By A. H. KOSCHMANN and M. H. BERGENDAHL - USGS 1968
The mining districts of Clark County are scattered through the many north-trending mountain ranges characteristic of this part of the State.
Although there is some indication of early small-scale mining by Indians and Spanish explorers, it was not until 1855, when the Mormon settlers began operating the Potosi mine in the Goodsprings district, that large-scale lode mining began. The Potosi is the oldest lode mine in the State (Vanderburg, 1937a, p. 9). Gold-silver deposits were discovered in the Eldorado district in 1857, and some time later, in the Goodsprings and Searchlight districts. These three districts produced most of the metals in the county.
Total recorded county production from 1908 through 1959 was 291,770 ounces. Of this total only 200 ounces was from placers; the remainder was from lode mines or a byproduct of silver, copper, and base-metal ores.
The Eldorado district is 6 miles wide and 12 miles long in the northern Opal Mountains in southeastern Clark County, about 25 miles south of Boulder City.
Mining began in this district in 1857, but it never received the publicity given many other areas, possibly because it was overshadowed by concurrent greater booms at the Comstock Lode, Eureka, and Ely (Ransome, 1907, p. 64). The major mines of the district were the Techatticup, Eldorado Rand, Crown Queen, Wall Street, Mocking Bird, Rambler, Rover, and Flagstaff.
The early production of the Eldorado district was estimated (Ransome, 1907, p. 65) at between $2 and $5 million, mostly in gold. From 1907 through 1959 the production was 101,729 ounces of lode and byproduct gold and 168 ounces of placer gold.
Gneiss and schist, possibly Precambrian in age, have been intruded by a mass of quartz monzonite and are flanked locally by patches of Tertiary volcanic rocks (Ransome, 1907, p. 65-68). Ores occur in fissures in the gneiss and schist and in the quartz monzonite. Most of the veins are small, but very persistent. The minerals present are pyrite, galena, and sphalerite in a gangue of quartz and some cal-cite. The gold and silver probably are associated with the sulfides; native gold has not been seen (Ransome, 1907, p. 76-79).
The Goodsprings (Yellow Pine) district comprises several hundred square miles in the southern Spring Mountain Range, in southwestern Clark County. The town of Goodsprings, in the center of the district, is 8 miles northwest of Jean and 28 miles southwest of Las Vegas.
Mormon missionaries are credited with the first discoveries in the district, and in 1856 work was begun at the Potosi mine. After several unsuccessful attempts to smelt the ore and recover lead, work was abandoned, and for the next several decades activity in the district consisted of desultory prospecting of gold-bearing iron gossans, copper-stained gossans, and lead veins. In the 1890's the district was reactivated, and considerable gold was mined from the Keystone, Bass, and Clementine properties.
In 1905 the completion of the railroad between Los Angeles and Salt Lake City provided the district with adequate shipping facilities, and the following year significant quantities of oxidized zinc minerals were recognized in the ores. These two events permitted a more orderly growth and development in the following years. Platinum was discovered in the Bass mine in 1914, but production of this element never fulfilled any of the expectations its discovery generated (Hewett, 1931, p. 69-71).
Gold is chiefly a byproduct of zinc-lead-silver ore. From 1902 through 1959 a total of 58,815 ounces of gold was produced; none of it was from placers.
The predominant bedrock consists of a thick section of Paleozoic and Mesozoic rocks that were folded, thrust faulted, and intruded by granitic dikes and sills (Hewett, 1931, p. 9-55). The Paleozoic rocks are predominantly limestone; the Mesozoic rocks are largely sandstone, shale, and conglomerate. Ores were deposited in breccia zones and fractures in limestone of pre-Permian age. Ore deposits are of three types: gold-copper with accessory cobalt, nickel-silver, and zinc-lead with accessory vanadium.
Gold deposits are in fractures in and near the intrusive bodies, copper deposits are in Devonian or older beds and are more remote from the intrusive bodies, and zinc and lead deposits occur in Lower Mississippian beds (Hewett, 1931, p. VIII). The gold deposits consist of pyritic fracture fillings, weathered to free gold and iron and manganese oxides; quartz is not present (Hewett, 1931, p. 89-90).
Located in southeastern Clark County, 40 miles south of Boulder City and 22 miles east of Nipton, Calif., the Searchlight district is one of the more recently developed in the State; the first production was recorded in 1898. The deposits have yielded gold and subordinate silver, copper, and lead.
Most of the production has come from the Duplex and the Quartette mines. The Quartette had a total yield worth well over $2,800,000 and the Duplex mine produced ore worth in excess of $650,000, mainly in gold (Callaghan, 1939, p. 161, 165).
The period of greatest activity in the district was 1902-16. After that time, activity steadily declined. Gold production from 1902 through 1959 was 246,997 ounces from the lode mines and only 26 ounces from placer workings.
The oldest rock of the district is gneiss of possible Precambrian age (Callaghan, 1939, p. 140-141). It is intruded by a large quartz monzonite body of Tertiary age and by andesite porphyry which may be an early facies of the quartz monzonite. The quartz monzonite is the most extensive rock in the district. A younger series of lava flows and volcanic (?) breccias lies on the eroded surface of the quartz monzonite and older rocks.
The veins are in fractured zones in the older rocks around the margin of the quartz monzonite. Most of the production has come from oxidized and weathered vein material which extends to depths of 800 feet, or more, in which galena is the only unweathered sulfide present. Unweathered vein material consists of a breccia of country rock cemented with vuggy quartz. Sphalerite, galena, and chalcopyrite occur in equal amounts in the quartz.
The oxidized vein material contains gold, traces of copper and chalcopyrite, galena, chalcocite, quartz, chalcedony, cuprite, hematite, cerussite, malachite, calcite, brochantite, limonite, leadhillite, chrysocolla, wulfenite, vanadinite, mottramite, hemimorphite (Callaghan, 1939, p. 152-153).
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