Mineralogy and Geochemistry of Desur Clay Deposit Hosted Within the Peninsular Gneiss, Northern Part of the Dharwar Craton of South India

The clay deposit which is hosted within the Peninsular Gneisses at Desur in Belgaum District of Karnataka is underlain by partially weathered granitic gneiss and overlain by soil horizon. Infra-Red and major oxide composition of clay samples indicate that kaolinite is the dominant clay mineral with subordinate abundance of illite. Quartz, chlorite, muscovite and montmorillonite also occur, but in minor abundance as admixtures in these clays. Clays occur as non-linear horizontal bodies which do not support the hydrothermal process for their formation. While the observed gradation from top to bottom is soil, clays and a weathered zone with fragments of precursor rock and hard and compact gneiss, which essentially indicates in-situ development of the weathered or residual clay profile. Geochemical comparison of Desur clays with that of the host granitic gneiss reveals that SiO₂, Fe₂O₃ CaO, Na₂O and K₂O oxides were mobile, while Al₂O₃ was immobile during the process of weathering. Kaolinite rich clay deposit of Desur was formed by the residual weathering of precursor granitic gneiss under tropical to sub-tropical humid conditions.