Journal of Geological Society of India (Online archive from Vol 1 to Vol 78)

P. K. Ramam ¹, P. Prakash ², P. F. Augustine ²

Affiliations
1 33/4 RT, Barkatpura, Hyderabad 500027, IN
2 Hyderabad 500027, IN

Abstract

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.

Full Text

   

P. Prakash ¹, E. V. R. Parthasaradhi ¹

Affiliations
1 Geological Survey of India, IN

Abstract

A study of aerial photographs taken before and immediately after the Great Assam Earthquake of 15th August 1950 revealed that the event had caused extensive landsliding in the northeastern India, including parts of catchments of Dihang and Subansiri rivers. Examination of the photographs of the same areas taken during 1959-60 and 1976-77 showed, that majority of the slopes that failed as a result of the earthquake, got stabilised to a large extent and some fresh landslides occurred during the period in a few areas.

Air-photo study shows that (i) the highly jointed nature of the Miri Quartzite has contributed to the maximum incidence of landslides in any particular lithological unit. (ii) The Main Boundary Fault and the system of faults parallel to it, in the Subansiri catchment have been reactivated during the Assam earthquake. (iii) In Dihang catchment, the MBF, and the Siang fracture have been reactivated.

In view of the possibility of fluid pressure exerted by impounding large quantities of water triggering off a major earthquake, it is suggested that construction of very large dams be avoided, even though the region has a very high hydel power potential.

Full Text

     

P. Prakash ¹, K. L. V. Ramana Rao ²

Affiliations
1 8-3-231/W/61. Srikrishna Nagar, Hyderabad-500 045, IN
2 Dept. of Geology, Andhra University, Visakhapatnam - 530 003, IN

Abstract

Bauxite cappings occur discontinuously, along a linear stretch amidst the Eastern Ghuts comprising khondalite and charnockite groups of rocks, in the States of Andhra Pradesh and Orissa. These cappings/deposits, by virtue of their proximity to the eastern coastline of India, are christened as the East Coast Bauxite deposits.

The East Coast Bauxites of Andhra Pradesh include the Anantagiri, Chintapalli, Gurtedu and Paderu groups of deposits. The Anantagiri group comprises Galikonda, Chittamgondi, Raktakonda and Kutuki deposits. The Chittamgondi bauxite deposit, charucterised by multi-directional slopes, is preserved in a sickle shaped synformal structure. Furthermore, the maximum thickness of bauxite, viz., 54 m, amongst the East Coast Bauxite deposits, investigated so far, has been recorded in it. As has already been established for other East Coast Bauxite deposits, the geomorphological setup and morphometry have played a pivotal role in the formation of the Chittamgondi bauxite deposit.

Keywords

Geomorphology, East Coast, Bauxite, Khondalite, Andhra Pradesh.

Full Text