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

R. Dhana Raju ¹, R. N. Prasad ², D. D. Pande ², A. Panneer Selvam ¹, Mary K. Kumar ¹

Affiliations
1 Atomic Minerals Division, Department of Atomic Energy, Bangalore-560 072, IN
2 Atomic Minerals Division, Department of Atomic Energy, Hyderabad-500 016, IN

Abstract

This study shows δ³⁴S values for the study of co-existing baryte and galena, respectively, are in the ranges of +6.9 to 8.0% and -6.0 to - 9.8%0. Such narrow ranges make biogenic sedimentary source for sulphur less likely and suggest magmatic source. Sulphur isotope values indicate a hydrothermal system with a T of ∼440°C, pH 5±1 and Log f0₂ of -34 to -37.

Keywords

Economic Geology, Sulphur Isotopes, Baryte, Galena, Tamil Nadu.

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A. Panneer Selvam ¹, R. N. Prasad ², R. Dhana Raju ¹, R. M. Sinha ²

Affiliations
1 Atomic Minerals Division, Department of Atomic Energy, Bangalore-560072, IN
2 Atomic Minerals Division, Department of Atomic Energy, Hyderabad-500016, IN

Abstract

Metaluminous granitoids of the South Khasi batholith (SKB) in the West Khasi Hills district of Meghalaya define a Rb-Sr whole-rock isochron age of 757 ± 60 Ma, with (⁸⁷Sr/⁸⁶Sr) of 0.71069 ±0.00092. SKB and other granitoids of Meghalaya like Mylliem, Nongpoh and Kyrdem have many common features such as the presence of basic enclaves of hornblende gneiss and amphibolite, lateto post-tectonic nature, predominance of biotite amongst mafic silicates, overall metaluminous nature and high (⁸⁷Sr/⁸⁶Sr) of more than 0.709. All these indicate much similarity in the genesis of their melts due to partial melting of lower crustal rocks. The Rb-Sr isochron ages of SKB and other granitoids in Meghalaya point to a major tectonomagmatic activity during ca. 760-480 Ma, which is almost coeval with ca. 800-500 Ma Mid-Upper.Pan-African activity. The data, thus imply the possible imprint of the widespread Pan-African activity in northeastern India, besides southern India.

Keywords

South Khasi Batholith (Meghalaya), Rb-Sr Isochron Age, Geochronology, Pan-African Activity.

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