California · Placer County
Past Producer

Ophir District

Placer County, California, United States
GoldSilverLeadCopper
⌖ Show on mapUSGS source ↗
Commodities
PrimaryGold, Silver
SecondaryLead, Copper
Commodity typeM
Deposit
Deposit typeHydrothermal vein
Model273: Low-sulfide Au-quartz vein
Orebody formTabular
Ore controlQuartz veins fill fractures developed in quartz diorite and metamorphosed mafic to intermediate volcanic rock. Lindgren (1892) observed that where the quartz veins intersected zones of metavolcanic rock enriched in pyrite and copper sulfides (termed ?iron belts?), the veins were more enriched in gold. Also, some localities where veins intersected were the sites of pockets or rich ore shoots.
Materials
Ore mineralsGold, Electrum, Pyrite, Chalcopyrite, Galena, Sphalerite, Arsenopyrite, Tetrahedrite, Molybdenite, Silver, Stibnite, Telluride
GangueQuartz, Calcite, Chalcedony
Geology
Host rockDiorite,Amphibolite · "Penryn Pluton", "Copper Hill Volcanics"
StructureBear Mountains Fault Zone
Tectonic settingMagmatic arc
AlterationCarbonate; calcite, sericite, pyrite, minor chlorite; formed as selvages a few inches to a few feet wide in wallrock immediately adjacent to quartz veins.
Economic & production
Development statusPast Producer
Discovery year1851
Identification
Deposit ID10310713
Alternate namesnumerous individual mines in this district
RegionNA
Data scoreA
Coordinates38.89111, -121.12278
References
Clark, W.B. and Carlson, D.W., 1956, Mines and mineral resources of El Dorado County: California Division of Mines, California Journal of Mines and Geology, v. 52, p. 408.Clark, W.B., 1970, Gold districts of California: California Divisions of Mines and Geology Bulletin 193, p. 102-103.Clark. W.B., and Lydon, P.A., 1962, Mines and mineral resources of Calaveras County, California: California Division of Mines and Geology County Report No. 2, p. 40.Earhart, R.L., 1988, Geologic setting of gold occurrences in the Big Canyon area, El Dorado County, California: U.S. Geological Survey professional Paper 1576, 13 p.Hobson, J.B., 1890, Ophir Mining District: 10th Annual Report of the State Mineralogist, California State Mining Bureau, p. 426-434.Irelan, W., Jr.,, 1888, Auburn District: 8th Annual Report of the State Mineralogist, California State Mining Bureau, p. 460-462.Knopf, A., 1929, The Mother Lode system of California: U. S. Geological Survey Professional Paper 157, 88 p.Koschmann, A.H., and Bergendahl, M.H., 1968, Principal gold-producing districts of the United States: U.S. Geological Survey Professional Paper 610, 283 p.Lindgren, W., 1892, The gold-silver veins of Ophir, California: U.S. Geological Survey 14th Annual Report, Part 2, p. 243-284.Lindgren, W., 1894, Sacramento Folio: U.S. Geological Survey Atlas of the U.S., Folio 5, 3 p.Logan, C.A., 1927, Placer County: 23rd Annual Report of the State Mineralogist, California State Mining Bureau, p. 247-251.Logan, C.A., 1935, Placer County: 31st Annual Report of the State Mineralogist, California Journal of Mines and Geology, p. 17-18.Logan, C.A., 1936, Gold mines of Placer County: 32nd Annual Report of the State Mineralogist, California Journal of Mines and Geology, p. 28-31.Olmsted, F.H., 1971, Pre-Cenozoic geology of the south half of the Auburn 15-minute quadrangle, California: U.S. Geological Survey Bulletin 1341, 30 p.Schweickert, R.A., Hanson, R.E., and Girty, G.H., 1999, Accretionary tectonics of the Western Sierra Nevada Metamorphic Belt in Wagner, D.L. and Graham, S.A., editors, Geologic field trips in northern California: California Division of Mines and Geology Special Publication 119, p. 33-79.Wagner, D.L. and others, 1981, Geologic map of the Sacramento Quadrangle, California: California Department of Conservation, Division of Mines and Geology Regional Geologic Map Series, Map No. 1A, scale 1:250,000.Waring, C.A., 1915, Placer County: 15th Annual Report of the State Mineralogist, California State Mining Bureau, p. 318-319.Zimmerman, J.E., 1983, The Geology and structural evolution of a portion of the Mother Lode Belt, Amador County, California: unpublished M.S. thesis, University of Arizona, 138 p.