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Chapter A 

Mineral Resources of the 

Table Top Mountain Wilderness Study Area, 

Maricopa and Pinal Counties, Arizona 

By JOCELYN A. PETERSON, GARY A. NOWLAN, 

WILLIAM F. HANNA, and JAMES A. PITKIN 

U.S. Geological Survey 

JOHN R. McDONNELL, JR. 

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 

DONALD PAUL HODEL, ·Secretary 

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director 

Any use of trade names and trademarks 

in this publication is for descriptive 

purposes only and does not constitute 

endorsement by the U.S. Geological Survey 

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON: 1988 

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 Table Top Mountain Wilderness 

Study Area, Maricopa and Pinal Counties, Arizona. 

(U.S. Geological Survey bulletin ; 1702-A) 

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

Bibliography: p. 

1. Mines and mineral resources-Arizona-Table Top 

Mountain Wilderness. 2. Table Top Mountain Wilderness 

(Ariz.) I. Peterson, jocelyn A. II. Series: Geological 

Survey bulletin ; 1702-A. 

QE75.B9 no. 1702-A 557.3 s 88-600497 

[TN24.A6) [553'.09791'73) 
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 part 

of the Table Top Mountain Wilderness Study Area (AZ-020-172), Maricopa and Pinal Counties, Arizona. 

CONTENTS 

Summary A1 

Abstract 1 

Character and setting 1 

Identified resources and mineral resource potential 1 

Introduction 2 

Appraisal of identified resources 3 

Mining history 3 

Mineral appraisal 3 

Assessment of mineral resource potential 5 

Geology 5 

Geochemistry 6 

Geophysics 8 

Gravity and magnetic data 8 

Aerial gamma-ray spectrometry 8 

Mineral and energy resources 9 

Proterozoic copper-gold-silver veins or polymetallic epithermal veins 9 

Pegmatites 11 

Monazite-bearing rocks 11 

Porphyry copper 11 

Geothermal energy 11 

Other commodities 12 

References 12 

Appendixes 

Definition of levels of mineral resource potential and certainty of assessment 16 

Resource/reserve classification 17 

Geologic time chart 18 

FIGURES 

1. Index map showing the location of the Table Top Mountain Wilderness Study 

Area, Maricopa and ·Pinal Counties, Arizona A2 

2. Map showing mineral resource potential and generalized geology of the Table Top 

Mountain Wilderness Study Area, Maricopa and Pinal Counties, Arizona 4 

3. Map showing locations of geochemical anomalies of the Table Top Mountain Wilderness Study Area 7 

4. Map showing locations of aeromagnetic anomalies in and near the Table Top 

Mountain Wilderness Study Area 10 

TABLE 

1. Statistics for anomalous elements from drainage samples collected in and near the 

Table Top Mountain Wilderness Study Area, Maricopa and Pinal Counties, 

Arizona A8 

Contents V 
MINERAL RESOURCES OF WILDERNESS STUDY AREAS: 

SOUTHWESTERN AND SOUTH-CENTRAL ARIZONA 

Mineral Resources of the 

Table Top Mountain Wilderness Study Area, 

Maricopa and Pinal Counties, Arizona 

By Jocelyn A. Peterson, Gary A. Nowlan, William F. Hanna, 

and James A. Pitkin 

U.S. Geological Survey 

John R. McDonnell, Jr. 

U.S. Bureau of Mines 

SUMMARY 

Abstract 

The part of the Table Top Mountain Wilderness Study 

Area (AZ-020-1 72) requested for mineral surveys by the U.S. 

Bureau of Land Management encompasses 34,400 acres in 

south-central Arizona. Field work was carried out by the U.S. 

Bureau of Mines in the spring of 1985 to appraise the known 

mineral resources and by the U.S. Geological Survey in the 

winter and spring of 1 986 to assess the mineral resource 

potential (undiscovered) of the study area. Samples from 

three prospects within the study area contain minor gold, 

silver, copper, lead, and zinc, but resources of these elements 

were not identified at these localities. Common variety sand 

and gravel deposits in the area are inferred subeconomic 

resources but are not likely to be developed. Areas of exposed Pinal Schist have low mineral resource potential for 

copper, gold, and silver in veins similar to those on the IC 

claims and for copper, lead, molybdenum, barite, and (or) 

tungsten in epithermal veins. The Oracle Granite has low 

potential for resources. of quartz, feldspar, mica, lanthanum (a · 

rare-earth element), uranium, thorium, and beryllium in 

pegmatites and low potential for resources of uranium, thorium, and lanthanum in accessory monazite. The entire study 

area has low potential for copper resources in porphyry 

copper deposits, but they would be more likely beneath the 

pediment of the southeastern .part of the study area. There is 

a low potential for resources of the evaporite minerals gypsum or anhydrite and halite, uranium in intermontane basins, 

placer tin, and oil and gas as suggested by geology, geochemistry, or leasing activity. The extreme northwest corner of the 

study area has a low potential for geothermal energy resources. 

. Publication authorized by the Director. U.S. Geological Survey, March 17, 1988. 

Character and Setting 

The Table Top Mountain Wilderness Study Area (AZ020-172) is in south-central Arizona about 35 mi eastsoutheast of Gila Bend, Ariz. (fig. 1) and 50 mi northeast 

of Ajo, Ariz. The area lies within the Sonora Desert section of the Basin and Range physiographic province, a 

region characterized by typically large mountain chains 

separated by deep, alluvial-filled valleys. The study area is 

underlain primarily by schist and quartz monzonite (fig. 2) 

of Proterozoic age (see geologic time chart in appendixes). 

Several peaks are covered by Tertiary basalt and clastic· 

sedimentary rocks; Table Top includes a thin layer of 

middle Proterozoic sedimentary rocks. Major stream beds, 

pediments, and intermontane valleys have a cover of alluvium. 

Identified Resources and Mineral Resource 

Potential 

The Table Top Mountain Wilderness Study Areas is 

not within any organized mining district, but there are 

several placer and lode claims within and along the western 

and northern parts of the area (McDonnell, 1986). No 

production has been recorded from these claims and they 

were inactive at the time of the field examination by the 

U.S. Bureau of Mines (USBM). There are also claims in 

the southeastern part of the study area. Of the three prospects sampled, all have low-level geochemical anomalies 

for copper, lead, zinc, gold, and (or) silver. There are no 

identified mineral resources in the study area. 

The Pinal Schist has low potential for resources of 

copper, gold, and silver in quartz veins similar to those on 

Mineral Resources of the Table Top Mountain Wilderness Study Area, Maricopa and Pinal Counties, Arizona Al 
the IC claims and for resources of copper, lead, molybdenum, barite, and (or) tungsten in epithermal veins (hereafter 

called polymetallic epithermal veins) (fig 2). The Oracle 

Granite has low resource potential for quartz, feldspar, 

mica, uranium, thorium, lanthanum (a rare-earth element), 

arid beryllium in pegmatites and a low potential for uranium, thorium, and rare-earth elements in accessory monazite. The study area has low potential for copper resources 

in porphyry copper deposits, although the pediment in the 

southeast comer seems to be more favorable. Low potential for resources of several commodities is suggested by 

the geology, geochemistry, or leasing activity. These include gypsum or anydrite and halite resources in evaporite 

deposits, uranium resources in the alluviated valleys, placer 

tin resources, and oil and gas resources. The extreme 

northwest comer of the study area has low potential for 

geothermal energy resources. 

I I. 

INTRODUCTION 

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

of Land Management (BLM) and is a joint effort by the 

U.S. Geological Survey (USGS) and the 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, 

claims, and mineralized areas. Identified resources are 

classified according to the system described by U.S. Bureau 

of Mines and U.S. Geological Survey (1980). Studies by 

the USGS are designed to provide a reasonable scientific 

basis for assessing the potential for undiscovered mineral 

resources by determining geologic units and structures, 

112°15' 112•oo· 

1 APPROXIMATE BOUNDARYV'ii:::-:---......::::::.....__~ I - - - - - - - - - - - - - - --- - - - - OF 

TABLE TOP MOUNTAIN 

WILDERNESS STUDY AREA 

(AZ-020-172) 

32°45' 

L I 

~I ! 

I t1r·-·-·' I l . :- -·-·-·- --, I 

LUKE AIR FORCE RANGE 1 

~PAPAGOlNDiANRESERVATION--------

8 0 5 IOMILES 

AREA OF f'M.P 

Figure 1. Index map showing location of the Table Top Mountain Wilderness Study Area, Maricopa and Pinal 

Counties, Arizona. • 

A2 Mineral Resources of Wilderness Study Areas-Southwestern and South-Central Arizona 
possible environments of mineral deposition, presence of 

geochemical and geophysical anomalies, and applicable 

ore-deposit models. Mineral assessment methodology and 

terminology as they apply to these surveys were discussed 

by Goudarzi (1984). See appendix for the definition of 

levels of mineral resource potential, certainty of assessment, and classification of identified resources. 

The Table Top Mountain Wilderness Study Area in 

south-central Arizona (AZ-020-172) encompasses 39,823 

acres, of which the BLM requested mineral surveys on 

34,400 acres. The area is centered on the rugged Table Top 

Mountains where elevations range from 4,737 ft at the 

summit of Table Top to 1 ,600 ft in the valleys peripheral to 

the mountains. The area can be reached by several dirt 

roads leading south from Interstate Highway 8 into Vekol 

Valley and into the unnamed valley along the north boundary of the study area. Much of the interior is inaccessible 

to vehicles. The arid climate supports typical southern 

Arizona desert fauna and flora. 

The study area is located about 35 mi east-southeast of 

Gila Bend, Ariz. (fig. 1), and 50 mi northeast of Ajo, Ariz., 

within the Sonora Desert section of the Basin and Range 

physiographic province, an area usually characterized by 

elongate mountain ranges separated by broad valleys. 

The USBM study began with a review of the literature 

related to mining in the table Top Mountains vicinity. 

BLM mining claim information ~d land status plats were 

examined as were mineral information and production data 

compiled by the USBM. Subsequent field work was undertaken to examine mines, prospects, and known mineral 

occurrences inside and within 2 mi of the study area. Three 

prospects within the study area were surveyed, mapped, 

and sampled. · 

The USGS mapped the geology of the study area in 

1986. The work helped to revise previous mapping by 

Dockter and Keith ( 1978) and reconnaissance mapping by 

R.M. Tosdal done as part of a regional study (Peterson and 

others, 1987b). Rock and stream-sediment samples were 

collected for geochemical analyses. Geophysical studies 

were based on interpretations of available published data. 

M.I. Hornberger assisted with the field work by the USGS. 

APPRAISAL OF IDENTIFIED RESOURCES 

By John R. McDonnell, Jr. 

U.S. Bureau of Mines 

Mining History 

The Table Top Mountain Wilderness Study Area is not 

within an organized mining district and has no recorded 

mineral production. The study area is 10-15 mi north of the 

Vekol mining district, where gold, silver, copper, lead, and 

zinc have been produced. Mineral deposits in the Vekol 

district formed along faults as replacements in Paleozoic 

limestone, dolomite, and shale (Denton and Haury, 1946; 

Arizona Department of Mineral Resources file data), structures and rocks that do not extend into the study area. 

Several unpatented placer and lode claims are within 

and along the west and north edges of the study area 

(McDonnell, 1986); the placer claims cover most of Vekol 

Valley to the west. No active mining operations were 

noted wi.thin the study area during the USBM field investigation, but results of past mining or prospe~ting were examined on the IC, Silver King, and Silver Queen claims 

and on an area in the southeastern part of the study area 

(fig. 2). 

American Rockwool, Inc., Casa Grande, Ariz., was 

mining basalt about 0.5 mi north of the study area (fig. 2) 

for use in manufacturing insulation. The rock was crushed 

and mixed with steel slag and coke in a furnace, melted at 

about 3,600 op and blown and spun into fibers. The loose 

fibers were used as blowing wool insulation or combined 

with resin to form insulation batts. Robert Corsentino 

(Plant Superintendent, American Rockwool, Inc., oral 

commun., 1985) said that the company has about a 10-yr 

reserve of the basalt at its quarry. He also indicated that the 

company empirically tested the basalt and that a detailed 

investigation of basalt in the surrounding area had not been 

made. As of March 10, 1986, the plant had stopped production and the company had no future start-up plans. 

Two sand and gravel pits are near the study area, one 

0.5 mi -to the north (fig. 2) and the other 2.5 mi to the 

northwest. Several smaller borrow pits ·are scattered near 

the north boundary along Interstate Highway 8. The material was used primarily in constructing interchanges and 

overpasses for the highway; some may also have been used 

in local building projects. 

Mineral Appraisal 

Three of the prospected localities within the Table Top 

Mountain Wilderness Study Area were sampled: the IC 

and Silver King claims and an unnamed shaft in the southeastern part of the study area (fig. 2). Samples collected at 

these prospects. included chip, select, and grab samples, 

which were analyzed for gold and silver by fire assay and 

inductively coupled plasma-atomic emission spectrometry, 

and for copper, lead, and zinc by atomic-absorption spectrophotometry. Samples were also analyzed for 40 elements by semiquantitative optical-emission spectrography. 

Analytical data are summarized by McDonnell (1986). 

Copper occurrences reported by Krason and others (1982) 

based on Stipp and others (1967) were searched for but not 

found. They may have been accidentally mislocated and 

'were intended to represent the IC, Silver King, aild Silver 

Queen claims, which were not shown by them. A sample 

of the basalt mined by American Rockwool, Inc., was also 

collected. 

Mineral Resources of the Table Top Mountain Wilderness Study Area, Maricopa and Pinal Counties, Arizona A3 
At the IC claims, quartz veins as thick as 3 ft and fault 

zones as wide as 6 ft contain visible chrysocolla exposed in 

pits, trenches, and shafts in the Pinal Schist. Bulldozer cuts 

disrupt much of the surface, making the extent of the veins 

and faults difficult to determine; additional mineralized 

rock may have been removed or covered. Samples from 

t}:le mineralized area contain minor gold, silver, copper, and 

zinc, but resource estimates could not be calculated from 

the scattered field and analytical data. 

A decomposed iron-oxide-stained quartz monzonite of 

the Oracle Granite is exposed in an 18-ft-deep shaft in the 

southeast comer of the study area (fig. 2). The iron-oxide 

stain is dispersed throughout the quartz monzonite and is 

probably due to the weathering of mafic minerals. No 

mineralized rock was apparent, but gold, copper, and zinc 

were detected in a chip sample from the quartz monzonite. 

The quartz monzonite exposed here is similar to quartz 

monzonite exposed on the Silver King and Silver Queen 

claims in the northern part of the study area, where 

occurrences of gold and silver in quartz-calcite veinlets 

have been reported by claimant Charles Irwin (oral and 

written commun., 1986). Prospecting on the claims has 

UC Qtz, Mica, Fsp [2) 

U B U, Th, REE, Be [2,3) 

tOracle granite unit, ex posed, 

and beneath thin gravel) 

APPROXIMATE BOU DAR Y OF 

TABLE TOP MOU TAIN 

WILDERNESS STUDY AREA 

UC Qtz, Mica, Fsp [2) U B U, Th, REE, Be [2,3) (AZ-020- 172) 

(Oracle granite unit, exposed, and beneath thi n gravel) 

4 MILES 

Figure 2. Mineral resource potential and generalized geology of the Table Top Mountain Wilderness Study Area, Maricopa 

and Pinal Counties, Arizona. 

A4 Mineral Resources of Wilderness Study Areas--Southwestern and South-Central Arizona 
been limited to surface sampling. The USBM sampled 

quartz-calcite veinlets that crop out on the Silver King 

claims but detected no gold and only minor silver, lead, and 

zinc; the veinlets are not well exposed on the Silver Queen 

claims. More detailed geologic, geochemical, and 

geophysical surveys, and possible exploratory drilling, 

would be needed to determine the economic significance of 

veins and faults in the study area. 

A sample of the basalt mined by American Rockwool, 

Inc., was collected and analyzed for whole-rock 

composition and metal content. . Because American 

Rockwool, Inc., made no formal analysis of the basalt, we 

attempted to determine why this particular basalt is useful 

in manufacturing insulation on the basis of the whole-rock 

analysis. Mineralogical and chemical studies of the basalt, 

however, did not reveal any special characteristic to 

indicate why this basalt is more suitable than others for 

making insulation. 

Sand and gravel occur in drainages and low-lying parts 

of the study area and are an inferred subeconomic resource. 

Nearby material was used in constructing Interstate 

Highway 8 and probably for other local building projects. 

Transportation costs and a low unit value restrict the 

market to local use, and sufficient material outside the 

study area will satisfy this demand. 

ASSESSMENT OF MINERAL RESOURCE 

POTENTIAL 

By Jocelyn A. Peterson, Gary A. Nowlan, 

William F. Hanna, and James A. Pitkin 

U.S. Geological Survey 

Geology 

The Table Top Mountain Wilderness Study Area is 

underlain primarily by Proterozoic igneous and 

metamorphic rocks, but several peaks are capped by 

Tertiary conglomerate and basalt (Peterson and others, 

1987b). The lower Proterozoic Pinal Schist covers most of 

the central part of the study area (fig. 2). It is a [megrained, strongly foliated muscovite-quartz schist that in 

places is chloritic. Metamorphic segregations of quartz are 

locally abundant and seldom absent. In the north half of 

the area the schist is intruded by a few small very dark 

green pods that are presumed to be altered diabase. The 

schist contains localized concentrations of secondary 

copper minerals, commonly in veinlets associated with 

small local faults or larger faults as at the IC claims. 

The middle Proterozoic Oracle Granite, which intrudes 

the Pinal Schist, crops out extensively on the edges of the 

EXPLANATION 

Geologic terrane having low mineral resource potential--See 

appendixes for definition of levels of mineral resource 

potential (L) and certainty of assessment (B,C) 

UB U,Sn 

UB Evap 

UB Geo 

UC Qtz, Mica, Fsp; UB U, Th, REE, Be--Oracle Granite 

unit, exposed, and beneath thin gravel 

UC Cu, Au, Ag, Pb, Mo, W, Bar--Pinal Schist unit 

Commodities 

Ag 

Au 

Cu 

Mo 

Pb 

REE 

Sn 

Th 

Be 

Silver 

Gold 

Copper 

Molybdenum 

Lead 

Rare-earth element lanthanum 

Tin 

Thorium 

Beryllium 

Figure 2. Continued. 

u 

Bar 

Evap 

Fsp 

Geo 

Mica 

O,G 

Qtz 

w 

Uranium 

Barite 

Evaporites 

Feldspar 

Geothermal 

Mica 

Oil and gas 

Quartz 

Tungsten 

[ ] 

1 

2 

3 

4 

5 

Qa 

Tb 

Yo 

Xp 

+Cu 

Deposit types 

Veins 

Pegmatites 

Disseminated monazite 

Porphyry copper 

Caliche 

Geologic map units 

Alluvium, talus, and gravel (Quaternary) 

Basalt and conglomerate (Tertiary) 

Oracle Granite (Middle Proterozoic) 

Pinal Schist (Early Proterozoic) 

Contact-Dashed where approximately 

located 

Fault-Dotted where concealed 

Shaft 

Quarry 

Copper occurrence 

Mineral Resources of the Table Top Mountain Wilderness Study Area, Maricopa and Pinal Counties, Arizona AS 
Table Top Mountains and on adjacent pediment surfaces, 

particularly pediments in the southeastern part of the study 

area. The unit is compositionally a quartz monzonite to 

rare granodiorite, but "granite" has been retained in the 

formal name of the unit. It is typically coarse grained, 

sometimes to the extent of forming small pegmatites of 

quartz-monzonitic composition. Elsewhere, there are larger 

pegmatites consisting mostly of quartz with some muscovite, although feldspar-dominant pegmatites are also present. Aplite is found locally. 

On Table Top below the Tertiary rocks is a thin layer 

of the middle Proterozoic Pioneer Formation of the Apache 

Group, the only formation of the group present in the study 

area. It consists of a fme-grained red sandstone with distinctive (and diagnostic) light-colored spherical areas 

throughout that are less than 0.5 in. in diameter and typically even smaller. 

Paleozoic and Mesozoic rocks are absent in the area. 

Unconformably resting on the Proterozoic rocks in the 

northern part of the area are scattered outcrops of a basaltic 

andesite, perhaps the same basaltic rocks as those at the 

American Rockwool, Inc., quarry. A Tertiary conglomerate crops out mostly beneath outcrops of basalt. Because 

it is poorly consolidated, it was readily eroded elsewhere. 

The subrounded to subangular clasts are derived from the 

Pinal Schist, Oracle Granite, Apache Group (including 

those formations of the group not present in the study area), 

and a variety of volcanic rocks that are not exposed in the 

area. Olivine basalt caps several of the peaks in the area 

and forms the somewhat flat top of Table Top. The unit is 

made up of several flows. 

Three unconsolidated Quaternary units are present in 

the area. Flanking some of the peaks are poorly sorted, 

semiconsolidated to unconsolidated, locally derived terrace 

gravels. More immediate to some of the mountains are 

talus slopes, which obscure underlying geology. Pediment 

surfaces are covered by alluvium, and major drainages 

contain alluvium. 

There are no major structures in the area. Minor faults 

were seen in the units of Proterozoic and Tertiary age on 

the west side of the area. The Pinal Schist has a strong 

schistosity that lacks a regional trend because of the intense 

small-scale folding that the unit has undergone. 

Evidence of alteration is scarce. The prospect in the 

Oracle Granite in the southeastern part of the ··area (shaft, 

fig. 2) has highly oxidized and slightly chloritized quartz 

monzonite. Chloritic areas are common throughout the 

Pinal Schist, sometimes associated with the copper oxides, 

but development of chlorite rather than muscovite could be 

the result of original compositional differences in the rocks 

from which the schist was derived. 

Geochemistry 

For the reconnaissance geochemical survey of the 

Table Top Mountain Wilderness Study Area, stream-sediment samples were collected at 72 sites and 11 samples of 

mineralized or altered rock were collected at seven sites. 

Stream-sediment and panned-concentrate samples derived 

from stream sediments, the sample media used for this 

study, represent a composite of material eroded from the 

drainage basin of the stream sampled. Three samples were 

collected at each site. One was dried and sieved through a 

30-mesh stainless-steel sieve. A 30-mesh sieve was used 

rather than the more conventional 80-mesh to lessen possible dilution by wind-blown material in this desert environment. The minus-30-mesh stream-sediment sample was 

analyzed for 31 elements by emission spectrographic methods and for antimony, arsenic, bismuth, cadmium, and zinc 

by other methods (see Adrian and others, 1987). The other 

two samples each consisted of 20 lb of stream sediment that 

were panned until about 3 oz or less remained. One of 

these raw panned-concentrate samples was further concentrated by heavy liquids and magnetic separations to produce 

a nonmagnetic heavy-mineral concentrate (called concentrate hereafter), which was then analyzed for the same 31 

elements by semiquantitative spectrographic methods. The 

other raw panned-concentrate sample was analyzed for 

gold by atomic absorption without further treatment. 

Anomalous element concentrations present in the study 

area, the lower and upper limits of determination, the range 

of concentrations, the 50th percentile value, and the threshold (highest background) concentrations are listed in table 

1. Threshold values were established by visually examining the data and comparing them with stream-sediment and 

concentrate sample data used as part of a mineral-resource 

assessment of the Ajo and Lukeville 1 by 2 quadrangles 

(Theobald and Barton, 1983, 1987). Analytical results, 

sample preparation and analytical methods, and references 

for the analytical methods are given in Adrian and others 

(1987). 

Geochemical data for the Table Top Mountain Wilderness Study Area suggest epithermal vein deposits and 

pegmatites. Probable pegmatite areas are underlain by the 

Oracle Granite and are characterized by anomalous beryllium, scandium, niobium, tin, lanthanum, and thorium. 

Areas that may contain epithermal vein deposits, on the 

other hand, are underlain mostly by the Pinal Schist. These 

areas are characterized by three suites of geochemically 

anomalous elements: barium, bismuth, molybdenum, and 

tungsten; lead; and copper, gold, molybdenum, and tungsten. 

Concentrate samples from area A (fig. 3) show a close 

association of anomalous concentrations of barium, bismuth, molybdenum, and tungsten. Some concentrate 

samples from the area also contain anomalous concentrations of copper and lead. One raw panned-concentrate 

sample contains. an anomalous amount of gold. One 

stream-sediment sample from area A contains an anomalous concentration of boron. Area A encompasses the IC 

claims (McDonnell, 1986) where chrysocolla is visible in 

quartz veins and fault zones. Mineralized rock samples 

A6 Mineral Resources of Wilderness Study Areas-Southwestern and South-Central Arizona 
from outcrops and dump material at the claims contain as 

much as 6.3 parts per million (ppm) gold, 12.5 ppm silver, 

200 ppm arsenic, 1,000 ppm bismuth, 3,000 ppm boron, 

and greater than 2 percent copper (McDonnell, 1986, fig. 4; 

Adrian and others, 1987, table 6). Geochemical data from 

area A fit some of the geochemical criteria for polymetallic 

epithermal vein deposits of the region but the known 

mineralization more closely resembles that of gold-silver 

quartz veins (Peterson and others, 1987a, p. 7-8). 

Several concentrate samples from area B (fig. 3) contain anomalous concentrations of lead. Also, one concentrate sample and the stream-sediment sample from the same 

site contain anomalous concentrations of barium and copper, respectively. Although area B is not as geochemically 

favorable for epithermal vein deposits as area A because of 

the fewer number of elements present in anomalous 

amounts, local outcrops of quartz veins and chrysocolla 

indicate some mineralization has taken place. 

Concentrate samples from area C (fig. 3) contain 

anomalous amounts of molybdenum and tungsten. One 

112"10' 

n•.ts'JO" 

32°44'30" 

raw panned-concentrate sample contains an anomalous 

amount of gold~ One minus-30-mesh stream-sediment 

sample contains an anomalous concentration of copper. 

Area C is somewhat favorable for polymetallic epithermal 

vein deposits or gold-silver quartz veins. 

Concentrate samples from area D (fig. 3) contain 

anomalous amounts of beryllium and scandium; this is an 

area underlain by the Oracle Granite where prominent 

quartz veins and pegmatites are located. Scandium is, in 

some cases, associated with pegmatites and is found in 

mafic minerals in other cases (Rankama and Sahama, 1950, 

p. 512). The presence of both pegmatites and anomalous 

beryllium and scandium concentrations in area D indicate a 

pegmatite association. Beryl, the most common beryllium 

mineral, is not present in concentrate samples because it 

has a low specific gravity. Thus, the beryllium is a constituent of some other mineral that is associated with the 

quartz monzonite or pegmatites. Anomalous amounts of 

scandium in concentrate samples from area E (fig. 3) 

probably reflect the presence of the known pegmatites in 

112°05' 

APPROXIMATE BOUNDARY 

OF 

TABLE TOP MOUNTAIN 

WILDERNESS STUDY AREA 

(AZ-020-172) 

4 MILES 

Figure 3. Geochemical anomaly map (alphabetically labeled areas) of the Table Top Mountain Wilderness Study Area, 

Maricopa and Pinal Counties, Arizona. See text for discussion of alphabetically labeled areas. See figure 2 for explanation 

of geologic map units. 

Mineral Resources of the Table Top Mountain Wilderness Study Area, Maricopa and Pinal Counties, Arizona A7 
the area. Concentrate samples from area F contain anomalous concentrations of niobium, tin, and thorium; this association of elements (Peterson and others, 1987a) suggests 

that pegmatites may be present in area F (fig. 3), although 

none were noted during geologic mapping. 

Four concentrate samples from the area have at least 

500 ppm lanthanum. The samples were collected in areas 

of Oracle granite. 

Tin is anomalous in concentrate samples from several 

scattered sites; all of these sites are on streams that have 

drainage basins entirely on pediments. Therefore, the 

anomalous tin values may reflect incipient placer tin deposits. 

Geophysics 

Gravity and Magnetic Data 

The area of the Table Top Mountain Wilderness Study 

Area is included in regional gravity (D.P. Klein, written 

common., 1987; Lysonski and others, 1981; Defense 

Mapping Agency Aerospace Center, 1974, 1975) and detailed magnetic (U.S. Geological Survey, 1980; D.P. Klein, 

written common., 1987) surveys having sufficient resolution to define anomalies of several square miles or larger. 

Contours of complete (largely terrain corrected) Bouguer 

gravity anomalies are defined by about 25 observations 

within and near the study area. Contours of total-intensity 

magnetic anomalies are defined by measurements made 

along nine east-west traverses spaced about 1 mi apart at a 

nominal altitude of 4,000 ft above sea level. 

The Bouguer gravity anomaly map is characterized by 

large-amplitude lows near the northwest and southwest 

comers of the study area and by a small-amplitude low near 

the southeast comer. All of these lows are associated with 

low-density basin sediments and minor associated basalt 

that is relatively vesicular, thin, or both. The sediment 

thickness beneath the large amplitude lows is about 1 ,500 

to 3,000 ft; thickness beneath the small-amplitude low is 

600 to 1,500 ft in the deepest parts of the basin (Oppenheimer and Sumner, 1980), on the basis of gravity modeling and well-hole data. The northeast and west-central 

parts of the study area are characterized by highs separated 

by a saddle. This zone is largely associated with moderTable 1. Statistics for anomalous elements from drainage samples collected in and near the Table Top 

Mountain Wilderness Study Area, Maricopa and Pinal Counties, Arizona 

[Results based on 72 samples. Concentrations determined by emission spectrographic methods except gold determined by 

atomic absorption. All values reported in parts per million except iron, which is in percent. N, not detected; L, detected 

but below limit of determinations; G, greater than 'upper limit of detrmination] 

Element Lower Limit Upper Limit Minimum Maximum 50th Threshold 

of of concentration concentration percentile concentration 

determination determination 

Minus-30-mesh stream sediments 

Boron 10 2,000 10 100 20 70 

Copper 5 20,000 7 50 7 30 

Iron 0.05 20 1.5 15 3 10 

Nonmagnetic heavy-mineral concentrate 

Barium 50 10,000 200 G 500 3,000 

Beryllium 2 2,000 N 20 2 7 

Bismuth 20 2,000 N 1,500 50 700 

Copper 10 50,000 N 100 10 70 

Lead 20 50,000 N 5,000· 30 200 

Molybdenum 10 5,000 N 100 N 15 

Niobium 50 5,000 ·N 100 N 50 

Scandium 10 200 N G 30 150 

Strontium 200 10,000 L 2,000 2000 1,000 

Thorium 200 5,000 N 1,000 N 200 

Tin 20 2,000 N 100 N 20 

Tungsten 100 20,000 N 5,000 N 500 

Gold-a 0.05' __ a N 0.19 N N 

1

Based on 10-g sample. 

aupper limit is open ended. 

A8 Mineral Resources of Wilderness Study Areas-Southwestern and South-Central Arizona 
ately dense components of the Pinal Schist locally intruded 

by Oracle Granite. 

The magnetic anomaly map is dominated by shortwavelength, large-amplitude anomalies, some of which are 

affected by topography. Most of the anomalies overlap two 

or more magnetic lithologic units; therefore, anomaly 

sources cannot be unambiguously identified by visual 

examination of the data. The strongest clue to the most 

likely anomaly sources is provided by measuring remanent 

and induced magnetization (average magnetic dipole 

moment per unit volume), which yields the total magnetization capable of generating an anomaly. One measurement each of total magnetization for the Oracle Granite, 

Pinal Schist, and olivine basalt was made. Samples of the 

olivine basalt and Pinal Schist have total magnetizations, 

respectively, about 17.5 and 2.5 times stronger than that of 

the Oracle Granite, which itself is weakly to moderately 

magnetic. Thus, on this basis, the large-amplitude mag~ 

netic anomalies are most likely caused by basalt. 

The lapping of magnetic anomalies over more than one 

magnetic unit is inferred to be caused largely by abnormal 

directions of average total magnetization. For example, 

most basalt crops out beneath steep anomaly flanks rather 

than beneath anomaly maxima. This offset of anomaly 

maxima with respect ·to source is caused largely by 

reversed to abnormally directed remanent magnetization, 

which is stronger in all three of the measured samples than 

induced magnetization. Specifically, anomalies A, B, C, D, 

and E (fig. 4) are singlet or doublet high and low anomalies 

probably caused largely by basalt, which is partly buri~d 

and which in other places is more· highly elevated than 

surrounding terrain and, thus, was close to the 

magnetometer sensor during the aerial survey. An elongate 

pair of east-trending anomalies, F and G (fig. 4), have a 

buried source; the inferred source is· basalt, possibly as 

feeder dikes, based on the short wavelength and high 

amplitude of these features. Other small-amplitude 

anomalies, such as H, I, J, K, and L (fig. 4), may be 

associated with the moderately magnetic Pinal Schist or 

Oracle Granite. 

Aerial Gamma-ray Spectrometry 

Aerial gamma-ray spectrometry measures the near-, .. 

surface (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 (1979). Flightline spacing was 

J 

usually at 3- to 6-mi intervals, which yields data suitable 

for producing contour and other maps at scales of 

1:500,000 and smaller. All NURE flight altitudes were 400 

ft above ground level. At this altitude terrestrial gamma 

radiation can be detected along a swath 800 ft wide along 

the flightline. Data for the region around 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. 

Spectrometric data described below were derived from the 

NURE report for the Ajo C by 2° quadrangle (U.S. 

Department of Energy, 1979). 

The Table Top Mountain Wilderness Study Area is 

characterized by radioelement concentrations of 1-2 percent 

K, 3-5 ppm eU, and 7-14 ppm eTh. These concentrations 

·are determined from ·three NURE flightlines that partially 

outline the study area on the north, south, and east and 

provide sparse control for defining radioelement 

distribution for the area. The concentrations detected are 

within normal ranges for the Proterozoic crystalline rocks, 

Tertiary sedimentary and volcanic rocks, and Quaternary 

materials that are present in the study area. The sparse 

flightline coverage of the study area, however, precluded 

deriving direct information on mineral resource potential 

. from the aerial gamma-ray data. 

Mineral and Energy Resources 

The Table Top Mountain Wilderness Study Area lies 

within a part of Arizona that has major porphyry copper 

and other types of deposits. There are small known copperbearing veins and pegmatites inside the area. Other types 

of deposits found nearby have a remote chance of being 

· present in the subsurface rocks. There is also permissive 

evidence for some types of deposits that are not currently 

known within the region. 

Proterozoic Copper-gold-silver Veins or Polymetallic 

Epithermal Veins · 

The area underlain by Pinal Schist has a low mineral 

resourc~ ·potential, with. a certainty level of C, for copper, 

gold, and .. silver resources in small quartz veins and for 

barite, molybdenum, lead, copper, and (or) tungsten 

resources in polymetallic epithermal veins, because of their 

scattered distribution and small size. Small copper-goldsilver quartz veins are present on the IC claims and 

elsewhere within exposures of the Pinal Schist but have had 

no recorded production. In appearance they resemble other 

gold-silver quartz veins in the region (Peterson and others, 

1987a), but they are thought to have originated in the 

Proterozoic as the region was metamorphosed (R.M. 

Tosdal, written commun., 1985). The veins are 

characterized by spotty chrysocolla and limonite 

pseudomorphs of sulfide minerals and a gangue of white 

quartz. These veins also contain small amounts of gold and 

Mineral Resources of the Table Top Mountain' Wilderness Study Area, Maricopa and Pinal Counties, Arizona A9 
silver (McDonnell, 1986). Host rocks are weakly 

sericitized and chloritized locally near the veins. Most of 

the veins are small, narrow, localized occurrences, 

commonly emplaced along small faults with an 

undetermined but probably small offset Geochemical data 

discussed above suggest that the Pinal Schist may contain 

polymetallic epithermal veins as well. 

In a regional survey (Barton and others, 1982), three of 

13 concentrate samples collected from the study area contain tungsten at detectable levels (100 ppm, 1,500 ppm, and 

3,000 ppm). The source of the tungsten is not known. The 

only nearby tungsten occurrence is in the Gunsight Hills 

about 50 mi to the southwest, where scheelite and quartz 

fragments litter the pediment surface over a Tertiary 

granitic pluton (Wilson, 1941). If there is a pluton 

genetically associated with tungsten in the study area, it is 

not exposed. Tungsten has already been evaluated as a 

possible constituent of polymetallic epithermal veins in the 

_,_()C) 

APPROXIMATE BOUNDARY 

OF 

TABLE TOP MOUNTAIN 

WILDERNESS STUDY AREA 

( AZ-020-1 72) 

EXPLANATION 

- -300 -

• • 

Aeromagnetic contour--In milligals 

Aeromagnetic low--Letters refer to text 

Aeromagnetic high--Letters refer to text 

Figure 4. Aeromagnetic anomaly map of the Table Top Mountain Wilderness Study Area and vicinity, Maricopa and Pinal 

Counties, Arizona. 

A 10 Mineral Resources of Wilderness Study Areas-Southwestern and South-Central Arizona 
Pinal Schist, but it could also form distinct veins containing 

only tungsten as a commodity. 

Pegmatites 

The area underlain by the Oracle Granite has a low 

potential, certainty level C, for resources of quartz, mica, 

and feldspar in pegmatites, and a low potential, certainty 

level B, for resources of lanthanum (a rare-earth element), 

uranium, thorium, and beryllium in pegmatites. Two types 

of pegmatites are present in the study area. Both are simple 

pegmatites; the complex zoned pegmatites that commonly 

contain rare minerals were not seen. The first type is 

compositionally the same as the Oracle Granite, but its 

crystals are much larger than those of the host rock. These 

pegmatites usually. form veins several feet long and a few 

inches wide. Their contacts with the host rock are sharp. 

These pegmatites have not been prospected. The second 

type of pegmatite is more prominent because it is typically 

made up mostly of white quartz, or less commonly 

feldspar, with some very coarse muscovite. These 

pegmatites are at least one foot to several feet wide; the 

larger ones can be traced along strike for several tens of 

feet. Although these could be mistaken for quartz veins, 

the presence of muscovite and the geochemical data for 

areas underlain by the Oracle Granite indicate that they are 

more likely pegmatites. A pegmatite on the Silver King 

claims is associated with narrow, black calcite veinlets. 

Pegmatites can be host to several commodities 

including quartz, feldspar, mica, gem quality minerals, 

rare-earth elements (including lanthanum), uranium, and 

thorium. The Table Top Mountains lie south of the major 

productive pegmatite belt of Arizona, but there has been 

one productive pegmatite southwest of the area at the San 

Antonio mine (Keith, 1974), where quartz was mined for 

use as silica flux in the New Cornelia Smelter at Ajo. 

Quartz from pegmatites within the study area may be 

suitable for such uses. Geochemical data for the area 

(Adrian and others, 1987; Barton al)d others, 1982) suggest 

that the pegmatites could also contain some rare-earth 

elements or uranium and thorium, and possibly beryllium, 

though the minerals that would commonly host these 

elements were not seen during the field investigations. 

Monazite-bearing Rocks 

The parts of the study area underlain by the Oracle 

Granite have a low potential, certainty level B, for 

resources of uranium, thorium, and lanthanum in monazite, 

an accessory mineral in the Oracle Granite and possibly in 

associated pegmatites (see previous section). Monazite is a 

rare-earth- and thorium-bearing mineral that can be present 

in granitic rocks, certain schists, and pegmatites. It can 

also accumulate in detrital material as placer deposits. 

Geochemical and mineralogical data from a regional study 

(Barton and others, 1982) indicate the presence of 

lanthanum; three of their 13 concentrate samples have 

greater than 2,000 ppm lanthanum, and monazite was 

identified in some samples. Two of the same samples also 

·contain 300 and 1,000 ppm thorium. Uranium was not 

measured. Four concentrate samples from the current study 

have at least 500 ppm lanthanum. 

Porphyry Copper 

The entire study area has low potential for copper 

resources in porphyry copper deposits, certainty level B. 

Porphyry copper and related skarn deposits are widespread 

throughout Arizona and several occur within 50 mi of the 

study area. These deposits can be hosted by a variety of 

rocks but are usually associated with Laramide (Late 

Cretaceous and early Tertiary) calcalkalic'intrusions. They 

typically contain large tonnages and low grades with 

disseminated, vein, or stockwork copper-sulfide minerals 

and have a characteristic alteration pattern (Titley, 1982; 

Lowell and Guilbert, 1970). 

In the Vekol Hills deposit about 15 mi south of the 

study area, the Pinal Schist and quartz monzonite 

(presumably the Oracle Granite) form a basement complex, 

which underlies the Apache Group and associated 

Proterozoic diabase. A Paleozoic sedimentary sequence 

nearby in the Vekol Mountains hosts skarn deposits. Late 

Cretaceous or early Tertiary porphyritic stocks, dikes, and 

sills intrude all the pre-Mesozoic units (Steele, 1978). 

Most of the ore is hosted by the pre-Mesozoic rocks with 

only minor mineralization in the porphyritic rocks. The 

sulfide minerals ,pyrite, chalcopyrite, and molybdenite are 

disseminated within the host rocks and fill fractures. There 

is little supergene enrichment. 

The study area is geologically similar to the setting for 

the Vekol Hills deposit except for the lack of Paleozoic 

sedimentary rocks. The place most likely to have a 

porphyry copper deposit is in the prospected area (shaft, 

fig. 2) where the weakly altered Oracle Granite might 

suggest a buried pluton and possibly a porphyry copper 

deposit. Porphyritic intrusions are not known to be present, 

which is why there is only a low rating and a low degree 

of certainty for such resources. However, intrusions could 

be present; it has been suggested that pegmatites west of 

the study area are genetically associated with younger 

plutons (Peterson and others, 1987a). If pegmatites in the 

study area are also associated with younger plutons, these 

plutons have not yet been exposed. 

Geothermal Energy 

No geothermal waters or leasing activity are known 

within the study area. Witcher and others (1982) showed 

no thermal springs or wells in or near the study area; they 

did not define the area as favorable for the discovery of 

Mineral Resources of the Table Top Mountain Wilderness Study Area, Maricopa and Pinal Counties, Arizona All 
geothermal resources. Krason ~d others (1982), however, 

suggested the possibility of favorability for geothermal 

resources in the northwest comer of the study ar~a based on 

a small-scale map published in Jones (1979). Therefore, 

the northwest comer of the study area has low potential, 

certainty level B, for geothermal resources. 

Other Commodities 

The periphery of the Table Top Mountains, and 

consequently of the study area, is flanked by pediment 

surfaces that become deep basins to the northeast and 

southwest. These pediments· have a low potential for 

resources of gypsum, anhydrite, or halite m evaporite 

deposits, certainty level B. The part of the basin about 7 

mi nor~east of the area has been designated as favorable 

for the presence of continental evaporite deposits because it 

lies within a structural area termed the Gila Low, which is 

known to· contain two evaporite deposits (Peterson and 

others, 1987a). Within the study area, evaporites are not 

likely because the basin is very shallow, However, in the 

Sauceda Mountains about 30 mi west of the study area, a 

celestite deposit of evaporite origin is exposed on the edge 

of the pediment (Moore, 1935) and. similarly shallow 

evaporite deposits could possibly exist in the Table Top 

area buried beneath the pediment surface. 

. Uraniu.m in the basins surrounding the Table Top 

Mountains is unlikely but possible. These areas have a low 

potential, certainty level B, for uranium. Uranium can form 

in sedimentary basins in several ways: in calcrete (Carlisle, 

1978), in tuffaceous lake-bed sediments (Davis and 

Hetland, 1956), and precipitated in caliche where the 

uranium is transient throughout the rainy season . (Bell, 

1956). The basin margins around Table Top Mountains are 

too shallow for the development of calcrete, and a lack of 

exposed tuffaceous .rocks makes lake-bed accumulations 

improbable. Thus, the most likely means of accumulating 

uranium in the study area is in caliche deposits. These 

accumulations ~e typically small and of low grade. For 

any such uranium deposits to develop, a suitable source 

area is required. Peterson and others (1987a) have 

designated the area north of the study area as being suitable 

as a uranium source region, and the study area itself may 

also be a source area. · 

Several scattered tin anomalies in the concentrate 

samples collected on the pediments suggest that there may 

be small amounts of placer tin present around the edges of 

the area. These areas have low potential, certainty level B, 

for tin. A source for this tin is not known. 

There have -been no reported oil or gas discoveries, but 

scattered parcels of Federal land are leased for oil and gas 

in and around the Table Top Mountains (McDonnell, 

1986). Ryder (1983) included the study area in a zone of 

"low to zero" potential and further indicated that in this 

zone hydrocarbons could accumulate only in the sedimentfilled basins, which are generally too shallow in the study 

area. Also, the study area consists mostly of intrusive, 

metamorphic, and volcanic rocks, which are not conducive 

to hydrocarbOn accumulation. Any hydrocarbons in nearby 

sedimentary rocks would likely have migrated or been 

destroyed through tectonic and magmatic activity. 

Therefore, we concur with Ryder's conclusions and assign 

a low potential, certainty level B, for oil and gas resources 

to the entire study area. 

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2° quadrangle, Arizona: U.S. Geological Survey Open-File 

Report 83-734, 40 p. 

__ 1987, Maps showing anomalous copper concentrations in 

stream sediments and heavy-mineral concentrations from 

the Ajo and Lukeville 1 o by 2' quadrangles, Arizona: U.S. 

Geological Survey Miscellaneous Field Studies Map MF1834-C, scale 1:500,000. 

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. Department of Energy, 1979, NURE aerial gamma-ray and 

magnetic reconnaissance survey Colorado-Arizona area, 

Salton Sea, Phoenix, El Centro, Ajo, Lukeville 

quadrangles: U.S. Department of Energy, Report GJBX12(80), v. II. 

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

the Papago area, Arizona: U.S. Geological Survey OpenFile Report 80-56, scale 1:250,000. 

Wilson, E.D., 1941, Tungsten deposits of Arizona: Arizona 

Bureau of Mines Bulletin 148, 54 p. 

Witcher, J.C., Stone, Claudia, and Hah.man, W.R., Sr., 1982, 

Geothermal resources of Arizona: Tucson, Arizona Bureau 

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

Mineral Resources of the Table Top Mountain Wilderness Study Area, Maricopa and Pinal Counties, Arizona A13 
J 
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. 

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Abstracted with minor modifications from: 

B c 

H/B H/C 

HIGH POTENTIAL HIGH POTENTIAL 

M/B M/C 

MODERATE POTENTIAL MODERATE POTENTIAL 

L/B L/C 

LOW POTENTIAL LOW POTENTIAL 

LEVEL OF CERTAINTY ... 

D 

H/D 

HIGH POTENTIAL 

M/D 

MODERATE POTENTIAL 

L/D 

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. 

A16 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 1------------ I 

----,---- Inferred 

-~-

MARGINALLY Marginal 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 respurce/reserve classification for minerals: U.S. Geological Survey Circular 831, p. 5. 

Mineral Resources of the Table Top Mountain Wilderness Study Area, Maricopa and Pinal Counties, Arizona A17 
GEOLOGIC TIME CHART 

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

EON ERA PERIOD EPOCH AGE ESTIMATES OF 

BOUNDARIES (in Ma) 

Quaternary 

Holocene 0.010 

Pleistocene 1.7 

Neogene Pliocene 5 

Cenozoic Subperiod Miocene 24 

Tertiary Paleogene Oligocene 38 

Subperiod Eocene 55 

Paleocene 66 

Cretaceous Late 

Early - 96 

138 

Late 

Mesozoic Jurassic Middle 

Early 

205 

Late 

Triassic Middle 

Early 

-240 

Permian Late 

Phanerozoic Early 

Late 

290 

Pennsylvanian Middle 

Carboniferous Early Periods -330 

Mississippian Late 

Early 360 

Late 

Devonian Middle 

Paleozoic Early 

410 

Late 

Silurian Middle 

Early 

435 

Late 

Ordovician Middle 

Early 

500 

Late 

Cambrian Middle 

Early 1

-570 

Late Proterozoic 900 Proterozoic Middle Proterozoic 1600 

Early Proterozoic 2500 

Late Archean 3000 

Archean 

Middle Archean 3400 

Early Archean 

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

pre-Archean2 

1Rocks older than 570 Ma also called Precambrian, a time term withoot specific rank. 21nformal time term without specific rank. 

A 18 Mineral Resources of Wilderness Study Areas-Southwestern and South-Central Arizona 

4550 

GPO 585-045/78054 
SELECTED SERIES OF U.S. GEOLOGICAL SURVEY PUBLICATIONS 

Periodicals 

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

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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. 

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Oil and Gas Investigations Charts show stratigraphic information 

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

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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. 
Peterson and others-MINERAL RESOURCES, TABLE TOP MOUNTAIN WILDERNESS STUDY AREA, ARIZONA-U.S. Geolo

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