Iso-dip Contouring: An Innovative Approach to Exploration for Concealed, Structure-controlled, Hydrothermal, Vein-type Uranium Mineralisation in Kanchankayi Sector of Kurlagere-Gogi-Gundanahalli Fault Zone, Yadgir District, Karnataka

Kanchankayi is located in the central part of the 55 km long Kurlagere-Gogi-Gundanahalli (KG) fault of Meso-Neoproterozoic Bhima basin of Southern India. Intensive integrated exploration in Kanchankayi has established a concealed, fracture-controlled, low-grade uranium deposit. Uranium mineralisation is mostly confined within the fractured limestone of Shahabad Formation and partly within fractured basement granite. Tectonic movements along the KG fault in Kanchankayi area have resulted in the northward thrusting of basement granite over the Bhima sediments forming a reverse fault geometry. Structural mapping and subsurface exploration has established that the uranium mineralisation is mainly confined to the fault zone. In general, the fault zone is characterised by steep southerly dipping to vertical limestone beds. Iso-dip contouring was attempted on the beds having equal angle of dip, with the premise that steep southerly dipping and vertical beds will reveal the trend and location of the fault zone on the surface. The iso-dip contour map reveals that the contour depicting the fault zone initially follows the basement-sediment contact and further NE i.e. towards Kanchankayi and transgresses into the Bhima sediments. This suggests that the fault zone, instead of following the basement-sediment contact, moves within the basin in Kanchankayi. Recent sub-surface exploration in Kanchankayi has corroborated this interpretation. The innovative approach in utilizing structural mapping and iso-dip contouring has not only given a new dimension to the exploration programme at Kanchankayi but also provided a model technique for exploration of concealed, structure-controlled, hydrothermal, vein-type uranium mineralisation in parts of Bhima basin.