The role of granites in volcanic-hosted massive sulphide ore-forming systems: an assessment of magmatic–hydrothermal contributions / Роль гранитов в вулканогенных системах, образующих массивные сульфидные руды VHMS: оценка магмо-гидротермального привноса

Assessment of geological, geochemical and isotopic data indicates that a significant subgroup of volcanichosted massive sulphide (VHMS) deposits has a major or dominant magmatic–hydrothermal source of ore fluids and metals. This group, which is typically characterised by high Cu and Au grades, includes deposits such as those in the Neoarchean Doyon-Bousquet-LaRonde and CambrianMount Lyell districts. These deposits are distinguished by aluminous advanced argillic alteration assemblages or metamorphosed equivalents intimately associated with ore zones. In many of these deposits, δ34Ssulphide is low, with a major population below −3‰; δ34Ssulphate differs from coexisting seawater and Δ34Ssulphate–sulphide∼20–30‰. These characteristics are interpreted as the consequence of disproportionation of magmatic SO2 as magmatic–hydrothermal fluids ascended and cooled and as a definitive evidence for a significant magmatic–hydrothermal contribution. Other characteristics that we consider diagnostic of significant magmatic–hydrothermal input into VHMS ore fluids include uniformly high (>3 times modern seawater values) salinities or very 18O-enriched (δ18O>5‰) ore fluids. <...>