The Conditions of Generation for the Au-Ag Epithermal Mineralization in the Amguema-Kanchalan Volcanic Field, Eastern Chukotka

This paper discusses the conditions of generation for the Au-Ag epithermal mineralization in the Amguema-Kanchalan Volcanic Field (AKVF), which is situated at the western termination of the East Chukchi flank zone of the Okhotsk-Chukchi Volcanogenic Belt (OChVB). The AKVF contains the potentially large Valunistoe Au-Ag deposit and several promising deposits and ore occurrences (Zhilnoe, Shakh, Gornoe, Ognennoe, and Osennee). Thermal and cryometric studies of fluid inclusions in quartz and calcite in epithermal veins showed that the solutions were dominated by Na and K chlorides. The epithermal mineralization was deposited by heterogeneous hydrothermal fluids with low salt concentrations (0.2-3.6 wt % equ. NaCl, under moderate temperatures 174-354 degrees C). The fluid pressure reached values of 30-160 bars, which is proper to depths of generation of 0.1-0.6 km under hydrostatic conditions. These results classify the epithermal mineralization studied here as a low sulfide one. Meteoric waters and magma chambers of andesitic magmas are the most likely sources of ore-forming fluids. The information furnished in this paper is of practical value for regional metallogenic predictions, as well as the search for and assessment of epithermal Au-Ag deposits.