Metallogeny of Low-K Tholeiitic Magmas in Volcanic Arcs: Inferences from Petrology, Geochemistry and Micromineralogy of the Modern Mutnovsky Volcano Lavas (Kamchatka, Russia)

Metallogeny of low-K tholeiitic magmas in volcanic arcs is poorly documented and understood. The Mutnovsky volcano in Kamchatka erupted low-K tholeiitic basalt, basaltic andesite, andesite and dacite formed through partial melting of a depleted mantle wedge beneath the active front of the Kamchatka arc, followed by fractional crystallization in subarc magmatic conduits. Mineral microinclusions in Mutnovsky lavas are dominated by Cu-Ag chlorides and sulfides (±cerussite, baryte, cassiterite and Sb oxide), which show, along with the bulk rock Ag, Sn and Sb concentrations, a general increase during magmatic differentiation. Mutnovsky rocks are characterized by higher cumulative proportions of Cu-Ag sulfides and chlorides in comparison with the neighboring rear-arc Gorely and Bakening volcanoes, emphasizing the importance of S- and Cl-bearing fluids for their metallogenic evolution. Microinclusions in Mutnovsky tholeiites display certain similarities with ore mineral associations from epithermal and porphyry deposits in Kamchatka. Together with the enrichment of Mutnovsky lavas in Ag, Cu and Sb in reference to the bulk continental crust, this indicates a potential link between low-K tholeiitic magmas and Cu-Ag (±Sb, Sn) mineralization in volcanic arcs.