Au-bearing gabbro-tonalite-granodiorite-granite plutons of the urals: Age, geochemistry, and magmatic and ore evolution

Abstract

Gabbro-tonalite-granodiorite-granite (GTGG) plutons productive for gold are suprasubduction intrusive bodies formed at an Andean-type active continental margin 410–380, 365–355, and 320–290 Ma ago. The Devonian plutons are situated in the southeastern marginal continental zone, whereas the Carboniferous plutons occur in the northwestern zone. All GTGG plutons are mantle-crustal. Their formation started with hydrous basic magmatism and was accompanied by such magmatism up to the final stage. Mantle-derived amphibole gabbro and diorite experienced partial melting (anatexis) in the lower crust under a pressure of 6–10 kbar, giving birth to the tonalite-granodiorite members of the GTGG series. The latter, in turn, were involved in anatexis with the formation of adamellite and granite, immediately accompanied by hydrothermal gold mineralization. The multistep anatexis is the main petrogenetic process responsible for the gold resource potential of GTGG plutons. In the process of anatexis occurring under high fluid saturation, gold was repeatedly removed from rocks into fluid, facilitating its concentration in ore deposits.