STRATIGRAPHIC SUCCESSION OF PRECAMBRIAN OF SINGHBHUM - EVIDENCE FROM QUARTZ PEBBLE CONGLOMERATE

Though the stratigraphic succession in the Precambrian of Singbhum-Ori ssa region of the Indian shield given by Saha et al. is widely accepte d, there are several contentious issues which have been hotly debated over the years. The occurrence of uraninite and pyrite bearing quartz- pebble conglomerate at the base of Iron Ore Group (IOG) as well as the Dhanjori Group has indicated the necessity for a revision in the stra tigraphic succession in view of the temporal significance of such cong lomerate the world over. The conglomerate contains a significant popul ation of zircon, chromite and shows a typical minor and trace element composition. The zircon has morphometric properties similar to those f ound in several members of the Singhbhum Granite Complex. The presence of detrital chromite and high Cr content indicate the occurrence of o lder mafics/ultramafics in the provenance along-with the Singhbhum Gra nite Complex. It is suggested that some mafic and ultramafic members p resently grouped within the IOG may represent such ''older greenstones ''. The IOG as well as the Dhanjori Group with basal QPC horizon lie o ver a basement of Singhbhum Granite-Greenstone Complex. From available evidences it is surmised that both IOG sensu stricto (the BIF sequenc e and associated ferruginous cherts, greywackes and acid-intermediate volcanics) and the Dhanjori Group represent late Archaean (2500-3000 M a) supracrustals and hence are nearly coeval. The Singhbhum Group nort h of the shear zone represents early Proterozoic supracrustals.