EXPLORATION PRACTICES FOR EAST COAST BAUXITES

R. KUMARDepartment of Geology

Andhra UniversityEmail:kumartecgeo.au@gmail.com

Abstract

EAST COAST BAUXITE DEPOSITS----------------------------------------------INTRODUCTION

The bauxite deposits of Andhra Pradesh and Orissa of India are termed as East Coast Bauxite by their virtue proximity to the eastern coast of India. Even though, the bauxite deposits of Andhra Pradesh were explored by the GSI and MECL, mining could not take place so far due to environmental and social concerns. Whereas in Orissa, NALCO is operating the Pachpatmalli bauxite deposit which is located at Koraput district, Orissa between North latitudes 18˚48΄ to 18˚54΄ and East latitudes 82˚57΄ to 83˚04΄.

Bauxite deposits of Eastern Ghats region have come to limelight during 1974 with the efforts of G.S.I and later detailed exploration programme taken up by MECL and other private aluminium companies showed that these East Coast Bauxite deposits are the richest and largest deposits in the world. Panchpatmli Bauxite mines is the captive mines of M/S NALCO is the largest deposit of Asia with a reserve of 310 mill. tonnes started its production since 1986 and is able to feed its 1.6MTPY alumina refinery successfully since it became operational and will suffice more than 30yrs from now.

The important deposits of Bauxite which are associated with the Eastern Ghat super group of rocks form the main component of the East Coast Bauxite deposits. These deposits occur within the 400 kms corridor with almost similar physical and chemical properties and close to the coast. The deposits are of lateritic type and owe their origin to in-situ chemical weathering of Khondalites and Charnockite, and more specifically Khondalites (Garnet-Sillimanite-Graphite gnisses and schists). The major Bauxite deposits of Orissa and Andhra Pradesh occur as a very gently undulating blankets, capping the parent rock on plateau tops in this unique Bauxite province and occur at elevations of 900-1400 mtrs above MSL. Bauxitisation is more pronounced in the case of Khondalites.

A generalized profile of East Coast Bauxite deposits is as follows:-----------------------------------------------------------------------------: SoilLateriteAluminousLaterite/BauxiteLithomarge/KaolineUnaltered Khondalite

-----------------------------------------Mineralogically, the bauxite column shows the presence of relics of feldspar, quartz etc. Neoformed minerals include gibbsite, kaolinite, goethite, hematite and traces of anatase.

The mineralogy of different zones studied in representative pit shows the association of major mineral constituents like Gibbsite, Goethite, Hematite, Kaolinite, Limonite and quartz. Gibbsite (AL 2O3,3H2O) is the most abundant mineral followed by Hematite and Goethite in the bauxite zone.

All of the studies reflect a complex alteration process responsible for the development of Pachpatmalli bauxite. Development of neogene minerals under different condition gives an idea of bauxite formation.

Distribution of ECB-------------------------The bauxite deposit in Pachpatmalli area developed in-situ cover khondalite parent rock, preserving some of the primary structures with an age Paleocene to Eocene.

Large deposits (1600million tonnes) of bauxite occur as thick capping over certain hills of Eastern Ghats in the states of Andhra Pradesh and Orissa. The bauxite bearing hills form a linear belt of 400kms in length and 30kms in width. The ECB comprises about 20 major group of deposits aligned in NE-SW direction. The southern part is stretched into Vishakhapatnam district of Andhra Pradesh whereas northern part falls in the Koraput and Kalahandi districts of Orissa.

Bauxite caps the Gandhamardan plateau over Khondalite on the border of Bolangir-Sambalpur districts.

The paper deals with the exploration methods to be deployed for Bauxite deposits, in particular to assess the quality and quantity to meet the refinery requirements.s