Lithostratigraphy of the Precambrian Rocks around Koira, Sundargarh District, Orissa

A group of little metamorphosed volcanic and sedimentary rocks of Precambrian age belonging to the 'Iron Ore Series' of Jones (1934), comprising lavas, tuffs, banded iron formation, shales and quartzite-sandstone is preserved in a narrow, low, northplunging synclinorium with a well defined horse-shoe closure facing south in Bonai Subdivision, Sundargarh district, Orissa. Detailed mapping carried out by the authors in the southern part of the belt (in Bonai) has thrown new light on the stratigraphic relations of these rocks. The group is designated here the Koira Group, is subdivided, on lithological grounds, into five formations.