Petrology of the Precambrian Banded Iron Formation of Gandhamardan Hill, West of Keonjhargarh, Orissa

The Precambrian Banded Iron Formation of Gandhamardan hill, Keonjhar district, Orissa, belongs to Noamundi Group. It is restricted largely to oxide facies of Lake Superior type. The sulphide facies in association with black chert is present in small amount. It is almost unmetamorphosed and exhibits many depositional and penecontemporaneous deformation sedimentary structures. A preliminary field and petrographic examination reveals that iron formation was initially deposited at least in major part as hematite-magnetite-chert rock in a near-shore epicontinental environment partially restricted from free-circulation of sea water. Iron and silica were precipitated almost contemporaneously largely due to physico-chemical changes in sea water. The presence of siliceous stromatolitic laminations and alga-like spheroid Archaeospheroides barbertonis similar to that of Fig Tree cherts, however, suggests biogenic activity during the deposition of the Banded Iron Formation.