Mineral composition and fluid regime of formation of the Yubileinoe gold deposit (Transbaikalian region, Russia)

Conclusions on the origin of the Yubileinoe gold deposit (Transbaikalian re gion) have been drawn on a base of the mineralogical and fluid inclusion st udies of samples from the gold quartz veins and the wall rock alterations. The deposit is considered to belong to a low-sulfide style according to a r atio of quartz and sulfide minerals. Processes of the metasomatic alteratio n of host rocks such as beresitisation and listvenitisation are manifested in the deposit area. The gold quartz veins are a most widespread and econom ically perspective type of ore mineralization. Several mineral paragenetic assemblages in the composition of the gold quartz veins were recognized. Th ey are (from early to late) quartz, quartz-pyrite, quartz-sphalerite-chalco pyrite-galena, and gold-telluride-quartz assemblages. The major amount of g old is found to occur as free gold or as inter growths. The gold fineness i s uniform and lies within 880 to 940. Results of a multidisciplinary study of fluid inclusions indicate that ore veins were formed from chlorine-beari ng (Cl- content is from 0.4 to 1.4 mol/kg H2O) carbonate-aqueous solutions with low salinity (5.0 to 5.5 wt % NaCl-equiv) and subordinate amount (in m ol/kg H2O) F- (0.1), SO42- (0.05), N-2 (0.2 to 1.0), and CH4 (0.01 to 0.06) at medium temperatures (270 to 300 degrees C) and high fluid pressures (2. 2 to 2.5 kbar).