Mineral resources of the Big Horn Mountains Wilderness Study Area, Maricopa County, Arizona

Abstract

At request of U.S. Bureau of Land Management, U.S. Geological Survey and U.S. Bureau of Mines conducted a mineral survey of approximately 21,500 acres of Big Horn Mountains Wilderness Study Area (AZ-020-099) in southwest part of Big Horn. Mountains in southwestern Arizona. In this report, area studied is referred to as wilderness study area, or simply the study Big Horn Peak, only geographic feature in region with a formal name, liesin central part of study area. Field work for this report was carried out in 1984 and 1985. Additional mapping in region surrounding study area and encompassing Big Horn and adjacent Belmont Mountains was conducted as part of a Cooperative Geologic Mapping Program (COGEOMAP) project, carried out jointly by U.S. Geological Survey and Arizona Bureau of Geology and Mineral Technology. The eastern boundary of study area includes part of an area of weakly mineralized rocks having moderate and low mineral resource potential for undiscovered gold, silver, lead, and zinc in hydrothermally altered areas that are found along Tertiary (about 1.7 to 66 million years before present, (or Ma); see Geologic time chart, last page of report) age high-angle normal faults and fractures and (or) Proterozoic-age (about 240 to 570 Ma) east-trending quartz veins. Similar areas of fault-controlled, hydrot her m ally mineralized rock in northeastern and northwestern parts of study area have low resource potential for undiscovered gold, silver, and copper. The mineral resource potential for undiscovered iron and titanium is considered low in northern part of study area because only negligible amounts of iron-titanium-oxide-bearing sands are present in Quaternary (about 0 to 2 Ma) drainages. On basis of temperatures obtained from nearby wells and absence of local magmatism less than 5 million years old, geothermal resource potential is low for entire study area. On basis of extrapolation of surficial bedrock exposures, oil and gas potential in study area is low and presence of geothermal resources is considered extremely unlikely. The resource potential for undiscovered agate resources is also considered low. Character and Setting The Big Horn Mountains Wilderness Study Area (AZ-020-099) encompasses approximately 21,500 acres in southwest part of Big Horn Mountains, located approximately 55 mi west of Phoenix, in westcentral Arizona (fig. 1). Situated in Basin and Range physiographic province, study area consists of rugged northwest-trending mountains and gently sloping alluvial valleys along mountains flanks. Elevation in study area ranges from about 3,480 ft