Mineral Resources of the Mount Nutt Wilderness Study Area, Mohave County, Arizona

Gray, Floyd- fgray@usgs.gov, Jachens, Robert C. jachens@usgs.gov, Miller, Robert J. rjmiller@usgs.gov, Turner, Robert L. · 1990 · Report

The Mount Nutt Wilderness Study Area (AZ-020-024) is located in the Black Mountains about 15 mi west of Kingman, Arizona. At the request of the U.S. Bureau…

Public-domain full text preserved in the Mountain Man Mining Library. Original source: pubs.usgs.gov.

Mineral Resources Mount Nutt Wilderness Study Mohave County, Arizona U. S. GEOLOGICAL SURVEY BULLETIN 1 737- D

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Chapter D Mineral Resources of the Mount Nutt Wilderness Study Area, Mohave County, Arizona By FLOYD GRAY, ROBERT C. JACHENS, ROBERT J. MILLER, ROBERT C. TURNER, ERIC K. LIVO, DANIEL H. KNEPPER, JR., and JOHN MARIANO U.S. Geological Survey CARL L. ALMQUIST U.S. Bureau of Mines U.S. GEOLOGICAL SURVEY BULLETIN 1737 MINERAL RESOURCES OF WILDERNESS STUDY AREAS: BLACK MOUNTAINS REGION, 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 : 1990 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 Mount Nutt wilderness study area. Mohave County, Arizona / by Floyd Gray ... [et al.]. p. cm. (U.S. Geological Survey bulletin : 1737) (Mineral resources of wilderness study areas Black Mountains region, Arizona : ch. D) Includes bibliographical references. Supt. of Docs, no.: I 19: 1737-D 1. Mines and mineral resources Arizona Mount Nutt Wilderness. 2. Mount Nutt Wilderness (Ariz.) I. Gray, Floyd. II. Series. III. Series: Mineral resources of wilderness study areas Black Mountains region, Arizona: ch. D. QE75.B7 no. 1737-D 557.3 s dc20 UN24.A6] [553 1 .09791'59] 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 part of the Mount Nutt Wilderness Study Area (AZ-020-Q24), Mohave County, Arizona.

CONTENTS Summary Dl Abstract Dl Character and setting Dl Identified mineral resources D2 Mineral resource potential D2 Introduction D3 Area description D3 Previous and present investigations D3 Acknowledgments D5 Appraisal of identified resources D6 Methods D6 Mining and mineral exploration history D6 Mines and prospects, mining claims and leases D6 Reserves and identified resources D6 Assessment of mineral resource potential D7 Geology D7 Stratigraphy D7 Structure D8 Brecciation and alteration D8 Geochemical studies D9 Methods D9 Results D9 Geophysical studies D10 Aeromagnetic data D10 Gravity data D10 Radiometric data D13 Remote sensing D13 Interpretation D13 Results D13 Mineral and energy resource potential D14 References cited D16 Appendixes D19 Definition of levels of mineral resource potential and certainty of assessment D20 Resource/reserve classification D21 Geologic time chart D22 FIGURES Index map showing location of Mount Nutt Wilderness Study Area, Mohave County, Arizona D2 Map showing mineral resource potential and generalized geology of Mount Nutt Wilderness Study Area, Mohave County, Arizona D4 Map showing aeromagnetic anomalies of Mount Nutt Wilderness Study Area, Mohave County, Arizona D12 Map showing areas of alteration minerals in Mount Nutt Wilderness Study Area, Mohave County, Arizona D15 TABLE Analyses of altered rock samples in and near Mount Nutt Wilderness Study Area, Mohave County, Arizona Dll Contents

Mineral Resources of the Mount Nutt Wilderness Study Area, Mohave County, Arizona By Floyd Gray, Robert C. Jachens, Robert J. Miller, Robert C. Turner, Eric K. Livo, Daniel H. Knepper, Jr., and John Mariano U.S. Geological Survey Carl L. Almquist U.S. Bureau of Mines SUMMARY Abstract The Mount Nutt Wilderness Study Area (AZ-020-024) is located in the Black Mountains about 15 mi west of Kingman, Arizona. At the request of the U.S. Bureau of Land Manage- ment, approximately 27,210 acres of the wilderness study area was evaluated for mineral resources (known) and min- eral resource potential (undiscovered). In this report, the area studied is referred to as the "wilderness study area" or simply "the study area;" any reference to the Mount Nutt Wilderness Study Area refers only to that part of the wilderness study area (27,210 acres) for which a mineral survey was requested. The U.S. Geological Survey and the U.S. Bureau of Mines conducted geological, geochemical, and geophysical surveys to assess the identified mineral resources and mineral re- source potential of the study area. Fieldwork for this report was carried out in 1987 and 1988. A gold resource totaling at least 56,000 troy oz has been identified at two sites in Secret Pass Canyon, less than 0.5 mi north of the study area. No other metallic mineral resources were identified inside the study area. An area near the center of the study area contains fire agate, a gem stone. On the basis of tonnage, site acces- sibility, and current production methods, this area is consid- ered an indicated subeconomic fire-agate resource for the foreseeable future. Sand and gravel are present in the study area. An area surrounding the Tincup mine and including a small portion of the extreme north-central part of the study area has high potential for gold and low potential for silver, lead, and mercury. Three areas in the extreme northwestern, north-central, and southwestern parts of the study area have Manuscript approved for publication, April 27, 1990. moderate potential for gold and low potential for silver, lead, and mercury. A small area near the known fire-agate re- source in the south-central part of the study area has low potential for fire agate. Large areas in the eastern and central parts of the study area have low potential for perlite and zeolite resources. The entire study area has no potential for oil and gas and no potential for geothermal resources. Character and Setting The Mount Nutt Wilderness Study Area is located just north of the town of Oatman, Arizona, approximately 15 mi west of Kingman, Arizona (fig. 1). It is situated between Arizona Highway 68 and old U.S. Highway 66. The study area has a total relief of about 3,000 ft; the highest points in the study area are an unnamed peak (Benchmark Nutt, 5,216 ft) and Mount Nutt (5,062 ft). The benchmark lies approximately 1 mi northeast of Mount Nutt. These peaks are surrounded by precipitous cliffs, small mesas, rough slopes, and several steep-walled canyons, the deepest of which is Grapevine Canyon. The area is underlain by Proterozoic (see "Appendixes" for geologic time chart) granite and gneiss that is overlain by or in fault contact with Tertiary volcanic rocks and Holocene sand and gravel. Small late Miocene rhyolitic intrusive bodies cut the older Tertiary rocks in several places in the study area and are typically associated with localized alteration. Volcanic rocks in the study area are cut by numerous, dominantly north-trending high-angle normal faults. Dilatant zones resulting from the intersections of these faults or from curved fault planes served to localize any hydrothermal alteration and gold mineralization that may have occurred. Mount Nutt Wilderness Study Area, Mohave County, Arizona D1

Identified Mineral Resources A gold resource totaling at least 56,000 troy oz was identified by Fischer-Watt Gold Co., Inc., at two sites in Secret Pass Canyon, one site just east of the study area and the other less than 0.5 mi north of the study area. A block of mining claims was located near the center of the study area for fire agate, a gem stone. Hand-sorted specimens, averaging $30-100 per Ib and rarely $1,000 or more, have been extracted from the site. On the basis of a rough size estimate, current production methods, and site accessibility, this deposit will be an indicated subeconomic fire-agate re- source for the foreseeable future. Sand and gravel in the study area have no qualities that would make them more valuable than abundant supplies available from established sources closer to existing markets. Mineral Resource Potential Geologic, geochemical, and geophysical studies show that the Mount Nutt Wilderness Study Area has an area with high potential for gold and low potential for sil- ver, lead, and mercury in the north-central part of the study area. Three areas in the northwestern, southwestern, and north-central parts of the study area have moderate poten- tial for gold and low potential for silver, lead, and mercury resources (fig. 2). That these areas are predominantly underlain by fractured, veined, and altered volcanic rocks suggests volcanic-hosted gold deposits may be present. The areas are cut by mostly north- to northwest-trending faults with localized areas of thin, irregular stockwork veins consisting of calcite and minor amounts of quartz; limonite staining and localized illitic alteration characterize the stockwork. Anomalous concentrations of elements including barium, silver, and lead and smaller concentra- tions of mercury and arsenic were detected in stream sedi- ments collected from drainages in these areas. Gold was consistently detected in rock samples from shears and fault zones within Secret Pass Canyon. Occurrences of gem-quality fire agate have been reported from a locality in the south-central part of the study area within rhyolite flows, but the potential for undiscovered agate resources is low in the region surround- ing the known deposit. Zeolite and perlite occur locally in the upper part of the volcanic section associated with thick tuff intervals and rhyolite flows, flow breccias, and intrusive bodies through- out the study area. Large areas in the central and eastern parts of the study area underlain by these volcanic rocks have low potential for perlite and zeolite resources. However, the low grade and difficult access to these per- lite- and zeolite-bearing beds in the study area would hin- der development of these commodities. The oil and gas resource potential of the study area was considered by Ryder (1983) to be low to zero. In this region, hydrocarbon source or reservoir rocks are limited to Tertiary and (or) Quaternary sedimentary basins that flank the mountain ranges. Within the study area, a Proterozoic schist, gneiss, and granite unit crops out or underlies expoAPPROXIMATE BOUNDARY OF MOUNT NUTT TiNESSSTUD' (AZ-020-024) FORT MOHAVE INDIAN RESERVATION Figure 1. Index map showing location of Mount Nutt Wilderness Study Area, Mohave County, Arizona. D2 Mineral Resources of Wilderness Study Areas: Black Mountains Region, Arizona

sures of Tertiary volcanic rock at shallow depths. There- fore, there is no resource potential for oil and gas within the study area. There is no potential for undiscovered geothermal energy within the study area because well temperatures (ap- proximately 30 °C) from the surrounding area are average for this region of the Basin and Range province (Bliss, 1983). INTRODUCTION This mineral survey was requested by the U.S. Bureau of Land Management and is the result of a coopera- tive effort by the U.S. Geological Survey and the U.S. Bureau of Mines. An introduction to the wilderness review process, mineral survey methods, and agency responsibili- ties was provided by Beikman and others (1983). The U.S. Bureau of Mines evaluates identified resources at individ- ual 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 a system that is a modification of that described by McKelvey (1972) and U.S. Bureau of Mines and U.S. Geo- logical Survey (1980). U.S. Geological Survey studies are designed to provide a scientific basis for assessing the potential for undiscovered mineral resources by determin- ing geologic units and structures, possible environments of mineral deposition, presence of geochemical and geophysi- cal anomalies, and applicable ore-deposit models. Goudarzi (1984) discussed mineral assessment methodol- ogy 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. Area Description The Mount Nutt Wilderness Study Area (AZ-020-024) covers approximately 27,210 acres in the desert highlands 15 mi west of Kingman and 8 mi east of the Colorado River. The terrain of the study area is rugged, rising from about 2,300 ft along the west side to sharp peaks above 5,000 ft with precipitous cliffs and rocky canyons. Grapevine Canyon is the deepest and most spec- tacular canyon and is over 1,000 ft deep at its east end. The Mount Nutt Wildernes Study Area lies in the Mohave desertscrub biome of the Warm-Temperate Desertland Biotic Community (Brown, 1982). The vegetation of the study area is dominated by the shrubs and cacti that are typical of southwest desert biomes. However, this study area also contains local areas of the Great Basin desertscrub biome. The dominant shrubs in the study area are Mohave indicators, such as creosotebush (Larreo tridentata),v/hi\.e bursage (Ambrosia dwnosa), brittlebush (Enceliafairnosa), and all-scale (Atriplex polycarpa); the Yucca (Yucca spp.) is the characteristic Mohave tree that flourishes in the study area. The Mohave desertscrub is especially rich in ephem- eral plants, many of which are endemic to the biome. Cholla (Opuntia spp.) and other cacti are well represented in the study area and are common in the large spaces be- tween the shrubs. Many of these cacti are endemic to the Mohave biome. Local areas of the Great Basin desertscrub biome contain California juniper (Juniperus californica), sagebrush (Artemisia spp.), and Torrey joint-fir (Ephedra torreyana). The area contains several species of lizards, small mammals, and birds. Rattlesnakes and desert tortoise are native to the study area. Other wildlife including deer, bobcat, kit fox, cottontail, and jack rabbit inhabit the re- gion; the northern part of the study area contains Bighorn sheep migratory/watering routes. The study area is easily accessible in the north by gravel roads from Arizona High- way 68, from the west by dirt roads off the Silver Creek road, and from the east by roads leading into Secret Pass Canyon from Sacramento Valley. Previous and Present Investigations Early reports on the geology and ore deposits of the Katherine and Oatman mining districts, which include parts of the study area, were given in Ransome (1923) and Lausen (1931). Thorson (1971a) described the stratigraphy and structure of volcanic rocks in the Oatman district. Clifton and others (1980) and W.P. Durning (written commun., 1980) modified the descriptions of Thorson (1971a). Recent studies on the geology and ore-deposit characteristics of the Oatman district were conducted by Smith (1984) and Dewitt and others (1986). The U.S. Geological Survey carried out field inves- tigations in the study area during 1987 and 1988. This work included geologic mapping at scales of 1:48,000 and 1:24,000, geochemical sampling, geophysical surveys, and examining outcrops for evidence of mineralization. The geochemical survey used rock and stream-sediment samples (including a fine fraction and heavy-mineral con- centrate) that were analyzed for 31 elements by semiquan- titative emission spectrography. Arsenic, antimony, cad- mium, zinc, and bismuth were analyzed by inductively coupled plasma-argon atomic-emission spectrometry. Gold was analyzed by electrothermal atomic-absorption spectroscopy and mercury by continuous-flow, cold-vapor atomic-absorption spectroscopy. Previously collected geo- physical data, which resulted from regional gamma-ray, gravity, and magnetic surveys, were compiled and analyzed for this study. X-band side-looking airborne radar data and stereoscopic Landsat thematic mapper (TM) images were interpreted for structural fabric, major tectonic elements, Mount Nutt Wilderness Study Area, Mohave County, Arizona D3

and potential areas of hydrothermal alteration using photo- graphic techniques. Further details on analytical proce- dures undertaken for this resource assessment are given in the appropriate sections that follow. The Mount Nutt Wilderness Study Area geologic map is generalized from mapping in the southern half by Thorson (1971a) and Clifton and others (1980) and the northern half from mapping done during the course of this 114° 23' M/B 11 ] Au L/C Ag, Pb, Hg H/C 11 ] Au

L/C Ag, Pb, Hg APPROXIMATE BOUNDARY OF MOUNT NUTT WILDERNESS STUDY AREA (AZ-020-024) M/B [ 1 ] Au L/C Ag, Pb, H L/C Per, Zeo Gold ore M/B [ 1 ] Au L/C Ag, Pb, Hg Goldroad Figure 2. Mineral resource potential and generalized geology of Mount Nutt Wilderness Study Area, Mohave County, Arizona. D4 Mineral Resources of Wilderness Study Areas: Black Mountains Region, Arizona

study (Floyd Gray and RJ. Miller, unpub. data, 1988; Gray and others, 1987). Altered and mineralized areas in the northern half were mapped in detail to characterize the extent and effect of hydrothermal activity in the study area. The U.S. Bureau of Mines carried out field investi- gations in 1987, including searches for mines, prospects, claims, and mineralized geologic structures (Almquist, 1989). Ninety-two chip, grab, and select samples and one panned-concentrate sample were collected. Acknowledgments The authors would like to thank Robert Harrison of the U.S. Bureau of Land Management and Perry Durning of Fischer-Watt Gold Co., Inc., for their information re- garding the geology and mining activity in the study area. In addition, the staff of the Kingman, Arizona Resource Area Office of the U.S. Bureau of Land Management provided logistical support, equipment, and facilities. EXPLANATION B Commodities Au Ag F Hg Pb Per Zeo Area having high resource potential (H) Tr Area having moderate resource potential Tc (M) Area having low resource potential (L) Ts Mine having identified fire-agate resource See text for discussion Tm Levels of certainty of assessment Data only suggest level of potential Data give good indication of level of potential Gold Silver Fire agate Mercury Lead Perlite Zeolites [ ] Deposit type Epithermal gold deposits in volcanic and volcaniclastic rock Map units Qal Alluvial deposits (Quaternary) Mostly stream sand and gravel; includes fanglomerate; also includes minor amounts of eolian and lacustrine sediment. May also include scattered low-lying bedrock outcrops Job Olivine basalt (Tertiary) Medium-grained, gray, granular to ophitic basalt with 1- to 3-mm phenocrysts of iddingsite (altered olivine) Tmf Meadow Creek and Flag Spring Trachytes, undivided (Tertiary) Alkalic to subalkalic quartz latite flows, agglomerates, and flow breccias Rhyolite (Tertiary) Rhyolitic flows, massive domes, plugs, and associated breccias and tuffs Cottonwood unit of Thorson (1971a) (Tertiary) Rhyolite to alkali rhyolite flow domes and flow breccias. May be correlative with unit Tr Sitgreaves Tuff (Tertiary) Volcaniclastic sedimentary rock including conglomerate and air-fall tuff Moss Porphyry (Tertiary) Rhyolite to rhyodacite porphyry stock. Contains phenocrysts of feldspar, quartz, and minor amounts of altered biotite. Intrudes the Alcyone Formation of Thorson (197 la, b) on west side of study area Trd Rhyodacite dikes and intrusive rocks (Tertiary) Argillically altered, limonite-stained intrusive rocks; commonly contains altered plagioclase and quartz phenocrysts Ta Antelope quartz latite unit of Thorson (1971a) (Tertiary) Rhyodacite to rhyolite flows and domes Tpa Porphyritic andesite (Tertiary) Porphyritic, plagioclase-rich andesite flows and flow breccias Tg Gold Road Latite (Tertiary) Andesitic to dacite flows, flow and vent breccias, and minor amounts of lithic air-fall tuff To Oatman latite unit of Thorson (1971a) (Tertiary) Dacite to andesitic basalt flows, tuffs, and flow breccias Tal Alcyone Formation of Thorson (1971a,b) (Tertiary) Rows, tuffs, and breccias of quartz latitic composition Pg Granite, schist, and gneiss (Proterozoic)

-- Contact Dashed where approximately located Fault Dashed where approximately located; dotted where inferred Mount Nutt Wilderness Study Area, Mohave County, Arizona D5

APPRAISAL OF IDENTIFIED RESOURCES By Carl L. Almquist U.S. Bureau of Mines Methods In March 1987 the U.S. Bureau of Mines conducted a mineral investigation of the Mount Nutt Wilderness Study Area. This investigation included a review of literature, unpublished U.S. Bureau of Mines and U.S. Bureau of Land Management files, mining claim, and land-status records; contact with mineral interest holders; a field ex- amination of the study area and vicinity; and an evaluation of sample analyses. Two U.S. Bureau of Mines geologists spent nine days in the study area and collected 92 chip, grab, and select samples and 1 panned-concentrate sample. The samples were analyzed by Chemex Labs, Inc., Sparks, Nevada. Gold content was determined by fire assay and neutron activation. Silver, arsenic, antimony, bismuth, cadmium, gallium, tellurium, copper, lead, zinc, and mo- lybdenum contents were determined by inductively coupled plasma-atomic emission spectrometry. All analytical data are reported in Almquist (1989). Mining and Mineral Exploration History The Oatman mining district, Arizona's third largest gold producer, extends into the southwestern part of the study area. In the early 1860's, a gold-bearing ore shoot was discovered in a prominent quartz vein outcrop 2.5 mi west of the study area at the Moss mine (Almquist, 1989, pi. 1). Shortly after this discovery, other gold-bearing veins were located nearby to the east and southeast, but nearly 30 years passed before the largest gold mines of the Oatman district were opened. In the early 1900's, develop- ment work was started at the Tom Reed, United Eastern, and Gold Road mines, which were by far the most produc- tive in the district. Ore production peaked in 1920 and then sharply declined in 1924 as gold ore grades decreased. Mining activity stagnated in the late 1920's, was revived in 1933 when the gold price increased to $35 per oz, and ceased in 1942 (Ransome, 1923; Lausen, 1931; and Durning and Buchanan, 1984). Recorded production, from 1870 to 1980, is 1,966,000 troy oz of gold, 1,147,000 troy oz of silver, and 60,000 Ib of copper from 4,073,000 short tons (st) of ore (Keith and others, 1983, p. 38-39). All the past-producing mines in the Oatman district are outside the study area. More gold-bearing veins are present in the Union Pass mining district, which extends into the northern part of the study area at the mouth of Secret Pass Canyon. Discov- eries in the district followed the Moss mine discovery at Oatman by about ten years, and mining activity coincided with the main period of activity at Oatman, but on a smaller scale. The most productive past-producing mines in the district are all northwest of the study area. Recorded pro- duction, from 1868 to 1943, is 128,000 troy oz of gold and 313,000 troy oz of silver from 704,000 st of ore (Keith and others, 1983, p. 52-53). An unknown tonnage of gold ore, reportedly con- taining from 0.43-0.57 oz/st, was produced from the Tin Cup mine, which is in Secret Pass Canyon less than 0.5 mi north of the study area (Almquist, 1989, pi. 1; Westervelt, written commun., 1987). Recent exploration work (1984-1988) by Santa Fe Pacific Mining, Inc., and Fischer- Watt Gold Company, Inc., which included drilling, resulted in the identification of approximately 460,000 st of ore with a grade of 0.110 troy oz gold/st at the Tin Cup mine and approximately 108,000 st of ore with a grade of 0.053 oz gold/st at a nearby site, a total resource of about 56,000 troy oz gold. As of early 1988, Fischer-Watt Gold Com- pany was continuing its exploration efforts in the Secret Pass area (F.L. Hillemeyer, Fischer-Watt Gold Company, Inc., Kingman, Ariz., oral commun., 1988). Mines and Prospects, Mining Claims and Leases There are numerous prospect pits, shallow shafts, and adits inside the study area but no mines with a history of metallic mineral production. Large blocks of unpatented mining claims, located on gold-bearing vein deposits in the Oatman and Union Pass mining districts, extend from the north, west, and south into the study area (Almquist, 1989, pi. 1). Mining claims have also been located on a gem- stone resource northeast of Mount Nutt, where fire agate was being mined on a small scale during the U.S. Bureau of Mines investigation. Ryder (1983, p. 19) rated the study area as having zero to low potential for the occurrence of petroleum, on the basis of prevalent Proterozoic crystalline rocks and Tertiary volcanic rocks. Approximately 5,160 acres were under lease for oil and gas at the time of the U.S. Bureau of Mines investigation (Almquist, 1989, pi. 1). Reserves and Identified Resources Host rocks, structures, and some types of alteration associated with gold deposits in the Oatman mining district are present in the southern and western parts of the study area. Although these characteristics suggest the presence of ore deposits and there has been some prospecting in the study area, no ore deposits have been discovered. Element concentrations that could indicate the presence of metallic mineral resources were not detected in U.S. Bureau of Mines samples from prospects and altered outcrops inside the study area (Almquist, 1989, table 1 and appendix), but D6 Mineral Resources of Wilderness Study Areas: Black Mountains Region, Arizona

these findings are not conclusive. In the Oatman mining district, most past-producing ore shoots are not exposed; their only surface expression is altered volcanic rock that gives no distinct geochemical anomaly (Durning and Buchanan, 1984). The gold ore deposits recently identified by drilling in the Secret Pass Canyon area are on the Frisco Mine fault, which is traceable for more than 2 mi into the study area (Almquist, 1989, pi. 1; fig. 2). Gold was detected in all U.S. Bureau of Mines samples collected from workings in the Secret Pass Canyon area, with concentrations as high as 0.880 and 0.354 oz/st (Almquist, 1989, table 1), but there are no known gold-bearing deposits in the study area. Deposits that were mined on the Mossback, Gold Ore, and Gold Trail mine veins are not traceable at the surface into the study area (Almquist, 1989, pi. 1). The northwest-trending Mossback vein dips about 80° SW and appears to be fault-terminated at a point near the east boundary. The Gold Ore and Gold Trail mine veins trend toward the study area, but their trace is obscured by vol- canic cover. A block of mining claims near the center of the study area was located for fire agate. Hand-sorted speci- mens, valued at $30-$ 100 per Ib, are packed out from the remote site and sold in small quantities. Exceptional indi- vidual specimens reportedly sell for $1,000 or more (Tom Dodge, claimant, oral commun., 1987). On the basis of a rough size estimate, current production methods, and site accessibility, this deposit will be a subeconomic indicated fire-agate resource for the foreseeable future. Inferred subeconomic resources of sand and gravel in the study area have no qualities that make them more valuable than abun- dant supplies available from established sources closer to existing markets. Therefore, development is unlikely. No other industrial-mineral commodities are present in the study area. ASSESSMENT OF MINERAL RESOURCE POTENTIAL By Floyd Gray, Robert C. Jachens, Robert J. Miller, Robert C. Turner, Eric K. Livo, Daniel H. Knepper, Jr., and John Mariano U.S. Geological Survey Geology Stratigraphy The Mount Nutt Wilderness Study Area is underlain by Proterozoic granite, schist, and gneiss and Tertiary volcanic and volcaniclastic rocks. Rhyolitic to rhyodacitic porphyries intrude the basement rocks and the lower to middle parts of the volcanic section. The geology shown in figure 2 is modified from Thorson (197la), Ransome (1923), Clifton and others (1980), Dewitt and others (1986), and Floyd Gray and RJ. Miller (unpub. data, 1988). Proterozoic rocks are exposed in scattered areas along the east side of the Mount Nutt Wilderness Study Area and in a northwest-trending fault-bounded block as much as 2 mi wide in the Secret Pass Canyon area. These rocks consist of medium- to coarse-grained biotite granite to quartz monzonite, weakly foliated gneiss, and schist. The granitic rocks are commonly porphyritic with feldspar phenocrysts as large as 2 in. in diameter; some rocks have a rapakivi texture. The granitic rocks are hypidiomorphic- granular and consist of potassium feldspar (approximately 55 percent), plagioclase (approximately 25 percent) and quartz (approximately 20 percent). They contain as much as to 6 percent biotite and nearly an equal amount of amphibole; they also contain minor amounts of magnetite and sphene locally. The feldspars in the granite, gneiss, and schist are slightly saussuritized, and they are typically altered to sericite and muscovite. Biotite is slightly altered to chlorite, and mafic minerals are partially replaced by iron oxide. The eastern contact of the Proterozoic rocks with the volcanic rocks is a depositional unconformity with the volcanic rocks dipping approximately 25-35° W. The western contact of the basement rocks and the overlying volcanic rocks is exposed just north of the study area and is an east-dipping low-angle normal fault. The oldest volcanic rocks of the study area are basalt and basaltic volcaniclastic rocks within the Alcyone For- mation of Thorson (197la, b), a sequence of mainly an- desite and trachyandesite (subalkalic quartz latite) flows exposed just inside the west boundary of the study area (fig. 2). The trachyandesite flows are typically dark por- phyritic rocks consisting of 65 percent groundmass and 35 percent phenocrysts of sanidine, plagioclase, and biotite and minor amounts of pyroxene and quartz. The middle volcanics unit of Thorson (1971a) un- conformably overlies the Alcyone Formation. Units com- prising the middle volcanics unit include the Oatman latite unit of Thorson (197 la) and the Gold Road Latite. The Oatman latite unit ranges in composition from dacite to andesitic basalt, but its average composition is subalkalic latitic andesite (Dewitt and others, 1986). The unit is composed of flows, flow breccias, and minor amounts of tuff and is exposed in the western part of the study area. The Gold Road Latite conformably overlies the Oatman latite unit and is composed of porphyritic subalkalic to alkalic flows and vent breccias; this unit is exposed throughout the study area. The middle volcanics unit is intruded by the Moss Porphyry, a small stock exposed west of the study area (Thorson, 1971a). The unit's composition ranges from porphyritic tonalite and monzodiorite to granodiorite. Numerous silicic, porphyritic north west-trending dikes and Mount Nutt Wilderness Study Area, Mohave County, Arizona D7

small sills similar to the Moss Porphyry are exposed in the northern part of the study area and suggest a more wide- spread intrusive episode that may include separate high- level plutonic bodies (Floyd Gray and RJ. Miller, unpub. data, 1988). The upper volcanics unit of Thorson (197la) uncon- formably overlies the middle volcanics unit and consists of the Antelope quartz latite unit of Thorson (1971a), Cotton- wood unit of Thorson (1971a), Flag Spring Trachyte, Meadow Creek Trachyte, and the dominantly volcaniclastic Sitgreaves Tuff. In the north half of the study area, the upper volcanics unit is correlated with a thick sequence of rhyolite flows and domes, welded tuffs, and small silicic plugs. The Antelope quartz latite and Cottonwood units are dominantly flows and domes of subalkalic rhyodacite to rhyolite and rhyolite to alkalic rhyolite, respectively (Dewitt and others, 1986). The Flag Spring Trachyte and Meadow Creek Trachyte are quartz latite flows, agglomer- ates, and flow breccias. The Sitgreaves Tuff is a volcani- clastic unit that contains conglomerate and air-fall tuff with abundant lithic fragments derived from the upper volcanics unit. The upper volcanics unit is unconformably overlain by flat-lying to gently east-dipping olivine basalt flows and interbedded conglomerate and silicic ash. Although ages are available for several units in and near the study area, the details of the timing of Tertiary volcanic events remains unclear. Thorson (1971a) reported conventional potassium-argon (K-Ar) ages of 18.6+0.9 Ma (million years before present) and 19.2+0.9 Ma for the Gold Road latite and Antelope quartz latite, respectively. This apparent inversion of the stratigraphy can be ac- counted for in the analytical uncertainty of the ages or by assuming that one or both represent minimum ages. Dewitt and others (1986) obtained an Ar-Ar age of 18.8+0.1 Ma on hornblende from the Moss Porphyry. This body intrudes the Alcyone (lower unit) and is chemically similar to the Cottonwood unit. DeWitt and others (1986) suggested that the Moss Porphyry may be coeval with the upper volcanics unit. A uranium-lead age of 18+4 Ma for the Moss Por- phyry (DeWitt and others, 1986) suggested that the intru- sion was coeval with the main period of volcanism and not late Miocene, as was suggested by Thorson (197 la). Ages from volcanic rocks in the northern part of the study area, correlated with the upper volcanic unit, are somewhat younger than the age reported by Thorson (1971a). Biotite from two samples of porphyritic andesite (unit Tpa, fig. 2) produced ages of 18.2+0.5 Ma and 18.4+0.5 Ma (RJ. Miller, unpub. data, 1989). A silicic dike, tentatively correlated with the upper part of the upper volcanic unit, has a K-Ar biotite age of 17.1+0.5 Ma (RJ. Miller, unpub. data, 1988) suggesting that the upper vol- canic unit may represent as much as 2 million years of volcanic activity. A brief quiescent period may have preceded eruption of mesa-capping basalts. This basalt is much thicker and more areally extensive south of the study area and has been dated by whole-rock K-Ar methods at 15.8±0.5 Ma (RJ. Miller, unpub. data, 1988). No volcanic units overlie this basalt in the southern Black Mountains. Quaternary units unconformably overlie Tertiary volcanic and older crystalline rocks. Flanking some of the peaks are poorly sorted, semiconsolidated to unconsoli- dated locally derived terrace gravels. Closer to some of the mountains are talus slopes that obscure underlying geology. Widespread pediment surfaces are covered by older allu- vium, and major drainage channels contain Quaternary alluvium. Structure Rocks within the study area are intensely faulted and tilted as a consequence of late Tertiary deformation related to extensional tectonism. The faults are generally north- to northwest-trending high-angle normal faults. The study area is divided into two areas that have different structural configurations. The south half of the study area (roughly from Mount Nutt south) is dominated by a large circular structural feature inferred to be a volcanic depression (Thorson, 197la; Clifton and others, 1980; Dewitt and others, 1986; Gray and others, 1987). This feature is older than the north- to northwest-trending fault set and is offset along them (Gray and others, 1987). The north half of the study area is dominated by north- to northwest-trending normal faults. The Tertiary volcanic cover is thinner in the northern part of the study area where a more closely spaced set of parallel faults is exposed. The general structural pattern suggests a faulted, southward-plunging horst cored by Proterozoic granitic rocks. Brecciation and Alteration Brecciation and localized alteration are coincident with Tertiary fault and fracture systems. The fault and fracture systems possibly served as conduits for circulating hydrothermal fluids driven by proximal rhyolitic magma- tism. Zones of intensely brecciated rocks from 5 ft to about 150 ft wide characterize most faults. Weak to moderate propylitic alteration is evident along more prominent nor- mal faults with irregular zones of illitic alteration; minor silicification is locally present along these faults. Altera- tion is mainly present in the lower part of the volcanic section; young bedded air-fall tuff, silicic breccias, and rhyolite plugs are virtually unaltered. Near the Frisco Mine fault, propylitic alteration is common adjacent to the fault in both granitic and volcanic rocks. The granitic rocks are intensely fractured near the fault and host an irregular D8 Mineral Resources of Wilderness Study Areas: Black Mountains Region, Arizona

stockwork vein system consisting of quartz, calcite, and minor amounts of fluorite. Volcanic rocks near the fault are propylitically altered and also are argillically altered in irregular patches. Rhyolitic to rhyodacitic dikes in the northern part of the study area are limonite stained and pervasively argilli- cally altered; the alteration resulted from acid fluid associ- ated with the breakdown of pyrite. The dikes are bleached white with irregular reddish brown to yellowish tan patches created by limonite staining. Moderate to intense argillic alteration is predominant in the eastern margin of the Moss Porphyry west of the study area. This silicic, high-level intrusion is typically bleached white to yellowish-brown or pinkish-white in this region. Geochemical Studies Methods A reconnaissance geochemical survey was con- ducted in the Mount Nutt Wilderness Study Area in the fall of 1986 and the spring of 1987. Reconnaissance surveys allow the evaluation of large areas for evidence of miner- alization. Reconnaissance surveys are not designed to find individual deposits, rather the spacing of samples allows large areas to be subdivided rapidly at low cost into zones of favorable geochemical provinces and mineralized tracts. Minus-80-mesh stream sediments, heavy-mineral concen- trates derived from stream sediments, and rocks were se- lected as the sample media in this study. Fifty-three sites were sampled for stream sediments and heavy-mineral concentrates and 27 rock samples were collected at 25 sites. The stream-sediment samples were collected from the active alluvium in the stream channel length of approxi- mately 50 ft. The stream sediments were sieved through an 80-mesh screen and pulverized to a fine powder before analysis. The heavy-mineral concentrates were sieved through a 10-mesh screen and then panned until most of the quartz, feldspar, clay-sized material and organic matter were removed. The remaining light minerals were sepa- rated from the heavy minerals with heavy liquid (bro- moform, specific gravity 2.8). Magnetite and ilmenite were removed from the resultant heavy-minerals fraction with a Franz Isodynamic electromagnetic separator; the remainder was separated into nonmagnetic and slightly magnetic frac- tions. The nonmagnetic fractions, which were used in this study, were ground to a fine powder before analysis. Stream sediments represent a composite of the rock and soil exposed upstream from the sample collection site. The heavy-mineral concentrate represents a composite of the heavy-mineral components of the rocks exposed in the drainage basin, which could include ore-forming and orerelated minerals. Analyses of the nonmagnetic fraction of the concentrate permits determination of the concentration of some elements that are not easily detected in bulk stream sediments. Rocks were collected from mineralized and unmineralized outcrops and stream float. Samples that appeared fresh and unaltered were collected to provide information on background geochemical values. Altered samples were collected to determine the suite of elements associated with the observed alteration or mineralization. The rocks were crushed and pulverized to a fine powder before analysis. The heavy-mineral concentrates, stream sediments, and rocks were analyzed for 31 elements by direct-current arc, semiquantitative, emission spectrographic analysis (Grimes and Marranzino, 1968; Crock and others, 1983). The rocks were also analyzed for antimony, arsenic, bis- muth, cadmium, and zinc by inductively coupled argon plasma-atomic emission spectroscopy (O'Leary and Viets, 1986); for gold by atomic absorption (Thompson and oth- ers, 1968); and for mercury by cold-vapor atomic-absorp- tion methods (Koirtyohann and Khalil, 1976). Analytical data and a description of the sampling and analytical tech- niques were compiled by J. Bullock (written commun., 1989). Results A plot of the anomalous values from the minus-80 mesh stream-sediment samples delineated an anomalous zone in the northwestern part of the study area. This zone is characterized by anomalous values for mercury (0.1-0.6 parts per million, ppm), gold (0.05-0.1 ppm), arsenic (10-18 ppm), lead (as high as 200 ppm), zinc (as high as 250 ppm), and barium (2,000-3,000 ppm). A second zone, in the southeastern part of the study area, is characterized by anomalous values for mercury (8-16 ppm) and molyb- denum (as high as 15 ppm). A third zone delineated from this sample medium is in the east to northeast part of the study area and is characterized by anomalous values of mercury (as high as 12 ppm) and zinc (230-250 ppm). Rock samples collected from altered volcanic rocks and altered silicic dikes in and adjacent to the north-central part of the study area yielded anomalous precious metal values (table 1). The rocks are characterized by anomalous values for gold of as much as 10 ppm (average value being approximately 1.43 ppm), silver (as high as 30 ppm), and mercury (as high as 84 ppm). Arsenic concentrations are weakly anomalous but low compared to the Sleeper and Buckhorn gold deposits (table 1). Weakly anomalous concentrations of trace elements, (mercury, arsenic, antimony, and molybdenum) were de- tected in scattered, altered rocks in and adjacent to the northwestern part of the study area. Mount Nutt Wilderness Study Area, Mohave County, Arizona D9

Geophysical Studies Three types of geophysical data from western Ari- zona (magnetic, gravity, and radiometric) were compiled and examined to aid in the assessment of the mineral re- source potential of the Mount Nutt Wilderness Study Area, Arizona. Detailed aeromagnetic and radiometric data are available along profile lines spaced about 1 mi apart. The sparsely distributed nature of the gravity data and the wide separation between aeromagnetic and radiometric profile lines make these data adequate for addressing the regional structural and tectonic setting of the study area but do not permit detailed statements about mineral resource potential at the deposit scale. Aeromagnetic Data An aeromagnetic survey of the study area and vicin- ity was flown in 1977 and compiled by Western Geophysi- cal Company of America under contract to the U.S. Depart- ment of Energy as part of the National Uranium Resource Evaluation (NURE) program (U.S. Department of Energy, 1979). Total-field magnetic data were collected along east- west flightlines spaced approximately 1 mi apart at a nominal height of 400 ft above the ground surface. Correc- tions were applied to the data to compensate for diurnal variations of the Earth's magnetic field, and the Interna- tional Geomagnetic Reference Field (updated to the month data were collected) was subtracted to yield a residual field that primarily represents the distribution of magnetite in the underlying rocks. The magnetic field of the Mount Nutt Wilderness Study Area is dominated by numerous short-wavelength (1-3 mi in width), high amplitude (200-400 nanoteslas) anomalies that are characteristic of areas of rugged relief in magnetic volcanic rocks. The mafic volcanic rocks that primarily underlie regions of rugged terrain within the study area appear to be strongly magnetic and cause large anomalies. These anomalies result both from lateral vari- ations of induced and remanent magnetization within the volcanic rocks and from variable separation between the magnetic sensor and the underlying rocks because a con- stant flight elevation could not be maintained above the ground surface. In contrast, the tuff units and rhyolitic rocks appear to be much less magnetic and cause magnetic lows. Most of these anomalies do not directly contribute to an understanding of the mineral resource potential of the study area. Two pronounced magnetic lows, one lying mostly outside the study area along its southwest edge and another that straddles the northwest corner of the study area, sug- gest mineralization may have occurred. The southwestern low lies over the Oatman mining district and extends less than 1 mi into the study area (anomaly 1, fig. 3). This low covers more than 15 mi1 and includes most of the deposits and claims in the district. The rocks encompassed by this low are significantly less magnetic than the igneous rocks in the surrounding area, probably as a result of hydrother- mal alteration that destroyed the magnetite in the rocks. The northwestern low (anomaly 2, fig. 3) is situated over exposures of rhyolite that include a group of rhyolite plugs. This low may be related to alteration associated with the intrusion of the rhyolite plugs, but it also partly indicates the magnetic character of the rhyolite that elsewhere in the study area appears to be only weakly magnetic. Gravity Data Gravity data in the vicinity of Mount Nutt Wilder- ness Study Area were obtained from Mariano and others (1986). Gravity stations are scattered at 1-3 mi intervals outside the study area, but only 12 stations are located within the study area boundary and most are aligned along a northeast-trending profile that crosses the center of the study area. The observed gravity data, based on the Inter- national Gravity Standardization Net datum (Morelli, 1974), were reduced to free-air gravity anomalies using standard formulas (Telford and others, 1976). Bouguer, curvature, and terrain corrections (to a distance of 103.6 mi from each station) at a standard reduction density of 2.67 g/ cm3 (grams per cubic centimeter) were made at each station to determine complete Bouguer gravity anomalies. The Bouguer gravity field over the study area and surrounding region shows shallow-density distributions related to near-surface geology and deep-crustal density distributions that correlate with topography in a manner consistent with the concept of isostasy. To isolate that part of the gravity field that arises from near-surface density distributions, an isostatic residual gravity map was con- structed from the Bouguer gravity data. The method used was removal of a regional gravity field computed from a model of the crust-mantle interface that assumes Airy-type isostatic compensation (Jachens and Griscom, 1985). Measurements were made on hand samples collected from outcrops in or near the study area to determine the densities of the major rock types. Fifteen samples of Proterozoic basement rock yielded an average density of 2.72±0.06 g/cm3. Twenty-six samples of unaltered Tertiary volcanic rocks yielded an average of 2.51±0.12 g/cm3, al- though this average should be used with caution because the density measurements on the volcanic rock samples showed considerable scatter. The gravity field in the vicinity of the Mount Nutt Wilderness Study Area primarily shows the thickness of low-density Cenozoic deposits that overlie higher density Proterozoic basement rock. An elongate gravity low about 4 mi wide and 6 mi long that is centered on Mount Nutt covers most of the study area. This low, which culminates D10 Mineral Resources of Wilderness Study Areas: Black Mountains Region, Arizona

Table 1. Analyses of altered rock samples in and near Mount Nutt Wilderness Study Area, Mohave County, Arizona [All samples are either from altered volcanic rocks in fault and fracture zones or from altered, hematite-stained silicic dikes. Analyses by J. Bullock and B. Anderson. N, not detected at detection limit (given in parentheses). --, not analyzed for. AH element concentrations measured in parts per million unless otherwise indicated. Au, gold; Ag, silver; Hg, mercury; As, arsenic; Sb, antimony; Cd, cadmium; Pb, lead; Zn, zinc; Mo, molybdenum] Sample Number WGT-3 WGT-13 WGT-15 WGT-21-7 WGT-30 WGT-34 WGT-35 WGT-37 7M136A 7M136B 7M136C 7M136D 7M136F 7M137 7M137B 7M137C 7M137D 7M137E 7M137F 7G105-1 7G105-2 7G105-3 7G105-4 7G105-5 7G106-1 7G106-3 7G 106-4 7G106-5 7G106-6 *7G102-1 *7G102-2 *7G102-3 '7G102-4 *7G103 Au Ag N(0.5) N(0.5) N(0.5) N(0.5) N(0.5) Hg As

Sb

Cd Pb <10 N(10) <10 <10 N(10) N(10) Zn

Mo N(5)

N(5)

N(5) N(5)

N(5) N(5) N(5) N(5)

N(5) N(5) N(5)

N(5) N(5) N(5)

N(5) N(5) N(5) N(5)

Deposits 1 Sleeper Analyses in parts per billion (ppb) 2Buckhorn 3 Buckhorn 4 Buckhorn 5 Buckhorn 6 Buckhorn 14 *Sample from rhyodacite dikes in study area. Means of surface-rock chemistry from Wood (1988, p. 300) 2 Average values of altered basaltic andesite (3-6 samples) and silicified fanglomerate (14 samples) from Monroe and others (1988) Mount Nutt Wilderness Study Area, Mohave County, Arizona D11

in values lower than -30 milligals (mGal), is bounded on the northeast by a gravity ridge having highest values of about -12 mGal and on the south and southwest by gravity highs of about -10 mGal. These highs are centered over outcrops of Proterozoic basement rock. Proterozoic base- ment rock is also exposed along the north boundary of the study area, an area where gravity values reach only about -18 mGal. An area with gravity values of about -22 mGal that bounds the low on the west is not associated with any Proterozoic basement exposures. A northeast-southwest trending structural trough is implied by low gravity values and, on the basis of model- ing, may contain as much as 1.5 mi of volcanic rock. Using a density contrast of 0.2 g/cm3 between Proterozoic basement and Tertiary volcanic rock, gravity-modeling results indicate that the structural trough is bounded on the northeast by a Proterozoic surface that dips gently south- west and on the southwest by a near-vertical interface. Northwest-trending faults have been mapped in Tertiary rock immediately above the inferred near-vertical south- west boundary and these faults parallel the gravity gradient that defines the edge of the trough. Although the gravity data are sparse and do not accurately define the extent of the inferred vertical boundary, it appears to lie within the deepest part of the magnetic low over the Oatman mining district. 114°30' 114°25' 114°20' MOUNT NUTT WILDERNESS STUDY AREA (AZ-020-024) Figure 3. Aeromagnetic anomalies of Mount Nutt Wilderness Study Area, Mohave County, Arizona. Contour interval, 20 nanoteslas; hachured in direction of magnetic low; anomalies labeled 1 and 2 are discussed in text. D12 Mineral Resources of Wilderness Study Areas: Black Mountains Region, Arizona

Radiometric Data Knowledge of natural radioelement distribution in the Mount Nutt Wilderness Study Area is based on an aerial gamma-ray spectrometry survey (U.S. Department of Energy, 1979) of the Kingman 1- by 2-degree quadrangle. The survey acquired gamma-ray data along 1-mi-spaced east-west flightlines at 400 ft above the ground for the eastern part of Kingman quadrangle. The line spacing represents about 15 percent coverage for the study area because an aerial gamma-ray system flown 400 ft above the ground effectively detects terrestrial gamma radiation from a swath 800 ft wide along a flightline. The coverage rep- resents a reconnaissance sampling of the near-surface (0- to 18-in. depth) distribution of the natural radioelements po- tassium (K), uranium (eU), and thorium (eTh). The prefix "e" (for equivalent) denotes the potential for disequilibrium in the uranium and thorium decay series. Examination of 1:500,000 and smaller scale radio- element maps made from the aerial-gamma-ray data for the eastern part of the Kingman quadrangle indicates that the study area is characterized by radioelement concentrations of 2.0 to 3.6 percent K, 2.5 to 3.5 ppm eU, and 12.5 to 20.0 ppm eTh. Relatively lower concentrations of 2.0 to 2.4 percent K, 2.5 to 3.0 ppm eU, and 12.5 ppm eTh are pres- ent in the southern part of the study area, and relatively higher concentrations of 2.4 to 3.6 percent K, 2.5 to 3.0 ppm eU, and 15 to 20 ppm eTh are present in the northern part. These concentrations likely reflect the distribution of the Proterozoic and Tertiary igneous rock that composes most of the bedrock of the study area. Generally, higher ra- dioelement concentrations relate to more silicic rock, and detritus derived from it. The study area includes part of the Oatman mining district at its southwest side and part of the Union Pass mining district (fig. 2) at the northeast side of Secret Pass Canyon (fig. 1). The southwest side of the study area is in the area of lower radioelement concentra- tions, and the northeast side is in the area of higher radio- element concentrations. There is no evidence that these concentrations relate to the mineralization that occurred in the mining districts. Remote Sensing Digital image data acquired by the thematic mapper (TM) system on the Landsat-4 satellite (Scene I.D. 40174-17383) were analyzed to detect and map areas that may contain hydrothermally altered rocks. The six bands of image data in the visible and near-infrared spectral bands were digitally processed to enhance spectral characteristics of minerals that commonly accompany alteration or are derived from the weathering of altered rocks. Those areas that have spectral characteristics suggesting the presence of alteration minerals were visually mapped on l:62,500-scale Applicon color ink-jet plots of the processed data. The broad bands of the TM data allow two groups of minerals to be identified, but the minerals within each group cannot be distinguished from each other. Group 1 minerals consist of the limonite minerals, particularly hematite, goethite, and jarosite. Hematite and goethite are not diagnostic of hydrothermal alteration because they are common weathering products of iron-bearing minerals in altered and unaltered rocks alike. However, concentrations of hematite or goethite that crosscut lithologic units do suggest alteration. Jarosite is diagnostic of hydrothermal alteration, regardless of whether or not it crosscuts litho- logic units. Group 2 minerals include the hydroxyl-bearing and (or) hydrated minerals (clay minerals, micas, gypsum, alunite, jarosite) and carbonates (calcite, dolomite). Al- though the minerals in Group 2 are not restricted to altered rocks, they are commonly important constituents of altered rocks or are derived from the weathering of altered rocks. Alteration halos of Group 2 minerals (micas and clay minerals), which can extend as far as 200 ft laterally from vein systems, (Durning and Buchanan, 1984) can be de- tected with remote sensing. Interpretation Visual interpretation of the masked TM color-ratio composite consists of identifying concentrations of Group 1, Group 2, and jarosite (included in both Group 1 and Group 2 minerals) in the study area. In general, areas of alluvium identified on the basis of outcrop patterns in available geologic maps and photo interpretation of the images were excluded from consideration. The areas of potentially hydrothermally altered rocks were manually outlined by visual interpretation of the color-ratio compos- ite image and the outlines were transferred to a 1:62,500- scale base map of the wilderness study area, which was used to compile figure 4. Results Areas that may depict hydrothermally altered rocks taken from the masked TM color-ratio composite image are shown in figure 4. Areas containing only Group 1 minerals are labeled "1"; those containing only Group 2 minerals are labeled "2;" and those containing both Group 1 and Group 2 minerals (and (or) jarosite) are labeled "3". Areas of widespread, apparently low concentrations of minerals of these groups are labeled "D" for dispersed. Another area (labeled "A") may represent an illitically altered area (Durning and Buchanan, 1984). Mine dumps, mill tailings, and (or) discharge in nearby stream beds are labeled "d." No pronounced alteration patterns within the central Oatman mining district just south of the wilderness study Mount Nutt Wilderness Study Area, Mohave County, Arizona D13

area are visible on the TM data. Traces of veining (through linear alignment of mine dumps) can be seen, but they were not plotted on figure 4. Ransome (1923), Lausen (1931), and Durning and Buchanan (1984) described the variability of the veining and surrounding alteration halos; surface expression of some of the most productive veins is very limited. However, the Mossback mine is associated with area "A" on the TM image. Propylitic alteration in the Oatman district is also associated with Group 1 elements (limonite) due to weathering of pyrite. Vegetation obscures only a small part of the rocks and soil in the study area. The areas of rugged topography in the study area, combined with the relatively low solar- elevation angle at the time the TM data were acquired (25 degrees), results in a small part of the study area being in deep to moderate shadow on the TM data. Vegetation and shadows, then, have only modestly limited the area of surface rocks and soil that could be spectrally analyzed for alteration minerals. A number of anomalous areas were identified and these anomalies, because of the masking effects of vegetation and shadows, may represent a part of slightly more extensive areas. Four types of potential dispersed alteration were delineated within the study area. Within the dispersed anomalies, locally more intense concentrations are present. (1) Group 2 and Group 3 elements are widespread on the west edge of the study area (fig. 4). Area "A" is described as a large area of illitic alteration by Durning and Buchanan (1984). The area just to the north appears to be a similar, though less intense, area of alteration possibly attributable to the underlying Moss Porphyry. (2) Moderate to strong potentially altered areas (Group 1 and Group 2) were delineated within the southern one- third of the study area (fig. 4). Some of the areas contain Group 2 cores. In general, the areas are located on south-facing slopes; shadows mask any characteristics of these elements on north-facing slopes. (3) Group 1 elements are widespread in the northern one- quarter of the study area (fig. 4). Weathering of one or more volcanic lithologic surfaces (volcanic flow rock?) possibly could be generating nonhydrothermal Group 1 products. However, Group 3 elements are also present in this area. (4) Combinations of type 2 and type 3 anomalies (above) occur in the middle of the study area (fig. 4). Areas of Group 1, Group 2, and combinations of Group 1 and Group 2 elements are localized within the more dis- persed alteration. Local high concentrations of Group 2 and Group 1 and Group 2 elements are present within the north-central region excluded from the study area. The relative importance of any one of the mapped anomalies is difficult to evaluate; however, proximity to areas of known alteration or mineralization is probably a good method for assessing the anomalies. Mineral and Energy Resource Potential An area in the extreme north-central part of the Mount Nutt Wilderness Study Area has high resource po- tential for gold and low resource potential for silver, lead, and mercury with a C certainty level. Three areas in the north-central, northwestern, and southwestern parts of the study area have moderate resource potential for gold with a B certainty level. These areas also have low potential for silver, lead, and mercury with a certainty level C. A small area in the south-central part of the study area has low potential, certainty level C, for fire agate. Large areas in the central and eastern parts of the study area have low potential for perlite and zeolite resources with a certainty level of C. The entire study area has no potential for oil and gas, certainty level D, and no potential for geothermal resources, certainty level D. The results of this study show that there is high mineral resource potential for gold in the extreme north- central part of the study area (fig. 2). A gold resource totaling at least 56,000 troy oz has been identified at two sites in the Secret Pass Canyon area. The main site (Tincup mine) is less than 0.5 mi outside the study area; the second site lies approximately 500 ft north of the study area. Most of the area is underlain by intensely faulted and fractured rocks that also extend into the wilderness study area. The fault structure is visible in the study area for over 2 mi. Altered, mineralized rocks exposed north of the study area are also present in the study area and are covered by unal- tered silicic tuff and flows. The thickness of this unaltered cover increases southward. Geochemical data suggest that the area is characterized by low but anomalous levels of arsenic and mercury in stream sediments and lead and sil- ver in heavy-mineral concentrates. The potential is inter- preted to be high because composite chip material and rock samples of altered rocks consistently yield anomalous concentrations of gold and low but detectable concentra- tions of gold suite elements (table 1) (see Berger, 1986). A certainty level C is assigned to the area because the fault trace is generally well exposed, and the geochemical data suggest that mineralization occurred in the area. Moderate resource potential for gold exists in three areas in the ex- treme northwestern, northeastern, and southwestern parts of the study area (fig. 2). This potential is suggested by anomalous concentrations of mercury, lead, barium, and arsenic. Scattered anomalous concentrations of gold, molybdenum, and zinc detected in stream sediments sug- gest that mineralization occurred. The potential is moder- ate because alteration patterns defined by remote sensing, faulting, and the anomalous trace-element suite are similar to the known gold deposits in the area. A certainty level of D14 Mineral Resources of Wilderness Study Areas: Black Mountains Region, Arizona

B is assigned to the areas because either potential host rocks are poorly exposed or examination of their surficial appearance suggests that they are only weakly altered and mineralized. Each of the areas mentioned above has a low potential for silver, lead, and mercury resources, certainty level C. The concentrations of these three elements are not large enough clearly to suggest the occurrence of potential resources of these commodities even as byproducts. Perlite and zeolite minerals occur in the upper part of the volcanic sequence associated with welded tuff se- quences and small rhyolitic plugs. This part of the sequence has a low potential for zeolite and perlite, certainty level C. Low grade and the lack of access to perlite and zeolite-bearing beds in the study area would hinder devel- opment of these commodities. Ryder (1983) assessed the oil and gas potential of the study area as zero to low on the basis of extensive occurrences of Proterozoic schist and gneiss which make up the basement rocks of the wilderness study area and which are unsuitable hydrocarbon source or reservoir rocks. There is no resource potential for oil and gas, certainty level D, in the study area. 114°25' 114°20' 35° 10' 35° 05' APPROXIMATE BOUNDARY OF MOUNT NUTT WILDERNESS STUDY AREA (AZ-020-024) 2 MILES J A D d EXPLANATION Group 1 minerals are hematite, goethite, and jarosite See text for discussion Group 2 minerals are hydroxyl- bearing and (or) hydrated minerals (including clay minerals, micas, gypsum, alunite, and jarosite) and carbonates (calcite and dolomite) See text for discussion Group 1 and 2 minerals Illite (Duming and Buchanan, 1984) Dispersed occurrence of mineral group Mine dumps and mine tailings Figure 4. Areas of alteration minerals in Mount Nutt Wilderness Study Area, Mohave County, Arizona. Mount Nutt Wilderness Study Area, Mohave County, Arizona D15

No geothermal resources were observed in or adja- cent to the study area (Witcher and others, 1982; Muffler, 1979). Although the study area contains numerous rhyolite and basalt intrusions and the study area is in a region judged to have undergone greater than normal heat flow during the Miocene to early Pliocene, the Miocene intru- sions in the study area are small and the entire region had most likely cooled to near ambient temperatures by the early Pliocene. Therefore, there is no potential for geother- mal resources, certainty level D. REFERENCES CITED Almquist, C.L., 1989, Mineral investigation of a part of the Mount Nutt Wilderness Study Area (AZ-020-024), Mohave County, Arizona: U.S. Bureau of Mines Open-File Report MLA 35-88, 20 p. Beikman, H.M., Hinkle, M.E., Frieders, Twila, Marcus, S.M., and Edward, J.R., 1983, Mineral surveys by the Geological Sur- vey and Bureau of Mines of Bureau of Land Management Wilderness Study Areas: U.S. Geological Survey Circular 901, 28 p. Berger, B.R., 1986, Descriptive model of hot-spring Au-Ag, in Cox, D.P., and Singer, D.A., eds., 1986, Mineral Deposit models: U.S. Geological Survey Bulletin 1693, p. 143-144. Bliss, J.D., 1983, Arizona: Basic data for thermal springs and wells as recorded in geotherm: U.S. Geological Survey Open-File Report 8327, 200 p. Brown, D.E., 1982, Biotic communities of the American south- west-United States and Mexico, Desert Plants, v. 4, no, 1 4, 342 p. Clifton, D.G., Buchanan, L.J., and Durning, W.P., 1980, Explora- tion procedure and controls of mineralization in the Oatman mining district, Oatman, Arizona: Society of Mining Engi- neers of AIME preprint 80-143, 38 p. Crock, J.G., Lichte, F.E., and Briggs, P.H., 1983, Determination of elements in National Bureau of Standards geological ref- erence material SRM 278 obsidian and SRM 668 basalt by inductively coupled argon plasma atomic emission spec- trometry: Geostandards Newsletter, no. 7, p. 335-340. Dewitt, E., Thorson J.P., and Smith, R.C., 1986, Geology and gold deposits of the Oatman district, northwestern Arizona: U.S. Geological Survey Open-File Report 86-638, 34 p. Durning, W.P., and Buchanan, L.J., 1984, The geology and ore deposits of Oatman, AZ: in Wilkins, Joe, Jr., ed., Gold and silver deposits of the Basin and Range province western U.S.A.: Arizona Geological Society Digest, v. 15, p. Goudarzi, G.H., 1984 Guide to preparation of mineral survey reports on public lands: U.S. Geological Survey Open-File Report 84-787, 51 p. Gray, Floyd, Jachens, R.C., Miller, R.J., and Mariano, John, 1987, An interpretation of the shallow crustal structure of the Black Mountains, northwest Arizona: computer-generated model- ing and structural compilation [abs.], Geological Society of America Abstracts with Programs, v. 19, no. 7, p. 682. Grimes, D.J., and Marranzino, A.P., 1968, Direct-current arc and alternating-current spark emission spectrographic field methods for the semiquantitative analysis of geologic materials: U.S. Geological Survey Circular 591, 6 p. Jachens, R.C., and Griscom, Andrew, 1985, An isostatic residual gravity map of California A residual map for interpretation of anomalies from intracrustal sources, in Hinze, W.J., ed., The utility of regional gravity and magnetic anomaly maps: Tulsa, Okla. Society of Exploration Geophysicists, 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 Technol- ogy Bulletin 194, 58 p. Koirtyohann, S.R., and Khalil, Moheb, 1976, Variables in deter- mination of mercury by cold vapor atomic absorption: Analytical Chemistry, v. 48, p. 136-139. Lausen, C., 1931, Geology and ore deposits of the Oatman and Katherine districts, Arizona: Arizona Bureau of Mines Bulletin 131, 126 p. Mariano, John, Helferty, M.G., and Gage, T.B., 1986, Bouguer and isostatic residual gravity maps of the Colorado River region, including the Kingman, Needles, Salton Sea, and El Centre quadrangles: U.S. Geological Survey Open-File Report 86-347, 6 sheets, scale 1:250,000, 1 sheet, scale 1:750,000. McKelvey, V.E., 1972, Mineral resource estimates and public policy: American Scientist, v. 60, p. 32-40. Monroe, S.C., Godlewski, D.W., and Plahuta, J.T., 1988, Geology and mineralization at the Buckhorn mine, Eureka county, Nevada: in, Schaffer, R.W., Cooper, J.J., and Vikre, P.G., eds., Bulk mineable precious metal Deposits of the western United States, symposium proceedings: Geological Society of Nevada, p. 273-291. Morelli, C.E., ed., 1974, The international gravity standardization net 1971: International Association of Geodesy Special Publication No. 4, 194 p. Muffler, L.J.P., 1979, Assessment of geothermal resources of the United States 1978: U.S. Geological Survey Circular 790, 163 p. O'Leary, R.M., and Viets, J.G., 1986, Determination of antimony, arsenic, bismuth, cadmium, copper, lead, molybdenum, sil- ver, and zinc in geologic materials by atomic absorption spectrometry using a hydrochloric acid-hydrogen peroxide digestion: Atomic Spectroscopy, v. 7, no. 1, p. 4 8. Ransome, F.L. 1923, Geology of the Oatman gold district, Ari- zona: U.S. Geological Survey Bulletin 743, 58 p. Ryder, R.T., 1983, Petroleum potential of wilderness lands in Arizona; in Miller, B.W., ed., Petroleum potential of wilder- ness lands in the western United States: U.S. Geological Survey Circular 902-C, p. C1-C21. Smith, R.C., 1984, Mineralogy and fluid-inclusion studies of epithermal gold-quartz veins in the Oatman district, north- western Arizona: Tucson, University of Arizona, M.S. the- sis, 233 p. Telford, W.M., Geldart, L.O., Sheriff, R.E., and Keyes, D.A., 1976, Applied Geophysics: New York, Cambridge Univer- sity Press, 960 p. Thompson, C.E., Nakagawa, H.M., and Van Sickle, G.H., 1968, Rapid analysis for gold in geologic materials, in Geological Survey Research 1968: U.S. Geological Survey Professional Survey Paper 600-B, p. B130-B132. D16 Mineral Resources of Wilderness Study Areas: Black Mountains Region, Arizona

Thorson, J.P., 197la, Igneous petrology of the Oatman district, Mohave county Arizona: Santa Barbara, University of Cali- fornia at Santa Barbara, Ph.D. dissertation, 189 p. 1971b, Igneous petrology of the Oatman district, Mohave county Arizona [abs.], Dissertation Abstracts, v. 32, no. 8, p. 4677-B. U.S. Bureau of Mines and U.S. Geological Survey, 1980, Prin- ciples of a resource/reserve classification for minerals: U.S. Geological Survey Circular 831, 5 p. U.S. Department of Energy, 1979, Airborne gamma-ray spec- trometer and magnetometer survey, Kingman quadrangle, (Arizona, California, Nevada): U.S. Department of Energy Open-File Report GJBX 59 (79), v. 2, variously paged. Witcher, J.C., Stone, Claudia, and Hahman, W.R., Jr., 1982, Geothermal resources of Arizona: Arizona Bureau of Geol- ogy and Mineral Technology Map 15-2, scale 1:500,000. Wood, J.D., 1988, Geology of the Sleeper gold deposit, Humboldt County, Nevada: in Schaffer, R.W., Cooper, J.J., and Vikre, P.O., ed., Bulk mineable precious metal deposits of the western United States, symposium proceedings: Geological Society of Nevada, p. 300. Mount Nutt Wilderness Study Area, Mohave County, Arizona D17

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 char- acteristics 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. 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. B Available information only suggests the level of mineral resource potential. Available information gives a good indication of the level of mineral resource potential. D Available information clearly defines the level of mineral resource potential. LU U C£ O CO LU o

LU5 A U/A UNKNOWN POTENTIAL B H/B HIGH POTENTIAL M/B MODERATE POTENTIAL L/B LOW POTENTIAL H/C HIGH POTENTIAL M/C MODERATE POTENTIAL L/C LOW POTENTIAL D H/D HIGH POTENTIAL M/D MODERATE POTENTIAL I/O LOW POTENTIAL N/D NO POTENTIAL LEVEL OF CERTAINTY Abstracted with minor modifications from: Taylor, R.B., and Steven, T.A., 1983, Definition of mineral resource potential: Economic Geology, v. 78, no. 6, p. 1258-1270. 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. D20 Mineral Resources of Wilderness Study Areas: Black Mountains Region, Arizona

RESOURCE/RESERVE CLASSIFICATION ECONOMIC MARGINALLY ECONOMIC SUB- ECONOMIC IDENTIFIED RESOURCES Demonstrated Measured Rese Indicated jrves Marginal Reserves Demonstrated Subeconomic Resources Inferred Inferred Reserves Inferred Marginal Reserves Inferred Subeconomic Resources UNDISCOVERED RESOURCES Probability Range Hypothetical Speculative Major elements of mineral 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. Mount Nutt Wilderness Study Area, Mohave County, Arizona D21

GEOLOGIC TIME CHART Terms and boundary ages used by the U.S. Geological Survey in this report EON Phanerozoic Proterozoic Archean pre-Archean2 ERA Cenozoic Mesozoic Paleozoic Late Proterozoic Middle Proterozoic Early Proterozoic Late Archean Middle Archean Early Archean PERIOD Neogene Subperiod Tertiary rSUCOfiCnG Subperiod Jurassic Triassic Permian Pennsylvanian Carboniferous Periods

Mississippian Devonian Silurian Ordovician Cambrian f3?i- - . EPOCH Holocene Pleistocene Pliocene Miocene Oligocene Eocene Paleocene Late Early Late Middle Early Late Middle Early Late Early Late Middle Early Late Early Late Middle Early Late Middle Early Late Middle Early Late Middle Early ACE ESTIMATES OF BOUNDARIES IN MILLION YEARS (Ma)

3Q

1 Oq

'-570

'Rocks older than 570 Ma also called Precambrian, a time term without specific rank, informal time term without specific rank. D22 Mineral Resources of Wilderness Study Areas: Black Mountains Region, Arizona

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