Geophysical survey in parts of the palaeoproterozoic hirapur basin, madhya pradesh: A prelude to subsurface uranium exploration

Abstract

The Palaeoproterozoic Bijawar sediments comprising mainly Hirapur Phosphorite and subordinate Karri Ferruginous formations non-conformably overlie the Bundelkhand Granitoid Complex in Luhani-Tigoda sector of the Hirapur Basin, Chattarpur and Sagar districts, Madhya Pradesh. Ground geophysical surveys viz. Time Domain Induced Polarization (TDIP) and magnetic surveys were conducted to assess the potentiality of the area for unconformity-Associated uranium mineralization∗ TDIP data reveal that the average chargeability in basement rocks (granitoids, dolerite, and schists) and the Bijawar sediments are 19 mV/V and 67 mV/V respectively. The zones associated with >50 mV/V chargeability and low resistivity have been identified as potential targets for subsurface mineralization. These anomalous zones do not show any correlation with the exposed lithologies, rather spread across them. Magnetic data indicate the presence of distinct magnetic low of the order of 300-500 nT. A sediment-filled down-faulted block (half- graben) has been inferred on the basis of interpretation of the observed anomaly, spatial disposition of the anomalous zones, and lithological correlation. Besides, the TDIP and magnetic data notably correlate well with each other. The integrated geophysical survey helped in delineating two 250-300 m wide basement conductors between Luhani and Tigoda in the Hirapur Basin. The conductors trend NE-SW and N-S/NNW-SSE, and intersect each other to the SE of Luhani. The basement conductors have been interpreted as variably clay-infiltrated fault/fracture, or disseminated sulphide mineralized linear structure in the basement. The N-S/NNW-SSE trending basement conductor shows dextral displacement in the south-western part. However, no evidence of displacement has been observed in the overlying sediments. Absence of any surface evidence but presence of distinct magnetic low of the order of 300-500 nT in conjunction with abrupt displacement of chargeability contours allowed recognition of the causative structure as basement fault. The basement faults often act as conduits for migration of hydrothermal fluids, and are therefore potential targets, especially their intersection zone, for uranium mineralization.