Malmyzh Cu-Au porphyry - flagship discovery in an emerging porphyry-epithermal belt, Russian Far East

摘要

The Sikhote-Alin Orogen in the Russian Far East consists of a collage of various aged accretionary prisms, turbidite basins and magmatic arcs active during the Cretaceous through Early Tertiary. The Orogen plays host to an emerging Cu-Au province referred to here as the East Sikhote-Alin metallogenic belt, which is characterised by numerous epithermal, skarn and porphyry-type deposits and prospects (see Figure 1). This belt of mineral deposits can be traced from the Amur River mouth in the north, 1600 km to the south. Commencement of this important metallogenic event is believed to be synchronous with a switch from an active transform margin to Andean-type arc magmatism in the mid Cretaceous, continuing through to the Early Tertiary. Deposits within and proximal to the belt vary from Sn-W-Cu porphyrylike systems of the Khingan-Okhotsk (95±10 Ma; Sato et al, 2002) and the Pb-Zn-W-B skarns in southern Primorye (103-105Ma; Sakhno et al, 2012), typically associated with reduced magmatism, through to large porphyry Cu-Au porphyry deposits such as Malmyzh, associated with oxidised magmatism. Recent SHRIMP zircon U-Pb ages of diorite, diorite porphyry and granodiorite porphyry stocks from Malmyzh include 97.3 - 99.3 Ma (Bukhanova and Collins, 2018), remarkably similar to those of the more reduced Khingan-Okhotsk deposits. Numerous small to mid-sized intermediate to low sulphidation epithermal deposits such as Mnogovershinnoye (dated at 68.1 Ma; Ishihara et al, 1996) mark the waning and likely extensional phases of the metallogeny, and can be seen throughout the Sikhote-Alin.