METAL-BEARING ADAKITES AS MAGMATIC PRECURSORS OF Cu–Au–Ag MINERALIZATION AT CONVERGENT PLATE BOUNDARIES ( <i>the Kamchatka example</i> )

The Valovayam and Tymlat adakites formed during the subduction of the Miocene oceanic lithosphere of the Komandorsky Basin beneath Northern Kamchatka, followed by their interaction with subarc mantle wedge peridotites. Postcollisional adakitic dacites from the Bakening Paleovolcano (Central Kamchatka) are related to the destruction and partial melting of the Mesozoic Kronotsky microplate paleoslab under the influence of the hot subslab asthenospheric mantle after the collision of the Kronotsky island arc. Minerals and volcanic glass in Kamchatka adakites contain predominant Cu–Ag–Au alloys and silver chloride microinclusions along with various sulfides, native metals, alloys, oxides, and hydroxycarbonates of chalcophile elements. Microinclusion associations in these adakites are similar to ore mineral assemblages in epithermal and porphyry deposits of the Russian Far East. The Kamchatka adakites show elevated silver and gold contents in comparison with back-arc basin and volcanic-arc lavas. These elements might have been sourced from the metabasites in the oceanic crust and metal-bearing pelagic sediments in the subducted slab. We conclude that adakites associated with the subduction of the young oceanic lithosphere (Northern Kamchatka) and the melting of the old oceanic lithosphere during the slab tear and break-off (Central Kamchatka) can be magmatic precursors of the Cu–Au-Ag mineralization in the Kamchatka region. We also suggest that adakite-related metallogenic processes are possible at the convergent plate boundaries in other settings, in particular, in the flat slab subduction setting.