A REVIEW OF RECENT PROGRESS IN UNDERSTANDING GOLD MINERALIZATION AND PETROLOGY AT THE ROUND MOUNTAIN GOLD MINE, CENTRAL NEVADA

The Round Mountain Gold Mine (RMGM), located in central Nevada, is one of the top 10 gold producing mines in the US, with annual production nearing 400,000 equivalent Au ounces. Gold is being extracted from a low sulfidation, volcanic-hosted ore deposit with the principle gold occurrence being interpreted as pyrite-hosted gold with lesser amounts from native gold. Recent efforts aimed at characterizing the occurrence and distribution of gold at the RMGM have focused on transmission electron microscopy (TEM) of native gold; scanning electron microscopy (SEM) study of the paragenesis of Paleozoic metasedimentary ores; and petrography and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) investigations of the trace element chemistry of pyrite throughout the deposit. From TEM, results indicate that macrocrystalline gold is largely the result of nanoparticle assembly. Nanoparticles of gold are observed in illite and titanium oxides. SEM work indicates that a complex (multi-staged) sequence of mineralization occurred in the Paleozoic ore. From this, minerals such as palygorskite and interstratified clay minerals may be problematic for transitioning to less environmentally impactful extraction methods. Minor amounts of gold telluride mineral have been observed in Paleozoic ore. From elemental mapping via LA-ICP-MS, complex growth textures associated with gold and arsenic (in addition to other trace elements, e.g. selenium) have been revealed. Current detailed mineralogical and petrographical characterization of lithic tuffs is providing additional constraints on the context, distribution, and origins of pyrite mineralization at the RMGM. Preliminary LA-ICP-MS elemental mapping of pyrite grains indicates potentially multiple stages of gold mineralization and pyrite inheritance, based on the initial zoning patterns observed. These textures are potentially relevant for better understanding of gold extraction. Results from these efforts are currently providing technical support for the mine that otherwise would not be readily available and creates context for testing the origin and distribution of gold as well as the petrologic history of the Round Mountain Gold Mine and surrounding areas.