Application of magnetic and Induced Polarization techniques in uranium exploration - A case study from Sunari-Sefraguwar sector, North Delhi Fold belt, Rajasthan

Magnetic and Induced Polarization (IP)/resistivity surveys were conducted in Jodpura-Sunari-Sefraguwar sector, Jhunjhunu district, Rajasthan to decipher the nature of structural features i.e., faults/fractures and sulphide rich zones favourable for uranium mineralisation. The Sunari-Sefraguwar sector is a part of albitite zone of East Khetri Basin of the North Delhi Fold Belt (NDFB) and is located about 25 Km NE of Rohil uranium deposit. The area exposes quartzite, quartz amphibole schist, quartz biotite schist and calc-silicate rocks as major litho-units belonging to Ajabgarh Group of Delhi Supergroup. Interpretation of magnetic data resulted in characterizing the lithological domains in the area. High amplitude magnetic anomalies of the order of 3000nT represent magnetite bearing quartz amphibole schist. The low magnetic zone delineated along the Sunari-Sefraguwar tract indicates a shear/fracture zone in the quartz biotite schist/quartz amphibole schist. Analysis of the reduced to the pole, derivative and band pass filtered images facilitated in mapping the concealed structural features trending in NW-SE, NE-SW and E-W direction. Three significant high charge ability zones (15-40 mV/V) trending NE-SW were delineated by IP/resistivity survey. The high chargeability zones are attributed to the presence of disseminated sulphide minerals in fractured quartz biotite schist/quartz amphibole schist. The correlation of low resistivity (<150 Ohm-m) and low magnetic zones (-180 to 250nT) with high charge ability (20-40 mV/V) towards south of Sefraguwar indicate shear/fracture zone with disseminated sulphide mineralisation. Inverted 3D-Voxel depth slices further indicate the depth extension of high charge ability (20-40 mV/V) zone beyond 300m. Based on the integrated analysis, potential target zones for uranium mineralisation have been identified for planning of boreholes in Sunari-Sefraguwar sector. Boreholes drilled based on the results of geophysical surveys intercepted significant mineralisation associated with sulphides in Quartz amphibole schist (QAS) to the south of Sefraguwar. (author)