GEOLOGICAL SURVEY CIRCULAR 753

Short Papers of the 

U.S. Geological Survey 

Uranium-Thorium Symposium, 

1977
Short Papers of the 

U.S. Geological Survey 

Uranium-Thorium Symposium, 

1977

Edited by John A. Campbell

GEOLOGICAL SURVEY CIRCULAR 753

Papers presented April 27-28, 1977,

at the Colorado School of Mines, Golden
United States Department of the Interior

CECIL D. ANDRUS, Secretory

Geological Survey

V. E. McKelvey, Director

First printing 1977 

Second printing 1977

Library of Congress catalog-card No. 77-600012

Free on application to Branch of Distribution, U.S. Geological Survey, 1200 South Eods Street, Arlington, VA 22202
PREFACE

This circular contains expanded abstracts for the 

technical papers presented at the 1977 Uranium and Thorium 

Research and Resources Conference, sponsored by the Branch 

of Uranium and Thorium Resources, U.S. Geological Survey. 

This Conference was held April 27 and 28, 1977, at the 

Colorado School of Mines, Golden. This was the second 

conference sponsored by the Branch the first was held in 

December of 1975.

Readers interested in additional information about a 

paper presented at the meeting should contact the author

directly. U.S. Geological Survey authors stationed in 

Denver can be reached by writing to Box 25046, Denver 

Federal Center, Denver, Colorado 80225. Authors stationed 

in Reston, Virginia, can be reached by writing to the U.S. 

Geological Survey, National Center, 12201 Sunrise Valley 

Drive, Reston, Virginia 22092. Current addresses for other 

authors appear at the beginning of their papers.

Any use of trade names and trademarks in this 

publication is for descriptive purposes only and does not 

constitute endorsement by the U.S. Geological Survey.

DODGE,SPENCER 

.MAINES.SAWATSKY

REYNOLDS.

6DLDHABEH.

6MAUGH

GEOGRAPHIC INDEX TO ARTICLES
CONTENTS

Page

Preface, by John A. Campbell III

Abbreviations VI

A geologic foundation for uranium resource assessment, 

Triassic Chinle Formation, southeast Utah, by 

Robert Lupe 1

Uranium mineralization during early burial, Newark 

basin, Pennsylvania-New Jersey, by C. E. TurnerPeterson-.- 3

Surface geophysical methods applied to uranium 

exploration in crystalline terranes, by Vincent J. 

Flanigan 5

Geophysical and petrologic studies of radioactive 

contact zones of pyroxenite dikes in nepheline 

syenite of the Ekiek Creek pluton, western Alaska, 

by Alan R. Wallace and John W. Cady 6

A theory for the origin of the Rifle-Garfield 

vanadium-uranium deposit, by C. S. Spirakis 8

A new structural model for humic material which shows 

sites for attachment of oxidized uranium species, 

by J. K. Jennings and J. S. Leventhal 10

Non-linear complex resistivity for the characterization of sedimentary uranium deposits, by Gary 

R. Olhoeft 12

Total-field magnetic surveying as an exploration tool 

for sedimentary uranium deposits, by Louis J. 

0'Connor and Bruce D. Smith 13

Origin of uranium in the middle Precambrian Estes 

Conglomerate, eastern Black Hills, South Dakota-- 

Inferences from lead isotopes, by F. Allan Hills 

and Maryse H. Delevaux 15

The role of borehole electrical measurements in 

uranium exploration, by Jeffrey Daniels and 

James Scott 17

How to plan an aerial gamma-ray survey, by J. A. 

Pitkin and J. S. Duval - 19

Composite images of radiometric data from south Texas 

and Wyoming, by J. S. Duval, J. A. Pitkin, and 

D. L. Macke 21

Two-mica granite and uranium potential in the 

Northern Appalachian orogen of New England, by 

Eugene L. Boudette 23

Ground-water flow and the shape of uranium roll 

deposits, by C. Gerald Warren 24

Page

Economic implications of a new hypothesis of origin 

of uranium- and copper-bearing breccia pipes, 

Grand Canyon, Arizona, by C. G. Bowles 25

Computer-enhanced images and geologic studies, 

southern Powder River Basin, Wyoming, by T. W. 

Offield, G. L. Raines, and D. L. Sawatzky 27

Characterization of fine-grained black uranium ores 

by transmission electron microscopy, by Gordon L. 

Nord, Jr. 29

Examples of uranium distribution graphics in geologic 

rock specimens illustrated with the radioluxograph, 

induced fission tracks, and other tracks methods, 

by J. R. Dooley, Jr., C. N. Conwell, Pieter Berendsen, 

J. K. Otton, C. T. Pierson, W. D. Hoisington, 

D. A. Lindsey, and J. N. Rosholt 32

Speculation on three possible modes of emplacement of 

uranium into deposits of the Midnite mine, Stevens 

County, Washington, by J. Thomas Nash 33

Conceptual-mathematical models of uranium ore formation in sandstone-type deposits, by Joel S. 

Leventhal and Harry C. Granger 34

Geology of uraniferous Tertiary rocks in the Artillery 

Peak-Date Creek basin, west-central Arizona, by 

James K. Otton 35

Uranium associated with iron-titanium oxide minerals 

and their alteration products in a south Texas 

roll-type deposit, by Richard L. Reynolds, Martin 

B. Goldhaber, and Richard I. Grauch 37

Uranium-lead apparent ages of uraniferous secondary 

silica as a guide for describing uranium mobility, 

by R. A. Zielinski, K. R. Ludwig, and D. A. Lindsey-- 39

Precambrian uranium associated with a metamorphosed 

massive sulfide body--Camp Smith area, New York, 

by Richard I. Grauch and David L. Campbell 41

The distribution of uranium in sediment samples as 

determined by multi-element analysis, by 

John D. Tewhey 43

Uranium deposits related to depositional environments 

in the Morrison Formation (Upper Jurassic), Henry 

Mountains mineral belt of southern Utah, by 

Fred Peterson 45

Low-level determinations of uranium and thorium by 

X-ray spectrometry, by Gerard W. James 47
Page

Determination of uranium in source rocks using radium 

in Crystal Springs, Great Salt Lake area, Utah, by 

J. Karen Felmlee and Robert A. Cadigan 48

Thinning of the Fox Hills Sandstone, Crook County, 

Wyoming A possible guide to uranium mineralization, 

by H. W. Dodge, Jr., and C. W. Spencer 50

Uranium exploration using helium detection A case 

study, by 6. M. Reimer 52

Geochemical interpretation of ore zonation at the Rifle 

vanadium mine, Colorado, by Dennis J. LaPoint and 

Gergeley Markos 53

Assay for uranium and measurement of disequilibrium 

by means of high-resolution gamma-ray borehole 

sondes, by Allan B. Tanner, Robert M. Moxham, and 

Frank E. Senftle - 56

Refinement of the thermodynamic properties of uranium 

minerals and dissolved species, with application to 

the chemistry of ground waters in sandstone-type 

uranium deposits, by Donald Langmuir and Kenneth 

Applin 57

Page

Uranium potential of sedimentary and igneous rocks in 

western and southwestern Oklahoma, by Al-Shaieb, 

Zuhair and John W. Shelton 61

New and recent results from the Canadian uranium reconnaissance program, by A. G. Darnley 63

Interpretation of uranium content of ground water in 

west-central Kansas, by L. R. Hathaway 65

Geochemical propsecting at the Ladwig uranium mine, 

near Golden, Colorado, by C. S. Fern's and 

Norman Bennett 66

Hydrogeochemistry of uranium in the Walker River Basin, 

California and Nevada, by D. L. Leach and 

L. V. Benson 68

Uranium and thorium distribution in continental 

Tertiary rocks of the Cook Inlet basin and some 

adjacent areas, Alaska, by Kendell A. Dickinson 70

A 252Cf-based borehole logging system for in-situ 

assaying of uranium ore, by D. K. Steinman, 

D. G. Costello, C. S. Pepper, W. E. Gober, D. B. 

Breuner, J. S. M. Wilson, J. C. Young, and 

Joseph John 72

Anomalous uranium in the waters of the Rio Ojo 

Caliente, New Mexico, by K. J. Wenrich-Verbeek 73

ABBREVIATIONS USED IN THIS CIRCULAR

angstroms

chemical activity (relative) 

atmosphere (pressure) 

calories per mole-degree

a

atm

cal/mol deg

cm centimeters 

cm/yr centimeters per year 

cps counts per second 

dc direct current 

AC- 0 Gibbs free energy (of formation 

of minerals from the elements)

AH,0 Enthalpy (of formation of minerals

from the elements)

Eh oxidation-reduction potential 

eTh equivalent thorium 

f>U equivalent uranium 

ft3 /s cubic feet per second 

g/cm3 grams per cubic centimeter 

g/min grams per minute 

GVW gross vehicle weight 

y ................................................... gamma

IP induced polarization 

kcal/mol kilocalories per mole 

keV kiloelectron volts

kg kilograms 

km kilometers 

km2-- square kilometers 

km 3 cubic kilometers 

kv kilovolts 

L alpha radiation from L energy level 

Ji./min liters per minute 

m meters 

m 3 cubic meters 

m/km meters per kilometer 

m 3 /s cubic meters per second 

m/\ milliamperes 

MeV megaelectronvolts 

mm millimeters 

rnn^ square mi 11 imeters 

mrad mi Hi radians 

m.y.~ million years 

pm micrometers (microns) 

MgA micrograms per liter 

wg/a--- - - - -micromicrograms per liter 

nm nanometers 

ohm-m ohm-meters 

pCi/Ji picocuries per liter
PCO " partial pressure of C02 s-- seconds 

pH hydrogen ion activity e Bragg angle 

ppb parts per billion vlf~ very low frequency 

ppm parts per million vs-- versus 

S°__ Entropy (of formation of minerals yr-- years

from the elements)

VII
A GEOLOGIC FOUNDATION FOR URANIUM RESOURCE ASSESSMENT, 

TRIASSIC CHINLE FORMATION, SOUTHEAST UTAH

BY ROBERT LUPE, U,S, GEOLOGICAL SURVEY, 

DENVER, COLO,

Lupe (1976) has described the spatial relationship 

between depositional environments and uranium mineralization 

in the Chinle Formation in the San Rafael SwelI-Canyon!ands 

area. A similar spatial relationship exists between rock 

texture and uranium, because texture is determined by 

sedimentary processes which are characteristic of certain 

depositional environments. This relationship between rock 

properties and uranium observed at the outcrop was extended

into the subsurface using textural data derived from logs of 

petroleum test wells to form the geologic basis for a 

resource assessment of unexplored areas (fig. 1).

Judging from the setting of known uranium deposits, 

areas with intermediate sandstone-mudstone ratios seem to be 

most favorable for uranium deposits (fig. 1). For purposes

of assessment, favorable ground in the Chinle, which covers

n 

a third of the study area, was subdivided into 50 km cells

SANDSTONE - SHALE RATIO - TOTAL FORMATION

109 C

+

HANKSVILLE

FAVORABLE GROUND

plj|40-70/ Sandstone/

I I c Lft J mudstone 

' '"

10

10 20 30 KILOMETERS

x 100

IQo, 5 } Magnitude,

38 4 .4

3J Kg.U3Og,in powers of 10.

110°

Figure 1. Sandstone/mudstone ratio map from measured surface 

sections and logs of petroleum test wells of the Chinle 

Formation, southeast Utah, showing significant uranium

deposits and favorable ground. The distribution of favorable 

ground is the comparison of known deposits to a composite 

of this map and a sandstone isopach map (not shown).
109»

I

-39°

SspK Productive cell, Kg. U 3 O8 , 

i^-^y- in powers of 10

 j Favorability, Kg. U3 O8 ,in powers of

20 30 50 Kilometers

Figure 2. Favorable and productive ground was subdivided

f Into cells. These 50-km cells Include mineralized areas

plus barren ground around a deposit. The cell was used 

1n the assessment to compare areas of unexplored ground

to productive ground. The distribution of speculative 

resources for the contour method Is contoured from the 

distribution of favorable ground and from the distribution 

of known deposits from figure 1.

(fig. 2). These cells center on areas of known 

mineralization and Include the surrounding barren ground 

which was explored as the result of the uranium discovery. 

The same size cells were also established in unexplored 

areas, and in explored but unproductive areas. It was 

decided arbitrarily that the cells should be 50 km2 (5 km by 

10 km extending lengthwise from the outcrop into the 

subsurface), but the areas explored around known deposits in 

the Chinle in the study area were typically about this size 

(«fl. 2).

Ideally, the true value for total uranium in explored 

areas should be the data base for an assessment of adjacent, 

unexplored areas, but that value may never be known. 

Therefore, this assessment, which used available production 

data, will reflect only the volumes and grades of uranium 

that have been produced. Production values for explored 

cells are shown on figure 2.

After subdividing favorable ground into cells, two 

different methods of assessment were used. In the first 

method, the equal volume method, it is assumed that 

unexplored areas contain deposits similar to those 

discovered in adjacent and geologically similar areas. 

Assessed resources are simply the ratio between the total

area of unexplored but favorable cells and the total area of 

productive cells, multiplied by production. The ratio of 

unexplored, favorable ground to productive ground is about 

2.25 (3,800 km2/!,700 km2 ), and approximately 30xl06 kg U308 

have been produced in the study area. Hence, 68x10 kg U,0g 

of a similar volume and grade to that produced 1s assessed 

for the area. If a better value for the amount of uranium 

in explored areas became known, then the amount of assessed 

resources could be multiplied by the ratio between the new 

value and the old to reach a more accurate assessment 

figure. Similarly, a change in cell size would change the 

ratio of the areas of favorable and productive ground.

The second assessment method, the contour method, is 

similar to the equal volume method but does not assume that 

unexplored areas contain deposits similar to those 

discovered; areas far from known deposits are credited with 

less uranium, because the assessment becomes more uncertain 

with Increased distance from known deposits (figs. 1 and 2). 

By the contour method, the value of each individual cell is 

determined by multiplying the values of the intersecting 

contours by the fraction of the cell they intersect. For 

example, if a cell has half Its area within the 103 kgU,00

A C ^ O

contour, plus a fourth each 1n the 10 - and 10 -kg-U,Og
contours, then the cell contains 103/2+104/4+105/4= 28,000

2 kg U30g within Its 50 km area (fig. 2). The total resource

value for the study area, the total of the values for all 

cells, is {]xl07 )+(3xl06 H7.5xl05 )+(21.5xl04 H41.5xl03 ) = 

approximately 14xl06 kg UgOg. However, the production data 

used for individual deposits is out of date. Production 

data for the entire area is current, so therefore, a better 

assessment value can be obtained by adjusting the old 

assessment value by the ratio between new and old production 

data: (14xl06 ) (30x106/13x1O6 ) = 32xl06 kg U30g.

The geographic distribution of favorable ground can be 

related to the distribution of other geologic features, such 

as regional structure (no relationship), potential source 

rocks in the Chinle (positive relationship), and subsurface 

gamma-ray anomalies (positive relationship).

Lupe, Robert, 1976, Depositlonal environments as a guide to

uranium mineralization in the Chinle Formation, San Rafael 

Swell, Utah: U.S. Geol. Survey Jour. Research, v. 5, 

p. 365-372.

URANIUM MINERALIZATION DURING EARLY BURIAL, NEWARK BASIN, 

PENNSYLVANIA-NEW JERSEY

BY C, E, TURNER-PETERSON, U,S, GEOLOGICAL SURVEY, 

DENVER, COLO,

Sedimentation 1n the Trlassic-Jurassic Newark basin was 

the result of infilling of a rift basin formed prior to 

continental breakup. Asymmetrical development of fades 

resulted from differential tectonism in an internally-drained 

lake basin. The Stockton Formation, which crops out along 

the southern margin, consists of conglomerate, gray 

fine-grained sandstone, red siltstone, and red mudstone. The 

Lockatong Formation, which crops out 1n the central part of 

the basin, contains analcimic black mudstone and carbonate 

rocks. The Brunswick Formation, which crops out along the 

northern margin of the basin, 1s composed predominantly of 

red si Itstone and mudstone, and local conglomerate.

The Lockatong Formation has a lacustrine origin, as 

documented by Van Houten (1962). The presence of carbonate 

rocks, black mudstone, sedimentary analcime, fish remains, 

and conchostracans suggests that a perennial alkaline lake 

existed in the basin. The Stockton and Brunswick Formations, 

long considered fluvial, are here considered largely marginal 

lacustrine deposits, based on facies relations, sedimentary 

structures, and a newly found fossil.

Laterally coalescing fans of conglomerate, derived from 

a crystalline highland to the south, compose the base of the 

Stockton Formation. Basinward from the southern margin, the 

next facies consists of thick beds of gray, fine-grained, 

flat-bedded, well-sorted sandstone of the Stockton, 

interpreted to be nearshore lacustrine in origin. A 

conspicuous lack of trough crossbeds, foresets, ripples, and 

other typical current features indicates that there was no 

fluvial plain between the aprons of coarse material on the 

fans and the fine-grained sandstone in the lake. 

Fine-grained detritus settled out of suspension farther from 

shore to form the red siltstone and burrowed red mudstone

facies of the Stockton. Black mudstone Included in the 

Lockatong Formation was deposited in the central euxinic part 

of the lake. Locally the red, fine-grained fades of the 

Stockton is absent and the offshore black mudstone is 

interbedded with the nearshore lacustrine sandstone. Thus, 

facies distribution along the southern border reflects a 

fan-to-lake transition with development of thick, well-sorted 

nearshore sandstone beds.

Fades development along the northern border was notably 

different. The fans in the Brunswick Formation are not 

coalesced, are restricted in areal extent, and are dominated 

by debris flow units. An abrupt fan-to-lake transition, 

without development of a nearshore sandstone, is indicated by 

interfingeMng of fanglomerate with green and black mudstone, 

conchostracan-bearing red mudstone, and mollusk-bearing 

limestone in the Brunswick Formation.

The differences in the facies along the two margins of 

the basin, as reflected in the Stockton and Brunswick 

Formations, are explained by the tectonic model proposed for 

the basin. Geophysical data suggest that en echelon normal 

faults occur near the northern border with their downthrown 

sides towards the basin (Sumner, written commun., 1975). 

Faulting is also present along the southern border but 

sedimentary overlap is more common. The tectonic differences 

that characterize the two borders directly affected facies 

distribution in the basin. The development of a nearshore 

lacustrine sandstone fades in the Stockton may be attributed 

to a gentle slope of the basin floor along the southern 

margin which permitted sorting of detritus delivered to the 

basin. In contrast, the interfingeMng of low-energy lake 

beds and coarse debris-flow units in the Brunswick Formation 

can be attributed to poor sorting on a steep slope,
maintained by recurrent faulting, along the northern margin 

of the basin. A similar situation was documented in Death 

Valley (Denny, 1965), where a playa, flanked on the east and 

west by fans, occupies a graben. Renewed faulting along the 

east side causes greater tilting and subsidence along that 

margin. The west side fans, in response, have been extended 

and the playas have encroached upon the more restricted fans 

on the east side.

Uranium mineralization in the Newark basin occurred in 

the offshore lacustrine black mudstones of the Lockatong 

Formation and the nearshore lacustrine sandstones of the 

Stockton Formation. Mineralization occurred during or 

shortly after deposition of the host rock, as indicated by 

geochemical considerations discussed below.

Two agents (hunric acids and aqueous sulfide) capable of 

fixing uranium were forming in the offshore black muds at the 

time of deposition. The bottom sediments of the central part 

of the lake were anaerobic, as indicated by the black color 

of the mudstones and the presence of pyrite. Ferroan 

dolomite in the offshore mudstone facies also indicates 

anoxic conditions because ferrous ions substitute for 

magnesium in dolomite only in reducing conditions. 

Sedimentary analcime indicates a high pH, perhaps as high as 

9.4, in the pore waters of the black muds. Ruinates are 

soluble in basic solutions and thus the solubilization of 

humic acids was favored in the pore fluids of the black muds. 

Simultaneously, bacterial anaerobic respiration resulted in 

the reduction of sulfate to bisulfide within the bottom 

sediments. Uranium was fixed near the sediment-water 

interface in the black muds, resulting in widespread 

medium-grade (0.01-0.02 percent U^Og) uranium deposits in the 

Lockatong.

Mineralization in the nearshore sandstone beds of the 

Stockton occurred shortly after deposition. The proximity of 

mineralized sandstone to black mudstone units suggests that 

the black mudstones played an important role in uranium 

mineralization. It is proposed that the reducing agents 

generated within the black muds (humic acids and aqueous 

sulfide) were expelled during compaction into the adjacent, 

more permeable nearshore sands, providing the reductants 

necessary for uranium fixation in those sands. Uranyl ions 

were carried into the basin by ground water from uranium-rich 

crystalline rocks south of the basin. Recent studies

(McBride and Pfannkuch, 1975) on ground water movement on the 

periphery of modern lakes demonstrate that seepage into a 

lake occurs largely in the nearshore zone. In a similar 

manner, uranium-bearing ground water passed into the 

nearshore sands and then upward into the lake. In this 

manner, large amounts of uranium-bearing ground water may 

have passed through the nearshore sands, where reductants 

expelled from the black muds would have caused the uranium to 

precipitate, resulting in localized mineralization (as much 

as 1.28 percent U,0P ) in the Stockton. <3 o

If the reductants were provided by expulsion of fluids 

from the compacting black muds, as is proposed here, certain 

time constraints are imposed on the model. The generation of 

aqueous sulfide in sediments is greatest at shallow depths, 

restricting its availability as a reductant to early burial 

stages. Further limitations are imposed on the depth and 

timing of fluid expulsion, because clays compact readily 

during early burial and expel most of the pore fluids at that 

time. Thus, compaction-induced lateral movement of the 

fluids containing aqueous sulfide and humic acids from the 

black muds into the adjacent, more permeable nearshore sands, 

and the resulting uranium mineralization, occurred during 

early burial.

The model proposed here for uranium mineralization in 

the Newark basin has several important implications: (1) 

black mudstones associated with uranium deposits in the 

Newark basin played an active geochemical role during 

mineralization, and (2) mineralization in the Stockton 

Formation occurred shortly after deposition of the host 

sandstone because agents necessary for fixing uranium were 

generated in the pore fluids only during early burial.

Denny, C. S., 1965, Alluvial fans in the Death Valley region, 

California and Nevada: U.S. Geol. Survey Prof. Paper 466, 

62 p.

McBride, M. S., and Pfannkuch, H. 0., 1975, The distribution of 

seepage within lakebeds: U.S. Geol. Survey Jour. Research, 

v. 3, no. 5, p. 505-512.

Van Houten, F. B., 1962, Cyclic sedimentation and the origin 

analcime-rich Upper Triassic Lockatong Formation, westcentral New Jersey and adjacent Pennsylvania: Am. Jour. Sci. 

v. 260, no. 8, p. 561-576.
SURFACE GEOPHYSICAL METHODS APPLIED TO URANIUM 

EXPLORATION IN CRYSTALLINE TERRANES

BY VINCENT J, FLANIGAN, U,S, GEOLOGICAL SURVEY, 

DENVER, COLO.

Complementary geophysical methods are demonstrated to 

be valuable in identification of areas favorable for the 

deposition of uranium in crystalline terranes. Geophysical 

surveys conducted in eastern Washington State and Colorado 

have aided in mapping lithologic units and structures where 

exposures are poor. The Swartzwalder Mine area, Jefferson 

County, Colo., was selected as a survey test area. This 

test area included a segment of the major north-west 

trending fault system known as the Rogers Fault West. 

Included in the test area is a contact between a hornblende 

gneiss and a mica-schist unit both of the Precambrian X 

Idaho Springs Formation (fig. 1). Within the mica schist 

there are about 6 m of alternating layers of magnetite and 

quartz (Young, oral commun., 1977).

The purpose of the geophysical survey was to identify 

the electrical and magnetic properties of the lithologic 

units and to delineate the geophysical expression of the 

Rogers Fault crossing the test area. The entire test area 

is covered with a thin veneer of overburden making surface 

geologic mapping difficult. At the Schwartzwalder mine, 

uranium minerals are being mined from a system of faults and 

fractures which lie between two branches of the Rogers fault 

system. In the mine area, the two Rogers faults (east and 

west) are about a kilometer apart. While it is not possible 

to detect uranium mineralization at depth using surface 

geophysical methods, the ability to identify favorable areas 

for mineralization warrants the inclusion of geophysical 

surveys in a uranium exploration program.

105° 17' 17"

39°

52'

27"

N

\

39° 

52' 

27" 

N

50 100 METERS 

_]_______I

Precambnan X Idaho / \ 10 

Springs Formation

Interlayered magnetite and quartz

Mica-schist

Hornblende gneiss

Figure 1 Figure 2
The test area is 275x265 m in extent and measurements 

were made on a 30.5 m grid across the area. Three methods 

were used to determine the electrical and magnetic nature of 

the rocks in the test area. Turam and VLF (very low 

frequency) electromagnetic methods measured the electrical 

character of the rocks. The magnetic character of the rocks 

was measured using a proton precession magnetometer. In 

addition, a single IP (induced polarization) profile was 

made across the contacts and structures delineated by the 

electromagnetic methods.

The electromagnetic methods indicated that the 

hornblende gneiss has an apparent resistivity of 1000 ohm-m 

or less (fig. 2) and the mica schist with the interlayered 

magnetite and quartz has apparent resistivities of from 1000 

to 2500 ohm-m. The contact between the two units can 

readily be seen from the electromagnetic data. A relief of 

12,000 gamma in the mica schist indicates concentrations of 

magnetite and also suggests the location of the contact 

between the two major rock types (fig. 3). The location of 

the Rogers Fault West is seen as a linear magnetic low, and 

has an associated conductive zone of less than 630 ohm-m. A 

second conductive zone was detected about 150 m south of the 

Rogers fault zone. The source of this anomaly is not 

readily apparent. The IP traverse crossing this area 

confirms the conductive nature of the area, and indicates a 

relatively good polarization characteristic in the 

conductive zone, suggesting possible sulfides in the 

near-surface rocks. Although there is no firm relationship 

between sulfide mineralization (mostly pyrite) and uranium 

mineralization, the geophysical data do indicate areas where 

more detailed study might be made. Figure 3

GEOPHYSICAL AND PETROLOGIC STUDIES OF RADIOACTIVE CONTACT

ZONES OF PYROXENITE DIKES IN NEPHELINE SYENITE OF THE

EKIEK CREEK PLUTON, WESTERN ALASKA

BY ALAN R, WALLACE AND JOHN W, CADY, 

U,S, GEOLOGICAL SURVEY, DENVER, COLO,

A ground geophysical, petrographic, and petrophysical 

study was made of a subsilicic composite pluton, the Ekiek 

Creek Complex of Miller (1972), in western Alaska to 

determine the sources of coincident total-count gamma-ray 

and aeromagnetic anomalies detected in aerial surveys. This 

pluton is related to a series of subsilicic intrusive stocks 

in western Alaska and the eastern Siberian peninsula 

(Miller, 1972), (fig. 1). Airborne radiometric studies of 

several of the stocks in Alaska indicate uranium 

mineralization, and ground surveys have shown low-grade 

uranium concentrations of as much as 92 ppm (Jones, 1976).

Owing to the lack of outcrops, the morphology of these 

stocks must be delineated by geophysical methods.

The project included data collection in the 3x5 km 

study area, and petrographic and petrophysical analyses of 

representative samples. Field geophysics Involved nine 

major east-west traverses, as well as a number of shorter 

crossing traverses, and totaled 35 line km of magnetic, VLF, 

and four-channel gamma-ray spectrometer measurements. 

Petrophysical work on the samples included measurements of 

remanent magnetism and magnetic susceptibility, density, and 

electrical resistivity. Detailed petrographic studies of
representative samples also were made.

The Ekiek Creek pluton is a composite stock of 

Cretaceous age which intruded Lower Cretaceous silicic 

stocks and volcanic rocks. It includes two major 

silica-undersaturated rock types, fine-grained pyroxenite 

and medium-grained nepheline syenite. Field relationships 

between the two are anomalous. The pyroxenite occurs as 

broad tabular bodies in the syenite, but contact zones show 

veins of syenite through pyroxenite, and syenite along 

joints in pyroxenite, suggesting that the syenite intruded 

the pyroxenite. Extensive iron oxide alteration was noted 

along the contact zones, but no ore minerals were observed.

EKIEK 

CREEK 

PLUTON

66°

««

 630

Alkaline Racks

Figure 1

Petrographic studies of the samples collected in the 

field show a metamorphosed contact zone in addition to 

unaltered pyroxenite and nepheline syenite. The felsic 

rocks contain major orthoclase and nepheline, and varietal 

biotite, aegerine, and sphene. Melanite, a titanium-rich 

andradite garnet, occurs in variable amounts as deep-brown 

euhedral crystals of seemingly igneous origin. Zeolites, 

sericite, and cancrinite are common alteration products. 

The felsic rocks grade texturally from fine-grained 

hypidiomorphic-granular rocks to coarse porphyries 

containing orthoclase phenocrysts. The felsic rocks contain 

less than 15 percent mafic minerals, not including melanite, 

and orthoclase is much more common than nepheline.

The pyroxenites are fine to medium grained in thin 

section, and are composed of predominant aegerine-augite and 

biotite, and minor orthoclase, nepheline, sphene, and 

zeolites. Melanite, significantly, is absent. Flow 

textures are present in a few of the samples.

In contact zones poikiloblastic mafic minerals commonly 

contain inclusions of fine-grained melanite and orthoclase. 

The orthoclase and garnet become more common near the 

syenite, and euhedral garnets along the contact are 

poikiloblastic with inclusions of aegerine-augite.

Microscopic contact relations between the pyroxenite and 

syenite show the syenite transecting preexisting flow 

structures in the pyroxenite.

Although many of the contact relations between the two 

major rock types suggest that the syenite, as the younger 

rock, intruded the pyroxenite, the tabular pyroxenite 1n the 

syenite points to the- pyroxenite being the youngest rock. 

The Increasing predominance of garnet and orthoclase in the 

pyroxenite near the contact indicates an interaction between 

the two rock types. It does not seem likely that the 

syenite, with a relatively low solidus temperature, could 

lonically diffuse through the pyrdxenite to produce the 

garnet and orthoclase. The reverse situation is more 

probable, with the pyroxenite assimilating the components of 

the syenite along the contact. The pyroxenite intruded the 

felsic crystalline mush, with some assimilation, and, owing 

to its higher solldus temperature, crystallized in the mush. 

Cooling produced shrinkage cracks Into which the felsic mush 

was drawn, forming what now appear to be dikes of syenite 1n 

pyroxenite.

As of this writing, the ground magnetometer, VLF, and 

gamma-ray data await position-recovery, and, in the case of 

magnetic data, smoothing before they can be contoured. 

Samples collected at about 45 rubble-crop exposures yield a 

generalized geologic map. However, a much more detailed 

geological map should result when geophysical contour maps 

become available.

Figure 2 shows ground magnetic, VLF, and gamma-ray 

profiles collected on an east-west traverse across the

1800 

Eo»t

Figure 2
pluton. Magnetic highs labeled A and B coincide with zones 

of high conductivity, indicated by the "tangent tilt angle" 

VLF profile.

Magnetic and VLF anomalies A and B coincide with 

occurrences of pyroxenite. Anomaly B was traced in detail 

and found to be continuous for 500 m south and 1,600 m north 

of the east-west traverse. It is believed to mark a 

north-south-striking tabular body of pyroxenite at least 

2,100 m long. Magnetic and VLF anomalies labeled A also 

occur on several east-west profiles, suggesting the presence 

of a second north-south tabular body, but the anomalies were 

not traced with the detail of anomaly B. Anomaly C did not 

show a clear VLF expression. Its appearance on several 

profiles suggests a possible third north-south-trending 

tabular body. Remanent magnetism and susceptibility 

measurements of samples show that the pyroxenite is more 

magnetic than the nepheline syenite.

The good correlation between the magnetic and VLF 

anomalies may occur because the ground is permanently 

frozen. Under ordinary temperature conditions VLF 

measurements are dominated by ionic conduction in water 

filled fractures. In frozen ground, however, ice-filled 

fractures would be non-conductive, and the VLF technique may 

be sensitive to changes in lithology.

The gamma-ray spectrometer traverses show zones of 

highest radioactivity along contacts between pyroxenite and

nepheline syenite. Total counts measured over the contacts 

are 6 to 10 times those of the background over the muskeg, 

and 1.5 to 2.5 times those measured over the rubble-crops of 

the pluton as a whole. Iron-oxide staining, perhaps 

indicating hydrothermal alteration, is prominent along the 

contact zones. Detailed profiling by gamma-ray spectrometer 

shows that iron oxide-stained rocks are more radioactive 

than average, but the highest readings were obtained over a 

sharp, unoxidized contact of pyroxenite against nepheline 

syenite.

On a scale of kilometers, aeromagnetic highs of the 

Ekiek Creek pluton and of other alkalic plutons north of the 

Selawik Hills correlate with radioactivity anomalies. On a 

scale of 10 to 100 m, radioactivity anomalies correlate with 

contact zones between pyroxenite and nepheline syenite. The 

pyroxenite is distinguished by magnetic and VLF conductivity 

highs. Thus magnetic and electrical measurements, on either 

scale, may be tools for locating possible uranium 

mineralization.

Jones, B. K., 1976, Uranium and thorium in granitic and 

alkaline rocks in western Alaska: Master's thesis, 

University of Alaska, 123 p.

Miller, T. P., 1972, Potassium-rich alkaline intrusive rocks 

of western Alaska: Geol. Soc. America Bull., v. 83, 

p. 2111-2128.

A THEORY FOR THE ORIGIN OF THE RIFLE-GARFIELD 

VANADIUM-URANIUM DEPOSIT

BY C, S, SPIRAKIS; U,S, GEOLOGICAL SURVEY, 

DENVER, COLO,

The Rifle-Garfield vanadium-uranium deposit, located in 

Garfield County, Colo., has been described in detail by 

Fischer (1960). The deposit occurs in eolian sandstones of 

Triassic and Jurassic age, and displays a distinct zonation 

of authigenic minerals, a feature whose origin has not been 

adequately explained in earlier works. In sequence, these 

zones are a 0.7-m-thick chromium-mica zone; a 0.1- to 

0.6-cm-thick zone of galena and clausthalite in solid 

solution; a 1.3- to 2.5-cm-thick barren zone; and a zone of 

low-valent vanadium and uranium minerals, which is generally 

about 2 m thick but may be as much as 9 m thick. This 

latter zone is dominated by very fine-grained mixed-layered 

vanadium mica-montmorillonite, vanadiferous chlorite, and 

the vanadium mica, roscoelite. Each zone forms a curved 

surface, which may be traced for about 3 km in its long 

dimension and a few hundred m in its short dimension.

In the vicinity of the ore deposit, the upper meter or 

so of the underlying Chinle Formation is bleached. This 

altered zone is characterized by a slight loss of total iron 

and a partial reduction of ferric iron. According to 

Fischer (1960), the localization of this bleaching around 

the deposit suggests a genetic link between the alteration 

and the formation of the ore deposit.

Fischer (1960) considered reactions at an interface 

between two solutions to be the most logical explanation for 

the formation of the deposit, but he realized it was 

difficult to explain how the interface could be maintained 

for a long enough time for the ore to develop. Also, an 

interface by itself does not explain the origin of the zones 

or the alteration. The zonation, the alteration, and the 

long-lived interface could all be effects of semipermeable 

membranes.
The membrane properties of layers of clay minerals 

appear to result from the interactions of dissolved species 

with the negatively charged sites on the surfaces of clay 

platelets (Kanshaw, 1962). An important consequence of 

these interactions 1s that most ions and molecules diffuse 

more slowly in- a membrane than in an open solution. Thus, 

these dissolved species diffuse away from a membrane faster 

than they do through it; hence, concentration gradients 

across a semipermeable membrane can be maintained and 

solutions of differing properties can be kept separate.

Another effect of a semipermeable membrane is the 

generation of pH changes on both sides of a membrane. One 

mechanism for generating pH changes with a membrane is 

described by Hartman (1947). As he points out, when an ion 

diffuses through a membrane, an ion of like charge must 

diffuse through in the opposite direction, or one of 

opposite charge must diffuse through in the same direction 

in order to maintain charge balance. When the diffusion of 

the hydrogen ion through the membrane is involved in 

maintaining charge balance, a pH change results.

A second mechanism for generating pH changes across a 

semipermeable membrane concerns the diffusion of H2C03 

through the membrane. Because H2C03 is uncharged, it has 

little interaction wi.th a membrane and diffuses through 

faster than other carbonate species. This relatively rapid 

diffusion of HgCOj from a high-carbonate solution on one 

side of a membrane into a low-carbonate solution on the 

opposite side of the membrane, causes a disequilibrium among 

the carbonate species on both sides of the membrane. On the

high-carbonate side, H+ and HCO, associate to replace the j. J 

lost H2CO,. In the process, H is removed from the solution

and the pH is raised. As more H-CO, forms, it in turn 

diffuses through the membrane. On the low-carbonate side of 

the membrane, excess H2C03 dissociates to H+ and HC03 and 

thereby decreases the pH.

In the case of the Rifle-Garfield deposit, the 

vanadium-uranium zone of the ore is a potential 

semipermeable membrane. Hanshaw (1962) showed that 

montmorillonite (which forms a major part of the 

vanadium-uranium zone) can act as an effective membrane, 

thus supporting the possibility that the vanadium-uranium 

zone can function as a semipermeable membrane. It is 

assumed here that the interface at which the ore 

precipitated was between a carbonate solution and a sulfate 

solution. This assumption is supported by the abundance of 

carbonate- and sulfate-dominated ground waters at shallow to 

moderate depths; by the work of Hostetler and Garrels 

(1962), which suggests that the mineralizing solutions of 

the Colorado Plateau were carbonate-rich; and by the 

presence of galena in the deposit. The significance of the 

galena lies in the incompatibility of lead with sulfur in 

most ground-water solutions (Anderson, 1975). This 

incompatibility suggests that they were transported in 

different solutions; I believe one of these was a sulfate

solution containing some H2S, and the other was a carbonate 

solution that transported lead along with uranium, vanadium, 

and selenium. It is also assumed that the sulfate solution 

had a lower Eh and pH than the carbonate solution. At the 

interface, the lower Eh and pH of the sulfate solution 

caused uranium and vanadium to precipitate. Once a 

sufficiently dense layer of vanadium silicates formed, it 

began to function as a semipermeable membrane.

The vanadium-silicate membrane kept the two solutions 

separate and maintained the position of the solution 

interface while the ore grew. Diffusion of H2C03 from the 

carbonate side to the sulfate side of the membrane created 

higher pH conditions on the carbonate side and lower pH

conditions on the sulfate side. As HCO, diffused from the J + 

carbonate side to the sulfate side of the membrane, H

diffused through in the same direction in order to maintain 

charge balance. This diffusion of H further increased the 

pH difference across the membrane.

On the sulfate side, where the pH, Eh, and carbonate 

content were lower, conditions were right for the 

precipitation of more vanadium and uranium minerals. Thus 

the vanadium-uranium zone grew by addition onto its sulfate 

side. On the carbonate side, the high pH generated by the 

membrane Increased the solubility of vanadium and uranium 

and inhibited their precipitation in a region adjacent to 

that side of the membrane. That is the region now 

represented by the barren zone.

Diffusion of hydroxyl ions and H2S away from the 

membrane established a pH gradient and a gradient in the hUS 

concentration on the carbonate side of the membrane. As 

lead and selenium diffused into the higher pH and higher H2S 

concentration near the membrane, they precipitated as galena 

and clausthalite, thus forming the galena-clausthalite zone.

It is suggested that silica, required for the 

precipitation of the chromium mica, was derived from the 

corroded quartz grains of the vanadium-uranium zone. The 

high pH near the membrane increased the solubility of silica 

and prevented the precipitation of the chromium mica in the 

barren zone. Farther from the membrane, the pH decreased 

and the chromium mica formed.

As the vanadium-uranium zone grew, chemical conditions 

within it changed. Leakage of the carbonate solution into 

the zone (which had formed on the sulfate side of the 

Interface) slightly raised the pH, Eh, and carbonate content 

of the older parts of the zone. The position of the older 

parts of the vanadium-uranium zone was such that the pH in 

the older parts was increased by the membrane effects of the 

younger parts of the zone. The increased pH, Eh, and 

carbonate content of the older parts of the membrane had 

little effect on the very stable vanadium silicates; 

uranlnite, however, was remobilized by these new conditions. 

The remobilized uraninite diffused farther toward the 

sulfate side where it reprecipitated and formed the observed 

zone of uranium enrichment on the edge of the
vanadium-uranium zone.

The acidic conditions generated on the sulfate side of 

the membrane may account for the alteration of the Chinle in 

that both the solubility of iron and the stability of 

ferrous compounds relative to ferric compounds increase in a 

more acidic environment.

The theory presented above, which involves diffusion 

through a semipermeable membrane that precipitated at a 

carbonatesulfate solution interface, provides a means of 

maintaining the interface despite mixing due to diffusion or 

flow, explains the possible origin of all of the observed 

zones, accounts for the alteration and its genetic link to 

the ore, and provides a reductant by the diffusion of H2S 

from the sulfate solution.

Anderson, G. M., 1975, Precipitation of Mississippi Valleytype ores: Econ. Geology, v. 70, no. 5, p. 937-943.

Fischer, R. P., 1960, Vanadium-uranium deposits of the Rifle 

Creek area, Garfield County, Colorado: U.S. Geol. Survey 

Bull. 1101, 52 p. [1961].

Hanshaw, B. B., 1962, Membrane properties of compacted clays: 

Unpub. PhD. thesis, Harvard University, 113 p.

Hartman, R. J., 1947, Colloid chemistry, 2d ed.: Boston, 

Houghton Miffin Co., 604 p.

Hostetler, P. B., and Garrels, R. M., 1962, Transportation

and precipitation of vanadium and uranium at low temperatures, 

with special reference to sandstone-type uranium deposits: 

Econ. Geology, v. 57, no. 2, p. 137-167.

A NEW STRUCTURAL MODEL FOR HUMIC MATERIAL WHICH SHOWS SITES 

FOR ATTACHMENT OF OXIDIZED URANIUM SPECIES

BY J, K, JENNINGS AND J, S, LEVENTHAL 

U,S, GEOLOGICAL SURVEY, DENVER, COLO,

The literature has many references to structureless 

uranium-organic associations. The organic material usually 

associated with the uranium ore is unsoluble, but it is 

commonly believed that this material was originally a 

humic-acid type. Humic acids are the soluble products of 

inorganic and biological degradation of plant material. 

Several structural representations of humic acids based on 

experimental chemical studies have been presented in the 

literature in the past. Unfortunately, these models are 

deficient, but as a result of physical and chemical studies 

in the last 10 years can now be brought up to date. Humic 

acids have the approximate elemental chemical composition of 

56 percent carbon, 34 percent oxygen, 6 percent hydrogen, 3 

percent nitrogen, and 1 percent sulfur. There are numerous 

ways these elements can be combined, depending on the source, 

age, environment of deposition, and preservation of the humic 

material. One of the simplest chemical formulas which can be 

written (C150 06Q H 18Q N6 S) gives a molecular weight of 

approximately 3,200, which is well within the normal

molecular weight range of humic acids (1,000 to 10,000).

The elements oxygen, hydrogen, nitrogen, and sulfur in 

humic acids are usually present as functional groups such as 

acid, COOH; hydroxyl, OH; phenolic hydroxyl, CgHgOH; amino, 

NH2 ; ketone, C=0; ester, COOR; ether, COC; and sulfhydryl, 

SH. Many of these groups can be positively or negatively 

charged (depending on the pH) or can share electrons 

(nitrogen, oxygen, and sulfur). By these mechanisms they can 

form ion-exchange and (or) chelate sites. These sites can 

interact with soluble oxidized uranium species such as U02+2 

U02 (C03 ) 2 -H202 , and U02 (OH) +1 . Figure 1 shows a structural* 

model of humic acid with the above sites; they are shown with 

positive or negative charges that would be available over the 

whole pH range of 4 to 10. It is important to realize that 

real humic acids are each different in size and shape, and 

that they are three dimensional having external protrusions 

and internal voids. Our model is simplified, but we believe 

it is the most correct presented to date, especially in 

reference to interaction with uranium.

10
H

H-C-0-H 

H-C-O-H 

H-C-O-H

>©

HO OH

Figure 1. Structural model of a humlc acid having a molecular : (on nitrogen and sulfur) show possible sites of uranium 

weight of approximately 5,000. The approximate chemical interaction, 

formula is C249°82H320N 13S2' The C1rc1ed + and ~ and the
-LINEAR COMPLEX RESISTIVITY FOR THE CHARACTERIZATION 

OF SEDIMENTARY URANIUM DEPOSITS

BY GARY R, OLHOEFT, U,S, GEOLOGICAL SURVEY, 

DENVER, COLO,

Measurement of variations in physical and chemical 

properties by mapping changes in the electrical resistivity 

of the ground is a well known technique whereby a known 

electrical current is used to stimulate the ground while the 

resultant voltage generated is separately measured. The 

ratio of the voltage to the current times a geometric 

constant is then the observed resistivity. If the 

measurement is done at dc (zero frequency), only one number 

is obtained, the dc resistivity. At non-zero frequencies, 

however, the resistivity is a complex quantity and the 

resultant terms are usually expressed as the real part of 

the complex resistivity ("real resistivity") and the phase 

angle between the applied current and the measured voltage. 

For measurements at several frequencies, there are further 

parameters such as the percent frequency effect (PFE) which 

is a measure of the variation of the real resistivity with 

frequency.

In all of these techniques, it is assumed that the 

resistivity is a linear function of voltage and a linear 

reciprocal function of current, in which case we say that 

the system is linear and obeys Ohm's law. Thus, if we plot 

current vs voltage at dc the result is a straight line for a 

linear resistivity material. If the frequency is non-zero 

and there is a significant phase angle, a plot of current vs 

voltage will result in an ellipse (with limits of a straight 

line for 0 mrad (milliradians) phase angle and a circle for 

1570.8 mrad phase angle). If the system has any non-linear 

components, the resultant plot will appear as a distorted 

line, ellipse or circle. The non-linear complex resistivity 

measurements described here are the result of driving a pure 

sine wave current into a sample, and studying the resultant 

voltage response for harmonic distortion.

Most unaltered materials, such as basalt or quartz 

sand, have extremely high resistivities when dry and low 

resistivities when in contact with water; in both cases the 

response is linear. This is due to the fact that the 

rock-water interaction in these materials is not very 

chemically active. In contrast, materials such as sulfides, 

clays, and zeolites are extremely chemically active at the 

water-rock interface either through direct 

oxidation-reduction reactions or through 

adsorption-desorption reactions (such as in the cation 

exchange process). The currents which result while these 

reactions are proceeding cause non-linear responses in such 

materials.

At very low current densities, when little chemical 

action is occurring, these materials may be linear. With 

increasing current density, chemical activity increases and 

the system becomes non-linear. The nature of the observed 

non-linearity is a direct function of the type of chemical 

reaction. Also, as the frequency of the applied current is 

varied, the non-linear response changes character and 

eventually disappears as the driving current begins to 

exceed the rate of the chemical reaction.

Detailed laboratory work has been proceeding on a 

series of very carefully acquired, handled, and prepared 

natural and synthetic materials which are respresentative of 

sedimentary uranium deposits. Strong differences have been 

observed between the linear response of quartz sand and the 

two most common types of non-linear response due to 

oxidation-reduction reactions (as occurring in sulfides) and 

due to adsorption-desorption reactions (as in the cation 

exchange process in clays and zeolites). Although the dry 

sulfide minerals may have non-linear responses due to their 

semiconducting nature, all of the observed non-linear 

responses reported here are due to reactions at the 

rock-water interface.

A single non-linear response for a typical sulfide such 

as pyrite is very complicated due to the occurrence of 

several different reactions. There is a hierarchy in the 

sequence of reaction as the current is increased and then 

decreased. This hierarchy allows observance of specific 

individual reactions. Each reaction occurs at a specific 

rate and is influenced by the chemical environment (such as 

the pH, Eh, and so on of the water). Further, some 

reactions are reversible while others are not. By observing 

the characteristic non-linear response of a sample as a 

function of frequency and interpreting that as the presence 

or absence, rate, and relative magnitude of various chemical 

reactions it thus becomes possible to identify several types 

of material (clay vs sulfide, for example), sorbable ions in 

solution, and to place limits on the oxidation state of the 

minerals as well as the Eh and pH of the ground water.

The laboratory work has already demonstrated that 

distinctions may be made between clays, sulfides, shales, 

and graphites. Also, the relative oxidation state is 

observable.

Although non-linear complex resistivity is useful as a 

laboratory tool, it does not appear that it will be 

successfully applied as a surface exploration technique.

12
The problems of divergent and widely varying current 

densities are very great. As a downhole logging tool, 

however, it shows exceptional promise. This is especially 

true in areas where an in situ or solution mining process 

must be tailored to the specific ground water and mineral 

chemistry of a given site. As a logging tool, non-linear 

complex resistivity should then be able to delineate and 

characterize an orebody as to variations in pH and Eh (by 

observing the changes in various sulfide chemical 

reactions), as to relative concentrations of clays and 

sulfides, as to the availability and mobility of sorbable 

ions, and possibly as to variations in cation exchange 

capacity.

There is a considerable amount of detailed laboratory 

work which has yet to be performed. It has already been 

demonstrated that clays and sulfides have very different 

non-linear responses, but it has yet to be shown whether or 

not individual sulfides (pyrite vs chalcopyrite) may be 

discriminated or whether individual clays (kaolinite vs

montmorillonite) may be discerned. It has been shown that 

the relative oxidation states of some materials are 

observable, but absolute calibrations should be possible.

Bockris, J. 0., and Reddy, A. K. N., 1970, Modern electrochemistry,

vols. 1 8 2: London, Plenum Press, 1432 p. 

Fink, J. B., 1976, Electrochemical experiments on base metal

sulfides, 52nd Annual Meeting of the Southwestern and

Rocky Mountain Division of the AAAS, Tucson, Arizona:

Preprint American Association for the Advancement of

Science, 18 p. 

Hall, S. H., 1975, A method of measuring rock electrode kinetics:

Jour. Electroanal. Chem., v. 59, p. 323-333. 

Katsube, T. J., Ahren, R. H., and Collett, L. S., 1973, Electrical

non-linear phenomena in rocks: Geophysics, v. 38, p. 106-124. 

Klein, J. D., 1976, A laboratory investigation of the non-linear

impedance of mineral-electrolyte interfaces: M.Sc. thesis:

Dept. of Geology and Geophysics, Univ. of Utah, Salt Lake

City, Utah, 94 p.

TOTAL-FIELD MAGNETIC SURVEYING AS AN EXPLORATION TOOL 

FOR SEDIMENTARY URANIUM DEPOSITS

BY LOUIS J, O'CONNOR AND BRUCE D, SMITH,

U,S, GEOLOGICAL SURVEY, DENVER, COLO,

Total-field magnetic surveying is a relatively simple 

and inexpensive geophysical exploration method. In order to 

test applications in the exploration for sedimentary uranium 

deposits, ground surveys have been conducted in several 

areas over known mineralization. Results indicate that 

magnetic surveying can detect subtle variations in the 

distribution of magnetic minerals in the sedimentary 

section. In many cases, these variations can be spatially 

related to uranium orebodies.

Induced magnetization is usually the primary source of 

magnetism in sedimentary rocks. The majority of magnetic 

anomalies are due to changes in the strength of the induced 

field caused by local variations in the quantity of magnetic 

minerals distributed in the rocks. The common magnetic 

minerals are Fe-Ti oxides, the most important being 

magnetite. Their distribution is controlled by the 

depositional processes of the sedimentary environment and by 

their possible alteration due to geochemical processes.

In the fluvial to transitional marine sandstones that 

most commonly host sedimentary uranium deposits, magnetic 

minerals can occur both as local concentrations associated 

with stream channels and as disseminated detrital grains.

The mechanical deposition of these minerals is dependent 

upon the size, shape, and mass of the grain and the velocity 

and sorting capability of the environment. Adler (1973); 

Adams, Curtis, and Hafen (1975); and Reynolds (1975) have 

discussed how oxidizing and reducing conditions, related to 

the formation of sedimentary uranium deposits, can alter 

detrital magnetic minerals. Of particular interest in the 

application of magnetic surveying techniques is the reported 

partial to complete destruction of magnetic minerals in the 

vicinity of some sedimentary uranium deposits and the 

correlation of low magnetic susceptibility with uranium 

(Ellis and others, 1968).

The ability of magnetic mapping to detect anomalies 

associated with sedimentary uranium deposits is dependent 

upon the contrast of magnetic properties (if any) of 

mineralized rocks with surrounding rocks and upon the size 

and depth of that zone of contrast. Increasing depth will 

decrease the size of an anomaly associated with a given 

source and increase the possibility of it being obscured by 

other magnetic sources. This factor limits the usefulness 

of surface magnetic methods in exploring for deeper uranium 

deposits. However, even when no anomalies can be directly

13
associated with fronts, valuable geologic information such 

as the location of channel sands and changes in facies can 

be inferred from magnetic data. This information could 

prove useful in indirectly guiding exploration.

Due to the relatively small quantities of magnetic 

minerals in sedimentary rocks, magnetic anomalies are 

typically small. In order to accurately detect these 

anomalies, two magnetometers with 1/4-gamma sensitivity were 

used in our surveys. One magnetometer was used as a local 

base station to monitor diurnal variations of the 

geomagnetic field, while the other instrument was used for 

field surveying. As a compromise between rapid surveying 

and the need for adequate details, readings were usually 

taken at 30 m intervals. If changes in magnetic levels 

across short distances were recognized in the field, 

intermediate readings were taken to fill in the details of 

the anomaly. The time correlation of base and field 

readings allowed the accurate removal of diurnal variations. 

Regional variations related to basement anomalies and to the 

spatial variation of the earth's field were removed by the 

subtraction of low order polynomial trend surfaces from the 

data. The residual fields represent the effect of local 

sources in the sedimentary section.

Two surveys were conducted in northern Colorado over 

roll fronts in the Upper Cretaceous Laramie Formation (fig.

109*

1, area 1). One survey was made on exposed Laramie with a 

roll front occurring in a sand unit approximately 15 m below 

the surface. A strong correlation was found between a sharp 

15-gamma negative anomaly and the mineralized zone. This 

anomaly probably results from the relative depletion of 

magnetic minerals in the vicinity of the roll front.

A second survey was made where approximately 45 m of 

the White River Formation (Oligocene} unconformably overlies 

the Laramie. Here mineralization occurs in the Laramie 

about 75 m below the surface. No magnetic anomalies could 

be directly associated with the ore. The lack of any 

distinctive magnetic signature may be due to the greater 

depth to the deposit, or to the absence of those conditions 

that produced the relatively low magnetic values in the 

previous case. Trends in the magnetic map do show a 

similarity to trends in the isopach of the ore sand. This 

may be the result of the concentration of magnetic minerals 

in the area of greatest sand deposition. Although not a 

direct guide to uranium, the ability to map trends in the 

thickness of the ore sand could still be useful where 

uranium mineralization can be related to such variations.

Two surveys were also conducted in the Powder River 

Basin. One survey in the central portion of the basin was 

directed at uranium deposits 45-50 m deep in the Eocene 

Wasatch Formation (fig. 1, area 2). A small negative 

anomaly correlates with the oxidized side of the zone of 

mineralization (fig. 2). The other area surveyed (fig. 1, 

area 3) has uranium mineralization in the Fort Union

37°

1 1

_ _ __ _ __ _ _ 1

xO i

' 1 1 l

i "2 1

i "3 r~

i i

i WYOMING \

~--~~~~~~~~~~B| i

r"

\

\ 

COLORADO i

1

\

i _____- -j- IT i

(Paleocene) and Wasatch Formations, ranging from near

surface to deeper than 150 m. Here the magnetic pattern is

complex, reflecting perhaps both the local complexity of the

geologic units and their alteration history, and uranluir

deposits are not marked by any consistent magnetic

signatures.

10 ';;***

4 X *. A / ^^*\ A ^ f^*^f ^^s- I v ^-\r~

« -10 L J

OXlDiZED *C=^« REDUCED ,0^.,.

MINERALIZED

Figure 2. Second residual magnetic profile, drillholes, and 

generalized relations of uranium ore in area 2. Minera

ization is at a depth of approximately 50 m. Bracket

indicates area of magnetic anomaly.

The depth, size, and magnetic properties of

m4na»al4-ra Unn anH the inf 1 nonrp. nf Inral npolnoic features

0 200 400 KILOMETERS are contro nj ng factors on the magnetic patterns observed in

surface surveys. Despite the complexities introduced by

Figure l. The location of study areas: Numbers indicate survey these local factors, the method, which involves only one or

areas discussed in text. two people and commercially available instruments, is rapid

14
and inexpensive and promises to be a useful exploration tool 

for sedimentary uranium deposits.

Adams, S. S., Curtis, H. S., and Hafen, P. L., 1975, Alteration 

of detrital magnetite-ilmenite in continental sandstones 

of the Morrison Formation, New Mexico, ^n_ Uranium exploration 

methods: Internat. Atomic Energy Agency, Vienna, p. 219-253.

Adler, H. H., 1973, Exploration for uranium in sandstones-- 

geochemical, remanant magnetic, and sulfur isotope 

applications, in^ Uranium exploration methods: Internat. 

Atomic Energy Agency, Vienna, p. 155-166.

Ellis, J. R., Austin, S. R., and Droullard, R. F., 1968,

Magnetic susceptibility and geochemical relationships as 

uranium prospecting guides: U.S. Atomic Energy Conn. 

R.I.D., rept. 4, 6.J.O. Grand Junction, Colo., 21 p.

Reynolds, R. L., 1975, Alteration of iron-titanium oxide

minerals associated with uranium deposits in sandstones, 

j[n_ Craig, L. C., Brooks, R. A., and Patton, P. C., eds., 

Abstracts of the 1975 Uranium and Thorium Research and

Resources Conference: U.S. Seol. Survey Open-File Rept. 

75-595, p. 38-39.

ORIGIN OF URANIUM IN THE MIDDLE PRECAMBRIAN ESTES 

CONGLOMERATE, EASTERN BLACK HILLS, SOUTH DAKOTA-- 

INFERENCES FROM LEAD ISOTOPES

BY F, ALLAN HILLS AND MARYSE H, DELEVAUX, 

U.S. GEOLOGICAL SURVEY, DENVER, COLO.

The middle Precambrian (or Precambrian X) Estes 

Conglomerate, which crops out approximately 23 km northwest 

of Rapid City, South Dakota, in Lawrence, Meade, and 

Pennington Counties, contains beds of well-sorted quartzand quartz-pebble conglomerate (oligprnlctic conglomerate), 

in which pyrite may form as much as 25 percent of the 

matrix. Commonly these beds are moderately radioactive 

(table 1) and locally they contain minor gold (table 2 and 

fig. 1).

The Estes Conglomerate lies unconformably upon the 

Benchmark Iron-formation (a banded quartz-taconite rock) and 

upon the Boxelder Creek Quartz!te (Bayley, 1970) both of the 

Nemo Group. Most pebbles and larger clasts in the Estes 

apparently were derived from these two formations. In its 

northernmost exposures, at the head of Little Elk Canyon, 

the Estes may lie unconformably upon the lower Precambrian

Table 1.--Uranium and thorium concentrations in weathered rocks,

calculated fresh-rock uranium concentrations, and 207Pb/Z06Pb

ages of Estes Conglomerate

Sample 

No.

BH-76-5b 

BH-76-133 

BH-76-14a 

BH-76-19 

BH-76-26

Weathered rock 

(Delayed neutron analyses)

U ppm

41 

11 

36 

21 

11

Th ppm

164 

700 

188 

173 

110

Th/U

4.0 

6.4 

5.2 

8.2 

10.0

Fresh-rock 9ri7 9ri, 

(calculated) ^0/Pb/^05Pb

U ppm

66 

114 

104 

77 

44

Th/U Age in m.y.

2.48 

6.14 

1.81 

2.25 

2.30

1925 

2150 

2075 

2000 

2810

(or Precambrian W) Little Elk Granite, although outcrops are 

poor and the contact relations are not firmly established. 

Quartz pebbles predominate over quartzite pebbles in 

oligomictic beds in the Estes at this locality, suggesting 

that the granite, and quartz veins within the granite, may 

have been the source rock for these oligomictic beds.

Pyrite, gold, and radioactive minerals in oligomictic

Table 2.--Gold content of samples of Estes 

Conglomerate containing >0.05 ppm Au 1

Sample No. Au (ppm) Sample No. Au (ppm)

BH-76-9b 0.16 

BH-76-14a 0.06 

BH-76-14d 0.05 

BH-76-14e 0.25 

BH-76-19 0.06

BH-76-20a 0.08 

BH-76-26 0.28 

BH-76-28a 1.39 

BH-76-28b 0.49 

BH-76-28C 0.37

samples reported by Hills (1977) were 

analyzed for Au. For the locations of barren 

samples, see his figures 2 and 5. Au 

determined by fire assay and atomic absorption 

by J. G. Crock, Joseph Haffty, and 

A. W. Haubert.

15
103°35' 103°30'

a 5E. a 6E.

Figure 1. Area of explosure of the Estes Conglomerate 

(stippled) with sample localities. (Geology adapted 

from Bayley, 1972).

beds of the Estes Conglomerate have been interpreted as 

heavy-mineral concentrates formed in placer deposits of 

early middle Precambrian age (Hills, 1977). However, the 

possibility that uranium was introduced into these 

conglomerates by more recent epigenetic processes cannot be 

ruled out on the basis of field and geochemical evidence. 

Intense weathering of outcrops, facilitated by oxidation of 

pyrite, would have eliminated any easily altered uranium 

minerals that originally were present, making mineralogical 

studies of samples from outcrop of little value in 

distinguishing between a syngenetic and an epigenetic origin 

for the uranium. The degree of weathering and oxidation of 

Estes Conglomerate appears to be greatest where the 

oligomictic beds originally contained the most pyrite 

(estimated from pyrite molds). Therefore, these same areas 

probably have the greatest potential for containing 

commercial-grade uranium.

Oxidation and leaching of the oligomictic conglomerates 

have obscured the answers to two important questions: (1) 

What process concentrated uranium in the Estes 

Conglomerate?; and (2) how much uranium is present below the 

zone of oxidation and leaching? Lead-isotope ratios from 

weathered samples provide tentative answers to these 

questions that may be useful in deciding whether a bore-hole 

program is warranted. According to the syngenetic or placer

hypothesis, the uranium has resided in the oligomictic beds 

since the early middle Precambrian, whereas according to the

epigenetic hypothesis, uranium was 

relatively recent time. The 206Pb/ 204Pb and

introduced 

207

at a 

Pb/ 204Pb

ratios should be higher than those for most ordinary rock

lead 

207r

if the syngenetic hypothesis is correct, and 

206r Pb/ Pb ages should be early or middle Precambrian.

The exact uranium content of the fresh rock cannot be 

determined from analyses of highly weathered samples because 

the uranium, as well as the lead and thorium, are depleted 

or enriched to some unknown extent in weathered samples. 

Nevertheless, if the age of a U-Th-Pb system is known or can 

be estimated from other data, the U/Th ratio responsible for 

producing the lead isotope system can be calculated with the 

following equation

238 206 U =

where ( 206Pb/ 208Pb)

U-Th-Pb system,

is radiogenic lead, t is the age of 

is the decay constant for 238U, and is

pop

the decay constant for Th. This equation is strictly 

true only where the U-Th-Pb system has remained closed until 

geologically recent times. 

The 238U/ 232Th ratios determined by equation (1) are 

not sensitive to errors in the independently determined age 

(t); errors as great as 500 m.y. produce variations of less

poo pop

than 5 percent in "BU/ Th, provided the lead is

poo pT.9

moderately radiogenic. However, the U/ Th ratio 

calculated may be in error because the degree of weathering 

and lead removal from uranium-rich phases may differ from 

that in thorium-rich phases.

The low solubility and low mobility of thorium in the 

weathering environment suggests that the fresh-rock uranium 

tenor can be estimated by using a chemical analysis for 

thorium in conjunction with the 238U/ 232Th ratio derived 

from equation (1). The effects of weathering (preferential 

loss of uranogenic lead, introduction of lead from nearby 

rocks, and mobility of thorium) and of Precambrian 

metamorphism (loss of lead) are most apt to cause 

underestimation of fresh-rock uranium, whereas loss of 

uranium early in the history of the sample (perhaps during 

metamorphism) would cause overestimation of fresh-rock 

uranium.

Five samples of weathered Estes Conglomerate (fig. 1)

yield the following 

from 38.65 to

208pb/ 204pb

ranges 

92.02; 207 Pb/204Pb

of isotope ratios: 206Pb/ 204Pb

than 

207

normal

Pb/ 206Pb ages

from 19.57 to 25.18; and 

These ratios are higher 

Precambrian rock leads and yield apparent 

that range from 1925 m.y. to 2810 m.y. 

(table 1).

Based on an assumed age of 2500 m.y. for the U-Th-Pb 

system and corresponding common lead ratios (Stacey and 

Kramers, 1975, Table 9), equation (1) yields apparent 

fresh-rock Th/U ratios that range from 1.8 to 6.1 and

16
fresh-rock uranium concentrations of as much as 114 ppm.

Geologic age, sedimentary characteristics, and the 

coherence of uranium, thorium, and gold in oligomictlc beds 

of the Estes Conglomerate support an interpretation of 

uranium in the Estes as fossil placer deposits, similar in 

origin to uraniferous conglomerate in the Elliot Lake 

District of Ontario and the Witwatersrand of South Africa. 

By their antiquity, the 207Pb/206Pb ages support the 

syngenetic or fossil placer hypothesis and appear to rule 

out the recent-eplgenetic hypothesis.

Although the semiquantitative estimates of fresh-rock 

uranium tenor, based on lead-isotope analyses of five 

samples, do not confirm that ore-grade rock is present, they 

Indicate that as much as 90 percent of the uranium 

originally present has been leached from the conglomerate. 

This suggests that part of the uranium may be present in 

soluble minerals, such as uranlnlte, and that economic 

concentrations may occur in the Estes where sedimentologic 

conditions and source rock were favorable. The Estes

Conglomerate, especially where it contains a high proportion 

of detritus from the Little Elk Granite, merits further 

examination by means of boreholes.

Bayley. R. W., 1970, Iron deposits of the Estes Creek area, 

Lawrence County, South Dakota, in_ Geological Survey 

research 1970: U.S. Geol. Survey Prof. Paper 700-B, 

p. B93-B101.

___1972, Preliminary geologic map of the Nemo district,

Black Hills, South Dakota: U.S. Geol. Survey M1sc. Geol. 

Inv. Map 1-712.

Hills, F. A., 1977, Uranium and thorium 1n the Middle Precambrlan 

Estes Conglomerate, Nemo District, Lawrence County, South 

Dakota A preliminary report: U.S. Geol. Survey OpenFile Rept. 77-55, 27 p.

Stacey, J. S., and Kramers, J. D., 1975, Approximation of

terrestrial lead isotope evolution by a two-stage model: 

Earth and Planetary Sc1. Letters, v. 26, no. 2, p. 207-221.

THE ROLE OF BOREHOLE ELECTRICAL MEASUREMENTS 

IN URANIUM EXPLORATION

BY JEFFREY DANIELS AND JAMES SCOTT 

U,S, GEOLOGICAL SURVEY, DENVER, COLO,

The only borehole electrical resistivity-related 

measurement that is commonly used in uranium exploration is 

the single-point resistance log. This measurement 1s used 

exclusively for stratigraphic correlation and, as such, is a 

valuable and inexpensive exploration tool. However, 

single-point measurements do not provide quantitative 

Information concerning the physical or lithologlc properties 

of the rocks.

Resistivity and induced polarization (IP) logs are also 

useful for stratigraphic correlation, and 1n addition they 

can provide information concerning the physical 

characteristics of rocks. Quantitative characterization of 

Hthologic conditions by use of these logs can be a useful 

indicator of favorable environments for uranium occurrence.

Figure 1 shows the single-point resistance and 

resistivity logs in an ore zone and outside of the ore zone 

for a uranium deposit 1n the Powder River Basin. The ore 

deposition is characterized by a high calcite cement content 

at the bottom of the ore sand, a depletion of calcite cement 

in the middle of the ore sand, and an increase in calcite 

cement at the top of the ore sand (off top of fig. 1). This 

is clearly illustrated by the resistivity logs in figure 1.

However, the single-point resistance logs do not clearly show 

the difference (1n spite of the fact that the recording 

sensitivity is much higher for the resistance logs). 

Although calcite cement near the bottom of the ore zone is 

indicated on the single-point resistance log, the log also 

shows spikes such as the one at a depth of 53 meters that are 

caused by variations in borehole diameter rather than 

lithology.

The primary advantage of using quantitative resistivity 

and IP logs, 1s the ability to use them for detecting 

anomalous concentrations of non-radioactive minerals 

associated with uranium mineralization. Figure 2 shows the 

correlation that was found between resistivity values and 

clay content in the ore sand of a south Texas uranium 

deposit. This figure indicates that, for this deposit, the 

total clay content of the sand can be estimated directly from 

the resistivity logs. This can be important in areas where 

the clay content varies in different parts of the roll front.

IP measurements respond to the presence of certain clay 

minerals (particularly montmorlllonite) and sulfldes such as 

pyrite. Since the amounts of montmorillonlte and pyrite vary 

across a uranium geochemlcal front, IP measurements can be

17
RESISTANCE, IN OHMS RESISTIVITY, IN OHM-METERS 

SINGLE POINT ELECTRODE NORMAL, 0.381 METER SPACING

33.5

14 21 28 20 40 60 80

i" 45.7

61.0

 HOLE I IN THE ORE ZONE

----- HOLE 2 ON THE REDUCED SIDE OF THE ORE ZONE

Figure 1. Comparison of single-point resistance and resistivity 

logs in the ore zone (hole 1) and outside of the ore 

zone (hole 2).

o

UJ

Ul 

O

0.

- 10

i-"

UJ

o 

o

0 10 100 

APPARENT RESISTIVITY, IN OHM-METERS

Figure 2. Correlation between resistivity and total clay

content for samples taken from the ore sand across a south 

Texas uranium deposit.

2 II 3 456TB 9 

DRILL HOLE SEPARATION AND NUMBER

200 400 600 800 1000

Figure 3. Relationship between induced polarization log

pyrite content, and montmorillonite content across a uranium 

deposit in south Texas.

used to locate the relative position of the uranium deposit 

with respect to a group of drill holes. Figure 3 shows the 

variation in pyrite, montmorillonite and IP response across a 

uranium deposit in south Texas. An increase in the 

montmorillonite and pyrite content correlates with an 

increase in the induced polarization response on the well 

logs.

Hole-to-hole measurements can make use of the 

quantitative response of well logging tools and can be used 

to minimize the number of drill holes necessary to locate on 

orebody. The electrical current source is placed in one 

drill hole and the electrical potential difference is placed 

in a hole at a large distance from the source hole. 

Potential difference measurements are made between bipole and 

electrodes, at discrete positions in the receiver hole. 

These resistivity and IP measurements give an indication of 

lithologic variations that exist between the boreholes.

HOLE-TO-HOLE RESISTIVITY AND IP MEASUREMENTS

HOLE LOCATION OF TRANSMITTER AND RECEIVER CABLES

RECEIVER II 

SOURCE 3 

SEPARATION 122m

RECEIVER 4 

SOURCE 9 

SEPARATION 214m

RECEIVER 9 

SOURCE 3 

SEPARATION 306m

IP RESPONSE, IN MILLIVOLTS/VOLT 

50 IOO ISO

5 K> 0 5 K)

APPARENT RESISTIVITY, IN OHM-METERS 

BARREN ACROSS ORE ACROSS ORE

Figure 4. Resistivity and induced polarization measurements 

across a uranium roll-type deposit in south Texas.

18
Interpretation of these measurements can eliminate 

unnecessary drilling and speed up the evaluation of marginal 

properties.

Examples of hole-to-hole measurements across two 

roll-type uranium deposits are illustrated in figures 4 and 

5. The measurements shown in figure 4 are from the same 

property in south Texas as the data shown in figure 3. The 

hole-to-hole measurements across the ore zone show an IP 

anomaly that is believed to be caused by an increase in 

pyrite and montmorillonite near the center of the deposit. 

The resistivity data are not significantly anomalous across 

the ore zone.

The hole-to-hole data for the Powder River Basin 

property (fig. 5) reflect a different lithologic setting. 

The resistivity shows an anomalous high value across the 

center that is caused by an increase in calcite cement at the 

oxidized-reduced geochemical interface of the roll front. 

The IP high on the reduced side of the roll front is probably 

caused by relatively higher sulfide and (or) montmorillonite 

content on the reduced side of the ore zone.

The preceding examples show how the use of quantitative 

types of well logging information can lead to a better understanding of the uranium environment and can ultimately yield 

savings of both time and money. It should be cautioned that 

as geologic characteristics change for each geographic area, 

borehole responses will also change from area to area.

APPARENT RESISTIVITY, IN OHM-METERS100 200

INDUCED POLARIZATION, IN MILLIVOLT/VOLTBARREN ACROSS ORE BARREN 

REDUCED OXIDIZED

Figure 5. Resistivity and induced polarization measurements 

across a uranium roll-type deposit in the Powder River 

Basin, Wyoming.

HOW TO PLAN AN AERIAL GAMMA-RAY SURVEY

BY J, A, PlTKIN AND J, S, DUVAL

U,S, GEOLOGICAL SURVEY, DENVER, COLO,

A number of parameters require consideration when an 

aerial gamma-ray survey is being planned. Some of the 

parameters to be considered are: the type of data to be 

obtained (gross-count or spectrometric), the ground interval 

between flight lines, the nominal survey flight altitude, 

and the detector volume to be used. Other factors not here 

discussed include instrumentation to be used, advance 

planning for flight operations, and scheme for data 

reduction.

The initial decision is whether the survey obtains 

gross-count or spectrometric data. The amount of money 

available is one consideration, as spectrometric surveys are 

more expensive than gross-count surveys by a factor of 3 or 

more. The goal of the survey is another factor to be 

considered. Gross count data provide aid for geologic 

mapping, but are less suitable for mineral exploration.

Spectrometric data separate the contributions of the 

components~K, U, and Th of the gross-count data, thereby 

providing more information and reducing the amount of ground 

follow-up required.

Target dimensions can be used to specify the desired 

flight line spacing and survey altitude, but other factors 

of a practical nature must also be considered. Coarse (>3 

km) line spacing can suffice for detection of broad, 

regional anomalies. Fine (<3 km) line spacing is needed to 

detect localized anomalies or to provide aid for detailed 

geologic mapping. Low topographic relief in sedimentary 

basins may permit decreasing the flight altitude while 

greater topographic relief in crystalline areas may 

necessitate increasing the flight altitude. However, target 

detectability or ground resolution decreases as the altitude 

increases, and the percentage of a survey area covered

19
decreases with decreasing altitude. Furthermore, gamma-rays 

are absorbed in air exponentially as the air column 

increases in thickness, which means that the observed count 

rate decreases and statistical error increases as the flight 

altitude increases.

The parameters controlling aerial gamma-ray surveying 

interact in a complex manner. A graph and a table are 

included to enable easier understanding of this interaction 

and to provide means by which surveys can be designed. 

Figure 1 shows the expected corrected count rate per liter 

of detector as a function of altitude above ground for 

specific radioelement concentrations and can be used to 

estimate corrected count rates provided by a given crystal 

volume. For example, at an altitude of 122 m and with a 

volume of 13.6 liters, the count rates are 24.1 cps (counts 

per second) for 1 percent K, 4.4 cps for 1 ppm eLI^, 11.9 cps 

for 1 ppm elL, and 1.4 cps for 1 ppm eTh. ell, uses only the 

1.76-MeV photopeak, while eU2 is a sum of the 1.12- and 

1.76-MeV photopeaks. The e for equivalent prefix is used 

because of the potential for disequilibrium in the U and Th 

decay series.

Table 1 complements figure 1 by showing how count rate 

error increases as detector volume decreases. Note the 

large error in U count rate caused by using only the 

1.76-MeV photopeak. Both the figure and the table, while 

based upon different concentrations, were compiled with data 

that were normalized to 122 m and had corrections applied 

for Compton scattering, airborne bismuth-214, cosmic 

radiation and aircraft background radiation. Other graphs 

(not included) illustrate the percentage of area covered by

an aerial survey for several flight altitudes as a function 

of flight-line spacing, the estimated ground resolution as a 

function of detector altitude, and the expected gross count 

rate per liter of detector as a function of altitude for two 

rock types.

All of these graphs and tables, together with a 

knowledge of the survey objectives, the type of terrain to 

be surveyed, and the available funds can be used to 

objectively select the survey parameters.

a: "Z. 

§0

O UJ

100 122 200 300

ALTITUDE OF DETECTOR ABOVE GROUND, IN METERS

Figure 1

1 2

Table 1.--Corrected count rates for K, U 1t U?, and Th showing estimated errors

for three detector volumes

[Constant ground concentrations are 1.1 percent K, 1.7 ppm eLI, and 4.5 ppm eTh. 

All data normalized to 122 m flight altitude]

Detector 

volume, 

in liters

54.5

27.3

13.6

K

106

53

26

, cps

±20.2

.1±13.4

.5± 9.1

K error, 

percent

±19

±25.2

±34.3

i 

UL cps

28±14.6

14±10.6

7± 8.1

14 error, 

percent

±52.2

±75.7

±115.7

2 

U

84

42

21

2 , cps U 2 error, 

percent

±21.6

.3±17.8

.2±12'.8

±25.7

±42

±60.4

Th

25

12

6

, cps Th error, 

percent

±7.8

.5±5.4

.2±3.7

±31.2

±43.2

±59.7

Assuming only the 1.76-MeV windows.

2 assuming summed windows centered at the 1.12- and 1.76-MeV photopeaks.

20
COMPOSITE IMAGES OF RADIOMETRIC DATA 

FROM SOUTH TEXAS AND WYOMING

BY J, S, DUVAL, J, A, PITKIN, AND D. L, MACKE 

U.S. GEOLOGICAL SURVEY, DENVER, COLO,

Aerial radiometric measurements of the apparent surface 

concentrations of potassium (K)» uranium (ell), and thorium 

(eTh) are usually presented as stacked flight-line profiles 

or, where line spacing permits, as contour maps. In either 

presentation, an interpreter must examine the profiles or 

maps individually and must then synthesize the data to 

produce a map related to geology or potential uranium 

mineralization. Even with the aid of a computer and the use 

of statistical techniques, such a synthesis is a difficult 

and subjective task.

A technique developed by the U.S. Geological Survey can 

be used to produce a single composite representation which 

synthesizes three components of the data (either K, eU, and 

eTh, or ell/eTh, ell/K, and eTh/K). The contour maps, in the 

form of. equally spaced grid points, are converted to 

gray-tone images in which each grid point becomes a picture 

element (pixel) and the density of the gray tones is 

proportional to the magnitude of the count rates. Each of 

the three components is assigned one of the primary colors 

(magenta, cyan, or yellow) and a transparent color copy of 

each component is made using the Diazo process. Overlaying 

the resulting color images produces a composite, false-color 

image that is a visual synthesis of the three components.

Composite color images have been produced using data 

from aerial surveys flown in an area around Freer, Tex. and 

in Converse County, Wyo. Figure 1A_ shows radiometric units 

determined from the composite image of the radioelements K, 

eU, and eTh using the data from an aerial gamma-ray survey 

near Freer, Texas (Schulz, 1975a); the figure also shows the 

geology and faults of the area (adapted from the Crystal City 

and Laredo Atlas Sheets of the Texas Bureau of Economic 

Geology, Austin, Tex.), and locations of known uranium 

mineralization. Each radiometric unit appears on the 

composite image as a relatively uniform, distinctive color or 

combination of colors. The radiometric units show good 

agreement with the mapped geology: units A and B correlate 

with the Oakville Sandstone, unit E with the Goliad Sand, 

units C and D with the Catahoula Tuff, units G and J with the 

Frio Clay, and units H and I with the Jackson Group. Unit M 

may correspond to some of the terrace deposits along the 

Nueces River, although the bulk of the mapped alluvium has 

the same radiometric character as does much of the Catahoula 

Tuff. The remaining radiometric units, F, K, L, N, and 0,

show up as subtle color variations, the specific colors being 

determined by the lithologic unit within which the areas lie. 

Of these five units, F and N show correlations with areas of 

known uranium mineralization. One hypothesis that might 

explain some of these subtle color variations is that they 

reflect differences in the geochemical character of the 

ground due to the presence of gases eminating from buried 

petroleum deposits. If this hypothesis is true, these areas 

can be interpreted as locations with a favorable environment 

for uranium deposition, because the petrolic gases act as 

reductants that precipitate uranium from the ground waters.

Figure IB. shows radiometric units determined from the 

composite image of the radioelements K, eU, and eTh using the 

data from an aerial gamma-ray survey in Converse County, Wyo. 

(Schulz, 1975b); in addition, the figure shows geology 

(adapted from Sharp and Gibbons, 1964), and locations of 

uranium mines. Each radiometric unit corresponds to a 

relatively uniform, distinctive color or combination of 

colors. The radiometric units show poor agreement with the 

mapped geology. Unit E correlates with eolian sand that is 

easily identified on standard aerial photographs. Unit F 

correlates with the water course of the Dry Fork of the 

Cheyenne River. Our tentative interpretation of the 

remaining radiometric units is that units A, B, C, D, and K 

represent distinctive lithologies or soils, and that units G, 

H, I, J, and L represent alteration zones, although much of 

unit I reflects the presence of open-pit mines. We suggest 

that locations where units I and J occur are likely targets 

for uranium exploration.

Schulz, K. A., 1975a, Airborne gamma-ray spectrometry and

aeromagnetic survey of the Freer area in Duval, Live Oak, 

McMullen, and Webb Counties, Texas: U.S. Geol. Survey 

Open-File Rept. 75-294, 5 p.

___1975b» Airborne gamma-ray spectrometry and aeromagnetic 

survey of part of the southern Powder River Basin in 

Converse County, Wyoming: U.S. Geol. Survey Open-File 

Rept. 75-661, 6 p.

Sharp, W. N., and Gibbons, A. B., 1964, Geology and uranium 

deposits of the southern part of the Powder River Basin, 

Wyoming: U.S. Geol. Survey Bull. 1147-D, 60 p.

21
Tertiary

Tw Wasatch Formation

Fort Union Formation 

Tfu upper part 

Tfl lower part

Quaternary

Qal Alluvium

Qt Terrace deposits 

Tertiary

Tg Goliad Sand

To Oakville Sandstone

Tc Catahoula Tuff

Tf Fno Clay

Tj Jackson Group

 Geologic contact

^ Location of known

uranium mineralization

Altered ground

r Red

w White

d Drab 

i^^^^ Geologic contact

A Uranium mine

Figure 1.--Map of radiometric units determined from composite from the Crystal City and Laredo Atlas Sheets of the 

Image of radloelements K, eU, and eTh for aerial Texas Bureau of Economic Geology, Austin, Tex. The 

gamma-ray surveys near (A) Freer, Tex., and (Bj Converse geology of B_was adapted from Sharp and Gibbons (1964). 

County, Wyo. The geology and faults of A_ were adapted

22
TWO-MICA GRANITE AND URANIUM POTENTIAL IN THE 

NORTHERN APPALACHIAN OROGEN OF NEW ENGLAND

BY EUGENE L, BOUDETTE, U,S, GEOLOGICAL SURVEY, 

RESTON, VA,

Northern Appalachian rocks make up a dissected 

northeastward-plunging orogenic system. Roots of the orogen 

are manifested by rocks of the infrastructure in southern 

New England. The present erosion surface intersects rocks 

of progressively higher crustal levels northeastward, 

reaching the suprastructure in Maine. Rocks of the orogen 

are buttressed to the west by the Precambrian rocks of the 

Grenville Series of the Adirondacks and contain discrete 

Precambrian terrains interspersed with predominantly 

Paleozoic rocks. The rocks may be subdivided into 

eugeosynclinal and miogeosynclinal successions and ascribed 

to major tectono-stratigraphic zones for purposes of 

long-range correlation.

At least two zone boundaries in the orogen can be 

interpreted to coincide with plate or intraplate sutures. 

An Early Ordovician orogenic culmination is documented by a 

Middle Ordovician unconformity. Orogenic events (older than 

Early Silurian) are traditionally ascribed to the Taconian. 

Events assigned to the Taconian vary in time from place to 

place, and a trampoline model can, in fact, be invoked in 

which the orogen was restless between (at least) the Early 

Cambrian and Carboniferous in both longitudinal and lateral 

anisotropic disharmonic motion.

The end of the Taconian is Interpreted to be signalled 

by the closing of an island arc against the continental 

Appalachians in Late Ordovician to Early Silurian time. The 

sedimentologic and plutonic geochronologic record Indicates 

that initial interplate collision probably occurred in Early 

to Middle Silurian time and was completed probably after the 

Late Mississipplan, a period which spans at least 80 m.y. 

and includes the entire Acadian orogeny.

Plate collisions caused the deformation in the 

Appalachian orogen. It was during an orogenic culmination 

that two-mica granite (Gauthier, 1973, 1974) was generated, 

probably by extraction from rocks called here informally 

migmatite which is exposed near the town of Massabesic in 

southeastern New Hampshire and in eastern Massachusetts. 

This migmatite was produced from the partial melting, during 

metamorphism, of eugeosynclinal detrital or volcanic rocks 

found west of the interplate suture. These rocks are part 

of the segment welded onto the ancestral Appalachians after 

the Taconian.

Eugeosynclinal deposition probably continued until 

emplacement of the synkinematic plutons during the Acadian. 

Plutonism probably coincided with emplacement of a hot 

mantle slice beneath the geosynclinal assemblage. This 

slice also provided the heat for the Acadian metamorphism.

This mantle material reacted, in part, with crustal host 

rock, was mobilized into sheets (Nielson and others, 1976), 

and crystallized into a gabbro-quartz monzonite intrusive 

suite of Early Devonian age.

Subsequent to the emplacement of the gabbro-quartz 

monzonite suite, westward!./ transported allochthons were 

stacked on site on thrust faults in the suprastructure. At 

the same time, two-mica granite was extracted from the 

migmatite by anatexis. The mobilized two-mica granite moved 

westward in sheets in association with the allochthons, 

possibly, in part, coring nappes. The two-mica granite 

composes a second intrusive suite and was assigned to the 

Devonian Concord Granite (Billings, 1956).

The Concord Granite crops out in three belts in New 

Hampshire, presumably in the infrastructure. The belts 

apparently coincide with antiformal flexures in allochthons 

which expose partial to complete sections of two-mica 

granite at least 1 km thick. The easternmost (Milford) belt 

closely parallels and appears to grade into the migmatite to 

the east wherein it is Interpreted to be rooted. The 

Central (Swenson) belt probably represents outliers of the 

same sheet (or sheets) making up the Milford belt. Granite 

in the Milford and Swenson belts is an excellent 

quarrystone. In these belts it is more massive than the 

foliated granite in the western Lake Sunapee belt.

The two-mica granite contains uranium minerals exposed 

in two parallel roadcuts along Interstate Route 89 (1-89) in 

New London, N. H., and the Lake Sunapee belt, reported first 

by William Bateman (oral commun., 1968) during the cutting 

of the highway grade. The mineralized pluton is everywhere 

strongly jointed and is intensely sheared at a few places. 

The pluton has a moderate systematic foliation probably 

formed partly by fTowage and partly by inherited relic 

foliation in screens dragged parallel to flowage. The 

foliation geometry suggests that the pluton is a 

subhorizontal sheet that has been antiformally arched along 

a north-south axis. This sheet probably was more than a 

kilometer thick in its central zone. Preliminary 

ground-gamma radiometry by W. A. Bothner (oral commun., 

1976) shows that the mineralized zone in the 1-89 roadcuts 

can probably be traced both northwest and southeast to the 

borders of the pluton. The proposed trend of the 

Boston-Ottawa geophysical lineament, a regional topographic 

photolinear, and the mineralized zone are all parallel.

Oxidized uranium minerals in a zone more than 4 m thick 

are exposed in the 1-89 cut. This occurrence of secondary 

uranyl-phosphate minerals resembles that of the Daybreak

23
mine near Spokane, Wash. Uranium minerals in the Lake 

Sunapee deposit occur mainly in fractures, local fault 

gouge, and biotitic schlieren. The granite is somewhat more 

fractured than correlative rock north and south on regional 

strike, but not conspicuously so. In the nearly 10 years 

since the mineralization was exposed by roadcuts and the 

water table was lowered, more than 90 percent of the yellow 

uranium minerals have been leached away by vadose ground 

water. The top of the original water table is believed to 

have fluctuated within the mineralized zone. It is possible 

that the uranium minerals have reprecipitated at the lowered 

(reestablished) water table.

Two-mica granite is recognized for its metallogenic 

specialization in tin, tungsten, beryllium, lithium, 

fluorine, and uranium. Uranium production in France and in 

the Iberian peninsula is from Variscan or Hercynian-age 

two-mica granites. Concord Granite can be compared with the 

uranium-producing granites of the Massif Central of France 

and fits the evolving international model for two-mica 

granites based upon an apparent anatectic origin, 

emplacement during an orthotectonic event, and probable 

requisite preconcentration of uranium in its parent rock, 

thought to be the migmatite.

Anomalous radioactivity is associated with the 

migmatite. The radioactivity pattern may partly be related 

to sulfide- magnetite-quartz-uraninite(?) veins and 

pegmatites which apparently also contain uranium oxides. 

The oxidized uranium deposit at Lake Sunapee obviously 

involves a secondary concentration of uranium. It is 

presently unknown if the oxidized uranium minerals were 

derived from orthomagmatic veins as in Massabesic area of 

New Hampshire and in Massachusetts and the Massif Central of 

France or younger hydrothermal veins as proposed by Page (in 

press) or a broadly disseminated source.

It is significant that carbonate-rich lamprophyre dikes 

are associated with the Concord Granite, especially as seen 

in the mineralized rock at Lake Sunapee. Carbonate

lamprophyre emplacement in Variscan granites is concurrent 

with uraniferous vein emplacement and transformation of 

parts of the granite to episyenite, and the mobility of the 

uranium is related to carbonate complexing (Poty and others, 

1974). Exploration on this basis should be focused on 

episyenite and lamprophyre zones, especially in the upper 

zones of the Concord sheets.

Application of the Variscan model to the Concord 

Granite requires that all three outcrop belts as well as the 

migmatite be considered potential ore terrane. Facies of 

the Concord Granite also intrude the migmatite in a 

situation interpreted to be auto-intrusion.

Gauthier, J.-C., 1973, Evolution granitique, development des 

granites a deux micas et geochimie des alcalins dans la 

Marche orientale (Massif Central Francais), L'evolution 

granitique: Sci. Terre, v. 18, no. 4, p. 317-352.

___1974, Evolution granitique, development des granites a 

deux micas et geochimie des alcalins dans la Marche 

orientale (Massif Central Francais), Geochimie des 

alcalins rares: Sci. Terre, v. 19, no. 2, p. 119-151.

Nielson, D. L., Clark, R. G., Lyons, J. B., Englund, E. <]., 

and Borns, D. J., 1976, Gravity models and mode of 

emplacement of the New Hampshire plutonic series, in 

Lyons, P. C., and Brownlow, A. H., eds., Studies in New 

England geology: Geol. Soc. America Mem. 146, p. 

301-318.

Page, L. R., (in press), Guides to prospecting for uranium 

and thorium in New Hampshire and adjacent areas: New 

Hampshire Dept. Resources and Econ. Devel. Bull.

Poty, B. P., Leroy, Jacques, and Cuney, Michel, 1974, Les 

inclusions fluids dans les minerals des gisements 

d'uranium intragranitiques du Limousin et du Forez 

(Massif Central, France), jn_ Formation of uranium ore 

deposits: Internet. Atomic Energy Agency Proc. Ser. 

No. STI/PUB/374, p. 569-582 [includes English summ.].

GROUND-WATER FLOW AND THE SHAPE 

OF URANIUM ROLL DEPOSITS

BY C, GERALD WARREN, U,S, GEOLOGICAL SURVEY, 

DENVER, COLO,

In this study the characteristics of ground-water flow 

were related to the shape of the oxidation front of 

sandstone-type orebodies. An understanding of this 

relationship provides a tool for studying the ground-water 

flow during the time that a deposit was forming. Many

ground-water flow patterns were evaluated to find the 

associated shape of the oxidation front. The type of 

ground-water flow that produced shapes similar to those 

found in actual deposits is postulated to represent the 

actual flow of ground water as the deposits formed.

24
The oxidized tongue associated with a roll-type uranium 

orebody was created by oxldants reacting with the pyrlte and 

other ore components. The rate at which the oxidized tongue 

advanced was controlled by the rate at which the oxldants 

were delivered to the oxidation front. Although all 

oxidants were delivered by ground water there were two 

separate and distinct processes Involved: (1) oxidants were 

transported by the moving ground water, (2) oxidants were 

moved by diffusion from regions of high concentration to 

regions of low concentration.

These delivery processes were described by a 

differential equation and solved by computer analysis. The 

results were displayed on microfilm 1n a graphical form 

resembling the shape of a roll front of an actual orebody. 

A movie showing the development of an oxidation front and

uranium orebody was obtained by recording successive 

computer-generated representations of the roll front.

In the movie, a bulge or roll develops in the oxidation 

front within the zone of maximum flow in the aquifer. 

Although parts of the orebody may lag behind 1n the less 

permeable zones of the aquifer, they are slowly destroyed by 

oxldants that are delivered by the diffusion process. In a 

simple homogeneous aquifer system the shape of the roll 

gradually achieves maturity and Us dimensions are a 

function of the ratio between flow velocity and diffusion. 

For example, an average ground-water velocity of 2x10 cm/s 

(6.3 m/yr) and an oxldant diffusion coefficient of 2xl05 

cm2/s will produce a C-shaped oxidation front with a profile 

about twice as wide as the height of the aquifer.

ECONOMIC IMPLICATIONS OF A NEW HYPOTHESIS OF ORIGIN OF

URANIUM- AND COPPER-BEARING BRECCIA PIPES,

GRAND CANYON, ARIZONA

BY C, G, BOWLES, U.S. GEOLOGICAL SURVEY, 

DENVER, COLO,

Uranium and copper ores have been mined 1n the Grand 

Canyon from breccia pipes developed within M1ss1ssipp1an to 

Permian formations, Including the Redwall Limestone 

(M1ss1ss1ppian), Supal Group (Pennsylvanlan and Lower 

Permian), and Hermit Shale (Lower Permian); weak 

mineralization occurs as well 1n the upper part of pipes 

within the Lower Permian Coconlno Sandstone, Toroweap 

Formation, and Kalbab Limestone. Some breccia pipes formed 

during Hesozolc time, but collapse may have begun as early 

as Late Permian time. Other pipes apparently were formed 

during erosion of the Grand Canyon and may be no older than 

middle to late Cenozolc. Recurrent collapse has also 

occurred 1n the older breccia pipes.

The breccia pipes 1n the Grand Canyon are generally 

believed to be either cryptovolcanlc structures or collapse 

structures formed by solution of limestone by hydrothermal 

waters. Copper and uranium deposits in these structures are 

attributed to hydrothermal mineralizing solutions. This 

view 1s derived from studies of the Orphan mine by Gabelman 

and Boyer (1958); Kerr (1958); Kofford (1969); Gornltz and 

Kerr (1970). Isotoplc studies by Miller and Kulp (1963) and 

Adler (1963), and fluid-Inclusion geothermometry by Gornltz 

(1969) suggest that the temperature during mineralization of 

the Orphan pipe may have been less than 100'C.

The following hypothesis proposes that formation of the 

breccia pipes and primary mineralization resulted from

low-temperature hypogene solutions that consisted either 

domlnantly or entirely of artesian ground water. However, 

secondary enrichment by either supergene or mesogene 

(mingled descending and ascending) solutions concentrated 

the metals 1n medium- to high-grade orebodles. This 

hypothesis rejects a cryptovolcanlc origin for the 

structures. Emphasis 1s placed upon the hydrologlc system 

believed to dominate the development and mineralization of 

most breccia pipes. Canyon cycles of erosion strongly 

influenced or controlled secondary enrichment.

The typical mineralized pipe developed 1n four stages:

(1) Initial solution and collapse 1n the Redwall Limestone;

(2) sloping into the overlying Supal Group and alteration by 

bleaching and carbonate cementation; (3) continued sloping 

and primary mineralization, consisting predominantly of 

pyrite, chalcodte, and uranlnlte; and (4) secondary 

enrichment.

Limestone solution and collapse within the Redwall 

Limestone began during the Hesozolc when northeastward 

tilting of the Colorado Plateau and the bevelling of 

Paleozoic strata southwest of the area now occupied by the 

Mogollon Rim permitted ground water to recharge the Redwall. 

Artesian pressure Initiated an upward flow of ground water 

along fractures 1n the limestone. The ground water, 

containing dissolved carbon dioxide and saturated with 

calcium and magnesium bicarbonate Is postulated to have
migrated upwards from the dolomltlc Whltmore Wash and 

Thunder Springs Members of the Redwall Limestone. Upon 

entering the calcitic Mooney Falls Member the water 1s 

believed to have mixed with other ground water that was 

saturated with calcium bicarbonate but which contained a 

smaller concentration of dissolved carbon dioxide. The 

mixing of waters having differing concentrations of 

dissolved solids and gases caused disequilibrium and 

undersaturation with respect to calcium carbonate (Bbgli, 

1964) and dissolution within the Mooney Falls Member. The 

water continued upwards into the overlying Horseshoe Mesa 

Member, which previously had been made highly transmissive 

during development of the pre-Pennsylvanian karst surface. 

Limestone solution in the upper Redwall formed chimneys 

filled with collapse breccia.

During stage 2 dissolution of the Redwall Limestone 

continued, and upward stoping extended the collapse 

structure Into the Supai. Accompanying alteration consisted 

of bleaching and carbonate cementation of the breccia and 

adjacent red beds. Collapse stoping in the Supai eventually 

intersected aquifers that had lower artesian pressures than 

were present in either the Redwall or the pipe, and aquifers 

in the Supai were thus recharged'by the artesian water.

Ground water from the Redwall Limestone contained 

reductants, probably dissoved hydrogen sulfide (H^S), 

bisulfide (HS1 ) and and sulfide (S2 ) ions, as well as 

organic carbon released from the dissolved limestone. 

Dissolved carbon dioxide and hydrogen sulfide were released 

from solution as the pressure of the water ascending in the 

pipe structure decreased. Release of dissolved carbon 

dioxide caused both the precipitation of calcite cement and 

an increase in the sulfide and bisulfide ion activity. 

Reducing solutions moved through the brecciated red beds and 

Into the sandstone aquifers; Iron was reduced and pyrite was 

precipitated. Where the reductants were not as abundant, 

oxidation of the dissolved sulfides formed an acidic 

solution that attacked and removed hematite, thus bleaching 

the breccia and the enclosing sandstone host rocks. Beyond 

the limits of bleaching a purplish-red halo of Iron and 

manganese oxides formed around some bleached zones.

Primary mineralization of the pipe marked the beginning 

of stage 3. As more aquifers 1n the Supai were penetrated 

by stoping and recharged by artesian flow, the pressure 

within the pipe decreased. Ground water carrying 

high-valence copper and uranium ions then entered the pipe 

from the lower sandstone aquifers of the Supai. Mixing of 

the ground water in the pipe with ground water from aquifers 

in the Supai caused iron, copper, and uranium ions to be 

reduced, and pyrite, chalcocite, and uraninite were 

precipitated in the pipe above the point of recharge by 

aquifers 1n the Supai. Iron was available in relatively 

large amounts in the ground water, and pyrite was readily 

precipitated.

The commencement of Grand Canyon erosion initiated

stage 4, in which secondary enrichment of uranium and copper 

in a supergene or mesogene environment was accompanied by 

renewed collapse in the breccia pipe. Beginning in Miocene 

time oxygenated vadose and ground water leached uranium and 

sulfide deposits within the breccia pipe, decemented breccia 

fragments, pipe-fill sediments, and adjacent sandstone host 

rocks, and dissolved limestone in adjacent beds. This 

decementation caused renewed collapse, slump, and 

redistribution of detrital material in the pipe. Within the 

zone of oxidation minerals were formed from high-valence 

copper and uranium, but farther below the water table 

secondary chalcocite and uraninite were precipitated in a 

reducing environment. The reductants may have been the 

primary sulfide minerals or the sulfide ions in artesian 

water that flowed from the breccia pipe into aquifers in the 

Supai and eventually discharged as springs into the Colorado 

River drainage.

The secondary enrichment process appears to be related 

mainly to the development of an extensive erosion surface 

known as the Esplanade. This surface formed in the Grand 

Canyon during middle to late Miocene or early Pliocene time. 

All known uranium and copper orebodies occur below the level 

of this ancient valley surface or below less extensive 

surfaces that formed in the eastern Grand Canyon during the 

same period of time.

Damming of the Colorado River by lava flows in the 

western part of the canyon during late Pliocene(?) and 

middle Pleistocene time may have contributed to supergene 

development of ores by reestablishing water tables at and 

below the Esplanade surface. Possibly the volcanic activity 

released hydrogen sulfide to the ground water to provide 

favorable conditions for ore deposition and enrichment. The 

economic significance, however, is speculative pending 

further studies.

The above hypothesis for the origin of uranium and 

copper-bearing breccia pipes in the Grand Canyon suggests 

that the best ore potential is limited to large breccia 

pipes that stoped through the upper part of the Supai Group 

into overlying formations. In these pipes primary 

mineralization during stage 3, followed by enrichment during 

stage 4, was most likely to form an ore deposit below the 

Esplanade surface. A greater enrichment and a more 

restricted vertical distribution of ore should be expected 

in pipes in areas where the Esplanade surface is especially 

well developed. Secondary enrichment probably decreases 

laterally away from the Colorado River. Copper and uranium 

deposits are more likely to be preserved in pipes downdip 

from the canyon where there has been little recharge of the 

Paleozoic aquifers since Miocene time.

Adler, H. H., 1963, Concepts of genesis of sandstone-type uranium 

ore deposits: Econ. Geology, v. 58, no. 6, p. 839-852.

Bbgli, A., 1964, Corrosion par melange des eaux: Internat. Jour. 

Speleology, v. 1, pt. 1-2, p. 61-70.

26
Gabelman, J. W., and Boyer, W. H., 1958, Relation of uranium 

deposits to feeder structures, associated alteration and 

mineral zones, !n_ Volume 2, Survey of raw material 

resources: Second United Nations Internat. Conf. on Peaceful 

Uses of Atomic Energy, Geneva 1958, Proc., p. 338-350.

Gornitz, V. M., 1969, Mineralization, alteration, and mechanism 

of emplacement, Orphan ore deposit, Grand Canyon, Arizona: 

Columbia Um'v. Ph.D. thesis.

Gornitz, V. M., and Kerr, P. F., 1970, Uranium mineralization 

and alteration, Orphan mine, Grand Canyon, Arizona: Econ. 

Geology, v. 65, no. 7, p. 751-768.

Hamblin, W. K., 1969, Late Cenozoic lava flows in the Grand 

Canyon of the Colorado River, Arizona, ij^ Geology and 

natural history of the Grand Canyon region: Four Corners

Geol. Soc. Field Conf., 5th, Powell Centennial River

Expedition, [Durango, Colo.]- 1969, p. 41-60. .* 

Kerr, P. F., 1958, Criteria of hydrothermal emplacement in

[Colorado] Plateau uranium strata: Internat. Conf. on

Peaceful uses of Atomic Energy, 2d, Geneva 1958, Proc.,

v. 2, p. 330-334. - ; 

Kofford, M. E., 1969, The Orphan mine, in_ Geology and natural

history of the Grand Canyon region: Four Corners Geol. Soc.

Field Conf., 5th, Powell Centennial River Expidition,

[Durango, Colo.] 1969, p. 190-194. 

Miller, D. S., and Kulp, J. L., 1963, Isotopic evidence on the

origin of the Colorado Plateau uranium ores: Geol. Soc.

America Bull., v. 74, no. 5, p. 609-629.

COMPUTER-ENHANCED IMAGES AND GEOLOGIC STUDIES, 

SOUTHERN POWDER R|IVER BASIN, WYOMING

BY T, W, OFFIELD, G, L, RAINES, AND D, L, SAWATZKY 

U,S, GEOLOGICAL SURVEY, DENVER, COLO,

Different surface geologic materials of interest in 

uranium exploration show varying reflectance characteristics 

and vegetation assemblages in computer-enhanced Landsat 

images of the southern Powder River Basin. Well-drained 

(sandy, coarse-grained) and poorly drained (clayey, 

fine-grained) soils are distinguished by conspicuous 

vegetation differences; a major vegetation change marks the 

line drawn by some mappers for the somewhat disputed contact 

of the Fort Union (Paleocene) and Wasatch (Eocene) 

Formations. Within the area underlain by generally 

coarse-grained sandstones of the Wasatch, numerous areas 

have vegetation like that of the Fort Union, suggesting the 

presence of inliers of the Fort Union or finer grained 

facies in the Wasatch. An intermediate vegetation and soil 

combination near the town of Bill, shown by subtle spectral 

contrast in a color-enhanced image of a single ratio of 

Landsat bands 5 and 6 (fig. 1), marks an area mapped by 

Sharp and Gibbons (1964) as a claystone-siltstone border 

facies of the Wasatch near the contact with the Fort Union.

Color enhancement of images produced from single ratios 

is achieved by compositing three color films each of which 

represents contrast stretches of three different segments of 

the image gray scale. This and other enhancements of the 

band 4 to band 5 ratio image, especially when .combined with 

enhanced versions of other band-ratio images, permit 

reasonably good discrimination of exposed hematite-stained 

materials in altered ground associated with uranium 

roll-front mineralization (fig. 2). The described

vegetation differences and red altered ground are not 

discernible in available high-altitude, color-infrared 

photographs. Field and laboratory measurements of spectral 

reflectance show that absorption bands characteristic of 

ferric iron are obvious in spectra of altered rocks and 

their overlying residual soils but are absent or minimal in 

spectra of unaltered materials. This is the basis of the 

detection of red altered ground using Landsat data. The 

field spectra show that bands not available on Landsat but 

available in aircraft scanners should permit better 

discrimination of hematite-stained, altered materials and 

possibly of calcite-cemented materials associated with 

uranium roll-fronts.

The Wasatch-Fort Union contact is conspicuous in 

nighttime thermal-infrared images available for a very short 

segment of the contact. A thermal boundary matches the 

contact shown on one of two geologic maps that depict the 

contact differently. Some of the thermal contrast relates 

to topographic changes with which the contact coincides in 

places, but where the contact departs from the topographic 

line so does the thermal boundary.

Enhanced Landsat images show many linear topographic 

elements 2 to 25 km long (fig. 3) and so regularly developed 

that they are inferred to represent geologic structure. 

Azimuth-frequency maxima occur at N. 75° E., N. 45° W., and 

N. 30° W. Northwest-trending lineaments are dominant on the 

east side of the basin and northeast-trending lineaments are 

dominant on the west side. The Box Creek-Monument Hill

27
- ' , '-"^ j^, , ^^gjfc^lgifc^ ..;^

i;rlM^^^1^^^. BLj: '*-- AS¥KL?«'V. ^_- '.' . * -- r.irf>~*r^'"'**'Sai Tf

l^lxtt^i *"^l^ii^%l^

Figure 1. Black-and-white copy of color-enhanced image of 

Landsat-band ratio 5/6. Tf, Fort Union Formation; Tw, 

Wasatch Formation; Twc, claystone facies of Wasatch 

(Sharp and Gibbons, 1964); small arrows mark 

approximate claystone-sandstone facies of Wasatch 

contact; long arrows mark major lineament. H, Highland 

mine; B, Bill; NB, North Pumpkin Butte. North 

approximately at top of image.

uranium area is located at the boundary of the two lineament 

domains. Lineaments in this uranium area match the 

northwest trend of subsurface folds and ore-sand, isopachs

Figure 2. Map outlining areas of red altered ground (from 

Sharp and Gibbons, 1964); x, distinctive iron 

discoloration seen in color-ratio composite image.

mapped at the Highland mine by Langen and Kidwe11 (1973). A 

color-enhanced image of a Landsat band 5 to band 6 ratio 

reveals a NNW-trending lineament marked by changes in 

vegetation and stream-course patterns (fig. 1). Alluviation 

in stream courses crossing the lineament suggests that 

downwarping has affected stream gradients. The line is

28
I06°00' I05°00'

43< 

30

43' 

00'

Figure 3. Map showing lineaments defined in Landsat images. 

0, Orpha, H, Highland mine; B, Bill; P, Pine Tree; NB, 

North Pumpkin Butte.

suspected of marking a subtle, relatively young structural 

sag parallel to and west of a postulated positive fold axis 

(Sharp and Gibbons, 1964). Uranium occurrences are 

scattered in a narrow belt west of this newly defined 

lineament, but the line marks the west limit of economic 

mineralization discovered so far. Limited well-water 

chemical data (Hodson and others, 1973) indicate a change in 

dominant type of dissolved solids from calcium bicarbonate 

west of the lineament to sodium sulfate or sodium 

bicarbonate in the uranium district east of the lineament. 

The lineament directly overlies a major downwarp axis 

defined from subsurface data (E. S. Santos, written commun., 

1976). We offer the hypothesis that a structural sag 

impeded the flow of uranium-bearing solutions and promoted 

major uranium deposition just east of the structure.

Hodson, W. 6., Pearl, R. H., and Druse, S. A., 1973, Water 

resources of the Powder River Basin and adjacent "areas, 

northeastern Wyoming: U.S. Geol. Survey Hydrol. Inv. 

Atlas HA-465.

Langen, R. E., and Kidwell, A. L., 1973, Geology and geochemistry of the Highland uranium deposit, Converse 

County, Wyoming: Wyoming Geol. Assoc. Earth Sci. 

Bull., v. 6, no. 4, p. 41-48.

Sharp, W. N., and Gibbons, A. B., 1964, Geology and uranium 

deposits of the southern part of the Powder River 

Basin, Wyoming: U.S. Geol. Survey Bull. 1147-D, 60 p.

CHARACTERIZATION OF FINE-GRAINED BLACK URANIUM ORES 

BY TRANSMISSION ELECTRON MICROSCOPY

BY GORDON L. NORD, JR., U.S. GEOLOGICAL SURVEY, 

RESTON, VA.

Mineralogical and geochemical investigations of primary 

uranium minerals (uraninite and coffinite) and of the 

mechanisms by which these phases oxidize to the yellow 

uranyl minerals have been greatly hampered by the 

fine-grained nature of the primary crystalline phases and 

the black amorphous colloidal nature of the products of the 

early oxidation steps. The high resolution (^2 A) of the 

transmission electron microscope (TEM) provides an 

opportunity to study these phases directly (electron 

petrography). In addition, TEM with scanning capability 

(STEM) can obtain electron diffraction data and X-ray energy 

spectra from crystallites as small as 100 A.

This technique has been used to study black organic 

material containing fine-grained coffinite (U(Si04) lx (OH)^x )

from the La Sal no. 2 mine, Mesa County, Colo. (the type 

locality, Stieff and others, 1956). The coffinite-bearing 

material was made into a 20-um-thick doubly polished thin 

section. Part of the thin section was further thinned to 

electron transparency ( 1 vn) by argon ion milling. Another 

part was used by H. T. Evans, U.S. Geological Survey, for 

determining the lattice constants of tetragonal coffinite (a 

= 6.938(1) A, c = 6.291(2) A) with a focusing Guinier powder 

camera) (fluorite standard). Figure la is a scanning 

electron micrograph of the thin-section surface showing the 

coffinite (light) as elongated grains (1-2 um wide, 10-15 pm 

long) filling collapsed plant-cell cavities in a 

carbonaceous matrix (dark). At higher magnification in the 

transmission electron microscope (fig. Ib), these grains

29
Figure 1. Electron micrographs of coffinite-bearing material, 

a, SEM image; b, transmission electron micrograph; 

c and d, bright- and dark-field images, respectively, 

of same area; e, dark-field micrograph showing the (TOO) 

faces of another grain; f, typical spectra from the SEM 

(Si(K } and U(L and M) peaks. The spectra in g-i were

obtained on a JEM 100C STEM. The electron beam size used 

for analysis is V100 A in diameter; therefore, a 

single crystal can be analyzed, g, from a coffinite 

single crystal; Cu peaks are from the sample holder, h, 

from an area high in uraninite; and i, from the carbonaceous 

matrix.
appeared as aggregates consisting of individual crystals 

ranging from 30 to 500 nm in size embedded in the more 

transparent carbonaceous matrix. The coffinite crystals 

were rounded, rather wheat-shaped, and elongated parallel to 

[001], and some had developed prism faces.

Figures Ic and Id are bright-field and dark-field 

electron micrographs, respectively, of an irregularly shaped 

single crystal of coffinite. Covering the surfaces of the 

coffinite grains were 5- to 15-nm particles which produced 

diffraction rings in the selected area electron diffraction 

(SAED) pattern (fig. Id, inset) overprinting the 

single-crystal diffraction spots of the coffinite grain. To 

obtain the dark-field micrograph in figure Id, the electron 

beam was tilted, allowing only the first and most intense 

diffraction ring of the particles to contribute to the 

image; no single-crystal spots were allowed. The dark-field 

image therefore shows intensity only from the particles; the 

coffinite phase is dark. These particles were found 

covering all the coffinite grains observed, and were 

determined to be cubic and to have a unit cell edge of a = 

5.46 A (the cell edge was determined using both the 

coffinite and evaporated gold as a standard), which is 

consistent with an unoxidized uraninite.

The single-crystal patterns from coffinite are 

consistent with its tetragonal symmetry. Figure le shows a 

squarish grain with the c-axis parallel to the electron 

beam. The inset SAED pattern shows the intense 200 and 020 

diffraction net in a square pattern. Note that the spots 

are broadened in an arc, which indicates the coffinite 

lattice is severely strained, perhaps becoming metamict.

Electron microprobe and qualitative X-ray 

energy-dispersive analyses in SEM (fig. If) and in a JEM 

100C STEM (fig. Ig) all show the presence of only U and Si 

in the coffinite. In particular the elements Ca, Th, and Pb 

were found to be below detectability (^0.1 weight percent)

in the electron microprobe. Spectra taken in the part of 

the grain with the most abundant particle phase (uraninite) 

show a significantly smaller Si peak (fig. Ih). Figure li 

is a spectrum taken from the carbonaceous matrix; no 

crystalline material was nearby. Peaks indicating the 

presence of Na, S, and Si are strong; a U peak much smaller 

than the Si peak is also present. It should be reemphasized 

that no microcrystalline phase (>2-5 nm), such as quartz, 

was detected in the carbonaceous matrix. Nor was quartz 

detected with the coffinite by electron diffraction.

The small uraninite particles are interpreted as 

reaction products from the breakdown of coffinite; the 

silica exists as an amorphous phase associated with the 

coffinite and the matrix. Brodin and Sidorenko (1974) found 

similar particles of uraninite derived from coffinite which 

were more highly oxidized (aQ = 5.37 A) than the uraninite 

in this study (aQ = 5.46 A). They interpreted the uraninite 

as a reaction product formed during the transformation of 

coffinite to a metamict state. A thermal spike is probably 

the driving force for this reaction. Alternatively, the 

breakdown of coffinite to fine-grained uraninite plus silica 

may be a necessary step in the sequence by which coffinite 

oxidizes to the yellow uranyl minerals, reflecting the 

inability of the coffinite structure to accept the smaller 

hexavalent uranium atom and its charge-compensating defect.

Brodin, B. V., and Sidorenko, G. A., 1974, Radiogennye pseudomorfozy 

po koffinitu [Radiogenic pseudomorphs after coffinite]: 

Vses. Mineralog. Obshch Zapiski, v. 103, no. 4, p. 470-475.

Stieff, L. R., Stern, T. W., and Sherwood, A. M., 1956,

Coffinite, a uranous silicate with hydroxyl substitution 

a new mineral: Am. Mineralogist, v. 41, nos. 9-10, 

p. 675-688.

31
EXAMPLES OF URANIUM DISTRIBUTION GRAPHICS IN GEOLOGIC ROCK

SPECIMENS ILLUSTRATED WITH THE RADIOLUXOGRAPH,

INDUCED FISSION TRACKS, AND OTHER TRACKS METHODS

BY J, R, DOOLEY, JR., C, N, CONWELL, PIETER BERENDSEN, 

J, K, OTTON, C, T, PIERSON, W, D, HOISINGTON,

D, A, LlNDSEY, AND J, N, ROSHOLT,

U,S, GEOLOGICAL SURVEY, DENVER, COLO.

Exploration for uranium and thorium has renewed 

Interest in rapid and specific methods for locating and 

Identifying the distribution of these elements In geologic 

materials. Fast photographic film along with the 

amplification provided by the Radloluxograph (Dooley, 1958; 

1972) can provide autoradlographs which graphically 

illustrate the distribution of the uranium-series and 

thorium-series Isotopes from sections of geologic specimens 

in a relatively short time. Radioluxographs of ore-grade 

material with as little as 1,000 ppm uranium can be made in 

a few minutes to a few hours. Detection of sub-ore-grade 

material containing as little as 10 ppm uranium and thorium 

can generally be made with the Radloluxograph in several 

days, but homogeneous distributions require somewhat longer 

autoradiographlc exposure times. This method is best suited 

for a quick and Inexpensive reconnaissance view of the 

uranium and thorium distribution on a "macro" scale.

Induced fission from a nuclear reactor or other 

high-flux source of neutrons can specifically detect uranium 

and, to a lesser extent, thorium from the fission tracks 

produced upon Lexan, mica, and other solid-state particle 

detectors (Fleischer and Price, 1963; Fleischer and others, 

1965; 1975). After being properly developed by chemical 

etching the detector serves as a fission-track map which can 

be viewed under the microscope and compared with the 

specimen which produced the tracks. Samples that are 

over-irradiated produce a high concentration of tracks which 

is visible to the unaided eye, and Is somewhat similar to an 

autoradlographic Image. Most reactors can only accommodate 

sample sections less than 2.5 cm in diameter and are 

generally used to study low uranium concentrations because 

of the reactor's capacity to produce high neutron fluxes. 

Alpha decay from the naturally occurring radlolsotopes and 

other Induced nuclear reactions can be recorded on cellulose 

nitrate and used for "micro" autoradlography If exposure to 

light and other photographic effects can be avoided. 

Microscopic examination of alpha-particle tracks on these

State of Alaska, Department of Natural Resources 

College Alaska. 

2 Kansas Geological Survey, Lawrence, Kansas.

Dartmouth College, Hanover, New Hampshire.

detectors and In nuclear photographic emulsions (Yagoda, 

1949) are almost always required and give better resolution 

than other "macro" methods of autoradlography.

Radioluxographs were made of sawed rock sections and 

drill cores. Polished sections and uncovered thin sections 

can be used with Induced fission tracks and other alpha 

track methods as well as with the Radloluxograph. 

Homogeneous distribution of 3 ppm uranium and 11 ppm thorium 

was found In a tektite with a Radioluxograph. 

Nonhomogeneous distributions of uranium and thorium are 

categorized into single accessory minerals; aggregates; 

concentrations along bedding, vein or fracture fillings; and 

mineral zoning localizations. High levels of single grain 

radioactivity dispersed within lower levels of homogeneous 

or nonhomogeneous radioactivity are best demonstrated with 

two autoradlographs of different exposure lengths. 

Semiquantitative determination of uranium can be made from 

comparing successive autoradiograph exposures of different 

time lengths or different neutron flux intensities and 

quantitative determinations can be made from track counting.

Dooley, J. R., Jr., 1958, The radioluxograph a fast, simple 

type of autoradiograph: United Nations Internet. Conf. 

Peaceful Uses Atomic Energy, 2d, v. 3, Paper 1762, p. 

550-553.

___1972, The high-speed radioluxograph with single-scintillation sensitivity for autoradlography of geologic 

samples [abs.]: Internet. Conf. Nuclear Photography 

and Solid State Track Detectors, 8th, Proc., v. II, 

p. 453, Bucharest, Romania.

Fleischer, R. L., and Price, P. B., 1963, Tracks of charged 

particles in high polymers: Science, v. 140, 

no. 3572, p. 1221-1222.

Fleischer, R. L., Price, P. B., and Walker, R. M., 1965,

Tracks of charged particles in solids: Science, v. 149, 

no. 3682, p. 383-393.

___1975, Nuclear tracks In solids: Univ. Calif. Press, 

605 p.

Yagoda, Herman, 1949, Radioactive measurements with nuclear 

emulsions: New York, John Wiley and Sons, Inc., 356 p.

32
SPECULATION ON THREE POSSIBLE MODES OF EMPLACEMENT OF

URANIUM INTO DEPOSITS OF THE MIDNITE MINE,

STEVENS COUNTY, WASHINGTON

BY J, THOMAS NASH, U,S, GEOLOGICAL SURVEY, 

DENVER, COLO,

Oxidized and reduced uranium minerals that make up the 

Midnite uranium deposits are localized in metapelite and 

metacarbonate rocks of the Precambrlan Y Togo Formation 

adjacent to a Cretaceous(?) porphyrltic quartz monzonite 

pluton (Becraft and Weis, 1963; Nash and Lehrman, 1975). 

The present distribution of uranium minerals 1s Interpreted 

to represent destruction and redistribution of earlier 

formed mineralized zones. Description of original (primary) 

uranium minerals and interpretation of their genesis 1s 

hampered by overprinting of later features and by a simple 

and nonspecific paragenesis that seems to have been repeated 

at several times. At least three modes of uranium 

emplacement, or combinations of them, seem possible.

One possibility Is penesyngenetlc accumulation of 

uranium in carbonaceous mud of the Togo Formation about 1300 

m.y. ago. As a result of mapping and relnterpretation of 

the stratigraphy of the mine area 1t now appears that the 

Togo was deposited 1n a marine shelf environment as a 

sequence of impure carbonate sediments overlain by 

carbonaceous mud and sand. The lower metacarbonate rocks of 

the Togo, about 1,100 m of chiefly diopslde hornfels and 

marble, are probably equivalent to the lower part of the 

Wallace Formation of the Belt Supergroup exposed about 180 

km to the east. Apparently overlying the metacarbonate 

rocks is a sequence of graphitic metapelite about 1,000 m 

thick that contains 1-3 percent Iron su(fides; the uranium 

deposits are 1n these rocks. This sedimentary sequence is 

similar to that of the Alligator Rivers region, Australia, 

described by Dodson and others (1974). The proposed 

syngenetlc uranium enrichment during lower Paleozoic 

sedimentation. If uranium accumulated in carbonaceous mud 

of the Togo Formation along with pyrite, it would later have 

been mobilized during two periods of metamorphism and have 

migrated toward the pTuton. This sequence of events should 

have left a record of anomalous uranium concentrations in 

equivalent strata outside of the mine area, and to my 

knowledge none has been observed. Moreover, petrologlc 

features of the pluton suggest that it crystallized at high 

water pressure and released water into its wall rocks; I 

consider it unlikely that uranium could have migrated In the 

opposite direction.

A second possibility, which I favor, is hydrothermal 

emplacement of uranium by postmagmatic fluids evolved from 

the porphyrltic quartz monzonite. Age and petrologlc data 

support this hypothesis. Age determinations on plutonic

rocks and a sample of pitchblende are approximately the 

same, about 100 m.y. (Becraft and Weis, 1963). The pluton 

is two-mica granite, has porphyrltic texture, and contains 

zones of pegmatite and aplite features Interpreted to 

Indicate crystallization at relatively high water pressure 

and release of water after saturation. Also, fission-track 

maps of thin sections Indicate that about 80 percent of the 

uranium in the pluton 1s associated with magnetite and very 

little is contained in refractory minerals such as zircon. 

On the basis of these observations I suggest the following 

sequence of events: during emplacement the magma became 

saturated with an aqueous phase, and this fluid was released 

along certain zones, some of which may have been established 

by preintruslon faults. The hydrothermal fluid possibly 

leached uranium from previously crystallized magnetite in 

the pluton and transported 1t into the contact aureole to 

create a zone of very low grade (O.OX percent) disseminated 

uranium mineralization. This process operated by diffusion, 

hence did not produce veins, and had a chemistry (low 

chlorine and sulfur) that precluded hydrogen metasomatic 

alteration typical of base-metal sulfide deposits. 

Subsequently, the low-grade protore was enriched to ore 

grade during middle to late Tertiary leaching and 

redistribution (Nash and Lehrman, 1975; Nash, 1975).

The third possibility, supergene emplacement, could 

have started in about the Oligocene, by which time the 

pluton had been exhumed. There 1s evidence for leaching of 

uranium in present-day weathering profiles 1n the pluton. 

Although freshest samples of the porphyritic quartz 

monzonite today contain about 16 ppm uranium (probably a 

minimum estimate of original content), a limiting parameter 

appears to be the amount of the pluton in a position 

suitable for leaching and ground-water transport Into the 

deposits. I estimate that only 0.2 to 0.3 km3 of the pluton 

could have been in the proper hydrologlc position, and this 

volume of rock probably could not provide enough uranium 

unless there was extremely favorable conditions for 

leaching, transport, and deposition. However, the supergene 

process may have added uranium to rocks previously 

mineralized by Cretaceous metasomatism.

Becraft, G. E., and Weis, P. L., 1963, Geology and mineral

deposits of the Turtle Lake quadrangle, Washington: U.S. 

Geol. Survey Bull. 1131, 73 p.

33
Dodson, R. G., Needham, R. S., Wilkes, P. G., Page, R. W., 

Smart, P. G., and Watchman, A. L., 1974, Uranium mineralization in the Rum Jungle-Alligator Rivers Province, 

Northern Territory, Australia, l£ Formation of uranium 

ore Territory, Internet. Atomic Energy Agency Proc. Ser., 

no. STI/PUB/374, p. 551-568.

Nash, J. T., 1975, Secondary enrichment of uranium at the

Midnite mine, Washington, TH Craig, L. C., Brooks, R. A., 

and Patton, P. C., eds., Abstracts for the 1975 Uranium 

and Thorium Research and Resources Conference: U.S. 

Geol. Survey Open-File Rept. 75-595, p. 32. 

Nash, J. T., and Lehrman, N. J., 1975, Geology of the Midnite 

uranium mine, Stevens County, Washington a preliminary 

report: U.S. Geol. Survey Open-File Rept. 75-402, 36 p.

CONCEPTUAL-MATHEMATICAL MODELS OF URANIUM ORE 

FORMATION IN SANDSTONE-TYPE DEPOSITS

BY JOEL S, LEVENTHAL AND HARRY C. GRANGER 

U.S. GEOLOGICAL SURVEY, DENVER, COLO,

Relatively simple calculations allow estimates to be 

made of the time required to produce a sandstone-type ore 

deposit of a given size using reasonable assumptions for the 

removal of uranium from igneous source rocks, for uranium 

content of ground water, ground-water flow rate, uranium 

entrapment efficiency, and host-rock porosity and density.

Mass balance calculations indicate that removal of half 

the uranium from a relatively small volume of source rock 

(7.7xl05 m3 ) having a specific gravity of 2.6 and originally 

containing 10 ppm uranium would yield 10 metric tons of 

uranium approximately equal to a deposit that contains 

26,000 pounds UgOg. This amount is equivalent to that 

obtainable by weathering and leaching a 300 m x 300 m area 

of granite to a depth of 8.5 m or a 3 km x 3 km area of 

volcanic ash about 8.5 cm thick. The time required to 

remove uranium from such source rocks depends, in part, on 

their porosity and permeability which, in turn, are related 

to either the grain size of the ash or the degree of 

fracturing of granite, and, of course, the solubility of the 

uranium. The amount of weathering and rainfall and the 

infiltration of meteoric water into the ground-water system

n

also need to be considered. It can be calculated that 10 

m of water containing 10 ppb uranium are needed to form a 

deposit that contains 10 metric tons of uranium. If the 

rainfall is 25 cm/yr, this amount of water would fall on the 

granite noted above in about 44,000 years and the ash in 440 

years. These are minimum estimates because the uranium may 

not be removed in this time, and it is unlikely that all the 

rainwater would enter the ground-water system. If only 10

percent of the rainwater infiltrated the rock, the above 

time periods would be increased by a factor of 10.

Using several reasonable assumptions, a calculation can 

be made of the time required to form a roll-type deposit 

that averages 5 m wide across the roll front and which 

contains 10 metric tons of uranium. If this deposit 

averages 0.25 percent uranium, it contains about 4,000 

metric tons of ore, and if this ore has a specific gravity 

of 2, it has a volume of about 2,000 m3 . The 109 m3 of 

ore-bearing solution needed to supply 10 metric tons of 

uranium, assuming a uranium content of 10 ppb and 100 

percent precipitation, is about 500,000 times the volume of 

the ore deposit.

The ore formed as the solution flowed through the 

5-m-wide orebody. If the hydraulic gradient is 9.4 m/km and 

the host rock is a medium-grained sandstone having a

permeability of 2 darcys, then the bulk water flow is 5.3

3 m/yr. That is about 5.3 m of water flowing through a

2 cross-sectional area of 1 m in a year. This means that

each year a volume of water about equal to the volume of ore 

percolates through the roll, and that it will take about 

500,000 years to form the assumed 0.25 percent uranium 

orebody. If the ore solution were richer and contained as 

much as 50 ppb uranium, it then would take only about 

100,000 years to form the same orebody.

A series of nomograms can be constructed in which known 

data can be used to determine variables and scientists can 

make their own estimates of the variables.

34
GEOLOGY OF URANIFERGUS TERTIARY ROCKS IN THE ARTILLERY 

PEAK-DATE CREEK BASIN, WEST-CENTRAL ARIZONA.

BY JAMES K. OTTON, U,S, GEOLOGICAL SURVEY, 

DENVER, COLO.

Uranium occurs In Tertiary rocks of the Artillery 

Peak-Date Creek basin 150 km northwest of Phoenix, Arizona. 

Although the original size and shape of the basin is unknown, 

it presently underlies an area 30 km wide that extends 80 km 

from the southern end of the McCracken Mountains southeast of 

an area of low hills near the intersection of U.S. Highway 93 

and State Highway 71 (fig. 1).

20 KILOMETERS

Figure 1. Index and generalized geologic map of the Artillery 

Peak-Date Creek basin area. Pattern, outline of present 

basin; light stipple, Tertiary to Holocene basin fill; 

dark stipple, Precambrian and Mesozoic basement rocks.

Lasky and Webber (1944, 1949) first mapped and described 

Tertiary rocks in the Artillery Mountains manganese district 

in the western part of the basin. More recently, Shackelford 

(1976), J. S. Gassaway (written .commun., 1972, 1976), I. 

Lucchita (oral commun., 1976) and the author have studied the 

rocks of the basin and adjacent areas.

The Tertiary rocks within the basin consist of Eocene(?) 

sedimentary and intermediate to mafic volcanic rocks 

belonging to the Artillery Formation named by Lasky and 

Webber (1944) who had assigned an Eocene(?) age to it and its 

probable lateral equivalents; lower Miocene silicic volcanic 

and tuffaceous sedimentary rocks; upper lower to middle 

Miocene(?) mafic to intermediate volcanic rocks, coarse 

clastic sedimentary rocks and tectonic breccias belonging to 

the Chapin Wash Formation named by Lasky and Webber (1944)

who assigned a Pliocene(?) age to it; upper Miocene(?) 

basalt; and upper Miocene(?) to Holocene sedimentary rocks. 

Facies relations within these units are complex, 

unconformities are common, and no unit can be traced 

continuously throughout the basin.

The Eocene(?) rocks of the basin are best exposed at the 

northwestern end and along the northeastern margin of the 

basin. The rest of the basin is largely covered by the 

Holocene sedimentary rocks. The maximum thickness ot the 

Tertiary section is about 2,500 m near the confluence of the 

Big Sandy River and the Santa Maria River (J. S. Gassaway, 

written commun., 1977). One drill hole 8 km south of the 

Anderson mine encountered 1,700 m of Tertiary sedimentary and 

volcanic rocks.

The rocks of the basin are generally tilted to the south 

or southwest and have been cut by normal faults. The 

predominant faults have a northwesterly trend, although 

east-west and northeast-trending faults have also been 

observed. Movement on the northwest-trend ing faults seems to 

have been recurrent throughout most of the history of the 

basin. Greatest offsets occur in the upper part of the 

Artillery Formation of the eastern part of the basin. 

Offsets are progressively smaller in younger rocks. 

Low-angle normal (?) faulting, interpreted as gravity glide 

faulting with a probable source in the Rawhide Mountains 

(Shackelford, 1976), has occurred at least once in the 

western part of the basin during deposition of the Chapin 

Wash Formation and may also have occurred during deposition 

of the upper part of the Artillery Formation. The 

sedimentary rocks of the basin have also been gently folded 

periodically.

A thin sheet of arkose and arkosic conglomerate of 

Eocene(?) age was the first Tertiary sediment deposited in 

the basin. This arkose is the lowermost unit of the 

Artillery Formation, and is generally well preserved in the 

western part of the basin but in the eastern part it is 

exposed only in isolated patches unconformably overlain by 

younger rocks. At the type locality in the Artillery 

Mountains in the western part of the basin, the Artillery 

consists of fine-grained calcareous sandstone and siltstone, 

successively overlain by volcanic pebble conglomerate, 

limestone, metavolcanic breccia, and limestone and basalt. 

Although exposures are not continuous to the east, the 

calcareous siltstone and limestone of the Artillery appear to 

intertongue with sandstone which, in turn, intertongues with 

andesitic(?) flows and agglomerates and other volcanic rocks.

35
An age of 43.3 m.y. has been obtained for the basalt 1n the 

upper part of the formation near Artillery Peak (J. S. 

Gassaway, written conunun., 1976).

Unconformably overlying the Artillery Formation are 

unnamed lower Miocene rocks. At the far western end of the 

basin these are silicic volcanics which have been dated at 

17.1 m.y. (J. S. Gassaway, written commun., 1977). In the 

vicinity of Artillery Peak, the lower Miocene unit consists 

of tuffs interbedded with sandstone. Throughout its western 

exposures the unit is thin. North of the mouth of Date Creek 

and east of the Big Sandy River, the tuffs and relatively 

fine-grained fluvial rocks grade into a thick section of gray 

calcareous boulder to sandy conglomerate and tan sandy 

conglomerate and sandstone which, in turn, grades into a 

red-brown Fe- and Mn-rich sandy conglomerate and sandstone 

near Palmerita Ranch. East of Palmerita Ranch these rocks 

intertongue with tuffaceous mudstones and siltstones and 

other rocks which form the mineralized unit at the Anderson 

Mine.

Overlying this lower Miocene unit is the Chapin Wash 

Formation. West of the Big Sandy River, the formation 

consists of basalt, conglomerate, a massive megabreccia and 

manganiferous conglomerate and sandstone. The base of the 

Chapin Wash appears to have been intruded by andesitic bodies 

near the confluence of the Big Sandy and Santa Maria Rivers. 

East of the Big Sandy River, the megabreccia and 

manganiferous clastic facies are absent. The basalt at or 

near the base of the formation has been dated at 15.9 m.y. 

(J. S. Gassaway, written commun., 1976).

The younger basin-fill rocks overlying these three units 

include an upper Miocene(?) basalt that locally caps a few 

mesas in the western end of the basin; upper Miocene(?) to 

Holocene fanglomerate that is several hundred feet thick in 

the central and southeastern part of the basin, but 

apparently has been largely removed by erosion in the western 

part of the basin; and Holocene alluvium.

At the Anderson Mine in the eastern part of the basin, 

uranium occurs in silicified, tuffaceous, locally 

carbonaceous lacustrine mudstones, calcareous mudstones, and 

siltstones. These lacustrine and overlying fluvial rocks 

compose a unit that ranges in thickness from 60 to 120 m in 

surface exposures, and thickens considerably downdip to the

south in the subsurface. This unit is here correlated with 

the unnamed lower Miocene silicic volcanic and tuffaceous 

sedimentary rocks in the western part of the basin.

Fossil plant material, consisting of thin beds of 

lignitic(?) material and silicified twigs, leaves, and roots, 

is abundant. Uranium occurs principally in thinly bedded 

siltstones rich in carbonaceous or silicified plant material. 

In many places these siltstones are highly stained by Fe- and 

Mn-oxides. Carnotite is the only uranium mineral yet 

recognized, and is probably secondary. The primary uranium 

phase has yet to be identified: in the mineralized 

carbonaceous rock it may be a urano-organic complex; and in 

the silicified rock it may be a urano-silica or urano-iron 

hydroxide complex.

Interbedded with the mineralized tuffaceous siltstones 

are unmineralized, thickly bedded, greenish-gray tuffaceous 

mudstones, white to light-gray tuffaceous calcareous 

mudstones with abundant calcareous microfossils, and sparse 

sandstone and siltstone. A thin conglomerate is observed 

locally at the base. The overlying fluvial rocks consist of 

upward coarsening gray to greenish-gray sandstones and sandy 

conglomerates. Virtually the entire unnamed lower Miocene 

unit is rich in tuffaceous material and is anomalous in 

uranium content.

Approximately 2 km west of Artillery Peak, uranium 

occurs in carbonaceous, calcareous siltstones and 

fine-grained sandstones immediately overlying the basal 

arkose of the Artillery Formation. The arkose overlies 

basement rocks which are rich in uranium and thorium in the 

Artillery Peak area.

Lasky, S. G., and Webber, B. N., 1944, Manganese deposits in 

the Artillery Mountains region, Mohave County, Arizona: 

U.S. Geol. Survey Bull. 936-R, p. 417-448.

___1949, Manganese resources of the Artillery Mountains 

region, Mohave County, Arizona: U.S. Geol. Survey Bull. 

961, 86 p.

Shackelford, T. J., 1976, Structural geology of the Rawhide 

Mountains, Mohave County, Arizona: Univ. Southern Calif. 

Ph.D. thesis, 176 p.

36
URANIUM ASSOCIATED WITH IRON-TITANIUM OXIDE MINERALS

AND THEIR ALTERATION PRODUCTS IN A SOUTH TEXAS

ROLL-TYPE DEPOSIT

BY RICHARD L, REYNOLDS, MARTIN B, GOLDHABER,

AND RICHARD I. GRAUCH, 

U.S. GEOLOGICAL SURVEY, DENVER, COLO,

Electron mlcroprobe and petrographlc studies have been 

conducted on a suite of ore-bearing samples from a roll-type 

uranium deposit 1n south Texas. Each sample from the nose 

and lower 11mb of the roll was separated Into size fractions 

less than and greater than 44 m, and each size fraction was 

further subdivided by bromoform density separation Into 

heavy and light mineral groups. Uranium In the light* 

fine-grained fraction appears to be predominantly associated 

with silicon, calcium, potassium, and aluminum. Uranium 1n 

the heavy fractions occurs primarily with titanium and Iron, 

and to a lesser extent with sulfur, calcium, and silicon. 

Uranium was frequently observed 1n association with a T10« 

phase that originates largely, 1f not exclusively, from the 

alteration of 1ron-t1tan1um (Fe-T1) oxide minerals. It Is 

possible that some uranium occurs as a silicate 

(coffinite?).

The T102 phase In the ore-bearing zones originated 

primarily by expulsion of T1 during the replacement of 

detrltal Fe-TI oxides (tltanomagnetlte and tltanohematlte) 

by Iron sulflde (FeS2 ) minerals (fig. 1). Uranium occurs In

association with T102 on the margins of relict Fe-TI oxide 

grains 1n various stages of conversion .to FeS? . Where 

replacement 1s complete, uranium-bearing T1CL surrounds the

Figure 1.--Tltanohematlte (light gray) replaced by pyHte (white) 

along grain margins and fractures within grain. T102 

(hazy, white phase) forms partial r1m around Iron 

sulflde. Grain from reduced rock remote from ore. Length 

of field 1s 158 m. Grain viewed 1n oil under reflected 

light.

Figure 2. Pyrlte (bright white) partly surrounded by T102 

(hazy, white). Grain from mineralized rock at nose of 

uranium roll. Long dimension of grain Is 29 m. 

(b) X-ray Image of sulfur distribution of grain shown 

In a. Fe distribution (not shown) Is Identical. Note 

that X-ray map Is mirror Image of photomicrograph In this 

as 1n following diagrams, (c) X-ray Image of titanium 

distribution. Corresponds to T102 phase shown In a. 

(d) X-ray Image of uranium distribution showing that the 

majority of uranium 1s coextensive with titanium.

37
sulfides (fig. 2). Uranium occurs not only in authlgenic 

TiOg surrounding altered Fe-Ti oxides, but also in TiOp, 

within the altered grains. Figure 3 illustrates a 

uraniferous TiOp phase that formed by the alteration of a 

detrital titanomagnetite. That this grain was originally 

titanomagnetite is indicated by ghosts of ilmenite lamellae 

along (111) crystallographic planes. Silicon in this grain

Figure 4. Ti(L (a) with small iron sulflde grain (white) at 

margin in lower right. .Note zonation (light-gray rim 

partly surrounding darker gray interior) within Ti02 - 

Long dimension of grain is 72 m. X-ray images show 

distribution of titanium (b), uranium (c), silicon (d), 

iron (e), and calcium (f). Note that light-gray rim is 

enriched in silicon and iron, whereas uranium is evenly 

distributed throughout the grain. (Uranium X-ray image 

(c) is shifted to right.)

Figure 3.~T102 (white areas in a) produced by alteration of 

titanomagnetite, with ghost ilmenite lamellae (dark gray) 

in trellis pattern. Long dimension of grain is 33 m) 

X-ray Images show distribution of titanium (b), uranium 

(c), and silicon (d).

Figure 5. Alteration of detrital titanohematlte in mineralized 

rock. Mottled light-gray and black phases consist of 

abundant titanium, iron, and sulfur with minor uranium, 

is relict of the original detrital grain. Iron sulfide 

(white) occurs on margin of grain by replacement and 

overgrowth and along fractures within grain. Length of 

field is 390 m.

38
is largely coextensive with uranium, which indicates the 

possible presence of a uranium silicate. Silicon and 

uranium also occur together along part of the margin of the 

Ti02 grain in figure 4. The interior of this grain, 

however, contains significant uranium but is much lower in 

silicon.

Alteration of Fe-Ti oxide minerals has not led in every 

case to the segregation of TiOo into a discrete phase. In 

some titanomagnetite and titanohematite grains in 

mineralized rock, we have observed other alteration phases 

(fig. 5), petrographically distinct from Ti02 , that contain 

abundant titanium, iron, and sulfur together with lesser 

amounts of uranium, silicon, and calcium.

Previous studies have established the association of 

uranium with titanium in hydrothermal vein and Precambrian 

quartz- pebble conglomerate uranium deposits (Fern's and 

Ruud, 1971; Roscoe, 1969). Our results demonstrate the 

affinity of uranium for titanium-bearing alteration products 

of Fe-Ti oxide minerals in a south Texas roll-type deposit.

Ferris, C. S., and Ruud, C. 0., 1971, Brannerite~its occurrences

and recognition by microprobe: Colorado School Mines

Quart., v. 66, no. 4, p. 1-85. 

Roscoe, S. M., 1969, Huronian rocks and uraniferous conglomerates

in the Canadian Shield: Canada Geol. Survey Paper 68-40,

205 p.

URANIUM-LEAD APPARENT AGES OF URANIFEROUS SECONDARY 

SILICA AS A GUIDE FOR DESCRIBING URANIUM MOBILITY

BY R, A, ZIELINSKI, K, R, LUDWIG, AND D, A. LINDSEY 

U,S, GEOLOGICAL SURVEY, DENVER, COLO,

The two case studies presented below illustrate the use 

of U-Pb isotope systematics to investigate the timing of 

migration of uraniferous silica saturated solutions. It is 

assumed that time of uranium mobilization is reflected in 

the U-Pb apparent ages of secondarily precipitated, 

uraniferous, cryptocrystalline silica. Apparent ages of 

secondary silica may be compared with ages of host rocks and 

nearby uranium deposits to further describe the timing of 

uranium migration in a particular area.

Case 1: Shirley Basin, Wyoming Chalcedony veinlets 

occur in silicified tuffaceous si Itstone and limestone beds 

near the base of the Oligocene White River Formation (NE 1/4 

sec. 21, T. 28 N., R. 79 W.). The veinlets are present as 

gray translucent fracture fillings less than 5 cm wide (fig. 

1A). The majority of veinlets closely parallel bedding 

although some small veinlets crosscut bedding at angles up 

to 90°. The silicified sequence of siltstone and limestone 

is as much as 14 m thick and represents a series of shallow 

lake sediments. This sequence covers an area of at least 

8x3 km in the central Shirley Basin (Harshman, 1972) and 

overlies major uranium deposits in Eocene sandstones. 

Fission-track maps of the veinlet selected for dating 

revealed a homogeneous distribution of uranium. Silica 

saturation of ground water probably resulted from the 

downward percolation of ground water through glassy tuff of 

the overlying White River Formation. Silica gel and uranium 

coprecipitated from solution to produce the uraniferous 

veinlets.

One of these veinlets was crushed, and inclusion-free 

material was hand picked from it and washed with water prior 

to analysis. Uranium and lead concentrations in this 

material, determined by isotope dilution, were 242 ppm and 

0.93 ppm, respectively. Apparent ages were slightly 

discordant: 18.8 0.3 m.y. for 206Pb/ 238U, and 20.1 0.8 m.y. 

for 207Pb/235U. The discordance results from either 

preferential loss of radioactive daughters of U or the 

presence of an unrecognized component of inherited 

Precambrian lead. The maximum possible age of the veinlets 

is that of the host rock (32.4 2.6 m.y. zircon fission-track 

age by C. W. Naeser). Radiometric ages as young as 24 3 

m.y. determined for nearby uranium deposits in the 

underlying sandstone (Ludwig, 1977) are compatible with the 

hypothesis that some uranium was derived from leaching of 

tuffs. Secondary silica and uranium ores which occur in the 

same host rock and are subjected to the same maximum age 

restrictions should provide tighter limits to the timing of 

uranium migration.

Case 2: Thomas Range. Utah Uraniferous opal veinlets 

1 cm wide occur in fractures in 38- to 39-m.y.-old 

rhyolitic ash-flow tuff at the Autunite No. 8 prospect (SW 

1/4 sec. 10, T. 13 S., R. 11 W.) in the Thomas Range. The 

veinlets may have been deposited by hydrothermal activity 

related to nearby beryllium, fluorspar, and uranium 

mineralization. Mineralization in the Thomas Range 

accompanied or followed topaz rhyelite volcanism that began 

21 m.y. ago and ended with extrusion of voluminous flows of

39
topaz rhyolite 6 to 7 m.y. ago (Lindsey, 1977). The areas 

of most intense mineralization occur in water-laid tuff 

associated with 21-m.y.-old rhyolite at Spor Mountain, but 

traces of mineralization are present in tuff interbedded 

with 6- to 7-m.y.-old rhyolites in the Thomas Range.

The opal veinlets in the Autunite No. 8 prospect were 

dated to obtain additional information concerning the age of 

mineralization and its relationship to volcanism in the 

Thomas Range. Fission-track maps (fig. 1BJ revealed U 

distribution to be very homogeneous within concentric growth 

zones (500-1,000 ppm U). The analyzed opal fragments 

contained 1,220 ppm uranium and 0.88 ppm lead, and gave 

nearly concordant apparent ages of 3.5 m.y. The results 

support the hypothesis that some, and possibly all, of the 

beryllium-fluorspar-uranium mineralization occurred after 

the eruption of voluminous topaz rhyolite 6-7 m.y. ago.

Harshman, E. N., 1972, Geology .and uranium deposits, Shirley 

Basin area, Wyoming: U.S. Geol. Survey Prof. Paper 745, 

82 p.

Lindsey, D. A., 1977, Epithermal beryllium deposits in waterlaid tuff, western Utah: Econ. Geology, v. 72, no. 2 

(in press).

Ludwig, K. R., 1977, Uranium daughter migration and U/Pb isotope 

apparent ages of uranium ores, Shirley Basin, Wyoming: 

Econ. Geology (in press).

Figure 1.--A, Cryptocrystalline silica veinlets in silicified 

tuffaceous siltstone, White River Formation, Shirley 

Basin, Wyoming. B., Fission-track image of the uranium 

distribution in uraniferous opal veinlets, Autunite No. 

8 prospect, Thomas Range, Utah. Area of view about 1 cm2

40
PRECAMBRIAN URANIUM ASSOCIATED WITH A METAMORPHOSED MASSIVE 

SULFIDE BODY-CAMP SMITH AREA, NEW YORK

BY RICHARD I, GRAUCH AND DAVID L, CAMPBELL 

U,S, GEOLOGICAL SURVEY, DENVER, COLO,

Precambrian uranlnlte is associated with a zoned massive 

sulfide body at the Phillips mine (Klemic and others, 1959) 

and, locally, in other zones along the contact between units 

of amphibolite gneiss and quartzo-feldspathic leucogneiss in 

the Camp Smith area, Putnam and Westchester Counties, New 

York.

The Camp Smith area is underlain by a complexly folded, 

interlayered sequence of metamorphosed (granulite facies) 

submarine volcanogenic, carbonate, pelitic rocks, and minor 

amounts of granitic and pegmatitic material. The three major 

rock units are amphibolite gneiss, quartz-feldspar-biotite 

leucogneiss, and quartz-feldspar-hornblende-(±biotite) 

leucogneiss. The amphibolite gneiss unit is variable in 

composition and appearance, ranging from massive dark-green 

amphibolite to banded hornblende-quartz-feldspar gneiss. 

Minor horizons of magnetite-rich amphibolite gneiss and 

scapolite-rich amphibolite gneiss are included in that unit. 

The biotite leucogneiss unit includes minor amounts of 

marble, graphitic calc-siHcate gneiss, graphitic metachert, 

biotite-garnet-quartz-feldspar gneiss, and 

amphibole-pyroxene-garnet-graphite skarn. Compositional 

variations within the hornblende leucogneiss are minor and 

are reflected by variations from 1:0 to 1:1 in the ratio of 

hornblende to biotite. All three of the major rock units 

host small amounts of quartz-feldspar pegmatite and 

hornblende-quartz-feldspar-(±pyroxene) pegmatite.

Uraninite is found in four different host rocks: 

magnetite-rich and scapolHe-rich layers in amphibolite 

gneiss; hornblende-pegmatite; and the outer, Cu-Ni-bear1ng 

zone of the massive sulfide body. Uraninite occurs in 

magnetite-rich layers as small euhedral to anhedral crystals, 

some of which are embayed by magnetite. In the 

scapolite-rich layers, uraninite occurs as minute inclusions 

in scapolite and hornblende. The magnetite- rich and 

scapolHe-rich layers appear to be near the contact between 

light and dark colored gneisses. Hornblende pegmatites, 

interpreted as being anatectic in origin, are most abundant 

near that contact. The pegmatites contain uraninite as 

anhedral inclusions in hornblende and apatite, and as large 

(up to 1 cm) euhedral crystals; uraninite unit cells range 

from 5.460 to 5.480 A. In the massive sulfide body uraninite 

is apparently restricted to the Cu-N1-bear1ng zone which in 

addition contains apatite, pyrrhotite, pyrite, chalcopyrite, 

marcosite, magnetite, and molybdenite. The core of the 

sulfide body 1s apparently massive pyrrhotite with little 1f 

any uraninite, pyrite, or chalcopyrite. The uraninite

occurrences mentioned above have two features in common: 

association of uraninite with apatite and proximity to the 

lithologic break between melanocratic and leucocratlc rocks. 

Minor concentrations of uranium are also found in small, 

presumably old, fractures near the Hthologic break.

The association of high uranium concentrations with the 

contact between melanocratic and leucocratlc rocks is also 

supported by geophysical work (manborne total field magnetic, 

E-mode VLF resistivity, and y-ray spectrometric surveys). 

Geophysical measurements were made at 20 m intervals on lines 

40 m apart over an area of about 400 by 800 m. The resulting 

contoured geophysical maps show some details not readily 

relatable relatable to known surface geology. Zones of 

sulfide mineralization often show some combination of high 

magnetic values, low resistivity, and high eU content (only 

the results from the uranium channel, eU, of the Y-ray 

spectrometer are considered). Proceeding across strike from 

northwest to southeast, we note the following, generalized, 

geophysical characteristics (fig. 1).

(1) A zone of high resistivity, low magnetic, and low 

eU values that probably contains little mineralization. 

Locally, however, there are low resistivity subzones that may 

be sulfide- or graphite-bearing.

(2) A narrow zone of low resistivity, high eU, and high 

magnetic values, that correlates with a uranlferous 

hornblende pegmatite.

(3) A zone of moderate-to-high resistivity, and 

moderate eU content that seems to typify the hornblende 

leucogneiss unit. The magnetic field in this zone 1s 

apparently uniform but its relative magnitude has not been 

evaluated.

(4) A zone that shows high resistivity and large 

variations in eU and magnetic values.

The close spatial association of uraninite, magnetite, 

and sulfides suggests an exploration target that should be 

readily identifiable through manborne and airborne 

geophysical techniques. Indeed, the Phillips mine area has 

been mapped as a major aeroradioactlvHy anomaly (Popenoe, 

1966).

The massive sulfide body at the Phillips mine 1s 

apparently a strata-bound body located near the interface 

between mafic and felslc metavolcanogenic rocks. Some of the 

mafic and probably most of the felsic rocks were originally 

deposited as clastic sediments with variable amounts of 

pelitic and carbonate components. It is proposed that during 

deposition of the sediments some mechanism, possibly the

41
1000

CO

CO

E 

E

CO 

D)

CD

O

Q) 

C 

D) 

CO

E

CO 

O

E

E

c

100 O^

>> *- 

>

CO

0)

LL

c 'E

CVJ

0> 

Q.

c

=3 

O 

O

I

O

amphibolitic / / // /

gneiss/ / // leucogneiss,

/ / // /amphibolitic gneiss

biotitic leucogneiss.7 // /

anpNbditic gneiss '

horittende pegmatite

LINE 280S

Figure 1. Geological cross section and related geophysical expression of a portion of the Phillips mine area

(geology modified from Klemic and others, 1959).

precipitation of apatite, caused widespread but low-grade 

concentration of uranium. This mechanism was presumably 

operative during the waning stages of massive sulfide

formation and the beginning stage of magnetite deposition. 

During subsequent granulite facies metamorphism uraninite was 

formed. This hypothesis appears to explain the association

42
of uraninite with apatite and the proximity of 

uranium-bearing rocks to the contact between melanocratic and 

leucocratic units. Other uranium occurrences (Grauch and 

Zarinskl, 1976) in the Hudson and Jersey Highlands may be 

explained by this model and seem to offer excellent targets 

for future exploration.

Grauch, R. I., and Zarinski, Katrin, 1976, Generalized descriptions of uranium-bearing veins, pegmatites, and disseminations 1n non-sedimentary rocks, eastern United States: 

U.S. Geol. Survey Open-File Rept. 76-582, 114 p.

Klemic, Harry, Eric, J. H., HcNitt, J. R., and McKeown, F. A., 

1959, Uranium in Phillips mine-Camp Smith area, Putnam and 

Westchester Counties, New York: U.S. Geol. Survey Bull. 

1074-E, p. 165-199.

Popenoe, Peter, 1966, Aeroradioact1v1ty and generalized geologic 

maps of parts of New York, Connecticut, Rhode Island, and 

Massachusetts: U.S. Geol. Survey Geophys. Inv. Map GP-359.

THE DISTRIBUTION OF URANIUM IN SEDIMENT SAMPLES 

AS DETERMINED BY MULTI-ELEMENT ANALYSIS

BY JOHN D, TEWHEY

EARTH SCIENCES SECTION

LAWRENCE LIVERMORE LABORATORY

LIVERMORE, CALIFORNIA 94550

A number of sediment samples collected from the Walker 

River, Winnemucca and Smoke Creek Basins, Nevada, as part of 

a National Uranium Resource Evaluation (NURE) program 

orientation study, were selected for detailed analysis in 

order to determine the nature of the uranium distribution in 

sediments from a semiarid environment. The results of this 

study suggest that an estimate of the Teachable versus 

nonleachable uranium in samples studied can be made on the 

basis of certain geochemical Indicators that are obtainable 

by means of multielement instrumental neutron activation 

analysis (INAA).

Sediment samples were split into seven size fractions 

ranging from 63 m to 2000 m and each fraction was subjected 

to a 30-element INAA (including uranium) to determine its 

bulk chemical characteristics. Each split was then subjected 

to a heavy-liquid separation to facilitate optical 

mineralogical analysis. Light fractions ( 3.19 g/cm3 ) 

consisted primarily of quartz, feldspar and mica; heavy 

fractions ( 3.19 g/cm3 ) commonly consisted of sphene, zircon, 

magnetite, hematite, epidote, augite, and hornblende. The 

contribution that each mineral made towards the total uranium 

content of the split was determined by using the average 

abundance of uranium in the mineral as given by Rogers and 

Adams (1972), or by analyzing representative mineral 

fragments from one of the larger size fractions by INAA. In 

the latter case, the contribution from Teachable uranium was 

minimized by (1) keeping a small ratio of surface area to 

mass by choosing several large grains for analysis rather 

than many small ones, and (2) by washing the grains prior to 

analysis. For each size fraction, the difference between the 

total uranium in the sample and the sum of the contributions

of the individual minerals was considered to represent the 

Teachable uranium (fig. 1AJ. The amount of Teachable uranium 

in the various size fractions determined by the procedure 

described above correlates reasonably well with the amount 

determined by acid-leaching experiments. The absolute amount 

of Teachable uranium as analyzed by leaching experiments is 

always less than the amount calculated on the basis of INAA, 

but the relative amounts in the various size fractions and in 

different samples as determined by the two methods are 

correlative (fig. 1A_ and B).

Through analysis of the INAA data for eight samples, it 

has been found that the amount of Teachable uranium in 

samples from the area studied can be correlated with certain 

geochemical parameters, such as Th/U ratios and Zr and La 

values. Sediment samples containing heavy res 1 state minerals 

often exhibit moderately high uranium concentrations and 

concomitant Tow values of Teachable uranium. In general, 

heavy reslstate mineraTs are characterized by having high 

Th/U ratios (Adams and Weaver, T958). The resistates from 

the area studied are also characterized by moderately high 

concentrations of Zr and the rare earth elements. In figure 

2, weighted Zr-La values (ppm Zr + 10 ppm La) are plotted 

against the Th/U ratio of fine- and coarse-grained size 

fractions of eight sediment samples. An indication of the 

percentage of Teachable uranium with respect to the total 

uranium concentration, as determined by acid Teaching 

experiments, is given for each sample. Note that samples 

with high percentages of Teachable uranium (solid circles) 

tend to be characterized by Tow Th/U ratios and low Zr-La 

values, and those exhibiting low values of Teachable uranium 

(open circles) tend to have higher Th/U ratios and Zr-La

43
10 Results oflNAA 

aual"i$

leachable U I |

U in mica 

U in feldspar

U in quartz

U in augite'

U in sphene

U in zircon

10 Results off acid-leaching

experiments leachable U \ 1

non-leachable U

B

1000 2000 63

Grain size (microns)

ooo

Figure 1. (A) Distribution of uranium 1n various size fractions of sediment sample from Walker River Basin (238) as 

determined by INAA. (B) Distribution of Teachable versus non-leachable uranium 1n sediment sample (238) as 

determined by acid-leaching experiments.

Grain size < 150|i......

Grain size > ISOji .... .

* 5 percent teachable U. 

> 5 percent teachable U. 

ppm U in sample.........

30O

 20

so

30

50

40

50

ISO 

ISO

100

13O

5»

500

Zr + 10La (ppm)

1000 20N 22N

Figure 2. Plot of Th/U versus Zr + 10 La (ppra) for fine- (small circle) and coarse- (large circle) size fractions of eight

sediment samples from Western Nevada Basins.

44
values. It Is suggested that, the data derived from 

multielement INAA can be used to estimate the amount of 

Teachable uranium in a sample without having to conduct 

costly and time-consuming acid-leaching experiments.

Adams, J. A. S., and Weaver, C. E., 1958, Thorium-to-uranium 

ratios as indicators of sedimentary processes Example of

concept of geochemical fades: Am. Assoc. Petroleum 

Geologists Bull., v. 42, no. 2, p. 387-430.

Rogers, J. J. W., and Adams, J. A. S., 1972, Geochemistry of

uranium, ij^Wedepohl, K. H., ed., Handbook of Geochemistry,

v. I1-3: New York, Springer-Verlag, p. 92-D-l to 92-D-2.

URANIUM DEPOSITS RELATED TO DEPOSITION ENVIRONMENTS IN THE

MORRISON FORMATION (UPPER JURASSIC), HENRY MOUNTAINS

MINERAL BELT OF SOUTHERN UTAH

BY FRED PETERSON, U,S, GEOLOGICAL SURVEY, 

DENVER, COLO,

Analysis of the depositional framework of the Morrison 

Formation in south-central Utah (fig. 1) shows that the 

environments of deposition played a significant role in the 

formation of uranium deposits in the region. The lower 

member (Peterson, 1974) and Salt Wash Member of the Morrison 

comprise a series of fluvial and lacustrine beds that are 

divided into three fluviolacustrine sequences (fig. 1). The 

sequences are distinguished from each other in vertical 

sections by differences in facies, crossbedding dip vectors, 

and stratification ratios (planar crossbedding/planar 

crossbedding plus horizontal bedding). The thickness of the 

sequences in the mineral belt are: lower sequence, 55-90 m; 

middle sequence, 7-12 m; and upper sequence, 38-87 m.

The lateral distribution of facies within these 

sequences progressing away from a highland source region, 

down an alluvial plain, and into a lacustrine area is listed 

below and shown on figure 1 (time 1). Important exceptions 

to this distribution occur at or near the uranium deposits, 

where some of the facies are absent (fig. 1).

Facies A: Chiefly braided-stream deposits consisting 

of trough-crossbedded, planar-crossbedded, and flat-bedded, 

gray to brown conglomerate and conglomeratic or pebbly 

sandstone. Also contains red mudstone and siltstone 

deposited on flood plains adjacent to the streams.

Facies B; Predominantly meandering-stream deposits 

consisting of trough-crossbedded gray to brown sandstone and 

pebbly sandstone containing fining-upward cycles and lateral 

accretion (point bar) units. Includes red mudstone and 

siltstone deposited on flood plains flood plains adjacent to 

the streams.

Facies C: Marginal-lacustrine strata consisting of 

laminated or locally burrowed light-gray sandstone deposited 

at or near the shoreline of lakes where silt and clay were 

washed away by wave-generated currents.

Facies D: Nearshore-lacustrine red beds consisting of 

laminated and burrowed red mudstone, siltstone, and 

sandstone deposited in shallow nearshore waters of lakes. 

Composed of clay, silt, and very fine-grained sand carried 

in suspension and deposited near the shoreline of lakes that 

probably had fluctuating shorelines.

Facies E: Offshore-lacustrine beds consisting of 

dark-gray mudstone containing fine-grained carbonized plant 

debris. These beds consist of suspended-load sediments 

deposited in the offshore part of lakes where anaerobic 

conditions were present in the bottom sediments.

Regional studies indicate that the three sequences were 

deposited on an extensive alluvial plain or in a relatively 

small lacustrine area that developed in the Henry structural 

basin. Sedimentation was chiefly by braided streams that 

originated in highlands southwest and west of the Henry 

basin, although meandering streams locally formed on the 

distal end of the plain where the gradients were low. Lakes 

formed in a persistent depositional low that formed in the 

vicinity of the mineral belt whenever the rate of basin 

subsidence exceeded the rate of sedimentation by fluvial 

processes. Deposition of most of the fluvial and 

marginal-lacustrine sandstone beds probably was under 

oxidizing conditions, as suggested by the associated red 

beds and the general lack of carbonized plant debris. 

However, deposition occurred under reducing conditions in 

the offshore and deeper parts of the lakes where anaerobic 

processes dominated. The reducing conditions were 

responsible for preservation of carbonized plant debris 

incorporated in the bottom muds, and the fluids within the 

muds were the source of the reductant necessary for the 

ore-forming process.

The uranium deposits occur as discontinuous tabular 

bodies up to a meter thick and a hundred or more meters wide

45
Ii

O T3 -< O>

rt- o> c/i c/i

-fc 3 O

Z in c= o

0> -i.

cn -H IB

n > -> u>

.

i I 5

_ . Q. _,.

00

rt- -* -i.

_ :V'f-,?Si.;>>

?<^C^

11 11 ll

ill 

11II

ill I

lower fluviolacustrine sequence
within braided-stream and marginal-lacustrine sandstone beds 

that are 2-9 m thick. Scattered carbonized plant debris is 

present in the sandstone at or near the ore deposits but is 

not preserved elsewhere in the same bed. Near the uranium 

deposits, thin beds of offshore-lacustrine gray mudstone 

less than 2 m thick lie directly above, below, or lateral to 

the sandstone (fig. 1), and thin lenses of the gray mudstone 

are also present locally within the sandstone.

Proximity of the uranium deposits to 

offshore-lacustrine gray mudstone in the lower and middle 

fluviolacustrine sequences indicates that these mudstones 

played an important role in the mineralization, and this, as 

well as the association with braided-stream sandstones 

suggests a model for the mineralization that is related 

primarily to the depositional environments. The hypothesis 

presented here is that uranium was transported in solution 

by oxidized ground water that flowed down the depositional 

slope of an alluvial plain through sands deposited by 

fluvial processes. The uranium was precipitated at the 

distal end of the alluvial plain in braided-stream or 

marginal-lacustrine sands in places where braided streams 

emptied directly into lakes, and where meandering-stream 

sands (facies B) and nearshore-lacustrine red beds (facies 

D) were not present. Precipitation of the uranium occurred 

within the sands at the interface between the oxidized 

uranium-bearing water and reducing fluids that migrated into 

the sands from the offshore-lacustrine gray muds. 

Carbonized plant debris in the sandstone at or near the 

orebodies apparently was preserved by the reducing fluids 

which migrated into these beds shortly after deposition. 

Lack of uranium deposits in meandering-stream sandstone beds 

probably is due to slower flow of ground water through these 

beds and the scarcity of offshore-lacustrine gray mudstone 

in proximity to these beds. No uranium deposits have been 

found in the upper fluviolacustrine sequence, which also 

contains braided-stream sandstone beds but lacks the 

offshore-lacustrine gray mudstone. This important

difference in the upper fluviolacustrine sequence 

strengthens the hypothesis that fluids in the gray mudstones 

in the underlying sequences were necessary for the 

mineralizing process.

The association of uranium deposits with lacustrine 

gray mudstone is similar to that described for lacustrine 

rocks of the Newark basin in Pennsylvania and New Jersey. 

According to Turner-Peterson (this volume), humic acids and 

aqueous sulfides were generated in offshore-lacustrine black 

muds of the Newark basin where anaerobic bottom conditions 

were present. Pore fluids containing these reducing agents 

were then expelled by compaction into the adjacent sands at 

the lake margin where intervening marginal-lacustrine red 

beds (facies D of this paper) were absent. The black muds 

could only play a role in the mineralizing process shortly 

after their deposition, because the reducing agents (humic 

acids and aqueous sulfides) were only produced within these 

muds while they were still buried at shallow depths. As 

applied to the Henry Mountains mineral belt, this explains 

the geochemical processes involved in generating the 

reducing fluids in the offshore-lacustrine gray muds. 

However, in this area the reducing fluids were expelled into 

braided stream sands as well as marginal-lacustrine sands, 

in places where either of these lay adjacent to the 

offshore-lacustrine gray muds.

This depositional model should be useful as an 

exploration guide to uranium deposits in unexplored 

subsurface parts of the Henry basin as well as in other 

regions where closely associated fluvial and lacustrine 

strata occur.

Peterson, Fred, 1974, Correlation of the Curtis, Summerville, 

and related units (Upper Jurassic) in south-central Utah 

and north-central Arizona [abs.]: Geol. Soc. America Abs. 

with Programs, v. 6, no. 5, p. 466-467.

LOW-LEVEL DETERMINATIONS OF URANIUM AND THORIUM BY 

X-RAY SPECTROMETRY

BY GERARD W, JAMES, KANSAS GEOLOGICAL SURVEY, 

LAWRENCE, KANSAS 66044

Rapid and accurate low-level determinations of uranium 

and thorium in geologic samples are essential to large-scale 

uranium exploration programs. Although X-ray spectrometric 

techniques have been utilized for the analysis of ore-grade 

rocks and ore concentrates for over 20 years, most previous

work has indicated X-ray methods (1) lack the sensitivity 

required for low-level analyses of exploration samples, and 

(2) require the addition of an internal standard for 

quantitative determinations. As a result, many government 

laboratories are utilizing automated neutron activation

47
techniques, and laboratories without access to reactor 

facilities are utilizing traditional fluorimetric, 

colorimetric, and counting methods of analysis.

More recent work, however, has demonstrated the rapid 

and accurate determination of low levels (0 to 100 ppm) of 

uranium and thorium in geologic samples by 

wavelength-dispersive X-ray emission spectrometry (James and 

Hathaway, 1976; James, 1977). This paper summarizes the 

results of these investigations.

All the data reported in these studies were obtained by 

utilizing a Philips 1410 vacuum spectrograph with an XRG 

3000-watt generator operated at 50 kV and 50 mA. Maximum 

sensitivities for the determination of uranium and thorium 

were achieved by employing a molybdenum target X-ray tube in 

combination with a LiFopQ ana lyz^ n 9 crystal, and measuring 

the uranium and thorium L radiation. Scattered background 

radiation was measured at 0.901 A. Sample preparation 

consisted of directly analyzing rock powders (10-gram samples 

ground to minus 200 mesh) in 50-mrn-diameter sample holders. 

Analytical count times were 50 seconds at the analyte and 

background positions. Data reduction involved comparing 

peak-to-background count-rate ratios of samples to analytical 

calibration curves, which were determined from the analyses 

of Ottawa sand samples spiked with a carnotite ore and from 

U.S. Geological Survey igneous rock standards.

Reproducibility studies indicated no significant errors 

were associated with the sample preparation (as long as the 

samples were ground fine enough to be homogeneous) and 

instrument operation. Hence, the detection limits and 

precision of the method could be directly estimated on the 

basis of standard counting errors, which are a function of 

counting time. For a total analysis time of 5 minutes on a

sequential spectrometer (two 50-second measurements at each 

of the three 29 positions), the two-sigma (95 percent 

confidence level) detection limits were 0.8 ppm uranium and 

1.0 ppm thorium.

The method was found to be applicable to a broad variety 

of igneous and sedimentary rock types. For most exploration 

samples, large variations in Si02» Fe2^3> CaCOg, and organic 

material did not have significant influences on the accuracy 

of the X-ray-predicted concentrations of uranium and thorium. 

Matrix effects were sufficiently corrected for by the 

peak-to-background ratio method, which utilizes scattered 

background radiation as an internal standard. Thus, one 

analytical calibration curve per element is applicable to all 

types of sandstones (unaltered, reduced, and oxidized) and 

most igneous and metamorphic rocks.

The main advantages of X-ray spectrometric techniques 

over other methods of analysis lie in the simplicity of the 

sample preparation and the rapidity of the analysis. In 

addition, X-ray spectrometers are capable of determining low 

levels of other indicator elements (e.g., selenium) and can 

be easily adapted for routine quality control applications of 

ore-grade levels as mined or as recovered in leach solutions.

James, G. W., 1977, Low level determinations of uranium and 

thorium in geologic samples by X-ray spectrometry: Anal. 

Chemistry (in press).

James, G. W., and Hathaway, L. R., 1976, Recent advances in 

analytical methods for determining uranium in natural 

waters and geological samples, j_n_ Exploration for uranium 

ore deposits: Internat. Atomic Energy Agency, Vienna, 

p. 311-320.

DETERMINATION OF URANIUM IN SOURCE ROCKS USING RADIUM 

IN CRYSTAL SPRINGS, GREAT SALT LAKE AREA, UTAH

BY J, KAREN FELMLEE AND ROBERT A, CADIGAN 

U,S, GEOLOGICAL SURVEY, DENVER, COLO,

The amount of uranium in source rock that would be 

required to produce the radium in the water of Crystal 

Springs, north of Brigham City, Utah, has been calculated in 

order to determine whether the source rock may have a 

potential for uranium concentrations of economic interest. 

This study is an outgrowth of reconnaissance sampling of 

mineral springs in Colorado, Utah, Arizona, and New Mexico in 

1975-76 (Cadigan and Felmlee, 1977). The area around the 

Great Salt Lake in the Basin and Range Province of Utah was 

revisited in May 1976. Water samples were collected from 11

springs for radium, uranium, and major- and minor-element 

analysis. Limited data are available (O'Connell and 

Kaufmann, 1976; Mundorff, 1970) for 4 other springs, making a 

total of 15 sites. Precipitate samples were collected from 8 

of the sites.

Radium in the water has a positive correlation (0.82) 

with total dissolved solids and with most of the major and 

minor ions. The three springs having the lowest salinity 

also have the lowest radium content, less than 1 ypg/l, and 

one of the briny springs, Crystal Springs, has the most

48
radium, 220-410 uug/1. Some springs on faults within 20 km 

west of the Wasatch Range have moderately high salinity and 

radium content, 20-140 wg/1. Others having moderately high 

salinity, however, have low radium, only 2-5 wg/1. Such 

deviations reflect variations in unmeasured parameters, such 

as uranium content of the source rock, that affect the radium 

content of the water.

Barium, copper, iron, and manganese in the precipitates 

are unusually abundant at some localities, notably barium and 

copper at Stinking Hot Springs and iron and manganese at Utah 

Hot Springs. These metals are known to be associated with 

hydrothermal mineral deposits. Many of the mineral springs 

near the Wasatch Range have moderately high radium contents, 

but only Stinking and Utah Hot Springs contain high barium or 

iron. Coprecipitation of radium with barium and iron has 

produced very radioactive precipitates at these two sites. 

Although Crystal Springs have no barium- or iron-rich 

radioactive precipitates, they exceed the other two sites in 

the radium content of their water. Therefore, it is used in 

the calculation of uranium in source rocks.

The amount of radium in the water at Crystal Springs 

exceeds by several hundred times the amount of radium that 

would be in equilibrium with the amount of uranium in the 

water. The amount of enrichment, called the radium 

enrichment factor (REF), can be calculated by using the known 

equilibrium ratio for radium-226 and uranium-238 and the 

measured radium and uranium per liter or minute at the 

spring. The REF at Crystal Springs is 430-440.

The REF in the water depends on the difference in leach 

between radium and uranium when they are removed from the 

source and transferred to the spring. Differential leaching, 

based on differences in response to such parameters as 

pressure, temperature, oxidation-reduction potential, ionic 

strength, and mineral phases, leads to disequilibrium within 

the rocks being leached. If the percentage of leach for the 

two elements is the same, equilibrium in the rocks is 

maintained and equilibrium amounts are dissolved in the 

water. Differential leaching in favor of radium results in 

an excess of radium in the water and a corresponding 

depletion at the source. Continued differential leaching 

eventually leads to extreme disequilibrium in the leached 

part of the rock. The disequilibrium is actually between 

radium and its direct parent, thorium-230, which is in 

relative equilibrium with uranium (O'Connell and Kaufmann, 

1976). Therefore, we calculate uranium in the source rocks 

by assuming that disequilibrium in the rocks is extreme (no 

equilibrium radium present) and that the only radium 

available for transport is the amount being produced each 

minute by thorium-230.

The calculations begin with known measured values at the 

spring: the concentration of radium in water, and the volume 

of water flow per minute. Multiplication of these values 

gives the rate at which the spring is yielding radium. We 

assumed that the amount of radium available for leaching is

the radium being produced each minute. In addition, we 

assumed that all of the available radium is leached and 

carried to the surface; in other words, we assumed that the 

rate of radium yield at the spring is equal to the rate of 

radium production at the source. The amount of thorium-230 

decaying to produce this radium can be calculated by using 

the half-life equation. The amount of uranium in equilibrium 

with the thorium-230 can then be determined by using the 

known equilibrium ratio.

Crystal Springs contain at least 220 wg/1 radium and 

flows at 6,800 1/min (Mundorff, 1970; Bjorklund and McGreevy, 

1974); therefore, the springs yield radium at l.SxlO6 g/min. 

By assumption, this rate of yield is equal to the rate of

radium production at the source. A production rate of 1.5x10

fi K

g/min radium is equivalent to the decay rate of 1.5x10

g/min thorium-230. The proportion of any amount of 

thorium-230 (half life 8.0x10 years) decaying each minute is 

1.7x10 . If 1.5x10 g thorium-230 decays each minute, then 

the amount of thorium-230 present is 9.3x10 g. Assuming 

secular equilibrium (1 g uranium balanced by 1.7x10 g 

thorium-230), the amount of uranium required to maintain the 

present production of radium at Crystal Springs is at least

g 5.5x10 g, or 5,500 metric tons.

The uranium occurs in either all or part of the total 

volume of rock involved in the flow of ground water to 

Crystal Springs. This volume can be estimated by using 

hydrologic data and geothermal techniques as applied to a 

flow model in the region of the springs. Regional 

ground-water flow is from the Wellsville Mountains in the 

Wasatch Range westward to the lower Bear River valley and the 

Great Salt Lake. Because the regional flow is westward, 

saline water in the basin sediments is not likely to flow 

eastward to contribute any large quantity of water to Crystal 

Springs. The water at the springs rises along a fault zone 

at the mountain front and is probably composed mostly of 

deeply circulating meteoric water that may have come in 

contact with a cooling magma chamber or with rocks heated by 

an intrusive igneous complex. Some magmatic water may enter 

the system at depth, but lack of hydrogen- and oxygen-isotope 

data makes evaluation of the contribution unfeasible.

The total volume of rock involved in the flow to Crystal 

Springs is on the order of 10 km3 . The mass of rock,

o i c

assuming an average density of 2.8 g/cm , is thus about 10 

g. The length of the volume is 5-10 km, the width is 1-3 km, 

and the thickness is 1-2 km. The length was measured 

parallel to the flow direction, or eastward from the springs; 

the width was measured perpendicular to the flow direction, 

along the surface-water divide; the thickness was measured by 

estimating depth of water circulation on' the basis of 

geothermometry (Fournier and Truesdell, 1973, 1974) and 

geothermal gradient (Bjorklund and McGreevy, 1974).

Whether the uranium is disseminated or concentrated in

g the source rock is uncertain. If the calculated 5.5x10 g 

uranium were disseminated in 10 g of rock, the content

49
would be 0.55 ppm, less than the crustal average of 2-4 ppm. 

Inasmuch as porosity and permeability in the 

sedimentary-metamorphic terrane of the Wellsvilie Mountains 

are controlled mostly by joints and fractures, water flowing 

through these openings comes in contact with only a small 

percentage of the total rock. By assuming that the radium is 

derived from uranium in restricted zones adjacent to 

fractures and joints, considerably higher potential grades of 

uranium in the rock can be calculated. The grade would be 

0.55 percent if the 5,500 metric tons of uranium were 

concentrated in 1 percent of a fracture system comprising 1 

percent of the volume of rock assumed to be leached by the 

spring water.

Bjorklund, L. J., and McGreevy, L. J., 1974, Ground-water 

resources of the lower Bear River drainage basin, Box 

Elder County, Utah: Utah Dept. Nat. Resources Tech. 

Pub. 44, 65 p.

Cadigan, R. A., and Felmlee, J. K., 1977, Radioactive

springs geochemical data related to uranium exploration: 

Jour. Explor. Geochemistry (in press).

Fournier, R. 0., and Truesdell, A. H., 1973, An empirical 

Na-K-Ca geothermometer for natural waters: Geochim. et 

Cosfflochim. Acta, v. 37, no. 5, p. 1255-1275.

___1974, Geochemical indicators of subsurface temperature part 2, Estimation of temperature and fraction of 

hot water mixed with cold water: U.S. Geol.'Survey Jour. 

Research, v. 2, no. 3, p. 263-270.

Mundorff, J. C., 1970, Major thermal springs of Utah: Utah 

Geol. and Mineralog. Survey Water-Resources Bull. 13, 

60 p.

O'Connell, M. F., and Kaufmann, R. F., 1976, Radioactivity 

associated with geothermal waters in the Western United 

States Basic data: U.S. Environmental Protection Agency, 

Office of Radiation Programs, Tech. Note ORP/LV-75-8A, 

25 p.

THINNING OF THE FOX HILLS SANDSTONE, CROOK COUNTY, WYOMIIJGA POSSIBLE GUIDE TO URANIUM MINERALIZATION

BY H, W, DODGE, JR., AND C, W, SPENCER 

U.S. GEOLOGICAL SURVEY, DENVER, COLO.

Uranium mineralization occurs in the Fox Hills Sandstone 

of Late Cretaceous age in the eastern Powder River Basin, 

northeastern Wyoming. The Fox Hills is a sequence of 

marginal marine to estuarine and possibly tidal-flat deposits 

which were deposited during the eastward regression of the 

Upper Cretaceous Pierre Sea. The Fox Hills Sandstone 

consists of an upper and lower unit in the area of 

mineralization. The lower unit is not known to contain 

uranium and consists of offshore-marine and transitional-marine shale, siltstone, and fine-grained sandstone 

that grade upward into submarine-shoreface and tidal-beach 

sandstones. The upper unit locally is uranium-bearing and is 

composed largely of organic, thin-bedded claystone, 

siltstone, and sandstone considered to be deposited 1n 

estuarine and possibly tidal-flat environments. The upper 

unit is interpreted to have been deposited during and 

following a period of fluvial erosion that cut into the 

previously deposited lower unit. The upper unit grades into 

the overlying Lance Formation (Upper Cretaceous) that is 

composed predominantly of fresh-water delta-plain deposits.

The marine-transitional lower unit of the Fox Hills 

thins both regionally and locally. There is a regional 

northward depositional thinning from about 200 m near Lance 

Creek in central Niobrara County, Wyo., to a thickness of

40-50 m in west-central Crook County, Wyo. This regional 

thinning is attributed to slightly greater subsidence rates 

in the south (Niobrara County) with resultant vertical 

repetition of early Fox Hills paleoenvironments; to the 

north, less rapid subsidence did not favor a thick 

accumulation of lower unit sediments. Local erosional 

thinning of this unit is seen in an isopach map of the lower 

unit of the Fox Hills, prepared from approximately 100 

petroleum test-well electric logs in west-central Crook and 

northeastern Campbell Counties, Wyo. The pattern of the 

isopachs shows an erosional thinning of the lower unit 

superimposed on the regional northward depositional thinning 

of the formation. The erosional pattern is interpreted to 

represent an easterly draining dendritic system as much as 20 

km wide, 25-30 km long, and as much as 40 m deep.

On the basis of cores and logs from exploratory holes, 

uranium mineralization is known to be present east of and 

associated with this easterly draining dendritic system. 

Interpretation of these cores shows mineralization in 

estuarine and associated sediments of the upper unit. It is 

believed that low-density plant matter was carried into 

estuaries and associated environments by high-energy fluvial 

systems. Upon reaching the low-energy drowned valleys, the

50
organic matter was dropped out of suspension. This organic 

material was a focal point for later uranium mineralization.

If these observations hold for this area they may also 

be true for other areas, leading to the proposition that 

regional thinning of regressive sandstones, coupled with 

evidence of fluvial-estuarine erosion and deposition, 

constitute a possible guide to the location of uranium 

mineralization.

Though the exact time of mineralization is not known, 

many alternatives could be offered for the uranium source and 

time of emplacement; however, on the basis of present data we 

interpret the following sequence of events for the area of 

mineralization:

1. Deposition of Upper Cretaceous marine shales of the 

Pierre Shale.

2. Shallowing of marine waters (regressive cycle).

3. Deposition of transitional and marginal-marine sediments 

(lower unit of Fox Hills Sandstone).

4. Development of a fluvial-estuarine system.

5. Deposition of locally organic-rich thin-bedded claystone, 

siltstone, and sandstone in estuarine and associated 

environments (upper unit).

6. Deposition of overlying fluvial and delta-plain deposits 

(Lance Formation).

7. Deposition of Tertiary Fort Union and Wasatch Formations.

8. Erosion and truncation of westward-dipping Fox Hills and 

younger formations.

9. Deposition of uranium-rich semi permeable White River 

Formation (Oligocene).

10. Uplift and ground-water leaching of uranium coupled with 

hydrodynamic flow into westward-dipping highly permeable 

lower unit of the Fox Hills.

11. Reduction and precipitation of uranium minerals in the 

adjacent organic-rich upper unit of the Fox Hills.

51
URANIUM EXPLORATION USING HELIUM DETECTION--A CASE STUDY

BY G, M, REIMER, U,S, GEOLOGICAL SURVEY, 

DENVER, COLO,

In order to provide a case study of the application of 

helium-detection methods to uranium exploration, a roll-type 

uranium deposit in Weld County, Colo., was investigated by 

both water and soil-gas sampling. The general geologic 

setting of the Weld County uranium deposit is discussed by 

Reade (1976). The deposit is low grade, near the surface, 

and below the ground-water table, which is about 10 m below 

the surface. Eighteen water samples and 200 soil-gas 

samples, collected in the vicinity of the uranium deposit, 

were analyzed for helium using the mobile helium detector 

developed by the U.S. Geological Survey (Reimer, 1976). This 

instrument consists of a small mass spectrometer installed in 

place of the rear seat for a four-door pickup truck. The 

inlet system of the spectrometer was modified slightly to 

accommodate the sample collecting scheme used for both water 

and soil gas. This mobile laboratory has the capability to 

analyze samples within a few minutes at the field location, 

and the results of the analyses can be used immediately to 

guide the direction of exploration.

Subsurface water samples were collected wherever a

source was available, such as domestic- or stock-supply

2 wells. Eighteen samples were collected from an 80-km area.

The shallow stock-supply wells, ranging from 3-10 m deep, 

showed low helium values. Domestic wells, about 25 m deep, 

that were on the down-gradient side of ground-water flow 

relative to the uranium deposit, had higher helium 

concentrations than those on the up-gradient side. 

All helium concentrations in the water samples analyzed in 

this Weld County study were anomalously high when compared to 

atmospheric-equilibrated values. The high values are 

consistent with the magnitude of anomalies found to be 

associated with other uranium deposits by Dyck (1976) and 

Pogorski, Quirt, and Blascheck (1976). Because the 

ground-water anomaly can be detected over a large area, 

helium detection using ground water may be an extremely 

valuable regional reconnaissance technique. Maintaining 

sampling control is difficult when collecting water, 

turbulence and mixing with air are the largest problems 

encountered. Those actions scrub the dissolved gases from 

the water and are, in fact, employed in the technique used to 

remove the gas from the sample for our analysis. 

Consequently, a certain degree of qualitative evaluation must 

be used in the interpretation of the analytical results. 

Shallow wells and turbulent water generally have low helium 

concentrations.

The soil-gas investigations incorporated two basic 

sampling patterns: (1) to obtain information on the regional

helium distribution, sample spacing was on 3.2- and 1.6-km 

centers; (2) in the immediate vicinity of the uranium 

deposit, sample spacing was on about 320-m centers. The 

range of helium values in the regional soil-gas study was 

distinctly greater than that of the values taken near the 

uranium deposit. This difference in range suggests that the 

background helium concentration changes regionally and widely

1 KILOMETER 

J

Figure 1.--Contour map of helium in soil gas in the vicinity 

of the Weld County, Colo., roll-type uranium deposit. 

Contour interval is 8 ppm. The base value for the atmosphere 

is 5,239 ppb. The highest anomaly is displaced about 

1.5 km from the roll front (cross-hatched area). 

Ground-water flow is presently to the southwest. Sample 

locations are shown by dots.

52
spaced soil-gas sampling does not provide much useful 

information, a direct contrast to the water-sampling results. 

The closely spaced soil-gas sampling over the uranium deposit 

produced a more consistent pattern. Parts of this survey 

were repeated on three separate occasions over a three-month 

period to allow us to consider the effects of the temporal 

variations in soil-gas helium content that have been observed 

in other studies (Reimer and others, 1976). These replicate 

surveys demonstrated the reproducibility of the pattern of 

the anomaly. The raw data indicated a density of higher 

helium values roughly centered about 2 km from the uranium 

roll front in the direction of ground-water flow. A very 

simple statistical averaging technique was used to enhance 

the plotted data. The value of any one sample point is 

influenced by the average of all the neighboring sample 

values, weighted by their relative distances from the central 

point. This statistical approach resulted in a contour map 

(fig. 1) that minimizes the effects of spurious values that 

may be the result of localized structural or other controls. 

The map summarizes the soil-gas data and demonstrates an 

important point, that the center of the anomaly may not 

correspond to the location of the ore deposit. In the Weld 

County study, ground-water flow is probably a factor 

controlling the displaced location of the anomaly.

The positive results of the preliminary studies indicate

that helium detection in both water and soil-gas samples can

make a significant contribution to an integrated geochemilcal

and geophysical exploration program.

Dyck, Willy, 1976, The use of helium in mineral exploration: 

Jour. Geochem. Explor., v. 5, no. 1, p. 3-20.

Pogorski, L. A., Quirt, 6. S., and Blascheck, J. A., 1976, 

Helium surveys A new exploration tool for locating 

uranium deposits: Toronto, Ontario, Chem. Proj. Ltd., Tech. 

Paper CPL-6/76, 27 p.

Reade, H. L., Jr., 1976, Grover uranium deposit a case history 

of uranium exploration in the Denver Basin, Colorado: 

Mtn. Geologist, v. 13, no. 1, p. 21-31.

Reimer, G. M., 1976, Design and assembly of a portable helium 

detector for evaluation as a uranium exploration instrument: 

U.S. Geol. Survey Open-File Rept. 76-398, 18 p.

Reimer, G. M., and Otton, J. K., 1976, Helium in soil gas and 

well water in the vicinity of a uranium deposit, Weld 

County, Colorado: U.S. Geol. Survey Open-File Rept. 76-699, 

10 p.

Reimer, G. M., Roberts, A. A., and Denton, E. H., 1976, Diurnal 

effects on the helium concentration in soil-gas and nearsurface atmosphere: U.S. Geol. Survey Open-File Rept. 

76-715, 9 p.

GEOCHEMICAL INTERPRETATION OF ORE ZONATION AT THE 

RIFLE VANADIUM MINE, COLORADO

BY DENNIS J, UPoiNT AND GERGELEY MARKOS

DEPARTMENT OF GEOLOGICAL SCIENCES

UNIVERSITY OF COLORADO

BOULDER, COLORADO 80309

The Rifle vanadium deposits are located along East Rifle 

Creek about 13 miles northeast of Rifle, Colo., on the 

southern flank of the White River Plateau. Fischer (1960) 

described the deposit and suggested that 

uranium-vanadium-lead-selenium-chromium mineralization 

occurred at an S-shaped interface between two fluids (fig. 

1), but he recognized no evidence to suggest the source of 

mineralizing solutions or the elements they contained.

The compositions reported in table 1 for vanadium clay 

minerals are based on analyses by Foster (1959), and the compositions of chromium clay minerals are assumed to be 

analogous to those of vanadium because of the similarity in 

site occupancy in the clay mineral structure. Thermodynamic 

calculations are computed according to the method described 

by Markos (1977); Gibbs free energies of clay minerals are

calculated using the method described by Tardy and Garrels 

(1974), and the Gibbs free energy for galena-clausthalite 

solid solution is estimated for Pb (SQ 5 SeQ 5 ) from data 

published by Coleman (1959).

Although we are discussing the mixing of two fluids, one 

of which is warm and saline, calculations are based on a 

temperature of 25°C, and the activity of water was set at one 

with no corrections for salinity, temperature, or pressure. 

It should also be noted that no attempt was made to calculate 

concentrations, which may have values significantly different 

from activities in saline waters. Changes of two orders of 

magnitude in the assumed activities do not alter the 

interpretations.

At the zone of fluid interaction, ore minerals 

precipitated due to three causes: (1) cooling of the brine,

53
Cross section of the deposit

meters 

30-

20-

I 0-

0-

Garfield Mine Rifle Mine

1 I

East Rifle Creek

mineralization

Morrison

Entrada

Glen Canyon

Chinle

west east 

2 km

Zonation

B

zone of Cr- silicates

zone of galena-clausthalite solid sol.

zone of V-silicates

zone of U enrichment

- ground water 

 brine

Figure 1. (A) Cross section of the Rifle vanadium deposit in 

Jurassic and TriaSsic rocks. Modified from Fischer 

(1960). (B) Idealized representation of metal zonation 

and directions of water movement.

(2) dilution of the brine, and (3) the availability of ions 

in amounts sufficient to form the observed minerals. The 

first two causes can only be evaluated indirectly at this 

time. As the brine' cooled and mixed with the ground water, 

chloride complexes became unstable and the water was 

oversaturated in elements carried as complexes.

Vanadium, as roscoelite, is the major ore mineral in the

Rifle deposit. In the formation of roscoelite, if vanadium

+4 +3 is carried as V , it can be reduced to V in the mica

structure. " which can be carried in 

,+3

Calculations show VT

J.O

to form 

the 

of the chromium zone. Mariposite forms

oxidizing ground water, will not be reduced to V 

mica. Likewise, Cr is required to form mariposite, 

dominant mineral

Table 1. Gibbe free energies of formation (calculated for this paper) and 

composition of minerals

Minerals fiGf k"l/»ole

(25°C, 1 atm)

A. Vanadium minerals 

V-mica-montmorillonite mixed layer mineral

<A1O.S7Vo!82FeO?2M8o.25) < S1 3.17A10.83)010<OH) 2K0.95 -1241 ' 16 

Roscoelite

<A1 1.13Vot72FeO?l%.05) < St3.25A10.75 )010< OH) 2Kb.8H0.1 

Montroseite VO(OH)

-1271.255 

-163.5

B. Chromium minerals 

Volkhonskoite

(A10.8Cro!6 Feo!4%.4) < Si 3.2A10.8 ) °10< OH >2K0.6 Ca0.1M80.1 

Mariposite

< A1 1.13 Cro!72Feo!lM80 .05 ) < S1 3.25A10.75)010< OH) 2K0.8H0.1 

C. Lead mineral 

Galena-clausthalite solid solution Pb(S ,Se ,) 0.5 0.5'

D. other 

Illite

(A1 1.85FVltfe0.05)(Si 3.25A10.75> 010 (OH) 2K0.8H0.1

0.8

0.6 H

0.4

0.2

Eh

-0.2-

-0.4-

-0.6

water 

oxidizes

Aqueous solution of 

Si, Al, V, Fe, Mg, K 

log aSl- * log Qp9 * log OM * log o^

log aAf --6 

log ay * -4 8 -6

10 12

Figure 2. The Eh-pH field for the formation of roscoelite 

from solution. An increase in the activity of vanadium 

expands the field for roscoelite. A low oxidation 

potential and neutral to alkaline pH is required to 

form roscoelite from solution.

54
easily over a broad range of Eh-pH conditions which 

roscoelite has a narrow stability field (fig. 2).

The equilibrium ratio of chromium to vanadium for 

coexisting mariposite and roscoelite is strongly pH dependent 

(fig. 3). The zonation of chromium and vanadium micas is 

therefore probably due to exhaustion of chromium in solution 

or to a rapid and pronounced decrease of pH. Both minerals 

are similar in composition and structure to illite, but the 

presence of chromium or vanadium prevents the precipitation 

of illite at pH values greater than six and eight, 

respectively.

In the vanadium zone, the relative stability between 

montroseite and roscoelite is controlled by pH and the 

activities of silica and aluminum. At low pH, unreasonably 

high amounts of silica are needed to form vanadium mica. 

Calculations indicate that vanadium montmorillonite is not 

formed from solution, but instead it is secondary, 

post-depositional transformation of roscoelite at a pH below 

6.5 to 7.1. Both chromium mica and montmorillonlte minerals 

are likely to form from solution; however, the chromium mica 

is preferred.

The small amounts of uranium present in the orebody make 

the determination of its mineralogy difficult (Fischer, 

1960). A study of potential source rocks and ore fluids 

suggest the uranium was carried in ground water as a 

carbonate complex. The absence of discrete uranium minerals 

may indicate that the uranium is adsorbed onto the vanadium 

clay minerals and calcite cement.

Galena-clausthalite solid solution forms when the sulfur 

activity and Eh are both relatively low in solution, and the 

solution is alkaline (Tischendorf and Ungethum, 1963). 

Selenium, entering a reducing environment with lead and 

sulfur available,will readily precipitate in a narrow zone. 

This suggests that the galena-clatisthalite zone represents 

the actual interface between the two solutions.

One of the fluids was a typical bicarbonate ground water 

that had a low temperature, slightly alkaline pH, and a high 

oxidation potential. Of the ore-forming elements, selenium 

and uranium may have been carried in this type of water. The 

overlying Morrison Formation of Jurassic age is proposed as 

the source of the water and these ore-forming elements. The 

second fluid was a warm, chloride brine which may have been 

derived from sediments of the Central Colorado Basin of late 

Paleozoic age. In the brine, major ions of importance were 

chloride, sodium, potassium, and magnesium. Iron, lead, 

chromium, and vanadium were also transported in this brine. 

Sulfur could have been transported in either fluid. Chemical 

calculations support the hypothesis that two fluids of very 

different composition interacted to cause the Rifle deposit.

0-

-2-\

-6-

-8-

-10

I_______I_______I

Roscoelite

6 8 

pH

10 12

Figure 3.--A comparison of equilibrium activities of vanadium 

and chromium in the formation of mica minerals as a 

function of pH. At pH 3.9 the activities of vandium 

and chromium are equal. At pH 7, mariposite will form 

even if the activity of chromium is as little as one 

millionth of the activity of vanadium.

Coleman, R. 6., 1959, The natural occurrence of galena-clausthalite solid solution series: Am. Mineralogist, v. 44. 

Fischer, R. P., 1960, Vanadium-uranium deposits of the Rifle

Creek area, Garfield County, Colorado: U.S. Geol. Survey

Bull. 1101, 52 p. 

Foster, H. D., 1959, Chemical study of the mineralized clays:

U.S. Geol. Survey Prof. Paper 320, p. 121-132. 

Markos, G., 1977, Geochemical alteration of plagioclase and

biotite in glacial and periglacial deposits: Univ. Colo.

Ph.D. thesis. 

Tardy, Y., and Garrels, R. M., 1974, A method of estimating

Gibbs energies of formation of layer silicates: Geochim.

et Cosmochim. Acta, v. 38, p. 1106-1116. 

Tischendorf, G., and UngethUm, H., 1963, Uber die bildungsbedingungen von clausthalit-galenlt und bemerkungen zur

selenverteilung im galenit in abhangigkeit vom redoxpotential und vom pH-wert: Chemie Erde, v. 23, p. 279-

311.

55
ASSAY FOR URANIUM AND MEASUREMENT OF DISEQUILIBRIUM 

BY MEANS OF HIGH-RESOLUTION GAMMA-RAY BOREHOLE SONDES

BY ALLAN B, TANNER, ROBERT M, MOXHAM, AND FRANK E, SENFTLE 

U,S, GEOLOGICAL SURVEY, RESIGN, VA, 22092

In-hole assay has been done by measurement of gamma 

radiation since the early days of uranium exploration. 

Because detectors used are most sensitive to the 

radioactivity of nuclides far down the decay chain of the 

uranium and thorium series, radioactive disequilibrium or 

significant concentrations of thorium result in assay erors 

that can be significant.

Gamma-ray detectors made of germanium have been in 

laboratory use for a decade. They are capable of resolving 

most of the numerous natural X-rays and gamma rays, and in 

principle they can measure uranium directly, without regard 

to the state of radioactive equilibrium. There has been 

some reluctance to use these high-resolution detectors in 

the field because they are expensive, require sophisticated 

electronics and data reduction, and must be cooled to 

liquid-nitrogen temperature for operation. The germanium 

detector has been adapted to the borehole environment by 

substituting melting propane (85 K) for boiling nitrogen 

(77 K) as the coolant, thus enabling the detector sonde to 

be sealed for operation underwater. In the 1975 Uranium and 

Thorium Research and Resources Conference, we reported the 

design of such a sonde and some laboratory borehole 

measurements made with it; we report here the results of 

field measurements made using it and an earlier sonde in 

boreholes in a uranium deposit near Pawnee, Bee County, Tex. 

The two sondes are intended for different uses: one houses

a high-purity, or "intrinsic," germanium disc about 5 mm

2 thick and 500 mm in area, and 1s best suited to measurement

of radiations in the range of the X-rays of the heavy 

elements and low-energy gamma rays; the other houses a 

lithium-compensated, or "Ge(L1), M germanium cylinder with a 

volume of 45 cm , and is suited to measurements of gamma 

rays of higher energy than the X-rays.

Because far fewer gamma rays per unit time are received 

from any one radioactive species than from all species 

combined, spectrometry requires longer counting periods than 

total counting to achieve the same statistical accuracy. 

Routine, top-to-bottom logging of a particular gamma-ray 

energy at a feasible speed of only a few meters per hour is 

unacceptably slow. For delimiting zones worth investigating 

by high-resolution spectrometry, we recorded total counts 

received during successive 10-second periods while the sonde 

moved continuously at about 1 m per minute. The resulting 

log is comparable in definition and statistical quality to 

the conventional scintillation log.

Having used rapid, total-count, continuous-motion 

logging to find the zones of greatest activity, we shifted 

to 10-minute accumulations of spectra in a pulse-height 

analyzer. The data were transferred to magnetic cassettes 

during movement of the sonde from one station to the next. 

Data reduction by the minicomputer takes about 5 minutes and 

could be done during the station if desired.

Assay for uranium was tried using the 63.3-keV gamma 

ray of 234Th and the 1001.4-keV gamma ray of 234mPa. The 

short half lives of these isotopes (24.1 days and 1.175 

minutes, respectively) imply that they reach equilibrium in

oop

a few months after deposition of the parent U and that 

they should be reliable measures of the concentration of the 

parent in solid deposits. Although nearly 10 times as many 

63.3-keV as 1001.4-keV gamma rays are emitted from a given 

sample, the 1001.4-keV gamma rays reach the detector from 

greater distances in the wall rock of a borehole, and the 

detector used is more efficient; consequently, the counting 

rates from the two gamma rays are nearly equal. The same 

general pattern of U distribution is inferred from logs 

of the 63.3-keV and the 1001.4-keV gamma rays, but they show 

significant differences in detail. We believe that the 

differences are due less to instrumental error than to the 

approximately fivefold difference in mass effectively 

sampled by the two detectors.

Calibration was done by comparing the intensity of the 

1001.4-keV gamma radiation at a location in the borehole 

with that from a core sample from the same location and, in 

turn, with that from standard samples. The result was 9 

percent lower than the result of fluorimetric analysis of 

the split of core closest to the same location. The 

combined sampling and analytical errors of the fluorimetric 

analysis may exceed the 9 percent difference.

The sensitivity of the method is estimated at about 80 

ppm U,0D when the 1001.4-keV gamma ray is measured for a 5 O

counting period of 10 minutes. We base the estimate on the 

concentration at which our data reduction program just 

rejects the 1001.4-keV peak when a one-standard-deviation 

test is imposed.

High-resolution gamma-ray spectrometry is unique 

because it offers an 1n situ method of determining the state 

of equilibrium in the 238U and 235U series by simultaneous 

measurements using a single detector. Of the six isotopes 

or groups capable of independent behavior over geologically 

important periods of time, five can be evaluated

56
unambiguously by at least one gamma ray; the remaining one,

ppc 9^K

Ra, can be evaluated if a correction is made for U. 

We investigated four boreholes alined approximately in 

the direction of the dip. The borehole most updip 

penetrated a thin upper ore zone and both "limbs" of a 

lower-ore-zone roll. The next hole penetrated a 3-m-thick 

upper ore zone and a 5-m-thick lower ore zone. The lower 

ore zone in this second hole contained the highest grade ore 

found in any of the four holes. The two holes farther 

downdip encountered progressively lower grades of ore in 

both ore zones. Spectra were taken in all ore zones of the 

first two holes and in the lower ore zone of the last two

holes.

222 214 The Rn group, as measured by Bi, is present in

excess of equilibrium at the inner boundaries of the roll

limbs in the first hole, at both boundaries of both ore

zones in the second hole, and at both boundaries of

mineralization in the two holes downdip. At each location,

222 the Rn group is deficient to some extent between the ore

226

zones. The results for Ra are not consistent enough to

222 apportion the causes of the uneven Rn group distribution 

between radium migration and radon migration.

An intermediate decay product, 230Th, in the 238U 

series, is relatively deficient in the middle of the lower 

ore zone in the hole penetrating the ore of highest grade, 

but is in relative excess toward the upper and lower 

boundaries of that zone. On the basis of preliminary 

determination of the relative intensities of the 63.3-keV

OOA 970

"HTh and 67.7-keV "uTh gamma rays in borehole geometry, we

oon

infer that Th is present in threefold or greater excess 

at the two locations. If this is true, U~and almost

poo

certainly U of commensurately higher concentration must 

have been dispersing from those locations for about the last 

80,000 years, a time span comparable to the half life of

OOT ?7R

The Pa group of the U series, controlled by the

OOT

34,300-year half life of Pa, is also apparently present 

in excess of equilibrium toward the lower boundary of the

main ore zone, as is the Th. However, an excess of the 

2^1 Pa group was not found near the upper boundary of this

zone. Such a difference in the relative proportions of 

230Th and the 231 Pa group could arise if leaching of the 

uranium isotopes from the upper part of the main ore zone 

had started earlier or progressed faster than in the lower 

zone.

REFINEMENT OF THE THERMODYNAMIC PROPERTIES OF URANIUM MINERALS

AND DISSOLVED SPECIES, NITH APPLICATION TO THE CHEMISTRY

OF GROUND NATERS IN SANDSTONE-TYPE URANIUM DEPOSITS

BY DONALD LANGMUIR! AND KENNETH AppLiN2

DEPARTMENT OF GEOSCIENCES

THE PENNSYLVANIA STATE UNIVERSITY

UNIVERSITY PARK, PA, 16802

Hostetler and Garrels (1962) examined the solubility of 

four uranium minerals dissolving to form seven 

uranium-bearing species in water. In our study, 

thermodynamic data have been collected and critically 

evaluated for a total of 25 minerals and 42 dissolved species 

of uranium. This expanded, updated listing permits a far 

more detailed appraisal of the low-temperature aqueous

The data show 

U*+ ) ions is

the rule in natural waters, and is more important than 

generally realized. The existence and stability of these 

complexes indicates that the mobility of uranium in water may 

be enhanced under a wide variety of conditions. The study

geochemistry of uranium than before possible. 

that complexing of uranyl (UO? ) and uranous

Professor of Geochemistry.

o

Graduate Research Assistant.

also shows that the solubility of uraninite (and coffinite) 

is about 8 to 10 orders of magnitude less than was indicated 

by Hostetler and Garrels. This suggests that, for a given Eh 

and pH, precipitation of these minerals can occur from ground 

waters far more dilute in uranium than usually assumed.

Table 1 lists the thermochemical data for uranium 

minerals and aqueous species at 25°C and 1 atmosphere total 

pressure. The data have been computed using values for 

non-uranium species listed in Wagman and others (1968, 1969, 

1971, and 1976) and Parker and others (1971); they are 

considered internally consistent, with the exception of AG^° 

for H2 P04 , which should be -270.17 kcal/mol. The 

thermochemical values for U , U02 + ions, and for uraninite, 

U02 67 (1/3 U,0g), and Y-UO, are the only ones accepted as 

given by their sources. Thermodynamic properties of all 

other solutes and solids have been computed or estimated from

57
TABLE 1. Thermochemical data for uranium minerals and aqueous species at 25°C and 1 atm total pressure 

[Parentheses on entropy (S°) values indicate uncertainty greater than +5 cal/mol deg. Enthalpies (AH°) calculated from these uncertain values ar

Mineral or

Aqueous Species

u4V

uo»r*

U(OH)|+

U(OH) 3

U(OH)«

U(OH)g

U 2 (OH)3*

U0,(c) uraninite

£

U02 (am)

U02 _ 67 (c)

USi04 (c) coffinite

USi04 (am)

UF3+ 

UF2+

UF2+

UF 3

UF:

4

UF 5

UF6~ 

6-U

UC1 3+

uso4 "

u(so4 )|

UHP04+

U(HP04 )^

U(HP04) 2 ' 

U(HP04 ) 4 "

U(HP04)2 -4H20(c)

CaU(P04 ) 2 -2H20(c)

ningyoite

2+

U02

U02OH+

U02 (OH)°

U02 (OH)-

U02 (OH) 2~

(U02 ) 2 (OH) 2+

(U02 ) 3 (OH) 5

Y-U03 (c)

U03 (am) gummite 

6-U02 (OH) 2 (c)

AH£

(Kcal/mol)

-141.3

-197.9

-259.7

(-322.9)

(-387.3)

(-451.4)

-259.3

 -

-284.8

-478

....

-216.3 

-292.7

-371.6 

-453.3

-532.5

-613.2

-168.3

(-341.5)

(-554.6)

(-439.1)

(-750.2)

(-1065) 

(-1389)

-1029

-1016

-243.5

-299.0

-361.6

(-418.6)

(-471.7)

-610.3

-1047

-292.5

-288.8 

-365.8

Afi«

(Kcal/mol)

-126.9

-182.7

-236.7

-289.0

-339.6

-388.5

-529.4

-246.6

-233.7

-268.5

-452.0

-439.2

-205.8 

-279.6

-352.0 

-424.5

-493.3

-563.1

-157.1

-309.9

-491.1

-403.6

-677.6

-949.7 

-1221

-910.9

-933.4

-227.7

-277.5

-324.3

-365.6

-402.9

-561.0

-945.2

-273.9

-270.2 

-332.7

S°

(cal/mol deg)

-99

-46

-16.5

(3)

(12)

(17)

-_--

18.41

 

22.51

28.4

 

-46 

-15

3 

12

17

20

-46

(-20)

(10)

(-15)

(15)

(25) 

(5)

85

70

-23.2

13.3

16.1

(19)

(22)

5.5

26.7

22.97

23.1 

29.9

Source

Fuger and Oetling, 1976.

Baes and Mesmer, 1976.

Do.

Do.

Do.

Do.

Do.

V. B. Parker, oral commun., 1977.

V. B. Parker, oral commun., 1977.

Ahrland and others, 1973. 

Do.

Do. 

Do.

Do.

Do.

Naumov and others, 1974

Ahrland and others, 1973.

Do.

Moskvin, Essen, and

Bukhtiyarova, 1967. 

Do.

Do. 

Do.

Do.

Muto, 1965.

Fuger and Oetling, 1976.

Nikitin and others, 1972.

Do.

Naumov and others, 1974.

Do.

Nikitin and others, 1972.

Baes and Mesmer, 1976.

Fuger and Oetling, 1976;

V. B. Parker, oral commun., 1977. 

Nikitin and others, ,1972; 

"uger and OetTfng, 19/6. 

NiRitin and others, 1972.

Mineral or

Aqueous Species

UOe(OH) 2 -H 20(c)

schoepite

U02C03(c) 

rutnerfordine

uo2co°

uo2 (co3 ) 2'

uo2 (co3 ) I'

U02 F+

U02 F2

nn c~ U02 F 3

UO.F2 -

uo 2 ci

uo2so^

U02 (S04 ) 2-

(U02 ) 3 (P04 ) 2 (c)

U02HP04 (c)

U02 HPOJ

U02 (HP04 ) 2 "

U02H 2POj

U02(H2P04)°

i in t u on ^ -

°2^ 2 4' 3 

H2(U02 ) 2(P04 ) 2(c)

H-autunite

Na 2 (U02 ) 2 (P04 ) 2 (c)

Na-autunite 

K2 (u02 ) 2 (P04 ) 2 (c)

K-autunite 

(NH4 ) 2 (U02 ) 2 (P04 ) 2

uramphite

Mg(U02 ) 2 (P04) 2 (c)

saleeite

Ca(U02 ) 2 (P04 ) 2 (c)

autunite

Sr(U02 ) 2 (P04 ) 2 (c)

Sr-autunite

Ba(U02 ) 2 (P04 ) 2 (c)

uranocircite 

FE(U02 ) 2 (P04 ) 2 (c)

bassetite

Cu(U02 ) 2 (P04 ) 2 (c)

torbernite

Pb(U02 ) 2 (P04 ) 2 (c)

AHt

(Kcal/mol )

-435.7

-404.7

-404.2

-563.3

(-737.8)

-323.1

-403.8

-486.0

-567.4

-282.2

-455.8

-672.2

-1328

-548.3

(-550.9)

(-865.9)

(-552.5)

(-870.6)

(-1188)

-1098

-1216

-1229

(c) - 

-1194

-1219

-1220

-1206

-1101

-1050

-1071

przhevalskite 

K2 (U02 ) 2 (V04 ) 2 -3H20(c)-1385

carnotite

iAGJ

(Kcal/mol)

-389.6

-373.3

-367.3

-502.8

-635.4

-3D1.1

-373.7

-446.4

-516.5

-259.4

-409.4

-589.4

-1237

-504.7

-499.5

-773.7

-502.0

-775.5

-1048

-1011

-1136

-1147

-1051

-1116

-1141

-1142

-1168

-1024

-972.8

-993.4

-1267

(cal/m

4

3

1

3

(

-

16

18

-4

10

25

92

38

(12

(30

(15

(20

(25

76

91

94

 

83

85

8

89

86

86

91

13
published empirical results (chiefly stability constants) 

consistent with the tabulated properties of U4+ and U022+ 

ions. Entropies of many aqueous species have been estimated. 

Entropies of coffinite and all the phosphate minerals have 

been estimated (probably to within ±5 cal/mol deg) using 

approaches described by Naumov and others (1974). Detailed 

explanation of the sources, methods of calculation and 

estimation of the data, and application of the data to 

uranium geochemistry will be presented in a future report.

The relative importance of different uranium complexes 

as a function of pH was assessed at 25°C and Prn =102 '° or

2 5 kOo

10 atm for some typical total ligand concentrations in 

ground water (F=0.2 or 0.3 ppm; Cl=10 ppm; S04=100 ppm; and 

P04=0.1 ppm). In the following discussion, complexes are 

termed "important" if they exceed 10 percent of the total 

concentration or uranous or uranyl species. A species is 

"predominant" if it comprises more than half the total of 

uranous or uranyl species. For uranous ion, calculations 

showed that the fluoride complexes are predominant at pH's 

below 3-4, and that hydroxyl complexes are predominant at 

higher pH's. Uranyl ion formed important complexes with

Figure 2. Increase in uraninite solubility caused by uranous 

fluoride complexing at 25°C.

100

10

Figure 1. Mole percent dissolved uranium vs pH for some 

uranyl complexes, at 25°C with PCQ =10"2 (A), and

rco. 3 (B).

iu

1.0

.8

.6

.4

.2

-2

-.4

-.61

Uraninite-solution 

boundaries at K)~ 6 M 

dissolved uranium species.

"H+G'denotesthe boundary of 

the uraninite stability field 

according to Hastetler 8 Cartels (1962) 

I i _i i i I I i

6 

PH

8 10 12

Figure 3.--The increased field of stability of uraninite indicated 

by our data (patterned area) compared with that indicated 

by data from Hostetler and Garrels (1962) (enclosed by 

line marked "H and 6").

59
fluoride and sulfate at pH's below 4.5-5.5. The fluoride

complexes predominated at pH's below about 4. The complex

2 UOpfHPO.)^ was surprisingly stable, and was the predominant

uranyl species between about pH 4.5 and 7.5. In the absence

of phosphate, uranyl carbonate complexes predominated at all

2 pH's above 4.5, but in the presence of U02 (HPO.) 2 they only

predominated above pH 7.5.

Figure 1 illustrates relations among some uranyl 

complexes. The increase in uraninite solubility caused by 

uranous fluoride complexing is shown on figure 2. The Eh-pH 

diagram on figure 3 compares the greater stability of 

uraninite indicated by our data to its stability computed 

using free-energy data listed in Hostetler and Garrels 

(1962).

Ahrland, S., Liljenzin, J. 0., and Rydberg, J., 1973, Solution 

chemistry [of the actim'des], in_ Comprehensive inorganic 

chemistry, v. 5, Actim'des, Master Index: New York, 

Pergamon Press, p. 465-635.

Baes, C. F., Jr., and Mesmer, R. E., 1976, The hydrolysis of 

cations: New York, John Wiley & Sons, 489 p.

Chukhlantsev, V. G., and Alyamovskaya, K. V., 1961, Solubility 

product of uranyl, beryllium and cerium phosphates: 

Vyssh. Ucheb. Zavedeniy Izv. Khimiia i Khimicheskaia 

Tekhnologiia, v. 4, p. 359-363.

Chukhlantsev, V. G., and Stepanov, S. I., 1956, Solubility of 

uranyl and thorium phosphates: Zhur. Neorganicheskoi 

Khimii, v. 1, p. 478-484.

Fuger, J., and Oetling, F. L., 1976, The chemical thermodynamics 

of actinide elements and compounds Part 2, The actinide 

aqueous ions: Vienna, Internat. Atomic Energy Agency, 

p. 16-20.

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.

Karpov, V. I., 1961, Solubility of neutral uranyl phosphate: 

Zhur. Neorganicheskoi Khimii, v. 6, p. 531-533.

Lietzke, M. H., and Stoughton, R. W., 1960, The solubility of 

silver sulfate in electrolyte solutions VII, Solubility 

in uranyl sulfate solutions: Jour. Phys. Chemistry, v. 64, 

p. 816-820.

Marcus, Y., 1958, Anion exchange of metal complexes the

uranyl phosphate system: United Nations Internat. Conf. 

Peaceful Uses Atomic Energy, 2d., Proc., v. 3, p. 465- 

471.

Moskvin, A. I., Essen, L. N., and Bukhtiyarova, T. N., 1967, 

Complexing of tetravalent thorium and uranium in phosphate

solutions: Zhur. Neorganicheskoi Khimii, v. 12, p. 3390- 

3392.

Moskvin, A. I., Shelyakina, A. M., and Periminov, P. S., 1967, 

Solubility product of uranyl phosphate composition and 

dissociation constants of uranyl phosphate complexes: 

Zhur. Neorganicheskoi Khimii, v. 12, p. 3319-3325.

Muto, T., 1965, Thermochemical stability of m'ngyoite: 

Mineralog. Jour., v. 4, no. 4, p. 245-274.

Muto, T., Hirono, S., and Kurata, H., 1968, Some aspects of 

fixation of uranium from natural waters: Japan Atomic 

Energy Research Inst. Report NSJ Transl. No. 91, from 

Mining Geology, 1965, v. 15, p. 287-298.

Naumov, G. B., Ryzhenko, B. N., and Khodakovsky, I. L., 1974, 

Handbook of thermodynamic data: Natl. Tech. Inf. Service, 

U.S. Dept. of Commerce, Springfield, Va., 328 p.

Nikitin, A. A., Sergeeva, Z. I., Khodakovsky, I. L., and

Naumov, G. B., 1972, Uranyl hydrolysis in a hydrothermal 

region: Geokhimiya, no. 3, p. 297-307.

Parker, V. B., Wagman, D. D., and Evans, W. H., 1971, Selected 

values of chemical thermodynamic properties: U.S. Natl. 

Bur. Standards Tech. Note 270-6, 119 p.

Sergeyeva, E. I., Nikitin, A. A., Khodakovsky. I. L., and 

Naumov, G. B., 1972, Experimental investigation of 

equilibria in the system UOj-COg-HpO in 25-200°C temperature interval: Geochemistry Internat., v. 9, p. 900-910.

Sillen, L. G., and Martell, A. E., 1964, Stability constants 

of metal-ion complexes: Spec. Pub. No. 17, The Chemical 

Society, Burlington House, London, 754 p.

Vesely, V., Pekarek, V., and Abbrent, M., 1965, Uranyl phosphates IV, Sorption of some four-valent cations on 

ammonium uranyl phosphate: Jour. Inorganic Nuclear 

Chemistry, v. 27, p. 1419-1425.

Wagman, D. D., Evans, W. H., Parker, V. B., and Schumm, R. H., 

1976, Chemical thermodynamic properties of compounds of 

sodium, potassium, and rubidium: U.S. Natl. Bur. 

Standards Interim Rept. 76-1034, 73 p.

Wagman, D. D., Evans, W. H., Parker, V. B., Halow, I., Bailey, 

S. M., and Schumm, R. H., 1968, Selected values of 

chemical thermodynamic properties: U.S. Natl. Bur. 

Standards Tech. Note 270-3, 264 p.

___1969, Selected values of chemical thermodynamic properties: U.S. Natl. Bur. Standards Tech. Note. 279-4, 

141 p.

Wagman, D. D., Evans, W. H., Parker, V. B., Halow, I., Bailey, 

S. M., Schumm, R. H., and Churney, K. L., 1971, Selected 

values of chemical thermodynamic properties: U.S. Natl. 

Bur. Standards Tech. Note 270-5, 49 p.

60
URANIUM POTENTIAL OF SEDIMENTARY AND IGNEOUS ROCKS 

IN WESTERN AND SOUTHWESTERN OKLAHOMA

BY AL-SHAIEB, ZUHAIR AND JOHN W, SHELTON

DEPARTMENT OF GEOLOGY

OKLAHOMA STATE UNIVERSITY

STILLWATER, OKLA,

Uranium anomalies In western and southwestern Oklahoma 

are present in Permian terrigenous clastic rocks and 

Cambrian Igneous rocks. Uranium anomalies are known to 

occur In slltstones of the Doxey Formation of western 

Oklahoma (Al-Shaieb and others, 1977), in the Post Oak 

Conglomerate near the Michita Mountains, and in dikes within 

the igneous complex of the Michita Mountains.

A carnotite-tyuyamunite-bearing zone is localized in 

the lower part of the Upper Permian Doxey Formation, which 

crops out in Custer, Mashita, Beckham, and Rogers Mills 

Counties. Outcrops of the Doxey are along both flanks of 

the Anadarko basin and near its center.

The Doxey Formation (160-190 ft thick) is characterized 

by alternating siltstones, mudstones, and shale. The host 

rock is composed of highly resistive, well stratified, 

pale-reddish-brown sandy siltstone beds, 15-150 cm thick. 

Subangular to angular quartz and feldspar grains are 

cemented by secondary gypsum and calcite. Ripple marks and 

small-scale crossbedding are major sedimentary structures. 

The Doxey Formation and the upper part of the underlying 

Upper Permian Cloud Chief Formation were deposited in 

tidal-flat environments. Many of these beds have been 

leached to a grayish-green or white color. They are 

fractured, and many fractures are filled with secondary 

gypsum and calcite. Lovett (1961) proposed that these 

gypsum-filled fractures formed as the result of 

post-depositional precipitation either by circulating ground 

water or by a sulfate-rich solution squeezed from an 

evaporite mash during lithification of the Cloud Chief 

Formation. Uranium occurs as spotty encrustations along 

bedding planes, as filling of small fractures, and as part 

of the cement in siltstones. The mineralization appears to 

be spatially related to grayish-green siltstone and also to 

the secondary gypsum disseminated in siltstones and filling 

fractures.

Factor analysis on several ground water samples shows a 

strong positive relationship between uranium, calcium, 

magnesium, sulfate, and total dissolved salts and a 

relatively weak negative relationship between uranium and 

HC03 . Figure 1 shows that the [U02 (C03 ) 2 2 HgO] 2 is the 

complexing agent in these waters. If the activities of 

carbonate species become low, the activity of the uranyl ion 

becomes high (Dall'Aglio and others, 1974). Evaporation 

would increase the activities of specific ion species until

Figure l.~Eh-pH of ground water in some Permian rocks of 

western Oklahoma on aqueous equilibrium diagram of the 

U-02-H 20-C02 system with total C02=10"3M. Dashed lines 

show boundaries for system with total C0o= 10 M. 

Modified from Hostetler and Carrels (1962).

the solubility products of carnotite and tyuyamunite are 

reached, resulting in precipitation of both.

The Post Oak Conglomerate represents the uppermost or 

Permian unit of a thick section of Pennsylvanian and Permian 

arkosic and carbonate detritus derived from the Wichita 

uplift. The Oklahoma Geological Survey considers it 

equivalent to the Hennessey Shale (Havens, 1977).

61
The Post Oak was divided by Chase (1954) into four 

phases, consisting of granite conglomerate, rhyolite 

conglomerate, limestone conglomerate, and granite-gabbro 

conglomerate with zeolite-opal cement. The first two of 

these comprise the greatest volume of the Post Oak. Granite 

conglomerate is present in several isolated patches north of 

the eastern part of the Wichita Mountain and as a larger 

more continuous belt to the south.

The conglomerate near the mountains consists of cobbles 

and boulders, commonly exceeding 30 cm in diameter, in a 

matrix of sandstone which displays many abrupt lateral and 

vertical changes in grain size. Medium-scale crossbedding, 

truncation, and cut-and-fill are the dominant sedimentary 

structures. In the outcrop belt south of the mountains, the 

size and percentage of cobbles and boulders decrease 

southward, as the amount of red and green shales and 

siltstones increases. Within 9 km of the mountains the Post 

Oak consists of lenticular fluvial sandstones and flood 

plain siltstones and claystones. The depositional 

environment is inferred to change southward from alluvial 

piedmont to alluvial plain.

Sandstones of the Post Oak are lithic arkoses and 

feldspathic litharenites, with angular grains and moderate 

to very poor sorting. Quartz, microperthite, and granitic 

rock fragments are the dominant constituents. Detrital iron 

oxides are present, and plagioclase and biotite are found in 

trace amounts. Zircon is generally present, along with rare 

sphene and allanite. Cementation history in the Post Oak is 

complex. Diagenetic clay, the earliest cement, is generally 

kaolinite, but mixed-layer illite-montmorillonite is also 

present. The clay was followed, in succession, by limonite 

and hematite, carbonate, and another generation of illitic 

clay. Barite is a rare cement. Commonly the sequence is 

not completely represented in any one sandstone.

The Post Oak shows low uranium contents ranging from 2 

to 8 ppm, and averaging 2.3 ppm. The highest uranium values 

are found in sandstones which are characterized by a matrix 

of silt and clay, and which occur immediately south of 

granite outcrops. It is suggested, therefore, that uranium 

within most of the Post Oak has been flushed from the ground 

waters which are responsible for the complex cementation. 

Uranium was retained only in those rocks which possessed a 

relatively impermeable clay matrix.

Uranium anomalies are present also in a coarse-grained, 

arkosic, channel sandstone 20 km south of the granitic rocks 

of the Wichita Mountains. The sequence, which is 3 m thick, 

consists of thin beds of sandstone, less than a meter thick, 

and interbedded yellow-red and green shale. The sandstone 

consists primarily of quartz, microperthite, and granophyric 

rock fragments cemented by iron oxides and sparry calcite. 

Apatite and zircon occur in minor quantities. The average 

uranium content of several samples is 60 ppm. However, no 

uranium minerals were identified.

Riebeckite-aeglrine pegmatite dikes, genetically 

related to the peralkallne Cambrian Quanah Granite, contain 

40 to 100 ppm uranium. A typical example of these dikes is 

located on the western edge of the U.S. Wildlife Refuge in 

the Wichita Mountains. This dike is north-trending and is 

essentially vertical (Anderson, 1955). It consists of an 

aplitic core with a xenomorphic, granular texture which 

grades outward into a coarsely crystalline phase, which in 

turn grades into the host rock. A pronounced banding is due 

to preferred orientation of black riebeckite and (or) green 

aegirine crystals and light-colored feldspars and to 

gradational texture. The dike is composed mainly of quartz, 

microperthite, orthoclase, albite, riebeckite, aegirine, and 

small quantities of hornblende. Two distinct generations of 

albite were observed: an early stage associated with 

K-feldspars and a later hydrothermal stage. Presumably 

hydrothermal, microcrystalline quartz, usually in the form 

of veins, cuts across primary minerals. An outstanding 

feature is the abundance of the alkaline-rich riebeckite and 

aegirine, which represent overlapping periods of 

crystallization. Much of the aegirine has undergone 

corrosion and resorption. Zircon is relatively abundant (up 

to 10 percent); it evidently was an early crystallization 

product. Iron oxides occur both as primary and secondary 

minerals.

Fission tracks show that the'uranium is associated with 

both aegirine-riebeckite and refractory minerals such as 

zircon and allanite. It was not determined whether uranium 

occurs as submicroscopic mineral inclusions in Na-rich 

minerals, or if it is fixed in their lattice structures. It 

is proposed that uranium in these dikes is related to a late 

uranium-rich hydrothermal stage which followed an early 

magmatic phase.

Al-Shaieb, Zuhair, Olmsted, R. W., Shelton, J. W., May, R. T., 

Owens, R. T., and Hanson, R. E., 1977, Uranium potential 

of Permian and Pennsylvanian sandstones in Oklahoma: 

Am. Assoc. Petroleum Geologists Bull., v. 61, p. 360-375.

Anderson, K. E., 1955, Pegmatites and miarolitic cavities of 

the Wichita Mountains, Oklahoma: Univ. Oklahoma M.S. 

thesis, 66 p.

Chase, W. W., 1954, Geologic note on Permian conglomerate

around Wichita Mountains, Oklahoma: Am. Assoc. Petroleum 

Geologists Bull., v. 38, p. 2028-2035.

Dall'Aglio, M., Gragnani, R., and Locardi, E., 1974, Geochemical factors controlling the formation of secondary 

minerals of uranium, jn. Nininger, R. D. (chairman), 

Formation of uranium ore deposits: Internat. Atomic 

Energy Agency, Proc. Ser., no. STI/PUB/374, p. 33-48.

Havens, J. S., 1977, Reconnaissance of the water resources 

of the Lawton quadrangle, southwestern Oklahoma: Oklahoma Geol. Survey Hydrologic Atlas 6 (in preparation).

62
Hostetler, P. B., and Garrels, R. M., 1962, Transportation of Lovett, F. F., 1961, Area! geology of the Quartermaster area, 

uranium and vanadium at low temperature, with reference Rogers Mills and Ellis Counties, Oklahoma: Univ. 

to sandstone-type uranium deposits: Econ. Geology, Oklahoma M.S. thesis, 81 p. 

v. 57, no. 2, p. 139-167.

RECENT RESULTS FROM THE CANADIAN URANIUM 

RECONNAISSANCE PROGRAM

BY A, G, DARNLEY 

GEOLOGICAL SURVEY OF CANADA

601 BOOTH ST, 

OTTAWA, ONT, K1A OES, CANADA

The Geological Survey of Canada (G.S.C.), which is a 

Branch of the Canadian Federal Department of Energy, Mines 

and Resources, was involved in developing new methods of 

exploration either specifically for uranium or with 

relevance to uranium throughout the 1960's when exploration 

for this element was at a low ebb. The principal methods 

developed were ground and airborne gamma-ray spectrometry, 

and various forms of regional geochemistry. These methods 

progressed from modest small-scale experiments to extensive 

test surveys conducted in several different areas known to 

contain uranium. This demonstrated the general suitability 

of the methods for rapid and efficient coverage of large 

regions. The operational experience made it possible to 

prepare detailed specifications of a common national 

standard for the execution of the work by several 

contractors.

Although exploration for uranium in Canada has been 

pursued by industry many times over the last 30 years, and 

'most accessible parts of the country have been examined, 

there has been no systematic record to indicate the 

thoroughness with which any nonmim'ng area has been 

searched. It can be safely assumed that while some areas 

have been explored to the limits of present-day capability, 

other areas have been very inadequately examined. 

Unfortunately, for the majority of exploration areas the 

thoroughness of past work is not clearly known, because of 

inadequate records. In these circumstances it is prudent 

for a national program to start from first principles, and 

assume that previous work has been conducted with methods 

less sensitive than those now available. By covering all 

areas, including those containing known mineralization, it 

is possible for a national program to use the response over 

known areas as the basis for interpreting results from the 

same methods over poorly known areas.

The first aim of the Uranium Reconnaissance Program Is 

to ensure that all regions in Canada where the crust

contains an above normal amount of uranium are known and 

adequately delineated. Evidence from G.S.C. studies in 

Canada and published information from elsewhere shows that 

the dimensions of these areas of above average uranium 

content are sufficiently large to be recognizable with 

widely spaced sampling Intervals. A small but important 

aspect of the Uranium Reconnaissance Program is the 

progressive provision of facilities for the standardization 

and calibration of exploration measurements. Past 

exploration work has entailed measurements of a qualitative 

or semi-quantitative type, at best, and this has prevented 

the compilation and comparison of results obtained in 

different places in different times. The Geological Survey 

of Canada is encouraging the adoption by the exploration 

fraternity of the recommendations recently published by the 

International Atomic Energy Agency (Technical Report No. 

174) relating to radiometric standards and calibration, and 

is providing the physical facilities to enable this to be 

done. Facilities for airborne and ground radiometric 

equipment are available and those for borehole equipment are 

under construction.

Over the last 10 years there has been an international 

evolution of ideas concerning the genesis of uranium ore 

deposits. These ideas, which to a considerable extent 

originated in France, came about partly from restudy of well 

known deposits, but also from the study of recently 

discovered deposits in Australia, West Africa, and Canada. 

These studies emphasized the Importance of surface 

weathering processes In moving and concentrating uranium, 

and the strong tendency of uranium deposits to be found In 

proximity to ancient major unconformities. These 

unconformities represent long periods of time during which 

rocks were subjected to weathering. The studies also 

suggested that one of the most favorable places to look for 

uranium deposits formed by these processes is in the 

vicinity of older rocks containing an above normal amount of

63
uranium. With such a working hypothesis an exploration 

program which seeks to delineate those areas of the country 

containing above normal amounts of uranium is likely to be 

successful in two ways. Firstly, those areas of above 

normal uranium content may themselves contain localities 

with a concentration sufficient to be economically 

interesting. Secondly, uranium derived from such areas may 

be concentrated in related younger rocks. The Canadian 

Uranium Reconnaissance Program rests upon the concept that 

most uranium deposits are geologically related to and occur 

in or .near regions of the crust containing higher than 

average amounts of uranium.

One important factor which contributed to the design of 

the Uranium Reconnaissance Program was the success achieved 

by the combined Federal-Provincial Aeromagnetic Program 

initiated in 1960. This program served two purposes: It 

was an aid to geological mapping especially in areas of poor 

bedrock exposure, and at the same time it clearly delineated 

the extent of base-metal-bearing greenstone belts and iron 

formations across the Canadian Shield.

The uranium program primarily depends upon airborne 

gamma-ray spectrometry and regional geochemistry, but other 

methods are not excluded if these serve the objectives of 

the program. The objectives are (1) to provide the mineral 

industry with high quality reconnaissance data to indicate 

those areas of Canada where there is the greatest 

possibility of finding new uranium deposits, and (2) to 

provide government with systematic and nationally consistent 

data to serve as a base for uranium resource appraisal. The 

program is expected to continue at least until 1985. 

Airborne gamma-ray spectrometry is primarily undertaken over 

relatively flat areas where there is some rock outcrop and 

generally thin overburden. High sensitivity equipment is 

being employed with a line spacing for reconnaissance 

purposes of 5 km; but in areas which are remote and may not 

be reached by the main program for a number of years, some 

advance reconnaissance work is being done from time to time 

at wider spacing in order to assign priorities for later, 

more detailed work. Airborne spectrometry is being used 

principally over the Shield, but also over other parts of 

the country where the topography does not prevent effective 

coverage by fixed-wing aircraft. In 1976 for example, the 

hilly area of New Brunswick surrounding the central 

Carboniferous basin was flown.

Regional geochemistry is the only method being used at 

present in mountainous areas, but it is also being used in 

parts of the country with extensive overburden and in areas 

considered particularly favorable for uranium occurrence. 

Because the agreement with the Provinces permits them to 

require searches for other elements besides uranium, in some 

districts geochemistry has priority in Order to fulfill this

commitment. Obviously gamma-ray spectrometry is of prime 

interest only for radioactive elements, whereas geochemistry 

has more general applicability. Eleven elements plus loss 

on ignition are normally measured. The list varies 

according to region, but it typically includes zinc, copper, 

silver, cobalt, nickel, lead, mercury, molybdenum, arsenic, 

iron, and manganese. Regional geochemistry is based upon 

stream-sediment, lake-sediment or bedrock analyses, and 

sample spacing is normally in the range of one sample per 

12.5 km . Water sampling is carried out wherever possible 

as part of the regional sampling program. This technique 

has a unique application to the analysis of subsurface 

waters to detect the presence of uraniferous material in 

otherwise unexposed horizons.

The results from the program are published as rapidly 

as they can be compiled, and are made available 

simultaneously by the Federal and Provincial authorities. 

There is a potential problem with the large amount of data 

required in the course of the program. The 1:250,000 map 

sheets of the National Topographic System (N.T.S.) are used 

as the basic blocks for the program. For each map sheet 

there are normally 12 geochemical and 9 geophysical 

parameters. Up to the end of 1976, standard airborne 

reconnaissance data had been published for 36 of the 

1:250,000 N.T.S. map sheets, and standard geochemical data 

for 24 map sheets. In addition, a preliminary airborne 

reconnaissance had been made over a million square 

kilometers in the District of Keewatin, and individual 

flight lines extended over other portions of the Shield. In 

1977, radiometric and (or) geochemical data will be released 

for 56 additional map sheets. Host of the work to date has 

been carried out in the western half of the Shield north and 

west of Lake Superior.

One of the conditions of the program is that steps are 

taken to monitor the usefulness of the results. This 

entails ascertaining the extent to which results lead to the 

discovery of uranium, and also whether improvements in 

technique are possible. In part this is done by feedback 

from the exploration industry, although the comments 

received are an incomplete record of events and opinion and 

sometimes indicate the data are not being used in the most 

efficient manner. For this reason the G.S.C. is undertaking 

a limited number of followup investigations on selected 

anomalies in several areas in order to provide an 1n-house 

assessment of the reconnaissance program. These 

investigations are undertaken with the agreement of 

companies or individuals holding the mineral rights. In 

general, work is only undertaken subject to agreement that 

the results of these investigations can be published within 

a reasonable period of time, so that everyone may benefit.

64
INTERPRETATION OF URANIUM CONTENT OF GROUND WATER 

IN WEST-CENTRAL KANSAS

BY L, R. HATHAWAY

KANSAS GEOLOGICAL SURVEY

LAWRENCE, KANSAS

The uranium content of ground water collected from 239 

pumping Irrigation wells during the summers of 1974 and 1975 

has been determined by X-ray fluorescence (Hathaway and 

James, 1975; 1976). Ground water from these wells is 

derived from (1) the Ogallala Formation (Tertiary), (2) 

undifferentlated Tertiary (Ogallala) and Quaternary 

sequences, and (3) Quaternary alluvial sediments along the 

Arkansas River in the west-central Kansas study area, which 

covers parts of eight counties. The bedrock formations from 

north to south (Pierre Shale to Dakota Sandstone) Increase 

1n age from Late to Early Cretaceous. The water table 

slopes regionally from west to east, and the water varies 

from an alkaline earth-bicarbonate type to an alkaline 

earth-sulfate type.

Previous determinations of the uranium content of 

ground water from the study area suggested an anomalously 

high regional background level (Scott and Baker, 1962, p. 

47). In the current study a uranium concentration range of 

2-172 ppb, with a mean of 14 ppb, was found. The area! 

distribution' of waters with uranium levels above 20 ppb 

appears closely related to a north-south-trending 

topographic depression (Scott-F1nney depression and Scott 

Basin) that is also reflected in bedrock contours, and to 

portions of the Arkansas River valley. These areas also 

contain saline soils and shallow water tables, and usually 

exhibit sulfate-type ground water and higher total dissolved 

solIds content. In the Scott Basin area the higher total 

dissolved solids level in the ground water appears to be 

related to leaching of soluble salts from the soils in the 

basin area (Hathaway and others, 1975). Water from the 

sandy areas south of the Arkansas River exhibits low uranium 

levels.

Several major chemical species and the total dissolved 

solids in the ground water show a positive correlation with 

uranium (table 1), which suggests the higher uranium values 

observed may result from an increased salt loading of soils 

and ground water in areas of shallow water tables. 

Correction for common correlation with total dissolved 

solids 1s found to reduce greatly the number of variables 

exhibiting a significant correlation with uranium (S102> F, 

Sr, and Mg). A comparison of uranium content with total 

dissolved solids suggests that water from the Scott Basin, 

some of the upland drainage areas, and the northern half of 

the Scott-F1nney depression exhibit a higher 

uranium-to-total-dissolved-sollds ratio than water from the

Table 1 . Correlations of several 

chemical species and total dissolved 

solids with uranium at the 95 percent 

significance level (>0.115)

Variable Correlation 

coefficient

SiO, 

HCO,

so4

Cl

Ca

Mg

Na

K

Sr

Total Dissolved Solids

0.138

0.376

0.249

0.366

0.343

0.317

0.392

0.376

0.378

0.384

0.372

southern half of the depression and the alluvium of the 

Arkansas River valley. This comparison also suggests that 

waters having two different compositions, both with 

relatively high uranium contents, exist 1n the study area. 

The relatively high uranium content of ground water from 

this area suggests that a regional anomaly exists for the 

aquifer and related systems in the Ogallala. Such an 

anamoly may result from leaching and dissolution of volcanic 

ash that contains about 6 ppm uranium (James, 1977) and 1s 

found in the Ogallala Formation (Swlneford and others, 

1955).

The significance of uranium anomalies in ground waters 

from similar settings needs to be interpreted carefully in 

view of the overall water chemistry and aerial variables 

such as soil associations, surface and bedrock topography, 

depth to water, and nature of the surface of the water 

table.

65
Hathaway, L. R. s and James, G. W., 1975, Use of chelating 

ion-exchange resin in the determination of uranium in 

ground water by X-ray fluorescence: Anal. Chemistry, 

v. 47, no. 12, p. 2035-2037.

___1976, Preconcentration of uranium in natural waters 

for X-ray fluorescence analysis: Advances in X-ray 

Analysis, v. 20 (in press).

Hathaway, L. R., Magnuson, L. M., Carr, B. L., Galle, 0. K., 

and Waugh, T. C., 1975, Chemical quality of irrigation 

waters in west-central Kansas: Kansas Geol. Survey 

Chem. Quality Ser. 2, 46 p.

James, G. W., 1977, Uranium and thorium in volcanic ash deposits of Kansas Implications for uranium exploration 

in the central Great Plains: Kansas Geol. Survey Bull. 

Ill, pt. 4 (in press).

Scott, R. C., and Baker, F. B., 1962, Data on uranium and 

radium in ground water in the United States 1954 to 

1957: U.S. Geol. Survey Prof. Paper 426, 115 p'.

Swineford, A., Frye, J. C., and Leonard, A. B., 1955, Petrography of the Late Tertiary volcanic ash falls in the 

central Great Plains: Jour. Sed. Petrology, v. 25, 

no. 4, p. 243-261.

GEOCHEMICAL PROSPECTING AT THE LADWIG 

URANIUM MINE, NEAR GOLDEN, COLORA.DO

BY C, S, FERRIS AND NORMAN BENNETT

CONSULTANTS

11427 W, 57TH AVE,

ARVADA, COLO, 30004

The Ladwig uranium mine is located approximately 4.8 km 

northwest of Golden in the Colorado Front Range. The 

geologic setting is similar to that of the Schwartzwalder 

uranium mine 6.4 km further north, although there are some 

important differences. Country rock consists of gneisses 

and schists of the 1.8- to 2.0-b.y.-old Idaho Springs 

Formation, and a pegmatite, the 1.4-b.y.-old Silver Plume 

Granite.

Rocks at the Ladwig mine consist principally of 

east-northeast-striking, steeply dipping 

garnet-biotite-quartz gneiss, biotite-quartz gneiss, 

biotitic schist, calc-silicate gneisses, minor pyroxenite, 

quartzite, and granite pegmatite. The mine is within the 

northwest-trending Hurricane Hill breccia reef fault zone, 

and the fault system goes through the mine area, but no 

fault has yet been mapped within 600 m. The principal vein 

in the mine strikes northwest and is roughly at the contact 

of pegmatite and garnet-biotite-quartz gneiss.

The original Ladwig mine was operated in 1955-56 by 

Denver-Golden Corp. Near its contact with 

garnet-biotite-quartz gneiss, highly fractured pegmatite was 

mineralized with pitchblende, gummite, and autunite at and 

near the surface. This was open-pit mined and nearly all 

the rock was shipped for milling. A shaft was sunk 

approximately 22.5 m from the floor of the pit; more ore was 

discovered, and was mined from a vein dipping 30°northeast 

near the bottom of the shaft. In 1967, Kerr-McGee Corp. 

undertook a radiometric and soil geochemical survey of the 

property that found additional anomalies. Angled core holes

were drilled to explore the strongest geochemical anomaly, 

and to test veins in the vicinity of the shaft. The 

strongest geochemical anomaly was found to represent a 

nearly vertical vein of pitchblende extending to a depth of 

at least 180 m. However, for various reasons, Kerr-McGee 

did not explore further. In 1969, Reserve Oil and Minerals 

Corp. acquired the property and drove a 900-m adit westward 

to the pitchblende vein discovered by Kerr-McGee. 

Exploratory mining and drilling has been conducted 

intermittently since then. This paper relates known 

pitchblende veins to some of the radiometric and geochemical 

anomalies found 10 years ago.

Initially a square 1,000 feet (305 m) on each side, 

centered on the old Ladwig shaft, was sampled for 

radioactivity and soil molybdenum content on a 25-foot 

(7.6-m) grid. The central grid was surrounded by a zone 500 

feet (152 m) wide, in which samples were taken at 100-foot 

(30.5-m) intervals. Anomalies in parts of this zone led to 

further sampling at 25-foot intervals. Care was taken to 

avoid contaminated areas.

Radiometry was conducted with an Eberline PRM-4 

scintillometer with a 50.8-mm crystal. A check station was 

monitored twice a day for changes in background value. The 

contour lines in figure 1 represent relative values and not 

multiples of "background value. The lowest value shown is 

considerably higher than background.

Soil samples were analyzed for molybdenum, a known 

associate of pitchblende 1n Front Range vein uranium 

deposits. Molybdenum, more stable than uranium in the

66
A,5 7 13 15 17 19 21 23 25 27.A

C

EM

EXPLANATION 

GEOCHEMISTRY 

 10 RADIOMETRY

MOLYBDENUM °

M

10-20 PPM 

20-50 PPM

MINE WORKINGS

100 M 

_I

0,5 7

-=*- VEINS PROJECTED TO SURFACE 

13 15 17 19 21 23 25 27,0

Figure 1

weathering environment, should Indicate the existence of 

uranium veins at depth. Background values of molybdenum are 

2 ppm. Values of 10 ppm or more were considered anomalous.

There 1s some degree of correlation between 

radioactivity and molybdenum In some areas, such as the two 

small southern anomalies, the strong NW-SE anomaly, and 

several small anomalies northeast of the strong one (fig. 

1). However, some molybdenum anomalies, such as the 

northwest part of the strong anomaly and the smaller NW-SE 

anomaly 1n the eastern part of the area, show no significant 

radioactivity. Conversely, anomalous radioactivity without 

corresponding molybdenum extends northeasterly from the main 

anomaly and also forms a large zone westward from the shaft. 

The presence of molybdenum without radioactivity may be 

assumed to mean that soil cover retains or acquires 

molybdenum more easily than it retains or acquires the 

radioactive daughters of uranium. However, radioactivity 

without molybdenum may mean contamination of the surface 

without migration of contaminating molybdenum.

Contamination of part of the area west of the shaft 1s 

likely.

Trenching of molybdenum anomalies showed that most are 

related to narrow radioactive veins. Most veins are nearly 

vertical and strike northwest, although some strike 

northeast and some dip at less than 45°. Drilling of one 

northwest-trending vein confirmed that the vein was 

mineralized.

Mine workings, anomalies, and the principal veins 

discovered are shown on figure 1. Of the northwesterly 

veins, only the westernmost one was extensively explored. 

Drilling from within the mine Indicates 1t may have a 

vertical extent of 600 m. The easternmost vein contains ore 

where intersected by other structures but is otherwise 

indistinct and weakly mineralized. It was found underground 

and has not been traced to the surface. In addition to 

steep veins there are a number of so-called "flat" veins, 

which dip generally less than 45 north to northeast.

The strongest soil molybdenum anomaly corresponds to

67
the westernmost northwest vein. Drilling has shown that the 

vein extends farther southeast than the surface anomaly. 

The northwestern part of the anomaly has not been explored 

at depth, but trenching indicates continuation of the 

structure. The other northwest veins do not provide sharp 

molybdenum anomalies at the surface, although there is a 

weak anomaly for one, and there is autunite in a trench 

between vertical extensions of two of them. The cause of 

the strong molybdenum anomaly trending northwest on the east 

side of the area is not known.

Northeast-dipping "flat" veins, normally less than a

foot in width, have been found at depth and in some 

trenches. Anomalies relating to these veins do not, of 

course, signify structures that may be projected vertically.

In conclusion, where uranium is suspected within a 

Colorado Front Range area with dimensions of several hundred 

meters, detailed soil sampling for molybdenum is a valuable 

supplement to radioactivity in locating pitchblende veins. 

At the Ladwig property the principal vein, not found by the 

original prospectors, showed a molybdenum geochemical 

expression more prominent than the radiometric expression.

HYDROGEOCHEMISTRY OF URANIUM IN THE WALKER RIVER 

BASIN, CALIFORNIA AND NEVADA1

BY D, L. LEACH AND L, V, BENSON

LAWRENCE LIVERMORE LABORATORY

UNIVERSITY OF CALIFORNIA

LIVERMORE, CALIF,

The Lawrence Livermore Laboratory is conducting a 

hydrogeochemical and stream sediment reconnaissance (HSSR) 

in seven western states as part of the National Uranium 

Resource Evaluation (NURE) program sponsored by the U.S. 

Energy Research and Development Administration. The 

objective of the NURE-HSSR program is to complete a 

systematic survey of the nation's surface water, ground 

water, and stream sediment for the purpose of evaluating the 

uranium resources of the United States. Orientation studies 

were conducted in the Basin and Range province, including 

the Walker River Basin in California and Nevada, to aid in 

the design of the NURE-HSSP survey for this environment. 

The specific objectives of this report are to (1) describe 

the geochemical transport system which governs the 

distribution of uranium in water in this environment, (2) 

evaluate the different water types (tributary, river, 

spring, well, and lake) as mediums for detecting uranium 

anomalies, (3) describe the possible temporal changes in 

uranium concentration, and (4) evaluate the possible effects 

of mining and agricultural activities on the 

hydrogeochemistry of uranium.

The Walker River Basin, with an area of approximately

2 11,000 km , lies along the western margin of the Basin and

This work was performed under the auspices of the U.S. 

Energy Research and Development Administration, under 

contract No. W-7405-Eng-48.

Range province. East Walker River and West Walker River 

head in the Sierra Nevada Mountains of California, flow 

through several small valleys, and merge to form the Walker 

River which terminates in Walker Lake. The entire drainage 

area forms a closed basin with no outlet to the sea.

Granitic, metavolcanic, and metasedimentary rocks of 

Mesozoic age are the basement rocks of the Walker Basin. 

Over much of the region they are buried by thick 

accumulations of Cenozoic sedimentary and volcanic rocks. 

Most of the exposed basement consists of quartz monzonite or 

granodiorite. A small number of uraniferous deposits and 

prospects are present along the East Walker River. 

Uranim'te, kasolite, and various secondary uranium minerals 

occur in three closely related settings: (1) quartz veins 

in granitic rocks containing silver, lead, copper, and iron 

sulfides; (2) altered granitic rocks adjacent to quartz 

veins; and (3) fault gouge zones. In addition, the 

Yerington porphyry copper deposit is located below the 

confluence of the East and West Walker Rivers.

Snow, tributaries, rivers, springs, wells, and lakes 

were sampled and analyzed for a spectrum of elements by 

neutron activation and other techniques. The rivers were 

sampled twice: in June during the high-runoff season, and 

in August during the low-flow regime. Each sampling was 

accomplished within a single day so that the chemistry of 

the system was "fixed" with respect to time.

Snow samples reveal the composition of the aqueous 

phase prior to its introduction into the surface and

68
subsurface hydrologlc systems. Of 26 snow samples collected 

from different sites 1n the east-central Sierra Nevada, 10 

were analyzed for uranium. Only one sample contained 

detectable uranium, Indicating the Insignificance of the 

flux of uranium via precipitation.

With the onset of spring, snowmelt is released to the 

tributary system. Along this segment of the transport path, 

the acidic fluid (pH ^5.6) reacts chemically with exposed 

granite, granodlorlte, and felslc volcanics, thereby 

releasing uranium. In the Sierran headwater region, 

concentration of uranium was found to be less than 2 ppb and 

often only a few tenths of a ppb. In tributaries north of 

the Sierran headwater region, concentrations in excess of 2 

ppb are common, and some are as high as 58 ppb, suggesting 

the presence of a uranium anomaly. Some of the snowmelt and 

tributary discharge recharges the subsurface ground-water 

system, a portion of which later emerges in springs. The 

distribution of uranium in springs is similar to the 

distribution found in tributaries. The concentration is 

typically less than 0.5 ppb, and is often below 

detectabillty in the Sierran headwaters. An area of springs 

rich 1n uranium with concentrations as great as 124 ppb 1s 

found in the center of the basin, about 35 km northeast of 

the anomalous area Indicated by the tributaries.

The East Walker River flows for about 75 km through the 

area of uranium occurrences with only a minor increase in 

uranium concentration. For the high-flow condition in June, 

the concentration Increased from 1.3 ppb upstream to 1.9 ppb 

downstream; and the August samples showed an Increase from 

1.5 to 1.9 ppb. The concentration of uranium increases 

gradually, as does the concentration of chloride and sodium 

through this region. River discharge measurements show that 

the river loses water 1n this region during low flow, 

whereas very little water is lost during high flow. In 

addition, the flow 1s apparently maintained at a high level 

during the normal low-level period in August by release from 

the Bridgeport Reservoir. Any anomalous uranium ground 

water that may be entering the East Walker River is 

apparently insignificant compared to the flux of low-uranium 

Bridgeport water. From the base of the Sierras to the 

convergence with the East Walker River, the uranium 

concentration 1n the West Walker River shows a similar 

Increase with distance of transport. For the June samples, 

the increase is from 1.8 ppb to 6.4 ppb, and for the August 

samples, from 0.9 ppb to 6.2 ppb. However, the increase in 

uranium concentration 1s more Irregular than that observed 

for the East Fork, and seems to be affected by areas under 

irrigation. Below the confluence with the East Fork, the 

Walker River flows through Mason Valley, which contains the 

Yerington porphyry copper mine on the west and large areas 

of irrigable agricultural lands on the east side of the 

river. Through this region, the uranium and most other 

dissolved components show a gradual increase in 

concentration towards Walker Lake. For uranium, the June

increase is from 3.7 ppb to 6.3 ppb, and the August increase 

1s from 6.7 to 15 ppb. These increases in uranium 

concentration with transport distance can largely be 

accounted for by evaporative concentration of river water 

through Irrigation procedures. Mass flux calculation show 

that chloride mass decreased by 10 percent through this 

region whereas uranium has a 25 percent increase in mass 

over the same distance. Assuming that chloride 1s as mobile 

as uranium, there 1s a net Increase in uranium relative to 

chloride of nearly 35 percent, which cannot be explained by 

simple evaporation through Irrigation procedures. 

Calculations on the amount of fertilizer used in Mason 

Valley requires that unreasonable amounts of fertilizer be 

added to the system to account for the large increase in 

uranium. Another potential source for uranium in the area 

is the Yerington copper deposit. However, the addition of 

uranium to the river system begins far upstream from the 

Yerington mine. The increase in uranium relative to 

chloride through the region may be due to selective leaching 

of uranium from soil and gravels by irrigation water, or 1n 

the lower reaches of the Walker Basin, to leaching of 

uranium-rich sediments from Pleistocene Lake Lahontan.

These data show that uranium is conserved and Increased 

in the river system, and that its mobility in that system is 

as high as chloride and sodium. Uranium does not appear to 

be appreciably absorbed by the stream sediments, and 

actually may be released from sediments by the leaching 

action of Irrigation water. Agricultural Irrigation 

significantly affects the uranium chemistry of the river 

system, particularly during the low-flow regime 1n August 

when irrigation is at maximum. In addition, the river data 

do not Indicate the presence of known uranium deposits. The 

chemistry of the river 1s dominated by either high flow of 

low-uranium tributary water or low flow of high-uranium 

agricultural water.

The mass transport system terminates at Walker Lake. 

Concentrations of most elements 1n the lake are considerably 

enhanced since Walker Lake functions as a large evaporating 

pan. The concentration of uranium 1s 130 ppb, which is high 

compared to other large surface bodies of water, and 

represents a total uranium mass of about 460,000 kg. The 

high concentration of uranium in Walker Lake can be 

attributed to the stability of the uranium-bicarbonate 

complex 1n the high-bicarbonate complex in the 

high-bicarbonate lake water. However, mass balance 

calculations on Walker Lake show that the uranium present in 

the lake water represents approximately 5 percent of the 

total uranium flux since the last playa stage some 5,000 

years ago. The remaining uranium has been removed by a 

downward flux of uranium into the sediments. This flux 1s 

driven by the absorption of uranium within the reducing 

sediments of Walker Lake.

The data presented provide some Insight into the mass 

transport of uranium within a closed hydro!ogic basin.

69
Uranium 1s an extremely mobile component In the stream 

waters and does not appear to be effectively removed by 

Interaction with the sediments. In terms of geochenrical 

reconnaissance, tributary water is effective in indicating 

surficial uranium sources, whereas spring water is effective

in locating buried deposits. Streams within the basin may 

not be effective in locating uranium anomalies, particularly 

if they receive little ground-water input and are modified 

by reservoirs and irrigation procedures.

URANIUM AND THORIUM DISTRIBUTION IN CONTINENTAL TERTIARY 

ROCKS OF THE COOK INLET BASIN AND SOME ADJACENT AREAS, ALASKA

BY KENDELL A, DICKINSON, U,S, GEOLOGICAL SURVEY, 

DENVER, COLO,

The distribution of uranium in potential host rocks may 

indicate whether the uranium was leached from potential 

source rocks and concentrated in the host rocks in the Cook 

Inlet area, Including the Susitna lowlands and the lower end 

of the Matanuska valley. Suitable uranium source rocks in 

the form of granite and tuff are present in the surrounding

area, and a large'thickness of continental sedimentary rocks 

containing carbonaceous material is found in the basin. The 

important question is whether or not uranium has been 

leached from the potential source rocks and concentrated in 

the potential host rocks. One approach to this problem, 

although not a proven technique, 1s to determine the present

Table 1.--Sources of samples for uranium and thorium analysis

Stratigraphic 

unit

Area Age Rock description in area of 

sampling

Sterling 

Formation.

Beluga 

Formation.

Tyonek 

Formation.

West Foreland 

Formation.

Kenai Group 

undi fferentiated.

Chickaloon 

Formation.

McNeil Canyon, Ninilchik beach Plioceneand Southern Kenai Peninsula. Miocene.

Homer bluff, Miocene. 

Southern Kenai Peninsula.

Capps Glacier and MioceneChuitna River, Oligocene. 

20-30 km northwest of Tyonek.

Beluga River, Eocene. 

17 km north of Tyonek.

Near Houston and PliocenePetersville. Oligocene.

Premier coal mine, Pal eocene. 

Glenn Highway, and 

Chickaloon River.

Sandstone, reddish-brown and gray; 

gray mudstone and shale; and coal 

Fluvial sequence.

Sandstone, gray and reddish-brown, 

fine- to medium-grained, some 

calcitic cement; gray shale and 

mudstone, and coal. Fluvial 

sequence.

Sandstone, light-brown, fine- to 

coarse-grained, conglomeratic; 

gray mudstone and coal. Fluvial 

sequences.

Siltstone and shale, gray, hard, 

micaceous.

Sandstone, brownish-gray, finegrained, hard and soft; and 

shale, gray, hard, micaceous.

Sandstone and conglomerate, gray 

and light-brown, soft and hard, 

arkosic: shale and mudstone, 

gray and brown; and coal.

70
distribution of uranium in the potential host rock to see if 

it has been mobilized by dissolution, transported, and 

redeposited. An advantage of this approach is that it 

provides background data that will aid in the recognition of 

areas affected by uranium mineralization.

A total of 57 samples of potential host rock were 

collected from various localities in the Cook Inlet area 

(table 1). Thorium and uranium were determined in these 

samples by the delayed-neutron method in the analytical 

laboratories of the U.S. Geological Survey at Lakewood, 

Colo. One measure of the precision of the data is the 

coefficient of variation for the counting statistics, which 

averaged 19 percent for thorium determinations and 4.5 

percent for uranium determinations.

The Cook Inlet basin is a structural fault-bounded 

basin in southern Alaska between the Alaska Range to the 

west and the Chugach Mountains and Kenai Mountains to the 

east. It is about 300 km long and 100 km wide. More than 

half of the area is submerged in Cook Inlet, which opens 

into the Gulf of Alaska to the southeast and the Shelikof 

Strait to the southwest. The Cook Inlet basin contains 

about 7,925 m of continental sedimentary rocks that compose 

the Tertiary Kenai Group and West Foreland Formation. 

Calderwood and Fackler (1972) have divided the Kenai Group, 

in ascending order, into the West Foreland Formation, 

Hemlock Conglomerate, Tyonek, Beluga, and Sterling 

Formations (table!). Later Magoon, Adkison, and Egbert 

(1976) removed the West Foreland from the Kenai; and their 

usage will be followed in this report. The Susitna 

lowlands, which are separated from the Cook Inlet basin by 

the Castle Mountain fault, may be a northern extension of 

the basin.

The Matanuska valley is a fault-bounded basin between 

the Talkeetna Mountains to the north and the Chugach 

Mountains to the south. The valley, which connects to the 

Cook Inlet basin along its northeast margin, contains about 

2,135 m of Tertiary continental sedimentary rocks. These 

rocks are divided into three formations, in ascending order, 

the Chickaloon, Wishbone, and Tsadaka (table 1; Magoon and 

others, 1976).

The thorium and uranium contents found in continental 

sedimentary rocks in the Cook Inlet area are remarkably 

uniform (table 2). The uranium content averaged about 2.4 

ppm and the range was from about 0.5 to 4.3 ppm. The 

thorium:uranium ratio averaged about 2.3, low compared to 

the general terrestrial ratio of 3-4, and low compared to 

many oxidized nonmarine sedimentary rocks that 

characteristically have ratios of more than 7 (Adams and 

Weaver, 1958). Shale, siltstone, and mudstone samples 

contain about 1 ppm more uranium than sandstone samples. 

This difference may have resulted from slightly more 

leaching of uranium from porous sandstone or adsorption by 

the clay, but it could also have resulted from depositional 

segregation of heavy uranium-bearing minerals into placer

Table 2.--Distribution of uranium and thorium in continental 

Tertiary rocks of the Cook Inlet basin, Susitna basin, and 

the southern part of the Matanuska Valley as shown by average values and ratios. 

[Numbers in parentheses are number of samples averaged.]

All samples

Sterling Formation

Beluga Formation

Tyonek Formation

West Foreland 

Formation

Kenai Group 

undifferentiated

Chickaloon Formation

Reddish-brown sandstone

Gray sandstone

^udstone, siltstone, 

and shale

Thorium 

(ppm)

5.59 (57)

5.27 (15)

5.22 (20)

6.14 (2)

8.95 (2)

4.69 (4)

$.68 (7)

4.16 (17)

4.34 (18)

6.84 (21)

Uranium 

(ppm)

2.38 (66)

2.13 (21)

2.24 (22)

4.00 (2)

2.97 (2)

1.97 (4)

2.85 (7)

2.01 (17)

1.99 (18)

2.88 (21)

Uranium: 

thorium 

ratio

2.30 (57)

2.19 (15)

2.38 (20)

1.51 (2)

3.01 (2)

2.37 (4)

2.22 (7)

2.12 (17)

2.18 (18)

2.42 (21)

deposits. Reddish-brown sandstone, which presumably was 

subjected to oxidation, has nearly the same uranium content 

as gray sandstone, indicating that the oxidation was 

insufficient to leach uranium from the sandstone.

The low uniform uranium content and the low 

thorium:uran1um ratio found in Tertiary sedimentary rocks of 

the Cook Inlet area may indicate that geochemical conditions 

have not been favorable for the formation of epigenetic 

uranium deposits in these rocks, but it is important to note 

that the samples collected and analyzed for this report may 

not adequately represent the large amount of potential host 

rocks. Not known yet, for instance, are the geochemical 

conditions that existed in the subsurface, especially around 

petroleum accumulations. Hayes, Harms, and Wilson (1976) 

reported rocks in the Sterling Formation that contain 

montmorillonite and some from which volcanic glass has been 

dissolved. None of these samples were evaluated in this 

report.

Adams, J. A. S., and Weaver, C. E., 1958, Thorium-to-uranium 

ratios as- indicators of sedimentary processes example 

of concept of geochemical facies: Am. Assoc. Petroleum 

Geologists Bull., v. 42, no. 2, p. 387-430.

Calderwood, K. W., and Fackler, W. C., 1972, Proposed stratigraphic nomenclature for Kenai Group, Cook Inlet basin, 

Alaska: Am. Assoc. Petroleum Geologists Bull., v. 56, 

no. 4, p. 739-754.

71
Hayes, J. B., Harms, J. C., and Wilson, T., Jr., 1976, Con- Magoon, L. B., Adklson, W. L., and Egbert, R. M., 1976, Map

trasts between braided and meandering stream deposits, 

Beluga and Sterling Formations (Tertiary), Cook Inlet, 

Alaska, i^ T. P. Miller, ed., Recent and ancient sedimentary environments in Alaska: Proc. Alaska Geol. Soc. 

Symposium, Anchorage, 1975, Proc., p. J-l-J-27.

showing geology, wildcat wells, Tertiary plant fossil 

localities, K-Ar age dates, and petroleum operations, 

Cook Inlet area, Alaska: U.S. Geol. Survey M1sc. Inv. 

Map 1-1019, scale 1:250,000.

A 252CF-BASED BOREHOLE LOGGING SYSTEM FOR 

IN-SITU ASSAYING OF URANIUM ORE

BY D, K, STEINMAN, D, G, COSTELLO, C, S, PEPPER, W, E, GOBER, 

D, B, BREUNER, J, S, M, WILSON, J. C, YOUNG, AND JOSEPH JOHN 

IRT CORPORATION, SAN DIEGO, CALIF, 92138

IRT Corporation, under contract with the U.S. Energy

Research and Development Administration (ERDA), has

252 constructed a prototype of a second-generation, Cf-based

direct uranium measurement system for borehole logging. 

Preliminary tests of this system have been conducted in the

laboratory and in the field. The technical feasibility of

252 using Cf sources for borehole logging of uranium was

first demonstrated by Kerr-McGee Corporation several years 

ago. The ERDA-sponsored program at IRT has been directed at 

building and testing a practical hardware system using 

252Cf. It is anticipated that the first commercial system 

could be available by June 1978.

Thermal neutron fission 1s used to uniquely identify 

any uranium present in the rock around a borehole. 

Uranium-235 undergoes fission upon capture of a thermal 

neutron. The fission products emit radiations such as beta 

rays, gamma rays, and neutrons during their decay to stable 

isotopes. Of these, the neutrons represent the most 

interference-free means of of uranium identification because 

the natural background sources of neutrons are very weak.

Californium-252 is a practical neutron source for 

assays, and has the desirable engineering features of small 

size and steady, maintenance-free output. It requires no

power and generates negligible internal heat. Neutrons from

25? the Cf source induce fission of the uranium in the rock

ooc

around the borehole, and delayed neutrons from the U 

fission are detected in the sonde to indicate the presence 

and concentration of uranium in the rock. This method, 

called delayed neutron activation analysis (DNAA), 1s 

sensitive because there is no background source of neutrons 

to mask the delayed neutrons from fission. The method is 

also selective, because the thermal neutrons can only induce 

nuclear fission in 235U.

The logging system consists of a sonde which contains 

the formation measurement subsystems, the sonde-support, the

source-storage cask which provides the biological shielding,

252 and the mechanism for transferring the Cf source between

the cask and the sonde. In addition, there is the logging 

truck containing the power supply, the logging winch, the 

teletype and plotter, and the electronic equipment used to 

control the sonde and to acquire, analyze, and display the 

data from the sonde. The sonde has a diameter of 5.7 cm, 

and it contains the measurement subsystem from which the 

delayed neutron signal, the monitor detector signals, and 

the natural gamma-ray signals are detected and conditioned 

for use by the uphole electronic units. Low-voltage dc 

power is supplied to the sonde through two conductors in the 

4HO logging cable. Signals and commands between the 

detectors in the sonde and the electronic units in the truck 

are sent through the other two conductors in the cable. The 

surface electronic units receive, process, and display the 

detector signals, and the system control unit, an LSI-11 

minicomputer, is able to reduce the data and display it in a 

form useful for uranium exploration or mine planning.

In keeping with the overall program goal of developing 

a practical, sensitive, economic, and safe uranium logging 

system, the following factors were considered: (1) 

acceptability to the uranium industry, (2) logistics of 

logging and maintenance, (3) sensitivity and precision of 

measurement, (4) cost of acquisition and operation, and (5) 

safety of operation.

To make the system acceptable to the uranium Industry, 

it was thought that its operation should represent as little

change as possible from current logging practice. In

252 addition, the intensity of the Cf neutron source had to

be minimal. A new activation technique permitted reduction

72
of the source size to a tenth of that used by Kerr-McGee 

with a net gain in sensitivity. All necessary information 

is obtained in a single pass through a borehole. The DNAA 

log is made with the sonde going upwards at 1.5 m/min. 

Logistically, a single vehicle with a GVW rating of 10,000 

pounds can transport the system, including the biological 

shield for the source. One technician can operate the 

system, with the aid of the system control unit. The system 

has sensitivity to 100 ppm U,0Q ; the neutron counts detected

?R? are equal to 9.1 per percent UgOg per ug totCf. With a 

source loading of 330 ug, a neutron count of 3,000 counts is 

obtained in 1 percent ore. The background counting rate is 

negligible, so sensitivity to less than 100 ppm U 30g is 

statistically useful. In addition to statistical precision, 

the system also includes a neutron flux monitor which 

measures the effects of the surrounding rock on the source 

neutrons and uses the resulting signals to correlate effects 

on the DNAA signal. The monitor signals are themselves 

useful as a lithology log. For safety, the design of the 

system minimizes both the exposure of the operator to the

source and the possibility of losing control of the source. 

A mechanism on the sonde permits retrieval of the source if 

the sonde becomes stuck in the borehole. The source is 

shielded and kept in a guiding channel during all loading 

and unloading operations to help prevent accidental loss. 

For each hole logged, the operator is exposed to an amount 

of radiation that is less than 3 .percent of the weekly 

maximum permitted by Federal law. Cost projections show 

that the system can be used for 45$ to 72$ per foot ($1.48 

to $2.36 per meter).

Field tests in 21 boreholes in the three major 

uranium-producing districts of the country show the system 

performs satisfactorily in temperatures from 0° to >32°C, in 

both cased and uncased holes, and with ore grades from less 

than 100 ppm to more than 1.5 percent UgOg. At many of the 

measured holes, core assays were available for comparison. 

Field tests also showed the system could be set up in less 

than 10 minutes and stored back on the truck in less than 7 

minutes.

ANOMALOUS URANIUM IN THE WATERS OF THE RIO OJO CALIENTE, 

NEW MEXICO

BY K, J, WENRICH-VERBEEK, U,S, GEOLOGICAL SURVEY., 

DENVER, COLO,

A high U value (15 ug/«.) found in water of the Rio Ojo 

Caliente, La Madera, Rio Arriba County, N. Hex., during a 

regional sampling technique study in August 1975 by the 

author, was further investigated in May 1976 to determine 

whether stream waters could be effectively used to trace the 

source of an anomaly. The associated stream sediments, 

sampled in 1975, contain only an average U content, 3-6 ppm 

(variation among replicate samples) and would not have been 

useful for isolating an anomalous area in a reconnaissance 

program (Wenrich-Verbeek, 1977).

Although uranium in the pegmatites was first reported 

in 1930, pegmatite deposits in the Petaca-Ojo Caliente area 

of northern New Mexico have been sources of commercial mica 

since the 17th century (Jahns, 1946). The rocks in the 

Petaca-Ojo Caliente area are predominantly Precambrian 

quartzites and quartz-mica schists with lesser amounts of 

Precambrian amphibole schists, meta-rhyolites, and a 

medium-grained granite. These units are transected by 

pegmatite bodies and quartz veins containing sparsely 

disseminated crystals of U minerals, notably samarskite. No 

Paleozoic or Mesozoic rocks are exposed in the area above La

Madera although the Tertiary Carson Conglomerate of Just 

(1937), and Tertiary and Quaternary Santa Fe Formation are 

present. Quaternary basalts cap many of the mesas and 

Quaternary alluvium has been deposited to form flat valley 

bottoms along some stretches of the Tusas and Vallecitos 

rivers.

Numerous thermal springs occur in this region of New 

Mexico. Some of them have been studied by Summers (1976, p. 

24-28) who reported limited Rn-222 determinations, but no U. 

Although the Rn in the hot springs of the Ojo Caliente area 

ranges from 820 to 9,400 pC/s,, no insight into the uranium 

content can be gained from these data because of the 

different solubility of radium, the direct parent of radon; 

uranium concentrations are frequently low in springs of high 

radium content.

A detailed study of the tributaries to the Rio Ojo 

Caliente above La Madera was conducted during a moderate 

discharge period, May 1976, so that small tributaries would 

contain water. The U.S. Geological Survey gaging station at 

La Madera was resampled, and due to the increased discharge, 

from 15 to 109 cfs, the water showed an expected decrease in

73
uranium concentrations from 15 to 3.3 vg/a. This example of 

changing uranium concentration with discharge emphasizes a 

major problem in water sampling, that is, maintenance of a 

constant discharge during the sampling of an entire study 

area. This problem is minimized if the uranium 

concentration is normalized by the similarly decreased 

conductivity (lOOxU/conductivity); under these conditions 

the uranium content of the Rio Ojo Caliente remains 

anomalous (greater than two standard deviations above the 

mean) with respect to other normalized values from its 

drainage basin. This particular anomaly is sufficiently 

large that even without normalizing the values the source of 

the uranium anomaly can readily be traced (fig. 1). Canada 

de la Cueva, a small tributary to the Ojo Caliente, was 

found to contain 40 ^g/j,whereas other tributaries contain <3 

vg/M. The source of the anomaly appears to be a hot spring

containing 60 v g/M that discharges into Canada de la Cueva; 

this is an unusually high value for hot springs, among the 

highest reported in the United States (J. K. Felmlee, oral 

commun., 1977).

From figure 1 it can be seen that other sites in the 

area have uranium values comparable with the Rio Ojo 

Caliente at the U.S. Geological Survey gaging station. Yet, 

when the values are normalized, only the Rio Tusas above the 

junction with Rio Vallecitos (1.04), the Rio Ojo Caliente at 

the gaging station (1.40), Canada de la Cueva (1.63), and 

the hot spring on Canada de la Cueva (3.80) are anomalous 

with respect to all other localities (<0.80). From these 

results it appears that the Rio Tusas above the junction 

with the Rio Vallecitos should also be studied in more 

detail. Between 1975 and 1976 the Rio Ojo Caliente at the 

U.S. Geological Survey gaging station ranged from 2.10 to 

1.40 normalized uranium. Thus, uranium values at this site, 

when normalized, maintain a constant relation to 

drainage-basin background values regardless of variation in 

discharge.

Correlations between uranium and other parameters are 

listed in table 1 for two groups of data: (1) all sample 

sites and (2) all sites except the hot spring and Canada de 

la Cueva, both containing uranium concentrations an order of 

magnitude greater than the other samples. Correlation 

coefficients of group 2 when compared with group 1 give a 

suggestion as to elements which may be present in the source 

rock contributing uranium to the ground water that feeds the 

hot spring at La Madera.

Table 1. Correlation coefficients between U and other parameters 

measured in water from the Rio Ojo Caliente Drainage 

basin, N. Hex.

[i - Correlation coefficient; n - Number of samples; ** Significant 

at the 99 percent confidence Unit; * Significant at the 95 percent confidence limit]

Figure 1

Parameter

Water Temperature

Conductivity

pH

Alkalinity

Hardneas

Ca

Mg

Na

K

F

As

Ba

B

Cu

Fe

Pb

Mn

Mo

Ni

Sr

V

Zn

Al

Li

Ti

Hg

Eh

All

r

0.67

0.73

-0.31

0.81

0.96

0.94

0.97

0.44

0.94

0.08

0.96

-0.11

0.87

0.58

-0.15

0.63

-0.18

0.59

0.40

0.92

0.59

0.07

-0.06

0.29

0.12

0.06

0.24

29 sites

n

29

29

21

29

28

26

28

28

28

29

25

29

17

27

29

25

25

9

15

29

25

25

29

25

25

25

25

Sign.

**

**

**

**

**

**

*

**

**

**

**

**

**

**

27 sites omitting 

anomalous U sites

_r

0.56

0.58

0.38

0.64

0.75

0.76

0.64

0.48

0.66

0.53

0.57

0.12

0.54

0.25

-0.30

0.82

-0.18

0.59

0.34

0.70

0.59

0.39

-0.20

0.48

-0.24

-0.34

0.10

n

27

27

19

27

26

24

26

26

26

27

23

27

16

26

27

18

25

9

23

27

23

23

27

23

23

23

27

Sign.

**

**

**

**

**

*

*

*

*

*

**

**

**

*

74
Uranium in the waters of the Rio Ojo Caliente drainage 

basin is most closely related to the alkalies and alkaline 

earths; calcium, magnesium, sodium, potassium, alkalinity, 

conductivity, and hardness all show significant correlations 

with uranium. R-mode factor analysis places them in the 

same factor group with uranium. This result is expected,

particularly for calcium which, in these samples, is related

2 to the C03 anion that has a large influence on the

solubility of uranium. Due to this association of uranium 

with the alkalies and alkaline earths, normalization of the 

uranium content by conductivity, which is controlled by the 

concentration of the major ions, should be effective in 

minimizing the effects of evaporation and dilution on the 

uranium content of surface waters.

The elements arsenic and boron show much higher 

correlation coefficients for the sample group including the 

high-uranium sites, although both have significant 

correlations without the high-uranium sites. This suggests 

that arsenic and boron are very high in the uranium source 

rock and (or) show solubilities similar to uranium. 

Previous studies (Wenrich-Verbeek, 1977a) have shown that 

arsenic and boron frequently correlate with uranium in 

water, so their solubilities are possibly very similar; 

their very high correlation coefficients, 0.96 and 0.87 

respectively, suggest also that they are high in the uranium 

source rock. The nonsignificant correlation of uranium with 

other metals may be as much, if not more, a function of 

differences in the other metals' soluble complexes and 

solubility constants from those of uranium as they are a 

function of the metals' occurrence, or lack of it, in the 

source rock.

Only a few anomalous values occur among the other 

elements and these are distributed primarily within two 

areas: (1) the hot spring and Canada de la Cueva contain 

anomalous concentrations of Ca, Mg, Na, K, As, B, and Sr, 

and (2) Carton de la Paloma contains anomalies of Na, Li, B, 

F, and Mo. The association of Mo with F, Li, B, and Na also 

occurs to the northeast of Ojo Caliente in the molybdenite 

deposit of Questa, N. Mex. Perhaps the Canon de la Paloma 

Mo anomaly should be studied further. The pegmatite at the 

Paloma Canyon mica prospect is albitized and contains 

fluorite perhaps contributing to the F and Na anomaly.

Conclusions: A uranium anomaly found in the waters of 

the Rio Ojo Caliente has been traced upstream along Canada 

de la Cueva to a hot spring. Hence surface-water sampling

has been shown to be an effective geochemical technique for 

tracing a stream stream-water uranium anomaly back to a 

ground-water source for the uranium and consequently has 

value as a tool for locating buried deposits. Normalizing 

uranium concentrations with conductivity proved extremely 

useful in negating the effect of a change in stream 

discharge from 15 to 109 cfs.

Although the Petaca-Ojo Caliente area has long been 

known for its samarskite occurrences in pegmatites, the 

uranium anomaly traced to the hot spring in Canada de la 

Cueva suggests the possibility that a uranium occurrence, 

perhaps a concentration from the uranium-bearing pegmatites 

up the drainages is present in the Tertiary-Quaternary 

sediments, or possibly deeper in the Precambrian, beneath 

the surface near La Madera, N. Mex. Additional sampling of 

the ground water and numerous springs, particularly those 

springs linearly alined along Canada de la Cueva from the 

anomalous hot spring, should prove valuable in delineating 

the anomalous area.

Jahns, R. H., 1946, Mica deposits of the Petaca district, Rio 

Arriba County, New Mexico, with brief descriptions of 

the Ojo Caliente district, Pio Arriba County, and the 

Elk Mountain district, San Miguel County: New Mexico 

Bur. Mines and Mineral Resources Bull. 25, 289 p.

Just, Evan, 1937, Geology and economic features of the pegmatites of Taos and Rio Arriba Counties, New Mexico: 

New Mexico School of Mines Bull. 13, 73 p.

Summers, W. K., 1976, Catalog of thermal waters in New Mexico: 

New Mexico Bur. Mines and Mineral Resources Hydrol. Rept. 

no. 4, 80 p.

Wenrich-Verbeek, K. J., 1977a, Uranium and coexisting element 

behavior in surface waters and associated sediments with 

varied sampling techniques for uranium exploration: 

Jour. Geochem. Explor. (in press).

___1977b, The effectiveness of stream-sediment sampling 

along the Rio Ojo Caliente, New Mexico, in Energy 

Resource and Development Administration Symposium on 

Hydrogeochemical and stream-sediment reconnaissance for 

uranium in the United States, Proc. (in press).

75

*U.S. Government Printing Office: 1977-777-102/12