THE GOLD-TUNGSTEN SKARN ORES OF THE ANDRYUSHKIN DEPOSIT (RUSSIA)

The geological structure and mineralogical-geochemical features of the gold-tungsten skarn of the Andryushkin deposit were studied, and the position of this deposit in the geological history of the Balei gold m ining district was defined. The deposit is located in a transverse hor st separating the western Nizhne-Udinsk on the west and the Shadoron o n the east depressions. The main structural element of the deposit is a sublatitudinal fault zone. Sheelite, gold-sheelite-sulfide, and gold -sulfide assemblages associated with metasomatic rocks of feldspar-qua rtz, propylite, and berezite assemblages are distinguished. Gold-tungs ten ores, composed of sheelite and gold-sheelite-sulfide assemblages, predominate in the skarn ore bodies. Gold-sulfide ores are subordinate and occur only in the apogranite berezites. The main ore minerals are native gold, sheelite, and minerals of Bi (bismuthite, lillianite, ko zalite, native bismuth). A high silver content sometimes occurs in the ores. The evolution path of the ore deposition corresponds to the tem perature lowering from 500 to 250 degrees C. The earliest was the shee lite assemblage. It was followed by the gold-sheelite-sulfide, and the n by gold-sulfide. The sheelite of the feldspar-quartz assemblage unde rwent intensive dissolution and could be an additional source of tungs ten for sheelite deposition during propylitization. Some preore proces ses are common. They formed contact hybridic rocks, amphybole-biotite hornfelses, and magnesian and calcareous skarns.