 

radioactivity measurements made in the Gas Hills area. 

A scintillation counter read 8 mr/hr on the surface 

and a trench sample of the uppermost 1 foot of 

sandstone contains 1.2 percent equivalent uranium 

and 1.87 percent uranium. The uranium is concentrated in a very light gray slightly clayey sandstone at about the same horizon as that at locality 3. 

The thickness of the uraniferous part of the sandstone is not known, but 50 feet to the southwest 

on the point of the spur along which the sandstone 

crops out, a ledge 5 feet thick is moderately 

radioactive. Meta-autunite, possible uranospinite, 

Ca(UO2)2(AsO4 ) 2 .8-12H2 O, and an unknown greenishyellow nonfluorescent mineral are disseminated in 

the coarse-grained sandstone near the surface. 

Readings of more than 1 mr/hr were obtained for 

a distance of 20 feet on each side of the spot that 

was sampled and lower readings for another 50 feet 

beyond that.

Locality 5 (SEiNEiNWi sec. 12. T. 32 N.. 

R. 91 W). Abundant meta-autunite, uranospinite(?), 

and possibly the unknown nonfluorescent greenishyellow uranium mineral are disseminated in a 

coarse-grained conglomeratic sandstone (fig. 2) 

at locality 5. A trench sample of 1 foot of 

rock at the surface contains 0.58 percent equivalent uranium and 0.25 percent uranium. At a 

depth of 5 feet a 1-foot channel sample contains 

0.19 percent equivalent uranium and 0.065 percent uranium. The deposit is in a very soft 

ferruginous conglomeratic sandstone about 50 feet 

stratigraphically below the uraniferous sandstone 

at locality 4. The sandstone is brown, coarse 

grained, and contains rounded pebbles of granite . 

as much as 2 inches in diameter. A scintillation 

counter reads 8 mr/hr at the surface point 

sampled, and indicates a high level of radioactivity for 20 feet in all directions. About 

400 feet to the southeast another occurrence of 

high radioactivity occurs in a similar sandstone.

Locality 6 (SEiSEjNEi sec. 14. T. 32 N.. 

R. 91 W).- The site of locality 6 fs Coyote 

Spring which issues from the basal conglomeratic 

sandstone of the Wind River formation where it 

overlaps northward onto a pre-Wind River hill 

of Mowry shale. The spring flows a 1-inch pipe 

full of clear cold water which contains 0.090 ppm 

uranium.

Locality 7 (fig. 3) (NEjSEj- sec. 22, T. 33 N.. 

R. 90 W). The site of locality 7 is in the Gas 

Hills area where Neil McNeice first discovered 

radioactive sandstone. The uranium is in the 

Wind River formation which overlies the Cody 

shale, strikes east, and dips 3° S. Exposures 

of the Wind River formation begin about 50 feet
Table 1. Analyses of samples from Gas Hills area1

Laboratory 

sample no.

99202

99201

99204

99205

206975

99206

99207

99209

99208

200929

99210

99212

58068

99211

58067

20697^

Locality

2

3

4

5

5

7

7

(AEG sample

loc. EWS-6).

7

(AEG sample

loc. EWS-2).

7

(AEG sample

loc. EWS-1).

7

8

(AEG sample

loc. EWS-8).

9

10

10

10

eU 

(percent)

0.051

.13

1.2

.58

.19

.21

.047

.19

.08

.52

.039

.06

.015

.078

.003

4.7

U 

(percent)

0.021

.050

1.87

.25

.065

.24

.014

.24

.096

.95

.041

.078

.018

.062

.003

6.72

V2 05 

(percent)

0.06

.06

.06

.06

.1

.06

.05

.06

.06

.05

.08

.12

.1

Se 

(ppm)

10

20

50

2

50

12

40

80

3

2

15

As 

(ppm)

150

50

750

400

1000

350

200

400

50

50

50

Location (fig. l), lith

C SW£ sec. 52, T. 33 N. , R. 90 

of carbonaceous shale in Wind 

SW£SE£SW£ sec. 1, T. 32 N., R. 

of sandstone in Wind River f

NE£NE£NW£ sec. 12, T. 32 N., R

of sandstone in Wind River fo

bly uranospinite, and an un

mineral present.

SE£NE£NW£ sec. 12, T. 32 N., R

of conglomeratic sandstone in 

autunite, possibly uranospini

fluorescent uranium mineral p

Channel sample of 1 ft of sand

NE^SE^ sec. 22, T. 33 N., R. 90 

sandstone in Wind River forma

36 ft SW of 99206. Channel sam

Wind River formation.

126 ft SW of 99207. Channel sa

Wind River formation.

8l ft SW of 99209. Channel sam

Wind River formation.

Pebble of basic igneous rock fr

Wind River formation.

NE£SEjLSW£ sec. 23, T. 33 N., R. 

of black Thermopolis shale.

NW£HE£SW£ sec. 17, T. 33 N., R. 

in middle Eocene sequence.

C SE£-NE£ sec. 27, T. 33 N., R. 

Wind River formation.

30 ft southwest of sample 58068

shale in Wind River formation

SE£SEjLNE£ sec. 27, T. 33 N., R. 

upper Eocene rocks above Wind 

NWlc?U' :L l\niJ-i- «*f»r» f*i T ~*& TJ T? 

XNW ^wn j^lvn^ oc5U. vJ, X . J7^ 1" . , -TV * 

of conglomeratic sandstone in 

1 Samples analyzed by the U. 5. Geological Surrey. Analysts: Furman, Dufour, Meadows, Mountjoy, and Vilson.
</."/.<««,,,:. j^.

X^^'«*^?£^*S&ass&*'*r

£ - ^ -J~. ^ --;,£__ 

^ . . .. ---v^ '>-.**- -:*- *- - .r*TS

Figure 2. Uraniferous sandstone in Wind River formation at locality 5. Sample of top foot contains 0. 25 percent

uranium and from the bottom foot 0.65 percent uranium.

above the Cody shale. A generalized estimated section is shown below, from top to bottom (fig. 3):

Unit 

no. Lithologic character

Sandstone, gray, medium-grained to 

coarse-grained, crossbedded, with 

hard and soft layers; forms intermittent ledges; contains many ferruginous uraniferous concretionary 

masses that cut across bedding 

and resemble the uranium-bearing concretions in the Pumpkin Buttes area. 

Some meta-autunite or uranospinite(?) is 

visible. A channel sample of 1 foot of 

sandstone contained 0.21 percent equivalent uranium and 0.2*4- percent uranium.

Shale, brown, carbonaceous, slightly radioactive.

Sandstone and claystone, greenish-brown, 

soft, interbedded.

Shale, dark brown, carbonaceous, 

slightly radioactive.

Sandstone and claystone, greenishbrown, soft.

Shale, brown, carbonaceous.

Sandstone and claystone, greenishbrown, soft.

Estimated 

thickness 

(feet) 

10

0.5

10

20

1

25

The uraniferous sandstone crops out extensively along the top of a broad upland area. A 

1-foot channel sample of this sandstone from AEC 

pit EWS-6, about 36 feet southwest of the measured

section, contained 0.047 percent equivalent uranium and 0.014 percent uranium. About 125 feet 

farther southwest, a 1-foot channel sample of 

sandstone at the same horizon in AEC pit to EWS-2, 

contained 0.19 percent equivalent uranium and 0. 24 percent uranium. Another 1-foot channel sample of 

sandstone taken from the same horizon 81 feet 

farther southwest, at AEC pit EWS-1 contained 

0.08 percent equivalent uranium and 0.096 percent 

uranium. This zone of ferruginous radioactive 

sandstone crops out for a distance of 450 feet 

farther southwest but the amount of radioactivity 

apparently decreases in that direction. High radioactivity was detected at a number of additional 

places southeast and east of locality 7 on the same 

ridge and in the same sandstone. A pebble of darkgray basic igneous rock from this locality contained 

0.52 percent equivalent uranium and 0.95 percent 

uranium. Concentric zones of alteration suggest 

that uranium soaked into the pebble from solutions 

in the surrounding sandstone.

Locality 8 (NEjSEJSWi- sec. 23. T. 33 N.. 

R. 90 W.). The black Thermopolis shale of Early 

Cretaceous age is the site of locality 8. A channel sample of the shale taken at AEC pit EWS-8 

contained 0.039 percent equivalent uranium and 

0.041 percent uranium. The shale dips west about 

35° and is overlain by essentially horizontal ferruginous conglomeratic sandstone in the Wind River 

formation. The radioactive zone is about 30 feet 

below the Muddy sandstone member. Neither the 

Muddy sandstone member nor the basal sandstone 

of the Wind River formation show more than a
Figure 3. Wind River formation at locality 7. Arrow marks zone of uraniferous sandstone.

ground cut on Cody shale.

Flats in left backnormal background radioactivity count. The radioactive zone in the Thermopolis shale extends for 

more than 50 feet north-south, and has a stratigraphic thickness of about 10 feet, but the radioactivity gradually diminishes in both directions 

from the pit where the sample was taken.

The sandstones of the Wind River formation were 

deposited in a steep narrow valley cut along the strike 

within the soft Thermopolis shale and flanked on the 

west by a resistant ridge of Mowry shale and on the 

east by resistant sandstone in the Cleverly formation. 

The writer believes that the uranium carried by 

ground water along porous sandstones in the Wind River 

formation could not escape laterally because of the 

confines of the pre-Wind River valley, and was deposited in carbonaceous shales in the nearly impervious 

underlying Thermopolis shale. Sandstones in the 

Cloverly formation on the east side of this pre-Wind 

River valley are slightly radioactive.

Locality 9 (NWJNEJSWj sec. 17. T. 33 N.. 

R. 89 W). A uranium occurrence in middle Eocene 

rocks is the site of locality 9. It is in the middle of 

an area where the background radioactivity is several 

times as high as the average in adjacent localities of 

pre-Tertiary rocks. The rocks are very ferruginous 

coarse-grained conglomeratic sandstones near the base 

of the middle and upper Eocene sequence. A 2-foot 

channel sample contained 0.06 percent equivalent uranium and 0. 078 percent uranium. These rocks crop 

out as dark-brown discontinuous ledges for half a mile. 

A reconnaissance section of the rocks is listed 

from top to bottom as. follows:

Unit 

no. Lithologic character

Conglomerate, gray; composed largely of 

"boulders of mouse-gray andesite*derived from volcanic rocks of middle 

Eocene age in the Rattlesnake Hills; 

conglomerate interbedded with a minor 

amount of chalky white crystal tuff; 

slightly radioactive.

Sandstone, yellowish-white, coarse-grained, 

slightly tuffaceous, soft, interbedded 

with conglomerate in which roundstones 

are of pre-Cambrian granite and Eocene 

volcanic rocks from the Rattlesnake Hills; 

slightly radioactive.

Volcanic conglomerate, mouse-gray, composed largely of "boulders of gray 

andesite porphyry derived from Eocene 

vents in the Rattlesnake Hills; some 

"boulders ^ feet in diameter; slightly 

radioactive.

Sandstone, pale yellow, very coarse

grained, arkosic, soft, with white tuff 

fragments; slightly radioactive.

Sandstone and conglomerate, gray to dark- 

"brown, with very ferruginous lenses in 

middle; some lenses 15 feet thick and 

100 feet long; a channel sample of 

2 feet of sandstone from one lens contained 0.06 percent equivalent uranium 

and 0.078 percent uranium; conglomerate 

intertongued with the sandstone contains rounded fragments of pre-Cambrian 

granite and Eocene andesite porphyry 

from the Rattlesnake Hills; some andesite 

"boulders are 3 feet in diameter.

Estimated 

thickness 

(feet) 

30

30

50

30
R.

Locality 10 (C SEJNE4- sec. 27. T. 33 N.. 

W.). A carbonaceous shale near the top of the

Wind River formation is the site of locality 10. A channel sample of 1 foot of shale contained 0.078 percent 

equivalent uranium and 0.062 percent uranium. This 

carbonaceous shale bed overlies coarse-grained 

greenish-yellow arkosic sandstone. The top of the bed 

grades upward through 6 inches of slightly carbonaceous 

shale to a greenish-gray plastic claystone. Leaves 

identified by R. W. Brown of the U. S. Geological Survey from this carbonaceous shale are: Ulmus sp., 

Leguminosites sp., Aralia sp., Quercus castaneopsis, 

and Zizyphus cinnamomoides and are considered to be 

of early or middle Eocene age. The carbonaceous shale 

is exposed in an area about 75 feet long and 25 feet wide 

but its uranium content suggests that uraniferous ground 

waters have been in the area and that higher grade deposits may be present in more favorable host rocks.

Locality 11 (NE cor, sec. 11. T. 32 N.. 

R. 90 W.). -The site of locality 11 is Cameron Spring 

which issues from the White River formation of Oligocene age, 100 feet or more above the base of the sequence, and 250 feet or more below the top. The water 

is clear, cold, and comes out along fractures in lighttan hard tuffaceous claystone. The water contains 

0. 010 ppm uranium.

Other localities of interest. A spring issues 

from a very ferruginous conglomeratic sandstone in the 

upper part of the Wind River formation in the NW-JSEl 

sec. 33, T. 34 N., R. 89 W. This spring flows about 

a 1-inch pipe full of clear cold water that contains 

0.073 ppm uranium. The presence of this much uranium is significant because the locality is at an altitude 

of about 6, 800 feet, higher than nearly all the uranium 

deposits found in the Gas Hills area, and is about 3 miles 

northeast of the Gas Hills, beyond the border of the 

area shown in figure 1.

A locality near the center of the SWi sec. 29, 

T. 33 N., R. 90 W. shows many places where metaautunite is concentrated in ferruginous coarse-grained 

soft porous sandstone in the middle part of the Wind 

River formation. A spectrographic analysis of a sample collected for mineralogic study showed more than 

10 percent uranium.

In the NWiSWiNWi sec. 6, T. 32 N., R. 90 W., 

there are localized concentrations of an unidentified 

calcium uranyl phosphate mineral, greenish-yellow in 

color, nonfluorescent, and which, according to 

L. B. Riley (personal communication, 1954), contains 

more than 10 percent uranium, 1-2 percent elemental 

phosphorus, traces of barium, and arsenic. The minerals are concentrated in and adjacent to a petrified log 

which is embedded in a coarse-grained gray sandstone 

in the middle of the Wind River formation. A channel 

sample of 1 foot of sandstone adjacent to the log contained 4. 7 percent equivalent uranium, 6. 72 percent 

uranium, and 0.1 percent V2 O 5 .

Another locality where considerable uranium minerals occur is about half a mile northeast of Coyote 

Spring (locality 6), in the southern part of the SEi sec. 12, 

T. 32 N., R. 91 W. Both meta-autunite and the 

unidentified greenish-yellow uranium mineral are present. The host rock is a ferruginous conglomeratic 

sandstone in the lower part of the Wind River formation 

northeast of a partly exhumed hill of Mowry shale surrounded by the Wind River formation.

ORIGIN OF URANIUM IN THE GAS HILLS AREA

Insufficient data are available on the occurrences 

of uranium minerals now known in the Gas Hills area 

to warrant a definite statement as to the origin of the 

deposits. It is apparent that these minerals were deposited in their present sites by water moving through 

ithe rocks and bringing uranium into an environment 

favorable for precipitation. The source of the uranium 

ions and the origin of the water that carried them can 

only be assumed at the present time.

The uranium deposits may be the result of hydrothermal solutions coming from the volcanic rocks in 

and south of the Rattlesnake Hills. These volcanic 

rocks are dacites, andesites, and alkalic rocks 

F. B. Van Houten (personal communication) and 

B. D. Carey, Jr., (1954) of middle and late Eocene age. 

There is no known evidence of hydrothermal activity in 

the Gas Hills area other than, possibly, the uranium 

deposits themselves. The writer prefers the theory that 

the uranium originally was a primary constituent in the 

ashes in the White River formation or younger Tertiary 

rocks in this area, that the uranium was leached out by 

ground water which transported it downward and laterally along sandstone aquifers in the middle Eocene sequence and the Wind River formation, and that the uranium concentrated wherever favorable host rocks were 

found. This theory of origin was likewise advocated 

for the uranium deposits in the Pumpkin Buttes area 

of northeastern Wyoming (Love, 1952, p. 17). The 

Oligocene and younger rocks once extended over the 

Gas Hills area and across the Wind River Basin, for 

remnants are found in the mountains on both sides. In 

the Pumpkin Buttes area, the Wasatch formation, which 

is the same age as the Wind River formation and has 

much the same lithology, contains uranium deposits and 

is overlain by the White River formation, which is uraniferous (Love, 1952).

Denson, Bachman, and Zeller (1951) have reported uraniferous lignites of Paleocene age overlain 

by the White River formation in South Dakota. 

J. R. Gill (personal communication) has found carnotite in the White River formation in the Slim Buttes 

area, South Dakota, and G. W. Moore and H. A. Tourtelot (personal communication) have found uranocircite 

and tyuyamunite in rocks of the White River formation 

in the Big Badlands of South Dakota. Miocene (?) rocks 

in the Miller Hill area, southern Wyoming, contain 

0.15 percent or more uranium (Love, 1953), and tuffaceous limestones of Pliocene (?) age in the Split Rock 

area, 16 miles south of the Gas Hills, contain0.023percent uranium (Love, 1952, unpublished report, supplemented by later field studies). Carnotite occurs in 

tuffaceous sandstones in the lower Pliocene(?) North 

Park formation of the Saratoga area.

In all of these areas, the possibility of hydrothermal activity that would form uranium deposits seems 

slight. The White River formation in the Gas Hills area 

is contributing above-normal amounts of uranium to 

ground water today (table 2) and may have supplied the 

uranium now found in the underlying rocks. The uranium in the water in the Wind River formation may come 

either from the White River formation or from secondary uranium minerals previously deposited by ground 

water in the Wind River formation.

Characteristics of the currently known deposits 

that need further investigation and that will assist in
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determining the origin and history of the deposits include (1) additional mineralogic studies of the metaautunite, uranospinite(?), and the unidentified calcium 

uranyl phosphate mineral, and (2) the relationship between the level of radioactivity expressed as percent 

equivalent uranium and the amount of uranium chemically determined.

The level of radioactivity of the samples expressed 

as percent equivalent uranium and uranium chemically 

determined is out of balance; in some samples the radioactivity is in excess of the uranium content and in others 

the radioactivity is deficient. In sample 99207 (table 1), 

the radioactivity of 0.047 percent equivalent uranium is more than 3 times the uranium content of 

0.014 percent, and in sample 99205, the equivalenturanium content of 0.58 percent is more than twice the 

uranium content of 0. 25 percent. In other samples, 

however, the uranium content is greater than the radioactivity expressed in percent equivalent uranium. For 

example, sample 99204 contains 1. 87 percent uranium 

but only 1. 2 percent equivalent uranium, and sample 

206974 contains 6. 72 percent uranium but only 4. 7 percent equivalent uranium. The significance of these variations may become apparent as more data accumulate, 

and should lead to a better understanding of the origin 

and history of the deposits.

POSSIBILITY OF INDUSTRIAL HEALTH HAZARD

Eleven samples were analyzed for selenium and 

arsenic, as well as for uranium (table 1). Beath (1946, 

p. 7-10)has described the occurrence of highly seleniferous tuffaceous strata of middle and late Eocene age 

in the Lysite area 30 miles north of the Gas Hills. The 

significant feature of this occurrence is the large amount 

of water-soluble selenium which indicates that it can be 

readily absorbed by human beings if it were to get into 

the lungs with dust. The percentage of water-soluble 

selenium in the uranium-bearing rocks of the Gas Hills 

area has not yet been determined so it is not known 

whether the selenium here constitutes a hazard. Trelease 

and Beath (1949, p. 240-242) describe the effects of 

selenium as an industrial health hazard and Voegtlin and 

Hodge (1949) discuss in considerable detail the studies 

of chronic inhalation of uranium compounds. Experiments by Beath and Rosenfeld (personal communication, 

1954) indicate that the action of selenium and uranium 

is synergistic, that is, the total effect is greater than 

the sum of the two effects taken independently.

SELECTED REFERENCES

Beath, O. A., Hagner, A. F., and Gilbert, C. S., 

1946, Some rocks and soils of high selenium content: 

Wyo. Geol. Survey Bull. 36, 23 p.

Carey, B. D., Jr., 1954, Geologic map and structure 

sections of the Rattlesnake Hills volcanic field, 

Natrona County, Wyoming: Wyo. Geol. Assoc. 

9th Ann. Field Conf. Guidebook map.

Love, J. D., 1952, Preliminary report of uranium deposits in the Pumpkin Buttes area, Powder River 

Basin, Wyoming; U. S. Geol. Survey Circ. 176.

_______1953, Preliminary report on uranium deposits in the Miller Hill area, Carbon County, 

Wyoming: U. S. Geol. Survey Circ. 278.

Love, J. D., Johnson, C. O., and others, 1945, Stratigraphic sections and thickness maps of Triassic 

rocks in central Wyoming: U. S. Geol. Survey Oil 

and Gas Chart 17.

10
Love, J. D., Thompson, R. M., and others, 1945, 

Stratigraphic sections and thickness maps of Lower Cretaceous and non-marine Jurassic rocks of central Wyoming: U. S. Geol. Survey Oil and Gas Chart 13.

Love, J. D., Tourtelot, H. A., and others, 1945, 

Stratigraphic sections and thickness maps of Jurassic 

rocks in central Wyoming: U. S. Geol. Survey Oil 

and Gas Chart 14.

______1947, Stratigraphic sections of Mesozoic rocks 

in central Wyoming: Wyo. Geol. Survey Bull. 38, 59p.

Love, J. S., Weitz, J. L., and Hose, R. K., 1952, 

Geologic map- of Wyoming: U. S. Geol. Survey map.

Thompson, R. M., Love, J. D., and Tourtelot, H. A., 

1949, Stratigraphic sections of pre-Cody Upper Cretaceous rocks in central Wyoming: U. S. Geol. Survey Oil and Gas Chart 36.

Trelease, S. F., and Beath, O. A., 1949, Selenium, 

its geological occurrence and its biological effects 

in relation to botany, chemistry, agriculture, nutrition, and medicine: 292 p. Published by the 

authors, Box 42, Schermerhorn Hall, Columbia 

University, N. Y.

Van Houten, F. B., Volcanic-rich middle and upper 

Eocene sedimentary rocks northwest of Rattlesnake 

Hills, central Wyoming: U. S. Geol. Survey Prof. 

Paper 264. [In preparation. ]

Voegtlin, Carl, and Hodge, H. C., 1949, Pharmacology 

and toxicology of uranium compounds: National 

Nuclear Energy Series, Manhattan Project, Tech. 

Sec., Div. 6, v. 1, pts. 3 and 4, Chronic inhalation 

and other studies, McGraw Hill Book Co.

UNPUBLISHED REPORTS

Denson, N. M., Bachman, G. O., and Zeller, H. D., 

1951, Summary of new information on uraniferous lignites in the Dakotas: U. S. Geol. 

Survey Trace Elements Memo. Rept. 175.

Love, J. D., 1952, Preliminary report on uraniumbearing Pliocene (?) rocks in the Split Rock area, 

central Wyoming: U. S. Geol. Survey Trace Elements Memo. Rept. 282.

Rachou, J. F., 1951, Tertiary stratigraphy of the 

Rattlesnake Hills, central Wyoming: [Unpublished master of arts thesis in files of Univ. 

Wyo. library. ]

Weeks, A. D., and Thompson, M. E., 1953, 

Identification and occurrence of uranium and 

vanadium minerals from the Colorado Plateaus: 

U. S. Geol. Survey Trace Elements Inv. 

Rept. 334.

11

INT.-DUP. see., HASH.. 0,0.71409