Tin, copper, and uranium at Majuba Hill, Nevada

Abstract

Uranium minerals occur with ores of copper, tin, and silver at Majuba Hill, Nevada. During World War I, the Majuba Hill mine produced about 4,000 tons of 12 percent copper ore, and during World War II about 23,000 tons of ore containing 2 to 4 percent copper and enough tin ore to furnish from 10 to 15 tons of metallic tin. No uranium has been produced. The bedrock geology of Majuba Hill consists of a complex; volcanic neck or plug composed of rhyolite porphyry, porphyritic rhyolite, quartz feldspar porphyry, breccia dikes, and irregular breccia masses. This plug intruded Triassic (?) sedimentary rocks, chiefly shale. The principal loci of ore deposition were (l) parts of the breccia bodies, particularly where they were porous and where they were silicified and tourmalinized, and (2) a few small pre-mineral fractures adjacent to the breccia masses, Intense hydrothermal alteration resulted in the formation of sericite, quartz, and tourmaline in the wall rocks. This was accompanied or followed by deposition of arsenopyrite, pyrite, cassiterite, fluorite, and several primary sulfide minerals of copper. All of the ore bodies exposed in the mine are highly oxidized, and a profusion of secondary minerals of copper and iron have been found. The only uranium minerals detected are the phosphates torbernite and matatorbernite and the arsenate zeunerite. These are widely disseminated throughout the mine in small amounts associated with the secondary minerals of copper and iron along minor fault surfaces, bedding planes in the shale, and in porous parts of the breccia. A primary uranium mineral has not been found. The secondary uranium minerals appear to be most abundant where copper ore is highest grade. Although unoxidized uranium ore has not been found, it is inferred from this relation that the deposition of the original uranium minerals favored those areas where primary copper mineralization was most intense. There may have been an intimate association of uranium with silver in the ore, but this has not been established. The U 3 O 8 content of samples of copper ore ranges from .0.002 to 0.30 percent. Because the bottom of the oxidized ore has not been reached in mining or exploration, the downward extensions of the known ore bodies of secondary minerals would appear to be worthy of investigation to determine the grade and extent of the primary ore.