FORMATION OF IGNEOUS COMPLEXES OF THE SALAIR PYRITE-POLYMETALLIC ORE FIELD (WEST SIBERIA)

Abstract

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°C) 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 A12O3 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.