PROPENSITY FOR MINERALIZATION IN VOLCANOES — EVIDENCE FROM MELT INCLUSIONS

Rocks and melt inclusions (MI) from 11 volcanic centers of the Kermadec-Tofua arc, in the South West Pacific, were petrographically studied prior to chemical analysis under the ion beam. The abundance of MI with daughter minerals are volcano-specific with the most abundant found in "U", Putoto, and Hinepuia volcanoes where >50% of MI contain daughter minerals. The B, Li, Cl and S contents in MI generally increase with the silica content of the rock. Fe, Ni, Mn, Cu and Zn are common in MI of all rock types but Mo, Hg and Cu have the highest concentrations in dacite-rhyodacites. The highest concentrations of B, Ti, V, Fe, Co and Mo occur in plagioclase MI; S, Ni, Ge and Hg in pyroxene MI; Cl and Li in quartz MI; and Cu, Zn and M in hornblende MI. Different ore-forming components in volcanic rocks can be correlated with rock composition, Cl/S and B/S of the melts, the presence and abundance of mineral sinks for various elements and the occurrence of hydrothermally altered rock at depth and on the seafloor.