Although relatively small, the sedimentary rock-hosted Sterling Mine has been the largest gold producer in the Bare Mountain district in southern Nye County, with total production of about 130,000 troy ounces between 1983 and 1996. Other gold production in the district has come from sedimentary and volcanic rock-hosted ore at the Mother Lode Mine (Mapa, 1990) and the Fluorspar Canyon deposits (Greybeck and Wallace, 1991) about 10 km north and northwest of the Sterling Mine. The district has also produced fluorspar and minor amounts of mercury.
At the Sterling Mine, mineralization is controlled by the intersection of north-northeast striking, high-angle normal faults with a thrust fault that separates siliciclastic rocks of the Late Proterozoic to Early Cambrian Wood Canyon Formation in the upper plate from carbonate rocks of the Middle Cambrian Bonanza King Formation in the lower plate. This mineralization is associated with an alteration assemblage that includes kaolinite, halloysite, illitesmectite, sericite, and alunite (Odt, 1983). Jarosite and limonite are present in most mineralized rock, but primary sulfide ore occurs in places and contains pyrite (Fig. 1 ), marcasite, arsenopyrite, and traces of sphalerite and galena (Joe Marr, personal communication, 1996). Samples ofunoxidized ore consist of quartz± dolomite± kaolinite and contain pyrite± marcasite± stibnite ±galena. On the basis of SEM examination, an unoxidized sample withl38 ppm gold contains pyrite with 1- to 2-micron-thick rims and veins of arsenian pyrite (see the figure below). Very rare micron-size gold is present, but the grade is too high to be accounted for by