Analysis of magnetic anomalies in relation to Placer deposits and basement configuration off Mirya bay, Central West coast of India

Abstract

The offshore ilmenite placers off Konkan, central west coast of India, have been surveyed by echosounding, shallow seismic profiling, magnetics, and seabed sampling. The magnetic data show two different types of anomalies: (1) N-S trending high amplitude long wavelength anomalies (250-350 nT, 240-420 m) extending 3 km west of a line joining Mirya head with the Bhagavati Port and (2) low amplitude short wavelength anomalies (100-120 nT, 200-300 m) located to the east in Mirya Bay. Magnetic modelling has been carried out for placer deposits, basement configuration, and basement relief. A first-order correlation between the short wavelength anomalies and the known heavy mineral concentrations is discernible; however, basement relief and/or intrabasement magnetization contrasts may also affect this. The high amplitude long wavelength anomalies may be due to dykes within the traps. The quantitative interpretation of the dyke anomalies indicates the magnetization contrast at depths of 50 and 100 m, respectively. The width varies from 150 to 200 m. The subbottom topography of the magnetic basement is shallow toward the coast and dips toward the inner shelf