Lincoln County Nevada Gold Production
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The Pioche district is 19 miles west of the Utah-Nevada State line; the town of Pioche is the county seat of Lincoln County.
This is primarily a silver-lead-zinc copper district; gold is produced as a byproduct. Production began in 1869 but did not reach bonanza proportions until about 1870. Hostile Indians and poor transportation facilities prevented large-scale operations for the first few years. Westgate (in Westgate and Knopf, 1932, p. 5) reported two periods of accelerated production: from 1869 to 1875, and from 1911 through 1958. In the early days two companies - the Meadow Valley Co. and Raymond & Ely - dominated mining in the district, but they were mostly inactive after 1875. The second period of activity was accelerated by the entrance of Combined Metals Reduction Co. into the district in 1915.
Gold production was not recorded before 1906, but in view of the fact that $17 million in metals was produced in 6 years in the early days (Young, 1950, p. Ill), considerable gold must have been produced before 1906. From 1906 to 1959, a total of 104,583 ounces of gold was mined in the district.
A thickness of 17,000 to 18,000 feet of Paleozoic sedimentary rocks is exposed in the Pioche district. These are, according to Westgate (in Westgate and Knopf, 1932, p. 6-7), in ascending order: the Prospect Mountain Quartzite and Pioche Shale (Lower Cambrian); Lyndon Limestone, Chisholm Shale, and Highland Peak Limestone (Middle Cambrian) ; the Mendha Limestone (Upper Cambrian) ; Yellow Hill Limestone and Tank Hill Limestone (Lower Ordovician) ; Eureka Quartzite (Middle Ordovician) ; Ely Springs Dolomite (Upper Ordovician) ; dolomite of Silurian age; Silverhorn and West Range Dolomites (Devonian), Bristol Pass Limestone; Peers Spring Formation, Scotty Wash Quartzite (Mississippian) ; and Bailey Spring Limestone (Mississippian and Pennsylvanian). Unconformably overlying the sedimentary rocks is a thick series of Tertiary or late Mesozoic lava flows consisting of dacite, latite, andesite, and a little rhyolite and basalt. Tuffs are interbedded with the flows. Locally, stocks and dikes of quartz monzonite cut the sedimentary rocks and lava flows which have been metamorphosed by the intrusions. The Paleozoic formations have been gently folded and the Paleozoic and pre-Pliocene(?) rocks have been shattered by block faults and thrusts.
Ore deposits, according to Knopf (in Westgate and Knopf, 1932, p. 45), are of three types: (1) silver-bearing fissure veins in Lower Cambrian quartzite, (2) argentiferous lenses and pods in granite porphyry dikes, and (3) replacement deposits of sulfides in limestone and dolomite units in the Pioche Shale, Lyndon Limestone, Mendha Limestone, and the Highland Peak Limestone. The deposit of the Combined Metals mine is in a limestone unit of the Pioche Shale. The deposits all seem to have been contemporaneous, having been formed between two periods of Tertiary dike injection (Knopf, in Westgate and Knopf, 1932, p. 51). The bonanza output of the initial years came from the fissure veins in the quartzite; more recently, interest has focused on the sulfide replacement ores. Minerals of the fissure veins are argentite, cerargyrite, cerussite, and galena in quartz gangue. The podlike deposits in porphyry dikes contain the same minerals as the fissure veins. The replacement deposits are masses of argentiferous pyrite, sphalerite, and galena (Knopf, in Westgate and Knopf, 1932, p. 48-50).