By A. H. KOSCHMANN and M. H. BERGENDAHL - USGS 1968
Beaver County, in southwestern Utah, contains extensive deposits of silver, lead, zinc, copper, and relatively small amounts of gold.
It is credited with the first mineral output in Utah, a few tons of lead ore produced from 1860 to 1863 at the Rollins mine in the Lincoln district (Butler and others, 1920, p. 503). It became important in mining when silver was discovered in the early 1870's in the San Francisco, Star, and Beaver Lake districts and remained important until 1926. Gold production was mainly from 1860 to 1950; total production from 1860 through 1959 was about 55,850 ounces. The San Francisco was the only district that produced more than 10,000 ounces.
San Francisco District
The San Francisco district, located in the San Francisco Mountains in the central part of Beaver County, has yielded 60 percent of the gold output of the county, mostly as a byproduct of base-metal ores. Records of early production are incomplete, but Butler (in Butler and others, 1920, p. 503) credited the district with a gold output of 21,822 ounces through 1917. Total production through 1959 was about 33,400 ounces.
Ore was discovered in about 1871, but the district was of little importance until the Horn Silver mine became productive in 1876 (D. B. Huntley, quoted by Butler, 1913, p. 111). For about 10 years this mine was one of the most successful in the State. Several other mines in the district also were active intermittently, depending on the fluctuating prices of base metals and silver.
The following description of geology and ore deposits is by D. M. Lemmon (written commun., 1963).
Sedimentary rocks exposed in the San Francisco Mountains are in three thrust plates. The top plate, which makes up Frisco Peak, is composed of upper Precambrian quartzite and argillite; the middle plate is Upper Cambrian and Ordovician dolomite, limestone, shale, and quartzite; and the lower plate is Mississippian and Pennsylvanian dolomite, limestone, and minor sandstone. After thrusting, the older rocks were largely covered by Tertiary volcanic rocks and then intruded by quartz monzonite.
The ore deposits that have yielded much of the byproduct gold are the silver-lead-copper-zinc replacement deposits in volcanic and carbonate rocks at the Horn Silver mine. At the surface, the main ore bodies are along a fault contact between Upper Cambrian carbonate rocks in the footwall and volcanic rocks in the hanging wall; the fault enters silicined carbonate at about 750 feet and remains in the altered sedimentary rocks to the 1,600-foot level. Deepest ore found was on the 1,200-foot level, but principal output was above the 1,000-foot level. The principal primary ore minerals are galena, pyrite, and sphalerite, and the less important ore minerals are chalcopyrite, sulfantimonides, and sulfarsenides. A large suite of secondary minerals is developed through oxidation and through secondary enrichment of sulfides. All the ore contains a small amount of gold, perhaps 0.01 to 0.02 ounce per ton.
The copper ore of the Cactus mine is in breccia pipes in quartz monzonite. The principal primary ore minerals are pyrite and chalcopyrite, and small amounts of tetrahedrite, bornite, and cosalite are present. The important gangue minerals are hematite, sericite, quartz, tourmaline, siderite, anhydrite, and barite. In 1905-12, gold recovery was about 0.008 ounce per ton from 1,230,302 tons of copper ore treated. The ratio of silver to gold recovered was about 22:1.
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