I 

Ground Magnetometer Surveys Over 

Known and Suspected Breccia Pipes on the 

Coconino Plateau, Northwestern Arizona 

U.S. GEOLOGICAL SURVEY BULLETIN 1683-C 

This research was funded by the 

Bureau of Indian Affairs 

in cooperation with the 

Hualapai Indian Tribe 
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Chapter C 

Ground Magnetometer Surveys Over 

Known and Suspected Breccia Pipes on the 

Coconino Plateau, Northwestern Arizona 

By BRADLEY S. VAN GOSEN and KAREN J. WENRICH 

Computer graphics by WILLIAM L. THOEN 

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 
DEPARTMENT OF THE INTERIOR 

DONALD PAUL HODEL, Secretary 

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director 

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, CO 80225 

Any use of trade names in this report is for descriptive purposes only and does 

not imply endorsement by the U.S. Geological Survey. 

Library of Congress Cataloging-in-Publication Data 

Van Gosen, B.S. (Bradley S.), 196QGround magnetometer surveys over known and suspected breccia pipes on 

the Coconino Plateau, northwestern Arizona. 

(U.S. Geological Survey bulletin ; 1683-C) 

Bibliography: p. 

1. Breccia-Arizona-Coconino County. 2. Magnetic prospectingArizona-Coconino County. 

I. Wenrich, Karen J. II. Title. Ill. Title: Ground magnetometer surveys over 

breccia pipes, Arizona. IV. Series: Geological Survey bulletin ; 1683-C 

QE75.B9 no. 1683-C 557.3 s ' 88-600259 

[QE471.15.87] [553.4'09791 '33] 
CONTENTS 

Abstract Cl 

Introduction C2 

Breccia pipes of northern Arizona C2 

Collapse features on the Hualapai Indian Reservation C6 

Mapping of suspected breccia pipes on the Hualapai Indian Reservation C7 

Magnetometer surveys over breccia pipes C7 

Methods CS 

Ground magnetometer results CS 

Mohawk Canyon pipe CS 

Pipe 562 en 

Feature 220 C12 

Feature 493 C14 

Feature 569 CIS 

Feature 570 C18 

Conclusions C19 

Acknowledgments C23 

References cited C24 

FIGURES 

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

.Indian Reservation, San Francisco volcanic field, and breccia pipes developed 

into mines C3 

2. Map of Hualapai Indian Reservation showing solution-collapse features C4 

3. Schematic cross section of a breccia pipe showing rock units that host breccia 

pipes in the Grand Canyon region of Arizona CS 

4. Map of Hualapai Indian Reservation showing collapse features surveyed by 

ground magnetometer C9 

5. Photograph of the Mohawk Canyon pipe ClO 

6. Geologic map of the Mohawk Canyon pipe showing location of ground 

magnetometer readings and drill holes en 

7. Total magnetic field profiles of ground magnetometer traverses at the 

Mohawk Canyon pipe C12 

8. Diagram showing three-dimensional model and contour plot of the ground 

magnetometer data for the Mohawk Canyon pipe C13 

9. Photograph of pipe 562 C14 

10. Map showing the location of ground magnetometer readings at 

pipe 562 CIS 

11. Total magnetic field profiles of ground magnetometer traverses at 

pipe 562 C16 

12. Diagram showing three-dimensional model and contour plot of the ground 

magnetometer data for pipe 562 C17 

13. Photograph of feature 220 C18 

Contents Ill 
14. Map showing location of ground magnetometer readings at 

feature 220 C19 

15. Total magnetic field profiles of ground magnetometer traverses at 

feature 220 C19 

16. Diagram showing three-dimensional model and contour plot of ground 

magnetometer data for feature 220 C20 

17. Photograph of feature 493 C21 

18. Map showing the location of ground magnetometer readings at 

feature 493 C22 

19. Total magnetic field profiles of ground magnetometer traverses at 

feature 493 C22 

20. Diagram showing three-dimensional model and contour plot of ground 

magnetometer data for feature 493 C23 

21. Photograph of feature 569 C24 

22. Map showing the location of ground magnetometer readings relative to the 

rim of feature 569 C25 

23. Total magnetic profiles of ground magnetometer traverses at 

feature 569 C26 

24. Diagram showing three-dimensional model and contour plot of ground 

magnetometer data for feature 569 C27 

25. Diagram showing computer modeling for the source of the dipole magnetic 

anomaly recorded along line 2 at feature 569 C28 

26. Photograph of feature 570 C29 

27. Map showing location of ground magnetometer readings at 

feature 570 C30 

28. Total magnetic field profiles of ground magnetometer traverses at 

feature 570 C30 

29. Diagram showing three-dimensional model and contour plot of ground 

magnetometer data for feature 570 C31 

TABLE 

1. Statistics for the data set of 531 ground magnetometer readings recorded 

during the study of six breccia pipes C10 

IV Contents 
BRECCIA PIPES IN NORTHERN ARIZONA 

Ground Magnetometer Surveys Over 

Known and Suspected Breccia Pipes on the 

Coconino Plateau, Northwestern Arizona 

By Bradley S. Van Gosen and Karen J. Wenrich 

Computer graphics by William L. Thoen 

Abstract 

The Colorado Plateau in northern Arizona is host to 

hundreds, possibly thousands, of solution-collapse breccia 

pipes; many contain concentrated deposits of copper, 

uranium, silver, lead, zinc, cobalt, and nickel minerals. These 

breccia pipes, which formed by solution and collapse within 

the Mississippian Redwall Limestone and by progressive 

upward stoping of the overlying strata, extend into the 

Triassic Chinle Formation. The discovery of high-grade 

uranium ore in some pipes, plus potentially economic 

concentrations of other byproduct metals, has stimulated 

mining and exploration throughout northern Arizona in recent 

years. 

More than 900 confirmed and suspected breccia pipes 

were mapped on the Hualapai Reservation from 1982 to 

1986. Mapping breccia pipes on the Coconino Plateau (on 

the eastern half of the reservation) is complicated by 

relatively recent karst development (sinkholes) on the Kaibab 

Limestone surface and collapses formed by dissolution of 

gypsum units within the Permian Kaibab Limestone and 

Toroweap Formation. Both types of collapse features have 

little economic value. 

Six known or suspected breccia pipes that crop out on 

the Coconino Plateau were surveyed by a ground magnetometer, which had a sensitivity of ±0.02 gammas. The 

Mohawk Canyon pipe contains surface copper mineralization and subsurface uranium mineralization; a dipole 

magnetic anomaly was recorded over the pipe, with the low 

magnetic area positioned N. 70° E. of the high magnetic area. 

Exploratory drilling at pipe 562 indicates a uraniummineralized pipe at depth; anomalously low magnetic values 

occur in the collapsed interior of the pipe. Surveys over 

Manuscript approved for publication May 20, 1988. 

feature 220, which appears to be a stratiform copper deposit 

(it is uncertain whether this deposit overlies a pipe), reveal an 

area of anomalously high magnetic values north of the 

feature and an area of low magnetic values near the 

excavated pit. Audio-magnetotelluric soundings and field 

observations at feature 493 suggest it is a breccia pipe that is 

enclosed by a moat, which was probably formed by Kaibab 

or Toroweap gypsum collapse; an east-west-oriented dipole 

magnetic anomaly was recorded at the central hill. The 

peanut-shaped morphology of feature 569 suggests that it 

represents the intergrowth of two breccia pipes. Two areas of 

anomalously high magnetic values and two areas of 

anomalously low magnetic values were detected within and 

bordering the collapse of feature 569, again suggesting that 

two coalescing breccia pipes underlie the collapse. Although 

audio-magnetotelluric soundings and surface morphology 

suggest that feature 570 overlies a breccia pipe, the magnetic 

gradient that was recorded here lacks the anomalies 

associated with the other collapses that have been surveyed. 

A dipole magnetic anomaly recorded along line 2 at 

feature 569 was modeled to determine the magnetic source. 

The best-fit model reveals that: (1) The magnetic source 

begins at the surface and extends to a depth of at least 50 m, 

(2) the source is slightly smaller than the surface diameter of 

the collapse, and (3) the magnetic susceptibilities recorded 

are typical of detrital magnetism in sedimentary rocks. 

The dipole magnetic anomalies that were recorded 

may reflect Triassic Moenkopi Formation downdropped into 

a less magnetic Kaibab Limestone host rock. In addition, the 

anomalously low magnetic values recorded, such as over 

pipe 562 and feature 220, may indicate the alteration of 

magnetic minerals within the reduced zones that are 

associated with the uranium ore deposits in mineralized 

breccia pipes. In this second scenario, replacement of the 

detrital ilmenite and magnetite within the bleached (reduced) 

rocks by nonmagnetic iron and titanium minerals, such as 

Ground Magnetometer Surveys Over Breccia Pipes, Arizona C1 
pyrite and leucoxene, creates a relative magnetic depletion 

over the pipe. 

INTRODUCTION 

The Colorado Plateau in northern Arizona is host 

to hundreds, probably thousands, of solution-collapse 

breccia pipes, many of which contain concentrated 

deposits of Cu, U, Ag, Pb, Zn, Co, and Ni minerals. The 

discovery of high-grade uranium ore in some of these 

pipes, and its association with potentially economic 

concentrations of the other byproduct metals, has stimulated mining and exploration for mineralized breccia 

pipes throughout northern Arizona in recent years. 

Bowles (1965) was the first to recognize the northern 

Arizona breccia pipes as solution-collapse features; 

earlier work had suggested the pipes were volcanic in 

origin. 

The recent interest in mineralized breccia pipes 

has been carried onto the 1,550-m? Hualapai Indian 

Reservation, which is located on the southwestern corner 

of the Colorado Plateau in northwestern Arizona (fig. 1 ). 

More than 900 confirmed and suspected breccia pipes 

were mapped on the Hualapai Reservation from 1982 to 

1986 (fig. 2; also see Wenrich, Billingsley, and Huntoon, 

1986, 1987; and Billingsley and others, 1986). Ground 

magnetometer surveys are one of several exploration 

techniques that have been used to distinguish potentially 

mineralized, deeper rooted breccia pipes from nonmineralized, shallow collapses and other circular features. 

Throughout this paper the terms "solution collapse," 

"structure," or "feature" are defined as those areas that 

apparently have undergone collapse due to dissolution of 

underlying rock, whereas the term "breccia pipe" refers 

specifically to dissolution of the Redwall Limestone that 

resulted in stoping and brecciation of the overlying rock. 

Note to reader: All measurement units presented 

in this paper are given in the unit in which the measurement was made during the study; that is, to provide 

smoother reading the corresponding conversions to feet 

or meters are not simultaneously provided. Feet may be 

calculated by multiplying meters by 3.281; meters may be 

calculated by multiplying feet by 0.3048. 

BRECCIA PIPES OF NORTHERN 

ARIZONA 

Breccia pipes formed as the result of solution and 

collapse within the Mississippian Redwall Limestone and 

collapse through progressive upward stoping of the 

overlying strata. An extensive karst system developed in 

the Redwall Limestone sometime after its depostion, and 

caverns that formed became filled with rubble and blocks 

C2 Breccia Pipes in Northern Arizona 

from the overlying strata. Continued upward stoping of 

the overlying strata produced a pipelike column of mixed 

lithologies, usually no more than 300 ft in diameter. The 

stoping and steep walls of the pipe produced extensive 

brecciation, which was generally most developed toward 

the center of the pipe. All breccia dropped downward 

into the pipe; no breccia clasts have been observed that 

occur above their normal stratigraphic position. 

Northern Arizona breccia pipes and the associated 

mineralized rocks transgress the entire upper Paleozoic 

section from the Misssissippian Redwall Limestone to 

the Triassic Chinle Formation of the Mesozoic section 

(fig. 3). No volcanic rocks are associated in time or space 

with the formation of the pipes. 

A steeply dipping (subvertical), circular stope 

fracture zone formed in the country rock along the 

perimeter of . each breccia pipe. This fracture zone is 

commonly mineralized, if the breccia pipe is mineralized, 

and it separates the breccia body from the relatively 

undisturbed wall rock. In this paper the stope fracture 

zone will be referred to as the "ring fracture," which is 

the term that has been applied by recent workers 

(Wenrich, 1985). 

The breccia pipes of the Colorado Plateau are 

abundant south of the Utah border to the Mogollon Rim 

(the southern margin of the plateau), west to the Grand 

Wash Cliffs (the western margin of the plateau), and east 

across the Marble Plateau of the Navajo Indian 

Reservation (fig. 1). No breccia pipes have been found 

east of the Echo Cliffs. The lavas of the San Francisco 

volcanic field bury terrane with a high potential for 

breccia pipes. Recent studies have identified the galliumand germanium-rich Apex Mine in the Beaver Dam 

Mountains of southwestern Utah as an oxidized Colorado Plateau-type collapse breccia pipe (Wenrich and 

others, 1987; Verbeek and others, 1987); this breccia 

body was previously interpreted as fault created (Kinkel, 

1951; Bernstein, 1986). This suggests that the Arizona 

pipes extend into the southern Basin and Range province 

in those areas underlain by the Redwall Limestone or 

equivalent units. 

The region best known for breccia pipes and most 

active for recent exploration is the Arizona Strip, which 

extends from the Grand Canyon northward to the Utah 

border. Figure 1 shows the location of several mineralized breccia pipes that have been mined within the 

Arizona Strip, including the three Hack Canyon mines, 

the Kanab North mine, the Pigeon mine, the Hermit 

mine, and the Pinenut deposit, all which went into, or are 

going into, operation during the 1980's. 

Recent exploration interest in mineralized breccia 

pipes of northern Arizona has resulted in numerous 

multidisciplinary studies, which are summarized and 

referenced here. 
<( 

0 

<( 

> 

w 

z 

Kingman •

BASIN AND RANGE 

14 13 

17~~~ 

6 

~~16 

50 100 KILOMETERS 

50 MILES 

111 o UTAH 11 Do 

ARIZONA 

COLORADO 

PLATEAU 

109° 

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

Colorado Plateau (Mogollon Rim), the San Francisco volcanic field (its lavas bury terrane with high potential for breccia pipes), 

and breccia pipes presently or previously developed into mines. 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 1 0 Riverview 

An extensive suite of elements are anomalously 

concentrated and commonly associated with the highgrade uranium ore in mineralized breccia pipes. A 

thorough discussion of breccia-pipe mineralization and 

geochemistry is provided in Wenrich (1985), and a 

discussion of geochemical exploration for mineralized 

pipes is provided in Wenrich (1986); also, photographs of 

several breccia pipes are shown in each of these papers. 

Except for the presence of uranium, many samples from 

the ore zone in Colorado Plateau pipes are strikingly 

similar in geochemistry and appearance to Mississippi 

Valley deposits; this is discussed in Wenrich (1985), 

Wenrich and others (1988), Wenrich and Pratt (1985), 

and Wenrich, Billingsley, and Van Gosen (1986). The 

paragenesis and formation of ore minerals from 

mineralized pipes are discussed in Wenrich and Pratt 

(1985). In some pipes a black, pore-filling pyrobitumen is 

associated with the ore minerals; the results of RockEval 

analyses of this pyrobitumen are presented in Wenrich 

15 Canyon 

and Pratt (1985) and Wenrich (1986). Geochemical 

analyses of organic material associated with the breccia 

pipes are discussed by Landais (1986). 

Using U-Pb isotope analyses, the minimum age of 

formation for uraninite from the Orphan mine breccia 

pipe was determined to be 141 Ma (Gornitz and Kerr, 

1970). U-Pb isotope measurements on samples from 

several northern Arizona breccia pipes suggest uranium 

mineralization occurred 200-220 Ma (Ludwig and 

others, 1986). The significance of these age determinations is also discussed in Wenrich (1985, 1986). 

Fluid inclusion studies have been conducted on 

dolomite, sphalerite, and calcite samples from mineralized pipes. The results show that the temperatures of 

the transporting fluids were 80-173 °C, with an average 

salinity of about 20 weight percent NaCl equivalent. 

Further discussion of fluid inclusion data is available in 

Wenrich (1985, 1986), Wenrich and Pratt (1985), and 

Rasmussen and others (1986). 

Ground Magnetometer Surveys Over Breccia Pipes, Arizona C3 
1WOO' 

T 

33 

N 

T 

32 

N 

T 

31 

N 

T 

29 

~~~~~~~hr-T~ N 

T 

28 

~~~~~~~~d N 

T 

27 

N 

T 

26 

N 

T 

25 

N 

T 

24 

~~~~~~~~~~~~~~~~~l-LID~~-1-~~~~~~DL~~_L~~N R 11 W R 10 W R 9 W R 8 W R 7 W R 6 W R 5 W 

Figure 2. This map of the Hualapai Indian Reservation and vicinity illustrates the density of solution-collapse features existing 

in northern Arizona. Over 900 confirmed and suspected breccia pipes have been mapped within and adjacent to the Hualapai 

Reservation. Vegetation is sparse on the western side of the reservation, which is reflected in the greater density of identified 

collapses. Area outlined in black (with tree symbol in the center) on eastern side of map is densely tree covered, which prevents 

recognition of most pipes. Future refinement of Landsat imagery may aid exploration for breccia pipes in these forested areas. 

Mineralized breccia pipes commonly occur in 

clusters, which suggests that each pipe in the cluster is 

connected by a common hydrogeochemical system. The 

density of pipe locations and possible hydrologic relations 

are discussed in Wenrich (1985, 1986). Huntoon (1986) 

discussed breccia pipe hydrology and provided good 

evidence for ascending mineralizing fluids. There is 

evidence for the structural alignment of pipes, especially 

on the Marble Plateau, and this is presented in Sutphin 

(1986) and in Sutphin and Wenrich (1983, 1986). This 

evidence for breccia-pipe alignments on the Marble 

Plateau was evaluated by Wheeler (1986). 

C4 Breccia Pipes in Northern Arizona 

The Surprise Canyon Formation was deposited in 

the Grand Canyon region during Late Mississippian and 

possibly Early Pennsylvanian time, sometime after the 

deposition of the underlying Redwall Limestone and 

before the deposition of the Supai Group (Billingsley and 

Beus, 1985). The Surprise Canyon was deposited in 

stream-eroded valleys and solution caverns within the 

Redwall Limestone karst surface. The relationship of the 

Surprise Canyon to the breccia pipes is discussed by 

Billingsley (1986). 

The production figures and mine history of the 

Orphan mine, a copper- and uranium-mineralized pipe 
:~Diameter of surface depression~: I I 

Average or range 

in thickness 

(in feet) 

(.) 

Cl) 

Cl) 

<{ 

a: 

1--

Chinle 

Formation 

Moenkopi 

Formation 

Kaibab 

Limestone 

Toroweap 

Formation 

I 

300 

Shinarump Member 0-200 

400-1200 

Harrisburg Gypsiferous 0-300 

Member 

Fossil Mountain 200-250 

Woods Ranch Member 90-120 

Brady Canyon Member 

Seli man Member---------r 

100-250 

~~~~LL~~~~~~~-----30-90 

z Coconino Sandstone 

<{ 

::2: 

a: 

w 

o.. Hermit Shale 

I _Jz 

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0.. 

0.. 

Cl) 

Cl) 

Cl) 

Cl) 

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0.. 

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0 

ctl 

0.. 

::J 

Cl) 

Esplanade Sandstone 

Wescogame Formation 

Manakacha Formation 

Watahomigi 

Surprise Canyon 

Formation 

( Mississippian I Penns y Ivan ian? l 

Redwall Limestone 

I 

oz 

> <l:: Temple Butte Limestone woz 

0-600 

50-1200 

300-500 

150-200 

180-230 

150-200 

0-380 

400-700 

0-450 

Figure 3. 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 study area for this report) represent 

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

that occur in the Coconino Plateau of the eastern Hualapai Reservation (from Wenrich, Billingsley, and Huntoon, 1986, which 

also provides unit descriptions). Some collapse features on the Coconino Plateau, such as collapse feature 493, have reddish 

centers which may be the result of downdropped Moenkopi sediments. 

Ground Magnetometer Surveys Over Breccia Pipes, Arizona CS 
in the Grand Canyon National Park, were presented in 

detail by Chenoweth (1986). His report provides an 

example of the "typical" ore reserves for a mineralized 

Colorado Plateau breccia pipe, plus a historical 

anthology. 

Results of detailed studies of particular 

mineralized pipes are available for (1) the Orphan mine 

(Gornitz and Kerr, 1970; Chenoweth, 1986); (2) the 

EZ-2 pipe (Krewedl and Carisey, 1986); 3) the Riverview mine (Chenoweth and Blakemore, 1961); (4) the 

Copper House mine (Bromfield, 1952); (5) the Copper 

Mountain mine (Osterstock and others, 1954); (6) the 

Copper House, Copper Mountain, and Parashant mines 

(Watkins, 1975); (7) the Hack Canyon mines (Casebolt 

and others, 1986); and (8) the Ridenour mine (Miller, 

1954; Verbeek and others, 1988). 

COLLAPSE FEATURES ON THE 

HUALAPAI INDIAN RESERVATION 

The Hualapai Indian Reservation is situated on the 

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

which is bounded on the west by the Grand Wash Cliffs; 

these cliffs are the western limit of breccia pipes for the 

Arizona Strip. The western half of the reservation lies on 

the Hualapai Plateau, which is capped by the Redwall 

Limestone. On the Hualapai Plateau no more than 500ft 

of rock strata is available to host an orebody, and little of 

it is sandstone. This is a problem because the orebodies 

that are found in mineralized breccia pipes in northern 

Arizona consistently occur within breccia composed 

dominantly of sandstone clasts. Thus, the Hualapai 

Plateau is considered to have relatively little potential for 

economically mineralized breccia pipes. The eastern half 

of the Hualapai Reservation occupies the western edge 

of the Coconino Plateau, which is capped primarily by the 

Harrisburg Gypsiferous Member of the Kaibab 

Limestone (fig. 3). The Coconino Plateau surface is 

underlain by at least 2,500 ft of strata which includes the 

sandstone units that commonly host orebodies within 

breccia pipes along the Arizona Strip. Thus, magnetometer surveys on the Hualapai Reservation were confined 

to collapse features exposed on the Coconino Plateau 

surface; specifically, all surveys were conducted on the 

Harrisburg Gypsiferous Member of the Kaibab 

Limestone. 

A map of the Hualapai Reservation (fig. 2), where 

more than 900 confirmed and suspected breccia pipes 

were mapped during 1982-1986, shows the density of 

collapse features that is typical in northern Arizona. The 

mapping of breccia pipes on the high plateaus capped by 

the Kaibab Limestone (such as the Coconino, Kaibab, 

and Marble Plateaus) is complicated by (1) relatively 

recent karst development on the Kaibab surface, and (2) 

C6 Breccia Pipes in Northern Arizona 

formation of collapse features by dissolution of gypsum 

units in the Harrisburg Gypsiferous Member of the 

Kaibab Limestone and the Woods Ranch Member of the 

underlying Toroweap Formation. Collapse features of 

the first type shall be referred to in this paper as 

"sinkholes", which are characterized by vertical walls that 

lack inward-dipping beds and a bottom that contains 

uncemented rubble; thus, sinkholes appear to be 

relatively recent karst features. Collapse features of the 

second type shall be referred to as "gypsum collapses," 

which on a plateau surface are difficult to distinguish 

from surface manifestations of the deep-rooted breccia 

pipes. Both gypsum collapses and sinkholes are 

considered to have little economic value because they 

appear to have formed after the regional mineralizing 

fluid phase that occurred sometime in the Triassic, and 

they do not extend downward into the sandstone units 

which most commonly host the orebodies. For this 

report, "breccia pipes" will refer only to those collapse 

features that appear to originate in the Redwall 

Limestone and are formed by the stoping and brecciation 

of the overlying strata. 

In canyons where a cross-sectional view of the third 

dimension is exposed, it is possible to distinguish gypsum 

collapses from Redwall breccia pipes. Locally a breccia 

pipe is exposed along a canyon rim, where a breccia 

column that crops out on the canyon wall is directly 

overlain by a circular, shallow, structural basin on the 

plateau. The surface expression of this structural basin 

has been enhanced by underlying gypsum dissolution, as 

fluid percolating through the pipe moved laterally into 

the gypsiferous units. This effect of increased dissolution 

adjacent to breccia pipes was observed in drill core from 

the Mohawk Canyon pipe (Wenrich and others, 1988), 

where the gypsiferous Woods Ranch Member of the 

Toroweap Formation was almost entirely removed from 

the breccia body. Thus, the collapse feature expressed on 

the plateau surface is generally much larger than the 

underlying breccia column. The Shadow Mountain 

collapse feature on the Marble Plateau is the largest 

(more than 1 mi in diameter) collapse feature known in 

northern Arizona. However, the known orebodies that 

occur in mineralized breccia pipes are much smaller, 

generally 100--400 ft in diameter. 

It is important to develop relatively inexpensive 

geochemical and geophysical exploration techniques, 

prior to drilling, that will distinguish uneconomic gypsum 

collapses from potentially economic, deep-seated breccia 

pipes. Ground magnetometer surveys are one of several 

exploration techniques that have been tested over 

suspected and known breccia pipes. Geochemical surveys 

tested (with mixed results, see Wenrich, 1986) include 

hydrogeochemical, soil geochemistry, helium soil-gas 

(Reimer, 1985; Reimer and Been, 1986), Bacillus cereus 

(bacteria), rock geochemistry, clay hydrocarbon, and 
thermoluminescence sampling surveys. Two geophysical 

techniques, scaler AMT (audio-magnetoteUuric) and 

E-field teHuric, have produced profile data that delineate 

mineralized breccia pipes from surrounding terrane 

(Flanigan, Tippens, and others, 1986). After suspected 

breccia pipes are mapped, geophysical profiles and 

geochemical surveys provide useful techniques for 

selecting drilling targets. 

'MAPPING OF SUSPECTED BRECCIA 

PIPES ON THE HUALAPAI INDIAN 

RESERVATION 

The selection of targets for exploration surveys on 

the Hualapai Reservation began with the mapping of 

suspected breccia pipes (fig. 2) on 1:24,000-scale color 

photographs; suspiciously circular features or alteration 

halos were chosen from the photographs and field 

checked. Many features were also spotted from a 

helicopter, especiaHy those pipes exposed in cliff faces 

that are not visible on the aerial photographs. The 

mapping of the Hualapai Reservation and vicinity is 

presented in Wenrich, Billingsley, and Huntoon (1986, 

1987) and Billingsley and others (1986). 

Exploration criteria for evaluating the potential of 

each coUapse feature were developed during the 

mapping project. The foUowing criteria are considered 

favorable indicators for a mineralized breccia pipe: 

(1) ConcentricaHy inward dipping beds. 

(2) A circular topographic pattern. This is commonly expressed as a topographicaHy high 

rim around a central depression. 

(3) Anomalous radioactivity. A count that is 2.5 

times background or higher is considered 

anomalous. 

( 4) Goethite pseudomorphs and molds of pyrite. 

(5) Colloform celadonite-stained chalcedony. 

( 6) Copper mineralization. This is 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 v~getation or color pattern. 

These criteria must be evaluated by field checking 

to verify the presence of a breccia pipe. Few pipes 

(including those features evaluated in this report) exhibit 

aH nine criteria on surface exposure, but the more 

criteria that are present, the more potential a suspected 

pipe is believed to have. 

MAGNETOMETER SURVEYS OVER 

BRECCIA PIPES 

Geophysical prospecting over breccia pipes is 

dependent on the principle that the pipe itself IS 

physicaHy distinct from the surrounding strata. 

Conductivity anomalies from AMT and E-field telluric 

profile data have successfuHy delineated breccia pipes 

(Flanigan, Tippens, and others, 1986). Transient or timedomain electromagnetic surveying has shown changes in 

resistivity between the breccia column and the adjacent 

country rock (Standish and Schmeling, 1986). ShaHow 

seismic studies across breccia pipes show promise in 

distinguishing the ring fracture, the inward-dipping beds, 

and the breccia mass from the surrounding strata 

(Hasbrouck, 1986). 

The sedimentary units that host breccia pipes can 

be expected to exert low magnetic intensities because of 

their detrital ilmenite. The uranium ore deposits within 

Colorado Plateau pipes are not known to contain 

magnetic minerals such as magnetite, ilmenite, and pyrrhotite. The deposits in these pipes contain such sulfide 

minerals as pyrite, marcasite, galena, arsenopyrite, millerite, gersdorffite, siegenite, and sphalerite, plus the 

copper sulfides chalcocite, covellite, chalcopyrite, enargite, tennantite, digenite, and djurleite. The magnetic iron 

sulfide, pyrrhotite, has not been found within pipe 

deposits, nor is it expected to be associated with the 

aforementioned lower temperature mineral assemblage. 

A petrographic study of the Moenkopi Formation 

by R.A. Cadigan (in Stewart and others, 1972) identified 

detrital magnetite, magnetite-ilemenite, and ilmenite, 

which "occur as black to brown, rounded to subangular, 

opaque grains." Preliminary thin section analyses by H.B. 

Sutphin (oral commun., 1987) indicate that the Moenkopi Formation contains a higher concentration of heavy 

minerals, including ilmenite and magnetite, than does the 

underlying Kaibab Limestone, Toroweap Formation, or 

Coconino Sandstone. Detrital ilmenite, which is more 

common than magnetite, may locally compose as much 

as 2 percent of the Moenkopi framework grains. In 

contrast, clastic horizons from the aforementioned 

underlying units generally contain only trace amounts, if 

any, of ilmenite or magnetite, and the carbonate horizons 

lack these minerals altogether. Thus, blocks of Moenkopi 

Formation that have been downdropped into a breccia 

pipe contained within the Kaibab Limestone or Toroweap Formation can be expected to exhibit a magnetic 

anomaly relative to the surrounding country rock. 

Ground Magnetometer Surveys Over Breccia Pipes, Arizona C7 
Modeling of magnetic anomalies can be used to 

estimate the depth of the anomaly. A best-fit magnetic 

model for the breccia pipe can be used to calculate. an 

anomaly depth on the order of tens or hundreds of feet; -

this depth indicates the amount of vertical downdropping 

of Moenkopi blocks to be expected within a breccia pipe. 

Model calculations that suggest shallower anomaly 

depths could still indicate the presence of downdropped 

Moenkopi sediments and thus the potential for a breccia 

pipe. If the relatively recent shallow collapse features on 

the Kaibab Plateau (sink holes and possibly gypsum 

collapses) formed after the Moenkopi sediments were 

stripped off the plateau surface, then Moenkopi breccia 

would not be expected within these features, nor would 

there be an associated magnetic anomaly. Thus, the 

effective use of magnetic surveys over suspicious collapse 

features may be limited to the Kaibab surface, where 

Moenkopi sediments form the upper part of the downdropped breccia column. 

Flanigan and others (1987) present preliminary 

results of a high-resolution aeromagnetic survey that was 

conducted over a section of the Coconino Plateau in the 

eastern Hualapai Reservation. Their data do not show 

any unique magnetic signature that coincides with the 

mapped collapse features, including three features that 

were surveyed by ground magnetometer and discussed in 

this paper-220, 569, and 570. The aeromagnetic data 

show no local magnetic anomaly at, or in the vicinity of, 

these three features; the data at these locations blend 

into the regional magnetic gradient. The surveys of 

Flanigan and others (1987) were flown 90 m above 

ground level with flight lines spaced 120 m apart; 

magnetic readings averaged every 22 m along each line. 

Apparently, either the aircraft was too high to detect the 

small amplitude of the magnetic anomalies of the pipes 

(attenuation due to distance) or the flight lines did not 

pass directly over any pipes. The aeromagnetic surveys 

did record magnetic anomalies that reflect several major 

faults shown on maps of the northeastern (Wenrich, 

Billingsley, and Huntoon, 1986) and southeastern 

(Billingsley and others, 1986) parts of the Hualapai 

Reservation. 

Methods 

The ground magnetometer surveys were 

conducted in June 1985 over two breccia pipes that have 

been confirmed by drilling-the Mohawk Canyon pipe 

and piAe 562-and over four suspected breccia 

pipes-220, 493, 569, and 570 (fig. 4). All of these 

surveys were conducted on the Coconino Plateau 

surface, which is capped by the Harrisburg Gypsiferous 

Member of the Kaibab Limestone. 

Each ground magnetometer survey was run in a 

grid pattern, with 3 or 4 lines transecting the feature, and 

C8 Breccia Pipes in Northern Arizona 

each line contained 20--30 evenly spaced readings. 

Station spacings for the individual readings along each 

line were adjusted to the size of the feature, from 10m at 

-feature 569 to 60 m at the larger fe-ature. 493. To ensure 

that- adeq!J:~te background data were obtained, each 

survey line extended outside the collapse on each side for 

at least the distance of the feature's radius; usually the 

lines extended outside the feature on each side for 

greater than its diameter. 

An EDA PPM-350 (proton precession total field) 

ground magnetometer was used; the manufacturerclaims a sensitivity of ±0.02 gamma and an absolute 

accuracy of ± 15 ppm within the conditions under which 

it was operated. An accompanying base-station 

magnetometer (EDA PPM-400) recorded total field 

measurements every 15 seconds during the operation, 

which allowed the station readings to be corrected 

for both diurnal variations and reference field values. 

These corrections were calculated automatically in 

the field by connecting the portable and base-station 

magnetometers. 

GROUND MAGNETOMETER RESULTS 

Mohawk Canyon Pipe 

The M~hawk Canyon pipe on the western side of 

Mohawk Canyon was discovered in 1983 and was rotary 

and core drilled during July-October 1984 by the U.S. 

Geological Survey in cooperation with the Bureau of 

Indian Affairs and the Hualapai Tribe (Wenrich and 

others, 1988). The upper 160ft of the pipe is exposed on 

two sides along the cliffs of Mohawk Canyon and a side 

tributary canyon (fig. 5). This exposure provides a crosssectional view of the beds of Harrisburg Gypsiferous 

Member of the Kaibab Limestone, which dip inward 

towards the center of the pipe, and of the gully that has 

been eroded along the circular ring fracture. Mineralized 

rock exposed on the surface within and adjacent to the 

inner ring fracture includes the secondary copper 

minerals malachite, azurite, brochantite, and chrysocol1a, 

plus goethite pseudomorphs and molds of pyrite. 

Somewhere around the turn of the century, these copper 

minerals were mined from two adits dug into the inner 

ring fracture on the eastern side of the pipe. Hand 

samples from the ring fracture (including the adits) 

contain anomalous concentrations of Ag (110 ppm), As 

( 400 ppm), Cu (1.4 percent), Fe (18 percent), Hg (0.3 

ppm), Mo (140 ppm), Ni (70 ppm), Pb (1.2 percent), Sb 

(106 ppm), Se (350 ppm), U (50 ppm), V (190 ppm), and 

Zn (1.2 percent). 

Five rotary and core holes were drilled into the 

Mohawk Canyon pipe; complete lithologic and geophysical logs are presented in Wenrich and others (1988). 
36° 15'-

35° 45' 

I I 4 

I I I I 12 16 KILOMETERS 

0 

0 

1.() 

GRAND CANYON 

• CAVERNS 

35° 30' 

Figure 4. Map of the Hualapai Indian Reservation showing the collapse features surveyed by ground magnetometer-the 

Mohawk Canyon pipe, pipe 562, and collapse features 493, 220, 569, and 570. All of these features are plotted on 1 :48,000-

scale topographic maps in Wenrich, Billingsley, and Huntoon (1986) and Billingsley and others (1986). 

The porosity inherent within this brecciated column 

caused numerous drilling problems including loss of 

circulation, large water consumption, and the loss of 

several hundred feet of casing and the drill stem into a 

cavern that was apparently 30 ft high. Brecciated core 

was recovered in the center of the pipe to a total depth of 

1,012 ft. The core is variably oxidized and reduced and in 

places contains abundant pyrite, goethite, and limonite 

and minor galena, sphalerite, arsenopyrite, and bravoite. 

These minerals are common within economically 

mineralized (uranium) breccia pipes. One rotary hole, 

which reached a total depth of 1,335 ft, contained a 1-ft 

interval of 0.52 percent eU3 0 8 at a depth of 1,191 ft 

within a 20-ft interval that averages 0.04 percent eU3 0 8 • 

While this amount of uranium mineralization does not 

represent an orebody, the Mohawk Canyon pipe merits 

further drilling to fully evaluate its economic potential. 

Because of the uranium mineralization and mineral 

assemblage discovered at this pipe, it is presently 

considered to be one of the pipes on the Hualapai 

Reservation that have the greatest potential for an orebody. 

Ground Magnetometer Surveys Over Breccia Pipes, Arizona C9 
Figure 5. The Mohawk Canyon pipe, exposed on the western rim of Mohawk Canyon. Beds of Harrisburg Gypsiferous 

Member of the Kaibab Limestone dip towards the center of the pipe, and drainages accentuate the circular ring fracture. The 

central portion of the pipe (between the drainages) is about 650ft wide. 

Four lines, each of which contained 21 magnetometer readings, were surveyed across the Mohawk Canyon 

pipe in 1985 subsequent to drilling (fig. 6). The pipe is 

bounded on the south and east by a shear cliff, thus 

limiting the survey. As shown in figure 7, the third and 

fourth magnetometer readings from the south on line 2 

are suspiciously anomalous-the third reading is 7 

standard deviations greater than the mean value of the 

ground magnetometer data set (table 1), and the fourth 

reading is 20 standard deviations greater than the mean 

-therefore these readings are considered to be erroneous. To record such high magnetic values, these 

readings must have been taken near metal objects 

(perhaps something that was buried during the postdrilling reclamation). These readings were therefore 

removed from the calculation of the contour and threedimensional plots shown in figure 8. All other magnetometer values recorded at the pipe lie within one 

standard deviation of the data-set mean and were 

included in figure 8. 

The contouring of lines 1-4, as shown in figure 8, 

reveals a dipole anomaly within the breccia pipe. The 

C1 0 Breccia Pipes in Northern Arizona 

Table 1. Statistics for the data set of 531 ground magnetometer readings recorded during the study of six breccia 

pipes 

[All values of total magnetic field are in gammas] 

Mean ........................ ............................................... . 

Standard deviation ................................................ . 

Minimum value recorded .................................... . 

(feature 570, line 3). Maximum value recorded .................................... . 

(Mohawk Canyon pipe, line 2). 

53,003.5 

27.6 

52,977.2 

53,554.6 

area of low magnetic values is positioned about N. 70° E. 

of the area of high values. Because the magnetic 

declination in this region is N. 15° E., the recorded 

anomaly does not exhibit the properties typical of a 

purely induced magnetic body (Dobrin, 1960, p. 

275-277). Moenkopi Formation rocks or fragments were 

not recognized within the drill core or chip samples 

recovered from the pipe; the exact nature of the magnetic 

source being detected is uncertain. 
Pkh 

Pkf 

Ptw 

MOHAWK CANYON PIPE 

LINE 4 3 2 

• • • • 

• • • • 

• • • • 

• • • • 

• • • • 

• • • • 

• • • • 

• • • • 

Pkh 

Ptw 0 100 FEET 

0 '-------' 50 METERS 

EXPlANATION 

Permian Kalbab Umestone, Harrisburg Gypslferous MemberCalcareous siltstone and fine-grained sandstone with minor 

micritic limestone; very pale orange; thin bedded to massive. 

Contains an 8-ft-thick marker bed composed of chert and 

chert breccia cemented by finely crystalline calcite. Forms 

alternating ledges and slopes. About 62 m (200 ft) thick. 

Permian Kalbab Umestone, Fossil Mountain Member-Very 

finely crystalline limestone containing abundant concentrically 

laminated chert nodules about 10 em In diameter; light 

brownish gray; massive. About 7 4 m (240 ft) thick. 

Permian Toroweap Formation, Woods Ranch MemberCalcareous sandstone and siltstone with minor micritic 

limestone and gypsum Interbeds; pale red to grayish orange; 

thin bedded. About 62 m (200 ft) thick. 

--- Contact, dashed where Inferred 

• u 

D 

oJ"OP 'o 

BOITOM 

• 

--< 

Surface trace of normal fault, dashed where Inferred; ball and 

bar on downthrown side 

Surface trace of reverst! fault, dashed where Inferred; U on 

upthrown side, D on downthrown side 

Drill hole with bottom location In map view 

Location of magnetometer reading 

Ad it 

Figure 6. Geologic map of the Mohawk Canyon pipe 

showing the location of ground magnetometer readings and 

drill holes. 

Pipe 562 

Pipe 562 is located just southeast of the Hualapai 

Reservation, and, as with the other pipes surveyed, 

occurs on the surface of the Coconino Plateau. This pipe 

has a morphology that is typical for breccia pipes exposed 

on the Coconino Plateau surface-a raised rim (about 7 

ft high) of rock outcrop of Harrisburg Gypsiferous 

Member of the Kaibab Limestone encloses a soilcovered, circular, depressed interior that consists of 

Moenkopi Formation sandstones and siltstones (fig. 9) . 

Mineralized rocks, breccia, and obviously dipping beds 

are not present at the surface of this feature. Union 

Pacific Resources (formerly Rocky Mountain Energy, 

Inc.) has driiied the feature intermittently from 1984 to 

1987; the results of the drilling indicate that the collapse 

is a uranium-mineralized breccia pipe. 

Four lines of magnetometer readings were conducted across the mineralized pipe; each line contained 

31-32 readings (fig. 10). The magnetometer survey was 

made subsequent to exploratory drilling at the pipe. As 

shown in figure 11, the three north-south lines (lines 1-3) 

display a local magnetic gradient which increases toward 

the south. The east-west line (line 4) shows a smaller, 

gradational magnetic increase toward the east. The 

anomalously high gamma value that is the fifth reading 

from the east on line 4 is 3.5 standard deviations above 

the mean and is thus considered to be an erroneous 

value-this reading was eliminated from the calculations 

that were used to create figure 12. 

In lines 2-4 anomalously low magnetic values 

occur over the collapsed interior of the pipe. A contour 

map of data from all four lines (fig. 12) shows that the 

centrally located magnetic lows are subtle relative to the 

local magnetic gradient, yet these anomalously low values 

are confined to an area that overlies the pipe. 

The anomalous magnetic low that was detected 

over the pipe could be related to an underlying uranium 

orebody. A bleached (reduced) zone is generally 

associated with the uranium ore deposits in Grand 

Canyon breccia pipes. Because organic matter has been 

found in only minor occurrences within these pipes, 

Gornitz and others (1988) proposed that Fe+ 3 is reduced 

by H2S and that H2S is the most likely reducing agent for 

the ore deposition. Bleaching by H2S-bearing fluids 

would alter the detrital ilmenite and magnetite to nonmagnetic iron and titanium minerals, such as pyrite and 

leucoxene. Ilmenite depletion within bleached rocks has 

been observed in at least four mineralized breccia pipes, 

including the Mohawk Canyon pipe (also see Wenrich, 

1986). In drill core recovered from the Mohawk Canyon 

pipe, a sharp oxidation/reduction contact occurs within 

the Permian Hermit Shale at a depth of 1,322 ft (Wenrich 

and others, 1988). Petrographic studies by H.B. Sutphin 

(oral commun., 1987) reveal that the oxidized side of this 

Ground Magnetometer Surveys Over Breccia Pipes, Arizona C11 
South North Scni.th. North 

53005 53012 

Inside pipe Background .. .. a 

a 53000 ~ 53008 

e 

Inside pipe Background 

" !! "' !! ~ 53004 

... 52995 

.. i 53000 u 

.. 52990 "' " c 

"' ~ 52996 e 

~ 0 

52985 ... ... 52992 

Line 1 Line 3 52980 52988 0 150 300 0 150 300 

53600 53006 

Inside pipe Background .. ~ 53500 a a ~ 53004 

:, 53400 !! !! 

~ 53300 ~ 53002 

u 

Ba.ckground 

~ 53200 i 53000 

c "' ~ 53100- a e ! 52998 

! 53000 0 

0 ... ... 52996 52900 

Line 2 Line 4 

52800 52994 0 150 300 0 150 300 

Distance, in meters 

Figure 7. Total magnetic field profiles of ground magnetometer traverses at the Mohawk Canyon pipe. Lines 1-4 are inde><ed 

to figure 6. The anomalously high magnetic readings in line 2 (third and fourth from south} are 7 and 20 standard deviations, 

respectively, above the mean of the ground magnetometer data set and thus are considered to be erroneous values; these 

readings were not used in the calculation of figure 8. 

contact contains about 0.5 percent ilmenite framework 

grains, whereas the reduced/pyritic side does not contain 

even a trace of ilmenite; instead it has been replaced by 

leucoxene. This replacement could explain the magnetic 

low found over pipe 562, which is known to contain 

subsurface uranium minerals and reduced zones. 

Feature 220 

Feature 220 (fig. 13) is one of seven copper 

prospects within the region south of Laguna graben. 

These prospects were mined intermittently from the 

early 1900's to the 1950's. They appear similar to the 

Jacob Lake prospect on the North Rim and the Anita 

Claims farther east, which consist of malachite- and 

azurite-impregnated chert breccias. Recent mapping 

indicates that these breccias are not tectonic or channel 

deposits but rather are intraformational breccias formed 

during deposition of the Harrisburg Gypsiferous 

Member of the Kaibab Limestone. The breccias near 

C12 Breccia Pipes In Northern Arizona 

feature 220 may be related to movement along the 

Toroweap and Aubrey faults during Kaibab deposition, 

as the breccias appear to thicken adjacent to the faults. 

The excavated copper-rich areas of these prospects 

are roughly circular, but the prospects lack other classic 

pipe morphologies, such as concentrically inward dipping 

beds. The geochemistry of rocks and soil taken from 

these prospects suggests that these copper deposits may 

have been formed by the same mineralizing fluids that 

created ore deposits in mineralized breccia pipes. 

Samples taken from these prospects contain anomalous 

concentrations of Ag, As, Co, Cu, Mo, Ni, Ph, Se, U, and 

Zn-a trace element assemblage similar to that found in 

mineralized breccia pipes. Most element concentrations 

are as high as those measured in uranium ore-bearing 

pipes, for example, 100 ppm Co, 300 ppm Ni, 410 ppm 

Ph, 4,200 ppm Zn, and 41 ppm U. There remains the 

possibility that these prospects are epigenetic copper 

deposits located over breccia-pipe orebodies in an 

intraformational breccia that was readily favorable for 

hosting copper mineralization. 
Figure 8. Three-dimensional model and contour plot of the ground magnetometer data shown in figure 7 for the Mohawk 

Canyon pipe. Heavy dashed line represents the outline of the breccia pipe. Note the magnetic dipole overlying the pipe. 

Five rotary holes were drilled into feature 220 by 

Western Nuclear Inc.; the drilling reports are stored in 

the Hualapai Tribal office files. Four of the holes were 

less than 200 ft deep, and hole 2 reached a total depth of 

297 ft. Hole 4 showed 100 cps (counts per second) 

radiation between 20 and 30 ft, but gamma logs of the 

remaining holes showed radiation less than 40 cps. 

Sparse copper and some limonite and hematite alteration 

were found in the core. The shallow depth reached by 

these holes did not permit us to determine whether a 

breccia pipe occurs at depth. 

Flanigan, Mohr, and others (1986) conducted a 

single northeast-southwest profile of AMT soundings 

across feature 220. Two conductive zones that reach the 

Ground Magnetometer Surveys Over Breccia Pipes, Arizona C13 
Figure 9. Pipe 562 has a morphology that is typical for breccia pipes exposed on the Coconino Plateau-a raised rim of 

Harrisburg Gypsiferous Member outcrop encloses a soil-covered, circular depression that is about 100m in diameter. View is 

to the southwest. 

surface were detected at stations located just northeast 

and southwest of the excavated pit area. A third 

conductive zone, which underlies resistive rocks, was 

recorded near the center of the pit area. Flanigan, Mohr, 

and others (1986) considered this profile data "not 

definitive", again leaving the genesis of the copper 

deposits in question. 

Three lines, each of which contained 22 ground 

magnetometer readings, were surveyed at feature 220, as 

shown in figure 14. A high magnetic reading was 

recorded near the northern end of every survey line (fig. 

15). The single-point positive anomaly near the northern 

end of line 2 is slightly more than one standard deviation 

above the mean; all other readings at the site occur within 

one standard deviation of the mean. Contouring the data 

for lines 1-3 (fig. 16) shows the nearly linear area of high 

magnetic values north of the prospect, plus a magnetic 

low near the excavated pit. These data suggest two 

hypotheses regarding a subsurface structure at feature 

220: (1) The copper deposit may extend at least another 

C14 Breccia Pipes in Northern Arizona 

250 m north of the excavated pit; and (or) (2) an actual 

breccia pipe may be to the north, and the copper 

mineralizing fluids migrated along the permeable 

intraformational breccia and formed the small copper 

deposit to the south of the breccia pipe. 

Feature 493 

Feature 493 (fig. 17), which is one of the largest 

collapses mapped on the Hualapai Reservation, has a 

diameter of about 500 m. The collapse is truncated on its 

western side by Mohawk Canyon. The collapse has a 

striking morphology-a central hill is encircled by a moat 

that is in turn surrounded by higher hills of Harrisburg 

Gypsiferous Member of the Kaibab Limestone. The 

mound-shaped central hill is rimmed by a circular ring of 

steeply inward dipping ( > 45°) red and white beds that 

enclose a center of dark-red soil. The dark-red soil is 

most probably an erosional remnant of downdropped 
PIPE 562 

LINE 1 2 3 

(

1. ·---e ~ _.,..........coLLAPSED INTERIOR 

LINE 4 1• e .1...........-- o o o o o o o o o o o o o oeo @ oeo o o o o o o o o o o o o o "--•-....!) 

0 100 METERS 

'--------' 

300 FEET 

Figure 10. Map showing the location of ground magnetometer readings at pipe 562. The dashed line represents the 

outline of the soil-covered, collapsed interior. The raised rim 

(not shown) that encircles the collapsed interior is about 75 m 

wide. 

Moenkopi Formation. The soil within the moat area 

appears to be weathered Kaibab Limestone. 

Along the cliff face, on the western edge of the 

co11apse, the gypsiferous Woods Ranch Member of the 

Toroweap Formation thins to zero thickness below the 

collapse. On the same cliff face a cave has formed below 

the collapse within the Fossil Mountain Member of the 

Kaibab Limestone. These solution features are evidence 

of the increased fluid movement and dissolution that 

occurred through this collapse. The increased dissolution 

also explains the large enclosing moat area, which is 

probably the result of lateral fluid movement into gypsiferous and calcareous units adjacent to the breccia pipe 

(as discussed earlier in the section on collapse features 

on the Hualapai Indian Reservation). 

Chemical analyses of rock samples from the central 

hill and from altered beds on the western edge of the 

collapse reveal few anomalous elements. Flanigan, Mohr, 

and others (1986) conducted AMT soundings within 

feature 493. The AMT data along a north-south traverse 

shows a very conductive zone about 50 m wide beneath 

the central hill (resistivity plots of the zone resemble the 

morphology of the Washington Monument). This 

conductive zone is enclosed by resistive rocks that are 

surrounded by a conductive zone near the rim of the 

feature. These data support a model in which the central 

hill with inward-dipping beds represents the breccia pipe, 

and the moat area represents the gypsum collapse 

formed by dissolution of the Toroweap adjacent to the 

pipe. 

As shown in figure 18, three north-south lines, each 

of which contained 23 ground magnetometer readings, 

were conducted across feature 493. A shorter line with 10 

readings, line 4, traversed the small central hill and 

crossed lines 1-3 at their midpoints. 

All the magnetic values (fig. 19) recorded at 

feature 493 lie within one standard deviation of the 

ground magnetometer data-set mean value. The most 

significant anomaly recorded here occurs in the vicinity 

of the central hill. An anomalous magnetic high was 

detected over the middle of the central hill, adjacent to an 

area of an anomalous magnetic low which is positioned 

50 m to the east, just outside the eastern rim of the 

central hill. These data (fig. 20) suggest that a magnetic 

body or source is associated with the central hill 

structure. More closely spaced north-south readings 

across and around the central hill would better delineate 

the orientation of this anomaly. As mentioned earlier, 

AMT soundings strongly suggest that the central hill 

represents the surface manifestation of a breccia pipe. 

The dark-red soil on the surface of the hill is likely 

downdropped Moenkopi sediments, which should exhibit 

a relatively higher magnetic response than the 

surrounding Kaibab Limestone. Thus; the magnetic 

anomaly recorded at the central hill may reflect the more 

magnetic Moenkopi sediments that collapsed into the 

breccia pipe. 

Feature 569 

The surface morphology of feature 569 (fig. 21) 

makes it one of the collapse structures most likely to 

overlie a breccia pipe in the National Tank area of the 

Hualapai Reservation (Wenrich, Billingsley, and Van 

Gosen, 1986). The collapse is a peanut-shaped depression enclosed by a low rim of Harrisburg Gypsiferous 

Member of the Kaibab Limestone. The interior of the 

collapse is covered by soil and brush, and the outside is 

rocky and covered with Kaibab float and some juniper 

and pinyon pines. The limited outcrop that rims the 

collapse appears to contain only flat-lying beds. 

A helium soil-gas survey was conducted over the 

collapse in March 1985; mean helium concentrations 

measured inside the depression were similar to concentrations obtained in a background area located 1,500 ft to 

the southwest (Reimer, 1985). A second helium survey 

was run over the collapse in June 1985 (G.M. Reimer, 

personal common., 1986). This time two samples from 

the eastern side of the depression were anomalous, but 

too few background samples were taken to adequately 

define "anomalous." 

Ground Magnetometer Surveys Over Breccia Pipes, Arizona C15 
53040 South North 

.. 

8 

a 

:, 53020 

! 

... 

;; i 53000 

a 

! 52980 

0 

... 

300 600 

53040 

., 

a 

~ 53020 

! 

:i 

.. 

~ 53000 

~ 

a 

~ 52980 

... 

Line 2 52960 0 300 600 

53040 

., 

a 

a 

:, 53020 

! 

... 

~ 

~ 53000 

~ 

a 

! 52980 0 

... 

52960 0 

53120 

., 

Ill 

a 531oo 

~ ! 53080 

... 

~ 53060 

.. 

~ 53040 

a 

~ 53020 

... 53000 

52980 -300 

South 

West 

I 

I 

I 

I 

I I 

1 Center 1 

I of I 

:collapse: 

I 

I 

I 

300 

I 

I 

I 

I 

I I 

I Center I 

I of I 

I Collapse: 

0 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

North 

Line 3 

600 

Ea.st 

Line 4 

300 

Distance, in meters 

Figure 11. Total magnetic field profiles of ground magnetometer traverses at pipe 562. Lines 1-4 are indexed to figure 10. 

The anomalously high gamma value that is the fifth reading from the east on line 4 is considered to be a false value because 

it is 3.5 standard deviations above the mean; this reading was eliminated in the calculation of figure 12. 

A northwest -southeast line of AMT soundings was 

measured across the long dimension of feature 569 by 

Flanigan, Mohr, and others (1986). A small conductive 

zone was recorded just southeast of the center of the 

collapse. Because of the small size of this zone, Flanigan, 

Mohr, and others (1986) considered the feature a 

"questionable breccia pipe." It is worth noting that the 

small conductive zone is located near the area of 

Reimer's two "anomalous" helium soil-gas samples. 

Four lines of ground magnetometer readings were 

recorded at feature 569 (fig. 22), including two northsouth lines that contained 26 and 27 readings and two 

east-west lines that contained 26 and 29 readings. All the 

values recorded here fall within one standard deviation of 

the mean. All four lines showed anomalously high 

magnetic values (fig. 23) that occur either within the 

depressed interior or near the rim of the collapse. 

Contouring of feature 569 data (fig. 24) reveals two areas 

of anomalously high values, two areas of anomalously 

low values, and a local magnetic gradient that increases 

towards the north. The overall pattern suggests that at 

least two dipole anomalies may be associated with the 

collapse, but if so, would be positioned in different 

orientations than those of bodies with strictly induced 

C16 Breccia Pipes in Northern Arizona 

magnetization. The surface morphology of the collapse 

and the presence of two dipole anomalies suggest that the 

feature represents the surface manifestation of two intergrown breccia pipes. While the data indicate that the 

collapsed interior of feature 569 is magnetica11y 

anomalous, the source of magnetism is uncertain; typical 

Moenkopi sediments have not been identified on the 

surface of the collapse. 

North-south line 2 (fig. 23), which displays the 

most pronounced dipole anomaly recorded during this 

study (Telford and others, 1976), was chosen for 

modeling of the magnetic source. SAKI, a Fortran 

program developed by Webring (1985), was used to 

model the data. The best-fit model (fig. 25) placed the 

top of the magnetic source at ground level. The magnetic 

source continued to a depth of at least 50 m (these closely 

spaced data could not be modeled for greater depths). 

The model approximated a rectangular prism (there was 

not enough information available for a more detailed 

shape) with a diameter of 30m (the width of the collapse 

feature along line 2 is about 50 m ). The model also fit 

best when the magnetic body was tilted slightly to the 

south at depth. Magnetic susceptibilities were estimated 

to be in the range of 10-5 to 10-4 emu/cm3 (electro-
;;o 0 

Figure 12. Three-dimensional model and contour plot of the ground magnetometer data shown in figure 11 for pipe 562. Note 

the area of low magnetic values over the collapsed interior of the pipe. 

Ground Magnetometer Surveys Over Breccia Pipes, Arizona C17 
Figure 13. Feature 220 is a bulldozed copper prospect (about 50 min diameter) among Ponderosa pine trees. The copper 

minerals appear to have formed a stratiform mineralized layer within an intraformational chert breccia. It is uncertain whether 

this deposit overlies a breccia pipe. View is to the northeast. 

magnetic units per cm3), which are typical values for 

detrital magnetism in sedimentary rocks (Clark, 1966). 

In summary, modeling of the magnetic data from 

feature 569 reveals that the magnetic source, which is 

slightly smaller than the surface diameter of the collapse, 

begins at the surface and extends to a depth of at least 50 

m. The magnetic susceptibilities recorded are typical of 

detrital magnetism in sedimentary rocks. 

Feature 570 

Feature 570 is very similar in surface morphology 

to pipe 562 described earlier, except that 570 is breached 

on one side (fig. 26). Its center is soil covered and 

surrounded on three sides by a circular rim about 15 ft 

high of rocks of the Harrisburg Gypsiferous Member. 

The rim is rockier than the interior of the collapse, but 

outcrop is generally absent throughout the feature. The 

morphology alone makes Feature 570 one of the best 

prospects for an underlying breccia pipe in the National 

C18 Breccia Pipes in Northern Arizona 

Tank area of the Hualapai Reservation (Wenrich, 

Billingsley, and Van Gosen, 1986). 

Flanigan, Mohr, and others (1986) conducted 

AMT soundings across feature 570 along east-west and 

north-south lines. Both lines recorded a conductive zone 

about 100 m in diameter that is centered in the middle of 

the collapse. The zone was recorded vertically about 900 

m through the entire depth of the profile. The conductive 

zone appears to split at depth, and the more conductive 

section plunges to the south and east. The data suggest 

an underlying, plunging breccia pipe; this plunge must be 

considered in future drilling plans for the pipe. 

Three north-south lines, each of which contained 

22 ground magnetometer readings, were traversed across 

the collapse (fig. 27). The magnetic data recorded here 

are the least variable data of all the features surveyed. A 

constant magnetic gradient appears in every survey line 

(fig. 28); the magnetic values increase toward the north. 

All the magnetic values recorded at feature 570 lie 

within one standard deviation of the mean (fig. 28). The 
LINE 2 3 

• • • 

• • • 

• • • 

• • • FEATURE 220 

• • • "Copper prospect" 

• • • 

• • • 

• • • 

• • • 

• • • 

• • • 

• ~.......--=--PIT AREA 

I ~~ • 

• ' . • • • 

• • • 

~ • • • ·N· • • ~ • 0 100 METERS 

• • • 

• • • 0 300 FEET 

• • • 

• • • 

• • • 

Figure 14. Map showing the location of ground magnetometer readings at feature 220. Patterned area represents 

the extent of the excavated pit. 

data here appear featureless and lack the localized, 

magnetically anomalous areas that are associated with 

the other collapses surveyed. Two subtle magnetic lows 

(fig. 29) occur just south of the collapsed interior of 570 

in lines 2 and 3. Yet similar subtle lows also appear north 

of and outside the collapse in lines 1 and 3. Overall, the 

magnetic data at 570 do not appear to suggest the 

presence of an underlying breccia pipe as do the AMT 

soundings at this site by Flanigan, Mohr, and others 

(1986). 

CONCLUSIONS 

Magnetic anomalies were detected at five of the six 

collapses surveyed: 

(1) The Mohawk Canyon pipe contains surface 

copper mineralization and subsurface uranium mineralization that has been confirmed by rotary drilling and 

coring. A dipole anomaly was recorded over the pipe, 

with the area of low magnetic values positioned about N. 

70° E. of the high value area. 

53015 

.. 

a 

e 

:, 53010 

..., 

~ 53005 

u 

"' 

~ 

9 53000 

.. 

0 

... 

.. 

52995 

53040 

l53030 

c 

-. 53020 

~ ~ 53010 

"' 

a 53000 

-;; 

0 

... 52990 

53020 

l53015 

~ 53010 

::!! 

= 53005 u 

"' 

~ 53000 

a 

! 52995 0 

... 

52990 

Line 1 

350 700 

350 700 

Line 3 

52985 .:r--..---,..--,--,..--..----r---.---.--r---r--..--,..--,--r--r----r---.---.--.--~ 

0 

South 

350 

Distance, in meters 700 North 

Figure 15. Total magnetic field profiles of ground magnetometer traverses at feature 220. Lines 1-3 are indexed to 

figure 14. The single high gamma reading on the north end of 

line 2 is slightly more than one standard deviation above the 

mean; all other readings at the site lie within the standard 

deviation. 

(2) Exploratory drilling at pipe 562 indicates that 

the collapse is a uranium-mineralized breccia pipe. 

Anomalously low magnetic values were detected over a 

portion of the collapsed interior of the pipe. 

(3) Feature 220 appears to be a stratiform copper 

deposit within an intraformational breccia. The deposit 

may overlie a breccia pipe; the exact structure of the 

deposit is uncertain. A nearly linear area of high 

Ground Magnetometer Surveys Over Breccia Pipes, Arizona C19 
53026 

53020 

~ 53014 

~ 53008 

~ 53002 

52996 

52990..-..-~ 

1c.O 

Figure 16. Three-dimensional model and contour plot of ground magnetometer data shown in figure 15 for feature 220. Note 

the area of high magnetic values north of the feature and the magnetic low in the vicinity of the excavated pit. 

magnetic values occurs north of the feature, and an area 

of low magnetic values exists in the vicinity of the 

excavated pit. 

( 4) AMT soundings and field observations at 

feature 493 suggest that the small hill in the center of the 

collapse, which is rimmed by steeply inward dipping beds, 

represents a breccia pipe, which is endosed by a gypsum 

collapse moat. The magnetic data reveal an east-westoriented dipole anomaly associated with the central hill. 

C20 Breccia Pipes in Northern Arizona 

(5) The surface morphology of feature 569 

indicates that some type of collapse is present here. 

Helium soil-gas surveys and AMT soundings were 

incondusive. The magnetic data shows two areas of 

anomalously high values and two areas of anomalously 

low values within and bordering the collapse, which 

suggests that this peanut-shaped depression may 

represent the surface manifestation of two intergrown 

breccia pipes. 
Figure 17. Feature 493. The collapse contains a small hill rimmed by circular, inward-dipping beds, which is encircled by a 

moat, in turn surrounded by higher hills. Entire feature, rim to rim, is about 500 m wide as viewed to the west with Mohawk 

Canyon in the background. 

( 6) The surface morphology of feature 570 

indicates a collapse that is about three-fourths enclosed 

by a circular, raised rim. AMT soundings suggest an 

underlying, plunging breccia pipe. The magnetic data 

reveal a featureless, constant local magnetic gradient that 

lacks the magnetic anomalies associated with the other 

collapses surveyed. 

A dipole magnetic anomaly recorded along line 2 

at feature 569 was modeled to determine the magnetic 

source. The best-fit model reveals that: (1) The magnetic 

source begins at the surface and extends to a depth of at 

least 50 m, (2) the source is slightly smaller than the 

surface diameter of the collapse, and (3) the magnetic 

susceptibilities recorded are typical of detrital magnetism 

in sedimentary rocks. 

Petrographic studies indicate the Moenkopi 

Formation contains a higher concentration of heavy 

minerals-including detrital grains of ilmenite, 

magnetite, and magnetite-ilmenite (ilmenite is most 

abundant)-than the underlying Kaibab Limestone and 

Toroweap Formation. The ±0.02-gamma sensitivity of 

the ground magnetometer used in this study allowed 

detection of subtle magnetic anomalies. These anomalies 

suggest magnetic susceptibilities that are typical for 

ilmenite- and magnetite-bearing sedimentary rocks. The 

dipole magnetic anomalies detected over collapses may 

reflect Moenkopi sediments of relatively higher magnetic 

content that have been downdropped into Kaibab 

Limestone host rock. Surface exposures of typical Moenkopi rocks are visible only at feature 493, but the 

precision of the instrument used requires little magnetic 

source to be present for detection. Thus, magnetic 

surveys over suspicious collapse features should be 

useful on plateau surfaces capped by the Kaibab 

Limestone, where Moenkopi sediments could downdrop 

into the breccia column. 

The anomalously low magnetic values recorded 

over the interior of pipe 562 and near the center 

(excavated pit) of feature 220 require a different 

explanation. These anomalous magnetic lows could 

reflect underlying mineral deposits. Bleached (reduced) 

zones are generally associated with the uranium ore 

deposits in Grand Canyon breccia pipes. A depletion of 

magnetic minerals-specifically ilmenite- has been 

Ground Magnetometer Surveys Over Breccia Pipes, Arizona C21 
LINE 2 3 

• • • 

• • 

• • 

• 

• 

• • 

• • 

• • • 

......... ........... . / ' 

• • . " 

e CENTRAL e • 

• • • 

• • 

• !---/ 

-- _ _.... 

• • 

• 

• • 

• • 

• • 

• • • 

• • 

FEATUHE 493 

'\ 

\~ 

\~ 

\o 

I 

I 

/ / 

\-n 

0 1o 1:: 

I~ 

If« 

~· 

-N-

~ 

~00 METERS 

~00 FEET 

Figure 18. Map showing the location of ground magnetometer readings at feature 493. The "rim of collapse" 

represents the crest of the hills surrounding the moat. 

observed within the bleached rocks of mineralized pipes. 

Framework ilmenite grains, which compose about 0.5 

percent of the oxidized breccia, are replaced by nonmagnetic iron and titanium minerals, such as pyrite and 

leucoxene, within the reduced/pyritic breccia. This type 

of ilmenite depletion could explain the magnetic lows 

found over pipe 562 (known to contain subsurface 

uranium minerals and reduced rock) and over feature 

220 (copper deposit). 

The magnetic declination in this region ·is N. 15° E. 

None of the dipole anomalies recorded in this study were 

oriented as would be expected for a strictly induced 

magnetic source, that is, aligned with the area of low 

magnetic values positioned about N. 15° E. of the area of 

high magnetic values. 

C22 Breccia Pipes in Northern Arizona 

53004 South North 

53003 Ba£kground Inside Feature 

53002 

53001 

Line1 53000+-~~~r-r-~~~-,-.~~~~-r-r~~~~ 

-660 

53007 

.. 

; 

a 

:. 53005 

.: 

i 53003 

a 

! 53001 0 

... 

660 

52999~~~~~~~~~~~~~~~~~~~~~ 

-660 

53008 

.. 

a 

a 

:.53006 

~ 53004 

c 

"' a 

~ 53002 

... 

0 660 

Line 3 53000T-~~~r-r-~~_,-,-,~~~~-r-r~~~~ 

-660 

53015 West 

; '53010. 

~ .: 5~005 

~ 

::: 53000 u 

.. 

c 

::52995 

a 

.. 

~ 52990 

0 

Moat Central Hill Moat 

660 

Ea.st 

Line 4 52985 +---r--,--+---r----.--.---....~...r-----..-----, 

0 75 ~0 225 

Distance, in meters 

Figure 19. Total magnetic field profiles of ground magnetometer traverses at feature 493. Lines 1-4 are indexed to 

figure 18. Note the anomaly detected in line 4. 
53014 

~ 53008 

: 53002 

< 

C) 62996 

5299.0 

~Cb~ 

Figure 20. Three-dimensional ~odel and contour plot of ground magnetometer data shown in figure 19 for feature 493. Note 

the east-west-oriented dipole anomaly associated with the central hill. 

Future drilling of the collapse features investigated 

in this report might help to evaluate the effectiveness of 

ground magnetometer surveys in distinguishing breccia 

pipes from shallow, unmineralized collapses. Although 

ground magnetometer surveys alone may not provide 

conclusive evidence for a subsurface, mineralized pipe, 

they seem useful in choosing drilling targets when 

combined with other geophysical techniques (primarily 

AMT). 

ACKNOWLEDGMENTS 

This study was part of larger project funded by the 

Bureau of Indian Affairs in cooperation with the Hualapai Indian tribe. We appreciate the conscientious 

manuscript reviews and suggestions by Viki Bankey (U.S. 

Geological Survey) and Dick Mead (Union Pacific 

Resources). We are also grateful to Hoyt B. Sutphin for 

sharing his prior experiences with ground magnetometer 

surveys over breccia pipes and especially for providing his 

Ground Magnetometer Surveys Over Breccia Pipes, Arizona C23 
Figure 21. Feature 569 is a soil- and brush-covered depression, about 80 m long, rimmed by sparse outcrops of flat-lying 

rocks of the Harrisburg Gypsiferous Member. Sparse juniper and pinyon pines surround the collapse. View is to the north. 

consultation concerning the petrology of the rock units 

within the region. We thank Lindrith E. Cordell for 

sharing his knowledge on magnetic anomalies and Vicki 

Bankey and Michael W. Webring for the computer 

modeling of the data. Joseph F. Mascarenas and Erin 

Nelson participated in the field collection of the data. 

REFERENCES CITED 

Bernstein, L.R., 1986, Geology and mineralogy of the Apex 

germanium-gallium mine, Washington County, Utah: 

U.S. Geological Survey Bulletin 1577, 9 p. 

Billingsley, G.H., 1986, Relations of the Surprise Canyon and 

Watahomigi Formations to breccia pipes in the Grand 

Canyon, Arizona: Geological Society of America 

Abstracts with Programs, v. 18, no. 5, p. 342. 

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. 

C24 Breccia Pipes in Northern Arizona 

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

plates, scale 1:48,000. 

Bowles, C.G., 1965, Uranium-bearing pipe formed by solution 

and collapse of limestone, in Geological Survey research, 

1965: U.S. Geological Survey Professional Paper 525-A, 

p. A12. 

Bromfield, C.S., 1952, Copper House Mining Company, 

Mohave County, Arizona, access road copper geology: 

Defense Minerals Exploration Administration, AR 126, 

5 p. 

Casebolt, L.L., Faurote, J.M., and Fillmore, D.M., 1986, 

Underground geologic evaluation-Hack Canyon breccia pipe uranium ore body, Mohave County, Arizona: 

Geological Society of America Abstracts with Programs, 

v. 18,no.5,p. 345. 

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

Canyon, Arizona, a case history of a mineralized, 

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

Report 86-510, 126 p. 

Chenoweth, W.L., and Blakemore, P.P., 1961, The Riverview 

mine, Coconino County, Arizona: Plateau, v. 33, 

p. 112-114. 

Clark, S.P., Jr., 1966, Handbook of physical constants: 

Geological Society of America Memoir 97, p. 548. 
LINE 1 2 

. LINE 3 ,---... • oooooooooooooo~~ooooooooooooo I • • ...._ \ . . \ LINE 4 0 0 0 0 0 0 0 o o...g__ ® o Oeo 0 o o o o o o o 0 o o o 

•, • I 

• ' • I '-•...._ .. /-RIM OF COLLAPSE 

0 50 METERS '---....J 

0 200 FEET 

FEATURE 569 

Figure 22. Map showing the location of ground magnetometer readings relative to the rim of feature 569. 

Dobrin, M.B., 1960, Introduction to geophysical prospecting 

[2d ed.]: New York, McGraw-Hill, p. 275-277. 

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

Michael, 1986, Electrical character of collapse breccia 

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

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

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

1986, Geophysical exploration criteria for collapse breccia pipes, northern Arizona: Geological Society of America Abstracts with Programs, v. 18, no. 5, p. 355. 

Flanigan, V.J., Webring, M.W., and Mohr, P.J., 1987, 

Preliminary geologic interpretation of the high resolution 

aeromagnetic map of part of the Coconino Plateau, 

Hualapai Indian Reservation, Arizona: U.S. Geological 

Survey Open-File Report 87-53, 8 p., 2 plates. 

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., Metallurgical Society, p. 281-301. 

Hasbrouck, W .P., 1986, Results of shallow siesmic studies across 

the collapse breccia pipe sites on the Hualapai 

Reservation, northern Arizona: Geological Society of 

America Abstracts with Programs, v. 18, no. 5, p. 360. 

Huntoon, P.W., 1986, Ground water flow directions in Colorado Plateau breccia pipes: Geological Society of America Abstracts with Programs, v. 18, no. 5, p. 363. 

Kinkel, A.R., Jr., 1951, Preliminary report on the Apex and 

Paymaster mines, Washington County, Utah: U.S. 

Geological Survey Open-File Report 90, 9 p. 

Krewedl, D.A., and Carisey, J.C., 1986, Contributions to the 

geology of uranium mineralized breccia pipes in northern 

Arizona: Arizona Geological Society Digest, v. 16, 

p. 179-186. 

Landais, P., 1986, Geochemical analyses of the organic matters 

associated with the breccia pipes in the Grand Canyon 

area: Geological Society of America Abstracts with 

Programs, v. 18, no. 5, p. 389. 

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

of uranium ores in collapse-breccia pipes in the Grand 

Canyon area, northern Arizona: Geological Society of 

America Abstracts with Programs, v. 18, no. 5, p. 392. 

Miller, R.D., 1954, Copper-uranium deposits at the Ridenour 

mine, Hualapai Indian Reservation, Coconino County, 

Arizona, Pt. 1: U.S. Atomic Energy Commission, 

RME-2014, p. 1-18. 

Osterstock, R.W., Tillman, C.G., and Young, W.E., 1954, 

Defense Minerals Exploration Administration Docket 

3075: J. and M. Leasing Co., Cox and Ross Claims, 

Copper Mountain Mine, Mohave County, Ariz., 33 p. 

Rasmussen, J.D., Cunningham, C.G., and Gautier, A.M., 1986, 

Primary fluid inclusions in sphalerite from the Hack 1 

and 2 mines, Mohave County, Arizona: Geological 

Society of America Abstracts with Programs, v. 18, no. 5, 

p. 404. 

Reimer, G .M., 1985, Helium soil-gas survey of a collapse 

feature on the Hualapai Indian Reservation, Arizona: 

U.S. Geological Survey Open-File Report 85-394, 15 p. 

Reimer, G.M., and Been, J.M., 1986, Helium soil-gas surveys of 

collapse features on the Hualapai Indian Reservation, 

Arizona: Geological Society of America Abstracts with 

Programs, v. 18, no. 5, p. 404. 

Standish, R.P., and Schmeling, B.D., 1986, The use of transient 

electromagnetics in exploration for mineralized breccia 

pipes: Geological Society of America Abstracts with 

Programs, v. 18, no. 5, p. 415-416. 

Stewart, J.H., Poole, F.G., and Wilson, R.F., 1972, Stratigraphy 

and origin of the Triassic Moenkopi Formation and 

related strata in the Colorado Plateau region, with a 

section on Sedimentary petrology, by R.A. Cadigan: U.S. 

Geological Survey Professional Paper 691, p. 61. 

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 83-908, 6 p., 2 

sheets, scale 1:50,000. 

___ 1986, Redwall Limestone joint control on Orphan 

mine-type breccia pipes on the Marble Plateau, Arizona: 

Geological Society of America Abstracts with Programs, 

v. 18, no. 5, p. 416. 

Telford, W.M., Geldart, L.P., Sheriff, R.E., and Keys, D.A., 

1976, Applied Geophysics: Cambridge, Great Britain, 

Cambridge University Press, p. 155-157. 

Ground Magnetometer Surveys Over Breccia Pipes, Arizona C25 
"' 8 

El 

South 

53040 

~ 53030 

~ 

..; 

~ 

~ 53020 

c 

01 

8 

~ 53010 ... 

North 

53000~~~-r-r,-~~-.~,-~~~-r~~ro~-r-ro 

.53025 

"' 8 

~ c 

- 53015 

~ u 

.. 

~ 

8 53005 

.. 

0 

... 

50 100 150 200 2 0 

Line 2 

"' 8 

If est 

53025 

~ 53015 

"0 

~ 53005 

u 

.. 

c 

:52995 

El 

.. 

0 

... 52985 

"' 8 

El 

~ 53005 

~ i 52995 

01 

8 

~ 52985 

... 

I 

I 

I 

I 

I I 

I Inside I 

:Collapse: Background 

I I 

110 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

Ea.st 

Line 3 

2 0 

Line 4 52995+-~-r~~-r~~-r+-~-r~~-r~~-r~~~ 52~5+-~-r~~-r~~r~,-~-r,-r4-r,-~-r,-~~ -3o uo 2 o -so do ' 240 Distance, in meters 

Figure 23. Total magnetic profiles of ground magnetometer traverses at feature 569. Lines 1-4 are indexed to figure 22. Note 

the dipole anomalies in lines 2 and 3 and the high gamma values in lines 1 and 4. All values recorded here fall within the 

standard deviation of the magnetometer data set. 

Verbeek, E.R., Grout, M.A., and Van Gosen, B.S., 1988, 

Structural evolution of a Grand Canyon breccia 

pipe-The Ridenour copper-vanadium-uranium mine, 

Hualapai Indian Reservation, Coconino County, Arizona: U.S. Geological Survey Open-File Report 88-6, 

75 p. 

Verbeek, E.R., Grout, M.A., Van Gosen, B.S., and Sutphin, 

H.B., 1987, Structure of the Apex mine, southwestern 

Utah: Geological Society of America Abstracts with 

Programs, v. 19, no. 5, p. 340. 

Watkins, T.A., 1975, The geology of the Copper House, Copper 

Mountain, and Parashant breccia pipes, western Grand 

Canyon, Mohave County, Arizona: Golden, Colo., Colorado School of Mines M.S. thesis, 91 p. 

Webring, Michael, 1985, SAKI-A Fortran program for 

generalized linear inversion of gravity and magnetic 

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

85-122, 108 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. 

C26 Breccia Pipes in Northern Arizona 

___ 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, 29 p., 2 plates, scale 1:48,000. 

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

The potential for breccia pipes in the National Tank area, 

Hualapai Indian Reservation, Arizona: U.S. Geological 

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

Wenrich, K.J., and Pratt, L.M., 1985, Paragenesis and 

conditions of formation of ore minerals from metalliferous breccia pipes, northern Arizona: Geological Society 

of America Abstracts with Programs, v. 17, no. 7, p. 7 4 7. 

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 CanyonLithologic and geophysical logs: U.S. Geological Survey 

Bulletin 1683-A, 66 p. 

Wenrich, K.J., Verbeek, E.R., Sutphin, H.B., Van Gosen, B.S., 

and Modreski, P.J., 1987, The Apex mine, Utah-A 

Colorado Plateau-type solution-collapse breccia pipe, in 

Sachs, J.S., ed., USGS research on mineral resources, 

1987; program and abstracts: U.S. Geological Survey 

Circular 995, p. 73-74, 76-77. 

Wheeler, R.L., 1986, Selecting reliable alignments of mapped 

points-Structural control of breccia pipes on the Marble 

Plateau, northern Arizona: Geological Society of America Abstracts with Programs, v. 18, no. 5, p. 422. 
53020 

~ 53010 

:E 

:E 53000 

< 

"52990 

~14111 

Figure 24. Three-dimensional model and contour plot of ground magnetometer data shown in figure 23 for feature 569. Note 

the two areas of anomalously high values and two areas of anomalously low values associated with the collapse. 

Ground Magnetometer Surveys Over Breccia Pipes, Arizona C27 
South Feature 569 - Line 2 North 

5.0-

(I) 

CG 

: Background 

-(I) 

t! 2.5-

c: 

c: 

... 

:g - • . ! 0 .... 

. ~ .... 

C» 

c: 

0) -2.5-

CG 

e 

-; 

.... 

~ -5.0-

0 

• • 

rOb served 

• values 

• 

• 

100 

• I 

Background 

• • • • • 

• • • 

• 

I I 1 

200 DISTANCE, IN METERS 

I 

of magnetic source 

Figure 25. Computer modeling for the source of the dipole magnetic anomaly recorded along line 2 at feature 569 (fig. 23). 

The model shown produced the calculated curve which best fit the observed data. The magnetic susceptibility used for the 

body was 0.001 emu/cm3 . Alternate models showed less fit between the curve and data but indicated that the source may 

continue to at least 50-m depth. 

C28 Breccia Pipes in Northern Arizona 
Figure 26. Feature 570 is a circular collapse about three-fourths enclosed by a raised rim of rocks of the Harrisburg 

Gypsiferous Member. The surface morphology of this collapse is similar to that of pipe 562 described earlier. Interior of collapse 

is about 140 min diameter. View is to the west. 

Ground Magnetometer Surveys Over Breccia Pipes, Arizona C29 
LINE 2 3 

• • • . . . . . . . . . . 

• • . . . . . . . . / . . I 

\ 

• • 

• • • 

• • 

• . . . • • 

• • • 

• • • 

' I 

FEATURE 570 

I-COLLAPSED INTERIOR 

I 

I 

0 100 METERS 

0 300 FEET 

Figure 27. Map showing the location of ground magnetometer readings at feature 570. The dashed line represents 

the inside base of the surrounding rim. The rim area (not 

shown) is about 50 m wide. 

C30 Breccia Pipes in Northern Arizona 

53030 

.. 

a 

~ 53020 

~ 53010 

~ 53000 

: i 52990 

0 

1-

52980 

53030 

.. i 53020 

c 

-. 53010 

~ ~ 53000 

;, 

a 5299o 

10 

0 

1- 52980 

53030 

; 53020 

e 

.. 

"' .: 53010 

., 

~ 53000 

.. i 52990 

a 

-;;; 52980 

0 

1-

52970 

Center of Collapse 

Center of Collapse 

Center of Collapse 

Line 1 

Line 2 

Line 3 

52960~,-~-r-r~~-,~~~~~~4-~-r-r~~-,---~ 

0 

South 

250 

Distance., in meters 500 

North 

Figure 28. Total magnatic field profiles of ground magnetometer traverses at feature 570. Lines 1-3 are indexed to 

figure 27. This magnetic data is the least variable data of all 

the features surveyed. Note the local magnetic gradient 

recorded in every line. 
en 5302 

~ 5300 

:1 52996 

~ 5298 

5297 

9o 

;]0 ~~ 

, '?>~ ';;o \A~ 't ~ 

Figure 29. Three-dimensional model and contour plot of ground magnetometer data shown in figure 28 for feature 570. The 

data show a local magnetic gradient but lack the magnetic anomalies associated with the other collapses surveyed. 

Ground Magnetometer Surveys Over Breccia Pipes, Arizona C31 

'tt U.S. GOVERNMENT PRINTING OFFICE: 1989-673-047/66036 
!P~Srr~~(dl~~~~~ 

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