Magnetic anomalies and their possible relation with heavy mineral placers and basement configuration in Mirya bay, Konkan coast, Maharashtra, India

Abstract

The offshore ilmenite placers off the Konkan coast have been explored in detail by echosounding, shallow seismic profiling and magnetic measurements followed by extensive sea bed sampling. The magnetic data show two different types of anomalies: (1) N-S trending high amplitude and long wavelength anomalies (250-350 nT, about 500-700 m) approximately on a line joining the Mirya Head with the Bhagvati Fort, Maharashtra, India and extending 3 km offshore, and (2) low amplitude and medium to short wavelength anomalies (100-120 nT, about 100 m) distributed in a zone 3 km seaward of the shoreline. The high amplitude long wavelength anomalies may be due to structures (dykes) within the Deccan Traps. An attempt has been made to correlate the magnetic patterns with known offshore heavy mineral placers in Mirya Bay. The low amplitude and medium to short wavelength anomalies may be correlated with the known heavy magnetic mineral concentrations in the bay although other effects cannot be ruled out. From the quantitative studies of the anomalies, the depth to the top of dykes is 50 m and 100 m in nearshore and offshore areas respectively, while the width varies from 150-250 m. The average depth to the magnetic basement is about 50 m.