Genesis of cordierite-gedrite-cummingtonite rocks of the northern portion of the khetri Copper Belt, Rajasthan, India

Abstract

The cordierite-gedrite-cummingtonite rocks occur in the zone of sulphide mineralization. Field and petrographic evidences suggest formation of these rocks from the chlorite ± garnet schists which are associated with them. Time relations between crystallization and deformation, as evident by textural relations, suggest that this transformation constitutes a progressive sequence in time during prograde metamorphism in the area. Bulk chemical compositions of the cordierite-gedrite-cummingtonite rocks plot in the compositional range of the chlorite schists in the AKF, ACF and AFM diagrams. The AFM diagram shows a discontinuity in the topology as revealed by the intersection of the coexisting garnet-chlorite join with the three-phase field of cordierite-gedrite-garnet, suggesting the reaction: Al-chlorite+quartz (±garnet)↔ gedrite+cordierite+H₂O. The reaction took place under conditions of P_H2 < P_s, brought about by dilution of pore fluid by B, Cl, F, S, etc., which reduce the activity of water.