Home – Home – Jornals – Russian Geology and Geophysics 2001 number 8

Study of melt inclusions in quartz phenocrysts from quartz porphyries has clarified the composition of acid magmas of the Salair ore field. We have established that low-alkali rhyodacite melts of tholeiitic series actively participated in the formation of igneous complexes hosting barite-polymetallic deposits. The high temperatures of acid melts (1050 - 1165 ^oC) evidence their relation with basaltic igneous systems. The Salair rhyodacite melts are shown to be geochemically similar to acid magmas of pyrite deposits in Tuva and the Southern Urals. A comparative analysis of the bulk chemical compositions of quartz porphyrites and melt inclusions in quartz phenocrysts has revealed that low-alkali rhyolites and rhyodacites of tholeiitic series are significantly metamorphosed to high-alkali andesite-dacites enriched in Na and Mg and depleted in Ca, with SiO₂, TiO₂, and Al₂O₃ being their "inert components". A petrochemical analysis of rocks and melt inclusions has shown that some of the igneous complexes of the Salair ore field might have formed in the setting of a developing back-arc basin.