VMS and porphyry copper deposits: products of discrete tectono-magmatic settings

摘要

VMS and porphyry copper deposits are considered to be incompatible ore types characteristic of discrete tectono-magmatic settings. VMS settings are extensional and typically marked by bimodal felsic-mafic volcanism, whereas porphyry copper deposits are generated in more compressive, constructional arcs dominated by andesitic-dacitic magmatism. Regional extension in back-arc, intra-arc or post-arc settings favours the development of deep seawater circulation and submarine basins, basic prerequisites for VMS formation. Rapid ascent of hot, dry, felsic magma, the product of crustal melting induced by injection of mafic magmas, minimises mixing and fractionation and appears to result in shallow dyke- and sill-like magma chambers. Steep cylindrical stocks of intermediate composition, which are fundamental to porphyry copper formation, appear to be absent, even where VMS systems possess high-sulphidation characteristics indicative of direct magmatic contributions.