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

D. Bhattacharya ¹, Madhuparna Roy ¹, G. B. Joshi ¹

Affiliations
1 Atomic Minerals Directorate for Exploration and Research, New Delhi-11 0066, IN

Abstract

Field observations, petromineralogical and geochemical studies on the locks of Jhirgadanpdi pluton indicate three phases of igneous activity, compositionally ranging from gianodiorite, Quartz-Monzonite to granite. The wide spread intermediate phase of this suite shows anomalous concentration of U, Ce and Th as compared to average granite and enrichment of K, Rb, Ba relative to Zr, Nb and Y. The radioactive minerals identified are thorite, uranothorite, allanite monazite and samaiskite Molybdenite and chalcopyite are the other are minerals Presence of REE (1 are earth element) minerals, distibution pattern of LIL (large Ion lithophile) elements, various elemental ratios and increasing metaluminous tendency indicate moderate degree of differentiation Petromineralogical study of rocks suggests partial melting of a magic source of lower crustal rocks Geochemical data suggests that the granitic rocks of the three phases are comagmatic. Available age data together with tectonic considerations indicate that the magmatic activity is relaled to the development of Mahakoshal greenstone belt which might have culminated with the emplacement of Post-Tectonic Jhirgadandi sulte (∼ 1800 Ma), possibly under the influence of a mantle plume.

Keywords

Jhirgadandi Granite Post-Tectonic, Mantle Plume Radloactive Minerals Sonbhadra District, Uttar Pradesh

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D. Bhattacharya ¹, G. B. Joshi ¹, G. S. Sharma ², D. B. Sen ³

Affiliations
1 Atomic Minerals Directorate for Exploration and Research, New Delhi-110066, IN
2 Atomic Minerals Directorate for Exploration and Research, Jaipur -302030, IN
3 Atomic Minerals Directorate for Exploration and Research, 313/4, Sector-56, Rail Vihar, Gurgaon, Haryana, IN

Abstract

Surface indications of uranium mineralisation associated with ferruginised brecciated rocks is traceable, intermittently, over a strike length of 25 km, exposed along the Jamual -Markundi Fault (JMF), at the tectonic contact of Neo- to Meso-Proterozoic Vindhyan Supergroup and Paleo-Proterozoic Mahakoshal Group between Gurdah and Mohariya, Sonbhadra and Sidhi districts of U.P. and M.P. respectively. Preliminary investigations reveal uranium (U₃O_g) content upto 610 ppm with little or no ThO₂. Uranium occurs in adsorbed state in the ferruginised groundmass of brecciated rock and probably related to hydrothermal activity. This is the first reported uranium occurrence from this unconformity related geological set up in the Son valley.

Keywords

Uranium mineralisation, Unconformity, Jamual-Markundi fault, Son-valley, U.P., M.P.

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T. P. S. Rawat ¹, G. B. Joshi ¹, Bhaskar Basu ¹, Nurul Absar ¹

Affiliations
1 Atomic Minerals Directorate for Exploration and Research, R.K. Puram, New Delhi -110 066, IN

Abstract

Black shale type uranium deposits, though of low grade (<0.001 to 0.05% U₃O₈), contain large uranium resources because of their immense volume. The Neoproterozoic-Cambrian Krol-Tal Himalayan sequence covering a cumulative area of about 1000 sq km in five different synclinal basins from Sirmour district, Himachal Pradesh in the west to Nainital district, Uttar Pradesh in east contain such black shale horizons. The uranium mineralisation found in black shale in the Nigalidhar syncline of Himachal Pradesh and its implication of being an indicator for search of such uranium deposits in Himalayas is discussed.

Keywords

Uranium, Black Shale, Proterozoic, Tal Group, Himachal Pradesh.

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D. Bhattacharyya ¹, G. B. Joshi ², Rakesh Sharma ³

Affiliations
1 Atomic Minerals Directorate for Exploration and Research, Bangalore, 560 072, IN
2 Atomic Minerals Directorate for Exploration and Research, Shillong – 793 011, IN
3 Atomic Minerals Directorate for Exploration and Research, Hyderabad – 560 016, IN

Abstract

Several small lensoidal bodies of felsic volcanics are exposed in a curvilinear pattern within the brecciated granitoids of Bundelkhand Gneissic Complex (BGC) at Mohar. Sub-surface data reveals extensive presence of these felsic volcanics below the sediment of Vindhyan Supergroup. It occurs like a sheet with thickness varying from 12 m to 134 m. Its lateral extent has been traced upto 4.8 km. Multiple flows of felsic magma are identified based on colour, granularity, cross cutting relations and cyclic distribution of multiple vesicular bands along the entire thickness of felsic magma. The felsic rock contains upto 13.21% K₂O. Chemical composition of these felsic volcanics varies across the column. Petrographically and chemically all these felsic volcanics are identified as rhyolite or rhyolite tuff.

Significant uranium mineralisation of 0.0165% eU₃O₈ average grade has been intercepted for 11.10 m thick with <0.005% ThO₂ within the felsic rock. Radiometric assay of a mineralised intercept (15 cm length) has revealed up to 0.15% U₃O₈ with disequilibrium in favour of parent. Uranium occurs as disseminated grains of coffinite - (Y) associated with pyrite, chalcopyrite, galena, molybdenite, hematite, fluorite, anglesite and cerrusite. Mineral assemblage and mode of occurrence of the uranium and other minerals in the host rock indicates its hydrothermal nature. This is the first reported uranium occurrence from the volcanogenic environment of Bundelkhand.

Keywords

Uranium Mineralisation, Felsic Volcanism, Mohar, Madhya Pradesh.

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