Formation of igneous complexes of the Salair pyrite-polymetallic ore field(West Siberia)

Study of melt inclusions in quartz phenocrysts from quartz porphyries has c larified the composition of acid magmas of the Salair ore field. We have es tablished that low-alkali rhyodacite melts of tholeiitic series actively pa rticipated in the formation of igneous complexes hosting barite-polymetalli c deposits. The high temperatures of acid melts (1050-1165 degreesC) eviden ce their relation with basaltic igneous systems. The Salair rhyodacite melt s are shown to be geochemically similar to acid magmas of pyrite deposits i n Tuva and the Southern Urals. A comparative analysis of the bulk chemical compositions of quartz porphyrites and melt inclusions in quartz phenocryst s has revealed that low-alkali rhyolites and rhyodacites of tholeiitic seri es are significantly metamorphosed to high-alkali andesite-dacites enriched in Na and Mg and depleted in Ca, with SiO2, TiO2, and Al2O3 being their "i nert components". A petrochemical analysis of rocks and melt inclusions has shown that some of the igneous complexes of the Salair ore field might hav e formed in the setting of a developing back-arc basin.