Geological and Geophysical Exploration for Offshore Ilmenite Placers off the Konkan Coast, Maharashtra, India

Abstract

Abstract The occurrence of heavy mineral placers on the Indian coasts is known but no systematic attempt has so far been made to explore their offshore extension. The Institute carried out detailed offshore surveys (Sextants and microwave position fixing system) of a 130 km long strip along the Konkan Coast (1889 1km echo sounding, 895 lkm of shallow seismic and 1228 lkm of magnetic followed by 1117 grab and 66 piston-gravity core samples). The coastal area is marked by 13 actuate bays and tidal inlets. The onshore sediments of these bays contain heavy mineral placers with in most cases extend to offshore also. The seabed in most of the bays is marked by even topography and the near shore sand covered areas are marked by steep gradient and the offshore clay covered areas by gentle gradients. The seabed in the bays down to a water depth of 9 to 12 m is largely covered by sand beyond which the sands are covered by clays. The surgical sands in these bays cover an area of 96 km2 and contain up to 91 per cent heavy minerals and 64 per cent of limonite. The dual frequency echograms, seismic profiles and short cores confirm the extension of the heavy mineral rich sands below the clays. The thickness of the heavy mineral rich sands ranges from 2 to 10 m and these cover total area of 436 km2 The magnetic surveys in this area indicate that the magnetic picture is largely related to the basement configuration and structural trends over which are superimposed the anomalies due to heavy mineral placers. The high frequency and low amp11tude and short wave length anomalies are perhaps due to heavy mineral placers. The offshore reserves and limonite are estimated to be about 4 million tons whereas estimates based on the 2 to 10 m thickness and spread of limonite bearing sands over an area of 436 km2, total reserves appears to be very large. The extensive onshore and offshore deposits offer encouraging possibilities for future integrated development. Introduction The occurrences of heavy mineral placers usually called "black sands" are known from many localities along the Indian Coast. The onshore placers along the west coast largely comprise high grade beach and low grade dune sands. The placers along the SW coast i.e., Kerala contain ilmenite, zircon, rutile, monazite and sillimanite and extent from Cape Comorin to Quilon. Further north on the west coast, onshore placers with varying proportions of ilmenite and magnetite and minor amounts of zircon and garnet have been reported from Konkan Coast, Maharashtra2 On the east coast, heavy mineral placers contain ilmenite, magnetite, monazite and garnet are reported from Tinnavelli, Ramnad and Tanjore in Tamilnadu3, Visakhapatnam, Yarda, Waltair and Bhimunipatnam in Andhra Pradesh4, Ganjam, Cuttack and Wheeler island off the mouth of Brahman river in Orissa5. The onshore reserves of limonite in India are estimated to be about 138 million tons7. The present production (1979) of heavy minerals from the beach sands of Kerala and Tamil Nadu Coast is about 0.165 million tons7.