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Mineral resources of the Orocopia Mountains Wilderness Study Area, Riverside County, California
| Content Provider | Semantic Scholar |
|---|---|
| Author | Haxel, Gordon B. Smith, David Branson Whittington, Charles Lynn Griscom, Andrew Diveley-White, D. V. Powell, R. E. Kreidler, Terry J. |
| Copyright Year | 1988 |
| Abstract | At the request of the U.S. Bureau of Land Management, approximately 34,172 acres of the Orocopia Mountains Wilderness Study Area (CDCA-344) were evaluated for mineral resources (known) and mineral 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 Orocopia Mountains Wilderness Study Area refers only to that part of the wilderness study area for which a mineral survey was requested by the U.S. Bureau of Land Management. The Orocopia Mountains Wilderness Study Area is located in southeastern Riverside County, California, about 25 miles southeast of Indio. Fieldwork for this report was conducted between 1982 and 1986. In 1982, there were about 20 unpatented mining claims within or adjacent to the wilderness study area. Identified resources in the Orocopia Mountains Wilderness Study Area include low-grade talc deposits of moderate size and a small, low-grade, low-tonnage quartz-vein gold deposit. Active exploration for gold, including geochemical sampling and exploratory drilling, was underway in the late 1980's, and a tract with high resource potential for disseminated gold in crystalline rocks is delineated in the central part of the Orocopia Mountains Wilderness Study Area. One small area in the southeast corner of the wilderness study area has moderate resource potential for gold in quartz veins associated with propylitically altered mafic dikes cut by fault zones. Other small tracts within the wilderness study area have low resource potential for gold in quartz veins, moderate resource potential for gold in placer Manuscript approved far publicatio:n, August 26, 1988. deposits, moderate resource potential for talc and fluorite, and moderate resource potential for gypsum and borates in evaporite strata. There is low resource potential for gold, copper, lead, zinc, and manganese in volcanogenic massivesulfide deposits and for copper and molybdenum in porphyry deposits. Moderate potential for geothermal energy resources is assigned to the southwestern two-thirds of the study area. There is no energy resource potential for oil, and gas in the study area. Character and Setting The Orocopia Mountains Wilderness Study Area is in southeastern Riverside County, about 25 mi southeast of Indio (fig. 1). The Orocopia Mountains comprise a small, rugged range on the northeast side of the northern Imperial Valley. The main part of the range lies about 6 mi northeast of the San Andreas fault zone. Major lithologic units in the Orocopia Mountains Wilderness Study Area are Early and Middle Proterozoic (see appendixes for geologic time chart) gneiss and migmatite; a Middle Proterozoic anorthosite-syenite complex; Proterozoic(?), Jurassic, and (or) Cretaceous granitoid rocks; the late Mesozoic Orocopia Schist; the Eocene marine Maniobra Formation (Crowell and Susuki, 1979); and the Oligocene(?) and early Miocene nonmarine Diligencia Formation (Crowell, 1975) (fig. 2). The principal structural features of the study area are the Late Cretaceous Orocopia thrust, which places the Proterozoic and Mesozoic plutonic and gneissic rocks over the Orocopia Schist, and the late Tertiary Clemens Well fault, a major right-slip fault. Both faults trend northwestward through the central part of the Orocopia Mountains. The Orocopia thrust was Mineral Resources of the Orocopia Mountains Wilderness Study Area, Riverside County, California El modified by middle to late Tertiary low-angle-normal and strike-slip faulting. Identified Mineral Resources Identified resources in the Orocopia Mountains Wilderness Study Area include low-grade talc deposits of moderate size and a small, low-grade, low-tonnage quartzvein gold deposit. Active exploration for low-grade, hightonnage disseminated gold deposits was underway during preparation of this report. Mineral Resource Potential In the central part of the study area, a northwest-trending strip, approximately 12 mi long and 0.75 to 1 mi wide, ,.... i..--·-·-, i i 116"00' L._."L.·-·-·-·-·-·-·, between the Orocopia thrust and the Clemens Well fault has high potential for disseminated gold in crystalline-rockhosted deposits. Geochemical sampling by industry indicates that rocks with anomalously high abundances of gold and arsenic (an alternative elemental indicator of gold mineralization) are widespread within this strip. A small area in the southeastern part of the study area between the Clemens Well fault and . the Diligencia Formation has moderate potential for disseminated gold in quartz veins and fault zones associated with propylitically altered mafic dikes (fig. 2). This area is underlain by Proterozoic gneiss. Small veins and pods of metamorphogenic white quartz are common in the late Mesozoic Orocopia Schist. Some of these veins are gold bearing; the Orocopia mine is developed in an unusually large gold-bearing quartz vein. The potential for gold in quartz veins within the Orocopia Schist is low. |
| File Format | PDF HTM / HTML |
| DOI | 10.3133/b1710E |
| Alternate Webpage(s) | https://pubs.usgs.gov/bul/1710e/report.pdf |
| Alternate Webpage(s) | https://doi.org/10.3133/b1710E |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
