Early Proterozoic Rare Metal and Tin Pegmatites near Kawadgaon, Bastar, M.P.: An Example of Vertical Pegmatite Zonation

Abstract The paper reports, for the first time, the occurrences of several almost non-metasomatized rare metal zoned pegmatites of small- to medium-dimensions near Kawadgaon in the Bastar. Columbite- tantalite and beryl occur mainly close to quartz core. Beryl is Ubiquitous. Replacement units are almost absent in the Be and Be-Nb-Ta pegmatites whereas, they are prominent in the cassiterite pegmatites. Spatial distribution of rare metal and tin pegmatites of the study area suggests a distinct vertical zonation. At lower level, Be and Be-Nb-Ta-minetalization took place whereas, at higher level, albitization and Sn-mineralization are observed. Tin seems to have behaved as incompatible element at lower level, where high K/Na ratios and reducing conditions attended the crystallization. With the fractionation of substantial amounts of microcline perthite in the Nb-Ta pegmatites at lower level, Na and volatiles have increased and enriched Sn to form cassiterite in association with albite in the upper level pegmatites. Non-albitized pegmatites do not contain any tin mineralization, which is suggestive of Na-Sn geochemical affinity. Systematic mining of pegmatites and their gravels will yield considerable quantities of cassiterite, besides columbite-tantalite and beryl.