PRECIOUS METAL BEARING ASSEMBLAGES IN THE ANN MASON PORPHYRY DEPOSIT, YERINGTON, NEVADA
There are four different mineralization zones in the deposit: chalcopyrite-bornite, chalcopyrite-pyrite, chalcopyrite>pyrite, and chalcopyrite<pyrite. Assay analyses by Entree Gold, who own the rights to the deposit, show an association of bornite-rich zones with higher concentrations of precious metals, including Au and Ag. The goal of this project is to determine the assemblages which host precious metals within the deposit, particularly in the bornite-rich region, by using petrographic descriptions, SEM EDAX analysis, and WDS microprobe analysis of thirty thin sections of drill core samples from the deposit. Our study finds that Au and Ag occur in telluride minerals along the borders of bornite grains in the chalcopyrite-bornite zone. Specifically, Ag and Au are found within a Ag-Te-Pb-Se-Au mineral, with Au concentrated along the outer rim of the grain. Other samples show Ag hosted in rutile alongside U in apatite. All Au and Ag have been found in the chalcopyrite-bornite zone.
In summary, accessory metals are hosted within different mineral assemblages in distinct mineralization zones within the deposit. These findings indicate that Au and Ag are transported and deposited separately from the major ore elements in the Ann Mason Deposit, or have been remobilized by later fluids. The conclusions of this research will be used in the extraction and processing of ore at Ann Mason when the deposit is developed, and contribute new data to the scientific literature on trace assemblages in porphyry deposits.