Use of shallow seismic surveys in the exploration of nearshore placers off Maharashtra coast, India

Abstract

Shallow seismic surveys were carried out for 520 lkm in 3 bays viz., Jaigad, Ambwah and Varwada along the Maharashtra coast in the western part of India. In total, 53 traverses were run across the shelf perpendicular to the coast upto about 20m were depth. These surveys water used for the first time in this country by the authors to determine (1) the lateral continuity of the placers below the clay, (2) the vertical thickness of placer sand and to use the same for the calculation of the inferred reserves and (3) to understand the nature and structure of the basement which is likely to throw some light upon the important and controversial subject to lake the evolution of the west coast of India. The continuity of the sand reflector below clay has been traced upto -17 to -18 m where a sudden fall in their level in almost in all the traverses has brought an end to that. The sand isopachs indicate on an average of 4 m thickness which has been, in place of borehole confirmation, directly used to evaluate the inferred ore reserves of ilmenite-magnetite placers. The continuity of the placer sand below the clay even upto -17 m and the 4 m thickness of the sand as deduced from the sand isopachs have boosted the inferred reserve potential from 5.27 to nearly 21 million tons