ORE-FORMING SYSTEMS IN VOLCANOGENIC-SEDIMENTARY SEQUENCES BY THE EXAMPLE OF BASE METAL DEPOSITS OF THE CAUCASUS AND EAST PONTIC METALLOTECT

Abstract

By the example of Alpine volcanogenic base metal deposits of the central part of the Alpine- Himalayan fold belt (East Pontic Metallotect and Caucasus), it has been demonstrated that their hydrothermal systems naturally emerge at various stages of active interaction of microplates-continental fragments of Eurasia and Gondwanaland. During the divergence stage, at the microplates-boundary zones within the marginal sea, hydrothermal-sedimentary Cu and polymetallic deposits have been formed; at the early convergence stage, within the paleo-island-arc systems, epigenetic Cu and in lesser extent, barite-polymetallic (Lesser Caucasus), and later both combined (hydrothermal-sedimentary and stockwork) and epigenetic (mainly Cu- and Zn-contain- ing) deposits have been originated (East Pontic Metallotect). In the beginning of collisional stage, in connection with antidrome volcanism within the back-arc volcanic structures, polyformational deposits (barite, barite-poly- metallic, Cu, Au) have been formed. This tendency persists during the whole collisional stage - in the withinplate and transplate Eocene volcanic depressions - mainly polymetallic deposits have been originated in which the increasing contents of Ag take place in comparison to Au. The authors share the opinion that the primarily- ano- malous environments for Cu-Zn deposits can have been "specialized" basic and medium-acidic volcanics whereas for baritic and barite polymetallic deposits gray colored and evaporitic sequences in the volcano-struc- ture pedestals with buried highly mineralized brines seem to be most favorable.