High-Field Strength Elements Geochemistry of Granite and Co-genetic Pegmatites of the Kawadgaon Area, Bastar Craton, Central India

Abstract

A geochemical study on granite and co-genetic pegmatites of the Kawadgaon area, Bastar craton, Central India reveals varying levels of enrichments of high-field strength elements (HFSEs) in both. However, granite has much higher contents of U, Th, Y, Zr, and rare-earth elements (REEs), whereas co-genetic pegmatites reveal anomalously high Nb and Ta contents. The data indicates a preferential enrichment of REEs in granite (av. 198 ppm). The chondrite-normalised REE plots of granite and co-genetic pegmatites show strongly fractionated patterns. Strong fractionation between light REE (LREE) and heavy REE (HREE) is brought out by high (LREE/HREE)N, (La/Lu)N, and (La/Yb)N ratios in granite and co-genetic pegmatites. Among LREEs, a strong fractionation is displayed by very high (La/Sm)N ratio (av. 5.69) in granite. Marked negative Eu anomalies in studied felsic rocks are attributed to fractionation of plagioclase feldspar. High La/Sc ratio in granite and decrease in Hf/Zr ratio from granite to co-genetic pegmatites are apparent, which are coherent with their behaviour in the sequence of fractionated felsic rocks. A preponderance of Nb and Ta in co-genetic pegmatites is due to their formation from still more fractionated melt leading to higher concentrations of these elements owing to their increased diffusion consequent to enrichment of fluxing components such as B, P, F, H2O in the residual pegmatitic fluids. The fertile nature of the investigated felsic bodies of the Kawadgaon area for rare-metals is revealed by anomalous abundances of Nb and Ta in them. A study of HFSEs abundances in felsic bodies of the region will help in exploration of rare metals and rare earths.