Noble Metal Mineralization and Pt-Parameters of Formation of the Ak-Sug Porphyry Au-Mo-Cu Deposit (Eastern Sayan)

Ore mineralization of the Ak-Sug porphyry Au-Mo-Cu deposit formed during three stages: 1) porphyry-copper mineralization with simple sulfides in quartz-sericite and quartz-sericite-chlorite metasomatites, 2) subepithermal Au-Bi-Te-Pd-quartz mineralization in quartz-sericite metasomatites, and 3) intermediate-sulfidation Au-Ag mineral assemblages with selenides, tellurides, and Sb and As sulfosalts in argillisites. The Ak-Sug deposit exhibits the features of the evolution of mineral assemblages, temperatures, composition, and fluid salinity during the transition from porphyry copper to the epithermal stage. At the early stages of the ore-forming process, the fluid was magmatic, whereas the later stages involved meteoric waters and the composition of the fluid transformed from high-saline (up to 32.9 wt % NaCl eq) CO2-aqueous-chloride to aqueous-chloride (from 7 to 1.4 wt % NaCl eq) with Na, K, and Mg carbonates and sulfates. A wide diversity of Au-Ag minerals of subepithermal and epithermal mineral assemblages is caused by variations in fS2, fSе2, and fTе2.