TRACING THE ORIGINS OF PYRITE AT THE ROUND MOUNTAIN GOLD MINE, NEVADA: A MINERALOGICAL AND CHEMICAL INVESTIGATION

Round Mountain is a low sulfidation epithermal type gold-silver deposit in Northern Nye County Nevada. The stratigraphy of Round Mountain consists of Paleozoic altered sedimentary bedrock, intruded by Cretaceous-aged granite, overlain by a sequence of variably-welded volcanic tuffs of Oligocene age, with younger alluvial sediment from adjacent mountain ranges on top. The majority of gold from Round Mountain is extracted via cyanide heap leaching of disseminated gold from the volcanic tuffs. Gold is well documented to be associated with arsenic-rich pyrites in the Carlin Trend deposits to the north of Round Mountain, and at other similar epithermal type deposits around the world. Gold is thought to be incorporated into the structure of pyrite via coupled substitution with arsenic, as nanoparticle inclusions, or possibly some combination of these mechanisms. Transmission Electron Microscopy studies on pyrite from Carlin Trend deposits show gold occurring as nanoparticle inclusions. The objective of this study is to document the spatial distribution and concentration of elements within pyrites from Round Mountain, specifically gold and arsenic. This approach ultimately aims to advance the understanding of the distribution of disseminated gold at Round Mountain. Energy dispersive X-Ray spectroscopy (EDS) elemental mapping of pyrites from Round Mountain ore reveal significant, yet heterogeneous, concentrations of arsenic associated with pyrites. To date, arsenic enrichment is concentrated toward the pyrite crystal boundary. While no gold has been detected via EDS in the studied samples, the presence of arsenic suggests that gold could be present at trace, yet still potentially economically significant, concentrations. Future work will therefore involve elemental mapping of pyrite via Laser Ablation Inductively Coupled Plasma Mass Spectrometry. Resolving the distribution of gold in pyrite could have implications for the efficiency of gold production at the Round Mountain mine and deposits of similar type worldwide.