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Pande, Dheeraj
- Radioactive Quartz-Pebble Conglomerates from Western Margin of Bonai Granite Pluton, Sundargarh District, Orissa - A New Find
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Authors
Affiliations
1 Atomic Minerals Directorate for Exploration and Research, Department of Atomic Energy, Khasmahal, Jamshedpur - 831 002, IN
1 Atomic Minerals Directorate for Exploration and Research, Department of Atomic Energy, Khasmahal, Jamshedpur - 831 002, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 73, No 4 (2009), Pagination: 537-542Abstract
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.
References
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- Playa Sediments of the Didwana Lake, Rajasthan: A New Environment for Surficial-Type Uranium Mineralisation in India
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Authors
Affiliations
1 Atomic Minerals Directorate for Exploration and Research, Western Region, Sector-V, Pratap Nagar Extn, Jaipur - 302 030, IN
1 Atomic Minerals Directorate for Exploration and Research, Western Region, Sector-V, Pratap Nagar Extn, Jaipur - 302 030, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 77, No 1 (2011), Pagination: 89-94Abstract
The Didwana playa, the second largest playa in the eastern part of the Thar desert, is 5.6 km long and 2.4 km wide and supports commercial salt production. The thickness of lake sediment package is reported to be 20 m and comprises fine grained clays and silts, with abundant calcite, gypsum, and halite,associated with hypersaline water. Isolated hills of graphitic phyllite and quartzite are seen on the western side of the lake. During the course of investigations for uranium in surficial environment of semi-arid terrain of Rajasthan, ground water sampling defined a NE-SW trending uranium halo encompassing the Didwana playa. Subsequent sampling of unlined dug wells, up to water table in central part of the playa, indicated uranium values up to 190 ppm and 2072 ppb in lake sediments and brine respectively. These values are of the order of 21 ppm and 192 ppb towards the southwestern periphery of the lake. The average uranium content, as inferred from 12 samples in the central part of the lake, is around 60 ppm over a thickness of 5 m. It appears that the uranium is loosely bonded to the sediments in amorphous form and is, hence, easily leachable. Samples of brine (n = 10), from both the central and southwestern portions of the lake, analysed high (1,67,500-3,00,000 mg/l) TDS, HCO3- (1128-8395 mg/l), and SO4(30,536-88,000 mg/l). These are of alkaline (pH: 7.2-9.3) and reducing (Eh: -200 to -340 mV) nature. Under these Eh-pH conditions below the groundwater table, and for such uranium bearing groundwater, precipitation of primary uranium is expected. It is, therefore, modelled that uranium in lake sediment package above water table is concentrated by evaporation process and by chemical reduction below the water table.As the sampling is so far confined to zones above water table, the above possibility is still to be examined. Features like high intrinsic uranium in lake (playa) sediments as well as groundwater, the alkaline and reducing nature of groundwater, which may facilitate precipitation of primary uranium below water table, and the large extent of the lake sediments (10 sq km × 20 m thickness) make the Didwana Lake, a potential candidate for hosting a surficial-type uranium occurrence of significance, for which samples below water table need to be generated. These studies are expected to establish the lake sediment environment in semi-arid tracts of Rajasthan as a new target horizon for locating surficial-type uranium mineralisation in India.