Delineation of Placer Deposits using DC resistivity, Induced Polarization and Radiometric methods along coastal Odisha, India

Coastal placer deposits of Odisha, India serve as a repository of heavy-minerals, which contains monazite. The mineral monazite consists of thorium and Rare Earth Element. As no geoelectric model of the area has been proposed, so dredge mining remains the only viable option for placer exploration. Our objective is to find out the placer prospective areas from the saline water saturated beach sands. In order to explore the area we conducted an integrated study comprising three geophysical techniques viz. DC resistivity, time domain induced polarization (IP) and radiometric method to get an idea of the lateral and vertical extension of the heavy mineral enriched placer deposits. The DC resistivity method can easily delineate the conductive zones which could be due to saline water saturated sand or clay or due to heavy mineral placers. The IP method can identify the chargeable heavy mineral placer deposits and saline water saturated clay. With the help of the radiometric method, the demarcation of the heavy mineral placer deposits can be done with ease. The 2D inverted model of DC data showed that the conductive zones were concentrated at shallow depths (10-15 m below the surface) and appeared on the surface in the form of black patches. The 2D inverted chargeability profile depicted some pockets in the shallow conductive zone with high chargeability values; most of the highly chargeable pockets corresponded to high gamma ray radiation count from the environmental survey meter. The zones (pockets) with high radiation counts from the survey meter confirmed the presence of heavy minerals. The mineralized zones had resistivity, chargeability values and survey meter readings in the range 0.1-1.1 Ωm, 20-30 mV/V and 4-9 µR/h respectively. The high conductivity, chargeability and radiation counts indicated the heavy mineral placer bearing area.