The following report summarizes the results of a brief geological examination made by the Geological Survey of the small uranium deposit in the Majuba Hill mine, Pershing County, Nevada.
"This report is a summary of the results of a brief geological examination made by the Geological Survey of the small uranium deposit in the Majuba Hill mine, Pershing County, Nevada."
Abstract: The tin and copper deposits at Majuba Hill, Pershing County, Nevada are in a partly brecciated plug of Tertiary rhyolite porphyry, which is altered nearly everywhere to quartz and sericite and in some places is intensely tourmalinized. The tin mineral, cassiterite, appears to be associated with the alteration, for the single concentration of it was formed by replacement of altered breccia. Brecciated and altered rock is, however, only a general guide to potentially tin-bearing ground, and not a specific guide to ore shoots, for most of such rock appears to contain only small amounts of cassiterite, widely and unevenly distributed. The known deposit, which is exposed only underground, is at most 20 by 20 by 10 feet in size, and may contain about 12,000 pounds of metallic tin. The deposit is cut off by a normal fault, which apparently is of small displacement, and the footwall segment has not been found. The copper deposit is in the same normal fault, about 300 feet south of the earlier-formed tin deposit. From it about 4,000 tons of 12 percent copper ore was mined in 1915-18, but none has been mined since and no copper ore is now in sight.
Abstract: The tungsten deposits of the Nightingale district are just within the western border of Pershing County, Nev., and in the Nightingale or Truckee Range, which lies east of Winnemucca Lake. The Tertiary volcanic rocks of the district rest unconformably upon intrusive granodiorite and steeply dipping metamorphosed limestones and slates of unknown age. The tungsten deposits are of the contact-metamorphic type: The ore consists of scheelite bearing tactite, a dark silicate rock that was formed by metamorphism of limestone at the granodiorite contact. Scheelite (calcium tungstate) is the only valuable mineral. The gangue minerals are epidote, quartz, pyroxene, garnet, calcite, tremolite, molybdenite, pyrite, pyrrhotite, chalcopyrite, arsenopyrite, apatite, and sphene. The bodies of tactite are generally tabular, and they extend downward steeply, because both the limestones and the granodiorite contact dip vertically or nearly so. The largest tactite body of the district is at the Nightingale mine; it attains a maximum thickness of 60 feet and is nearly a thousand feet long, but only for part of its length is it thick enough and rich enough to be potentially minable. That it continues downward below the mine workings, which extend to a depth of 128 feet, is shown by nine drill holes put down by the Bureau of Mines, United States Department of the Interior, in 1940, all of which encountered tactite at depths of, 260 to 350 feet. The mine has produced about 12,000 tons of ore, and its ore bodies contain the principal reserve of the district. In 1938 the reserves of the entire district were estimated to be about 50,000 tons of ore averaging between 0.25 and 0.50 percent of W03. Later diamond drilling by the Bureau of Mines indicated that the principal tactite body continues to at least twice the depth hitherto explored by the mine workings.
From abstract: Uranium is associated with copper and tin ores in the Majuba Hill area, Antelope mining district, in the central part of the Antelope Range, Pershing County, Nev. About 23, 000 tons of copper and 200 tons of tin ore, a small quantity of lead-silver ore, and some arsenic-silver ore have been produced from the Majuba Hill mine, the Last Chance mine, and a mine in sec. 34, T. 33 N., R. 31 E.
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