Implications of Magnetic Properties in the Concentration and Distribution of REEs in Beach Placer Monazites: A Case Study from Chhatrapur Coast, Odisha

Abstract

The concentration of monazite, a rare earth and thorium phosphate, in the heavy mineral-bearing sands of Chhatrapur coast varies from 0.09 to 0.16%. Under the microscope, monazite displays color variation from colorless to various shades of yellow, green and brown. The color variation is further reflected in the chemistry of individual grains. Such monazites of distinct colors and different chemistry also show variation in their paramagnetic properties. Representative detrital monazites separated under varied magnetic field strength were analysed for their rare earth elements, Th and U content. The electron probe micro analysis (EPMA) data indicate that monazites separated under low magnetic field strength (separated at 0.80 amps) are characterized by their higher Nd, Sm, HREE, Y and U as well as low Th content, whereas those separated at 1.10 amps contain low Nd, Sm, HREE with negligible Y and U content as well as higher Th content. The wider variation in the concentration of different rare earths in varied magnetic field strength is a function of varied magnetic susceptibility of individual elements. Hence, the physical method for separation of monazite using magnetic properties may facilitate to segregate the monazites of a particular chemical composition with respect to their constituent elements like U, Th and rare earths based on their magnetic properties.