TIME-SPACE RELATIONSHIPS BETWEEN MAGMATISM, HYDROTHERMAL ALTERATION, AND MINERALIZATION IN THE BERLIN AND BUFFALO CANYON AREAS OF THE UNION DISTRICT, NEVADA

Buffalo Canyon is a gold prospect located near the historic Berlin mining area in northern Nye County, Nevada, where gold, silver, copper, lead and zinc were mined from mesothermal quartz veins. Buffalo Canyon contains the more recently discovered Everson deposit, a poorly defined gold occurrence based off 40 RC holes. The district includes a series of intrusions hosted in greenschist facies Triassic metasedimentary and metavolcanic rocks. These previously undated intrusions vary in composition from diorite to granodiorite and granite. LA-ICPMS U-Pb dating of zircons has revealed distinct intrusive events in the Jurassic, Cretaceous, and Oligocene. Metaluminous, biotite-pyroxene diorite stocks to porphyritic granodiorite dikes have been dated to 159.59+4.5 Ma and 159.38+0.94 Ma respectively. Peraluminous, ilmenite bearing, equigranular granite and coarse grained leucogranite dikes and plugs have been dated to 78.9+1.8 Ma and 81.05+0.44 Ma respectively. An unaltered quartz monzonite dike has been dated to 25.66+0.26 Ma, similar to Oligocene ignimbrites exposed just east of Buffalo Canyon. The country rocks are altered to pyrrhotite-bearing biotite hornfels. Biotite hornfels is overprinted by sodic-calcic alteration that is likely related to Jurassic intrusive activity, and consists primarily of actinolite + albite + epidote + apatite + tourmaline in veins and disseminated patchworks. Sericite + tourmaline alteration is hosted in and spatially associated with Cretaceous granitic rocks. Free gold within low sulfide, 1-10cm thick, sheeted, blocky to elongate blocky crack-seal quartz veins with locally developed sericite + tourmaline selvages defines the bulk of the Everson gold mineralization. The quartz veins cross-cut all mapped Jurassic intrusive rocks and sodic-calcic veins. The veins have a Au-Bi-(Te) signature and high Au:Ag (>1:1), which is distinct from 10-50 cm thick mesothermal quartz veins in the Berlin area, which have an Au-Ag-Cu-Pb-Zn-Sb signature and a Au:Ag of 1:7 on average. Base metal veins, including pyrite + pyrrhotite + tourmaline and arsenopyrite + chalcopyrite + galena + tourmaline have also been recognized. The presence of reduced, peraluminous granites spatially associated with Au-Bi-(Te) quartz veins bears similarity to intrusion related deposits of Alaska and the Yukon.