Petrography and Geochemistry Study of Bauxite in the part of Kollimalai in Namakkal District, Tamil Nadu

SanthaKumar.K, Aravindan.S, Bharathiraja.S

Abstract: Bauxite is a rock consisting mainly of aluminum hydroxide minerals; it is the principal source of alumina (A1₂O₃) from which aluminum metal is smelted by electrolytic process. Bauxite occurs in Kolli hill along the Eastern Ghat range of Tamil Nadu, Which essentially consists of the charnockite and the associated rocks of the Achaean age. It is formed due to residual weathering and lateritization of Archean charnockites. In the Study area Bauxite is soft, whitish red to brown aluminum ore mineral mainly consist of hydrous aluminum oxides and aluminum hydroxides and laterites are mostly found in humid tropic climatic condition due to intense weathering of Host rock. Most authors agree that bauxite forms by weathering under conditions favorable for the retention of alumina and the leaching of other constituents from the host rock. From the above literature review aim of the present work is to study occurrence of bauxite in Kolli hills in Namakal District of Tamil Nadu. Objectives are to study ore petrography of Bauxite and XRF study to get weight percentage of oxide ores. In the field observation a sharp contact between brownish red laterite at the top followed by pinkish white Gibbsite as Bauxite ore at the bottom further underlined by lithiomorphs as basement weathering. From Petrographic study, it is possible to identify the constitute of Gibbsite occurrence with pale brown colour with weak pleochroism and moderate relief as main Aluminous ore mineral and Goethite with opaque lusture, whitish blue colour with imperfect cleavage and ubiquitous due to residual weathering of above aluminous ore from Charnockite basement. Microscopic study also shows the brownish yellow colour, Oolitic structure and weak pleochroism for Diaspore ore. Deep brown colour and opaque luster without any structure can be identified as pisolitic Cliachite. It is characterized by very high Fe₂O₃ constitute of 83% by weight, low Al₂O₃ of 14 % & 0.36 % of TiO₂ portrays it as Iron rich laterite at Selurnadu (Table.1, Fig.7). It is also characterized by medium Al₂O₃ of 39.67 weight %, medium high Fe₂O₃ concentration of 55.32 % & 1.61 % of TiO₂ by weight conveys it as a medium grade bauxite at Thinanur. Low Al₂O₃ weight % of 25.73, high Fe₂O₃ concentration of 71.58 % & 0.23 % of TiO₂ by weight indicate it as medium low grade bauxite (aluminous laterite) at Ariyurnadu. Above geochemistry reveals the site specific ore percentage of Bauxite within study area kolli malai.