COMBINED GEOCHEMICAL INVESTIGATIONS OF THE PESTRINSK SILVER-BEARING FIELD (NORTHEAST RUSSIA)

Magmatic and hydrothermally altered rocks, the ore mineralization, and associated endogenous and exogenous geochemical fields of concentrati on (GFC) of local (deposit) and regional (ore field) orc-magmatic syst ems (OMS) were studied. Combined geochemical investigations were condu cted in the area of the Pestrinsk silver-bearing field, where silver, tin, and rare metal mineralization is widely manifested. Existing conc epts on the geochemical specialization of magma were confirmed. Endoge nous GFC of different scales discovered within the Pestrinsk OMS are c losely associated through the ore matter source with the acid magma ch amber that formed the Upper Cretaceous rhyolite-granite complex, By th eir origin, GFC are magmatogenous formations, and similar to casks of rhyorite-granite associations, they are specialized for Ag, Sn, W, Mo, and complex ores (tin-rare metal, tin-silver, and silver-palymetallic GFC). The zonal character of different-scale OMS is established. It i s pronounced especially distinctly in the composition and structure of endogenous GFC. Geochemical zonality represents a general feature of ore-bearing systems, and it does not depend on their scales. An import ant role in the study of GFC of OMS belongs to secondary geochemical f ields, that is, to exogenous GFC, and in particular to lithochemical d ispersion flows and secondary halos, The results obtained suggest that the composition and structure of exogenous GFC match well the composi tion and structure of eroded and drained objects, and features of zona l development are in many cases reflected in the composition and struc ture of exogenous GFC. Combined geochemical investigations indicate th at modern methods of prediction and exploration for ore mineralization could not be based on the study and evaluation of separate anomalies alone. They should take into account CFC of different genesis (exogeno us and endogenous) and scales (local and regional) in the frame of the whole OMS.