Petrographic, geochemical, and geochronological investigation of gold mineralization at the Lone Tree gold mine, Battle Mountain, Nevada, A

Abstract

The Lone Tree gold deposit, located in the Battle Mountain district in Humboldt County, Nevada, is hosted in siliciclastic rocks positioned stratigraphically above the Roberts Mountains thrust fault. The gold mineralization is spatially associated with and cross-cuts several rhyolite dikes in the mine. Both the dikes and siliciclastic host rocks are variably argillized, sericitized, and silicified. The gold mineralization is associated with an alteration assemblage of quartz, sericite, pyrite, and arsenopyrite. Clay alteration and dolomitization were also observed with the gold mineralization. The strongest geochemical correlations to the gold mineralization are silver, arsenic, antimony, copper, and mercury. Electron microprobe characterization of sulfides at Lone Tree identified gold-bearing arsenopyrite, pyrite, and sphalerite. Arsenopyrite was the most common ore mineral and showed the highest gold grades. The ore texture is commonly gold-rich arsenopyrite rims around less mineralized pyrite cores, which are disseminated throughout the host rock and in veinlets and breccias. Chalcopyrite, tennantite and most of the sphalerite does not contain detectable gold, whereas most of the pyrite and arsenopyrite was above the EMP detection limit with respect to gold. Although most of the gold occurs in the quartz and sulfide breccia veins, some gold also occurs in rhyolitic dikes crosscutting the sedimentary rocks, with elevated grades at the dike margins where alteration is strongest. CA-TIMS analysis of zircon grains indicate that the intrusions were emplaced during the Eocene (40.95 ± 0.03 Ma), providing a maximum age of mineralization.