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

Ajay Kumar ¹, S. N. S. Birua ¹, Dheeraj Pande ¹, A. R. Nath ¹, P. V. Ramesh Babu ¹, S. A. Pandit ¹

Affiliations
1 Atomic Minerals Directorate for Exploration and Research, Department of Atomic Energy, Khasmahal, Jamshedpur - 831 002, IN

Abstract

Several radioactive quartz-pebble conglomerate (QPC) occurrences at the western margin of Archaean Bonai granite and overlying Iron Ore Group (IOG) rocks have recently been located over a total strike length of 8-10 km intermittently in a NE-SW to E-W trend with steep dips due north- west to north in parts of Sundargarh district of Orissa. The QPC samples have analysed up to 0.039% U₃O₈ and 0.035% ThO₂ with high concentration of Y (74 to 518 ppm), La (<100 to 880 ppm), Cr (126 to 633 ppm), Zr (137 to 1250 ppm) and Pb (31 to 581 ppm). Cellulose Nitrate (CN) film studies of few QPC samples indicated adsorbed uranium over goethite and infiltrated ferruginous material (limonite), secondary uranium as encrustation and fracture filling and discrete sub-rounded grains of monazite, zircon, allanite and rare xenotime in the matrix of QPC as radioactive phases. Higher content of Th over U, elevated concentration of Y and La in QPC eliminates the possibility of its low temperature product by epigenetic processes. Poor correlation of U with elements like Pb, Y, Zr, La and Cr can be explained due to surficial leaching of uranium from QPC after its deposition as reflected by adsorbed U over iron- oxides and low U/Th ratio in QPC in the area.

Keywords

Quartz-Pebble Conglomerate, Bonai Granite, Radioactive Minerals, Orissa.

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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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