Physico-chemical parameters from melt inclusions for the formation of the massive sulfide deposits in the Altai–Sayan Region, Central Asia

Abstract

Studies of quartz-hosted melt inclusions from rhyolitic dacite and andesite rocks showed that high-temperature (910–1180°C) felsic melts of normal alkalinity, which correspond to a tholeiitic K–Na series, played an active role during the formation of volcanogenic massive sulfide deposits of the Altai–Sayan Region. High temperatures can be explained by felsic melts degassing in open volcanic systems and heating by ascending basaltic magma. Considerable variation in the H2O content in magmatic systems of the Altai–Sayan volcanogenic massive sulfide deposits (0.08–4.30 wt%) has been established. REE patterns of quartz-hosted inclusions from volcanic rocks of the Altai–Sayan volcanogenic massive sulfide deposits display distinct negative Eu anomalies, which suggest plagioclase fractionation during differentiation of the melt. They are similar to the patterns of quartz-hosted inclusions of the Yaman–Kasy deposit (marginal sea setting) in the South Urals and to island arc rhyolites. Analyses of melt inclusions showed high values of Cu—up to 4100 ppm at the Yubileinoe deposit (Rudny Altai) and up to 3230 ppm at the Kyzyl–Tashtyg deposit (East Tuva). Comparison of data on melt inclusions has shown that some physical and chemical parameters of the magmas that generate volcanogenic massive sulfide and porphyry Cu deposits can be quite similar within certain limits.