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JP R OFE SISI 0N A J, PAt*fcR,
GEOLOGY AND URANIUM DEPOSITS,

SHIRLEY BASIN AREA,

WYOMING
Uranium ore roll at contact of altered-sandstone tongue (yellowish green) and unaltered sandstone (gray), Petrotomics Co. 

Section 9 pit, phase 7, north wall. Height across nose of roll is about 7 feet.
Geology and Uranium Deposits, 

Shirley Basin Area, Wyoming

By E. N. HARSHMAN

GEOLOGICAL SURVEY PROFESSIONAL PAPER 745

A study of the geochemistry and genesis 

of the uranium deposits and their 

relation to regional stratigraphy, 

structure, and hydrology

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1972
UNITED STATES DEPARTMENT OF THE INTERIOR 

CECIL D. ANDRUS, Secretary

GEOLOGICAL SURVEY 

V. E. McKelvey, Director

Library of Congress catalog-card No. 72-600017

First Printing 1972 

Second Printing 1978

For sale by the Branch of Distribution, U.S. Geological Survey 

1200 South Eads Street, Arlington, VA 22202
CONTENTS

Page

Abstract... .-....................................................................... 1

Introduction......................................................................... 2

Location and accessibility.......................................... 2

Physical features........................................................ 2

Local industries........................................................... 4

Climate and vegetation.............................................. 5

Early culture............................................................... 5

Previous work.............................................................. 6

History and fieldwork................................................. 6

Acknowledgments........................................................ 7

Stratigraphy........................................................................ 7

Precambrian igneous and metamorphic rocks....... 8

Paleozoic...................................................................... 9

Madison Limestone............................................. 11

Post-Madison erosion.......................................... 11

Casper Formation............................................... 12

Paleozoic and Mesozoic.............................................. 13

Goose Egg Formation........................................ 13

Mesozoic........................................................................ 13

Red Peak Formation........................................... 13

Alcova Limestone.......... ................................... 13

Jelm Formation................................................... 14

Sundance Formation.......................................... 14

Morrison Formation........................................... 15

Cleverly Formation............................................. 16

Thermopolis and Mowry Shales........................ 17

Frontier Formation.. ................................... 18

Niobrara Formation........................................... 18

Steele Shale.......................................................... 18

Cenozoic........................................................................ 19

Fort Union (?) Formation................................. 19

Wind River Formation....................................... 19

Wagon Bed Formation....................................... 24

White River Formation..................................... 26

Arikaree Formation........................................... 32

High terrace gravel............................................ 34

Low terrace gravel.............................................. 34

Alluvium............................................................... 34

Silicification of sedimentary rocks........................... 34

Structure.. .. . .........................................-.. ...,. 35

Page 

Structure Continued

Landslides..................................................................... 35

Faults.... .............................................. 35

Folds.............................................................................. 36

Ground water.... ............................................................ 37

Ore deposits.......................................................................... 41

Uranium deposits in sandstone................................. 41

Paleotopographic control................................... 42

Relation to altered-sandstone tongues............. 44

Character of alteration...................................... 46

The ore bodies...................................................... 50

Physical character...................................... 50

Mineralogy and mineral distribution....... 53

Paragenesis of the ore and

associated minerals................................. 57

Distribution of elements and compounds 58

Uranium and equivalent uranium.... 59

Iron........................................................ 60

Selenium.. ...................................... 62

Sulfate.................................................. 63

Carbon................................................... 63

Manganese............................................ 63

Phosphate.. . . 63

Arsenic.................................................. 65

Copper................................................... 65

Vanadium............................................. 65

Beryllium.. ................................. 65

Lead ........ ..................................... 66

Mercury..... . 66

Miscellaneous elements....................... 66

Geochemistry........................................................ 67

Solution, transportation, and

deposition of elements.. .. . 68

Genesis of the deposits 70

Age............... ........... .. .................. 73

Uranium deposits in other rocks........ ................... 73

Monazite deposits in Tertiary rocks........................ 74

Construction materials.. .................................................. 74

References cited .............................................. ............. 74

Index........................................... .. 79

ILLUSTRATIONS

FRONTISPIECE. Photograph of uranium ore roll at contact of altered-sandstone tongue and unaltered sandstone. 

FIGURE 1. Index map of Wyoming, showing Shirley Basin area............ ............... . ................ .. 

2. Map showing limits of the Shirley Basin area, and some of the geographic features

described in this report................. ... ................................................... ... ........................

Page

3

4
VI CONTENTS

Page

FIGURES 3-22. Photographs:

3. Erosion in Bates Hole............................ ..... .. . ............................................................................ 5

4. Tipi rings in eastern part of Basin..........-.. ..................................................................................... 6

5. Ring of unknown designation associated with tipi rings................................................................ 6

6. Diabase dikes intruding Precambrian granite........... ...................................................................... 9

7. Basal sandstone unit of the Madison Limestone................................................................................ 11

8. Solution breccia in well-developed karst surface............................................................................... 12

9. Crossbedded sandstone near base of Cleverly Formation............................................................... 16

10. Ripple-marked mudstone in middle unit of Cleverly Formation.................................................. 17

11. Large granite boulders in basal conglomerate of Wind River Formation.................................... 21

12. Petrotomics Co. Section 9 pit, showing lithology of Wind River Formation.............................. 22

13. Petrotomics Co. Section 15 pit, showing lithology of Wind River Formation............................ 22

14. Petrotomics Co. Section 15 pit, showing contorted lignite.............................................................. 23

15. Basal part of the White River Formation......................................................................................... 27

16. White River Formation......................................................................................................................... 29

17. Diastem between the upper and lower members of the White River Formation...................... 29

18. Basal part of upper member of White River Formation.... .............-............................ ............. 32

19. Basal part of Arikaree Formation...................................................................................................... 34

20. Thick old alluvium............................................................................................................................... 34

21. Large landslide block in the White River Formation....................................................................... 36

22. Gentle fold in the White River Formation. ....... .................................... .......................... 37

23. Contour map of the top of the ground-water table in part of the Shirley Basin...................................... 38

24. Photograph showing small roll on the upper surface of an altered-sandstone tongue. ...................... 42

25. Map of part of the Shirley Basin, showing paleogeology and paleotopography........................................ 43

26. Photograph showing channel sandstones cutting lignite and siltstone beds.................... ....................... 44

27. Map showing relation of altered-sandstone tongues to paleotopography.................................................... 45

28. Graph showing cumulative and frequency distribution curves for three samples from the

ore-bearing sandstone interval.................... .................................................................................... 46

29. Photograph showing contact between unaltered sandstone and altered-sandstone tongue.... 49

30. Sections showing simple "C" roll and two complex rolls.. .. ..................................................................... 51

31. Section of small ore body on bottom of altered-sandstone tongue.....- ...................................................... 51

32-34. Photographs:

32. Crosscutting contact between altered sandstone and ore................................................................ 52

33. Ore at edge of altered-sandstone tongue..........................................,. ........................................... 53

34. Strong control of ore by permeable crossbeds................................................................................... 53

35-38. Photomicrographs:

35. Replacement of feldspar by pyrite........... ........................................................................................ 54

36. Pyrite and uraninite in high-grade ore............................................................................................... 54

37. Pyrite-marcasite and uraninite rims on quartz sand grains.......................................................... 55

38. Twinned ferroselite crystals..........-.....-........-....-...-...........--...----..- ....- . . . 56

39. Photograph of calcite-cemented ore-bearing sandstone, showing carbonaceous material in core. . 56

40. Photomicrographs showing replacement of feldspar by calcite in high-grade ore.................................... 56

41. Photomicrograph of calcite-cemented concretion, showing rim and outer skin of uraninite 57

42. Sketch showing graphic summary of mineral deposition in the Shirley Basin.. . 58

43. Cross sections at the edges of altered-sandstone tongues, showing uranium and

equivalent-uranium contents....................................--..-.-.-...........-.-.-...-......................-...-..-...-. 60

44. Graph showing equilibrium relations of 175 samples of mineralized sandstone from Shirley Basin...... 61

45-50. Sections through ore bodies showing:

45. Contents of uranium, of ferrous, ferric and total iron, and of ferrous iron in

sulfide and nonsulfide minerals..................................... .................................................... 62

46. Selenium contents...............................................-...-...-.........-........................-.-.-.............. 62

47. Uranium and sulfate contents......................--....-.........................-................... 64

48. Organic-carbon, mineral-carbon, and manganese contents... ... ... . . 64

49. Uranium, selenium, arsenic, and sulfide-sulfur contents.................................................................. 65

50. Copper and vanadium contents........................................-............................................ . .. 66

51. Diagrams showing possible paths of circulation of ore-bearing solutions in the Shirley Basin area.... 71

52. Diagram showing postulated Eh and pH conditions for a unit of solution during transportation

and deposition of uranium and other elements................ ..................................................... 72

53. Graph showing total Pb/U ratios of 15 high-grade ore samples from the Shirley Basin.. 73
CONTENTS VII

TABLES

Page

TABLE 1. Stratigraphic units in the Shirley Basin area.............................................................................................................. 10

2. Chemical analyses of water samples................................................................................................................................ 40

3. Size-frequency data on 23 samples of altered, ore-bearing, and unaltered sandstone............. .......................... 46

4. Physical and mineralogical data on 39 samples of unaltered, altered, and ore-bearing sandstone......... ........ 47

5. Principal differences between altered and unaltered sandstone.....-....... ................................................................. 50

6. Uranium and pyrite contents of some Shirley Basin ores from Utah Construction and Mining Co.

mine and Petrotomics Co. Section 9 pit.................................................................................................................. 54

7. Uranium and phosphate contents and U/P20s ratios for a suite of samples from the

Petrotomics Co. Section 9 pit.-...................................................................................................................... ......... 63

8. Uranium leached from samples of igneous rocks from mountain ranges that flank the Shirley Basin.......... 67

GEOLOGY AND URANIUM DEPOSITS, 

SHIRLEY BASIN AREA, WYOMING

By E. N. HARSHMAN

ABSTRACT

The Shirley Basin area is in Albany, Carbon, Converse, and 

Natrona Counties, Wyo., about 35 airline miles south of Casper. It is accessible over two improved and many local dirt 

roads. The area may be divided into four geographic units or 

subareas: the Shirley Basin, Bates Hole, Bates Creek drainage area, and the Laramie Mountains. Perennial streams 

drain all four sub-areas, although summer flows are low.

Maximum relief is in Bates Hole, an erosional depression, 

where altitudes range from about 6,100 feet along Stinking 

Creek to about 8,000 feet on Chalk Mountain in the southwest 

corner. Altitudes in the Shirley Basin, the subarea of economic interest, range from about 6,900 feet along the Little 

Medicine Bow River on the southeast to about 7,800 feet along 

the north rim of the basin.

The Shirley Basin contains one of the major uranium ore 

reserves in the United States, and as of late 1969 the deposits 

were being mined by Kerr McGee Corp., Petrotomics Co., and 

Utah Construction and Mining Co. Most of the ore is milled 

locally.

Rocks in the Shirley Basin area range in age from Precambrian to Quaternary. The Precambrian rocks crop out in 

the core of the Laramie Mountains and are part of an ancient 

terrane that was folded, metamorphosed, and subsequently 

invaded by granitic batholiths and mafic dikes. The intrusive 

activity was followed by a long period of erosion, and by the 

end of Precambrian time the region was reduced to a nearly 

flat surface.

Throughout the Paleozoic Era and much of the Mesozoic, 

the area was part of a stable foreland that lay along the east 

side of the Cordilleran geosyncline. Epicontinental seas repeatedly transgressed the area from the west and northwest, 

and a thick series of marine, littoral, and continental sediments was deposited in the Shirley Basin area. The formations, from oldest to youngest, are (1) the Madison Limestone 

of Mississippian age, (2) the Casper Formation of Pennsylvanian and Permian age, (3) the Goose Egg Formation of 

Permian and Triassic age, (4) the Red Peak, Alcova, and 

Jelm Formations of Triassic age, and (5) the Sundance and 

Morrison Formations of Jurassic age.

Near the end of the Jurassic Period the western shores of 

the epicontinental seas migrated eastward, and great amounts

of clastic material, eroded from highlands to the west, were 

deposited along the shores of, or in, the Cretaceous seas. From 

oldest to youngest the rocks of Cretaceous age of the Shirley 

Basin are (1) the Cloverly Formation, principally of continental origin, and (2) the Thermopolis, Mowry, Frontier, 

Niobrara, and Steele Formations, principally of marine and 

deltaic origin.

The Laramide orogeny deformed the area at the close of 

the Cretaceous, and the seas withdrew for the last time. 

Erosion of the newly formed mountains began in the Paleocene and continues now. The clastic debris that had been 

eroded from the highlands to the east and west of the Shirley 

Basin was deposited on an erosional surface which was cut 

into Cretaceous and older rocks. Formations of Tertiary age 

present in the area are, from oldest to youngest: Fort 

Union(?), Wind River, Wagon Bed, White River (two members) , and Arikaree. Quaternary formations include several 

stages of stream gravels and alluvium.

The pre-Tertiary rocks have been folded and faulted on a 

minor scale. A syncline trends southeastward through the 

western part of the area. Dips of the rocks on the eastern 

limb of the syncline are 2°-12° SW., and on the western limb 

the dips are northeastward and somewhat flatter. The area 

was domed in late Tertiary time; exposed Tertiary rocks dip 

about 1° N. and have been broken by a few faults that show 

small displacements.

The ground-water table in the area lies from a few feet to 

100 feet or more below the surface. Ground water is tributary 

to the surface drainage system and has a southerly gradient 

of 10-30 feet per mile. The principal anions in the ground 

water are sulfate and bicarbonate; radioelements include 

uranium, radium, and radon. Measurements of pH range from 

6.6 to 8.3 and have a mean and median of about 7.7.

The uranium deposits in the Shirley Basin are of major 

significance and constitute about one-sixth of the Nation's 

ore reserves. They are in the Wind River Formation of early 

Eocene age in two thick sandstone intervals which are separated by siltstone and silty claystone beds. The deposits bound 

large tongues of altered sandstone, commonly in so-called roll 

forms at the margins and as tabular layers on the top and 

bottom surfaces, a spatial relationship useful as an exploration guide. Ore bodies range from a few hundred tons to a few 

hundred thousand tons and in ore grade, as mined, from 0.1 

to 0.7 percent UgOg. High-grade ore may contain as much as 

20 percent U3 08 .

1
GEOLOGY AND URANIUM DEPOSITS, SHIRLEY BASIN AREA, WYOMING

The edges of the altered-sandstone tongues in the Shirley 

Basin area separate oxidized iron minerals within the tongues 

from reduced iron and uranium minerals in the material surrounding them. For this and other reasons, the ore-bearing 

solutions that produced this alteration are thought to have 

been oxidizing. The geochemistry of the ore and associated 

minerals and the arkosic nature of the ore-bearing sandstones 

suggest that these solutions were alkaline. Hydrogen sulfide 

of biogenic origin is believed to have played an important part 

in forming the ore deposits, although precipitation of the ore 

minerals may have been caused by nonbiogenic reactions. Ore 

deposition probably took place at least 500 feet and perhaps 

as much as 1,500 feet below the ground surface.

Uraninite is the only identified ore mineral; accessory minerals are abundant pyrite and minor amounts of marcasite, 

calcite, hematite, native (?) selenium, and an unidentified sulfate mineral. Altered sandstone contains goethite, limonite, 

and ferroselite. Uraninite and pyrite coat sand grains and fill 

interstices between sand grains; there is some replacement of 

the arkose by pyrite.

Many elements in the ore, and in altered and unaltered 

sandstone near ore, show a systematic distribution about the 

edge of the altered-sandstone tongue. These elements include 

uranium, iron, selenium, carbon, beryllium, sulfur, copper, and 

vanadium.

The sequence of events that gave rise to the Shirley Basin 

ore deposits is believed to have been as follows: (1) Downward percolation of vadose waters that leached uranium from 

weathered granite in nearby highlands and (or) from the 

tuffaceous constituents of rocks overlying the ore-bearing 

intervals, (2) lateral movement of this water through the 

most permeable beds of the Wind River Formation, (3) reaction of the oxidizing ore-bearing solutions with the rocks 

through which they moved, causing a lowering of the Eh and 

pH of the solutions and deposition of the ore and associated 

minerals, and (4) passage of the spent ore-bearing solutions 

beyond the zone of deposition and out of the basin.

The zone of ore deposition is considered to have been a 

dynamic feature, migrating basinward by oxidation and solution on the updip side of the ore body and reduction and 

deposition on the downdip side. A rather sharp drop in the 

pH of the ore-bearing solution probably occurred at the edge 

of the altered sandstone tongue when pyrite was oxidized by 

the ore-bearing solutions.

The age of the Shirley Basin uranium deposits is not well 

documented, but the best evidence suggests that it is about 

18 million years.

INTRODUCTION 

LOCATION AND ACCESSIBILITY

The Shirley Basin area is in southeastern Wyoming 

in Carbon, Natrona, Albany, and Converse Counties 

(fig. 1). Casper, the second largest town in Wyoming, 

is about 33 airline miles north of the center of the 

area, and Medicine Bow, on the main line of the 

Union Pacific Railroad, is 32 miles to the south.

The area is traversed by several improved roads 

and many unimproved roads and trails (fig. 2). State

Highway 487, a paved all-weather road that is maintained throughout the winter, passes from north to 

south through the western part of the area. The old 

Casper-Medicine Bow road serves the eastern and 

north-central parts of the area; it is graded, gravel 

surfaced, and, in part, maintained throughout the 

winter. The Shirley Ridge road, which connects the 

Shirley Basin mining area with State Highway 487, 

passes from east to west through the central part of 

the area; it is graded, gravel surfaced, and maintained throughout the winter. Most of the other 

roads and trails are impassable during periods of 

heavy snow, and some are impassable to all but fourwheel-drive vehicles, even in the summer months.

PHYSICAL FEATURES

The Shirley Basin area lies between the Laramie 

Mountains on the northeast and the Shirley Mountains on the southwest. It is an area of low to moderate relief that comprises four distinct geographic 

units (fig. 2). These and other physical features 

are shown on the geologic map of the Shirley Basin 

area (Harshman, 1968b).

The Shirley Basin, the focal point of this investigation, is by far the largest and economically the 

most important of these geographic units. The basin 

is not well defined, but generally it is considered to 

lie in the Little Medicine Bow River drainage and 

to be bounded on the northwest by Bates Hole, on 

the north by the south edge of the Bates Creek drainage area (Dugway Rim), and on the east by the west 

flank of the Laramie Mountains. The south and southwest boundaries are outside of the area investigated. 

In this report, about 10 square miles of terrain near 

the southwest corner of the area is considered a part 

of the Shirley Basin even though it is drained by 

Dry Creek, a westward-flowing tributary of the North 

Platte River. The Shirley Basin is an area of low 

relief eroded in rocks of Cretaceous and Tertiary age. 

Altitudes range from slightly below 6,900 feet along 

the Little Medicine Bow River in the southeastern 

part of the basin to about 7,800 feet on the Dugway 

Rim at the north boundary. The Little Medicine Bow 

River, a perennial stream that rises on the west 

flank of the Laramie Mountains, flows southward 

through the basin and joins the westward-flowing 

Medicine Bow River near the town of Medicine Bow. 

Owing to the low, rolling character of the terrain, 

exposures in the Shirley Basin are poor except in 

very limited areas along the Little Medicine Bow 

River and its major tributaries and along the southern slope of the Dugway Rim.
PHYSICAL FEATURES

Bates Hole, a prominent erosional feature in the 

northwestern part of the area, is drained by Stinking 

Creek and its tributaries. Stinking Creek is an intermittent stream that flows northward and joins the 

North Platte River about 30 miles northwest of the 

area. Relief in Bates Hole is moderate; altitudes 

range from about 6,100 feet along Stinking Creek at 

the north edge of the area to slightly over 8,000 feet 

on Chalk Mountain near its western edge. The floor 

of Bates Hole is composed of Cretaceous shales; in 

the walls are excellent exposures of Tertiary rocks 

ranging in age from Eocene to Miocene. Although 

Stinking Creek is a small intermittent stream, erosion of the soft rocks composing the rim of Bates 

Hole has been exceedingly rapid. That piiion pine 

trees are supported on their stiltlike roots and have 

their crowns as much as 6 feet above the present 

ground surface (fig. 3) indicates that the rim of

Bates Hole has receded as much as 10 feet during 

the lifespan of the trees probably not more than a 

few hundred years.

The Bates Creek drainage area lies north of the 

Shirley Basin, east of Bates Hole, and west of the 

Laramie Mountains. It is a high-standing almost terracelike area drained by northward-flowing Bates 

Creek and carved in rocks of Tertiary age. Altitudes 

range from about 7,000 feet on the northwest to 

about 7,800 on the east. Steep-walled narrow canyons 

dissect the northwestern part of the area; elsewhere 

dissection has been minor, and the component rocks 

are poorly exposed. Bates Creek reservoir, in the 

north-central part of the area, stores water for a 

short time after the spring runoff, but owing to excessive leakage through underlying permeable rocks, 

it is generally dry by midsummer.

HOT SPRINGS 

| Thermopolis

I L,H£;Ki!iJNlNJl CHEYENNE | 

I

464-170 O - 72 - 2

FIGURE 1. Shirley Basin area (shaded), Wyoming.
GEOLOGY AND URANIUM DEPOSITS, SHIRLEY BASIN AREA, WYOMING

106°30' 

^n, R. 81 W. R. 80 W. R. 79 W. R. 78 W.

106°00' 

R. 77 W. R. 76 W.

FIGURE 2. Limits of the Shirley Basin area, and some of the geographic features described in this report.

The west flank of the Laramie Mountains extends 

into the northeastern part of the mapped area. Exposed here are coarse-grained granitic rocks, diabase 

dikes, and metamorphic rocks of Precambrian age 

and limestone, sandstone, quartzite, and shale of 

Paleozoic age. Altitudes range from about 7,200 feet 

along the toe of the west flank of the Laramie Mountains to slightly above 8,400 feet in the northeast 

corner of the mapped area.

The west flank of the Laramie Mountains is dissected by numerous steep-walled canyons, some of 

which were cut by early Tertiary streams. These canyons were subsequently filled with clastic sediments, 

principally of Oligocene (White River) age. Recent 

erosion has removed, or is removing, this old canyon 

fill. The reexcavation of the higher reaches of the 

early Tertiary drainage system and the superimposition of the present drainage system on this old system 

have produced drainage abnormalities. For example, 

in the northeast corner of the mapped area Deer, 

Texas, and Curry Creeks flow southwestward down 

the west flank of the Laramie Mountains to an area

about 3 miles west of the topographic divide. Here 

Curry Creek joins Texas Creek and Texas Creek 

joins Deer Creek. Deer Creek then reverses its direction of flow, passes eastward through the topographic 

divide in a steep-walled canyon, and discharges into 

the North Platte River at the foot of the east slope 

of the Laramie Mountains.

LOCAL INDUSTRIES

Mining and sheep and cattle grazing are the principal enterprises in the area. Winters are severe, and 

grazing is limited to the summer months.

In late 1968 two mines were operating in the Shirley Basin. The Petrotomics Co., after terminating 

mining in sec. 9, was operating an open-pit mine in 

sec. 15, T. 27 N., R. 78 W.; the ore was being processed on the property. In sec. 28, T. 28 N., R. 78 W., 

the Utah Construction and Mining Co. was extracting 

uranium in situ by introducing sulf uric acid through 

holes drilled to the ore-bearing sandstone, pumping 

out the uranium-bearing solution, and removing the 

uranium by ion exchange. Additional open-pit mines
EARLY CULTURE

are planned by Utah Construction and Mining Co. 

and by Kerr-McGee Corp.

Tourism is minimal, and the area has no commercial establishments where room, board, and fuel 

for vehicles may be purchased. The area is hunted 

for sage grouse, deer, and antelope (American pronghorn) .

FIGURE 3. Pinon pine tree killed by erosion in Bates Hole. 

Crown of tree (arrow) about 6 feet above present ground 

surface.

CLIMATE AND VEGETATION

The Shirley Basin area ranges from arid in the 

lower reaches to semiarid in the higher reaches on 

the west flank of the Laramie Mountains. There are 

no official gaging stations, but the average annual 

precipitation is 12.12 inches at Casper, 14.03 inches 

at Bates Creek, and 12.97 inches at Medicine Bow. 

More than half the total precipitation falls during 

the period April through July. Summers are short; 

snowstorms may occur as late as June and as early 

as September. Strong winds are common.

Temperatures are moderate in the summer and 

severe in the winter. On hot summer days the temperature may reach 90° F; summer nights are 

cool. Winter temperatures as low as 45° F have 

been recorded at mining camps in the Shirley 

Basin, but periods of severe cold are generally interspersed with periods of moderate temperatures. That 

the temperature of ground water issuing from springs 

or being pumped from shallow wells ranges from 43° 

to 50° F, suggests an average annual temperature 

of about 45° F for the Shirley Basin area.

Vegetation is typical of high plains. It consists of 

sagebrush, squirreltail and other grasses, and pricklypear on flat or gently rolling terrain; pinon pine,

scrub fir, juniper, and aspen on the north slopes of 

the canyons at the edge of Bates Hole; and pine, 

spruce, fir, and aspen on the west flank of the Laramie Mountains. Deciduous trees, other than aspen, 

are not prevalent in the area, even along the perennial streams.

EARLY CULTURE

Tipi rings are numerous in the Shirley Basin and 

attest to early occupation of the area by nomadic 

Indians. The observed rings are 10-20 feet in diameter, generally in groups of 10 or more, and of both 

the simple- and multiple-course types. For the most 

part, they are on broad spurs or on high bluffs overlooking lower areas where game may have been 

plentiful at one time. Water is not available now at 

any of the sites, but there are springs within a few 

miles of all of them.

Well-preserved rings were observed on two spurs 

in the SEi^NW^ sec. 23, T. 27 N., R. 77 W., and 

less-well-preserved rings are along the erosional 

bluffs that extend several miles eastward from the 

SW. cor. sec. 28, T. 27 N., R. 80 W., and from sec. 32, 

T. 29 N., R. 77 W. Several of the rings in sec. 23 

are shown in figure 4. The ring in the foreground 

is about 13 feet in diameter and consists of several 

courses of sandstone boulders, obtained locally from 

outcrops of the Cloverly Formation. The boulders 

are 6-14 inches in maximum dimension. Similar 

rings can be seen higher on the spur, and other rings 

extend several hundred feet down the spur from the 

area shown in the photograph. The rings in this 

area contain only an isolated rock or two within the 

circle, but one ring on the south rim contains what 

appears to be a hearth.

The ring shown on figure 5, unlike any other seen 

in the area, consists of many sandstone slabs, most 

of which are carefully set on end in the ground so 

that they tilt inward. The ring, 2 feet in thickness 

and about 8 feet in diameter, is near the sandstone 

outcrops shown in figure 4 (upper right). The soil 

inside the ring contains, and is covered by, flint 

chips and a few broken artifacts.

Artifacts are abundant in the Shirley Basin area, 

particularly close to sources of flinty materials. On 

the top of a prominent hill (VABM Holiday) in the 

SE. cor. sec. 14, T. 27 N., R. 77 W., numerous flinty 

chips and rejected artifacts are near outcrops of 

silicified Cloverly sandstone. Near the spring in the 

NW14SW^ sec. 12, T. 28 N., R. 77 W., about 100 

feet below a silicified zone at the top of the Madison 

Limestone, an area of an acre or more contains piles 

of flint chips and broken or imperfect artifacts.
GEOLOGY AND URANIUM DEPOSITS, SHIRLEY BASIN AREA, WYOMING

FIGURE 4. Tipi rings on flat-topped spur in eastern part of 

the Shirley Basin. Ring in foreground is about 13 feet in 

diameter.

FIGURE 5. Ring of unknown designation but associated with 

tipi rings shown in figure 4. Ring is about 8 feet in diameter, and soil within it contains many flint chips.

PREVIOUS WORK

The geology and mineral resources of the Laramie 

Basin, Wyo., were described by Darton and Siebenthal (1909), and their reconnaissance map, at a 

scale of about 1 inch=7 miles, includes four townships in the southeast corner of the area discussed in this report. Although the configuration 

of their contact between Tertiary and Cretaceous 

rocks in T. 27 N., R. 78 W., and the Wi/2 T. 27 N., 

R. 77 W., is approximately correct, it is shown about 

6 miles north of its proper position and appears to 

have been misplotted by one township.

The Shirley Basin area was investigated by Konkel (1935), Peterson (1935), Roehler (1958), Riedl 

(1959), and Shipp (1959) as part of the requirements for advanced degrees at the University of 

Wyoming. The ore deposits and their origin were 

discussed by Adler (1964), Bailey (1965), Harshman (1961, 1962, 1966, and 1968a), Melin (1964), 

and Rosholt, Harshman, Shields, and Garner 

(1964).

Miscellaneous Geologic Investigations Map 1-539 

(Harshman, 1968b) shows the 450-square-mile Shirley Basin area discussed in this report and is referred to frequently in the following discussions of 

the geology and ore deposits of the area.

HISTORY AND FIELDWORK

Uranium was discovered in the Shirley Basin in 

1955 when the Teton Exploration Drilling Co. of 

Casper, Wyo., found ore-grade material while drilling just west of the Little Medicine Bow River in 

sees. 2 and 3, T. 27 N., R. 78 W. The discovery 

attracted only minor attention until the summer of 

1957, when several thousand claims were staked 

in an area of about 150 square miles. Extensive 

drilling was started immediately, and by the end 

of 1959, more than 1 million feet of drilling had 

been completed. Most holes were drilled through 

the ore-bearing Wind River Formation and a few 

tens of feet into the underlying pre-Tertiary rocks. 

Most holes were probed, and for these, resistivity, 

gamma-ray, and, for some holes, self-potential logs 

were prepared. Lithologic logs, based on 5-foot 

sample intervals, were made by most property 

owners.

By the spring of 1959 it was evident that the 

Shirley Basin contained one of the Nation's major 

reserves of uranium ore, and mining companies 

made plans to exploit the deposits. Utah Mining 

Corp. (now Utah Construction and Mining Co.) 

constructed surface facilities and in the summer of 

1959 started to sink a 12i/£-foot-inside-diameter concrete-lined circular shaft on their property in sec. 

28, T. 28 N., R. 78 W. Because of heavy inflow of 

water, the shaft was plugged at a depth of 365 feet, 

and development work was started at the 330-foot 

level. The first Shirley Basin uranium ore was produced in March 1960 from development headings in 

the Utah Construction and Mining Co. mine.

In July 1960 the Petrotomics Co. began to strip 

3 million yards of overburden in preparation for 

mining large high-grade uranium ore bodies on their 

property in sees. 4 and 9, T. 27 N., R. 78 W. The 

first ore was mined from this property in December
STRATIGRAPHY

1960. Ore from the Utah mine was shipped to the 

Lucky Me mill in the Gas Hills; ore from the Petrotomics Co. pit was processed outside the area until 

October 1962 when a mill employing solvent-extraction techniques was completed on the property.

In late 1964, after a 4-year period of research, 

Utah Construction and Mining Co. abandoned underground mining in favor of in situ leaching of the 

ore-bearing sandstone with sulfuric acid introduced 

through drill holes. The uranium in the pregnant 

solution pumped from the leached area is recovered 

by ion-exchange techniques.

Ore was discovered by exploratory drilling on 

other properties in the Shirley Basin, but no new 

mines were activated until the summer of 1965 when 

Centennial Development Co. completed a shaft in 

sec. 26, T. 28 N., R. 78 W., on the Nail Lease of the 

Homestake Mining Co. Activity on this property 

was suspended after about 1 year of developmental 

work and experimental mining.

In October 1966, Petrotomics Co. started a new 

open pit in sec. 15, T. 27 N., R. 78 W. The first ore 

from this pit was mined in September 1967 from 

high-grade ore bodies about 180 feet below the 

ground surface.

The Shirley Basin project was started in the fall 

of 1959 after drilling by private individuals and 

mining companies indicated that the basin contained 

one of the Nation's largest uranium ore reserves. 

Advanced copies of topographic maps became available late in the summer of 1960, and geologic mapping was started in the eastern part of the area. 

Summer fieldwork continued through 1964 and included regional mapping and studies of uranium 

deposits in the Utah Construction and Mining Co. 

underground mine and the Petrotomics Co. Section 

9 open pit. Short periods were spent in the field in 

1965, 1966, and 1967 in reconnaissance mapping to 

the east of the area covered in this report and in the 

continued study of the ore deposits exposed by mining operations.

Concurrent with regional mapping and ore-deposits studies, considerable subsurface data were 

compiled from drill-hole cuttings and from waterdepth measurements made in several hundred drill 

holes.

The writer was assisted in the summers of 1960- 

62 by J. W. Hasler, Jay Hodges and A. P. Butler, 

and Robert B. Laughon, respectively.

ACKNOWLEDGMENTS

The author especially thanks the fine people of 

the area whose cooperation and friendliness aided in

this investigation. Among them are Weston Bourrett, Robert Melin, Robert Bailey, and Jack Bailey 

of Utah Construction and Mining Co.; Norman 

Grant, G. K. Coats, Robert Cypert, and Robert Odell 

of Tidewater Oil Co. and subsequently of Petrotomics Co.; Richard Lisco of the Teton Exploration 

Drilling Co.; Cotter Ferguson of Gas Hills Uranium 

Co.; Fred Groth and Dean Webb of Kerr-McGee 

Corp.; and Page Jenkins, consultant. Dr. Paul McGrew, University of Wyoming, made rapid field 

identifications of vertebrate-fossil collections. These 

identifications were valuable as a guide in day-today mapping in the Bates Hole area.

The author is grateful to many Geological Survey 

colleagues who have contributed to this study by 

criticism and discussion.

Analytical data essential for the study of the ore 

deposits and the alteration associated with them 

were furnished by G. T. Burrow, Ardith J. Bartel, 

Nancy M. Conklin, E. F. Cooley, E. J. Fennelly, 

Dorothy Ferguson, I. C. Frost, A. J. Gude, J. C. 

Hamilton, M. W. Solt, Lorraine Lee, H. H. Lipp, 

Violet Merritt, Wayne Mount joy, H. M. Nakagawa, 

L. E. Patten, L. F. Rader, D. L. Skinner, Barbara 

Tobin, Roberta Wilkey, and E. J. Young. Samples of 

ground water were analyzed in the Denver laboratories of the U.S. Geological Survey.

STRATIGRAPHY

Rocks in the Shirley Basin area are of both igneous and sedimentary origin and range in age from 

Precambrian to Cenozoic (table 1). Quaternary surficial deposits fill some of the valleys and form terraces related to at least two erosion cycles earlier 

than the present. The sedimentary rocks, particularly those of Tertiary age, are widespread at the 

surface and are the host rocks for the uranium 

deposits. Igneous and metamorphic rocks of Precambrian age and sedimentary rocks of Paleozoic 

age crop out only in the northeastern part of the 

area, on the western flank of the Laramie Mountains. 

Rocks of Mesozoic age crop out in Bates Hole and 

along the southern border of the area, where erosion 

has removed the Tertiary rocks.

The Shirley Basin is structurally simple. It is an 

erosional feature whose position is governed to some 

extent by a broad syncline in the pre-Tertiary rocks. 

The synclinal axis trends northwestward, parallel 

to the erosional axis of the basin, and lies 9-10 

miles west of the basin axis. Paleozoic, Mesozoic, 

and, to a lesser extent, Tertiary rocks have been 

broken by faults that show small displacements.
8 GEOLOGY AND URANIUM DEPOSITS, SHIRLEY BASIN AREA, WYOMING

Two faults with displacements of about 100 feet 

are just west of the project area.

PRECAMBRIAN IGNEOUS AND METAMORPHIC ROCKS

The principal igneous and metamorphic rocks in 

the Shirley Basin area are biotite granite, diabase, 

and granite gneiss, all of Precambrian age. These 

rocks form the core of the Laramie Mountains, and 

they are exposed in the northeastern part of the 

mapped area. Deep drill holes show that similar 

rocks underlie the Shirley Basin at a depth of as 

much as 5,000 feet.

The granite ranges in texture from coarse-grained 

porphyritic to aplitic, but the compositions of the 

various facies are similar. Most common is a medium- to coarse-grained pink facies composed of 

quartz, feldspar, and very minor amounts of ferromagnesian minerals, principally biotite. In some 

places this facies becomes porphyritic and contains 

feldspar crystals as much as 3 inches long. Less 

common in the report area are irregular or dikelike bodies of pink or light-gray aplitic granite.

The granite weathers to a coarse sandy soil that 

forms a thin mantle over the somewhat rounded 

bedrock surfaces. In most places erosion keeps pace 

with disintegration, and therefore moderately fresh 

granite is close to the surface. However, intensely 

weathered surfaces are found in some places where 

the granite has recently been exposed by removal 

of the overlying Paleozoic rocks. The weathered 

rock is unmistakably related to a pre-Mississippian 

erosion surface characterized by intense weathering.

Three prominent joint sets that have broken the 

granite govern the shape of several granite pinnacles 

in the northeast corner of the mapped area. The 

most prominent joints are vertical, strike N. 40°- 

50° E., and give rise to the linearity that is so 

prominent on aerial photographs of the area. These 

joints appear to be tension fractures, for some of 

them are occupied by diabase dikes or quartz veins. 

Another set of joints is vertical and strikes within 

a few degrees of north. These joints appear to have 

been tight at the time of diabase intrusion, although 

one of them is occupied by a dike about 10 feet wide 

and 2 miles long. The third, and least conspicuous, 

set of joints is approximately horizontal and may 

have been caused by relief of stress following erosion of the upper part of the granite.

Thin sections of the granite contain quartz, potassium-feldspar (microcline and orthoclase), plagioclase, and biotite, listed in decreasing order of 

abundance. The potassium-feldspars show incipient

alteration to kaolin or sericite; the plagioclase, composition about Ab80 , shows moderate alteration. In 

some thin sections biotite has been completely altered 

to chlorite, and a part of the plagioclase has been 

altered to epidote. The feldspars, and to a lesser extent the quartz, contain small amounts of hematite, 

giving rise to the pink color of the granite.

Diabase dikes, common in the part of the Laramie 

Mountains included in the mapped area, are easily 

recognized on aerial photographs (fig. 6). The dikes 

range in width from a few inches to 300 feet; some 

have been traced for more than 6 miles. The dikes 

have been intruded along strong joints that strike 

about N. 45° E. and offered easy access toward the 

surface at the time of emplacement. The dikes are 

virtually vertical. One diabase dike that trends about 

N. 15° W. and dips vertically occupies a fracture 

that has offset several northeast-trending diabase 

dikes. No other northerly trending dikes are known 

in the area.

In flat or gently rolling terrain the diabase dikes 

may not crop out. They weather more rapidly than 

granite and generally occupy saddlelike depressions 

or troughs filled with a greenish-brown fine-grained 

soil which supports a luxuriant growth of sagebrush, but few conifers. All but the very narrow 

dikes have indurated the adjacent granite, and differential weathering has given rise to two parallel 

ridges that define the dike walls.

In hand specimen the dike rock is a greenish-gray 

ophitic intergrowth of feldspar and a pyroxenelike 

dark mineral. The rock is extremely tough and appears to be unaltered. In thin section the rock is 

shown to be a quartz diabase in which the original 

pyroxene has been completely converted to greenishgray pleochroic hornblende. Quartz occurs as micrographic intergrowths with alkali feldspar and is the 

latest product of crystallization. The alteration of 

pyroxene to hornblende is considered to be deuteric. 

The plagioclase is considerably altered but approximates labradorite in composition.

Metamorphic rocks, common in parts of the core 

of the Laramie Mountains, are sparse in the mapped 

area. Several small irregular masses and dikelike 

bodies of granite gneiss were noted during field 

mapping in the northeastern part of the Shirley 

Basin area. These are composed of quartz, potassium 

feldspar, plagioclase, and a dark mineral, generally 

biotite. The component minerals are roughly alined. 

The rock is probably older than the granite, although 

possibly it represents a slightly metamorphosed 

part of the granite itself.

Several minor quartz veins are present in the area. 

One, shown on the geologic map (Harshman, 1968b),
STRATIGRAPHY, PALEOZOIC 9

is offset by a northwest-striking diabase dike and 

thus is older than the dike. A short distance east of 

the mapped area, a 5-foot-wide quartz vein has been 

emplaced parallel to the north wall of a northeasttrending diabase dike and from a few inches to 30 

feet from it. This quartz vein also appears to be 

younger than the dike. Both veins are bull quartz 

containing no other visible minerals.

PALEOZOIC

In the Shirley Basin area the oldest sedimentary 

rocks are limestone, dolomite, sandstone, and quartzite strata of Mississippian, Pennsylvanian, and 

Permian age. No rocks of Cambrian, Ordovician, 

Silurian, or Devonian age have been recognized; if 

deposited in the area, they were subsequently removed by erosion.

Stratigraphic nomenclature for rocks of Paleozoic 

age on the west flank of the Laramie Mountains has 

undergone considerable change. Darton (1908) used 

the name Casper Formation to identify a sequence 

of sedimentary rocks of Carboniferous age that crop 

out on the west flank of the Laramie Mountains, 

overlie the Precambrian granite, and underlie the 

Satanka Shale (the lower part of the Goose Egg 

Formation of this report). Knight (1929), Miller 

and Thomas (1936), Thomas (1948), Thompson and 

Thomas (1953), Agatston (1954), Maughan and 

Wilson (1960), Maughan (1963), and others proposed various restrictions on the use of the name 

Casper. Current usage, followed in this report, 

restricts the name Casper Formation to the upper 

part of the stratigraphic interval described by Darton ; the lower part is termed the Madison Limestone.

£>*£*'' - -7'f;'

CTMKB3 isSMIsfeis r *

>

.-*.; .

FIGURE 6. Aerial photograph of diabase dikes (pCd) intruding Precambrian granite ( p g) in T. 27 N., Rs. 75-76 W.

White River Formation (Twr) laps on granite (at left corners).
10 GEOLOGY AND URANIUM DEPOSITS, SHIRLEY BASIN AREA, WYOMING

TABLE 1. Stratigraphic units in the Shirley Basin area

Geologic time unit

Cenozoic

Mesozoic

Paleozoic

Quaternary

Tertiary

Holocene

Pleistocene

Miocene

Oligocene

Late 

and 

Eocene middle

Early

Cretaceous

Jurassic

Triassic

Permian

Pennsylvanian

Mississippian

Precambrian

Rock unit

Stream alluvium and 

terrace gravel

Arikaree Formation

White River 

Formation

Wagon Bed Formation

Wind River Formation

Steele Shale

Niobrara Formation

Frontier Formation

Mowry Shale

Thermopolis Shale

Cloverly Formation

Morrison Formation

Sundance Formation

Jelm Formation

Alcova Limestone

Red Peak Formation

Goose Egg Formation

Casper Formation

Madison Limestone

Approximate 

thickness 

(ft)

0-50

180

750

150

500

2,000

900

860

110

185

200

200

240

125

20

580

400

650

150

Description

Surficial deposits of silt, sand, and gravel; 

in some areas includes terrace gravel.

Tuffaceous siltstone, sandstone, conglomerate, and fresh-water limestone of fluvial 

and lacustrine origin.

Upper member tuffaceous siltstone and 

conglomerate; fluvial and lacustrine. 

Lower member tuffaceous siltstone and 

claystone; predominantly fluvial and lacustrine.

Tuffaceous siltstone, sandstone, conglomerate, and limestone; fluvial and lacustrine.

Silty claystone, siltstone, arkosic sandstone, 

and conglomerate; fluvial.

Thin-bedded carbonaceous shale, lenticular 

sandstones near top.

Thin-bedded carbonaceous shale, in part calcareous.

Thin-bedded carbonaceous shale and sandstone; Wall Creek Sandstone Member at 

top.

Thin-bedded siliceous shale; contains fish 

scales.

Thin-bedded carbonaceous shale; Muddy 

Sandstone Member near base.

Sandstone, moderately cemented, even-bedded to crossbedded; carbonaceous shale in 

middle.

Variegated waxy mudstone and siltstone; 

sandstone near base; limestone concretions.

Thin-bedded and fissile shale, sandstone, and 

sandy limestone.

Shale and ledge-forming sandstone; red to 

buff.

Crinkly limestone and limy sandstone.

Siltstone and shale, red; sparse sandstone.

Siltstone and sandstone, red; interbedded 

limestone.

Dolomitic limestone and sandstone; overlain 

by crossbedded sandstone and quartzite.

Dolomitic limestone; cherty near top; conglomerate and sandstone at base.

Granitic and metamorphic rocks and mafic dikes.
STRATIGRAPHY, PALEOZOIC 11

MADISON LIMESTONE

The name Madison Limestone was first used by 

Peale (1893) to identify a 1,250-foot-thick series of 

massive, laminated, and siliceous dolomitic limestone beds exposed in the Three Forks area of the 

Madison Range in southwestern Montana. The formation thins by truncation southward from the type 

locality and pinches out southeast of the Shirley 

Basin area. The Madison Limestone is of Mississippian age.

Many divisions of the Madison have been proposed, but none of them are entirely satisfactory 

for field mapping in the Shirley Basin area. The 

Madison Limestone was mapped (Harshman, 1968b) 

as a single unit in the area, but it may be divided 

into three distinctive lithologic units with a combined thickness of about 150 feet. The basal unit, 

considered by some geologists to be Cambrian in 

age but herein considered to be Mississippian as 

proposed by Maughan (1963), is composed of arkosic sandstone, conglomerate, and quartzite. It ranges 

in thickness from 10 to 20 feet and was derived, 

for the most part, from the granitic rock on which 

it rests. It was deposited on an old weathered 

remarkably flat erosion surface cut in granitic and 

metamorphic rocks. Local irregularities in this surface account for variations in thickness. The lower 

unit is generally dark brown or dark reddish brown 

and is composed of quartz and feldspar grains and 

pebbles in a sandy or silty matrix. The coarse fraction is subangular to rounded, and some of the 

material appears to have been derived from areas 

close to the place of deposition. Pebbles, where present, are generally in the lower part of the unit, and 

in most places they grade upward into finer grained 

material. In some areas this unit is a well-cemented 

quartzite; in others it is only moderately cemented, 

and the rock is friable. Crossbeds are common and 

range from a fraction of an inch to about 15 inches 

in thickness.

The basal unit resists erosion and characteristically crops out in a nearly vertical low cliff or forms 

flat dip slopes (fig. 7).

A sequence of thin-bedded pink, purple, and gray 

dolomitic limestone and dolomite overlies the lower 

unit. In most places the contact with the underlying 

sandstone or quartzite is poorly exposed; however, 

in the exposures examined the contact is rather well 

defined, grading upward in a few inches from 

sandstone, through calcareous sandstone and sandy 

dolomite, to dolomite. The contact appears to be 

conformable.

Individual beds in the middle unit are 2-6 inches 

thick and persist laterally. Some beds contain as 

much as 5 percent coarse sand; others contain almost 

none. The sandy beds weather to -a rough, pitted 

surface. In some places the rock contains small vugs 

filled with calcite or quartz crystals; in other places 

it contains small veinlets or irregular masses of 

cherty silica. The middle unit is about 70-90 feet 

thick.

The upper unit consists of dolomitic limestone 

beds, similar to those in the middle unit, interspersed with lenticular masses and persistent beds of 

chert. The chert is greenish gray to brownish gray, 

is generally fossiliferous, and occurs as beds that 

range in thickness from about 1 inch to about 24 

inches. The contact between the middle and upper 

units is indistinct, and in most places the first welldefined chert bed is underlain by 15-20 feet of 

strata containing thin beds or small lenticular masses of chert. The upper unit ranges from 50 to about 

75 feet in thickness; the variation appears to be 

due to erosion of the upper part of the upper unit.

FIGURE 7. Outcrop of basal sandstone unit of Madison 

Limestone in sec. 16, T. 29 N., R. 77 W. Base of exposure 

rests on Precambrian granite; top is calcareous sandstone 

in contact with dolomitic limestone unit.

POST-MADISON EROSION

The top of the Madison Limestone is separated 

from the base of the Casper Formation by a welldeveloped erosional unconformity. In some places a
12 GEOLOGY AND URANIUM DEPOSITS, SHIRLEY BASIN AREA, WYOMING

few inches to a few feet of poorly cemented red sand, 

silt, or sandy silt separates the two formations; in 

other places, for example one-third mile south of 

the Taylor Ranch in sec. 2, T. 28 N., R. 77 W., where 

a well-developed karst topography formed in the 

top of the Madison Limestone, as much as 20 feet 

of solution or collapse breccia mixed with red sand 

and silt separate the two formations (fig. 8). Workings of the Night Owl uranium prospect have explored uranium-bearing apatite associated with 

chert emplaced along the old karst surface in sec. 

12, T. 28 N., R. 77 W. The chert in the uranium 

deposits is not genetically related to the chert in 

the upper part of the Madison Limestone.

FIGURE 8. Solution breccia in well-developed karst surface, 

NE% sec. 2, T. 28 N., R. 77 W. Light-colored material is 

brecciated Madison Limestone; dark-colored material is red 

sand and silt filling voids and caverns.

CASPER FORMATION

The Casper Formation, as used in this report, consists of all strata overlying the Madison Limestone 

and underlying the Opeche (lowest) Shale Member 

of the Goose Egg Formation. The Casper Formation 

is considered to be Early, Middle, and Late Pennsylvanian and Early Permian in age although the 

Lower Pennsylvanian strata are absent in the report area. The Casper is similar in lithology to the 

combined Tensleep Sandstone and Amsden Formation, but Keefer and Van Lieu (1966) considered it 

to be appreciably younger than these formations.

In the Shirley Basin area the entire thickness of 

the Casper Formation is not exposed at any one

place, and therefore the formation must be described 

from several partial sections in outcrops slightly 

more than a mile apart. Because of abrupt lithofacies changes along the strike of individual beds, 

correlation between the several partial sections may 

be inexact, and all of the strata described may not 

be present in any one area.

The Casper Formation in the northeastern part 

of T. 28 N., R. 77 W., may be divided into two units 

having a total thickness of about 650 feet. The 

lower unit is about 300 feet thick and consists of 

pink, purple, and gray dolomitic limestone and 

dolomite and tan to reddish-brown dolomitic sandstone, sandstone, and quartzite. Beds in the carbonate rocks range in thickness from 1 inch to 3 

feet and contain considerable siliceous material as 

irregular chert masses and as dispersed grains of 

coarse-grained sand. Weathered beds have very 

rough pitted and gnarled surfaces and form a series 

of prominent ledges. Laterally there is considerable 

change in lithology, and some of the dolomite beds 

grade into dolomitic sandstone or even quartzite 

within a few hundred feet. The clastic rocks are in 

beds 1-6 inches thick; generally they are evenly 

bedded. In most areas they are well-cemented sandstone, but in some places they contain enough silica 

cement to class them as quartzite. Crossbedded sandstone is present in some areas. From about 110 to 

140 feet above the base of the lower unit in sees. 

1 and 2, T. 28 N., R. 77 W., there are two red, 

crossbedded, and moderately well cemented sandstone beds that have good lateral continuity and 

have been used in correlating the various partial 

sections measured in the area. These two sandstone 

beds, separated by a 6-foot-thick sequence of thinbedded sandy dolomite, may represent the base of 

the upper unit of the Casper Formation as used by 

Agatston (1954). From the top of the red beds to 

the top of the lower unit the strata consist of principally sandy dolomitic limestone that contains several 

thin jasper beds 1-6 inches thick as well as chert 

nodules 1-3 inches in diameter.

The upper unit is about 350 feet thick and consists of sandstone and quartzite which, near the 

base, are interbedded with minor amounts of dolomite and dolomitic limestone. The clastic rocks are 

in beds a fraction of an inch to a few feet thick; 

crossbeds are common in some areas. The arenaceous 

rocks are fine to medium grained, siliceous, and 

generally buff, tan, or reddish brown and are moderately well to extremely well cemented. Intense 

cementation occurs along certain beds in some 

places, and it cuts across bedding planes in other 

places.
STRATIGRAPHY, MESOZOIC 13

PALEOZOIC AND MESOZOIC

GOOSE EGG FORMATION

The Goose Egg Formation was first described and 

named by Burk and Thomas (1956) from exposures 

near the Goose Egg Post Office, 11 miles southwest 

of Casper in Natrona County, Wyo. Maughan 

(1964) extended the use of the name into the 

southeastern part of the State. The formation is of 

Permian and Triassic age and comprises that part 

of the red-bed sequence that is inter stratified with 

carbonate- and sulfate-bearing rocks. In southeast 

Wyoming, Maughan proposed the following members, listed in ascending order: Opeche Shale, Minnekahta Limestone, Glendo Shale, Forelle Limestone, 

Difficulty Shale, Ervay, Freezeout Shale, and Little 

Medicine. Only the lowest four members, of Permian 

age, are exposed in the Shirley Basin; the upper 

four members, of Permian and Triassic age, are 

covered either by alluvium or by rocks of Tertiary 

age.

The best exposures of the Goose Egg Formation 

are in sec. 15, T. 28 N., R. 77 W. Here the Opeche 

Shale Member rests on the Casper Formation with 

no apparent angular discordance. The contact is 

sharp, and in many places it is marked by carbonate 

(siderite?)-cemented iron-stained round sandstone 

concretions i/^-1 inch in diameter. The Opeche is 

about 70 feet thick in the area and consists of red 

siltstone beds less than 2 inches thick interbedded 

with a few sandy siltstone beds. At about 60 feet 

above the base of the Opeche is a bed of pink to 

yellowish-red sandy dolomitic limestone about 2 feet 

thick.

Beds equivalent to the Minnekahta Limestone 

Member at the type locality crop out about 70-97 

feet above the base of the Goose Egg Formation. In 

ascending order, they consist of 11 feet of interbedded gray to pink dolomitic limestone, limy sandstone, and red sandy siltstone; 9 feet of purple limy 

siltstone and red silty sandstone; 3 feet of gray 

to purple dolomitic limestone containing quartz-lined 

vugs; and 5 feet of purple limestone grading upward 

into purple siltstone.

Overlying the Minnekahta are thin-bedded red 

and reddish-orange siltstone beds about 66 feet 

thick the Glendo Shale Member of the Goose Egg 

Formation. Gray-green spots, characteristic of this 

shale over much of eastern Wyoming, are present 

in the exposures.

The Forelle Limestone Member, which overlies 

the Glendo, is about 21 feet thick and from the base 

upward consists of 12 feet of gray thin-bedded crenulated or "crinkly" dolomitic limestone interbedded

with limy sandstone, 7 feet of red sandy siltstone 

and sandstone, and 2 feet of gray crenulated sandy 

dolomitic limestone. The limestone strata of this 

member form a broad dip slope; they are the highest 

beds in the Goose Egg Formation exposed in the 

Shirley Basin, but electric logs of wells drilled in 

the area show that the overlying members of the 

Goose Egg Formation are present in the subsurface. 

The thickness of the Goose Egg Formation, determined from electric logs, is about 400 feet.

MESOZOIC

RED PEAK FORMATION

The name Red Peak was first used by Love (1939) 

to identify a sequence of. red siltstone and finegrained sandstone beds exposed along Red Creek a 

few miles west of Red Peak, in the southern part of 

the Absaroka Range in Fremont County, Wyo. Love 

considered the Red Peak to be a member of the 

Chugwater Formation of Triassic age. High and 

Picard (1967) and Pipiringos (1968) raised the 

name to formational rank. As used in this report, 

which follows the proposals of Pipiringos, the Red 

Peak Formation includes all strata in the interval 

between the underlying Goose Egg Formation and 

the overlying Alcova Limestone and is Early Triassic in age.

Only the upper part of the Red Peak Formation 

is exposed in the Shirley Basin area; the rest of the 

strata are covered either by rocks of Tertiary age 

or by soil. The exposures in the mapped area are 

generally obscured by talus blocks of the overlying 

Alcova Limestone, but about 2 miles northeast of 

the southeast corner of the area, the exposed strata, 

from bottom upward, are as follows: 6 feet of 

brick-red thin-bedded siltstone; 6.6 feet of salmonred thin-bedded calcareous siltstone, bleached to 

pale green along joints; 1.5 feet of white silty finegrained crossbedded calcareous sandstone containing 

red and yellow concretions about 1 inch in diameter; 

and 1.2 feet of white and pale-pink fine-grained thinbedded calcareous sandstone.

Electric logs of wells indicate that several sandy 

beds are present in the middle and lower parts of the 

Red Peak Formation in the Shirley Basin area and 

that the total thickness of the formation approximates 580 feet.

ALCOVA LIMESTONE

The name Alcova Limestone was used by Lee 

(1927) for an 8-foot-thick limestone exposed in the 

red-bed sequence near Alcova, Wyo. He considered
14 GEOLOGY AND URANIUM DEPOSITS, SHIRLEY BASIN AREA, WYOMING

the Alcova to be a member of the Chugwater Formation. Pipiringos (1968) established the Alcova as a 

formation in the Chugwater Group, and it is so 

used in this report.

Most of the Alcova Limestone is covered by rocks 

of Tertiary age. In the few exposures in the eastern 

part of the mapped area, the Alcova is about 8-19 

feet thick and consists of gray or brownish-gray 

"crinkly" or contorted slabby limestone. However, 

in a few places outside the area the lower part of the 

formation consists of massive sandy limestone beds 

1-2 feet thick. The Alcova is a resistant unit in an 

easily eroded sequence of red beds and generally 

forms hogbacks and dip slopes. The contacts of the 

Alcova Limestone with the overlying and underlying formations appear to be conformable.

About 2 miles east of the southeast corner of the 

mapped area, in the southern part of sec. 4, T. 

26 N., R. 76 W., the Alcova Limestone crops out in 

the steep walls of a small creek. Here the limestone 

has thinned to about 6 feet, and part of the thicker 

stratigraphic interval normally composed of limestone contains considerable sandy and silty material. 

In the next exposure, about one-half mile to the 

southeast, the Alcova Limestone is absent, and the 

Jelm rests on the Red Peak Formation.

Although described separately in this report, the 

Alcova Limestone and the Red Peak Formation are 

shown as a single unit on the geologic map of the 

Shirley Basin area (Harshman, 1968b).

JELM FORMATION

The name Jelm Formation was first used by 

Knight (1917) to identify a 250-foot-thick sequence 

of strata exposed near the foot of the east slope of 

Jelm Mountain in Albany County, Wyo. Previously this sequence had been included in the top 

part of the Chugwater Formation. In later years, 

beds in the top of the Jelm were excluded from the 

formation. Pipiringos (1968) defined the Jelm 

Formation in south-central Wyoming as including 

the Upper Triassic rocks that lie above the Alcova 

Limestone and below the Popo Agie Formation, or 

below the Sundance Formation in areas where the 

Popo Agie is absent. He recognized a lower and 

an upper member, the Red Draw Member and Sips 

Creek Member, respectively; his usage is followed 

in this report.

The Jelm Formation is well exposed only in a 

small rounded knob in sec. 28, T. 28 N., R. 77 W. 

The Red Draw Member is about 60 feet thick and 

comprises a sequence of interbedded brick-red, reddish-brown, or white siltstone, claystone, and sandstone strata containing some greenish-gray finegrained beds. Some of the beds contain calcareous 

cement, and some beds are ripple marked. The 

alternation of hard and soft beds in the lower 

member gives rise to overhanging ledges. The contact of the Red Draw Member with the underlying 

Alcova Limestone, which is poorly exposed in the 

creek at the foot of the hill, appears to be sharp and 

conformable. Pipiringos (1968) believed that on a 

regional basis the contact may be disconformable.

The upper part of the hill is composed principally 

of tan and buff well cemented crossbedded and slabby sandstone, provisionally assigned to the Sips 

Creek Member. These beds are about 27 feet in total 

thickness. The conglomerate that separates the Red 

Draw and Sips Creek Members of the Jelm Formation in many other places in Wyoming (Pipiringos, 

1968) could not be seen in this exposure, nor could 

the zone of chert pebbles that in many places is at 

the base of the overlying Sundance Formation. Lacking these diagnostic marker beds, it is impossible 

to definitely identify these strata. Although they are 

shown as Jelm on the geologic map (Harshman, 

1968b), possibly the crossbedded sandstone beds 

near the top of the hill are basal Sundance indurated 

by silica leached from the tuffaceous White River 

Formation that once overlay the area; or possibly 

the Sips Creek Member of the Jelm is absent in this 

area, and the entire 27-foot-thick sandstone sequence 

is abnormally indurated basal sandstone of the Sundance.

Electric logs of wells drilled about 5 miles to the 

west show that the Jelm in that area is about 125 

feet thick.

SUNDANCE FORMATION

The Sundance Formation was named by Darton 

(1899) from exposures of shale and thin-bedded 

sandstone of Late Jurassic age in the Black Hills of 

South Dakota. Subsequently, the name was applied 

to rocks of similar lithology and age in eastern and 

central Wyoming. Lee (1927) noted the similarity 

between the lowest sandstone beds in the Sundance 

Formation and the entire Nugget Sandstone of 

southwestern Wyoming, and Bartram (1930), Imlay (1947), Pipiringos (1948), and others correlated 

the two sandstone units. Love, Denson, and Botinelly 

(1949) questioned the correlation and showed that a 

marked unconformity separates the lowest sandstone 

beds of the Sundance from the Nugget Sandstone. 

Pipiringos (1968), in part following Imlay's (1947) 

nomenclature in the Black Hills, recognized seven 

members for the Sundance Formation and described 

in detail the widespread erosion surface, almost
STRATIGRAPHY, MESOZOIC 15

everywhere characterized by chert pebbles, that 

separates the Sundance Formation from the underlying rocks.

The Sundance Formation in the eastern part of 

the Shirley Basin area is about 250 feet thick, as 

shown by the width of outcrop and by electric logs 

of wells. The Sundance is poorly exposed on the 

surface; the best exposures are in sec. 13, T. 27 N., 

R. 77 W., and sec. 28, T. 28 N., R. 77 W. Six of the 

seven members of the Sundance can be identified in 

sec. 13.

As mentioned in the discussion of the Jelm Formation, the chert pebbles that mark the contact between the Jelm and the overlying Canyon Springs 

Sandstone Member (lowest member) of the Sundance Formation were not found, and without them 

the precise position of the contact cannot be determined. As mapped (Harshman, 1968b), the Canyon 

Springs is about 25 feet thick and comprises a 

sequence of white to buff fine- to medium-grained 

crossbedded sandstone beds that contain rounded 

quartz and chert grains. In the southern part of the 

area, the sandstone is massive and friable and is 

similar to the Canyon Springs 10 miles to the south, 

where the member is about 27 feet thick (G. N. 

Pipiringos, oral commun., 1967). In sec. 13, T. 27 

N., R. 77 W., the sandstone beds are highly indurated and slabby, and are thus atypical. The cementation probably is due to downward migration of silica 

leached from the White River Formation. The electric log of a drill hole 7 miles to the west shows the 

Canyon Springs Member to be about 45 feet thick 

in that area.

The Stockade Beaver Shale Member has not been 

definitely recognized on the surface in the Shirley 

Basin, and possibly it is not present in the outcrop 

area. It is identifiable on the log of a well drilled in 

sec. 14, T. 27 N., R. 78 W., and it may crop out in the 

creek near the SE. cor. sec. 13, T. 27 N., R. 77 W. 

However, this area was disturbed by considerable 

faulting, and the greenish-yellow shale and siltstone 

in thi3 small exposure may be a part of the Pine 

Butte Member of the Sundance Formation. A 35- 

foot-sequence of greenish-gray shale and siltstone, 

interbedded with thin sandstone and limestone, exposed in the Freezeout Hills 12 miles southwest of 

the Shirley Basin, was considered by Pipiringos 

(1957) to be Stockade Beaver. He now (oral commun., 1969) considers these strata to be part of the 

Hulett Sandstone Member. On the log of the well 

in sec. 14, the Stockade Beaver is about 25 feet 

thick.

The Hulett Sandstone, Lak, and Pine Butte Members of the Sundance are poorly exposed in sec. 13,

T. 27 N., R. 77 W., and faults and associated dip 

changes hamper estimation of exposed thicknesses of 

the separate members. Their combined thickness is 

estimated to be about 80 feet. In the well drilled in 

sec. 14, 7 miles to the west, the combined thickness 

is about 78 feet. The Hulett Sandstone Member comprises a sequence of beds of fine- to medium-grained 

calcareous buff to white sandstone that contains 

many subrounded to rounded and frosted sand 

grains and some glauconite. A few beds are ripple 

marked. The Lak Member is similar to the Hulett in 

the physical character of the rocks, but has a very 

distinctive pink or orange-red color, discernible even 

where moderate soil cover obscures the bedrock. 

The Pine Butte Member comprises a sequence of 

buff to white fine- to medium-grained calcareous 

sandstone strata interbedded with greenish-gray 

shale. The sandstone is ripple marked, and some 

beds contain glauconite and fossil trails of crawling 

organisms.

The Redwater Shale Member is fairly well exposed in the Shirley Basin area, particularly in 

small gullies that cut the gentle slopes characteristic 

of this member. It comprises a series of greenishor yellowish-gray thin-bedded shale and siltstone 

beds containing some interbedded limy sandstone 

and limestone concretions. The limestone concretions are in the more shaly beds whereas the limy 

sandstone occurs with the siltstone. At least two 

limestone strata composed largely of coquina shells 

are present in the upper part of the Redwater, and 

belemnites are common in the lower part. The Redwater is about 100 feet thick in the outcrop area 

and in the well drilled in sec. 14.

The Windy Hill Sandstone Member of the Sundance Formation is 8-10 feet thick and comprises a 

sequence of medium-grained thin-bedded oolitic buff 

to gray sandstone layers which are generally ledge 

forming and ripple marked. Regional studies by 

Pipiringos (1968) show that this member rests 

disconformably on the underlying Redwater Shale 

Member of the Sundance Formation.

MORRISON FORMATION

The name Morrison Formation was first used by 

Eldridge in Emmons, Cross, and Eldridge (1896) to 

describe a 200-foot-thick sequence of fresh-water 

marl beds of Late Jurassic age exposed in the 

vicinity of Denver, Colo.; the type locality is near 

the town of Morrison. The name is now used for 

rocks of similar age and lithology in an area extending from Oklahoma and Arizona north to South 

Dakota and Montana.
16 GEOLOGY AND URANIUM DEPOSITS, SHIRLEY BASIN AREA, WYOMING

In the Shirley Basin, the Morrison Formation is 

about 200 feet thick and comprises a sequence of 

nonmarine clayey siltstone, siltstone, and finegrained sandstone strata. The contacts with the 

underlying Windy Hill Sandstone Member of the 

Sundance Formation and with the overlying lower 

sandstone unit of the Cleverly Formation are 

conformable.

The formation is poorly exposed or covered by 

Tertiary rocks. The best exposures are on the steep 

back slopes of the Cleverly hogbacks in the southeastern part of the mapped area. Here, the lower 

20 feet of the Morrison consists of buff slightly calcareous medium-grained sandstone interbedded with 

buff to yellow siltstone. The sandstone and siltstone 

are ripple marked; the siltstone contains mud 

cracks. An upper unit, about 180 feet thick, consists of clayey siltstone which is generally dark gray 

with a greenish cast but contains a few green, 

maroon, and red zones. Interbedded with the siltstone are thin lenticular beds of fine-grained limestone, almost lithographic, and thin zones of brown 

and buff concretions.

The upper few feet of the Morrison Formation, 

in the few places where not covered with talus from 

the overlying cliff-forming sandstones of the Cloverly Formation, is in sharp contact with the Cleverly.

CLOVERLY FORMATION

The Lower Cretaceous Cleverly Formation, first 

described by Barton (1904) from outcrops in the 

Bighorn Basin near Cleverly, Wye., is well exposed in the Shirley Basin area. It is divisible into 

three major stratigraphic units which, though not 

shown separately on the geologic map of the area, 

(Harshman, 1968b), are easily distinguishable on 

the surface and on subsurface resistivity logs. A 

complete section of Cleverly is exposed along Spring 

Creek in the western part of sees. 6 and 7, T. 26 N., 

R. 76 W., just south of the southeast corner of the 

mapped area. There the lower unit rests on Morrison 

siltstone with a sharp conformable contact. It is 

about 93 feet thick, and its basal part comprises 30 

feet of white to buff fine- to medium-grained somewhat friable sandstone having a few conglomerate 

interbeds containing pebbles as much as 2 inches in 

diameter. The sand grains are subrounded to 

rounded, and many are frosted. Some of the sandstone is crossbedded (fig. 9). Chert pebbles are common in the lower 20 feet of the sandstone. Individual 

beds range in thickness from a few inches to several 

feet, and bedding is irregular. Although all of this 

sandstone was mapped as Cloverly, the basal few

feet may belong in the underlying Morrison Formation, for similar sandstones are present at the top of 

the Morrison in areas southwest of the Shirley Basin.

FIGURE 9. Crossbedded sandstone near base of. Cloverly 

Formation, SW% sec. 6, T. 26 N., R. 76 W.

Overlying the somewhat friable sandstone is about 

45 feet of massive cliff-forming tan sandstone that 

is medium to fine grained, well cemented, and 

slightly crossbedded. The sand grains are rounded, 

some are frosted. The top of the lower sandstone 

unit comprises a 15- to 20-foot-thick sequence of 

well-bedded buff quartzose fine- to medium-grained 

well-cemented sandstone. Some of these sandstone 

beds grade laterally into carbonaceous shale.

The middle unit is about 20 feet thick and comprises, from the bottom upward, a sequence of 

fissile dark-gray carbonaceous shale and interbedded 

silty sandstone; fine-grained crossbedded well-cemented buff sandstone; and dark-gray fissile to 

blocky shale containing hard indurated claystone 

beds, thin bentonitic beds, and concretionary ironstone. Mud cracks and ripple marks are common 

(fig. 10). Changes in thickness of the middle unit 

occur where the lower shale beds are replaced by 

sandstone.

The uper unit is about 37 feet thick and consists 

of fine- to medium-grained white to buff quartzose 

sandstone in beds that range in thickness from 2 

inches to 2 feet.

Resistivity logs from wells drilled in sees. 12 and 

14, T. 27 N., R. 78 W., show that the Cloverly in 

that area has thickened to as much as 200 feet, 

principally owing to thickening of the sandstone 

in the lower unit.
STRATIGRAPHY, MESOZOIC 17

FIGURE 10. Ripple-marked mudstone characteristic of the 

upper part of the middle unit of the Cleverly Formation in 

the Shir ley Basin area, NW% sec. 24, T. 27 N., R. 77 W.

THERMOPOLIS AND MOWRY SHALES

The Thermopolis and Mowry Shales were not 

differentiated in the geologic mapping of the Shirley 

Basin area, although these formations can be recognized on electric logs of wells and in exposures near 

the Cram Ranch a mile or so south of the southeast 

corner of the mapped area (Harshman, 1968b). 

Neither formation is well exposed in the mapped 

area, and the descriptions that follow are based on 

the Cram Ranch exposures.

The Thermopolis Shale was named by Lupton 

(1916) from exposures of shale and sandstone near 

the town of Thermopolis, Wyo. As then defined, the 

Thermopolis was considered to be of Late Cretaceous 

age. It was overlain conformably by the Mowry 

Shale and underlain conformably by the Cleverly 

Formation. It is now known to be of Early Cretaceous age. The name "Mowrie beds" was first used 

by Darton (1904) to describe a sequence of hard 

light-gray shale and thin-bedded sandstone strata 

exposed on the east side of the Bighorn Mountains 

in Johnson County, Wyo. Darton included the 

Mowrie (now Mowry) beds in the Benton Formation. The Mowry was also considered to be of Late 

Cretaceous age, but it is now known to be of Early 

Cretaceous age. The Muddy sand, formerly of 

drillers' terminology, is considered to be a formal 

unit, the Muddy Sandstone Member of the Thermopolis Shale (Hintze, 1915).

In the Shirley Basin area the comformable contact 

between the Cleverly Formation and the overlying

Thermopolis Shale is marked by a 3-foot-thick zone 

of gradation from ripple-marked fine-grained buff 

sandstone through shaly thin-bedded gray finegrained sandstone to black fissile shale. That part 

of the Thermopolis that underlies the Muddy Sandstone Member comprises dark-gray to black fissile 

carbonaceous shale of marine origin. It is about 60 

feet thick in the Cram Ranch area, and 19 feet above 

the base it contains a 2-foot-thick bed of radiating 

acicular aragonite crystals. The Thermopolis Shale 

underlying the Muddy Sandstone Member in a well 

in sec. 14, T. 27 N., R. 78 W., is about 55 feet thick.

The black fissile Thermospolis Shale is overlain by 

a 6-foot-thick zone of silty thin-bedded sandstone 

that weathers gray to buff and an 8-foot-thick irregularly bedded medium- to fine-grained buff to 

light-gray silty sandstone the Muddy Sandstone 

Member of the Thermopolis Shale. Individual beds 

range in thickness from a fraction of an inch to 6 

inches, are well indurated, and generally form 

ledges. Some exposures contain ripple marks.

Overlying this sandstone are brownish-gray thinbedded fine-grained silty sandstone beds interbedded with thin-bedded siltstone and shale. The 

siltstone contains some carbon flecks and a few 

pyrite crystals. The rocks in this interval, which is 

approxima'tely 50 feet thick, are poorly indurated, 

underlie low flat areas, and have few outcrops. At 

the top of this sequence is a 2-foot-thick bed of silty 

lignite associated with several thin limy sandstone beds that contain mud cracks and what look 

like root tubes. This 50-foot-thick sequence of beds 

appears to be of paludal origin and is considered to 

be part of the Thermopolis Shale, although some of 

the sandy beds near the base of the sequence may 

be properly included in the Muddy Sandstone 

Member.

Overlying the lignite is a transitional zone, about 

60 feet thick, comprising sandy siltstone and silty 

shale interbedded with typical dense siliceous Mowry 

Shale. In this zone the amount of siltstone and silty 

shale decreases upward. These strata are arbitrarily 

included in the upper part of the Thermopolis, and 

thus the total thickness of the Muddy Sandstone 

Member and the upper part of the Thermopolis Shale 

is about 125 feet.

The Mowry Shale is about 110 feet thick in the 

Shirley Basin area. It is a gray dense siliceous laminated shale which contains abundant marine fish 

scales and is interbedded with bentonite beds as 

much as 2-3 feet thick, some of which retain a shaly 

structure. Associated with some of the bentonite 

are shale beds as thick as 6 inches that contain considerable calcium carbonate.
18 GEOLOGY AND URANIUM DEPOSITS, SHIRLEY BASIN AREA, WYOMING

The Mowry Shale is resistant to erosion and generally forms long narrow ridges which weather 

yellow or off-white and are contorted by surface 

creep or incipient landsliding. Large blocks of Mowry Shale, their slide planes lubricated by bentonite, 

slid as much as one-half mile on the steep pre-Wind 

River erosion surface. They are now partly buried 

by Tertiary clastic rocks.

FRONTIER FORMATION

The Frontier Formation, a name used by Knight 

(1902) for rocks exposed in southwestern Wyoming 

near the town of Frontier, comprises a sequence of 

dark-gray carbonaceous shale, silty shale, and sandstone strata underlain by the Mowry Shale and 

overlain by the Niobrara Formation. It is Late Cretaceous in age.

Exposures of the Frontier are poor in the Shirley 

Basin area, for the soft nature of the formation gives 

rise to a rolling grass-covered terrain. The hard 

siliceous Mowry Shale crops out in prominent ridges, 

and where these ridges are cut by small gullies the 

lower few feet of the Frontier is exposed in sharp 

contact with the Mowry Shale. In some areas the 

basal 5 feet of the formation consists of reddish- or 

purplish-gray siltstone and sandy siltstone, in part 

concretionary, and containing considerable siderite 

or hematite. The beds are 1-2 inches thick. In 

other areas the ironstone is not present, and the 

basal part of the Frontier consists of gray thinbedded silty sandstone and shale. Generally within 

5-10 feet above the base of the formation the typical 

dark-gray thin-bedded shale predominates.

Data from electric logs of wells drilled in the area 

and from the few poor exposures along ridges and 

gullies indicate that the lower part of the Frontier 

Formation is principally dark-gray carbonaceous 

thin-bedded shale and that the upper part is similar 

shale interbedded with gray to brownish-gray fineto medium-grained thin-bedded sandstone.

At the top of the Frontier Formation is a series 

of fine- to medium-grained sandstone beds that 

weather buff to greenish gray and are interbedded 

with dark-gray shale. These beds constitute the Wall 

Creek Sandstone Member of the Frontier Formation. 

The sandstone beds near the top of the Wall Creek 

Member crop out in a tributary of Slate Draw in 

sec. 32, T. 27 N., R. 77 W. At this place they are 

medium to coarse grained, siliceous, greenish brown, 

and slabby to crossbedded and contain considerable 

biotite and an occasional glauconite grain. The sandstone is cemented by calcium carbonate, silt, and 

clay. These beds are resistant to erosion and generally form a conspicuous ridge both on the present 

surface and on the surface now buried by Tertiary 

rocks. Although sandstone blocks cover the ground 

surface, outcrops along the ridge are poor. Electric 

logs of wells drilled in the area show the Wall 

Creek Member to be about 110 feet thick. Data from 

the width of outcrop, the dip of the beds, and electric 

logs of wells indicate a total thickness of 860 

feet for the Frontier Formation.

NIOBRARA FORMATION

The name Niobrara Formation was first used by 

Meek and Hayden (1862, p. 418-423) to identify 

a sequence of limy shale strata exposed along the 

Missouri River near the mouth of the Niobrara 

River in Knox County, Nebr. The formation is of 

Late Cretaceous age.

In the Shirley Basin area the Niobrara Formation 

crops out only in the SW. cor. T. 27 N., R. 77 W., 

where erosion has stripped the cover of Tertiary 

rocks. The formation weathers readily and is poorly 

exposed in isolated spots along Slate Draw and the 

Little Medicine Bow River. The contact of the 

Niobrara and the underlying Wall Creek Sandstone 

Member of the Frontier Shale is not exposed, but in 

Slate Draw, about 150 feet downstream from the 

approximate position of the contact (equivalent to 

about 10 ft stratigraphically above the base of the 

formation), the Niobrara consists of dark-gray thinbedded noncalcareous clay shale, some of which is 

fissile. About 500 feet downstream from the contact, 

the Niobrara contains some thin limy sandstone beds 

intercalated in the thin shale beds. About 1,500 feet 

downstream (120 ft stratigraphically above the base 

of the formation), typical thin-bedded to fissile 

silvery-gray calcareous spotted shale beds are exposed.

Cuttings from exploratory drill holes indicate that 

the upper part of the Niobrara Formation consists 

principally of black calcareous shale, in some places 

tending to be fissile and exhibiting the small white 

spots characteristic of the so-called spotted shale. 

However, some of the upper shale seems to be noncalcareous. The contact between the Niobrara Formation and the overlying Steele Shale is not exposed 

in the mapped area, but data from electric logs of 

wells indicate that the Niobrara Formation in the 

Shirley Basin area is about 900 feet thick.

STEELE SHALE

The Steele Shale, named by Darton, Blackwelder, 

and Siebenthal (1910) from exposures along the
STRATIGRAPHY, CENOZOIC 19

North Platte River near Fort Steele in Carbon 

County, Wyo., underlies most of Bates Hole, and 

it crops out along the southwest edge of the mapped 

area. The Steele may be divided into a lower 

part that consists principally of thin-bedded to 

fissile dark-gray clay shale having minor amounts 

of lenticular sandstone and dark-brown concretionary sandy ironstone and an upper part in which a 

considerable amount of lenticular sandstone is interbedded with the shale. The upper, sandstonebearing part is exposed only along the south edge 

of the mapped area, near the synclinal axis, where 

the cover of rocks of Tertiary age has been removed 

by erosion. The sandstone is light gray, tan weathering, poorly sorted, siliceous, medium grained, and 

calcite cemented. Many of the sandstone beds contain invertebrate fossils; it was from a sandstone 

ledge in the NW^SE^SW^ sec. 35, T. 27 N., R. 

79 W., that the Late Cretaceous ammonite Hoplitoplacenticeras was taken (Cobban, 1963). This is the 

only known record of this genus in the Western 

Interior of the United States.

The Steele Shale is very soft and easily eroded. 

It is generally covered with a soft puffy soil mantle 

which obscures the character and attitude of the 

underlying rock. Landslides ranging from small to 

very large are common in this incompetent shale.

Cretaceous formations younger than the Steele 

Shale have not been recognized in the Shirley Basin 

area, and if they were ever present in the region, 

they have been removed by erosion. The maximum 

remaining thickness of Steele Shale is probably in 

the general area of the syncline shown on the geologic map (Harshman, 1968b) ; there it may range 

from 1,500 to 2,000 feet.

CENOZOIC

FORT UNION (?) FORMATION

Rocks of Paleocene age have not been identified 

in the Shirley Basin, but they may be present in 

the southern part of the mapped area. A sequence 

of varicolored soft sandy siltstones, in part carbonaceous, is exposed in a landslide block at the south 

edge of the area in sees. 4 and 5, T. 26 N., R. 79 W. 

Similar sandy siltstones were noted in drill cuttings 

from an exploratory hole about 3 miles to the east 

in sec. 36, T. 27 N., R. 79 W. In both places the 

varicolored rocks fill channels eroded in Steele Shale 

and are overlain by Wind River rocks of contrasting 

physical appearance. The rocks do not contain ancient pollen, and no other fossils have been found in 

them. Studies of the meager heavy minerals from

three samples were inconclusive but do not rule out 

the possibility that these rocks are remnants of the 

Fort Union Formation deposited in stream channels 

and protected from the extensive erosion that preceded deposition of the Wind River Formation. The 

maximum thickness of these rocks is about 50 feet.

WIND RIVER FORMATION

The terms "Wind River deposits" and "Wind River 

group" were first used by Meek and Hayden (1862, 

p. 433, 447) to identify a series of beds of continental origin exposed in the Wind River Basin and to 

the west of the Wind River Range. These beds were 

provisionally placed above the "Fort Union" or 

"Great Lignite Group" and below the "White River 

group." St. John (1883, p. 228) first used the term 

"Wind River formation," and Sinclair and Granger 

(1911, p. 104-105) divided the formation into the 

Lysite (lower) and Lost Cabin (upper) Members, 

lithologically and faunally distinct units in the 

northeastern part of the Wind River Basin.

The Wind River sediments were deposited in a 

basinlike depression eroded in rocks of Paleozoic 

and Mesozoic age. The position of the depression was 

controlled to some extent by the position of a 

synclinal axis about 10 miles west of and approximately parallel to the axis of the depression.

The pre-Wind River basin had considerable relief 

and was drained by a well-developed system of major 

and tributary streams. The trunk stream, probably 

a tributary of the ancestral North Platte River, 

drained northwestward through the basin along a 

line extending from the northeastern part of T. 

26 N., R. 78 W., through the center of T. 27 N., 

R. 78 W., and the southwestern part of T. 28 N., 

R. 78 W., to the northeastern part of T. 28 N., R. 

79 W. Major tributaries originated far to the west 

on the flank of the newly formed Granite Mountains 

and to the east on the flank of the young Laramie 

Mountains. Locally, relief on the old surface was as 

much as 300 feet in a lateral distance of about onefourth mile, and over broad areas relief was as much 

as 1,500 feet in 12 miles.

The erosion surface is probably of Laramide age, 

but the age cannot be precisely determined from 

data gathered during this investigation. The surface 

was cut in rocks as old as Late Cretaceous (Steele 

Shale), and it is buried beneath rocks as young as 

early Eocene (Wind River). Although the basin 

configuration was probably established before deposition of the Wind River Formation, erosion on 

the basin flanks took place concurrently with deposition on the basin floor. Thus, the. old erosion

464-170 O - 72 - 4
20 GEOLOGY AND URANIUM DEPOSITS, SHIRLEY BASIN AREA, WYOMING

surface becomes progressively younger with increasing height on the basin flanks. The term "preWind River erosion surface" is used, however, for 

the sake of brevity and because post-Wind River 

erosion probably caused only a slight modification of 

the pre-Wind River erosion surface.

Abrupt changes in lithology and thickness are 

characteristic of the Wind River Formation in the 

Shirley Basin. The thickest section is along a northwesterly trending zone in the central part of the 

basin where 450-550 feet of siltstone and sandstone 

overlies a major valley on the pre-Wind River erosion surface. In and near this zone the Wind River 

Formation consists of interbedded fine- and coarsegrained rocks, in about equal amounts, interbedded 

with considerable lignitic material. Westward the 

formation thins, as the old erosion surface rises, and 

the proportion of coarse clastic debris increases as 

the source of the sediment is approached. Eastward 

the formation thins rapidly as it laps on the steep 

flank of the Laramie Mountains. Lithologic data, 

though scanty, suggest that the Wind River does 

not coarsen as it laps eastward on the older rocks.

In the Shirley Basin the Wind River Formation 

is widespread and has great economic importance. 

It underlies or crops out in about two-thirds of the 

mapped area and it is the host for the uranium 

ore deposits. The Lysite and Lost Cabin Members 

of the Wind River Formation cannot be recognized 

lithologically in the Shirley Basin area, nor can 

they be distinguished on the basis of the fossil 

vertebrates and plants collected during this investigation.

The Wind River Formation crops out over most of 

the south half of the area investigated, but exposures 

are generally poor owing to the friable nature of 

the rocks, the low-rolling topography, and the sand 

and soil at the surface. Fair natural exposures are 

present along the south edge of the basin, where 

the lower part of the Wind River crops out in an 

erosional escarpment locally known as the "south 

rim." Fair natural exposures also occur along the 

south edge of Bates Hole, in the west-central part 

of the area, where Stinking Creek has exposed and 

eroded the Tertiary rocks in the steep walls of the 

hole. Two mine pits, one in sec. 9 and the other 

in sec. 15, T. 27 N., R. 78 W., expose a considerable 

part of the Wind River Formation in the central 

part of the Shirley Basin. The general character 

of the rocks throughout the basin can be determined 

from cuttings and resistivity logs of exploratory 

drill holes.

In the southwestern part of the area, along the 

south rim, the lower part of the Wind River Formation consists principally of a gray boulder conglomerate and coarse arkosic sandstone that weathers 

buff to rusty yellow. Drill cuttings indicate that a 

few silty interbeds, generally greenish gray and 

rarely purplish red, are present in areas a few miles 

north of the south rim. There is little or no cement 

in the coarse clastic debris, and it might properly 

be called sand, gravel, and boulders. The silty rocks 

have some clay binder, but they are not indurated; 

they have been compacted by the weight of the 

rocks which once overlay the area.

The gravel, cobbles, and boulders in the conglomerate are well rounded, and boulders are as much 

as 7 feet in diameter, although those more than 3 

feet in diameter are rare. The large boulders are 

Precambrian granite; the smaller ones are granite 

or Paleozoic and Mesozoic quartzite, chert, sandstone, limestone, siliceous shale, or other types of 

indurated rock that in early Eocene time flanked 

the granite cores of the mountain ranges. A few 

small boulders of Precambrian diabase are also in 

the conglomerate, but without exception they are 

intensely weathered and disintegrate with the slightest blow of a hammer.

At the west edge of the mapped area, and for 

about 10 miles eastward along the south rim, the 

conglomerate is at or very close to the base of the 

Wind River Formation. Where not at the base, the 

conglomerate overlies silty material that fills small 

stream channels on the pre-Wind River erosion 

surface. Farther to the east the lower part of the 

Wind River Formation laps on the flank of the basin, 

and an increasingly thick wedge of silty shale separates the conglomerate from the base of the Wind 

River Formation.

At the south edge of Bates Hole, particularly 

along State Highway 487, outcrops are principally 

in a coarse-grained sandy facies of the Wind River 

Formation. A basal conglomerate, of well-rounded 

gravel and boulders as much as 3 feet in diameter 

composed of granite and of indurated rocks of 

Paleozoic and Mesozoic age, rests on the eroded 

surface of the Steele Shale. The conglomerate is 5- 

15 feet thick in the outcrops examined. In most 

places the conglomerate is overlain by 100-200 feet 

of sandstone and some interbedded conglomerate, 

but in a few places considerable siltstone is present 

in this lower interval. The upper 100-200 feet of 

the Wind River Formation in this area contains 

considerable clayey siltstone, generally in beds 5-20 

feet thick intercalated with sandstone. Most of the 

siltstone is greenish gray, but toward the top of 

the sequence some is reddish brown or light red.

The Wind River Formation has a maximum thickness of about 425 feet at the south end of Bates 

Hole. Northward it maintains its lithologic char-
STRATIGRAPHY, CENOZOIC 21

acter, but it thins as it laps on a ridge on the preTertiary erosion surface. The minimum thickness on 

the east side of Bates Hole is probably about 15 

feet, in sec. 27, T. 29 N., R. 80 W., where the 

formation is almost totally obscured by extensive 

landslide blocks of the overlying White River siltstone. On the west side of Bates Hole, in sec. 3, 

T. 28 N., R. 81 W., west of the mapped area, the 

Wind River Formation thins in a similar manner.

On the flat-topped ridge just north of Lawn Creek, 

sec. 8, T. 29 N., R. 80 W., the Wind River basal 

conglomerate contains granite boulders as much as 

26 feet in greatest dimension (fig. 11). They are 

exposed along the edge of the ridge for about 1 

mile and were apparently deposited on, and slightly 

above, a pre-Wind River erosion surface that now 

has a northeasterly dip of about 15 feet per mile. 

The dip of this surface was probably not much 

greater at the time of deposition of the boulders.

FIGURE 11. Large granite boulders in basal conglomerate of ' 

Wind River Formation, overlying Steele Shale, in Bates 

Hole, sec. 8, T. 29 N., R. 80 W. The nearly flat erosion 

surface on Steele Shale (Ks) is overlain by rocks of Tertiary (Tr) age (right center).

About 2 miles to the west, in sees. 11 and 12, T. 29 

N., R. 81 W., similar boulders are found in the basal 

conglomerate of the Wind River Formation. Between 

the two localities the Wind River Formation has 

been eroded, but it is assumed that at one time the 

boulders extended continuously for at least 3 miles, 

perhaps much more. The boulder outcrop pattern is 

sinuous and about 300 feet wide. The nearest granitic sources are now about 10 miles to the northeast 

and 14 miles to the southwest; they were at least 

that distant in early Eocene time when the boulders

were transported and deposited. The boulders were 

apparently carried by streams flowing eastward 

from the Granite Mountains; however, their size 

and their distance from the source are difficult to 

reconcile with the low stream gradients believed 

to have been extant at the time of their deposition. 

There is no evidence that they were carried in 

mudflows.

The best exposures of the Wind River Formation 

in the Shirley Basin area are in the Petrotomics Co. 

open pits, one in sec. 9, and the other in sec. 15, T. 27 

N., R. 78 W. The Section 9 pit exposes about 160 

feet of strata in the upper part of the formation, 

in an interval from about 100 feet to about 260 

feet below the reconstructed Wind River-White 

River contact. A measured section of this exposure 

follows:

Measured section, north wall, phase 2,1 Petrotomics Co. 

Section 9 pit

Feet 

Top of exposure.

Wind River Formation:

1. Clayey siltstone, buff to yellow, light-brown,

olive-green .-. . ... ._......... ....... ... 12.0

2. Clayey siltstone, dark-brown, yellow, lignitic,

gypsiferous; a few thin sandy gray interbeds 4.9

3. Sandstone, fine- to medium-grained, poorly 

cemented, buff; a few thin lignitic clay 

interbeds .. ._ __............ ........_......... .... 5.5

4. Clayey siltstone, yellowish-green to bluish-gray;

a few thin gypsiferous beds and lignitic beds.... 13.8

5. Clayey siltstone, greenish- and bluish-gray.......... 10.7

6. Sandstone, medium-grained, poorly cemented,

yellow; trace of carbon.......................................... 5.5

7. Clayey siltstone, gray-green; trace of carbon........ 19.9

8. Siltstone, yellowish-green.......................................... 5.6

9. Silty claystone and siltstone, gray and

dark-green ......................................... .................. 13.0

10. Claystone, red, blocky...............-......... ................... 1.3

11. Silty claystone, gray-green........................................ 2.4

12. Silty claystone, reddish-purple to yellowishgreen, blocky.......... ..................... .......... .......... 6.9

13. Siltstone and silty claystone, greenish-gray.......... 25.4

14. Silty claystone, red, orange..... .............................. 2.7

15. Sandy siltstone, gray, pyritic; slight

CaC03 cement................................................. 3.2

16. Sandstone, unaltered, gray, pyritic, mediumto very coarse-grained; in part crossbedded; 

compacted but uncemented. Carbonaceous 

material chiefly on cross beds. This is the 

upper ore-bearing sandstone . 30.0

Total measured Wind River Formation .162.8 

Bottom of exposure.

1The pit was excavated in 10 separate units termed "phases."

The Petrotomics Co. Section 15 pit exposes about 

185 feet of strata in the interval about 200-385 feet 

below the top of the Wind River Formation. A 

composite section on the west wall of this exposure 

follows:
22 GEOLOGY AND URANIUM DEPOSITS, SHIRLEY BASIN AREA, WYOMING

Measured section, west wall, Petrotomics Co. Section 15 pit

Feet

Top of exposure. 

Wind River Formation:

1. Topsoil, brown, sandy.. ........................................... 3.0

2. Gravel, pink; 1%-in. maximum diameter.............. .5

3. Sandstone, very coarse grained, poorly

cemented, greenish-yellow..... .............................. 6.0

4. Claystone, silty, yellowish-green; contains 

lenses of poorly cemented very coarse 

grained sandstone.................................................... 15.0

5. Sandstone, siliceous, poorly cemented, yellow;

gravel as much as 3 in. in diameter.................... 4.0

6. Silty claystone, green; interbedded with

brown lenticular lignite beds. ......................... 4.0

7. Sandstone, very coarse grained, crossbedded, 

yellow to buff; some gravel as much as 1 in. 

in diameter; channels cut in upper part............ 22.5

8. Clayey siltstone, dense, blocky, gray-green............ 15.0

9. Lignite, silty, dark-gray............................................ 6.5

10. Claystone, silty, blocky, green; sandy in

lower third................................................................ 17.5

11. Sandstone, medium- to very coarse-grained, 

silty, crossbedded, gray; calcite cement 

in top beds-.... ....................................................... 10.5

12. Lignite, silty, dark-gray............................................ 1.5

13. Claystone, silty, blocky, green; sandy in

some beds.................................................... ........... 21.0

14. Sandstone, very coarse grained, poorly

cemented, crossbedded, gray.................................. 10.5

15. Lignite, silty, dark-gray............................................ 1.0

16. Siltstone, clayey, greenish-gray; interbedded 

in lower half with fine-grained gray 

sandstone .................................................................. 14.0

17. Sandstone, very coarse grained, crossbedded, 

pyritic, carbonaceous, uncemented, gray. 

This is the lower ore-bearing sandstone............ 33.5

Total measured Wind River Formation .......186.0

Bottom of pit.

Both pits are in a belt that overlies the lowest 

part of the pre-Wind River erosion surface, an area 

that apparently remained topographically low as the 

basin gradually filled with Wind River sediments. 

In periods of low water, sand and silt were deposited 

in the area in stream channels and as overbank 

deposits, and decaying vegetation accumulated in 

transitory swamps. In periods of high water, large 

channels were cut in the newly deposited sediment, 

later to be filled with crossbedded sand and gravel. 

Figures 12, 13, and 14 show the general character 

of this material after compaction and slight lithification.

The sandstone in this part of the basin is poorly 

sorted and medium to very coarse grained and is 

composed principally of quartz and potassium feldspar (orthoclase and microcline) in about equal 

amounts. It contains an average of about 2.5 percent by weight of heavy minerals and a few percent 

clay, principally montmorillonite and kaolinite.

FIGURE 12. Southeast wall, phase 7, Petrotomics Co. Section 

9 pit, showing: lignite (li) and siltstone (si) in upper part 

of wall, large sand-filled channel (chs) cut in silty sandstone 

(sis) and lignite (li), and altered ore-bearing sandstone 

(obs) of Wind River Formation in lower part of pit 

sec. 9, T. 27 N., R. 78 W.).

FIGURE 13. Northwest wall, Petrotomics Co. Section 15 pit, 

showing lignite (li), siltstone (si), silty sandstone (sis), 

sandstone (ss), and ore-bearing sandstone (obs) of Wind 

River Formation (NE^i sec. 15, T. 27 N., R. 78 W.).

About 100 feet of strata which once overlay the 

exposures in the Section 9 pit is exposed in small 

gullies and bluffs in sees. 3 and 4, T. 27 N., R. 78 W., 

north of the pit, and on the west side of the Petrified 

Forest area in sees. 11,12, 13, and 14, east of the pit. 

North of the pit the rocks are predominantly silty 

shale, interbedded with minor amounts of sandstone
STRATIGRAPHY, CENOZOIC 23

and, near the top of the formation, siliceous pebble 

conglomerate. Generally the siltstone contains considerable lignite and the petrified trunks of trees as 

much as 3 feet in diameter. The lignitic material 

weathers to a dark reddish brown with orange and 

purple tones, a color characteristic of this interval. 

The strata in the Petrified Forest area are somewhat 

sandier than those in sees. 3 and 4 but are characterized by the same strong colors, lignitic siltstone, and 

petrified trees.

Data from exploratory drilling in and near the 

Section 15 pit show that the interval of Wind River 

Formation between the bottom of the pit and the 

underlying Niobrara Formation comprises sandstone, conglomerate, and very minor amounts of 

shaly siltstone.

FIGURE 14. Contorted lignite in west wall of Petrotomics 

Co. Section 15 pit. Because overlying beds are undisturbed, 

contortion is probably due to compaction and flowage of 

lignitic material shortly after deposition. (NE1^ sec. 15, 

T. 27 N., R. 78 W.)

Rocks in the southeastern part of T. 27 N., R. 

78 W. contrast with the characteristic heterogeneous mixture of fine- and coarse-grained rocks of 

most of the central part of the Shirley Basin. In 

this area the entire Wind River Formation, as much 

as 300 feet thick, is composed of medium to very 

coarse grained sandstone having few or no siltstone 

partings. Several large tributary streams, flowing 

down the west flank of the early Tertiary basin, 

joined the trunk stream in this area, and sand was 

probably deposited when the carrying power of the 

water decreased abruptly where the tributary 

streams joined the trunk stream.

The Wind River Formation in the Shirley Basin 

is characterized by yellow-weathered sandstone outcrops, greenish-gray shale, significant amounts of 

lignite in the shale and coalified material in the

sandstone, a lack of volcanic constituents in the 

clastic rocks, and the almost complete absence of 

diabase in the conglomerate. In the central part of 

the basin the conglomerate contains no diabase, and 

the pebbles are composed principally of dense siliceous rock. On the flanks of the basin near the 

source of the detritus, the conglomerate contains 

cobbles of intensely weathered diabase and moderately weathered coarse-grained granitic rocks. In 

contrast, the White River and younger formations 

throughout the basin contain fresh hard pebbles, 

cobbles, and boulders of coarse-grained diabase and 

granitic rocks. The degree of weathering and disintegration of the coarse-grained rocks probably 

reflects climatic differences at the time of deposition 

of the various formations moist, semitropical in 

early Eocene time, becoming semiarid in late Oligocene time.

The conglomerate gradually changes in composition from the base of the Wind River Formation 

upward. Most conglomerate beds in the basal part 

of the formation contain cobbles and boulders 

from the dense sedimentary units of the Paleozoic 

and Mesozoic formations, and in a few places the 

conglomerate is composed almost entirely of these 

rocks. With increasing distance above the base of 

the formation, the amount of granitic material increases, and the granitic material becomes the 

principal constituent in the conglomerate at the 

top of the formation. This gradual change in the 

lithology of the conglomerate reflects the gradual 

erosion of the sedimentary rocks from the flanks 

of the granite cores and the exposure of the cores 

in the uplifts bordering the Shirley Basin as well 

as the gradual burial of the sedimentary rocks low 

on the flanks.

Fossil vertebrates collected from the Wind River 

Formation and identified by Frank C. Whitmore 

(written commun., 1961, 1962, 1965) are as follows:

NE% sec. 19, T. 27 N., R. 76 W., Albany County, Wyo. 

Phenacodus cf. primaevus Cope 

Hyrachyus sp. 

Crocodile scutes 

Garpike scales

SW% sec. 31, T. 27 N., R. 79 W., Carbon County, Wyo. 

Coryphodon sp.

SW% sec. 15, T. 29 N., R. 80 W., Natrona County, Wyo.

Hyrachyus sp.

Brontops sp. 

SWM sec. 23, T. 28 N., R. 80 W., Natrona County, Wyo.

cf. Coryphodon

Hyracotherium sp.

Fossil pollen collected from lignitic material in the 

Utah Construction and Mining Co. mine and Petro-
24 GEOLOGY AND URANIUM DEPOSITS, SHIRLEY BASIN AREA, WYOMING

tomics Co. Section 9 pit were identified by Estella 

Leopold (written commun., 1964, 1967) as follows:

SW 1^ sec. 28, T. 28 N., R. 78 W., Carbon County, Wyo. 

(USGS paleobotany loc. D4012)

Cicatricosisporites1

Eleagnus

Platycarya

Dinoflagellates and hystrix1

A qiiilapo llenites1

Nyssa type

Caryapo llenites

Monosulcites (reticulate form)

Tilia

Corrugatisporites

Pistillipollenites

Proteacidites (round form) *

NE% sec. 9, T. 27 N., R. 78 W., Carbon County, Wyo. (USGS 

paleobotany loc. D3426)

Platycarya

Castanopsis

Osmunda

Pterocarya

Carya

Nertera

Ulmus

cf. Tilia

cf. Nyssa

EucommiaC!)

Fossil leaves collected by R. V. Bailey from carbonaceous shale about 200 feet above the base of the 

Wind River Formation in the Utah Construction 

and Mining Co. mine were identified by Jack A. 

Wolfe (written commun., 1962) as follows: 

Lygodium kaulfussii Heer

Eugenia(l) cf. #.(?) americana (Lesq.) MacGin

Fossil evidence shows the Wind River Formation 

to be of early Eocene age and to have been deposited 

in a tropical or semitropical climate. It is predominantly fluvial in origin although lacustrine 

f acies are present, particularly near the top of the 

formation.

WAGON BED FORMATION

The Wagon Bed Formation, of middle and late 

Eocene age, is present in the eastern and western 

parts of the Shirley Basin, but it was completely removed by pre-lower Oligocene erosion in the central 

part. The name Wagon Bed was first used by Van 

Houten (1964) to identify middle and upper Eocene 

deposits in the Beaver Divide area of Fremont 

County, Wyo. Contrary to Van Houten's philosophy 

that deposits "accumulated separately in different 

structural basins * * * should be assigned to different formations," the name Wagon Bed is herein

1Forms probably redeposited from Upper Cretaceous sediments.

extended to the Shirley Basin to identify deposits 

similar in age and lithology to those described by 

Van Houten.

Rocks of middle and late Eocene age had not been 

recognized in the area prior to the start of the 

Shirley Basin project, but they had been recognized 

in the Alcova Dam area, about 24 miles to the northwest, by N. M. Denson (oral commun., 1961). Where 

present, the Wagon Bed Formation conformably 

overlies the lower Eocene Wind River Formation 

and is unconformably overlain by the Oligocene 

White River Formation. It consists of a series of 

interbedded coarse-grained arkosic sandstone beds 

and silicified claystone beds, generally light greenish 

yellow and sufficiently indurated to form prominent 

ledges that contrast with the rounded slopes of the 

overlying and underlying softer formations. Red 

hematitic splotches or concretionary stains are characteristic of most exposures. The beds in the formation have considerable lateral continuity, and the 

bedding is fairly well defined.

The top of the Wagon Bed Formation is probably 

everywhere an erosion surface, and the original 

maximum thickness of the formation is unknown. 

The maximum measured thickness of the Wagon Bed 

in the Shirley Basin area is about 155 feet in an 

exposure in the SEi/4 sec. 15, T. 27 N., R. 77 W., 

Albany County, Wyo. This may approach the original maximum thickness. A measured section of this 

exposure follows:

Measured section of Wagon Bed Formation in the Shirley 

Basin area, SEl/4 sec. 15, T. 27 N., R. 77 W., Albany County,

Wyo.

Feet

Top of exposure. 

Wagon Bed Formation:

1. Claystone, silty, indurated, silicified,

light-olive-green ....................................................... 17

2. Sandstone, very coarse grained, poorly sorted, 

siliceous, clay-cemented, off-white; orange 

and red stains in irregular patches........................ 2

3. Claystone, silty, indurated, light-tan; contains

scattered coarse sand grains.......... ....................... 11

4. Sandstone, very coarse grained, siliceous,

clay cemented, off-white............................. ............ 28

5. Sandstone, very coarse grained; interbedded

with silty, light-olive-green claystone...... ........... 8

6. Conglomerate, crossbedded, poorly sorted, buff; 

light-pink irregular stains, pebbles to 

yz in. in diameter......... ............................ .. .. . 12

7. Sandstone, very coarse grained, poorly sorted, 

clay-cemented; some intercalated claystone 

beds ......................... ... .... . 8

8. Claystone, silty, indurated, light-tan; contains

a few very coarse sand grains....... ...................... 11

9. Sandstone, very coarse grained, clay-cemented........ 3

10. Claystone, silty, silicified, light-olive-green;

some coarse sand grains....... ................ .... 8
STRATIGRAPHY, CENOZOIC 25

Feet

Wagon Bed Formation Continued

11. Sandstone, very coarse grained, clay-cemented........ 4

12. Claystone, indurated, silicified; interbedded

with sandy claystone; weathers nodular.............. 32

13. Sandstone, very coarse grained, clay-cemented;

red and orange concretionary stains...................... 2

14. Claystone, silty, silicified, light-olive-green.............. 4

15. Conglomerate, sand, and gravel; siliceous;

pebbles to 2 in. in diameter..................................... 5

Total measured Wagon Bed Formation............155

Conformable contact. 

Wind River Formation.

Lake beds, mostly fresh-water limestone, are 

present in the basal part of the Wagon Bed Formation in two areas in the Shirley Basin. In and near 

sees. 5 and 6, T. 27 N., R. 77 W., a lower nodular 

fresh-water limestone about 2 feet thick overlies a 

very coarse grained off-white sandstone of the Wind 

River Formation. The limestone is overlain by 6 feet 

of pink-hued and greenish-yellow silty claystone and 

interbedded coarse to very coarse grained sandstone. 

Above the claystone are nodular limestone, sandy 

limestone, and limy sandstone beds having a total 

thickness of 3 feet. Windblown Holocene sand overlies the upper limestone.

In sees. 24 and 25, T. 27 N., R. 77 W., and for 2 

miles eastward, limestone beds as much as 44 feet 

thick are exposed in several small cuestas. The 

lowest exposed limestone rests on siltstone or on 

what appears to be a lignitic soil in the Wind River 

Formation. A measured section of the thickest exposure follows:

Measured section of the lower part of the Wagon Bed Formation in the NEy4 sec. 30, T. 27 N., R. 76 W., Albany County,

Wyo.

Feet

Top of exposure. 

Wagon Bed Formation:

1. Limestone, medium-gray, poorly bedded;

contains fossil gastropods..........................................15

2. Clay, silty, yellowish-buff; calcareous at top..............13

3. Limestone, poorly bedded, white, fossiliferous..........16

Total measured lower part of the Wagon

Bed Formation..........................................................44

Conformable contact. 

Wind River Formation.

The indistinct contact between the Wind River 

and Wagon Bed Formations is difficult to see in the 

field. In the eastern part of the area, the contact has 

been placed at the base of the lowest fresh-water 

limestone or, in the absence of lacustrine rocks, 

at the base of the lowest clay-cemented tuffaceous 

sandstone bed. Vertebrate fossil evidence shows the 

limestone to be early middle Eocene in age, and 

heavy mineral studies by N. M. Denson (oral commun., 1966) show a distinct mineralogical break

at the base of the lowest sandstone of the Wagon 

Bed.

In the western part of the Shirley Basin the 

lacustrine deposits and the clay-cemented sandstone 

beds are absent, and the Wagon Bed Formation 

comprises a 40- to 100-foot-thick sequence of silicified bentonitic claystone and tuffaceous silty claystone. A measured section on the east side of Chalk 

Mountain follows:

Measured section of the Wagon Bed Formation on Chalk

Mountain in the SEy4 sec. 13, T. 28 N., R. 81 W., Carbon

County, Wyo.

Feet

White River Formation.

Unconformity.

Wagon Bed Formation:

1. Claystone, silty, blocky, indurated; tan and

sandy at base, greenish tan at top.....--- ................10

2. Siltstone, tuffaceous, silicified, nodularweathering, off-white; forms ledges............. ........ 13

3. Claystone, silty, silicified, brown to pale-green..........18

4. Siltstone, tuffaceous, silicified, nodularweathering, off-white; forms ledges........................13

5. Siltstone, tuffaceous, indurated, nodular, tan............10

,Total measured Wagon Bed Formation..................64

Conformable contact. 

Wind River Formation.

At some places in the Shirley Basin area, although not at the measured sections, the contact 

between the Wagon Bed and the overlying White 

River Formation is marked by a 14 - to i^-inch-thick 

bed of translucent silica that weathers in small 

chips and litters the slopes below the outcrop. The 

material is not fluorescent. It is epigenetic and was 

probably leached from the overlying White River 

Formation and deposited on the impermeable upper 

bed of the Wagon Bed Formation.

In the Beaver Divide area in Fremont County, 

Wyo., many of the tuffaceous beds of the Wagon 

Bed Formation have been altered to various zeolite minerals. Samples of tuffaceous members of the 

Wagon Bed Formation from the Shirley Basin were 

examined by R. A. Sheppard, who reported (oral 

commun., 1967) the absence of zeolites in all samples 

and the presence of relatively fresh shards and 

considerable glass in some of them. He postulated 

that the highly alkaline environment necessary for 

the formation of zeolites has not existed in the 

Shirley Basin area since deposition of the Wagon 

Bed sediments.

Vertebrate fossils are sparse in the Wagon Bed 

Formation in the Shirley Basin area, and only one 

diagnostic fossil was found. It was identified by G. 

Edward Lewis (written commun., 1965) as "a fragment of the front part of a right mandibular ramus 

of Notharctus tenebrosus Leidy with the alveoli of
26 GEOLOGY AND URANIUM DEPOSITS, SHIRLEY BASIN AREA, WYOMING

/C, PT, and P2 ; the roots of P3 ; and the complete P4 and MX." This lemuroid primate is a characteristic faunal element of the lower part of the 

middle Eocene Bridger Formation of Wyoming.

Lithologically similar strata in the Beaver Divide 

area of Wyoming were shown by Van Houten (1964) 

to be of middle and late Eocene age. Since the middle Eocene fossil was near the base of the Wagon 

Bed Formation in the Shirley Basin, these strata 

are here considered to be of middle and late Eocene 

age. However, it is possible that the rocks are principally middle Eocene and that the late Eocene was 

a period of erosion, during which the middle Eocene 

deposits were removed from the central part of the 

Shirley Basin area.

WHITE RIVER FORMATION

The terms "White River deposits, formations, or 

beds" were used by Meek and Hayden (1858) to 

describe fine-grained clastic rocks on the east side 

of the Missouri River near the confluence with the 

White River in South Dakota. The use of the name 

has been extended to similar deposits in Nebraska, 

Wyoming, Colorado, North Dakota, and Montana. 

Darton (1898) divided the White River Group into 

the Chadron (lower) and Brule (upper) Formations. In central Wyoming, the term White River 

Formation, in preference to White River Group, is 

generally used for rocks of Oligocene age that 

practice is followed in this report.

The White River Formation is exposed in much of 

the northern part of the mapped area; it is particularly well exposed on the steep slopes of Bates Hole. 

For mapping, the formation has been divided into a 

lower member of fine-grained rocks and an upper 

member of interbedded fine- and coarse-grained 

rocks.

The lower member is predominantly fine-grained 

tuffaceous siltstone, although in some areas there 

is considerable claystone, sandstone, tuff, conglomerate, or fresh-water limestone near the base. It 

is as much as 400 feet thick in exposures along the 

east side of Bates Hole, and drilling east of these 

exposures indicates that it may be slightly thicker 

in that area. The upper member consists of tuffaceous siltstone interbedded with very coarse grained 

sandstone and boulder conglomerate. Thicknesses of 

as much as 350 feet in the upper member have been 

measured along the east side of Bates Hole.

The lower member rests unconformably on rocks 

of the Wagon Bed or older formations in the eastern 

part of the Shirley Basin area; on rocks of the Wind 

River Formation in the central part of the area,

where the Wagon Bed Formation was completely 

removed by late Eocene or early Oligocene erosion; 

and on rocks of the Wagon Bed Formation in the 

western part of the area. There is no apparent angular discordance between the White River Formation and older rocks of Tertiary age. The contact 

between the White River and the older formations 

is sharp and easily recognized in the field except 

where the White River rests on the eroded surface 

of the Wind River. In these areas there is considerable reworked material in the base of the White 

River, and the contact is difficult to locate precisely.

In the eastern part of the area the base of the 

White River Formation contains many channel-fill 

conglomerate beds composed of poorly sorted coarsegrained sand, subangular to angular pebbles, generally less than 1 inch in diameter, and a few 

rounded cobbles as much as 6 inches in diameter. 

The pebbles and cobbles are principally granitic 

rocks, but in some areas as much as 15 percent of 

the material may be limestone, chert, diabase, and 

quartzite. In Tps. 27 and 28 N., R. 77 W., many 

short narrow sinuous ridges or irregular masses 

of conglomerate, too small to be shown on the map, 

rest on a slightly tilted dipslope of Wagon Bed 

rocks. These are erosional remnants of White River 

deposits that filled shallow channels in the top of 

the Wagon Bed Formation. Similar conglomerate 

beds northeast of the Holiday Ranch (northeast of 

the mapped area) contain an early Oligocene vertebrate fauna (P. 0. McGrew, oral commun., 1964).

Overlying the channel conglomerate in this eastern part of the area or, where the conglomerate is 

absent, resting on the eroded surface of the Wagon 

Bed Formation, is a monotonously uniform sequence 

of tuffaceous siltstone and mudstone beds which are 

generally pinkish gray, pale tan, or off white and 

which range in thickness from an inch or less to 

several feet. Individual beds have considerable continuity and were apparently deposited on flood 

plains or in shallow playa-type lakes. The siltstone 

weathers to a blocky rubble that forms small talus 

slopes below ledgy outcrops.

On the western flank of the Laramie Mountains, 

the White River Formation laps on many of the 

older Mesozoic and Paleozoic rocks, and in some 

places detritus from the older rocks is incorporated 

in the White River Formation. This is particularly 

true near paleooutcrops of the soft, easily eroded 

Red Peak or Goose Egg Formation where the White 

River is a brick-red siltstone having an appearance 

strikingly similar to that of the red beds on which 

it laps. Near paleooutcrops of Mowry Shale, the 

White River may consist principally of shale frag-
STRATIGRAPHY, CENOZOIC 27

ments cemented with the silty material that elsewhere composes the lower member of the formation. 

High on the flanks of the basin, where the White 

River Formation laps on the old indurated rocks 

such as the Precambrian granite, Madison Limestone, or Casper Formation, the contact is sharp, 

and almost no detritus from the older rocks is incorporated in the onlapping part of the White 

River. This fact suggests rapid deposition of White 

River sediments on a surface undergoing minimal 

weathering and erosion.

In the central part of the Shirley Basin area, the 

White River Formation rests on the eroded surface 

of the Wind River Formation, and the contact has 

no apparent angular discordance. From the southeast corner of Bates Hole eastward to the Little 

Medicine Bow River, the Wind River-White River 

contact is difficult to locate on the surface, for the 

outcrops are poor and there is no distinctive lithologic break between the two formations. Data from 

exploratory drilling south of Moss Agate Ridge were 

used to determine the location of the contact in that 

area. The contact was selected at the base of a 

chocolate-brown claystone that overlies a very coarse 

grained off-white sandstone. Similar chocolatebrown claystone, half a mile north of the Utah Construction and Mining Co. shaft, contained White 

River (Chadron) vertebrate fossils. East of sec. 33, 

T. 28 N., R. 78 W., the brown clay is not present, or 

at least it was not recognized in drill cuttings, and 

for a distance of almost 2 miles there is no distinctive bed near the contact that can be used as a 

horizon marker. The mapped position of the contact in this area is therefore only approximate. 

Northward along the east side of Bates Hole, the 

contact is not sharp due to some reworked Wind 

River sand incorporated in the base of the White 

River, but the zone of questionable designation is 

only a few feet thick.

A sequence of tan, brown, green, or red clayey 

siltstone beds directly overlies the Wind River Formation in much of the central part of the Shirley 

Basin area. These rocks are plastic and waxy and 

weather to steep slopes covered with blocky chips 

and spherical masses of clayey siltstone. They are 

well exposed in the Wi/2 sec. 15, T. 29 N., R. 80 W., 

where they are overlain by the tuffaceous siltstone 

that makes up the bulk of the lower unit of the 

White River Formation, and in the NEi/4 sec. 21, 

T. 28 N., R. 79 W., where they are overlain by a 

sequence of lake beds. At some intervening points 

the clayey siltstone beds are absent, and tuffaceous 

siltstone rests directly on the eroded surface of the 

Wind River Formation. In sec. 15 the clayey siltstone beds are chocolate brown or pale green and 

blocky and are interbedded with coarse-grained 

arkosic tuffaceous sandstone. The clayey siltstone 

beds range in thickness from 10 to 20 feet; the 

sandstone beds, from 5 to 15 feet. The sequence is 

about 100 feet thick, and it is capped by a ledgeforming sandstone. In sec. 21 the clayey siltstone 

beds are mottled red and green and contain sparse, 

isolated, coarse quartz grains. Here the sequence is 

about 50 feet thick and contains some sandstone in 

the lower part. The clayey siltstone beds have been 

seen at the base of the White River Formation only 

where the Wagon Bed Formation has been completely eroded and the White River rests on the eroded 

surface of the Wind River Formation. These beds 

are a distinctive lithologic unit, and they are thought 

to be the earliest Oligocene deposits in the area, perhaps similar in age to the Yoder Formation of 

Schlaikjer (1935) in eastern Wyoming (P. O. McGrew, oral commun. 1964).

In the southeast corner of Bates Hole, and for 

about 5 miles eastward, a sequence of lacustrine 

acidic tuff, tuffaceous siltstone, and silicified limestone beds overlies the basal White River clayey 

siltstone (fig. 15). These beds are as much as 45 

feet thick, are resistant to erosion, and form the 

prominent cuesta known as Moss Agate Ridge. The 

sediments now comprising these beds were deposited 

in a shallow lake at least 5 miles long and 2 miles 

wide, and perhaps much more extensive. The base 

of the lake-bed sequence is 50-75 feet above the base

FIGURE 15. Lower part of the lower member of the White 

River Formation at the southeast corner of Bates Hole (sec. 

21, T. 28 N., R. 79 W.), showing clayey siltstone (cs) at the 

base of the White River Formation and lake-bed sequence 

(Ib) overlying clayey siltstone and underlying Moss Agate 

Ridge, an erosional cuesta extending 5 miles southeast of 

this exposure.
28 GEOLOGY AND URANIUM DEPOSITS, SHIRLEY BASIN AREA, WYOMING

of the White River Formation. The lower part of 

the lakebed sequence is silty limestone replaced in 

part by silica leached by ground water from the 

overlying tuff and tuffaceous siltstone and deposited 

in the rocks directly overlying impervious claystone.

A section from the base of the White River Formation through the lake-bed sequence follows:

Section of base of White River Formation measured in sec. 21, 

T. 28 N., R. 79 W., at the southeast corner of Bates Hole

Feet

Top of exposure. 

White River Formation:

1. Tuffaceous siltstone, blocky, buff to light-tan;

in beds 1-6 in. thick................................................ 11.5

2. Sandy siltstone, massive, indurated,

calcareous, light-tan; forms ledges ............ . 2.5

3. Tuffaceous siltstone, sandy, blocky, pale-pink

and brown, thin-bedded.......................................... 17.0

4. Sandstone, fine- to medium-grained, silty, 

tuffaceous, crossbedded, off-white; beds 

about % in. thick.................................................... 3.0

5. Sandstone, crossbedded, off-white; pebbles

as much as % in. in diameter................................ .5

6. Siltstone, blocky, light-brown.................................... 3.5

7. Tuff, massive, white to pinkish-white; grades

to bedded tuffaceous siltstone at top.................... 3.0

8. Siltstone, blocky, tuffaceous, pinkish-brown.......... 4.0

9. Sandstone, very coarse grained, siliceous;

contains calcite-cemented siltstone pebbles

1 in. in diameter...................................................... .5

10. Marl, off-white; replaced in large part by

silica; dendritic manganese ............................... 2.5

11. Claystone, silty, pink- and green-mottled,

blocky ........................................................................ 3.5

12. Chalcedony (moss agate) ; thin claystone

interbeds .................................................................. 1.0

13. Claystone and clayey siltstone, bentonitic, 

blocky, red- and green-mottled. Banded 

silica in top 5 ft ................................................... 55.5

Total measured base of White River

Formation ........................................................108.0

Unconformity.

Wind River Formation.

A section of the lake-bed sequence measured in 

the bank of Spring Creek in sec. 19, T. 28 N., R. 78 

W., about 4 miles east of the Bates Hole measured 

section, contains 36 feet of strata comprising principally calcareous siltstone, silty limestone, and tuffaceous siltstone, all somewhat silicified. The lake 

beds were originally more extensive than at present, 

as shown by the fact that they end abruptly on the 

east, south, and west in exposures 30-70 feet thick, 

obviously carved by erosion, perhaps starting in the 

Pleistocene. On the north, the lake beds phase out 

laterally by a gradual change in f acies to the floodplain tuffaceous siltstone characteristic of most of 

the lower member of the White River Formation.

The upper part of the lower member of the White 

River Formation in the central part of the area, as 

in the eastern part, comprises a 300- to 350-footthick sequence of light-pink, tan, or off-white tuffaceous siltstone and mudstone beds. Beds range in 

thickness from a fraction of an inch to several 

feet, and relatively thin beds can be traced laterally for several thousand feet. Thick beds or groups 

of beds have been traced as far as 2 miles.

A section of the lower member of the White River 

Formation follows:

Section of lower member of White River Formation measured 

in sec. 26, T. 29 N., R. 80 W., on the east side of Bates Hole

Feet

Upper member, White River Formation.

Conformable contact.

Lower member, White River Formation:

1. Siltstone, tuffaceous, off-white; in beds as

much as 5 ft thick...........___............ ... . ... -- 54

2. Siltstone, off-white to light-tan; sandy at top;

beds a few inches to 5 ft thick......... .. 67

3. Siltstone. off-white to light-tan; beds 2 in.

to 3 ft thick.............................. ................................116

4. Siltstone, light-tan, massive.. - 57

5. Siltstone, tuffaceous, off-white, thin-bedded

(interpreted from drill cuttings). . 36

Total measured lower member of

White River Formation 330

Unconformity.

Wind River Formation.

The lower two-thirds of the lower member of the 

White River Formation weathers in even, steep 

slopes covered by blocky and rounded siltstone 

fragments. The upper third weathers in almost 

vertical cliffs due in part to cementation of the 

siltstone and in part to protection from erosion 

offered by the moderately indurated siltstone and 

conglomerate in the upper member. The character 

of the east side of Bates Hole near triangulation 

station Rimo (sec. 26, T. 29 N., R. 80 W.) is shown 

in figure 16.

In the western part of the area, the lower member 

of the White River Formation rests unconformably 

on the Wagon Bed Formation without angular 

discordance. The lake beds and silty claystone 

present in the central part of the area are absent 

in the western part, and the lower member is composed entirely of siltstone, tuffaceous siltstone, and 

minor amounts of fine-grained sandstone. The lower 

member, as measured on Chalk Mountain in sec. 

31, T. 28 N., R. 80 W., is about 265 feet thick. The 

combined thickness of the lower member and the 

Wagon Bed Formation in the Chalk Mountain section is 331 feet, about the same as the thickness of 

the lower member on the east side of Bates Hole, 

where the Wagon Bed Formation is missing.
STRATIGRAPHY, CENOZOIC 29

FIGURE 16. Lower member (Twrl) of the White River 

Formation, showing rubble-covered steep slopes of lower 

two-thirds and steep cliffs of upper third of member. Cliffforming beds of upper member (Twru). Looking north on 

east side of Bates Hole (NE% sec. 27, T. 29 N., R. 80 W.).

Thin sandstone dikes in mudstone, similar to the 

mudstone dikes described by Rich (1962) in the 

White River Formation in the Clarkson Hill area 

15 miles northeast of Bates Hole, are present in the 

lower member along the west side of Bates Hole. 

One, exposed in sec. 6, T. 27 N., R. 80 W., is 2 

inches wide and 75 feet long and is filled with 

medium- to coarse-grained sand. It pinches out 

downward, but upward it ends abruptly at the lower 

contact of a sandy siltstone bed of the lower member. There is no apparent displacement of beds cut 

by the dike. It may represent a shrinkage crack 

formed prior to deposition of the overlying sandy 

beds and filled concurrently with the deposition of 

the sandy material.

The upper member of the White River Formation 

is well exposed on both sides of Bates Hole, and the 

lower part of this member forms the north rim 

of an erosional scarp that extends from Bates Hole 

eastward, along the Carbon-Natrona County line, 

to the west flank of the Laramie Mountains. The 

upper member has a consistent lithology over most 

of the Shirley Basin area and comprises tuffaceous 

siltstone beds, similar to those in the lower member, 

interbedded with conglomerate and coarse-grained 

arkosic sandstone beds composed principally of Precambrian granitic and metamorphic rocks. Over 

most of the area the upper member is separated 

from the lower one, by a well-defined break in sedimentation, representing an interruption of very 

short duration which did not necessarily occur over 

the entire area. It is considered to be a diastem

rather than an unconformity. Relief on the eroded 

surface of the lower member in some places is as 

much as 50 feet, but generally it is a few tens of 

feet or less. Figure 17 shows the configuration of 

the contact in the steep wall of the south fork of 

Chalk Creek in sec. 9, T. 29 N., R. 79 W.

FIGURE 17. View showing diastem between the upper (Twru) 

and lower (Twrl) members of the White River Formation 

exposed in Chalk Creek (NE% sec. 9, T. 29 N., R. 79 W.). 

Steep rock wall is about 100 feet high.

Over much of the outcrop area the base of upper 

member is marked by tuff beds, conglomerate beds, 

or both, but for about 1 mile in sec. 26, T. 29 N., R. 

80 W., the contact is poorly defined by a tuffaceous 

siltstone; there appears to have been no break in 

sedimentation in this area.

The upper member contains from three to five 

beds of coarse-grained sandstone and conglomerate 

that generally range in thickness from a few feet 

to about 20 feet, although a 50-foot-thick conglomerate bed is exposed on the west side of Bates Hole 

in sec. 25, T. 28 N., R. 81 W. The conglomerate is 

composed principally of arkosic sand and of pebbles, 

cobbles, and boulders of granite, diabase, and metamorphic rocks. Very few rocks younger than Precambrian were noted in the exposures, although in 

a few places pebbles of siltstone eroded from the 

White River Formation are present in the conglomerate. The coarse material is as much as 18 

inches in diameter and is rounded to subangular. 

The degree of rounding increases as diameter 

decreases. The fine-grained material consists of individual quartz and feldspar grains or grain aggregates, remarkably fresh and generally angular. 

The sandstone is crossbedded.
30 GEOLOGY AND URANIUM DEPOSITS, SHIRLEY BASIN AREA, WYOMING

No individual conglomerate bed in the upper 

member is continuous throughout the area, and in 

the southeastern part of sec. 13, T. 29 N., R. 80 W., 

no conglomerate beds are in the member. In the 

very good exposures along the east side of Bates 

Hole, individual conglomerate beds can be seen 

to extend for a few thousand feet to several miles. 

Some conglomerate beds terminate abruptly in what 

appear to be the steep banks of stream channels; 

others thin and terminate in what must have been 

a gravelly sheet wash. One thick conglomerate bed 

splits into two thinner ones which are separated by 

about 15 feet of siltstone. In the erosional scarp 

extending eastward from Bates Hole to the Laramie 

Mountains, single conglomerate beds near the base 

of the upper member, or at least a basal zone of 

interbedded acidic tuff and conglomerate beds about 

50 feet thick, extend the entire distance, about 15 

miles (fig. 18).

The conglomerate beds are intercalated in a sequence of well-bedded tuffaceous siltstone, mudstone, 

and fine-grained sandstone almost identical with the 

beds in the lower member. Individual fine-grained 

beds range in thickness from a few inches to several feet, and the aggregate thicknesses of the beds 

between the conglomerate beds range from 5 to 50 

feet. The fine-grained rocks are somewhat darker 

in the upper member than in the lower member, and 

the upper member, particularly from a moderate 

distance, is noticeably darker than the lower member.

Two measured sections of the upper member, one 

on the west side of Bates Hole and the other on the 

east side, follow:

Section of upper member of the White River Formation on

Chalk Mountain measured in sec. 31, T. 28 N., R. 80 W., on

the west side of Bates Hole

Feet Arikaree Formation.

Conformable contact.

Upper member, White River Formation:

1. Siltstone, massive, tan; stringers and

pockets of sand and gravel; calcareous 

concretions ............................................................ 37.0

2. Sand and gravel; boulders of white granite

and diabase as much as 12 in. in diameter........ 10.0

3. Siltstone, tan; calcareous concretions.................. 18.5

4. Sand and gravel; cobbles of white granite

and diabase as much as 6 in. in diameter........ 3.5

5. Siltstone, tan, massive, and interbedded

fine-grained sandstone.......................................... 8.0

6. Sand and gravel; pink and white granite 

and diabase; rounded to subangular; 

maximum diameter about 14 in.......................... 22.0

7. Siltstone, tan, thin-bedded, and fine-grained

off-white sandstone. . . .. . 28.0

8. Sand and gravel; red and pink granite

pebbles; maximum diameter about 2 in.. . 8.0

Upper Member, White River Formation Continued Feet 

9. Siltstone and sandstone, thin-bedded, tan

to off-white.............................................................. 28.0

10. Conglomerate; pink and white granite and 

diabase pebbles; rounded to subangular;

1 in. in maximum diameter................................ 8.0

11. Siltstone and sandstone, fine-grained, tan... .. 49.0

12. Conglomerate; pink and white granite and 

diabase pebbles; subangular to rounded, 

crossbedded; some rounded tuff pebbles

2 in. in maximum diameter................................ 11.0

Total measured upper member of the

White River Formation................................231.0

Conformable contact.

Lower member, White River Formation.

Section of upper member of the White River Formation 

measured in sec. 26, T. 29 N., R. 80 W., near triangulation

station Rimo, on the east side of Bates Hole 

Arikaree Formation. 

Conformable contact. 

Upper member, White River Formation:

1. Siltstone, massive, tan................................................ 39

2. Conglomerate; red granite cobbles as much

as 8 in. in diameter.................................................. 3

3. Siltstone, massive, tan................................... . ... 28

4. Siltstone, tan, and fine-grained off-white to 

pink sandstone; interbedded with silty 

limestone lenses; beds as much as 2 ft thick......133

5. Conglomerate; red granite and diabase clasts;

boulders as large as 12 in. in diameter................ 4

6. Sandstone, fine-grained, silty, thin-bedded.............. 8

7. Siltstone, sandy, massive, tan. . . . . . 18

8. Sandstone, off-white; gravel as much as

*/i in. in diameter..................... . .. .............. 3

9. Siltstone, tan, massive .. . 8

10. Conglomerate and sandstone, crossbedded.. . 7

11. Siltstone, tuffaceous, thin-bedded, tan;

interbedded with sandstone having gravel

as much as % in. in diameter..... ................. .. 19

12. Conglomerate and sandstone, crossbedded; 

red granite cobbles as large as 8 in. in 

diameter; some siltstone pebbles.......................... 11

13. Siltstone, tan to off-white, calcareous.. . 66

14. Siltstone, massive, tan......... 12

Total measured upper member of the __ 

White River Formation.. ....... .. . 359

Conformable contact.

Lower member, White River Formation.

The conglomerate in the upper member of the 

White River Formation on the east side of Bates 

Hole is significantly different from that on the west 

side. Although granitic rocks are the principal components of the conglomerate in both areas, the character of the granite cobbles and boulders suggests 

that the clastic debris was derived from two separated lithologically distinct sources. On the east 

side of Bates Hole the clastic debris is composed 

principally of the pink granite and gray diabase 

that characterize the northern end of the core of 

the Laramie Mountains, and it is almost certain 

that the conglomerate was deposited in fans by
STRATIGRAPHY, CENOZOIC 31

streams flowing westward from the Laramie 

Mountains.

In sharp contrast, the debris in the conglomerate 

on the west side of Bates Hole is composed principally of light-gray or white granite and gray diabase, 

rock types characteristic of the core of the 

mountains southwest and west of the Shirley Basin 

area. The clear implication is that this conglomerate 

was deposited by easterly flowing streams that originated on the northeast flank of the south end of the 

Granite Mountains.

These data indicate that in Oligocene time the 

position of the major stream that drained the low 

area between the Granite and Laramie Mountains 

was near Bates Hole, or about 10 miles west of its 

position in early Eocene time.

Previous workers have misidentified rocks in the 

upper member of the White River Formation in the 

Shirley Basin area. Roehler (1958) and Shipp 

(1959) considered them to be part of an unnamed 

sequence of Miocene age; Peterson (1935) and Konkel (1935) termed them the Arikaree Formation; 

and Love, Weitz, and Hose (1955), Weitz and Love 

(1952), and Weitz, Love, and Harbison (1954), in 

compiling State and county geologic maps, showed 

them as part of an undivided sequence of Miocene 

and Pliocene age.

Vertebrate fossils, most of which were collected 

near the base of the upper member but some of 

which were as much as 160 feet above the base, show 

that this sequence of siltstone, sandstone, and conglomerate beds is, in fact, of middle Oligocene age 

(Orellan provincial age of Wood and others, 1941) 

and that it is the central Wyoming equivalent of the 

Brule Formation of eastern Wyoming and western 

Nebraska. The change in lithology from the finegrained rocks in the lower member to the intercalated fine- and coarse-grained rocks of the upper 

member suggests uplift of the source areas in the 

Laramie and Granite Mountains, vigorous erosion 

and transportation by streams flowing from the 

mountains, and deposition of extensive alluvial fans 

on the flood plains at the foot of the mountain fronts.

Rocks equivalent to the upper member of the 

White River Formation probably are more extensive 

than commonly believed, and their recognition is 

imperative if the geologic history of the region is 

to be correctly interpreted. For example, Rich 

(1962) stated that middle and upper Oligocene 

(Brule) rocks are absent in the Clarkson Hill area 

of Natrona County, 15 miles northwest of Bates 

Hole, either not having been deposited or, if deposited, having been removed by post-early Oligocene 

to pre-early Miocene erosion. However, the lower few

hundred feet of a sequence he designated as lower 

and middle Miocene is lithologically similar to the 

upper member of the White River Formation in the 

Bates Hole area, and the fossil evidence of early 

Miocene age was from rocks about 500 feet above 

the base of the sequence. Possibly, therefore, some of 

the rocks included in the base of the lower and middle Miocene sequence by Rich are actually of middle 

and late Oligocene age. Furthermore, reconnaissance mapping and studies of heavy mineral concentrates from fine-grained rocks by Denson (1965; 

oral commun., 1967) have lead him to conclude that 

the upper member of the White River Formation 

can be recognized almost continuously from the 

Shirley Basin westward to the Gas Hills area in 

Fremont County, as well as in eastern Wyoming 

along the east flank of the Laramie Mountains.

Vertebrate fossils were collected from the lower 

75 feet of the lower member of the White River 

Formation and from the lower 160 feet of the upper 

member. They were identified by F. C. Whitmore 

and G. Edward Lewis (written commun., 1961, 

1962, 1963, 1965) as follows:

Upper member:

Sees. 4, 5, and 8, T. 28 N., R. 79 W.

Leptomeryx evansi Leidy

Palaeolagus haydeni Leidy

Fragments of bones of rhinoceros and camel 

Sec. 31, T. 29 N., R. 79 W., and sees. 25, 26, and 27, T. 29 

N., R. 80 W.

Hyracodon nebrascensis Leidy

cf. Poebrotherium

Metamynodon sp.

Subhyracodon occidentalis (Leidy)

Leptauchenia sp.

Poebrotherium sp.

Leptomeryx cf. evansi Leidy

Stylemys sp. 

Lower member:

Sees. 15, 22, and 27, T. 29 N., R. 80 W.

Brontops sp.

cf. Menodus

Leptomeryx, between L. yoderi and L. evansi in size

Hesperocyon cf. gregarius (Cope)

Hesperocyon cf. paterculus (Matthew)

Leptomeryx sp. 

Sec. 8, T. 27 N., R. 76 W.

cf. Agriochoerus

In the western parts of Nebraska and South 

Dakota, rocks of Oligocene age are assigned to the 

White River Group. In the group, two formations, 

the Chadron (lower Oligocene) and the Brule (middle and upper Oligocene), are recognized, and the 

Brule was subdivided by Schultz and Stout (1955) 

into the Orella (middle Oligocene) and the Whitney 

(upper Oligocene) Members. In central Wyoming 

these formations are not easily recognized on the
32 GEOLOGY AND URANIUM DEPOSITS, SHIRLEY BASIN AREA, WYOMING

basis of lithology, and the name White River Formation is generally used for the Oligocene rocks. Correlation between the twofold division of the White 

River Formation used in this report and the divisions of the White River Group used in Nebraska 

and South Dakota is uncertain. Fossil evidence 

indicates that the lower part of the lower member in 

the Shirley Basin area is Chadronian provincial age 

and that the lowest part of the upper member is 

Orellan provincial age. The faunal discontinuity is, 

therefore, somewhere in the middle or upper part of 

the lower member. Roehler (1958) suggested that 

in Bates Hole the discontinuity lies about 50-150 

feet above the base of the White River sequence, 

at the base of the lake beds described earlier in this 

report. Rich (1962) presented evidence that the discontinuity is at least 600 feet above the base of the 

White River Formation in an area 15 miles northwest of Bates Hole. It is possible, but by no means 

certain, that the Chadron-Brule faunal discontinuity 

corresponds with the lithologic discontinuity between the upper and lower members of the White 

River Formation in the Shirley Basin area.

No fossils of late Oligocene (Whitneyan provincial age) age were found prior to or during this 

investigation. However, since no fossils have been 

found in the upper 200 feet of the upper member, 

possibly beds equivalent to the Whitneyan are present near the top of the upper member.

FIGURE 18. Tuff bed (tu) overlying lowest conglomerate bed 

(egI) at base of the upper member of the White River Formation in sec. 31, T. 29 N., R. 77 W. Note channeling of 

conglomerate and tuff.

Stratigraphic and faunal evidence suggests that 

the White River Formation was deposited on flood 

plains and in fanlike deposits near the mountain

fronts. Ash was deposited directly as ash falls or 

as reworked material washed in and mixed with 

detritus from surrounding upland areas. The environment appears to have ranged from semiarid 

desert to stream border-savannah and from temperate to subtropical.

ARIKAREE FORMATION

The name Arikaree Formation was first used by 

Darton (1898) to identify a series of gray sands 

which overlies the Gering Formation and underlies 

the Ogallala Formation and which is characterized 

by layers of dark-gray concretions, many of which 

are tubular. These rocks are present in eastern 

Wyoming and western Nebraska, and the name 

was taken from the Arikaree Indians, a tribe that 

once occupied the area in which the formation was 

found. The name was generally restricted in use 

to areas east of the Laramie Mountains until Sato 

and Denson (1967) applied it to lower Miocene 

rocks in central Wyoming. Their usage is followed 

in this report.

In the Shirley Basin area the Arikaree Formation overlies the upper member of the White River 

Formation with apparent conformity. The Arikaree 

consists of a series of light-gray tuffaceous fineto medium-grained calcareous sandstone, lenticular 

conglomerate, and fresh-water limestone beds. The 

rocks are moderately indurated and generally erode 

to form steep cliffs.

Rocks of the Arikaree Formation are exposed in 

the northwestern and western parts of the mapped 

area, where they have a maximum thickness of 

about 175 feet. They underlie the flat dip slope 

of Chalk Mountain and several small outliers to 

the north, and they cap prominent ridges in the 

high area northeast of Bates Hole. The Arikaree 

Formation in the Shirley Basin area is the basal 

part of a sequence of clastic and volcanic rocks 

which was originally much thicker, but which has 

now been largely removed by Quaternary erosion. 

Data on the original thickness of the Arikaree 

Formation in the Shirley Basin area are lacking, 

but Denson (1965) estimated that lower and middle 

Miocene rocks in central Wyoming averaged about 

1,000 feet in thickness.

The contact between the Arikaree and the upper 

member of the White River Formation is well 

defined in most areas, but in some places it is gradational. The Arikaree rocks are generally light shades 

of gray; the White River rocks are light tan, brown, 

and pink. In some areas there are lenticular conglomerate beds at the base of the Arikaree Forma-
STRATIGRAPHY, CENOZOIC 33

tion, but for the most part the basal beds are 

sandstone.

Figure 19 shows the indurated cliff-forming sandstone beds at the base of the Arikaree Formation 

in the area northeast of Bates Hole. The exposure 

is principally tuffaceous, arkosic sandstone that 

contains a few subangular to rounded cobbles and 

boulders of gray granite and diabase, as much as

18 inches in diameter. Some beds contain considerable calcium carbonate as a cementing material, 

and these beds weather in ellipsoidal concretionary 

forms. Blue-black magnetite grains, characteristic 

of the Arikaree Formation over much of central 

Wyoming, are present in the sandstone, particularly 

near the base of the exposure. A section measured 

about 1 mile north of the exposure shown in figure

19 follows.

Section of Arikaree Formation measured in NWfy sec. 7, T. 

29 N., R. 79 W., Natrona County, Wyo.

Feet

Top of exposure. 

Windblown sand. 

Arikaree Formation:

1. Sandstone, tuffaceous, arkosic, white, poorly 

cemented; contains pebbles and boulders as 

much as 10 in. in diameter (poor outcrops)...... 15.0

2. Sandstone, tuffaceous, arkosic, light-gray, 

rounded frosted grains; noticeable black 

opaque grains; calcareous cement. Irregular 

bedding 1 in. to 10 ft thick; weathers to 

gnarled surface dotted with very coarse 

sand grains ........................_...........-. ..........-.... . 92.0

3. Sandstone, light-gray, arkosic; frosted grains;

traces of calcareous cement (poor outcrops).... 25.5

4. Sandstone, tuffaceous, light-gray; contains 

pebbles and boulders as much as 6 in. 

in diameter, interbedded with silty sandstone.... 34.0

5. Sandstone, tuffaceous, light-gray, silty; 

numerous black opaque grains; poor 

cementation (poor outcrops)....................... 3.5

6. Sandstone-conglomerate, off-white, crossbedded; 

subangular to rounded cobbles as much as 

6 in. in diameter.... .................................. ...... 5.0

Total measured Arikaree Formation. .175.0

Conformable contact. 

White River Formation.

Chalk Mountain, at the center of the west edge 

of the mapped area, is capped by an 80-foot-thick 

sequence of arkosic sandstone, conglomerate, freshwater limestone, and tuffaceous siltstone beds of a 

light-gray hue. The siltstone and to a lesser extent 

the sandstone and conglomerate contain calcareous 

cement. No fossils have been found in these strata, 

but because of their stratigraphic position, their 

light-gray color, the presence of considerable calcareous cement, and a probable Granite Mountain 

source of the clastic debris, they have been mapped

as Arikaree. The possibility remains that these 

strata are a calcareous facies at or near the top 

of the upper member of the White River Formation a facies not exposed elsewhere in the Shirley 

Basin area.

A section measured on the east slope of Chalk 

Mountain follows:

Section of Arikaree Formation measured on the east slope of 

Chalk Mountain, sec. 31, T. 28 N., R. 80 W.

Feet 

Top of exposure.

Arikaree Formation:

1. Fresh-water limestone, silicified, irregularly

bedded, white ................................................................13

2. Conglomerate, poorly cemented, rounded to 

subangular, light-gray; boulders as much 

as 12 in. in diameter............. ................................14

3. Fresh-water limestone, silicified, irregularly

bedded, gray-white ...................................................... 7

4. Conglomerate, poorly cemented, rounded to

subangular, crossbedded, light-gray; cobbles

as much as 10 in. in diameter; interbedded

with sandy calcareous, off-white siltstone.

Beds 5-12 ft thick.....-....-....-... ................ 46

Total measured Arikaree Formation. .80

Conformable contact. 

White River Formation.

No fossils were found in the rocks mapped as 

Arikaree in the Shirley Basin area although they 

were looked for diligently. The identification of 

these strata as part of the lower Miocene Arikaree 

Formation is based on their stratigraphic position, 

their lithologic similarity to well-dated strata in 

the Clarkson Hill (Rich, 1962) and Beaver Divide 

(Van Houten, 1954) areas, respectively 15 and 60 

miles to the west, and on the fact that this unit, 

according to Denson (1965), is

strikingly similar to the Arikaree Formation as defined by 

Darton *** has been mapped discontinuously from the vicinity 

of Oregon Buttes along the southwest flank of the Wind River 

Mountains [Range] through central and southeastern Wyoming into northwestern Nebraska.

The Arikaree Formation in the Shirley Basin area 

is of fluvial, lacustrine, and eolian origin. These 

are the youngest eolian sands in the Tertiary rock 

sequence. The clastic parts of the formation were 

derived from a granitic and metamorphic terrane 

of Precambrian age which lay to the west of the 

area and which now forms the core of the Granite 

Mountains. Volcanic material, in part ash falls and 

in part reworked ash from the highlands to the 

west, constitutes a significant part of the rocks. 

The heavy-mineral suites from the fine sandstones 

exposed in sec. 7, T. 29 N., R. 79 W., contain about 

40 percent each of augite and brown hornblende. 

About 90 percent of the minerals are of volcanic 

origin (N. M. Denson, oral commun., 1967). Relief
34 GEOLOGY AND URANIUM DEPOSITS, SHIRLEY BASIN AREA, WYOMING

in the sediment source areas appears to have been 

considerably less than in Oligocene time but was 

still sufficient to produce sheet gravel and fluvial 

conglomerate in the outwash plain.

FIGURE 19. Cliff-forming calcareous-cemented sandstone 

(Ta) at base of Arikaree Formation in sec. 18, T. 29 N., 

R. 79 W., northeast of Bates Hole. The White River Formation, upper member (Twru), is covered by talus.

HIGH TERRACE GRAVEL

At several places in Bates Hole, as well as in the 

area drained by the Little Medicine Bow River and 

its tributaries, terrace gravel caps ridges or hills 

that rise a few tens to as much as 100 feet above 

the general terrain. These deposits consist of poorly 

stratified sand and gravel; the gravel is rounded to 

subangular and composed principally of granitic 

and metamorphic rocks. The terrace gravel in the 

Bates Hole area contains boulders and cobbles of 

sandstone from the upper member of the White 

River Formation and probably is reworked from 

the sandstone and conglomerate exposed in the 

rim of Bates Hole. It may be of Pleistocene age, 

but no definitive age data are available.

In the Little Medicine Bow drainage area, the 

high terrace gravel deposits cap ridges south of 

the toe of the erosional scarp along the NatronaCarbon County line. These deposits probably are 

reworked from the conglomerate and sandstone 

exposed in the scarp, and they are assumed to be 

of Pleistocene age.

Inasmuch as the high terrace gravel is thin and 

of limited aerial extent, it was not mapped as a 

separate geologic unit.

LOW TERRACE GRAVEL

Terrace gravel is present along the Little Medicine Bow River, Stinking Creek, Elk Creek, and

some of the other streams in the area. Most of the 

material is probably reworked from the soft Tertiary rocks in the headwaters of these streams, but 

some of the material in the terraces along the Little 

Medicine Bow River may have been derived directly 

from the older rocks on the west flank of the 

Laramie Mountains. Where the low terrace gravel 

deposits are of sufficient size and thickness to be 

mapped, they have been included with the alluvium.

ALLUVIUM

Old alluvium, now being dissected by streams, 

is present throughout the Bates Hole area and, to 

a lesser extent, in the area drained by the Little 

Medicine Bow River. It is primarily fine-grained 

material eroded from soft Cretaceous and Tertiary 

rocks. It reaches a thickness of as much as 30 feet 

in some of the main tributaries of Stinking Creek, 

and it extends far into their upper reaches (fig. 20). 

Two stages of alluviation older than the present 

one can be recognized along Stinking Creek in the 

Bates Hole area. The old alluvium is younger than 

the high terrace gravel and probably is Holocene 

in age.

Alluvium is now being deposited by streams as 

flood-plain deposits and channel fill. Most of it is 

fine-grained material derived from the soft rocks 

in the drainage basins of the major streams and 

their tributaries.

FIGURE 20. Exposure of thick old alluvium now being 

actively dissected by Lawn Creek in NEx/4 sec. 10, T. 29 N., 

R. 80 W.

SILICIFICATION OF SEDIMENTARY ROCKS

At some places in the Shirley Basin the permeable rocks of several pre-Tertiary formations con-
STRUCTURE 35

tain abnormally large amounts of siliceous cement. 

These indurated rocks are generally on topographically high areas that are now, or once were, only 

a short distance below the lowest beds of the White 

River Formation.

An example of intense silicification can be seen 

atop the hogback in sees. 14 and 24, T. 27 N., R. 

77 W., where the lower, permeable sandstone of the 

Cloverly Formation has been silicified to such an 

extent that the Indians used it for making implements. Westward, down the dip slope of the hogback, 

the same beds grade into the normal well-cemented 

sandstone characteristic of the Cloverly Formation. On a small hill in the N^ sec. 28, T. 28 N., 

R. 77 W., sandstone beds at the top of the Jelm 

Formation (or perhaps at the base of the Sundance) are so indurated by silica cement that 

positive identification is not possible. In contrast, 

these same beds at other places are poorly to moderately cemented sandstone. At some places in the 

northeastern part of the mapped area, the solution 

breccia on the old karst surface at the top of the 

Madison Limestone has been replaced and cemented 

with such large amounts of silica that it can be 

confused with one of the thick chert beds in the 

upper part of the Madison Limestone.

Silicified rock at or slightly above the base of 

the White River Formation and at the top of the 

Wagon Bed Formation is common in the Shirley 

Basin and has been described in the discussions of 

the lithology of these two formations. The silicification almost certainly resulted from leaching of 

silica from the tuffaceous rocks higher in the section, 

downward migration of the silica-bearing ground 

water, and deposition of silica at or near the base 

of the formation. It seems reasonable to assume that 

the same general process gave rise to the abnormally high silica content of the permeable rocks of 

pre-Tertiary age that closely underlie, or at some 

earlier time underlay, the White River Formation.

STRUCTURE 

LANDSLIDES

Landslides of two ages have been differentiated 

on the geologic map of the Shirley Basin area. The 

older slides consist of large blocks of sandstone or 

shale that have slid on underlying claystone and 

have come to rest as far as half a mile laterally 

from their place of origin. Rocks of the Cloverly 

and Mowry Formations generally constitute the 

slide blocks. Some of the detached blocks are only 

slightly disturbed; others have been considerably 

broken and tilted. The older slides are found only 

in the eastern third of the Shirley Basin area.

Many of the slide blocks are partly buried by 

rocks of Tertiary age, and the undisturbed material 

upon which the slide rests is not exposed. Where the 

underlying rock is exposed, for example in sec. 20, 

T. 28 N., R. 77 W., and sec. 24, T. 27 N., R. 77 W., 

the material underlying the landslide debris is of 

pre-Tertiary age, generally rocks of the Morrison, 

Sundance, or Frontier Formations. This fact, the 

fact that the early Eocene was a time of moist 

climate, and the fact that relief in the Shirley Basin 

area was greatest just before deposition of the 

Wind River Formation all suggest that the landslides probably occurred in late Paleocene or earliest 

Eocene time. The slides are definitely pre-middle 

Eocene, as shown by the fact that debris from the 

slide blocks is incorporated in the lower part of the 

Wagon Bed Formation where it laps on and partly 

buries those blocks. Similar landslides were described by Gill (1962).

Landslides of Quaternary age, a few of which are 

now active, are present in many places in the Shirley 

Basin area. These young landslides are most common in the Bates Hole area, where gravitational 

forces and over-steepened slopes in rocks of the 

White River Formation and the Steele Shale have 

caused rock failure and sliding on a large scale. 

Quaternary slides are far less common in the 

central and eastern parts of the area, where they 

occur principally in rocks of Tertiary age. Slides in 

the Steele Shale are generally small but may affect 

as much as one-half square mile of surface area. 

Slides in the White River Formation are generally 

large, and masses of landslide debris covering a 

square mile or more of surface area are present 

along the steep eastern and western walls of Bates 

Hole. The larger landslide areas comprise many 

contiguous landslide blocks. A large landslide block 

on the west side of Bates Hole is shown in figure 21.

FAULTS

The Paleozoic, Mesozoic, and, to a lesser extent, 

the Tertiary rocks were affected by small-scale 

faulting. A prominent fault zone mapped (Harshman, 1968b) in sees. 13, 23, and 24, T. 27 N., R. 

77 W., comprises a down-dropped block bounded by 

two high-angle normal faults and broken by several 

subsidiary parallel and transverse faults. Drag on 

the beds adjacent to one of the bounding faults indicates predominantly dip-slip movement which appears to have been 50-60 feet. These faults cut rocks 

ranging in age from Early Triassic (Red Peak 

Formation) to Early Cretaceous (Thermopolis 

Shale), and they are blanketed by rocks of early 

Eocene age (Wind River Formation). The faults
36 GEOLOGY AND URANIUM DEPOSITS, SHIRLEY BASIN AREA, WYOMING

appear to be of Laramide age. Gouge and breccia 

zones along the faults are minimal or absent. Some 

of the faults contain banded silica or silicified breccia, the float from which aids in locating the faults 

in areas of poor outcrops and thin soil cover.

In the east-central part of the mapped area, several small faults cut rocks of the lower part of the 

Goose Egg Formation (Permian), and in the northeast corner of the area, small faults displace Precambrian diabase dikes and fracture the Madison 

Limestone (Mississippian). Inasmuch as these faults 

do not extend into the adjacent or nearly adjacent 

rocks of Tertiary age, they too are considered to 

be of Laramide age.

In the Bates Hole area, where exposures are good 

and individual sedimentary beds have lateral continuity, a few small faults have displaced beds in 

the Miocene Arikaree Formation. These faults have 

steep dips, have displacements of 10-20 feet, and 

are of short strike length. However, in the Chalk 

Mountain area, 500-6,500 feet west of the west 

edge of the mapped area, two major high-angle 

normal (?) faults displace rocks of the Arikaree 

Formation 70-300 feet to form a graben. These 

faults can be traced laterally for 10,000-25,000 feet.

Faults are rare in the mine workings in the 

central part of the basin. None were noted in the 

Utah Construction and Mining Co. mine workings or 

in the Petrotomics Co. Section 9 pit. One fault 

having about 5 feet of displacement has been exposed in the Section 15 pit. In some exposures in 

the Petrotomics Co. pits, beds have been displaced 

by slumping on paleostream banks and by squeezing and flowage during diagenesis of the newly 

deposited sediments, but beds a few feet above and 

below the distorted rocks show no displacement. 

Sketchy data on the paleotopography of the preWind River erosion surface in the northeastern part 

of T. 27 N., R. 79 W., show an abrupt rise toward 

the west. The rise may have resulted from displacement along a Tertiary fault, but for lack of confirming surface and subsurface data, the feature 

has been considered to be erosional and is so shown 

on the geologic map of the area.

FOLDS

A syncline traverses the western part of the Shirley Basin area. The trace of the axis on the eroded 

surface of the Steele Shale, shown on the geologic 

map (Harshman, 1968b), is parallel to and about 

10 miles west of the axis of the topographic basin. 

Rocks on the east limb of the syncline strike about 

N. 40° W. and dip 2°-12° SW.; rocks on the west 

limb strike north or northwestward and dip 2° -8°

E. Rocks of Tertiary age do not appear to have been 

folded, but because of poor exposures and irregular 

bedding in the Wind River Formation, it is impossible to state with certainty that the lowest Eocene 

rocks were entirely unaffected.

Attitudes observed in outcrops of Steele Shale 

in the Bates Hole area and along the south edge of 

the mapped area suggest that the fold is considerably tighter in the northern part of the area than 

in the southern part and that it plunges southward. 

It should be pointed out, however, that attitudes 

observed in Steele Shale may be misleading, owing 

to the instability of steep slopes in this formation 

and the expansiveness of the shale constituents.

In most of the Shirley Basin area the Tertiary 

rocks dip l°-2° N. These dips reflect a slight northward tilt of the area since original deposition. At 

the extreme west edge of the mapped area, and for 

several miles westward, there is a gradual change 

in the dip of the Tertiary rocks from northeastward 

to northwestward and finally to southwestward. 

These changes resulted from collapse, in an area 15- 

20 miles to the west, probably along major structures bounding the north flanks of the Shirley and 

Seminoe Mountains. The axis of this broad flat 

anticline in the Tertiary rocks lies several miles west 

of the mapped area. The fold is apparent in good 

exposures of conglomerate beds at the base of the 

upper member of the White River Formation in 

sec. 15, T. 28 N., R. 81 W. (fig. 22).

FIGUKE 21. Large landslide block (Ib) in the White River 

Formation on the west side of Bates Hole (sec. 13, T. 28 N., 

R. 81 W.). The contact between the upper (Twru) and 

lower (Twrl) members of the White River Formation lies 

just above and parallel to the upper edge of the slide. The 

large white blocks at the break in slope (indicated by 

arrows) are masses of conglomerate from upper member.
GROUND WATER 37

FIGURE 22. Gentle fold in beds of conglomerate at the base 

of the upper member of the White River Formation, sec. 15, 

T. 28 N., R. 81 W., about 1 mile west of the west edge of 

the mapped area. Looking northwest.

GROUND WATER

Because ground water was believed to play an 

important part in the genesis of uranium deposits, 

in their subsequent modification, and, under certain 

conditions, in their ultimate destruction, studies 

were made to determine the hydrology and chemical 

nature of ground water now flowing in the Shirley 

Basin. These data are used in this report to speculate 

on the character of the ground water at the time 

the ore deposits formed.

Depths to ground water were measured in about 

600 holes drilled in a 200-square-mile area of the 

Shirley Basin. Most of the measurements were made 

in the fall of 1959, before dewatering in preparation 

for mining had disturbed the normal ground-water 

regimen. All measurements were made with a device 

consisting of a reel, weighted probe, two-wire conductor, milliammeter, and battery power source. 

Depths were recorded to the nearest 0.5 foot. Surveyed collar altitudes were available for some of 

the holes, but most altitudes were taken from topographic maps, and they may be in error by as much 

as 5 feet.

Measurements of the depth to water were made 

in holes in which the water level was believed to 

have stabilized. Most depths were recorded in holes 

drilled a year prior to measurement; in more recently drilled holes, measurements were made at monthly intervals until consecutive readings were similar. 

To avoid false readings on surface water collected 

above a blocked section of hole, all holes were probed 

to make certain that they were open for several 

tens of feet below the water level. Measurements 

were made in the months June through September, 

a period of gradual rise of the ground-water table 

following the spring runoff. Utah Construction and 

Mining Co. records on observation wells in the

southern part of T. 28 N., R. 78 W., show the 

annual fluctuations of the water table to be 

about 2 feet.

Ground water in the Shirley Basin is unconfined, 

and the water table, in a general way, reflects the 

surface topography. In the eastern part of the 

mapped area, where data on the ground water are 

available, there are three perennial streams. Two of 

them, the Little Medicine Bow River and the lower 

reach of Sand Creek, have cut below the main 

ground-water body, and they are gaining streams. 

The third, Spring Creek, is fed from and flows on a 

perched body of water. It is a gaining stream with 

respect to the perched water, but it may be a losing 

stream with respect to the main body of ground 

water. Contours on the main ground-water table, 

plotted on a topographic base, are shown in figure 23. 

The water table slopes southward at gradients of 

20-30 feet per mile in the flat part of the basin and 

100-150 feet per mile under the steep north rim.

Ground-water studies were made by the Utah 

Construction and Mining Co. for dewatering their 

mine and subsequently for the control of the solvent 

used in their solution mining process. These data 

show that: the upper and lower sandstone intervals, 

as well as most of the individual lenticular sandstone beds, are interconnected; perched water is 

present above some of the shale beds; in the area 

of study, ground water is moving south under a 

gradient of about 20 feet per mile; and some of the 

sandstone beds have permeabilities of as much as 

1,000 meinzer units.

Water samples were collected from springs, 

pumped wells, and drill holes in the Shirley Basin 

area. Each sample was split between two 2-liter hard 

glass containers. One sample was treated with acetic 

acid and chloroform to keep uranium in solution and 

to prevent algal growth; the other sample was left 

untreated. Samples from drill holes were taken with 

a thief sampler suspended on a wire cable, and during the sampling process, small amounts of material 

from the drill-hole walls Were dislodged and fell 

into the water. Suspended material introduced in 

this manner was removed by filtering at the sample 

site, before acidification, to minimize changes in 

the true chemical composition of the water sample. 

Temperature and pH measurements were made at 

the sample sites. A colorimeter using chlorophenol 

red, brom thymol blue, cresol red, and thymol blue 

dyes was used to determine pH; probable accuracy 

was 0.1-0.2 pH units.

The analytical results for 42 water samples, 

grouped according to the geologic formations from 

which the samples were taken, are shown in table
38 GEOLOGY AND URANIUM DEPOSITS, SHIRLEY BASIN AREA, WYOMING

2. The locations for 35 of the samples are shown Average composition of water samples from the 

in figure 23. White River and Wind River Formations differs

R. 78 W.

42°22'30

7 %/ \ \

CONTOUR INTERVAL 50 FEET 

DATUM IS MEAN SEA LEVEL
GROUND WATER 39

markedly. Water from the White River Formation 

is moderately hard, moderately mineralized, and

of the calcium sodium bicarbonate type. The water 

from the Wind River is higher in silica and lower

r

R. 78 W. R. 77 W.

12679 10 s 

24,33^34 

37,38,42XB

Shaft

'_ PETRQTQMICS COMPANY 

lection^ /

it /

FIGURE 23. Contours drawn on the top of the ground-water table for a part of the Shirley Basin, Carbon County. Dashed 

where approximate; interval is 50 feet. X, ground-water sample locality. Base modified from Harshman (1968b).
40 GEOLOGY AND URANIUM DEPOSITS, SHIRLEY BASIN AREA, WYOMING

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:O

d

o\2

88

o

oo

o

om

O

+*>

moo 

<s<s

mo

Ots 

vpvo

ON 00

W5W

<sco

^ 

*j

Micromicrocuries 1per 

2Parts billion. per 
URANIUM DEPOSITS IN SANDSTONE 41

in magnesium, sodium, sulfate, chlorine, dissolved 

solids, noncarbonate hardness, radium, and uranium. The Wind River water is of the calcium sulfate 

and sodium bicarbonate type. It contains moderate 

amounts of dissolved solids and is moderately to 

very hard. The average pH of water from both the 

White River and the Wind River Formations is 

about 7.7. White River water samples in group 1 

were taken near the base of the upper member; the 

samples in group 2 were taken near the base of the 

lower member. Water from the two members is 

similar, but that from the lower member contains more sodium, sulfate, and uranium and somewhat less phosphate than does that from the 

upper member.

Ground-water samples from the Wind River 

Formation are much less uniform in chemical composition than samples from the White River Formation. For example, in samples from the Wind River 

Formation, calcium ranges from 13 to 126 ppm 

(parts per million), sodium from 7.6 to 268 ppm, 

bicarbonate from 94 to 280 ppm, sulfate from 24 

to 508 ppm, and uranium from 0.3 to 420 ppb; pH 

ranges from 6.6 to 8.4. Water samples from the 

Wind River Formation have been grouped in table 2 

according to the geologic environment from which 

they were taken. Group 1 samples were taken from 

the ore-bearing sandstone in the vicinity of large 

ore bodies and from 200-300 feet below the water 

table. They are similar in composition and contain calcium, sodium, bicarbonate, and sulfate as 

the principal constituents. Their average uranium 

content is the same as that in the water samples 

from the lower part of the White River Formation, 

but the radium content is greater by almost two 

orders of magnitude.

Group 2 samples were taken from exploratory 

drill holes in the western part of the Shirley Basin, 

where uranium ore lies near the base of the Wind 

River Formation and at or slightly below the 

ground-water table. The principal constituents of 

group 2 samples are the same as for group 1, but 

the amounts present range widely.

Ground-water samples from the White River 

Formation, groups 1 and 2, and from the Wind River 

Formation, group 1, appear to be in equilibrium 

with the geologic environments from which they 

were taken. Wind River samples, group 2, appear 

not to be similarly in equilibrium.

ORE DEPOSITS

Uranium is the only mineral commodity of major 

economic importance in the Shirley Basin area.

Large high-grade roll-type deposits occur in sandstone, and very small deposits occur in brecciated 

limestone in the karst surface at the top of the 

Madison Limestone. The Shirley Basin contains, in 

addition to uranium, deposits of monazite and construction materials.

«

URANIUM DEPOSITS IN SANDSTONE

The major uranium deposits in the Shirley Basin 

are in a well-defined belt of Wind River sandstone 

that was physically and chemically favorable for ore 

deposition. The belt extends for a distance of 6 

miles northwestward through the central part of 

the area. The uranium deposits are in several sandstone intervals of the Wind River Formation of 

early Eocene age. They are roll-type deposits and 

lie at the margins of large tongues of altered sandstone (fig. 24) formed by the flow of ore-bearing 

solutions through the host rock. The tongues are 

irregular in plan and section, and areas of greatest 

irregularity generally contain the best ore deposits. 

Individual ore bodies contain from a few tons to 

several hundred thousand tons of ore; grades, as 

mined, range from 0.1 to 0.7 percent U3O8.

The principal ore mineral, uraninite, is either 

fine grained or sooty. It is associated with pyrite, 

marcasite, native (?) selenium, ferroselite, hematite, 

calcite, and organic material. The ore and associated 

minerals coat sand grains and fill interstices between grains.

West of the mineralized belt, exploratory drilling 

has shown deposits of large size and medium grade 

to be present in sandstone-filled channels in the old 

pre-Wind River erosion surface and in bedded sandstones close to the base of the Wind River Formation. The mineralogy of this ore may be similar to 

that of the ore in the main mineral belt, but at the 

time this report was prepared very few data were 

available on these deposits. They appear to be related to altered sandstone, but the nature of the 

relation is unclear, and the character of the alteration appears unlike that in the mineral belt to the 

east. Meager data from drill cuttings in sees. 35 

and 36, T. 28 N., R. 79 W., sees. 1, 2, 3, 9, and 

10, T. 27 N., R. 79 W., and sees. 1, 2, and 3, T. 

27 N., R. 80 W., indicate that altered sandstone in 

this area contains considerable pyrite and that the 

feldspar in the arkose has been kaolinized. The 

milky-white color of the altered sandstone in this 

area contrasts with the greenish yellow color of the 

altered sand in the mineral belt to the east but is 

similar to altered sandstone described by King and 

Austin (1966) from the Gas Hills area and by Mrak
42 GEOLOGY AND URANIUM DEPOSITS, SHIRLEY BASIN AREA, WYOMING

(1968) in the Powder River Basin. Preliminary 

data indicate that disequilibrium may complicate 

ore-reserve estimates. These deposits are not discussed further in this report.

PALEOTOPOGRAPHIC CONTROL

* The major ore deposits in the Shirley Basin overlie the lowest part of the pre-Wind River erosion 

surface (fig. 25). Most of the deposits lie west of 

a prominent ridge on the old surface, but a few 

lie east of breached or low areas in the ridge. The 

ridge is formed by the indurated Wall Creek Sandstone Member of the Frontier Formation of Late 

Cretaceous age. It ranges in height from about 

400 feet near the north end of the mineral belt 

to about 100 feet near the south end, and it is buried 

beneath as much as 350 feet of Tertiary rocks. 

Southeast of the mineral belt the cover of Tertiary 

rocks has been removed by erosion, and the Wall 

Creek forms a prominent discontinuous ridge on 

the present surface.

The Wall Creek Sandstone Member separates the 

very soft, easily eroded shales of the Steele and 

Niobrara from the less easily eroded shales of the 

Frontier and Mowry. This difference in ease of 

erosion governed the configuration of the pre-Wind 

River erosion surface and the position of the lowest 

part of the basin. The paleotopography of the orebearing part of the Shirley Basin is shown by the 

red overprint on the geologic map of the area 

(Harshman, 1968b). The main or trunk stream that 

drained the area flowed northwestward, and it lay 

west of the ridge of the Wall Creek Sandstone Member. Major tributaries from both the east and the 

west joined the trunk stream in the area now containing the ore bodies. The presence of thick lignite 

beds interbedded with siltstone and cut by large 

crossbedded channel sandstone west of the ridge 

(fig. 26) indicates that the lowest part of the aggrading basin remained west of the ridge throughout much of Wind River time.

The coincidence of the lowest part of the basin 

and the favorable belt probably relates to the enFlGURE 24. Small roll on the upper surface of an altered-sandstone tongue in Wind River Formation in the Petrotomics Co. 

Section 9 pit. A, altered sandstone; U, unaltered sandstone; O, ore. Photograph by Emerson Kemp, Kerr-McGee Corp.
PALEOTOPOGRAPHIC CONTROL, URANIUM DEPOSITION 43

vironment at the time the Wind River sediments 

were being deposited west of the sandstone ridge.

Early in the depositional cycle, swampy flood-plain 

conditions developed along the trunk stream, and

106°07'30°

EXPLANATION

Niobrara Formation

Frontier Formation

Mowry and Thermopolis Shales

4+

HOMESTAKE MINING 

COMPANY Contact on pre-Wind River 

erosion surface, approximately 

located, showing dip

Contour drawn on pre-Wind 

River erosion surface

vrval 100 feet; datum, is mean

sea level 

0 2000 4000 6000 FEET

I I I

PETROTOMICS COMPANY 

- Section^

KERR-McGEE COR, , AC A

Pit

R. 78 W. R. 77 W.

FIGURE 25. Map of a part of the Shirley Basin showing paleogeology, paleotopography, and approximate locations of the 

principal ore deposits (pick-and-hammer symbol) with respect to the ridge of Wall Creek Sandstone Member, Frontier 

Formation.
44 GEOLOGY AND URANIUM DEPOSITS, SHIRLEY BASIN AREA, WYOMING

these conditions persisted through most of Wind 

River time. During periods of high water the tributary streams, flowing down the relatively steep 

slopes of the basin, carried considerable coarse 

clastic debris. Upon reaching the relatively flat 

flood-plain area in the lower part of the basin, this 

debris was deposited on and interbedded with the 

lignitic siltstone and lignite being deposited by the 

trunk stream. As a result of this depositional environment, strata in the lower part of the basin, 

just west of the ridge, consist of fine-grained 

siltstone and silty lignite interbedded with coarsegrained permeable channel sandstone a rock sequence that was favorable for uranium deposition 

at a later time.

FIGURE 26. Exposure in Petrotomics Co. Section 9 pit, showing a lower sandstone-filled channel (csl) cut in siltstone 

(si) and ore-bearing sandstone (obs) ; an upper sandstonefilled channel (csu) is cut in lignite (Ii), silty sandstone 

(ssi), and the lower channel sandstone (csl).

RELATION TO ALTERED-SANDSTONE TONGUES

The ore deposits in the mineral belt all lie at or 

near the margins of large tabular bodies of greenish-yellow altered1 sandstone. The outlines, in plan 

view, of the two principal altered tongues are shown 

in figure 27. The lower tongue is in a single sandstone interval that overlies the pre-Tertiary erosion 

surface. The upper tongue is in two sandstone intervals which in some places are separated by 30- 

40 feet of sandy siltstone and which in other places

irrhe term "altered" is used in the widely accepted sense to refer to those 

physical and chemical changes, excluding mineralization, effected by an orebearing solution on the rock through which it passed. "Unaltered" denotes 

a lack of such changes.

rest one on the other. The upper and lower altered 

tongues are separated by 50-75 feet of siltstone, 

lignitic siltstone, and silty claystone.

The upper altered tongue ranges in thickness 

from a few feet near its western edge to about 70 

feet several thousand feet from the edge. The upper 

and lower surfaces are generally concordant with 

the low dip of the Wind River Formation, but in 

many places the contact between altered and unaltered sandstone or altered sandstone and ore cuts 

sharply across sedimentary structures. The upper 

altered-sandstone tongue is 5 miles long in a northwesterly direction and as much as 3 miles wide. At 

one time it may have been somewhat longer, but 

south of the Petrotomics Co. Section 9 pit the tongue 

passes into the zone of recent weathering, and is 

obliterated. The upper altered tongue is about 90- 

150 feet below the surface in the Petrotomics Co. 

Section 9 pit, 350 feet deep in the Utah Construction 

and Mining Co. section 28 mine, and 450 feet deep 

2 miles farther north in sec. 20, T. 28 N., R. 78 W. 

The western edge of the tongue drops about 325 

feet in altitude in a distance of 4i/^ miles and thus 

plunges northwestward about 70 feet per mile.

The lower tongue has recently been exposed by 

mining operations in sec. 15, T. 27 N., R. 78 W., 

and in most aspects it is similar to the upper one. 

It lies beneath the southeastern part of the upper 

tongue but does not extend as far to the northwest. 

Drilling in sees. 15 and 16, T. 27 N., R. 78 W., 

about 2 miles south of the Petrotomics Co. Section 

9 pit, shows that the siltstone and silty claystone 

beds that separate the upper and lower sandstone 

intervals reach the ground surface in that area, and 

that to the south the upper sandstone tongue has 

been eroded.

Both of the altered-sandstone tongues end abruptly on their southwest sides. Near the western edges 

of the tongues there is no apparent difference in the 

permeabilities of the altered and unaltered sandstone, and it is probable that the limits of alteration 

were governed by chemical rather than physical 

changes in the host rock. In sharp contrast, the 

altered-sandstone tongues gradually fade out eastward along an irregular indistinct zone of decreasing 

permeability in the unaltered sandstone; therefore, the termination of the tongues eastward seems 

to result from physical as well as chemical changes 

in the host sandstone. For a short distance north 

from the Utah Construction and Mining Co. property, the eastern edge of the upper altered-sandstone tongue and the sandstone bed in which the 

tongue formed abut the buried ridge of Cretaceous 

rocks discussed earlier in this report. There is no
URANIUM DEPOSITS AND ALTERED-SANDSTONE TONGUES 45

ore at the contact of the altered sandstone and the 

Cretaceous shale and sandstone.

Factors controlling the geographic positions of 

the altered-sandstone tongues in the Shirley Basin

R. 78 W. 106°07'30° R. 77 W.

EXPLANATION

Edge of altered sandstone 

tongue

Dashed where approximately located

Contour drawn on pre-Wind 

River erosion surface

Interval 100 feet; datum is mean 

sea level

UTAH CONSTRUCTION AND 

MINING COMPANY

HOMESTAKE MINING 

COMPANY

KERR-McGEE CORP

PETRDTOMICS COMPANY 

15

FIGURE 27. Map showing relation of altered-sandstone tongues to paleotopography and the location of principal mines

at edges of altered-sandstone tongues.
46 GEOLOGY AND URANIUM DEPOSITS, SHIRLEY BASIN AREA, WYOMING

are not known, but possibly these tongues are related spatially to major streams that drained the 

west flank of the Laramie Mountains in Eocene 

time. Both tongues plotted in figure 27 extend to, 

and span, the mouth of a major valley in the preWind River erosion surface. Paleocontours and reconnaissance mapping east of the Shirley Basin 

project area indicate that the valley was formed 

by a major stream that extended at least 15 miles 

east of the center of the Shirley Basin (Denson and 

Harshman, 1969). The character of the sediment 

carried by this major tributary stream and deposited at, and downstream from, its confluence with 

the trunk stream may have been one of the factors 

that controlled the position of the altered tongues. 

However, a more important factor may have been 

the fact that the downward- and laterally migrating 

uranium-bearing ground water moved more easily 

through the material filling this major stream channel than through the material in which the channel 

was cut.

Alteration is generally limited to the highly transmissive thick sandstone intervals of the Wind River 

Formation. The effect of the permeability (a coefficient that is independent of thickness) of any 

particular bed on the configuration and position of 

the altered tongue is difficult to assess. Twentythree samples of sandstone (seven unaltered, two 

ore-bearing, and 14 altered) were selected for study 

to determine if size analyses would indicate differences in the permeabilities of the three sample 

groups. Table* 3 summarizes the size-frequency data 

of the samples after separation on a standard set 

of screens of decreasing class interval ^2 (ASTM

TABLE 3. Size-frequency data on 23 samples of altered, orebearing, and unaltered sandstone

[Data computed according to methods described by Pettijohn (1957, p. 

35-38). Grain size, in millimeters]

Grain size

Sample Mode

Coefficient

Median Sorting, Skewness, Kurtosis,

Unaltered sandstone

304

305

306

307

308

309

310

0.33

.42

.46

.44

.46

.48

.55

0.42

.46

.48

.48

.51

.48

.39

1.32

1.31

1.31

1.36

1.36

1.38

1.93

1.02

0.99

.97

.93

.93

.96

.79

0.203

.212

.206

.188

.207

.201

.199

Ore-bearing: sandstone

312

316

324

329

333

336

341

344

348

349

350

351

352

353

354

355

0.59

.57

0.57

.57

.57

.59

.35

.50

.35

.46

.33

.55

.54

.35

.35

.33

0.64

.59

Altered

0.54

.55

.55

.65

.40

.44

.40

.44

.43

.54

.46

.42

.40

.40

1.44

1.47

sandstone

1.35

1.53

1.37

1.58

1.52

1.46

1.83

1.46

1.46

1.46

1.50

1.48

1.52

1.41

1.02

.94

0.90

1.00

.94

1.15

.98

.99

1.03

.99

.97

.84

.83

.90

.91

.91

0.186

.237

0.168

.250

.179

.236

.227

.213

.240

.207

.212

.209

.246

.222

.220

.245

sieve scale). Figure 28 shows typical frequency and 

cumulative distribution curves for the three groups 

of the samples. Unaltered, altered, and ore-bearing 

sandstones are similar in their principal physical 

parameters. The sandstones are well sorted, slightly 

skewed toward the fine sizes, and moderately peaked. 

Although these data indicate no significant difference between altered and unaltered sandstone, it 

is probable that gross permeability, not the permeability of any small segment of the sandstone 

interval, controlled the position of the tongues.

0.5 0.25 0.125 0.0625 

GRAIN DIAMETERS, IN MILLIMETERS

0.03125

FIGURE 28. Cumulative and frequency distributions of three 

samples of sandstone from the ore-bearing sandstone interval, Petrotomics Co. Section 9 pit.

CHARACTER OF ALTERATION

Color is the most striking difference between 

altered and unaltered sandstone. This color difference is well illustrated in the frontispiece photograph. In some exposures the color contrast is 

strong and easily recognized, in others it is subtle 

and can be seen only in sandstone containing considerable silty material. Unaltered sandstone, where 

unweathered, is generally medium to light gray. 

Altered sandstone is generally greenish yellow, although in some areas it is orange, red, or reddish 

brown. When samples of gray unaltered sandstone 

and greenish-yellow altered sandstone are screened, 

silt and clay retain the diagnostic color. The minus200-mesh, or 0.074-mm (millimeter), fraction of a 

sample of altered sandstone constitutes only 3.3 

percent of the sample, but this fraction contains
URANIUM DEPOSITS, ALTERATION 47

about 36 percent of the iron in the bulk sample. 

In sharp contrast, the minus-200-mesh fraction of 

unaltered sandstone contains only 12 percent of the 

iron in the bulk sample. X-ray analyses of the 

Tractions of altered sandstone smaller than 0.002 mm 

in diameter show these materials to be montmorillonite that is high in iron; the same size fractions 

of unaltered sandstone are montmorillonite that is 

low in iron. These data suggest that the color distinctions between altered and unaltered sandstone 

are a result of the amount and oxidation state of 

iron in the fine-grained fractions of the rocks.

To determine the changes in the sandstone which 

were due to alteration by the ore-bearing solutions, 

39 samples of sandstone were tested for the relative 

amounts of clay, silt, and sand (by weight), the 

content of acid-soluble material (by weight), and 

the principal heavy minerals (by weight and by 

grain count). The data from the study are in table 

4. The heavy minerals were separated in bromoform,

and the heavy-mineral percentages were determined 

by counts on mineral grains ranging from 0.044 to 

0.250 mm in diameter. Depending on the shape, 

diameter, and specific gravity of the grains, the 

amount of any mineral may differ considerably 

from the grain count. For example, in samples 214 

and 215 the percentages (by grain count) of hornblende and epidote are about equal, but because 

most of the epidote is in large spherical grains and 

most of the hornblende is in small tabular grains, 

the amount (by volume) of epidote in the sample 

is at least three times that of hornblende.

The black opaque mineral contents of ore, altered 

sandstone, and unaltered sandstone shown in table 

4 are not directly comparable. Uraninite, absent in 

altered and unaltered sandstone, is present with 

other black opaque minerals of the ore samples. An 

estimate of the sedimentary (syngenetic) black 

opaque minerals for each ore sample is shown in 

parentheses in the table.

TABLE 4. Physical and mineralogical data on 39 samples of unaltered, altered, and ore-bearing sandstone

Total sample

(percent by weight)

Sample

Acid soluble

 o 

c 

a

Ol

Is

&o

<M

<° -~.

O C O B 

O

Smaller than 

(clay) 0.008 mmIn 0.044-250 to

fraction mm 

by weight (percent 

Hornblende

Grains per

Epidote

U

Heavy minerals

100 grains in 0.044- to

Zircon Sphene Biotite

0.250-mm fraction

Zoisite and

sillimanite Miscellaneous Black opaque minerals 1

Pyrite

Goethite andhematite

Unaltered sandstone

183

186

198

199

200

201

202

203

214

215

268

179

184

251

252

253

254

255

256

257

258

259

180

189

190

194

216

217

260

265

266

270

1.47

1.67

31.54

2.60

1.31

2.12

7.22

4.81

1.21

1.15

4.37

1.17

2.47

1.75

2.40

1.92

1.04

1.75

1.25

1.08

.82

1.32

0.73

1.80

5.53

3.58

1.57

1.87

3.23

.70

4.17

1.23

95.39

94.05

58.62

81.53

95.04

94.86

86.95

88.12

96.65

96.84

87.78

96.26

95.89

95.22

91.53

94.47

95.91

94.29

94.75

95.52

95.78

94.38

95.96

95.97

90.62

90.32

95.28

94.49

94.63

90.61

87.86

90.45

2.27

2.70

9.30

13.06

2.50

2.22

4.50

3.93

1.59

1.45

6.53

1.80

1.28

2.04

4.70

2.32

2.25

2.47

2.91

2.52

2.46

3.34

2.61

1.62

2.80

5.15

2.27

2.69

1.63

7.23

6.29

7.04

0.87

1.58

.54

2.81

1.15

.80

1.33

3.14

.55

.56

1.32

0.77

.36

.99

1.37

1.29

.80

1.49

1.09

.88

.94

.96

0.70

.61

1.05

.95

.88

.95

.51

1.46

1.68

1.28

2.45

2.80

2.63

3.10

2.90

3.14

1.64

2.47

4.04

3.57

1.95

Altered

2.86

.90

3.41

1.90

5.18

1.15

2.04

1.73

1.90

2.10

1.30

Altered

1.71

3.78

2.88

1.47

2.54

1.93

1.38

1.87

1.53

1.71

30

19

12

31

40

46

23

40

27

33

1

sandstone

42

25

28

37

24

36

33

32

36

42

35

sandstone

28

31

35

2

23

36

29

1

0

0

Unaltered sandstone that

181

182

187

193

261

262

263

1.97

1.71

2.27

2.21

5.36

7.35

9.19

96.12

96.32

94.84

95.43

87.92

85.07

84.08

1.54

1.41

2.15

1.89

5.55

6.29

5.44

0.37

.56

.74

.47

1.17

1.29

1.29

2.77

2.49

7.23

2.88

2.52

1.32

2.07

38

25

9

17

0

0

0

34

31

44

3

27

19

28

18

23

35

37

more than

23

25

28

38

45

38

39

25

37

35

44

closer than

40

33

30

29

44

29

30

42

46

42

15

7

1

26

12

7

5

12

15

3

13

5 ft from

17

21

10

16

20

14

14

21

16

16

5

5 ft from

11

11

17

12

14

14

5

15

26

26

0

2

1

2

0

3

1

1

1

4

1

ore

0

4

5

0

1

0

1

6

3

1

3

ore

0

2

0

0

3

7

1

4

1

6

2

2

1

1

1

2

9

2

2

2

5

12

2

4

0

3

2

1

0

0

0

0

6

2

3

1

0

3

5

2

5

4

0

0

15

0

1

1

1

1

0

0

1

2

0

0

0

0

0

0

0

0

1

3

0

1

0

0

7

0

0

6

0

1

1

0

0

1

1

1

1

0

2

2

4

0

3

3

1

2

2

1

5

3

0

1

1

0

1

3

1

1

0

3

0

1

0

1

0

2

1

0

0

0

0

0

1

0

0

3

2

0

1

2

2

0

0

0

0

0

0

1

0

0

0

4

1

0

5

6

3

3

3

8

5

5

5

2

6

4

6

19

6

5

6

8

8

5

4

7

5

3

2

3

8

8

18

6

4

6

13 0

32 0

23 0

31 0

14 0

13 0

27 0

21 0

25 0

19 0

31 0

0 0

0 14

0 0

0 0

0 0

0 1

1 0

0 1

0 0

0 1

0 2

6 3

17 0

12 0

1 48

0 0

2 0

4 8

14 3

12 5

10 4

contains more than 0.1 percent U

20

23

14

22

4

19

10

16

19

3

29

5

12

4

2

0

6

0

2

3

4

0

1

0

0

0

0

0

0

8

0

0

0

0

0

1

0

0

1

0

1

1

0

0

1

2

0

0

4

22(6)

2(2)

24(10)

4(3)

9(4)

17(8)

24(10)

1 0

22 0

43 0

25 0

80 0

44 4

53 0

1 Figures in parentheses exclude uraninite.
48 GEOLOGY AND URANIUM DEPOSITS, SHIRLEY BASIN AREA, WYOMING

Table 4 quantifies some of the differences between 

altered and unaltered sandstone observed in the field. 

Pyrite, present in unaltered sandstone in significant 

amounts, has been largely destroyed in the altered 

sandstone, and it has been deposited with uranium 

in the ore bodies. Pyrite constitutes about 23 percent (by grain count) of the heavy-mineral suite 

in unaltered sandstone, 38 percent in ore-bearing 

sandstone, 8 percent in altered sandstone within 

5 feet of ore, and only 0.9 percent in altered sandstone more than 5 feet from ore. Chemical analyses 

for sulfide sulfur, run on about 200 samples of 

ore and host rock, confirm the conclusions based 

on heavy-mineral counts and show that sulfide minerals (pyrite and minor amounts of marcasite are 

the only known sulfide minerals associated with ore) 

constitute 0.19-2.75 percent (by weight) of the unaltered sandstone, 0.20-17.60 percent of ore, 0.04- 

0.77 percent of altered sandstone near ore, and 0.02- 

0.04 percent of the sandstone more than 5 feet 

from ore.

Early work in the Shirley Basin (Harshman, 

1962) suggested that the black opaque minerals in 

the altered sandstone had been partly destroyed 

by the ore-bearing solutions. Subsequent work has 

shown this to be untrue. Data in table 4 indicate that 

the black opaque minerals from altered and unaltered sandstone are similar, and that they 

constitute 4.5-7.0 percent of the heavy-mineral concentrate. Magnetite is present in each of the samples. 

The weight percent of heavy minerals in the unaltered sandstone is greater than in the altered 

sandstone (2.8 versus 2.2 and 2.1 percent), but this 

reflects differences in pyrite, not differences in the 

black opaque mineral contents.

Alteration by ore-bearing solutions, particularly 

acid ones, generally produces fine-grained material, 

so alteration in the Shirley Basin might have resulted in an increase in the clay content of the sandstone. The first indication that this was not the case 

came when clay-sized particles (less than 0.002 mm 

in diameter) were separated from altered- and unaltered-sandstone samples for identification of the 

clay minerals in the two rocks. Almost without exception, the amount of clay obtained from 500-gram 

samples of altered sandstone was slightly less than 

that obtained from equal weights of unaltered sandstone. Size analyses of the 39 samples listed in 

table 4 show that unaltered sandstone contains an 

average of 1.33 percent by weight of particles less 

than 0.008 mm in diameter (clay and very fine 

grained silt), and that altered sandstone contains 

only 1.00 percent of the same sized particles. Comparable data from the samples listed in table 3

show that particles less than 0.044 mm in diameter 

comprise 1.47 percent of unaltered sandstone and 

1.08 percent of altered sandstone. These data suggest that alteration decreased the amount of finegrained material in the rock, but the apparent 

decrease may have resulted from inadequate sampling. It seems certain, however, that alteration did 

not result in an increase in the amount of very fine 

grained constituents in the sandstone.

Destruction of much of the calcium carbonate in 

altered sandstone is apparent in exposures near the 

margins of the altered tongues. It is confirmed by 

the contents of acid-soluble constituents listed in 

table 4 and by analyses for mineral carbon in about 

100 samples taken in ore and host rocks. Acidsoluble constituents comprise 2.79 percent of the 

unaltered sandstone (sample 198, table 4, omitted 

in calculating this average), 2.44 percent of the 

altered sandstone near ore, and 1.54 percent of the 

altered sandstone more than 5 feet from ore. Analyses for mineral carbon, converted to CaC03 , 

show that calcium carbonate constitutes 2.25 percent of the unaltered sandstone, 2.00 percent of the 

altered sandstone near ore, and 0.15 percent of the 

altered sandstone several tens of feet from ore. 

Analyses for acid-soluble constituents and for mineral carbon were made on different suites of samples 

and are therefore not directly comparable. Because 

calcite is generally in concretions rather than distributed throughout the rocks, few sandstone beds 

contain calcium carbonate in amounts approaching 

the averages given above.

Field and laboratory evidence shows that carbonaceous material, common in the Wind River Formation throughout the lower part of the Shirley Basin, 

has been almost completely destroyed in the alteredsandstone tongues. Figure 29 is a photograph taken 

in the Petrotomics Co. Section 9 pit where a vertical 

cut exposed the contact between altered and unaltered sandstone along the lower surface of an 

altered tongue. The photograph shows considerable 

dark carbonaceous trash in crossbedded unaltered 

sandstone below the contact; the amount of trash 

decreases rapidly on the same crossbeds in the 6- 

to 8-inch interval in altered sand above the contact, 

and at a point about 1 foot above the contact the 

trash has been completely destroyed. Carbonaceous 

material in unaltered sandstone is generally vitreous 

and shows the structure of the woody material 

from which it was derived. In marked contrast, the 

carbonaceous material in altered sandstone near the 

contact is generally sooty and shows no relict structure. Carbonaceous material at the contact, or in 

altered sandstone very near the contact, may have
URANIUM DEPOSITS, ALTERATION 49

a vitreous core and an altered sooty shell. Within 

the altered-sandstone tongue, at distances of more 

than 10 feet from the edges, carbonaceous material 

is rare, and where found, it generally consists of 

small sooty nodules containing considerable silt 

and clay.

Chemical analyses confirm the field evidence that 

alteration destroyed carbonaceous material once 

present in the sandstone. Because of its erratic 

distribution, the organic-carbon content of unaltered 

sandstone ranges between wide limits, but most, 

samples contain a few tenths of a percent and a 

few contain as much as 2 percent organic carbon. 

The organic carbon content of altered sandstone, 

on the other hand, is generally less than 0.10 percent near the margins of the tongues and less than 

0.02 percent a few feet from the margins.

The Fe+2/Fe+3 ratios in the sandstone host rocks 

changed considerably during the ore-forming process. Analyses of samples from three roll-type ore 

bodies, two in the Petrotomics Co. Section 9 pit

and one in the underground mine of the Utah Construction and Mining Co., show that unaltered sandstone, presumably unaffected by the ore-bearing 

solutions, has a Fe+2/Fe+3 ratio ranging from about 

2.0:1 to 4.5:1. In marked contrast, the altered sandstone more than 5 feet from ore has a ratio ranging 

from about 1.5:1 to less than 0.4:1 and generally 

less than 1:1. The total-iron contents of altered 

and unaltered sandstone are approximately the 

same. The ore contains much more total iron than 

does either the altered or the unaltered sandstone. 

Fe+2/Fe+3 ratios in ore range from about 4.5:1 

to more than 100:1 and reflect the large amount of 

pyrite deposited with uranium in the ore bodies.

A marked difference in selenium content distinguishes altered from unaltered sandstone. Several 

hundred samples of unaltered, unmineralized sandstone from the ore-bearing intervals and from 

strata in the pit walls above those intervals were 

analyzed turbidimetrically for selenium. They contain 0.5-4 ppm selenium. The higher amounts are

V r

r -x

.- --. . ?& *,

FIGURE 29. Vertical exposure in Petrotomics Co. Section 9 pit, showing contact (dashed) between altered (A) and unaltered 

(U) sandstone on lower surface of altered-sandstone tongue. Dark streaks in unaltered sandstone are carbonaceous materials on crossbeds.
50 GEOLOGY AND URANIUM DEPOSITS, SHIRLEY BASIN AREA, WYOMING

generally in the fine-grained carbonaceous rocks; 

the lower amounts are in the sandstone and conglomerate. The nature of the selenium in these rocks 

is unknown; it may be in the native state. In altered 

sandstone a few feet or more from the edges of the 

altered tongues, selenium constitutes 10-40 ppm 

of the altered rock, and thus is about 1 order of 

magnitude more abundant than in unaltered sandstone. Inasmuch as selenium forms relatively insoluble compounds with iron, this selenium probably 

is associated with limonite and goethite, common in 

the altered sandstone. High concentrations of selenium at the margins of the altered-sandstone 

tongues and in the ore are described in the discussion of mineralogy and mineral distribution.

There is some evidence that copper has been 

leached from the altered-sandstone tongues. Analyses on one suite of samples from the Petrotomics 

Co. Section 9 pit show that altered sandstone contains an average of 3 ppm copper (range, 1-7 

ppm) and that unaltered sandstone contains 10 

ppm (range, 2-15 ppm) . However, two other sample 

suites, one from the Petrotomics Co. Section 9 pit 

and the other from the Utah Construction and Mining Co. mine, show little difference in the copper content of altered and unaltered sandstone.

Table 5 summarizes the principal differences between altered and unaltered sandstone in the Shirley 

Basin.

TABLE 5. Principal differences between altered and unaltered sandstone

Altered sandstone Unaltered sandstone

Color.......................................Greenish yellow, Gray.

orange, red. 

Montmorillonite. ...............High in iron.....................Low in iron.

Pyrite.....................................Largely destroyed............Present in significant

amounts. 

Calcite......................... .............................do.................... Do.

Carbonaceous material...........................do.................... Do.

Copper............................ .....Some leaching ?................Present in small amounts.

Selenium...............................10-40 ppm.. ....................1 ppm or less._________

THE ORE BODIES 

PHYSICAL CHARACTER

The major ore bodies in the Shirley Basin are 

at the edges of the altered-sandstone tongues in 

zones that separate altered from unaltered sandstone. Their inner contacts with altered sandstone 

are generally sharp, and their outer contacts with 

unaltered sandstone are gradational. An ore body, 

in its simple form, is crescent shaped in section, 

and in plan it is elongate parallel to the margin of 

the altered tongue. Ore boundaries generally cut 

bedding of the host rock at steep angles, although

the horns of the crescent may be peneconcordant 

with the bedding. Fischer (1942) used the term 

"roll" to describe vanadium-uranium ore bodies in 

Colorado and Utah which had curved edges, and 

Shawe (1956) discussed the shape and genetic 

significance of rolls. These ore bodies differ somewhat in form and perhaps in origin from those in 

the Shirley Basin. The term, however, has been extended to describe the crosscutting ore bodies found 

in the Wyoming basins. Many of the ore bodies in 

the Shirley Basin are complex and consist of several 

rolls and lenticular bodies connected by thin bands 

or layers of ore. A simple roll-type ore body is 

shown in figure 30Z?; more complex ore bodies are 

illustrated in figure 30,A and C.

Although ore is found only in a zone along the 

altered-unaltered sandstone contact, the contact is 

not everywhere bordered by ore-grade material. 

Samples of both altered and unaltered sandstone, 

taken a few inches from the contact, have contained 

as little as 0.02-0.05 percent uranium.

Most of the ore in the Shirley Basin is in rolltype ore bodies at or near the edges of the tongues, 

but some ore is in tabular, lenticular, or roll-like 

bodies on the top and bottom surfaces of the 

tongues. These bodies are generally smaller than 

those at the margins, but they may be of high grade. 

A small body of ore, about 1,200 feet east of the west 

edge of the upper altered-sandstone tongue, is shown 

in figure 31. The ore is associated with a small irregular body of unaltered sandstone that extends 

upward into the lower part of the altered-sandstone 

tongue. The unaltered sandstone contains considerable silt, and it therefore has a low transmissivity, 

which accounts for its presence within the altered 

tongue. Continued flow of the ore-bearing solutions 

would have eventually altered this sandstone and 

destroyed the ore associated with it. Ore, associated 

with irregular bodies of this type and perhaps with 

islands of unaltered sandstone, is common near, or 

within several thousand feet of, the edges of the 

altered tongues.

Individual ore bodies in the Shirley Basin are 

not extensive, either in lateral dimension or in total 

tonnage. The largest known deposits, which extend 

as much as 200 feet from the edge of the alteredsandstone tongues, are as much as 30 feet thick and 

extend a few hundred to as much as 2,500 feet 

laterally along the edges of the tongues (Melin, 

1964, fig. 4). Ore bodies of this size contain several 

hundred thousand tons of ore. The grade of mineralized sandstone ranges from a few thousandths of a 

percent to as high as 20 percent for small samples.
PHYSICAL CHARACTER OF ORE BODIES 51

Ir-aitered sandstone \ 

" "~~ Bottom of pit

 ;. Alte/ed- ; '.;.. 

sand.stppev.V-.M Ore v-^^-'-^v-^:-:-/'-/^^

B

HORIZONTAL AND VERTICAL SCALE

FIGURE 30. Sections at the west edge of the upper altered-sandstone tongue. A and C, two complex rolls in the Petrotomics 

Co. Section 9 pit; B, a simple "C" roll in the Utah Construction and Mining Co. mine.

'.- .40 feet-'.', 

tp'oyprlyjrig 

.' .siltstbhe-':

ore f : //--/-'.;:-:-:-"----'-'vv:.v--;v'-"-'::-:^::-:: : ::-:-

Unaltered silty sandstone with calcite concretions and lignite

10 30 FEET

HORIZONTAL AND VERTICAL SCALE

FIGURE 31. Small ore body on bottom of altered-sandstone tongue, about 1,200 feet back from edge of tongue, Petrotomics

Co. Section 9 pit.
52 GEOLOGY AND URANIUM DEPOSITS, SHIRLEY BASIN AREA, WYOMING

Average grades of material mined range from about 

0.10 to 0.70 percent U3O8 . This spread in grade of 

ore mined reflects economic factors relating to mining and beneficiation costs at individual properties 

and not to geologic factors. The highest grade ore 

may be adjacent to the altered-sandstone tongue, 

or it may be separated from the tongue by a few 

feet of lower grade ore. In this characteristic, the 

Shirley Basin deposits are similar to those described 

by Kashirtseva (1964) in undesignated areas in the 

U.S.S.R., but they are dissimilar to those described 

by King and Austin (1966) in the Gas Hills where 

they found that the peak values of uranium and 

many of its associated elements always occur several feet beyond the edge of the altered tongue.

The boundaries of the ore bodies, particularly 

the boundaries between ore and altered sandstone, 

are almost everywhere broad curved features that 

cut sedimentary structures at sharp angles. The 

positions and shapes of these boundaries seem to be 

controlled by broad geochemical processes influenced

only to a very minor extent by local permeability 

of the host rock. Ore deposition, on the other hand, 

has been influenced to a considerable extent by the 

relative permeability of different parts of the host 

rock, and in many places the ore minerals accentuate permeability differences along crossbeds, bedding planes, and scours. The broad crosscutting 

character of the ore-altered sandstone contact is 

well shown in the frontispiece and in figures 32 and 

33; the effect of permeability differences is shown 

on the two figures. In figure 34 is a somewhat 

atypical ore body that shows no broad crosscutting 

features but instead shows a strong control of ore 

deposition by crossbedding in the host rock.

Some ore bodies at the margins of the alteredsandstone tongues are asymmetric in cross section. 

Although exceptions are common, there appears to 

be some tendency for the highest grade and largest 

amount of ore to occur on the lower limb of an 

asymmetric roll. By far the largest amount and 

highest grade ore in the roll shown in figure 32 is in

FIGURE 32. Exposure on north wall, phase 1, Petrotomics Co. Section 9 pit, showing crosscutting contact between altered 

sandstone (A) and ore (dark gray) and accentuation of crossbedding by ore minerals. Thickness of ore zone is about 10 

feet in this exposure.
MINERALOGY OF ORE BODIES 53

the lower limb, as is true for the rolls shown in 

figure 30. Ore not at the margins of the altered 

tongues seems to be about equally distributed on the 

top and bottom surfaces of the tongues.

FIGURE 33. Exposure on north wall, phase 1, Petrotomics 

Co. Section 9 pit, showing ore at edge of altered-sandstone 

tongue (A). Contact between altered sandstone and ore cuts 

crossbeds at high angles, but ore tends to be of high grade 

on crossbeds. Ore at this place is about 12 feet thick and 

contains 1-2 percent uranium.

FIGURE 34. Exposure in west wall, phase 1, Petrotomics Co. 

Section 9 pit, showing strong control of ore by permeable 

crossbeds in the host sandstone and no sharply defined 

crosscutting boundary of the ore body.

Roll-type uranium deposits have been divided into 

zones or sections by some authors. Kashirtseva 

(1964) used the terms "bypass," "black ore," and 

"gray ore" for subzones of ore progressively distant 

from the edge of an altered-sandstone tongue. King 

and Austin (1966) divided the mineralized rock

into a "rich ore section," "intermediate section," 

and "protore." Some of the Shirley Basin deposits 

could be divided in a similar manner, but as the 

highest grade ore may occur in the "intermediate 

zone" and the "black ore" may not be the highest 

grade, such an unnatural division seems inadvisable 

here. Mineralogical and elemental zonation which 

has genetic significance has been recognized in the 

Shirley Basin deposits and is discussed later in 

this report.

MINERALOGY AND MINERAL DISTRIBUTION

The Shirley Basin deposits are of simple mineral 

composition. The principal epigenetic minerals in 

the ore are pyrite (FeS2 ), marcasite (FeS2 ), uraninite (U02 ), ferroselite (FeSe2 ), native (?) selenium 

(Se), hematite (Fe203 ), and calcite (CaC03 ). The 

ore is unoxidized, and it contains no secondary 

uranium minerals.

Pyrite is the most abundant epigenetic mineral in 

the sandstone host rock and has the widest distribution. It is present in unaltered sandstone far from 

ore, in ore, and in altered sandstone near ore. Unaltered sandstone contains about 1 percent pyrite, 

most of which is disseminated through the rock; 

some pyrite surrounds clay balls, cements gravelly 

crossbeds, or replaces carbonaceous material. Pyrite 

in unaltered sandstone is untarnished and is in 

euhedral or subhedral grains a few hundredths of 

a millimeter in diameter or in grain aggregates as 

much as 1 mm in diameter. A few pyrite grains or 

grain aggregates are as much as 5 mm in diameter. 

Most of the identifiable grains are either cubes, 

octahedrons, or cubes modified by octahedral faces; 

pyritohedrons have not been recognized. Much 

of the fine-grained pyrite is attached to the sand 

grains, but some of it replaces clay in the host 

rock. This epigenetic pyrite is unrelated to the oreforming processes, and it is considered as a "background of mineralization" on which the ore deposits 

were superimposed.

Pyrite is abundant in the ore and commonly is 

more abundant than uraninite; there is no consistent 

ratio, however, between uranium and sulfide-sulfur 

contents of ore samples (table 6).

Sandstone having the highest pyrite content is 

most commonly in ore adjacent to the margins of 

the altered-sandstone tongues, but in some places 

it is separated from the altered sandstone by a few 

feet of material with a lower pyrite content. On the 

outer extremity of the ore deposits, pyrite extends 

farther from the altered-sandstone tongues than does 

any other epigenetic mineral, with the possible exception of calcite.
54 GEOLOGY AND URANIUM DEPOSITS, SHIRLEY BASIN AREA, WYOMING

TABLE 6. Uranium and pyrite contents of some Shirley 

Basin ores from Utah Construction and Mining Co. mine 

and Petrotomics Co. Section 9 pit

Sample

120

124

126

127

131

187

193

196

277

324

337

342

394

403

Uranium 

(percent)

2.34

2.50

.16

1.04

10.74

.22

.63

19.2

1.50

.45

4.62

.38

.84

.51

Sulfide sulfur

Per nt Percent equivalent U/S ratio 

pyrite

1.41

.98

.45

.34

.87

1.33

.41

6.93

.52

.17

6.40

.69

.72

1.06

2.64

1.84

.84

.64

1.63

2.49

.77

12.99

.98

.32

12.00

1.29

1.35

1.99

1.66

2.55

.36

3.06

12.34

.17

1.54

2.77

2.88

2.65

.72

.55

1.17

.48

Pyrite occurs in the ore as small euhedral to 

subhedral crystals, as small aggregates of grains, 

as coatings on sand grains, and as botryoidal masses 

filling open spaces in the host rock. The crystal 

forms of the small pyrite grains and grain aggregates are difficult to determine, but cubes and cubes 

modified by octahedral faces appear to be most common. Most of the euhedral pyrite is untarnished or 

only slightly iridescent, but the pyrite coatings on

FIGURE 35. Feldspar (F) replaced by pyrite (p) along cleavage and fractures. Silvery-gray mineral is uraninite (U).

sand grains are tarnished iridescent to bluish black. 

The tarnish may be due to the intimate association 

of pyrite and uraninite in these coatings.

Microscopic studies of polished and thin sections 

of ore show that single rims of mineral material 

on sand grains generally consist of pyrite. If multiple rims surround sand grains, the inner or inner 

and outer rims are pyrite, and the middle rim is 

uraninite. Replacement of feldspar by pyrite is 

common (fig. 35). Figure 36 shows pyrite in highgrade calcite-cemented ore.

In altered sandstone, pyrite is present in significant amounts only in a zone a few feet wide adjacent 

to ore. At other places in the altered tongues, pyrite 

is absent or is present only in trivial amounts 

(table 4). It forms small euhedral to anhedral 

grains or grain aggregates, similar to those in 

unaltered sandstone but with the important distinction that many of the grains in altered sandstone 

are corroded and have irregular outlines. Generally 

this pyrite is more tarnished than that in unaltered 

sandstone, although some bright untarnished grains

-HI

FIGURE 36. Pyrite (P) as irregular grains in uraninite (U) 

.and in rims surrounding quartz grains (qz). Pyrite and 

uraninite fill open spaces in high-grade calcite-cemented ore 

(C) from Petrotomics Co. Section 9 pit.
MINERALOGY OF ORE BODIES 55

are mixed with the tarnished ones. The very small 

pyrite grains that are attached to the sand grains 

of unaltered sandstone are not present in altered 

sandstone.

King and Austin (1966) described morphologic 

differences in pyrite from altered, unaltered, and 

ore-bearing sandstones in the Gas Hills area of 

Wyoming. These differences are not characteristic 

of similar rock units in the Shirley Basin, although 

selected samples may show some of the differences 

they described.

Marcasite is a very minor constituent in ore and 

seems to be most abundant in ore near the contact 

with altered sandstone. It can be visually identified 

only in polished and thin sections of ore, where it is 

in the form of small irregular or lathlike grains 

intergrown with pyrite or isolated grains dispersed 

through calcite. In polished sections it contrasts 

with pyrite by having a less brassy color, a less 

pitted surface, and strong anisotropism. Its presence 

in ore has been confirmed by X-ray diffraction 

techniques. The distribution of marcasite is similar 

to that of pyrite.

Uraninite is the only uranium-bearing mineral 

that has been identified in the Shirley Basin ore, but 

coffmite may be present and unidentified. Some uranium may be present as an organic-uranium compound or chelate, but because of the very complex 

nature of this geochemical field, investigations to determine the presence or absence of such compounds 

were not attempted. X-ray diffraction studies indicate that the uraninite contains considerable UO3 , 

probably formed by auto-oxidation of UO2 . Uraninite 

coats grains of the host sandstone, fills interstices 

between grains, and in some places fills fractures in 

grains or replaces grains particularly feldspar. 

It was deposited through a zone much wider than 

the selenium zone but narrower than the zone in 

which pyrite and marcasite were deposited.

Uraninite forms the inner rim on sand grains 

in a few samples of ore, but in most samples it 

forms an outer rim on pyrite-marcasite or, if three 

rims are present, the middle rim between two pyritemarcasite rims. In a few polished sections of ore, 

minute veinlets of pyrite-marcasite cut through 

uraninite. They are so small that it is impossible to 

establish continuity with either the inner or the 

outer pyrite-marcasite rim, but they probably represent late (outer rim) pyrite-marcasite that fills 

shrinkage cracks in uraninite. Other interpretations are possible. Figure 37 shows the relations 

just described.

Selenium is abundant in a very narrow zone 

astride the contact between altered sandstone and

ore. The zone is sharply defined, and in some places 

the selenium content drops from 0.10 percent to a 

few parts per million in a distance of about 1 

foot. The selenium-bearing mineral in ore probably 

is native selenium. One sample 6 inches from the 

altered-sandstone tongue contained a number of 

small reddish-gray radiating acicular crystals associated with pyrite; these crystals probably were 

native selenium, but they were too small and too 

few to be positively identified. Native selenium has 

been described from similar deposits in Russia 

(Kashirtseva, 1964) and at Ambrosia Lake, N. Mex. 

(Granger, 1963).

Ferroselite has been identified in altered sandstone near the contact with ore. It occurs in twinned 

clusters attached to sand grains or to clay. The 

clusters range from a few hundredths to as much 

as 0.2 mm in diameter. Similar ferroselite clusters 

have been described in the Powder River Basin 

uranium deposits (Granger, 1966). The quantities 

of ferroselite in altered sandstone and of native ( ?) 

selenium in ore-bearing sandstone do not appear to

FIGURE 37. Polished section of ore from Petrotomics Co. 

Section 9 pit, showing pyrite-marcasite (P) and uraninite 

(U) rims on quartz sand grains (qz); small veiniets of 

pyrite-marcasite (vp) cut some of the uraninite rims.
56 GEOLOGY AND URANIUM DEPOSITS, SHIRLEY BASIN AREA, WYOMING

be sufficient to account for the selenium content of 

these rocks. Perhaps the fragile ferroselite crystal 

aggregates were broken in preparation and separation of the samples, and thus became unidentifiable, 

or perhaps some of the selenium is contained in the 

pyrite. Typical twinned ferroselite crystals are 

shown in figure 38.

FIGURE 38. Twinned ferroselite crystals in heavy mineral 

separate from altered sandstone in Petrotomics Co. Section 

9 pit.

Calcite occurs as a cementing material in ore 

and in a zone or halo in unaltered sandstone surrounding ore. It is less uniformly distributed 

through the host sandstone than are the other epigenetic minerals, and in most places it occurs in 

concretionary masses ranging from a few inches to 

15 feet in maximum dimension. The calcite cement 

in most places is localized around large accumulations of carbonized plant debris; one such 

concretionary mass is shown in figure 39. These 

concretions are generally streaked with hematite, 

and they may contain uranium. Those that do not 

contain uranium may have a rind of high-grade 

friable uranium ore. In some places, small calcitecemented masses of sandstone, which appear to be 

corroded remnants of larger concretions, are in 

zones a few feet to as much as 10 feet wide that 

border, and extend slightly into, altered-sandstone 

tongues.

Studies of thin and polished sections of ore show 

that calcite may be younger or older than uraninite.

In samples of high-grade ore, taken from the Petrotomics Co. Section 9 pit about half way between the 

inner and outer edges of the ore body, calcite replaced feldspar rimmed by uraninite or pyrite or 

both. Replacement ranged from incipient to complete, and the calcite within the rim is optically 

continuous with that outside the rim. The younger 

age of the calcite with respect to the uraninite and 

pyrite is unquestionable. The observed relations are 

shown in figure 40.

FIGURE 39. Calcite-cemented slab of ore-bearing sandstone 

in waste dump from the Petrotomics Co. Section 9 pit, 

showing large percentage of carbonaceous material in slab. 

Concretionary masses of this type generally are in a halo 

around ore.

FIGURE 40. Thin sections of high-grade calcite-cemented ore 

from Petrotomics Co. Section 9 pit, showing degrees of 

replacement of feldspar by calcite. A, Feldspar (F) rimmed 

by uraninite-pyrite (up) and incipient replacement of feldspar by calcite (C). B, As in A, but considerable replacement of feldspar by calcite. C, As in A, but complete 

replacement of feldspar by calcite, leaving only uraninitepyrite rim "floating" in calcite. Quartz (Q) is rimmed by 

uraninite but is not replaced by calcite.
PARAGENESIS OF THE ORE 57

Calcite, definitely older than uraninite, was described by Melin (1964) in the ore bodies at the 

Utah Construction and Mining Co. mine, and small 

calcite concretions, barren in their interior but enclosed in an altered rim by a skin 'of high-grade ore, 

have been noted near the outer edge of ore bodies 

in the Petrotomics Co. Section 9 pit. Calcite in these 

samples is older than uraninite. Part of a small concretion enclosed in ore is shown in figure 41.

Hematite is almost everywhere associated with 

calcite, and it is restricted to the outer parts of the 

ore bodies or to a zone not more than 10-20 feet 

from ore on the unaltered side. It occurs in streaks, 

bands, and irregular masses, and it ranges in color 

from brick red to purplish red and in length from 

a few inches to several feet. About half of the

hematite coats grain surfaces; the remainder occurs as grains and irregular masses along cleavage 

planes of feldspar, biotite, hornblende, and other 

ferruginous minerals and rarely as isolated grains 

in calcite. Many of the hematite grains have dark 

metallic centers, others have rectangular outlines; 

these facts suggest that this hematite resulted from 

alteration of pyrite, marcasite, or perhaps magnetite. Some fresh pyrite is associated with hematite-bearing calcite.

In addition to the minerals just described, several 

elements show a systematic distribution in and near 

the ore deposits. Their mineralogy is not known, and 

they are discussed under "Distribution of Elements."

FIGURE 41. Calcite-cemented concretion showing unaltered 

barren medium-gray core (C), slightly darker gray altered 

rim (A), and outer skin of uraninite (U).

PARAGENESIS OF THE ORE AND ASSOCIATED MINERALS

Only the paragenetic relations of the minerals 

deposited by the ore-bearing solutions are discussed 

in this section of the report; sedimentary and diagenetic minerals, including diagenetic pyrite in unaltered sandstone (see p. 53), are not considered.
58 GEOLOGY AND URANIUM DEPOSITS, SHIRLEY BASIN AREA, WYOMING

Pertinent to this discussion is the concept, to be 

developed later in the report, that the zone of ore 

deposition was dynamic and moved slowly downdip, 

in the direction of flow of the ore-bearing groundwater, by oxidation and solution on the upstream 

side of the zone and by reduction and deposition on 

the downstream side.

Figure 42 is a graphic summary of the data on 

mineralogy and mineral distribution. It is an approximation in which the ends of the arrows on the 

left side of the figure show the points at which the 

ore-bearing solution, as it moved away from the 

altered-sandstone tongue, started to deposit each 

element or compound. The arrow lengths show the 

relative widths of the intervals through which 

deposition occurred, and the arrowheads show the 

points at which deposition stopped.

Because the zone of deposition was dynamic, the 

sequence of mineral deposition from a unit of solution moving through the zone differs from that at 

a given point in the zone.

Native selenium was the first mineral deposited 

from a unit of solution flowing from the altered 

sandstone through the zone of deposition (from left 

to right, fig. 42). Pyrite and marcasite, uraninite, 

and calcite, in that order, were the next minerals 

to form, and they mostly overlapped one another. 

Hematite was probably the last mineral to form, 

although the point at which deposition started, or

the point at which other iron-bearing minerals 

started to alter to hematite, is not known with 

accuracy.

The sequence of mineral deposition at a given 

point in the host rock is almost the reverse of that 

from a unit of solution. Iron sulfide is deposited first 

at a given point, followed by hematite, calcite, and 

uraninite as the zone of deposition moves forward. 

Native selenium, the first mineral to form from 

the unit of solution, is the last to be deposited at a 

given point.

DISTRIBUTION OF ELEMENTS AND COMPOUNDS

Analyses of many samples of roll-type ore bodies, 

and the altered and unaltered sandstones associated 

with them, show that several elements and compounds are systematically distributed in and near 

the ore and that some elements and compounds show 

consistent correlations with each other. An understanding of these distribution patterns is prerequisite to an understanding of the processes of ore 

emplacement, and, therefore, data on the distribution of several elements and compounds are discussed 

in detail.

For the convenience of the reader, minute 

amounts of most ore constituents will be expressed 

in parts per million, and larger amounts will be 

expressed in percentages; 1 ppm is equal to 0.0001 

percent.

Direction of flow of ore-bearing solution

Zone of mineral deposition

FIGURE 42. Summary of mineral deposition in the Shirley Basin. Arrow lengths show relative positions and widths of zones 

in which various minerals were deposited; dashed lines are possible deviations from normal conditions. No scale.
DISTRIBUTION OF ELEMENTS AND COMPOUNDS IN ORE BODIES 59

The reference point for the discussion will be the 

terminal edge of the altered-sandstone tongue, variously called: (1) A solution interface or front by 

King and Austin (1966), (2) a redox interface by 

Adler (1964), and (3) an altered-unaltered sandstone interface or contact by Bailey (1965), Melin 

(1964), and Harshman (1962, 1966). The edge of 

the altered-sandstone tongue in the Shirley Basin 

is not now, and probably never was, a boundary 

between two solutions of different character, nor was 

it a redox interface for all of the elements in the 

deposits. For these reasons the physically descriptive term "edge of altered-sandstone tongue" will be 

used in this report to describe the reference point. 

The distribution of elements was determined from 

samples taken in suites across the terminal edges of 

altered-sandstone tongues in the Utah Construction 

and Mining Co. mine and the Petrotomics Co. Section 9 pit. Sampling intervals were as short as 2 

inches and as long as 10 feet. All samples were 

analyzed spectrographically for 51 elements and 

chemically for total iron, ferrous iron (corrected 

for iron in FeSo), ferric iron (by difference), mineral carbon, organic carbon, selenium, sulfide sulfur, 

sulfate sulfur, and total sulfur, as well as for uranium and equivalent uranium. Analyses for phosphate, arsenic, magnesium, and mercury were made 

on selected samples or sample suites.

URANIUM AND EQUIVALENT URANIUM

Figure 43 illustrates the distribution of uranium 

and its daughter products in four typical Shirley 

Basin ore bodies. Uranium is distributed unevenly 

in each of the four rolls, being most abundant at 

the margins of the altered-sandstone tongues and 

gradually decreasing in amount away from the 

tongues. This contrasts with the ore rolls in the 

Gas Hills district of Wyoming where King and Austin (1966) reported that the peak values of uranium and many of its associated elements do not 

occur at the front, but several feet beyond it, within 

the mineralized zone.

The uranium content of unmineralized sandstone 

ranges from about 4-8 ppm (0.0004-0.0008 percent), a value based on analyses of samples of 

unweathered sandstone that is exposed above the 

ore-bearing interval in the walls of the Petrotomics 

Co. Section 9 pit and of samples of sandstone from 

the ore-bearing interval that are considered to be 

unaltered.

Altered sandstone generally contains only slightly more uranium than does unaltered sandstone, but 

in a few places the outer few inches, or in rare instances the outer few feet, of the altered tongue 

contains ore-grade material. Where the edges of the 

tongues are of ore grade, the uranium content of 

altered sandstone decreases rapidly away from the 

edge and drops to a normal content of 6-15 ppm 

(0.0006 to 0.0015 percent) uranium in samples 

10 feet or more from the edge.

Uranium is not in equilibrium with its daughter 

products in most of the Shirley Basin deposits. 

Values from radiometric analyses (beta-gamma, 

expressed as percentages of equivalent uranium) 

exceed those from chemical analyses (fluorimetric, 

expressed as percentages of uranium) on samples of 

poorly mineralized sandstone, both altered and unaltered, and values from chemical analyses exceed 

those from radiometric analyses on samples of ore 

and of ore-grade altered sandstone (0,1 percent or 

more uranium). The character of the disequilibrium 

thus seems to depend on the uranium content of a 

sample rather than on the type of material sampled. 

In general, in sandstone with less than about 0.07 

percent uranium, the U/eU ratio will be less than 1, 

and in sandstone with more than 0.1 percent uranium, the same ratio will be more than 1. There are 

exceptions to this generalization. The equivalent-uranium and uranium contents of 175 samples of 

altered and unaltered sandstone and of ore are 

plotted in figure 44. A plot of the equivalent-uranium and uranium contents of 290 samples from the 

Ambrosia Lake area of New Mexico shows similar 

U/eU ratios (Granger and others, 1961).

If roll-type deposits originate from a continuing 

process of oxidation, transportation, and reduction 

of uranium in flowing ground water, then a residuum of daughter products in the altered-sandstone 

tongue could result if uranium were more readily 

leached from the sandstone than its daughter products. It appears that in the Shirley Basin such 

differential leaching may have taken place; taking 

into account the normal imbalance that is characteristic of all low-grade mineralized samples, there is 

still some factor which causes the imbalance of 

equivalent uranium and uranium to be much greater 

in the altered-sandstone samples than it is in the 

unaltered samples. This is well shown in figure 44, 

where almost all the analyses of altered sandstone 

lie at a greater distance from the line representing 

equilibrium conditions than do the corresponding 

analyses of unaltered sandstones which have similar 

uranium contents. The degree of imbalance of uranium and equivalent uranium in samples of poorly 

mineralized sandstone should be useful in determining the presence of alteration in drill cuttings and 

drill cores.
60 GEOLOGY AND URANIUM DEPOSITS, SHIRLEY BASIN AREA, WYOMING

Unaltered sandstone

: 0.058

;:.o.o5o Unaltered sandstone':

10

I

15 20 FEET

::.llrnal.t.ere'd::sahdstone;

Ore

1.50 0.93 0.37 °-^9 .' .' .: '. .-.'.'. .'.:'M2I' : 0.017.''.-0.022.. __ __ 

'.' ' ' '. '.'.'/. 0.017Y-; 0.050 \.-0.063\- ' A /1.25 /0.6:

 '' ' ' ' ^'-'-'-^-'-'t'-.\^'r-/-J.'A'.'-i';VV-j-'-'|/| .1/1.1

 -.._ .. - } : '-I'./.- \t-\..vi'} \ \ \\ I i\ i i'

: ..Altered//-.-. o.oos/-.- opjo/ pji//! 40 / \0 57 \o.33

 .sandstone' '.'.--0.012-;.' o.o ^^

Unaltered, sandstone :

10 FEET

FIGURE 43. Cross sections at the edges of altered-sandstone tongues, showing positions and contents of samples. Percentages 

of uranium (numerator) and equivalent uranium (denominator) expressed as the fraction U/eU.

IRON

Iron is the most abundant epigenetic element in 

the ore deposits. It combines with sulfur to form 

pyrite and marcasite in the ore and unaltered sandstone and with silica and alumina to form highiron montmorillonite in the altered sandstone. Iron 

combined with oxygen forms the hematite associated with calcite concretions in ore and unaltered 

sandstone and the goethite and limonite in the 

altered-sandstone tongues.

The distribution of uranium, of ferrous, ferric, 

and total iron, and of ferrous iron in sulfide and 

nonsulfide minerals in a typical roll is shown in

figure 45. Unaltered sandstone contains about 0.8 

percent total iron, about two-thirds of which is in 

the ferrous state. Ferrous iron is about equally 

divided between sulfide and other iron-bearing minerals. The high total iron and high ferrous iron in 

sample 308 are due to a concentration of pyrite 

around carbonaceous material in the sandstone.

The ore is enriched in iron, most of which is in 

the ferrous state and is present as the minerals 

pyrite and marcasite. Sample 319 has considerable 

ferrous iron in minerals other than pyrite, and, since 

this sample is also high in S04 , the iron may be 

present in a ferrous sulfate mineral as yet unidentified in the Shirley Basin deposits. Ferric iron is
DISTRIBUTION OF ELEMENTS AND COMPOUNDS IN ORE BODIES 61

50.0

10.0 

EXPLANATION

x 

Altered sandstone

0.005 -

0.001

0.001 0.005 0.01 0.05 0.1 0.5 1.0 

EQUIVALENT URANIUM (eU), IN PERCENT

10.0 50.0

FIGURE 44. Equilibrium relations of 175 samples of mineralized sandstone from Shirley Basin.

virtually absent in high-grade ore near the margins 

of the altered-sandstone tongues; it is present in 

minor amounts near the outer edges of ore bodies. 

Altered sandstone generally contains 0.8-0.9 percent total iron, about the same as does unaltered 

sandstone. At the edge of the altered tongue, total 

iron decreases somewhat in amount; most of it is in 

the ferrous state, some in pyrite and some in other 

iron-bearing minerals. A few tens of feet from the 

edge of the tongue the amounts of ferrous and ferric

iron are about equal, and the amount of ferrous 

iron in pyrite becomes almost nil. Pertinent to the 

problem of origin of uranium deposits are (1) the 

high Fe+2/Fe+3 ratio in unaltered sandstone compared with the same ratio in altered sandstone, 

(2) the low-ferric and high-ferrous iron contents of 

ore, (3) the decrease of ferric iron toward the edge 

of the altered tongue, and (4) the similarity 

between total-iron contents of altered and unaltered 

sandstone.
62 GEOLOGY AND URANIUM DEPOSITS, SHIRLEY BASIN AREA, WYOMING

SAMPLE NUMBERS

CO <£> «i *

CO tO ^f *

CO CO fO P

Top of bench 

^Bottom of pit

2 2

Uranium

Ferrous iron

""^Ferric iron

Total iron

/Ferrous iron in nonsulfide minerals 

, Ferrous iron in sulfide minerals

FIGURE 45. Section through ore body in Petrotomics Co. Section 9 pit, showing locations of samples and the distribution of uranium, of ferrous, ferric, and total iron, and of ferrous iroh in sulfide and nonsulfide minerals.

SELENIUM

Selenium in amounts of more than 100 ppm is 

found only in a narrow zone, generally less than 5 

feet wide, astride the contact of ore and altered 

sandstone. Samples from this zone contain as much 

as 3,000 ppm (0.3 percent) selenium. The highselenium zone is not necessarily symmetrical with 

respect to the contact, and the greatest amount of 

selenium may be either in ore or in altered sandstone. The selenium content of ore and of altered 

sandstone decreases abruptly away from the contact. High-grade ore and altered sandstone generally 

contain, respectively, 2-10 and 10-50 ppm selenium 

10-20 feet from the contact. In small or low-grade 

deposits the amount of selenium decreases in much 

shorter distances.

Unaltered sandstone contains i/^-l ppm selenium, 

probably in the crystal lattice of the pyrite. In sharp 

contrast, altered sandstone farther from the edge 

of the tongue contains 10-40 ppm selenium. Here

the selenium is thought to be associated with the 

limonite or goethite.

Figure 46 shows the distribution of selenium 

across a small ore body in the Shirley Basin.

6 FEET

FIGURE 46. Section through ore body in Utah Construction 

and Mining Co. mine, showing locations of samples and 

their selenium contents, in parts per million.
DISTRIBUTION OF ELEMENTS AND COMPOUNDS IN ORE BODIES 63

SULFATE

Significant differences in the sulfate content of 

altered sandstone, unaltered sandstone, and ore are 

shown by analytical data on sample suites across 

uranium deposits in the Shirley Basin. Samples of 

altered sandstone from the Utah Construction and 

Mining Co. mine and from the Petrotomics Co. 

Section 9 pit contain 0.03-0.09 percent sulfate. 

Samples of unaltered sandstone from both workings contain 0.04-0.30 percent sulfate. In the altered 

sandstone the sulfate-bearing mineral or minerals 

are not known, but in unaltered sandstone some of 

the sulfate is present as gypsum.

Most of the uranium ore contains from a few 

hundredths to a few tenths of a percent sulfate, but 

one sample from a roll in the Petrotomics Co. Section 9 pit contained 3.33 percent. This ore sample 

(319), when leached in 150 cubic centimeters of 

distilled water for 10 hours on a steam bath (95°C) 

gave rise to a filtrate of pH 4, saturated with calcium 

sulfate and enriched in iron. Analytical data are inconclusive on possible elements combined with sulfate in the ore, and polished sections of ore contain 

no identifiable sulfate mineral. The presence of a 

ferrous sulfate compound is suspected. The sulfate 

contents of samples from two rolls are shown in 

figure 47.

There is no positive correlation between the 

amount of sulfate and other elements, including 

uranium, in the sample suites, although sandstone 

high in uranium generally is relatively high in sulfate. The amount of sulfate in altered sandstone is 

generally less than that in either ore or unaltered 

sandstone, but the U/S04 ratios in both unaltered 

and altered sandstone are much less than 1. The 

same ratio in ore is generally more than 1. This 

contrasts with the findings in the Gas Hills by King 

and Austin (1966, p. 79), who stated that "a low 

uranium value and a U308/S04 ratio of greater than 

or near unity would indicate a sample from the 

barren interior."

CARBON

Carbon is present in the ore bodies in two principal forms as mineral carbon in calcium carbonate 

and as organic carbon in fossil plant debris. Figure 

48 shows the distribution of mineral and organic 

carbon and manganese in an ore body in the Petrotomics Co. Section 9 pit. In this sample suite, as in 

others from the Shirley Basin, altered sandstone contains much less organic carbon than does unaltered 

sandstone or ore. Also in this suite, the sample with 

the most uranium contains the most organic carbon, 

a relation that does not persist throughout the basin:

although some samples of high-grade ore contain 

considerable organic carbon, others are low in 

organic carbon, and many samples high in organic 

carbon contain insignificant amounts of uranium. 

Mineral carbon, as calcite cement, is present in 

concretionary masses in ore and in unaltered sandstone in a halo around ore. The distribution of calcite was discussed under "Mineralogy and Mineral 

Distribution."

MANGANESE

Manganese distribution in a typical ore body is 

shown in figure 48. Manganese contents range from 

70 to 2,000 ppm, and there is little or no concentration of this element in the ore. However, there appears to be a good correlation between manganese 

and calcite, for almost without exception samples 

high in mineral carbon, be they from ore, altered 

sandstone, or unaltered sandstone, are high in 

manganese.

PHOSPHATE

Samples from the Shirley Basin deposits contain 

from a few hundredths to as much as 0.11 percent 

P2 05 . High phosphate generally accompanies high 

uranium, but the correlation is not direct, for the 

U/P205 ratios range from 28.0 in the highest grade 

ore to 0.02 in weakly mineralized sandstone. Both 

altered and unaltered sandstone contain about 0.05 

percent P205 . The phosphate-bearing mineral or 

minerals have not been identified, but the wide variation in the U/P205 ratios and the fact that the 

amount of phosphate exceeds that of uranium by 

two orders of magnitude in altered and unaltered 

sandstone indicates that a significant amount of 

phosphate is not contained in uranium-bearing 

minerals.

The uranium and phosphate contents and the 

U/PoOs ratios of the samples shown in figure 45 are 

listed in table 7.

TABLE 7. Uranium and phosphate contents and

ratios for a suite of samples from the Petrotomics Co. Section 9 pit

[Locations of samples are shown, by sample number, in fig. 45]

Sample

304

305

306

307

308

309

310

312

316

319

324

329

333

336

341

348

349

350

351

Uranium 

(percent)

0.002

.002

.001

.001

.002

.001

.075

.72

1.30

3.07

.45

.054

.010

.006

.006

.007

.002

.001

.002

PsOs 

(percent)

0.067

.051

.051

.043

.043

.045

.066

.084

.046

.110

.077

.034

.041

.083

.050

.050

.050

.051

.053

U/PsOs ratio

0.03

.04

.02

.02

.05

.02

1.14

8.57

13.54

27.91

5.84

1.59

.24

.07

.12

.14

.04

.02

.04
64 GEOLOGY AND URANIUM DEPOSITS, SHIRLEY BASIN AREA, WYOMING

CM CM .-I rt CM 1-1 in

8

0 O o o o r*^

q p q q q q

d d d d d d d

0_OO^finiot^coa)OCM 10

^ 5 O O O O O O fc 1-1 1-1 -!

OOOOOOOOOOOOOOOO 00

-Top of bench

. !> . . :o: .CM; -CM 

 . .'.p-'. :.'.p;'.p-'.'-2 ^ _;

 -« - '.p. ;.'o-'

oo oo oo 

d d d d

00 00

d d

6 FEET 

J

FIGURE 47. Sections through ore rolls in Petrotomics Co. Section 9 pit (upper) and in the Utah Construction and 

Mining Co. mine (lower), showing locations of samples and their uranium and sulfate contents, in percent.

FIGURE 48. Section through ore body in Petrotomics Co. Section 9 pit, showing locations of samples and their organiccarbon (Corg), mineral-carbon (Cm m), and manganese (Mn) contents.
DISTRIBUTION OF ELEMENTS AND COMPOUNDS IN ORE BODIES 65

ARSENIC

The arsenic and uranium contents of a suite of 

samples from an ore body in the Petrotomics Co. 

Section 9 pit are shown in figure 49. Arsenic ranges 

from 30 to 50 ppm in ore-grade material; it averages 

about 5 ppm in unaltered sandstone and less than 

1 ppm in altered sandstone. In this ore body, the 

distribution of arsenic correlates well with that of 

sulfide sulfur, less well with that of uranium, and 

not at all with that of selenium.

Arsenic in a suite of samples across an ore body 

in the Utah Construction and Mining Co. mine shows 

a fair correlation with uranium, a lack of correlation with selenium, and only a fair correlation with 

sulfide sulfur. Altered sandstone in this suite contains 2-5 ppm arsenic, and ore having as much as 

0.30 and 0.41 percent sulfide sulfur contains only 1 

ppm arsenic considerably less than in the Petrotomics Co. ore body in sec. 9. The distribution of 

arsenic in the Shirley Basin deposits suggests that 

some of the arsenic is contained in pyrite and that 

some also may be associated with other minerals.

COPPER

The distribution of copper has been determined 

from analyses of several hundred samples from ore 

bodies in the Utah Construction and Mining Co. 

mine and in the Petrotomics Co. Section 9 pit. 

Spectrographic analyses, having a threshold detection limit of 1 ppm, indicate that altered sandstone 

contains 2-7 ppm copper; the larger amounts are 

within a few feet of the edges of the altered tongues, 

and the smaller amounts are farther from the edges. 

Ore and unaltered sandstone contain from a few

to as much as 20 ppm copper and an average of 

about 10 ppm. The copper contents of a typical roll 

are shown in figure 50.

On the basis of available data, it seems probable 

that the ore-bearing solutions leached copper from 

the altered sandstone but did not redeposit it within 

the ore bodies.

VANADIUM

Most of the uranium deposits in the Tertiaryfilled basins of Wyoming contain little vanadium; 

the Shirley Basin is no exception. The highest grade 

ore samples contain about 0.15 percent vanadium 

and have U/V ratios as high as 100:1, although in 

much of the ore, uranium exceeds vanadium by a 

factor of 20-25. The vanadium content of altered 

sandstone near the margins of the tongues is 100- 

150 ppm, but it drops rapidly away from the 

margins to 15-50 ppm. U/V ratios in altered sandstone range from about 20:1 near the margins of 

the tongues to about 0.5:1 away from the margins.

Unaltered sandstone contains 15-50 ppm vanadium, about the same as altered sandstone away 

from the margins of the tongue. U/V ratios in 

unaltered sandstone, similar to those in altered 

sandstone away from the margin of the tongues, 

range from 0.5:1 to 1:1.

The vanadium contents of samples across a typical 

roll in the Petrotomics Co. Section 9 pit are shown 

in figure 50.

BERYLLIUM

The maximum beryllium content of any analyzed 

sample of sandstone from the Shirley Basin is 3 

ppm in a sample of high-grade ore; most samples 

contain 1.5 ppm or less beryllium.

Top of bench

^-^ij'ii^ : '' :;^\^::'l^[-Y-^V-^

clstpirie'j;;v^-f' /^JV-Y-''-''^-'^'-'.''.'.''.-^'.' ':-.' ' ;' '.-."'.'. ' \'\':'.'-\'-:'-^ :' '. ' ' ' ' ^--.

^Bottom of pit

O z 300 

ZO

Gee 200

ZLU <CL

Sulfide sulfur

QhQQI?

FIGURE 49. Section through ore body in Petrotomics Co. Section 9 pit, showing locations of samples, and their uranium,

selenium, arsenic, and sulfide-sulfur contents.
66 GEOLOGY AND URANIUM DEPOSITS, SHIRLEY BASIN AREA, WYOMING

/Top of bench

^:-v!^^^^

 ' ' '.' '.' .' '.[. / ;.'.- . .'Altered sandstone.'.. .

^Bottom of pit

2000

FIGURE 50. Section through ore body in Petrotomics Co. Section 9 pit, showing locations of samples and their copper and

vanadium contents.

Spectrographic analyses of 180 samples of sandstone from the Utah Construction and Mining Co. 

mine and Petrotomics Co. Section 9 pit show beryllium as not detectable (less than 1 ppm) in all 42 

unaltered-sandstone samples, detectable in only two 

of 53 altered-sandstone samples, but, in sharp contrast, detectable in 30 of 85 ore samples. Statistically, there seems to be little doubt that beryllium 

was transported and deposited with uranium from 

the ore-bearing solutions.

LEAD

Spectrographic analyses on 86 ore samples, 42 

unaltered-sandstone samples, and 52 altered-sandstone samples show that lead contents are considerably higher in ore than in altered and unaltered 

sandstone. Ore samples that contain 0.10-19.2 percent uranium correspondingly contain 0.0015-0.02 

percent lead; their average lead content is 0.0051 

percent. A suite of 15 ore samples, all containing 

more than 2 percent uranium and averaging 4.83 

percent uranium, contains an average of 0.0122 

percent lead. It is apparent that the highest lead 

contents are paired with the highest uranium 

contents.

The analyses show almost no difference in the 

lead contents of altered and unaltered sandstone. 

Altered sandstone contains 15-30 ppm lead and 

averages 16 ppm. Unaltered sandstone contains 10- 

20 ppm lead and averages 15 ppm.

Undoubtedly most of the lead results from inplace radioactive decay of U235, U238, and thorium,

but some common lead and radiogenic lead may have 

been transported to the site of deposition by the 

ore-bearing solution.

MERCURY

Mercury analyses, sensitive to 5 ppb, were made 

by the atomic-absorption method on a suite of 24 

samples from the ore roll shown in figure 50. Unaltered sandstone contains an average of 36 ppb 

mercury (range 30-50 ppb) ; altered sandstone, an 

average of 40 ppb (range 20-70 ppb) ; and ore, an 

average of 37 ppb (range 30-40 ppb). These differences are insignificant, and at this locality at 

least, there is no mercury halo associated with a 

large high-grade uranium ore body.

MISCELLANEOUS ELEMENTS

Analytical data on elements, other than those just 

discussed, are not conclusive with respect to correlation with other elements or distribution in the 

roll features. Barium may be slightly more abundant in the ore than in unaltered sandstone (0.133 

versus 0.091 percent), and barite crystals with high 

alpha activity have been observed associated with 

carbonized plant debris in the Utah Construction 

and Mining Co. mine. Some of the rock-forming 

elements, particularly potassium and sodium, may 

be depleted in the ore, but this apparent depletion 

is probably due to dilution by the addition of elements such as uranium, iron, and calcium to the 

ore-bearing sandstone.
GEOCHEMISTRY OF ORE DEPOSITS 67

GEOCHEMISTRY

An acceptable concept of origin for the Shirley Basin uranium deposits must explain their 

restricted stratigraphic distribution, their spatial relations to large bodies of altered sandstone, the systematic distribution of their component minerals, 

and their physical parameters. It must encompass 

the source of the uranium and associated elements, 

the nature and hydrodynamics of the ore-bearing 

fluid, the method of precipitation of the ore minerals, 

and the disposition of the spent ore fluid. Because 

the ore bodies were formed eons ago, any discussion 

of their origin is speculative and interpretative. 

There is, however, a large body of data on the 

Shirley Basin deposits that can be used to keep 

speculation within reasonable bounds and, it is 

hoped, to help interpret correctly some of the complex factors pertinent to genesis of the deposits.

The ore bodies are clearly epigenetic, as shown by 

the fact that parts of most of them cut the host 

sandstone beds at sharp angles. In a few places the 

ore minerals are distributed along the crossbeds, 

and in these places the ore gives the false impression of being syngenetic. Figures 32 and 33 show 

ore that cuts across bedding as well as ore that 

"pseudomorphs" bedding.

Unfortunately, evidence is much less clear as to 

the source of the uranium now concentrated in the 

deposits, the character of the solutions that transported the uranium, and the reasons for uranium 

deposition in the ore bodies. Possible sources of the 

uranium and associated elements in the Shirley 

Basin deposits are (1) magmatic hydrothermal solutions, (2) the arkosic Wind River sandstone that 

is the host for the deposits, (3) the granite in the 

cores of the mountain ranges that flank the basin, 

and (4) the White River and younger formations, 

which overlie or once overlay the area, and more 

particularly the tuffaceous components of these 

rocks.

Magmatic hydrothermal solutions appear to be 

the least likely source of the elements in the ore inasmuch as no evidence of hydrothermal activity of 

Tertiary age exists in or near the basin, no igneous 

activity of Tertiary age is known within 50 miles 

of the basin, and no deposits of probable hydrothermal origin and Tertiary age occur in the mountain ranges that flank the basin. Possibly some 

contribution of elements to the ore-bearing solution was made by the intermixing of ground water 

and magmatic fluids, but it is unlikely that such 

contributions were significant.

The arkosic material that forms the permeable, 

ore-bearing part of the Wind River or Wasatch

Formation has been considered by some geologists 

(Melin, 1964; Rackley and others, 1968) to be the 

source of the uranium and other elements in some 

of the Wyoming deposits. Data on the ore, altered 

sandstone, and unaltered sandstone in the Shirley 

Basin, much of which is given in an earlier section 

of this report, indicate that this was not the source 

for these deposits. The uranium content of the 

altered sandstone in the Shirley Basin is slightly 

greater than that of the unaltered sandstone, an impossible situation if the altered arkose were the 

source of uranium in the ore bodies. Furthermore, 

in the Shirley Basin as in the Gas Hills, the altered 

sandstone contains 10-50 times more selenium than 

does the unaltered sandstone, which is clear evidence 

that the arkose is not the source of the selenium in 

the deposits and suggestive that it was not the 

source of the uranium so intimately associated with 

selenium.

Samples of granitic rocks from the cores of the 

Laramie and Shirley Mountains, rocks considered 

to be the sources of the arkoses in the Shirley Basin, 

contain several parts per million uranium, some of 

which is shown by laboratory tests to be loosely held 

and readily available for solution by percolating 

water. One sample of gabbro and 11 of granite were 

crushed to about one-eighth inch in order to separate, but not grind, the component mineral grains. 

Five grams of the crushed material was placed in 

a funnel, and 50 ml (milliliters) of a leach solvent 

was dripped through it in a 10-hour period. The 

solvent was similar to present-day Shirley Basin 

ground water; it contained 0.3 g (grams) of Na2S04 

and 0.15 g of Na2C03 in 1 liter of water, and it was 

brought to a pH of 7.98 by the addition of C02. 

The results of the experiment are shown in table 8.

TABLE 8. Uranium leached from samples of igneous rocks 

from mountain ranges that flank the Shirley Basin

[...., not calculated because value for ppm leached uranium is not precise

enough]

Sample Total uranium

(ppm)

Leached uranium

ppm percent

Granite

85

86

87

88a

88b

89

90

91

160

161

162

7.0

2.0

1.0

2.0

2.0

1.5

.5

1.0

.2

3.0

.4

0.039

.008

.009

.005

.010

.008

<.005

.007

<.005

.027

<.005

0.6

.4

.9

.2

.5

.5

.7

.9

Gabbro

163 0.4 <0.005

The period of contact between the solvent and 

the crushed granite was short, yet as much as 0.9 

percent of the uranium was leached from material 

containing a few parts per million uranium. These 

tests indicate that readily soluble uranium was
68 GEOLOGY AND URANIUM DEPOSITS, SHIRLEY BASIN AREA, WYOMING

available to ground water early in the weathering 

of granite, and it probably was removed; the uranium remaining in the arkose after its deposition in 

the basin possibly was quite insoluble and in large 

part unavailable for solution by ground water. It 

seems probable, therefore, that the granite, as it 

weathered in place, was a source of some of the 

uranium in the Shirley Basin deposits, but the importance of this particular source is not known.

Volcanic ash has been considered by many to be 

a source of copper, uranium, selenium, and some 

other elements in sedimentary rocks and soils. As 

early as 1938, Koeberlin proposed that "red bed" 

type deposits of copper, vanadium-uranium, and 

silver were formed by the leaching of these metals 

from volcanic ash, transportation by ground water 

to shallow basins, and precipitation by the reducing 

action of organic matter or bacteria. Beath (1943) 

implied that uranium, selenium, and other metals 

in sandstone deposits in the Yellow Cat area of Utah 

were of volcanic origin, and Beath, Hagner, and 

Gilbert (1946) related the high selenium content 

of some Wyoming soils to the high selenium content 

of tuffaceous beds in the Tertiary rocks of Wyoming. Denson, Bachman, and Zeller (1951) proposed 

that uranium associated with lignite in North Dakota and South Dakota was leached from the tuffaceous White River Formation, and Love (1952) 

concluded that the uranium in the deposits he discovered in the Powder River Basin was deposited 

from descending vados water that had leached 

uranium from the overlying White River Formation. Many earth scientists have proposed similar 

origins for the metals in sandstone-type uranium 

deposits.

The tuffaceous rocks of the White River and 

younger formations that overlie, or once overlay, 

the Shirley Basin area probably were the source of 

some of the elements in the ore deposits. Water that 

was taken from springs at the base of the upper 

member of the White River Formation and that has 

not been in contact with other rocks contains 8-10 

ppb uranium, and water from springs near the base 

of the lower member, where tuffs predominate, contains 19-52 ppb uranium. These data show that the 

White River Formation is contributing uranium 

to the present-day ground water, so these rocks 

must be considered as a probable source of some 

of the uranium in the Shirley Basin ore deposits.

The source of the uranium being leached from 

the White River Formation is not definitely known, 

but there is reason to believe that much of it comes 

from the tuffaceous rather than the clastic fraction 

of the rock, although both fractions contain 5-10

ppm uranium. Lipman (1965) reported that volcanic glass, upon hydration, looses certain constituents to circulating water, particularly sodium and 

silica. It is possible that uranium, as well as silica 

and calcium, may be lost. There are no data on the 

extent to which the clastic fraction of the tuffaceous 

rocks contribute constituents to ground water, but 

it seems probable that uranium and associated elements are contained in quartz, feldspar, and heavy 

minerals, such as zircon, or they may be absorbed 

on clays, and thus the contribution of the clastic 

fraction is probably small.

The cited evidence as to the source of the uranium 

and associated elements in the Shirley Basin ore 

deposits is circumstantial, but it does suggest that 

the source was multiple and included the granitic 

rocks in the cores of the mountains that flank the 

basin as well as the tuffaceous fraction of the White 

River and younger formations that overlie or once 

overlay the area.

SOLUTION, TRANSPORTATION, AND DEPOSITION OF ELEMENTS

Hostetler and Garrels (1962) showed that in the 

presence of C02 and at low temperatures and pressures, uranium is soluble in either the 4- or the 

6-valent state, depending on the pH and Eh of the 

solution. Transportation in the 4-valent state is possible at Eh values of about -f 0.3 volt or less and at 

pH values of less than about 3. Transportation in the 

6-valent state is possible in acidic or alkaline solutions at minimum Eh values of about -f 0.3 and 

 0.4 volt. The amount of C02 in solution affects the 

solubility of uranium and the limits of pH and 

Eh values at which it is easily transported. The wide 

range of conditions under which uranium is soluble 

makes this element a poor indicator of the character 

of the transporting medium and the genetic 

processes responsible for the Shirley Basin deposits. 

However, other factors such as the geochemical environment of the basin, the character of alteration 

produced by the ore-bearing solutions, and the geochemistry of elements associated with uranium 

greatly restrict the conditions under which the 

deposits could have been formed.

The permeable part of the Wind River Formation, 

in which the uranium deposits are found and 

through which the ore-bearing solution migrated, 

is an arkose containing considerable orthoclase and 

microcline, some plagioclase, 1-5 percent acid-soluble 

material (mostly calcium carbonate), and 50 percent 

or more quartz. The White River and Arikaree 

Formations that overlie, or once overlay, the Wind 

River have clastic components similar to those in
GEOCHEMISTRY OF ORE DEPOSITS 69

the Wind River, but in addition they contain considerable volcanic ash in the form of fairly pure 

tuff beds or as glass shards dispersed through siltstones. Both the arkosic and the tuffaceous rocks 

are alkaline and would tend to buffer the pH of 

ground water flowing through them. Garrels and 

Christ (1965) showed that water in contact with 

CaC03 generally has a pH of 8 or more, the exact 

value depending on the partial pressure of C02 in 

the system and other factors. Hemley and Jones 

(1964) discussed at length the increase in alkalinity 

caused by the hydrolysis of silicate minerals such as 

feldspar. Laboratory and theoretical data show that 

alteration of silicic glass releases silica and alkali 

ions to ground water and produces pH values of 8 

or more (Hay, 1963). The theoretical considerations are confirmed by the pH measurements of 

actual ground water in the Shirley Basin (table 2), 

where 39 of 40 water samples from the Tertiary 

rocks have pH values greater than 7.0; the average 

of the 40 samples is 7.7, and the median is 

about 7.75.

Ground water flowing through the basin today is 

alkaline, and the environment through which it flows 

is conducive to alkalinity, so if the present is a key 

to the past, it seems reasonable to conclude that the 

ore-bearing solutions were alkaline.

Transportation of elements in oxidizing solutions 

is suggested by the character of the alteration produced as the solutions passed through the ore-bearing sandstone. Pyrite is present in the unaltered 

sandstone in amounts approaching 1 percent, but in 

altered-sandstone tongues a few tens of feet from 

their edges it has been almost totally removed (total 

sulfur is less than 0.02 percent). Carbonaceous trash 

sparingly distributed through the unaltered sandstone has been almost completely destroyed in the 

altered sandstone, both visually and chemically. 

Goethite and limonite are present in some samples of 

altered sandstone, but not in unaltered sandstone. 

Fe+2/Fe+3 ratios in altered sandstone are about 

1:1 or less, but in unaltered sandstone they are at 

least 2:1; total-iron contents of the two types of 

sandstone are similar. These data suggest that the 

ore-bearing solutions were oxidizing with respect to 

iron and carbon.

Oxidizing alkaline ore-bearing solutions are suggested by the geochemistry of the ore elements at 

low temperatures and pressures. Selenium appears 

to be one of the most diagnostic elements with 

respect to character of the solution in which it 

moved. It is intimately associated with ore and must 

be considered as having been deposited with uranium from the ore-bearing solutions. Data summarized by Lakin (1961) show that, under conditions 

extant in natural environments, selenium can be 

taken into solution and transported only under 

oxidizing alkaline conditions. Although the selenite 

ion ((Se203 ) ~ 2 ) is readily formed under moderate 

oxidation potentials in either acid or alkaline solutions, it is almost immediately immobilized by reacting with the ferric ions in ground water to form 

an insoluble precipitate having a composition 

approximating a basic ferric selenite. Selenate ion 

is soluble in most natural waters, but it is formed 

only under restricted Eh and pH conditions. In acid 

solutions selenate ion is formed only under conditions of acidity far greater than can be expected 

in the most rigorous natural environments. However, in solutions of about pH 7 and greater, the 

oxidation potentials in near-surface waters will 

oxidize selenium to selenate, and probably solutions 

of this character dissolved and transported the 

selenium in the Shirley Basin deposits. Selenium 

possibly migrates in ground water as a complex with 

sulfur (Goleva and Lushnikov, 1967) rather than 

as selenate ion. Laboratory investigations of this 

method of selenium transport and the implications 

with respect to uranium deposits in sandstones indicate that the complexes are stable in alkaline oxidizing solutions and unstable in acid reducing solutions 

(Warren, 1968; Granger and Warren, 1969).

The distribution of beryllium, discussed earlier 

in this report, indicates it was a component of the 

ore-bearing solution. The geochemistry of this element at low temperatures and pressures is not 

well known, but Beus (1962) suggested that it is 

transported in alkaline solutions as a complex with 

chlorine, fluorine, or carbonate. Govorov and Stunzhas (1963) showed that alkalic carbonatoberyllate 

complexes are stable in the pH range 6.8 to 11.8 at 

temperatures of about 80°-210°C and that a decrease in the alkalinity of the solvent causes precipitation of beryllium compounds. These data 

suggest that beryllium was transported in alkaline 

solutions, but they do not preclude transportation 

in solutions of other character.

In addition to the positive, though indirect, evidence that the ore-bearing solutions were alkaline 

and oxidizing, there is evidence that they were not 

acid. Acidic solutions, particularly if they were 

sufficiently acid (pH <3) to transport uranium in 

the 4-valent state and if they percolated through the 

ore-bearing arkosic members of the Wind River 

Formation in sufficient volume to account for the 

uranium deposits in the Shirley Basin, would have 

produced considerable alteration of feldspar minerals, particularly plagioclase. Alteration of feldspar
70 GEOLOGY AND URANIUM DEPOSITS, SHIRLEY BASIN AREA, WYOMING

in the thin sections of the rocks in the altered-sandstone tongues is minimal and can be accounted for 

by a temporary acidic "front" produced by oxidation 

of pyrite in the ore body, a process described later 

in this report.

A second major objection to the ore-bearing solutions being acid is the difficulty of generating them 

in great volume and over a considerable period of 

time. A magmatic source of acid emanations seems 

unlikely for reasons discussed earlier. Oxidation of 

pyrite produces sulf uric and carbonic acid, but available data show that more than enough carbonate 

(>2.5 percent) is present in the Wind River Formation to neutralize the acid produced by oxidation 

of the small content of pyrite (1± percent). Carbonized plant material in the arkosic sandstone seems 

too sparse for one to postulate that the ore-bearing 

solutions contained large amounts of humic acids, 

and there are difficulties in transporting uranium 

and associated elements in solutions made acid by 

humic compounds.

The data presented in the preceding paragraphs 

weigh heavily in favor of the supposition that the 

ore-bearing solutions were neutral to somewhat alkaline and oxidizing with respect to iron, selenium, 

uranium, carbon, and associated elements.

The ore deposits appear to have resulted from a 

reduction in the Eh of the transporting fluid, although a drop in pH may have been a contributing 

factor in their formation. The large amount of 

ferrous iron and the small amount of ferric iron in 

the ore, the presence of ferroselite in ore and in 

altered sandstone near ore, the reduced chemical 

state of the ore minerals, and the general nature of 

the environment in which ore is found, all topics 

discussed earlier in this report, suggest that the 

zone of deposition was strongly reducing with respect to the ore elements. The nature of the reductant is not known. Lindgren, Graton, and Gordon 

(1910) postulated that the red-bed copper deposits 

of New Mexico might have originated through reduction of copper by H2S of biogenic origin. More 

recently Jensen (1958), Cheney and Jensen (1966), 

and others theorized that H2S of biogenic origin accounts for the sulfur in the pyrite intimately associated with uranium in the Wyoming deposits. 

Research now under way in the U.S. Geological 

Survey (Granger and Warren, 1969) shows that 

pyrite associated with uranium ore may form in 

the absence of bacteria by inorganic reactions between iron and several dissolved sulfur-bearing 

compounds formed by oxidation of disseminated 

pyrite of biogenic origin. Bacterial reduction of 

sulfate is essential to this concept, but the final reduction of the elements to form ore is independent 

of bacterial activity.

Grutt (1957) proposed that natural gas may 

have been the reductant for the ore deposits in the 

Gas Hills area of Wyoming. The Wall Creek Sandstone Member of the Frontier Formation underlies 

the ore-bearing areas of the Shirley Basin and contains oil and gas in some parts of Wyoming. Where 

the western and southern edges of the lower alteredsandstone tongue pass over the Wall Creek, there 

is no noticeable increase in the amount or grade of 

ore above the paleooutcrop, and it seems unlikely 

therefore that gas escaping from this sandstone was 

the reductant for these deposits.

Organic matter in situ, and perhaps redistributed 

organic compounds not recognized in this investigation, may have been the loci for deposition of 

some uranium and pyrite. However, the poor correlation between carbon and uranium, discussed in 

an earlier section of this report, suggests that carbon 

itself has not played an important roll in the formation of the deposits.

Although available data do not define the reductant responsible for the uranium deposits in the 

Shirley Basin, they are compatible with the concept 

that H2S of biogenic origin was an important 

factor in ore genesis, either directly or through 

intermediate sulfur compounds formed by oxidation 

of an early biogenic pyrite.

GENESIS OF THE DEPOSITS

The Shirley Basin deposits are young, simple in 

form and mineralogy, and apparently unaltered by 

weathering or by significant redistribution of uranium. In addition, they have an obvious spatial and 

genetic relation to large tongues of altered sandstone. This detailed study of the deposits and of the 

environment in which they were formed was therefore undertaken in the hope that it would yield 

data on ore genesis more easily interpreted than 

similar data from older and more complicated deposits. Most of these data have been presented earlier in this report; here, these data are used to 

set up a genetic model for the Shirley Basin uranium 

deposits.

Conditions favorable for solution, transportation, 

and deposition of uranium probably came into being 

in late Miocene or early Pliocene time when the 

Shirley Basin, as we know it today, was buried 

beneath as much as 1,800 feet of clastic and tuffaceous roclrs ranging from Eocene to Miocene in 

age. During mid-Tertiary time, ground-water flow, 

particularly in formations as deeply buried as the 

Wind River, was probably very slow, and ingress
GEOCHEMISTRY OF ORE DEPOSITS 71

of vadose water into the Wind River may have been 

limited by the thick sequence of flat-lying Tertiary 

rocks that overlay the area. There is ample geologic 

evidence, in areas surrounding the Shirley Basin 

(Denson, 1969), that late Miocene time was marked 

by uplift of the mountain ranges and renewed erosion of rocks in the uplifts and on the flanks. The 

low northerly dip of rocks of Tertiary age now exposed in the Shirley Basin is thought to have originated at this time, a seemingly minor event that 

may have produced the hydraulic gradient necessary 

for the flow of uranium-bearing ground water 

throughout the permeable beds of the Wind River 

Formation.

Soon after uplift, ground water that carried 

uranium and other elements is thought to have 

percolated downward through the overlying rocks 

and then to have moved laterally along the permeable beds of the Wind River Formation, somewhat as 

shown in figure 51A. Later, after erosion of the 

Tertiary rocks on the flanks of the uplift, the uranium-bearing ground water may have entered the 

Wind River Formation directly by a path similar

to that shown in figure 5LZ?. The oxygenated ground 

water would at first be out of equilibrium with the 

reduced environment through which it moved, but 

oxidation of the rock components, particularly pyrite, and fossil wood would quickly produce conditions approximating equilibrium in an oxidized zone 

at and slightly downstream from the area of groundwater ingress. This zone, at first very small, would 

gradually expand in the direction of ground-water 

flow, and an interface would be established between 

reducing conditions in the downdip part of the 

aquifer and oxidizing conditions in the updip part. 

More correctly, several interfaces would be established, the position of each determined by the combined effect of Eh and pH changes on the solubility 

of various elements. The interface most commonly 

discussed, and incorrectly referred to as the interface or the solution front, is one between oxidized 

and reduced forms of iron, or, pyrite and goethite 

in the Shirley Basin area. Easily distinguished iron, 

uranium, and selenium interfaces occur in the Shirley Basin; iron, uranium, selenium, and molybdenum 

interfaces occur in the Gas Hills. Deposition of an

Altered sandstone

Pre-Tertiary rocks

Siltstone

LJ n a Itered; sa n dsto n e

Pre-Tertiary rocks B

FIGURE 51. Possible paths of circulation of ore-bearing solutions in the Shirley Basin area. Arrows indicate direction of

ground-water flow.
72 GEOLOGY AND URANIUM DEPOSITS, SHIRLEY BASIN AREA, WYOMING

element carried by ground water appears to have 

occurred most rapidly at the redox interface for 

that element and less rapidly as the solution moved 

through the reducing zone. There was an overlap 

in the deposition of the several ore elements.

Changes in Eh have been considered by most 

geologists to be the principal cause of deposition in 

sandstone-type uranium deposits. However, the EhpH diagrams of Garrels and Christ (1965), applicable to uranium deposits, and those of Hostetler and 

Garrels (1962) show that pH changes may be of 

equal importance in precipitation of some of the 

component minerals. The writer, in an earlier publication (Harshman, 1966), pointed out the genetic 

similarities between secondary sulfide deposits and 

uranium deposits in sandstone and postulated that 

oxidation of pyrite accompanying uranium ore would 

cause a sharp drop in pH near the redox interface 

for iron. Figure 52 is reproduced from that earlier 

publication to illustrate the postulated Eh and pH 

conditions in and near the Shirley Basin deposits.

Lisitsyn and Kuznetsova (1967) and Germanov 

and Panteleyev (1967) collected ground-water 

samples, from below the permanent water table, in 

traverses extending from altered sandstone, through 

ore and mineralized sandstone, and into unaltered 

sandstone. The first two investigators sampled a 

zone of "epigenetic mineralization" (uranium is not 

mentioned) ; the latter investigators sampled uranium deposits similar in most aspects to the roll-type 

deposits of the Shirley Basin. The Eh and pH values 

determined by these investigators for the zones in 

the Russian deposits are remarkably similar to those 

postulated for similar zones in the Shirley Basin.

Any mineralized zone established early in the 

cycle just described would be small and of low tenor. 

It would migrate in the direction of ground-water 

flow, generally downdip, by oxidation and solution 

on the updip side of the zone and reduction and redeposition on the downdip side. A continuous external supply of uranium and associated elements 

in the ground water passing through the zone of 

deposition would cause the mineralized zone to grow 

in both size and grade and to eventually reach the 

magnitude of present-day ore bodies.

The genetic processes proposed for the Shirley 

Basin deposits and the multiple migration-accretion 

theory of Gruner (1956) have some broad similarities, but they have very basic differences. The first 

step in the multiple migration-accretion theory is 

the formation of a large body of mineralized sandstone of very low tenor. Repeated cycles of uplift, 

exposures, oxidation, migration, and deposition redistribute the uranium from the original mineralized-sandstone body into an increasingly higher 

grade deposit that finally reaches ore grade. This 

is a discontinuous process, and it does not require 

the addition of "new" uranium after the first large 

low-grade deposit forms. In marked contrast, the 

Shirley Basin ore bodies are thought to have started 

with very small low-grade deposits that grew in 

size and grade by redistribution of the uranium in 

them and the continuous addition of "new" uranium 

to them. Though oxidation and reduction are essential to the concept, the entire process takes place 

at depth, and repeated uplift and exposure play no 

part in it. The process would continue until the 

supply of uranium and associated elements was 

exhausted, the environment causing deposition was 

destroyed, or the hydrodynamic system was 

disrupted.

The shape of the altered-sandstone tongues, the 

shape and position of the ore bodies, and the distribution of the elements in and near ore suggest that 

the ore-bearing solutions in the Shirley Basin were 

moving northwestward at the time of ore deposition. 

Today the ground-water flow is southward at gradients of 10-30 feet per mile, and the divide that 

separates northerly from southerly flowing ground 

water lies 5 miles or more north of the ore deposits,

Altered sandstone :'. '. ' -.: -.' ' .-.'

Direction of flow of ore-bearing solution

FIGURE 52. Postulated Eh and pH conditions for a unit of solution during transportation and deposition of

uranium and other elements, Shirley Basin.
URANIUM DEPOSITS IN OTHER ROCKS 73

near the south-facing erosional scarp that marks 

the contact between the upper and lower members 

of the White River Formation shown on the geologic 

map (Harshman, 1968b). It is postulated that the 

ore deposits were formed by northwesterly flowing 

ground water when the ground-water divide was 

south of the altered-sandstone tongues, and that the 

ore-forming processes were disrupted when the 

divide migrated northward and the direction of 

ground-water flow reversed.

AGE

The Shirley Basin deposits are in rocks of early 

Eocene age, and thus they are less than 50 million 

years old; how much less is not known. Radioactivity disequilibrium studies by Dooley, Tatsumoto, and Rosholt (1964) indicate that the deposits 

are more than 250,000 years old. In an effort to 

narrow the gap between these two limits, total Pb/U 

ratios of 15 ore samples that contained more than 

2 percent uranium were determined and are plotted 

in figure 53. The average content of these samples

EXPLANATION

 

Individual sample

x 

Average of 15 samples

0.001 0.005 0.01 

LEAD, IN PERCENT

0.05

FIGURE 53. Total Pb/U ratios of 15 high-grade ore samples 

from the Shirley Basin. (Isochrons plotted from Stieff and 

others, 1959.)

is 4.83 percent uranium and 0.0122 percent lead, 

amounts that suggest an age of about 18 million 

years. Ages determined in this manner are subject 

to considerable error, but from the geologic viewpoint an age of about 18 million years is reasonable,

for in late Miocene time there was uplift of the 

mountain ranges bounding the Shirley Basin, accompanied by vigorous renewed erosion. This uplift 

is thought to have been the event that spawned the 

hydrodynamic cycle responsible for the ore deposits.

URANIUM DEPOSITS IN OTHER ROCKS

Although the largest and economically most significant uranium deposits in the Shirley Basin are 

in sandstone, small deposits of ore-grade material 

are associated with jasper along the karst surface at 

the top of the Madison Limestone. Ore and accessory minerals are apatite, goethite, chalcedony, calcite, and quartz. They fill open spaces in a limestone 

breccia that characterizes the karst surface, and 

they replace some of the limestone fragments. The 

apatite is very fine grained or cryptocrystalline, and 

it is intergrown with fine-grained goethite. In some 

samples apatite intergrown with goethite is in 

rhomb-shaped aggregates, pseudomorphous after 

either calcite or dolomite rhombs.

A small pit excavated near the center of sec. 12, 

T. 28 N., R. 77 W., exposes the mineralized karst 

surface to a depth of about 6 feet in an area of high 

surface radioactivity. A selected sample of the ore 

contained "0.26 percent U3O8 and had an equivalent 

uranium (eU) of 0.22 percent U3O8. Autoradiographs of thin slabs of the ore show that the uranium is associated with the iron-bearing apatite, not 

with the chalcedony. A spectrographic analysis of 

the ore showed Si and Ca to be the major constituents and the contents of other elements, in percent, 

to be as follows: P, 5.0; Al, 0.07; Fe, 2.0; Mg, 

0.05; Na, 0.03; Mn, 0.1; Ni, 0.015; Ba, 0.02; Pb, 

0.02; Sr, 0.05; V, 0.015; Ti, Co, Cr, Cu, Mo, Y, 

Yb, 0.0002-0.005.

The karst surface is not everywhere mineralized 

or radioactive, and the deposits appear to be restricted to a part of the surface that was close to or in 

direct contact with the White River Formation that 

once overlay the entire area. The deposits are believed to have been formed by vadose waters that 

leached uranium and associated elements from the 

White River Formation. These solutions moved along 

the most permeable zones in the karst surface and 

deposited uranium-bearing apatite, chalcedony, and 

other associated minerals as fillings of open spaces 

or as replacements of carbonate minerals.

Anomalously high radioactivity has been noted 

near the base of the Wagon Bed Formation in the 

SE*4 sec. 25, T. 28 N., R. 78 W. Several cuts were 

bulldozed prior to 1959 to explore the anomaly, but 

nothing of economic interest seems to have been 

found. A selected sample of the most radioactive
74 GEOLOGY AND URANIUM DEPOSITS, SHIRLEY BASIN AREA, WYOMING

material in these pits contained 0.001 percent 

uranium.

MONAZITE DEPOSITS IN TERTIARY ROCKS

Several areas of high radioactivity in Tps. 27 

and 28 N., Rs. 79, 80, and 81 W., were found as a 

result of airborne surveys made by geologists Page 

Jenkins and Darby Hand in the summer of 1953. 

The areas lie just south of the south rim of Bates 

Hole in a region of Tertiary rocks (shown on geologic investigations map 1-539, Harshman, 1968b). 

The cause of the high radioactivity was first thought 

to be uranium but was subsequently shown to be 

monazite in the sandy and conglomeratic beds of 

the Wind River and White River Formations or in 

alluvium derived from these beds. Page Jenkins 

(written commun., 1953-54), who explored the 

areas in 1953 and 1954 and collected about 230 

samples from shallow holes drilled on a rectangular 

pattern, furnished the following data on these monazite deposits.

The exploration program showed that minor 

amounts of monazite are present in the coarsegrained rocks over an area of about 40 square miles 

and that six areas contained considerably greater 

amounts. Estimates of the monazite content of 

samples were based on the weight of heavy minerals 

in each 5-pound sample of sand and on a determination that the composite of the heavy-mineral 

separates contained 52 percent monazite. Monazite 

contents ranged from a few hundredths of a pound 

to 1.43 pounds per ton of sand; most samples contained less than 1 pound per ton. The composite 

samples of concentrates contained about 34.5 percent rare-earth oxides and 1.61 percent Th02. The 

monazite therefore contained about twice these 

amounts.

The coarse-grained facies of the Wind River and 

of the White River Formations in this western part 

of the Shirley Basin were derived from light-colored 

granites now exposed farther to the west in the 

Shirley and Granite Mountains. The monazite 

probably originated in these rocks of Precambrian age.

CONSTRUCTION MATERIALS

Materials for road and concrete structures are 

available in the Shirley Basin area. The Shirley 

Ridge road, which leads from State Highway 487 

to the mining area, has been surfaced with silicified tuff obtained from pits along Moss Agate Ridge. 

This material requires no processing before being 

used on the road.

Sand and gravel can be obtained from the coarsegrained beds of the Wind River Formation at many 

points in the Shirley Basin. Concrete made from 

these materials seems to be of fair quality, although 

the high silica content of the gravels may cause some 

adverse reaction with high alkali cement.

REFERENCES CITED

Adler, H. H., 1964, The conceptual uranium ore roll and its 

signiricance in uranium exploration: Econ. Geology, v. 

59, no. 11, p. 46-53.

Agatston, R. S., 1954, Pennsylvanian and Lower Permian of 

northern and eastern Wyoming: Am. Assoc. Petroleum 

Geologists Bull., v. 38, no. 4, p. 508-583.

Bailey, R. V., 1965, Applied geology in the Shirley Basin 

uranium district, Wyoming: Wyoming Univ. Contr. Geology, v. 4, no. 1, p. 27-35.

Bartram, J. G., 1930, Triassic-Jurassic red beds of the Rocky 

Mountain region: Jour. Geology, v. 38, no. 4, p. 335-345.

Beath, O. A., 1943, Toxic vegetation growing on the Salt 

Wash member of the Morrison formation: Am. Jour. 

Botany, v. 30, no. 9, p. 698-707.

Beath, O. A., Hagner, A. F., and Gilbert, C. S., 1946, Some 

rocks and soils of high selenium content: Wyoming Geol. 

Survey Bull. 36, 23 p.

Beus, A. A., 1962, Beryllium Evaluation of deposits during 

prospecting and exploratory work [translated from Russian] : San Francisco, W. H. Freeman and Co., 161 p.

Burk, C. A., and Thomas, H. D., 1956, The Goose Egg Formation (Permo-Triassic) of eastern Wyoming: Wyoming 

Geol. Survey Rept. Inv. 6, 11 p.

Cheney, E. S., and Jensen, M. L., 1966, Stable isotope geology 

of the Gas Hills, Wyoming, uranium district: Econ. 

Geology, v. 61, no. 1, p. 44-71.

Cobban, W. A., 1963, Occurrence of the Late Cretaceous ammonite Hoplitoplacenticeras in Wyoming, in Short papers 

in geology and hydrology: U.S. Geol. Survey Prof. Paper 

475-C, p. C60-C62.

Barton, N. H., 1898, Preliminary report on the geology and 

water resources of Nebraska west of the one hundred and 

third meridian: U.S. Geol. Survey 19th Ann. Rept., pt. 4, 

p. 719-785.

_____1899, Jurassic formations of the Black Hills of South 

Dakota: Geol. Soc. America Bull., v. 10, p. 383-396; abs. 

in Am. Geologist, v. 23, p. 94 (1899) ; Science, new ser., 

v. 9, p. 103 (1899).

_____1904, Comparison of the stratigraphy of the Black 

Hills, Bighorn Mountains, and Rocky Mountain front 

range: Geol. Soc. America Bull., v. 15, p. 379-448; abs. 

in Science, new ser., v. 17, p. 292 (1903).

-1908, Paleozoic and Mesozoic of central Wyoming:

Geol. Soc. America Bull., v. 19, p. 403-470.

Barton, N. H., Blackwelder, Eliot, and Siebenthal, C. E., 

1910, Description of the Laramie and Sherman quadrangles [Wyoming]: U.S. Geol. Survey Geol. Atlas, Folio 

173, 17 p.

Barton, N. H., and Siebenthal, C. E., 1909, Geology and mineral resources of the Laramie Basin, Wyoming: U.S. 

Geol. Survey Bull. 364, 81 p.
REFERENCES CITED 75

Denson, N. M., 1965, Miocene and Pliocene rocks of central 

Wyoming, in Cohee, G. V., and West, W. S., Changes in 

stratigraphic nomenclature by the U.S. Geological Survey, 1964: U.S. Geol. Survey Bull. 1224-A, p. A70-A74.

_____1969, Distribution of nonopaque heavy minerals in 

Miocene and Pliocene rocks of central Wyoming and parts 

of adjacent States, in Geological Survey research 1969: 

U.S. Geol. Survey Prof. Paper 650-C, p. C25-C32.

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 Rept. (to the U.S. Atomic 

Energy Comm.) TEM-175, 10 p.

Denson, N. M., and Harshman, E. N., 1969, Map showing 

areal distribution of Tertiary rocks, Bates Hole-Shirley 

basin area, south-central Wyoming: U.S. Geol. Survey 

Misc. Geol. Inv. Map 1-570.

Dooley, J. R., Jr., Tatsumoto, Mitsunobu, and Rosholt, J. N., 

1964, Radioactive disequilibrium studies of roll features, 

Shirley Basin, Wyoming: Econ. Geology, v. 59, no. 4, 

p. 586-595.

Emmons, S. F., Cross, Whitman, and Eldridge, G. H., 1896, 

Geology of the Denver Basin in Colorado: U.S. Geol. 

Survey Mon. 27, 556 p.

Fischer, R. P., 1942, Vanadium deposits of Colorado and 

Utah, a preliminary report: U.S. Geol. Survey Bull. 

936-P, p. 363-394 [1943].

Garrels, R. M., and Christ, C. L., 1965, Solutions, minerals, 

and equilibria: New York, Harper and Row, 450 p.

Germanov, A. I., and Panteleyev, V. M., 1967, Behavior of 

organic matter in ground water during infiltrational 

epigenesis: Akad. Nauk SSSR Izv. Ser. Geol., no. 12, 

p. 113-120; English translation, Internat. Geology Rev., 

v. 10, no. 7, p. 826-832 (1968).

Gill, J. R., 1962, Tertiary landslides, northwestern South 

Dakota and southeastern Montana: Geol. Soc. America 

Bull., v. 73, no. 6, p. 725-735.

Goleva, G. A., and Lushnikov, V. V., 1967, Selenium distribution in underground waters of ore deposits and some 

types of mineral waters: Geokhimiya, no. 4, p. 438-445; 

English translation, Geochemistry Internat., v. 4, no. 2, 

p. 378-385 (1967).

Govorov, I. N., and Stunzhas, A. A., 1963, Mode of transport 

of beryllium in alkali metasomatism [English translation] : Geochemistry, no. 4, p. 402-409.

Granger, H. C., 1963, Mineralogy, in Geology and technology 

of the Grants uranium region: New Mexico Bur. Mines 

and Mineral Resources Mem. 15, p. 21-37.

 1966, Ferroselite in a roll-type uranium deposit, 

Powder River basin, Wyoming, in Geological Survey research 1966: U.S. Geol. Survey Prof. Paper 550-C, p. 

C133-C137.

Granger, H. C., Santos, E. S., Dean, B. G., and Moore, F. B., 

1961, Sandstone-type uranium deposits at Ambrosia Lake, 

New Mexico An interim report: Econ. Geology, v. 56, 

no. 7, p. 1179-1210.

Granger, H. C., and Warren, C. G., 1969, Unstable sulfur 

compounds and the origin of roll-type uranium deposits: 

Econ. Geology, v. 64, no. 2, p. 160-171.

Gruner, J. W., 1956, Concentration of uranium in sediments 

by multiple migration-accretion: Econ. Geology, v. 51, 

no. 6, p. 495-520.

Grutt, E. W., Jr., 1957, Environment of some Wyoming uranium deposits, in Advances in nuclear engineering: Nuclear Eng. and Sci. Cong., 2d, Philadelphia, Proc. 2d 

Conf., v. 2, p. 313-323.

Harshman, E. N., 1961, Paleotopographic control of a uranium mineral belt, Shirley Basin, Wyoming, in Short 

papers in the geologic and hydrologic sciences: U.S. Geol. 

Survey Prof. Paper 424-C, p. C4-C6.

_____1962, Alteration as a guide to uranium ore, Shirley 

Basin, Wyoming, in Short papers in geology, hydrology, 

and topography: JJ.S. Geol. Survey Prof. Paper 450-D, 

p. D8-D10.

_____1966, Genetic implications of some elements associated with uranium deposits, Shirley Basin, Wyoming, in 

Geological Survey research 1966: U.S. Geol. Survey Prof. 

Paper 550-C, p. C167-C173.

_____1968a, Uranium deposits of the Shirley Basin, Wyoming, in Ridge, J. D., ed., Ore deposits of the United 

States, 1933-1967 (Graton-Sales volume) : New York, 

Am. Inst. Mining, Metall., and Petroleum Engineers, v. 1, 

p. 849-856.

_1968b, Geologic map of the Shirley basin area, Albany, Carbon, Converse, and Natrona Counties, Wyoming: 

U.S. Geol. Survey Misc. Geol. Inv. Map 1-539.

Hay, R. L., 1963, Stratigraphy and zeolitic diagenesis of the 

John Day Formation of Oregon: California Univ. Pubs. 

Geol. Sci., v. 42, no. 5, p. 199-262.

Hemley, J. J., and Jones, W. R., 1964, Chemical aspects of 

hydrothermal alteration with emphasis on hydrogen metasomatism: Econ. Geology, v. 59, no. 4, p. 538-567.

High, L. R., Jr., and Picard, M. D., 1967, Rock units and 

revised nomenclature, Chugwater Group (Triassic), western Wyoming: Mtn. Geologist, v. 4, no. 2, p. 73-81.

Hintze, F. F., Jr., 1915, The Basin and Greybull oil and gas 

fields: .Wyoming Geologist's Office Bull. 10, 62 p.

Hostetler, P. B., and Garrels, R. M., 1962, Transportation 

and precipitation of uranium and vanadium at low temperatures, with special reference to sandstone-type uranium deposits: Econ. Geology, v. 57, no. 2, p. 137-167.

Imlay, R. W., 1947, Marine Jurassic of Black Hills area, 

South Dakota and Wyoming: Am. Assoc. Petroleum 

Geologists Bull., v. 31, no. 2, p. 227-273.

Jensen, M. L., 1958, Sulfur isotopes and the origin of sandstone-type uranium deposits [Colorado Plateau and 

Wyo.] : Econ. Geology, v. 53, no. 5, p. 598-616.

Kashirtseva, M. F., 1964, Mineralic and chemical zonality in 

uranium infiltration ore occurrences: Sovetskaya Geologiya, no. 10, p. 51-65.

Keefer, W. R., and Van Lieu, J. A., 1966, Paleozoic formations in the Wind River Basin, Wyoming: U.S. Geol. 

Survey Prof. Paper 495-B, 60 p.

King, J. W., and Austin, S. R., 1966, Some characteristics 

of roll-type uranium deposits at Gas Hills, Wyoming: 

Mining Eng., v. 18, no. 5, p. 73-80.

Knight, S. H., 1917, Age and origin of the red beds of southeastern Wyoming [abs., with discussion by Erasmus Haworth and E. B. Branson]: Geol. Soc. America Bull., 

v. 28, no. 1, p. 168-169.

______1929, The Fountain and the Casper formations of the

Laramie Basin; a study on genesis of sediments: Wyoming Univ. Pub. Sci. Geology, v. 1, no. 1, p. 1-82.

Knight, W. C., 1902, The petroleum fields of Wyoming: Eng. 

and Mining Jour., v. 73, p. 720-723.
76 GEOLOGY AND URANIUM DEPOSITS, SHIRLEY BASIN AREA, WYOMING

Koeberlin, F. R., 1938, Sedimentary copper, vanadium-uranium, and silver in southwestern United States: Econ. 

Geology, v. 33, no. 4, p. 458-461.

Konkel, Phillip, 1935, The geology of the northeast portion 

of the Laramie Basin, Little Medicine district, Wyoming: 

Wyoming Univ. unpub. M.A. thesis, 59 p., map.

Lakin, H. W., 1961, Geochemistry of selenium in relation to 

agriculture, in Selenium in agriculture: U.S. Dept. Agriculture Handb. 200, p. 3-12.

Lee, W. T., 1927, Correlation of geologic formations between 

east-central Colorado, central Wyoming, and southern 

Montana: U.S. Geol. Survey Prof. Paper 149, 80 p.

Lindgren, Waldemar, Graton, L. C., and Gordon, C. H., 1910, 

The ore deposits of New Mexico: U.S. Geol. Survey Prof. 

Paper 68, 361 p.

Lipman, P. W., 1965, Chemical comparison of glassy and crystalline volcanic rocks: U.S. Geol. Survey Bull. 1201-D, 

24 p.

Lisitsyn, A. K., and Kuznetsova, E. C., 1967, Role of microorganisms in development of geochemical reduction barriers where limonitization bedded zones wedge-out: Akad. 

Nauk SSSR Izv. Ser. Geol., no. 1, p. 31-44; English 

translation, Internat. Geology Rev., v. 9, no. 9, p. 1180- 

1191 (1967).

Love, J. D., 1939, Geology along the southern margin of the 

Absaroka Range, Wyoming: Geol. Soc. America Spec. 

Paper 20, 134 p.

_______1952, Preliminary report on uranium deposits in the

Pumpkin Buttes area, Powder River Basin, Wyoming: 

U.S. Geol. Survey Circ. 176, 37 p.

Love, J. D., Denson, N. M., and Botinelly, Theodore, 1949, 

Geology of the Glendo area, Wyoming: U.S. Geol. Survey 

Oil and Gas Inv. Prelim. Map 92, 2 sheets.

Love, J. D., Weitz, J. L., and Hose, R. K., 1955, Geologic map 

of Wyoming: U.S. Geol. Survey.

Lupton, C. T., 1916, Oil and gas near Basin, Big Horn County, 

Wyoming: U.S. Geol. Survey Bull. 621-L, p. 157-190.

Maughan, E. K., 1963, Mississippian rocks in the Laramie 

Range, Wyoming, and adjacent areas, in Short papers in 

geology and hydrology: U.S. Geol. Survey Prof. Paper 

475-C, p. C23-C27.

_____1964, The Goose Egg Formation in the Laramie 

Range and adjacent parts of southeastern Wyoming, in 

Geological Survey research 1964: U.S. Geol. Survey Prof. 

Paper 501-B, p. B53-B60.

Maughan, E. K., and Wilson, R. F., 1960, Pennsylvanian and 

Permian strata in southern Wyoming and northern Colorado, in Weimer, R. J., and Haun, J. D., eds., Rocky Mtn. 

Assoc. Geologists Guide to the geology of Colorado: Denver, Colo., p. 34-42.

Meek, F. B., and Hayden, F. V., 1858, Descriptions of new 

species and genera of fossils, collected by Dr. F. V. Hayden in Nebraska Territory, under the direction of Lieut. 

G. K. Warren, U.S. Topographical Engineer; with some 

remarks on the Tertiary and Cretaceous formations of 

the north-west, and the parallelism of the latter with 

those of other portions of the United States and Territories: Acad. Nat. Sci. Philadelphia Proc., 1857, v. 9, 

p. 117-148.

_____1862, Descriptions of new Lower Silurian (Primordial) , Jurassic, Cretaceous, and Tertiary fossils, collected 

in Nebraska Territory by the Exploring Expedition under 

the command of Capt. Wm. F. Raynolds, U.S. Topographical Engineer, with some remarks on the rocks 

from which they were obtained: Acad. Nat. Sci. Philadelphia Proc., 1861, v. 13, p. 415-447.

Melin, R. E., 1964, Description and origin of uranium deposits 

in Shirley Basin, Wyoming: Econ. Geology, v. 59, no. 5, 

p. 835-849.

Miller, A. K., and Thomas, H. D., 1936, The Casper formation 

(Pennsylvanian) of Wyoming and its cephalopod fauna: 

Jour. Paleontology, v. 10, no. 8, p. 715-738.

Mrak, V. A., 1968, Uranium deposits in the Eocene sandstones 

of the Powder River basin, Wyoming, in Ridge, J. D., 

ed., Ore deposits of the United States, 1933-1967 (Graton-Sales volume) : New York, Am. Inst. Mining, Metall., 

and Petroleum Engineers, v. 1, p. 338-848.

Peale, A. C., 1893, The Paleozoic section in the vicinity of 

Three Forks, Montana, with petrographic notes by G. P. 

Merrill: U.S. Geol. Survey Bull. 110, 56 p.

Peterson, A. F., 1935, Geology of the Shirley Basin and Bates 

Hole region, Carbon County and Natrona County, Wyoming: Wyoming Univ. unpub. M.A. thesis, 70 p., map.

Pettijohn, F. J., 1957, Sedimentary rocks [2d ed.] : New York, 

Harper & Bros., 718 p.

Pipiringos, G. N., 1948, Marine Jurassic and related rocks of 

Laramie Basin, Wyoming [abs.]: Geol. Soc. America 

Bull., v. 59, no. 12, pt. 2, p. 1399-1400.

_____1957, Stratigraphy of the Sundance, Nugget and 

Jelm formations in the Laramie Basin, Wyoming: Wyoming Geol. Survey Bull. 47, 63 p.

-1968, Correlation and nomenclature of some Triassic

and Jurassic rocks in south-central Wyoming: U.S. Geol. 

Survey Prof. Paper 594-D, 26 p.

Rackley, R. I., Shockey, P. N., and Dahill, M. P., 1968, Concepts and methods of uranium exploration, in Black Hills 

area, South Dakota, Montana, Wyoming Wyoming Geol. 

Assoc. Guidebook, 20th Field Conf., 1968: Casper, Wyo., 

Petroleum Inf., p. 115-124.

Rich, E. I., 1962, Reconnaissance geology of Hiland-Clarkson 

Hill area, Natrona County, Wyoming: U.S. Geol. Survey 

Bull. 1107-G, p. 447-540.

Riedl, Gary, 1959, Geology of the eastern portion of Shirley 

Basin, Albany and Carbon Counties, Wyoming: Wyoming 

Univ. unpub. M.S. thesis, 49 p., map.

Roehler, H. W., 1958, Geology of Bates Hole, Wyoming: 

Wyoming Univ. unpub. M.S. thesis, 58 p., map.

Rosholt, J. N., Harshman, E. N., Shields, W. R., and Garner, 

E. L., 1964, Isotopic fractionation of uranium related to 

roll features in sandstone, Shirley Basin, Wyoming: 

Econ. Geology, v. 59, no. 4, p. 570-585.

St. John, O. H., 1883, Report on the geology of the Wind 

River district: U.S. Geol. and Geog. Survey Terr. (Hayden) 12th Ann. Rept., pt. 1, p. 173-269.

Sato, Yoshiaki, and Denson, N. M., 1967, Volcanism and 

tectonism as reflected by the distribution of nonopaque 

heavy minerals in some Tertiary rocks of Wyoming and 

adjacent States, in Geological Survey research 1967: U.S. 

Geol. Survey Prof. Paper 575-C, p. C42-C54.
REFERENCES CITED 77

Schlaikjer, E. M., 1935, A new basal Oligocene formation, pt. 

3 of Contributions to the stratigraphy and palaeontology 

of the Goshen Hole area, Wyoming: Harvard Coll. Mus. 

Comp. Zoology Bull., v. 76, p. 69-94.

Schultz, C. B., and Stout, T. M., 1955, Classification of Oligocene sediments in Nebraska A guide for the stratigraphic collecting of fossil mammals: Nebraska Univ. 

State Mus. Bull., v. 4, no. 2, p. 17-52.

Shawe, D. R., 1956, Significance of roll ore bodies in genesis 

of uranium-vanadium deposits on the Colorado Plateau, 

in Page, L. R., Stocking, H. E., and Smith, H. B., compilers, Contributions to the geology of uranium and 

thorium by the United States Geological Survey and 

Atomic Energy Commission for the United Nations International Conference on Peaceful Uses of Atomic Energy, Geneva, Switzerland, 1955: U.S. Geol. Survey Prof. 

Paper 300, p. 239-241; also in United Nations, 1956, 

Geology of uranium and thorium, v. 6, p. 335-337.

Shipp, B. G., 1959, Geology of an area east of Bates Hole, 

Carbon County and Albany County, Wyoming: Wyoming 

Univ. unpub. M.S. thesis, 69 p., map.

Sinclair, W. J., and Granger, Walter, 1911, Eocene and Oligocene of the Wind River and Bighorn basins [Wyo.]: Am. 

Mus. Nat. History Bull., v. 30, p. 83-117.

Stieff, L. R., Stern, T. W., Oshiro, Seiki, and Senftle, F. E., 

1959, Tables for the calculation of lead isotope ages: U.S. 

Geol. Survey Prof. Paper 334-A, p. 1-40.

Thomas, H. D., 1948, Summary of Paleozoic stratigraphy of 

the Wind River Basin, Wyoming, in Wyoming Geol. 

Assoc. Guidebook, 3d Ann. Field Conf., Wind River 

Basin, 1948: p. 79-95.

Thompson, M. L., and Thomas, H. D., 1953, Systematic 

paleontology of fusulinids from the Casper formation, pt. 

2 of Fusulinids of the Casper formation of Wyoming: 

Wyoming Geol. Survey Bull 46, p. 15-56.

Van Houten, F. B., 1954, Geology of the Long Creek-Beaver 

Divide area, Fremont County, Wyoming: U.S. Geol. Survey Oil and Gas Inv. Map OM-140, 2 sheets.

_____1964, Tertiary geology of the Beaver Rim area, Fremont and Natrona Counties, Wyoming: U.S. Geol. Survey 

Bull. 1164, 99 p. [1965].

Warren, C. G., 1968, The synthesis of ferroselite from an 

aqueous solution at low temperature: Econ. Geology, v. 

63, no. 4, p. 418-419.

Weitz, J. L., and Love, J. D., 1952, Geologic map of Carbon 

County, Wyoming: U.S. Geol. Survey.

Weitz, J. L., Love, J. D., and Harbison, S. A., 1954, Geologic 

map of Natrona County, Wyoming: Wyoming Geol. Survey.

Wood, H. E. 2d, chm., and others, 1941, Nomenclature and 

correlation of the North American continental Tertiary: 

Geol. Soc. America Bull., v. 52, no. 1, p. 1-48.

INDEX

A Page 

Absaroka Range, Red Peak .......................... 13

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

Airborne surveys .............................................. 74

Alcova Dam, Wyo.............................................. 24

Alcova Limestone ............................................ 1, IS

Alluvium ............................................................ 34

Alteration, deuteric .......................................... 8

sandstone .................................................... 46

feldspar ...................................................... 8, 69

Alumina .............................................................. 60

Ambrosia Lake, N. Hex.................................. 55, 59

Ammonites ........................................................ 19

Amsden Formation .......................................... 12

Analyses, atomic-absorption .......................... 66

beta-gamma ............................................ 59

chemical .................................................... 49, 59

fluorimetric ................................................ 59

radiometric ................................................ 59

spectographic .................................... 59, 65, 73

turbidimetric .............................................. 49

X-ray ........................................................ 47, 55

Apatite .............................................................. 12, 73

Aragonite ............................................................ 17

Arikaree Formation ........................................ 32

faults ............................................................ 36

measured sections .................................... 33

nomenclature ............................................ 31

stratigraphic position ............................ 1

volcanic ash .............................................. 69

Arikaree Indians .............................................. 32

Arkose ........................................................ 41, 67, 68

Arsenic ................................................................ 65

Artifacts ............................................................ 5

Ash, volcanic ...................................... 32, 33, 68, 69

Augite ................................................................ 33

Auto-oxidation .................................................. 55

Autoradiographs .............................................. 73

B

Bailey, R. V., fossil collection........................ 24

Barium ................................................................ 66

Bates Creek .................................................... 1, 3, 5

Bates Hole ........................................................ 1, 2. 3

airborne survey ........................................ 74

Arikaree Formation ................................ 32

Cretaceous shales ...................................... 3

faults .......................................................... 36

gravel .......................................................... 34

landslides .................................................... 35

measured sections .................................. 28, 30

Mesozoic outcrops .................................. 7, 19

Tertiary rocks .......................................... 3

White River Formation .......................... 26

Wind River Formation ............................ 20

Beaver Divide, Wyo.................................. 24, 25, 33

Belemnites .......................................................... 15

Benton Formation ............................................ 17

Bentonite ............................................................ 17

Beryllium .................................................... 2, 65, 69

Bicarbonate ........................................................ 1, 39

Bighorn Basin .................................................. 16

Bighorn Mountains .......................................... 17

Biotite .......................................................... 8, 18, 57

Black Hills, S. Dak............................................ 14

Black ore ............................................................ 53

Breccia zones .................................................... 36

[Italic page numbers indicate major references]

Page 

Bridger Formation .......................................... 26

Brule Formation ............................................ 26, 31

Orella Member .......................................... 31

Whitney Member ...................................... 31

Butler, A. P., assistance .................................. 7

Bypass, uranium zonation ............................ 53

Calcite, accessory ore mineral ................ 2, 41, 73

concretions ........................................ 56, 60, 63

epigenetic mineral .................................... 53

in depositional sequence ........................ 58

in uranium deposits ................................ 56

ore cementation ...................................... 54, 63

vugs .............................................................. 11

Calcium ...................................................... 39, 66, 68

Calcium carbonate ...................... 17, 18, 33, 48, 68

Canyon Springs Sandstone Member,

Sundance Formation ................ 15

Carbon, analyses .............................................. 59

in uranium deposits ................................ 63

mineral .............................................. 48, 59, 63

organic .............................................. 49, 59, 63

relation to solutions .............................. 69, 70

replacement by pyrite ............................ 53

systematic distribution ............................ 2

Wind River Formation .......................... 48

Carbonate ........................................................ 69, 70

Carbonate minerals .......................................... 73

Casper Formation ............................................ 12

nomenclature ............................................ 9

stratigraphic position ...................... 1, 11, 27

Casper, Wyo ....................................................... 2, 6

Centennial Development Co............................ 7

Chadron Formation ........................................ 26

Chadronian provincial age .............................. 32

Chalcedony ........................................................ 73

Chalk Mountain .............................. 1,3,28,32,36

measured sections ............................ 25, 30, 33

Chemistry, ground water ............................ 41, 69

Chert, Madison Limestone .......................... 11, 12

White River Formation .......................... 26

Chlorine ............................................................ 41, 69

Chlorite .............................................................. 8

Chugwater Formation .................................... 13

Chugwater Group ............................................ 13

Clarkson Hill, Wyo.................................... 29, 31, 33

Clay ....................................................... 18, 48, 53, 68

kaolin .......................................................... 8, 41

kaolinite .................................................... 22

montmorillonite ................................ 22, 47, 60

sericite ........................................................ 8

Claystone ............................................................ 44

Cleverly Formation .................................. 16

Jelm Formation ...................................... 14

slide surface .............................................. 35

Wagon Bed Formation .......................... 24

White River Formation .......................... 26

Wind River Formation ............................ 21

Climate .................................................. 5, 23, 24, 35

Cleverly Formation ........................................ 16

slide blocks ................................................ 35

stratigraphic position .............................. 1

tipi rings .................................................... 5

Coffinite .............................................................. 55

Page 

Colorado, Morrison Formation ...................... 15

vanadium-uranium ore bodies .............. 50

Concrete ............................................................ 74

Concretions ...................................................... 32, 48

calcite ................................................ 56, 60, 63

ironstone .................................................... 16, 19

limestone .................................................. 15, 16

sandstone ................................................ 13, 15

Conglomerate, Arikaree Formation.............. 32

Cleverly Formation .................................. 16

Madison Limestone .................................. 11

Wagon Bed Formation ........................ 24, 26

White River Formation ................ 26, 29, 74

Wind River Formation ........................ 20, 23

Construction materials .................................... 41

Copper ............................................ 2, 50, 65, 68, 70

Coquina shells .................................................... 15

Cordilleran geosyncline .................................. 1

Cram Ranch ...................................................... 17

Crossbeds, Casper Formation ........................ 12

Cleverly Formation ................................ 16

Frontier Formation ................................ 18

Jelm Formation ........................................ 14

Madison Limestone .................................. 11

ore minerals .............................................. 67

pyrite cementation .................................. 53

White River Formation .......................... 29

Culture ................................................................ 5

Curry Creek ...................................................... 4

Deer Creek ........................................................ 4

Denson, N. M., reconnaissance mapping.... 31

rock and heavy-mineral studies .......... 24, 25

Deposition of ore. See Uranium, deposition. 

Diabase ...................................................... 23, 26, 30

dikes ........................................................ 4, 8, 36

Precambrian .............................................. 8, 20

Difficulty Shale Member, Goose Egg

Formation .................................. 13

Dikes, diabase .............................................. 4, 8, 36

mafic ............................................................ 1

sandstone .................................................... 29

Dissolved solids, ground water ...................... 41

Dolomite, Casper Formation .......................... 12

Madison Limestone .................................. 11

Drainage, present .......................................... 1, 2, 4

Tertiary .......................................... 4,19, 30, 43

Drill-hole cuttings ............................ 18, 19, 20, 27

Dry Creek .......................................................... 2

Dugway Rim ...................................................... 2

E

Economy ............................................................ 4

Elements, distribution .............................. 2, 58, 72

See also names of specific elements. 

Elk Creek .......................................................... 34

Environment of deposition ............................ 44

Epidote .............................................................. 8, 47

Equivalent uranium ........................................ 59

Ervay Member, Goose Egg Formation........ 13

Faults ...................................................... 1, 7, 15, 55

Feldspar, alteration ........................................ 8, 69

79
80 INDEX

Page 

Feldspar Continued

arkose ........................................................ 41, 68

calcite replacement .................................. 56

hydrolysis .................................................. 69

microcline ............................................ 8, 22, 68

occurrence with hematite ...................... 57

orthoclase ............................................ 8, 22, 68

plagioclase ............................................ 8, 68, 69

pyrite replacement .................................. 54

uranium contents ...................................... 68

Ferroselite ............................................ 2, 41, 53, 55

Fish scales .......................................................... 17

Fluorine .............................................................. 69

Folds ........................................................ 1, 7, 19, S6

Forelle Limestone Member, Goose Egg

Formation .................................. 13

Fort Steele, Wyo............................................. 19

Fort Union Formation .................................... 1, 19

Fort Union Group ............................................ 19

Fossils, Agriochoerus ...................................... 31

ammonites .................................................. 19

Arikaree Formation ................................ 33

belemnites .................................................. 15

Brontops sp .............................................. 23, 31

camel bone fragments .............................. 31

coquina shells ............................................ 15

Coryphodon sp .......................................... 23

crocodile scutes ........................................ 23

fish scales .................................................. 17

garpike scales ............................................ 23

Hesperocyon gregarius .......................... 31

Hesperocyon paterculus .......................... 31

Hoplitoplacenticeras ................................ 19

Hyrachyus sp ............................................ 23

Hyracodon nebrascensis .......................... 31

Hyracotherium sp .................................... 23

leaves .......................................................... 24

Leptauchenia sp ...................................... 31

Leptomeryx evansi .................................. 31

Menodus ...................................................... 31

Metamynodon sp ...................................... 31

Notharctus tenebrosus ............................ 25

Oligocene .................................................... 32

Palaeolagus haydeni ................................ 31

Petrotomics Co, sec. 9 pit ...................... 23

Phenacodus primaevus .......................... 23

Poebrotherium sp .................................... 31

pollen ........................................................ 19, 23

primate ........................................................ 25

rhinocerous bone fragments ................ 31

root tubes .................................................. 17

Steele Shale ................................................ 19

Slylemys sp ................................................ 31

Subhyracodon occidentalis .................... 31

trails ............................................................ 15

Utah Construction and Mining Co.

open-pit mines .......................... 23

White River Formation ........................ 27, 31

Wind River Formation .......................... 23

wood ............................................................ 71

Fractures, tension ............................................ 8

Freezeout Shale Member, Goose Egg

Formation .................................. 13

Frontier Formation ........................................ 18

natural gas ................................................ 70

paleotopography ...................................... 42

stratigraphic position ............................ 1

underlying landslides .............................. 35

Wall Creek Sandstone Member .... 18, 42, 70

Frontier, Wyo.................................................... 18

Gabbro ................................................................ 67

Gas, natural ..............____........._............... 70

Gas Hills, altered sandstone ........................ 41, 67

interfaces .................................................. 71

Lucky Me mill .............................__....... 7

natural gas ................................................ 70

Page 

Gas Hills Continued

pyrite .......................................................... 55

uranium occurrence .............................. 52, 59

uranium-sulfate ratio .............................. 63

White River Formation .......................... 31

Geochemistry .................................................... 2, 67

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

Geologic history .............................................. 1

Gering Formation ............................................ 32

Glauconite ........................................................ 15, 18

Glendo Shale Member, Goose Egg

Formation .................................. 13

Gneiss, Precambrian ........................................ 8

Goethite, accessory to uranium ore ............ 73

altered sandstone .................................... 2, 69

association with iron .............................. 60

association with selenium .................... 50, 62

interface ...................................................... 71

Goose Egg Formation .................................. 13, 26

faults ..............................._......................... 36

nomenclature ............................................ 9

stratigraphic position ............................ 1

Gouge zones ...................................................... 36

Granite .................................................. 2, 30, 67, 74

Granite, batholith ............................................ 1

boulders ...................................................... 20

Laramie Mountains ...................... 4, 8, 30, 67

Precambrian, Arikaree Formation ...... 33

composition ........................................ 8

Laramie Mountains ........................ 4, 8

source of monazites ........................ 74

stratigraphic position ...................... 27

White River Formation ................ 27, 29

Wind River Formation .................. 20

Granite Mountains .................... 19, 21, 30, 33, 74

Gravel .................................................................. 34

Gray ore .............................................................. 53

Great Lignite Group ...................................... 19

Ground water .................................................... 1

chemistry ................................................ 41, 69

dissolved solids .......................................... 41

hardness ...................................................... 39

ore-bearing solutions ............................ 59, 69

pH .................................................. 1, 37, 69, 71

sampling techniques ................................ 37

temperature .............................................. 37

Tertiary flow .............................................. 70

Wind and White River Formations .... 38, 41

Gypsum .............................................................. 63

H

Hand, Darby, airborne survey .................... 74

Hardness, ground water ................................ 39

Hasler, J. W., assistance ................................ 7

Hematite ............................................................ 57

accessory ore mineral .............................. 2, 41

calcite concentrations .............................. 56

epigenetic mineral .................................... 53

Frontier Formation ................................ 18

in depositional sequence .......................... 58

Precambrian granite .............................. 8

Hodges, Jay, assistance .................................. 7

Hogbacks .................................................... 14,16, 35

Holiday Ranch .................................................. 26

Holocene alluvium ............................................ 34

Homestake Mining Co...................................... 7

Hornblende .......................................... 8, 33, 47, 57

Hulett Sandstone Member, Sundance

Formation .................................. 15

Hydrogen sulfide .............................................. 2, 70

Hydrology .......................................................... 37

Hydrothermal activity .................................... 67

Igneous activity ................................................ 67

Igneous rocks .................................................... 7, 67

Indians ........................................................ 5, 32, 35

Industry .........................

Intermediate section .....

Iron ...................................

Page

4

. 53

60

analyses ...................................................... 59

color of alteration .................................... 46

effect on depleted ore elements ............ 66

Fe+2/Fe+3 ratio ........................................ 49, 69

reducing environment ........... 70

systematic distribution ............................ 2

Ironstone .................................................... 16, 18, 19

Iron sulfide ..............................................-...... 58

J, K

Jasper, Casper Formation ............................ 12

Madison Limestone .................................. 73

Jelm Formation ........................................ 1, H, 35

Jelm Mountain ................................................ 14

Jenkins, Page, airborne survey ................ 74

Joints .................................................................. 8, 13

Kaolin .................................................................. 8, 41

Kaolinite ............................................................ 22

Kerr McGee Corp ............................................ 1, 5

Lak Member, Sundance Formation ........ 15

Lake beds .................................................. 25, 27, 32

Landslides ........................................................ 35

Laramide orogeny ............................................ 1

Laramie Mountains .................................... 1, 2, 4

Arikaree Formation ................................ 32

drainage ...................................................... 19

granitic rocks ............................................ 67

Paleozoic rocks ........................................ 4

Precambrian core .................................... 8

terrace gravel ............................................ 34

White River Formation ........................26, 30

Laughon, Robert B., assistance ................ 7

Lawn Creek ...................................................... 21

Leaching ................................................ 2, 59, 67, 73

copper .......................................................... 65

in situ ..................... . .. ........ .. . 4

Lead .................................................................... 66, 73

Leaves, fossil .................................................... 24

Leopold, Estella, fossil identification ........ 24

Lewis, G. Edward, fossil identification .. 25, 31 

Lignite .............................................................. 42, 68

Thermopolis Shale .................................... 17

Wind River Formation ........................ 23

Limestone, Alcova Limestone ...................... 13

Arikaree Formation ................................ 32

Casper Formation .................................. 12

concretions ................................................ 15, 16

cuestas ............ ....... ..... ................. 25

Goose Egg Formation ............................ 13

Madison Limestone ................................ 11, 41

Sundance Formation .............................. 14

Wagon Bed Formation .......................... 24

White River Formation ........................ 26

Limonite, association with iron .................. 60

association with selenium .................... 50, 62

in altered sandstone ................................ 2, 69

Little Medicine Bow River, altitude ........ 1

area of drainage ........................................ 2

ground water ............................................ 37

Niobrara Formation ................................ 18

terrace gravel .......................................... 34

Wind River-White River contact ...... 27

Little Medicine Member,

Goose Egg Formation ............ 13

Location, Shirley Basin .............................. 2

Logs. See Well logs. 

Lost Cabin Member,

Wind River Formation ........ 19

Lucky Me mill .................................................. 7

Lysite Member, Wind River Formation 19
INDEX 81

M Page 

Madison Limestone ........................................ 11

artifacts ...................................................... 5

karst topography .................................... 12, 35

jasper .................................................. 73

uranium ............................................ 41, 73

nomenclature ............................................ 9

stratigraphic position .............................. 1, 27

Madison Range, Mont .................................... 11

Magnesium ........................................................ 41

Magnetite .................................................... 33, 48. 57

Manganese .......................................................... 63

Marcasite ............................................................ 55

accessory ore mineral .............................. 2, 41

altered sandstone .................................... 48

association with hematite .................... 57

association with iron .............................. 60

epigenetic mineral .................................. 53

in depositional sequence ...................... 58

Marl, Morrison Formation ............................ 15

Measured sections, Arikaree Formation .... 33

Bates Hole ................................................ 28, 30

Chalk Mountain ...................................... 25, 30

Petrotomics Co. sec. 9 pit .................... 21

Petrotomics Co. sec. 15 pit .................. 22

Wagon Bed Formation ........................ 24, 25

White River Formation ........................ 28

Medicine Bow River ........................................ 2

Medicine Bow, Wyo............................................ 2, 5

Mercury .............................................................. 66

Metamorphism, Precambrian ............ 4, 7, 29, 33

Microcline .................................................... 8, 22, 68

Minerals, accessory to ore .................... 2, 47, 57

altered sandstone .................................... 2

black opaque ............................................ 47, 48

distribution ................................................ 58

epigenetic .......................................... 53, 60, 72

sequence of deposition .......................... 58

syngenetic .................................................. 47

See also specific mineral names. 

Mining. See Uranium, extraction. 

Minnekahta Limestone Member,

Goose Egg Formation ........ 13

Miocene, uranium deposition ...................... 70

Missouri River ................................................ 18, 26

Molybdenum ...................................................... 71

Monazite .... ..... ............................................. 41, 74

Montana, Madison Range ............................ 11

Montmorillonite ........................................ 22, 47, 60

Morrison, Colo.................................................... 15

Morrison Formation ................................ 1, 15, 35

Moss Agate Ridge ........................................ 27, 74

Mowrie beds ...................................................... 17

Mowry Shale .................................................... 17

paleotopography ...................................... 42

slide blocks ................................................ 35

stratigraphic position ................................ 1

White River Formation ........................ 26

Mud cracks ...................................................... 16,17

Muddy Sandstone Member,

Thermopolis Shale .................... 17

Mudstone, Morrison Formation .................. 15

White River Formation ................ 26, 28, 29

Multiple migration-accretion theory ........ 72

N, O

Nail Lease .......................................................... 7

Nebraska, Arikaree Formation .................... 32

Brule Formation ...................................... 31

Niobrara Formation .............................. 18

New Mexico, Ambrosia Lake ...................... 55, 59

red-bed copper deposits .......................... 70

Night Owl uranium prospect ........................ 12

Niobrara Formation ................................ 1, 18, 42

Niobrara River, Neb ...................................... 18

North Dakota, lignite .................................. 68

North Platte River ........................................ 2, 19

Nugget Sandstone .......................................... 14

Page 

Ogallala Formation ........................................ 32

Opeche Shale Member,

Goose Egg Formation ........ 12, 13

Oregon Buttes .................................................. 33

Orella Member, Brule Formation .............. 31

Orellan provincial age ................................ 31, 32

Organic material ............................................ 41, 70

See also Carbon. 

Orthoclase .................................................... 8, 22, 68

Oxidation ............................................ 58, 69, 70, 71

Paleocontours .................................................... 46

Paleotopography ............................................ 36, 42

Petrified Forest, Wyo ...................................... 22

Petrotomics Co .................................................. 1, 6

solvent-extraction techniques .............. 7

Petrotomics Co. open-pit mine,

sec. 9, altered sandstone ........ 44

calcite .................................................. 57

carbonaceous material .................... 48

copper .................................................. 50

distribution of elements ................ 59

Fe+2/Fe+s ratio .................................. 49

fossils .................................................. 23

measured section .............................. 21

sulfate .................................................. 63

sec. 15 .......................................................... 4

measured section .............................. 22

Phosphate ........................................................ 41, 63

Pine Butte Member, Sundance Formation 15 

Plagioclase .................................................... 8, 68, 69

Pollen ................................................................ 19, 23

Popo Agie Formation .................................... 14

Potassium .......................................................... 66

Powder River Basin ................................ 42, 55, 68

Precambrian rocks .......................................... 1

diabase ........................................................ 8, 20

gneiss .......................................................... 8

granite, Arikaree Formation ................ 33

composition ........................................ 8

Laramie Mountains ........................ 4, 8

source of monazites ........................ 74

White River Formation ................ 27, 29

Wind River Formation ................ 20

igneous ........................................................ 7, 8

Laramie Mountains ................................ 4, 8

metamorphism ............................ 4, 7, 8, 29, 33

Protore ................................................................ 53

Pseudomorphs bedding .................................... 67

Pyrite .................................................................. 53

accessory ore mineral ............................ 2, 41

alteration .................................................. 48, 69

association with arsenic ........................ 65

association with hematite .................... 57

association with iron ............................ 49, 60

association with selenium .................... 62

in depositional sequence .......................... 58

oxidation .................................................... 70

Thermopolis Shale .................................... 17

Q

Quartz .................................................... 8, 22, 68, 73

veins ............................................................ 8

vugs .............................................................. 11

Quartz diabase .................................................. 8

Quartzite ............................................................ 26

Casper Formation .................................. 12

Madison Limestone ................................ 11

R

Radioactive dating ........................................ 73

Radioactive decay ............................................ 66

Radioactivity .................................................. 73, 74

Radioelements. See Uranium,

Radium, and Radon. 

Radium ................................................................ 1, 41

Page 

Radon .................................................................. 1

Reconnaissance mapping ............................ 31, 46

Red beds .................................................... 26. 68, 70

Alcova Limestone .................................... 13

Goose Egg Formation .................................. 13

Red Creek ........................................................ 13

Red Draw Member, Jelm Formation ...... 14

Red Peak, Absaroka Range ........................ 13

Red Peak Formation .................................... 13, 26

faults .......................................................... 35

stratigraphic position ............................ 1, 14

Redox interface .............................................. 59, 72

Reduction .................................................. 58, 70, 71

Redwater Shale Member,

Sundance Formation .............. 15

References cited .............................................. 74

Rich ore section .............................................. 53

Rimo, triangulation station ........................ 28

Ripple marks .................................... 14, 15, 16, 17

Roads .................................................................. 2

Russia, selenium deposits .............................. 55

uranium deposits .................................... 52, 72

Sand ...................................................... 12, 22, 25, 74

Sand Creek ........................................................ 37

Sandstone .......................................................... 42, 56

Alcova Limestone .................................... 13

alteration .................................................... 46

Arikaree Formation ................................ 32

Casper Formation .................................... 12

Cleverly Formation ................................ 16

concretions ................................................ 13, 15

dikes ........................................................._. 29

Frontier Formation ................................ 35, 42

Goose Egg Formation ............................ 13

ground water .......................................... 37, 41

Jelm Formation ...................................... 14, 35

Madison Limestone ................................ 11

Morrison Formation ................................ 15

Niobrara Formation .............................. 18

permeability ............................................ 46, 52

Red Peak Formation ............................ 13

slide blocks ................................................ 35

Steele Shale .............................................. 18

Sundance Formation .............................. 14

Thermopolis Shale .................................. 17

transmissivity .......................................... 46, 50

Wagon Bed Formation .......................... 24

White River Formation ........ 26, 29, 34, 74

Wind River Formation ........................ 20, 41

Satanka Shale ................................................ 9

Sedimentation, Laramie Mountains .......... 4

Oligocene .................................................... 4

Paleozoic .................................................... 7, 9

Tertiary ...................................................... 7

Selenium .................................................... 65, 62, 70

accessory ore mineral ............................ 2, 41

altered sandstone .................................... 49, 67

association with arsenic ........................ 65

epigenetic .................................................. 53

from volcanic ash .................................. 68

in depositional sequence ........................ 58

Seminoe Mountains .......................................... 36

Sericite .................................-. .... - .. 8

Shale, Cleverly Formation ....._..................... 16

Frontier Formation ................................ 36

Jelm Formation ...................................... 14

Mowry Shale ............................................ 17, 42

Niobrara Formation .............................. 18, 42

perched water .......................................... 37

slide blocks ................................................ 35

spotted ........................................................ 18

Steele Shale .............................................. 18, 42

Sundance Formation .............................. 14

Thermopolis Shale ....._. .......................... 17

Wind River Formation .......................... 23
82 INDEX

Page 

Shards ................................................................ 25

Shirley Basin, location .................................. 2

structure .................................................... 7

Shirley Mountains .......................................... 2, 67

Siderite ............................................................ 13, 18

Silica .................................................... 25, 39, 60, 68

Silicate minerals .............................................. 69

Silicification ...................................................... 34

Silt ........................................................ 12,18, 22, 50

Siltstone ............................................................ 42, 44

Arikaree Formation ................................ 32, 68

Fort Union Formation .......................... 19

Frontier Formation ................................ 18

Goose Egg Formation ............................ 13

Jelm Formation ...................................... 14

Morrison Formation .............................. 15

Red Peak Formation .............................. 13

Sundance Formation ............................ 14

Thermopolis Shale .................................... 17

Wagon Bed Formation .......................... 24

White River Formation ........................ 26

Wind River Formation .......................... 21

Silver .................................................................. 68

Sips Creek Member, Jelm Formation .... 14

Size frequency .................................................. 46

Slate Draw ........................................................ 18

Slide blocks and surfaces ................................ 35

Sodium ........................................................ 39, 66, 68

Solution ............................................................ 58, 68

Solution front .................................................. 59, 71

Solution interface .......................................... 59, 71

South Dakota, Black Hills ............................ 14

lignite ........................................................ 68

Sundance Formation................................ 14

White River .............................................. 26

South rim erosional escarpment ................ 20

Spring Creek ............................................ 16, 28, 37

Steele Shale ...................................................... 18, 42

landslides .................................................... 35

stratigraphic position ............................ 1, 20

Stinking Creek ...................................... 1, 3, 20, 33

Stockade Beaver Shale Member,

Sundance Formation ................ 15

Stratigraphic sequence ................................ 1, 10

Structure, Shirley Basin ................................ 7

Subsurface data ................................................ 7

See also Well logs. 

Sulfur, analyses .............................................. 59

association with iron ............................ 60

association with pyrite ........................ 70

association with selenium .................... 69

sulfate ........................................................ 63

accessory ore mineral .................... 2

analyses .............................................. 59

bacterial reduction ............................ 70

ground water .................................... 1, 41

sulfide, altered sandstone ...................... 48

analyses .............................................. 59

association with arsenic ................ 65

correlation with uranium contents 53 

Eh and pH ........................................ 72

systematic distribution .......................... 2

Sundance Formation ................................ 1, 14, 35

Surveys, airborne ............................................ 74

Tensleep Sandstone ........................................ 12

Teton Exploration Drilling Co...................... 6

Page 

Texas Creek ...................................................... 4

Thermopolis Shale .................................... 1, 17, 35

Thermopolis, Wyo ............................................ 17

Thorium .............................................................. 66

Three Forks, Mont ........................................ 11

Tipi rings .......................................................... 5

Topography ............................................ 1, 2, 19, 33

karst ............................................ 12, 35, 41, 73

Transmissivity .................................................. 46

Triangulation station Rimo ........................ 28

Tuff, White River Formation .................... 26, 68

U

Union Pacific Railroad ................................ 2

Uraninite ............................................................ 55

association with black

opaque minerals ........................ 47

epigenetic mineral ................................ 53

in depositional sequence ........................ 58

principal ore mineral ............................ 2, 41

Uranium, age .................................................. 2, 73

analyses .................................................... 50

association with vanadium .................. 65

deposition, dynamic ........................ 58, 71, 72

deposition, environment ...................... 44, 68

equivalent .................................................. 59

extraction .................................................. 4

in situ leaching ................................ 4

ion exchange .................................... 4, 7

solvent-extraction techniques ........ 7

genesis of ore .................................. 37, 57, 67

model .................................................. 70

problems .............................................. 61

grade of ore .................................... 1, 41, 50, 52

ground water ............................................ 41

minerals .............................................. 2, 41, 47

depositional sequence .................... 58

reserves .........................................._.......... 1, 6

roll-type deposits .................................... 50

boundaries .......................................... 52

Fe+2 /Fe+3 ratio ................................ 49

formation .......................................... 72

location ................................................ 1

solubility .................................................... 68

source ........................................................ 67, 68

transportation .......................................... 68, 70

zonation ...................................................... 53

U.S.S.R. See Russia.

Utah Construction and Mining Co ............ 1

development headings ............................ 6

mining methods .................................... 4, 5, 7

observation wells .................................... 37

Utah Construction and Mining Co. mine,

altered-sandstone tongue ........ 44

arsenic ........................................................ 65

calcite .......................................................... 57

copper .......................................................... 50

distribution of elements ........................ 59

Fe+2/Fe+3 ratio ...................................... 49

sulfate ........................................................ 63

Utah Construction and Mining Co.

open-pit mines, fossils .......... 23

Utah, vanadium-uranium ore bodies ........ 50

Yellow Cat area ...................................... 68

VABM Holiday ................................................ 5

Vanadium ............................................ 2, 50, 65, 68

Page 

Vegetation .................................................... 5, 8, 22

Veinlets, pyrite-marcasite ............................ 55

Veins, quartz ................'......................... ........ 8

Volcanic ash ...................................... 32, 33, 68, 69

Vugs .................................................................... 11

W

Wagon Bed Formation ................................ 24

fossils .......................................................... 25

measured section .................................... 24, 25

radioactivity ............................................ 73

silicified rock ............................................ 35

stratigraphic position ............................ 1, 28

Wall Creek Sandstone Member,

Frontier Formation ........ 18, 42, 70

Wasatch Formation ........................................ 67

Water table ........................................................ 37

Well logs, electric ............................ 13, 14, 15, 18

gamma-ray ................................................ 6

lithologic ......................... ........................... 6

resistivity ............................................ 6, 16, 20

self-potential ............................................ 6

Wells, observation .......................................... 37

White River, S. Dak ...................................... 26

White River Formation ................................ 26

comparison with Wind

River Formation .................... 23

fossils ........................................................ 27

ground water ............................................ 38

landslides .................................................... 35

measured sections .................................. 28, 30

monazites .................................................. 74

sandstone .................................................... 34

silica source ............................................ 14, 25

stratigraphic position ............................ 1

uranium source ...................................... 67, 73

White River Group ...................................... 19, 26

Whitmore, Frank C.,

fossil identification ................ 23, 31

Whitneyan provincial age ............................ 32

Whitney Member, Brule Formation ........ 31

Wildlife .............................................................. 5

Wind River Basin ............................................ 19

Wind River deposits .................................... 19

Wind River Formation .................................. 19

carbonate .................................................... 70

drilling ........................................................ 6

faults and landslides .............................. 35

fossils .......................................................... 23

ground water ............................................ 38

host of uranium deposits ................ 1, 41, 67

monazite deposits .................................... 74

sand and gravel ...................................... 74

stratigraphic position .................... 1, 25, 27

Wind River Group ........................................ 19

Wind River Range ...................................... 19, 33

Windy Hill Sandstone Member,

Sundance Formation .............. 15

Wolfe, Jack A., fossil identification ........ 24

X, Y, Z 

X-ray diffraction ............................................ 47, 55

Yellow Cat area, Utah .................................. 68

Yoder Formation ....................... ......... ............ 27

Zeolites .............................................................. 25

Zircon ....................................................... ........ 68

U. S. GOVERNMENT PRINTING OFFICE: 1978 782-066