Linkages between volcanotectonic settings, ore-fluid compositions, and epithermal precious-metal deposits / Связи между вулканотектоническими условиями, составом рудных флюидов и эпитермальными месторождениями драгоценных металлов

Epithermal Au and Ag deposits of both vein and bulk-tonnage styles may be broadly grouped into high-sulfidation (HS), intermediate-sulfidation (IS), and low-sulfidation (LS) types based on the sulfidation states of their hypogene sulfide assemblages. The HS and LS types may be subdivided using additional parameters, particularly related igneous rock types and metal content.Most HS deposits are generated in calc-alkaline andesitic-dacitic arcs characterized by near-neutral stress states or mild extension, although a few major deposits also occur in compressive arcs characterized by the suppression of volcanic activity. Rhyolitic rocks generally lack appreciable HS deposits. Highly acidic fluids produced the advanced argillic lithocaps that presage HS mineralization, which itself is due to higher-pH, moderate- to low-salinity fluids. Similar lithocaps in the Bolivian Sn-Ag belt, some mineralized with Ag and Sn, accompany reduced, ilmenite-series magmatism.