Abstract

Scheelite mineralization in the granulite-facies supracrustal sequences of the Kerala Khondalite Belt, southern India is reported. The supracrustal sequences where the mineralization is found comprise granulite-grade metasediments which underwent metamorphism at ~550 Ma. The mineralization is assumed to have formed by late-stage metasomatism that overprinted the regional metamorphism of the country rock (garnet-biotite gneiss) and occurs along a quartz vein that intrudes the regional foliation. The paragenetic data from the vein demonstrate unambiguously a separate cycle of hydrothermal activity, resulting in metasomatism and mineralization. Scheelite is found in both the altered host rock along the foliation plane and in the quartz vein. Fluid inclusions preserved in the vein suggest that the mineralizing fluids were saline-aqueous in composition, while those in the country rocks were redominantly CO2-rich. The mineral chemistry and bulk-rock chemical composition of the mineralized domain reveal the unusual enrichment of Ca in the mineralised zone with the depletion of K. We propose that fluid discharging from a crystallizing deep-seated magma, mixing with deep circulating Ca-bearing palaeo-groundwater gave rise to the deposition of scheelite. The scheelite mineralization and the quartz vein emplacement occurred after the Pan-African regional metamorphism.

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