Mineral Resource.s of the 

Ragged Top Wilderness Study Area, 

Pima Countyt,Arizona 

' - . . I • 

- U.S. GEOLOGICAL SU.RVEY BULLETIN 1702-H 

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Chapter H 

Mineral Resources of the 

Ragged Top Wilderness Study Area, 

Pima County, Arizona 

By GARY A. NOWLAN, JOCELYN A. PETERSON, 

.JAMES A. PITKIN, and WILLIAM F. HANNA 

U.S. Geological Survey 

TERRY J. KREIDLER 

U.S. Bureau of Mines 

U.S. GEOLOGICAL SURVEY BULLETIN 1702 

MINERAL RESOURCES OF WILDERNESS STUDY AREAS: 

SOUTHWESTERN AND SOUTH-CENTRAL 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 publication is for descriptive purposes only 

and does not imply endorsement by the U.S. Government 

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1989 

For sale by the 

Books and Open-File Reports Section 

U.S. Geological Survey 

Federal Center, Box 25425 

Denver, CO 80225 

Library of Congress Cataloging-in-Publication Data 

Mineral resources of the Ragged Top Wilderness Study Area, Pima County, 

Arizona I by Gary A. Nowlan ... [et al.] 

p. em. -(Mineral resources of wilderness study areassouthwestern and south-central Arizona ; ch. H)(U.S. Geological Survey 

bulletin ; 1702-H) 

Bibliography: p. 

Supt. of Docs. no. : I 19.3:1702-H 

1. Mines and mineral resources-Arizona-Ragged Top Wilderness. 

2. Ragged Top Wilderness (Ariz.) I. Nowlan, G.A. II. Series. Ill. Series: U.S.· 

Geological Survey bulletin ; 1702-H. 

QE75.89 no. 1702-H 557.3 s-dc20 89-600134 

[TN24.A6] [5531

.09791 1.77] CIP 
STUDIES RELATED TO WILDERNESS 

Bureau of Land Management Wilderness Study Areas 

The Federal Land Policy and Management Act (Public Law 94-579, October 21, 

1976) requires the U.S. Geological Survey and the U.S. Bureau of Mines to conduct 

mineral surveys on certain areas to determine the mineral values, if any, that may be 

present. Results must be made available to the public and .be submitted to the President 

and the Congress. This report presents the results of a mineral survey of the Ragged Top 

Wilderness Study Area (AZ-020-197), Pima County, Arizona. 
CONTENTS 

Summary 

Abstract 

Hl 

Hl 

Character and setting Hl 

Identified resources Hl 

Mineral resource potential H3 

Introduction H3 

Character and setting H3 

Previous investigations H4 

Present study H4 

Acknowledgments H4 

Appraisal of identified resources H4 

Mining and leasing activity H4 

Appraisal of sites examined HS 

Ragged Top mine HS 

Barite prospects HS 

Other prospects H6 

Sand and gravel H7 

Summary H7 

Assessment of mineral resource potential H7 

Geology H7 

Geochemistry Hll 

Geophysics Hl4 

Gravity and aeromagnetic data H14 

Aerial gamma-ray spectr9metry HlS 

Mineral and energy resource potential HlS 

Vein deposits HlS 

Porphyry copper deposits H16 

Uranium in the Apache Group H16 

Thorium, rare-earth elements, quartz, feldspar, and mica in granite H16 

Energy resources H16 

References cited Hl6 

Appendixes 

Definition of levels of mineral resource potential and certainty of assessment H20 

Resource/reserve classification H21 

Geologic time chart H22 

FIGURES 

1. Index map showing location of Ragged Top Wilderness Study Area, Pima County, 

Arizona H2 

2. Map showing mineral resource potential, geology, U.S. Bureau of Mines sampling 

sites, and locations of mines and prospects of Ragged Top Wilderness Study 

Area H8 

3. Map showing stream-sediment and rock sample sites and areas of geochemical 

anomalies, Ragged Top Wilderness Study Area H12 

4. Bouguer gravity anomaly map of Ragged Top Wilderness Study Area H14 

5. Aeromagnetic map of Ragged Top Wilderness Study Area Hl4 

Contents V 
TABLES 

1. Selected geochemical data for U.S. Bureau of Mines samples from mines and prospects 

in and near Ragged Top Wilderness Study Area, Pima County, Arizona H6 

2. Geochemical statistics for elements present in anomalous amounts in drainage-basin 

samples collected in 1987 in and near Ragged Top Wilderness Study Area, Pima 

County, Arizona H13 

VI Contents 
Mineral Resources of the 

Ragged Top Wilderness Study Area, 

Pima County, Arizona 

By Gary A. Nowlan, Jocelyn A. Peterson, James A. Pitkin,- and William F. Hanna 

U.S. Geological Survey 

Terry J. Kreidler 

U.S. Bureau of Mines 

SUMMARY 

Abstract 

The Ragged Top Wilderness Study Area (AZ- 020-197), 

for which mineral surveys were requested by the U.S. Bureau 

of Land Management, encompasses 4,460 acres in southcentral Arizona. Throughout this report, "study area" includes the wilderness study area and adjacent terrain where 

samples were collected. Field work was carried out in 1987 

by the U.S. Bureau of Mines and the U.S. Geological Survey 

to appraise the identified (known) resources and assess the 

mineral resource potential (undiscovered) of the wilderness 

study area. The study area includes the northern part of a 

mineralized area that includes the Silver Bell porphyry copper 

deposits. Despite this proximity to a major mine and the 

presence of several mines and prospects within and near the 

study area, no metallic resources were identified; exposures 

of mineralized rock are generally erratic and small. Sand and 

gravel are present in minor amounts, but they have no unique 

qualities and other supplies are closer to markets. 

Part of the southwest corner of the study area has high 

resource potential for gold, silver, lead, vanadium, barite, 

molybdenum, copper, and zinc in vein deposits. Adjacent 

parts of the study area to the north, west, and south have 

moderate resource potentfal for zinc, lead, barite, molybdenum, gold, silver, and copper in similar veins. Part of the east 

side of the study area has low resource potential for gold, 

barite, lead, silver, 'zinc, and copper in veins. The· southern 

part of the study area has moderate resource potential for 

copper, silver, gold, and molybdenum in porphyry copper 

deposits. The east-central part of the study area has low 

resource potential for uranium deposits in veins and disseminated in Proterozoic sedimentary. rocks. The northern part of 

the study area has low resource potential for thorium and 

rare-earth elements such as lanthanum in monazite or other 

Manuscript approved for publication, May 2, 1989. 

accessory minerals in Proterozoic granite and for quartz, 

feldspar, and mica for industrial uses in pegmatites within 

granite. The study area has no potential for oil and gas or for 

geothermal energy resources. 

Character and Setting 

The Ragged Top Wilderness Study Area (AZ020-197) (fig. 1) is located about 35 mi northwest of 

Tucson, Ariz., on the northeast side of the Silver Bell 

Mountains, a small range within the Basin and Range 

physiographic province. The study area lies partially in the 

northern part of the recently identified Silver Bell caldera, 

which provides the structural setting with which the Silver 

Bell porphyry copper deposits are associated (Sawyer,· 

1987). The study area is underlain by Proterozoic (see 

geologic time chart in "Appendixes") granitic and sedimentary rocks, Cretaceous volcanic rocks and granodiorite porphyry, and Tertiary rhyolite. A veneer of pediment gravels 

covers much of the granite north of Ragged Top. 

Identified Resources 

No metallic mineral resources were identified in the 

study area; exposures of mineralized rock are erratically 

distributed and small. The study area lies northeast of the 

Siiver Bell mining district, which has produced copper 

since 1865, but little mining has occurred within the study 

area. Blocks of claims have been established in the study 

area and along the southwest boundary. Among these 

claims is the Ragged Top mine, which reportedly produced 

some zinc-lead-copper ore (Cruver and others, 1982). 

South-southwest of the Ragged Top mine are two barite 

prospects, and other small prospects are present in and near 

the west side of the study area. 

Mineral Resources of the Ragged Top Wilderness Study Area, Arizona Hl 
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Figure 1. Index map showing location of Ragged Top Wilderness Study Area, Silver Bell mining district, southern boundary of Silver Bell caldera, and selected mines and 

prospects, Pima County, Arizona. 
There are no oil and gas leases near the study area, and 

appropriate reservoir rocks are absent. Sand and gravel are 

not likely to be developed because other equally suitable 

material is present closer to markets. 

Mineral Resource Potential 

Primarily on the basis of strong geochemical anomalies, part of the southwest comer of the study area, which 

includes the Ragged Top mine area and known barite 

prospects, has high resource potential for gold, silver, lead, 

vanadium, barite, molybdenum, copper, and zinc in vein 

deposits (fig. 2). The adjacent parts of the study area to 

the north, west, and south, with less intense geochemical 

anomalies, have moderate resource potential for zinc, lead, 

barite, molybdenum, gold, silver, and copper in similar 

veins. An area of weak geochemical anomalies on the east 

side of the study area may also contain such veins; this area 

has low resource potential for gold, barite, lead, silver, zinc, 

and copper. The southern part of the study area has 

moderate resource potential for copper, silver, gold, and 

molybdenum in porphyry copper deposits; propylitic alteration is present in some rocks south of the Ragged Top fault, 

and three porphyry-copper ore bodies are known to the 

southwest within 2 mi of the study area. The east-central 

part of the study area has low resource potential for uranium, either in veins or disseminated throughout Proterozoic sedimentary rocks. Elsewhere in Arizona, similar 

Proterozoic rocks contain uranium. The northern part of 

the study area, underlain by granite, has low resource potential for thorium and rare-earth elements such as lanthanum in monazite or other accessory minerals and has low 

resource potential for quartz, feldspar, and mica for industrial uses in pegmatites. The study area has no potential for 

oil and gas or for geothermal energy resources. 

INTRODUCTION 

This mineral survey was requested by the U.S. Bureau 

of Land Management (BLM) and is the result of a coopera· 

tive effort by the U.S. Geological Survey (USGS) and the 

U.S. Bureau of Mines (USBM). An introduction to the 

wilderness review process, mineral survey methods, and 

agency responsibilities was provided by Beikman and others (1983). The USBM evaluates identified resources at 

individual mines and known mineralized areas by collecting data on current and past mining activities and through 

field examination of mines, prospects, and mineralized 

areas. Identified resources are classified according to a system that is a modification of that described by McKelvey 

(1972) and U.S. Bureau of Mines and U.S. Geological 

Survey (1980). USGS studies are designed to provide a 

scientific basis for assessing the potential for undiscovered 

mineral resources by determining geologic units and structures, possible environments of mineral deposition, presence of geochemical and geophysical anomalies, and applicable ore-deposit models. Goudarzi ( 1984) discussed 

mineral assessment methodology and terminology as they 

apply to these surveys. See "Appendixes" for the definition 

of levels of mineral resource potential and certainty of assessment and for the resource/reserve classification. 

Character and Setting 

The Ragged Top Wilderness Study Area (AZ020-197) (fig. 1) is located in south-central Arizona about 

35 mi northwest of Tucson. It covers 4,460 acres on the 

northeast side of the Silver Bell Mountains. The mountains 

are within the Sonora Desert region of the Basin and 

Range physiographic province, which in this part of Arizona ~s characterized by north- to northwest-trending 

mountain ranges separated by broad valleys. The valleys 

are made up of gravel-veneered pediments and local, deep, 

gravel-filled basins. The stutly area is underlain by two 

very different geologic terranes\_ The terrane north of the 

prominent Ragged Top fault (~. 2) is composed of 

Proterozoic granitic and sedimentary rocks, and the terrane 

south of the fault is composed of Cretaceous volcanic, 

sedimentary, and intrusive rocks associated with the Silver 

Bell caldera and a later porphyry copper system. Extruded 

along the Ragged Top fault is a dome of Tertiary rhyolite 

that forms the rugged pinnacles of Ragged Top, for which 

the wilderness study area and the fault are named. Ragged 

Top is the collective name for 3,907-ft Ragged Peak, 

nearby 3,200-ft Wolcott Peak (U.S. Bureau of Land Management, 1987, p. 115), and adjacent lower peaks. The 

topography of Ragged Top is steep and rugged, while the 

wilderness study area elsewhere consists of relatively flat 

pediments or gentle hills. 

The study area is accessible from Interstate 10 by the 

A vra Valley road from Rillito or by a gravel road running 

southwest from Red Rock, which is about 15 mi northwest 

of Rillito. Gravel roads providing easy access are present 

along the east, west, and north boundaries of the wilderness 

study area, and all parts of the study area are within walking distance of these roads. The climate is arid with hot 

summers and moderate winters; precipitation falls during 

summer thunder storms or winter rains. 

The Ragged Top Wilderness Study Area lies in the 

Arizona upland subdivision of the Sonoran Desertscrub 

biotic community (Brown, 1982). The vegetation is dominated by shrubs; large intervening spaces contain layers of 

cacti. Trees found in the sudy area include the foothill palo 

verde (Cercidium microphyllum), cat-claw acacia (Acacia 

greggiz), mesquites (Prosopis spp.), and ironwood (Olneya 

tesota). Most of the 20 species of cacti largely confined to, 

or best represented in, the Arizona upland subdivision are 

found here. The most spectacular cacti of the Sonoran 

Desert, the saguaro (Carnegiea gigantea), are found in 

large numbers in the study area and locally become a dense 

Mineral Resources of the Ragged Top Wilderness Study Area, Arizona H3 
saguaro forest (Brown, 1982). The study area contains a 

population of Arizona rosewood (Vauquelinia californica) 

plants. Harris' hawks (Parabuteo harrisii) nest in the 

saguaro, and there is a small population of desert bighorn 

sheep ( Ovis canadensis nelsonz) in the area. 

Previous Investigations 

Mining began in the Silver Bell Mountains in 1865, 

and by the early 1900's the disseminated copper mineralization within the district was recognized as having economic potential. Consequently, this area has received scrutiny by many people over the decades. Of particular note 

are the studies by Watson (1964 ), Richard and Courtright 

(1966), and Graybeal (1982), who described the porphyry 

copper deposits and discussed the structure and petrology 

of the Silver Bell Mountains. Recently, Sawyer (1987) 

interpreted the porphyry copper deposits as being structurally related to a Cretaceous caldera. Joseph (1982) described epithermal veins north of the main porphyry copper 

mineralization. Geologic quadrangle mapping of the Vaca 

Hills 15-minute quadrangle (Banks and Dockter, 1976) 

covers the west one-quarter of the study area. 

Present Study 

For the current study, USBM personnel reviewed 

sources of mineral information that include published and 

unpublished literature, USBM files, and mining claims and 

oil-and-gas lease records at the BLM State office in Phoenix,.Ariz. 

Field work by the USBM consisted of mapping and 

sampling mines and prospects. In all, 24 samples were 

collected: 16 from the Ragged Top mine, 4 from prospects 

within the wilderness study area, and 4 from prospects 

outside the area. All samples were analyzed for gold, silver, and 32 other elements by neutron activation; 4 of them 

were analyzed for copper, lead, zinc, manganese, molybdenum, and silver by direct coupled plasma emission spectroscopy, and 20 were an~lyzed for copper, lead, and zinc 

by wet chemistry and atomic absorption. Bondar-Clegg of 

Lakewood, Colo., performed the analyses; complete analytical data are available for inspection at the U.S. Bureau 

of Mines, Intermountain Field Operations Center, Building 

20, Denver Federal Center, Denver, CO 80225. 

Geologic interpretations of the study area and vicinity 

are based on dissertations by Watson (1964) and Sawyer 

(1987) and an unpublished map by D.A. Sawyer. Geologic 

interpretations of Precambrian rocks in the west one-quarter of the study area are based on mapping by Banks and 

Dockter (1976). USGS personnel conducted a reconnaissance geochemical survey of the study area in March 1987. 

On the basis of initial findings, more samples were collected in December 1987. Geophysical interpretations are 

based on published data. 

Acknowledgments 

We thank D.A. Sawyer for sharing information based 

on his Ph.D. study of the Silver Bell caldera and its relation 

to the porphyry copper mineralization and for assistance in 

sample collection; however, interpretations and conclusions 

are those of the authors. Personnel at the BLM Phoenix 

District Office provided helpful discussions on the mineral 

occurrences in the study area. 

APPRAISAL OF IDENTIFIED RESOURCES 

By Terry j. Kreidler 

U.S. Bureau of Mines 

Mining and Leasing Activity 

The nearest mining district is the Silver Bell, about 1 

mi southwest of the study area (fig. 1). The first production, in 1865, was oxidized copper ore that contained minor 

lead-silver concentrations and was mined from skarn at the 

Boot (Mammoth) mine, about 2 mi southwest of the study 

area. Production from vein and replacement ore bodies 

similar to those at the Boot mine continued intermittently 

until 1930. By 1909 the economic possibilities of lowgrade disseminated copper in igneous rocks were recognized, and over the next 3 years extensive chum drilling 

partially delineated the Oxide and El Tiro ore bodies of the 

Silver Bell mine, 2 mi south and southwest of the study 

area, which at that time were subeconomic. ASARCO 

began further exploration drilling on the Silver Bell porphyry copper deposits in 1948 and started production in 

1954 (Richard aRd Courtright, 1966, p. 157). The mine has 

not operated since 1984; the only production since then has 

been from precipitate recovery (ASARCO, annual report, 

1986). Total production from the district between 1885 and 

1981 was 1.3 billion lb of copper, about 50 million lb of 

lead, zinc, and molybdenum combined, about 6 million oz 

of silver, and about 2,000 oz of gold (Keith and others, 

1983, p. 48). Another porphyry copper body, the North 

Silver Bell ore body, is in T. 11 S., R. 8 E., sec. 33, about 

1 mi southwest of the study area (fig. 1). The company 

plans to develop the deposit pending higher copper prices 

(S.A. Anzalone, ASARCO, Inc., Tucson, Ariz., written 

common., 1987). 

Although 65 mining claims lie wholly or partly in the 

wilderness study area, little mining has taken place (fig. 1); 

44 of those claims have been staked since the release of a 

USGS report in October 1988 (McHugh and others, 1988). 

The history of the Ragged Top mine, on the west boundary, 

is not known except that it was previously called the Franco 

Riqueza claims and reportedly produced some copper:-leadzinc ore (Cruver and others, 1982, p. 98). Two barite 

prospects, also near the west boundary, include one pit and 

H4 Mineral Resources of Wilderness Study Areas: Southwestern and South-Central Arizona 
one shallow shaft about 0.5 mi west-southwest of the 

Ragged Top mine. 

There are no oil and gas leases in or near the· study 

area. Ryder (1983) rated the petroleum potential of the 

study area as zero because the underlying Mesozoic and 

Tertiary igneous rocks are unsuitable source rocks; heat 

associated with them would have destroyed any hydrocarbons that may have existed. 

Appraisal of Sites Examined 

No metallic mineral resources were identified in the 

study area. The Ragged Top mine, two barite prospects, 

and five other prospect pits were examined. Geochemical 

anomalies in the samples from these sites (table 1) indicate 

that the southwestern part of the study area is possibly in 

the outer part of the propylitic alteration zone surrounding 

the three known ore bodies of the Silver Bell mine. 

However, the geochemical anomalies could also have resulted from a later, independent mineralizing hydrothermal 

event. The inferred subeconomic sand and gravel resources 

have no unique qualities, and similar materials are present 

- closer to markets. 

Ragged Top Mine 

The Ragged Top mine is in an embayment on the west 

boundary of the wilderness study area (fig. 2). Workings 

consist of two adits and a shallow prospect shaft. The 

upper adit, 95ft long, was driven along a mineralized zone 

and ends in a partially collapsed and filled winze, now only 

30 ft deep. The lower adit, about 500 ft long and 70 ft 

below the upper adit, intersects the mineralized zone approximately 300ft from the portal (Kreidler, 1987, fig. 2). 

Sixteen samples were taken in the adits, all but two from 

the mineralized zone. 

A 200-ft-diameter alteration zone surrounds the deposit. From a distance, this zone appears yellowish orange 

because sulfide minerals, particularly pyrite, have been 

oxidized during weathering. 

Sphalerite, galena, and minor amounts of chalcopyrite 

are present in the mineralized zone as small irregubirly 

shaped pods and veinlets that fill fractures in a weathered 

and altered granodiorite porphyry. A select sample of 

sulfide minerals was taken from several veinlets and pods 

in both levels to ascertain the base-metal content of the ore 

minerals; the sample contains 29 percent zinc, 15.3 percent 

lead, and 1.56 percent copper (table 1, No. 3). However, 

the average metal content (0.95 percent lead, 0.82 percent 

zinc, and 0.24 percent copper) of the remaining 13 samples 

from the mineralized zone shows the low concentration of 

metals, even though lead and zinc contents are locally high 

(table 1). 

Of the 13 mineralized samples, 3 contain concentrations of gold and silver much higher than the other samples 

(table 1, Nos. 8, 11, and 14). The 10 low-gold samples 

average about 140 parts per billion (ppb) gold, whereaS the 

3 anomalous samples average nearly 4,000 ppb. The 10 

low-si,lver samples average about 12 parts per million 

(ppm) silver, while the 3 anomalous samples average 190 

ppm. 

Arsenic and barium, highly mobile elements in a 

mineralizing environment, are often used as geochemicalprospecting tools to locate deposits of base and precious 

metals. The arsenic content (8 to 41 ppm; table 1) of all 

samples from the Ragged Top mine is higher than average. 

The barium content (600 ~ 1,100 ppm; table 1) of 10 

samples, inciuding the two unmineralized ones, is higher 

than average. The average content for an igneous rock of 

intermediate composition is 2 ppm arsenic and 500 ppm 

barium (Levinson, 1980, p. 865). 

The erratic distribution and small exposures of mineralized rock at the Ragged Top mine preclude the identification of base- or precious-metal resources. 

Barite Prospects 

Two barite prospects are approximately 2,500 ft westsouthwest of the Ragged Top mine (fig. 2, Nos. 19-21). 

The northernmost working, a partly collapsed shaft 

about 30 ft deep, was sunk on a 4.5-ft-wide, vuggy quartz 

vein that strikes N. 15°-20° E., dips vertically, and contains 

pods of barite. The barite pods vary from a few inches to 

.about 1.5 ft long. Other minerals in the vein are pyrite, 

hematite, and limonite. The vein can be traced on the 

surface for about 20 ft before it disappears beneath alluvium. A select sample of barite pods contains 48.6 percent 

barium, equivalent to 82.6 percent barite, (table 1, No. 20); 

a grab ~mple of vein quartz collected from dump material -

contains 5,100 ppm barium (0.86 percent barite), less than 

5 ppb gold, and 9 ppm silver (table 1, No. 19). 

The second working, about 700 ft southwest of the 

shaft, is a prospect pit (fig. 2·, No. 21) on a 2- to 6-ft-wide 

quartz-barite vein. Although not directly traceable on the 

surface, it appears to be an extension of the vein exposed 

at the shaft. The vein strikes N. 21° E. and dips vertically. 

Unlike the vein at the shaft, the quartz and barite here are 

more evenly distributed . A sample of the vein contains 4.8 

percent barium (8.2 percent barite) (table 1, No. 21). 

No barite resources were identified. The lowest commerical grade in use today is 92 percent barite (BaS04

) 

(equivalent to a specific gravity of 4.2) for drilling fluids; 

other uses require grades between 95 and 98 percent 

(Brobst, 1983, p. 486, 496). Barite exposed in the prospect 

pit is too low grade to be of commercial interest. Selective 

mining of the vein and hand sortirig of the barite pods at the 

shaft would yield concentrate containing about 80 percent 

BaSO 4 and would require further processing to reach minimum commercial grade. Even so, the limited exposure and 

unknown extent of the pod-bearing part of the vein indicate 

Mineral Resources of the Ragged Top Wilderness Study Area, Arizona HS 
Table 1. Selected geochemical data for U.S. Bureau of Mines samples from mines and prospects in and near Ragged Top 

Wilderness Study Area, Pima County, Arizona 

[Gold (Au), silver (Ag), bariwn (Ba), and arsenic (As) determined by neutron activation, detection limits 5 parts per billion (ppb), 5 parts per million 

(ppm), 100 ppm, and 1 ppm, respectively; copper (Cu), lead (Ph), and zinc (Zn) determined by wet chemistry and atomic absorption, detection limits 

0.01 percent for all elements; *, outside area boundary; -, not detected; na, not analyzed; >, greater than] 

Sample 

Map No. Type or 

(fig. 2) length (in.) 

Au 

(ppb) 

Ag 

(ppm) 

Cu Pb Zn Mn 

(percent) 

Ba 

(ppm) 

As 

(ppm) 

North of wilderness study area 

*1 

*2 

Grab 

26 

na 

0.14 

na 

0.02 

na 

0.01 

27.5 

.3 

>3 pet 

1,100 

489 

71 

Ragged Top mine, mineralized zone 

*3 

*4 

*5 

*6 

*7 

*8 

*9 

*10 

*11 

*12 

*13 

*14 

*15 

*16 

Select 

45 

62 

55 

44 

42 

45 

38 

48 

30 

33 

54 

52 

42 

58 

66 

24 

35 

75 

4,050 

70 

84 

3,660 

597 

240 

4,270 

140 

170 

8 

7 

7 

25 

190 

10 

140 

36 

5 

-240 

10 

12 

1.56 

.08 

.01 

.01 

.13 

1.37 

.20 

.69 

.21 

.19 

.04 

.06 

.16 

15.3 

.21 

.05 

.01 

1.12 

4.42 

.56 

2.32 

.41 

3.15 

.26 

.85 

.61 

29.0 

.49 

.08 

.14 

1.39 

.98 

.54 

2.70 

1.06 

1.65 

.22 

.83 

.58 

760 

820 

1,100 

890 

250 

390 

850 

700 

380 

600 

300 

850 

20 

34 

24 

33 

28 

35 

39 

34 

33 

41 

39 

29 

33 

38 

Ragged Top mine, nonmineralized zone 

*17 

*18 

37 

39 

64 

11 .01 

.01 

.01 

1,100 

880 

38 

8 

Barite prospects 

19 

20 

21 

Grab 

Select 

35 

9 

na 

na 

.1 

na 

na 

.02 

na 

na 

na 

na 

na 

5,100 

48.6 pet 

4.8 pet 

27 

45 

16 

Ncar southwest corner of wilderness study area 

*22 

23 

*24 

27 

55 

42 

170 

220 

34 

63 

280 

1.3 

.02 

1.8 

that a drilling program would be required to evaluate the 

extent and grade of the barite deposit. The most crucial 

factor in any further development of this vein would be in 

establishing. a local market for the final product. This 

seems unlikely as barite has not been mined in Arizona for 

several years and, as of September 1987, all domestic barite 

production comes from bedded and residual deposits (S.G. 

Ampian, U.S. Bureau of Mines, oral commun., 1987). 

Other Prospects 

Two prospect pits were found outside the northwest tip 

of the study area (fig. 2, Nos. 1, 2). At locality 1, psi4.2 

.23 

3.3 

3.1 

.26 

4.5 

na 

na 

na 

1,400 

3,200 

1,800 

10 

lomelane, a manganese mineral, covers the dump of a small 

pit dug in a volcanic rock of intermediate composition. 

None was seen in place, however, indicating that the 

manganese probably occurred in an isolated pod. A sample 

from the dump contains 27.5 percent manganese and more 

than 3 percent barium (table 1, No. 1). No resources were 

identified. The second pit, dug in an altered volcanic rock 

of intermediate composition, contains thin veinlets of 

quartz or calcite with no sulfides. A chip sample from the 

pit contains 1,100 ppm barium and 71 ppm arsenic but 

does not contain any appreciable metal concentrations 

(table 1, No. 2). 

H6 Mineral Resources of Wilderness Study Areas: Southwestern and South-Central Arizona 
Three prospect pits are in or near the southwest comer 

of the wilderness study area. The northernmost pit (fig. 2, 

No. 22) is in highly altered granodiorite porphyry. No 

major structure is apparent. Malachite and azurite coat 

fractures, and the rock is heavily iron stained, but no sulfide minerals were seen. A chip sample from the pit contains anomalous concentrations of copper, lead, and zinc 

(table 1, No. 22). The two other prospect pits, along the 

south boundary of the wilderness study area (fig. 2, Nos. 

23, 24), are in altered, highly fractured volcanic rocks of 

intermediate composition. At both localities, fracture surfaces are stained by iron oxides; at locality 24, malachite, 

azurite, and a black amorphous mineral, possibly an oxidized copper mineral, were also observed. Sample 23 does 

not contain any anomalous metal concentrations. Sample 

24, however, contains anomalous concentrations of copper, 

lead, and zinc similar to those of sample 22 (table 1). 

Samples 22 to 24 contain 34 to 220 ppb gold, and samples 

22 and 24 contain 63 and 280 ppm silver, respectively. No 

resources were identified. 

All samples from the prospects discussed in this section contain anomalous amounts of barium, and all but two 

(Nos. 23, 24) contain anomalous arsenic. 

Sand and Gravel 

The Sonoran Desert is one of nature's great repositories of sand and gravel, and this study area is no exception. 

Sand and gravel are high-volume, low-unit-value commodities that require a local market for economic development. The occurrences in the Ragged Top Wilderness 

Study Area have no unique properties that would make 

them more valuable than other deposits closer to markets. 

Summary 

No unique mineral resources were identified in the 

Ragged Top Wilderness Study Area. The erratic distribution and generally small exposures of mineralized rock at 

the Ragged Top mine preclude the identification of resources. The barite-bearing quartz veins and the sand and 

gravel deposits are not now, or in the foreseeable future, of 

commercial value. There are no oil and gas leases. 

ASSESSMENT OF MINERAL RESOURCE 

POTENTIAL 

By Gary A. No~lan, jocelyn A. Peterson, james A. Pitkin, and 

William F. Hanna 

U.S. Geological Survey 

Geology 

The Ragged Top Wilderness Study Area can be evaluated for mineral resource potential only by considering the 

broader area that includes the Silver Bell porphyry copper 

deposits which are immediately to the south and which 

reflect geologic processes that have affected the study area. 

Thus, some geologic units are discussed below even though 

they do not crop out within the study area (fig. 2). 

The study area is separated into two main geologic 

terranes by the major west-northwest-trending Ragged Top 

fault Rocks north of the fault are correlated with the 

Middle Proterozoic granite and Middle Proterozoic sedimentary rocks of the Apache Group. South of the Ragged 

Top fault are Late Cretaceous volcanic, sedimentary, and 

intrusive rocks related to the formation of a caldera and the 

intrusion of rocks related to the porphyry copper system. 

Descriptions of the northern terrane are mainly from Watson (1964) and those of the southern terrane are mainly 

from Sawyer (1987). 

The Proterozoic granite consists of porphyritic granite 

and cross-cutting, fine- to medium-grained granite (Banks 

and Dockter, 1976). The granite is composed mainly of 

quartz, orthoclase, plagioclase, and biotite and has minor 

chlorite, epidote, magnetite, apatite, and zircon. Near 

Ragged Top it has abundant iron-oxide minerals after 

magnetite and pyrite, and it contains some resistant quartz 

veins (Watson, 1964). 

Proterozoic diabase is seen only in the granite as dikes 

and sills, too small to show at the map scale, and most 

likely predates deposition of the Apache Group. The rock 

consists mostly of small altered plagioclase laths and pyroxene, most of which have been altered to biotite, chlorite, 

and muscovite (Watson, 1964). The plagioclase and pyroxene form subophitic intergrowths. Quartz was introduced 

by later hydrothermal activity. These rocks contain veinlets of quartz, calcite, and iron-oxide minerals. 

Sedimentary rocks of the Apache Group overlie the 

granite along an erosional unconformity.- At the base of the 

Apache Group is a rounded pebble conglomerate of red to 

orange chert pebbles in a white siliceous matrix that is 

equivalent to the Barnes Conglomerate Member of the 

Dripping Spring Quartzite (Watson, 1964). Overlying the 

conglomerate are interbedded white quartzite and tan silty 

quartzite; one bed of silty rocks is colored red by hematite. 

These· quartzite beds represent the upper part of the Dripping Spring Quartzite. No other formations of the Apache 

Group are present in the study area. 

South of the Ragged Top fault (Sawyer, 1987) the 

oldest Late Cretaceous unit is the El Tiro biotite granite 

unit, containing perthitic potassium feldspar, quartz, plagioclase, and biotite. It predates formation of the Silver Bell 

caldera. This unit is present southwest of the study area, 

along the southwest side of the Silver Bell Mountains. 

The Confidence Peak tuff unit consists of ash-flow tuff 

greater than 3,000 ft thick within the caldera. The tuff 

contains 5 to 20 percent lithic clasts and is compositionally 

a low-silica rhyolite. It contains abundant phenocrysts of 

plagioclase, quartz, and biotite plus a small amount of irontitanium-oxide minerals. Large blocks of Paleozoic rocks 

Mineral Resources of the Ragged Top Wilderness Study Area, Arizona H7 
32° 

27' 

30" 

r < ' 

15 \ 

' I 

M/C Zn, Pb, 

7 

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24 - 'rl( 

H/C~u, Ag~ Pb, V, 

a, Mo, Cu, Zn, [ 1] ...:. c 

f 

( I 

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EXPLANATION 

Geologic terrane having high mineral resource potential (H) for Au, 

Ag, Pb, V, Ba, Mo, Cu, and Zn in vein deposits 

Geologic terrane having moderate mineral resource potential (M) for 

precious and base-metal commodities, as listed, in vein deposits 

Geologic terrane having moderate mineral resource potential (M) for 

Cu, Ag, Au, and Mo in porphyry copper deposits 

Geologic terrane having low mineral resource potential (L) for Th 

and REE in granite and for quartz, feldspar, and mica in 

pegmatite 

Geologic terrane having low mineral resource potential (L) for Au, 

Ba, Pb, Ag, Zn, and Cu in vein deposits 

Geologic terrane having low mineral resource potential (L) for U 

Levels of certainty of potential 

Data only suggest level of potential 

Data give good indication of level of potential 

Commodities 

Ag Silver Peg Quartz, feldspar, and mica 

Au Gold REE Rare-earth elements 

Ba Barite Th Thorium 

Cu Copper U Uranium 

Mo Molybdenum V Vanadium 

Pb Lead Zn Zinc 

Deposit types 

[1] Vein deposits 

[2] Porphyry copper deposits 

Description of map units 

Oa Alluvium and talus (Quaternary) 

Trr Rhyolite of Ragged Top (Tertiary) 

Kgdp Grano~iiorite porphyry (Cretaceous) 

Ksb Silver Bell volcanics unit of Sawyer (1987) (Cretaceous) 

Kcr Claflin Ranch Formation of Richard and Courtright (1966) (Creta- ceous) 

Kcp Confidence Peak tuff unit of Sawyer (1987) (Cretaceous) 

Ya 

Yg 

Apache Group (Middle Proterozoic}-Sandstone and conglomerate 

Granite (Middle Proterozoic) 

( ) Parentheses indicate unit overlain by thin pediment gravels 

---Contact 

---Fault 

Mining activity 

Mining claims located before Oct. 1988 

Mining claims located Oct. 1988-Feb. 1989 

Prospect-Number refers to sampling site, table 1 

Shaft 

Ad it 

Figure 2, Mineral resource potential, geology, U.S. Bureau of Mines sampling sites, and locations of mines and prospects of Ragged 

1988. Geology modified from David A. Sawyer (written commun., 1987). Base from U.S. Geological Survey, 1:24,000 Silver Bell 

Top Wilderness Study Area, Pima County, Arizona. Mineral resource data compiled by Gary A. Nowlan and Jocelyn A. Peterson, 

East and Silver Bell West quadrangles, 1988. 

H8 Mineral Resources of Wilderness Study Areas: Southwestern and South-Central Arizona Mineral Resources of the Ragged Top Wilderness Study Area, Arizona H9 
in a matrix of the Confidence Peak tuff unit are present 

locally. This unit extends into the southern part of the 

wilderness study area (fig. 2). 

Overlying the Confidence Peak tuff unit is the Claflin 

Ranch Formation (Richard and Courtright, 1966) consisting 

of volcaniclastic sedimentary rocks. The Claflin Ranch 

Formation is more than 2,300 ft thick at its type section in 

the study area (sec. 26, T. 11 S., R. 8 E., Silver Bell West 

quadrangle) (Sawyer, 1987), where it is composed of volcaniclastic sedimentary rocks, debris-flow deposits, and 

primary pyroclastic ash-fall .and ash-flow deposits. Elsewhere in the Silver Bell Mountains it is mostly composed 

of primary and reworked pyroclastic flow and fall deposits 

and minor intercalated sedimentary rocks. This unit covers 

about 0.5 mF in the southwest comer of the wilderness 

study area. 

The Silver Bell volcanics unit is a diverse sequence of 

andesitic and dacitic rocks that overlie and locally interfinger with the Claflin Ranch Formation. These volcanic 

rocks include flows, domes, hypabyssal intrusions, and 

related volcaniclastic debris-flow deposits and sedimentary 

rocks. The volcaniclastic rocks include heterogeneous 

matrix-supported mudflow deposits and monolithologic 

clast-supported traction breccias of andesite and dacite 

composition. . Flows and domes are high-potassium dacites 

containing phenocrysts of plagioclase and biotite with 

quartz, hornblende, or pyroxene locally. These rocks represent deposits from a postcollapse composite volcano. 

They are present in the southern part of the wilderness 

study area, directly south of Ragged Top. 

Granodiorite porphyry intrudes both the Confidence 

Peak tuff unit and the Claflin Ranch Formation. The largest intrusion is southwest of Ragged Top, partly within the 

wilderness study area, where it is largely truncated by the 

Ragged Top fault. The mineralogy of these intrusions is 

similar to that of the dacite in the Silver Bell volcanics 

unit, but the plutons are more phenocryst rich. The granodiorite porphyry has undergone strong propylitic alteration 

with the development of epidote. These plutons may be the 

cores of andesitic stratovolcanoes of the Silver Bell volcanics unit. 

The youngest Late Cretaceous volcanic unit is the 

Mount Lord Volcanics, a densely welded tuff containing 

phenocrysts of sanidine, plagioclase, and quartz. The tuff 

is a compound cooling unit as thick as 650 ft. Field evidence suggests that this unit is an outflow facies from a 

source outside the Silver Bell caldera, and geochemical 

considerations support the conclusion that these rocks are 

unrelated to the caldera. This unit is found south and west 

of the study area. 

The last Cretaceous igneous event was intrusion of the 

plutons and dikes associated with the porphyry copper 

deposits. These rocks range from monzodiorite to granodiorite to quartz monzodiorite porphyry; porphyry copper 

mineralization is most closely related to the quartz monzodiorite porphyry. These plutons were intruded along an arc 

on the southwest side of the Silver Bell Mountains along 

the exposed caldera ring faults. They do not crop out 

within the wilderness study area. 

The jagged pinnacles of Ragged Top represent an 

eroded Oligocene flow-banded rhyolite dome extruded 

along the Ragged Top fault. The rhyolite contains sanidine, plagioclase, and biotite phenocrysts. Lithologically 

similar dikes found south of Ragged Top, nearer the porphyry copper deposits, are probably coeval. This rhyolite 

postdates movement on the Ragged Top fault, as it exhibits 

no displacement 

Pediment gravels and alluvium consist of poorly 

sorted, unconsolidated sand and gravel of local derivation. 

They primarily form a thin veneer over Middle Proterozoic 

granite in the northern part of the study area. 

· The major structures and lithologies of the southern 

part of the wilderness study area resulted from Late Cretaceous caldera volcanism. The follow~ng interpretations are 

from $awyer (1987). TheEl Tiro biotite granite unit was 

intruded 73 million years ago (E. W. James and D .A. 

Sawyer, unpub. data cited by Sawyer, 1987, p. 32), prior to 

formation of the caldera. Collapse of the caldera coincided 

with the eruption of the Confidence· Peak tuff unit, which 

formed a thick tuff sequence within the caldera and a thin 

outflow facies exposed in the West Silver Bell Mountains 

about 7 mi west of the study area. Large blocks of Paleozoic sedimentary rocks were enclosed within parts of the 

intracaldera tuff during caldera collapse. The volcaniclastic 

sediments of the Claflin Ranch Formation were derived 

from the reworking of unconsolidated tuff in the uppermost 

part of the Confidence Peak tuff unit. Pyroclastic flows 

and fallout materials higher in the Claflin Ranch Formation 

indicate the close temporal and genetic ties between the 

intracaldera tuff of the Confidence Peak tuff unit and the 

Cbiflin Ranch Formation. Thus, the Claflin Ranch Formation is considered the moat-filling sedimentary material of 

the caldera. Ring faults outline the structural margin of the 

caldera and controlled the emplacement of several plutons 

of the porphyry-copper-forming system. These may have 

been preexisting regional faults that were reactivated during caldera formation. The Silver Bell volcanics unit forms 

a post-collapse composite volcano and associated rocks that 

were deposited on the intracaldera accumulation. Granodi- a 

orite porphyry intrusions may be the roots of such composite volcanoes or may have formed during magmatic resurgence following caldera collapse. After intrusion of the 

granodiorite porphyry, but before intrusion of the quartz 

monzodiorite porphyry suite, the Mount Lord Volcanics 

were deposited from a source outside the Silver Bell 

Mountains. Monzodiorite porphyry intrusions predate the 

mineralization, but grade into later porphyry-copper-related 

quartz monzodiorite porphyries. The hydrothermal activity 

associated with the porphyry copper mineralization accompanied the final Late Cretaceous intrusive activity. 

Hl 0 Mineral Resources of Wilderness Study Areas: Southwestern and South-Central Arizona 
The Ragged Top fault is a major structural feature that 

bisects the study area. Movement along the fault was 

largely strike slip and truncated the north edge of the 

caldera structure. 

Geochemistry 

Stream-sediment samples represent a composite of 

material eroded from all parts of the drainage basin of the 

stream sampled. Panned-concentrate samples derived from 

stream sediment contain selectively concentrated minerals 

that may include ore-related elements that are not easily 

detected in stream-sediment samples. Samples of drainage 

sediment were collected in March 1987 at 11 sites on 

ephemeral streams in the study area (fig. 3). At each 

stream site three samples were collected. One, here called 

a stream-sediment sample, was air dried and then sieved 

through a 30-mesh stainless-steel sieve. A 30-mesh, rather 

than the more conventional 80-mesh, sieve was used to 

lessen the possible dilution effects of wind-blown material 

in this desert environment. The other two samples, each 

derived from 20 lb of stream sediment, were panned until 

1 to 4 oz remained and are here called concentrate samples. 

One of these samples was further concentrated by heavy 

liquids and magnetic separations to produce a nonmagnetic 

heavy-mineral-concentrate sample consisting of accessory 

minerals such as zircon, sphene, and apatite, and nonmagnetic ore minerals. The other concentrate sample received 

no further treatment before chemical analysis for gold and 

is here called a raw panned-concentrate sample. 

The stream-sediment samples and nonmagnetic heavymineral-concentrate samples were analyzed by emission 

spectrography for more than 30 elements. The streamsediment samples were also analyzed (1) for gold by graphite-furnace atomic absorption, (2) for arsenic, bismuth, 

cadmium, antimony, and zinc by inductively coupled 

plasma spectroscopy, and (3) for uranium by fluorimetry. 

The raw panned-concentrate samples were analyzed for 

gold by flame atomic absorption. 

Gold analyses of raw panned-concentrate samples have 

several advantages over gold analyses of nonmagnetic 

heavy-mineral-concentrate samples. The first advantage is 

that a large sample of raw panned-concentrate (from 6 to 27 

g in this study) is analyzed, and thus problems of inhomogeneity are lessened. In contrast, only 5 mg of nonmagnetic heavy-mineral concentrate are analyzed. The second 

advantage is that preparation of raw panned-concentrate 

samples for analysis takes only a few simple steps, so 

chances of losing gold particles are minimized. The third 

advantage is that the analytical sensitivity for gold is less 

than its average bedrock crustal abundance (0.002--0.005 

ppm, Rose and others, 1979, p. 557) if the gold concentration of the raw panned-concentrate sample is converted to 

its concentration in the original stream sediment. The 

'analytical method used in the analysis of raw panned-concentrate samples will detect 0.05 ppm gold in a 10-g 

sample (table 2). 

Additional concentrate samples were collected at 15 

sites in December 1987, and-28 samples of mineralized and 

altered bedrock were also collected then. The concentrate 

samples were collected and treated in the same manner as 

the previous ones except that, in most cases, only 10 lb of 

stream sediment were panned. To establish bedrock background concentrations, analysis of the mineralized and altered rocks was supplemented by the analysis of seven 

samples of relatively unaltered bedrock that had been collected in 1982 by D.A. Sawyer. Rock samples were analyzed by semiquantitative direct-current arc emission spectrography for more than 30 elements. In addition, they 

were analyzed for arsenic, bismuth, cadmium, antimony, 

and zinc by inductively coupled plasma-atomic emission 

spectroscopy, for mecury by cold-vapor atomic absorption, 

for telllurium and thallium by flame atomic absorption, for 

fluorine by ion selective electrode, and for tungsten by visible spectrophotometry. 

Sampling locations, tabulations of the analytical results, descriptions of sample preparation methods, descriptions of rock samples, and descriptions and references for 

the analytical methods are given by McHugh and others 

(1988). 

Table 2 lists selected elements determined in each type 

of drainage sample, the lower and upper limits of determination, the range of concentrations, the 50th percentile 

value, and the threshold (highest background) concentrations. Threshold values were established by both subjectively and statistically examining the data and by comparing the data with geochemical data from mineral resource 

assessments of the Ajo and Lukeville 1° by 2° quadrangles 

(Theobald and Barton, 1983, 1987) and the Table Top 

Mountain, Baboquivari ·Peak, and Coyote Mountains ·Wilderness Study Areas (Peterson and others, 1988; Nowlan 

and others, 1989). 

Three geochemically anomalous areas were delineated 

on the basis of analyses of concentrate and stream-sediment 

samples (fig. 3). Extremely high concentrations of gold, 

silver, lead, vanadium, barium, and strontium characterize 

most concentrate samples from area A (McHugh and others, 1988). Some concentrate samples also contain anomalous concentrations of molybdenum, copper, zinc, cadmium, and bismuth. Concentrations of lead, vanadium, 

barium, and strontium are as high as 1 percent (10,000 

ppm) or greater. Concentrations of gold, silver, and copper 

are 1,000 ppm or greater. Concentrations of zinc, molybdenum, and bismuth are as high as 300-700 ppm, and the 

concentration of cadmium is as high as 70 ppm. The most 

intensely anomalous part of area A is on the southwest 

slopes of Ragged Top. The relative significance of the 

anomalous elements (listed above) in area A, as judged 

from the number and magnitude of anomalous concentrations, is Au=Ag>Pb=V>Ba=Sr>(Mo>Cu>Zn>Cd=Bi). 

Mineral Resources of the Ragged Top Wilderness Study Area, Ar~zona Hll 
Only minimal prospecting has occurred near the most intensely anomalous part of area A, and the source of the 

anomaly is unknown. 

Anomalous area B adjoins the north, west, and south 

margins of area A. The intensity of the geochemical 

anomalies is less in area B than in area A, and there are no 

anomalous concentrations of vanadium, cadmium, and 

bismuth. Area B is divided into two parts, B-north and Bsouth. The suites of anomalous elements in B-north and Bsouth are similar except that B-north lacks anomalous 

concentrations of strontium and B-south lacks anomalous 

concentrations of copper, and the order of importance of 

anomalous elements is essentially the opposite. The relative significance of anomalous elements in B-north is 

Zn=Pb>Ba> (Ag=Ao>Cu>Mo), and that in area B-south is 

I 

\ 

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I 

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I 

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I 

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---......... , 

Mo>Sr>Ba>(Ag=Au>Pb=Zn). The geochemistry of drainage samples from anomalous area B is consistent with the 

mineralogy of veins that have been prospected or mined in 

that area. Mineralized rock samples collected by the 

USBM from the Ragged Top mine in area B-north contain 

as much as 4 ppm gold (Kreidler, 1987). Mineralized and 

altered rocks collected in area B by the USGS contain from 

0.002 ppm to as much as 0.38 ppm gold (McHugh and 

others, 1988). Seven samples of relatively least altered 

Upper Cretaceous rocks collected in and near area B contain less than 0.001 ppm gold. 

Anomalous area C lacks the geochemical intensity of 

areas A and B. Concentrations of gold and silver are 

generally near the lower limits of determination, and concentrations of barium are not universally greater than 

" \ 

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APPROXIMATE BOUNDARY 

OF 

RAGGED TOP WILDERNESS 

STUDY AREA 

(AZ-020-197) 

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EXPlANATION 

• Rock sample 

e Nonmagnetic heavy-mineral-concentrate, raw 

. panned-concentrate, and mlnus-230-mesh streamsediment samples 

A Nonmagnetic heavy-mineral-concentrate and raw 

panned-concentrate samples, only 

• Raw panned-concentrate sample, only 

---- Drainage basin boundary 

Figure 3. Stream-sediment and rock sample sites and areas of geochemical anomalies in Ragged Top Wilderness Study Area, Pima 

County, Arizona. Anomalous area A, B, and C discussed in geochemistry section of. text. 

H12 Mineral Resources of Wilderness Study Areas: Southwestern and South-Central Arizona 
Table 2. Geochemical statistics for elements present in anomalous amounts in drainage-basin samples collected in 1987 

in and near the Ragged Top Wilderness Study Area, Pima County, Arizona 

[Results based on 26 raw panned-concentrate samples, 25 nonmagnetic heavy-mineral-concentrate samples,. and 11 stream-sediment samples, 

except as noted. Concentration determined by emission spectrographic methods except that Au-a was determined by atomic absorption and 

Sb-i and Zn-i were determined by inductively coupled plasma spectroscopy. ppm, parts per million; 50th percentile, concentrations in onehalf of samples were equal to or lower than this number; N, not detected; G, greater than upper limit of determination; L, detected below 

lower limit of determination; <, less than value shown] 

Limits of Determination (ppm) 

Element Lower Upper Minimum 

Concentration (ppm) 

Maximum 50th 

percentile 

Threshold 

Raw panned concentrate 

Gold (Au-a) 10.05 <0.02 150 <0.05 <0.05 

Nonmagnetic heavy-mineral concentrate 

Gold (Au) 20 1,000 N G N N 

Silver (Ag) 1 10,000 N 1,000 N N 

Barium (Ba) 50 10,000 700 G G 3,000 

Bismuth (Bi) 20 2,000 N 300 N N 

Cadmium (Cd) 50 1,000 N 70 N N 

Copper (Cu) 10 50,000 N 1,000 20 30 

Molybdenum (Mo) 10 5,000 N 500 N N 

Lead (Pb) 20 50,000 L G 700 700 

Strontitim (Sr) 200 10,000 N G 700 1,500 

Vanadium (V) 20 20,000 30 15,000 150 500 

Zinc (Zn) 500 20,000 N 700 N N 

Minus-30-mesh stream sediment 

Gold (Au)' 0.001 

Silver (Ag) .5 

Barium (Ba) 20 

Copper (Cu) 5 

Lead (Pb) 10 

Antimony (Sb-i) 2 

Zinc (Zn) 200 

Zinc (Zn-i) 2 

1 Based on 1 0-gram sample. 2 Upper limit is open ended. 

' Based on eight samples. 

(2) 

5,000 

5,000 

20,000 

20,000 

(2) 

10,000 

(2) 

10,000 ppm as is the case in areas A and B. Area C is 

unique in that antimony is anomalous in several samples of 

stream sediment; concentrations are as high as 14 ppm. 

The relative significance of anomalous elements in area C 

is Au=Sb>Ba>Pb>(Ag=Bi>Zn=Cu). Samples of quartz 

veins, diabase, and altered granite from area C contain from 

less than 0.001 ppm to 0.044 ppm gold. 

The Proterozoic igneous and sedimentary terrane north 

of the Ragged Top fault is geochemically different from the 

Late Cretaceous volcanic-intrusive-sedimentary terrane 

south of the fault. Area A and most of area B are south of 

the Ragged Top fault. Mildly anomalous area C, which lies 

mostly north of the Ragged Top fault, is primarily underlain by Proterozoic granite, diabase, and sedimentary rocks. 

Drainage samples from areas north of the Ragged Top fault 

<0.001 0.01 0.001 <0.001 

N .5 N N 

300 1,500 500 500 

20 70 30 30 

30 300 50 50 

<2 14 <2 <2 

N 200 N N 

31 150 77 60 

have high, but not anomalous concentrations of beryllium, 

boron, gallium, scandium, tin, uranium, and yttrium. 

The suites of elements found in anomalous concentrations in samples from areas A, B, and Care consistent with 

an interpreted occurrence of polymetallic or epithermal 

veins conforming to one or more of several mineral deposit 

models (Cox, 1986; Mosier and others, 1986a, b, c). The 

geochemical patterns of areas A and B (fig. 3) suggest 

zoning related to a mineralized area southwest o{ Ragged 

Top. Another possiblity is that multiple independent stages 

of vein mineralization may have occurred. Such veins may 

have resulted from the mineralizing proce·sses that produced the nearby Late Cretaceous North Silver Bell porphyry copper deposit, from processes associated with the 

Oligocene extrusion of the rhyolite of Ragged Top, or both. 

Mineral Resources of the Ragged Top Wilderness Study Area, Arizona H13 
More work is needed to determine the temporal relation of 

mineralization in and near the study area. 

Geophysics 

Gravity and Aeromagnetic Data 

The Ragged Top Wilderness Study Area is covered by 

regional gravity (Lysonski and others, 1980; Defense 

Mapping Agency Aerospace Center, 1974, 1975) and aeromagnetic (U.S. Geological Survey, 1980) surveys having 

sufficient resolution to define anomalies with areas of 

several square miles. Complete (terrain-corrected) 

Bouguer gravity anomalies were determined from 13 observation points immediately surrounding the study area and 

from about 15 additional points outside of but within 1.2 mi 

of the area shown in figure 4. Magnetic anomalies were 

determined from total-field measurements made along 

seven east-west flightlines, three of which intersect the 

study area itself (fig. 5), spaced 1 mi apart at a nominal 

altitude of 4,000 ft above sea level. 

The Bouguer gravity anomaly map (fig. 4) is dominated by a quasi-linear gradient of almost 3.2 milligals/mi. 

Anomaly values decrease southwestward along the common flank of a broad high centered north of the study area 

and a local low centered about 3 mi southwest of the area. 

The high is probably associated with the moderately dense 

Proterozoic granite that extends in the subsurface northFigure 4. Bouguer gravity anomaly map of vicinity of Ragged 

Top Wilderness Study Area, Pima County, Arizona. Contour 

interval 1 milligal. Dots represent gravity observation points. 

northeast of the study area and the Cretaceous granodiorite 

porphyry that extends to the south-southwest. Alternatively, the high may be associated with the Tertiary rhyolite. Anomaly values decline northwest of the high to a 

region about 6 mi northwest of the study area where lowdensity basin fill is at least 2 mi thick. Likewise, anomaly 

values decrease east of the high to a region 10 mi east of 

the study area where similar basin fill reaches a thickness 

of about 2 mi (Oppenheimer and Sumner, 1980). The low 

in the southwest corner of figure 4 is unusual in that it is 

a local small-amplitude feature that owes its geometry 

partly to a small-amplitude high farther southwest, which 

may be associated with moderately dense Paleozoic sedimentary rocks. Thus, the low is attributable to a veneer of 

low-density sediments that abut sedimentary rocks to the 

southwest. The region of most intensive mining and prospecting in the Silver Bell district underlies the dominant 

gradient rather than a high or low. Unfortunately, the 

gravity observation points are too sparsely distributed to 

determine whether a characteristic microgravimetric signature has been superposed on this gradient in this region. 

The magnetic anomaly map (fig. 5) is characterized by 

four main features: (1) a prominent east-trending high that 

transects the center of the study area and extends discontinuously to a high in the northeast comer of the figure; 

(2) a large-amplitude northwest-striking low immediately 

southeast of the area; (3) a cluster of circular highs southwest of this low; and ( 4) a broad low that occupies the 

111°32' 

32° 

28' ~,n-...;~---==~ 

32° 

26' 

32° 

24' 

111°30' 111°28' 111°26' 

Figure 5. Aeromagnetic anomaly map of vicinity of Ragged 

Top Wilderness Study Area, Pima County, Arizona. Contour 

interval 20 nanoteslas; hachures indicate closed area of lower 

anomaly value. Flightline traces are dashed. 

H14 Mineral Resources of Wilderness Study Areas: Southwestern and South-Central Arizona 
southwest comer of the figure and is directly west of the 

large-amplitude low and its neighboring cluster of circular 

highs. Two caveats should be noted: (1) these magnetic 

anomalies are strongly influenced by the topography of 

exposed magnetic rocks because the survey was flown at a 

constant barometric elevation, and (2) many of the contours 

defining anomaly shape near maximums or minimums are 

between flightlines and are inferred by interpolation. 

However, the anomaly map remains useful for correlating 

anomalies to known or inferred sources. 

The prominent east-trending magnetic high appears to 

correlate spatially much more with mapped Cretaceous 

granodiorite porphyry, presumed to be moderately to 

strongly magnetic, than with mapped Proterozoic granite, 

known to be weakly to moderately magnetic elsewhere in 

central and southern Arizona. However, the anomaly 

closely parallels the trace of the Ragged Top fault and the 

outcrop of the rhyolite emplaced along the fault. If the 

rhyolite is magnetic, the somewhat discontinuous extension 

of this high northeast of the study area raises the possibility 

that intrusive equivalents of the rhyolite may underlie the 

region in the northeast comer of the figure. Geologic 

mapping indicates that the Cretaceous granodiorite does not 

extend in~o the subsurface north of the Ragged Top fault. 

The large-amplitude northwest-trending magnetic low 

probably is not associated with reversely magnetized volcanic or intrusive rocks as are many other lows in southern 

Arizona. Rather, it appears to be a polarization feature over 

relatively nonmagnetic tuffs and sedimentary rocks, 

coupled to the cluster of circular highs south of the low. 

The cluster of highs is caused by normally magnetized 

intrusive rocks of intermediate composition. The region of 

intensive mining and prospecting in the Silver Bell district 

underlies a magnetic gradient rather than a high or low, just 

as is the case with the gravity anomaly map. It is possible 

that this magnetic gradient, forming the northeast margin of 

the broad low in the southwest comer of figure 5, is underlain by pervasively altered rocks associated with the porphyry copper mineralization. 

The regional geophysical data do not suggest regional 

evidence that anomaly features, and thus causative sources, 

of the Silver Bell mining district extend northeastward into 

the wilderness study area. Rather, these gradients extend 

only to areas southwest and immediately south of the study 

area. 

Aerial Gamma-Ray Spectrometry 

Aerial gamma-ray spectrometry measures the nearsurface (less than 2 ft) distribution of potassium (K), uranium (eU), and thorium (eTh). The e (for equivalent) 

prefix denotes the potential for disequilibrium in the uranium and thorium decay series. Because the distribution of 

these elements is controlled by geologic processes, aerial 

gamma-ray measurements can be used in geologic mapping, mineral exploration, and understanding of geologic 

processes. 

The spectrometry data used for this report were obtained between 1974 and 1981 for the National Uranium 

Resource Evaluation (NURE) program of the U.S. Department of Energy. Flightline spacing was usually at 3- to 6-

mi intervals, which yields data suitable for producing 

contour and other maps at scales pf 1:500,000 and smaller. 

All NURE flights were 400 ft above ground level. At this 

altitude, terrestrial gamma radiation can be detected along 

a swath 800 ft wide along the flightline. One north-south 

flightline crosses the east side of the study area. Spectrometry data that include the study area are presented on 

contour maps and color-composite image maps (Duval, 

1983) at scales of 1:500,000 and 1:1,000,000. The data 

described below were derived from the NURE report for 

the Tucson 1 o by 2° quadrangle (Texas Instruments, Inc., 

1978). 

Radioelement maps that include the Ragged Top Wilderness Study Area indicate that it is characterized by 

radioelement concentrations of 2.0 to 2.5 percent K, 3 to 4 

ppm eU, and 8 to 12 ppm eTh. These concentrations are 

probably of reasonable (not anomalous) levels for the 

Proterozoic crystalline rocks, Cretaceous volcanic, sedimentary, and intrusive rocks, and Tertiary intrusive rocks 

that are present in the study area. There is no indication 

that these concentrations relate in any way to alteration 

patterns of the Silver Bell porphyry copper system. The 

sparse flightline coverage of the study area precludes deriving any direct information on mineral resource potential 

from the aerial gamma-ray data. 

Mineral and Energy Resource Potential 

Vein Deposits 

An area near the southwest comer of the Ragged Top 

Wilderness Study Area has high resource potential, certainty level C, for gold, silver, lead, vanadium, barite, 

molybdenum, copper, and zinc in vein deposits (fig. 2). An 

area north, west, and south of this area of high potential has 

moderate resource potential, certainty level C, for barite, 

copper, gold, lead, molybdenum, silver, and zinc. These 

two areas have been distinguished primarily on the basis of 

geochemical anomalies found during this study. Known 

mines and prospects in that part of the study area, however, 

already indicate possible mineral resource potential. An 

additional area on the east side of the study area has low 

resource potential, certainty level B, for gold, barite, lead, 

silver, zinc, and copper in vein deposits on the basis of 

geochemical studies. 

Deposits at the Ragged Top mine and the barite prospects lie within areas designated here for vein deposits. 

Joseph (1982) conducted a detailed study of the barite and 

base-metal veins and concluded that they were formed by 

Mineral Resources of the Ragged Top Wilderness Study Area, Arizona H15 
a hydrothermal system younger than, and distinct from, the 

system that formed the Silver Bell porphyry copper deposits. Joseph determined that an early stage of quartz deposition that cemented breccias was followed by quartz-calcite-hematite-barite-fluorite-vein mineralization. This early 

mineralization is cut by late-stage fluorite-barite-galenasphalerite-quartz-calcite veins. Outcrop patterns suggested 

to Joseph (1982) that the early veins fill fault zones and 

fractures that show right-lateral offsets, whereas the later 

veins are present along normal faults. Her fluid-inclusion 

studies indicate that the hydrothermal- fluids ranged from 

370 to 160 oc and that mineral deposition probably was a 

result of simple cooling. Whether the possible hydrothermal system on the east side of the study area is related to 

the veins on the west side is unknown. 

Porphyry Copper Deposits 

The part of the study area south of the Ragged Top 

fault has moderate resource potential for copper, silver, 

gold, and molybdenum, certainty level B, in porphyry 

copper deposits. The known porphyry copper ore bodies in 

the mining district have been emplaced along bounding 

faults on the southwest side of the caldera structure, which 

the Ragged Top fault truncates on the north. Although no 

porphyry copper deposits have been found to date in the 

study area, the margin of the North Silver Bell deposit is 

about 1 mi southwest of the study area. Propylitic alteration in the southwestern part of the study area could be 

related to the known porphyry ore bodies or possibly to a 

buried, as yet undiscovered, ore body. Without detailed 

mapping of the alteration, sophisticated geophysical studies, and a drilling program, it is difficult to determine 

whether or not a porphyry copper deposit might lie buried 

beneath the volcanic and sedimentary rocks of the study 

area. 

Uranium in the Apache Group 

Outcrops of the Apache Group, here solely composed 

of Dripping Spring Quartzite, have low resource potential, 

certainty level B, for uranium. One stream-sediment 

sample from the northeast side of the wilderness study area 

contains a threshold concentration of 7.5 ppm uranium. In 

Gila County, Ariz., the Dripping Spring Quartzite hosts 

uranium deposits (Granger and Raup, 1959; Nutt, 1982). 

The uranium-bearing stratiform disseminated ore bodies 

were formed during diagenesis of volcaniclastic potassiumrich carbonaceous siltstone deposited in an intertidal environment (Nutt, 1982). Later intrusion of diabase sills 

remobilized the uranium into veins. The rocks of the study 

area have been given only low resource potential for uranium for several reasons. First, the closest known deposits 

are in Gila County, more than 50 mi away. Second, most 

of the exposed rocks are coarser than siltstone and appear 

to be clastic rather than volcaniclastic. Third, the diabase 

in this area intrudes only the Proterozoic granite and thus 

may be older than the Apache Group in this region (Watson, 1964). Fourth, uranium concentrations in streamsediment samples from near outcrops of the Apache Group 

are generally within the normal range for granite, sandstone, and shale (1.7-3.9 ppm; Rose and others, 1979, p. 

578). 

Thorium, Rare-Earth Elements, Quartz, Feldspar, and Mica 

in Granite 

The Proterozoic granite north of the Ragged Top fault 

has low resource potential, certainty level B, for thorium 

and rare-earth elements such as lanthanum in. monazite or 

other accessory minerals and for industrial quartz, feldspar, 

and mica in pegmatites. There is little evidence within the 

study area that the granite contains these commodities 

because geochemical indications of rare-earth elements and 

thorium are slight and because the pegmatites in the granite are very small and uncommon relative to pegmatites 

seen elsewhere in Proterozoic rocks of southern Arizona 

(Peterson and others, 1988). 

Energy Reso-urces 

The Ragged Top Wilderness Study Area has no potential, certainty level D, for oil and gas or for geothermal 

energy resources because the area lacks suitable reservoir 

rocks and because, in the case of oil and gas, any hydrocarbons would likely have been destroyed by heat generated 

during the Cretaceous igneous activity. 

REFERENCES CITED 

Banks, N.G., and Dockter, R.D., 1976, Reconnaissance geologic 

map of the Vaca Hills quadrangle, Arizona: U.S. Geological 

Survey Miscellaneous Field Studies Map MF-793, scale 

1:62,500. 

Beikman, H.M., Hinkle, M.E., Frieders, Twila, Marcus, S.M., and 

Edward, J.R., 1983, Mineral surveys by the Geological Survey and the Bureau of Mines of Bureau of Land Management 

wilderness study areas: U.S. Geological Survey Circular 901, 

28 p. 

Brobst, D.A., 1983, Barium minerals, in Lefond, S.J., ed., Industrial minerals and rocks: New York, American Institute of 

Mining, Metallurgical, and Petroleum Engineers, p. 485-501. 

Brown, D.E., 1982, Biotic communities of the American Southwest-United States and Mexico: Desert Plants, v. 4, no. 1-4, 

342 p. 

Cox, D.P., 1986, Descriptive model of polymetallic veins, in Cox, 

D.P., and Singer, D.A., eds., Mineral deposit models: U.S. 

Geological Survey Bulletin 1693, p. 125. 

Cruver, S.K., Wodzicki, Antoni, and Krason, Jan, 1982, Geology, 

energy and mineral resources assessment of the Wymola area, 

Arizona: Geoexplorers International, Denver, Colo., U.S. 

Bureau of Land Management contract, 109 p. 

Defense Mapping Agency Aerospace Center, 1974, World relaH16 Mineral Resources of Wilderness Study Areas: Southwestern and South-Central Arizona 
tive gravity reference network, North America, Part 2: Defense Mapping Agency Aerospace Center Reference Publication 25, with supplement updating gravity values to the International Gravity Standardization Net, 1971, 1,635 p. 

---1975, Holding, storage, and retrieval of gravity data: 

Defence Mapping Agency Aerospace Center Publication 

RP-75-003, 33 p. 

Duval, J.S., 1983, Composite color images of aerial gamma-ray 

spcctometric data: Geophysics, v. 48, no. 6, p. 722-735. 

Goudarzi, G.H., 1984, Guide to preparation of mineral survey 

reports on public lands: U.S. Geological Survey Open-File 

Report 84-787, 42 p. 

Granger, H.C., and Raup, R.B., 1959, Uranium deposits in the 

Dripping Spring Quartzite, Gila County, Arizona: U.S. Geological Survey Bulletin 1046-P, p. 415-486. 

Graybeal, F.T., 1982, Geology of the El Tiro area, Silver Bell 

mining district, Pima County, Arizona, in Titley, S.R., ed., 

Advances in geology of the porphyry copper deposits, southwestern North America: Tucson, University of Arizona Press, 

p. 487-505. 

Joseph, N.L., 1982, Epithermal veins in the Silver Bell district, 

Pima County, Arizona: Tucson, University of Arizona, M.S. 

thesis, 52 p. 

Keith, S.B., Gest, D.E., DeWitt, Ed, Toll, N.W., and Everson, 

B.A., 1983, Metallic mineral districts and production in Arizona: Arizona Bureau of Geology and Mineral Technology 

Bulletin 194, 58 p. 

Kreidler, T.J., 1987, Mineral investigation of the Ragged Top 

Wilderness Study Area (AZ-020-197), Pima County, Arizona: U.S. Bureau of Mines Mineral Land Assessment OpenFile Report MLA 80-87, 14 p., 1 plate. 

Levinson, A.A., 1980, Introduction to· exploration geochemistry: 

Wilmette, Ill., Applied Publishing Ltd., 924 p. 

Lysonski, J.C., Sumner, J.S., Aiken, C.L.V., and Schmidt, J.S., 

1980, Complete residual Bouguer gravity anomaly map of 

Arizona: Arizona Bureau of Geology and Mineral Technology, scale 1:500,000. 

McHugh, J.B., Nowlan, G.A., Sawyer, D.A., and Bullock, J.H., 

Jr., 1988, Analytical results and sample locality map for 

stream-sediment, panned-concentrate, and rock samples from 

the Ragged Top Wilderness Study Area, Pima County, Arizona: U.S. Gelogical Survey Open-File Report 88-587, 21 p. 

McKelvey, V.E., 1972, Mineral resource estimates and public 

policy: American Scientist, v. 60, no. 1, p. 32-40. 

Mosier, D.L., Berger, B.R., and Singer, D.A., 1986a, Descriptive 

model of Sado epithermal veins, in Cox, D.P., and Singer, 

D.A., eds., Mineral deposit models: U.S. Geological Survey 

Bulletin 1693, p. 154. 

Mosier, D.L., Sato, Takeo, Page, N.J, Singer, D.A., 'and Berger, 

B.R., 1986b, Descriptive model of Creede epithermal veins, in 

Cox, D.P., and Singer, D.A., eds., Mineral deposit models: 

U.S. Geological Survey Bulletin 1693, p. 145. 

Mosier, D.L., Singer, D.A., and Berger, B.R., 1986c, Descriptive 

model of Comstock epithermal veins, in Cox, D.P., and 

Singer, D.A., eds., Mineral deposit models: U.S. Geological 

Survey Bulletin 1693, p. 150. 

Nowlan, G.A., Haxel, G.B., Hanna, W.F., Pitkin, J.A., DiveleyWhite, D.V., McDonnell, J.R., Jr., and Lundby, William, 

1989, Mineral resources of the Baboquivari Peak and Coyote 

Mountains Wilderness Study Areas, Pima County, Arizona: 

U.S. Geological Survey Bulletin 1702-E, 30 p. 

Nutt, C.J., 1982, A model of uranium mineralization in the Dripping Spring Quartzite, Gila County, Arizona [abs.]: Geological Society of America Abstracts with Programs, v. 14, no. 4, 

p. 220. 

Oppenheimer, J.M., and Sumner, J.S., 1980, Depth-to-bedrock 

map, Basin and Range province, Arizona: Tuscon, University 

of Arizona, Laboratory of Geophysics, scale 1:500,000. 

Peterson, J.A., Nowlan, G.A., Hanna, W.F., Pitkin, J.A., and 

McDonnell, J.R., Jr., 1988, Mineral resources of the Table 

Top Mountain Wilderness Study Area, Maricopa and Pinal 

Counties, Arizona: U.S. Geological Survey Bulletin 1702-A, 

18 p. 

Richard, Kenyon, and Courtright, J.H., 1966, Structure and mineralization at Silver Bell, Arizona, in Titley, S.R., and Hicks, 

C.L., eds., Geology of the porphyry copper deposits, southwestern North America: Tucson, Ariz., University of Arizona 

Press, p. 157-163. 

Rose, A.W., Hawkes, H.E., and Webb, J.S., 1979, Geochemistry 

in mineral exploration, 2d ed.: London, Academic Press, 657 

p.-

Ryder, R.T., 1983, Petroleum potential of wilderness lands in 

Arizona, in Miller, B.M., ed., Petroleum potential of wilderness lands in the western United States: U.S. Geological 

Survey Circular 902-C, p. C1-C22. 

Sawyer, D.A., 1987, Late Cretaceous caldera volcanism and 

porphyry copper mineralization at Silver Bell, Pima County, 

Arizona: geology, petrology and geochemistry: Santa Barbara, University of California Santa Barbara, Ph.D. dissertation, 383 p. 

Texas Instruments, Inc., 1978, Aerial radiometric and magnetic 

reconnaissance survey of portions of Arizona-New Mexico, 

Tucson quadrangle: U.S. Department of Energy Report 

GJBX-23(79), v. 2-C. 

Theobald, P.K., and Barton, H.N., 1983, Statistical parameters for 

resource evaluation of geochemical data from the Ajo 1° by 2° 

quadrangle, Arizona: U.S. Geological Survey Open-File 

Report 83-734, 40 p., 1 plate. _ 

---1987, Maps showing anomalous copper concentrations in 

stream sediments and heavy mineral concentrates from the 

Ajo and Lukeville 1° and 2° quadrangles, Arizona: U.S. 

Geological Survey Miscellaneous Field Studies Map 

MF-1834-C, scale 1:500,000. 

U.S. Bureau of Land Management, 1987, Arizona Mohave draft 

wilderness environmental impact statement: U.S. Bureau of 

Land Management, Phoenix District Office, Arizona, unpublished report, 196 p. 

U.S. Bureau of Mines and U.S. Geological Survey, 1980, Principles of a resource/reserve classification for minerals: U.S. 

Geological Survey Circular 831, 5 p. 

U.S. Geological Survey, 1980, Composite aeromagentic map of 

the Papago area, Arizona: U.S. Geological Survey Open-File 

Report 80-56, scale 1: 250,000. 

Watson, B.N., 1964, Stucture and petrology of the eastern portion 

of the Silver Bell Mountains, Pima County, Arizona: Tucson, 

University of Arizona, Ph.D. dissertation, 168 p. 

Mineral Resources of the Ragged Top Wilderness Study Area, Arizona H17 
APPENDIXES 
DEFINITION OF LEVELS OF MINERAL RESOURCE POTENTIAL 

AND CERTAINTY OF ASSESSMENT 

LEVELS OF RESOURCE POTENTIAL 

H HIGH mineral resource potential is assigned to areas where geologic, geochemical, and geophysical characteristics indicate a geologic environment favorable for resource occurrence, where interpretations of data 

indicate a high degree of likelihood for resource accumulation, where data support mineral-deposit models 

indicating presence of resources, and where evidence indicates that mineral concentration has taken place. 

Assignment of high resource potential to an area requires some positive knowledge that mineral-forming processes 

have been active in at least part of the area. 

M MODERATE mineral resource potential is assigned to areas where geologic, geochemical, and geophysical 

characteristics indicate a geologic environment favorable for resource occurrence, where interpretations of data 

indicate reasonable likelihood for resource accumulation, and (or) where an application of mineral-deposit models 

indicates favorable ground for the specified type(s) of deposits. 

L LOW mineral resource potential is assigned to areas where geologic, geochemical, and geophysical characteristics 

define a geologic environment in which the existence of resources is permissive. This broad category embraces 

areas with dispersed but insignificantly mineralized rock, as well as areas with little or no indication of having 

been mineralized. 

N NO mineral resource potential is a category reserved for a specific type of resource in a well-defined area. 

U UNKNOWN mineral resource potential is assigned to areas where information is inadequate to assign a low, 

moderate, or high level of resource potential. 

LEVELS OF CERTAINTY 

A Available information is not adequate for determination of the level of mineral resource potential. 

8 Available information only suggests the level of mineral resource potential. 

C Available information gives a good indication of the level of mineral resource potential. 

D Available information clearly defines the level of mineral resource potential. 

r 

_,J 

< 

~ 

z 

LU 

~ 

0 

Cl.. 

LU 

u 

0:: 

::J 

0 

V') 

LU 

0:: 

u.. 

0 

_,J 

LU 

> LU 

_,J 

A 

U/A 

UNKNOWN POTENTIAL 

Abstracted with minor modifications from: 

8 c 

H/8 H/C 

HIGH POTENTIAL HIGH POTENTIAL 

M/8 M/C 

MODERATE POTENTIAL MODERATE POTENTIAL 

U8 L/C 

LOW POTENTIAL LOW POTENTIAL 

LEVEL OF CERTAINTY .... 

D 

H/D 

HIGH POTENTIAL 

M/D 

MODERATE POTENTIAL 

UD 

LOW POTENTIAL 

N/D 

NO POTENTIAL 

Taylor, R.B., and Steven, T.A., 1983, Definition of mineral resource potential: Economic Geology, v. 78, no. 6; p. 1268-1270. 

Taylor, R.B., Stoneman, R.J., and Marsh, S.P., 1984, An assessment of the mineral resource potential of the San Isabel National Forest, south-central Colorado: U.S. 

Geological Survey Bulletin 1638, p. 40-42. 

Goudarzi, G.H., compiler, 1984, Guide to preparation of mineral survey reports on public lands: U.S. Geological Survey Open-File Report 84-0787, p. 7, 8. 

H20 Mineral Resources of Wilderness Study Areas: Southwestern and South-Central Arizona 
RESOURCE/RESERVE CLASSIFICATION 

IDENTIFIED RESOURCES UNDISCOVERED RESOURCES 

Demonstrated Probability Range 

Inferred 

Measured Indicated Hypothetical Speculative 

I Inferred 

I 

ECONOMIC Reserves 

Reserves 

I - I ----~---- 1----------- -~-

MARGINALLY Marginal Inferred 

Marginal ECONOMIC Reserves Reserves ____ _L ____ 1------------ I I -~-

SUB- Demonstrated Inferred 

Subeconomic Subeconomic 

ECONOMIC Resources Resources I I I 

Majorelementsofmineral resource classification, excluding reserve base and inferred reserve base. Modified from McKelvey, V.E., 1972, Mineral 

resource estimates and public policy: American Scientist, v. 60, p. 32-40; and U.S. Bureau of Mines and U.S. Geological Survey, 1980, Principles 

of a resource/reserve classification for minerals: U.S. Geological Survey Circular 831, p. 5. 

Mineral Resources of the Ragged Top Wilderness Study Area, Arizona H21 
GEOLOGIC TIME CHART 

Terms and boundary ages used by the U.S. Geological Survey in this report 

EON ERA PERIOD EPOCH 

Quaternary 

Holocene 

Pleistocene 

Neogene Pliocene 

Cenozoic Subperiod Miocene 

Tertiary Paleogene Oligocene 

Subperiod Eocene 

Paleocene 

Cretaceous Late 

Early 

Late 

Mesozoic Jurassic Middle 

Early 

Late 

Triassic Middle 

Early 

Permian Late 

Phanerozoic Early 

Late 

Pennsylvanian Middle 

Carboniferous Early Periods 

Mississippian Late 

Early 

Late 

Devonian Middle 

Paleozoic Early 

Late 

Silurian Middle 

Early 

Late 

Ordovician Middle 

Early 

Late 

Cambrian Middle 

Early 

Late Proterozoic 

Proterozoic Middle Proterozoic 

Early Proterozoic 

Late Archean 

Archean Middle Archean 

Early Archean 

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - (3800?)- - - - - - - - - - - - - - - - - -

pre-Archean2 

1Rocks older than 570 Ma also called Precambrian, a time term without specific rank. 2lnformal time term without specific rank. 

H22 Mineral Resources of Wilderness Study Areas: Southwestern and South-Central Arizona 

AGE ESTIMATES OF 

BOUNDARIES IN 

MILLION YEARS (Ma) 

0.010 

1.7 

5 

24 

38 

55 

66 

- 96 

138 

205 

-240 

290 

-330 

360 

410 

435 

500 

1-570 

900 

1600 

2500 

3000 

3400 

4550 
SELECTED SERIES OF U.S. GEOLOGICAL SURVEY PUBLICATIONS 

Periodicals 

Earthquakes & Volcanoes (issued bimonthly). 

Preliminary Determination of Epicenters (issued monthly). 

Technical Books and Reports 

Professional Papers are mainly comprehensive scientific reports of 

wide and lasting interest and importance to professional scientists and engineers. Included are reports on the results of resource studies and of 

topographic, hydrologic, and geologic investigations. They also include 

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

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

geographic coverage than Professional Papers. They include the results 

of resource studies and of geologic and topographic investigations; as well 

as collections of short papers related to a specific topic. 

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

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

investigations in all phases of hydrology, including hydrogeology, 

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

Clr'culars present administrative information or important scientific 

information of wide popular interest in a format designed for distribution 

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

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

publications, and they are also available for publi~ inspection at 

depositories indicated in USGS catalogs. 

Open-File Reports include unpublished manuscript reports, maps, 

and other material that are made available for public consultation at 

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

cited in other publications as sources of information. 

Maps 

Geologic Quadrangle Maps are multicolor geologic maps on 

topographic bases in 7 1/2- or 15-minute quadrangle formats (scales mainly 1 :24,000 or 1 :62,500) showing bedrock. surficial, or engineering geology. Maps generally include brief texts; some maps include structure 

and columnar sections only. 

Geophysical Investigations Maps are on topographic or planimetric 

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

techniques, such as gravity, magnetic, seismic, or radioactivity, which 

reflect subsurface structures that are of economic or geologic significance. 

Many maps include correlations with the goology. 

Miscellaneous Investigations Series Maps are on planimetric or 

topographic bases of regular and irregular areas at various scales; they 

present a wide variety of format and subject matter. The series also includes 7 1/2-minute quadrangle photo geologic maps on planimetric bases 

which show geology as interpreted from aerial photographs. Series also 

includes maps of Mars and the Moon. 

Coal Investigations Maps are geologic maps on topographic or 

planimetric bases at various scales showing bedrock or surficial geology, stratigraphy, and structural relations in certain coal-resource areas. 

Oil and Gas Investigations Charts show stratigraphic information 

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

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

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

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

environmental studies or wilderness mineral investigations. 

Hydrologic Investigations Atlases are multicolored or black-andwhite maps on topographic or planimetril. bases presenting a wide range 

of geohydrologic data of both regular and irregular areas; principal scale 

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

Catalogs 

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

the conditions indicated below from the U.S. Geological Survey, Books 

and Open-File Reports Section, Federal Center, Box 25425, Denver, 

CO 80225. (See latest Price and Availability List.) 

"Publications of the Geological Survey, 1879-1961" may be purchased by mail and over the counter in paperback book form and as a 

set of microfiche. 

"Publications of the Geological Survey, 1962- 1970" may be purchased by mail and over the counter in paperback book form and as a 

set of microfiche. 

"Publications of the U.S. Geological Survey, 1971- 1981" may be 

purchased by mail and over the counter in paperback book form (two 

volumes, publications listing and index) and as a set of microfiche. 

Supplements for 1982, 1983, 1984, 1985,1986, and for subsequent 

years since the last permanent catalog may be purchased by mail and 

over the counter in paperba~k book form. 

State catalogs, "List of U.S. Geological Survey Geologic and 

Water-Supply Reports and Maps For (State)," may be purchased by mail 

and over the counter in paperback booklet form only. 

"Price and A vallabllity List of U.S. Geological Survey Publications," issued annually, is available free of charge in paperback booklet form only. 

Selected copies of a monthly catalog" New Publications of the U.S. 

Geological Survey" available free of charge by mail or may be obtained 

over the counter in paperback booklet form only. Those wishing a free 

subscription to the monthly catalog "New Publications of the U.S. 

Geological Survey" should write to the U.S. Geological Survey, 582 

National Center, Reston, VA 22092. 

Note.--Prices of Government publications listed in older catalogs, 

announcements, and publications may be incorrect. Therefore, the 

prices charged may differ from the prices in catalogs, announcements, 

and publications. 
Nowlan and others--MINERAL RESOURCES OFT~! RAGGED TOP WILDERNESS STUDY AREA, ARIZONA-U.S. Geologic