Laterite-Bauxite of Paduvari Plateau, South Kanara, Karnataka State

The different litho-units of the weathering profile of Paduvan Plateau show clear gradation contacts and contain relics of nearly all the minerals which are native to the underlying granitic gneiss. Mineralogically, the latent profile is dominated by gibbsite with kaolinite compared to lithomarge and goethite-hematite in the ferruginous laterite horizons. There is evidence of development of gibbsite both by the direct alteration of feldspar of the precursor rock and by the desilication of kaolinite. Four stages of transformation represented by altered gneiss, lithomarge, laterite and aluminous laterite bauxite are maintained in the weathering profile. As compared with the basalt derived laterite profiles, the Paduvari occurrence is characterised by relatively strong depletion of soda and potash and enrichment of ferrides. The field, petrographic mineralogical and geochemical data provide enough evidence of formation of Paduvan laterite profile by the in-situ chemical weathering of the underlying granitic gneiss and the aluminous laterite-bauxite by the 'in-situ chemical reworking' of laterite.