THE DAITARI-TOMKA BASIN - ITS STRUCTURAL AND STRATIGRAPHIC EVOLUTION AND GENESIS OF ASSOCIATED IRON ORES

摘要

The Daitari-Tomka Range, Orissa forms a palaeo-proterozoic basin of Iron Formation and iron ores and attracted attention in the sixties of the last century because of its proximity to Paradip port for exporting iron ores. The basin is isoclinally and coaxially folded with different axial planar orientations. High axial plunge and synchronous cross folding In each episode of folding have been the important features. The sediments, with maximum thickness at Daitari-Baliparbat sector, thins down to both sides. In the east it gets terminated off Tungaisuni folding back at Tomka east while in the other side the BIF continues up to south-west of Harichandanpur when it has thinned down to the status of non-entity and the basin closes. The SGC is at the base and these sediments were deposited to its south peripherally and the sequence is divided into lower metaperites, BIF with its variations and upper metapelites. This sequence is overlain by gritty quartzite of Dhanjori age disconformably and also angular unconformabiy in the region, while to the west of Keonjhar town (beyond this area) it rests on eroded SGC non-conformably. A host of ultramafites intrude the sequence, the last but one being cr-ultra basic respectively of which interrelationship with BJF-2 sequence is not very clear although indirect evidence suggests its intrusion. The other two are folded along with the sediments. Pyroxenite is the last intrusion. In north Orissa, north of Sukinda Thrust, three BIF sequences (1,2,3) chronologically exist and - Daitari-Tomka Range is considered as intermediate because of clear stratigraphic, structural and metamorphic character-differenes between them. Remanent magnetic studies were made to understand the genetic characters of the Daitari iron Ore bodies. The small ore bodies are intra-BIF while Daitari deposit is infra-BIF. All of them have undergone enrichment. The dolerites of the Daitari basin seem to be atleast an older phase of Newer dolerites those criss-cross the SGC besides intruding into the Dhanjori sequence. Newer dolcrite is older to the Kolhans but younger to Dhanjori quartzite.