RARE EARTH ELEMENT AND THORIUM ASSAYING IN PARTS OF THE EAST COAST, INDIA

The beach placer deposits along the Eastern Coastal region of India have an immense potential for extraction of heavy minerals. Minerals like ilmenite, rutile, garnet, zircon, monazite, sphene, sillimanite, etc. are very common in the region. This enrichment is dependent upon the geology of the hinterland rocks in the area of the coastal deposits. The Eastern Ghats mobile belt lying adjacent to the said coastal region is the main factor behind the heavy mineral enrichment. The typical rock types of this region are charnockite, khondalite and granite. The accessory minerals present in these rocks are the primary source of heavy minerals, to the beach placers. This indicates that the Eastern Ghats Mobile Belt is the source rocks of the beach placers along the eastern coastal region of the country. The coastal sedimentary processes play the primary role behind the sorting and deposition of the light and the heavy minerals. This sorting takes place mostly along the swash zone of the coast, and depends primarily on the coastal morphology of the area. Among the heavy minerals the presence of Monazite and Zircon indicates the presence of Rare Earth Elements along with the presence of Thorium and Uranium.

Sand samples collected from two different locations along the beach have been used to study the Rare Earth Element Concentration, present in the beach sands with the help of an ICPMS analysis. As compared to the crustal REE concentration, the beach sand shows about 88 times enrichment of LREE concentration, 138 times enrichment of MREE concentration and 85 times enrichment of HREE concentration. Radio-elemental analyses of these samples have also been undertaken with the help of a High Purity Germanium detector (HPGe). The result indicates a much higher enrichment of Thorium compared to Uranium, which infers the presence of higher concentration of Monazite than Zircon. Furthermore, the extent of metamictization in Monazites should be higher than Zircon. The comparison of the total REE (TREE) concentration with the Thorium concentration of the sample shows a positive correlation. Thus, prospecting of Thorium can be considered as a rapid field assay for estimating the concentration of REE in the area under study.