Gold Deposit in the Butarny Granitoid Stock, Russian Northeast

摘要

The Butarny gold deposit is situated in the central part of the Khurchan—Orotukan Zone oftectonomagmatic activation, which is traced for 150 km in the near-meridional direction, and localized in the slightly eroded Late Jurassic granitoid stock of the same name. The explored orebodies are quartz veins and pinnate veinlets with low-grade pocket-disseminated sulfide (mainly arsenopyrite) mineralization containing native gold. The Bi-bearing gold-pyrite-arsenopyrite and the quartz-lollingite-arsenopyrite-stibnite-jamesonite stages of the veined low-sulfide ore formation have been distinguished. The main mineral assemblage consists of arsenopyrite, native gold, and native bismuth. The minerals—carriers of gold were deposited during the final stage of ore-bearing quartz crystallization at 334-245°C from low-concentrated pneumatolytic-hydrothermal carbonated fluid containing CO2 and CH4 (5.8-2.2 and 1.6-0.5 mol/kg of solution, respectively). The ore-bearing fluid had variable salinity (5.3—2.2 wt % NaCl equiv). It is quite probable that the gas-saturated fluid participated in transport and precipitation of ore matter. Its density varies from 1.02 to 0.77 g/cm3. The pressure is estimated at 1600 to 780 bar. The fluid regime of ore formation at the Butarny deposit is similar to that of typical intrusion-related gold deposits. The Au tenor of beresitized granodiorite, numerous quartz veinlets, and extensive Au-bearing weathering mantle allow us to suggest stockwork mineralization.