A PETROGRAPHIC STUDY OF THE SHOSHONE GRANITE, CENTRAL NEVADA: NEW INSIGHTS IN MESOZOIC ARC MAGMATISM AND OLIGOCENE MINERALIZATION AT THE ROUND MOUNTAIN GOLD MINE
Fieldwork was conducted in March 2022 and defined a sampling transect away from the RMGM to the east and southeast. Six hand samples and thin sections from from this sampling locations were investigated to assess potential mineralogical and compositional variations. The modal minerology of samples include: 1) 40% quartz, 40% microcline, 20% muscovite, <1% plagioclase feldspar, trace oxides (biotite is notably absent); 2) 30-40% quartz, 25-30% microcline, 10% plagioclase feldspar+biotite, 5% muscovite, sanidine, and minor oxides, <1% apatite+zircon; 3) 30-40% quartz+ microcline, 5-10% biotite, 5% plagioclase feldspar, muscovite, and oxides, and <1% zircon+apatite; 4) 50% quartz, 15% microcline, 10% biotite, <5% plagioclase+oxides, <1% chlorite, apatite, and zircon; 5) 30-35% quartz, 20-25% microcline and plagioclase feldspar, 10% biotite, 5-10% muscovite, <5% oxides, <1% apatite+zircon; 6) 30-40% quartz and microcline, 5-10% plagioclase feldspar and muscovite, <5% oxides, and <1% biotite+apatite.
Ongoing and future work involves a detailed SEM-EDS study to identify growth zones in apatite and zircon for potential in-situ U-Pb analyses, and to investigate the potential occurrence of pyrite which has been documented in samples of the Shoshone Granite from the RMGM pit. These datasets will help constrain the timing of Mesozoic arc-related magmatism and further characterize the nature of Oligocene-aged mineralization.