Tungsten-bearing manganese deposit at Golconda, Nevada

Abstract

The tungsten deposit lies just above the former high water level of Quaternary Lake Lahontan and a short distance east of Golconda, Nevada. Tungsten-bearing manganiferous and ocherous deposits underlie calcareous tufa. The tungsten ores lie blanketlike on an erosion surface which truncates tilted Triassic sediments. Beneath the blanket deposits are veins of similar mineralization which are thought to have provided the source of the overlying ores. The blanket deposits are sufficiently large and contain enough tungsten to justify economic development. The ore minerals are colloidal in origin, tungstic acid having been adsorbed in psilomelane and Iimonite while both were gels. Both the ore-bearing layers and the tufa are considered to be chiefly of hot spring origin rather than the result of precipitation from Lake Lahontan. A jarosite-bearing vein containing small amounts of tungsten crops out at a slightly higher elevation where the hot springs deposit has been removed by erosion. The vein cuts steeply inclined limestone which has been considerably altered to chert and highly silicified with the production of quartzose masses. This vein is thought to be indicative of a still lower level of mineralization than the veins immediately below the blanket deposits. It is believed mineralization started with chertification and silicification but ultimately resulted in precipitation of tungsten, iron, manganese, and tufa. The source of the tungsten is not exposed, but the existence of scheelite deposits in the vicinity suggests the possibility of underlying scheelite or perhaps wolframite-bearing veins.