By A. H. KOSCHMANN and M. H. BERGENDAHL - USGS 1968
Tooele County, which is in northwestern Utah, contains a variety of mineral deposits. Gold is the chief mineral commodity; through 1959 a total of about 1,257,000 ounces was produced from the four major districts of Camp Floyd, Ophir-Rush Valley, Clifton, and Willow Springs. Lead, silver, arsenic, and tungsten are also mined.
CAMP FLOYD DISTRICT
The Camp Floyd (Mercur) district, in the southern part of the Oquirrh Mountains about 55 miles southwest of Salt Lake City, is unlike the other major mining districts of Utah. It is primarily a gold district and silver and mercury are byproducts.
The district is the third largest gold producer in the State; total output through 1959 was about 1,115,000 ounces.
The first mineral location in the area was a gold placer claim, and the district was organized in 1870. Placer mining, however, was unsuccessful because of the low grade and lack of water. Early discoveries of rich silver lodes also proved to be disappointing (Gilluly, 1932, p. 123). Interest in the area declined to the extent that the town of Lewiston, which had a population of 1,500 in the 1870's, became largely deserted. The Mercur lode, at first unsuccessfully worked as a mercury deposit, had a high content of gold, but the gold could not be recovered by the amalgamation treatment commonly used at that time. In 1890 attempts to treat the Mercur ore by the newly developed cyanide process were successful. As a result, prospectors again swarmed into the district, the town of Mercur was built on the old site of Lewiston, and new mines were developed rapidly. This period of prosperity lasted from 1890 to 1917, during which time the Mercur, Delamar, Geyser-Marion, Sacramento, Sunshine, Overland, Daisy, and La Cigale mines were the chief producers (Gilluly, 1932, p. 123-124). Mines were closed from 1917 through 1931, but in 1932 some were reactivated, and in 1933 a 500-ton cyanide plant was constructed to treat old tailings. Enthusiasm generated by increased prices in 1934 caused a significant resurgence of activity that lasted until 1945, when the mines again were closed. No production was reported from 1949 through 1959.
The Oquirrh Mountains consist of Paleozoic sedimentary formations, totaling more than 22,000 feet in thickness; the formations are deformed into northwest-trending open folds, are intruded by various igneous rocks, and are cut by numerous normal faults. In the Camp Floyd district, which is along the west flank of the mountains, Mississip-pian formations, consisting of the Deseret Limestone, Humbug Formation, Great Blue Limestone, and Manning Canyon Shale, are folded into the Ophir anticline (Gilluly, 1932, pi. 12). Two small stocks and several sills of Eagle Hill rhyolite, of Tertiary age, cut the sedimentary rocks just south of the town of Mercur (Gilluly, 1932, p. 58).
The major ore deposits of the district are bedded replacement deposits of gold and gold-mercury in the Great Blue Limestone. Silver and silver-lead replacement deposits and gold and gold-mercury fissure veins are of subordinate importance. The principal minerals of the gold-bearing replacement deposits are pyrite, realgar, orpiment, and cinnabar. The gangue is mostly jasperoid but contains small amounts of barite and calcite. The gold is too fine grained to be seen and its mode of occurrence is not known, although analyses have shown a relationship between it and carbon (Butler and others, 1920, p.394).
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