Sunshine Mining District, Tooele County, Utah, USAi

Regional Level Types
Sunshine Mining District	Mining District
Tooele County	County
Utah	State
USA	Country

The Sunshine (South Mercur) mining district is located on the southern slopes of the Oquirrh Mountains, about 18 mi southeast of Tooele and just south of the Mercur district, in Tooele and Utah Counties. Sunshine is a significant district having an estimated 21,000 ounces of Au produced between 1898 and 1910 (Gilluly, 1932). The area also produced a significant amount of refractory clay to the east in the Clay Canyon area, Utah County. Total district metal production at modern metal prices is estimated at $23 million. The Overland and Sunshine underground mines are the largest historical Au producers.
The Oquirrh Mountains are one of the easternmost ranges in the Basin and Range Province. The main Sunshine Au orebodies underlie Sunshine Canyon. The Au deposits occur in the Mercur member clastic carbonate of the Mississippian Great Blue Limestone, just below the carbonaceous Long Trail Shale Member. The deposits are on the east limb of the asymmetrical Ophir thrust-cored anticline stratigraphically analogous to the Au orebodies in the Mercur district to the north. At Sunshine, the host Mercur member bed dips 20° to 25° east and the ore is associated with northwest-trending, high-angle faults. The resulting elongated, tabular Au deposits rake moderately to the southeast. The ores are largely oxidized to a depth of about 150 ft but become more carbonaceous and refractory at depth. Alteration associated with the mineralization is primarily silicification and decalcification. Iron oxides are common and arsenic oxides occur locally, typically with Au values. The Au ores are anomalous in As (500–4000 ppm), Hg (1–10 ppm), Sb (25–100 ppm), and Tl (7–31 ppm) (USGS Model 26a).
The Sunshine district was extensively explored in the 1980s and 1990s, resulting in the delineation of three small Au resources. On the north, the Overland deposit is located at the Overland mine shaft and under the canyon to the west; its footprint is about 900 ft in an east-west direction and 950 ft north-south. The next deposit to the south, and the smallest, is Red Cloud located near the old Sunshine town site; it is about 700 ft north-south by 270 ft east-west. The Sunshine deposit at the old Sunshine mine, the southernmost and largest of the three deposits, is centered just north of the Sunshine shaft, and is about 1300 ft north-south by 700 ft east-west.
Roughly 1 mi east of Sunshine Canyon, Clay Canyon has an unnamed shale in the upper Great Blue Limestone that has been variably altered to clay, including illite, kaolinite, halloysite, smectite, variscite, and crandallite (Shubat, 1988). Clay Canyon trends northwesterly parallel to a series of faults. The clay has been exploited for fire brick, largely by the Interstate Brick Company. Very limited geochemical sampling of the clay mines showed weak Au to 0.09 ppm, As to 74 ppm, Sb to 29 ppm, and Zn to 590 ppm.