Sources of rare earths and prospects for a viable REE deposit in river sediments of Kerala, southwest India

Studies on rare earth elements (REEs) of river sedi-ments from Kerala, India indicate that the average to-tal REE (Sigma REE) of clay and silt-sized fractions is much higher than in Post-Archaean average Australian Shale (PAAS). Peak high Sigma REE for the clay fraction is found in the rivers of central Kerala and, for the silt fraction, it is in south and central Kerala. Sigma REE shows a mod-erate to strong correlation with Mn and P and, no cor-relation with Al, Fe and Ti in both size fractions. Sigma REE also shows no correlation with heavy metals in the clay fraction but a strong correlation in silt fraction. PAAS-normalized REE shows MREE-enrichment in almost all the samples. Further, LREE-enriched and HREE-depleted REE patterns are characteristic of sediments from south and central Kerala, and HREE-enriched or flat REE patterns are characteristic of sediments fromnorth Kerala. Weak positive or weak negative Ce anomalies are characteristic of the sediments. The Eu anomaly is negative in a few silt fractions from south Kerala and positive in all other sediments. Sm/Nd ratiosare high in the clay fraction and decrease with increasing Sigma REE for the sediments of central Kerala. REE enrichment and REE patterns are related to the felsic component and heavy mineral content in the sediments of south Kerala, adsorbed REE associated with the weathering products of laterites in the sediments of central Kerala, and the dominance of mafic component in the sediments of north Kerala. The river sediments of central Kerala may serve as a viable REE deposit because of their high REE content, inexpensive mining, easy recovery and extraction of REE. Only 21 out of 41 rivers of Kerala were analysed in this study. Detailed exploration in other rivers may expand and confirm the potential REE deposits and their economic viabi-lity. This REE deposit is different from the placer sand deposits on the beaches of south Kerala.