High quality uranium discovered in Karnataka

The atomic minerals division (of the Department of Atomic Energy) in Hyderabad has discovered high quality uranium in the Bhima basin near Hogivillage in Gulbarga district of Karnataka recently, giving a fillip to India's nuclear power programme.

The area where the new uranium deposits were discovered forms part of a proterozoic (1800 million to 650 million years old) basin, which is known to hold major uranium deposits in Canada and Australia.

The uranium deposits discovered two years ago by the AMD in Lambapur in Nalgonda district of Andhra Pradesh occur in the basin which is also a proterozoic basin.

AMD director K K Dwivedy said that, based on available geological information like stratigraphy (disposition of rock beds), lithology (rock types) and radiometric data, the area was taken up for detailed investigation involving regional sampling and radiometric checking.

The main rock types in the region were lime stone (locally known as Shahabad stones) and shale with thin beds of arenite (sand stones).

Dwivedy said the unconformity contact between these rocks and the underlying granite were chosen as a target area for uranium mineralisation.

He said some borewells drilled in the area for water some time back indicated the presence of high uranium values. The bore wells were subsequently probed using a gamma ray probe. This led to the discovery of high order radioactivity with values up to 0.12 per cent in one of the bore wells. Subsequent core drilling has confirmed mineralisation in the form of uranite and coffinite stone near granite contact, he added.

He said uranium mineralisation was also controlled by a fault in the granite basement in the peripheral parts of the basin. Mineralisation occurred at a shallow depth of less than 60 metres from the surface.

Uranium mineralisation was also associated with dark-coloured basic rocks in the granite. This clearly showed the role of solution movement along the unconformity surface (gap in sedimentation), which had acted as a channel way for the passage of rich fluids containing sufficient uranium to give rise to ore-grade concentration.

Considering that some faults continued below the sediments towards the basin, Dwivedy said there was good scope for sub-surface exploration to locate economically viable uranium deposits. This occurrence near the basin margin added a new variant to the long list of uranium deposit types.

The AMD has intensified sub-surface exploration (in the Bhima basin) to get an idea about the controls of mineralisation and the extent of deposits.

The first borehole (drilled recently) has given three ore zones, two of them having grades better than the Jaduguda uranium deposits in Bihar.

Dwivedy said once the probes are completed, the Bhima basin area would be the fourth promising uranium mining area in the country, the other three being Singhbum district (Bihar), West Khasi hills (Meghalaya) and Nalgonda district (Andhra Pradesh).

Scientists from 26 countries including the United States and Canada who participated in a meeting of the International Atomic Energy Agency in Vienna last week, appreciated the new uranium deposit types discovered at Bhima basin, when a paper was presented on the subject by Dwivedy.

On further prospects of high-grade uranium deposits in India, Dwivedy said the data collected during the current field season (of the AMD) has indicated the possibility of yet another deposit near Wahkyn in Meghalaya. It is expected to have better grade and tonnage than the existing uranium deposits near Domiasat, also in Meghalaya.

He said Wahkyn was located near the confluence of the Wahblei and Kinsiang rivers. Based on limited drilling in the Wahkyn region, the average ore grade has been determined to be 0.15 per cent uranium oxide.

He said though the prospects of finding additional reserves of uranium in the Yellapur-Peddagattu area of Nalgonda district were high, restrictions in carrying out exploration in the reserve forest area has slowed down AMD's efforts in the region.

He hoped that necessary clearance would be given by the state forest department for exploratory drilling. The year 1996-97, he said, has been a "very" successful field season for uranium exploration in India.

UNI