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B. N. Srivastava ¹, V. K. Shrivastava ¹, V. S. C. Rao ¹, G. P. Vyas ¹, G. S. Mehta ²

Affiliations
1 Affiliation not given, IN
2 Medical College, Jabalpur, IN

Abstract

Abstract not Given.

Keywords

No Keywords given

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U. K. Pandey ¹, D. V. L. N. Sastry ¹, B. K. Pandey ¹, Madhuparna Roy ², T. P. S. Rawat ², Rajeeva Ranjan ³, V. K. Shrivastava ³

Affiliations
1 Atomic Mineral Directorate for Exploration and Research, Geochronology Lab., Begumpet, Hyderabad - 500 016, IN
2 Atomic Mineral Directorate for Exploration and Research, Northern region, New Delhi - 110 066, IN
3 Atomic Mineral Directorate for Exploration and Research, Central Region, Nagpur - 440 001, IN

Abstract

The Dargawan gabbros intrusive into the Moli Subgroup of Bijawar Group, yielded Rb-Sr whole rock isochron age of 1967 ± 140 Ma. Based on the oldest age from overlying Lower Vindhyan (1.6Ga) and the underlying youngest basement ages (2.2 Ga), the time range of Bijawar sedimentation may be assigned as 2.1-1.6 Ga (Paleoproterozoic). Sm-Nd Model ages (T_DM), obtained, for Dargawan gabbros, is c. 2876 - 3145 Ma. High initial ⁸⁷Sr/ ⁸⁶Sr ratio of 0.70451 (higher than the contemporary mantle) and negative ε_Ndi (at 1.9 Ga) value of -1.5 to -4.5, indicate assimilation of Archaean lower crustal component by the enriched mantle source magma at the time of gabbroic intrusion. The dolerite, from Damdama area, which is intrusive into the basement and overlying sediments of Chandrapur Group in the central Indian craton, yielded Rb-Sr internal isochron age of 1641 ± 120 Ma. The high initial ⁸⁷Sr/⁸⁶Sr ratio of 0.7098 and ε^Ndi value of -3.5 to -3.7 (at 1.6 Ga) is due to contamination of the mantle source magma with the overlying sediments. These dolerites have younger Sm-Nd Model ages (T_DM) than Dargawan gabbros as c. 2462 - 2675 Ma, which is similar to the age of the Sambalpur granite, from which probably sediments to this part of Chattisgarh basin are derived. Hence mixing of sediments with the Damdama dyke during its emplacement, gives rise to high initial ⁸⁷Sr/⁸⁶Sr and low initial ¹⁴³Nd/¹⁴⁴ ratios for these dykes. The c. 1600 Ma age indicates minimum age of onset of the sedimentation in the Chandrapur Group of Chattisgarh basin. Both the above mafic intrusions might have taken place in an intracratonic rift related (anorogenic) tectonic setting. This study is the first reliable age report on the onset of sedimentation in the Chandrapur Group. The total minimum time span of Chandrapur and Raipur Group may be 1.6 Ga to 1.0 Ga (Mesoproterozoic). The unconformably underlying Shingora Group of rocks of Chhattisgarh Supergroup thus indicates Paleoproterozoic age (older than 1.6 Ga). Most part of the recently classified Chattisgarh Supergroup and Bijawar- Vindhyan sequence are of Mesoproterozoic-Paleoproterozoic age and not of Neoproterozoic-Mesoproterozoic age as considered earlier. Petrographic study of basic dykes from Damdama area (eastern margin of Chattisgarh Supergroup) indicated presence of primary uranium mineral brannerite associated with goethite. This is the evidence of mafic intrusive providing geotherm and helping in scavenging the uranium from the surrounding and later alterations causing remobilisation and reconcentration of pre-existing uranium in host rocks as well as in mafic dyke itself otherwise mafic rocks are poor source of uranium and can not have primary uranium minerals initially. It can be concluded that mafic dykes have role in uranium mineralisation although indirectly.

Keywords

Geochronology, Age of Sedimentation, Uranium Mineralisation, Northern and Central Indian Cratons.

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D. K. Sinha ¹, Shekhar Gupta ¹, K. Nautiyal ¹, V. R. Akhila ¹, V. K. Shrivastava ¹, A. K. Padhi ¹, M. B. Verma ¹

Affiliations
1 Atomic Minerals Directorate for Exploration and Research, Hyderabad 500 016, IN

Abstract

Recent exploration efforts in Kudada-Turamdih area has brought to light, for the first time, serpentinizedperidotite- hosted uranium mineralization (up to 0.188% U₃O₈) of polymetallic nature (U–Cr—Ni–Mo–REE–Fe–Mg) in the domain of Singhbhum Shear Zone (SSZ). The peridotite has been emplaced into the Iron Ore Group (IOG) and represents late phase activity in the IOG. Exploratory drilling has established substantial lateral (600 m) and downdip (1000 m) continuity of the mineralization. Subhedral to anhedral disseminated uraninite grains (10–600 μm) with cell dimensions of 5.4498 to 5.4650 Å suggest crystallization in meso to hypo-thermal range (300– 500°C). Magnetite, chromite, molybdenite, cobaltite, nickeline, vaesite, cerussite, pyrite and chalcopyrite have also been identified in the REE enriched (Av. 1457 ppm) uraniferous peridotite. Presence of MgO (18–28%), Cr (295–3165 ppm), Ni (222–9530 ppm), Au (11–30 ppb), Pt (47–95 ppb) and As (15–755 ppm) suggests komatiitic parentage of host rock. Discovery of polymetallic mineralization in serpentinized peridotite, a hitherto unknown geological environment, opens up scope for further research and enhancement of uranium resources in the SSZ.

Keywords

Polymetallic, Mineralization, Serpentinized Peridotite, Singhbhum Shear Zone, Uranium.

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