USGS2003
Geochemistry maps showing the distribution and abundance of 18 elements in about 1,400 rock samples, both mineralized and unmineralized, from the southern Toquima Range, Nev., indicate major structural and lithologic controls on mineralization, and suggest sources of the elements. Radiometric age data, lead mineralogy and paragenesis data, and lead-isotope data supplement the geochemical and geologic data, providing further insight into timing, sources, and controls on mineralization. Major zones of mineralization are centered on structural margins of calderas and principal northwest-striking fault zones, as at Round Mountain, Manhattan, and Jefferson mining districts, and on intersections of low-angle and steep structures, as at Belmont mining district. Paleozoic sedimentary rocks, mostly limestones (at Manhattan, Jefferson, and Belmont districts), and porous Oligocene ash-flow tuffs (at Round Mountain district) host the major deposits, although all rock types have been mineralized as evidenced by numerous prospects throughout the area. Principal mineral systems are gold-silver at Round Mountain where about 7 million ounces of gold and more than 4 million ounces of silver has been produced; gold at Gold Hill in the west part of the Manhattan district where about a half million ounces of gold has been produced; gold-mercury-arsenic-antimony in the east (White Caps) part of the Manhattan district where a few hundred thousand ounces of gold has been produced; and silver-lead-antimony at Belmont where more than 150,000 ounces of silver has been produced. Lesser amounts of gold and silver have been produced from the Jefferson district and from scattered mines elsewhere in the southern Toquima Range. A small amount of tungsten was produced from mines in the granite of the Round Mountain pluton exposed east of Round Mountain, and small amounts of arsenic, antimony, and mercury have been produced elsewhere in the southern Toquima Range. All elements show unique distribution patterns that suggest specific sources and lithologic influences on deposition, as well as multiple episodes of mineralization. Principal episodes of mineralization are Late Cretaceous (molybdenum and tungsten in and near granite; silver at Belmont and Silver Point mines), early Oligocene [tourmaline and base- and precious-metals around the granodiorite of Dry Canyon stock as well as at Manhattan(?)], late Oligocene (gold at Round Mountain and Jefferson), and Miocene (gold at Manhattan). Most likely principal sources of molybdenum, tungsten, silver, and bismuth are Cretaceous granites; of antimony, arsenic, and mercury are intermediate-composition early Oligocene intrusives; and of gold are early and late Oligocene and early Miocene magmas of the volcanic cycle. Lead may have been derived principally from Cretaceous granitic magma and Paleozoic sedimentary rocks. Several areas prospective for undiscovered mineral deposits are suggested by spatial patterns of element distributions related to geologic features. The Manhattan district in the vicinity of the White Caps mine may be underlain by a copper-molybdenum porphyry system related to a buried stock; peripheral high-grade gold veins and skarn deposits may be present below deposits previously mined. The Jefferson district also may be underlain by a copper-molybdenum porphyry system related to a buried stock, it too with peripheral high-grade gold deposits. The Bald Mountain Canyon belt of small gold veins has potential for deeper deposits in buried porous ash-flow tuff similar to the huge Round Mountain low-grade gold-silver deposit. Several other areas have potential for a variety of mineral deposits. Altogether the geochemical, geochronologic, mineralogic, and geologic evidence suggests recurring mineralizing episodes of varied character, from Late Cretaceous to late Tertiary time, related to a long-lived hot spot deep in the crust or in the upper mantle. Granite plutons of Late Cretaceous age were minerali