The Fertile Granite at Allapatna, Mandya District, Karnataka : A Possible Parent to Rare Metal Pegmatites of Southern Karnataka

The Allapatna granite has been found to be a low-calcic (CaO-0.85%), peraluminous (A/C+N+K ratio = 1.04) and potassic type (K₂O=4.75%), enriched in Rb(362), Ga(25), Cs(3), Nb( 19), U(l3), Ta(18), Th(38), Pb(55) and strongly depleted in Ba(333). Such abundances together with low K/Rb ( 118.9), Ba/Rb (0.92) and Th/U (2.92), and high Rb/Sr (3.45) ratios than normal granite indicate their highly fractionated and fertile character and strongly suggests that the Li-Cs-Ta (LeT) rich rare metal bearing pegmatites of Marlagalla and nearby areas may have been derived from such a parental granitic magma.