Vestiges of Khondalite in Some Bauxite Profiles, Visakhapatnam District, Andhra Pradesh

Vestiges of khondalite (garnet-sillimanite gneiss) occur sporadically in some bauxite profiles of Visakhapatnam district, Andhra Pradesh. Based on their mode of occurrence, the vestiges may be classified into (i) outcrop island, and (ii) sub-crop intercalation types. Neither of them has lateral nor downward persistence. Their occurrence within the residuum is by no means anomalous; instead, they are in conformity with the natural laws governing the processes of residual chemical weathering (RCW). Either the litho-textural and structural fabric of the vestige itself is resistant to RCW or the vestige may be circumscribed by a zone of impeded drainage that prevents thorough leaching locally. These vestiges are comparable to the kaolinised nepheline syenite pockets, within the bauxite residuum, of the well known Arkansas deposits in U.S.A., and the boulders of parent basic rock in the bauxite deposits of Sarawak.