U.S. GEOLOGICAL SURVEY CIRCULAR 1069 

Short Papers of the 

U.S. Geological Survey 

Uranium Workshop, 1990 
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Short Papers of the 

U.S. Geological Survey 

Uranium Workshop, 1990 

Edited by KENDELL A. DICKINSON 

Papers presented March 20, 1990, at the Denver Federal Center 

and at the Sheraton Hotel, Lakewood, Colorado 

U.S. GEOLOGICAL SURVEY CIRCULAR 1069 
U.S. DEPARTMENT OF THE INTERIOR 

MANUEL LUJAN, JR., Secretary 

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director 

Any use of trade, product, or firm names in this publication is for descriptive purposes only and 

does not imply endorsement by the U.S. Government 

UNITED STATES GOVERNMENT PRINTING OFFICE: 1992 

Free on application to 

Book and Open-File Report Sales 

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Library of Congress Cataloging-in-Publication Data 

U.S. Geological Survey Uranium Workshop (1990 .: Denver Federal Center and 

Lakewood, Colo.) 

Short Papers of the U.S. Geological Survey Uranium Workshop, 1990 I edited by 

Kendell A. Dickinson. 

p. em. -- (U.S. Geological Survey Circular; 1 069) 

"Papers presented March 20, 1990, at the Denver Federal Center and at the Sheraton 

Hotel, Lakewood, Colorado." 

Includes bibliographical references. 

1. Uranium ores-United States-Congresses. 2. Uranium ores-GeologyUnited States-Congresses. I. Dickinson, Kendell A., 1931- • II. Geological 

Survey (U.S.) Ill. Title. IV. 1itle: Short papers of the US Geological Survey 

Uranium Workshop, 1990. 

V. Series. 

TN490.U7U54 1990 

553.4'932'0973-dc20 
PREFACE 

By Kendell A. Dickinsonl 

This Circular contains abstracts and short articles from oral presentations and posters 

presented at the 1990 Uranium Workshop sponsored by the Branch of Sedimentary Pro· 

cesses, U.S. Geological Survey. The workshop was held on March 20, 1990, at the U.S. 

Geological Survey on the Denver Federal Center and at the Sheraton Hotel, Lakewood, 

Colorado. The last workshop of this type was held in 1977 and was titled the Uranium and 

Thorium Resource and Research Conference. 

Readers interested in additional information about papers presented at the meeting 

should contact the authors directly. Mailing addresses for each author may be found in the 

footnotes on the first page of each paper contained in this Circular. 

Interest in uranium was unexpectedly high at the workshop considering the present 

(March 1990)low spot price for U30 8 and the recent unpopularity of nuclear power. Most 

people realize, however, that nuclear power will continue to play an important energy role 

both in the United States and abroad. The workshop played an important role in providing 

a platform for the exchange of ideas, especially in areas such as surficial uranium deposits 

and breccia pipe deposits. The growth of knowledge in these fields has been substantial 

since interest in uranium waned as the National Uranium Resource Evaluation (NURE) 

program ended in the early 1980's. 

It is important that knowledgeable and experienced uranium geologists in both industry 

and government be available to make many of the important uranium-related decisions that 

lie ahead-this would be especially important in the event of a future national energy crisis. 

Manuscript approved for publication June 18, 1991. 1

U.S. Geological Survey, Box 25046, Mail Stop 939, Denver Federal Center, Denver, Colorado 80225. 

Preface Ill 

CONTENTS 

The State of the U.S. Uranium Industry in 1989 

by William L. Chenoweth 1 

U.S. Uranium Reserve Assessment 

by Taesin Chung 2 

Uranium Resources in New Mexico 

by Virginia T. McLemore and William L. Chenoweth 3 

New Assessments of Uranium Endowment for Two Regions in the United States 

by Warren !.Finch, Charles T. Pierson, Richard B. McCammon, James K. Otton, 

Hoyt B. Sutphin, and Karen J. Wenrich 7 

Uranium Endowment Estimate Calculations 

by Richard B. McCammon 12 

Uraniferous Wetlands-Young Uranium Deposits 

by Douglass E. Owen 14 

Response of Douglas Fir to Uraniferous Ground Water: A Case Study with Implications 

for Environmental Monitoring 

by Robert A. Zielinski and R. Randall Schumann 16 

Uranium Series Disequilibrium in a Young Surficial Uranium Deposit, Northeastern 

Washington 

by Robert A. Zielinski, Charles A. Bush, and John N. Rosholt 18 

Geology of the Holocene Surficial Uranium Deposit of the North Fork of Flodelle Creek, 

Northeastern Washington 

by Samuel Y. Johnson, James K. Otton, and David L. Macke 21 

Arid-Land Surficial Ur~ium Deposits-A Review of Examples and Their Modes of 

Occurrence 

by Sigrid Asher-Bolinder and James K. Otton 23 

Hydrogeology of San Juan Basin Uranium Deposits-The Brine-Interface Model 

Revisited 

by Richard F. Sanford 26 

Uranium Mineralization and Favorability in the Oligocene Chadron Formation, 

Southeastern Wyoming and Northwestern Nebraska 

by Paula L. Hansley and Kendell A. Dickinson 21 

Uranium in Phosphate Rock-With Special Reference to the Central Florida Deposits 

by James B. Cathcart 32 

Organic Matter and Uranium in Solution-Collapse Breccia Pipes of Northern Arizona and 

San Rafael Swell, Utah 

by Karen J. Wenrich and James G. Palacas 36 

Gold-Bearing Collapse-Breccia Pipe, Copper Mountain, Northwestern Arizona 

by Paul Adamek, H.J. Behr, and Edmund von Pechmann . Sl 

Relationship Between Collapse History and Ore Distribution in the Sage Breccia Pipe, 

Northwestern Arizona 

by Neal A. Brown, Richard H. Mead, and Jay M. McMurray 54 

Contents V 

The State of the U.S. 

Uranium Industry in 1989 

By William L. Chenoweth1 

The domestic uranium industry continues to operate at 

a reduced level due to low prices and increased foreign competition. The Secretary of Energy declared the industry to be 

nonviable for the period from 1984 to 1988, and a similar 

declaration is expected for 1989. Exploration and development drilling continues at the rate of 2 to 3 million ft per year 

in areas of producing mines and recent discoveries: northwest Arizona, northwest Nebraska, south Texas, Wyoming, 

southwest Colorado, and southeast Utah. Production of uranium concentrate during 1989 is estimated at 13.8 million 

pounds of uranium oxide (U 30 8) (fig. 1). For 1989, conventional mining methods account for approximately 55 percent 

of the production in New Mexico, Arizona, Utah, Colorado, 

and Wyoming (fig. 1), while the remaining 45 percent comes 

from solution (in situ) mining, from mine-water recovery, 

and from by-products of copper production and the manufacture of phosphoric acid 

50,----------------------------------, 

"" 40 

0 

::> "' 

~ 30 z 

:::> 

0 

0. 

u. 

~ 20 z 

0 

::; 

..J 

~ 10 

EXPlANATION 

0 In Situ' and By-Product 

0 Conventional ____r--1---1---

•1n Situ includes solution mining, f--f- mine water, and heap leaching r-

-

~~ 

I-- I-- -

-~--- I-- I-- I--

1968 70 72 74 76 78 80 82 84 86 1988 

CALENDAR YEAR 

Figure 1. United States uranium concentrate production, 

1968-1989. Data from Energy Information Administration 

(1989). Production for 1989 is estimated. 

1

707 Brassie Drive, Grand Junction, Colorado 81506. 

During 1989, underground mining took place in the 

Grand Canyon region of Arizona; Ambrosia Lake area, New 

Mexico; Crooks Gap, Wyoming; and in the Uravan mineral 

belt of Colorado and Utah. Due to the high vanadium content of the ores in the Uravan area (as much as 10 times the 

uranium content), vanadium is the principal metal recovered, 

and uranium is considered a by-product. Two open-pit 

mines were operating in 1989: one in Shirley basin, Wyoming, and another in McMullen County, Texas. Solution 

mining was done in the Powder River Basin, Wyoming, and 

in south Texas. The Crow Butte project in Dawes County, 

Nebraska, should receive final permits for commercial operation in 1990. Uranium is recovered from water circulating 

through inactive underground mines at Ambrosia Lake, New 

Mexico. Uranium is also recovered from the manufacture of 

phosphoric acid at plants in central Florida and southern 

Louisiana. The plants in Louisiana process phosphate rock 

that is barged in from Florida. Uranium that was recovered 

from phosphate operations amounted to approximately 3 

million pounds ofU30 8 in 1989 (22 percent ofthe total U.S. 

production). A plant that recovered uranium from copper 

leach solutions at Bingham Canyon, Utah, was placed on 

standby in early 1989. Unmined deposits, such as those in 

the Church Rock, New Mexico, area, are being investigated 

for the possible application of solution-mining technology. 

In 1989, ore from conventional mines was processed at 

four mills: Shirley basin, Wyoming; Blanding, Utah; 

Ambrosia Lake, New Mexico; and Hobson, Texas. In January 1990, both the Shirley basin and Ambrosia Lake plants 

were placed on standby. The Shirley basin mill will reopen 

in mid-1990, when stripping is completed and mining commences at a new open pit in the Shirley basin. Late in 1989, 

the Section 23 mine at Ambrosia Lake, New Mexico, closed, 

and the Sunshine Bridge uranium recovery plant in Louisiana was placed on standby. In early 1990, the last underground mine (Mt. Taylor) at Ambrosia Lake closed, and 

several solution mining operations in Wyoming and Texas 

were placed on standby. Uranium concentrate production in 

1990 could drop to approximately 8 million pounds of U30s. 

The discovered uranium resources in the United States 

are quite large, and the potential to discover additional 

resources is excellent. However, higher prices and a strong 

market will be necessary for their exploitation. 

REFERENCE CITED 

Energy Information Administration, 1989, Uranium Industry 

Annual 1988: U.S. Department of Energy Report 

DOFJ EIA-0478(88), 121 p. 

The State of the U.S. Uranium Industry in 1989 1 
U.S. Uranium Reserve 

Assessment 

By Taesin Chungl 

The uranium raw materials program ofthe U.S. Department of Energy (DOE) was formerly conducted through its 

Grand Junction Office (GJO). In 1983, the resources of GJO 

were drastically reduced, and the activity for uranium information gathering and reporting, including reserve assessment, was transferred to the Energy Information 

Administration (EIA). EIA is an independent unit of DOE 

concerned with information gathering and analysis. Undiscovered uranium resource evaluations are performed by the 

U.S. Geological Survey through an interagency agreement 

with DOE established in 1983. 

. !~fo~tion on uranium reserves and related industry 

act1v~t1es ts released by EIA in publications, primarily the 

Uramum Industry Annual, which summarizes the findings of 

the annual survey questionnaire. Additional information is 

re~e~sed in a report entitled Domestic Uranium Mining and 

Mtlhng Industry as part of the annual industry viability 

assessment. Information is also provided in collaboration 

with the joint activities of the International Atomic Energy 

Agency, especially in the periodic publication Uranium 

Resources, Production, and Demand, which covers worldwide uranium activities. EIA presents its findings at various 

technical meetings such as the U.S. Council for Energy 

Awareness annual uranium seminars. 

Uranium reserve assessments developed by EIA since 

1984 are largely dependent on data provided from replies to 

the annual questionnaires sent to industry. Companies report 

'~economic" reserves as well as production data and exploration and marketing activities. 

Reserves or reasonably assured resources at various 

co~t levels are determined by analysis of the property-level 

estimates of reserves completed by GJO as of December 31, 

1983. EIA adjustments to the GJO estimates include dele1

Project Manager, Uranium Resources, Nuclear and Alternate Fuels 

Division, Energy Information Administration, U.S. Department of Energy, 

Washington, D.C. 20585. 

2 Short Papers of the U.S. Geological Survey Uranium Workshop, 1990 

tion of properties that are reported as mined out, subtraction 

of production, and "erosion" adjustments that recognize 

losses from reserves of higher cost reserves as production 

proceeds. Currently, EIA does not estimate reserves of individual property from basic drill hole data. 

Increasing concern and some criticism has been 

expressed concerning the methodology in use by EIA and 

that the types of information being developed are not as reliable as before. Estimation techniques employed by companies providing reserve estimates are not uniform. Credibility 

is affected by reliance on company estimates made with a 

variety of techniques and assumptions and the adjustment of 

EIA reserve files without consideration of the fundamental 

developments at each property. Reliance on questionnaires 

has reduced the high level of trust formerly maintained 

between industry and GJO. As the needs for data and the 

resources available to make uranium reserve estimates have 

changed, alternate approaches recommended by independent reviewers are being considered. The overall recommendation includes modifying the survey questionnaire, 

auditing company-supplied information on a property-byproperty basis, and reestablishing ore deposit parameters to 

more closely define reserves in light of current conditions. 

The EIA continues to work towards implementation of an 

improved system of uranium reserve estimation. A redesigned survey questionnaire is currently under final review. 

Proposed changes include a shorter and more concise scope 

and a more realistic survey for in-situ leach operations. Priorities for company reviews on a property-by-property basis 

have been established; these priorities are based on those 

companies that have the largest reserves or active properties 

and on reserves appropriate for exploitation by new mining 

methods. Meetings with individual companies to verify 

reserves and to discuss estimation techniques have been 

scheduled. EIA staff will be utilized for all future reserve 

assessments. Cataloging and evaluation of basic data in EIA 

files has begun. 

EIA has developed in-house microcomputer software 

programs to provide a reserve estimation capability independent of the estimates provided by companies. The programs 

were written to estimate reserves from basic drill hole data. 

EIA is continuing to make improvements on the reserve estimation system using an on-site contractor and support from 

Oak Ridge National Laboratory. 
Uranium Resources in 

New Mexico 

By Virginia T. Mclemore1 and 

William L. Chenoweth2 

For nearly three decades (1950's-1970's), the Grants 

uranium district produced more uranium than any other district in the world, while other areas in New Mexico yielded 

minor quantities of uranium ore. The total uranium production in New Mexico from 1948 through 1989 was more than 

327 million pounds ofU30 8 concentrate. New Mexico contains most of the Nation's uranium resources even though 

declining market conditions have forced closure of all uranium mines in the State (January, 1990). New Mexico contains about 89 million pounds of U30 8 in economic reserves 

as of December 31, 1988, or 24 percent of the total economic 

reserves in the United States (fig. 1). Economic reserves are 

estimated by individual companies and are submitted to the 

Energy Information Administration (EIA), U.S. Department 

of Energy. Figures reported by the EIA do not include all 

120 million pounds of uranium in reserves at the Mt. Taylor 

mine that is owned by Chevron Resources Co. (Alief and 

Kern, 1989). New Mexico also contains about 177 million 

pounds of U30 8 in the $30 per pound forward-cost category 

and 447 million pounds of U30 8 in the $50 per pound forward-cost category of 61 percent and 45 percent of the total 

domestic reasonably assured resources as estimated by the 

EIA (fig. 1) (Energy Information Administration, 1989). 

Reasonably assured resources are estimates of grade and tonnage in known deposits that can be recovered within given 

production-cost ranges. 

Most of New Mexico's uranium resources occur in 

sandstones of the Morrison Formation (Upper Jurassic), 

which produced more than 338 million pounds ofU308 from 

1948 to 1989. Three types of uranium deposits occur in the 

Morrison Formation: primary, redistributed, and remnant 

uranium deposits. Primary uranium deposits are less than 8 

ft thick, average more than 20 percent U30 8, are low in vanadium, have sharp ore-to-waste boundaries, and are inti1

New Mexico Bureau of Mines and Mineral Resources, Socorro, 

New Mexico 87801. 

~07 Brassie Drive, Grand Junction, Colorado 81506. 

mately associated with humate (McLemore and Chenoweth, 

1989). The ore at the Mt. Taylor mine (fig. 2) is of the primary type. Redistributed uranium deposits are younger than 

primary uranium deposits, are typically more than 8 ft thick, 

have diffuse ore-to-waste boundaries, are brownish to lightgray because they contain less humate material than primary 

deposits, and are formed from primary deposits by a regional 

oxidation front. The Mary No. 1 deposit (fig. 2) is a redistributed uranium deposit. Remnant uranium deposits are the 

preserved remains of primary deposits that are left behind in 

oxidized sandstones after the oxidation front that formed 

redistributed deposits moves downdip. Blackjack No. 1 is an 

example of a remnant deposit. Smaller uranium deposits 

found in New Mexico include other sandstone deposits, 

limestone uranium deposits, other sedimentary rocks hosting 

uranium deposits, vein-type uranium deposits, and igneous 

and metamorphic rocks containing disseminated uranium 

(McLemore and Chenoweth, 1989). Sandstone uranium 

deposits in the Morrison Formation, and possibly those in the 

Dakota Sandstone (Upper Cretaceous), have potential for 

future development. 

Exploration for uranium has essentially ceased in the 

State (January, 1990). However, a few companies are examining the Grants district deposits for solution-mining potential (in situ leach). Since 1963, Homestake and Kerr McGee 

(now Rio Algom Mining Corporation) have extracted uranium from water circulated through uranium mines: about 

5.9 million pounds of U30 8 or 1.8 percent of the total uranium production from New Mexico has been produced from 

mine water. Solution mining has been tested at a few deposits in New Mexico. This type of mining has lower costs and 

fewer environmental problems than conventional mining 

methods. 

New Mexico has significant uranium reserves and 

resources, especially in the Grants uranium district (fig. 1). 

However, these deposits are much lower in grade and somewhat deeper than Proterozoic unconformity-type deposits in 

Canada and Australia. Future development of uranium 

resources in New Mexico will depend upon (1) an increase 

in the price for uranium, (2) the lowering of production costs · 

for uranium, perhaps by the use of solution mining (Holen 

and Hatchell, 1986, 1988), (3) discovery of higher grade 

deposits or a rise in the mining-grade cutoff, and (4) help for 

mining companies with the complex tasks of applying for 

permits and licenses and implementing required environmental regulations. 

Uranium Resources in New Mexico 3 
U N I 0 N 

R I 0 A R 

I i----1 

' I 

' , I 

~~-- ' _,_ _I --;t"ucumcori 

O R RANCE 

___ ___ __ ] 

L I N 

°Co rr izoto 

-, 

'------1 

r----

33·~----------~~~~~~~~~4---+-----~~~~=t~~==~ ~~tt~ 0 A lomogordo 

0 E R 0 

D y 

I 

32'~----~--~~---------+--~--- --~--~------------ ~-L--------~--~-------

- - --- ...L. 

-------J 

50 100 MI LE S 

50 100 KILOMETERS 

-

EXPlANATION 

Areas containing economic reserves and 

reasonably assured resources 

Areas containing undiscovered or 

potential resources 

Areas that may contain speculative resources, 

but more data will be required for proper 

assessment of the potential 

Figure 1. Uranium potential in New Mexico in 1989 (from Mclemore and Chenoweth, 1989; portions modified from U,S, 

Department of Energy, 1980). location numbers refer to table 1. The international terminology for the classification of uranium 

resources, recently adopted by the DOE, is used in this figure (Energy Information Administration, 1989). 

4 Short Papers of the U.S. Geological Survey Uranium Workshop, 1990 
c: 

iil 

= c:· 

3 

~ 

I'D 

! 

c 

.. 

Q 

Ill 

s· 

z 

I'D 

~ 

~ ~-s 

Cl1 

Table 1. Uranium districts in New Mexico shown on figure 1 

[Adapted from McLemore and Olenoweth, 1989] 

District or Area 

1. Laguna, Grants uranium district 

2. Marquez, Grants uranium district 

3. Bernabe Montano, Grants uranium district 

4. Ambrosia lake, Grants uranium district 

5. Smith lake, Grants uranium district 

6. Church Rock, Grants uranium district 

7. 

8. 

9. 

10. 

11. 

12. 

13. 

14. 

15. 

16. 

17. 

18. 

19. 

20. 

21. 

22. 

23. 

24. 

25. 

26. 

27. 

28. 

Nose Rock, Grants uranium district 

Chaco Canyon area, Grants uranium district 

Carrizo Mountains, Shiprock district 

Chuska Mountains, Shiprock district 

Tocito Dome area 

Abiquiu 

Mesa Portales area 

Collins-Warm Springs district 

Vermejo Park area 

Black Mesa area 

Ogallala Formation in eastern New Mexico 

Hagan Basin area 

Manzano Mountains-Manzanitas Mountains area 

Socorro area (Aqua Torres, Marie No. 1, lucky Don, 

little Davie mines) 

Ladron Mountains 

Hook Ranch-Riley area 

Red Basin-Pietown area 

Telegraph district 

Malone district 

Lordsburg Mesa area 

Gold Hill district 

Bound Ranch area 

Type of Deposit 

Sandstone deposit in Morrison Formation, limestone deposit 

Sandstone deposit in Morrison Formation, Limestone deposit 

Sandstone deposit in Morrison Formation, Limestone deposit 

Sandstone deposit in Morrison Formation, limestone deposit, 

Sandstone deposit in Dakota Sandstone 

Sandstone deposit in Morrison Formation, limestone deposit 

Sandstone deposit in Morrison Formation, Sandstone deposit 

in Dakota Sandstone 

Sandstone deposit in Morrison Formation 

Sandstone deposit in Morrison Formation 

Sandstone deposit in Morrison Formation 

Sandstone deposit in Morrison Formation, limestone deposit 

Sandstone deposit in Morrison Formation 

Sandstone deposit in Dakota Sandstone 

Sandstone deposit in Tertiary rocks 

Sandstone deposit in Morrison Formation 

Possible epithermal vein, granitic rocks or pegmatites 

Fracture-controlled uranium deposits 

Possible surficial uranium deposit 

Sandstone in Tertiary rocks 

Possible vein-type or disseminated magmatic deposit 

Fracture-controlled uranium deposits 

Fracture-controlled uranium deposits 

Sandstone in Cretaceous-Tertiary rocks 

Sandstone in Cretaceous-Tertiary rocks 

Epithermal vein 

Epithermal vein 

Surficial uranium deposit 

Pegmatite 

Epithermal vein 

----... 
~MARY 

RIO ALGOM MILL• 

N 

1 

5 MILES 

Figure 2. Location map of uranium mines mentioned in the 

text, Grants uranium district, New Mexico. 

6 Short Papers of the U.S. Geological Survey Uranium Workshop, 1990 

REFERENCES CITED 

Alief, M.H., and Kern, R.A., 1989, Mt. Taylor mine, in Lorenz, J.C. 

and Lucas, S.G., ed., Energy Frontiers in the Rockies: Albuquerque Geological Society, p. 28. 

Energy Information Administration, 1989, Uranium Industry 

Annual1988: U.S. Department of Energy, Report DOFJEIA-0478(88), 121 p. 

Holen, H.K., and Hatchell, W.O., 1986, Geological characterization of New Mexico uranium deposits for extraction by in 

situ leach recovery: New Mexico Bureau of Mines and Mineral Resources, Open-File Report 251,93 p. 

Holen, H.K., and Hatchell, W.O., 1988, Bibliography of uranium in 

situ leach technology: New Mexico Energy, Minerals and 

Natural Resources Department, Bureau of Economic 

Geology, Report of Investigation No.4, 48 p. 

McLemore, V.T., and Chenoweth, W.L., 1989, Uranium resources 

in New Mexico: New Mexico Bureau of Mines and Mineral 

Resources, Resource Map 18, 36 p. 

U.S. Department of Energy, 1980, An assessment report on uranium in the United States of America: U.S. Department of 

Energy, Report GJ0-111-80, 150 p. 
New Assessments of 

Uranium Endowment for 

Two Regions in the 

United States 

By Warren I.Finch, 1 Charles T. Pierson, 1 

Richard B. McCammon,2 James K. Otton, 1 

Hoyt B. Sutphin,3 and Karen j. Wenrich1 

The U.S. Geological Survey began a program to assess 

the undiscovered uranium endowment in selected areas of 

the United States as a result of a 1984 Memorandum of 

Understanding between the U.S. Department of Energy and 

the U.S. Department of the Interior. Uranium endowment is 

defined as the uranium estimated to be present in rock with 

a grade of at least 0.01 percent U30 8. The economic portion 

of endowment is calculated using a higher grade cutoff, commonly 0.10 percent U308. A proposed new assessment program is outlined in the report by Finch and McCammon 

(1987); the new assessments are intended to supplement and 

update those made by the U.S. Department of Energy (1980) 

during their National Uranium Resource Assessment 

(NURE) Program. Since 1984, the U.S. Geological Survey 

has developed a new assessment method called the depositsize-frequency (DSF) method (Finch and McCammon, 

1987); this technique is a modification of the NURE method. 

Two regions have been assessed using the DSF method: the 

Colville-Okanogan area, Washington and Idaho, and the 

Grand Canyon region, Arizona and Utah. 

The DSF method consists of a modification of the 

NURE uranium endowment (U) estimation equation 

(U=AxFxTxG), where factors F and Tare replaced by a single factor (see McCammon, this volume). In this equation, 

F is the fraction of area (A) that is favorable for endowment, 

and T equa.; the number of short tons of endowed rock per 

unit area. The combined F and T factor is the summation of 

the estimates of the number of deposits of different size within the area being assessed, or, in other words, the spatial density of deposits; hence, the name "deposit-size-frequency." 

The distribution of the average grade (G) of endowment is 

the same in both methods. The DSF method requires (1) that 

a deposit-size-frequency (a matrix of the lower limit, most 

likely value, and upper limit for the number of deposits in 

each size class) be established in a control area, which is a 

well-known to fairly well known area, and (2) that the geo1

U.S. Geological Survey, Box 25046, Mail Stop 939, Denver Federal 

Center, Denver, Colorado 80225. 2

U .S. Geological Survey, Mail Stop 920, National Center, Reston, 

Virginia 22092. 

3

USPCI, 5665 Ratiron Parkway, Boulder, Colorado 80301. 

logic factors that produced this frequency be determined. 

Using these requirements for a control area, the assessor estimates the size frequency of undiscovered deposits for the 

favorable area based on similarity to the control area. The 

probabilistic estimates in 5 percent intervals between 5 and 

95 percent of undiscovered uranium endowment are calculated using the computer program TENDOWG (McCammon and others, 1988). These estimates for two regions are 

shown in figures 2, 3, and 4. 

The undiscovered uranium endowment was estimated 

in 1986 for "young organic-rich uranium deposits" in the 

Colville-Okanogan favorable area in the Sandpoint and Spokane 1 °X2° quadrangles, Washington and Idaho (fig. 1). 

These uranium deposits occur in surficial organic-rich fluvial, alluvial, and lacustrine sediments laid down during the 

last 15,000 years (Johnson and others, 1985). The deposits 

average from 0.03 to about 0.10 percent u3o8 and contain 

from a few hundred pounds to as much as a million pounds 

of U308. The uranium endowment in the Colville-Okanogan favorable area is estimated to lie between about 6,700 

and 122,000 short tons of contained u3o8, and the mean undiscovered uranium endowment is 35,300 short tons u3o8 

(Finch, Otton, and others, 1990), as shown by the probability 

distribution of estimated short tons in figure 2. The uranium 

endowment is divided about evenly between the Sandpoint 

and Spokane quadrangles. 

Figure 1. Index map showing the location of the NTMS 1 °x2° 

quadrangles mentioned in this report. (Cedar City, 1; Grand Canyon, 2; Marble Canyon, 3; Williams, 4; Flagstaff, 5; Prescott, 6; 

Holbrook, 7; St. Johns, 8; Sandpoint, 9; Spokane, 1 0) 

New Assessments of Uranium Endowment for Two Regions in the United States 7 
1.0.----------.----------.---------~----------.----------.----------.----------, 

Mean undiscovered uranium 

endowment, in short tons U308: 

~ Sandpoint and Spokane 1 o x 2° quadrangles 35,300 1- 0.7 z 

w 

:E 

~ 

8 

fE 0.6 

:E 

:::> 

z 

<( 

a:: 

:::> 

(!) 0.5 z 

0 

w 

w 

u 

X 

w 

LL 0.4 0 

~ :::i 

iii 

<( 

m 

0 

a:: 

Q.. 

0.2 

0.1 

o.o OL__ _______ 2_0_,0L0_0 _______ 4_0_,0L0-0 _______ 6_0_,0L_0_0 _______ 8_0_,0L0-0 _____ 1_0_0.J...,0_0_0 ______ 1_2_0.J...,0_0_0 ______ 1_4__,0,000 

URANIUM ENDOWMENT (U), IN SHORT TONS U308 

Figure 2. Plot of the probability distribution of estimates of undiscovered uranium endowment for the Colville-Okanogan 

area, Sandpoint and Spokane 1 °x2° quadrangles, Washington and Idaho. The odds are 9 to 1 that the true unconditional 

endowment (in short tons U30 8) is between the values plotted for the 5 and 95 percent probabilities. 

The undiscovered uranium endowment was estimated 

in 1987 for the solution-collapse breccia pipes in the Grand 

Canyon region in the Grand Canyon, Marble Canyon, Williams, Flagstaff, Prescott, Holbrook, and St. Johns 1 °X2° 

quadrangles in Arizona and the Cedar City 1 °X2° quadrangle 

in Utah (fig. 1). The uranium deposits occur in nonvolcanic 

breccia pipes that formed as a result of solution collapse into 

8 Short Papers of the U.S. Geological Survey Uranium Workshop, 1990 

the Mississippian Redwall Limestone and by stoping of the 

overlying Pennsylvanian, Permian, and Triassic rocks (Wenrich, 1985). Most of the uranium deposits are high grade by 

U.S. standards, averaging between 0.43 and 0.65 percent 

U30 8. Typical deposits contain 125,000 to 500,000 short 

tons of ore, yielding 1 million to 6 million pounds of U308. 

The uranium endowment was estimated for 26 favorable 
1.0.------------.------------~----------~------------~------------~----------~ 

0.9 

0.8 

5' 

;: 0.7 z 

w 

~ 

~ 

8 

~ 0.6 

~ 

::;:) 

z 

<( 

a: 

::;:) 

(!) 0.5 z 

0 

w 

w 

u 

X 

w 

:5 0.4 

~ ~ 

iii 

<( 

al 

~ 0.3 c.. 

0.2 

0.1 

Mean undiscovered uranium 

endowment, in short tons U308: 

Grand Canyon 1 ox 2° quadrangle 536,000 

Williams 1 o x· 2° quadrangle 320,000 

Flagstaff 1 o x 2° quadrangle 248,000 

Marble Canyon 1 o x 2° quadrangle 1 24,000 

Holbrook 1 o x 2° quadrangle 62,900 

0·0o.__ _________ 2_o_o.~-.o_o_o ________ 4_o_o...L.o_o_o _______ 6o_o_j.-oo_o ________ 8_o_oi._.o_o_o _______ ,-.o-o..Lo-.o-o_o ______ 1_.2_o_Jo.ooo 

URANIUM ENDOWMENT (U). IN SHORT TONS U308 

Figure 3. Plots of the probability distribution of estimates of undiscovered uranium endowment for the Grand Canyon, Williams, Flagstaff, Marble Canyon, and Holbrook 1 °x2° quadrangles, Grand Canyon region, Arizona. For each quadrangle, the 

odds are 9 to 1 that the true unconditional endowment (in short tons U30 8) is between the values plotted for the 5 and 95 

percent probabilities. 

areas that total16,728 mi2 within the eight quadrangles. Figures 3 and 4 show the probability distributions of estimated 

short tons of uranium endowment within the eight quadrangles. About 41 percent of the mean uranium endowment is 

in the Grand Canyon 1 °X2° quadrangle, where most of the 

mining activity has occurred. About 93 percent of the endowment is within the Grand Canyon, Marble Canyon, Williams, and Flagstaff 1 °X2° quadrangles. The undiscovered 

mean endowment in the Prescott and St. Johns 1 °X2° quadrangles is insignificant because of their small favorable 

areas. The mean uranium endowment for the entire region 

totals about 1,300,000 short tons U30 8 (Finch, Sutphin, and 

New Assessments of Uranium Endowment for Two Regions in the United States 9 
5 

;::- 0.7 z 

w 

~ 

§ 

z 

w 

~ 

~ 

z 

<( 

a: 

::::> 

(!) 

z 

i5 

w 

w 

u 

X 

w 

u. 

0 

~ ::::; 

iii 

<( 

IXl 

0 

a: 

a.. 

Mean undiscovered uranium 

endowment, in short tons U308: 

Cedar City 1 o x 2° quadrangle 23,300 

St. Johns 1 o x 2° quadrangle 600 

Prescott 1 o x 2° quadrangle 400 

St. Johns 

Prescott 

5,000 10,000 15,000 20,000 25,000 30,000 35,000 40,000 45,000 50,000 

URANIUM ENDOWMENT (U), IN SHORT TONS U308 

Figure 4. Plots of the probability distribution of estimates of undiscovered uranium endowment in the Cedar City 1 °x2° 

quadrangle, Utah, and the St. Johns and Prescott 1 °x2° quadrangles, Arizona. For each quadrangle, the odds are 9 to 1 

that the true unconditional endowment (in short tons U30 8) is between the values plotted for the 5 and 95 percent probabilities. 

others, 1990). This value is about eight times the total endowment of 158,000 short tons U30 8 estimated for these 

breccia pipes by the U.S. Department of Energy 1980 NURE 

Program (U.S. Department of Energy, 1980). The larger 

USGS uranium endowment value is due to three factors: (1) 

The DSF method allows for greater partitioning of input data 

and results in less biased (generally larger) estimates, (2) significantly greater knowledge of the grade and tonnage of deposits discovered since 1980, and (3) greatly improved 

understanding of the geology of the region. 

10 Short Papers of the U.S. Geological Survey Uranium Workshop, 1990 
REFERENCES CITED 

Finch, W.l., and McCammon, R. B., 1987, Uranium resource 

assessment by the Geological Survey: Methodology and 

plan to update the national resource base: U.S. Geological 

Survey Circular 994, 31 p. 

Finch, W.I., Otton, J.K., McCammon, R.B., and Pierson, C.T., 

1990, The 1986 estimate of undiscovered uranium endowment for surficial uranium deposits in the Sandpoint and 

Spokane NTMS 1 °x2° quadrangles, Washington and Idaho: 

U.S. Geological Survey Open-File Report 90--2, 17 p. 

Finch, W.l., Sutphin, H.B., Pierson, C.T., McCammon, R.B., and 

Wenrich, K.J., 1990, The 1987 estimate of undiscovered uranium resources in solution-collapse breccia pipes in the 

Grand Canyon region of northern Arizona and adjacent Utah: 

U.S. Geological Survey Circular 1051, 19 p. 

Johnson, S.Y., Otton, J.K., and Macke, D.L., 1985, Geology of the 

north fork of Flodelle Creek drainage basin and surficial uranium deposit, Stevens County, northeastern Washington: 

U.S. Geological Survey Open-File Report 85-443, 38 p. 

McCammon, R.B., Finch, W.I., Pierson, C.T., and Bridges, N.J., 

1988, The microcomputer program TENDOWG for estimating undiscovered uranium endowment: U.S. Geological Survey Open-File Report 88-653, 11 p., 1 diskette. 

U.S. Department of Energy, 1980. An assessment report on 

uranium in the United States of America: U.S. Geological 

Survey Open-File Services, Denver, Colorado, U.S. Department of Energy GJ0-111 (80), 150 p. 

Wenrich, K.J., 1985, Mineralization of breccia pipes in northern 

Arizona: Economic Geology, v. 80, p. 1,722-1,735. 

New Assessments of Uranium Endowment for Two Regions in the United States 11 
Uranium Endowment 

Estimate Calculations 

By Richard B. McCammon1 

On September 20, 1984, the Memorandum of Understanding (MOU) between the Energy Information Administration (EIA) of the U.S. Department of Energy (DOE) and 

the U.S. Geological Survey (USGS) of the U.S. Department 

of Interior (DOl) was signed. This MOU was a continuant 

to the MOU between DOE and DOl dated November 12, 

1983, that provided for continuing the assessment of the 

Nation's uranium resources following the national assessment by DOE during the period 1974-1983 under the 

National Uranium Resource Evaluation (NURE) program. 

The 1984 EIAIUSGS MOU returned to the USGS the full 

responsibility for uranium resource assessment. 

The equation that was used to estimate the uranium 

endowment in each of the 704 favorable areas identified in 

the NURE program was defined as follows: 

U = AxFxTxGxP 

where 

U is the unconditional uranium endowment in short 

tons of U308 above a cutoff grade of 0.01 percent 

U30g, 

A is the projected surface area of favorable ground in 

square miles, 

F is the fraction of A that is underlain by endowment 

T is the short tons of endowed rock per square miie 

withinAxF, 

G is the average grade of endowment, in decimal form, 

and 

P is the probability of occurrence, a factor that 

expresses the likelihood that one or more deposits 

actually exist within the favorable area. 

The equation was applied using values of A, F, T, G, 

and P obtained from the principal scientist by a team of elicitors. Factor A was treated as a constant and assigned a single value. Factors F, T, and G were treated as random 

v~ab~es whose values were estimated by the principal scientist m each of three categories: lower (5 percent probability), most likely (mode), and upper (95 percent probability). 

Factor P, the probability of occurrence, was a single number 

estimated by the principal scientist. The computer program 

that was used to calculate the unconditional uranium endowment (U) has been described by Ford and McLaren (1980). 

Principal scientists, who were usually geologists, had 

great difficulty in estimating values for factors F and T. Factor T is essentially a measure of the size of the deposits and 

1

U.S. Geological Survey, Mail Stop 920, National Center, Reston 

Virginia 22092. ' 

depends upon the area, density, and thickness associated 

with the deposits. It was difficult for the geologist to conceptualize the size of undiscovered deposits in terms of short 

tons per square mile. Factor F was even more difficult to 

judge because, to estimate F, it was necessary for the geologist to estimate the projected surface area of undiscovered 

deposits. More often than not, estimates for F were obtained 

by asking the principal scientist how many more deposits of 

a particular type of deposit were likely to exist in the favorable area. Using data for known deposits, estimates for both 

F and T were then derived. 

It is more natural for a geologist to think in terms of the 

number and size of undiscovered deposits when being asked 

to make subjective judgments about the undiscovered 

resources within an area. The difference between this 

approach and the approach adopted in the NURE program is 

perhaps best seen in figure 1. The drawing in figure 1 illustrates that factor F is an abstraction and does not lend itself 

to identifiable and measurable geologic features, such as the 

character of sedimentary or structural forms in the area. The 

post-NURE characterization of undiscovered deposits in figure 1 has been adopted by the USGS and has resulted in a 

modified NURE method called the deposit-size-frequency 

(DSF) method. The method has been described by Finch and 

McCammon (1987). The equation that is now used to estimate the uranium endowment in a favorable area is defined 

as follows: 

where 

k is the number of deposit-size classes, 

nic/Ac is the spatial density (number of deposits per 

unit area) of deposits of size Ti (short tons of 

endowed rock) in the ith deposit-size class within a 

control area Ac, 

Ac is the control area from which estimates of Die/ Ac 

are taken, 

L is the optional scaling factor that expresses the relation between the endowment in the favorable area 

and that in either the control area or in some designated subarea for which estimates of the number of 

deposits in different size classes have been made, 

and 

U, A, G, and Pare defined as before. 

n. 

The equation is applied using values for A, k, ~c ,Ti, G, c 

L, and P obtained from the principal scientist by a team of 

elicitors. Factors A, G, and Pare obtained as before. Factor 

k and each Ti are treated as a constant and assigned a single 

12 Short Papers of the U.S. Geological Survey Uranium Workshop, 1990 
Uraniferous WetlandsYoung Uranium Deposits 

By Douglass E. Owen 1 

Wetlands are common in montane and subalpine settings in the western United States, and accumulations of peat 

and organic-rich sediments in these environments range 

from less than 30 em to more than 10 m thick. Wetlands 

form along spring lines in valley floors and adjacent to 

springs and seeps, or where drainage has been restricted by 

glacial moraines, debris slides, or beaver dams. Some of 

these wetlands contain significant concentrations of uranium 

because uranium is readily sorbed from the water by the 

abundant organics present in wetland sediments. Sorption is 

highly efficient because the uranyl ion (U02

2

+) forms strong 

complexes with the abundant humic and fulvic acids present 

in wetland sediments. Geochemical enrichment factors 

(GEF) of 10,000 to 1 or greater are well documented to exist 

between the peat/organic-rich sediments and the uraniumbearing waters that carry uranium into the wetlands. 

Of 145 wetlands sampled by the U.S. Geological Survey (USGS) in the Rocky Mountains of Colorado, 30 percent 

of the wetlands contained moderate uranium concentrations 

(20 to 99 ppm, maximum observed values), 15 percent contained high concentrations (100 to 999 ppm), and 1 percent 

contained very high concentrations ( 1,000 to greater than 

3,000 ppm). All values are reported on a dry-weight basis 

and are from auger samples taken over one-foot intervals. 

Elsewhere, USGS scientists assessed the uranium content of 

two small wetlands near Lake Tahoe in the Carson Range of 

Nevada. Average grades of 1,500 ppm and 800 ppm uranium were determined and total uranium contents were calculated at 15,000 and 24,000 kg, respectively. The only 

wetland uranium deposit in the United States that has been 

mined is the Flodelle Creek deposit in northeastern Washington State. The USGS estimates that this deposit contains 

450,000 kg of uranium; however, only about 500 kg of uranium was produced before ore processing problems and the 

low price of uranium forced closure of the mine. 

Because the sorptive processes responsible for concentrating uranium and other metals in organic-rich wetland 

sediments are reversible, both anthropogenic and natural disturbances may have serious environmental consequences. If 

a wetland is partly or completely drained, the subsequent 

oxidation of organic-rich sediments may rapidly liberate 

metals that have been accumulating from very dilute solutions for thousands of years; this could impact the quality of 

1 U.S. Geological Survey, Box 25046, Mail Stop 939, Denver Federal 

Center, Denver, Colorado 80225. 

local ground and surface waters. Acid leaching caused by 

mine drainage into wetlands (there are more than 10,000 

abandoned mines in Colorado alone) and the over-liming or 

addition of certain types of phosphate fertilizers to hydric 

soils may also release uranium from wetlands into water systems. Because uraniferous wetlands are of environmental 

and health concern, extraction of uranium for the purposes of 

protecting the environment and safeguarding public health 

may be justified. In addition, profit may be realized from the 

sale of the extracted uranium. 

The wetlands studied are of late Pleistocene to 

Holocene age; therefore, their uranium is in gross disequilibrium (excess) compared with its more radioactive daughter 

products. Because of their low radioactivity, these deposits 

generally are not detected with airborne or hand-held 

gamma-ray spectrometers or scintillometers. As a consequence, exploration must be based on specialized radiometric methods (delayed neutron activation) or on direct 

chemical measurements of uranium content. Two beneficial 

consequences of the low radioactivity associated with uraniferous wetlands are: (1) Radioactivity of tailings will be 1 to 

10 percent of that in conventional mines of similar grade, 

and (2) radiation hazard to the miners will be minimal. 

Reconnaissance for uraniferous wetlands is performed 

most effectively by measuring the uranium content of spring 

waters that feed wetlands and by examining existing data for 

uranium in ground water, such as that from the National Uranium Resource Evaluation program (NURE). Even with a 

GEF that is greater than 10,000 to 1, waters entering wetlands should contain at least 20 ppb uranium to concentrate 

significant amounts of uranium. For example, if incoming 

waters have a uranium concentration of 25 ppb and the operative GEF is 20,000 to 1, then the potential uranium concentration in peaty sediments is approximately 500 ppm. 

Ground water uranium concentrations greater than 20 ppb 

also indicate that the country rocks in the area are fertile; i.e., 

they contain significant quantities of labile uranium. Limited experience suggests that highly fractured granitic rocks 

with moderate to high concentrations of uranium and a history of deep weathering and recent glaciation are likely to be 

sources of labile uranium. Once a uraniferous wetland is 

identified, exploration is continued by sampling wetland 

sediments by hand auger: The auger samples are dried and 

analyzed for uranium content. Individual wetland uranium 

deposits tend to be small (less than 500,000 kg) and of modest average grade (0.05 to 0.12 percent); therefore, exploration must focus on finding clusters of deposits rather than on 

finding one large or exceptionally high grade deposit. 

The economic feasibility of development at a particular 

deposit will depend upon local hydrology, vegetation cover, 

land use, nature of uranium fixation, access, and the prevailing price of uranium. The only uraniferous wetland in the 

United States to be mined for its uranium, Flodelle Creek, 

used heap leaching to extract uranium from organic-rich sed14 Short Papers of the U.S. Geological Survey Uranium Workshop, 1990 
A 

A 

NURE 

T=A x F x Tc 

Where: T = Short tons of endowed rock 

F = Fraction of A with unspecified 

area underlain by endowed rock 

Tc =Short tons/ unit area of endowed 

rock 

Deposit outline 

0 

0 

B 

0 

0 nic 

Ac 

0 

Ac Log T 

Post-NURE 

k n· 

T=A{I: (-f-) Ti} i= 1 c 

Where: k= Number of deposit-size classes 

Ti=Short tons of endowed rock in 

size class i 

nic/ Ac=The spatial density (number of deposits per 

unit area) of deposits of size Ti (short tons of 

endowed rock) in the ith deposit-size class 

within a control area Ac 

Ac=The control area from which estimates of nic/ Ac 

are taken 

Figure 1. Comparison of F in A, NURE with 8, post-NURE representation of endowment. The reader is referred to Finch 

and McCammon (1987) for a complete explanation of terms. Modified after Finch and McCammon (1987). 

nic value. Factors A and L are treated as random variables c 

whose values are estimated by the principal scientist as 

lower (5 percent probability), most likely (mode), and upper 

(95 percent probability) values. The computer program to 

calculate U using this equation is described by McCammon 

and others (1988). 

In effect, factors F and T have been replaced with factors that relate explicitly to the number and size of undiscovered deposits within a favorable area. By asking the 

principal scientist to estimate these factors, the DSF method 

not only further segregates the estimate of endowment as 

compared to the NURE method, but it also emphasizes more 

of the everyday experience of exploration geologists. The 

DSF method is particularly well suited to frontier areas 

where information concerning undiscovered uranium deposits is scant. Finally, the DSF method preserves continuity 

with the NURE method: by allowing k to equal 0, a principal 

scientist can estimate F and T as before, making the calculation of U using the DSF method indistinguishable from the 

calculation ofU using the NURE method. The compatibility 

of the two methods serves to preserve the estimates of 

endowment made in the NURE program and ensures continuity in making new assessments using the DSF method. 

REFERENCES CITED 

Finch, WJ., and McCammon, R.B., 1987, Uranium resource 

assessment by the Geological Survey: Methodology and 

plan to update the national resource base: U.S. Geological 

Survey Circular 994, 31 p. 

Ford, C.E., and McLaren, R.A., 1980, Methods for obtaining distribution of uranium occurrence from estimates of geologic features: U.S. Department of Energy Report GJBX-165(80), 

121 PMcCammon, R.B., Finch, W.I., Pierson, C.T., and Bridges, N.J., 

1988, The micro-computer program TENDOWG for estimating undiscovered uranium endowment: U.S. Geological 

Survey Open-File Report 88-653, 11 p. 

Uranium Endowment Estimate Calculations 13 
iments. In situ leaching of uranium from uraniferous 

wetlands is a possible alternative method of mining. Lixiviants composed of ammonium bicarbonate and ammonium 

carbonate (both of which are strong fertilizers) are environmentally benign and are relatively efficient in removing uranium from wetland sediments. An advantage of in situ 

leaching is that it leaves the wetland intact, thus preserving 

the extractive capacity of the wetland. However, in situ 

leaching is impractical in wetlands with heavy shrub cover 

or where wetland hydrology short circuits the leach cycle by 

rapid loss or addition of fluids. Both in situ and heap leaching could utilize a mobile processing plant with ion 

exchange columns carried on flat bed semitrailers. This type 

of processing is compatible with the exploitation of numerous small deposits that may be present in a particular favorable area. 

In addition to adding to the U.S. uranium resource base, 

the identification of these young uranium deposits provides 

opportunities to better understand processes leading to the 

formation of syngenetic uranium deposits. The study of 

uraniferous wetlands also provides data for models of contaminant transport in organic-rich surficial environments 

and has implications for both radionuclide and toxic waste 

disposal. 

Uraniferous Wetlands- Young Uranium Deposits 1 S 
Response of Douglas Fir to 

Uraniferous Ground Water: 

A Case Study with 

Implications for 

Environmental Monitoring 

By Robert A. ZielinskP and 

R. Randall Schumann2 

The positive biogeochemical response of plants to concealed uranium deposits is well documented in the geologic 

literature. The apparent uptake of uranium by plants is 

undoubtedly aided by its high solubility in oxidizing waters 

as uranyl-carbonate or uranyl-phosphate complexes or as 

complexes with humic or fulvic acids. The relative solubility of uranium compared to other heavy metals of economic 

interest may confound efforts to precisely locate buried 

deposits because plant or soil media can record rather wide 

dispersion of uranium from a particular source. However, 

the explorationist' s problem of uranium dispersion by 

ground water may be turned to the advantage of environmental scientists. For example, biogeochemical indications of 

uranium dispersal from buried natural or man-made sources 

might supplement more direct, but more limited, measurements of ground water quality and flow patterns. 

This field study was designed to further test the hypothesis that biogeochemical sampling may be used to map the 

transport of uranium by shallow, uraniferous ground water. 

We sampled Douglas fir [Pseudotsuga menziesii (Mirb.) 

Franco] and associated soils in a small drainage containing 

anomalously uraniferous surface and ground water (Zielinski and others, 1987). The objective of this study was to test 

whether the distribution of biogeochemical anomalies exhibited any regularity that could be related to observed or 

inferred pathways of ground water movement in the drainage. The results, which were elaborated by Zielinski and 

Schumann (1987), strongly suggest that, in areas containing 

uraniferous water, the magnitude of biogeochemical anomalies is highly influenced by the degree of root zone exposure 

to such waters. 

The study was confined to slopes surrounding the upper 

reaches of the north fork of Flodelle Creek, Stevens County, 

Washington. This very limited drainage basin (4.1 km2) 

contains abundant labile uranium, as evidenced by anoma1

U .S. Geological Survey, Box 25046, Mail Stop 424, Denver Federal 

Center, Denver, Colorado 80225. 2

U .S. Geological Survey, Box 25046, Mail Stop 939, Denver Federal 

Center, Denver, Colorado 80225. 

lously uraniferous surface and ground waters (20-320 ppb 

U) and by the occurrence of uranium enrichments (0.01-0.9 

weight percent U) in organic-rich valley-fill sediments 

(Johnson and others, 1987). The valley slopes are underlain 

by a two-mica monzogranite of Cretaceous age that is covered by 1-2 m of relatively permeable glacial till. Topographic relief in the drainage is about 183 m, and slopes are 

generally 30-65 percent. The well-drained slopes are vegetated primarily by Douglas fir: this dictated the choice of 

this species for sampling. 

Douglas fir was sampled at 200-ft (61 m) intervals 

along a series of slope traverses designed to provide continuous coverage of both sides of the upper 2 km of the valley. 

Additional shorter traverses allowed for the sampling of 

some slopes at different elevations. A subset of six samples 

was collected in the vicinity of a slope spring. All129localities were visited during a dry five-day period in August 

1985. At each site we noted the elevation and collected at 

least 400 g of 30-50 em lengths of the most recent growth 

(twigs and needles). At every fifth site we collected a soil 

sample of silt-loam from a depth of 15-25 em-this is well 

within the root zone of the trees sampled. 

All plant matter was first air-dried at 40 oc and then 

shaken and sieved to separate twigs and needles. Separates 

were ashed to yield approximately 1 g of ash for analysis. 

Soil samples were also air dried and sieved to remove plant 

litter or occasional particles larger than fine sand. All uranium analyses of plant ash and soils were done by a delayed 

neutron method that had a detection limit of 0.2 ppm and an 

estimated precision of ±10-30 percent (relative standard 

deviation). 

The uranium content of needle ash ranged from 0.2 to 

5.8 ppm. Analysis of the positively skewed frequency distribution by two statistical methods provided an estimated 

threshold value of 1.0 ppm; this value was exceeded by 27 of 

the 129 determinations. Most of the anomalously uraniferous samples were located on the west side of the valley, on 

lower parts of the slope, and in two distinct sections of slope 

traverses. 

The entire data set was evaluated by statistical methods 

to determine the degree of correlation between the uranium 

in needle ash and other measured variables (table 1). A 

strong positive correlation with the uranium in twig ash suggests that twigs are an equally acceptable sample medium. A 

strong negative correlation with elevation data supports the 

indication that uraniferous samples tend to be located on 

lower slopes. A lack of correlation with the uranium content 

in soils suggests that soil-bound uranium is not readily available for uptake by the root system. Finally, a negative correlation with ash content of needles suggests that needles are 

not significantly contaminated by windblown dust. 

The locations of anomalous samples are readily 

explained using a model that accounts for the observed or 

inferred movement of shallow ground water in the drainage. 

16 Short Papers of the U.S. Geological Survey Uranium Workshop, 1990 
Table 1. Correlation coefficient matrix1 based on analysis of Douglas fir and associated soils, north fork, Flodelle Creek, 

Washington 

Ash Ash Log[U] Log[U] Logu] Ele¥ation Delta 

Content Content Needle Tvig Soil Elevation 

of of Tvigs Ash Ash 

Needles 

(129) (29) (129) (29) (29) (122) (122) 

Ash Content of Needles 

Ash Content of Tvigs 0.60 

Log (U] Needle ash -0.30 -0.20 

Log (U] Tvig ~ 0.07 -0.17 0.88 

Log(U] Soil -0.41 -0.31 0.16 -0.08 

Elevation 0.23 -0.06 -0.60 -0.67 -0.18 

Delta Elevation 0.11 0.19 -0.67 -0.65 -0.16 0.85 

1 Values in bold print are significant at the 99% level of confidera, ~ on the possible number of paired 

values for each correlation. Tbe number of determinations of each variable are given in parentheses. Elevation 

values do not iD::lllie seven samples collected mar b slope spring that vere considered to be strongly influenced 

by the spring. Delta elevation values are tb3 estimated ~ights above the '98lley floor. 

Anomalous samples were situated as follows: (1) in the 

immediate vicinity of a slope spring on the west side of the 

valley, (2) along a linear trend that includes the spring and 

parallels the strike ·of the valley (this suggests a structurally 

controlled zone of upwelling water), (3) at the toe of an alluvial fan deposited by an intermittent tributary stream (some 

ground water seeps were observed in a trench cutting the toe) 

and, ( 4) at lower slope sites that were more likely to experience prolonged water saturation and greater fluctuations in 

the water table related to subsurface runoff. The lack of 

anomalous samples near the drainage divide (an area of the 

valley bottom where the water table is relatively deep) is 

consistent with the model. 

The results of this study confrrm that biogeochemical 

sampling may be used to monitor the transport of anomalous 

amounts of uranium by shallow ground water. This method 

of environmental monitoring deserves further investigation, 

particularly if it can be expanded to include other plant species or other elements. 

REFERENCES CITED 

Johnson, S.Y., Otton, J.K., and Macke, D.L., 1987, Geology of the 

Holocene surficial uranium deposit of the north fork of 

Flodelle Creek, northeastern Washington: Geological Society of America Bulletin, v. 98, p. 77-85. 

Zielinski, R.A., Otton, J.K., Wanty R.B., and Pierson, C.T., 1987, 

The geochemistry of water near a surficial organic-rich uranium deposit, northeastern Washington State: Chemical 

Geology, v. 62, p. 263-289. 

Zielinski, R.A., and Schumann, R.R., 1987, Response of Douglas 

fir (Pseudotsuga menziesil) to uraniferous groundwater in a 

small glaciated drainage, northeastern Washington State: 

Journal of Geochemical Exploration, v. 27, p. 281-298. 

Response of Douglas Fir to Uraniferous Ground Water: A Case Study 17 
Uranium Series 

Disequilibrium in a Young 

Surficial Uranium Deposit, 

Northeastern Washington 

By Robert A. Zielinski,1 Charles A. Bush/ and 

John N. Rosholt3 

Concentration of uranium in surficial, organic-rich sediments is a recently recognized phenomenon that has both 

economic and environmental implications. Wetlands in 

which locally uraniferous ground water intercepts accumulations of highly sorbant organic matter, such as peat, are 

particularly favorable settings for surficial uranium accumulations. Despite uranium concentrations as high as several 

thousand parts per million (ppm) in dried peats, their low 

raqioactivity thwarts exploration efforts based on conventional radiometric methods. Emplacement of uranium in late 

Pleistocene or Holocene time is simply too recent to permit 

significant buildup of radioactive daughter products such as 

226Ra or 214Bi. Complete buildup of equilibrium abundances of uranium daughter products takes approximately 

400,000 years. 

Although daughter product abundances are low, they 

are amenable to measurement by specialized radiometric 

techniques such as high-resolution gamma-ray spectrometry 

and thin-source alpha spectrometry. In this study, we performed such measurements on core samples from a uraniferous peat in northeastern Washington State. The results 

indicate the relative mobility of uranium and some of its 

chemically diverse daughter products in this surficial environment and permit calculation of apparent U-series ages of 

uranium emplacement. The U-series ages can be compared 

to independently determined depositional ages of host peats 

to develop a history for uranium mineralization at the site. 

The core site is located along the uppermost reach of the 

north fork of Flodelle Creek, Stevens County, Washington 

(Johnson and others, 1987). Organic-rich valley-fill sediments from this drainage contain as much as 9,000 ppm U 

(dry basis) and were the target of an aborted mining effort in 

the early 1980's. Sediments at the core site were undisturbed 

by mining, which was restricted to wider parts of the valley 

farther downstream. The peat and organic-rich silt and sand 

at the core site were deposited in a shallow pond that formed 

1

U .S. Geological Survey, Box 25046, Mail Stop 424, Denver Federal 

Center, Denver, Colorado 80225. 2

U .S. Geological Survey, Box 25046, Mail Stop 963, Denver Federal 

Center, Denver, Colorado 80225. 

3

Deceased 1991. 

when unconsolidated glacial till slumped off the valley 

slopes and restricted drainage. A continuous piston core 5.0 

em in diameter and 292 em in length was collected and split 

into 16lithologically distinct intervals. Composite samples 

representing each interval were dried, crushed and homogenized prior to analysis (Zielinski and others, 1986). The 

depositional age of the sediments was estimated by identification of the 6, 700-7 ,000-year-old Mazama ash at a depth of 

50-55 em (Zielinski and Otton, 1986) and by recognition of 

glaciofluvial sediments of approximately 12,000-15,000 

years B.P. at the bottom of the core. Additional age control 

was indirectly available from 14C dating that was used at 

other sites in the drainage to confirm the identification of the 

Mazama ash. 

Uranium concentrations determined by a delayed neutron method range from 140 to 2, 790 ppm on a dry weight 

basis and are positively correlated with organic matter content (fig. 1). In contrast, thorium concentrations show a 

much narrower range of less than 10 to 40 ppm and are not 

correlated with organic matter content. These observations 

and previous results from size-fraction analyses and fissiontrack radiography (Otton and Zielinski, 1986) indicate preferential enrichment of uranium in finer grained organic matter. The degree of uranium enrichment is substantial, 

considering that the estimated uranium content of locally 

derived silicate detritus is less than 20 ppm. 

The uranium isotopic composition of the core samples, 

~s ~etermined by radioisotope dilution-alpha spectrometry, 

mdtcated a rather narrow range of 234uP38u activity ratios 

of 1.30-1.38. These alpha activity ratios are similar to the 

values of 1.27-1.38 reported for modem springs in the drainage (Zielinski and others, 1987). These results suggest that 

local waters had a uniform isotopic composition throughout 

the history of the deposit. An alternative explanation 

requires equilibration of the entire sediment column with 

modem waters; however, such uniform open-system access 

of uranium to the sediment column is unlikely considering 

the lithologic diversity of the samples and the evidence for 

approximate closed-system behavior of 234U and its immediate daughter 230n presented below. 

Apparent uranium emplacement ages for ten intervals 

of core were calculated using the measured decay-generated 

buildup of 230n daughter relative to 234U parent. After correction for the generally minor contributions of detrital 

230rrb, the apparent ages show a general increase as a function of depth and are in fair agreement with the estimated 

ages of host sediments (fig. 2). For example, apparent ages 

of intervals C ·and E bracket that of interval D, which contains the Mazama ash. With the exception of the deepest 

interval which may be receiving modem input of uranium 

from upwelling water, the trend of age with depth 

approaches the limiting age of basal, post-glacial sediments 

of 12,000-15,000 years B.P. These observations indicate 

that most of the measured intervals approximate closed sys18 Short Papers of the U.S. Geological Survey Uranium Workshop, 1990 
DEPTH 

CM IN 

ORGANIC CONTENT 

(LOSS ON IGNITION) 

u 

(ppm) 

0---.-----

10 

50- 20 

30 

100- 40 

50 

150- 60 

70 

200- 80 

90 

250-

100 

110 

300- 120 

/} 

----

A 

B 

c 

D 

E 

F 

G 

H 

J 

K 

L 

M 

N 

0 

p 

Q 

R 

EXPLANATION 

'-1 ~____J' Peat [:.:-,.:::<::·::·] Sand ·· ··· ··· ... 

r ' >v v l Volcanic ash t ~ (Mazama) 

~ . ·= "} Coarse granular 

~ ...... ;d sand 

t~~~ Clayandsilt h Wood fragments 

Figure 1. Generalized lithologic log of the studied core. Histograms indicate the concentrations of organic matter and uranium in the sampled intervals. Intervals 0, P, and Q were 

combined for subsequent analyses. 

A 

...J 

<( 

> 

a: B w 

f-

~ 

Cl 

w 

...J c 0.. 

::;; D <( 

(/) E LL 

0 F I 

f0.. 

w 

Cl G 

w H > 

f= 

::s 

w 

a: K 

L 

M 

N 

O, P, Q 

R 

l I I I I I I 

·- EXPLANATION 

. Uncorrected (with 1 sigma errors) 

.. "Corrected" for detrital 230Th 

....... 

........... 

MAZAMA ASH I 

......__. 

~ 

.,.,.._.._. 

.. 

s~ GLACIAL SEDIMENTS 1 

0 2,000 4,000 6,000 8,000 10,000 12,000 14,000 

APPARENT U·SERIES AGE, IN YEARS 

Figure 2. Apparent 230rhP34U ages of ten measured intervals, corrected for detrital 230rh and plotted as a function of 

depth. Ruled intervals provide independent estimates of depositional age and are included for comparison. Letters refer to 

intervals shown on figure 1. 

terns with respect to 234U and 230nt and record a period of 

uranium uptake early in their depositional history. This history of uranium uptake spans the entire post-glacial period 

and is probably occurring today in the shallower intervals 

and, perhaps, in the deepest intervals. Present access of 

uraniferous water to the site is as surface flow and as plumes 

of upwelling ground water that emerge as open spring pools. 

The core site is within a few m of one such pool that has concentrations of dissolved uranium in excess of 300 ppb (Zielinski and others, 1987). 

The abundances of other uranium daughters, in addition 

to 230nt, are similarly 10-100 times below that required for 

radioactive equilibrium. These other decay-generated species are not, however, as immobile as thorium and are subject to additional redistribution in the sediment column. For 

example, deficiencies of 226Ra daughter (t112=1602 y) 

Geology of the Surficial Uranium Deposit of the North Fork of Flodelle Creek, NE. Washington 19 
relative to 23D-rb parent occur in most of the deepest intervals 

and are too large, based on the elapsed time since sediment 

deposition and uranium emplacement. This implies some 

redistribution of decay-generated radium, resulting in a net 

loss of radium from the studied core. The residence of this 

mobilized radium is unknown, but radium may accumulate 

in clay-rich intervals in or below the cored section. 

Deficiencies of 226Ra relative to 210pb are observed 

throughout the core. These deficiencies probably result from 

recent radium loss as described above and (or) preferential, 

core-wide gain of deeper sourced 222Rn gas that streams 

upward and leaves a trail of relatively immobile and longer 

lived 21 0pb daughter (t112=22.3 y). Upwelling ground water 

carries radon gas to the site of the open spring pool (Otton 

and Reimer, 1991). In addition, sorption of minor amounts 

of radium on clays in the underlying post-glacial sediments 

may provide local, deep sources of radon daughter. 

Our results suggest that 23<>rh!234U dating of uraniferous peats may provide minimum ages for underlying glacial 

tills. Although radiocarbon dating is commonly employed 

for peats formed within the last 40,000 years, measurements 

of 230uv234U can extend the datable range to approximately 

the last 350,000 years. 

REFERENCES CITED 

Johnson, S.Y., Otton, J.K., and Macke, D.L., 1987, Geology of the 

Holocene surficial uranium deposit of the north fork of 

Flodelle Creek, northeastern Washington: Geological Society of America Bulletin, v. 98, p. 77-85. 

Otton, J.K., and Reimer, G. M., 1991, Radiogenic and other gases 

in shallow ground waters of uraniferous Holocene alluvium, 

Flodelle Creek, Washington, in Gunderson, L.C.S., and 

Wanty, R.B., eds., Field studies in radon geology: U.S. Geological Survey Bulletin 1971, 330 p. 

Otton, J.K., and Zielinski, R.A., 1986, Movement and fixation of 

uranium on organic matter in a late Quaternary uranium 

deposit, Stevens County, Washington, in Carter, L.M.H., ed., 

V. E. McKelvey Forum on Mineral and Energy 

Resources-1986: U.S. Geological Survey Circular 974, p. 

49-50. 

Zielinski, R.A., Bush, C.A., and Rosholt, J.N., 1986, Uranium 

series disequilibrium in a young surficial uranium deposit, 

northeastern Washington, U.S.A.: Applied Geochemistry, v. 

1, p. 503-511. 

Zielinski, R.A., and Otton, J.K., 1986, Volcanic ash in organic-rich 

surficial uranium deposits of northeastern Washington and 

westernmost Nevada: U.S. Geological Survey Open-File 

Report 86-342, 13 p. 

Zielinski, R.A., Otton, J.K., Wanty, R.B., and Pierson, C.T., 1987, 

The geochemistry of water near a surficial organic-rich uranium deposit, northeastern Washington State, U.S.A.: 

Chemical Geology, v. 62, p. 263-289. 

20 Short Papers of the U.S. Geological Survey Uranium Workshop, 1990 
Geology of the Holocene 

Surficial Uranium Deposit 

of the North Fork of Flodelle 

Creek, Northeastern 

Washington 

By Samuel Y. Johnson, 1 James K. Otton, 1 and 

David L. Macke2 

The north fork of Flodelle Creek drainage basin in 

Stevens County, northeastern Washington (fig. 1), contains 

the first surficial uranium deposit to be mined in the United 

States. The uranium was leached from granitic bedrock and 

1 U.S. Geological Survey, Box 25046, Mail Stop 939, Denver Federal 

Center, Denver, Colorado 80225. 2

U.S. Geological Survey, Box 25046, Mail Stop 921, Denver Federal 

Center, Denver, Colorado 80225. 

Spokane River 

50 KILOMETERS 

precipitated or adsorbed in organic-rich pond sediments. 

The distribution of the pond sediments and the uranium they 

contain was strongly influenced by relict glacial topography, 

slope processes, and beaver activity. 

The Cordilleran ice sheet covered the north fork of 

Flodelle Creek drainage basin during the Fraser (late Wisconsin) glaciation (fig. 1). Till and outwash were deposited 

on the valley slopes and floor as ice receded. Outwash incision and melting of stagnant ice led to formation of a terrace 

and kames. Shortly after deglaciation, a small (about 50 by 

20 m) pond (the spring pool of fig. 1B) formed in the upper 

part of the valley when unconsolidated glacial sediment 

slumped off the valley slopes and restricted drainage. Fluvial processes dominated in the central and downstream 

parts of the valley for several thousand years after deglaciation even though drainage was partly restricted by kames. 

Beavers occupied and built dams on the wide outwash plains 

beginning about 5,000 years B.P. Beaver ponds in the central part of the basin subsequently filled with sediment and 

were abandoned, whereas downstream ponds remained relatively free of clastic input and are presently occupied by beavers. The Meadow mine (figs. 1B, 2) occupies the site of a 

former beaver-pond complex. 

1 KILOMETER 

0 0.5 MILE 

EXPlANATION 

Valley floor-Sand. silt, muck 

Kames-Pebbly sand 

Terrace-Pebbly sand 

Valley slopes-Till 

Figure 1. A, Map showing the location of the north fork of Flodelle Creek drainage basin (FC). Dashed line shows approximate 

limit of lobes of the Cordilleran ice sheet during the Fraser glaciation. Other abbreviations are: CRL, Columbia River lobe; CRS, 

Colville River sublobe; LPR, Little Pend Oreille River; OL, Okanogon lobe; and PRS, Pend Oreille sublobe. 8, Map of surficial 

deposits of the north fork of Flodelle Creek (NFC) drainage basin. Contours in feet. 

Geology of the Surficial Uranium Deposit of the North Fork of Flodelle Creek, NE. Washington 21 
Ponds in the drainage basin trapped fine-grained, 

organic-rich sediments. These organic-rich sediments provide a suitable geochemical environment for precipitation 

and adsorption of uranium leached from granitic bedrock 

into ground, spring, and surface waters. Uranium concentrations in organic-rich sediments in the spring pool and 

Meadow mine (fig. 2) are as high as 8,960 and 1,020 ppm, 

respectively. Processes of pond formation have thus been 

important in the development of surficial uranium deposits 

(/) 

a: 

w 

1-

w 

:2 

Idealized 

section 

H 

-5100 ±100 yr B.P. 

Sample location 

map 

200 METE RS 

400 FEET 

in the north fork of Flodelle Creek drainage basin and may 

have similar significance in other areas. 

REFERENCE CITED 

Johnson, S.Y., Otton, J.K., and Macke, D.L., 1987, Geology of the 

Holocene surficial uranium deposit of the north fork of 

Flodelle Creek, northeastern Washington: Geological Society of America Bulletin, v. 98, p. 77-85. 

EXPlANATION 

• Peat. muck 

EJ Clay 

G Silt. very fine 

. :~~ 4 sand 

•158 E.J Fine to medium 

•85.8 sand 

• 245 53] Coarse to granular 

sand 

•83.4 Ash 

•248 Uranium, In parts 

per million 

38 

. •444 

•270 

•382 

•174 

•147 

•105 

•86.7 

Figure 2. Stratigraphy and uranium (U) concentration (determined by delayed neutron activation) of samples taken along the axis 

of the Meadow mine in the north fork of Flodelle Creek drainage basin. Stratigraphic units F, G, H, and I are described in detail in 

Johnson and others (1987). Unit G is the Mazama ash. Ages shown for the upper part of unit F and the lower part of unit Hare 14C 

dates on organic matter. Modified from Johnson and others (1987). 

22 Short Papers of the U.S. Geological Survey Uranium Workshop, 1990 
Arid-Land Surficial 

Uranium Deposits-A 

Review of Examples and 

Their Modes of Occurrence 

By Sigrid Asher-Bolinder1 and james K. Otton1 

Surficial uranium deposits are formed in near-surface 

sedimentary environments and are predominantly syngenetic. They are generally Tertiary to Holocene in age, and 

deposits less than 500,000 to 250,000 years old may be deficient in gamma- and beta-active uranium (U) daughter products. Present-day arid and semiarid regions containing 

surficial uranium deposits are characterized by climatic conditions in which potential evaporation exceeds actual precipitation by factors of 5 to 20. 

Figure 1 indicates the localities of several arid-land 

surficial uranium deposits (ALSUDS). Classification of 

ALSUDS has been based on depositional environments 

(Toens and Hambleton-Jones, 1984; Otton, 1984), on dominant associated mineralogies or organic-rich materials specific to climate and physical setting (Carlisle, 1984), or on 

processes leading to deposition of the uranium deposits 

(Boyle, 1984). As with other mineral deposits, ALSUDS 

result from: (1) physical and chemical processes that liberate U from its source terrain, (2) transport mechanisms that 

carry U in solution to suitable environments, and (3) physical 

and (or) chemical concentration and trapping mechanisms · 

that can deposit U. 

The source terrains for ALSUDS are generally igneous 

rocks of felsic to intermediate composition (such as granite, 

granodiorite, welded or airfall tufO or felsic metasedimentary rocks. Source rocks may contain 2-50 ppm U, some of 

which is dissolved and transported by surface waters or shallow ground waters during or following physical and chemical weathering. Physical processes that make U available for 

chemical weathering include grusification, regolith development, jointing, faulting, and glacial scouring. Uranium dissolves in slightly acidic to alkaline oxidizing waters and 

forms complexes of uranyl carbonates or phosphates. 

Although surface stream flow is an obvious transport 

mechanism for U-bearing waters, flow from springs and 

seeps and subsurface flow through soil, regolith, or sediment 

also provide a significant flux of U to areas of concentration 

and precipitation. 

The high ratio of evaporation to precipitation in arid 

and semiarid regions is primarily responsible for the concen1

U.S. Geological Survey, Box 25046, Mail Stop 939, Denver Federal 

Center, Denver, Colorado 80225. 

tration of U and other cations in surface waters and in shallow subsurface waters. Upwelling of subsurface waters into 

the vadose zone may be caused by topographic, lithologic, or 

structural barriers to subsurface hydrologic flow. Subsurface waters may rise to the surface in lake and playa basins 

or stream valleys, especially along buried topographic highs. 

Basinward fining of sediments may result in loss of permeability and upwelling of subsurface waters at the lacustrine 

or deltaic margin. Springs and seeps may form in areas of 

differential permeability such as along faults and flexures. 

The concentration of U relative to other ~ons, the speciation of other ions, and the pH and Eh of the solution determines whether U can be removed from that solution and in 

what form it will accumulate. Uranium minerals in 

ALSUDS commonly include carnotite and, less commonly, 

autunite, tyuyamunite, and schroeckingerite. Carnotite 

(K2(U02h(V04h·3H20) can form only when there is adequate potassium, vanadium, and U in solution; it is stable 

over a fairly broad pH range, from approximately 3 to 8.7. 

Adsorption of uranyl and uranous ions by organic matter, 

diatomite, clays, or iron or manganese oxyhydroxides is controlled to some degree by the water's pH (optimally 4-7 for 

organic matter and 5-7 for clays), the degree ofhumification 

of organic matter, and Eh. In strongly alkaline waters, U 

may remain complexed with carbonates, inhibiting adsorption ofU unless the Eh of the environment is strongly reducing (Boyle, 1984). As U-bearing waters well up into the 

zone of evaporation Pcaz drops, and decreased confining 

pressures cause destabilization of uranyl carbonate complexes, making U more available for precipitation or adsorption. 

The physical and chemical mechanisms responsible for 

U concentration operate in several environments common to 

arid and semiarid climates. In western Australia and 

Namibia, in recent and (or) ancient fluvial systems, carnotite-bearing nonpedogenic calcrete has accumulated in the 

centers of low-gradient valleys where U-rich groundwaters 

intersect the evaporative zone (Carlisle and others, 1978). 

The Yeelirrie calcrete U deposit (Cameron, 1984) and those 

in the Namib Group of Namibia (Hambleton-Jones, 1984a) 

are among the best known examples. The long-term tectonic 

stability and surface exposure in those areas have produced 

deeply weathered, permeable regoliths that are the source of 

U. Below the zone of evaporation, these regoliths also allow 

lateral and downstream migration of slightly acidic, U-bearing ground waters. As these waters migrate toward the zone 

of evaporation in the valley center, they become progressively more alkaline and saline. At the basin center, valleyfill calcrete and associated carnotite precipitate as cements 

and grain coatings in fluvial sediments. Because carnotite is 

more soluble than calcrete, it is redissolved and redistributed 

in the valley center by infrequent summer rains. Rains, confined largely to the summer months, are rapidly evaporated 

if they do not quickly percolate below the zone of evaporation. In contrast, in cooler and (or) wetter climates, or in less 

Arid-Land Surficial Uranium Deposits-A Review of Examples and Their Modes of Occurrence 23 
60' 

Q, 

J '.;Q 

!:~, 

Lake Ma1tland Yeeilrne}CJ 

Lake Raes1de 

Lake Way 

\;1 

Figure 1. Arid and semiarid regions of the world (patterned) showing arid-land surficial uranium deposits mentioned in the text. 

Modified from Meigs (1953). 

porous soils, soil moisture remains in the zone of evaporation and promotes formation of pedogenic calcrete within the 

soil column (Carlisle and others, 1978). Pedogenic calcrete 

is a less favorable host for carnotite accumulation than valley 

fill calcrete because lateral and downstream movement of 

ground water is reduced, and U is not transported to a site of 

high evaporation where concentration can occur. 

Another environment suited to the concentration and 

deposition of ALSUDS is the closed or partially closed basin 

that may contain playas, alkaline lakes, deltas, or marshes 

associated with springs having year-round flow. Within 

these sedimentary environments, U may be deposited as carnotite, or it may be adsorbed onto organic- or oxyhydroxiderich, clayey, or diatomaceous material (Carlisle, 1980). 

Examples of ALSUDS in closed or restricted basins include 

carnotite-bearing deltaic, fluvial, and playa sediments of 

Lakes Maitland (Cavaney, 1984), Raeside (Gamble, 1984), 

and Way (French and Allen, 1984) in western Australia. The 

lacustrine and playa basins of the south-central dry belt of 

British Columbia (Culbert and others, 1984) trap U in 

organic matter and clays under both oxidizing and reducing 

conditions. The Kannikwa and Henkries deposits of South 

Africa host U in reduced, organic-rich diatomaceous earth 

(Hambleton-Jones, 1984b). In Fish Lake Valley, Nevada, U 

is concentrated by organic-rich marsh sediments (Macke and 

others, 1990). 

In ALSUDS, as in other surficial uranium deposits, disequilibrium may be noted between the chemical values of U 

in a deposit and the equivalent values of U suggested by radiometric assay methods. This disequilibrium may be 

explained in two ways: Either the U is so recently deposited 

as to have had insufficient time for the ingrowth of gammaand beta-active daughters, or the U has been leached from its 

original site of deposition, leaving unsupported radioactive 

daughters behind. These factors complicate the assessment 

of potential ALSUDS deposits and emphasize the relatively 

ephemeral nature of such deposits. Any short-term influx of 

groundwater may produce gradients in pH, Eh, and salinity 

that can lead to differential solution and precipitation of U. 

Longer-term changes in climate or base level can affect local 

and regional groundwater levels, either further concentrating 

U or carrying it away. Given these factors, ALSUDS may be 

seen as possible sources of contamination of water supplies 

in semiarid to arid regions, or they may be seen, in a longer 

view, as transient preconcentrators that may have supplied 

dissolved U to more conventional sedimentary U deposits 

developed in the past. 

REFERENCES CITED 

Boyle, D.R., 1984, The genesis of surficial uranium deposits, in 

Toens, D., project leader, Surficial uranium deposits, Report 

of the working group on uranium geology organized by the 

International Atomic Energy Agency: Vienna, Austria, 

ReportlAEA-TECDOC-322, p. 45-52. 

24 Short Papers of the U.S. Geological Survey Uranium Workshop, 1990 
Cameron, E., 1984, 'flie Yeelirrie calcrete uranium deposit, Westem Australia, in Toens, D., project leader, Surficial uranium 

deposits, Report of the working group on uranium geology 

organized by the International Atomic Energy Agency: 

Vienna, Austria, Report IAEA-TECDOC-322, p. 157-164. 

Carlisle, Donald, 1980, Possible variations on the calcrete-gypcrete 

uranium model: U.S. Dept. of Energy Open-File Report 

GJBX-53(80), 38 p. 

Carlisle, Donald, 1984, Surficial uranium occurrences in relation to 

climate and physical setting, in Toens, D., project leader, 

Surficial uranium deposits, Report of the working group on 

uranium geology organized by the International Atomic 

Energy Agency: Vienna, Austria, Report IAEA-TECDOC-322, p. 25-35. 

Carlisle, Donald, Merifield, P.M., Orme, A.R., Kohl, M.S., Kolker, 

0., 1978, The distribution of calcretes and gypcretes in 

southwestern United States and their uranium favorability 

based on a study of deposits in Western Australia and South 

West Africa (Namibia): U.S. Dept of Energy Open-File 

Report GJBX-29(78), 274 p. 

Cavaney, R.J., 1984, Lake Maitland uranium deposit, in Toens, D., 

project leader, Surficial uranium deposits, Report of the 

working group on uranium geology organized by the International Atomic Energy Agency: Vienna, Austria, Report IAEA-TECDOC-322, p. 137-140. 

Culbert, R.R., D.R. Boyle, and Levinson, A.A., 1984, Surficial uranium deposits in Canada, in Toens, D., project leader, Surficial uranium deposits, Report of the working group on 

uranium geology organized by the International Atomic 

Energy Agency: Vienna, Austria, Report IAEA-TECDOC-322, p. 179-191. 

French, R.R., and Allen, J.H., 1984, Lake Way uranium deposit, 

Wiluna, western Australia, in Toens, D., project leader, Surficial uranium deposits, Report of the working group on uranium geology organized by the International Atomic Energy 

Agency: Vienna, Austria, Report IAEA-TECDOC-322, p. 

149-156. 

Gamble, D.S., 1984, The Lake Raeside uranium deposit, in Toens, 

D., project leader, Surficial uranium deposits, Report of the 

working group on uranium geology organized by the International Atomic Energy Agency: Vienna, Austria, Report IAEA-TECDOC-322, p. 141-148. 

Hambleton-Jones, B.B., 1984a, Surficial uranium deposits in 

Namibia, in Toens, D., project leader, Surficial uranium 

deposits, Report of the working group on uranium geology 

organized by the International Atomic Energy Agency: 

Vienna, Austria, Report IAEA-TECDOC-322, p. 205-216. 

Hambleton-Jones, B.B., 1984b, Surficial uranium deposits in South 

Africa, in Toens, D., project leader, Surficial uranium deposits, Report of the working group on uranium geology organized by the International Atomic Energy Agency: Vienna, 

Austria, Report IAEA-TECDOC-322, p. 221-229. 

Macke, D.L., Schumann, R.R., and Otton, J.K., 1990, Uranium distribution and geology in the Fish Lake surficial uranium 

deposit, Esmeralda County, Nevada: U.S. Geological Survey Bulletin 1910,22 p. 

Meigs, P., 1953, World distribution of arid and semi-arid homoclimates, in UNESCO Reviews of Research on Arid Zone 

Hydrology: Arid Zone Resources, vol. XI, p. 326-345. 

Otton, J.K., 1984, Surficial uranium deposits: summary and conclusions in Toens, D., project leader, Surficial uranium 

deposits; Report of the working group on uranium geology 

organized by the International Atomic Energy Agency: 

Vienna, Austria, Report IAEA-TECDOC-322, p. 243-247. 

Toens, D., and Hambleton-Jones, B.B., 1984, Definition and classification of surficial uranium deposits, in Toens, D., project 

leader, Surficial uranium deposits, Report of the working 

group on uranium geology organized by the International 

Atomic Energy Agency: Vienna, Austria, Report 

IAEA-TECDOC-322, p. 9-14. 

Arid-Land Surficial Uranium Deposits-A Review of Examples and Their Modes of Occurrence 25 
Hydrogeology of San Juan 

Basin Uranium DepositsThe Brine-Interface Model 

Revisited 

By Richard F. Sanford1 

For many years geologists thought that tabular-type 

uranium deposits in Triassic and Jurassic sedimentary rocks 

of the Colorado Plateau formed at the interface between two 

solutions of different salinity, although the evidence was 

largely circumstantial. A more recent hypothesis, the lacustrine-humate model, proposed that just one fluid was 

involved in uranium precipitation, and this fluid moved 

downward from the mudflat facies of a paleolake into underlying fluvial sands. New hydrogeologic modeling and comparison with modern hydrogeologic systems suggest that at 

least three compositionally distinct fluids existed during uranium deposition in the Upper Jurassic Morrison Formation 

and that two of these fluids caused uranium deposition by 

mixing at a brine interface in zones of ascending regional 

flow. This new model integrates, for the first time, observed 

associations of uranium deposits with fluvial sandstones, 

underlying evaporites, overlying lacustrine mudstones, and 

syndepositional topographic depressions. 

Reconstruction of the Late Jurassic paleogeography 

and paleohydrology of the southwestern United States indicates that the San Juan Basin area was the discharge zone for 

a 400,000-km2 drainage basin that extended to the Mogollon . 

highlands. Recharge to the Morrison Formation had three 

main sources: (1) deep gravity- and compaction-driven flow 

of meteoric and formation water, (2) shallow, gravity-driven 

flow of meteoric water, and (3) shallow density-driven flow 

of playa-lake water. 

Deep ground water originated as infiltration of meteoric 

water in the distant Mogollon highlands, flowed north and 

east toward the basin, and discharged at the playa margin. 

Compaction of sediments yielded minor additional deep 

ground water. The deep ground water that was thus discharged was saline due to reaction with detrital grains and 

dissolution of evaporite minerals, especially anhydrite from 

the Middle Jurassic Todilto Limestone. Infiltration by direct 

recharge at the outcrop yielded shallow ground water that 

became slightly alkaline and saturated with calcium carbonate during downdip flow toward the basin. This relatively 

fresh ground water rose, discharged at the lake shoreline, and 

formed a buoyant lens above the denser, saline ground water. 

Under some conditions, density-driven playa-lake water 

descended through the lake sediments, moved outward 

through the Westwater Canyon Member of the Morrison 

Formation, and then rose and discharged at the playa lake 

margin. Reaction of this fluid with volcanic ash produced 

characteristic alkaline-lake mineral assemblages in lacustrine muds and underlying fluvial sands. The regional topographic low and the hydrologic barrier created by the playa 

lake caused a regional upward flow and discharge at the carbonate mudflat zone bordering the playa lake. 

The Grants uranium region closely coincides with the 

zone of discharge and mixing of the three ground-water 

types. The association of uranium deposits with lacustrine 

mudstones can best be explained by the tendency of ground 

water to discharge at topographic depressions in which 

standing water often accumulates. Deposits such as the 

Jackpile Sandstone Member of the Morrison and Paguate 

Tongue of the Dakota Sandstone, which are not overlain by 

lacustrine mudstones, were also created in zones of discharge and mixing; only the topographic depression is 

revealed by thickened sediments characteristic of syndepositional subsidence. The flow system around topographic 

depressions also explains the association of uranium deposits with underlying evaporites and supports the brine-interface model. 

In contrast, no hydrogeologic simulations or modern 

analogs have suggested any systematic downward flow in 

the mudflat facies as required by the lacustrine-humate 

model. Further, diagenetic evidence is either consistent with 

different flow directions or contradicts the model of downward flow. For example, the pattern of iron-titanium oxide 

destruction in the Westwater Canyon Member is equally 

consistent with downward flow from the Brushy Basin 

Member of the Morrison or with lateral, down-dip flow from 

the outcrop. Abundant pedogenic calcite in the mudflat is 

strong evidence of upward-flowing, discharging ground 

water. 

Geologists exploring for sedimentary uranium deposits 

should look first in uranium provinces where fluvial sandstones overlie evaporites. Within these areas, syndepositional topographic lows, lacustrine mudstones, thicker 

fluvial sandstone, and low mudstone to sandstone ratios indicate favorable zones for the occurrence of tabular uranium 

deposits. 

26 Short Papers of the U.S. Geological Survey Uranium Workshop, 1990 
Uranium Mineralization 

and Favorability in the 

01 igocene Chadron 

Formation, Southeastern 

Wyoming and 

Northwestern Nebraska 

By Paula L. Hansley1 and 

Kendell A. Dickinson 1 

INTRODUCTION 

Anomalies on oil well gamma-ray logs of the basal 

sandstone of the Oligocene Chadron Formation led to the 

discovery of the Crow Butte uranium deposit near Crawford, 

Nebraska, in 1980 (fig. 1) (Collings and Knode, 1984). The 

N 

1 

WYOMING 

0 Douglas 

: 

I 

I 

I 

0 Rapid City 

SOUTH 

DAKOTA 

r---------,----

1 

l c?t~ETSY I 

1 0 Crawford \ 

• 

A~D-·E Crow Butte 

I c Deposit I L--___J 

I 

I 0 

NEBRASKA 

0 Scottsbluff 

50 MILES I 

0 CHEYENNE I I 

I 

0 ~0 KILOMETERS 

Figure 1. Index map showing locations of the Crow Butte 

uranium deposit and east-west cross section, A-E. 

1 U.S. Geological Survey, Box 25046, Mail Stop 939, Denver Federal 

Center, Denver, Colorado 80225. 

ore-bearing basal sandstone (average grade > 0.25 weight 

percent uranium) averages 13 m in thickness, and estimated 

reserves are in excess of 40 million pounds U30 8 (Gjelsteen 

and Collings, 1988; Collings, oral commun., 1990). Ferret 

Exploration Company of Nebraska, Inc., began mining the 

ore by an in situ leaching process early in 1991. 

The only part of the White River Group known to be 

favorable for commercial-size uranium deposits is the basal 

Chadron sandstone. Compilation of electric log data has 

revealed other areas that are potentially favorable for uranium where the basal Chadron sandstone is relatively thick. 

STRATIGRAPHY AND GEOLOGIC SETTING 

The Oligocene White River Group is divided into the 

Chadron Formation and the overlying Brule Formation in 

northwestern Nebraska (fig. 2); however, the White River is 

GEOLOGIC STRATIGRAPHIC THICKNESS 

AGE COLUMN (FEET) 

Harrison 

and 

Miocene c. Monroe ::J Creek 0 

t5 Formations 

Q) undivided ~ Ill 

""' 0-400 

~ Gering 

Formation 

Brown 

siltstone 

beds 

Brule 

Formation Whitney 0-400 

Member 

c. 

Oligocene ::J 

~ (!) Orella Qj 

> Member 

a: 

~ 

:.c 200-500 

~ 

Chadron 

Formation 

Basal 0-100 

sandstone 

Eocene Interior 

Paleosol 0-10 

Upper Pierre 

Cretaceous Shale 1500 

Figure 2. Stratigraphy of the White River Group in the vicinity of the Crow Butte uranium deposit, northwestern Nebraska (based on Swinehart and others, 1985). 

Uranium Mineralization in the Chadron Fm., SE. Wyoming and NW. Nebraska 27 
20 

H 

A 

0 

20 

H 

50 

Arikaree Formation 

0 50 

Basal Chadron Sandstone, 

White River Group 

White River 

Group 

Pierre Shale 

20 

H 

c 

0 50 

D 

0 50 

Figure 3 (above and facing page). East-west cross section (see fig. 1) showing development of the basal 

Chadron sandstone in the vicinity of the Crow Butte deposit. From Dickinson (1990). 

28 Short Papers of the U.S. Geological Survey Uranium Workshop, 1990 
SEA LEVEL +4000' 

Arikaree Formation 

White River 

Group 

--- 20 

H 

E 

Basal Chadron Sandstone, 

White River Group 

0 

Selfpotential 

20 

-H+ 

50 

ELECTRIC LOG 

EXPLANATION 

Resistivity 

ohms m2/m 

0 50 

millivolts 16-inch normal 

Vl 

=> 

0 

w 

u 

~ w 

0:: 

u 

0:: 

w 

0.. 

0.. 

=> 

"' c 

"' u 

0 

~ 

"' c 

"' u 

0 

.!:!' 

6 

Uranium Mineralization in the Chadron Fm., SE. Wyoming and NW. Nebraska 29 
undivided in Wyoming. The basal Chadron sandstone, 

which is found throughout southeastern Wyoming and 

northwestern Nebraska, was deposited in ancient braided 

stream channels that eroded into the underlying Upper Cretaceous Pierre Shale. Near Crawford, the uranium-bearing 

basal Chadron sandstone is overlain by an impervious red 

clay unit in the upper part of the Chadron Formation. The 

sandstone channels are scattered throughout southeastern 

Wyoming, northwestern Nebraska, and possibly parts of 

southwestern South Dakota and northeastern Colorado. The 

channel system containing the Crow Butte uranium deposit 

has been traced from the vicinity of Douglas, Wyoming, 

eastward and southward to the area south of Crawford, 

Nebraska, by Dickinson and Wise (1989), Gjelsteen and 

Collings (1988), and Dickinson (1990). 

The basal Chadron sandstone is as much as 350 ft thick 

in the vicinity of the Crow Butte deposit, but its thickness 

rarely exceeds 100ft in other areas. A cross section based 

on electric log data of the White River Group in the vicinity 

of the Crow Butte deposit is shown on figure 3. 

SANDSTONE PETROLOGY 

In the Crow Butte deposit, the basal Chadron sandstone 

is a coarse-grained, tuffaceous, arkosic litharenite composed 

of poorly sorted angular quartz, plagioclase, and potassium 

feldspar grains and igneous rock fragments that are loosely 

packed in a vitric matrix dominated by rhyolitic volcanic ash 

(Hansley and others, 1989). Major nonopaque heavy minerals are zircon, garnet, and tourmaline with minor amounts of 

staurolite, epidote, apatite, and biotite; ilmenite and magnetite are the major opaque heavy minerals. Fresh glass shards 

and feldspar grains and minor authigenic smectite/illite (> 90 

percent expandable) indicate that very little diagenetic alteration has taken place. 

URANIUM ORE MINERALOGY 

The highest uranium concentrations are in the clay fraction of the sandstone matrix where uranium occurs in submicroscopic coffinite crystals, 2 J.l.m or less in length (fig. 4). 

Uranium is also present in the amorphous matrix with Si, P, 

V, Fe, Ca, and AI. Coffinite is closely associated with abundant authigenic pyrite and marcasite. Most of the uranium 

ore remains in a reduced state; however, local oxidation of 

primary ore and sulfide minerals has produced tyuyamunite, 

metatyuyamunite, carnotite, and zippeite. 

GENESIS OF URANIUM ORE 

The occurrence of uranium-bearing matrix in sandstone 

interstices and between mica plates indicates that ore formaFigure 4. Scanning electron photomicrograph of typical 

poorly formed, micron-size coffinite crystal (c) in uraniumbearing matrix of Crow Butte ore. 

tion took place before compaction, not long after deposition 

of the basal Chadron sandstone. Uranium was probably 

derived from alteration of abundant rhyolitic volcanic ash in 

the White River Formation (Group)-this ash contains an 

average of 8 ppm uranium in Wyoming (Zielinski, 1983). 

According to Gjelsteen and Collings (1988), ore formed at 

oxidation/reduction fronts in a manner similar to that of 

Wyoming-type roll-front deposits. We propose that oxidizing ground water carrying uranyl dicarbonate complexes 

moved downdip through permeable basal Chadron channel 

sandstones and that uranium precipitated on the margins of 

the channels where a reducing environment was encountered. The reducing environment was caused by concentrations of woody fragments and associated humic organic 

matter in the Chadron. Bacterially mediated reduction of 

so4 in the presence of organic matter (e.g., decaying plant 

matter) produced H2S and led to chemical reduction and precipitation of uranium and ore-stage iron disulfides. Reduction of uranyl complexes coupled with high silica activity 

(created by alteration of rhyolitic ash) resulted in formation 

of coffinite. A schematic diagram showing our proposed 

roll-front model for ore formation is shown on figure 5. 

SUMMARY AND CONCLUSIONS 

The Crow Butte uranium orebody has been interpreted 

to be a roll-front deposit that formed during early diagenesis. 

The only part of the White River Group known to be favor30 Short Papers of the U.S. Geological Survey Uranium Workshop, 1990 
Figure 5. Proposed roll-front model for formation of Crow Butte uranium deposit. 

able for commercial-size uranium deposits is the basal sandstone of the Chadron Formation. The occurrence of uranium 

ore in this basal sandstone may be related to its thickness. 

Subsurface mapping in southeastern Wyoming and southwestern Nebraska has revealed areas where the sandstone 

may provide environments favorable for the occurrence of 

uranium orebodies 

REFERENCES CITED 

Collings, S.P., and Knode, R.H., 1984, Geology and discovery of 

the Crow Butte uranium deposit, Dawes County, Nebraska: 

Practical Hydromet '83: 7th Annual Symposium on Uranium 

and Precious Metals, American Institute of Metallurgical 

Engineers, p. 5-14. 

Dickinson, K.A., 1990, Distribution of the basal clastic unit of the 

Oligocene Chadron Formation in the Alliance 2° quadrangle, 

northwestern Nebraska: U.S. Geological Survey Open-File 

Report 90-416. 

Dickinson, K.A., and Wise, R.A., 1989, Distribution of the basal 

clastic unit of the Oligocene White River Formation in the 

Torrington and Newcastle 1 °X2° quadrangles, Wyoming, 

Nebraska, and South Dakota: U.S. Geological Survey, OpenFile Report 89-552, 4 p. 

Gjelsteen, T.W., and Collings, S.P., 1988, Relationship between 

groundwater flow and uranium mineralization in the Chadron Formation, northwest Nebraska: Wyoming Geological 

Association Guidebook, 39th Field Conference, p. 271-284. 

Hansley, P.L., Collings, S.P., Brownfield, I.K., and Skipp, G.L., 

1989, Mineralogy of uranium ore from the Crow Butte uranium deposit, Oligocene Chadron Formation, northwestern 

Nebraska: U.S. Geological Survey Open-File Report 

89-225, 28 p. 

Swinehart, J.B., Souder, V.L., DeGraw, H.M., and Diffendal, R.F., 

Jr., 1985, Cenozoic paleogeography of western Nebraska, in 

Flores, R.M., and Kaplan, S.S., eds., Cenozoic paleogeography of the west-central United States: Rocky Mountain Section, Society of Economic Paleontologists and 

Mineralogists, p. 187-206. 

Zielinski, R.A., 1983, Tuffaceous sediments as source rocks for 

uranium- a case study of the White River Formation, Wyoming: Journal of Geochemical Exploration, v. 18, p. 

285-306. 

Uranium Mineralization in the Chadron Fm., SE. Wyoming and NW. Nebraska 31 
Uranium in Phosphate 

Rock-With Special 

Reference to the Central 

Florida Deposits 

By James B. Cathcartl 

Uranium is a trace constituent of all apatites in amounts 

that characteristically range from 30 to 300 parts per million 

(ppm). Although the discovery that phosphate rock is radioactive was made at about the turn of the century, it was not 

until uranium was used in atomic weapons that the U.S. Geological Survey began an examination of all sources of the 

metal, and it was confrrmed that the phosphate deposits of 

the United States contain from 60 to 350 ppm uranium. Subsequent detailed examinations of the Florida and western 

United States deposits resulted in many published reports 

that are listed in a phosphate bibliography (Bridges and others, 1983). 

Phosphate is found in three distinct types of deposits: 

guano or derived from guano, apatite of igneous origin, and 

marine phosphorite deposits. Data on resources, production, 

and uranium content are shown in table 1; locations are 

shown on figure 1. 

Guano, the excreta of bats and sea birds, contains 10 

ppm uranium or less, and total resources are trivial. Guanoderived deposits result when dissolved phosphorus reacts 

with underlying rocks to form hydroxyapatite or aluminum 

and iron phosphate minerals. Uranium content ranges from 

10 to 80 ppm, but the higher concentrations are found only 

when the hydroxyapatite is altered to fluorapatite by seawater. Resources and production are limited. 

Deposits of igneous apatite occur as intrusive masses, 

marginal differentiates, veins, and pegmatites. The largest 

deposits are intrusive masses associated with alkalic rocks. 

The apatite content of these rocks ranges from a few percent 

in some veins to as much as 80 percent in intrusive sheets, 

and resources in individual deposits range from a few thousand to millions of tons. Uranium contents usually range 

from 10 to 50 ppm, but a sample of apatite from the magnetite deposits at Mineville, New York, contained 7,900 ppm 

uranium. 

Marine phosphorite deposits are known throughout the 

world and range in age from Precambrian to Holocene. Economic deposits are restricted to late Precambrian-Cambrian, 

1

U.S. Geological Survey, Box 25046, Mail Stop 939, Denver Federal 

Center, Denver, Colorado 80225 (Retired). 

Ordovician, Permian, Late Cretaceous-Eocene, and Miocene ages. These deposits form large phosphogenic provinces in which resources total hundreds of billions of tons. 

The deposits form in tectonically stable basins at low latitudes that are open to oceanic upwelling and are away from 

large sources of clastic diluents. Total potentially minable 

resources are scores of billions of tons. These deposits contain uranium in amounts that range from 10 to 400 ppm, and 

individual samples contain as much as 5,300 ppm. The apatite fraction in unaltered deposits ranges from 60 to 90 ppm 

uranium. Uranium is present in the phosphate minerals apatite and crandallite as U(IV) substituting for calcium in the 

mineral structure. A small amount of uranium as U (VI) may 

be adsorbed on the apatite surface. 

The distribution uranium in the Florida uranium deposits demonstrates that these deposits are syngenetic. Primary 

phosphate pellets in the middle Miocene Peace River Formation contain an average of90 ppm uranium, whereas the uranium content of the pellets in the Bone Valley Formation, 

reworked from the Peace River in a marine environment, average about 120 ppm. The coarser pebble fraction contains 

about 150 ppm, and compound pebbles that show several cycles of reworking contain as much as 500 ppm. 

In the Florida deposits (fig. 2), uranium content is highest in the coarsest phosphate nodules that are low in P205 

and is lowest in the finest size phosphate pellets that are high 

in P20 5• Leaching by acid stream water has removed both 

uranium and P20 5 from phosphate grains in deposits in the 

stream valleys; uranium content there is less than 50 ppm. 

The relation of high U to low P20 5 in the coarse fraction and low U to high P20 5 in the fine fraction is consistent 

in millions of tons in one mine area and in individual drill 

hole samples, and the relation holds regardless of the relative 

amounts of the two fractions. When data from only one size 

fraction are studied, the relation of U to P20 5 is positive. 

Data analyzed collectively from all size fractions show almost no correlation between U and P20 5• These relations indicate that primary uranium was not introduced into the 

deposit after deposition of the phosphate: had this been the 

case, we would expect to see the highest uranium concentrations associated with phosphate that is high in P20 5, is fine 

grained, and has a large surface area. For example, in an area 

where acid ground water was draining into a sinkhole filled 

with phosphate rock, the fine-grained phosphate contained 

5,300 ppm U, while the coarser material contained only 

about 1,000 ppm U. 

Apatite is soluble in acid solutions, and under acid 

ground-water conditions, both phosphate and uranium are 

dissolved. When the phosphorite is high in carbonate, apatite is not dissolved until almost all of the carbonate is removed: phosphate is then dissolved and P20 5 in solution 

moves downward and may replace underlying carbonate 

rock. Uranium tends to be enriched in the replacement 

32 Short Papers of the U.S. Geological Survey Uranium Workshop, 1990 
EXPlANATION 

• GUANO-DERIVED DEPOSITS 

1. Christmas Island 

2. Nauru 

.& IGNEOUS APATITE DEPOSITS 

1. Brazil carbonatite deposits 

2. Phalaborwa, South Africa 

3. Kola Peninsula, USSR 

4. Eppiwala, Sri Lanka 

• MARINE PHOSPHORITE DEPOSITS 

1. Triassic-Permian, Alaska 

2. Permian, Northwest United States 

3. Ordovician, Tennessee 

Figure 1. World-wide distribution of major phosphate deposits. 

deposits; amounts of as much as 1,000 ppm have been 

reported in secondary apatite hardpan deposits. 

Intensive acid weathering of sandy phosphorites dissolves apatite and produces zones rich in aluminum phosphate minerals. These deposits are characterized by the 

change of apatite to crandallite and finally to wavellite. Uranium is enriched in these deposits and is preferentially associated with crandallite and apatite at the base of the zone of 

weathering. Because wavellite is continually formed from 

crandallite, the uranium in crandallite is mobilized and 

moves downward, further enriching the underlying apatite 

that may contain as much as 1,000 ppm U. Isopleth maps of 

uranium and P20 5 content in coarse phosphate grains in the 

land pebble district clearly show the effects of acid leaching. 

4. Miocene-Florida, Georgia, and 

North Carolina 

5. Cretaceous, Colombia 

6. Precambrian, Brazil 

7. Miocene, Baja California, Mexico 

8. Ordovician, USSR 

9. Cretaceous-Eocene, North Africa 

10. Precambrian, Upper Volta 

11. Cretaceous-Eocene, Near East 

12. Precambrian, Karatau, USSR 

13. Cambrian-Precambrian, India, China 

14. Cambrian-Precambrian, Mongolia 

15. Cambrian, Australia 

The contour lines are similar to topographic contours: they 

are deeply indented upstream and form closed contours in 

the interstream divides. Samples from stream valleys contain only about 50 ppm uranium and 20-25 percent P205, 

whereas the interstream divides are underlain by phosphate 

that contains as much as 250 ppm uranium and 35 percent 

P20s. 

The phosphate rock in the southern extension of the 

land pebble district has been leached only in the northern 

part of the area. Most of the phosphate is in the Peace River 

Formation, a siliciclastic unit of the middle part of the Hawthorn Group. The uranium content of the phosphate in this 

formation ranges from 60 to 110 ppm and averages about 90 

ppm. Uranium content of the phosphate pellets of the 

Uranium in Phosphate Rock-With Special Reference to the Central Florida Deposits 33 
Table 1. Phosphate resources, production, and uranium content 

[Leaders(--), no data available; Avg., average uranium concentration (in percent)] 

Location Resources Production Uranium concentration 

(metric tons) (metric tons) (percent) 

Guano and guano-derived phosphate 

Worldwide 150x 1o6 1.5x 1o6 0.001-0.008 

Igneous phosphate 

Worldwide 3x 109 28x 1o6 0.001-0.005 

Marine phosphorites 

Florida, land pebble district lx 109 

Florida, southern extension 3x 109 

North Florida-South Florida 2x 109 

North Carolina 2x 109 

Western U.S. lOx 109 

Africa 45x 109 

Asia lOx 109 

Europe lOx 109 

Latin America 6x 109 

TOTALS 89x 109 

carbonate rock in the underlying Arcadia Formation is only 

about 60 ppm. Deposits of phosphate rock in northern and 

eastern Florida are similar to the deposits in the land pebble 

district and its southern extension. 

Hardrock phosphates are secondary deposits of apatite 

that remained after the rocks of the Hawthorn Group were 

eroded from the crest of the Ocala uplift. The deposits were 

formed when acid waters dissolved phosphate, and P20 5 in 

solution was precipitated on and replaced the underlying 

limestone. The apatite crusts and replacement bodies have 

been reworked in Pleistocene and Holocene time and form 

small, erratically distributed phosphate deposits. Uranium 

contents range from 60 to about 100 ppm, but the P20 5 content of rock produced from these deposits is about 35 percent. 

0.003-0.030 

Avg. ( + 1 mrn) 0.015 

Avg. (-1+0.1 mrn) 0.010 

0.003-0.010 

Avg. 0.005 

46.5x 1o6 0.004-0.011 

Avg. 0.006 

0.004-0.011 

Avg. 0.006 

0.004-0.023 

Avg. 0.009 

52x 106 0.004-0.023 

Avg. 0.009 

16x 1o6 0.003-0.020 

Avg. 0.008 

18x 1o6 0.005-0.021 

Avg. 0.006 

lx 1o6 0.002-0.012 

Avs. 0.008 

135x 1o6 0.002-0.015 

Avg. 0.008 

River pebble deposits occur as bars and in floodplains 

of modem streams that drain phosphate deposits. These deposits are small and low in both P20 5 and U because of 

leaching by acid stream water. 

Uranium is being recovered today from two phosphoric 

acid plants. One is at the border of Polk and Hillsborough 

Counties in Florida, and one, using Florida rock, is at Uncle 

Sam, Louisiana. Each plant produced about 1 million 

pounds of uranium in 1988. 

REFERENCE CITED 

Bridges, N.J., Jones, M.Y., Lee, A.I.N., Bowen, R.W., and Sheldon, R.P., 1983, Bibliography of the geology of sedimentary 

phosphorite and igneous apatite: U.S. Geological Survey 

Open-File Report 83-841,926 p. 

34 Short Papers of the U.S. Geological Survey Uranium Workshop, 1990 
I 

HILLSBOROUGH HIG 

EXPlANATION 

Location of phosphorite deposits 

Location of hard rock phosphate areas 

--+-- Structural axes 

. JOHNS PLATFORM 

() 

BREVARD 

PLATFORM 

SOUTH FLORIDA 

EMBAYMENT 

Figure 2. location of major structural features and known phosphate areas in Florida. 

0 

Uranium in Phosphate Rock-With Special Reference to the Cent~al Florida Deposits 35 
Organic Matter and 

Uranium in SolutionCollapse Breccia Pipes of 

Northern Arizona and San 

Rafael Swell, Utah 

By Karen J. Wenrichl and James G. Palacas2 

INTRODUCTION 

Organic matter is commonly associated with uranium 

orebodies throughout the Colorado Plateau. Extensive studies have been done on such associations because many authors believe that the organic matter played a major role in 

the ore-forming process, particularly in the San Juan Basin 

(Squyres, 1980; Leventhal, 1980; Hatcher and others, 1986). 

According to Hatcher and others (1986), humic acids were 

important in the formation of the San Juan Basin ores; the 

humic-type organic matter presumably acted as a reductant 

for uranium-bearing oxidizing groundwaters that subsequently deposited uraninite or coffinite. 

The uranium--organic matter association is particularly 

striking in many of the uranium deposits in Arizona. Uranium ore in the Upper Triassic Shinarump Member of the 

Chinle Formation in Monument Valley (fig. 1A) is restricted 

primarily to carbonaceous sandstone and conglomerate beds, 

and similarly in the Cameron area (fig. 1A), to sandstones 

and conglomerates that contain varying amounts of organic 

matter, including carbonaceous fossil logs. Along the southem edge of the Colorado Plateau in Arizona at the Promontory Butte deposit, uranium mineralization occurred in 

coalified plant fossils along bedding planes within the Supai 

Group (Wenrich and others, 1989). 

Nevertheless, not all organic-rich uranium deposits on 

the Colorado Plateau are believed to have originated from reduction by organic compounds. Breit and Goldhaber (1989) 

1

U.S. Geological Survey, Box 25046, Mail Stop 939, Denver Federal 

Center, Denver, Colorado 80225. 2

U .S. Geological Survey, Box 25046, Mail Stop 971, Denver Federal 

Center, Denver, Colorado 80225. 

suggested that vanadium-uranium deposits in the Morrison 

Formation in southwestern Colorado and southeastern Utah 

formed by reduction and precipitation that occurred through 

reaction with localized, strongly reducing (sulfidic) pore waters. 

In contrast to more classical sandstone-hosted Colorado 

Plateau uranium deposits, the uranium orebodies located 

within solution-collapse breccia pipes in the southwestern 

comer of the Colorado Plateau do not display any consistent, 

obvious organic matter-uranium association. These pipes 

formed by solution collapse into caverns within the Mississippian Redwall Limestone (for stratigraphic column see 

Brown and others, this volume) and subsequent stoping and 

brecciation of the overlying Pennsylvanian, Permian, and 

Triassic strata (Gomitz and Kerr, 1970; Wenrich, 1985; 

Krewedl and Carisey, 1986; Wenrich and Sutphin, 1989). 

With the exception of the Upper Mississippian/Lower Pennsylvanian Surprise Canyon Formation and the Lower Permian Brady Canyon Member of the Toroweap Formation, none 

of the other upper Paleozoic units are known to contain 

abundant organic matter within northwestern Arizona. The 

Surprise Canyon Formation fills channels cut into the Redwall Limestone across northwestern Arizona; these channels 

contain some black shales containing 1 percent organic carbon (K.J. Wenrich, unpub. data). Although breccia pipes 

that host uranium ore bodies do not generally contain any significant amounts of organic matter, several pipes clustered 

around the Kanab Creek-Hack Canyon area in Arizona (fig. 

1B) are known to contain solid bitumen. Because of this association, Landais (1989) studied the effects of biodegradation on these solid bitumens in the Arizona pipes and in the 

Temple Mountain pipe in Utah; he concluded that biodegraded, migrated, organic material (formerly liquid petroFigure 1 (facing page). A, Index map showing the location of 

several uranium districts on the Colorado Plateau that contain 

organic matter. 8, Index map of northern Arizona showing the 

locations of plateaus, Hualapai Indian Reservation, breccia 

pipes developed into mines, pipes containing bitumen that 

have not been developed into mines, and the San Francisco 

volcanic field that buries terrane with high potential for mineralized breccia pipes. Numbers refer to the following mines: (1) 

Copper House, (2) Copper Mountain, (3) Cunningham, (4) 

Grand Gulch, (5) Grandview, (6) Hack Canyon (includes old 

Hack, Hack 1, Hack 2, and Hack 3 mines, and Toroweap 

source-rock sample HB-821-C83), (7) Old Bonnie Tunnel, (8) 

Orphan, (9) Ridenour, (1 0) Riverview, (11) Savannic, (12) Snyder, (13) Pigeon, (14) Kanab North, (15) Canyon, (16) Pinenut, 

(17) Hermit, (18) Arizona 1, and (19) Mohawk Canyon. 

36 Short Papers of the U.S. Geological S&,Jrvey Uranium Workshop, 1990 
A 

0 Kingman 

SALT LAKE 

CITY0 

0 PHOENIX 

BASIN AND RANGE PROVINCE 

50 100 KILOMETERS 

50 MILES 

0 oENVER 

!MATE BOUNDARY 

OF COLORADO PLATEAU 

Color0 o'o Holbrook 

Organic MaHer and Uranium in Solution-Collapse Breccia Pipes of Northern Arizona and San Rafael Swell, Utah 37 
Figure 2. The Temple Mountain breccia pipe resides within the north half of Temple Mountain, which is located along the crest 

of the San Rafael Swell. View is to the northeast. The pipe is dissected and well exposed on the back side of the left-most butte 

in this photograph. 

leum) can interact favorably with uranium-bearing solutions 

to cause deposition of uranium minerals. 

Despite the well-documented association of uranium 

with humic-type organic matter, uranium is not as commonly associated with unaltered hydrocarbon concentrations 

(commercial oil accumulations). One of the questions addressed in this study was whether the solid bitumens in the 

northern Arizona breccia pipes and the Temple Mountain 

pipe were responsible for the associated uranium deposits. 

Even if bitumen did not influence uranium mineralization, 

determination of the source of the bitumen is important for 

exploration and research in uranium-rich breccia pipes. For 

instance, if the source of oils for the bitumens migrated over 

long distances, then such permeable channel ways may have 

been available for uranium and base-metal transport. Thus, 

another objective of the present study was to determine, 

through comparisons of bulk organic-chemical composition, 

saturated hydrocarbon distributions, biomarker distributions, and carbon isotopes, whether the solid bitumen andrelated oils from these two spatially separated breccia pipes are 

genetically related~ Insights gained from this investigation 

into the nature of bitumen migration pathways may aid in the 

understanding of passageways through which uranium and 

other metals are transported in solution. Information may 

also be gained concerning the source of these metals. In the 

past, source rocks for uranium have been assumed to be 

those that are nearby and contain a volcanic component. For 

example, Krewedl and Carisey (1986) proposed that the 

Chinle Formation, with its inherently higher uranium content, was the source rock for the breccia pipe uranium deposits in northern Arizona. 

ORGANIC MATTER AND 

URANIUM ASSOCIATION 

With the exception of a black, glassy, solid bitumen, 

few carbonaceous fossil logs, coalified plant fossils, or other 

visually obvious concentrations of organic matter have been 

38 Short Papers of the U.S. Geological Survey Uranium Workshop, 1990 
Figure 3. "Asphaltite" from a mine in the Temple Mountain breccia pipe. 

observed within the Arizona breccia pipes. Apparently unaltered oils have been encountered while drilling in such 

pipes as the Hack 2. Landais (1989) showed a gas chromatogram for "unaltered oils" from the "Arizona breccia pipes" 

but did not cite a specific location. 

The black, glassy, solid bitumen of the Arizona pipes 

contrasts with the duller asphaltite collected from the Temple Mountain breccia pipe, Utah (figs. 1A, 2), and the tar 

sand from Flat Top, Utah (fig. 1A), that was observed to flow 

down a sun-baked rock surface at or above 75°F (25°C). 

The Temple Mountain collapse-breccia pipe may have an origin different from that of the Arizona breccia pipes in that 

the bottom of the pipes may not terminate in Redwall Limestone. The Temple Mountain breccia pipe (fig. 2), which occurs in Jurassic (younger than the uranium mineralization of 

Arizona pipes) and Triassic rocks, contains abundant solid 

bitumen (referred to as "asphaltite" by Kerr and others, 

1957; fig. 3). According to Hawley and others (1965), "The 

asphaltite probably contains an average of a few percent uranium***." An analysis of pure asphaltite made during this 

study showed 809 ppm uranium in the asphaltite, in contrast 

to the Arizona bitumen, which generally contains< 10 ppm 

uranium (table 1). Although the Temple Mountain asphaltite 

sample appeared as pure as the Arizona bitumen, it is possible that it was not, considering the lower total organic carbon 

content (table 1). In addition to asphaltite, there is abundant 

plant debris (fig. 4) at Temple Mountain that also contains 

anomalously high uranium concentrations. The disparity in 

results between the Arizona pipes that contain essentially no 

uranium in the bitumen and the Temple Mountain asphaltite 

that appears to contain several hundred ppm uranium may be 

due to plant debris (normally high in uranium) intermixed 

with asphaltite in the Temple Mountain breccia. 

Elemental analyses of 418 surface and subsurface, oxidized and reduced samples collected from mineralized and 

unmineralized Arizona breccia pipes show no significant 

correlation between organic carbon and uranium (fig. 5, correlation coefficient = 0.02). The organic carbon-uranium 

correlation coefficient for 103 samples (a subset of the 418 

samples shown in fig. 5) collected from subsurface, reduced 

rock (much of it mineralized) was -0.07. A down-hole plot 

through reduced, poorly mineralized rock within the 

Organic Matter and Uranium in Solution-Collapse Breccia Pipes of Northern Arizona and San Rafael Swell, Utah 39 
Figure 4. Organic carbon and uranium-rich plant debris from a mine in the Temple Mountain breccia pipe. Horizontal field of 

view is 3ft. 

Mohawk Canyon pipe (fig. 6) shows little correlation between organic carbon and uranium (correlation coefficient= 

-0.02). Likewise, as discussed above, there is no significant 

correlation between uranium and organic carbon for samples 

that contain abundant bitumen material. Indeed, samples of 

pure bitumen contain less than 10 ppm uranium (table 1). 

DISTRIBUTION AND GENERAL 

CHARACTERISTICS OF SOLID BITUMEN 

In the northern Arizona breccia pipes, solid bitumen 

was exceptionally abundant in the Pigeon pipe, now mined 

out, (fig. 7; fig. 18, site 13) but was less common at several 

other breccia pipes. Irregularly shaped pieces of solid, black, 

glassy bitumen, 4-8 em in diameter (fig. 8), were found at 

several mine levels within the Pigeon pipe. They were located within the uranium breccia-pipe orebody and were associated with clasts of both the Lower Permian Hermit Shale 

and Esplanade Sandstone. Significant amounts of bitumen 

were also found at the Clearwater pipe (located a few miles 

northwest of the Pigeon pipe; fig. 18}, which, although mineralized, has not yet been delineated as an orebody. Minor 

amounts of solid bitumen were identified at Pinenut (Reid 

and Rasmussen, 1990), Kanab North, Hack 2, Hack 3, and 

Hermit (fig. 18, sites 16, 14, 6, 6, and 17, respectively) (Pat 

Hillard, Energy Fuels Nuclear, oral commun., 1990). The 

EZ-1 pipe, also located near the Pigeon pipe, contains bitumen (D.A. Krewedl, Pathfinder Mines, oral commun., 

1988). To date, no solid bitumens have been recognized at 

the Canyon pipe (fig. 18, site 15) (Pat Hillard, Energy Fuels 

Nuclear, oral commun., 1990), yet uranium deposits are 

present. With the exception of the Sage breccia pipe, located 

on the South Rim of the Grand Canyon, where very minor 

amounts of bitumen have been identified (Richard Meade, 

40 Short Papers of the U.S. Geological Survey Uranium Workshop, 1990 
Table 1. Elemental chemical analyses of samples from the Pigeon and Temple Mountain breccia pipes 

[Results were determined by inductively coupled argon plasma emission spectroscopy (ICP) except for: U, determined by delayed neutron analysis; organic 

C, calculated as (total C) -(carbonate C); Si02 and FeT03 determined by quantitative X-ray fluorescence (the "T' in FeT03 indicates total Fe reported as 

Fe203); totalS determined by combustion with infrared detection; trace metals in pure bitumen sample 455-J-CSS were determined by semi-quantitative 

emission spectroscopy. Leaders(··) indicate no data] 

Pigeon breccia pipe Temple Mountain breccia pipe Pure bitumen sameles 

Element samples containing varying samples containing varying amounts Pigeon Temple Mtn 

analyzed amounts of solid bitumen of asehaltite or carbonaceous elant debris breccia eie! breccia eiee 

455-J-CSS 455-N-C85 1194-A-C87 1194-C-C87 1194-D-C87 455-J-C85 455-T-caa 1194-M-C87 

Ag (ppm) ...................... <2.0 49 6.0 3.0 <2.0 <0.5 <0.5 <0.5 

As (ppm) ....................... llO 3,500 620 210 2,100 <1,000 <20 64 

Organic C (%) ................. 3.26 2.76 61.5 61 31.2 85.6 87.3 n.s 

Cd (ppm) ...................... < 2.0 23 <2.0 <2:0 170 <50 <4 19 

Ce (ppm) ......................... 14.2 58 4.0 <2.9 98 <200 <8 <8 

Co (ppm) ........................ 23.6 310 9.5 20.5 180 <5 <2 78 

Cr(ppm) ......................... 70 170 12 5.0 210 3 2 6 

Cu (ppm) ...................... 270 2,600 210 65 32 <1 2 13 

FeT03 (%) ....................... 0.57 14.SH 1.73 0.31 t.4H <0.01 

Hg (ppm) ...................... <0.14 1.10 0.28 0.08 0.10 0.70 

Mo (ppm) ......................... 8.0 820 15 3.0 <2.0 <3 <4 6 

Ni (ppm) ....................... 170 1,300 11 57 260 so 140 94 

Pb (ppm) ......................... 49 1,700 170 90 810 so <8 330 

TotalS (% ) ....................... 0.39 12.8 1.95 1.37 2.89 5.74 5.16 2.07 

Sb (ppm) ........................... 2.55 9.32 8.21 <200 <100 <100 

Si02 (%) ......................... 87 54H 3.37 1.49 35H 

U (ppm) .......................... 88.8 9,470 30.5 331 62,800 7 809 

V(ppm) .......................... 41 130 300 110 6,700 100 230 19,000 

Zn (ppm) ..................... .385 5,600 16.2 230 2,100 15 23 2,900 

H Results are semi-quantitative for this sample due to matrix interferences 

Union Pacific Resources, oral commun., 1990), all of the 

pipes containing significant amounts of bitumen are clustered together near Snake Gulch and Kanab Creek (fig. 1B). 

Solid bitumen appears to have been introduced into the 

pipes late in the paragenetic mineral sequence (Wenrich and 

others, 1990). Among the sulfides, only some late-stage 

sphalerite (fig. 9) has been identified as contemporaneous 

with (or later than) the bitumen. From the paragenetic relations, uraninite appears to have precipitated prior to the bitumen. A large set of U-Pb isotopic analyses from the Hack 2, 

Hack 3, Pigeon, Kanab North, EZ-1, EZ-2, Arizona 1, Pinenut, and Canyon pipe orebodies shows that the main uranium-mineralizing event occurred roughly 200 Ma (Ludwig 

and Simmons, 1988). However, data from the Canyon and 

Pinenut pipes indicate at least one earlier period of mineralization at about 260 Ma (Ludwig and Simmons, 1988). Fluid 

inclusion filling temperatures on sphalerite from seven different Arizona breccia pipes range from 80-173 °C; the salinities are high: 70 percent of the salinities are> 19 weight 

percent NaCl equivalent and the remaining 30 percent range 

from 9 to 12 weight percent NaCl equivalent (Wenrich, 

1985; Wenrich and Sutphin, 1989). Fluorescent orange-yellow petroleum inclusions were observed by Jim Reynolds 

(written commun., 1985) in sphalerite from the Pigeon 

pipe-within this sample, petroleum was observed in vugs 

and microfractures within quartz, indicating that petroleum 

postdates deposition of the quartz. 

The solid bitumen is sulfur rich. Elemental chemical 

analyses of a pure, solid bitumen sample from the Pigeon 

pipe yielded 85.6 percent carbon (precision of 1 percent) and 

3.74 percent sulfur; the bulk of the remaining fraction is 

probably hydrogen with minor amounts of nitrogen and oxygen. The bitumen contains few trace elements in concentrations over 3 ppm (table 1); exceptions to this are: Ba (50 

ppm), Ni (50 ppm), Pb (50 ppm), V (100 ppm), Zr (15 ppm), 

and Si (70 ppm). This paucity of trace metals within the bitumen contrasts sharply with the "asphaltite" from the San 

Rafael Swell discussed by Hawley and others (1965) and 

shown in table 1. Samples of bitumen from the Temple 

Mountain pipe contain 1.9 percent vanadium in contrast to 

100 and 230 ppm for bitumen from two Pigeon pipe samples. 

Likewise U, Zn, and Pb are significantly higher in the TernOrganic Matter and Uranium in Solution-Collapse Breccia Pipes of Northern Arizona and San Rafael Swell, Utah 41 
z 

0 

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EXPLANATION 

6. Oxidized samples 

e Unoxidized samples 

• 

•• 

• • 

6. • 

ORGANIC CARBON CONTENT, IN PERCENT 

Figure 5. Uranium concentration (in ppm) versus organic carbon content (in percent) for 418 surface (oxidized) and subsur· 

face (unoxidized-still in their primary, reduced condition) samples collected from mineralized and unmineralized northern 

Arizona breccia pipes. Correlation coefficient is 0.02. The 103 subsurface, reduced samples show no more of a significant 

correlation between uranium and organic carbon than do the 418 mixed group of oxidized and reduced samples. 

pie Mountain pipe bitumen than the Pigeon pipe bitumen. 

Elemental chemical analyses of five bulk rock samples containing varying amounts of solid bitumen and three pure bitumen samples are presented in table 1. The bulk rock 

samples are provided to illustrate the high metal concentrations that are intimately associated with the bitumen and, 

hence, should have been available for scavenging by the bitumen. Yet, analyses of pure bitumen (table 1) show that the 

bitumen did not adsorb or chelate most of these metals. The 

principal exceptions to this are vanadium and nickel, which 

are commonly associated with petroliferous substances. 

ORGANIC GEOCHEMISTRY OF 

SOLID BITUMENS 

Bulk Organic Chemical Characteristics 

Gas chromatographic analyses of saturated hydrocarbon fractions (fig. 1 0) from both Temple Mountain and Pigeon pipe are characterized by a depletion of nonnal (n)-

alkanes and a conspicuous hump of unresolved branched and 

cyclic alkanes. Such compositional features strongly indi42 Short Papers of the U.S. Geological Survey Uranium Workshop, 1990 
URANIUM CONCENTRATION. IN PARTS PER MILLION 

20 40 60 

1--

w 

w 

u.. 

~ 

:i 

b: 

w 

0 

Mohawk Canyon pipe 

Hole 5 

=-- -o 

ORGANIC CARBON CONTENT, IN PERCENT 

Figure 6. Down-hole plots of uranium concentration (in ppm, shown by open circles) and carbon content (in percent, shown 

by asterisks) for drill hole 5 in the Mohawk Canyon pipe. Note the absence of any significant correlation between uranium 

and carbon (correlation coefficient is -0.02). 

cate the effects of biodegradation and, to some extent, water 

washing (Connan, 1984; Landais, 1989). Bulk chemical 

fractions of chloroform extracts of solid bitumens (J.G. Palacas, unpub. data, 1990) from both areas show some differences. These apparent compositional differences between 

the Arizona and Utah solid bitumens are probably the result 

of one or more depositional or post-depositional processes: 

(I) bacterial degradation (biodegradation), (2) radiation 

damage, (3) thermal alteration in the presence of sulfur, or 

(4) derivation from different source rocks. 

Biomarker Distributions 

Biomarker distributions of extracts of solid bitumens in 

breccia pipes from northern Arizona and Temple Mountain, 

Utah, and tar sands from Flat Top (San Rafael Swell) and 

Circle Cliffs, Utah (figs. 1A and 18) are from unpublished 

data of J.G. Palacas, 1990. These biomarkers include: (1) 

tricyclic and pentacyclic terpanes (rnlz 191), (2) steranes 

(m/z 217), and (3) combined triaromatic (rnlz 231) and 

monoaromatic (m/z 253) steroids. Figure 11 shows 

Organic Matter and Uranium in Solution·Collapse Breccia Pipes of Northern Arizona and San Rafael Swell, Utah 43 
Figure 7. Pigeon pipe and mine headframe. Beds on left side of photograph dip inward toward the center of the basin. The 

collapse basin that has formed over the breccia pipe is about one-half mi in diameter, whereas the Pigeon pipe itself is only 240 

ft in diameter. 

biomarkers for the terpanes and steranes of samples from 

some of these areas along with biomarkers of an extract from 

the Toroweap Formation, which is believed by Landais 

(1986, 1989) to be a source rock for the solid bitumens in 

northern Arizona breccia pipes. From this diagram, it can be 

seen that the Pigeon pipe bitumen, Temple Mountain pipe bitumen, and the Circle Cliffs tar sand have similar biomarker 

distributions. The only apparent difference is the relatively 

lower amounts of pentacyclic terpanes in the Pigeon pipe 

sample-this is attributable to the greater degree of biodegradation (fig. 1 0). In contrast, the Toroweap rock extract has 

a low tricyclic to pentacyclic ratio (fig. llA); this signature 

is different from any of the other samples. Another disparity 

may be observed between the sterane distributions (fig. liB) 

in which the Toroweap sample has an abundance of diasteranes relative to regular steranes; in particular, peaks DS and 

DR have a distribution opposite to that observed in the hydrocarbon deposits from all three of the other areas. 

Carbon Isotopes 

Carbon isotopic values (313C per mil PDB) of aromatic 

hydrocarbons and saturated hydrocarbons are similar for the 

Pigeon pipe and Temple Mountain pipe solid bitumens and 

Flat Top tar-sand oils (fig. 12). This indicates a similarity of 

organic chemical composition and, in tum, suggests a similar 

or common source; this same conclusion is suggested by the 

44 Short Papers of the U.S. Geological Survey Uranium Workshop, 1990 
Figure 8. Bitumen associated with pyrite in the Pigeon pipe. Note how the pyrite is fractured and offset while the bitumen is not, 

indicating that the pyrite is older than the bitumen. 

biomarker correlations. Although the Toroweap Formation 

has the potential to be a local source rock for northern Arizona solid bitumens, no obvious carbon isotope correlation 

seems to exist between the Toroweap source rock and the Pigeon pipe bitumens. 

SOURCE OF SOLID BITUMENS 

Similar 313C values and (or) biomarker distributions of 

Pigeon pipe and Temple Mountain pipe solid bitumens to 

those of the tar-sand oils at Flat Top and other parts of the 

San Rafael Swell, Circle Cliffs, and Tar Sand Triangle (fig. 

IA) indicate that most, if not all, of these hydrocarbon substances were derived from the same source or from similar 

source facies either through long-distance or short-distance 

migration. The distinctly lighter 313C values (fig. 12), somewhat dissimilar biomarker distributions (fig. 11), and lower 

maturity levels of the Toroweap Formation hydrocarbons 

from northern Arizona indicate that the bitumens associated 

with breccia pipes in northern Arizona do not have their 

source in either the local Permian Toroweap Formation or in 

stratigraphically younger, less mature formations. 

If the source of bitumen involved local vertical migration, then older, more deeply buried, and more mature rock 

than the Permian Toroweap might qualify as an alternative 

source. If this scenario is viable, then the question arises: 

Can either Paleozoic rocks older than the Pennsylvanian or 

Precambrian rocks be possible source rocks? To date, based 

Organic Matter and Uranium in Solution-Collapse Breccia Pipes of Northern Arizona and San Rafael Swell, Utah 45 
Figure 9. Reflected light photomicrograph of chalcopyrite (ccp) and globules of bitumen (b) surrounded by later sphalerite (S). 

Horizontal field of view is 1 .29 mm. 

on published data and unpublished information gleaQed from 

field work by one of the authors and from other geoscientists 

who have worked in the Grand Canyon area, there is no evidence for the presence of viable petroleum source rocks of 

Paleozoic age older than the Toroweap Formation in the vicinity of the pipes; the only exception to this is the Upper 

Mississippian/Lower Pennsylvanian Surprise Canyon Formation channels that cover less than 1 percent of the Grand 

Canyon region (in plan view). Reynolds and others (1988) 

and Palacas and Reynolds (1989) recently discovered that a 

5,300-ft section of unmetamorphosed Late Proterozoic 

Chuar Group rocks exposed in the eastern part of the Grand 

Canyon, Arizona, has good to excellent oil source-rock potential. More than 1,000 ft of dark gray, organic-rich mudstones and siltstones contain as much as 9 weight percent 

organic carbon. This area of the eastern Grand Canyon lies 

within the Arizona breccia pipe province. These Chuar 

Group rocks are believed to be present beneath some of the 

plateaus (Coconino, Kaibab, Kanab, Marble, and Shivwits) 

that are known to contain collapsed breccia pipes to the south 

and north of the Grand Canyon in northern Arizona; Chuar 

Group rocks are also likely to exist into the subsurface of 

southern Utah (M.W. Reynolds and J.G. Palacas, unpub. 

data, 1990; Chidsey and others, 1990). Preliminary organic 

geochemical analyses (J.G. Palacas and M.W. Reynolds, 

unpub. data, 1990) show some faint similarities to the breccia pipe bitumens in saturated hydrocarbon and biomarker 

distributions, but no clear-cut source rock-solid bitumen 

correlations have been ascertained. However, approximately the upper 450 ft of the Chuar (upper half of the Walcott 

Member of Kwagunt Formation), also considered to be organic rich, have not yet been sampled. Until these Precambrian rocks are fully evaluated, they cannot be completely 

excluded as possible sources for the breccia pipe bitumens. 

In summary, particularly in south-central Utah, the confinement of tar-sand oils and solid bitumens principally to a 

stratigraphically narrow interval (Lower Permian White Rim 

Sandstone Member of the Cutler Formation to Lower and 

46 Short Papers of the U.S. Geological Survey Uranium Workshop, 1990 
A 

B 

c 

455-T-CSS 

Pigeon pipe 

1194-D-C87 

Moss Back Member 

Chinle Formation 

Circle Cliffs, Utah 

Moenkopi Formation 

Figure 10. Gas chromatograms of saturated hydrocarbons. 

All chromatograms are C9+ saturated hydrocarbon fractions. 

Pr, pristane; Ph, phytane; numbered peaks are n-alkanes. A, 

Solid bitumens in the Pigeon uranium-bearing breccia pipe, 

northern Arizona; 8, Solid bitumens in Chinle Formation at the 

Temple Mountain uranium-bearing breccia pipe, south-central 

Utah; C, Bitumen or "heavy oils" of tar sands in Moenkopi Formation, Circle Cliffs, Utah. 

Middle(?) Triassic Moenkopi Formation), similar biomarker 

signatures, and similar molecular maturity indices (Tm!fs, 

SIR ratios of C29 steranes and ratios of triaromatic to 

monoaromatic steroids; J.G. Palacas, unpub. data, 1990) 

suggest that these widely separated surface to near-surface 

hydrocarbon deposits are genetically related. Hence, they 

are derived from either a single, extensive, organically rich 

source-rock facies through long-distance migration or from 

various, similar, local source-rock facies. In any case, whatever hydrocarbon source rock is responsible for these deposits, it must have been one capable of generating huge 

amounts of petroleum. Estimated present combined oil-inplace reserves within the San Rafael Swell, Circle Cliffs, and 

Tar Sand Triangle areas amount to at least 8 and possibly as 

much as 18 billion barrels of tar-sand oils (Ritzma, 1973; 

Campbell and Ritzma, 1982)-the estimated volume of 

heavy oils and bitumens prior to alteration and destructive 

processes totals about 16 to perhaps as much as 35 billion 

barrels of oil. However, source rocks capable of generating 

such an enormous volume of oil have not, as yet, been identified in this area. 

CONCLUSIONS 

Comparisons of saturated hydrocarbon gas chromatograms, biomarker distributions, and carbon isotope data for 

(1) extracts of solid bitumens from solution-collapse breccia 

pipes at Temple Mountain, Utah, and (2) bitumens or "heavy 

oils" in tar-sand deposits from Flat Top, Circle Cliffs, and 

Tar Sand Triangle, Utah, indicate that the solid bitumens of 

Temple Mountain are definitely genetically linked to the pervasive tar-sand oils located throughout south-central Utah. 

Although a similar link can be made to the northern Arizona 

Pigeon pipe, such a conclusion is somewhat more tenuous 

because of the degree of biodegration of its solid bitumens. 

Because uranium ores in these Colorado Plateau solution-collapse breccia pipes are sometimes associated with 

solid bitumen, uranium as well as the other associated metals 

(Ag, Co, Cu, Mo, Ni, Pb, Zn, and V) in these orebodies may 

well have followed the same migration path as the oils. Most 

of the solid bitumen found in northern Arizona breccia pipes 

occurs in pipes clustered together near Snake Gulch and 

Kanab Creek (fig. 1B), suggesting a local source. Yet one of 

the most likely source-rock candidates, according to Meyer 

and others (1989) and Landais (1989), in the nearby 

vicinity-the Brady Canyon Member, Toroweap 

Formation-is dissimilar in hydrocarbon distributions and is 

less thermally mature than the pipe bitumens, suggesting that 

the local Toroweap is not the source of the bitumens. With 

the exception of the localized Surprise Canyon Formation, 

most of the remaining rock in the Paleozoic section in the 

nearby vicinity below the Toroweap contains no obvious organic-rich source-rock units. However, another possibility 

Organic Matter and Uranium in Solution-Collapse Breccia Pipes of Northern Arizona and San Rafael Swell, Utah 47 
455-T-CSS 

Pigeon pipe 

22 

21 

1194-D-C87 

Chinle Formation 

21 

23 

23 

Circle Cliffs-Moenkopi Formation 

Tricyclics 

23 

19 

A3 

Tm 

Toroweap Formation-Northern Arizona 

Tm 

20 21 23 

48 Short Papers of the U.S. Geological Survey Uranium Workshop, 1990 

455-T-CSS 

Pigeon pipe 

81 

1194-D-C87 

Chinle Formation 

Diasterane 

Region 

82 

Regular Steranes 

Circle Cliffs-Moenkopi Formation 

Toroweap FormationNorth.ern Arizona 

DS 

DR 
Figure 11 (facing page). A, Tricyclic and pentacyclic terpanes 

(m/z 191 ); 8, Sterane (m/z 217) distributions. A 1 and 81, Solid 

bitumens in Pigeon breccia pipe, northern Arizona; A2 and 82, 

Solid bitumens in Chinle Formation at Temple Mountain breccia pipe, Utah; A3 and 83, Bitumens or "heavy oils" of tar 

sands in Moenkopi Formation, Circle Cliffs, Utah; A4 and 84, 

Toroweap Formation extract. Peaks 19-29 are tricyclic terpanes; peaks Ts to C35 are pentacyclic terpanes; Ts = 18a(H) 

trisnorneohopane; Tm = 17a(H) trisnorhopane. DS and DR are 

C27 13f3(H), 17a(H) 205 and 20R diasteranes, respectively. 

is that long-distance lateral migration was responsible for 

transporting the hydrocarbons that eventually formed the bitumen deposits. If this were so, then a more mature Toroweap or comparable source-rock facies under greater burial 

depth or under higher geothermal gradients located west and 

northwest of the breccia pipes could be the probable source. 

An alternative to long-distance lateral migration is vertical 

migration: If the source were local, then an older, more 

deeply buried, more mature local rock unit might be an alternative source. A good candidate might be the Late Proterozoic Chuar Group, which has been shown to have good to 

excellent oil source potential by Reynolds and others (1988) 

and Patacas and Reynolds (1989). Some similarities exist 

between the Chuar Group and the breccia pipe bitumens, but 

they were not striking enough to conclude that the Chuar 

Group rocks were the source for the breccia pipe bitumens. 

Because the source rock for the oils is not a local source such 

as the Permian Toroweap or younger rocks, the same scenario may well exist for the uranium and associated metals in 

the breccia pipe ore bodies. There is no firm evidence to suggest that the oils and other metals followed the same migration path and had the same source rock, but, if they are 

related, the best uranium source rock is not the nearby Triassic Chinle Formation as proposed by Krewedl and Carisey 

(1986). 

ACKNOWLEDGMENTS 

The authors wish to thank Benny Law for his constructive review and suggestions that improved the manuscript. 

Bradley Van Gosen compiled the uranium and organic carbon geochemical data for the 418 samples from breccia pipes 

in Arizona as well as the down-hole data for the Mohawk 

Canyon breccia pipe. David Detra assisted in providing a 

rapid, accurate, inorganic geochemical analysis of the pure 

bitumen samples, and Eric Michael, Paul Lillis, David King, 

Ted Daws, and Augusta Warden provided the organic 

-27~--~~----~~-----~~--~~----~~----~ 

(/) 

z 

0 

~-28-

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a: 

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0 

a: 

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c 

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0 

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EXPLANATION 

• Pigeon pipe solid bitumen, 

northern Arizona 

o Temple Mountain solid bitumen, 

Utah 

0 Tar sand, Flat Top, Utah 

o Toroweap Formation, o 

northern Arizona 

00 

0 

-

-

-

-

-32.~---~~---~~--~~----~~----~~~--~ -32 -31 -30 -29 -28 -27 -26 

8 13C o;oo PD8 SATURATED HYDROCARBONS 

Figure 12. Plot of a13C values of saturated hydrocarbons versus 

aromatic hydrocarbons for solid bitumen samples from Pigeon 

pipe, northern Arizona and Temple Mountain breccia pipe, Utah. 

For comparative purposes, isotope values are also plotted for one 

tar-sand sample (Flat Top, Utah) and for one Toroweap Formation 

possible source-rock sample (northern Arizona). 

geochemical analyses. Thanks also go to Harry Dembicki, 

Marathon Oil Company, for providing metastable ion monitoring data. 

REFERENCES CITED 

Breit, G.N., and Goldhaber, M.B., 1989, Hematite-enriched sandstones and chromium-rich clays--clues to the origin of vanadium-uranium deposits in the Morrison Formation, 

southwestern Colorado and southeastern Utah, USA, in Uranium Resources and Geology of North America, [Proceedings of a technical committee meeting organized by the 

International Atomic Energy Agency and held in Saskatoon, 

Canada, 1-3 September 1987]: Vienna, International Atomic Energy Agency, p. 201-225. 

Campbell, J.A. and Ritzma, H.R., 1982, Geology and petroleum 

resources of the major oil-impregnated sandstone deposits of 

Utah, in Ball, Douglas, Marchant, L.C., and Goldburg, 

Arnold, eds., The OICC Monograph Series: Tar Sands: 

Interstate Oil Compact Commission, p. 27-43. 

Chidsey, T.C., Allison, M.L., and Palacas, J.G., 1990, Potential for 

Precambrian source rock in Utah [abs.]: Bulletin of the 

American Association Petroleum Geologists, v. 74, no. 8, p. 

1,319. 

Connan, J., 1984, Biodegradation of crude oils in reservoirs, in 

Brooks, J. and Welte, D., eds., Advances in Petroleum 

Organic Matter and Uranium in Solution-Collapse Breccia Pipes of Northern Arizona and San Rafael Swell, Utah 49 
Geochemistry: New York, Academic Press, v. 1, p. 

299-335. 

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

alteration, Orphan mine, Grand Canyon, Arizona: Economic 

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

Hatcher, P.G., Spiker, E.C., Orem, W.H., Romankiw, L.A., Szeverenyi, N.M., and Maciel, G.E., 1986, Organic geochemical 

studies of uranium-associated organic matter from the San 

Juan Basin: a new approach using solid state 13C nuclear 

magnetic resonance, in Turner-Peterson, C.E., Santos, E.S., 

and Fishman, N.S., eds., A Basin Analysis Case Study: the 

Morrison Formation, Grants Uranium Region, New Mexico: 

Tulsa, Oklahoma, American Association of Petroleum Geologists Studies in Geology No. 22, p. 171-184. 

Hawley, C.C., Wyant, D.G., and Brooks, D.B., 1965, Geology and 

uranium deposits of the Temple Mountain district, Emery 

County, Utah: U.S. Geological Survey Bulletin 1192, 154 p. 

Kerr, P.F., Bodine, M.W., Jr., Kelly, D.R., and Keys, W.S., 1957, 

Collapse features, Temple Mountain uranium area, Utah: 

Geological Society of America Bulletin, v. 68, p. 933-982. 

Krewedl, D.A., and Carisey, J.C., 1986, Contributions to the geology of uranium mineralized breccia pipes in northern Arizona: Arizona Geological Society Digest, v. 16, p. 179-186. 

Landais, P., 1986, Geochemical analyses of the organic matter 

associated with the breccia pipes in the Grand Canyon area 

[abs.]: Geological Society of America Abstracts with Programs,v. 18,no.5,p.389. 

Landais, P., 1989, Biodegradation of oils in uranium deposits, in 

Metallogenesis of Uranium Deposits, [Proceedings of a technical committee meeting on metallogenesis of uranium 

deposits organized by the International Atomic Energy 

Agency and held in Vienna, 9-12 March 1987]: Vienna, 

International Atomic Energy Agency, p. 43-62. 

Leventhal, J.S., 1980, Organic geochemistry and uranium in Grants 

Mineral Belt, in Rautman, C.A., compiler, Geology and Mineral Technology of the Grants Uranium Region, 1979: New 

Mexico Bureau of Mines and Mineral Resources Memoir 38, 

p. 75-85. 

Ludwig, K.R. and Simmons, K.R., 1988, Progress in U/Pb isotope 

studies of collapse-breccia pipes in the Grand Canyon 

region, northern Arizona [abs.]: Geological Society of 

America Abstracts with Programs, v. 20, no. 7, p. A139. 

Meyer, A.J., Landais, P., Brosse, E., Pagel, M., Carisey, J.C., and 

Krewedl, D., 1989, Thermal history of the Permian formations from the breccia pipes area (Grand Canyon region, Arizona): Geologische Rundschau, v. 78, no. 1, p. 427-438. 

Palacas, J.G. and Reynolds, M.W., 1989, Prelimiary petroleum 

source rock assessment of the Late Proterozoic Chuar Group, 

Grand Canyon, Arizona: Bulletin of the American Association of Petroleum Geologists, v. 73, no. 3, p. 397. 

Reid, A.R. and Rasmussen, J.D., 1990, The use of soil-gas C02 in 

the exploration for sulfide-bearing breccia pipes in northern 

Arizona: Journal of Geochemical Exploration, v. 38, p. 

87-101. 

Reynolds, M.W., Palacas, J.G., and Elston, D.P., 1988, Potential 

petroleum source rocks in the Late Proterozoic Chuar Group, 

Grand Canyon, Arizona, in Carter, L.M.H., ed., USGS 

Research on Energy Resources--1988, Program and 

Abstracts, [V .E. McKelvey Forum on Mineral and Energy 

Resources]: U.S. Geological Survey Circular 1025, p. 

49-50. 

Ritzma, H.R., 1973, Location map, oil-impregnated rock deposits 

of Utah: Utah Geological and Mineralogical Survey Map 33. 

Squyres, J.B., 1980, Origin and significance of organic matter in 

uranium deposits of Morrison Formation, San Juan Basin, 

New Mexico, in Rautman, C.A., compiler, Geology and 

Mineral Technology of the Grants Uranium Region, 1979: 

New Mexico Bureau of Mines and Mineral Resources Memoir 38, p. 86-97. 

Wenrich, K.J., 1985, Mineralization of breccia pipes in northern 

Arizona: Economic Geology, v. 80, no. 6, p. 1,722-1,735. 

Wenrich, K.J., Chenoweth, W.L., Finch, W.I., and Scarborough, 

R.B., 1989, Uranium in Arizona, in Jenney, J.P., and Reynolds, S.J., eds., Geologic Evolution of Arizona: Arizona 

Geological Society Digest 17, p. 7 59-794. 

Wenrich, K.J., and Sutphin, H.B., 1989, Lithotectonic setting necessary for formation of a uranium-rich, solution-collapse 

breccia pipe province, Grand Canyon region, Arizona, in 

Metallogenesis of Uranium Deposits, [Proceedings of a technical committee meeting on metallogenesis of uranium 

deposits organized by the International Atomic Energy 

Agency and held in Vienna, 9-12 March 1987]: Vienna, 

International Atomic Energy Agency, p. 307-344. 

Wenrich, K.J., Van Gosen, B.S., and Sutphin, H.B., 1990, Genesis 

and distribution of uraninite in solution-collapse breccia 

pipes, northwestern Arizona, in Carter, L.M.H., ed., USGS 

Research on Energy Resources--1990, Program and 

Abstracts, [Sixth Annual V.E. McKelvey Forum on Mineral 

and Energy Resources]: U.S. Geological Survey Circular 

1060, p. 86-91. 

50 Short Papers of the U.S. Geological Survey Uranium Workshop, 1990 
Gold-Bearing CollapseBreccia Pipe, Copper 

Mountain, Northwestern 

Arizona 

By Paul Adamek, 1 H.j. Behr,2 and Edmund von 

Pechmann3 

INTRODUCTION 

The Grand Canyon region of the Colorado Plateau is 

the site of hundreds of collapse-breccia pipes that commonly 

contain anomalous amounts of U, base metals, and Ag. 

These pipes became targets for an extensive exploration program carried out during the 1970's and 1980's, resulting in 

the discovery of a number of uranium orebodies. Out of hundreds of pipe occurrences presently known, only one, the 

Copper Mountain pipe, contains gold in amounts as high as 

150 ppm. Although attempts to mine gold at Copper Mountain were made during the 1950's, the occurrence was not 

mentioned in the literature until done so by Wenrich and Silberman (1984) and Wenrich (1985). The Copper Mountain 

pipe was explored by Uranerz U.S.A., Inc. between 1985 and 

1987. The results of the Uranerz program are briefly outlined in the first part of this paper. 

Because Uranerz has been engaged in a regional exploration of collapse-breccia pipes, it was only natural to ask 

whether other pipes on the southwestern Colorado Plateau 

might host significant gold accumulations. To answer this 

question, gold abundances in several pipes were investigated 

and fluid inclusions were studied to determine if the mineralizing fluids active in the collapse-breccia pipes were likely 

to have transported and deposited gold. Results of these 

studies are described in the· latter parts of this paper. 

THE COPPER MOUNTAIN PIPE 

The Copper Mountain collapse-breccia pipe in the lower Andrus Canyon on the Shivwits Plateau is deeply eroded 

and is exposed at an elevation of 970 m to 1 ,040 m at the 

stratigraphic level of the lower part of the Esplanade Sand1

Uranerz USA, Inc., 165 South Union Blvd., Suite 280, Lakewood, 

Colorado 80228. 2

University of Goettingen, Institute of Geology and Dynamics of the 

Lithosphere, Goldschmidstr. 3, D-3400, Goettingen, Germany 

~ranerzbergbau-GmbH, 5300 Bonn 1, 367 Koelnstrasse, Postfach 

170210, Germany. 

stone and lower formations of the Supai Group. The pipe 

structure plunges about 45° to the southeast and consists of a 

polymictic breccia core, approximately 100m in diameter, 

surrounded by a zone of severely broken wallrock which includes two isolated lensoidal bodies of polymictic breccia. 

The outer limit of the pipe structure is marked by hematitefilled ring fractures. Dolomitization of the core is pervasive. 

Bleached and dolomitized sandstones with anomalous Ag, 

As, Ba, Co, Cu, Ni, Zn, and U contents surround the pipe, 

forming an alteration halo up to 250 m wide. Copper and 

uranium reach peak concentrations in breccias within the 

southeastern peripheral zone of the pipe core. The central 

portion of the core is metal poor. 

Very strong supergene oxidation affected the pipe 

down to an elevation of about 920 m to 960 m, causing almost complete replacement of sulfides by limonite and secondary minerals of Cu, Zn, Ag, and Cd. 

Anomalous gold concentrations occur exclusively 

within the limonitic zone and, similar to other metals, are 

concentrated along the southeast margin of the breccia core 

in an arcuate body up to 50 m wide (the 0.14 ppm Au isopleth was arbitrarily used for this delineation). Within the 

partly eroded arcuate body, a zone between elevations of988 

m and 998 m is particularly enriched and contains an average 

of 4.37 ppm Au and 19.25 ppm Ag; the maximum gold concentration is a much as 150 ppm. Above and below this 

zone, the average grade is approximately 0.9 ppm Au and 8.7 

ppm Ag. The amount of the gold contained within the enriched zone was estimated to be about 300 kg. 

In a data set of 52 samples collected from drill cores 

from holes drilled in the pipe core, Au shows positive correlation at the greater than 95 percent significance level with 

Ag (r=0.760), Zn (r=0.677), and Pb (r=0.527). Likewise, Ag 

is significantly correlated with Pb (r=0.903) and Zn 

(r=0.901). The mineral assemblage is dominated by a matrix 

consisting of goethite and lepidocrocite and contains very 

fine grained particles of disseminated gold associated with 

acanthite and smithsonite. Gold is mainly hosted by goethite 

with which it sometimes forms rhythmically grown aggregates. Dendritic grains up to 50 J..lm long are a characteristic 

habit of the gold. Other minerals ocurring in the gold assemblage at Copper Mountain are Co-carbonates, covellite, 

hemimorphite, and greenockite and relics of pyrite, marcasite, chalcopyrite, and bornite. 

STUDY OF GOLD ABUNDANCE IN 

NON-OXIDIZED COLLAPSE-BRECCIA PIPES 

More than 300 samples from 12 uranium-bearing pipes 

in the Grand Canyon region were collected and assayed for 

Au (samples from Hack 1, 2, and 3, Pigeon, Kanab North, 

and Canyon pipes collected courtesy of Energy Fuels Corp.; 

see fig. 1). 

Gold-Bearing Collapse-Breccia Pipe, Copper Mountain, Northwestern Arizona 51 
N 

UTAH __ 

- ----'"ARizoN"A----

•CANYON 

50 100 KILOMETERS 

Figure 1. Map of northwestern Arizona showing locations of 

collapse-breccia pipes mentioned in this paper. 

Disregarding some values that occur close to the analyticallimit, only one pipe, the Orphan, was found to more consistently contain gold in enhanced amounts. Out of 18 

non oxidized samples analyzed from the Orphan, 10 contained identifiable Au (> 5 ppb ). Because all samples were 

collected from dumps, no details can be given about their position within the pipe. The four samples with the highest 

gold content contain 0.010 ppm to 0.045 ppm Au, 3 ppm to 

44 ppm Ag, 0.55 percent to 1.615 percent U, Pb+Zn+Cu between 0.67 percent and 8.55 percent, and As 0.10 percent to 

1.35 percent. No correlation between Au and other elements 

has been established, nor does there appear to be a special relationship between Au and certain lithological types. All 

gold-bearing samples show a variable degree of silicification; however, this is also a common feature of nonauriferous pipes. Quartz overgrowths on detrital quartz grains were 

determined to be one of the oldest mineral phases in the breccia pipes. 

FLUID INCLUSION STUDIES ON 

COLLAPSE-BRECCIA PIPES 

Fluid inclusion studies on samples from Orphan, Hack 

2, Kanab North and Cunningham pipes (fig. 1) were carried 

out by one of the authors (H.J. Behr) at the University of 

Goettingen, Germany. Results of these studies have been 

used to determine whether the collapse-breccia pipes are 

likely to host significant gold accumulations. On the basis of 

more than 100 determinations of fluid inclusion characteristics, the following fluid systems were distinguished (fig. 2): 

System (a) is a hypersaline (melting temperature, Tm, 

-28 to -35 °C), higher temperature (homogenization temperature, Th, 250 to > 350 °C) fluid system that contains 

C02. The fluid occurs in healed microfractures formed after 

~ -30 

w 

a: 

::J 

~ a:u 

Wo 

~~ 

~ -10 l!) 

z 

~ w 

~ 

....... 

.~ ... • System (b) . . . .... ~ .. !·~ .. 

CDOJ.cP 0 

~ System (c) 

0 

System (a) 0 8J 0 

8 oOg~~O O 0 

100 150 200 250 300 

HOMOGENIZATION TEMPERATURE (Th). 

IN oc 

Figure 2. Measured homogenization temperature (Th) versus 

melting temperature (Tm) for inclusion fluids from collapsebreccia pipes, northwestern Arizona 

the emplacement of detrital grains in pipes and as inclusions 

in the quartz overgrowths. Some of the fluid inclusions 

show critical homogenization conditions and boiling phenomena, in the course of which the C02 phase separated 

completely from the solution. The fluids have a complex 

composition characterized by a combination ofNaCl+KCl+ 

CaC12. System (a) was the earliest occurring fluid system in 

the breccia pipes. 

System (b) is a medium-salinity fluid system (Tm, -10 

to -23 °C) with Th between 120 and 160 oc (fig. 2). These 

fluids were identified in primary inclusions in dolomite and 

sphalerite, in secondary inclusions in quartz, and in microfractures. The fluids have a simple composition characterized by NaCI. System (b) appears to be the most 

volumetrically significant and the most persistent fluid system in the breccia pipes. 

System (c) is a late, low-salinity fluid system {Tm, 0 to 

3 °C) with Th between 50 and 120 oc (fig. 2). 

System (d) is a pure C02 system that has been released 

by the H20-C02 fluids (this system is not shown on fig. 2). 

Mixed systems consisting of fluids (b) and (c) and C02 

are located at the intersections of microfractures and at the 

margins of grains. 

DISCUSSION AND CONCLUSIONS 

There is little doubt that the present enrichment in gold 

at Copper Mountain has been caused by multiphased supergene processes similar to those described in western Australia by Butt (1989) and Mann (1984). Nothing, however, is 

known about the initial abundance of gold in this pipe. Even 

52 Short Papers of the U.S. Geological Survey Uranium Workshop, 1990 
if it is assumed that most of gold that is presently concentrated in the enriched zone was remobilized from the eroded 

parts of the Copper Mountain pipe, pipe volume calculations 

imply that the initial gold endowment of this pipe had been 

higher than that observed in the Orphan mine. 

The complex salinity composition of the earliest fluid 

system distinguished in the pipes of the Grand Canyon region suggests that the high salt component of the mineralizing fluids was derived from deep basinal brines that were 

seated immediately above the basement or in fractures within the basement. These brines were probably activated by 

and intermixed with a deeper, higher temperature, lower salinity, COr rich system. The rising fluids may have carried 

both gold and base metals. However, due to high salinity, 

their pH was relatively low regardless of C02 content, and 

consequently, the gold solubility was low as well (Hedenquist and Henley, 1985). If the results of our fluid inclusion 

studies are characteristic for all collapse-breccia pipes in the 

Grand Canyon region, it may be concluded that these pipes 

do not represent a likely host for gold deposits. The Copper 

Mountain pipe may be an exception in which the ore-forming solutions had somewhat different characteristics better 

suited for gold transfer and concentration. 

REFERENCES CITED 

Butt, C.R.M., 1989, Genesis of supergene gold deposits in the lateritic regolith of the Yilgarn block, western Australia, in The 

Geology of Gold Deposits: The Perspective in 1988: Economic Geology Monograph 6, p. 460-490. 

Hedenquist, J.W., and Henley, R.W., 1985, The importance of C02 

on freezing point measurements of fluid inclusions: evidence from active geothermal systems and implications for 

epithermal ore deposition: Economic Geology, v. 80, p. 

1,379-1,406. 

Mann, A.W., 1984, Mobility of gold and silver in lateritic weathering profiles: some observations from western Australia: 

Economic Geology, v. 79, p. 38-49. 

Wenrich, K.J., 1985, Mineralization of breccia pipes in northern 

Arizona: Economic Geology, v. 80, p. 1,722-1,735. 

Wenrich, K.J., and Silberman, M.L., 1984, Potential precious and 

strategic metals as by-products of uranium mineralized breccia pipes in northern Arizona: American Association of 

Petroleum Geologists Bulletin, v. 68, p. 954. 

Gold-Bearing Collapse-Breccia Pipe, Copper Mountain, Northwestern Arizona 53 
Relationship Between 

Collapse History and Ore 

Distribution in the Sage 

Breccia Pipe, Northwestern 

Arizona 

By Neal A. Brown, 1 Richard H. Mead, 1 and Jay 

M. McMurray1 

The Sage breccia pipe is located on the Coconino Plateau approximately 90 miles northwest of Flagstaff, Arizona 

(fig. 1 ). The pipe is exposed on the eroded surface of the 

Kaibab Limestone just above the Fossil Mountain MemberHarrisburg Member contact and manifests itself as a bowlshaped depression several hundred ft in diameter with inwardly dipping Harrisburg sedimentary rocks encircling the 

collapse area. 

Pipe formation began during or shortly after deposition 

of the Supai Group and caused 50 ft of thinning in the upper 

part of the Esplanade Sandstone on the northern side of the 

pipe and a corresponding thickening of the Hermit Shale section. Pipe formation continued, probably intermittently, 

through the Permian, as evidenced by secondary brecciation 

of pre-existing sandstone flows. However, one of the most 

active periods of stoping and pipe formation occurred during 

the deposition of the Lower Permian Kaibab Limestone. 

Breccia fragments from the Fossil Mountain Member have 

been observed in core at depths as great as 1,560 ft; this indicates a vertical displacement of over 1 ,000 ft. The Sage 

pipe is similar to other collapse breccia pipes in northern Arizona that have their roots in cave systems in the Redwall 

Limestone. Stoping of successively younger units caused 

the upward propagation of the pipe and provided the pipefilling breccia. The Sage pipe extends at least 2,500 ft (762 

m) vertically; the horizontal dimensions range from 100 to 

300ft (30.5 to 91 m), depending on variations in host-rock 

stratigraphy (fig. 2). 

Acidic, reducing solutions migrated laterally through 

the Redwall cave system until they encountered fault or frac1

Union Pacific Resources-Minerals, 8774 Yates Drive, Suite 100, 

Westminster, Colorado 80030 

his figure A 8 Areaof 

0 

I 

• SAGE PIPE 

10 

I 

N 

1 

20 MILES 

I 

Figure 1. Index map showing a portion of northwestern Arizona and the location of the Sage pipe. 

tore zones that provided vertical pathways for upward stoping and caused decementation of carbonate-cemented grains 

and iron reduction and removal. At Sage, the 80° SW. 

plunge of the pipe is believed to be related to the fracture or 

fault on the northern side of the pipe along which the solutions ascended. The ascending solutions dissolved the carbonate cement in Supai sediments resulting in collapse and 

deposition of sand and silt breccias and flows on the underlying breccia pile. The stoping processes involved both 

chemical disaggregation and mechanical failure of roof and 

wall rocks. This combination produced a complex mixture 

of rock types observed in the Sage core: these rock types include purely mechanical breccias, silty-sandy slurries, and 

flows resulting from chemical disaggregation or decementation of sandstones and siltstones. The solutions eventually 

stoped upward through the Hermit Shale, depositing a blanket of Hermit-derived siltstone breccias and flows on the 

growing debris pile at the bottom of the pipe. Due to the 

54 Short Papers of the U.S. Geological Survey Uranium Workshop, 1990 
KAIBAB LS 

Pk 

TOROWEAP FM 

Pt 

COCONINOSS 

Pc 

HERMIT 

SHALE 

Ph 

ESPLANADE SS 

Pe 

WESCOGAME FM 

IPw 

MANAKACHA FM 

IPm 

WATAHOMIGI FM 

IPwh 

REDWALL LS 

Mr 

Figure 2. Schematic cross section of the Sage pipe showing 

constriction through the Hermit Shale interval, expansion 

through the Esplanade Sandstone interval, and internal geometry of the breccia zones. Rock types in the pipe below the 

Watahomigi Formation are inferred. The representation depicts pipe gnometry near the end of Permian time. 

TOROWEAP FM 

Pt 

I COCONINO 

ss 

Pc: 

HERMIT 

SHALE 

Ph 

ESPLANADE SS 

PE1 

WESCOGAME FM 

IPw 

MANAKACHA FM 

IPm 

WATAHOMIGI FM 

IPwh 

REDWALLLS 

Mr 

Figure 3. Schematic cross section of the Sage pipe showing 

the Coconino-derived sand flow (Pc) encased in impermeable 

silstone breccias derived from the Hermit Shale. 

Relationship Between Collapse History and Ore Distribution in the Sage Breccia Pipe, Northwestern Arizona 55 
Annular ---+ 

ore 

ore 

COCONINO 

ss 

Pc 

HERMIT 

SHALE 

Ph 

ESPLANADE SS 

Pe 

WESCOGAME FM 

IPw 

MANAKACHA FM 

IPm 

WATAHOMIGI FM 

IPwh 

REDWALLLS 

Mr 

Figure 4. Schematic representation of the Sage pipe at the 

end of the Permian showing overthickening of the Harrisburg 

(Pkh) in the pipe and the location of the Hermit ore, sand flow 

ore, and annular ore zones. 

plunge of the pipe, the debris pile became asymmetrical and 

created long continuous breccia zones and flows, resembling 

talus piles, that dip to the southwest. As stoping progressed 

upward into the Coconino Sandstone, the sand was decemented and poured down into the underlying void and was 

deposited as a permeable wedge-shaped sand flow in the 

lower Hermit-derived level of the pipe (fig. 3). Subsequent 

stoping attacked the Hermit Shale on the hanging wall side 

of the pipe and deposited a large impermeable silt breccia 

pile on top of the Coconino-derived sand flow. Ensuing 

stoping then dissolved and brecciated Toroweap and Kaibab 

rocks. 

Bedded sandstones of the Harrisburg Member in the upper 60 ft of the pipe are thicker than equivalent units outside 

the pipe. These overthickened, unbrecciated units were deposited in a paleodepression centered over the pipe and indicate that stoping within the pipe had stopped by middle 

Harrisburg time (fig. 4 ). 

Uranium mineralization at Sage occurs primarily within the portion of the pipe at the Hermit and Esplanade horizons. Ore-grade mineralization occurs vertically for nearly 

700ft. Uranium ore occurs in three distinct environments 

(fig. 4) including: (1) upper Hermit ore, (2) sand flow ore, 

and (3) annular ore. 

The upper Hermit ore generally occurs near the pipe 

contact with the surrounding unbrecciated Hermit Shale. 

This ore is hosted in Coconino-derived sand flow and breccia that was deposited above the main sand flow ore zone. 

The sand flow ore zone accounts for 60 percent of the ore reserves at Sage. Nearly all of the sand flow "encased" between the two silt flows (labeled "Ph" on fig. 4) is ore 

bearing. Annular ore occurs along the pipe contact with the 

Esplanade Sandstone similar to the Orphan pipe occurrences. The best annular ore grade and maximum thickness generally occurs near the shoulder of the pipe as it flares out into 

the Supai Group. 

Uranium was deposited in permeable breccias and 

flows that were strongly reduced and contained minor hydrocarbon. In conclusion, the mineral distribution at Sage is directly related to the permeability of the internal breccias and 

flows and, to a lesser extent, to the ring fracture zone. 

56 Short Papers of the U.S. Geological Survey Uranium Workshop, 1990 

*U.S. GOVERNMENT PRINTING OFFICE: 1992-673-049/46044 


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