An integrated geophysical approach for gold from Wayand-Nilambur granulite terrain, Kerala (India)

Abstract

The Wayand-Nilambur granulite terrain in Kerala (India) is well-known for vein-type gold mineralization within the quartz veins. Based on the previous geological, petro-physical and geophysical characteristics of Wayand-Nilambur gold deposit, the integrated geophysical survey was carried out to delineate the favourable prospecting zones. In the present study, detailed ground geophysical surveys, that is, magnetic, electrical resistivity/chargeability surveys were carried out in an area of 2 km² in Kattikallu and Kalkulam blocks to delineate the ore deposits in terms of depths and extensions through the structural shear zone, locate the anomalous sources and the geometry of the Au-rich sulphide zone and its depth continuity in the subsurface. These surveys brought out prominent resistivity and chargeability zones over known magnetite-quartz veins that are associated with low-grade sulphide bands at the central part of the Kattikallu block. The prominent potential zone is characterized by strong bipolar magnetic anomalies over the quartz veins. Based on the 2D inversion of resistivity data, the resistivity low zone of order 80–600 Ω m and chargeability of 21–25 mV/V are observed at a depth range of 5–20 m. In Kalkulam block, the magnetic survey has also brought out high intensity anomaly zones over quartz veins, the same quartz veins are mapped by high chargeability of 10–35 mV/V and low resistivity of 185–400 Ω m. The dipole-dipole configuration produces two parameters, that is, resistivity and chargeability, these methods distinguish the anomalies along the two selected profiles in the study area. An attempt was made for combining the resistivity and chargeability values to identify the anomalous zone boundaries. The results of inversion indicated that the conductive bodies are located at the subsurface, with depths ranging from 5 to 25 m. Based on this integrated geophysical study, we suggested two borehole sites for further geo-scientific studies in view of mineralization.