The Bauxite Deposits of Anantagiri, Visakhapatnam District, Andhra Pradesh

Bauxite forms cappings at altitudes varying from 1090 to 1445 m above mean sea level, over the garnet-sillimanite gneisses near Anantagiri in Visakhapatnam district, Andhra Pradesh. Major cappings occur on Galikonda, Raktakonda, Katuki and Chittamgondi hills while those near Kottavalasa are relatively small. Bauxite is either light to dark brown or pink in colour and moderately hard with crystalline gibbsite occuring in varying proportions. The average thickness of bauxite in the various cappings may range between 3 and 15 m, while the maximum thickness encountered is about 50 m on Galikonda. A typical profile of the bauxite residuum in the area consists of a lateritic bauxite underlain by partially lateritised khondalitic gneiss or lithomarge followed by kaolinised and unaltered khondalitic gneiss. These bauxites are low in silica and titania and relatively high in iron oxide when compared to those derived from the Deccan basalts. The development of bauxite over the sillimanite rich gneisses, relict foliation, pseudomorphs of gibbsite after sillimanite, garnet and felspar, and the unaltered partings of the bed rock within the bauxite residuum, reveal that these bauxites' are formed from tbe in situ transformation of the subjacent garnet-sillimanite gneiss (khondalite). While the lithology and physical properties of these gneisses are congenial for lateritisation/bauxitisation on a regional scale, the preservation of some of the cappings with remarkable thickness may be attributed to a favourable structural setting. It is surmised that these bauxites are of post Mio-Pliocene age.