Mineralization of galena in an aplitic albitite from carbonatite complex of Tiruppattur, Tamil Nadu, India

Abstract

A 10cmx10cmx10cm galena and associate albite from an aplitic albitite vein cutting across a skarn rock, near Garigaipalli village, in the carbonatite complex of Tiruppattur, Tamil Nadu, India were collected and studied for systematic variations in chemical composition from the central portions to outer peripheries. The compositions of albite grains show a linear trend of crystallizations from Ne 81 Ks 0 Qz 29 to Ne 48 Ks 0 Qz 52. Co-variation diagrams of Pb-S, Na 2 O-PbO, (Ca+Na+K)-(Si+Ti+Al +3) and (Ca+Na+K)-S show sequences of crystallizations of albite and galena with miscibility gaps between them. These components in albite and galena negatively vary in opposite directions in these diagrams. Galena mineralization might have been initiated just after immiscible separation of sulphide phases from silicate phases but prior to initial crystallization of albite Tf3 at higher temperature. During the course of crystal growths under the influence of crystal field stabilization forces, mixed pattern of arrangement of individual early formed and late formed microcrystals together was taken place. Incorporations of volatiles into the voids of subsolidus crystal originated pits of galena and albite, play critical role on the increase of viscosity of residual magma and it depends upon the rate of cooling. Progressive depletion of Al, Na, K and S contents in sequentially crystallized albite and galena indicates that residual magma was enriched with these constituents and Si. After this co-magmatic differentiation the residual magma fractionated into silica oversaturated granitic magma as end product.