THE TAINSKOE GOLD DEPOSIT (EASTERN SAYAN, RUSSIA) - A NEW EXAMPLE OF THE PORPHYRY GOLD TYPE

Abstract

A new gold deposit in Eastern Sayan located in a granitoid stock cutting hyperbasites of the Il'chir ophiolitic cover is described. Three types of ore bodies are distinguished: quartz-vein, quartz-muscovite-pyrrhotite, and veinlet-disseminated. Their common features are the dominance of pyrrhotite among sulfides, the abundance of kustelite, and presence of tellurides and carbonaceous matter in ores and host granitoids (0.14-0.58 wt %). Mineral-forming fluids, of the Tainskoe deposit were presented by water-salt and mostly vapor phases and were heterogenic. The temperature of mineral formation decreased from more than 400°C for veinlet-disseminated to 280-120°C for quartz-vein and quartz-muscovite-pyrrhotite types with the pressure reaching 950-770 bars. The salt composition of fluids for all the ores was similar in terms of main salt components, but the salt concentration decreased from 29-28 to 28-23 wt % from the veinlet-disseminated type to the quartz-vein one. Methane dominated in the composition of the vapor phase. The ores are though to belong to the porphyry gold type (so-called reduced porphyry gold type) connected with island-arc magmatism. The latter was characteristic of the formation of granitoids among hyperbasites and the carbonate-shale sequence enriched with carbonaceous matter of both biogenic and mantle origin.