Informatics Publishing Limited

C. N. Rao ¹, K. Srinivasan ², Amit Roychowdhuri ³

Affiliations
1 Department of Geology and Geophysics, I.I.T., Kharagpur, IN
2 Knoxville, Tenesse, US
3 Oil and Natural Gas Commission, Agartala, IN

Abstract

Phyllites from the Cumbum Formation are exclusively made up of 2 M polymorph of illite. The 2 M polymorph, the most stable phase in the temperature range of 200-300°C, is comidered to be due to its heritage from the source area, having been derived from high-grade metamorphic Eastern Ghat and Dharwarian provenances. The Illite Crystallinity Jndex shows progressive improvement with depth as well as nearness to the Pb-Zn mineralised zone. The crystallinity Index averaging 0.4°2θ is consistent with anchizone of metamorphism. The progressive increase in the crystallinity and size with depth and in the proximity of the mineralized zone suggest that the mineral suffered post-depositional recrystallisation effected by the depth of burial, uplift and folding in the eastern margin of the Cuddapah basin and subsequent hydrothermal activity concomitant with the Pb-Zn mineralisation at Bandlamotu.

Keywords

Illite, Cumbum Formation, Cuddapah, Andhra Pradesh.

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