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Rajeev Bidwai ¹, S. Srinivasan ¹, L. K. Nanda ¹, Atanu Banerjee ¹, P. N. Bangroo ¹, A. K. Rai ², P. S. Parihar ²

Affiliations
1 Atomic Minerals Directorate for Exploration and Research, Western Region, Jaipur 302 030, IN
2 Atomic Minerals Directorate for Exploration and Research, Hyderabad 500 016, IN

Abstract

No Abstract.

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Rajeev Bidwai , S. Srinivasan , L. K. Nanda , Atanu Banerjee , P. N. Bangroo , A. K. Rai , P. S. Parihar

Abstract

No Abstract.

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G. S. Yadav ¹, A. Muthamilselvan ², T. S. Shaji ³, L. K. Nanda ⁴, A. K. Rai ⁴

Affiliations
1 Jamshedpur 831 002, IN
2 Center for Remote Sensing, Bharthidasan University, Tiruchirappalli 620 023, IN
3 Thiruvananthpuram 659 012, IN
4 Hyderabad 500 016, IN

Abstract

No Abstract.

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A. Yugandhara Rao ¹, K. Vijay Raj ², O. P. Yadav ², L. K. Nanda ³, A. K. Rai ³, P. S. Parihar ³

Affiliations
1 Atomic Minerals Directorate for Exploration and Research, Vishakapatnam 530 007, IN
2 Atomic Minerals Directorate for Exploration and Research, Jaipur 302 033, IN
3 Atomic Minerals Directorate for Exploration and Research, Hyderabad 500 016, IN

Abstract

Magnesium-bearing calcretes of soft-gritty and hard pan varieties containing uranium concentrations from 16 to 74 ppm with <10 ppm of thorium are located along the Saraswati palaeochannel at Khemasar village, Churu district, Rajasthan. The uraniumbearing calcretes are exposed over an areal extent of 300 m × 200 m with thickness of up to 2 m in an interdunal depression. The silty sand layer occurring below the calcrete horizon suggests that it is a valley-fill calcrete, deposited along a palaeochannel. This occurrence of uraniferous Mg-calcrete in the Saraswati river palaeochannel opens up a large area for uranium exploration in the calcrete environment of Thar Desert. These calcretes are composed of 15.94% to 25.39% CaO, 7.15% to 22.39% MgO and Sr/Ba ratio up to 66.98. There is a positive correlation of U with Sr/Ba and MgO. The high Sr/Ba ratio and MgO indicate water of saline nature and high rate of evaporation. Ephemeral centripetal drainage mixing with the dissected palaeochannel waters and groundwaters, under arid climatic conditions might have resulted in the formation of this kind of uranium-bearing calcrete in fluvio-lacustrine environment.

Keywords

Fluvio-Lacustrine Environment, Khemasar, Magnesian Calcrete, Surficial Type Uranium.

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K. Ramesh Kumar ¹, Dheeraj Pande ¹, Arpan Misra ¹, L. K. Nanda ¹

Affiliations
1 Atomic Minerals Directorate for Exploration and Research, Western Region, Sector-V, Pratap Nagar Extn, Jaipur - 302 030, IN

Abstract

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.

Keywords

Didwana, Playa, Lake Sediments, Uraniferous Brines, Rajasthan.

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B. Nagabhushanam ¹, S. Durai Raju ², K. L. Mundra ³, S. D. Rai ¹, R. K. Purohit ¹, M. B. Verma ¹, L. K. Nanda ¹

Affiliations
1 Atomic Minerals Directorate for Exploration and Research, Hyderabad 500 016, IN
2 Atomic Minerals Directorate for Exploration and Research, Beach Sand and Offshore Investigations, Thiruvananthapuram 695 012, IN
3 Atomic Minerals Directorate for Exploration and Research, Western Region, Jaipur 302 033, IN

Abstract

The Ambadongar sub-volcanic carbonatite alkali complex is located about 140 km east of Vadodara, Chhota Udepur district, Gujarat, India and falls in Survey of India Toposheet No. 46 K/1. The complex intrudes Bagh sandstone (Cretaceous) and overlying Deccan basalts (Eocene) and is situated in the Narmada rift zone. The carbonatites came into prominence in the early 1960s with significant discoveries of fluorite and conspicuous radioactivity located near Chhota Udepur, at Ambadongar, the erstwhile Baroda district, Gujarat. Earlier workers have clarified many aspects of the carbonatite complex.

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A. K. Patel ¹, H. Yalla ¹, M. B. Verma ¹, A. K. Jain ², L. K. Nanda ¹

Affiliations
1 Atomic Minerals Directorate for Exploration and Research, Hyderabad 500 016, IN
2 Atomic Minerals Directorate for Exploration and Research, Western Region, Jaipur 302 033, IN

Abstract

The Proterozoic Delhi Supergroup rocks of North Delhi Fold Belt (NDFB) is one of the prime targets for base metals, uranium and other economic mineral prospects.

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