U.S. GEOLOGICAL SURVEY CIRCULAR 1051 

The 1987 Estimate of 

Undiscovered Uranium Endowment in 

Solution-Collapse Breccia Pipes in the 

Grand Canyon Region of 

Northern Arizona and Adjacent Utah 
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The 1987 Estimate of 

Undiscovered Uranium Endowment in 

Solution-Collapse Breccia Pipes in the 

Grand Canyon Region of 

Northern Arizona and Adjacent Utah 

By W.l. Fl NCH, H.B. SUTPHIN, C.T. PIERSON, 

R.B. McCAMMON, and K.j. WENRICH 

Work done in cooperation with the Energy Information 

Administration, U.S. Department of Energy 

U.S. GEOLOGICAL SURVEY CIRCULAR 1051 
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: 1990 

Free on application to the Books and Open-File Reports Section, 

U.S. Geological Survey, Federal Center, Box 25425, Denver, CO 80225 

Library of Congress Cataloging-in-Publication Data 

The 1987 estimate of undiscovered uranium endowment in solution-collapse 

breccia pipes in the Grand Canyon region of northern Arizona and adjacent 

Utah I by W.l. Finch ... [et al.]. 

p. em. - (U.S. Geological Survey circular; 1051) 

"Work done in cooperation with the Energy Information Administration, U.S. 

Dept. of Energy." 

Includes bibliographical references (p. ) 

Supt. of Docs. no.: I 19.4/2:1051 

1. Uranium ores-Arizona-Grand Canyon Region. 2. Uranium 

ores-Utah-Washington County. 3. Breccia-Arizona-Grand Canyon 

Region. 4. Breccia-Utah-Washington County. I. Finch, Warren Irvin, 

1924- . II. United States Energy Information Administration. 

TN490.U7A15 1990 

553.4'932'097913-dc20 90-3340 

CIP 
CONTENTS 

Executive summary 1 

Introduction 2 

Post-NURE advances in the knowledge of solution-collapse breccia-pipe uranium 

deposits 3 

Geology and other characteristics of solution-collapse breccia pipes 4 

Method of estimating the uranium endowment 4 

The Hack-Pinenut control area S 

Endowment in the Hack-Pinenut control area 10 

Determination of favorable and unfavorable areas 10 

Favorable area A 11 

Favorable area B 11 

Favorable area C 11 

Favorable area D 12 

Unfavorable area E 12 

Basalt -covered areas 12 

Elicitation 12 

Undiscovered uranium endowment in the principal areas 16 

Additional undiscovered uranium endowment in the basalt -covered areas 16 

Total endowment in the Grand Canyon breccia-pipe province 16 

Selected references l8 

FIGURES 

1. Index map showing the locations of the 1 o x 2° quadrangles in Arizona and 

Utah assessed in this report 3 

2. Map showing locations of selected solution-collapse breccia pipes and areas 

favorable for uranium endowment in parts of eight 1° x 2° quadrangles in 

northern Arizona and adjacent Utah 6 

3. Schematic cross section of a typical solution-collapse breccia pipe and 

stratigraphic section in the Grand Canyon region, Arizona 8 

4. Map of the Hack-Pinenut control area for uranium-bearing collapse-breccia 

pipes in northern Arizona 9 

TABLES 

1. Estimated grade distribution, G, and size-frequency distribution for the HackPinenut control area 10 

2. Land areas and estimated L factors of favorable areas 13 

3. Undiscovered uranium endowment in the principal areas 14 

4. Undiscovered uranium endowment in the basalt-covered areas 17 

Contents Ill 

The 1987 Estimate of Undiscovered Uranium Endowment in 

Solution-Collapse Breccia Pipes in the 

Grand Canyon Region of Northern Arizona and Adjacent Utah 

ByW.I. Finch, H.B. Sutphin, C.T. Pierson, 

A.B. McCammon, and K.J. Wenrich 

EXECUTIVE SUMMARY 

In accordance with the Memorandum of Understanding 

(MOU) dated September 20, 1984, between the U.S. 

Geological Survey of the U.S. Department of the Interior and 

the Energy Information Administration of the U.S. 

Department of Energy, the Geological Survey is to provide 

estimates of uranium endowment for selected areas of the 

United States on a mutually planned and agreed-upon 

schedule. This report summarizes the estimates of 

undiscovered uranium endowment of solution-collapse breccia pipes in Pennsylvanian and Permian rocks of the Grand 

Canyon region in eight 1 ox 2° quadrangles located in 

Coconino, Mohave, Yavapai, and Navajo Counties, Ariz., and 

in Washington County, Utah. These new estimates for the 

eight quadrangles were made in 1987, and for six of the 

quadrangles they supersede the estimates of uranium 

endowment for this type of deposit given in the 1980 national 

resource assessment report (U.S. Department of Energy, 

1980). The estimates were generated using the depositsize-frequency (DSF, option C) method, a modified NURE 

(National Uranium Resource Evaluation) method, developed 

in accordance with the MOU (Finch and McCammon, 1987). 

In order to assess the uranium endowment for the 

region, we established the Hack-Pinenut control area in one 

of the main mining areas. Data on production, reserves, and 

estimated additional resources were used to establish 

various deposit-size classes above the grade-cutoff of 0.01 

percent U30 8 as well as to estimate the numbers of deposits 

in each size class. The mean uranium endowment in the 

control area was calculated to be 16,429 tons UsOe. 

The areas assessed for uranium endowment are 

divided into two groups: (1) the principal favorable areas, 

where the host formations are either exposed or only thinly 

covered with sedimentary rocks, and (2) the basalt-covered 

favorable areas, where successful exploration for breccia 

pipes is virtually impossible with present-day technology. 

The principal favorable areas contain potentially economic 

Manuscript approved for publication February 27, 1990 

resources; however, we conclude that the basalt-covered 

favorable areas should be considered in the same manner as 

areas deeper than 5,000 ft were treated in the NURE 

program, that is as uneconomic given present-day 

technology. 

For the purpose of the assessment, the Grand Canyon 

region was divided into four areas of differing favorability, A, 

B, C, and D, and one unfavorable area, E. The areas overlain 

by either Tertiary sedimentary rocks or Quaternary sediments 

are shown as subdivisions of areas A and B (A., Ba), but are 

included for purposes of estimating the total endowment of 

the principal areas. Each favorable area was divided into 

subareas along 1°X2° quadrangle boundaries. The 

endowment was estimated in 17 separate principal areas that 

total 13,291 mi2 • These areas do not correspond everywhere 

with the favorable areas used in the 1980 NURE assessment 

report (U.S. Department of Energy, 1980). The probability 

distribution of the endowment for each principal favorable 

area is given in our report. The mean endowment as 

calculated from the probability distribution for each of the 

principal favorable are~s is as follows: 

Favorable area 

Grand Canyon 

Cedar City 

Williams 

Marble Canyon 

Flagstaff 

Holbrook 

St. Johns 

Prescott 

A 

D 

A 

A 

As 

B 

Bs 

D 

A 

D 

A 

B 

c 

B 

c 

c 

B 

Tons UsOa 

482,148 

8,691 

23,265 

187,127 

22,590 

26,547 

4,053 

3,615 

123,066 

694 

94,744 

58,769 

1,759 

11,551 

25,308 

583 

405 

Executive Summary 1 
The total endowment for the principal areas of the Grand 

Canyon breccia-pipe region has a mean value of about 

1 ,000,000 tons UsOa. Additional endowment in the nine 

basalt-covered areas that total 3,437 mi2 has a mean value of 

about 240,000 tons U30e. Thus, the total endowment in the 

Grand Canyon region of the 26 areas encompassing a land 

area of 16,728 mi2 has a mean value of about 1,300,000 tons 

UsOe, about eight times the 158,000 tons estimated total 

endowment for breccia pipes in the 1980 NURE assessment. 

The DSF method used here has resulted in an 

endowment increase over the NURE endowment estimate by 

about twice the amount exp·ected from a previous DSF and 

NURE comparison (Finch and McCammon, 1987, p. 16). 

This larger endowment estimate is due primarily to three 

factors: (1) the DSF method allows for greater partitioning of 

the input data for calculating endowment and, thus, it tends 

to result in a less biased (generally larger) estimate (i.e., it 

evens out the inherent human tendency to underestimate 

parameters in order to be •on the safe side•); (2) our 

knowledge about the distribution of grade and tonnage of 

newly discovered and mined deposits is significantly greater 

than it was in 1980; and (3) our understanding of the geology 

of the region and of the deposits has improved greatly as a 

result of the past seven years of USGS study funded mainly 

by the Bureau of Indian Affairs of the U.S. Department of the 

Interior. 

The large endowment estimated for the principal areas 

alone is significant because it is nearly as large as the 1980 

NURE estimated endowment for the San Juan Basin, 

historically the most productive uranium-producing region in 

the United States. However, a reassessment of the San Juan 

Basin using the DSF method would probably yield an 

estimate much larger than the 1980 NURE estimate. 

Nevertheless, we conclude that the Grand Canyon region 

has the potential of becoming the second most important 

uranium-producing region in the United States. If exploration 

technology is developed to discover uraniferous pipes below 

the basalt cover, the Grand Canyon region could eventually 

become even more important. 

INTRODUCTION 

On September 20, 1984, a 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 the Interior (DOl) was signed. The 

MOU "describes the implementation of an agreement 

for assistance from the USGS in the assessment of U.S. 

potential uranium resources in support of EIA's work 

under Public Law 97-415 (January 4, 1983) to develop 

and provide information about the viability of the 

domestic uranium mining and milling industry" (Finch 

and McCammon, 1987). This MOU is a continuant to the 

MOU between DOE and DOl dated November 12, 

1983, that called for a plan to conduct research on data 

collected under the National Uranium Resource 

Evaluation (NURE) program and to provide for 

continuing the assessment of the Nation's uranium 

resources. The Geological Survey is to provide estimates 

of unconditional uranium endowment for selected areas 

of the United States on a mutually planned and agreed 

schedule. Endowmene is used in this report to mean the 

inplace resource, some of which is discovered and the 

remainder of which is undiscovered. This report is 

concerned primarily with the undiscovered part. 

In 1985, a modified NURE resource assessment 

method, called the deposit-size-frequency (DSF) 

method, was developed (Finch and McCammon, 1987). 

The first project to use this method was an assessment of 

surficial uranium deposits in Washington and Idaho 

(Finch and others, 1990). The assessment of the 

undiscovered uranium endowment for the Grand 

Canyon region described here also used the DSF 

method. 

The chief purpose of this report is to convey the 

1987 USGS assessment of the undiscovered uranium 

endowment in solution-collapse breccia pipes in the 

Grand Canyon region, which is in eight 1 o x 2° 

quadrangles located in Coconino, Mohave, Yavapai, and 

Navajo Counties, Arizona, and in Washington County, 

Utah (fig. 1 ). We discuss those aspects of the 

characteristics and geology of the uranium deposits that 

might be helpful to mining engineers, metallurgists, and 

mineral economists; explain the rationale for the 

determination of favorable areas; and review the method 

of estimating the endowment. Further information is 

available from the referenced material. 

The roles of the different authors in this 

assessment were as follows: H.B. Sutphin was the 

principal scientist. KJ. Wenrich provided geological 

expertise concerning the uranium deposits. The 

elicitation was carried out in the manner described in 

Finch and McCammon (1987) in two major sessions 

conducted by W.I. Finch, C.T. Pierson, and R.B. 

McCammon with the principal scientist. Pierson 

calculated the endowment distribution for each favorable 

area. McCammon calculated the total endowment for the 

region and checked all endowment calculations. Sutphin 

prepared figures 2 and 4. 

We acknowledge the consultation of Luther Smith, 

EIA, on many aspects of the development of the 

assessment. We are particularly appreciative of Mr. I. W. 

Mathisen, Jr., Energy Fuels Nuclear, Inc., Denver, Colo., 

for providing exploration drill-hole logs and calculations 

1

Uranium endowment: the uranium that is estimated to occur 

in rock with a grade of at least 0.01 percent UsOe. Unconditional 

endowment is based on the assumption that one or more deposits exist 

in the favorable area. 

2 1987 Estimate of Undiscovered Uranium Endowment, Grand Canyon Region, Arizona-Utah 
1 w 112° 11 oo 108° 

,----- ----~---'--;-=---------. 

i I WYOMING 

I 

I I, n

UTAH 0 

~ ~ 5 ~-------+--------~--~--~-

! \ 8 

3aol1-

1 

-----1-----------+----~t-----1 ! A# \ I <? I 37°r--------------+--

1 ~,~ . ·~-.~ I 

60 ,.. __ I f)~ti§> ~~I I 

100 200 MILES 

Figure 1. Index map showing the locations of the 

1 o x 2° quadrangles in Arizona and Utah assessed in this 

report. 

ofU30s reserve data at a 0.03 percent U30s cutoff grade 

for each mineralized hole for his company's entire 

exploration program. These data were essential for us to 

develop three useful candidates for control areas and to 

select the best one of the three. 

The numerical results tabulated in this report are 

computer generated (McCammon and others, 1988) and 

are presented either as probability distributions or 

calculated means, and no attempt was made to round to 

significant figures. Tons used in this report are short tons. 

POST-NURE ADVANCES IN THE 

KNOWLEDGE OF SOLUTION-COLLAPSE 

BRECCIA-PIPE URANIUM DEPOSITS 

Since the completion of the NURE assessments of 

the Grand Canyon region in 1980 (U.S. Department of 

Energy, 1980), both exploration and mining have 

increased greatly, and significant advances have been 

made in our knowledge of the geology and distribution of 

uraniferous solution-collapse breccia pipes in northern 

Arizona. 

The study of the breccia pipes in northern Arizona 

has been an ongoing project since 1976, when it was part 

of the USGS Uranium and Thorium Resource Program. 

Wenrich participated in the assessment of the Flagstaff 

quadrangle for the NURE program (Wenrich-Verbeek 

and others, 1982). From 1979 to 1981, Wenrich and 

Sutphin participated in the uranium assessment of the 

Navajo Reservation funded by the Bureau of Indian 

Affairs of the U.S. Department of the Interior by locating 

and mapping breccia pipes on the Marble Plateau (Sutphin and Wenrich, 1983, 1988; Sutphin, 1986). In 1982, 

the USGS undertook an intensive study of the uranium 

potential of the Hualapai Indian Reservation for the 

Bureau of Indian Affairs. This effort, in progress in 1987, 

included the following studies: (1) preparation of 

detailed breccia-pipe and geologic maps (scale 1:48,000) 

of the entire Reservation, divided into four mapsnortheast (Wenrich, Billingsley, and Huntoon, 1986), 

southeast (Billingsley and others, 1986), northwest 

(Wenrich, Billingsley, and Huntoon, 1987), and 

southwest (in preparation) parts of the Reservation; (2) 

detailed studies of favorable breccia pipes on the 

Reservation (Wenrich, Billingsley, and Van Gosen, 1986, 

1987, 1990), including geophysical (Senterfit and others, 

1985; Flanigan and others, 1986), helium soil gas 

(Reimer, 1985), and magnetometer studies (Van Gosen 

and Wenrich, 1989); (3) drilling of the Mohawk Canyon 

pipe (Wenrich, Van Gosen, and others, 1987) and Blue 

Mountain breccia pipe (Van Gosen and others, 1989); 

and ( 4) general studies of the breccia pipes throughout 

northern Arizona (Wenrich, 1985, 1986a, 1986b; Gornitz 

and others, 1988; Van Gosen and Wenrich, 1987; and 

Wenrich and Sutphin, 1989). 

These additional studies and maps, along with 

company confidential exploration and mining data, have 

increased our knowledge of breccia-pipe density and ore 

grade exponentially since 1980, when the previous 

assessment was completed. At that time, only one highgrade (average grade = 0.43 percent U30s) breccia-pipe 

orebody, the Orphan mine, had been mined. In addition, 

the Hack Canyon mine had produced about 1,400 tons of 

ore at an average grade of 0.18 percent U30s (U.S. 

Atomic Energy Commission publicly released 

production records, 1972). Whether there were other 

Post-NURE Advances In the Knowledge of Solution-Collapse Breccia-Pipe Uranium Deposits 3 
mineralized pipes of high-grade ore similar to those at 

the Orphan mine was not public knowledge. Company 

confidential data on high-grade ore from the Hack No. 2 

mine was available to DOE in 1979, but not to Wenrich 

when she assessed the Flagstaff quadrangle. Since 1980, 

five other mines, the Hack Nos. 1, 2, and 3, Pigeon, and 

Kanab North have gone into production (figs. 2, 4), at 

least ten more deposits have been delineated, and several 

mining projects are in various stages of lease application 

or development. 

Exploration and mining in the breccia-pipe 

province have been intense since 1980. Between 1980 

and the end of 1986, Energy Fuels Nuclear, Inc., has 

mined ore that yielded about 5,000 tons of UJOs at an 

average grade of about 0.65 percent U30s, and in 1987 it 

had six breccia-pipe mines in operation (Mathisen, 

1987). Other companies have smaller but still successful 

exploration programs, yet none of them had operating 

mines in 1987. Because of the high grade of breccia-pipe 

ores, they were in 1987 one of the main sources of 

conventionally mined uranium in the United States. 

GEOLOGY AND OTHER 

CHARACTERISTICS OF SOLUTIONCOLLAPSE BRECCIA PIPES 

Hundreds of solution-collapse breccia pipes are 

found in Paleozoic rocks of northern Arizona in the 

southwest part of the Colorado Plateau province (fig. 2; 

also see Sutphin and Wenrich, 1989). They formed as 

the result of solution collapse within the Mississippian 

Redwall Limestone and sloping of the overlying 

Pennsylvanian, Permian, and Triassic rocks (fig. 3). The 

pipes extend upward as far as the lower members of the 

Upper Triassic Chinle Formation. U/Pb isotope studies 

on ore from several pipes in the northern part of the 

region by Ludwig and others (1986) indicated a Late 

Triassic age of mineralization (similar to that of 

sandstone ores of the Chinle in eastern Utah), but more 

recent study on one pipe, the Canyon pipe (fig. 2A ), in 

the southern part indicated an Early Permian age (Ludwig and Simmons, 1988). The main ore-bearing horizons 

in the pipes are adjacent to the upper part of the Supai 

Group, the Hermit Shale, and the Coconino Sandstone. 

Areas underlain by these formations are considered 

favorable for breccia pipes and for uranium deposits. 

However, pipes are sparse to absent where the Redwall is 

less than 50 ft thick. 

The pipes are commonly 300ft or less in diameter, 

but their expression at the ground surface above may be 

as shallow structural and topographic basins as large as a 

mile in diameter. Some pipes form prominent features at 

the surface, whereas others are difficult to discern from 

the surface and can be verified only by pattern drilling 

over a suspected area. All of the pipes positively 

identified at the time of the assessment are plotted on 

figure 2. Many pipes on the flat Esplanade Sandstone and 

Redwall Limestone surfaces have been exposed by 

erosion and are relatively easy to detect. As a result, the 

plateaus capped by these formations have a greater 

density of identified pipes than do the higher plateaus 

capped by Kaibab Limestone. Consequently, the density 

of pipes shown in figure 2 is not uniform. 

The rocks on the Marble Plateau are very well 

exposed, and mapping of pipe locations there provides a 

good measure of pipe density. This density is 0.28 pipes 

per mi2, which is considered to be typical for the region. 

In areas where bedrock exposures are poor due to 

alluvial veneer and forest cover, a similar distribution is 

assumed and was used as a basis to estimate pipe density 

in each favorable area. This assumption was especially 

useful in setting up the Hack-Pinenut control area. 

Most of the breccia-pipe uranium deposits that 

have been mined are high grade by U.S. standards, 

averaging between 0.43 and 0.65 percent U30s. Typical 

ore-bearing pipes contain 105,000-500,000 tons of ore, 

yielding 500--3,000 tons of U30s. The boundaries of 

orebodies most commonly are sharp and in some cases 

correspond to the limits of brecciated rock. Low-grade 

rock (0.01-0.05 percent U30s) is generally a small part 

of the entire deposit. The average grade of mineralized 

rock in breccia pipes is higher than that of most 

sandstone deposits (generally 0.10-0.25 percent U30s) 

to the north and east in the Colorado Plateau province. 

The unoxidized uranium ore consists of uraninite 

associated with abundant pyrite. Concentrations of silver, 

cobalt, copper, nickel, lead, and zinc are sufficiently high 

that these metals could become viable byproducts of 

mining some uranium ore. The ore is low in carbonate 

(average less than 5 percent). Copper has been produced 

from some pipes, particularly from those highly oxidized 

and exposed in and below the Esplanade Sandstone 

(Chenoweth, 1986). 

METHOD OF ESTIMATING THE 

URANIUM ENDOWMENT 

The uranium endowment was estimated using the 

deposit-size-frequency (DSF) method described in detail 

by Finch and McCammon (1987). Briefly, the DSF 

method is a modification of the NURE uranium 

endowment (U) estimation equation, U =A •F•T•G, in 

which factors F and T (F =fraction of area, A, that is 

favorable for endowment; T = tons of endowed rock per 

unit area) are replaced by a single factor. This factor, 

shown in the equation below, is the summation of the 

estimates of the number of deposits in different depositsize classes within the area being assessed, or, 

equivalently, the spatial density of deposits; hence, the 

name "deposit-size-frequency." The grade distribution 

4 1987 Estimate of Undiscovered Uranium Endowment, Grand Canyon Region, Arizona-Utah 
(G) of the endowment is the same in both methods. The 

DSF method requires that a deposit-size-frequency (a 

matrix of deposits in each size class) be established in a 

well-known to fairly well-known area, called the control 

area, and that the geologic 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. Three options, A, B, and C, 

are available for a given assessment (Finch and McCammon, 1987). The choice as to which option to use 

depends on the level of knowledge about the control area 

and the level of exploration of the region being assessed. 

Option C is used where the favorable area can be 

delineated in detail only in part so that the number and 

size of deposits within the control area, Ac, can be 

estimated. Option C is applicable to the Grand Canyon 

assessment, and the modified equation is: 

U= A I·~ (Anic) Tija. L 

1•1 c 

where: 

U =unconditional uranium endowment in tons of 

U30s above a cutoff of 0.01 percent U30s, 

A =favorable area in square miles, 

k =number of deposit-size classes, 

n;c/Ac = spatial density (number of deposits/unit 

area) of deposits of size T; (tons of endowed rock 

in the ith deposit-size class) within a control area 

Ac, 

Ac =control area from which estimates of n;c/Ac are 

taken, 

G =grade distribution of endowment, in decimal 

fraction form, and 

L =optional scaling factor that expresses the 

relation between the endowment in the favorable 

area and that in either the control area or some 

designated subarea for which estimates of the 

number of deposits in different size classes have 

been made. 

Option C requires that the principal scientist 

establish the size-frequency distribution of deposits in a 

well-known or control area, Ac, and the relations of the 

deposit -size-frequency distribution to measurable controlling geologic factors, such as breccia pipes. Using these 

relations, the principal scientist first establishes the 

number and range of the size classes, and then for each 

size class estimates the lower limit, most likely value, and 

upper limit for the number of deposits in the control 

area, Ac. The favorable area, A, is measured, and the 

grade distribution, G, is estimated. Finally, the lowest, 

most likely, and highest values for the scaling factor, L, 

which relates the endowment of the favorable area to that 

of the control area, are estimated. Using these estimates, 

obtained by elicitation, as input into the DSF equation 

and the TENDOWG program (McCammon and others, 

1988), which is a modification of the program by Ford 

and McLaren (1980), one can calculate the probability 

distribution of undiscovered uranium endowment in a 

given area. The total endowment for any number of 

subareas, such as all those in a quadrangle, can be 

calculated using the same TENDOWG program. 

For this study, the summation of estimates made 

for many subareas by a single investigator is assumed to 

be perfectly correlated. This is an extension of the basic 

premise in the DSF method for which a perfect 

correlation is assumed among the estimates of the 

number of deposits within each size class. 

THE HACK-PINENUT CONTROL AREA 

Production records and exploration data provided 

by Energy Fuels Nuclear, Inc., on three areas consisting 

of about four townships each-(1) Hack-Pinenut (T. 

36-37 N., R. 4-5 W.), (2) Pigeon-Kanab North (T. 38-39 

N., R. 2-3 W.), and (3) Orphan-Canyon (T. 28-29 N., R. 

3 E.; E2/3 T. 28-29 N., R. 2 E.; E1/3 T. 30--31 N., R. 

2 E.)-were considered in selecting a control area. The 

Hack-Pinenut area (fig. 4), which is controlled entirely by 

Energy Fuels Nuclear, Inc.2

, was selected as the control 

area because more information was available concerning 

pipe distribution, density of exploration, production, and 

ore reserves for it than for the other two areas. On the 

basis of these data, Sutphin established four size classes 

(table 1) and estimated the numbers of deposits in each 

class. The density of pipes estimated to occur in the 

Hack-Pinenut control area is 0.23 pipes per mi2

, which 

matches well the density of 0.28 per mi2 determined for 

the well-exposed Marble Plateau area (fig. 2B ). In 

contrast to the control area of four townships used here, 

the 1980 DOE assessment used a single mine, the Hack 

No. 2 mine, as a grade-tonnage model for the control 

area. 

The lower, most likely, and upper gradedistribution estimates used in this assessment are 0.06, 

0.17, and 0.44 percent U30s, respectively (table 1). 

These grade-distribution levels were estimated using all 

of the data currently available in 1987 for some of the 

most thoroughly explored areas, namely the three areas 

mentioned above as candidates for control area. The 

Orphan-Canyon area has the lowest average grade, 0.06 

percent U30s, which is used for the 5th percentile 

(lower) grade-distribution estimate. The average grade 

for all three areas combined ( 468 mi2

) is 0.17 percent 

U30s, which is used as the 50th percentile, or most likely 

2

0ne Tabor Center, Suite 2500, 1200 17th Street, Denver, CO 

80202. 

The Hack-Pinenut Control Area 5 
114° 

37 o CEDAR CITY 

GRAND 

CANYON 

1° X 2° 

quadrangle 

A 

@Tank 

® Lynx 

~learwater • 

0 

p;~on 0 o

00 

0 

. . . 

@fcorpion 

• Ash fork 

A 

Jacob Lake 

• 

A 

Canyon 

.. ~~hale 

New Year~ ;ue NE 

Black Box 

Figure 2 (above and facing page). Map showing locations of selected solution-collapse breccia pipes and 

areas favorable for uranium endowment in parts of eight 1 ox 2° quadrangles in northern Arizona and adjacent 

Utah. A, Cedar City, Grand Canyon, Williams, and Prescott quadrangles; 8, Marble Canyon, Flagstaff, 

Holbrook, and St. Johns quadrangles. The Hack-Pinenut control area is shown in greater detail in figure 4. See 

Sutphin and Wenrich (1989) for an update of breccia-pipe locations. 

6 1987 Estimate of Undiscovered Uranium Endowment, Gran_d Canyon Region, Arizona-Utah 
Tap 

® 

... ® 

Auto 

B 

MARBLE CANYON 

1° X 2° quadrangle 

EXPlANATION 

Collapse breccia pipe 

® Uranium-mineralized pipe and 

name of mine, prospect, or 

claim (see figure 4 for pipe 

names in the control area) 

A Favorable area designation 

Ab Favorable area covered by basalt 

flows 

As Favorable area covered by Tertiary 

sedimentary rocks and (or) 

Quaternary sediments 

• City or town 

Volcanic necks, plugs (excluded 

from favorable areas) 

r----r7. Stratigraphic contact 

10 

Geographic and (or) stratigraphic 

boundary of favorable areas 

20 MILES 

~i---------------~----------------------------------~F~LAWGSTSTAAFFFFI 360 

1° X 2° quadrangle 

INDEX MAP 

cf c 

The Hack-Pinenut Control Area 7 
1 1 Average thickness !+-Diameter of surface depression~1 or range in thickness 1 1 (in feetl 

r-~----------~--------~1 ~~~~~~~~~----------~ 

(.) 

CIJ 

CIJ 

<( 

a: 

IChinle 

Formation 

Moenkopi 

Formation 

Kaibab 

Limestone 

Toroweap 

Formation Brady Canyon Member 

300 

400-1200 

S e I i man Member =======:Jf.;Sjt:~$5~hf~btk~SP$;===~3~0:-_:9~0~==J z Coconino Sandstone 0-600 <( 

:::!! 

a: 

UJ 

a... Hermit Shale 

I 

....Jz 

>-<( CIJ_ 

zz 

Z<C 

UJ> 

a... 

z 

<( 

a... 

a... 

CIJ 

CIJ 

en 

en 

:::!! 

a. 

:J 

0 

.... 

~ 

Esplanade Sandstone 

Wesco ation 

Manakacha Formation 

Redwall Limestone 

oz 

> < Temple Butte Limestone 

~z 

50-1200 

300-500 

150-200 

180-230 

400-700 

0-450 

Figure 3. Schematic cross section of a typical solution-collapse breccia pipe and stratigraphic section in the Grand 

Canyon region (modified after Van Gosen and Wenrich, 1989). 

estimate. The Hack-Pinenut area's average grade of 0.44 

percent U30s is used as the 95th percentile (upper) 

grade-distribution estimate. This area is the most 

thoroughly explored and contains the greatest density of 

known ore-bearing pipes. The grade for the PigeonKanab North area (0.61 percent U30s) is higher than that 

of the Hack-Pinenut area but is based on data from only 

four pipes, two of which are active mines. 

The estimated grade distribution used in this 

assessment has considerably greater values than were 

used in the NURE assessment for several reasons. The 

1980 NURE assessment used 0.05, 0.16, and 0.20 

8 1987 Estimate of Undiscovered Uranium Endowment, Grand Canyon Region, Arizona-Utah 
112° 39' 25" 

36°38' 31" R.SW. R.4W. 

T.37N. 

@ 

Wild band 

• 

SIN 506 

• 

Hack1 

2~ Top ~@• Hack 

• • Copper lady 

.tdas> J\ndv 

Ida 2 \ 

State 35-5-32 

0 

OJ Tank 

0 

®wizard 

SIN 686 

AI NO 

0 

• SIN 20 

Yucca 

i 

State 37-4-16 

• SIN 22 

Sunshine 

• 

~---------------------------------+------------------------~~------~ 

T.36N. 

Little Rob 

• 

Nate 

0 

®Lostcalf 

Wildcat 

o• 

JHA 

Timpo 

0 

SIN 208 

• 

@Arizona 1 3 

2~inenut 

0 2 MILES 

EXPLANATION 

• Breccia pipe o Possible breccia pipe @ Mineralized breccia pipe 

Figure 4. Map of the Hack-Pinenut control area for uranium-bearing collapse-breccia pipes in northern Arizona. See 

figure 2A for the location in the Grand Canyon 1°X2° quadrangle. 

percent U30s as the lower, most likely, and upper values 

in the grade distribution. Study of considerable data from 

Energy Fuels Nuclear, Inc's., exploration drilling 

indicates that there probably are no large bodies of 

mineralized rock having average grades in the 0.01 to 

0.09 percent U30s range within the stratigraphic interval 

under consideration in our assessment. However, drilling 

below the mined-ore horizon at the Orphan mine 

discovered a large body containing about 9,500,000 tons 

of rock with an average grade of 0.02 percent U30s 

(Chenoweth, 1986). The amount of low-grade ( < 0.10 

U30s) material in ore-grade deposits is small, as is shown 

by the unpublished 1979 DOE graph of the distribution 

of uranium inventory by grade for the Hack No. 2 

deposit, where, at a 0.01 percent U30s cutoff, the 

inventory3 is 20 percent of the total inventory and has an 

average grade of 0.21 percent U30s. We judge that the 

low DOE grade-distribution estimate used in 1980 was 

tempered by experience with the lower grades of 

sandstone deposits on the Colorado Plateau. We believe 

that the grade distribution estimated in our report is 

reasonable and might even be conservative. 

8

Uranium inventory is the preproduction tons UaOs at and 

above minimum grade of 0.01 percent UaOs contained in discovered 

mineralized material. 

The Hack-Pinenut Control Area 9 
Table 1. Estimated grade distribution, G, and size-frequency distribution for the Hack-Pinenut control area, Ao= 141 mj2 

(fig 2A) 

GIClde Distribution (G) Size-frequency distribution 

Percent U308 at 0.01% cutoff Size class Sizc.HWs interval Number of deposits 1 

(k) (tons of mineralized rock above 

cutoff of 0.01% U30g) 

Lower Most likely Upper Lower Midpoint2 PoljS) Lower Most likely Upper (0.05) value (0.95) (0.05) (0.05) value (0.95) 

0.06 0.17 0.44 1 1 1.4x1o2 2xto4 s 14 16 

2 2xlo4 6.3xlo4 2xtoS 3 4 6 

3 2xtoS 6.3xtoS 2xto6 2 3 4 

4 2xto6 6.3xto6 2xto7 0 1 1 

TOrAL 10 22 27 

1 Odds are 9 to 1 that the true numbers lie within the lower and upper estimates. 

2Midpoints of size-class intervals for size classes 1-4 are calculated and rounded as the geometric mean of the upper and lower 

limits. 

ENDOWMENT IN THE HACK-PINENUT 

CONTROL AREA 

On the basis of the data in table 1, the calculated 

results for the probability distribution and the mean 

unconditional uranium endowment are as follows: 

Probability Tons Probability Tons 

UaOs UaOs 

0.05 4,337 0.55 15,990 

.10 5,929 .60 17,229 

.15 7,221 .65 18,561 

.20 8,380 .70 20,043 

.25 9,471 .75 21,696 

.30 10,529 .80 23,636 

.35 11,577 .85 25,994 

.40 12,633 .90 29,129 

.45 13,710 .95 34,063 

.50 14,824 

Mean = 16,429 tons U30s 

DETERMINATION OF FAVORABLE AND 

UNFAVORABLE AREAS 

The areas assessed in this report are divided into 

two groups: (1) the principal group, in which the host 

formations are either exposed or only thinly covered with 

sedimentary rocks, and (2) a secondary group, in which 

the host formations are covered by thick Tertiary and 

Quaternary basalt. Because of the extremely small size of 

the pipes (about 300 ft in diameter; uranium deposits 

within the pipes are even smaller in areal extent but large 

in vertical extent) and their low average density of 

occurrence (one in 3-4 mi2

), random drilling exploration 

in basalt -covered areas would be more expensive than 

drilling through only sedimentary rocks and also would 

have an extremely low success rate, perhaps only one 

discovery in 1,500 holes. Geophysical or geochemical 

techniques, not yet developed, could significantly 

increase this success ratio. We considered excluding 

basalt-covered areas as not being viable for assessment 

and treating them the same way areas deeper than 5,000 

ft were treated in the 1980 NURE assessment. 

Nevertheless, we have estimated the uranium 

10 1987 Estimate of Undiscovered Uranium Endowment, Grand Canyon Region, Arizona-Utah 
endowment for basalt-covered areas, except for volcanic 

vent areas that are entirely unfavorable. This will allow 

EIA to apply an economic model to the basalt-covered 

areas and will permit comparison with the 1980 NURE 

estimates, which included the basalt-covered areas. The 

amount of uranium in these areas (estimated mean 

undiscovered endowment = 240,000 tons U30s) may be 

an incentive to develop geophysical or geochemical tools 

to locate pipes beneath basalt cover. 

The favorable areas were determined on the basis 

of the distribution of uranium-bearing strata and breccia 

pipes within the strata and on other geologic factors. 

Solution-collapse breccia pipes penetrate strata from the 

Mississippian Redwall Limestone through the lower part 

of the Upper Triassic Chinle Formation (fig. 3). The 

uranium-ore horizon is generally adjacent to the upper 

part of the Supai Group, the Hermit Shale, and the 

Coconino Sandstone. The division of the breccia-pipe 

province into smaller areas of favor ability is based on: (1) 

occurrence of known breccia pipes; (2) presence of 

favorable upper Paleozoic strata; and (3) thickness of the 

Redwall Limestone. Feeder vents to basalt flows, such as 

in the San Francisco volcanic field, are considered 

unfavorable. 

Areas underlain by strata younger than the 

Wescogame Formation and strata south and west of the 

mapped surface contact between the Petrified Forest 

Member and the overlying Owl Rock Member of the 

Chinle Formation are considered in differing degrees 

favorable for uranium-bearing breccia pipes. The 

favorable area is divided into areas A, B, C, and D (fig. 

2). Areas where favorable strata are overlain by Tertiary 

sedimentary rocks and by basalt flows are differentiated 

and labelled by subscript "s" or "b," respectively. The 

unfavorable area is labelled E on figure 2. 

Small parts of favorable areas A and B are covered 

by Quaternary sediments and Tertiary sedimentary 

rocks. A thick wedge of Quaternary alluvial gravel, sand, 

and silt covers the down-faulted Kaibab Limestone west 

of the Aubrey Cliffs in favorable area A. Tertiary 

sedimentary rocks cover the Kaibab surfac~ in the vicinity 

of the Mount Floyd volcanic field in favorable areas A 

and B. These rocks crop out beneath Miocene volcanic 

rocks and consist of as much as 165 ft of lacustrine 

limestone (Young, 1982). Locally the limestone contains 

interbedded sandstone and siltstone. 

Favorable Area A 

Area A is the most favorable area for the 

occurrence of uranium-bearing breccia pipes, although it 

excludes the Hack-Pinenut control area (fig. 2). 

Favorable area A contains many plateaus both north and 

south of the Grand Canyon. The plateaus are capped 

primarily by the Kaibab Limestone, although some are 

partially capped by younger rocks of the Moenkopi and 

Chinle Formations. The eastern and northern edges of 

area A are delineated by the top of the Petrified Forest 

Member of the Chinle Formation, because breccia pipes 

have not been observed in any of the younger, overlying 

strata. The western edge of area A is drawn at the base of 

the Hermit Shale, and thus the inner gorge of the Grand 

Canyon is excluded. The southern margin of area A is 

along a line approximately 10 mi south of the southernmost known pipes. In the Flagstaff 1 o x 2° quadrangle this 

line also corresponds to the south edge of favorable area 

A, as shown in the NURE report (Wenrich-Verbeek and 

others, 1982). 

Favorable Area B 

Favorable area B contains the full section of 

favorable Paleozoic and Triassic formations, and thus 

contains rock favorable for the occurrence of uraniumbearing breccia pipes. It is considered less favorable than 

area A only because no pipes have been confirmed there. 

Within area B, the Redwall Limestone thins toward the 

southeast, and where the Redwall is thinner than a 

critical thickness (arbitrarily designated as 50 ft ), 

dissolution may have been insufficient to have caused 

sloping and collapse of the overlying strata. This could 

explain why no pipes have been recognized in area B, but 

the lack of identified pipes could also be because this 

area has not been explored intensively. Alluvial and 

vegetative cover are thicker than in area A and may 

decrease the possibility of detecting any pipes that may 

exist. The south edge of area B (the boundary between B 

and C) is drawn along the 50-ft isopach of the Redwall 

Limestone (McKee and Gutschick, 1979). 

Favorable Area C 

Area C has very low favorability for the occurrence 

of uranium-bearing breccia pipes. The overlying Paleozoic section is present, but the Redwall thins from 50 to 

0 ft in the area. This thickness of Redwall was probably 

inadequate for more than minor collapse, certainly not 

enough to produce the brecciation of 2,000 ft of overlying 

strata. The several solution-collapse features (not shown 

on fig. 2) that do occur in the eastern half of area C 

probably are the result of evaporite dissolution within the 

upper Paleozoic redbeds, specifically limestone and gypsiferous units of the Permian Schnebly Hill Formation 

Qateral equivalent of the Coconino Sandstone). These 

pipes are not considered favorable for uranium for two 

reasons: (1) they probably formed some time after the 

mineralizing event that produced the uranium-bearing 

Determination of Favorable and Unfavorable Areas 11 
Redwall-related pipes, and (2) no northern Arizona 

uranium orebody or other significantly mineralized rock 

is known to occur in any solution-collapse feature except 

those rooted in the Redwall Limestone. Several circular 

depressions in the western part of area C have promising 

pipe-like surface expression, and they are located outside 

the evaporite facies mentioned above. 

Favorable Area D 

Area D has a lower favorability for the occurrence 

of uranium-bearing breccia pipes than does area B in that 

it does not contain the total section of strata favorable for 

mineralization, but it is adjacent to area A, so the rocks 

should have been subjected to the same dissolution and 

mineralization events as those in area A. Area D is 

defined by the outcrop of the Esplanade Sandstone and 

contains other rocks of the Supai Group, but all overlying 

strata have been stripped off by erosion. The lower parts 

of the Orphan, Pigeon, and Kanab North orebodies 

extend down into Esplanade Sandstone, so area D may 

contain significant uranium-mineralized rock, but the 

total mineralized body remaining in any one pipe would 

be smaller than in one formed in a full section of strata. 

Unfavorable Area E 

Area E is underlain by pipe-bearing Paleozoic 

strata consisting solely of the Redwall Limestone. Even 

though numerous pipes are present, these pipes have 

been eroded far below the main uranium-ore-bearing 

horizon. The Grandview copper mine (fig. 2B), mined at 

the turn of the century, is in a breccia pipe in the Redwall 

Limestone on the boundary between areas E and D. 

Uranium does occur in this pipe, but the uraniumbearing rock appears to be in finely comminuted 

sandstone of the Supai that has dropped down into the 

Redwall. Area E is unfavorable for uranium, except for 

small, insignificant secondary concentrations, primarily 

in sandstone blocks of the Supai downdropped during 

erosion. Area E is restricted to the Grand Wash Cliffs 

region and to the inner part of the Grand Canyon and its 

tributary canyons (fig. 2). 

Basalt-Covered Areas 

The volcanic rock of the San Francisco and Mount 

Floyd volcanic fields covers much of favorable area B and 

laps into favorable areas A and C. The age of the Mount 

Floyd volcanic field is 9.8 (Arney and others, 1985) to 2.6 

Ma ( L.D. Nealey, oral commun., 1989), whereas that of 

the San Francisco volcanic field is somewhat younger, 

ranging from 6 Ma (Damon and others, 1974) for 

Anderson Mesa to 1250 A.D. for the eruption of the red 

cinders at the summit of Sunset Crater (E.M. Shoemaker 

and D.E. Champion, written commun., 1978). The San 

Francisco volcanic field is dominated by San Francisco 

Mountain, a stratovolcano composed of andesite, dacite, 

rhyodacite, and rhyolite flows and pyroclastic deposits. It 

is surrounded by more than 600 basaltic cinder cones and 

associated flows and by scattered silicic domes and dome 

complexes. The large cones and vents are shown on 

figure 2 as unfavorable areas because any breccia pipes 

that may have once existed beneath them probably were 

obliterated by volcanic explosions and magma movement 

associated with the volcanic eruptions. In addition, the 

high heat flow associated with such volcanic activity 

probably would have altered, remobilized, or removed 

the uranium deposits. 

The favorable basalt-covered areas labelled At,, Bb, 

and C on figure 2 are underlain by host rocks similar to 

these in the adjacent uncovered areas. Thus, they have 

the same favorability as adjacent areas for the occurrence 

of uranium endowment. The thickness of the basalt in 

areas At,, Bb, and C ranges from about 5 ft along 

margins of flows to more than 300 ft near vents, on the 

basis of descriptions in Moore and Wolfe (1976). The 

basalt -covered areas are considered an essentially nonviable resource under present conditions because of the 

difficulty of exploring beneath the basalt cover for the 

small targets of pipes and their contained uranium 

deposits. Present-day geophysical techniques are 

inadequate to locate hidden pipes. The basalt -covered 

areas are assessed as having a uranium endowment in 

addition to the principal favorable areas. 

ELICITATION 

Elicitation for the assessment was carried out with 

the principal scientist, H.B. Sutphin, in two sessions, 

April13 and 20, 1987. Several follow-up discussions were 

held, and the final essential input for calculations was 

received on June 11, 1987. The elicitations were made by 

W.I. Finch, C.T. Pierson, and R.B. McCammon. The 

sessions were attended by K.J. Wenrich. The results of 

the elicitations are given in tables 1 and 2. 

The total area favorable for uranium endowment is 

16,728 mi2

, which is nearly 16 percent less than the total 

area of 19,879 mi2 designated as favorable in the 1980 

NURE assessment. This difference is due to designating 

volcanic vents as unfavorable and removing them from 

basalt-covered areas (fig. 2) and to refinements in 

identifying favorable areas. A large area deleted from the 

favorable category as defined in the NURE assessment is 

area E on figure 2. 

12 1987 Estimate of Undiscovered Uranium Endowment, Grand Canyon Region, Arizona-Utah 
Table 2. Land areas and estimated L factors of favorable areas 

Lfactor 

Favorable area Land area Lower Most likely Upper 

(mi2) (0.05) (0.95) 

Grand Canyon A 4,290* 0.90 0.99 1.00 

Ab 399 .90 .99 1.00 

D 589 .10 .13 .15 

Cedar City A 207 .90 .99 1.00 

Williams A 1,665 .90 .99 1.00 

As 201 .90 .99 1.00 

Ab 232 .90 .99 1.00 

B 393 .45 .55 .75 

Bs 60 .45 .55 .75 

Bb 748 .45 .55 .75 

D 245 .10 .13 .15 

Marble Canyon A 1,095 .90 .99 1.00 

Ab 1 .90 .99 1.00 

D 47 .10 .13 .15 

Flagstaff A 843 .90 .99 1.00 

Ab 173 .90 .99 1.00 

B 870 .45 .55 .75 

Bb 1,085 .45 .55 .75 

c 166 .01 .10 .15 

Cb 17 .01 .10 .15 

Holbrook B 171 .45 .55 .75 

Bb 311 .45 .55 .75 

c 2,388 .01 .10 .15 

Cb 471 .01 .10 .15 

St. Johns c 55 .01 .10 .15 

Prescott B 6 .45 .ss .75 

Total area 16,728 

*Excludes Hack-Pinenut control area. 

Elicitation 13 
.... 

-.... 

«&» 

C» Table 3. Undiscovered uranium endowment in the principal areas .... 

m 

I [Values are in tons UsOs. For each favorable area in a quadrangle, the odds are 9 to 1 that the true unconditional endowment in tons of UsOs is between the values given for the 5 percent and 

3 95 percent probabilities] • ;r 

0 

c -::s Orand Canyon CedarOty Williams Marble Canyon Q. 

i Favorable area ... A D A A As B Bs D A D 

.. 

~ CD Probability Q. 

c 

.. 0.05 126,950 2,238 6,126 49,272 5,948 6,758 1,032 931 32,404 179 • ::s 

E" .10 173,610 3,066 8,377 67,380 8,134 9,287 1,418 1,275 44,313 245 

3 .15 211,470 3,741 10,204 82,073 9,908 11,339 1,731 1,556 53,976 298 m 

::s 

Q. .20 245,450 4,349 11,844 95,264 11,500 13,185 2,013 1,809 62,651 347 

i .25 277,460 4,923 13,388 107,690 13,000 14,928 2,279 2,048 70,821 393 

3 

CD 

J .30 308,510 5,481 14,886 119,740 14,455 16,623 2,538 2,280 78,746 437 

G) 

.. .35 339,280 6,037 16,371 131,680 15,896 18,309 2,795 2,511 86,599 482 

• ::s .40 370,270 6,597 17,866 143,710 17,348 20,014 3,056 2,744 94,510 526 Q. 

~ .45 401,910 7,171 19,393 155,990 18,831 21,761 3,322 2,983 102,580 572 ::s .50 434,630 7,766 20,972 168,690 20,364 23,575 3,599 3,230 110,940 620 -g 

::s 

:a .55 468,920 8,392 22,626 181,990 21,970 25,485 3,891 3,491 119,690 670 cZ 

0 .60 505,320 9,058 24,383 196,120 23,676 27,527 4,203 3,768 128,980. 723 ~ .65 544,480 9,778 26,272 211,320 25,511 29,744 4,541 4,067 138,980 780 

~ .70 588,090 10,576 28,376 228,240 27,554 32,188 4,914 4,399 150,110 844 

I .75 636,770 11,482 30,725 247,140 29,835 34,986 5,341 4,776 162,530 916 

' c 

&r .80 693,870 12,538 33,480 269,300 32,510 38,243 5,839 5,215 177,110 1,000 :r 

.85 763,370 13,837 36,834 296,270 35,766 42,290 6,456 5,755 194,850 1,104 

.90 855,750 15,566 41,291 332,130 40,095 47,762 7,292 6,475 218,430 1,242 

.95 1,001,400 18,337 48,321 388,670 46,920 56,558 8,635 7,628 255,610 1,463 

Mean 482,148 8,691 23,265 187,127 22,590 26,547 4,053 3,615 123,066 694 
!!! 

c; 

i 

0 

~ 

... 

Ul 

Table 3. Undiscovered uranium endowment in the principal areas-Continued 

Flagstaff Holbrook 

Favorable area ... A B c B c 

Probability 

0.05 24,947 14,961 263 2,941 3,782 

.10 34,115 20,558 417 4,041 5,994 

.15 41,554 25,101 551 4,934 7,929 

.20 48,233 29,188 678 5,737 9,753 

.25 54,523 33,046 802 6,495 11,536 

.30 60,623 36,799 926 7,233 13,322 

.35 66,669 40,532 1,053 7,967 15,142 

.40 72,760 44,307 1,182 8,708 17,010 

.45 78,976 48,173 1,317 9,468 18,951 

.so 85,407 52,189 1,460 10,258 21,002 

.55 92,144 56,418 1,613 11,089 23,205 

.60 99,297 60,938 1,779 11,977 25,586 

.65 106,990 65,844 1,960 12,942 28,196 

.70 115,560 71,256 2,164 14,006 31,135 

.75 125,130 77,449 2,400 15,223 34,529 

.80 136,350 84,660 2,678 16,640 38,521 

.85 150,010 93,619 3,027 18,401 43,544 

.90 168,160 105,730 3,502 20,782 50,378 

.95 196,780 125,200 4,284 24,609 61,631 

Mean 94,744 58,769 1,759 11,551 25,308 

St. Johns Prescott Total endowment for principal areas 

c B 

87 103 277,790 

138 142 382,080 

183 173 466,680 

225 201 542,630 

266 228 614,180 

307 254 683,600 

349 280 752,430 

392 306 821,820 

436 332 892,680 

484 360 966,040 

534 389 1,043,000 

589 420 1,124,700 

649 454 1,212,900 

717 491 1,310,700 

795 534 1,420,800 

887 584 1,549,400 

1,003 646 1,706,800 

1,160 729 1,915,900 

1,419 863 2,248,200 

583 405 1,074,910 
UNDISCOVERED URANIUM 

ENDOWMENT IN THE PRINCIPAL AREAS 

The probability distribution of the undiscovered 

unconditional uranium endowment for each favorable 

area in the eight 1 o x 2° quadrangles is given in table 3. 

ADDITIONAL UNDISCOVERED URANIUM 

ENDOWMENT IN THE BASALT-COVERED 

AREAS 

The probability distribution of the undiscovered 

unconditional uranium endowment for each of five 

1° x 2° quadrangles having basalt cover is given in table 4. 

TOTAL ENDOWMENT IN THE GRAND 

CANYON BRECCIA-PIPE PROVINCE 

From the previously given individual estimates, the 

probability distribution of the undiscovered 

unconditional uranium endowment for the entire 

northern Arizona breccia-pipe province, including both 

the principal and basalt- covered areas, was calculated 

using the computer program TENDOWG (McCammon 

and others, 1988), which assumes that estimates in the 

subareas are perfectly correlated. The computergenerated probability distribution of the unconditional 

uranium endowment for the entire province is as follows: 

Probability Tons Probability Tons 

UaOs UaOs 

0.05 338,740 0.55 1,274,900 

.10 466,410 .60 1,375,100 

.15 569,870 .65 1,483,200 

.20 662,730 .70 1,602,900 

.25 750,230 .15 1,738,300 

.30 835,120 .80 1,896,100 

.35 919,320 .85 2,089,600 

.40 1,004,200 .90 2,347,000 

.45 1,090,900 .95 2,757,200 

.50 1,180,700 

The odds are 9 to 1 that the true endowment is between 

338,740 and 2,757,200 tons U30s in the region. The 

mean or expected value for the unconditional 

endowment is 1,315,390 tons U30s. A small part of this 

endowment has been discovered. 

The mean endowment of the Hack-Pinenut control 

area, which is in addition to the above total, is 16,429 tons 

U30s distributed in an area of 141 mi2

• Part of this 

endowment has been discovered. 

The depths to the endowed strata range from 500 ft 

to more than 2,000 ft in most areas. Only in favorable 

area D are the depths less than 500 ft. The depths 

generally are greater in basalt -covered areas than in 

adjacent areas. 

The mean total endowment of the 17 principal 

favorable areas in the Grand Canyon region is 1,074,910 

tons U30s distributed, in an area of 13,291 mi2

• 

Additional endowment in the nine basalt-covered areas 

has a mean value of 240,473 tons U30s distributed in an 

area of 3,437 mi2• The basalt-covered areas probably 

contain no economically viable resources. Nevertheless, 

the mean total endowment for the 26 favorable areas is 

1,315,390 tons U30s distributed in an area of 16,879 mi2

• 

The 1980 NURE mean total endowment in a comparable 

area, but measuring 19,728 mi2

, is 158,000 tons U30s. 

Thus, the new estimate is eight times larger than the 

NURE estimate. In the test case reported by Finch and 

McCammon (1987), the DSF method was compared to 

the NURE method using the same principal investigator, 

and the result of the DSF method was 4.4 times more 

than that calculated using the NURE method. This 

difference can probably be attributed to the DSF method 

allowing for greater partitioning of the input data into 

many estimates of grade and size of deposits, rather than 

a single F factor as in the NURE method for calculating 

endowment. This tends to result in a less biased 

(generally larger) estimate (i.e., it evens out the inherent 

human tendency to underestimate in order to be "on the 

safe side"). 

In addition to the partitioning character of the DSF 

method, the eight-fold increase may be explained by 

several other factors. Since 1980, knowledge of the 

distribution of grade and tonnage of newly discovered 

and mined deposits has increased significantly. 

Furthermore, knowledge of the geology of the Grand 

Canyon region and the deposits has increased several 

fold. For this assessment, the entire region was assessed 

by a single principal investigator with much greater 

knowledge of the uranium deposits and their geology 

(increased consistency promoted a more perfect 

correlation). For the NURE assessments, six 

investigators participated; of these only one had much 

experience with the geology and the breccia-pipe 

deposits, and the others probably had a "sandstonedeposit bias" that probably lowered input values. 

The large endowment reported here for the 

principal areas alone is significant because it is nearly as 

large as the 1,281,000 tons U30s reported in the 1980 

NURE estimate for the entire San Juan Basin (McCarnmon and others, 1986, p. 351). However, a reassessment 

of the San Juan Basin using the DSF method would 

probably yield an estimate much larger than the 1980 

NURE estimate. Nevertheless, we conclude that the 

principal areas have the potential of becoming the second 

most important uranium-producing region in the United 

States. If exploration technology is developed to explore 

the basalt -covered areas, the Grand Canyon region 

could become an even more important uranium province 

in the United States. 

16 1987 Estimate of Undiscovered Uranium Endowment, Grand Canyon Region, Arizona-Utah 
Table 4. Undiscovered uranium endowment in the basalt-covered areas 

(Values are in tons of UsOs. For each favorable area in a quadrangle, the odds are 9 to 1 that the true unconditional endowment in tons of UsOs is between the values given for the 5 percent 

and 95 percent probabilities] 

Total endowment for 

Grand Canyon Williams Marble Canyon Flagstaff Holbrook basalt-covered areas 

Favorable area ... At, Ab Bb Ab Ab Bb Cb Bb Cb 

Probability 

0.05 11,807 6,865 12,863 30 5,119 18,658 27 5,348 746 61,158 

.10 16,147 9,389 17,675 40 7,001 25,639 43 7,349 1,182 84,358 

.15 19,668 11,436 21,581 49 8,528 31,304 56 8,973 1,564 103,160 

.20 22,829 13,274 25,095 57 9,898 36,401 69 10,434 1,924 120,040 

.25 25,806 15,005 28,412 65 11,189 41,212 82 11,813 2,275 135,960 

.30 28,694 16,684 31,638 72 12,441 45,892 95 13,154 2,628 151,430 -t .35 31,555 18,348 34,848 79 13,682 50,548 108 14,489 2,986 166,780 0 

!: .40 34,438 20,024 38,093 86 14,932 55,256 121 15,838 3,355 182,290 m .45 37,380 21,735 41,418 94 16,207 60,078 135 17,221 3,738 198,150 :s 

0. 

0 .50 40,424 23,505 44,870 101 17,527 65,086 150 18,656 4,142 214,590 ~ 

3 

ell .55 43,613 25,359 48,506 109 18,910 70,360 165 20,168 4,577 231,890 :s 

.. 

3" .60 46,998 27,327 52,392 118 20,378 75,997 182 21,784 5,046 250,330 .. .65 50,640 29,445 56,611 127 21,957 82,116 201 23,537 5,561 270,290 :r 

ell 

C) .70 54,696 31,803 61,264 137 23,715 88,866 222 25,472 6,141 292,230 ; 

:s .75 59,224 34,436 66,588 148 25,679 96,589 246 27,686 6,810 317,460 0. 

0 

I» .80 64,535 37,524 72,788 162 27,981 105,580 274 30,264 7,598 346,680 :s 

'< 

0 

:s .85 70,999 41,283 80,491 178 30,784 116,750 310 33,466 8,588 382,850 

I:D 

.. .90 79,591 46,278 90,905 199 34,509 131,860 359 37,796 9,936 431,110 ell .95 93,140 54,157 107,650 233 40,384 156,150 439 44,757 12,156 509,020 (') 

(') 

ii" 

-b Mean 44,843 26,074 50,528 112 19,443 73,292 180 21,008 4,992 240,473 -ij" 

ell 

""0 

.. 

0 

< 3" 

(') 

Cl 

-..... 
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petrographic and K-Ar age data to accompany 

reconnaissance geologic strip map from Kingman to 

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Billingsley, G.H., Wenrich, KJ., and Huntoon, P.W., 1986, 

Breccia pipe and geologic map of the southeastern 

Hualapai Indian Reservation and vicinity, Arizona: U.S. 

Geological Survey Open-File Report 86-458-B, 26 p., 2 

pl., scale 1:48,000. 

Bowles, C.G., 1977, Economic implications of a new hypothesis 

of the origin of uranium- and copper-bearing breccia 

pipes, Grand Canyon, Arizona (abs.], in Campbell, J.A., 

ed., Short papers of the U.S. Geological Survey: U.S. 

Geological Survey Circular 753, p. 25-27. 

Chenoweth, W .L., 1986, The Orphan Lode Mine, Grand 

Canyon, Arizona, a case history of a mineralized, 

collapse-breccia pipe: U.S. Geological Survey Open-File 

Report 86-510, 91 p., 35 p. appendices. 

Damon, P .E., Shafiqullah, Muhammad, and Leventhal, J .S., 

1974, K-Ar chronology for the San Francisco volcanic 

field and rate of erosion of the Little Colorado River, in 

Karlstrom, N.V., and others, eds., Geology of Northern 

Arizona: Geological Society of America Rocky Mountain 

Section Guidebook, p. 221-235. 

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.l., 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 ox 2° quadrangles, 

Washington and Idaho: U.S. Geological Survey OpenFile Report 90-2, 19 p. 

Flanigan, V J ., Mohr, Pam, Tippens, Charles, and Senterfit, 

Michael, 1986, Electrical character of collapse breccia 

pipes on the Coconino Plateau, northern Arizona: U.S. 

Geological Survey Open-File Report 86-521, 50 p. 

Ford, C.E., and McClaren, A.R., 1980, Methods for obtaining 

distnbutions of uranium occurrence from estimates of 

geologic features: U.S. Department of Energy Report 

GJBX-165(80), 121 p. 

Gornitz, Vivian, and Kerr, P.F., 1970, Uranium mineralization 

and alteration, Orphan Mine, Grand Canyon, Arizona: 

Economic Geology, v. 65, p. 751-768. 

Gornitz, Vivian, Wenrich, K.J., Sutphin, H.B., and VidaleBuden, Rosemary, 1988, Origin of the Orphan mine 

breccia pipe uranium deposit, Grand Canyon, Arizona, in 

Vassiliou, A.H., Hausen, D.M., and Carson, D.J., eds., 

Process Mineralogy VII-As applied to separation 

technology: Warrendale, Penn., The Metallurgical 

Society, p. 281-301. 

Holm, R.F., 1986, Field guide to the geology of the central San 

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J.D., et al., eds., Geology of central and northern 

Arizona: Geological Society of America, Rocky 

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Huntoon, P.W., 1981, Fault controlled ground-water 

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Krewedl, D.A., 1986, Contnbutions to the geology of uranium 

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Ludwig, K.R., Rasmussen, J.D., and Simmons, K.R., 1986, Age 

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1986, Estimation of uranium endowment in the Westwater Canyon Member, Morrison Formation, San Juan 

Basin, New Mexico, using a data-directed numerical 

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American Association of Petroleum Geologists Studies 

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McCammon, R.B., Finch, W.l., Pierson, C.T., and Bridges, NJ., 

1988, The micro-computer program TENDOWG for 

estimating undiscovered uranium endowment: U.S. 

Geological Survey Open-File Report 88-653, 11 p., 1 

diskette. 

McKee, B.D., 1982, The Supai Group of Grand Canyon: U.S. 

Geological Sutvey Professional Paper 1173, 504 p. 

McKee, B.D., and Gutschick, R.C., 1979, Histocy of the Redwall Limestone of northern Arizona: Geological Society 

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18 1987 Estimate of Undiscovered Uranium Endowment, Grand Canyon Region, Arizona-Utah 
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collapse features on the southern Marble Plateau, 

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breccia pipes on the southern Marble Plateau, Arizona: 

U.S. Geological Survey Open-File Report 83-908, 6 

p., 2 pl. 

___ 1988, Map showing structural control of breccia pipes 

on the southern Marble Plateau, Arizona: U.S. 

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northwestern Arizona, U.S. Geological Survey Bulletin 

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northern Arizona: U.S. Geological Survey Open-File 

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___ 1986b, Uranium mineralization of collapse breccia 

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Fuchs, Helmut, ed., Vein type uranium deposits: 

International Atomic Energy Agency, Vienna, 

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trU.S. GOVERNMENT PRINTING OFFICE: 1990-773-047/06054 

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Breccia pipe and geologic map of the northeastern 

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pl., scale 1:48,000. 

___ 1987, Breccia pipe and geologic map of the 

northwestern Hualapai Indian Reservation and vicinity, 

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

86-458-C, 32 p., 2 pl., scale 1:48,000. 

Wenrich, K.J., Billingsley, G.H., and Van Gosen, B.S., 1986, 

The potential for breccia pipes in the National Tank area, 

Hualapai Indian Reservation, Arizona: U.S. Geological 

Survey Open-File Report 86-592-A, 45 p. 

___ 1987, The potential for breccia pipes in the National 

Tank area, Hualapai Indian Reservation, Arizona: U.S. 

Geological Survey Bulletin 1683-B, 45 p. 

___ 1990, Potential breccia pipes in the Mohawk Canyon 

area, Hualapai Indian Reservation, Arizona: U.S. 

Geological Survey Open-File Report 90-15, 67 p. 

Wenrich, K.J., Van Gosen, B.S., Balcer, R.A., Scott, J.H., 

Mascarenas, J.F., Bedinger, G.M., and Burmaster, Betsi, 

1987, A mineralized breccia pipe in Mohawk Canyonlithologic and geophysical logs: U.S. Geological Survey 

Bulletin 1683-A, 72 p. 

Wenrich-Verbeek, K.J., Spirakis, C.S., Billingsley, G.H., Hereford, Richard, Nealey, L.D., Ulrich, G.B., Verbeek, E.R., 

and Wolfe, E.W., 1982, National Uranium Resource 

Evaluation, Flagstaff quadrangle, Arizona: U.S. 

Department of Energy Report PGJ-014(82), 483 p. 

Wenrich, K.J., and Sutphin, H.B., 1989, Lithotectonic setting 

necessaty for formation of a uranium rich, solution 

collapse breccia pipe province, Grand Canyon Region, 

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Technical committee meeting on metallogenesis of 

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Young, R.A., 1982, Paleogeomorphologic evidence for the 

structural histoty of the Colorado Plateau margin in 

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Mesozoic-Cenozoic tectonic evolution of the Colorado 

River Region, California, Arizona, and Nevada: San 

Diego, Cordilleran Publishers, p. 29-39. 

Selected References 19 

SELECTED SERIES OF U.S. GEOLOGICAL SURVEY PUBLICATIONS 

Periodicals 

Earthquakes & Volcanoes (issued bimonthly). 

Preliminary Determination of Epicenters (issued monthly). 

Technical Books and Repons 

Professional Papers are mainly comp!'ehensive scientific reports of 

wide and lasting interest and importance to p!'Ofessional scientists and engineers. Included are reports on the results of resoUICe studies and of 

topographic, hydrologic. and geologic investigations. They also include 

collections of related papers addressing different aspects of a single scientific topic. 

Bulletins contain significant data and interpretations that are of lasting scientific interest but are generally more limited in scope or 

geographic coverage than Professional Papers. They include the results 

of resourcesmdies and of geologic and topographic investigations; as well 

as collections of short papers related to a specific topic. 

Water-Supply Papers are comprehensive reports that present significant interpretive results of hydrologic investigations of wide interest 

to professional geologists, hydrologists, and engineers. The series covers 

investigations in all phases of hydrology, including hydrogeology, 

availability of water, quality of water, and use of water. 

Cb'culars present administrative infonnation or important scientific 

infonnation of wide popular interest in a fonnat designed for distribution 

at no cost to the public. Infonnation is usually of short-term interest. 

Water-Resources Investigations Reports are papers of an interpretive namre made available to the public outside the fonnal USGS publications series. Copies are reproduced on request unlike fonnal USGS 

publications, and they are also available for public inspection at 

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and other material that are made available for public consultation at 

depositories. They are a nonpermanent form of publication that may be 

cited in other publications as soUICeS of infonnation. 

Maps 

Geologic Quadrangle Maps are multicolor geologic maps on 

topographic bases in 71/2-or 15-minutequadranglefonnats (scales mainly 1:24,000 or 1 :62,500) showing bedrock, surficial, or engineering geology. Maps generally include brief texts; some maps include structure 

and columnar sections only. 

Geophysical Investigations Maps are on topographic or planimetric 

bases at various scales; they show results of smveys using geophysical 

teclmiques, such as gravity, magnetic. seismic, or radioactivity, which 

reflect subsurface strucmres that are of economic or geologic significance. 

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Miscellaneous Investigations Series Maps are on planimetric or 

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which show geology as interpreted from aerial photographs. Series also 

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Coal Investigations Maps are geologic maps on topographic or 

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Oil and Gas Investigations Charts show stratigraphic information 

for certain oil and gas fields and other areas having petrolemn potential. 

Miscellaneous Field Studies Maps are multicolor or black-andwhite maps on topographic or planimetric bases on quadrangle or irregular areas at various scales. Pre-1971 maps show bedrock geology 

in relation to specific mining or mineral-deposit problems; post-1971 

maps are primarily black-and-white maps on various subjects such as 

environmental studies or wilderness mineral investigations. 

Hydrologic Investigations Atlases are multicolored or black-and ... 

white maps on topographic or planimetric bases presenting a wide range 

of geohydrologic data ofboth regular and irregular areas; principal scale 

is 1:24,000 and regional studies are at 1:250,000 scale or smaller. 

Catalogs 

Permanent catalogs, as well as some others, giving comprehensive listings of U.S. Geological Survey publications are available under 

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