Granite Mountain Mining District, Dugway Range, Tooele County, Utah, USAi

Regional Level Types
Granite Mountain Mining District	Mining District
Dugway Range	Mountain Range
Tooele County	County
Utah	State
USA	Country

The Granite Mountain (Granite Peak) mining district is located about 85 mi west of Provo in south-central Tooele County. The district is an insignificant Pb-Ag producer with some fluorite production. The El Dorado mine is believed to be the largest producer.
Granite Peak is an isolated mountain located in the Great Salt Lake Desert of the Basin and Range Province of west-central Utah. Granite Peak is principally composed of an exposed 25 sq mi Jurassic (about 149 Ma) granite-granodiorite complex (Clark and others, 2009). The upper part of the complex is a foliated granodiorite underlain by a less strained and more leucocratic granite. Both intrusive phases are cut by pegmatite and aplite dikes and quartz veins.
Pegmatite dikes are common throughout the Granite Peak intrusive complex and are estimated to form up to 10% to 15% of the intrusive rock volume, being more prevalent in the upper foliated granodiorite. The pegmatite dikes typically strike approximately N. 35° E. and dip 55° to 70° W. The pegmatites range from small stringers, to pods, to larger tabular, zoned dikes and some individual dikes can be traced for up to half a mile. Accessory minerals generally constitute about 1% of the pegmatites and the minerals include garnet, tourmaline, beryl, samarskite, zircon, apatite, and hematite. Three zones are recognized in the pegmatites: borderwall, intermediate, and core. Samarskite and beryl occur in greatest abundance at the inner margin of the intermediate zone, adjoining the quartz-dominant core. The core is reportedly 97% quartz and 2% microcline. The Desert Queen prospect on the west side of Desert Peak was briefly examined by the Mica Corporation of America in the 1940s for muscovite, some of which had books reaching 6 inches across.
Mineralization at the El Dorado mine occurs in a north-trending, steeply east-dipping quartz vein. The vein is in a fault which it shares with a green, medium-grained, “diorite” dike. The dike is altered to chlorite-sericite-pyrite (Butler and others, 1920). Both the hanging wall and footwall of the fault are leucocratic granite. Butler and others (1920) believe that the dike predates the vein and Clark and others (2009) date the dike as Miocene (~8 Ma). The quartz vein is banded and contains galena, chalcopyrite, fluorite, and some Ag-Au values (Butler and others, 1920).
The area is in the southern part of the U.S. Army Dugway Proving Ground with no public access.