·The Potential of Breccia Pipes 

in the .National Tank 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 SU·RVEY BULLETIN 1683-B 
Aerial photograph on cover shows typical surface expression of breccia pipe in the National Tank area, 

as well as local terrain and vegetation. Hualapai Indian Reservation~ Arizona. 
Chapter B 

The Potential of Breccia Pipes 

in the National Tank 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-B 

BRECCIA PIPES IN NORTHERN ARIZONA 
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 report is for 

descriptive purposes only and does not imply endorsement by the 

U.S. Geological Survey. 

UNITED STATES GOVERNMENT PRINTING OFFICE: 1989 

For sale by the 

Books and Open-File Reports Section 

U.S. Geological Survey 

Federal Center 

Box 25425 

Denver, GO 80225 

Library of Congress Cataloging-In-Publication Data 

Wenrich, Karen J. 

The potential of breccia pipes in the National Tank Area, Hualapai Indian 

. Reservation, Arizona. · 

(Breccia pipes in northern Arizona;ch. B) (U.S. Geological Survey bulletin ; 

1683-B) 

Bibliography: p. 

Supt. of Docs. no.: I 19.3:1683-B 

1. Breccia-Arizona-Mohave County. 2. Breccia-Arizona-Coconino 

County. I. Billingsley, George H. II. Van Gosen, B.S. (Bradley S.), 

196o-. Ill. Title. IV. Series. V. Series: U.S. Geological Survey bulletin ; 

1683-B. 

QE75.B9 no. 1683-B 557.3 s [552'.5) 88-600344 

[QE471.15.B7] 
CONTENTS 

Abstract Bl 

Introduction Bl 

Acknowledgments B2 

Breccia pipes of northern Arizona B3 

Pipes on the Hualapai Indian Reservation B6 

The National Tank area B7 

Mapping of collapse features in the National Tank area B7 

Description of specific collapse features in the National Tank area Bl2 

Conclusions B32 

References cited B33 

FIGURES 

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

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

Francisco volcanic field B2 

2. Stratigraphic column showing rock units that host breccia pipes in the 

Grand Canyon region of Arizona B3 

3. Map of the Hualapai Indian Reservation showing confirmed and suspe~ted 

breccia pipes mapped in the National Tank area between 1982 and 

1986 B4 

4. Geologic map of the National Tank area showing collapse features B8 

5-11. Photographs: 

5. Collapse feature 525 Bl2 

6. Collapse feature 531 Bl3 

7. Collapse feature 534 B14 

8. Collapse feature 537 BlS 

9. Collapse feature 538 B16 

10. Collapse feature 539 B17 

11. Collapse feature 569 Bl8 

12. Graphs of ground magnetometer traverse over collapse feature 569 Bl9 

13. Photographs of collapse feature 570 B20 

14. Photographs of collapse feature 571 B21 

15. Graphs of soil sampling survey results from collapse feature 571 B24 

16-26. Photographs: 

16. Collapse feature 572 B25 

17. Collapse feature 573 B26 

18. Collapse feature 57 4 B27 

19. Sink Tank (collapse feature 575) B28 

20. Collapse feature 576 B29 

21. Collapse feature 998 B29 

22. Collapse features 1107 and 1108 B30 

23. Collapse feature 1114 B30 

24. Collapse feature 1115 B31 

25. Collapse feature 1116 B31 

26. Collapse feature 1119 B32 

Contents Ill 
TABLES 

1. Collapse features mapped in the National Tank area BlO 

2. Chemical analyses of soil samples collected from collapse feature 571 B22 

IV Contents 
BRECCIA PIPES IN NORTHERN ARIZONA 

The Potential of Breccia Pipes in the . 

National Tank Area, Hualapai 

Indian Reservation, Arizona 

By Karen J. Wenrich, George H. Billingsley, and 

Bradley S. Van Gosen 

Abstract 

The Hualapai Indian Reservation lies on the 

southwestern corner of the Colorado Plateau in northern 

Arizona. Thousands 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 potential byproduct concentrations of Ag, 

Pb, Zn, Cu, Co, and Ni in some of these pipes, has stimulated 

exploration and mining activity in northern Arizona despite 

the depressed market for most of these elements. 

More than 900 confirmed and suspected breccia pipes 

were mapped on the Hualapai Reservation between 1982 

and 1986. Although breccia pipes are easily recognized 

within canyons where their vertical dimension is exposed, 

large expanses of northern Arizona are composed of undissected high plateaus. Recognition of pipes in these areas is 

particularly important because mining access to the plateaus 

is significantly better than to the canyons and the greater 

volume of overlying sandstones provided more host rock for 

ore precipitation by mineralizing fluids. Shallow structural 

basins on these plateaus are commonly the surface 

expression of the upper part of breccia pipes. 

The National Tank area on the Hualapai Indian 

Reservation, Arizona, was selected to demonstrate the high 

density of collapse features (suspected to be breccia pipes) 

that lie on these plateaus. Because most of the area is 

soil-covered and rock outcrops are few, soil geochemical, 

helium-soil gas, Bacillus cereus, and geophysical surveys 

were used to evaluate the potential that mapped collapse 

features are breccia pipes rather than more shallow-rooted 

solution features. Circular erosion patterns and vegetation 

changes are the only visible signs of collapse structures in 

the National Tank area. Twenty-five collapse features were 

mapped and described within this area; of these, three-534, 

Manuscript approved for publication, February 14, 1989. 

569, and 570-appear to have the greatest potential to be 

breccia pipes. 

INTRODUCTION 

The Colorado Plateau of northern Arizona is host 

to thousands of breccia pipes, many of which were 

mineralized by Cu-, U-, Ag-, Pb-, Zn-, Co-, and Nibearing fluids. Despite the depressed uranium market, 

the level of exploration activity for mineralized breccia 

pipes in north-central and northwestern Arizona has 

remained high. 

The Hualapai Tribal Council requested in 1985 

that the U.S. Geological Survey select two areas of 

potentially mineralized breccia pipes on the Hualapai 

Reservation (fig. 1) that the tribe could consider leasing 

to the mining community. The selection was based on 

maximum number of collapse features per area and 

distance from residential communities. The two areas 

selected represent, in general, two very different 

exposures of breccia pipes: (1) In the Mohawk Canyon 

area, mineralized rock is commonly exposed in cliff faces 

and along canyon bottoms in 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 motor vehicle. (2) In 

the National Tank area, mineralized rock is not exposed; 

in fact, little rock of any sort is exposed, and most of the 

area is soil-covered. Consequently, mapping is restricted 

to recognition of collapse features at the surface, which 

may or may not be mineralized at depth. However, most 

of the area is readily accessible by road. The National 

Tank area is the focus of this report; the Mohawk Canyon 

area is discussed in a separate report (Wenrich, Billingsley, and Van Gosen, 1990). 

The Potential of Breccia Pipes, National Tank Area, Hualapai Indian Reservation, Arizona 81 
-< 

0 

-< 

> 

w 

z 

K1ngman • • 

RANGE 

14 13 

17~~~ 

6 

~~16 

50 100 KILOMETERS 

50 MILES 

UTAH 

ARIZONA 

Area of 

figure 1 

COLORADO 

PLATEAU 

Winslowe Colorado 

San Francisco 

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

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

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

1. Copper House 6. Hack Canyon 11. Savanic 16. Pinenut 

2. Copper Mountain 7. Old Bonnie 12. Snyder 17. Hermit 

3. Cunningham 8. Orphan 13. Pigeon 

4. Grand Gulch 9. Ridenour 14. Kanab North 

5. Grandview 10. Riverview 15. Canyon 

More than 900 confirmed and suspected breccia 

pipes were mapped on the Hualapai Resexvation 

between 1982 and 1986 (fig. 3). This density of collapse 

features is not unique to the Hualapai Resexvation, the 

western edge of this pipe-rich region in Arizona, but 

extends eastward where a similar concentration of pipes 

had been mapped earlier on the Marble Plateau (Verbeek and Wenrich-Verbeek, 1980; Wenrich-Verbeek 

and Verbeek, 1980; Sutphin and Wenrich, 1983; Sutphin, 

1986). Thus, throughout the paper the tenns solution 

collapse, stiUcture, or feature are defined as those areas that 

apparently collapsed due to dissolution of any underlying 

rock, whereas the tenn breccia pipe refers specifically to 

82 Breccia Pipes In Northern Arizona 

dissolution of the Redwall Limestone, which resulted in 

stoping and brecciation of the overlying rock 

Acknowledgments 

This project was funded by the U.S. Bureau of 

Indian Affairs in cooperation with the Hualapai Tribe. 

Much appreciation goes to Hoyt B. Sutphin who 

provided mapping assistance in the early stages of this 

project. His continued assistance, enthusiasm, and 

exchange of ideas contributed to many of our 

conclusions. Joseph F. Mascarenas and Betsi Burmaster 

collected many of the soil samples over these collapse 
0 

(/) 

(/) 

<( 

0::: 

1-

z 

<( 

:E 

0::: 

w 

a. 

Thickness range, 

in feet 

c 

'~Petrified . ' Forest Member and , .. -:- •' :~.! c .~ .... $, sandstone and mudstone ':::: .... ~ ·- as eoo-1000 

f.++?~ .. ~~~~~r.~ .. ~~+r+.+.t4t'+.. ~ ~ 0 cb o Shlnarumo Member t1 o oo u. o-ao 

px;.:~~~~~P.J : ·; ~~~Cf2,:~:~ 0J f4.. 400-1200 //:(i·>.\:>}11:·:\::~.:·.((:} .. f }\/::#./:·:r::;-}):':} ~:; :' ·: :·:.' 'i ·· :· (#..;:::::;. 

1 Kaibab Limestone 1 1 250-500 

I T 'i i 'i I I 

I T I I ~ I I ...•. ,,.,. .... , ...... ·:" .'··.: ....... ..... .. ..... , ..... , ... ;. ..... ·. :·.-.·::.·:·:: :·:.· .. :.-:·; .. ,· .. :· :: .. ,:-:·"·:·. 

• Toroweap Formation 1 1 250-300 .:· . :~··:· :·:·· • : ...... :: ': . .. •; . . . :,. .:·.:·.:·.->::·.. . ·.·.,·· ..·. :.~· . ·: : .·. .·::::'::.::·::·:: 

;··· .. :: ~~~~r4 ~~~~i ~~. ;,·x ... \··; o-650 

- ---- ----------------

-_-__:-_-__: Hermit Shale ::-_--:__-_-__ 50-1400 

-----------------

600-700 

I • • • I 1 

w ~~~L-Redwall Limestone_•.......,~ (/) ' I I I 

550-700 

:E 

Figure 2. Stratigraphic column showing rock units that host breccia pipes in the Grand Canyon region of Arizona. The 

thickness shown for each unit is that characteristic of the area shown in figure 1. 

features. Earl R. Verbeek critically reviewed the 

manuscript and his suggestions were greatly appreciated 

and incorporated. 

BRECCIA PIPES OF 

NORTHERN ARIZONA 

The breccia pipes of northern Arizona differ from 

classic breccia pipes in that there are no volcanic rock 

associations in time or space; instead, they result from 

solution collapse within the Redwall Limestone and 

stoping of the overlying strata. Dissolution of the Redwall 

Limestone created caverns into which blocks of overlying 

strata collapsed, leading to gradual upward stoping of a 

rubble-filled, approximately 300ft (100m) in diameter, 

pipe-like structure. The pipes and associated mineralized 

rock transgress formational boundaries from the Mississippian Redwall Limestone through the Triassic Chinle 

Formation (fig. 2)-a vertical distance on the order of 

4,000 ft (1,300 m). No pipes have been observed in rock 

below the base of the Whitmore Wash Member of the 

Redwall Limestone during this study, nor during studies 

by Huntoon and others (1981, 1982) and Billingsley and 

The Potential of Breccia Pipes, National Tank Area, Hualapai Indian Reservation, Arizona 83 
R 16 W R 15 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 

N 

T 

29 

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

T 

28 

~~~~fs~'2~ ~ N 

R 8 W R 7 W R 6 W R 5 W 

T 

27 

N 

T 

25 

N 

Figure 3. The National Tank area is located on the eastern edge of the Hualapai Indian Reservation (outlined by rectangle). 

More than 900 confirmed and suspected breccia pipes were mapped on the Hualapai Reservation between 1982 and 1986. 

The western side has sparse vegetation, which is reflected in the greater density of identified collapses. This area provides an 

example of the solution collapse density when detailed mapping is completed. Area outlined in black (shown with a tree symbol 

in the center) on east side of map is densely tree covered, preventing recognition of most pipes. 

Huntoon (1983). 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 

84 Breccia Pipes in Northern Arizona 

breccia slid downward and is, therefore, by definition, a 

fracture (see fig. 1b, Wenrich, 1985). This nearly vertical 

fracture is referred to here as the ring fracture. 

The breccia pipes of northern Arizona extend to 

the Utah State line and 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 theHua-
lapai Indian Reservation, through Coconino National 

Forest to the Marble Plateau of the Navajo Reservation 

(fig. 1). No pipes are known east of the Echo Cliffs. 

Perhaps the area best known for breccia pipes is the 

Arizona Strip extending from the Grand Canyon 

northward to Utah; the flurry of mining ventures during 

the past 7 years, including the Hack Canyon mines, 

Kanab North mine, and the Pigeon mine, has brought 

recent prominence to this region. Pipes undoubtedly also 

exist along the southern margin of the Colorado Plateau, 

but for the most part are buried beneath the lavas of the 

San Francisco volcanic field. 

Mining activity in breccia pipes of the Grand 

Canyon region began during the 19th century; at that 

time essentially all ore produced was copper. It was not 

until1951 when high gamma radioactivity was discovered 

on the Orphan mine dump (Chenoweth, 1986) that these 

mines were first recognized to contain uraniummineralized rock. Metals produced from one or more 

pipes during the past century include Cu, U, Ag, Au, Pb, 

and Zn (Foord and others, 1978). Uranium ore from 

mines within these pipes is exceptionally high grade; 4.26 

million lbs U30 8 , composed primarily of uraninite, was 

removed from the Orphan mine averaging 0.43 percent 

U30 8 (Chenoweth, 1986). Other mined breccia pipes 

have, or had, grades and tonnages similar to those of the 

Orphan mine. All active mines are presently being 

operated essentially for their uranium content, although 

silver could be extracted as a byproduct in some if an 

appropriate mill were available; the Orphan mine 

produced 107,000 ounces of Ag from the copper ore 

from 1962 through 1969 at a grade of 0.35-0.45 oz/ton 

(ounces per ton; 11-14 ppm) (Chenoweth, 1986). 

Analyses of uranium-mineralized rock from breccia 

pipes throughout the Grand Canyon region routinely 

yield silver values of 10-100 ppm; some samples contain 

as much as 1,150 ppm (35 oz/ton) (Wenrich, 1985). 

Dissolution of the Redwall Limestone began 

during the Late Mississippian, creating an extensive karst 

terrain. The breccia pipes include strata up through the 

Triassic Chinle Formation, but no pipes have been 

observed to extend into younger rocks. Thus, it is 

probably safe to assume that formation of breccia pipes 

by sloping began at least by Early Pennsylvanian time and 

continued until, or at least was reactivated, in the Triassic. A minimum age of 141 m.y. (latest Jurassic-earliest 

Cretaceous) was determined for uraninite from the 

Orphan mine by U-Pb dating (Gornitz and Kerr, 1970). 

Preliminary U-Pb isotope data for uraninite from the 

Hack breccia pipes suggest a main period of 

mineralization of roughly 200 m.y. ago (late Triassicearly Jurassic) (Ludwig and others, 1986). The 200 m.y. 

age is in better agreement with the break in observed 

mineralized rock between the Triassic and Jurassic; that 

is, there are known pipes with Triassic strata but none 

with Jurassic or younger rock. 

Geological and geochemical controls on the 

mineralization of these breccia pipes are poorly 

understood at present. A more detailed discussion of the 

mineralogy and geochemistry of breccia pipes in 

northern Arizona is provided by Wenrich and Sutphin 

(1989). There is little doubt that pipe locations are in part 

structurally controlled, particularly on the Marble 

Plateau (Sutphin and others, 1983; Sutphin and Wenrich, 

1983), and that the pipes occur in clusters. Clustering of 

mineralized pipes is especially obvious in the .Hack 

Canyon area, where the Hack I, II, III, and old Hack 

Canyon mines (four separate pipes) all occur within one 

square mile (2.5 km2

) of each other. This proximity 

implies a hydrologic connection between multiple pipes 

and suggests that the mineralizing fluids circulated 

through all four pipes at the same time. Such a 

connecting system can be observed in a Redwall cave, 

with over a mile of passages, located on the west side of 

Peach Springs Canyon. Here the bottoms of four breccia 

pipes, aligned in a straight row and equally spaced, form 

broad chimneys in the ceiling of one passage (Wenrich 

and Sutphin, 1989) 

An extensive suite of elements is anomalously 

concentrated in mineralized rock within breccia pipes 

throughout northern Arizona. This association is 

remarkably consistent from pipe to pipe: Ag, As, Ba, Cd, 

Co, Cs, Cu, Hg, Mo, Ni, Pb, Sb, Se, Sr, V, Zn, and, less 

commonly, the rare-earth elements. In addition to this 

suite of elements, a black glassy pyrobitumen is found 

with the brecciated rock in many mineralized pipes, 

including the Mohawk Canyon pipe (Wenrich and others, 

1988). This material appears to have solidified after such 

associated minerals as pyrite and barite. Samples from 

the breccia pipes containing pyrite and pyrobitumen are 

visually indistinguishable from samples collected from 

Mississippi Valley-type deposits (Wenrich and others, 

1988). 

Primary and secondary fluid inclusions in sphalerite, dolomite, quartz, calcite, and anhydrite from several 

pipes scattered across northern Arizona yield filling 

temperatures that range from 86° to 222 °C. Salinities of 

fluids included in sphalerite are consistently higher than 

10 weight percent NaCl equivalent. Sphalerite 

(secondary inclusions) filling temperatures range from 

86° to 173 °C; dolomite (primary inclusions) from 130° 

to 145 °C; quartz (secondary inclusions within the 

silicified spire of the Blue Mountain pipe) from 275° to 

305 oC; and anhydrite (primary inclusions) from 187° to 

The Potential of Breccia Pipes, National Tank Area, Hualapai Indian Reservation, Arizona 85 
222 °C. These fluid-inclusion filling temperatures and 

salinities are also in agreement with those found in 

Mississippi Valley-type deposits, suggesting a similar 

genesis for pipe minerals such as sphalerite and galena, 

and the Co and Ni phases. Nevertheless, the absence of 

known uranium occurrences in Mississippi Valley-type 

deposits (D.L. Leach, oral commun., 1985) contrasts 

sharply with the pipe mineralogy. This does not preclude 

the base-metal breccia pipe assemblage from having a 

similar genesis to Mississippi Valley-type deposits, as the 

uraninite is paragenetically later than the base metal 

minerals in the breccia pipes and may well have 

precipitated from later mineralizing fluids. These data 

suggest that the base metals were probably precipitated 

from a moderately low-temperature brine solution, 

which exceeded the temperature that would be expected 

from the normal geothermal gradient on the Colorado 

·Plateau with a burial depth of 3,000-5,000 ft (900-1,500 

m). The quartz may well have crystallized from a latestage (later than all ore precipitation) silicification event, 

which only occurs in some pipes, such as the West 

collapse on the Marble Plateau and the Blue Mountain 

pipe. 

Pipes On The Hualapai 

Indian Reservation 

The Hualapai Indian Reservation is situated in the 

southwestern corner of the Colorado Plateau (fig. 1 ). 

The western half of the reservation, located 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 (175 m) of possible rock thickness is 

available to host an orebody and little of it is sandstone. 

Most is limestone, which generally is an unfavorable host 

for uranium 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 capped, 

for the most part, by the Harrisburg Gypsiferous 

Member of the Kaibab Limestone. This thick stratigraphic column of rock, in excess of 2,500 ft (800 m ), 

provides ample host rock for potential mineral deposits. 

In addition, this plateau surface lies at the same horizon 

as that above most breccia pipes hosting orebodies in 

northern Arizona. 

Mapping collapse features as 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 

86 Breccia Pipes In Northern Arizona 

development in the Kaibab Limestone and solution 

collapses formed where gypsum is dissolved from the 

underlying Toroweap Formation, or from the Harrisburg 

Gypsiferous Member of the Kaibab Limestone. 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. In contrast, collapse 

features with inward-tilted beds and alteration 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. · 

Although the dissolution of gypsum in the Toroweap.Formation and ofboth 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 (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 circulation can be seen 

in the core from the Mohawk Canyon pipe (Wenrich and 

others, 1988); here the 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 may well account 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 100 to 300 ft (most commonly 

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

features on plateau surfaces are as much as 1,300 ft 

across (most notable is the Pigeon pipe, fig. 1). The 

largest known collapse-Shadow Mountain collapse on 

the Marble Plateau-is more than one mile in diameter, 

and is located within a mile of Shadow Mountain, a 

Tertiary basaltic cinder cone. The actual Shadow 

Mountain breccia pipe may be no more than the average 

250 ft in diameter, but the Tertiary solutions associated 

with the volcanism must have caused extensive recent 

dissolution of some of the formations underlying the pipe 

(such as large-scale dissolution of the Redwall or Muav 
Limestones, as there is no soluble rock within the Toroweap and Kaibab on the Marble Plateau). Thus, locating 

the actual breccia pipe, and perhaps an orebody, will be 

more difficult at Shadow Mountain than in a small 

collapse, such as 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 pipe size on lower plateaus, 

because the lower plateaus are capped mostly by 

insoluble rock such as the Esplanade Sandstone. This 

increase in solution co11apse beneath the upper plateaus, 

which are capped by soluble Late 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 mapping. Mapping 

on the Hualapai Reservation began on 1:24,000 color 

aerial photographs, and was then field checked. Many 

pipes exposed along cliff faces are not recognizable on 

vertical aerial photographs and are best spotted from a 

helicopter. 

The fol1owing exploration criteria are considered 

favorable indicators of mineralized breccia pipes: 

1. Concentrical1y inward-dipping beds. 

2. A circular topographic pattern. This pattern is 

commonly expressed as a topographicaJiy high 

rim around a central depression. 

3. Anomalous radioactivity; 2.5 times background or higher is considered anomalous in 

this report. 

4. Goethite pseudomorphs and molds of pyrite. 

5. Co11oform 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 co11apse feature mapped from the 

air is a breccia pipe, these criteria must be checked in the 

field. Few pipes exhibit aJI these criteria on surface 

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

certainty that the feature is a breccia pipe as opposed to 

a 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 would 

promote 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 

occasional exposure of a breccia pipe in a canyon wa11 

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 coJiapse 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 this 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 NATIONAL TANK AREA 

The National Tank area (fig. 3) lies within the 

National Tank 71

h-minute topographic quadrangle, on 

the Coconino Plateau along the eastern edge of the 

Hualapai Reservation. The area is capped almost entirely 

by the Harrisburg Gypsiferous Member of the Kaibab 

Limestone; the Fossil Mountain Member is exposed only 

in a small canyon in the northwest corner (fig. 4). The 

area is essentially undissected. Relative to much of the 

Hualapai Reservation, this area has significant vegetation 

cover, primarily rangeland grasses, pinyon pine, and 

juniper. 

Mapping of Collapse Features in the 

National Tank Area 

Most of the National Tank area is soil-covered with 

little rock outcrop, which makes use of any of the first 

eight exploration criteria difficult. Circular topographic 

patterns and vegetation changes are the only observable 

features that permit mapping of collapse structures in the 

area. Because of the extremely limited rock outcrop, it is 

impossible to determine from the surface whether these 

are breccia pipes that extend downward into the Redwall 

Limestone or are merely co11apse features that may 

bottom in the Kaibab Limestone or Toroweap 

Formation. Nevertheless, this area is of potential 

economic importance because (I) all features are readily 

The Potential of Breccia Pipes, National Tank Area, Hualapai Indian Reservation, Arizona 87 
35° 

57' 

30" 

35° 

52' ~--~~~--~~7V~~~~~~--~~~~~~----~~-L~--~~ 

30" 

KILOMETER 

Figure 4 (above and facing page). Geologic map of the National Tank area showing 

collapse features. 

88 Breccia Pipes in Northern Arizona 
DESCRIPTION OF MAP UNITS 

~( ~ ALLU~f~~. (~~~~:E~~~-~ravel. Not all alluvium is shown 

KAIBAB LIMESTONE (LOWER PERMIAN)--

Harrisburg Gypsiferous Member--Slope- and ledge-forming gray and pale-red 

shales and gypsiferous siltstone interbedded with gray, ledge-forming 

limestone and dolomitic sandstone. Includes in lower part intraformational breccia beds of ripup chert clasts recemented with chert 

~ ~ KAIBAB LIMESTONE (LOWER PERMIAN)-- Fossil Mountain Member--A yellowish-gray fossiliferous cherty limestone 

and sandy limestone, forms cliff 

SYMBOLS 

CONTACT BETWEEN MAP UNITS 

FAULT--

Dashed where position uncertain; dotted where concealed; bar and ball on 

downthrown side; 20 indicates approximate stratigraphic offset in feet 

STRIKE AND DIP OF BEDS 

.-... --t----.111 AXIAL TRACE OF ANTICLINE 

0 538-C? COLLAPSE FEATURES--

Collapse feature number used in text to identify each collapse 

COLLAPSE FEATURE CLASSIFICATION 

• C2 Concentric, inward-dipping beds; no visible alteration 

C4 Distinctly circular feature, either due to vegetation or topography; no 

visible alteration or dipping beds 

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

obvious dipping beds, alteration, vegetation change or topography 

delineation 

accessible by four-wheel drive vehicle (the paved Supai 

highway passes through the middle of the area), and (2) 

the entire 2,500 ft (800 m) of stratigraphic sequence are 

present, permitting maximum preservation of any orebody that might be present. 

The collapse features were originally mapped from 

1:24,000 color aerial photographs. In the National Tank 

area, 25 features (fig. 4) have been mapped, field 

checked, verified as collapse features, and are considered 

likely to be breccia pipes. Many of these features appear 

circular from low-altitude aerial photographs and from 

directly overhead in a helicopter, but once on the ground, 

the circular nature of the feature is difficult to recognize. 

In most cases this circular nature is merely a circular 

color patch, although a few features do appear to have 

inward-tilting beds. Unfortunately, recognition of such 

features depends almost entirely on the vegetation, which 

is uniformly brown, except during summer when the 

centers of the collapse structures tend to be greener than 

surrounding areas. The greener centers are due in some 

cases to the negative topographic expression of some 

features, so that water drains into them. In other cases it 

is probably due to the highly fractured rock, which could 

permit enhanced water movement into the overlying soil. 

In any event, mapping in these areas of high plateaus 

where rock outcrops are few should be restricted to the 

summer months during the monsoon season when 

vegetation within the collapse structures are green. 

The Potential of Breccia Pipes, National Tank Area, Hualapai Indian Reservation, Arizona 89 
m 

.... 

0 

m 

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CD 

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CD 

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Table 1. Collapse features mapped in the National Tank area, Hualapai Indian Reservation, Arizona. The surface expression of all these collapse features is in the 

Harrisburg Gypsiferous Member of the Kaibab limestone 

7 lh -minute 

Feature topographic 

No. quadrangle Location 

525 National Tank Sec. 23, 

T. 30 N., R. 6 W. 

531 National Tank Sec. 15, 

T. 30 N., R. 6 W. 

534 National Tank Sec. 13, 

T. 30 N., R. 6 W. 

537 National Tank Sec. 22, 

T. 30 N., R. 6 W. 

538 National Tank Sec. 27, 

T. 30 N., R. 6 W. 

539 National Tank Sec. 27, 

T. 30 N., R. 6 W. 

569 National Tank Sec. 21, 

T. 29 N., R. 6 W. 

570 National Tank Sec. 20, 

T. 29 N., R. 6 W. 

571 National Tank Sec. 22, 

T. 29 N., R. 6 W. 

572 National Tank Sec. 22, 

T. 29 N., R. 6 W. 

573 National Tank Sec. 14, 

T. 29 N., R. 6 W. 

574 Supai Camp Sec. 12, 

T. 29 N., R. 6 W. 

575 National Tank Sec. 10, 

T. 29 N., R. 6 W. 

Lat, 

Long 

35° 58' 11" I 

112° 53' 58" 

35° 59' 00", 

112° 54' 32" 

35° 58' 4311 

112° 52' s4" 

35° 58' 16"' 

112° 54' 5311 

35° 57' 40", 

112° 54' 42" 

35° 57' 32"' 

112° 54' 51" 

35° 53' 08"' 

112° 55' 40" 

35° 52' 34"' 

112° 56' 2911 

35° 53' 06", 

112° 54' 28 

35° 53' 24"' 

112° 54' 26" 

35° 53' 38"' 

112° 53' 36" 

35° 52' 37"' 

112° 52' 25" 

35° 54' 07", 

112° 54' 44" 

Collapse 

category1 Comments 

C4 Circular depression; no outcrop; reddish-soil and-vegetation in a 

complete circle (fig. 5). 

C4 Circular depression of sagebrush 80 percent surrounded by a treeC4 

C? 

C? 

C? 

C4 

C4 

C4 

C? 

C4 

C4 

C? 

covered rim and reddish soil (fig. 6). 

Circular depression. Outcrop on north side dips invard (fig. 7). 

Slight bovl-shaped depression; no outcrop; soil and vegetation 

change (fig. 8). 

Very questionable; reddish soil patch (fig. 9). 

Circular pattern of sagebrush; slight bovl-shaped depression 

(fig. 10). 

Oblong, closed reddish soil-covered depression, rimmed by hill 

of Kaibab float (fig. 11). -

Semicircular shape; reddish soil in center; raised, white soilcovered rim (fig. 13). 

Circular depression;·darker soil and denser vegetation within 

depression; surrounded by a rim of lighter-colored soil (fig. 14). 

Circular~ fairly green patch of grass surrounded by sagebrush 

(fig. 16). 

Circular depression with grass patch inside (fig. 17). 

Large, reddish soil-covered center surrounded by circular to 

elliptical hill vith·some trees (fig. 18). 

Sink Tank; possibly a C2; outcrop has tilted beds (fig. 19). 
~ 

~ 

~ 

~ 

0 

~ ~ 

~ 

~ 

~ 

m 

; 

n 

n 

~ 

~ 

~· 

~ 

~ 

z 

a 

0 

~ 

~ 

~ ~ 

~ 

~ 

; 

~ 

X 

c 

m 

~ 

~ 

~ 

576 

998 

1107 

1108 

1109 

1110 

1111 

1114 

1115 

1116 

1119 

1124 

National Tank 

National Tank 

National Tank 

Dike Tank 

National Tank/ 

Dike Tank 

National Tank 

National Tank 

National Tank 

National Tank 

National Tank 

National Tank 

National Tank 

Sec. 3, 

T. 29 N., R. 6 W. 

Sec. 23, 

T. 29 N., R. 6 W. 

Sec. 21, 

T. 29 N., R. 6 W. 

Sec. 28, 

T. 29 N., R. 6 W. 

Sec. 21, 28, 

T. 29 N., R. 6 W. 

Sec. 21, 

T. 29 N., R. 6 W. 

Sec. 13, 

T. 29 N., R. 6 W. 

Sec. 15, 

T. 29 N., R. 6 W. 

Sec. 32, 

T. 30 N., R. 6 W. 

Sec. 32, 

T. 30 N., R. 6 W. 

Sec. 28, 

T. 30 N., R. 6 W. 

Sec. 17, 

T. 30 N., R. 6 W. 

~ 1Collapses are categorized as follows: m . ~ 

35° 55' 27" 

112° 54' .SJ" 

35° 52' 47" 

112° 53' s9" 

35° 52' 33" 

112° 55' l7'' 

35° 52' 28" 

112° 55' l8" 

35Q 52' 30" 

112° 55' l1" 

35° 52' 32" 

112° 55' 52" 

35° 54' 01" 

112° 52' 47'' 

35° 53' 44", 

112° 54' 38" 

35° 56' 45", 

112° 56' 34" 

35° 56' 47", 

112° 56' 28" 

35° 56' 55", 

112° 56' 1311 

35° 59' 00"' 

112° 56' 46" 

C? 

C4 

C2 

C2 

C? 

C? 

C? 

C4 

C4 

C4 

C4 

C? 

Depression with reddish soil; two-thirds surrounded by a ridge 

(fig. 20). 

Slight bowl in center filled with soil surrounded by a very low 

bill on three sides. Some gravels present; covered with 

basalt float (fig. 21). 

Central hill surrounded by a concentric drainage and outer rim 

of Harrisburg Gypsiferous Member dipping inward 12°-15° (fig. 22). 

Adjacent to 1107. A slight depression which is identical in 

size and shape to 1107. Inward-dipping beds of Harrisburg 

Gypsiferous Member (fig. 22). 

Large semicircular ridge with some trees bounding a broad, low 

grassy plain. Adjacent to 1108. 

Well-developed circular drainage around a central small hill 

covered with Kaibab float. 

Arcuate row of trees surrounding a grassy plain on 3 sides. 

A green grassy slight depression which contrasts sharply with 

the surrounding browner grassland (fig. 23). 

Fairly well-developed closed depression. Small goethite 

concretions present (fig. 24). 

Small depression of grass amid sagebrush surrounded by 

scattered junipers (fig. 25). 

Reddish soil-covered depression with grass and sagebrush 

surrounded by scattered junipers (fig. 26). 

Irregular shaped depression with grass and sagebrush surrounded 

by scattered junipers. 

~ C2 = Concentric, inward-dipping beds; no visible alteration 

~ C4 = Distinctly circular feature, either due to vegetation or topography; no visible alteration or dipping beds 

< C? = Questionable. A circular feature appears to be present, but with no obvious dipping beds, alteration, vegetation change, or 

~ topography delineation. 0 

F 

·~ 

~ 

i 

~ 

m 

m 

.... 
.... I 

Figure 5. Collapse feature 525 (indicated by arrow) has been classified as a C4 because of its concentric drainage and 

vegetation growth. Photographed from a helicopter; view to the northwest. 

The 25 collapse features listed in table 1 merit 

further study. Each feature is numbered on table 1 and is 

identified by that number on figure 4. The collapses are 

grouped into three categories-C2, C4 and C?-based 

on their surface expression. Those features that show (1) 

concentric, inward-dipping beds are classified as 

"collapse 2" (C2); (2) a centripetal and concentric 

drainage or a concentric vegetation pattern, but no 

outcrop, are classified as "collapse 4" (C4); and (3) those 

which appear to be, at best, only a somewhat circular 

color change, or are otherwise questionable are classified 

as "collapse ?" (C?). None of the 25 collapse features 

showed any evidence of anomalous surface gamma 

radioactivity or supergene copper mineralization. 

Collapse 562, similar in surface expression to 

collapses 569 and 570, was drilled intermittently between 

1984 and 1986 by Rocky Mountain Energy. This ollapse 

is about one mile southeast of the reservation boundary, 

just south of the sharp bend along the eastern boundary. 

812 Breccia Pipes in Northern Arizona 

Another similar collapse, 564 (fig. 3), was drilled in 1986 

by Energy Fuels Nuclear. All four collapses have a white 

circular rim around a central depression that contains 

reddish soil. This slightly raised rim may be due to 

silicification from fluids moving along the ring fracture of 

the breccia pipe, and, hence, may be a favorable 

exploration criterion for locating breccia pipes. 

Description of Specific Collapse Features 

in the National Tank Area 

525-C4.-This feature is readily discernible as a 

circular structure but appears to be merely a sink hole 

(fig. 5). The mapped area is a circular depression that is 

intermittently filled with water and rimmed by vegetation 

darker than the surrounding terrain. Nevertheless, 

because of the dissolution of the Harrisburg Gypsiferous 

Member of the Kaibab Limestone and the Woods Ranch 
Figure 6. Collapse feature 531 (indicated by arrow), photographed from a helicopter, is expressed as a depression bordered 

on three sides by a low rim of Kaibab Limestone crowned with junipers. View to the west. 

Member of the Toroweap Formation above known breccia pipes on the Coconino Plateau, unequivocal 

distinction between sink holes and breccia pipes from 

surface evidence becomes impossible. This feature does 

not have the vertical walls of a classical sink hole, but 

then there is no outcrop and the unconsolidated soil 

cover could have accumulated in the hole. Soil samples 

were collected from this feature in May 1986, but the 

data have not yet been compiled and plotted. 

531-C4.-This feature was mapped as a solution 

collapse because of its raised arcuate rim around a nearly 

closed basin (fig. 6). The basin contains sagebrush and 

the rim supports a denser growth of junipers than does 

the surrounding landscape. The rim of Kaibab Limestone 

resembles the rim around collapse features 562, 564, 

569, and 570. Feature 562 is a mineralized breccia pipe, 

and hence the other three features have good potential 

too. Nevertheless, the depression and rim in feature 531 

are not as pronounced or complete as they are in collapse 

features 562, 564, 569, or 570. This area has no outcrop. 

Soil samples were collected from this feature in May 

1986, but the data have not yet been compiled and 

plotted. Audio-magnetotelluric soundings do not show 

any significant conductive zone beneath the center of the 

collapse, although two minor zones occur beneath the 

rim. 

534-C4.-This locality is a more obvious circular 

feature than features 525 or 531, although the relief of 

the rim does not look pronounced in either the helicopter 

photograph (fig. 7 A) or the aerial photographic view (fig. 

7B). ·. lfe feature is a relatively large almost-closed 

depression, although there is no enhanced vegetation 

growth. Some rock outcrops along the rim and dips 

inward on the north side. 

Because many such collapse features on the high 

plateaus are covered by soil and low ground vegetation, 

with little outcrop, soil geochemistry appears to be an 

inexpensive means of acquiring additional information 

on the possible presence of subsurface mineralization. 

Good analytical accuracy, precision, and low detection 

limits are necessary because soil anomalies over the 

breccia pipes are very low level. Soil surveys were made 

The Potential of Breccia Pipes, National Tank Area, Hualapai Indian Reservation, Arizona 813 
~ ... 

·. 

: 

..... ... ... ~. ~ -:1" .... '"' .. • . .. . ·,:"-• ..... . .. ·~.~ -M-, . ": ~· • . .- .. a._ . . ...... , • • 

. :.-. . , 

Figure 7. Collapse feature 534 (indicated by arrow) is an obvious circular feature, although there are no distinct concentric 

vegetation or soil patterns. Outcrop of Kaibab Limestone on north side dips inward. A, Photograph from a helicopter (view to 

the southwest). B, low-altitude aerial photograph shows the feature belongs in the C4 category. Up on the photo is to the west. 

814 Breccia Pipes in Northern Arizona 
Figure 8. Collapse feature 537 (indicated by arrow). Photograph was taken from a helicopter. The feature is in the right center 

of the picture and stands out because of the darker green circular vegetation patch. 

of collapse feature 534 in 1984 and 1986. Preliminary 

results from the 1984 study show some significant 

element anomalies in the soil over the structure. Of the 

33 elements determined for 23 samples, Co, Cu, Fe, Mn, 

Ni, Pb, and Zn appear to increase in the soil over the 

collapse compared with soil of the surrounding terrain 

and Mg appears to decrease. With the exception of Mn, 

all the elements enriched in the soil over the collapse are 

ones that are commonly enriched in, or form, the breccia 

pipe orebodies. 

Helium surveys over breccia pipes have shown 

mixed success. Positive helium anomalies were observed 

over one known mineralized pipe but not over another. 

Collapse feature 534 is one of the few collapse features 

surveyed that showed a helium anomaly, although it was 

only twice background. 

Slingram and very low frequency (VLF) data, a 

time-domain electromagnetic (TDEM) profile, and an 

electric section are presented in Senterfit and others 

(1985). The TDEM data show a distinct change in 

resistivity at a depth of about 960 ft (290 m); this is 

approximately the same depth as the top of the Seligman 

(sandstone) Member of the Toroweap Formation in the 

center of the Mohawk Canyon breccia pipe (Wenrich and 

others, 1988). At the margin of the Mohawk Canyon 

pipe, the Seligman Member was encountered more than 

100ft (at a depth of approximately 825ft) higher than in 

the center of the pipe. So, because the rocks within the 

Mohawk Canyon pipe have been downdropped more 

than 100 ft, the top of the Seligman Member within the 

center of the pipe is at about 925 ft. If the units are 

approximately the same thickness in the National Tank 

area as at the Mohawk Canyon pipe about 15 miles away, 

the top of the Seligman Member in the middle of this 

structure is perhaps 130 ft lower than in the adjacent 

section. Hence, structure 534 is likely a breccia pipe. 

The results from soil geochemistry, helium soil gas, 

and TD EM geophysical surveys for collapse feature 534 

all appear encouraging. Further studies may prove this to 

be a mineralized breccia pipe. 

The Potential of Breccia Pipes, National Tank Area, Hualapai Indian Reservation, Arizona B15 
..... 

... .. , 

.... 

• • J 

• A "'I "" 4 .. • -· 

. . 

. ... 

."• . . . . . . ~ 

.... . .. . · . 

Figure 9. Collapse feature 538 (indicated by arrow). Photograph was taken from a helicopter. The feature is located in the 

center of the picture as a 2-in. by 1.5-in. circular darker patch that appears from this oblique view as two smaller dark patches. 

Dark patches on the right side of the photograph are cloud shadows. 

537-C?.-This feature (fig. 8) is similar to 525 in 

that it is a circular depression. The depression apparently 

accumulates water more than the surrounding terrain, as 

the vegetation within it is greener and forms a green 

circle. The soil appears to be a slightly redder than the 

soil in the surrounding terrain. This collapse feature has 

about the same low probability as 525 of being a breccia 

pipe. 

538-C?.-On the aerial photograph this area 

appears as an anomalous, round, reddish soil patch. Yet, 

from the helicopter (fig. 9) it is difficult to recognize 

anything that resembles a distinctly circular feature; on 

the ground there is little to distinguish the feature from 

the surrounding terrain. The area in question is shown in 

the center of figure 9 where it is about 2 in. by 1.5 in.; the 

oblique angle from which the photograph was taken 

distorts the circularity of the patch. This feature is 

probably the most questionable of the 25 collapse 

features listed in table 1. 

816 Breccia Pipes In Northern Arizona 

539-C?.-This feature is almost as questionable as 

538. It is a circular patch of sagebrush (fig. 10) that 

appears somewhat greener than the surrounding terrain 

during the summer months, as if water were 

accumulating in a slight depression. 

569-C4.-Based on surface morphology, this 

collapse structure is one of the more favorable features in 

the National Tank area, in that it has a closed depression 

surrounded by a low rim of Harrisburg Gypsiferous 

Member of the Kaibab Limestone. This feature also 

resembles, except for its more elliptically shaped 

depression, collapse feature 562 drilled by Rocky 

Mountain Energy. As is commonly the case, the collapse 

structure is not as obvious in a photograph from a 

helicopter (fig. 11A), as it is in a low-altitude aerial 

photograph (fig. 11B). Unfortunately, there is little 

outcrop, and the few exposed beds appear to be flat lying, 

in contrast to the more favorable characteristic of 

inward-tilted beds. 
. . . - •' .... . .. ... . . . . ·. : •:. .~ . 

Figure 10. Collapse feature 539 (indicated by arrow), photographed from a helicopter, has a slightly greener circular patch 

of sage just to the right of center. 

A preliminary soil survey completed over this 

structure in July 1984, was not very informative because 

only seven samples were collected. The sparse data 

suggest that Mn, Ni and Sr may be enriched in the soil 

over the collapse, as compared with the surrounding 

terrain, and Ca, Mg, and Pb may be depleted. 

A helium soil-gas survey was completed over this 

structure in March 1985 (Reimer, 1985). The mean 

helium concentration measured inside the depression 

was identical to that of the background area, 1,500 ft to 

the southwest. A similar survey (also in March, 1985), 

run over a structure known to be a mineralized breccia 

pipe (feature 562) showed that helium concentrations 

were approximately 50 ppb higher in the pipe than 

around it (Reimer, 1985); in addition, in the central part 

of the mineralized pipe the helium values were more than 

200 ppb higher than background. In June 1985, a second 

helium survey was made over collapse feature 569 (G.M. 

Reimer, written commun., 1986); a couple of samples, 

from the east side of the peanut-shaped depression, 

were anomalous, but an inadequate number of 

background samples were collected to accurately define 

"anomalous." 

Audio-magnetotelluric soundings over collapse 

569 detected a conductive zone lying southeast of the 

center of the depression (Flanigan and others, 1986). 

Although Flanigan and others (1986) believed this 

conductive zone to be small, and thus they suggest the 

feature is "a questionable breccia pipe," it is interesting 

to note that this zone is the same area where Reimer 

detected the highest helium soil-gas measurements. A 

ground magnetometer survey conducted over collapse 

569 detected two areas of anomalous high magnetic 

values and two areas of anomalous low magnetic values 

(probably two separate dipole anomalies), suggesting 

that the feature's peanut shape may represent the surface 

manifestation of two intergrown breccia pipes (Van 

Gosen and Wenrich, 1989). 

570-C4-This collapse structure is nearly identical 

in morphology to the drilled feature 562, except that it is 

The Potential of Breccia Pipes, National Tank Area, Hualapai Indian Reservation, Arizona 817 
Figure 11. Collapse feature 569 (indicated by arrow) is a semi-closed depression, surrounded by a low rim mantled by 

junipers and pinyon pines. The view in both photographs is to the north. A, Photograph taken from a helicopter; B, 1:24,000 

aerial photograph (but reproduced at a different scale) shows feature 569 as a distinct circular white rim of rocks mantled by 

scattered trees, surrounding a peanut-shaped closed depression. 150 ft by 300 ft. 

818 Breccia Pipes in Northern Arizona 
A 

rn 

a:l 

Collapse feature 569 - Line 2 53026 

Inside Ba.ckground Colla.pse Ba.ckground 

53005 

529115 -f--r---r-......-.---r-......-.---r-..,.-,.---r-+-..-.-.,..-,.-+-.,..-,.~T"'""T"~T"'""T"-.-,....., 

- 0 1 0 0 

South. 

53016 

63006 

Distance, in meters 

Collapse feature 569- Line 4 

Ba.ckground 

Inside 

Colla.pse Ba.ckground 

North. 

~ 62996 

~ 

52985 

52~6~---r-......-.---r-..,.-,.---r-..,.-,.~..,.-,.-r.,..-,.-.-~~T"'""T"~T"'""T"-.-r, 

- 0 1 0 0 

West 

B 

Distance, in meters Ea.llt 

Figure 12. Ground magnetometer traverse over collapse 

feature 569. A, North-south. Note the strong positive and 

negative (dipole) anomaly. B, East-west. Note the positive 

anomaly over the center of the pipe. 

not a closed depression. Rather it is breached on one 

side. The depression is bordered on three sides by a rim 

of Kaibab Limestone. Both near-surface (fig. 13A) and 

low-altitude (fig. 13B) aerial views show a distinctly 

circular feature with a raised rim of what appears to be 

whiter Kaibab Limestone. 

Soil sampling traverses across collapse 570 show 

significant positive enrichments that are 1.5-10 times 

background for Cu, Pb, and Zn concentrations in soil 

over the center of the collapse. Concentrations of Ag and 

Tl are also anomalous but to a lesser degree. 

Over collapse 570, AMT soundings reveal a pipeshaped, strongly conductive zone with a diameter of 

about 300 ft, extending to a depth of at least 1,900 ft 

(Flanigan and others, 1986). The most conductive part of 

the breccia pipe throat appears to plunge to the 

southwest. The shape of the highly conductive zone of 

this collapse is similar to that of the EZ-2 ore-containing 

breccia pipe (also shown in Flanigan and others, 1986). 

This apparent tilt to the presumed breccia pipe should be 

incorporated into the design of any future drilling 

project; that is, if a breccia pipe orebody is present, it is 

probably located under the southwest part of the 

depression. Ground magnetometer surveys over this 

coiiapse feature reveal a relatively featureless, consistent 

local magnetic gradient, thus providing weaker evidence 

than the AMT soundings for an underlying breccia pipe 

(Van Gosen and Wenrich, 1989). 

A helium soil-gas survey over collapse 570 shows 

no significant anomalies within the feature (G.M. 

Reimer, written commun., 1986). Helium surveys don't 

appear to provide definitive results even over known 

orebodies, so the helium results for collapse 570 do not 

particularly deter from the favorable AMT and soil 

survey results. This collapse has perhaps the greatest 

potential for being a breccia pipe .of the 25 described 

here. In addition to the favorable geochemical and geophysical surveys, the morphology is similar to that of 

breccia pipes 562 and 564. 

57J-C4.-Collapse feature 571 is approximately 

half the size of 570, but is also a circular depression 

surrounded by a white rim (fig. 14A,B). The soil inside 

this 10- to 13-ft-deep depression is somewhat darker than 

the surrounding terrain, and the vegetation growth 

denser. 

A soil survey conducted over this collapse structure 

showed significant anomalies that suggest that this 

feature is at least a sink hole, if not a mineralized breccia 

pipe. Samples shown in figures 15A-Hwere all collected 

approximately 4 in. (10 em) below the surface. The 

samples were dry-sieved through 80 mesh (177 m) 

stainless steel sieves to remove the large rock chips and 

coarse organic debris. Four traverses were made across 

the feature, and four background samples were collected, 

each about 100 ft beyond the margin of the pipe. The 

background samples are consistently lower in metal 

content th~m the samples taken within the feature; metal 

content of samples taken in the ring fracture (100-150 ft 

from center) is as low as the background samples, with 

the exception of Cu and Mg. Supergene copper minerals 

are commonly found in the ring fracture of mineralized 

pipes, so it would not be surprising to find a Cu anomaly 

in the soil overlying the ring fracture in a mineralized 

pipe. The raw data are shown in table 2. Of the 29 

elements determined, all but 3 appear to be positively 

enriched over the center of the collapse as compared with 

background samples from outside the collapse. Of these, 

15-Al, Ba, Co, Ce, Cr, Cu, Fe, Mg, Mn, Pb, Sc, Tl, V, Y, 

and Zn-are strongly enriched in soil within the 

The Potential of Breccia Pipes, National Tank Area, Hualapai Indian Reservation, Arizona 819 
Figure 13. A, This photograph, taken several hundred feet above the ground surface from a helicopter, of collapse 570 shows 

a low rim of white rock (Harrisburg Gypsiferous Member of the Kaibab Limestone) bordering a depression on three sides. The 

depression is about 600ft in diameter. View is to the west. B, This low-altitude view of collapse feature 570 (indicated by arrow) 

looks very similar to the helicopter view, except that with the smaller scale it is apparent that this feature has a slightly greater 

concentration of trees on its slightly whiter rim of rock than the adjacent terrain. View is to the southwest. 

820 Breccia Pipes in Northern Arizona 
Figure 14. Collapse feature 571 (indicated by arrow). A, Photograph taken from a helicopter shows a 10- to 13-ft-deep 

depression surrounded by a white rim. View is to the northeast. B, In this low-altitude aerial photograph, 571 resembles a small 

sink hole, with darker vegetation than the surrounding terrain. View is to the northwest. 

The Potential of Breccia Pipes, National Tank Area, Hualapai Indian Reservation, Arizona 821 
Table 2. Chemical analyses of soil samples collected from collapse feature 571 

[Latitude 35°53'6" longitude 112°54'06". Sample numbers with an "R" rather than a "C" in the 5th digit 

are analytical replicate samples of the preceding sample that has the same first four digits. Leader ( - ) 

indicates no data. All but two analyses are by inductively coupled argon emmission plasma spectroscopy; 

uranium and thorium are by delayed neutron. All analytical values are reported in parts per million unless 

otherwise noted] 

~ample Distance Al% As Ba Be Ca % Ce Co Cr 

Sample depth from center 

number Traverse (in.) (ft) 

1 571ASC84 All 4 0 6.6 <10 560 2 1.0 15 17 65 

2 571BSC84 All 8 0 7.2 {10 580 2 1.1 77 14 71 

3 571CSC84 NE-SW 4 75 4.9 {10 480 1 5.6 54 11 53 

4 571DSC84 NE-SW 8 15 4.6 (10 450 1 8.5 50 10 48 

5 571ESC84 NE-SW 4 75 s.s (10 550 1 0.9 61 10 52 

6 571PSC84 NE-SW 8 75 5.9 (10 570 2 0.9 63 12 62 

7 571GSC84 NW-SE 4 75 4.9 (10 500 1 0.6 55 8 47 

8 571HSC84 NW-SE 8 75 5.3 (10 520 1 0.6 56 11 53 

9 571ISC84 NW-SB 4 15 5.3 {10 500 1 3.0 60 9 55 

10 571JSC84 NW-SE 4 15 5.1 {10 480 1 4.7 61 10 52 

11 571JSRC4 NW-SE 8 75 5.1 (10 480 1 4.7 61 9 52 

12 571KSC84 N-S 4 so 5.7 (10 590 1 1.1 72 13 63 

13 571LSC84 N-S 4 100 4.7 <10 490 1 4.4 53 8 45 

14 57IOSC84 N-S 4 50 5.7 (10 590 2 0.9 67 12 62 

15 571PSC84 N-S 4 100 5.2 (10 520 1 0.8 61 11 57 

16 571RSC84 E-W 4 50 6.6 (10 630 2 0.9 77 16 68 

17 571SSC84 E-W 4 100 4.6 <10 500 1 1.1 58 9 52 

18 571USC84 E-W 4 50 5.9 (10 580 2 1.1 6 13 62 

19 571VSC84 E-W 4 100 5.1 {10 480 1 5.1 62 9 49 

BACKGROUND SAMPLES 

20 571MSC84 N-S 4 300 4.9 (10 480 1 1.7 53 8 51 

21 571MSRC4 N-S 4 300 5 (10 500 1 1.8 62 8 50 

22 571NSC84 N-S 8 300 5.1 (10 470 1 2.2 55 8 51 

23 571QSC84 N-S 4 300 4.8 20 500 1 0.6 59 8 51 

24 571TSC84 E-W 4 300 4.8 (10 510 1 0.7 62 9 50 

25 571WSC84 E-W 4 300 5.3 <10 550 2 0.8 71 11 58 

Sample no. Cu Fe % Ga Hg K% La Li Mg% Mn Na % Nb Nd Ni 

1 571ASC84 35 3.3 16 1.9 39 34 1.1 1200 0.71 11 32 33 

2 571BSC84 37 3.5 18 0.03 2.2 40 37 1.1 1100 0.67 11 36 36 

3 571CSC84 23 2.2 12 2.1 30 28 1.2 480 0.50 6 27 38 

4 571DSC84 23 2.1 11 1.9 28 27 1.2 390 0.46 7 28 37 

5 571ESC84 21 2.5 12 2.3 33 28 0.8 710 0.70 9 28 24 

6 571FSC84 26 2.8 11 2.3 36 30 0.9 710 0.69 7 28 26 

7 571GSC84 23 2.3 11 2.0 31 30 0.6 460 0.44 8 26 23 

8 571HSC84 33 2.5 12 1.8 33 31 0.7 480 0.49 7 30 25 

9 571ISC84 26 2.4 13 2.0 33 28 1.1 560 0.58 8 30 25 

10 571JSC84 27 2.3 12 2.2 32 27 1.1 500 0.54 8 30 24 

11 571JSRC4 28 2.3 12 2.0 31 27 1.1 510 0.55 6 29 25 

12 571KSC84 22 2.6 15 2.2 39 28 0.9 790 0.72 <4 30 39 

13 571LSC84 20 2.1 12 1.7 28 24 0.8 380 0.59 7 28 22 

14 5710SC84 25 2.7 12 2.4 37 28 0.8 810 0.73 8 29 25 

15 571PSC84 22 2.4 13 2.2 34 27 0.8 530 0.55 (4 28 36 

16 571RSC84 34 3.3 15 2.1 42 35 0.9 1200 0.75 10 36 32 

17 571SSC84 19 2.2 11 1.7 31 25 0.8 460 0.51 7 28 23 

18 571USC84 26 2.7 15 2.3 36 30 1.0 790 0.71 11 32 42 

19 571VSC84 23 2.3 12 1.8 32 26 1.0 470 0.60 8 28 25 

BACKGROUND SAMPLES 

20 571MSC84 17 2.3 12 1.8 31 34 0.6 360 0.41 8 28 24 

21 571MSRC4 19 2.4 13 1.7 35 34 0.6 370 0.45 7 33 25 

22 571NSC84 17 2.4 13 0.04 1.4 33 35 0.6 360 0.38 8 31 25 

23 571QSC84 18 2.3 11 2.0 32 31 0.5 420 0.48 9 27 23 

24 571TSC84 15 2.2 12 1.9 37 30 0.6 370 0.40 6 31 35 

25 571WSC84 16 2.5 13 1.8 39 31 0.7 560 0.58 6 32 23 

822 Breccia Pipes In Northern Arizona 
Table 2. Chemical analyses of soil samples collected from collapse feature 

571-Continued 

Sample no. P % Pb 

1 571ASC84 0.09 19 

2 571BSC84 0.09 16 

3 571CSC84 0.10 14 

4 571DSC84 0.09 12 

5 571ESC84 0.08 16 

Sc Se 

10 

11 <0.1 

7 

7 

8 

Sr Th 

140 12 

130 12 

130 8 

130 7 

130 10 

12.4 

8.9 

10.0 

11.3 

Ti % 

0.37 

0.38 

0.27 

0.24 

0.30 

u 

(DN) 1 

2.9 

2.6 

2.3 

2.8 

V Y Yb 

64 24 2 

6i 25 2 

48 16 2 

45 15 2 

50 19 2 

Zn 

120 

120 

62 

55 

75 

6 571FSC84 0.08 19 9 

7 571GSC84 0.04 16 7 

8 571HSC84 0.04 25 7 

9 571ISC84 0.09 13 8 

10 571JSC84 0.10 14 7 

130 9 9.3 0.32 3.1 

100 10 11.0 0.26 2.2 

110 12 11.1 0.28 2.6 

120 10 10.2 0.29 3.1 

120 9 9.6 0.27 2.6 

54 20 

50 17 

53 19 

51 19 

48 18 

2 77 

2 55 2 62 2 66 

2 62 

11 571JSRC4 0.09 12 7 

12 571KSC84 0.09 17 9 

13 571LSC84 0.08 13 7 

14 5710SC84 0.07 18 8 

15 571PSC84 0.06 15 8 

120 9 9.6 0.27 2.9 

140 9 10.7 0.33 3.0 

130 9 11.7 0.27 2.6 

140 12 11.2 0.32 3.0 

120 9 10.8 0.28 2.9 

49 18 

52 22 

44 15 

55 20 

51 19 

2 62 

2 88 

2 56 

2 73 

2 65 

16 571RSC84 0.07 21 11 

17 571SSC84 0.11 13 6 

18 571USC84 0.11 18 9 

19 571VSC84 0.08 14 7 

150 12 13.1 0.39 3.0 

110 11 10.6 0.27 2.6 

140 10 11.7 0.32 2.8 

140 9 10.1 0.28 2.5 

66 25 

44 18 

56 20 

49 16 

3 110 

2 58 

2 79 

2 64 

BACKGROUND SAMPLES 

20 571MSC84 0.05 16 7 

21 571MSRC4 0.05 14 7 

22 571NSC84 0.05 14 7 

23 571QSC84 0.06 17 7 

24 571TSC84 0.03 15 7 

25 571WSC84 0.04 15 8 

100 11 11.4 0.27 

110 13 9.4 0.28 

2.6 

3.0 

52 20 

54 19 

55 10 

51 19 

53 18 

53 21 

2 53 

2 56 2 54 2 56 

2 50 

0.2 100 9 0.27 

100 10 11.0 0.29 

110 10 9.3 0.27 

130 11 10.6 0.31 

3.3 

2.6 

2.7 2 99 

1DN• Analyses by delayed neutron. 

depression as compared with soil on the rim or outside 

the feature. Of the above elements, Co, Cu, Fe, Pb, V, 

and Zn (fig.15A-H) are ones that are enriched in breccia 

pipe orebodies; thus, their enrichment in the soil suggests 

similar underlying mineralized rock. Nevertheless, the 

enhancement of so many elements within the collapse 

depression soil may reflect a false anomaly; that is, the 

depression may have permitted development of a thicker 

soil horizon containing more organic material, or Fe + 

Mn oxides, that adsorb metals. So, the anomalies may not 

reflect a mineralized breccia pipe but rather enrichment 

of metals due to better adsorption conditions. 

Figure 15/ shows a comparison of Cr content in 

soils collected from two different soil depths. Soil 

samples were collected at both 4-in. and 8-in. depths and 

are plotted for comparison. Apparently neither level is 

consistently more enriched in Cr than the other (the 

results are similar for most of the other metals); so, the 

4-in. depth is preferable to sample because of greater 

ease and speed in sample collection. 

Although the soil overlying this structure is 

enriched in many metals relative to the surrounding 

terrain, whether the movement of ground water within a 

shallow sink hole could also cause such low-level metal 

enrichment, or whether the enrichment is due to upward 

movement of metals from a mineralized breccia pipe 

beneath, is unclear. In any event, the soil survey over 

collapse feature 571 appears favorable enough to merit 

additional study. 

A helium soil-gas survey showed some anomalies 

along the rim of the collapse feature. Nevertheless, this 

feature had relatively low helium and the background 

was exceptionally low, as compared with other collapse 

features surveyed for helium on the Hualapai 

Reservation. 

Bacillus cereus soil bacterial surveys were 

completed over collapse feature 571 (N.L. Parduhn, 

written commun., 1986). When penicillin concentrations 

of 10 ppm were used during the B. cer~us assay a distinct 

B. cereus low occurred over the collapse feature. This low 

is in contrast to surveys completed over known 

mineralized pipes that contain high concentrations over 

the breccia pipe orebody. 

Collapse feature 571 AMT soundings did not yield 

results that were as encouraging as for many of the other 

collapses studied on the Hualapai Reservation. The 

The Potential of Breccia Pipes, National Tank Area, Hualapai Indian Reservation, Arizona 823 
18 

A 

(/) 

1-

a: 15 z < 0 a.. :::::; 

~ ...J 

~ 

~- a: 

< w 

a.. lXI 10 ...J 

0 

u 

35 c 

(/) 

1- 30 a::z 

~Q ...J z:::! 

-~ 25 

cia: Ww 

Ita.. 

0 20 u 

15 

1.3 

1- E z 

w 

u 

a: 

w 

a.. 

~ 

~-

:::> 

u; 

w 

z 

(!) 

< 0 .5 ~ 

z 22-r----------~------~----------------~ 

0 

:::::; 

...J 

~ 20 

a: 

w 

a.. 

(/) 

II: 

< a.. 

~ 

a' 

15 

G 

Pb PPM 

~ 12~---.--~---,r---+---~--~---r--~ 400 200 0 200 400 

DISTANCE IN FEET FROM CENTER 

a NE-SW • NW-SE 

(/) 

II: 

<z 

a..o 

• N-S 

70-

~ 3so-

~-~ 

=>a: 

~~ 0 

a: 5 so-

• E-W 

0 

I 200 

0 

'!' 

70 B - (/) 

1-

a: 

~z 60 0 z:::::; 

- ...J 

~-~ 

2a:: 

~w 

oa.. 50 

a: 

:J: 

u 

40 

3 .4 

D 

1-

z 

w 3 u 

a: 

w 

a.. 

~ 

2 • 2.s 

0 

!!: 

13 ,-----------------~------------------, 

(/) 

II: 

<o 

a.. z 0 . 1 

z< 

-~ ·o 

ffi~ 

~ffi ~a.. < 0.05 

~ 

F 

z 130-r-------------------r------~----------~ 

o H :::::; 

...J 

~ 

a: 

w 

a.. 

(/) 

II: 80 

< a.. 

~ 

u 

z 

N 40-+----r----r----r----r----r---~--~~--~ 

400 200 0 200 400 

DISTANCE IN FEET FROM CENTER 

oNE - SW •NW-SE • N- S •E-W 

Cr PPM 

• 

D 

0 200 400 

DISTANCE IN FEET FROM CENTER 

! Sample depth= 4 in. II!' Sample depth= 8 in. 

824 Breccia Pipes In Northern Arizona 
...... ... .. ~ .. .. . .. • .,. •• • . • • • !"• ...... s-· • • •• • f 

•• . . . 

• 

Figure 16. Collapse 572 (indicated by arrow), photographed from a helicopter, is a shallow depression surrounded by a white 

halo in the soil. The presently low center suggests recent dissolution. 

conductivity anomalies that are present have a much 

lower intensity than those at other features, and instead 

of underlying the center of the collapse there appears to 

be a high under the rim on both sides of the traverse 

(Flanigan and others, 1986). The absence of a good 

conductivity high under the center of this feature 

suggests that the soil metal anomalies may be more of a 

reflection of increased soil development over a sink hole, 

Figure 15 (facing page). Soil sampling survey results from 

collapse feature 571. Distance across the pipe is plotted on 

the abscissa; "0" represents the center of the pipe. The edge 

of the pipe is located 150 ft from "0"; the pipe is 300 ft in 

diameter (shown as shaded area). Concentrations of the 

metals: A, Co; 8, Cr; C, Cu; D, Fe; E, Mg; F, Mn; G, Pb; and 

H, Zn are shown on the ordinate. A comparison is shown for 

Cr ( I) between samples taken at 4-in. depth and at 8-in. 

depth. Samples from the same locality are shown with the 

same shape symbol, but different size. 

and subsequent metal enrichment, than a reflection of a 

mineralized breccia pipe. Additional studies should be 

completed over this feature before it is determined to be 

unfavorable for ore. 

572-C?.-This feature appears as a dark, circular 

vegetation patch (fig. 16). It resembles a recent sink hole 

in that it does not appear to have a raised rim around it, 

although there is evidence of a white halo in the soil (fig. 

16). There is not a high probability of a breccia pipe 

beneath this recent solution feature, although the 

probability certainly is higher than at features 538 and 

539. 

573-C4.-This feature (figs. 17A,B) is similar to 

572, but is more pronounced and circular. It is 

intermittently filled with water and probably represents a 

recent sink hole. The white rim of soil surrounding the 

feature suggests that this feature is more than a recent 

sink hole. A soil sampling survey was completed over the 

feature, but the results are not yet available. 

The Potential of Breccia Pipes, National Tank Area, Hualapai Indian Reservation, Arizona 825 
Figure 17. Collapse feature 573 (indicated by arrow). A, 

Photograph taken from a helicopter, suggests a modern sink 

hole. B, This low-altitude aerial photograph shows feature 

573 (indicated by arrow) to be located on a ridge of Kaibab 

Limestone. 

574-C4.-This collapse feature has a large reddish 

center surrounded by a somewhat elliptical tree-covered 

rim. It lies outside the Hualapai Indian Reservation by 

approximately 400 ft, as can be seen from the road and 

fence line that follows the reservation boundary (fig. 18). 

The ring of trees growing on a slightly raised rim suggests 

that this may be a deeper seated solution feature rather 

than just a recent sink into the Kaibab Limestone or 

Toroweap Formation. 

575-C?.-This collapse feature is clearly a recent 

sink hole (fig. 19), as reflected by its name-Sink Tank. 

What. is not clear, though, is whether this is. a deeper 

seated solution feature that has long been a conduit for 

fluid movement. This fluid movement would have 

accentuated recent dissolution of the upper Paleozoic 

formations within the National Tank area, an actively 

spreading tectonic basin (P.W. Huntoon, written commun., 1986). Sink Tank is filled intermittently with water. 

576-C?.-This feature appears from the air (fig. 

20) to be a depression filled with reddish soil. There also 

appears to be an increase in tree growth; junipers are 

826 Breccia Pipes in Northern Arizona 
. '·,; ... 

.. .. :· ' .... 

Figure 18. Collapse feature 574 (indicated by arrow), shown in this view from a helicopter, is not located on the Hualapai 

Indian Reservation, but is less than 400 ft beyond the fence line. The structure is delineated by the circular ring of trees that 

probably lies along the ring fracture, which suggests a deeper seated feature rather than merely a recent sink hole. View is to 

the east. 

more concentrated within this feature than outside it. 

The collapse may be only a sink hole, although a ridge 

with spotty outcrops of Kaibab Limestone borders part of 

the depression. 

998-C4.-This collapse feature is merely a circular 

depression (fig. 21 ), but not a closed basin because it 

drains on the east side. It nevertheless is a conspicuous 

depression on the other three sides, and resembles the 

"amphitheaters" formed by erosion of breccia pipes in 

canyon areas. 

1107-C2.-An elongate depression with a 

concentric drainage around a central hill forms this 

collapse (fig. 22). Beds of the Harrisburg Gypsiferous 

Member of the Kaibab Limestone dip inward toward a 

central hill. Such rock exposure is rare in the National 

Tank area and collapses 1107 and 1108, immediately to 

the southeast, are the only collapses in the National Tank 

area with inward-dipping beds. Soil-sample traverses 

made over this feature reveal no significant anomalies 

compared with background samples. The AMT 

soundings were also completed, but the results did not 

show a strongly conductive zone under collapse site 1107 

(Flanigan and others, 1986). 

1108-C2.-Collapse 1108 (fig. 22) sits adjacent to 

1107 and exhibits a similar morphology of inwarddipping beds, although outcrop is more sparse at 1108 

and there is no central hill. As with the soil-sample 

traverses at 1107, those at 1108 show no strongly 

significant anomalies. Some elements did appear to be 

slightly enriched over 1108 as compared with the 

background, at least more so than at 1107. The AMT 

soundings were similar to 1107 and showed no strongly 

conductive zones under 1108 (Flanigan and other, 1986). 

1109-C?, 1110-C?, 1111-C?.-All three of these 

collapse features are considered questionable. This is 

particularly so with feature 1109, which is near 1108 and 

1107, but is merely an arcuate hill with sparse junipers 

bordering a soil covered flat. Collapse 1110 has a nearly 

circular drainage around a hill that, when viewed from 

the air, visually appears quite circular. Kaibab Limestone 

on the central hill appears to be flat lying. Collapse 1111 

The Potential of Breccia Pipes, National Tank Area, Hualapai Indian Reservation, Arizona 827 
Figure 19. Photograph of Sink Tank (indicated by arrow) (collapse feature 575) taken from a helicopter. Whether there is a 

deeper seated breccia pipe under the more recent karst feature is not known. View is to the northwest. 

is merely a soil-covered, treeless flat, three-quarters 

enclosed by a rim of trees. 

1114-C4.-Collapse 1114 (fig. 23) is a slight 

depression whose grasses are greener than those on the 

surrounding flat area. This feature is perhaps more 

questionably a breccia pipe than some of the others in the 

C4 category. No geophysical surveys were made over this 

collapse, and the only geochemical surveys are soil for 

which the data are not yet available. 

1115-C4.-This collapse is a relatively welldeveloped, closed basin (fig. 24). No geophysical surveys 

have been made on this collapse, and the only geochemical surveys are soil; computer processing of the data is 

not completed. This feature appears quite favorable for 

further exploration; it is the only collapse in the National 

Tank area where goethite nodules were found. 

1116-C4.-This collapse forms a well-developed 

small depression filled by sagebrush amongst a terrain of 

sparse junipers (fig. 25). It is located adjacent to the 

northeast of 1115. This is the type of morphology, but on 

a much smaller scale, that is expressed on the surface by 

the Canyon pipe, a known uranium orebody. 

828 Breccia Pipes in Northern Arizona 

1119-C4.-This collapse is morphologically 

identical to collapse 1116 (fig. 26). The depression is 

filled by reddish-brown soil and surrounded by scattered 

junipers. The center of the feature contains some red 

chert, whereas outside the depression the ridge contains 

typical white to cream Kaibab Limestone that caps most 

of the surrounding plateau. Because the exposed 

surrounding Kaibab at the same topographic horizon as 

that of the depression does not contain red chert, the 

center of the depression was probably downdropped 

from a higher stratigraphic position. Soil geochemistry 

traverses were made over this collapse, but the data have 

not yet been processed. The AMT soundings reflect a 

narrow vertical (about 1,800 ft deep) conductive zone 

that appears to go to the Redwall Limestone, and the 

feature is therefore probably a breccia pipe. 

1124-C?.-Collapse 1124 is very questionable and 

represents an irregular-shaped depression with grass and 

sagebrush surrounded by scattered junipers. 

[Figs. 20-26 follow. "Conclusions" begins on page B32.] 
Figure 20. Photograph from a helicopter of collapse feature 576 (indicated by arrow). The surface morphology of the structure 

is a depression containing reddish-white soil. Note the stand of junipers in the right center of the photograph. 

Figure 21. Photograph from a helicopter of collapse feature 998 (indicated by arrow). The only surface expression here that 

may indicate a possible underlying breccia pipe is the depression that is lower than the surrounding plateau on three sides. 

The Potential of Breccia Pipes, National Tank Area, Hualapai Indian Reservation, Arizona 829 
Figure 22. View from a helicopter to the southwest of collapse features 1107 (indicated by right arrow) and 1108 (indicated 

by left arrow). Both are basins elongated in an east-west direction. 

Figure 23. View from a helicopter to the southwest of collapse feature 1114 (indicated by arrow). This shallow depression with 

green grasses contrasts with the surrounding browner, less densely vegetated terrain. 

830 Breccia Pipes in Northern Arizona 
Figure 24. Collapse feature 1115 (indicated by arrow) forms a fairly well-developed closed depression with a lower lying 

drainage of sage enclosing (on three sides) a central hill of sparse junipers. View from a helicopter is to the south. 

Figure 25. View from a helicopter to the south of collapse feature 1116 (indicated by arrow). This feature, adjacent and 

immediately east of collapse 1115, forms a slight depression of sage that contrasts with the surrounding terrain of sparse 

junipers. 

The Potential of Breccia Pipes, National Tank Area, Hualapai Indian Reservation, Arizona 831 
Figure 26. View from a helicopter to the east of collapse feature 1119 (indicated by arrow), which has a morphology and 

vegetation cover identical to collapse 1115. 

CONCLUSIONS 

The National Tank area has good access, 

particularly when compared with most other areas in 

northern Arizona where breccia pipes can be recognized. 

The asphalt Supai road bisects the area and would 

provide good mining access. Unfortunately, the area has 

little outcrop, no surface mineralized rock, and no 

anomalous gamma radioactivity in the soil or rock in 

excess of 2.5 times background. 

Collapse features 562 and 564 (for locations see 

fig. 3) have been drilled by Rocky Mountain Energy and 

Energy Fuels, respectively. The persistence with which 

these features have been drilled over the past several 

years suggests strongly that they are both breccia pipes. 

Within the National Tank area, collapse features 570 ~"d · 

569 most strongly resemble these drilled features:· In 

addition, 531 and 534 also have some morphologic 

similarities. 

In the National Tank area, several collapse features 

(1116, 1119, and, to a lesser extent, 998) resemble the 

Canyon pipe but are somewhat smaller. The Canyon pipe 

is a known orebody expressed on the surface as a circular 

832 Breccia Pipes in Northern Arizona 

depression of grass and sage surrounded by Ponderosa 

pines. Perhaps this depression of grass and sage suggests 

that mineralized pipes produce a sufficient trace-metal 

halo above the orebody to prevent the growth of trees. 

The reliability of soil geochemistry as a tool for 

locating breccia pipes has not yet been determined. The 

results from feature 571 leave doubt as to whether 

anomalous values over depressions might simply be a 

result of increased thickness of fine-grained soil, and 

hence more metal adsorption, compared with the 

surrounding terrain where the "soil" tends more to be 

fine-grained chips of Kaibab Limestone. Yet of the 33 

elements determined for collapse feature 534, only Co, 

Cu, Fe, Mn, Ni, Pb, and Zn appear to be significantly 

enriched over the collapse as compared with the 

background terrain. Because these metals are all ones 

that are enriched in breccia pipe orebodies, soil 

geochemistry may be a useful tool in breccia pipe 

exploration. 

Audio-magnetotelluric (AMT) soundings appear 

to show vertical conductive zones over several of the 

more morphologically favorable collapse structures. The 

AMT soundings are very favorable for collapse feature 
570, in that they closely resemble the results from the 

EZ-2 sutvey, a known breccia pipe orebody (Flanigan 

and others, 1986). In fact, 570 appears to even have a 

slight tilt to the upper part, as does EZ-2. The AMT 

results for 569 are encouraging, whereas those for 531, 

571, 1107, and 1108 are not, although the 571 W-E 

traverse closely resembles the results from the 562 N-S 

traverse (Flanigan and others, 1986). The TDEM data 

from a geophysical sutvey on collapse structure 534 show 

a distinct change in resistivity at a depth of about 960 ft 

(290m); this is approximately the same depth as the top 

of the Seligman Member of the Toroweap Formation in 

the center of the Mohawk Canyon breccia pipe (Wenrich 

and others, 1985). Outside of the Mohawk Canyon pipe 

the top of the Seligman Member lies about 100 ft 

stratigraphically higher. This suggests that collapse 

structure 534 is downdropped to the same level as the 

Mohawk Canyon pipe, which is lower than the 

surrounding terrain, and thus is probably a breccia pipe. 

Ground magnetometer traverses over feature 569 show 

dipole highs and lows that would be expected over a 

narrow vertical body of rock heterogeneous from the 

surrounding rock. 

Initial results from B. cereus sutveys for most of the 

collapse features did not appear particularly useful (N.L. 

Parduhn, written commun., 1986). Then penicillinamended agars were prepared and many of the B. cereus 

traverses showed significant highs over collapses 

compared with the background. Helium soil-gas sutveys 

over several collapse structures were not as promising as 

some of the other techniques. 

Within the National Tank area two northeast 

alignments of pipes are quite striking. Toward the top of 

the area six collapse features (1115, 1116, 1119, 539, 538, 

and 534) are aligned in a N. 56° E. direction. At the 

bottom of the National Tank area, four collapses (570, 

569, 1114, and 574) are perfectly aligned in nearly the 

same direction-N. 53° E. This alignment may be useful 

for exploration; that is, if collapse feature 570 is a 

mineralized breccia pipe, which it well may be, then there 

is a good chance that 569, 1114, and 574 are also. The 

northeast alignments on the Marble Plateau mapped by 

Sutphin and Wenrich (1983) tend to be closer toN. 40° E. 

Perhaps the basement structures, which they suggest 

control the pipe locations, have been slightly rotated 

westward toward the Grand Wash Cliffs (edge of the 

Colorado Plateau). 

Of the 25 features described from the National 

Tank area, collapses 534,569, and 570 appear to have the 

most potential as mineralized breccia pipes. Collapse 

features 1107 and 1108 have concentrically inwarddipping beds and thus have excellent potential for being 

breccia pipes rather than recent collapses. Features 525, 

531, 571, 572, 573, 574, 575, 576, and 1114 are 

undoubtedly at least recent karst features, but the 

possible presence of Underlying breccia pipes still needs 

to be assessed. Features 537, 538, 539, 998, 1109, 1110, 

1111, and 1124 are not even certain to be collapse 

structures. Additional sutveys and techniques are needed 

for all features. Additional soil, helium, Baei/lus cereus, 

magnetometer, AMT, and TDEM sutveys over all 

features would be most helpful. Of these techniques, the 

natural source, scaler audio-magnetotelluric (AMT) is 

the most promising. 

REFERENCES CITED 

Billingsley, G.H., Jr., and Huntoon, P.W., 1983, Geologic map 

of Vulcans Throne and vicinity, western Grand Canyon, 

Arizona: Grand Canyon Natural History Association, 

scale 1:48,000. 

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

Canyon, Arizona-A case history of a mineralized, 

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

Report 86-510, 63 p. 

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

Michael, 1986, Electrical character of c91Iapse breccia 

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tru.S. GOVERNMENT PRINTING OFFICE: 1990-n3-047/06035