Ophir Mining District, Tooele County, Utah, USAi

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

Soldiers stationed at Fort Douglas in Salt Lake City discovered the district in 1865. These soldiers were attracted to the area by stories of Native Americans finding a metal to help make bullets. They found outcroppings of lead ore and located the St. Louis Lode, now known as the Hidden Treasure mine. Little work was done in the district until the early part of 1870, when the town of Ophir and the mining district were organized after silver-rich ore was located on Silveropolis Hill by W.T. Barbee (the same man who discovered the ore deposits at the Silver Reef mining district). Several days later, additional discoveries were made on nearby Lion Hill. Some of these mines included the Zella (which comprised the Zella, Mountain Tiger, Silver Chief, and Rockwell claims) and Mountain Lion mines. Approximately 2500 mineral occurrences were found, but only about 150 actually resulted in any mining activity. Many of the mines worked small ore deposits and were exhausted toward the end of 1880, with the exception of the Ophir Hill Consolidated, Hidden Treasure, and Cliff mines. The Ophir Hill Consolidated and Hidden Treasure mines were active until 1971 and had major periods of production during 1901-27 and 1936-71.

The Ophir mining district is in the southwestern Oquirrh Mountains about 33 mi south-southwest of Salt Lake City. The Ophir district was organized in the 1860s as a bonanza Ag camp and mining continued sporadically into the early 1970s. The Ophir district is about the tenth most productive in Utah. Ophir is credited with production of about 2.8 million tons of ore averaging 6.2% Pb, 1.5% Zn, 0.8% Cu, 237 ppm Ag, and 0.21 ppm Au, recovered. Total district metal production at modern metal prices is estimated at $877 million. The Ophir Hill mine in Ophir Canyon is the largest producer in the district with about 1.5 million tons of production followed by the Hidden Treasure mine at 300,000 tons (Rubright, 1978).
The Ophir district lies on the Bingham–Park City mineral belt of the Basin and Range Province. The southwestern Oquirrh Mountains are geologically dominated by the asymmetrical Ophir thrust-cored anticline. This fold is part of a north-northwest- trending, Mesozoic fold belt characterized by thrust-cored, asymmetrical, closed anticlines and synclines with a wavelength of about 35,000 ft and amplitude of 15,000 ft (Gilluly, 1932).
Mineralization in the Ophir district is largely confined to a northwest-trending belt less than 1 mi wide and over 3 mi long, approximately coincident with the crest of the Ophir anticline. The ore deposits of the Ophir district are dominantly distal skarns, carbonate replacement deposits, and veins. The dominant ore controls are the intersections of northerly trending fissures and favorable host horizons, principally the Cambrian Ophir Formation, Mississippian Gardison Limestone, and Mississippian lower Great Blue Limestone. A series of poorly exposed Eocene-age monzonite and rhyolite plugs, dikes, and sills intrude near the anticlinal crest and may be related to ore (Gilluly, 1932).
The Ophir district is unusual because it is, in part, a vertically zoned mining district. Past production ranges from distal, sediment-hosted Ag-Au-Pb ±Ba deposits high on Lion Hill to the south, through medial, Pb-Zn-Ag carbonate replacement deposits in Dry Canyon to the north, to Ag-Pb-Cu distal skarns in the bottom of Ophir Canyon and continuing north under Dry Canyon. The Ophir Hill Ag-Pb-Cu distal skarn is the most important mine in the district (Gilluly, 1932; Rubright, 1978). The primary ore/sulfide minerals are galena, sphalerite, argentite, chalcopyrite, acanthite, tetrahedrite, pyrite, pyrrhotite, arsenopyrite, wolframite, and fluorite. The bulk of the remaining district production has come from numerous Ag-Pb-Zn vein and replacement deposits (USGS Model 22c). Several companies have explored the Ophir district for a porphyry system like those found in the adjoining Bingham and Stockton districts, but no significant results have been released.