I 

The Potential of Breccia PipeS 

in the Mohawk Canyon Area, 

Hualapai Indian Reservation, AriZona 

This research was funded by the 

Bureau of Indian Affairs 

in cooperation with the 

Hualapai Indian Tribe 

U.S. GEOLOGICAL SURVEY BULLETIN 1683-D 
View looking north at the central half of the Mohawk Canyon Area. Mohawk Canyon extends 

along the eastern edge of the photograph; the Mohawk-Stairway fault has created the linear 

drainage along the bottom of this part of the canyon. The Mohawk Canyon pipe is exposed in 

the Kaibab Limestone visible in the foreground at the top eastern edge of the cliff (road on the 

plateau can be seen leading to the pipe}. The pipe can be detected by the white bleached area 

that appears even lighter than the normal pale yellow to buff color of the Kaibab Limestone. 
Chapter D 

The Potential of Breccia Pipes 

in the Mohawk Canyon Area, 

Hualapai Indian Reservation, Arizona 

By KAREN J. WENRICH, GEORGE H. BILLINGSLEY, and 

BRADLEY S. VAN GOSEN 

This research was funded by the 

Bureau of Indian Affairs in 

cooperation with the 

Hualapai Indian Tribe 

U.S. GEOLOGICAL SURVEY BULLETIN 1683 

BRECCIA PIPES IN NORTHERN ARIZONA 
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 

For sale by the 

Books and Open-File Reports Section 

U.S. Geological Survey 

Federal Center 

Box 25286 

Denver, CO 80225 

library of Congress Cataloging-in-Publication Data 

Wenrich, Karen J. 

The potential of breccia pipes in the Mohawk Canyon Area, Hualapai Indian 

Reservation, Arizona I by Karen J. Wenrich, George H. Billingsley, and 

Bradley S. Van Gosen. 

p. cm.-(Breccia pipes in northern Arizona ; ch. D) (U.S. Geological 

Survey bulletin ; 1683-D) 

Includes bibliographical references (p. ). 

Supt. of Docs. no.: 119.3:1683-D 

1. Breccia-Arizona-Mohawk Canyon. 2. Geology, StratigraphicPaleozoic. 3. Geology, Stratigraphic-Triassic. . Geology-ArizonaMohawk Canyon. I. Billingsley, George H. II. Van Gosen, B.S. (Bradley S.). 

1960- . Ill. Title. IV. Series. V. Series: U.S. Geological Survey bulletin ; 

1683-D. 

QE75.B9 no. 1683-D 

[QE471 .15.B7) 

557.3 s-dc20 

[552'.5) 90-21154 

CIP 
CONTENTS 

Abstract Dl 

Introduction Dl 

Breccia pipes in northern Arizona D2 

Breccia pipes in the Hualapai Indian Reservation D4 

The Mohawk Canyon area D7 

Mapping of collapse features D7 

Collapse features/breccia pipes exposed at the top of the Redwall 

Limestone DlO 

Collapse features/breccia pipes exposed along Supai slopes and the Esplanade 

erosion surface D21 

Collapse features/breccia pipes exposed in the Hermit Shale, Coconino 

Sandstone, and Toroweap Formation D28 

Collapse features/breccia pipes exposed on the Kaibab Limestone-capped 

plateaus D29 

Conclusions D36 

Acknowledgments D37 

References cited D38 

FIGURES 

1. Index map of northern Arizona showing the locations of plateaus, Hualapai 

Indian Reservation, breccia pipes developed into mines, and the San Francisco 

volcanic field D2 

2. Schematic cross section of a breccia pipe with stratigraphic units shown D3 

3. Map of the Hualapai Indian Reservation illustrating the density of solutioncollapse features existing in northern Arizona DS 

4. Schematic diagram showing the various types of solution-collapse features 

found in northwestern Arizona D6 

5. Geologic map of the Mohawk Canyon area showing breccia pipes and collapse 

features DS 

6-26. Photographs showing: 

6. Breccia pipes 593, 594, collapse feature 1030, breccia pipes I 032, I 034, 

I035, collapse features I076, I077, 1080, 1082 D22 

7. Breccia pipe 1033, Leisegang-banded and brecciated outcrop in 

pipe 1033 D24 

8. Hemimorphite D24 

9. Collapse features 1078, 1086 D24 

I 0. Collapse feature 1084 D24 

11. Collapse feature 1081 D25 

I2. Collapse feature 240 D25 

13. Collapse feature 1085 D25 

I4. Breccia pipe 239 D25 

15. Breccia pipe 495 D26 

I6. Breccia pipe 236 D26 

17. Breccia pipe 237 D27 

18. Breccia pipe 1031 D28 

Contents Ill 
TABLES 

19. Breccia pipe 238, brecciated rock from the breccia column in 

pipe 238 D28 

20. Breccia pipe 242, breccia in pipe 242, large goethite nodules altered from 

pyrite concretions in pipe 242 D29 

21. Breccia pipe 241, the breccia column in pipe 241, a close-up view of the 

breccia from pipe 241 D30 

22. Collapse features 592, 1101, 1087, I088, I089, I090, I092, 1099, IIOO, 

117I, II73 D32 

23. Collapse feature 249, collapse feature 249 enlarged from a I :24,000 

aerial photograph D34 

24. Collapse feature 1I 02, Fe-rich gossan at the surface of collapse feature 

II02 D35 

25. Collapse feature 493, collapse feature 493 enlarged from a I :24,000 

aerial photograph, the Woods Ranch Member of the Toroweap Formation 

thinning to 30-ft thickness near collapse feature 493 D36 

26. The Mohawk Canyon pipe as viewed from a southern distant perspective, 

a close-up view of the Mohawk Canyon pipe D38 

1. Collapse features/breccia pipes mapped in the Mohawk Canyon area Dll 

2. Chemical analyses of rock samples collected from collapse structures in the 

Mohawk Canyon area DIS 

IV Contents 
BRECCIA PIPES IN NORTHERN ARIZONA 

The Potential of Breccia Pipes 

in the Mohawk Canyon Area, 

Hualapai Indian Reservation, Arizona 

By Karen j. Wenrich, George H. Billingsley, and Bradley S. Van Gosen 

Abstract 

The Hualapai Indian Reservation is on the southwestern 

corner of the Colorado Plateau in northern Arizona. Hundreds 

of solution-collapse breccia pipes crop out in the canyons and 

on the plateaus of northern Arizona. The pipes originated in 

the Mississippian Redwall Limestone and stoped their way 

upward through the upper Paleozoic strata, locally extending 

into the Triassic Moenkopi and Chinle Formations. The occurrence of high-grade U ore, associated with potentially economic concentrations of Cu, Ag, Pb, Zn, V, Co, and Ni in some 

of these pipes, has stimulated mining activity in northern 

Arizona despite the depressed market for most of these metals. 

Forty-six of the niore than 900 confirmed and suspected 

breccia pipes that have been mapped on the Hualapai Indian 

Reservation are in the Mohawk Canyon area. The Mohawk 

Canyon area has most of the various breccia-pipe morphologies on the Hualapai Indian Reservation; in addition, the area 

contains the greatest number of mineralized pipes on the 

reservation. Rocks in the area span the entire Paleozoic 

sequence of the Grand Canyon, from the Cambrian Tapeats 

Sandstone to the Permian Kaibab Limestone. 

Identified collapse features (possible breccia pipes) and 

known breccia pipes in the Mohawk Canyon area are presently collared in one of three horizons: (1) the top of the 

Redwall Limestone (13 collapse features/breccia pipes), (2) the 

Esplanade erosion surface or along the cliffs formed by any 

Supai Group formation (14 collapse features/breccia pipes), or 

(3) the top of the Coconino Plateau capped by the Kaibab 

Limestone (19 collapse features/breccia pipes). The 13 structures that crop out within the Redwall Limestone are considered to have little or no economic potential. Two breccia 

pipes, 241 and 242, have significant mineralized rock exposed 

on the Esplanade erosion surface; unfortunately, their economic potential is questionable because of their inaccessibility 

Manuscript approved for publication September 21, 1990. 

at the bottom of Mohawk Canyon. In contrast, four features, 

249, 493, 494, and 1102, on the Coconino Plateau have the 

greatest potential for being U-bearing breccia pipes and are 

accessible. All warrant further exploration: 249 exhibits excellent circular surface morphology; 493 also has similar·circular 

morphology with concentric inward-dipping beds, but in 

addition, audio-magnetotelluric profiles show a vertical, 

strongly conductive zone (possibly a breccia core) beneath the 

collapse feature; 1102 contains the most radioactive surface 

exposure found anywhere on the reservation-18 times background; and 494 (the Mohawk Canyon pipe) was drilled by the 

U.S. Geological Survey in 1984 and proven to contain at least 

1 foot of core containing 0.52% U30 11 • 

INTRODUCTION 

The Colorado Plateau of northern Arizona is host to 

thousands of solution-collapse breccia pipes. Many of these 

pipes were mineralized by Cu-, U-, Ag-, Pb-, Zn-, Co-, and 

Ni-bearing fluids. Despite the depressed U market, the level 

of exploration activity for mineralized breccia pipes in 

north-central and northwestern Arizona remained high 

throughout the 1980's. The polymetallic, high-grade U ore, 

averaging as much as 0.74% U30 8 in the Canyon pipe 

(Casadevall, 1989), has made these deposits attractive, even 

at $15 per lb of U. Although the breccia pipes have also 

been mined in the past 100 years for Cu, Ag, Pb, V, and Zn, 

U has been the only commodity to tum a significant profit. 

During the 1980's mining cycle in the Grand Canyon, none 

of these base metals were mined as byproducts of U for 

several reasons: (1) the U mill, in Blanding, Utah, is more 

than 300 mi (miles) from the mines, so transportion costs 

must be offset by high metal prices-none of these base 

metals commanded an impressive price during this period; 

(2) the mill does not have a circuit for any of these metals 

except V; and (3) the base-metal enrichments are sporadic; 

Breccia Pipes, Mohawk Canyon Area, Hualapai Indian Reservation, Arizona 01 
Kingman • 

1 DO KI LOMETERS 

50 MILES 

COLORADO 

PLATEAU 

Figure 1. Index map of northern Arizona showing the locations of plateaus, Hualapai Indian Reservation, breccia pipes 

developed or being developed into mines, and the San Francisco volcanic field (patterned area) that buries terrane with high 

potential for breccia pipes. Numbers refer to the following mines: 

1 . Copper House 6. Hack Canyon 

2. Copper Mountain 7. Old Bonnie Tunnel 

3. Cunningham 8. Orphan 

4. Grand Gulch 9. Ridenour 

5. Grandview 10. Riverview 

for example, Ag is as high as 100 ppm (parts per million) in 

many samples but is more commonly below 20 ppm in 

unoxidized U ore collected from North Rim mines. 

The Hualapai Tribal Council requested in 1985 that 

the U.S. Geological Survey select and publish summary 

reports on two areas on the Hualapai Indian Reservation 

(fig. 1) that contain high concentrations of breccia pipes and 

have good potential for hosting U orebodies. The selection 

was based on the density of collapse features and the 

proximity to residential communities. The two areas 

selected represent two different exposures of breccia pipes: 

( 1) In the Mohawk Canyon area (this report), mineralized 

rock is commonly exposed in cliff faces and along canyon 

bottoms within all formations from the Permian Kaibab 

Limestone to the Mississippian Redwall Limestone (fig. 2). 

Much of this area is not easily accessible and cannot be 

reached by four-wheel-drive vehicles. Mapping of such 

terrain, specifically the tens of miles of cliff exposure, can 

only be done by viewing aerial photographs, and by 

D2 Breccia Pipes in Northern Arizona 

11. Savanic 16. Pinenut 

12. Snyder 17. Hermit 

13. Pigeon 18. Arizona 1 

14. Kanab North 

15. Canyon 

observations from a helicopter. (2) In the National Tank 

area (Wenrich, Billingsley, and Van Gosen, 1989), mineralized rock is not exposed; in fact, little rock of any type is 

exposed, and most of the area is soil covered. Consequently, 

mapping of breccia pipes is restricted to recognition of 

circular features on soil-capped plateaus. 

BRECCIA PIPES IN NORTHERN ARIZONA 

The breccia pipes of northern Arizona differ from 

classic breccia pipes, those formed from volcanic or gaseous 

explosions, in that no volcanic rock is associated with the 

pipes in time or space, nor is there any evidence of upward 

movement of clasts. Instead, the pipes result from solution 

collapse within the Redwall Limestone and stoping of 

overlying strata. Dissolution of the Redwall Limestone 

created caverns into which blocks of overlying strata 

collapsed, leading to gradual upward stoping of a rubble-
I 

!~Diameter of surface depression~: I 

Average or range 

in thickness 

(in feet) I I 

.---.---------------------------~ ,.~~~~~~~~~~----------------~ 

0 

(/) 

(/) 

<( 

a: 

fChinle 

Formation 

Moenkopi 

Formation 

Kaibab 

Limestone 

Toroweap 

Formation 

Shinarump Member 

Harrisburg Gypsiferous 

Member 

Fossil Mountain 

Woods Ranch Member 

Brady Canyon Member 

300 

0-200 

·· 400-1200 

. . . . . . 

.'.·:::· ··.~ ·.·:·~:-. 

250 

125 

S e I i man Member -------------f. 

250 

~~~~~~~~~~--------40------~ 

z 

<( 

~ 

a: 

w 

a.. 

I 

...Jz 

>-<( 

(/)_ 

zz 

Z<( 

w> 

a.. 

z 

<( 

a.. 

a.. 

(/) 

(/) 

(/) 

(/) 

~ 

Coconino Sandstone 

Hermit Shale 

a. 

:J 

0 

ro 

a. 

:J 

(/) 

Esplanade Sandstone 

Wescogame Formation 

Manakacha Formation 

Watahomigi 

Surprise Canyon 

Formation 

( Miss iss i p pi an I Penns y Ivan ian? ) 

Redwall Limestone 

I 

oz 

> <( Temple Butte Limestone 

~z 

50 - 160 

700 - 800 

450 

150 

200 

170 

0- 250 

400 - 600 

400 

Figure 2. Schematic cross section of a breccia pipe (based on cliff exposures in the Grand Canyon of Arizona). The unit 

thicknesses shown for the Triassic Chinle and Moenkopi Formations (not present in the Mohawk Canyon area) represent their 

thickness ranges in the Grand Canyon area. The unit thicknesses for the Paleozoic strata correspond to thicknesses present in the 

Mohawk Canyon area (from Wenrich and others, 1986, which also provides unit descriptions). Some collapse features in the 

Mohawk Canyon area, such as collapse feature 493, have distinct reddish-orange soil developed in their center. This soil may be 

weathered from downdropped Moenkopi strata. Modified from Van Gosen and Wenrich (1989). 

Breccia Pipes, Mohawk Canyon Area, Hualapai Indian Reservation, Arizona 03 
filled, approximately 250-ft (feet) diameter pipelike structure. The pipes and associated mineralized rock transgress 

formation boundaries from the Mississippian Redwall 

Limestone through the Triassic Chinle Formation (fig. 2), a 

vertical distance of about 4,000 ft. The stoping produced 

extensive brecciation of the rock within the steep walls of 

the pipe. At no level in any pipe have breccia clasts been 

observed from deeper beds; all material has been dropped 

into the pipe from stratigraphically higher units. As a result 

of collapse, brecciated rock within each pipe abuts generally 

well-stratified, undeformed sedimentary rock; the plane 

demarking this contact is obviously one along which the 

breccia slid downward and is, therefore, a fracture (Wenrich, 1985, fig. I b). This nearly vertical fracture is referred 

to throughout this report as the "ring fracture." 

The breccia pipes of northern Arizona extend from 

the Utah state line south to the Mogollon Rim (the southern 

margin of the Colorado Plateau). They are abundant from 

the edge of the Grand Wash Cliffs (the western margin of 

the Colorado Plateau) across the Hualapai Indian Reservation and the remainder of the Coconino Plateau to the 

Marble Plateau of the Navajo Indian Reservation (fig. 1). 

The pipes in the Mohawk Canyon area are typical of those 

in northwestern Arizona. They are exposed at various 

stratigraphic horizons from the Redwall Limestone to the 

Kaibab Limestone, which caps the Coconino Plateau. Many 

are known to have been mineralized. 

Mining activity in breccia pipes of the Grand Canyon 

region began during the 1860's, but prior to 1940 all of the 

production was for Cu, Pb, Zn, Ag, and minor Au. As of 

1987, more than 17,275,000 pounds of U30 8 have been 

mined from northern Arizona breccia pipes, and 13,000,000 

pounds have been mined since 1980 (Wenrich, Chenoweth, 

and others, 1989). The deposits are small and of high grade; 

the average diameter of the mined breccia pipes is about 250 

ft, and ore mined between 1980 and 1986 averaged 0.65% 

U30 8• The breccia pipes mined as of 1990 have contained 

between I and 7 million pounds of U30 8 each (I.W. 

Mathisen, oral commun., 1988). Uraninite is the ore 

mineral; pyrite, chalcopyrite, sphalerite, galena, and bravoite are other commonly associated metallic minerals. Less 

common metallic minerals are nickeline, rammelsbergite, 

millerite, gersdorffite, vaesite, siegenite, marcasite, arsenopyrite, tennantite, enargite, luzonite, lautite, bornite, chalcocite, djurleite, digenite, nukundamite, and covellite. 

Common gangue minerals are calcite, dolomite, and barite. 

Both the ore and gangue minerals occur primarily in the 

sandy matrix supporting the breccia clasts. Primary and 

secondary fluid inclusions in sphalerite, dolomite, and 

calcite yield filling temperatures that range from 80 to 

173°C. Their corresponding salinities are consistently more 

than 9 weight percent NaCl equivalent and generally more 

than 18 weight percent NaCI equivalent. A large set of U-Pb 

isotopic analyses from nine orebodies shows that the main 

U-mineralizing event occurred roughly 200 Ma ago; data 

04 Breccia Pipes in Northern Arizona 

from two of these pipes, however, indicate at least one 

earlier period of mineralization roughly at 260 Ma (Ludwig 

and Simmons, 1988). Additional descriptions of breccia 

pipes and their mineralization are in Wenrich, Chenoweth, 

and others (1989); Van Gosen and Wenrich (1989); Wenrich and Sutphin (1989); Gornitz and others (1988); Krewedl and Carisey (1986); Wenrich (1985, 1986); and Gomitz 

and Kerr (1970). 

BRECCIA PIPES IN THE HUALAPAI INDIAN 

RESER VA liON 

The Hualapai Indian Reservation is on the southwestern comer of the Colorado Plateau (fig. 1 ). The western 

half of the reservation, which is on the Hualapai Plateau and 

bounded on the west by the Grand Wash Cliffs, is capped by 

the Redwall Limestone. No more than 500 ft of possible 

rock thickness is available to host an ore body, and little of 

the rock is sandstone. Most is limestone, which generally is 

an unfavorable host for U mineralization; thus, the Hualapai 

Plateau is not considered favorable for economic breccia 

pipes and has been eliminated for potential drilling targets. 

In contrast, the eastern part of the reservation occupies the 

western edge of the Coconino Plateau, which is mostly 

capped by the Harrisburg Gypsiferous Member of the 

Kaibab Limestone. This thick rock sequence, in excess of 

2,500 ft, provides ample host rock for potential mineral 

deposits. In addition, this plateau surface occupies the same 

stratigraphic horizon as does the plateau surface above most 

breccia pipes hosting orebodies in northern Arizona. 

More than 900 confirmed and suspected breccia pipes 

have been mapped on the Hualapai Indian Reservation 

(fig. 3). This density of collapse features/breccia pipes is not 

unique to the Hualapai Indian Reservation, which lies at the 

western edge of the pipe-rich region in Arizona. This region 

extends eastward where a similar concentration of collapse 

features/breccia pipes has been mapped on the Marble 

Plateau (Sutphin and Wenrich, 1983). A map of breccia 

pipes across northwestern Arizona by Sutphin and Wenrich 

(1989) shows large areas with only a few pipes and some 

areas with no pipes; most of northwestern Arizona and 

especially these areas of low pipe density have not been 

mapped in detail. The only data available for areas 

containing few or no pipes is what was provided by the 

exploring mining companies. 

Mapping collapse features as surface manifestations 

of breccia pipes on high plateaus (such as the Coconino, 

Kaibab, and Marble Plateaus) capped by the Kaibab 

Limestone or younger units is complicated both by karst 

development in the Kaibab and solution-collapse features 

formed where gypsum dissolved from the underlying Toroweap Formation or from the Harrisburg Gypsiferous 

Member of the Kaibab Limestone (fig. 4). Thus, throughout 

this paper the terms "solution collapse," "structure," or 
1WOO' 

R 16 W R 14 W R 13 W R 12 W R 11 W R 10 W R 9 W 

T 

33 

N 

T 

32 

N 

T 

31 

N 

T 

30 

~~~mE;~~--Jj;_j N 

R 8 W 

T 

29 

~~~~~~~--~~-r N 

R 7 W R 6 W R 5 W 

T 

28 

N 

T 

27 

N 

T 

26 

N 

T 

25 

N 

T 

24 

N 

Figure 3. Map of the Hualapai Indian Reservation illustrating the density of solution-collapse features existing in northern 

Arizona made apparent when detailed geologic mapping is conducted. More than 900 confirmed and suspected breccia pipes 

have been mapped within and adjacent to the reservation. Vegetation is sparse on the western side of the reservation, which is 

reflected in the greater density of identified collapses. Outlined area with a tree symbol in the center on the eastern side of mJp 

area is densely tree covered, preventing recognition of most pipes. Solution-collapse features shown as black squares were 

mapped prior to the present study by G.H. Billingsley; solution-collapse features shown as black circles were mapped by the 

authors during the present study (1982 to 1988). 

"feature" are defined as those areas that apparently 

collapsed due to dissolution of any underlying rock, 

whereas the term "breccia pipe" refers specifically to 

dissolution of the Redwall Limestone, which resulted in 

sloping and brecciation of the overlying rock. Where the 

term "breccia pipe/collapse feature" is applied, either a 

collapse feature or a breccia pipe, or both, have been 

observed. It is generally assumed that those collapse 

features resembling ordinary sink holes-with vertical 

walls, no tilted beds, and a bottom covered by uncemented 

rubble-are recent karst landforms. An example of such a 

feature in the Mohawk Canyon area is the sinkhole (591) 

shown on the geologic map (fig. 4). In contrast, collapse 

features with inward-tilted beds and altered rock appear to 

be favorable indicators of concealed breccia pipes. 

Unfortunately, drilling results indicate that not all collapses 

possessing these favorable characteristics have breccia 

pipes beneath them, suggesting that geochemical- and 

geophysical-exploration techniques should be used before 

drilling (Wenrich, 1986; Flanigan and others, 1986). 

Breccia Pipes, Mohawk Canyon Area, Hualapai Indian Reservation, Arizona D5 
GYPSUM COLLAPSE IN THE 

HARRISBURG GYPSIFEROUS MEMBER 

OF THE KAIBAB LIMESTONE---, 

GYPSUM COLLAPSE IN THE 

WOODS RANCH MEMBER OF 

THE TOROWE!AP FORMATION----+---~ 

SOLUTION-WIDENED FRACTURE 

ALLUVIUM--1 

1 INWARD-DIPPING 

MARBLE PLATEAU ,_-BEDS 

TOROWEAP FORMATION 

COCONINO SANDSTONE 

ESPLANADE SANDSTONE 

LOWER PART, SUPAI GROUP 

REDWALL LIMESTONE 

Figure 4. Types of solution-collapse features in northwestern Arizona. (1) breccia pipes that bottom in the Redwall Limestone; 

(2) collapse due to dissolution of gypsum beds in the Woods Ranch Member of the Toroweap Formation; (3) collapse due to 

dissolution of gypsum beds in the Harrisburg Gypsiferous Member of the Kaibab Limestone; and (4) collapse (with vertical sides, 

as opposed to the gently sloping sides of the other three collapse types) due to recent sinkholes in the limestone beds of the Kaibab 

Limestone. 

Although the dissolution of gypsum in the Toroweap 

Formation and of both limestone and gypsum in the Kaibab 

Limestone is a complicating factor, the process apparently 

enhances the surface expression of those features that are, 

indeed, breccia pipes. Most of the lower plateau surfaces, 

most notably the Esplanade surface (generally located near 

or at the top of the Esplanade Sandstone, fig. 2), do not 

have the density of features exposed that the Kaibab-, 

Moenkopi-, and Chinle-capped plateaus have. Initially, this 

greater density of features might appear to suggest that most 

features on these latter plateaus are merely sinkholes within 

the Kaibab and Toroweap. To the contrary, apparently the 

presence of a breccia pipe increases the movement of fluids 

not only within the pipe itself but also laterally in various 

formations adjacent to the pipe. The effects of enhanced 

06 Breccia Pipes in Northern Arizona 

circulation can be seen in the core from the Mohawk 

Canyon pipe (494, fig. 5) (Wenrich and others, 1988)~ here 

the entire 100 ft of gypsiferous Woods Ranch Member of 

the Toroweap Formation has been almost entirely removed 

from the brecciated column. Dissolution of the upper 

soluble units in the vicinity of pipes accounts for the 

discrepancy in size between the pipes and the much larger 

collapse features that are commonly mapped above them. 

All known orebodies range from I 00 to 500 ft (most 

commonly about 250 ft) in diameter, whereas many of the 

collapse features on plateau surfaces are as much as I ,300 ft 

across. One notable example, which contained an economic 

orebody that is now mined out, is the Pigeon pipe (mine 13, 

fig. 1); the pipe diameter is about 250 ft, yet its overlying 

collapse structure is approximately 0.5 mi in diameter. The 
largest known collapse, Shadow Mountain collapse on the 

Marble Plateau, is more than 1 mi in diameter, and is about 

1 mi north-northeast of Shadow Mountain (fig. 1 ), a 

Tertiary basaltic cinder cone. The actual Shadow Mountain 

breccia pipe may be no more than the'average 250 ft in 

diameter-the Tertiary solutions associated with the nearby 

volcanism may have caused extensive recent dissolution of 

some of the formations underlying the collapse (such as 

large-scale dissolution of the Red wall or Muav Limestones, 

as there is no gypsiferous rock within the Toroweap and 

Kaibab on the Marble Plateau). 

Thus, locating the actual breccia pipe, and perhaps an 

orebody, is more difficult in a Shadow Mountain-sized 

collapse than in a small collapse, such as that which overlies 

the Mohawk Canyon pipe. Exploration for mineralized 

breccia pipes may be more successful on the upper plateaus 

where dissolution has enlarged the collapse within the upper 

Paleozoic units, in some places more than ten times the 

actual breccia-pipe size, than on the lower plateaus that are 

capped mostly by insoluble rock such as the Esplanade 

Sandstone. This increase in solution collapse within the 

upper plateaus, which are capped by soluble Lower Permian 

and younger rocks, emphasizes the importance of mapping 

all solution features in these areas. 

Many exploration criteria for detecting mineralized 

breccia pipes were developed during geologic mapping of 

the Hualapai Indian Reservation. Mapping began on 

1 :24,000-scale low-altitude color aerial photographs; pipes 

delineated on the photographs were then field checked. 

Many pipes exposed along cliff faces are not recognizable 

in the deep shadows along the cliffs on aerial photographs 

and are best identified from a helicopter. 

The following exploration criteria are considered 

favorable indicators of mineralized breccia pipes: 

1. Concentrically inward-dipping beds. 

2. A circular topographic pattern. This pattern is 

commonly expressed as a topographically high 

rim around a central depression. 

3. Anomalous radioactivity; 2.5 times background 

or higher was considered anomalous during the 

mapping. 

4. Goethite pseudomorphs and molds of pyrite. 

5. Colloform celadonite-stained chalcedony. 

6. Copper mineralization expressed on surface 

exposure as the supergene minerals malachite, 

azurite, brochantite, and chrysocolla. 

7. Breccia, other than intraformational breccias. 

8. Anomalous concentrations in surface samples of 

such trace elements as Ag, As, Cd, Co, Cu, Mo, 

Ni, Pb, Se, V, and Zn. 

9. A circular vegetation or color pattern. 

To verify that a collapse feature mapped from the air 

is actually a breccia pipe, these criteria were checked in the 

field. Few pipes exhibit all these criteria on surface 

exposure, but the more that are present, the greater the 

certainty that the feature is a deep-seated breccia pipe as 

opposed to a shallower collapse structure. 

Although breccia pipes are easily recognized within 

canyons where they are exposed in cross section, large 

expanses of northern Arizona are composed of undissected 

high plateaus. Recognition of pipes in these areas is 

particularly important because ease of access promotes 

mining that would be difficult or uneconomic in the 

canyons. In addition, pipes exposed in canyon walls have 

commonly lost much of their rock, including mineralized 

rock, to erosion and perhaps their metals to leaching. 

Shallow structural basins on the adjacent plateaus are 

probably surface expressions of the upper part of breccia 

pipes. This assumption is supported by the exposure in 

places of a breccia pipe in a canyon wall directly beneath a 

shallow structural basin on the plateau surface (Wenrich, 

1985, fig. 5). Because the ring fracture, which delineates the 

actual pipe, is well exposed in less than half the mapped 

collapse features, and in order to be consistent throughout 

the mapped area, the boundaries of the breccia pipes were 

mapped as the outermost extent of inward-dipping beds. It 

should be emphasized that the area mapped as a solution 

collapse can be as much as five times the size of the actual 

breccia pipe, due to dissolution of the Toroweap and Kaibab 

adjacent to the pipe. 

THE ·MOHAWK CANYON AREA 

The Mohawk Canyon area (fig. 3) is in the National 

Canyon IS-minute, the Vulcans Throne 71/2-minute, and the 

Vulcans Throne SE 7lf2-minute quadrangles in the northeastern corner of the Hualapai Indian Reservation. Rocks in 

the area span the entire Paleozoic sequence of the Grand 

Canyon, from the Cambrian Tapeats Sandstone to the 

Permian Kaibab Limestone (fig. 5). The area is dissected by 

Mohawk Canyon and parts of the Colorado River and 

Prospect Valley. Both Mohawk Canyon and Prospect 

Valley are fault-controlled canyons. Several breccia pipes 

identified in this area contain mineralized rock with 

anomalous concentrations of U, Cu, Ag, As, Pb, and Zn. 

Mapping of Collapse Features 

Most of the collapse structures identified within this 

area are exposed along cliffs; this exposure provides 

sufficient outcrop in three dimensions so that many of these 

collapses have been positively identified as breccia pipes. 

Nineteen of the structures occur on plateaus capped by the 

Kaibab Limestone; outcrop is sufficiently sparse that 

circular erosion patterns and occasional inward-dipping 

beds are the only guides to their recognition as collapses. 

All of the mapped collapse structures fall within three 

Breccia Pipes, Mohawk Canyon Area, Hualapai Indian Reservation, Arizona 07 
IPs 

Qbc 

36° 

07' 

30" 

Q1173-C2 

1172-C?Q 

Pk 

0 0.5 1 MILE 

I ,•, I ''I I I I I 

0 0.5 1 KILOMETER 

Pk 

Pk 

1092-C2 

< 

z 

Geology from Wenrich 

and others ( 19861 

Figure 5 (above and two following pages). Geologic map of the Mohawk Canyon area, Hualapai Indian Reservation, showing 

breccia pipes and collapse features. This area is shown on the geologic and breccia pipe map of the northeastern Hualapai Indian 

Reservation by Wenrich and others (1986). 

08 Breccia Pipes in Northern Arizona 
EXPlANATION 

. SURFICIAL AND VOLCANIC DEPOSITS B Alluvium (Holocene)-Silt, sand, gravel, and eolian 

deposits 

~ . Basaltic cinders and ash (Pleistocene) 

Basalt flows (Pleistocene) 

Intrusive volcanic rocks (Pleistocene)-lncludes dikes, 

plugs, and sills 

~ 

~ Travertine (Pleistocene and Pliocene?)-Includes local calcareous cemented talus commonly in and adjacent 

to travertine 

SEDIMENTARY ROCKS 

Moenkopi Formation (Lower Triassic)-Timpoweap 

Member: Light-brown limestone and chert conglomerate with coarse-grained sandstone matrix; 

clasts are rounded to subrounded. Clasts are eroded 

and contain fossils from the Harrisburg Member of 

the Kaibab Limestone. Forms a cliff 

Kaibab Limestone (Lower Permian)-Harrisburg Gypsiferous and Fossil Mountain Members, undivided; 

Harrisburg Gypsiferous Member consists of slopeforming gray and pale-red shale and gypsiferous 

siltstone interbedded withgray, ledge-forming limestone and dolomitic sandstone; Fossil Mountain 

Member consists of cliff-forming, yellowish•gray, 

cherty, fossiliferous limestone 

Toroweap Formation (Lower Permian)-From top to 

bottom, includes Woods Ranch, Brady Canyon, and 

Seligman Members, undivided; Woods Ranch is palered and gray siltstone interbedded with gray to white 

gypsum, and forms a slope; Brady Canyon consists of 

gray fossiliferous cherty limestone that forms a cliff, 

gradational contacts with Woods Ranch and Seligman 

Members; Seligman consists of pale-red and yellowwhite sandstone of Coconino Sandstone below, thinbedded, medium- to fine-grained quartz sand and 

forms a recess beneath the Brady Canyon cliff 

Coconino Sandstone (Lower Permian)-Yellowishwhite, fine-grained, cross-stratified sandstone. Forms 

prominent light-colored cliff 

Unconformity 0 Hermit Shale (Lower Permian)-Red-brown, slopeforming, fine-grained siltstone and sandstone; fills 

local channels on Esplanade Sandstone 

Unconformity · 

Supai Group (Permian and Pennsylvanian) 

Unconformity 

Esplanade Sandstone (Lower Permian)-Light-red to 

red-brown, cliff-forming, cross-stratified, medium- to 

fine-grained sandstone. Includes slope-forming redbrown siltstone above and below main sandstone cliff 

unit 

Wescogame, Manakacha, and Watahomigi Forma· 

tions, Undivided (Pennsylvanian)-Wescogame 

Formation: Red to pale-red siltstone and shale 

interbedded with thick beds of fine-grained, calcareous sandstone. Forms slope with ledges in upper 

part and a cliff or series of ledges in lower part. Unit 

unconformable with underlying Manakacha Formation. Manakacha Formation: Reddish-brown, thickbedded, fine-grained sandstone with some gray 

cross-bedded dolomitic sandstone. Also consists of a 

few beds of purple-red and gray shale. Forms cliff in 

lower part, slope and ledges in upper part. Unconformable with underlying Watahomigi Formation. 

Watahomigi Formation: Interbedded gray-purple 

calcareous shale and siltstone with gray limestone. 

Limestone contains bands of red and white chert. 

Forms slope with ledges in upper part 

Unconformity '--

Surprise Canyon Formation (Upper Mississippian)-

Dark-red-brown and orange-brown siltstone and 

sandstone interbedded with chert conglomerate and 

hematitic quartz sandstone in lower part. Also 

consists of thin- bedded, yellowish-gray, crystalline 

limestone and gray conglomeratic limestone in upper 

part. Forms slope with some ledges 

Unconformity 

Redwall Limestone (Mississippian)-Includes the 

Horseshoe Mesa, Mooney Falls, Thunder Springs, 

and Whitmore Wash Members, undivided. Lightgray, cliff-forming, thick-bedded, fossiliferous limestone and dolomite. Contains a few beds of chert 

(white), especially in the Thunder Springs Member 

Unconformity 

Temple Butte Limestone (Upper and Middle? Devonian)-Interbedded light-gray to purple dolomite, 

dolomitic sandstone, sandy limestone, reddish-brown 

siltstone, and gray sandstone. Forms series of ledges 

and cliffs 

Unconformity 

~ Muav Limeston~ (Middle Cambrian)-Mottled gray and 

purple dolomitic limestone; lower part contains 

tongues of Bright Angel Shale and a few beds of 

rusty-brown coarse-grained sandstone. Forms series 

of alternating slopes and cliffs about 1,200 ft thick El Bright Angel Shale (Middle Cambrian)-Green and 

purple-red fissile siltstone interbedded with a few 

light-brown, coarse-grained, thin sandstone beds. 

Unit forms a slope with ledges of dolomite and 

sandstone. Gradational contacts with the Muav 

Limestone and the Tapeats Sandstone. Thickness 

15(840) 

+ 

about 400ft 

Tapeats Sandstone (Middle and Lower Cambrian)-

Brown medium- to coarse-grained sandstone and 

pebble conglomerate. Contains a few thin beds of 

green Bright Angel Shale. Forms ledges, not fully 

exposed; estimated 200 ft thick 

Contact 

Fault-Dashed where position uncertain; dotted where 

concealed; bar and ball on down thrown side; number 

shows approximate stratigraphic offset, in feet; 

num.ber in parentheses shows estimated stratigraphic 

offset prior to Holocene deposits 

Monocline-Line showing axis located approximately 

midway between top and bottom hinges of fold; 

dashed where position uncertain; dotted where 

Breccia Pipes, Mohawk Canyon Area, Hualapai Indian Reservation, Arizona 09 
* D 

595 

B 

M 

C1 

C2 

concealed. Length of arrow indicates relative distance 

between hinges 

Volcanic vent-Approximately located 

Outline of collapse feature-Showing number used in 

text 

Strike and dip of beds 

Collapse-feature classification 

Brecciated rock observed in the field 

Mineralized rock (either visible copper or surface 

gamma radiation more than 2Y2 times background 

level present) 

Concentric, inward-dipping beds and visibly altered 

rock (bleaching or limonite staining) 

Concentric, inward-dipping beds; no visibly altered 

rock 

C3 Visibly altered rock; no visible dipping beds 

C4 Distinctly circular feature, either due to vegetation or 

topography; no visibly altered rock or dipping 

beds 

C? A circular feature appears to be present but with no 

obvious dipping beds, altered rock, vegetation 

change, or topographic delineation 

groups: (1) those that are exposed at the top of the Redwall 

Limestone surface along the inner gorge and side tributaries 

to the Colorado River (13 features), (2) those that are 

exposed on the Esplanade surface or along the cliffs in other 

formations of the Supai Group (14 features), and (3) those 

that crop out on the Coconino Plateau as circular features 

and shallow basins on the Kaibab Limestone-capped plateau 

surface (19 features). 

The collapse features in the Mohawk Canyon area 

we~e initially mapped on 1 :24,000-scale color aerial photographs. These features were then field checked, and 46 of 

them were either confirmed as breccia pipes (breccia was 

observed in outcrop) or were considered to be at least 

collapse structures (possible breccia pipes) (table 1, fig. 5). 

A photograph of each of 40 of the 46 mapped collapse 

features allows readers to make their own assessment of the 

potential for these collapse structures to be actual breccia 

pipes (figs. 6-26). Even poorly exposed collapse features 

are included so that readers can find the exact location of 

each collapse feature or breccia pipe described in this paper. 

Those features that are believed by the authors to have good 

potential to be breccia pipes are described in detail. 

Unfortunately, photographs were not available to illustrate 

all field observations that were considered important; nevertheless, a photograph of a collapse feature is commonly 

valuable to other geologists whose criteria might be 

different from those the authors used during this study. 

Geochemical studies were completed on rock samples 

collected from breccia pipes that were categorized as 

mineralized. The concentrations of 55 elements (plus loss 

Dl 0 Breccia Pipes in Northern Arizona 

on ignition) were determined on each sample (table 2). 

These samples generally represent the high-grade material 

from each pipe, collected because they contain gamma 

radiation exceeding 2.5 times background, malachite or 

azurite, goethite, or pyrite. The most accurate analytical 

method used to determine each element is shown in table 2, 

unless the method was not used on a sample; then the results 

from the next-best method are shown. For example, 

Au-HBR (hydrobromic acid digestion with atomic absorption) was only available for five samples, so ICP (inductively coupled argon plasma emission spectroscopy) results 

are listed for the other samples. 

Collapse Features/Breccia Pipes Exposed at 

the top of the Redwall Limestone 

The 13 collapse features/breccia pipes· within the 

Redwall Limestone are considered to have little or no 

economic potential, even though mineralized rock was 

observed at the surface in two of them. This judgment is 

based on the small possible thickness of potential host rock, 

which at most would not exceed 700 ft, and, more 

important, the Redwall is not known to contain U minerals. 

Uranium has not been mined from the Redwall in any 

breccia pipe, although other metals have been (most notably 

copper from the Grandview mine, fig. 1 ). For those pipes in 

this group that contain elevated gamma radiation, the 

anomalies are entirely restricted to downdropped sandstone 

blocks from the Surprise Canyon Formation or the lower 

part of the Supai Group. 

Twelve of the 13 collapse features are readily recognized at the top of the Redwall Limestone cliff. Collapse 

structures 593, 594, 1030, 1032, 1034, 1035, 1076, 1077, 

1080, and 1082 (fig. 6), and 595 and 596 (no photographs 

available) are expressed as amphitheaters eroded back into 

the Redwall cliff and (or) the overlying Watahomigi 

Formation. The thirteenth, 1033, is subtly exposed in a 

gully. Six of these 13 structures are confirmed to be breccia 

pipes. Many of the remaining 7 collapse structures/pipes 

have little outcrop, and only after careful field work does it 

become apparent that what outcrop is present contains beds 

that tilt radially inward. In several of the 13 features, the 

basal part of the Watahomigi Formation dips radially 

inward toward the center of the amphitheater, and (or) is 

dropped down into the Redwall Limestone. Because the 

basal part of the W atahomigi Formation is composed of 

limestone in the Mohawk Canyon area, this unit is as 

unfavorable as the Redwall as a host for U mineralization. 

In contrast to these two limestone units, the organic-rich 

stream-channel deposits of the Mississippian Surprise 

Canyon Formation (Billingsley and Beus, 1985) (fig. 2) 

were good host rocks for U and copper mineralization, 

although only gamma radiation slightly in excess of six 

times background (150 cps (counts per second)) and minor 

I' 
= ... 

t!l 

n 

n 

;;· 

., 

-c· 

t!l 

~ 

~ 0 

=r 

~ ~ 

n 

ll.l 

::I 

~ ::I 

> ;; 

~ 

:I 

c:: 

ll.l 

iii 

"C 

!!!. 

= c.. 

Ai" 

::I 

~ 

t!l 

Ill 

t!l 

~ 

a s· 

... = 

?:' 

j:;j" 

0 

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~ .... 

Table 1. Collapse features/breccia pipes mapped in the Mohawk Canyon area, Hualapai Indian Reservation. 

Feature/ 

PiJ2e No. 

236 

237 

238 

239 

240 

24I 

242 

249 

493 

494 

495 

592 

guadran~le 

National Canyon 

( 15-minut e). 

National Canyon 

(IS-minute). 

National Canyon 

(IS-minute). 

National Canyon 

(IS-minute). 

National Canyon 

(IS-minute). 

National Canyon 

(IS-minute). 

National Canyon 

(IS-minute). 

Vulcans Throne SE 

(7 If2 -minute). 

National Canyon 

(15-minute). 

Vulcans Throne and 

Vulcans Throne SE 

(7 If2 -minute). 

National Canyon 

(IS-minute). 

Vulcans Throne 

(7 1f2 -minute). 

Section, 

TownshiJ2, Ran~e 

None ••••••••••••••• 

None ••••••••••••••• 

None ••••••••••••••• 

None ••••••••••••••• 

None ••••••••••••••• 

Section 7, 

T. 32 N., R. 6 W •

Section 23, 

T. 32 N., R. 7 W. 

Section 33, 

T. 32 Ny• R. 7 W. 

Section 8, 

T. 32 N., R. 6 W. 

Section 26, 

T. 32 N. I R. 7 w. 

None ••••••••••••••• 

Section 29, 

T. 32 N. , R. 7 W. 

Latitude and 

Longitude 

36° 13' 09"" 

112° 57' 43"" 

36° 12' 47"" 

112° 57' 52"" 

36° I2' 40"" 

112° 57' 06"" 

36° I2' 43"" 

112° 13' 32"" 

36° 12' 09"" 

112° 59' 28"" 

36° 10' IS"" 

112° 58' 12"" 

36° 09' 01"" 

112° 59' 56"' 

36° 06' 46"" 

113° 02' 25"" 

36° 10' 04"" 

112° 57' I8"" 

36° 07' 30"" 

II3° 00' 24"" 

36° 12' 30"" 

112° 57' 57"" 

36° 08' 08"" 

113° 02' 59"" 

Category1 

C3, B ••• 

C3, B ••• 

CI, B ••• 

C1, B, M 

C3 •••••• 

C3, B, M 

C3, B, M 

C2 •••••• 

C2 •••••• 

C1, B, M 

Cl, B, M 

C? • • • • • • 

Unit(s)2 

Esplanade, 

lower Supai. 

Lower Supai ••• 

Esplanade, 

lower Supai. 

Esplanade ••••• 

Esplanade ••••• 

Lower Supai ••• 

Esplanade, 

lower Supai. 

Kaibab •••••••• 

Kaibab •••••••• 

Kaibab •••••••• 

Lower Supai. •• 

Kaibab •••••••• 

Comments 

Beds down hillslope within pipe dip 28° N.; conglomeratic 

breccia; bleached center and limonite alteration; massive 

calcite. 

Bleached; conglomeratic breccia. 

Distinct circular topographic shape; no dipping beds. 

Pink- and yellow-stained breccia. 

Sharp contact between bleached and unbleached rock; welldeveloped concentric jointing. 

Two tall pinnacles of breccia surrounded at their base by 

breccia with more rounded clasts, downdropped in an amphitheater. Goethite nodules with malachite rims in breccia. 

Brecciated sandstone with pyrite-bearing siderite concretions. 

Concentric bands of outcropping Kaibab Limestone; distinct 

circular topographic shape, concentric drainage around a 

circular hill; bleached; chert breccia (may be intraformational). Limonite pseudomorphs after pyrite. 

Central hill with inward-dipping (60°) beds of Moenkopi 

Formation(?); concentric depression around hill surrounded 

by a concentric rim (breached on two sides); dissolution of 

Harrisburg Member and Woods Ranch Member gypsum in west slope 

and cliff below collapse. 

Drilled by u.s. Geological Survey in 1984 (Wenrich and others, 

1988); U and Cu minerals present; 19th-century Cu prospect. 

Concentric ring fractures with semicircular drainage eroded 

along one inner ring fracture. Limonite pseudomorphs and 

molds after pyrite. Concentric radially inward dipping beds. 

Dipping beds; bleached; limestone breccia clasts; limonite; 

hematite. 

Dipping beds that may be a collapse into the Toroweap Formation 

gypsum; pale-reddish-orange, crossbedded sandstone (Moenkopi 

Formation?). Largest collapse feature in the Mohawk Canyon 

area. 
0 

-to.) 

~ Table 1. tl) 

n 

n 

;· Feature/ 

"'1:1 Pipe No. 

-s· 

tl) 593 (/) 

;· 

z 

0 594 ::l 

::r 

tl) 

... 

= 

?: 595 

j:;j" 

0 

= Dol 596 

1030 

1031 

1032 

1033 

1034 

1035 

1076 

1077 

1078 

il. 

Collapse features/breccia pipes mapped in the Mohawk Canyon area, Hualapai Indian Reservation-Continued. 

Quadrangle 

Vulcans Throne 

(7 1f2 -minute). 

Vulcans Throne 

(7 1f2 -minute). 

Vulcans Throne 

(7 1f2 -minute). 

Vulcans Throne 

(7 1;2 -minute). 

National Canyon 

(7 1;2 -minute). 

National Canyon 

(iS-minute). 

National Canyon 

(15-minute). 

National Canyon 

(iS-minute). 

National Canyon 

(15-minute). 

National Canyon 

(15-minute). 

Vulcans Throne 

(7 1f2 -minute). 

Vulcans Throne 

(7 lf2 -minute). 

Vulcans Throne 

(7 1f2 -minute). 

Section, 

Township, Range 

None ••••••••••••••• 

None ••••••••••••••• 

None ••••••••••••••• 

None ••••••••••••••• 

None ••••••••••••••• 

None ••••••••••••••• 

None ••••••••••••••• 

None ••••••••••••••• 

Section 12, 

T. 32 N., R. 7 W. 

Section 12, 

T. 32 N., R. 7 W. 

None ••••••••••••••• 

None ••••••••••••••• 

None ••••••••••••••• 

Latitude and 

Longitude 

36° 12' 06" 

113° 02' 54" 

36° 12' 25" 

113° 02' 39" 

36° 12' 42" 

113° 02' 30" 

36° 12' 55" 

113° 01 I 18" 

36° 12' 07" 

112° 58' 27" 

36° 11' 52" 

112° 14' 20" 

36° 11' 09" 

112° 58' 59" 

36° 11' 08" 

112° 59' 19" 

36° 10' 23" 

112° 58' 56" 

36° 10' 28" 

112° 58' 50" 

36° 11' 27" 

113° OS' 02" 

36° 11' 19" 

113° 04' 55" 

36° 11' 24" 

113° 04 '02" 

Category1 

C1, B ••• 

C2, B ••• 

Cl •••••• 

C2 •••••• 

C3 •••••• 

C3, B, M 

C2, B ••• 

C3, B, M 

C1, B ••• 

C4, B ••• 

C2 •••••• 

C? • • • • • • 

C1 •••••• 

Unit(s)2 

Lower Supai, 

Redwall. 

Redwall •••••• 

Lower Supai, 

Redwall. 

Lower Supai, 

Redwall. 

Esplanade, 

lower Supai, 

Surprise 

Canyon, 

Redwall. 

Esplanade, 

Watahomigi. 

Lower Supai, 

Redwall. 

Lower Supai, 

Redwall. 

Lower Supai, 

Redwall. 

Redwall •••••• 

Lower Supai, 

Surprise 

Canyon, 

Redwall. 

Lower Supai, 

Redwall. 

Lower Supai •• 

Comments 

Amphitheater shaped; dipping beds; limonite stains in mediumgrained sandstone. 

Steeply dipping beds; cave in limonite-stained Redwall directly 

~ below pipe. 

Dipping beds; oxidized and bleached; some very small limonitestained spots in the Supai Group. 

Dipping beds? Drainage widens here. 

Amphitheater in the Redwall Limestone with Surprise Canyon 

Formation sediments and one limonite-rich patch exposed. 

Entirely covered with alluvium except for small gully with 

limonite-stained soil and breccia; breccia contains goethite 

and pyrite concretions. Entire gully has anomalous gamma 

radioactivity. 

Amphitheater with Horseshoe Mesa Member of the Redwall Limestone 

strata dropped down into Mooney Falls Member of Redwall 

Limestone. Small breccia outcrop in center of amphitheater; 

minor dip to bedding. 

Limonite and hematite in side of gully; brecciated Horseshoe 

Mesa Member of Redwall Limestone; Surprise Canyon Formation on 

top. 

Very slightly dipping beds; limonite-stained breccia of 

Horseshoe Mesa Member dropped into Mooney Falls Member. 

Amphitheater with breccia in Mooney Falls Member and 20 ft of 

Horseshoe Mesa Member on top. 

Horseshoe Mesa Member barely dipping back into hillslope; 

Surprise Canyon Formation dipping inward. 

Altered and brecciated, possibly related to lava in the area. 

One bleached bed of Wescogame Formation with a very slight dip 

observed. 
.. = 

~ 

n 

n 

;· 

""C:C -a· 

~ 

~ :r 

~ :II:" 

n 

~ 

~ ::s 

~ ~ 

~ 

:::t 

c 

AI 

Dr 

"'C 

!!. 

5" 

a. 

iii" 

::s 

~ 

~ ~ 

~ 

~ a· 

~ 

> .. 

j:i" 

0 

::s 

AI 

c 

.... 

w 

Table 1. Collapse features/breccia pipes mapped in the Mohawk Canyon area, Hualapai Indian Reservation-Continued. 

Feature/ Section, 

Pipe No. Quadrangle Township, Range 

1080 

1081 

1082 

1084 

1085 

1086 

1087 

1088 

1089 

1090 

1092 

1099 

1100 

llOI 

Vulcans Throne 

(7 If2 -minute). 

Vulcans Throne 

(7 If2 -minute). 

Vulcans Throne 

(7 lf2 -minute). 

Vulcans Throne 

(7 Itz -minute). 

National Canyon 

(IS-minute). 

National Canyon 

(IS-minute). 

National Canyon 

(IS-minute). 

National Canyon 

(IS-minute). 

National Canyon 

(IS-minute). 

National Canyon 

(IS-minute). 

National Canyon 

(IS-minute). 

Vulcans Throne SE 

(7 Itz -minute). 

Vulcans Throne SE 

(7 If2 -minute). 

Vulcans Throne SE 

(7 lf2 -minute). 

None ••••••••••••••• 

None ••••••••••••••• 

None ••••••••••••••• 

None ••••••••••••••• 

Section 25, 

T. 32 N., R. 7 W. 

Section 35, 

T. 32 N., R. 7 W. 

Section 3I, 

T. 32 N., R. 6 W. 

Section 29, 

T. 32 N., R. 6 W. 

Section 29, 

T. 32 N., R. 6 W. 

Section 29, 

T. 32 N., R. 6 W. 

Section 17, 

T. 32 N., R. 6 W. 

Section 33, 

T. 32 N., R. 7 W. 

Section 33, 

T. 32 N., R. 7 W. 

Section 5, 

T. 31 N., R. 7 W. 

Latitude and 

Longitude 

36° I2' so·· 

113° 01 I 16" 

36° I2' 07" 

113° 00' 54" 

36° I3' 34" 

113° 01' 42" 

36° I2' 43" 

113° 00' I8" 

36° 07' 30" 

1I2° 13' 57" 

36° 06' 49" 

112° 59' 4I" 

36° 07' I7" 

112° 57 I 30" 

36° 07' 41" 

1I2° 57' I8" 

36° 08' 00" 

II2° 57' 01" 

36° 08' OI" 

II2° 57' 24" 

36° 09' 2I" 

112° 57' 08" 

36° 06' 41" 

I13° 02' 35" 

36° 06' 33" 

II3° 02' 40" 

36° 05' 54" 

113° 03' 19" 

Category1 

C2 •••••• 

CI •••••• 

C2 •••••• 

C2 •••••• 

CI, M ••• 

C?. • • • • • 

C2 •••••• 

C2 •••••• 

C2 •••••• 

C2 •••••• 

C2 •••••• 

Ct •••••• 

CI •••••• 

C?. • • • • • 

Unit(s)2 

Lower Supai, 

Redwall ••••• 

Esplanade, 

lower Supai. 

Lower Supai, 

Surprise 

Canyon, 

RP.dwall ••••• 

Esplanade ••••• 

Esplanade, 

lower Supai. 

Esplanade ••••• 

Kaibab •••••••• 

Kaibab •••••••• 

Kaibab •••••••• 

Kaibab •••••••• 

Kaibab •••••••• 

Kaibab •••••••• 

Kaibab •••••••• 

Kaibab •••••••• 

Comments 

Dipping beds of Redwall Limestone; lobe of travertine dips 

into gully. 

Very large collapse feature (second largest in Mohawk Canyon 

area), on plateau surface and spanning gully; very 

bleached, dipping beds. 

Beds of Horseshoe Mesa Member of Redwall Limestone and 

Surprise Canyon Formation dip into an amphitheater. 

Beds consistently dipping into a closed b~sin. 

Bleaching and limonite staining; base of gully and exposed part 

of pipe is Wescogame Formation. Minor inward dip (toward 

amphitheater). 

Circular drainage around hill; some bleaching. No obvious 

dipping of beds. 

Beds of Harrisburg Member dipping moderately to steeply into 

gully. 

Dipping beds all around the feature in Harrisburg Member; 

Fe-stained chert. 

Dipping beds in Harrisburg Member. 

Dipping beds in Harrisburg Member; no outcrop on three 

sides. 

Very slight bowl at top of Harrisburg Member; on cliffs below 

collapse, Woods Ranch Member of Toroweap Formation is 

largely dissolved away. 

In chert of Harrisburg Member; dipping beds; abundant 

limonite and hematite stains on exposed outcrop and float. 

Dipping Harrisburg Member bed8; limonite stains on chert. 

Dipping Harrisburg Member beds on one side of circular hilt • 
~ ~ 

t:O 

... 

~ 

n 

n 

Ai" 

~ -e· 

~ 

s· 

z 

~ 

:r 

~ 

= 

~ j;;j" 

0 

= Dl 

Table 1. 

Feature/ 

Pipe No. 

1102 

1170 

1171 

1172 

1173 

1174 

1175 

Collapse features/breccia pipes mapped in the Mohawk Canyon area, Hualapai Indian Reservation-Continued. 

Section, 

Quadrangle TownshtgL Range 

Vulcans Throne SE 

(7 lj2 -minute). 

Vulcans Throne SE 

(7 liz -minute). 

Vulcans Throne SE 

(7 liz -minute). 

Vulcans Throne SE 

(7 1;2 -minute). 

Vulcans Throne SE 

( 7 liz -minute). 

Vulcans Throne SE 

(7 liz -minute). 

Vulcans Throne SE 

(71/2-minute). 

Section 8, 

T. 31 N., R. 7 W. 

Section 34, 

T. 32 N., R. 7 w. 

Section 33, 

T. 32 N,, R. 7 w. 

Section 3, 

T. 31 N., R. 7 w. 

Sect ion 4, 

T. 31 N., R. 7 w. 

Section 3, 

T. 31 N., R. 7 w. 

Section 9, 

T. 31 N., R. 7 w. 

Latitude and 

Longitude 

36° OS' 3S" 

113° 03' 40" 

36° 06' 47'" 

113° 01' 29" 

36° 06' 34'' 

113° 01' 4S" 

36° 06' 03" 

113° 01' 23" 

36° 06' 14" 

113° 02' OS" 

36° OS' 42" 

113° 01' 31" 

36° OS' 33" 

113° 01' 47" 

Category1 

C1, M •••• 

C?. • • • • • • 

C2 ••••••• 

C? • • • • • •. 

C2 ••••••• 

C? • • • • • • • 

C2 ••••••• 

Unit(s) 2 Comments 

Kaibab •••••••• Beds dipping consistently around a gully; outcrops of darkorange Fe-rich gossan with radioactivity of 18 times 

background level (SSO counts per second); a possible 

drilling target for U ore in the Harrisburg Member. 

Kaibab •••••••• Harrisburg Member beds dip into stream meander on one side 

of pipe. 

Kaibab •••••••• Concentric Harrisburg Member strata dip radially inward, 

Kaibab •••••••• Harrisburg Member beds dip down hillslope on one side of 

pipe. 

Kaibab •••••••• Concentric Harrisburg Member strata dip radially inward. 

Goethite cubes are pseudomorphous after pyrite. 

Kaibab •••••••• Slightly inward dipping beds of Harrisburg Member on two sides 

of pipe. 

Kaibab •••••••• Harrisburg Member beds dip inward, forming a basin. 

l Refer to "COLLAPSE FEATURE CLASSIFICATION" in figure S. 

2 Geologic unit or units in which collapse feature/breccia pipe crops out. 
Table 2. Chemical analyses of rock samples collected from collapse structures in the Mohawk Canyon area, Hualapai Indian Reservation. 

[The first three or four digits of the sample number, preceding the dash. are the pipe number shown in table 1.] 

Total organSample Latitude Longitude Ag ppm Al 2o3 % As ppm Au ppm Ba ppm Be ppm Total C% ic C%** 

No. ICP XRF AA HBR ICP ICP CID 

237-A-C82 36°12'47" 112°57'52" <2 2.45 4700 * <8 140 (1 0.08 0.03 

238-A-C83 36°12'40" 112°57'06" <2 4.13 99 * <8 1100 (1 0.05 0.05 

239-A-C83 36°12'44" 112°58'46" (2 2.17 100 * (8 200 (1 6.36 0.15 

241-A-C82 36°10'15" 112°58'12" 170 1.4 5000 0.23 46 (1 0.06 0.04 

241-B-C82 36°10'15" 112°58'12" 14 2.21 870 (0.05 47 (1 0.1 0.01 

242-A-C82 36°09'01" 112°59'56" 11 3.23 6800 (0.05 19 (1 0.06 0.02 

242-B-C82 36°09'01" 112°59'56" 3 3.88 2800 * (8 7 (1 (0.01 (0.01 

249-A-C83 36°06'46" 113°02'25" (4 0.69 105 *(20 160 (2 0.23 0.07 

493-A-C83 36°10'04" 112°57'18" (2 0.56 4 * (8 28 (1 12.2 (0.01 

493-B-C83 36°10'04" 112°57'18" <4 (0.1 6.8 *(20 150 <2 0.84 0.09 

= 

~ 494-A-C83 36°07'30" 113°00'24" (10 0.49 36 *<40 150 (5 0.17 0.05 

6:i. 494-B-C83 36°07'30" 113°00'24" <2 14.4 72 *<40 350 (5 0.88 0.06 

~ 494-C-C83 36°07'30" 113°00'24" 100 2.24 400 (0.05 210 (5 1.58 0.57 

j. 495-A-C83 36°12'32" 113°57'50" 4 8.47 3300 * (8 100 (1 0.07 0.05 

~ 593-A-C83 36°12'06" 113°02'54" 21 5.07 5800 (0.05 460 8 0.31 0.19 

~ 

g. 1031-A-C85 36°11'52" 112°59'05" <2 0.69 * 490 * <8 54 (1 0.10 (0.01 

~ 1031-B-C85 36°11'52" 112°59'05" (2 1.78 * 830 * (8 46 <1 0.04 0.04 

~ 1033-A-C85 36°11'08" 112°59'19" (2 5.56 *1900 * (8 23 (1 0.09 (0.01 

Q 1085-A-C85 36°07'27" 112°59'03" <2 6.96 * (10 * (8 270 1 4.29 0.19 

~ 1088-A-C85 36°07'41" 112°57'18" <2 1.57 * 190 * <8 1700 (1 0.13 0.04 0 

::s 

> 1102-A-CBS 36°05'35" 113°03'40" <2 1.00 * 650 * (8 76 <1 0.11 0.05 

~ 1102-B-C85 36°05'35" 113°03'40" (2 0.55 * 570 * <8 120 <1 0.01 <0.01 ~ ------- ~ - Not determined 

~ * ICP data 

~ ** Total organic C% calculated by (total C%)-(total C% as co3 ) 

e!. t INAA data 

~ tt LOI-900= loss on ignition at 900°C 

~ § DN data 

~ ICP = inductively coupled argon plasma emission spectroscopy 

~ XRF = X-ray fluorescence 

~ AA = atomic absorption 

~ HBR = sample digested in hydrobromic acid and bromine and analyzed using AA 

~ CID = combustion with infrared detection 

g CT = coulometric titration > INAA = induced neutron activation analysis 

~ ISE = ion selectiv~ electrode 

g DN = delayed neutron activation analysis 

11.1 

g 

(,/1 
0 

.... 

0"1 

= 

~ t"l 

t"l 

;· 

"'1:1 

-s· 

1'1) 

II> 

5" 

z 

0 

.. 

s1'1) 

.. 

:::1 

:!:' N. 

0 

:::1 

Dol 

Table 2 . Chemical analyses of rock samples collected from collapse structures in the Mohawk Canyon area, Hualapai Indian Reservation-Continued. 

[The first three or four digits of t_he sample number, preceding the dash, are the pipe number shown in table I] 

Total --c% 

Sample as co3 CaO% Cd ppm Ce ppm Co ppm Cr ppm Cs ppm Cu ppm Dy ppm Er ppm 

No. CT XRF ICP ICP ICP ICP AA ICP ICP ICP 

2 3•7 -A-C8 2 0.05 0.44 <2 <4 <I 32 <I 140 <4 <4 

238-A-C83 (0.01 <0.02 (2 23 3 26 <I 180 <4 <4 

239-A-C83 6.21 15. 6 <2 t 6.98 t 12.9 15 t 0.63 190 (4 <4 

241-A-C82 0.02 0.23 15 t 6 t 2.25 11 t 0. 31 10000 t 1.6 <4 

241-B-C82 0.09 0.43 20 <4 <I 76 <I 8800 <4 <4 

24 2 -A-C8 2 0.04 0.51 <2 t 22 t 7.75 42 t 1. 32 460 t 1.5 <4 

242-B-C82 (0.01 0.79 (2 <4 <I 19 1 70 19 <4 

249-A-C83 0. 16 2.61 <4 (8 <2 62 <I 330 <8 <8 

493-A-C83 12. 2 30 (2 <4 13 20 <I 70 <4 (4 

493-B-C83 0.75 3 2. 3 <4 t 1. 7 t 0.94 7 t 0.09 37 (8 <8 

494-A-C83 0. 1 2 0.63 (10 (20 (5 31 (1 40 (20 (20 

494-B-C83 0.74 2.28 (10 t 3 3. 2 t 5.32 140 t 1 1. 4 20 (20 (20 

494-C-C83 l. 01 2.8 30 t 26.5 t 1 1. 9 330 t l. 2 7 14000 (20 (20 

49 5 -A-C8 3 0.02 0.41 (2 56 9 140 1 20 8 <4 

593-A-C83 0. 1 2 0.91 (2 t 9.54 t 38.6 81 t 2. 18 380 39 4 

1031-A-C85 0. 11 1. 7 1 5 t 1.8 t 7 21 t 0.99 120 

1031-B-C85 <O. 01 0.94 5 t 2.6 t 7.2 3 1 t 0.68 92 

1033-A-C85 0.09 0.61 <2 t 43 t 31 53 t 1.1 120 

1085-A-C85 4. 1 19.8 <2 t 40 t 4.5 35 t 7.8 4 

1088-A-C85 0.09 0.72 10 t 5. 1 t 2.5 16 t 0.25 26 

1102-A-C85 0.06 1. 6 9 (2 t 1 1 tl10 59 t 0.57 49 

1102-B-C85 0.03 l. 31 (2 t 5.9 t 11 43 t 0.29 25 
Table 2. Chemical analyses of rock samples collected from collapse structures in the Mohawk Canyon area, Hualapai Indian Reservation-Continued. 

[The first three or four digits of the sample number, preceding the dash, are the pipe number shown in table 1] 

Sample Eu ppm F% T-Fe 2 o3 z1 Ga ppm Gd ppm Hf ppm Hg ppm K2 o% LOI-900tt La ppm 

No. ICP ISE XRF ICP ICP INAA AA XRF ICP 

237-A-C82 <2 0. 01 11.9 <4 (10 - 0. 1 1 0.34 2.8 4 

238-A-C83 <2 0.02 0.49 s <10 - 0.02 0.67 2.03 14 

239-A-C83 t o.ss 0.02 0.61 <4 t 2. 3 7 6.S6 0. 19 0.81 2 3. 5 t 6.S7 

241-A-C82 t 0.34 0.01 1 l. 9 <4 <10 4.66 0.06 0.44 4.S8 t s. 1 

241-B-C82 <2 <O. 01 O.S9 <4 <10 - 0.08 0. 1 9 1. 7 7 4 

~ I'D 

n 242-A-C82 t 0.28 0.02 S6.S <4 10 4.94 0.47 0.93 16.7 t 9.66 n 

Dj" 242-B-C82 <2 <O. 01 3S. s <4 <10 - 0.49 O.S9 20.9 8 

-,::, 249-A-C83 <4 0.14 1.S8 (8 <20 - 0.02 0.07 1.4 1S ~- 493-A-C83 <2 0.03 l. OS <4 <10 - 0. 0 1 0. 1 s 44.4 <2 I'D 

.. "' 4 9 3 -B-C8 3 t 0.03 <0.01 0.06 (8 <20 0.2S <0.01 o.os - t 0.81 

~ 0 

~ 494-A-C83 <10 o. 01 2.68 <20 <SO - o.os 0.07 1.2S <10 llJ 49.4-B-C83 t O.S1 0.33 1S.2 (20 <SO 7.46 0.20 4.6 1 l. s t 19. 3 ~ :~':"' 494-C-C83 t 0.67 0.16 18 <20 t 3.S 2.81 0.30 0.3S 12. 2 t 27.4 

n 495-A-C83 <2 0.02 9.82 16 <10 - 0.2S 0.43 S.S9 28 llJ 

::I S93-A-C83 t 0.32 o.os 63.5 19 <10 1. 81 0. 1 7 o. 7 6 12.05 t 5.7 -< 0 

::I 

?: 1031-A-C8S t 0.27 0.01 59.9 <4 - 0.91 0.04 0. 17 14.4 t 4. 2 

I'D 1031-B-C8S t 0. 11 0.04 6 3. 7 s - 3.4 <O. 14 o.so 10.6 t 3.7 ~ 1033-A-C8S t 0.86 0.02 15 6 - 16 (0.14 0.34 5. 91 t 20 

:::t 1085-A-C85 t 0.79 0.06 0.99 10 - 6.2 <0.02 2.6S 1 7. s t 23 c 

llJ 1088-A-C85 t 0.12 0.02 4.96 <4 - 0.69 <O. 14 0.09 2. 1 1 t 4.6 iii" 

"'C 

e!. 1 1 0 2_-A- C 8 5 t 0.47 0. 10 3. 2 1 4 - 7.6 <O. 14 0. 16 1. 9 3 t 1 1 

:; 1102-B-C85 t Q. 0.24 0.08 2.52 <4 - 3. 1 <O. 14 0.11 1. 48 t 7. 7 

Di. 

::I 

;::IC 2 1 I'D T-Fe 2 o3 = Total iron reported as Fe 2 o , 3 I'D 

... 

< 

~ 

s· 

.. = 

> 

... 

i:r 

0 

::I 

llJ 

g 

~ 
0 

... 

00 

~ t1) 

l"l 

l"l 

~· 

"'1:1 

-s· 

t1) 

II> 

3' 

z 

~ 

=-

~ :I 

~ N' 

0 

:I 

llol 

Table 2. Chemical analyses of rock samples collected from collapse structures in the Mohawk Canyon area, Hualapai Indian Reservation-Continued. 

[The first three or four digits of the sample number, preceding the dash, are the pipe number shown in table 1] 

Sample Li ppm Lu ppm MgO% Mn ppm Mo ppm Na% Nb ppm Nd ppm Ni ppm 

No. AA INAA XRF ICP ICP ICP ICP ICP ICP 

237-A-C82 * 3 - o. 2 1 <4 39 (0.005 <4 (20 40 

238-A-C83 23 - 0.45 9 2 0.08 <4 8 7 

239-A-C83 5 - 10. 1 240 34 0.09 <4 t 8.4 19 

241-A-C82 * 3 <0.085 0.26 5 270 0.05 <4 t 3.7 30 

241-B-C82 *10 - 0.34 3 1 2000 0. 10 <4 <20 15 

242-A-C82 6 0. 13 0.67 <4 140 0.12 7 t 14 39 

242-B-C82 7 - 0. 1 <4 8 0.01 5 <20 35 

249-A-C83 14 - 0.24 82 14 0.06 <8 <8 16 

493-A-C83 * 4 - 19.3 720 5 0.06 <4 <4 16 

493-B-C83 * <4 0.01 1.02 51 6 0.05 <8 <8 <4 

494-A-C83 7 - 0.23 40 <10 0.06 <20 (20 20 

494-B-C83 99 0. 51 3.94 60 (10 0.29 <20 t 1 6. 1 130 

494-C-C83 10 0. 18 2.34 70 140 0.41 <20 t 13.7 70 

495-A-C83 37 - 0. 19 14 5 0.04 <4 21 30 

593-A-C83 9 0. 18 0.94 180 1 1 0.06 14 t 3.3 92 

1031-A-C85 * 8 - 0.50 100 65 0.06 - t 3.3 87 

1031-B-C85 * 6 o. 0 77 o. 55 <4 1 10 0.08 - t 1.3 51 

1033-A-C85 *2 2 0.41 0.57 23 4 0.24 - t 18 78 

1085-A-C85 *17 0.29 1. 0 9 100 <2 0.09 - t 19 30 

1088-A-C85 * 11 0.045 0.14 68 4 0.02 - t 2.5 19 

1102-A-C85 * 1 1 0. 1 5 0. 14 51 760 o. 0 2 - t 7.2 420 

1102-B-C85 * 7 - <0.10 31 450 0.02 - t 5.7 73 

P% 

ICP 

0.02 

0.008 

0.007 

0.07 

o. 11 

0.02 

0.01 

0.63 

o. 03 

(0.01 

0.07 

0.18 

o. 6 2 

0.04 

0.03 

<0.005 

0.009 

0. 0 2 

o. 0 2 

0. 10 

0.49 

0.41 
Table 2. Chemical analyses of rock samples collected from collapse structures in the Mohawk Canyon area, Hualapai Indian Reservation-Continued. 

[The first three or four digits of the sample number, preceding the dash, are the pipe number shown in table l] 

Sample Pb ppm Rb ppm Total-S% Sb ppm Sc ppm Se ppm Si0 2% Sm ppm Sr ppm Ta ppm 

No. ICP AA CID INAA ICP AA XRF ICP ICP ICP 

237-A-C82 60 7 0.03 - <2 20 79.7 (50 51 <40 

238-A-C83 67 12 0.02 - <2 0.6 91 <10 48 <40 

239-A-C83 80 12 <O. 01 23.2 t 2.59 0.2 46 t 2.28 44 t 0.21 

= 241-A-C82 4000 <5 0.54 541 t 0.8 580 76.4 t 1. 16 330 t 0. 13 "'t 

~ 241-B-C82 6300 (5 o. 19 - <2 4.9 92.3 <SO 45 <40 n 

n 

r;;· 242-A-C82 130 1 7 15.3 3 7. 7 t 2. 17 89 21.3 t 1. 57 62 t 0.36 ""CC 242-B-C82 40 16 28.3 - <2 15 37.8 (50 25 40 -s· 

~ 249-A-C83 (8 (10 (0.01 - <4 0. 1 90.4 <20 38 <80 ~"' 493-A-C83 <4 <10 <O. 01 - <2 <O. 1 3. 7 6 <10 90 <40 

c 

~ 493-B-C83 <8 t <2.5 1 7 0.54 t 0. 13 <O. 1 2.26 t 0.085 380 t 0.02 

=- Ill 

~ 494-A-C83 50 <10 0.01 - <10 1.5 92.3 (50 20 <200 ~ 

n 494-B-C83 130 100 0.02 2.22 t 8.86 4.6 4 5. 5 t 2.96 870 t 1. 32 Ill 494-C-C83 12000 <10 0.22 106 t 2.4 350 53.7 t 3. 6 2 1600 t 0.26 = -< 495-A-C83 6 c <10 0. 19 - 11 0.5 71.6 <10 160 (40 

= 593-A-C83 9 <10 0.27 4 3. 1 t 4.89 4.8 16.5 t 0.7 110 t 0.26 

~ ~ 1031-A-C85 230 - 7.44 6.6 t 1.1 300 22 t 0.81 79 t 0.034 .!» 

::t: 1031-B-C85 350 t 2.4 0. 7 1 13 t 1.4 170 22.3 t 0.35 42 t 0. 15 c 1033-A-C85 39 t 9. 2 0. 15 13 t 4. 1 <10 70.9 t 3.9 150 t 0.57 Ill 

rJ" 1085-A-C85 12 - 0.02 0.42 t 7.4 0.2 50.4 t 4. 1 150 t 0.59 "'C 1088-A-C85 51 t 4.8 0.09 1.1 t 0.62 1.9 89.5 t 0.54 57 t 0.062 ~-

5' 

c.. ll02-A-C85 130 - <0.01 25 '(2 1.4 90.3 t 2.2 63 t 0.20 ;· 1102-B-C85 94 - 0.05 7 <2 1.0 9 2. 9 < l.JL- 56 t_ 0. 1 1 = 

~ 

, 

~ 

~ < 

~ s· 

~= 

~ j;j" 

c 

= Ill 

g 

I.C 
0 

t,J 

= 

~ ~ 

~ 

~ 

iii' 

.., 

-ti' 

~ 

"' :;· 

z 

~ 

:r 

~ 

= 

.. > 

§' 

= Slol 

Table 2. Chemical analyses of rock samples collected from collapse structures in the Mohawk Canyon area, Hualapai Indian Reservation-Continued. 

[The first three or four digits of the sample number, preceding the dash, are the pipe number shown in table 1] 

Sample Tb ppm Th ppm Ti% Tm ppm U ppm V ppm y ppm Yb ppm Zn ppm 

No. ICP INAA ICP INAA DN ICP ICP ICP AA 

237-A-C82 (20 §(2.7 0.06 - 3.92 19 2 <1 29 

238-A-C83 <20 §<2.3 0.10 - 2.36 1 7 3 (1 28 

239-A-C83 t ·o. 3 5 2.68 0.05 0. 1 9 1 14 51 8 t 1. 16 15 

241-A-C82 (20 2.7 0.04 - 303 35 3 t 0.88 950 

241-B-C82 (20 *<4 0.06 - 3 3. 9 47 7 <1 140 

242-A-C82 t 0.28 3.63 0. 12 0.14 34.2 30 <2 t 0.89 27 

242-B-C82 <20 § 4. 1 0. 14 - 1.58 14 <2 (1 17 

249-A-C83 <40 §(2.7 0.01 - 5.44 14 21 (2 23 

493-A-C83 (20 §(1. 8 o. 0 2 - 1. 7 9 28 (2 <1 65 

493-B-C83 t 0.02 0.13 (0.01 - 0.32 5 <4 t 0.06 39 

494-A-C83 (1 00 § (3. 1 <0.03 - 4.97 60 <10 <5 440 

494-B-C83 t 0.37 18. 8 0.26 0.46 16. 7 90 20 t 3.37 2200 

494-C-C83 t 0. 4 5 3.03 0.09 0.22 49.5 290 20 t 1. 2 9 16000 

495-A-C83 <20 §16.5 0.52 - 4. 15 130 1 1 2 6 

593-A-C83 t 0.2 3.49 0. 1 0 - 14. 6 2400 6 t 1. 1 5 110 

1031-A-C85 t 0.64 0.64 0.02 - 29.6 170 4 t 0.54 t 130 

1031-B-C85 t 1.9 1. 9 0.05 - 41.8 58 <2 t 0.45 t 280 

1033-A-C85 t 0.6 5. 1 0. 1 5 - 1 2. 3 240 16 t 2.5 t 72 

1085-A-C85 t 0.54 5.8 o. 16 - 3.81 36 13 t 2 t 120 

1088-A-C85 t 0.088 0.59 0.01 - 1. 83 52 3 t<0.34 t 2300 

1102-A-C85 t 0.27 2.6 0.05 - 202 160 10 t 0.97 t 400 

1102-B-C85 t 0.16 1.5 0.03 - 165 68 5 t 0.47 t 230 

Zr ppm 

INAA 

185 

<116 

(56 

12 

238 

208 

<190 

53 
malachite have been observed. Nevertheless, this radioactivity level is in sharp contrast to that of the Redwall 

Limestone, which has not been observed during any study 

by the authors to be greater than 20 cps. Strata of the 

Surprise Canyon Formation have collapsed into at least 3 of 

these 13 collapse features (fig. 6). It is interesting to note 

that throughout the Hualapai Indian Reservation a geographic association exists between the Surprise Canyon 

Formation and the breccia pipes (Wenrich and others, 1986, 

1987; Billingsley and others, 19S6). The Surprise Canyon 

was deposited within the Mississippian karst that developed 

on the Redwall Limestone surface. Evidence that post 

Surprise Canyon collapse occurred within the ·pipes is 

suggested by the tilting of Surprise Canyon strata into 

underlying brecciated Red wall. Only one of the 13 Red wall 

breccia pipes was categorized as "mineralized" ("M" in 

table I), although a limonite-stained, weathered sandstone 

from the lower part of the Supai Group in pipe 593 (fig. 6A) 

did emit gamma radiation equal to two times background. A 

chemical analysis of this material (sample 593-A-C83, 

table 2) shows anomalous concentrations of Ag (21 ppm), 

As (5,800 ppm), Co (39 ppm), Cu (380 ppm), Fe203 

(64%), Hg (0.17 ppm), Ni (92 ppm), U (15 ppm), V 

(2,400 ppm), and Zn (II 0 ppm). These are all elements that 

are commonly anomalous within mineralized breccia pipes. 

Within this group of 13 collapse features/breccia 

pipes exposed in the Redwall Limestone, one breccia 

pipe-I 033-was mineralized by sufficient U to show 

radioactivity of more than 2.5 times background on the 

surface. Pipe 1033 is mostly covered by alluvium, in that the 

only rock exposure is a minor limonite-stained outcrop 

located in a gully (fig. 7A). Some Surprise Canyon 

Formation is associated with brecciated Horseshoe Mesa 

Member of the Redwall Limestone. A pinkish-yellow 

vuggy, calcareous sandstone of the Surprise Canyon 

Formation emitted gamma radiation that exceeded fourtimes background level; Liesegang bands are also prevalent 

in this outcrop (fig. 7 B). Geochemical analysis of this 

sandstone (sample 1 033-A-C85, table 2) shows anomalous 

amounts of As (1,900 ppm), Co, Cu, Hg, Ni, V, and Zn. 

Collapse Features/Breccia Pipes Exposed 

Along Supai Slopes and the Esplanade 

Erosion Surface 

Collapse features/breccia pipes exposed within Supai 

Group rocks are commonly recognized by bleaching of the 

otherwise red Supai rock. Four of the 14 features have 

significant mineralized rock exposed at the surface; 8 of the 

14 have exposed breccia and thus are confirmed breccia 

pipes. Although a sufficient volume of rock necessary to 

host an orebody is present beneath these surficial circular 

features, most of the features are exceptionally inaccessible, 

lying at the bottom of Mohawk Canyon; this inaccessibility 

limits their economic potential. 

Mineralized rock exposed at the surface, as in pipes 

239, 241, 242, and 1031 (fig. 5), is weathered, and the 

primary ore-zone minerals, such as uraninite, pyrite, chalcopyrite, sphalerite, or galena have been oxidized. The primary Cu minerals have oxidized, and Cu presently occurs in 

malachite, azurite, and brochantite. The pyrite has oxidized 

to goethite, which commonly occurs as concretions or cubic 

pseudomorphs after the original pyrite; in places where the 

oxidation is incomplete, the centers of the concretions 

contain remnant pyrite. Sphalerite has oxidized, and the Zn 

presently occurs in surface outcrop as hemimorphite (fig. 8) 

or smithsonite. 

The Supai Group collapse structures/breccia pipes are 

discussed below in order of increasing U potential. 

1078, 1086.-These features (fig. 9) have few of the 

recognition criteria for collapse-feature identification, and 

hence have low potential as mineralized breccia pipes. They 

have bleached sandstone, and feature I 078 has some minor 

inward dip to the beds. 

1 084.-Although this collapse structure (fig. I 0) in 

the uppermost Esplanade Sandstone has no exposed breccia, 

or altered or mineralized rock, it forms a completely closed 

basin with concentrically inward-dipping beds. Surface 

radioactivity was slightly elevated (1.5 times background). 

1081.-This collapse is relatively large with extensive bleaching of the Esplanade Sandstone (fig. 11 ). The 

beds dip inward toward the canyon from all sides; there is 

no breccia, anomalous radioactivity, or any evidence of 

mineralized rock. 

240.-0nly the bleaching of the Esplanade Sandstone 

and concentric fractures delineate this collapse (fig. 12). 

There is a sharp contact between the bleached and unbleached sandstone, but the most striking feature of this 

collapse is the concentric jointing, which bounds the 

collapse on the northeast side. Such jointing is suggestive of 

the concentric ring fractures observed at the Mohawk 

Canyon pipe (Wenrich and others, 1988). 

1085.-This collapse is a large structure (fig. 13) 

located within the exposed top and base of the Wescogame 

Formation. The Esplanade Sandstone is bleached, and some 

pale-yellow limonite staining occurs in a Wescogame 

limestone bed. This unit emitted a maximum gamma 

radiation of three times background. Geochemical analysis 

of a sample from this anomalous area (sample 

1 085-A-C85, table 2) shows essentially no enrichment of 

any of the metals commonly found in breccia pipes, except 

for minor enrichment in Zn (120 ppm). 

239.-This breccia pipe (fig. 14) can be identified 

aJong the slopes of the Supai Group formations through its 

bleached rock with minor tilting of beds, and the small mass 

of breccia exposed a short distance above the Red wall cliff. 

The breccia is stained pink and yellow by hematite and 

limonite alteration. Geochemical analysis of a sample 

Breccia Pipes, Mohawk Canyon Area, Hualapai Indian Reservation, Arizona 021 
022 Breccia Pipes in Northern Arizona 

Figure 6 (above and following page). The amphitheater style of 

erosion of breccia pipes/collapse features exposed along the 

top of the Redwall Limestone cliff, Hualapai Indian Reservation. Pipe and feature localities are shown in figure 5. 

A, Breccia pipe 593; view is about 600ft wide. B, Breccia pipe 

594; view is about 700ft wide. C, Collapse feature 1 030; view 

is about 700 ft wide. D, Breccia pipe 1 032; view is about 

600 ft wide. E, Breccia pipe 1 034; view is about 700 ft wide. 

F, Breccia pipe 1 035; view is about 400ft wide. G, Collapse 

feature 1 076; view is about 600 ft wide. H, Collapse feature 

1 077; view is about 1,000 ft wide. I, Collapse feature 1 080; 

view is about 700 ft wide. J, Collapse feature 1 082; view is 

about 900 ft wide. 
Breccia Pipes, Mohawk Canyon Area, Hualapai Indian Reservation, Arizona D23 
Figure 7. A, Breccia pipe 1033 can be recognized as a pipe 

only by limonite-stained, brecciated outcrops in a gully of 

Surprise Canyon Formation and Horseshoe Mesa Member of 

the Redwall Limestone, Hualapai Indian Reservation. View is 

about 500 ft wide. B, Liesegang-banded and brecciated 

outcrop of Surprise Canyon Formation in breccia pipe 1033. 

Figure 8. Hemimorphite, such as this botryoidal mass, 

commonly forms from surface weathering of primary sphalerite when a breccia-pipe orebody is exposed to oxidation by 

canyon erosion, Hualapai Indian Reservation. 

024 Breccia Pipes in Northern Arizona 

Figure 9. A, Collapse feature 1078 contains some ble;:1ched 

rocks and minor inward dip (arrows) of several beds of 

Wescogame Formation, Hualapai Indian Reservation. View is 

about 800ft wide. B, Collapse feature 1086 (dashed line) lies 

in the Esplanade Sandstone. The only evidence of a possible 

collapse is the bleached Esplanade and a circular gully around 

a hill. Collapse as outlined is about 700ft long. 

Figure 10. Collapse feature 1084 forms essentially a closed 

basin with concentrically inward-dipping beds of Esplanade 

Sandstone. Collapse occupies most of the foreground in this 

photograph. View is about 400 ft wide. 
Figure 11. Collapse feature 1081, Hualapai Indian Reservation, is relatively large with extensive bleaching of the 

Esplanade Sandstone (note the bleached Esplanade on all sides 

of the widened gully; collapse occupies the entire field of 

view). View is about 700 ft wide. 

Figure 12. Collapse feature 240, Hualapai Indian Reservation, shows a striking series of concentric fractures that mark 

its northeastern boundary. 

Figure 13. Collapse feature 1085 (dashed I ine), Hualapai 

Indian Reservation, was identified by bleached Esplanade 

Sandstone and limonite staining in the Wescogame Formation. 

View is about 700 ft wide. 

Figure 14. Breccia pipe 239, Hualapai Indian Reservation, 

has a small mass of breccia (B). View is about 1,000 ft wide. 

(239-A-C83, table 2) of fine- to medium-grained sandstone 

emitting gamma radiation of five times background (85 cps) 

reveals anomalous values for: As (1 00 ppm), Cu (190 ppm), 

Hg (0.19 ppm), Pb (80 ppm), Sb (23 ppm), U (114 ppm), 

and V (51 ppm); these values are not as anomalous as those 

in a Surprise Canyon sample from Redwall collapse feature 

593 (sample 593-A-C83, table 2). 

495.-This breccia pipe (fig. 15) contains highly 

fractured, highly oxidized, bleached sandstone. The breccia 

is composed of limestone and chert fragments with hematite 

squeezed between the clasts. Geochemical analysis of a 

sample (495-A-C83, table 2) that was three times background in sutface radioactivity shows significantly anomalous concentrations of As (3,300 ppm), Cr (140 ppm), Hg 

Breccia Pipes, Mohawk Canyon Area, Hualapai Indian Reservation, Arizona 025 
Figure 15. Breccia pipe 495, Hualapai Indian Reservation, is 

expressed on the surface as bleached rock in a slight recess of 

the hillslope (initial stages of formation of an amphitheater 

along the pipe ring-fracture zone). Pipe as outlined is about 

500ft long. 

(0.25 ppm), and V (130 ppm). Despite the anomalous 

surface radioactivity, the U concentration in this sample was 

only 4 ppm. 

236.-This breccia pipe (fig. 16) is easily located by 

its well-defined surface expression; the breccia pipe sits 

within an eroded amphitheater of Esplanade Sandstone. The 

center of the pipe is bleached and in places stained yellow 

by limonite. Massive calcite is abundant throughout the 

breccia that appears conglomeratic (pipe 241 (fig. 21) has 

similar breccia). No anomalous radioactivity or mineralized 

rock was observed. 

237.-This breccia pipe (fig. 17) is essentially identical to pipe 236 in morphology, stratigraphic horizon, 

alteration, and breccia. Although no anomalous radioactivity was detected, geochemical analysis of a limoniteand hematite-stained sandstone (sample 237-A-C82, 

table 2) shows anomalous amounts of As (4,700 ppm), 

Cu (140 ppm), Fe20 3 (12%), Pb (60 ppm), and Se 

(20 ppm). 

1031.-Alluvium extensively covers this breccia pipe 

(fig. 18) on the slope above the Redwall Limestone cliff; the 

only significant outcrop is a small area of limonite-stained 

sandstone in the upper part of the Watahomigi Formation. 

This sandstone emitted gamma radiation in excess of eight 

times background and contains goethite concretions with 

unaltered pyrite cores. In places, despite the intense 

Figure 16. Breccia pipe 236, Hualapai Indian Reservation, has the ideal pipe morphology: a plug of breccia (B) within an 

amphitheater that has eroded along the ring fracture of the breccia pipe. The plug of breccia is about 200 ft wide. 

026 Breccia Pipes in Northern Arizona 
Figure 17. Breccia pipe 237, Hualapai Indian Reservation, is similar to 236 in morphology, stratigraphy, alteration, and breccia 

(8). Also, it lies directly across from pipe 236 on the opposite side of a tributary canyon to Mohawk Canyon. The mass of breccia 

is about 250 ft wide. 

weathering of the pipe, pyrite was exposed on the surface of 

the outcrop. Two samples containing goethite and pyrite, 

and emitting anomalous gamma counts, were geochemically analyzed (samples 1 031-A-C85 and 1 031-B-C85, 

table 2). Results showed the Fe20 3 content of the two 

samples to be around 60%; As, Cu, Mo, Ni, Pb, Se, U, V, 

and Zn were also present in anomalous concentrations. 

238.-The breccia pipe (fig. 19) is expressed on the 

surface as a bleached amphitheater of Esplanade Sandstone. 

The bleached-unbleached rock contact is sharp. Concentric 

joints encircle the amphitheater, marking the pipe boundary 

where they die out. Brecciated rock (fig. 19B) lies on 

the floor of the amphitheater. No anomalous gamma 

radioactivity was detected in the pipe. Chemical analyses of 

a fine-grained sandstone (sample 238-A-C83, table 2) from 

the pipe show anomalous amounts of few elements except 

for Ba (1,100 ppm), Cu (180 ppm), and Pb (67 ppm). 

242.-This breccia pipe (fig. 20) is one of the two 

most interesting found in the Esplanade Sandstone in the 

Mohawk Canyon area. The breccia column is clearly visible 

in the cliff of Esplanade Sandstone (fig. 20A). The breccia 

is composed of angular fragments of sandstone in a wellcemented matrix (fig. 20B). Large goethite nodules (fig. 

20C), 1 to 3 in. in diameter, are common; these concretions 

have pyrite in their cores and gamma radioactivity in excess 

of 2.5 times background. Chemical analyses of pyrite 

concretions (samples 242-A-C82 and 242-B-C82, table 2) 

show anomalous values of Ag (11 and 3 ppm), As (6,800 

and 2,800 ppm), Cu (460 and 70 ppm), Fe20 3 (57 and 

36%), Hg (0.47 and 0.49 ppm), Mo (140 ppm), Pb (130 and 

40 ppm), Se (89 and 15 ppm), and U (34 ppm). 

241.-This breccia pipe (fig. 21) is the most interesting of the Mohawk Canyon area collapse features 

exposed below the Kaibab Limestone surface, in part 

because of the two silicified pinnacles (fig. 21A) and in part 

because surface samples arc mineralized. This is the only 

pipe in the Mohawk Canyon area with silicified spires 

similar to the Blue Mountain pipe (pipe 287 in Billingsley 

and others, 1986; Van Gosen and others, 1989) and pipe 237 

(Wenrich and others, 1986) located to the south and west on 

the Hualapai Indian Reservation and previously drilled by 

Western Nuclear in the 1970's. Except for the Orphan mine, 

none of the other U-producing breccia pipes have had 

exposures of silicified breccia. Such exposures subject the 

pipes to oxidation and removal of much of the ore body. The 

brecciated column of pipe 241 abuts against undeformed 

Breccia Pipes, Mohawk Canyon Area, Hualapai Indian Reservation, Arizona D27 
Figure 18. Breccia pipe 1031, Hualapai Indian Reservation, 

is almost totally covered by alluvium except for this small 

outcrop containing goethite (g) and pyrite nodules that emitted 

gamma radiation exceeding eight times background level. 

028 Breccia Pipes in Northern Arizona 

sandstone (fig. 21B). The breccia itself has a conglomeratic 

appearance of rounded cobbles in a well-cemented matrix 

(fig. 21 C). The chemical analyses of breccia samples 

(241-A-C82 and 241-B-C82, table 2) speckled with green 

malachite show anomalous concentrations of most elements 

commonly enriched in breccia-pipe orebodies: Ag ( 170 and 

14 ppm), As (5,000 and 870 ppm), Cu (1 and 0.9%), Mo 

(2,000 and 270 ppm), Pb (6,300 and 4,000 ppm), Sb (541 

ppm), U (303 and 34 ppm), and Zn (950 and 140 ppm). 

Collapse Features/Breccia Pipes Exposed in 

the Hermit Shale, Coconino Sandstone, and 

T oroweap Formation 

No collapse structures have been observed to date 

(1990) in the Mohawk Canyon area between the Esplanade 

surface and the Kaibab Limestone. This absence of features 

is probably because: (1) many of the pipes top out by the 

time they reach the Esplanade Sandstone; (2) there is little 

exposure of the red slope-forming Hermit Shale, which is 

commonly covered by alluvium; and (3) the vertical cliffs of 

Coconino Sandstone and Toroweap Formation expose little 

rock of these units relative to the total exposure of 

Esplanade along its flat erosion surface; in addition, any 

bleaching in the already white cliff-forming Coconino 
Sandstone and Brady Canyon Member of the Toroweap 

Formation could be easily overlooked. Even though fewer 

pipes stoped all the way to the Kaibab Limestone, 

dissolution of gypsum in the underlying Toroweap and 

gypsum and limestone in the Kaibab accentuate and enlarge 

any surface expression of pipes that did reach the Coconino 

Plateau surface. This surface consists of at least as much 

exposed rock in the Mohawk Canyon area as does the 

Esplanade erosion surface, yet it contains 19 collapse 

features in contrast to the 14 expo.sed along the Esplanade 

surface. Of course, some of the 19 Kaibab collapse features 

probably extend no deeper than the Harrisburg Gypsiferous 

Member of the Kaibab Limestone or the Woods Ranch 

Member of the Toroweap Formation (fig. 4). These 

shallow-seated collapses are most likely the "Kaibab" 

collapses listed under "Category" in table 1 as "C?." 

Collapse Features/Breccia Pipes Exposed on 

the Kaibab Limestone-Capped Plateaus 

Within the Mohawk Canyon area, on this part of the 

Coconino Plateau, the highest plateau surfaces are capped 

by the Harrisburg Gypsiferous Member of the Kaibab 

Limestone. The redbeds composing the top 200 ft of 

Harrisburg have been stripped from this part of Arizona, 

leaving the white bottom 100 ft of Harrisburg to cap the 

Coconino Plateau. 

Despite the exposure of mineralized rock in some of 

the Esplanade collapses, such as 241 and 242, collapse 

structures 249, 1102, 493, and 494 (listed in increasing 

order of favorability), exposed on the Kaibab Limestone 

surface (Coconino Plateau), are considered to be the pipes 

with the most potential for U ore in the Mohawk Canyon 

area. Compared to other features in the area, they are by far 

Figure 19 (above and facing page). Breccia pipe 238, Hualapai Indian Reservation. A, The pipe is expressed on the 

surface as a bleached amphitheater with the breccia column 

exposed on the amphitheater floor. View is about 600ft wide. 

B, Brecciated rock from the breccia column in pipe 238. Note 

the minor vugs throughout the breccia. 

Figure 20. Breccia pipe 242, Hualapai Indian Reservation. 

A, Breccia (B) is clearly visible in the cliff of Esplanade 

Sandstone. View is about 700 ft wide. B, The breccia is 

composed of angular fragments of sandstone within a vuggy, 

well-cemented matrix. C, Large goethite nodules (g), with 

remnant pyrite cores and anomalous gamma radioactivity, 

altered from pyrite concretions. 

Breccia Pipes, Mohawk Canyon Area, Hualapai Indian Reservation, Arizona D29 
the most accessible, and if an orebody is present, the total 

tonnage of U 30 8 is believed to be greater than that which 

might remain in the dissected pipes exposed along the 

Esplanade cliffs and Esplanade erosion surface. 

Fourteen of the 19 collapse features found on the 

Kaibab Limestone-capped plateau have inward-dipping 

beds; 10 of these features have no anomalous radioactivity, 

altered or mineralized rock, or breccia. Other than the four 

Kaibab collapses that contain altered, radioactive, or brecciated rock, geophysical, geochemical, or drilling surveys 

would be needed to determine whether the other features 

formed due to an underlying breccia pipe or merely from 

dissolution of the Kaibab Limestone or Toroweap Formation. It is known from drilling at pipe 494 that the 

Woods Ranch (gypsum-bearing) Member of the Toroweap 

Formation has been almost totally removed (Wenrich and 

others, 1988) within the pipe, despite its presence in the cliff 

exposure on either side of the pipe. In the cliffs adjacent to 

some of these 15 "C2" or "C?" (fig. 5) collapses, the Woods 

Ranch Member can be seen to thin to only a few feet. 

Whether the draping of the overlying beds and dissolution 

of this member is due to weathering along the canyon face, 

causing localized collapse, or is due to fluids moving 

through a breccia pipe and dissolving these units, cannot be 

determined without drilling or AMT (audio-magnetotelluric) geophysical surveys. Beds of Harrisburg Gypsiferous 

D30 Breccia Pipes in Northern Arizona 

Member dip inward at collapse structures 592, 1101, 1170, 

1172, 1174, 1087, 1088, 1090, 1189, 1175, 1092, 1099, 

1100, 1171, and 1173 (listed in increasing order of potential 

as breccia pipes). All of these collapse structures except 

1170, 1172, 1174, and 1175 are shown in figure 22. 

592, 1101, 1170, 1172, and 1174.-All five of these 

features are considered very questionable as breccia pipes. 

They are all exposed in the Harrisburg Gypsiferous Member 

of the Kaibab, are vaguely circular on the 1 :24,000-scale 

aerial photographs, and have minor inward dip of some of 

the strata. 

1087,1088,1089,1090,1092,1099, 1100,1171,and 

1173 .-All nine of these collapse features have beds with a 

significant inward dip and appear more circular on the aerial 

photographs than the five features listed above. Also, 

features 1088 and 1100 have some iron-stained chert, and 

1099 has abundant limonite-stained rock within the pipe. 

Soil geochemical surveys were completed over features 

1171 and 1174; the results will be released in a separate 

report. Geochemical analysis of an iron-stained sample 

(1 088-A-C85, table 2) from collapse feature 1088 shows 

minor enrichment of As (190 ppm), Ba (1 ,700 ppm), Cd 

(1 0 ppm), and Pb (51 ppm), and a significant enrichment of 

Zn (2,300). 

249.-This feature is a classic example of a small hill 

of flat-lying strata completely encircled by concentrically 
Figure 21 (above and facing page). Breccia pipe 241, Hualapai Indian Reservation. A, The pipe is expressed on the surface 

as two silicified pinnacles of breccia on the floor of an 

amphitheater eroded out of the Esplanade Sandstone. View is 

about 700 ft wide. B, The breccia column (B) abuts against 

untilted sandstone (SS). C, The breccia has the appearance of 

a conglomerate. Photograph is of the area in figure 21 B that the 

man is pointing to. 

inward-dipping beds; a moat lies between the hill and the 

dipping beds (fig. 23). This exposure of Harrisburg Gypsiferous Member appears bleached, although such alteration is 

difficult to identify in a rock that is normally white (such as 

this part of the Kaibab Limestone). Chert breccia is present, 

although it is possibly an interfmmational breccia of the 

Harrisburg and unrelated to pipe brecciation. No anomalous 

radioactivity or mineralized rock is apparent. A sample of 

hematite-stained chert breccia (90% Si02) was submitted 

for geochemical analysis (sample 249-A-C83, table 2). 

Although not visibly mineralized, it did contain elevated As 

(1 05 ppm) and Cu (330 ppm) concentrations. A soil 

geochemical survey was completed over this feature, but the 

data will be presented in a separate report. The geochemical 

results (table 2) along with the collapse morphology, 

specifically the moat (which may represent the more easily 

dissected ring-fracture zone of a deep-rooted breccia pipe), 

make this feature a favorable target for further exploration. 

1102.-At this collapse feature, the beds of Harrisburg Gypsiferous Member dip inward toward a central 

drainage (fig. 24A). The morphology is not distinctly 

circular as it is at feature 249 (described above). Small 

outcrops and float of gold to orangish-brown Fe-rich 

silicified gossan are scattered about the center of this feature 

(fig. 24B). The measured gamma radioactivity reached 550 

cps (18 times background) over the gossan. Except for the 

Blue Mountain pipe (pipe 287, Billingsley and others, 1986; 

Van Gosen and others, 1989), this feature has the highest 

surface radioactivity found anywhere on the Hualapai 

Indian Reservation; such levels of gamma radiation are 

particularly rare on the Kaibab erosion surface. Two 

samples from the gossan (11 02-A-C85 and 1102-B-C85, 

table 2) were geochemically analyn·d and indicate a striking 

enrichment of elements commonly associated with brecciapipe orebodies: As (650 and 570 ppm), Co (110 and 11 

ppm), Mo (760 and 450 ppm), Ni (420 and 73 ppm), Pb 

(130 and 94 ppm), Sb (25 and 7 ppm), U (202 and 165 

ppm), V (160 and 68 ppm), and Zn (400 and 230 ppm). Soil 

geochemical samples were collected over this feature, but 

the results will be discussed in a separate report. An AMT 

geophysical survey was completed by Flanigan and others 

(1986). The two (east-west and north-south) AMT cross 

sections indicate three vertical conductive zones that extend 

from about 300 ft to 2,400 ft below the collapse surface 

exposure. Flanigan believed that the central conductive 

zone represented the pipe core, and the outer two zones the 

ring fractures. Hence, Flanigan and others (1986) concluded 

that feature 1102 was a deep-seated breccia pipe. These 

AMT results and the anomalous surface geochemistry 

certainly suggest that collapse 1102 holds excellent 

economic potential as aU-mineralized breccia pipe. 

493.-This is one of the larger collapse fea~ures in the 

Mohawk Canyon area, about one-third mile in diameter. 

Like feature 249, this structure is a classic example of a 

small hill almost totally encircled by a moat that is 

surrounded by higher hills (fig. 25) of Harrisburg Gypsiferous Member. The central hill contains concentric sets of 

Breccia Pipes, Mohawk Canyon Area, Hualapai Indian Reservation, Arizona 031 
Figure 22 (above and facing page). Collapse features in the 

Mohawk Canyon area, Hualapai Indian Reservation, on the 

Kaibab Limestone-capped plateau that are expressed solely as 

inward-dipping beds, with no evidence of surface alteration, 

brecciation, or mineralization. Photographs taken from a helicopter. A, Collapse feature 592; dashed line shows feature. 

Collapse as outlined is about 2,500 ft wide. B, Collapse feature 

1101; dashed line shows feature. View is about 900 ft wide. 

C, Collapse feature 1 087; dashed line shows feature. View is 

about 1,000 ft wide. D, Collapse feature 1088. The entire field 

of view is within the collapse; the junction of the gullies is the 

center of the collapse. View is about 700ft wide. E, Collapse 

032 Breccia Pipes in Northern Arizona 

feature 1 089; dashed line shows feature. View is about 600ft 

wide. F, Collapse feature 1 090; dashed line shows feature. 

View is about 500 ft wide. G, Collapse feature 1 092; dashed 

line shows feature. View is about 1,000 ft wide. H, Collapse 

feature 1 099; dashed line shows feature. View is about 800ft 

wide. I, Collapse feature 11 00; the entire foreground is within 

the collapsed area. View is about 1,000 ft wide. J, Collapse 

feature 1171; note the concentric inward-dipping beds in the 

center of the photograph. Diameter of the collapse as viewed 

is about 800ft. K, Collapse feature 1173; dashed line marks the 

area of collapse and inward-dipping beds. Length of the 

collapse as outlined is about 700 ft. 
perfectly circular rings of unusually steep (nearly vertical 

toward the center), inward-dipping beds around a center of 

red soil. This red soil could be downdropped Triassic 

Moenkopi Formation strata; if so, there has been more than 

200 ft of downdrop at the present Harrisburg erosion level 

because the upper 200ft of red Harrisburg (the stratigraphic 

distance between the present plateau surface and the Moenkopi Formation) has been stripped from the plateau surface. 

Only the basal 100 ft of white Harrisburg remains, capping 

the plateau surfaces in the Mohawk Canyon area. 

A ground magnetometer survey over this feature 

yielded an anomalous magnetic high over the middle of the 

central hill, adjacent to an area of an anomalous magnetic 

low, just outside the eastern rim of the central hill (Van 

Gosen and Wenrich, 1989). These data suggest that the 

central hill contains a significant thickness of sedimentary 

rocks, such as the redbeds of the Harrisburg or the Moenkopi Formation, that are more magnetic than the rock of the 

surrounding hillsides. 

Along the Mohawk Canyon cliff on the extreme 

western edge of the collapse, the gypsiferous Woods Ranch 

Member thins to about 30 ft in thickness just beneath the 

collapse (fig. 25C). Also, a cave, just beneath the collapse in 

the Fossil Mountain Member of the Kaibab Limestone (fig. 

25C), attests to increased dissolution directly beneath this 

structure. Geochemical analyses of samples ( 493-A-C83 

and 493-B-C83, table 2), taken, respectively, from the 

central ring of inward-dipping beds and from gypsumbearing altered beds on the western edge of the collapse, 

show essentially no anomalous elements (the most anomalous element was Cu at 70 ppm). Such low concentrations 

of ore-bearing metals are discouraging in contrast to 

samples from some other pipes in the Mohawk Canyon area 

(table 2). A soil geochemical survey was also completed 

over this collapse; the results will be published in a separate 

report. 

Breccia Pipes, Mohawk Canyon Area, Hualapai Indian Reservation, Arizona 033 
Fourteen AMT soundings by Flanigan and others 

(1986) were completed over collapse 493. The north-south 

cross section illustrates a striking, perfectly vertical zone of 

very high conductivity from about 100ft below the surface 

of the collapse down to the base of the survey, 3,000 ft. 

Such results strongly suggest that not only is feature 493 a 

breccia pipe, but it is also entirely vertical, without the 

034 Breccia Pipes in Northern Arizona 

Figure 23 (above and facing column). Collapse feature 249, 

Hualapai Indian Reservation. A, The small hill is completely 

encircled by concentrically inward-dipping beds. Between the 

hill and the concentric beds is a moat that perhaps represents 

the more easily eroded ring-fracture zone surrounding a 

downdropped plug overlying a breccia core. Photograph taken 

from a helicopter. The diameter of the outline made by the 

concentric beds is about 1,000 ft. B, View of collapse feature 

249 on a 1 :24,000-scale aerial photograph (center of figure). 

bending shape that plagues many pipes (such as pipe EZ-2, 

AMT profile shown by Flanigan and others, 1986), making 

orebody delineation very difficult. Hence, the vertical, 

highly conductive zone beneath the collapse (AMT results), 

the collapse morphology, and the dissolution of the 

underlying Toroweap (see the section on "Woods Ranch 

dissolution in Mohawk Canyon pipe," Wenrich and others, 

1988) suggest that feature 493 has good potential as a 

U-mineralized breccia pipe, and it certainly warrants 

exploratory drilling. 

494 (Mohawk Canyon pipe).-This breccia pipe (fig. 

26) is considered to have the greatest potential for an 

orebody of any pipe on the Hualapai Indian Reservation. It 

was originally identified as a collapse by the senior author 
Figure 24. Collapse feature 1102, Hualapai Indian Reservation. A, Strata of Harrisburg Gypsiferous Member dip slightly 

inward toward a central drainage (center of photograph). 

Collapse as outlined is about 300 ft long. B, Small outcrops 

and float of orange-brown, Fe-rich gossan (G) emitted gamma 

radioactivity exceeding 18 times background level. 

in June 1983 while mapping collapse structures in the 

Mohawk Canyon area. Although the tum-of-the century 

Grand Canyon miners probably did not recognize this area 

as a breccia pipe, they obviously discovered its Cu minerals 

(malachite, azurite, and chrysocolla) during the 19th century-this timing is suggested by the square nails in the 

timbers that are lying about on the ground near two adits 

driven into the west side of Mohawk Canyon, at the cliff 

edge. The ad its lie on the outermost ring fracture of the pipe. 

An AMT survey could not be made over this pipe 

because of its proximity to the cliff. A soil survey was 

completed; the results will be released in a separate report. 

A ground magnetometer survey revealed a dipole anomaly 

(Van Gosen and Wenrich, 1989). The dipole high is over the 

core of the pipe, suggesting that the downdropped core may 

contain some of the redbeds (presently bleached) of the 

Harrisburg Gypsiferous Member, which have been stripped 

from the surrounding areas. In fact, lithologic logs from 

drilling indicate 210 to 255 ft of Harrisburg in the core 

(Wenrich and others, 1988)-only the basal 100ft are the 

normally white, less magnetic, Harrisburg. 

The pipe was selected for exploratory drilling during 

July-November 1984 because it exhibited the following 

exploration criteria: 

1. Concentrically inward-dipping beds of Kaibab 

Limestone (fig. 26B). 

2. A circular drainage pattern. 

3. Anomalous surface radioactivity-as much as 

five times background. 

4. Goethite pseudomorphs and molds of pyrite. 

5. Colloform celadonite-stained chalcedony. 

6. Supergene Cu minerals, such as malachite, 

azurite, brochantite, and chrysocolla. 

7. Breccia. 

8. Anomalous concentrations in surface exposure of 

several elements (Cu ore sample, 494-C-C83, 

table 2), such as Ag (100 ppm), As (400 ppm), Cr 

(330 ppm), Cu (1.4%), Fe20 3 (18%), Hg (0.3 

ppm), Mo (140 ppm), Ni (70 ppm), P (0.62%), 

Pb (1.2%), Sb (106 ppm), Se (350 ppm), Sr 

(1 ,600 ppm), U (50 ppm), V (290 ppm), and Zn 

(1.6% ). 

Five holes were drilled. The gamma log from one hole, 

penetrating to a depth of 1,335 ft, shows a 1-ft interval of 

0.52% eU30 8 at a depth of 1,191 ft and a 20-ft zone 

averaging 0.04% U30 8 from 1,191 to 1,211 ft of depth 

(Wenrich and others, 1988); this depth is the same stratigraphic horizon as the top of orebodies in active brecciapipe mines, located on similar plateaus capped with the 

Harrisburg Gypsiferous Member of the Kaibab Limestone. 

Zones of sulfide mineralization in the drill core include 

crystals of galena, 1-3% pyrite, and minor bravoite. A 

detailed discussion of the drilling results, including lithologic and geophysical logs, can be found in Wenrich and 

others (1988). Although the 1-ft-thick zone of high-grade U 

is hardly an orebody, the grade of 0.52% eU30 8 is near the 

average grade mined from those northern Arizona breccia 

pipes that host orebodies (Mathisen, 1987). Sufficient 

mineralized rock was verified in the Mohawk Canyon pipe 

that additional drilling is warranted to determine whether an 

orebody is present. 

Breccia Pipes, Mohawk Canyon Area, Hualapai Indian Reservation, Arizona 035 
CONCLUSIONS 

The Mohawk Canyon area has a greater concentration 

of surface-mineralized collapse features than anywhere else 

on the Hualapai Indian Reservation. Those collapse features 

exposed in the Redwall Limestone and overlying lower part 

of the Supai Group are not considered to have any potential 

036 Breccia Pipes in Northern Arizona 

Figure 25 (above and facing column). Collapse feature 493, 

Hualapai Indian Reservation. A, A small hill of concentrically 

inward dipping beds is almost totally encircled by a moat that 

is surrounded by higher hills. Rim to rim, the feature is about 

1,600 ft wide. B, photograph of 493 taken from low-Z~Ititude 

aerial photography (1 :24,000 scale); dashed line shows 

feature. Note the outer concentric ring of beds on the central 

hill. C, The Woods Ranch Member of the Toroweap Formation 

thins to about 30 ft in thickness near collapse feature 493 

(arrow). Also notice the cave (C) in the Fossil Mountain 

Member of the Kaibab Limestone just below the coiiJpse 

feature. The western edge of the collapse can be recognized by 

the amphithPC~ter beginning to develop at the top of the cliff. 
for U orebodies. Of the 46 collapse features mapped in the 

area, 6 should undergo additional exploration surveys, 

including the Mohawk Canyon pipe (494) that was drilled 

and discovered to contain U concentrations as high as 0.52 

percent eU 30 8. Three of the six features, 241, 242, and 494, 

are confirmed breccia pipes that have been mineralized. The 

other three, 249, 493, and 1102, have not been dissected by 

canyons, so no brecciated rock is exposed, although 1102 

has an Pe-rich gossan developed on its surface that is more 

radioactive than any other examined rock exposed on the 

Hualapai Indian Reservation (except at the Blue Mountain 

pipe). 

Brec?ia pipes 241 and 242 lie on the Esplanade 

erosion surface at the bottom of Mohawk Canyon, and 

although they are known to have been U mineralized, they 

have two negative economic considerations: (1) They are 

inaccessible by vehicle and difficult to reach even on foot; 

and (2) the top 1,500 ft of rock, that rock which hosts most 

of the ore in all of the past or presently active breccia-pipe 

U mines, has been eroded away. The other four favorable 

features crop out on the Coconino Plateau and are 

reasonably accessible; 493 and 494 have roads to them. 

Classic breccia-pipe morphologies are developed over 249, 

493, and 494. 

The morphology of collapse feature 249 strongly 

suggests the presence of an underlying breccia pipe. Such 

morphology, of concentric inward-dipping beds of the 

Harrisburg Gypsiferous Member of the Kaibab Limestone 

enclosing a moat that surrounds a central hill of flat-lying 

strata, probably results from a ring-fracture zone (less 

resistant to erosion) underlying the "moat". This ringfracture zone bounds an underlying breccia pipe. Although 

249 is not considered as favorable a feature as 1102, 493, 

and 494 for hosting a U orebody, it should certainly be 

explored further. 

The dissolution of the Woods Ranch Member of the 

Toroweap Formation, adjacent to and under feature 493 

(similar to what was observed while drilling feature 494), 

makes this structure a favorable target, as do ( 1) the AMT 

results that show a vertical, pipe-shaped zone of high 

conductivity lying beneath the surface collapse structure, 

and (2) the nearly vertical, inward-dipping beds that enclose 

red soil at the center of the collapse. The red soil is either 

weathered Harrisburg Gypsiferous Member (upper 200 ft of 

redbeds in the Kaibab Limestone) or Moenkopi Formation, 

suggesting that ( 1) a minimum of 40 ft of downdrop 

occurred if the soil is weathered Harrisburg strata (the red 

soil is about 40 ft below the top of the enclosing basal 

100 ft of white Harrisburg), or (2) 200 ft of downdrop 

occurred if it is weathered Moenkopi Formation. 

The anomalous gamma radioactivity of 18 times 

background at the surface of feature 1102, as well as the 

exceptionally elevated concentrations of As, Co, Mo, Ni, 

Pb, Sb, U, V, and Zn in the Pe-rich gossan, make this feature 

an excellent exploration target for an ore body. The geochemical results of 165 ppm U for the sample that emitted 

gamma radioactivity of 18 times background suggests that, 

at least for the surface exposure, the U gamma radioactivity 

and U content are approximately in chemical equilibrium. 

That is, the background U concentration in this rock is about 

4-8 ppm. The high conductivity zones delineated underneath this feature by an AMT survey also strongly suggest 

that this is a breccia pipe (Flanigan and others, 1986) rather 

than a near-surface, unmineralized gypsum or limestone 

collapse. 

Collapse feature 494 is considered to have the greatest potential for a U orebody on the Hualapai Indian 

Reservation because it has been proven through drilling to 

be both U mineralized and a breccia pipe. A 1-ft interval of 

0.52 percent eU30 8 (which as shown at feature 1102 is in 

approximate chemical equilibrium) was found in drilling, 

along with minerals such as bravoite, galena, and pyrite that 

are always associated with the uraninite ore in northern 

Arizona breccia pipes. 

It is interesting to note that these six favorable 

structures lie in a northeast-trending zone (fig. 5), similar to 

breccia-pipe alignments on the Marble Plateau shown by 

Sutphin and Wenrich (1983) and Sutphin (1986). Wenrich 

and others (1986) pointed out a similar northeast alignment 

of the Ridenour mine and three other mineralized pipes· just 

to the west of the Mohawk Canyon area. 

Finally, any additional exploration in this area should 

concentrate on ( 1) additional drilling of pipe 494 (see 

Wenrich and others, 1988, for recommended sites); 

(2) exploration surveys such as those for Bacillus cereus or 

helium soil gas, plus magnetometer surveys over features 

249, 493, and 1102, and an·AMT survey over 249; and 

(3) exploratory drilling of 493 and 1102. 

ACKNOWLEDGMENTS 

This study was funded by the U.S. Bureau of Indian 

Affairs in cooperation with the Hualapai Tribe. Much 

appreciation goes to Hoyt Sutphin who provided mapping 

assistance in the early and late stages of this project. His 

continued assistance, enthusiasm, and exchange of ideas 

contributed to many of our conclusions. Chuck Spirakis 

critically reviewed the manuscript, and his suggestions were 

greatly appreciated and incorporated. Also, special thanks to 

helicopter pilots Mike Bertoldi and Dana Morris for safely 

and competently transporting us in hazardous flying 

conditions to all 46 collapse features in the study area. 

Breccia Pipes, Mohawk Canyon Area, Hualapai Indian Reservation, Arizona 037 
REFERENCES CITED 

Billingsley, G.H., and Beus, S.S., 1985, The Surprise Canyon 

Formation-An Upper Mississippian and Lower Pennsylvanian(?) rock unit in the Grand Canyon, Arizona, in 

Stratigraphic notes, 1984: U.S. Geological Survey Bulletin 

1605-A, p. A27-A33. 

Billingsley, G.H., Wenrich, K.J., 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 plates, scale 

1:48,000. 

Casadevall, W.P., 1989, Exploration geology of Canyon breccia 

pipe south of Grand Canyon, Arizona [abs.]: American 

Association of Petroleum Geologists Bulletin, v. 73, no. 9, 

p. 1150. 

Flanigan, V.J., Mohr, Pamela, Tippens, C.L., and Senterfit, R.M., 

1986, Electrical character of collapse breccia pipes on the 

Coconino Plateau, northern Arizona: U.S. Geological 

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

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

and alteration, Orphan mine, Grand Canyon, Arizona: 

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

Gornitz, V., Wenrich, K.J., Sutphin, H.B., and Vidale-Buden, R., 

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. 

038 Breccia Pipes in Northern Arizona 

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. I 6, p. 179-

186. 

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. 

Mathisen, I.W., Jr., 1987, Arizona Strip breccia pipe programExploration, development, and production [abs.]: American 

Association of Petroleum Geologists Bulletin, v. 71, no. 5, 

p. 590. 

Sutphin, H.B., 1986, Occurrence and structural control of collapse 

features on the southern Marble Plateau, Coconino County, 

Arizona: Flagstaff, Ariz., Northern Arizona University M.S. 

thesis, 139 p. 

Sutphin, H.B., and Wenrich, K.J., 1983, Structural control of 

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

Geological Survey Open-File Report 83-90R, 6 p., 2 plates, 

scale 1:50,000. (Superseded by Sutphin, H.B., and Wenrich, 

K.J ., 1988, Map showing structural control of breccia pipes 

on the southern Marble Plateau, north-central Arizona: U.S. 

Geological Survey Miscellaneous Investigations Series Map 

1-1778, 2 plates, scale 1 :50,000.) 

___ 1989, Map of locations of collapse-breccia pipes in the 

Grand Canyon region of Arizona: U.S. Geological Survey 

Open-File Report 89-550, I plate, scale 1:250,000. 
Figure 26 (above and facing page). Breccia pipe 494 (Mohawk Canyon pipe), Hualapai Indian Reservation. A, The pipe shows 

up as a small bleached point on the Kaibab Limestone cliff (arrow). Fault-controlled Mohawk Canyon can be seen to the right 

heading north towards the Colorado River. This photograph was taken during drilling of the Mohawk Canyon pipe in 1984. B, 

Concentric beds of Harrisburg Gypsiferous Member of the Kaibab Limestone dip radially into the ring-fracture zone (eroded to 

form the drainage). This photograph was taken prior to drilling. The distance between the drainages in this view is about 650ft. 

Van Gosen, B.S., and Wenrich, K.J., 1989, Ground magnetometer 

surveys over known and suspected breccia pipes on the 

Coconino Plateau, northwestern Arizona: U.S. Geological 

Survey Bulletin 1683-C, 31 p. 

Van Gosen, B.S., Wenrich, K.J., Sutphin, H.B., Scott, J.H., and 

Balcer, R.A., 1989, Drilling of aU-mineralized breccia pipe 

near Blue Mountain, Hualapai Indian Reservation, northern 

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

89-0100, 80 p. 

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

Arizona: Economic Geology, v. 80, no. 6, p. 1722-1735. 

___ 1986, Geochemical exploration for mineralized breccia 

pipes in northern Arizona, U.S.A.: Applied Geochemistry, 

v. 1, no. 4, p. 469-485. 

Wenrich, K.J., Billingsley, G.H., and Huntoon, P.W., 1986, 

Breccia pipe and geologic map of the northeastern Hualapai 

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

Survey Open-File Report 86-458-A, 29 p., 2 plates, 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 

plates, scale 1 :48,000. 

Wenrich, K.J., Billingsley, G.H., and Van Gosen, B.S., 1989, The 

potential of breccia pipes in the National Tank area, 

Hualapai Indian Reservation, Arizona: U.S. Geological 

Survey Bulletin 1683-B, 34 p. (Supersedes U.S. Geological 

Survey Open-File Report 86-592-A, 1986, 45 p.). 

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. 759-794. 

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: Vienna, International 

Atomic Energy Agency Technical Committee Meeting, 

9-12 March, 1987, IAEA-TC-542/20, p. 307-344. (Also 

released as U.S. Geological Survey Open-File Report 

89-173, 1989, 33 p.). 

Wenrich, K.J., Van Gosen, B.S., Balcer, R.A., Scott, J.H., Mascarenas, J.F., Bedinger, G.M., and Burmaster, Betsi, 1988, 

A mineralized breccia pipe in Mohawk Canyon, ArizonaLithologic and geophysical Jogs: U.S. Geological Survey 

Bulletin 1683-A, 66 p. (Supersedes U.S. Geological Survey 

Open-File Report 85-469, 1985, 72 p.). 

Breccia Pipes, Mohawk Canyon Area, Hualapai Indian Reservation, Arizona 039 

* U.S. GOVERNMENT PRINTING OFFICE: 1992-774-049/66016