GEOLOGICAL SURVEY CIRCULAR 344 

URANIUM IN THE POISON BASIN 

AREA, CARBON COUNTY 

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 344 

URANIUM IN THE POISON BASIN AREA, CARBON COUNTY, WYOMING 

By James D. Vine and George E. Prichard 

This report concerns work done on 

behalf of the U.S. Atomic Energy 

Commission and is published with 

the permission of the Commission. 

Washington, D. C., 1954 

Free on application to the Geological Survey, Washington 26, D. C. 

URANIUM IN THE POISON BASIN AREA, CARBON COUNTY, WYOMING 

By James D. Vine and George E. Prichard 

CONTENTS 

Abstract ••••••••.••••.•••••.•.•••••••••••• 

Introduction •••.••••••...•••••..•...•.•.•.• 

Geography .................................. . 

Geology ••••••••••••••.•••.••••••••••.•••.• 

Stratigraphy ••••••••••••.•••.••••.•••..•.•• 

Wasatch formation· •.•••.••...••••••••• 

Green River 

formation •••••••••••••••..•••••••••. 

Page 

1 

1 

2 

3 

3 

3 

4 

Stratigraphy-Continued 

Browns Park formation • • • • • . • • • • • • • • • 

Uranium occurrences ••••••••••••••••••••••• 

Origin of the uranium •••••••••••••••••••••• 

Significance of the Poison Basin area 

in the search for uranium •••••••••••••••••• 

Literature cited •••••••••••.•••••••••••••••• 

Unpublished reports .•.•.••••••••••••••••••• 

Page 

4 

4 

7 

7 

7 

7 

ILLUSTRATIONS 

Page 

Figure 1. Geologic map of Poison Basin and adjacent areas........................................... • 2 

2. Sketch map of part of Poison Basin area • • • • • • • • • • • • • • • . • • • . • • • . • • • • • • . • . • • • • • . • • • • • . . • • • • • 3 

3. Close view of Poison Buttes •. •........................................................... •• 5 

TABLE 

Page 

Table 1. Analyses of samples •••••••.••...•••.•.••..•...•..•.•••••.••••..•.•••. , • • • • • • • • • • • • • • • • • • 6 

ABSTRACT 

Uranium minerals were found on October 15, 1953, 

about 6 miles west of Baggs in the Browns Park formation of the Poison Basin area, Carbon County, Wyo. 

A number of small occurrences are present over an 

area of several square miles in sees. 4 and 5, T. 12 N., 

R. 92 W., and sees. 32 and 33, T. 13 N., R. 92 W. 

Uranophane-bearing sandstones contain as much as 

3. 21 percent uranium in select samples. The occurrences cannot be evaluated because their dimensions 

and average grade have not been determined. The 

presence of uranium, however, is significant because 

it indicates that uranium deposits may be present in the 

Browns Park formation and also in the underlying 

formations unconformably overlapped by the Browns 

Park. 

INTRODUCTION 

The Poison Basin area is located 6 miles west of 

Baggs on the southeast flank of the Washakie Basin in 

southwestern Carbon County, Wyo. Unusually high 

1 

radioactivity in the Browns Park formation of Miocene(?) 

age was discovered by the writers on October 15, 1953, 

as a result of a reconnaissance with a car-mounted 

recording scintillation detector. The area was investigated because of the occurrence of uranium in rocks 

of Miocene(?) age in the Miller Hill area, Carbon County, 

Wyo., about 35 miles to the northeast (Love, 1953). 

Several days after the discovery of uranium, an 

airborne radioactivity survey was made in the i_tnmediate 

area by the U. S. Atomic Energy Commission, and a 

few weeks later another airborne radioactivity survey 

was made of a large area in southern Wyoming, including this area, by the U. S. Geological Survey 

(Henderson, 1954). · 

The area was revisited on October 19 and 20, 

1953, to collect samples, locate land corners, and 

map the deposits. Prichard returned to the area on 

November 14 with aerial photographs to map the geology. 

On February 7 and 8 Vine examined the localities of 

1

U. S. Atomic Energy Commission airborne anomaly location map of 

Carbon County, Wyo., posted in AEC offices in Denver, Colo., and Douglas, 

Wyo., on November 15, 1953. 
the radioactivity anomalies recorded by the U. S. Geological Survey airborne radioactivity survey. 

The reconnaissanc~ of the Poison Basin area was 

made on behalf of the Division of Raw Materials of the 

U. S. /J +omic Energy Commission. 

GEOGRAPHY 

The Poison Basin area is a small topographic basin 

tributary to. the Little Snake River, which drains a 

large region west of the Continental Divide on both sides 

of the Colorado-Wyoming boundary and flows across 

northwestern Colorado to join the Colorado River 

drainage system. 

A small group of low hills locally known as 

Poison Buttes derive their name from the fact that 

vegetation in the area is toxic to livestock. Investigation 

0 4 MILES 

r·"J-- ---------; 

;.__J ' I : WYOMING I 

__!L-.J. o; 

\ 

/ ... J 

.·· Twcb \ 

c 

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j 

0 

i 

. 

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of the vegetation and of the sandstone on which it is 

growing has indicated that the content of selenium, 

the principal toxicant, is unusually high (Beath, and 

others, 1946, p. 13). Because a high percentage of the. 

selenium is in a water-soluble form, suitableprecautions 

should be taken by persons working in the area or processing the samples to prevent the inhalation of seleniumbearing dust. Selenium-bearing dust can be a deadly 

poison to human beings. 

The region is easily accessible by car from Baggs, 

Wyo. , one of several ranching towns in the valley of Little 

Snake River. To reach the area from Baggs proceed north 

on State Highway 330 about 1 mile and turn west on a graveled 

county road. Proceed on the main traveled road about 

4. 5 miles to a road junction and take the right fork. Proceed 

another 1. 5 miles to pit 1. The occurrences are located 

insecs. 4and5, T. 12N., R. 92W., andsecs. 32and 

33, T.13N., R. 92W.,about3milesnorthofthe Colorado 

border (figs. 1 and 2). 

EXPLANATION 

r~Q·" ~~ Alluvium 

~ . 

Browns Pork formation 

~ t 

Grnn River ond Wasatch formations 

>-

0:: 

<I[ 

z 

0:: 

.., 

.... 

<I[ 

::I 

a 

>-

0:: 

<I[ 

i= 

T. 

13 

N. 

T. 

~--~ .... ~~12 N. 

g T9r: Main body of G;nn River fm. .., 0:: 

.., Twcb: Cathedral Bluffs tongue of Wasatch fm . .... Tt: Tipton tonQue of Green River fm. 

Tw: Main body of Wasatch fm. 

i f,Tfu.·l 

-------- Contact 

Oashtld whtiTtl approxlmaftll}' locaftld 

u / /o 

Fault 

l Fort Union formation Cl) 

.. i ::I 

~ 0 

.., .. a.U u a." Lance formation <I[ 

::::~; .... u .., 

..-0 0:: 

u 

Otlshtld wlltiTtl tlfiPIYJ.Ilimaftll}' IHaftld RIHiioactive locality 

Figure 1. -Geologic map of Poison Basin and adjacent areas, Carbon County, Wyo. 

2 

Goa * well 
The nearest railroad is the Denver and Salt Lake 

line at Craig, Colo. about 41 miles south ofBaggs. · 

The Union Pacific Railroad is at Creston, Wyo. , about 

50 miles north of Baggs. The only residents in the 

area live along the alluvial plain of the Little Snake River 

to the south. Sheep and cattle ranching are t{le chief 

industries, although several oil and gas test wells have 

been drilled in the vicinity. 

GEOLOGY 

The Poison Basin area is a topographic basin 

eroded chiefly from the Browns Park formation of 

probable Miocene age (fig. 2). The Browns Park 

was deposited on an erosion surface developed on 

gently dipping and truncated beds of the Wasatch 

and Green River formations of Eocene age. These 

formations comprise the outer rim of the Washakie 

Basin, a structural depression between the Rock Springs 

uplift on the west and the Sierra Madre Mountains on 

the east. Later movement along an east-trending 

fault zone, which extends across the entire south side 

of the Washakie Basin, has folded and faulted all of 

these strata (Bradley, 1945). A second group 

of faults, which strike north or northwest, is 

probably younger. 

:::::::: :Tw:::::: · · 

::::::::::<::::::: 

Both lower and upper Tertiary igneous intrusions 

are found in the Elkhead Mountains of Colorado 15 to 

50 miles southeast of.Baggs, Wyo. (Gale, 1910). The 

Hahns Peak mining district, about 45 miles southeast 

of Poison Basin has produced gold, silver, lead, and 

copper from vein deposits in rhyolite, latite, and 

andesite porphyry (Gale, 1906). 

STRATIGRAPHY 

Although no stratigraphic studies were made 

during this reconnaissance, the rocks exposed in this 

area were described by Bradley (1945) and the following 

descriptions are summarized chiefly from his work. 

All the exposed rocks are of Tertiary age and 

include the Wasatch, Green River, and Browns Park 

formations. 

Wasatch formation 

The Wasatch formation of Eocene age is the 

oldest rock sequence exposed in the vicinity of Poison 

Basin. It consists of several thousand feet of fluviatile 

deposits, chiefly sandy gray mudstone containing 

EXPLANATION > a:: 

cr ..... z 1:::: a:: ~ ILl 

~ 1-

Alluvium cr 

::> 

~ 0 

Cb 

~ ~ >- \) a:: -~ Browns Pork formation cr ~ .... Cb em a:: 1:::: ILl 

~ . .... 

~ wasatch formation 

.-® 

Location of test pits 

--------

Approximate contact 

_e 

Dip and strike of beds 

X 

Fault 

Geologic mapping by J.D. Vine and G. E. Prichard. 

Base compiled from aerial photographs 

Figure 2. -Sketch map of part of Poison Basin area showing location of test pits. 

3 
irregular lenses of sandstone. The main body of the 

Wasatch is chiefly gray (banded with red), green, and 

yellow. The upper part of the Wasatch interfingers 

with the Green River formation and a unit of the 

Green River known as the Tipton tongue separates the 

main body of the Wasatch from its upper unit, the 

Cathedral Bluffs tongue. In the Poison Basin area, 

the Tipton tongue, although well developed to the north 

and west, has thinned to a feather edge. The Cathedral 

Bluffs tongue consists chiefly of gray mudstone, banded 

with red, and is probably about 1, 000 feet thick. 

Green River formation 

The Green River formation of Eocene age consists of 

lacustrine, thin-bedded mar !stone, oil shale, and carbonaceous shale containing numerous fresh water fossils 

including fish, gastropods, and ostracods. These strata 

interfinger with and overlie the Wasatch formation. The 

Tipton tongue, which is separated from the main body 

of the Green River by the Cathedral Bluffs tongue of 

the Wasatch, is the principal unit of the Green River 

formation exposed in the Poison Basin area. The 

Tipton tongue consists chiefly of soft, brown, papery, 

fossiliferous shales about 75 feet thick north of 

Poison Basin but becomes sandy and carbonaceous, and 

loses its identity in the area south and west of Poison Basin. 

Browns Park formation 

The Browns Park formation of probable Miocene 

age was deposited on an erosion surface of slightly tilted 

Eocene rocks. Outliers of the Browns Park formation 

occur along the south flank of the Washakie Basin as 

well as in areas to the east, south, and west. They 

were probably once continuous with the Browns Park 

formation of northwestern Colorado and northeastern 

Utah where the formation overlies rocks as old as 

pre-Cambrian at the east end of the Uinta Mountains. 

At the base of the Browns Park formation is a 

conglomerate about 75 feet thick consisting largely of 

quartzite pebbles and cobbles in a sandy matrix. Above 

the conglomerate is a thick series of soft, white, highly 

crossbedded sandstone and tuffaceous sandstone. This 

rna terial weathers into a loose sand that covers much 

of the Poison Basin area. Beds of dense quartzite form 

the top of the formation exposed in this area. Bradley 

(1936) states that the lower part of the Browns Park 

formation along the south side of the Washakie Basin 

consists largely of glassy tuffs, although this lithology 

was not observed during the reconnaissance of the 

Poison Basin area. No figures are available on the 

total thlckness of the Browns Park formation and although more than 1, 000 feet may be present elsewhere 

the top has been subjected to erosion in thePoisonBasin 

area and it is estimated that only about 300 feet of strata 

remain. 

Bradley (1936, p. 182-184) discusses the origin 

of the Browns Park formation and considers that the 

rounded and frosted sand grains, prominent crossbedding, and wind-faceted cobbles are probable evidence 

that the material was wind blown. In the Poison Basin area 

widely divergent strike and dip readings taken on a few 

isolated exposures of crossbeddect sandstones in the 

Browns Park formation make structural interpretation 

difficult. 

4 

URANIUM OCCURRENCES 

Sandstone containing as much as 3 percent uranium occurs in the Browns Park formation in isolated 

exposures on a group of low hills known as Poison Buttes 

and in the surrounding area in sees. 4 and 5, T. 12 N., 

R. 92 W., and sees. 32 and 33, T. 13 N., R. 92 W., 

6th principal meridian (fig. 3). Uranophane, 

Ca(U0 2 )zSi 20 7 • 6H20, has been identified by R. S. Jones, 

W. F. Outerbridge, and A. J. Gude 3d as the principal 

uranium mineral in three select samples. Schroeckingerite, NaCa3(U0 2)(C0 3)a(S0 4)F. 10H20, has been 

identified as the principal uranium mineral in one 

sample. These minerals are known at other nearby 

localities in Wyoming. Uranophane is the principal 

uranium mineral in the Miller Hill area, Carbon County, 

Wyo. (Vine and Prichard, 1953). Schroeckingerite is 

the principal uranium mineral that occurs along 

Lost Creek in the Great Divide Basin, Sweetwater County, 

Wyo. (Sheridan and others, 1952). Samples for analysis 

were collected from 11 shallow pits dug at several 

places of high radioactivity on Poison Buttes and adjacent hills. The location of most of these pits are 

shown on figure 2. All analyses are listed in table 1. 

Pit 1. Radioactive loose brown sand lies 

on the bedrock for several hundred feet along 

the north side of the main east-trending road. 

About 18 inches of brown, friable, mediumgrained sandstone containing fracture coatings and 

disseminations of uranophane was exposed in a 

pit dug at a place of high radioactivity. Sample VW3-

91 is an 18-inch channel sample of this sandstone 

and contains- o. 43 percent equivalent uramum and 

0. 39 percent uranium. Channel samples, VW3-470, 

VW3-471, and VW3-472, through 6 feet of the 

radioactive zone contain an average of 0. 068 percent equivalent uranium, but only 0. 016 percent 

uranium. The most radioactive part of the rock. 

consists of a dark-brown lens of sandstone about 

2 inches thick containing fracture coatings of 

uranophane. Sample VW3-89 was collected from 

this lens and contains 0. 86 percent equivalent 

uranium and 0. 90 percent uranium. An unidentified 

black mineral colors a 1- to 2-inch streak through 

the radioactive zone. A grab sample from this 

black streak, sample VW3-401, contains 0. 5 percent equivalent uranium and 0. 69 percent uranium. 

A second sample from this same zone, VW3-473, 

contains 1. 5 percent equivalent uranium and 1. 31 percent uranium. 

Directly overlying the sandstone in pit 1 

is a bed of medium- to coarse-grained c·rossbedded sandstone about 8 feet thick that appears 

to strike east and dips about 35 ° north. 

Pit 2. An 18-inch zone of reddish-brown 

radioactive sandstone was uncovered at pit 2. 

No yellow uranium minerals were observed. A 

12-inch channel sample from this pit, sample VW3-94, contains 0. 024 percent equivalent 

uranium and 0. 004 percent uranium. A grab 

sample from the most radioactive part of the 

same pit contains 0. 25 percent equivalent uranium and 0. 011 percent uranium. The sandstone 

exposed in the pit appears to dip less than 5° 

but a nearby outcrop of sandstone at the top 

of the hill dips about 35° and strikes about 

N. 30° E. 
·Figure 3. -Close view of Poison Buttes looking southwest. Arrow indicates approtimate location of pit 3. 

Pit 3 was dug in a highly radioactive zone which 

appeared to be parallel to the dip of the beds on the 

side of a hill. Digging uncovered a reddish-brown 

and greenish-gray, friable sandstone. The greenish 

tint in part of the sand may be due to disseminated 

uranium minerals. A 12-inch channel sample from 

this pit, sample VW3-95, contains 0. 7 percent equivalent uranium and 0. 69 percent uranium. 

Pit 4. Soft, friable, light greenish-gray, massive 

sandstone at the top of a small hill is highly radioactive 

about 6 inches below the surface. The greenish tint of 

the sandstone may be due to disseminated uranium 

minerals. A 12-inch channel sample from this zone, 

sample VW3-96, contains 0. 1 percent equivalent 

uranium and 0. 018 percent uranium. 

Pit 4A was dug in a highly radioactive zone 

about 25 feet southeast of pit 4 on the same hill. Friable 

sandstone in the pit contains fracture coatings of yellow 

uranophane. A sample, VW3-97, of selected yellowstained sandstone fragments contains 1. 5 percent 

equivalent uranium and 3. 21 percent uranium. This 

. sample contains the highest percent uranium of any 

of the samples collected from the Poison Basin area. 

Pit 4B, on the same hill as pits 4 and 4A, was 

dug about 50 feet southeast of pit 4. This pit uncovered 

a 2-inch thick lens of radioactive, reddish-brown sandstone, estimated to be about 15 feet stratigraphically 

lower than the sandstone sampled in pit 4A. A grab 

sample, VW3-98, collected from this lens contains 

0, 13 percent equivalent uranium and 0. 027 percent 

uranium. 

Pit 5 was dug along a zone of moderately radioactive, light-gray sandstone similar in appearance to 

that encountered in pit 4. A 12-inch channel sample, 

VW3-99, from this pit contains 0. 037 percent equivalent uranium and 0, 021 percent uranium. A grab 

sample, VW3-474, from the same pit shows a trace 

of unidentified yellow mineral. It contains 0. 39 per-

.cent equivalent uranium and 0. 26 percent uranium. 

Pit 6. A fine-grained sandstone with a pale 

yellowish tint was uncovered in this pit. The 

5 

yellowish stain may be due to a uranium mineral disseminated through the matrix of the sandstone. A 6-inch 

channel sample, VW3-400, from this sandstone contains 0. 34 percent equivalent uranium and 0. 016 percent uranium. 

Pits 7-11 were located and sampled in February 

1954, after the area had been prospected by claim 

holders. Only pits 8 and 11 fall within the area shown 

on fig. 2. 

Pit 7was dug in a highly radioactive zone 

2 feet in diameter. A 12-inch channel sample from 

this pit, VW3-475, contains 0. 052 percent equivalent 

uranium, and 0. 013 percent uranium. The pit is located 

about 1, 200 feet north of the quarter corner between 

sec. 32, T. 13 N., and sec. 5, T. 12 N., R. 92 W. 

Pit 8. A bulldozer trench about 75 feet long and 

6 feet deep was dug in essentially barren sandstone 

except for one small mineralized zone at its southern 

end. On the east wall of the trench and about 3 feet 

below the ground surface, a yellow fluorescent mineral 

occurs in the sandstone. A 12-inch channel sample, 

VW3-476, of the mineralized zone contains 0. 033 percent equivalent uranium, and 0. 017 percent uranium. 

The mineral has been identified as schroeckingerite. 

Pit 8A is located about 300 feet north of pit 8. 

A grab sample, VW3-477, of brown sandstone from the 

pit contains 0. 018 percent equivalent uranium and 

0. 004 percent uranium. ~ 

Pit 9, about 3 feet deep, is located about 650 feet 

north-northeast of pit 8. Three channel samples, 

VW3-478, VW3-479, and VW3-480, were collected to 

represent the 3-foot interval of exposed sandstone. 

The average percent equivalent uranium content of 

these samples is about 0.1, but the average uranium 

content is only 0. 087 percent. 

Pit 10. A bulldozer trench about 10 feet deep 

was dug about 450 feet northeast of the northwest 

corner of sec. 4, T. 12 N., R. 92 W. At the bottom 

of the bulldozer trench a 3-foot hole was dug and a 

channel sample collected, VW3-481. This sample, 
Table 1.--Analyses of samples collected from the Poison Basin area 

Pit Equivalent Uranium 

no. Field no. Lab. no. uranium (percent) (percent) 

l VW3-89 D98776 0.86 0.90 

l VW3-9l D98777 .43 .39 

l VW3-40l D99839 .so .69 

l VW3-470 204323 .026 .004 

l VW3-471 204324 .14 . 020 

l VW3-472 204325 . 039 .025 

l VW3-473 204325 1.5 1.31 

2 VW3-93 D99831 .25 .011 

2 VW3-94 D99832 .024 .004 

3 VW3-95 D99833 -70 .69 

4 VW3-96 D99834 .10 .018 

4A VW3-97 D99835 1.5 3.21 

4B VW3-98 D99836 .13 .027 

5 VW3-99 D99837 .037 .021 

5 VW3-474 204327 -39 .26 

6 VW3-400 D99838 .34 .016 

7 V'w3-475 204328 .052 .013 

8 VW3-476 204329 .033 .017 

8A VW3-477 204330 .018 .004 

9 VW3-478 204331 .073 .016 

9 VW3-479 204332 .19 .19 

9 VW3-48o 204333 .051 .056 

10 VW3-48l 204334 .008 .004 

ll VW3-482 204335 .073 .019 

representing a 3-foot zone, contains 0. 008 percent 

equivalent uranium, and 0. 004 percent uranium. 

V205 

(percent) 

<0.05 

< . 08 

--------- f----------

---------

---------

---------

.08 

.06 

.16 

.13 

.10 

.11 

.08 

--------- .08 

---------

---------

---------

---------

--------- 1----------

f----------

f----------

As Se 

(ppm) (ppm) Description 

250 30 Grab sample. Dark-brown uranophane-bearing sandstone. 

200 20 18 inches . Brown sandstone. 

----- ----- Grab sample. Black sandstone. 

----- ----- 24 inches. Top of 6 feet of 

sandstone. 

----- ----- 24 inches • Next 2 feet sandstone. 

----- ----- 24 inches • Bottom 2 feet sandstone. 

-----1------ Grab sample. Black sandstone. 

250 15 Grab sample. Reddish-brown 

sandstone. 

150 12 12 inches. Reddish-brown sandstone. 

-----r------ 12 inches. Brown and green 

sandstone. 

50 40 12 inches. Greenish-gray sandstone. 

100 8o Grab sample. Uranophane-bearing 

sandstone. 

----- ~----- Grab sample. Reddish-brown 

sandstone. 

----------- 12 inches. Gray sandstone. 

--------..--- Grab sample. Brown sandstone. 

----------- 6 inches. Yellowish sandstone. 

1----------- Grab sample. Brown sandstone. 

1-----1------ 12 inches. Schroeckingeritebearing sandstone. 

1----------- Grab sample. Brown sandstone. 

1----------- 12 inches. Top foot of 3 feet 

sandstone. 

1-----1------ 12 inches. Next foot sandstone. 

1-----1------ 12 inches. Bottom foot sandstone 

f----- ------ 36 inches. Brown sandstone. 

1-----1------ 12 inches. Brown sandstone. 

Pit 11. A limonite-stained sandstone at the top 

edge of a bulldozer trench about 900 feet northeast of 

pit 1 is highly radioactive. A 1-foot channel sample, 

VW3-482, of this sandstone contains 0. 073 percent 

equivalent uranium and 0. 019 percent uranium. 

from this general trend. Some of this divergence may 

be due to large-scale crossbedding similar to that along 

the south side of Washakie Basin which Bradley (1936, 

p. 182) describes. Erratic dips, however, may also 

be structural in origin. Some of the zones of radioactive, 

friable sandstone may be localized along faults or other 

structural features. Detailed geologic mapping, stratigraphic studies, and extensive trenching will probably 

be necessary to determine the structure. 

All the pits were dug on or near the tops of low 

hills where the bedrock is fairly well exposed. Radioactivity is relatively high throughout the area, but it 

is not known whether the uranium minerals follow 

stratigraphic zones which might be continuous beneath 

soil cover between the hills. The dominant structural 

trend throughout the region appears to be east-west 

but locally the attitude of the rocks is widely divergent 

6 

The radioactive disintegration products of uranium 

are not in balance with the uranium contained in most 

of the samples collected. This is shown by the U:eU 

ratio, which ranges from 2.1:1 to 1:22.7 for the samples 

collected. This probably indicates a relative instability of the uranium or its radioactive disintegration 

products in the present environment. 
ORIGIN OF THE URP....NIUM 

The occurrence of uranium in the Poison Basin 

area is similar to several other areas in Wyoming including the Pumpkin Buttes (Troyer and others, 1953), 

Red Desert (Sheridan and others, 1952, and Masursky 

and Pipiringos, 1953), Miller Hill (Love, 1953), and 

Gas Hills (unpublished rept., Love, 1953) areas. They 

all contain surface deposits of secondary (yellow) uranium minerals in Tertiary strata remote from igneous 

activity but within or below Tertiary tuffaceous sandstones. In each instance the origin of the uranium is 

in doubt but most geologists favor an epigenetic origin, 

that is, they believe uranium was deposited at the 

present site by ground-water solutions passing through 

the rock long after the rock itself was deposited. The 

nature and origin of the ground-water solutions is a 

point of controversy. Some believe that the solutions 

were hydrothermal and ascended from a hidden source 

deep within the earth. According to this hypothesis 

various minerals in solution are deposited in a sequence 

depending on their solubility as the temperature and 

pressure of the solution decrease toward the earth's 

surface. Others believe that descending meteoric 

waters percolating through Tertiary tuffaceous sandstones that contain disseminated uranium have redistributed and concentrated uranium at certain favorable 

places.. The locus of concentration may be determined 

by a combination of several factors including (1} chemical reactions with the rocks and (2} rate and direction 

of flow of the solutions as determined by structural 

features and permeability of the rocks. 

Much more study will be required before a 

definite statement is warranted regarding the origin 

of the uranium in the Poison Basin area. However, 

before accepting any hypothesis it would be well to 

consider the following: ( 1) The Poison Basin area is at 

least 15 miles fr:om known igneous activity and 45 miles 

from the Hahns Peak mining district, though situated 

adjacent to an east-trending fault zone which could 

have provided access to ground waters of relatively 

deep origin. (2) Uranium occurs within a sequence 

of rocks characterized by material of volcanic origin. 

(3) No features unequivocally characteristic of hydrothermal deposits were observed. (4) The similarities 

between the Poison Basin area and several other 

widely scattered occurrences in Wyoming suggest a 

large uraniferous province. A single hidden source 

adequate to supply hydrothermal solutions over that 

large an area seems improbable as does also the 

requisite number of hidden sources if each area is 

independent. In contrast, there was a tremendous 

volume of volcanic debris spread over Wyoming and 

most of the adjacent states during middle and late 

Tertiary time, more than adequate to supply the 

uranium contained in these scattered occurrences. 

SIGNIFICANCE OF THE POISON BASIN AREA IN 

THE SEARCH FOR URANIUM 

'fhe occurrence of uranium minerals in the 

Browns Park formation of the Poison Basin area is 

the second reported occurrence in this formation, the 

first being in the Browns Park formation of Miocene(?) 

age in the Miller Hill area, about 35 miles 

to the northeast of Poison .Basin (Love, 1953). 

There is some doubt, however, regarding the 

correlation of the rocks in the two areas, 

and it is possiole that the uranium in the 

7 

Miller Hill occurrences may be in a slightly younger formation. Nevertheless, the occurrance of uranium minerals 

in the Browns Park formation indicates that the large area 

covered by this formation in northwestern Colorado and 

adjacent parts of Wyoming and Utah can now be considered 

as favorable for prospecting. Similarly, although no 

uranium is yet known in the strata directly under lying 

the Browns Park in the Poison Basin area, it seems possible 

that uranium may have been leached from tuffaceous sandstone and redeposited at favorable places in the older rocks. 

A map by Bradley ( 19 36, pl. 34) shows what he believes to 

be the restored surface on which the Browns Park formation 

was deposited and this map should provide a useful guide to 

prospecting in areas only recently stripped of the Browns 

Park as well as in areas where the formation is present. 

The occurrence of uranium in the Poison Basin 

area coincides remarkably with an area known to be 

high in selenium content (Beath, and others, 1946, 

p. 13). The association of the two elements is probably 

not due to chemical combination in a specific mineral 

but probably is best explained by a common origin. 

Selenium indicator plants have been useful guides to 

uranium prospecting in many areas and although the 

two elements do not always occur together, the association may be sufficiently common to continue prospecting 

for uranium in other areas of known high selenium 

content. 

LITERATURE CITED 

Beath, 0. A., Hagner, A. F., and Gilbert, C. S., 

1946, Some rocks and soils of high selenium content: 

The Geological Survey of Wyoming, Bull. 36. 

Bradley, W. H., 1936, Geomorphology of the north 

flank of the Uinta Mountains: U. S. Geol. Survey 

Prof. Paper 185-I, p. 163-204. 

1945, Geology of the Washakie Basin, 

-""'sw-e-et.,...w_a...,.ter and Carbon Counties, Wyo. , and 

Moffat County, Colo.: U. S. Geol. Survey Oil and 

Gas Inv. Prelim. Map 32. 

Gale, H. S., 1906, The Hahns Peak gold field, 

Colorado, in Emmons, S. F., and Eckel, E. C., 

Gold and silver: U. S. Geol. Survey Bull. 285-A, 

p. 28-34. 

1910, Coal fields of northwestern Colorado --an-d~n-o_r.,.,.theastern Utah: U. S. Geol. Survey Bull. 415. 

Love, J. D., 1953, Preliminary report on the uranium 

deposits in the Miller Hill area, Carbon County, 

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

UNPUBLISHED REPORTS 

Henderson, J. R., 1954, Airborne radioactivity survey of 

parts of Baggs SW and Baggs SE quadrangles, Carbon 

and Sweetwater Counties, Wyo.: U. S. Geol. 

Survey Trace Elements Memo. Rept. 743. 

Love, J. D., 1953, Uranium in the Gas Hills area, 

Fremont and Natrona Counties, Wyo. -a preliminary report: U. S. Geol. Survey Trace Elements 

Memo. Rept. 708. 

Masursky, Harold, and Pipiringos, G. N., 1953, 

Uranium-bearing coal in the Red Desert, Great Divide 

Basin, Sweetwater County, Wyo. : U. S. Geol. 

Survey Trace Elements Memo. Rept. 601. 

Sheridan, D. M., Collier, J. T., and Sears, R. S., 1952, 

Results of exploration at Lost Creek schroeckingerite 

deposit, Sweetwater County, VJ.yo. : U. S. Geol .. 

Survey Trace Elements Memo. Rept. 288. 
Troyer, M. L., McKay, E. J., Soister, P. E., and 

Wallace, S. R., 1953, Summary of investigations 

of uranium deposits in the Pumpkin Buttes area, 

Johnson and Campbell Counties, Wyo. : U. S. Geol. 

Survey Trace Elements Memo. Rept. 345. 

8 

Vine, J. D. , and Prichard, G. E., 1953, Miller Hill area, 

Carbon County, Wyo., in Geologic investigations 

of radioactive deposits, Semiannual progress report, June 1 to November 30, 1953: U. S. Geol. 

Survey Trace Elements Inv. Rept. 390, p. 91. 

INT.-DUP·. SEC .. lASH .. D.c.6681!5