Delineation of extension of uranium mineralization zone using resistivity and Very Low Frequency electromagnetic surveys around South Purulia Shear Zone, India

During a random radiometric survey, nuclear radiation was detected near exposed rocks in an open-pit phosphate-mine at Beldih (Purulia, W.B.), India. Radiometric analysis of rock samples reveals a significant concentration of uranium. Geological study suggests that Beldih phosphate mine lies near the South Purulia Shear Zone (SPSZ). Shear zones in the region are E-W striking elongated zone and associated with uranium mineralization (famous Singhbhum shear zone for several uranium mines). Electrical resistivity (profiling and sounding) and Very Low Frequency (VLF) electromagnetic surveys were performed around Beldih mine to delineate the suitable conducting zones which may be associated with uranium mineralization. Significant lateral extension of possible source is delineated; it could be exploited later on a large scale for commercial utilization. It is observed that gradient resistivity profiling (GRP) survey is the most suitable technique to explore the nearly vertical conducting structure. The GRP measurements were carried out at different locations. A good correlation of low resistive zones on various GRP was observed from the measured data. The study concludes that subsurface structures are nearly vertical and have alternate resistive and conducting bands. An inclined bore-hole drilled confirms the presence of alternate resistive and conducting structures and uranium mineralization is detected in conducting bands. This suggests that GRP can be conducted for precise location of the target zone. This will help in planning bore holes for drilling to find the exact thickness, lateral and vertical extent of the deposit for commercial utilization. VLF measurements were also carried out along various profiles. Even though VLF observation was quite noisy due to presence of power lines in the area; this method can be used to map the area and model the data for actual sub-surface conducting zones in less noisy areas as a support for drilling works.