Informatics Publishing Limited

T. Radhakrishna ¹, G. V. S. Poornachandra Rao ², J. G. Mitchell ³, A. S. Venkatesh ²

Affiliations
1 Centre for Earth Science Studies, Trivandrum 6950 10, IN
2 National Geophysical Research Institute, Hyderabad 500 007, IN
3 School of Physics, University of New Castle Upon Tyne, Ne 17 RU, GB

Abstract

Palaeomagnetic data on the basic dyke rocks of Palachal (Cannanore district) and Agali (Palghat district) regions of Kerala in the southwestern part of India are presented. Palachal dyke has obtained stable vectors of D and I at 200Oe and possesses a single thermally discrete component with blocking temperatures at the Curie temperature of magnetite, whereas the Agali dyke has shown unstable behaviour to the AF and thermal demagnetisation tests. The Palachal dyke possesses a southwest negative NRM remanence (D = 225.5°; 1 = 48.5°; K = 48.52; α 95 = 7.24) and a pole position (44°N; 135°E) which is closer to that of Gwalior Traps (1830 ± 200m.y.) or Group IV dykes of Proterozoic age. K-Ar ages of 1668 ± 31 m.y. and 1660 ± 25m.y. have been obtained for the Palachal dyke and it is compatible with the Palaeomagnetic results. The basic dyke activity jn the southwest is not solely related to the rifting of western continental margin of India as earlier suggested but is in part of Proterozoic age.

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R. K. Upadhyay ¹, S. Asokan ², A. S. Venkatesh ³

Affiliations
1 Natural Resources Division, Bengal Energy Limited, Kolkata - 700 071, IN
2 Minerals and Materials Division, Everest Industries Limited, Mumbai - 400 072, IN
3 Department of Applied Geology, Indian School of Mines, Dhanbad - 826 004, IN

Abstract

The eastern limb of horse shoe shaped "Bonai Synclinorium" in India hosts Banded Iron Formations (BIFs), consisting of major high grade iron deposits. Phosphorus (P) gets adsorbed in the iron ore by way of ion exchange mechanism of clay minerals and hydrated secondary iron oxide minerals. Its concentration is lesser in hard ores and blue dust types of ores, while the highest in case of lateritic ores. P content reduces with increase in iron (Fe) content in individual ore types. Along the eastern limb, phosphorus content gradually reduces from north to south direction. Since phosphorus is mainly associated with secondary lateritization process, its concentration is very high in top weathered profile and along the weaker zones.

Keywords

Bonai Synclinorium, Phosphorus, Lateritization, Iron Ore Deposits, Orissa.

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G. S. Yadav ¹, U. K. Pandey ², S. L. Aravind ³, P. K. Panchal ³, A. S. Venkatesh ⁴, P. R. Sahoo ⁴, A. K. Chaturvedi ², A. K. Rai ², P. S. Parihar ²

Affiliations
1 Atomic Minerals Directorate for Exploration and Research, Jamshedpur 831 002, IN
2 Atomic Minerals Directorate for Exploration and Research, Hyderabad 500 016, IN
3 Atomic Minerals Directorate for Exploration and Research, Jaipur 302 030, IN
4 Department of Applied Geology, Indian Institute of Technology (Indian School of Mines), Dhanbad 826 004, IN

Abstract

Uranium mineralization in Bichun area, Jaipur district, Rajasthan, India is hosted by albitites within the Banded Gneissic Complex (BGC). Detailed mineralogical and EPMA studies reveal the presence of davidite along with brannerite and uraninite. The U-Pb concordia upper intercept age of 933 ± 13 Ma and Pb-Pb isochron age of 930 ± 4 Ma, on pure davidite fractions indicate the timing of uranium mineralizing event to be ca. 930 Ma. The timing of uranium mineralization can be correlated with the Grenvillian orogeny (ca. 1000 Ma). The Sm-Nd model age (T_DM) of daviditeis varies from 1851 to 2200 Ma with ε_{Ndi(930 Ma)} ranging from -10.7 to -15.5 which shows that the Palaeoproterozoic rocks with crustal component (either within BGC or basement granite) are the source for uranium.

Keywords

Albitite Zone, Davidite, Geochronology, Orogeny, Uranium Mineralization.

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Ajay Kumar ¹, A. S. Venkatesh ², P. V. Ramesh Babu ³, S. Nayak ³

Affiliations
1 Atomic Minerals Directorate for Exploration and Research, Department of Atomic Energy, Jamshedpur-831002, IN
2 Atomic Minerals Directorate for Exploration and Research, Department of Applied Geology, Indian School of Mines, Dhanbad-826004, IN
3 Atomic Minerals Directorate for Exploration and Research, Hyderabad-500016, IN

Abstract

Petrographic and EPMA studies reveal the presence of discrete grains of uraninite and pyrite are being reported for the first time in quartz-pebble conglomerates from western margin of Bonai granite pluton, Sundargarh district, Orissa. Uraninite grains (2-3 μ in size) are subrounded to muffin shaped which show variation in UO₂ (63.86 to 71.73 wt %), ThO₂ (5.48 to 6.42 wt %) and RE₂O₃ (1.57 to 2.23 wt %). Pegmatitic source of uraninite is revealed by comparing UO₂, ThO₂, PbO, CaO content and ratios of UO₂/ThO₂ and CaO/ThO₂ in uraninites from pegmatite and other environments and areas. Subrounded to muffin shape of uraninite, their association with subrounded pyrite and heavies like zircon, tourmaline, chromite, monazite, magnetite and their comparable chemistry with well established quartz-pebble conglomerates of India and world are indicative of their detrital origin. Pyrite, minor chalcopyrite and rare galena are observed as sulphide phases in conglomerate. Variable shapes of pyrite, their low Co (up to 0.16 wt %) and Ni contents (up to 0.09 wt %) and Co/Ni ratio less than 1.0 (mean = 0.63) favours sedimentary/diagenetic origin.

Keywords

Quartz-Pebble Conglomerate(QPC), Uraninite, Pyrite, Bonai Granite Pluton (BGP), Orissa.

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