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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Yamuna Singh ¹, K. D. P. Singh ¹, R. N. Prasad ¹

Affiliations
1 Atomic Minerals Directorate for Exploration and Research, Department of Atomic Energy, Begump et, Hyderabad - 5000 16, IN

Abstract

Whole-rock Rb-Sr isochron dating of pink potassic (av.5% K₂O) granite from Dharmawaram, Karimnagar district, Andhra Pradesh, defines an isochron corresponding to an age of 2237±46 Ma with initial ⁸⁷Sr/⁸⁶Sr ratio of 0.71052±0.00084. The data suggest possible emplacement of potassic granite of Dharmawaram during early Proterozoic at ca. 2237 Ma. Further, high initial ⁸⁷Sr/⁸⁶Sr isotopic ratio of granite also indicates involvement of silicic crustal material in its genesis.

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R. Dhana Raju ¹, R. N. Prasad ², D. D. Pandey ², A. V. Jeyagopal ², R. D. Deshmukh ¹

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

Abstract

Baryte at Vemula near to the southwestern margin of Cudapah Basin occurs as a vein-type deposit discordant to both the carbonate rocks of Vempalle formation and its intrusive dolerite. S-isotopic data on the baryte have a range of δ³⁴S_CDT between +16.2‰ and +23.3‰ whereas the coexisting chalcopyrite has a restricted range between +10.9‰ and +11.4‰. The average value of δ³⁴S of Vemula baryte (+20.8‰) differs much from that of magmatic rocks (0‰ to +2.5‰), metamorphic rocks (+3‰) and sediments of continental margins, platform areas and geosynclines (-12.5‰ -17,1‰), but is similar to that of sea water (+20‰) which appears to be the source for sulphur. The narrow range of δ³⁴S of baryte and chalcopyrite points to a uniform source with their sulphur possibly derived from sea water sulphate by bacteriogenic reduction.

Keywords

Economic Geology, Baryte, Sulphur Isotope, Cuddapah Basin, Andhra Pradesh.

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