Petrology and Geochemistry of Mixed Oxide-Silicate Facies Banded Iron Formations from Sandur Schist Belt, India

Mixed oxide-silicate facies banded iron formations are found as thin bands in the Eastern Volcanic Block of the Sandur schist belt They consist of haematite, magnetite, cummingtonite-grunerite and chert/quartz. Chemical constituents are SiO₂, Fe₂O₃ and FeO with no appreciable concentration of any other oxide. This composition is reflected in their trace and REE data, such as high order depletion in geochemical twins like Zr-Hf, V-Sc and Nb-Ta. The REE patterns are highly depleted (ΣREE 0.96 to 9.98 ppm) with Nd/Yb varying between 2 and 5. Cherty BIFs from this belt, metamorphosed to lowest greenschist facies. show almost identical geochemistry. The available data from this belt and other places indicate that unless impurities from terrigenous and volcaniclastic sources are present, metamorphism from lowest greenschist facies to granulite facies does not make an appreciable change in their trace and REB constituents.