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).
The Clifton (Gold Hill) district is in the Clifton Hills near the Utah-Nevada boundary. Its ore deposits are varied and contain a wide range of valuable metal constituents. Besides gold, the deposits have yielded significant amounts of copper, lead, silver, and smaller amounts of tungsten, bismuth, molybdenum, and arsenic (Nolan, 1935a, p. 119).
The first mineral discoveries were made in 1858, but hostile Indians discouraged any mining in the area until 1869. In 1871 a smelter was built, and small amounts of silver, lead, and gold were produced for a few years. Interest was renewed in the area in 1892 when a mill was constructed to treat ores from the Cane Springs, Alvarado, and Gold Hill mines; total gold production from these mines from 1892 through 1895 was worth $207,896 (V. C. Heikes, in Butler and others, 1920, p. 475).
Intermittent activity continued to 1917, when the completion of rail facilities enabled the deposits to be exploited on a larger scale. Much activity was maintained through 1934, after which production again dropped. The district was virtually idle from 1945 through 1959. Total recorded gold production from 1892 through 1959 was about 26,000 ounces.
The rocks of the Clifton district consist of a thick section of Paleozoic sedimentary rocks, chiefly dolomite and limestone, that range in age from Early Cambrian through Permian. These rocks are intruded by a stock of quartz monzonite and dikes of porphyry and aplite of Tertiary age. Five cycles of folding and faulting, beginning in Late Cretaceous or Eocene time and continuing to the time of the quartz monzonite intrusion, created a complex structural terrain that was further modified by normal faults of more recent age (Nolan, 1935a, p. 4-64).
The ore deposits of the district are of several diverse mineralogical and genetic types. Nolan (1935a, p. 97-103) classified them as:
1. Pipelike deposits locally containing tungsten and molybdenum.
- Veins characterized by silicate minerals in the gangue.
- Veins containing chiefly quartz and metallic sulfides.
- Veins containing chiefly carbonate minerals with or without quartz.
3. Replacement bodies:
- Arsenic minerals dominant.
- Copper-lead-silver minerals dominant.
The replacement bodies yielded most of the mineral wealth of the district; however, most of the gold came from veins in limestone beds near their contact with the quartz monzonite stock. These veins are characterized by abundant wollastonite and small amounts of zoisite, vesuvianite, garnet, and diopside. Chalcopyrite is the most abundant sulfide and is accompanied by pyrite, bornite, arsenopyrite, and galena. Quartz and calcite are locally abundant, and native gold is present in small quantities.
OPHIR-RUSH VALLEY DISTRICT
The Ophir-Rush Valley (Stockton) district, in the central part of the west flank of the Oquirrh Mountains between the Camp Floyd district to the south and the Bingham district to the north, is known chiefly for lead, silver, copper, and zinc. Gold was recovered chiefly as a byproduct of the base-metal ores; total production through 1959 was about 104,000 ounces.
Silver deposits were found in 1864 in Rush Valley by soldiers of the California Volunteers stationed at a nearby military post known as "Camp Relief." Efforts at smelting the ore at first met with small success and the mines were abandoned by the end of 1865. After the Civil War the original claim owners, who were soldiers, were discharged and returned to their homes; however, mining laws were amended to make their claims permanently valid. This action retarded development of the district for several years (Gilluly, 1932, p. 117-118).
Lead deposits were found in the Ophir area in 1865, but very little work was done on claims until 1870. Additional discoveries of silver-lead ores in the early 1870's in the Ophir and Rush Valley areas caused a brief period of prosperity that lasted until about 1880 at Ophir and until 1890 at Rush Valley (V. C. Heikes, in Butler and others, 1920, p. 363-366).
Beginning in 1904, production increased sharply. Zinc was first recovered from ores in the Ophir area in 1911 and from the Rush Valley mines in 1913. Activity has continued, with periodic fluctuations, through 1959.
Most of the exposed rock in the district consists of sedimentary formations that range in age from Cambrian to Pennsylvanian. The Cambrian rocks, about 2,500 feet thick, consist of the Tintic Quartzite at the base, the Ophir Formation, Hartmann Limestone, Bowman Limestone, and Lynch Dolomite. The Devonian System is represented by about 185 feet of Jefferson (?) Dolomite. Rocks of Mississippian age are the Deseret Limestone, Humbug Formation, and Great Blue Limestone. The Manning Canyon Shale is of Mississippian and Pennsylvanian age and is overlain by the Oquirrh Formation of Pennsylvanian age (Gilluly, 1932, p. 6-38).
The rocks are folded into a northwest-trending anticline, the Ophir anticline, and are broken by fissures and faults, especially in the vicinity of Ophir Canyon, where a northeast-trending zone of faults has offset the axis of the Ophir anticline and the sedimentary beds about 2,000 feet. Northwest-trending normal faults are parallel to the west front of the Oquirrh Mountains (Gilluly, 1932, p. 69-74). Small intrusive stocks, dikes, plugs, and sills of monzonite, rhyolite, andesite, lamprophyre, and nepheline basalt cut the sedimentary formations.
The most important ore deposits are in the Honorine mine, just east of the town of Stockton. The ore bodies are in bedded replacement deposits in limestone beds of the Oquirrh Formation where these beds intersect faults or fissures. Primary ore consists of pyrite, galena, sphalerite, chalcopyrite, and arsenopyrite in a gangue of quartz and lime silicate minerals. Oxidized ore contains cerussite, plumbojarosite, jarosite, malachite, smithsonite, aurichalcite, pyromorphite, and limonite (Gilluly, 1932, p. 160-162).
In the Ophir area, the chief deposits are in replacement bodies in Mississippian limestones, especially the Great Blue Limestone. A few deposits occur in the Ophir Formation and the Jefferson (?) Dolomite. With local exceptions, these deposits contain the same minerals as the replacement deposits in the vicinity of Stockton. Fissure veins occur throughout the district, but they are of little economic importance (Gilluly, 1932, p. 136-137).
WILLOW SPRINGS DISTRICT
The Willow Springs district is in the southern part of the Deep Creek Range in the southwestern corner of Tooele County. Through 1959 it produced about 11,650 ounces of gold, lead, silver, and some copper.
The district was organized in 1891, but for many years it made only a few small shipments of silver ore (Nolan, 1935a, p. 167). Its period of greatest activity was that of recorded production, 1934-50. The ore shipped during this period consisted of high-grade lead-silver and gold ores. The district was virtually idle from 1951 through 1959.
Metamorphic rocks of Precambrian age are the oldest exposed rocks. They are nonconformably overlain by the Goshute Canyon Formation of Precambrian or Cambrian age. Completing the Cambrian sequence are the Prospect Mountain Quartzite, Pioche Shale, Abercrombie Formation, Young Peak Dolomite, Trippe Limestone, Lamb Dolomite, Hicks Formation, and lower part of the Chokecherry Dolomite. The upper part of the Chokecherry Dolomite and the Fish Haven Dolomite represent the Ordo-vician System, and the Laketown Dolomite, the Silurian. Devonian formations exposed in the district are the Sevy Dolomite, Simonson Dolomite, and Guilmette Formation.
In the northern part of the district, younger rocks, including the Woodman Formation, Ochre Mountain Limestone, Manning Canyon Formation of Mississippian age, and the Oquirrh Formation of Pennsylvanian age, are faulted against the lower Paleozoic units (Nolan, 1935a, pi. 1; Bick, 1959, p. 1065-1068). All the sedimentary formations are cut by faults that trend west or northwest and are deformed into a westward-tilted block by north-trending normal faults.
The ore deposits are in replacement veins and in bedded replacement deposits. The ores were probably completely oxidized at the surface and were rich in silver. Some of the vein ore examined by Nolan (1935a, p. 167-168) contained quartz, tetrahedrite, and galena.