Mineral Explorations of Cu-Pb-Zn deposits of Sikar District, Rajasthan, India

The Geophysical methods are one of the indirect techniques to understand the subsurface geology and its associated features. In geophysical exploration, measurements will be taken on the earth�s surface/ boreholes to determine distributions of physical properties at depths that reflect subsurface geology. Magnesium-bearing calcretes of soft-gritty and hard pan varieties containing uranium concentrations from 16 to 74 ppm with less than10 ppm of thorium are located along the palaeochannel at Narsingpuri to Gumansingke Dani village, Sikar district, Rajasthan. The uranium- bearing calcretes are exposed over an area extent of 300m and 200 m with thickness of up to 2 m in an inter- dunal depression. The silty sand layer occurring below the calcrete horizon suggests that it is a valley-fill cal- Crete, deposited along a palaeochannel. This occur- rence of uraniferous Mg-calcrete in the Palaeochannel opens up a large area for ura- nium 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 indi- cate water of saline nature and high rate of evapora- tion. Ephemeral centripetal drainage mixing with the dissected palaeochannel waters and groundwater�s, under arid climatic conditions might have resulted in the formation of this kind of uranium-bearing calcrete in fluvio-lacustrine environment.