METAL-BEARING ADAKITES AS MAGMATIC PRECURSORS FOR COPPER-GOLD-SILVER MINERALIZATION AT CONVERGENT PLATE BOUNDARIES (THE KAMCHATKA EXAMPLE)
P.К. Kepezhinskas1, A.I. Khanchuk2, N.V.Berdnikov1, N.V.Potapova1, V.O.Krutikova1
Keywords: Kamchatka; subduction; slab tear and break-off; adakites; microminerals; Cu-Au-Ag mineralization; epithermal and porphyry deposits
Abstract
Valovayam and Tymlat adakites were formed during subduction of the Miocene oceanic lithosphere of the Komandorsky Basin beneath the North Kamchatka followed by the interaction with mantle wedge peridotites. Post-collisional adakitic dacites from the Bakening paleo-volcano (Central Kamchatka) are related to the destruction and melting of the Mesozoic Kronotsky microplate paleo-slab due to the influence of hot sub-slab 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 chalcophile sulfides, native metals, alloys, oxides and carbonate hydroxides. Microinclusion assemblages in adakites are broadly comparable to the ore mineral associations in epithermal and porphyry deposits from the Russian Far East. Kamchatka adakites display elevated silver and gold contents in comparison with back-arc basin and volcanic arc lavas, which could be sourced from the metamorphosed oceanic crust and metalliferous pelagic sediments in the subducted slab. We conclude that adakites associated with subduction of the young oceanic lithosphere (North Kamchatka) and the old lithospheric slab tear and break-off (Central Kamchatka) can be magmatic precursors for the copper-gold-silver mineralization in the Kamchatka region. We also propose that adakite-related metallogenic processes may occur in the other convergent plate margin settings, for example, in the flat slab subduction environments.
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