THE GENETIC DIVERSITY AND CONVERGENCE OF EPITHERMAL GOLD-SILVER MINERALIZATION

Abstract

The majority of researchers believe that epithermal deposits form in near-surface (300--500 m) and low-temperature (50--200oC) conditions from hot solutions in open fissures. The facts that have been accumulated to date suggest that epithermal deposits are associated with postaccretionary volcanogenic belts, subduction zones, and tectonomagmatic reactivation regions. However, some researchers include epithermal deposits into a single genetic model (porphyry copper ore-forming system), in which gold--silver deposits are divided into low- and high-sulfidation types [1]. This model does not appear to encompass the entire diversity of gold--silver deposits (Fig. 1, Table 1). The obvious association of epithermal deposits with global structures, which governed the Pacific and Mediterranean volcanism, provoked an illusion of the formation of ore material in the adular--chalcedony-quartz veins from deep (subcrustal or lower crustal) sources. Convergence of the adular--chalcedony--quartz veins depends on the near-surface physicochemical conditions of the deposition of mineral aggregates. Our works have revealed that the epithermal deposits were no less developed in ancient epochs, beginning from the Precambrian. The degree of preservation of near-surface deposits inversely correlates with their age. Moreover, gold--silver deposits demonstrate a paragenetic relationship with gold--sulfide, massive sulfide, ferruginous--quartzite, uranium--polymetal, and porphyry copper--molybdenum ore associations (complexes) and gold ore associations of basic--ultrabasic complexes (Table 2).