The Tainskoe gold deposit (Eastern Sayan, Russia) - A new example of the porphyry gold type

A new gold deposit in Eastern Sayan located in a granitoid stock cutting hy perbasites of the Il'chir ophiolitic cover is described. Three types of ore bodies are distinguished: quartz-vein, quartz-muscovite-pyrrhotite, and ve inlet-disseminated. Their common features are the dominance of pyrrhotite a mong sulfides, the abundance of kustelite, and presence of tellurides and c arbonaceous matter in ores and host granitoids (0.14-0.58 wt %). Mineral-fo rming fluids, of the Tainskoe deposit were presented by water-salt and most ly vapor phases and were heterogenic. The temperature of mineral formation decreased from more than 400 degreesC for veinlet-disseminated to 280-120 d egreesC for quartz-vein and quartz-muscovite-pyrrhotite types with the pres sure 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 d ecreased 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 cha racteristic of the fort-nation of granitoids among hyperbasites and the car bonate-shale sequence enriched with carbonaceous matter of both biogenic an d mantle origin.