Integrated geophysical study for mapping Pb–Zn sulfide deposits in Asu River Group shales in Nkpuma-Ekwoku, Abakaliki area, southeastern Nigeria

The responses of the lead-zinc (Pb–Zn) ore-bearing veins in the Asu River Group shales in Abakaliki area to ground magnetic, resistivity, and induced polarization (IP) methods of geophysics were studied in Nkpuma-Ekwoku. Results of the study indicate that low magnetic susceptibility values are associated with shallow tectonic structures within the sedimentary basin which could host sulfide ores, while high susceptibility values suggest shallow intrusive/volcanic rocks. The ore-bearing veins within the sedimentary rocks have susceptibilities of ≤ 1.2 nT, while their resistivity and IP values are ≤ 80 Ωm and ≥122 ms respectively. The ores display mineral zoning in their electrical data profile. The primary occurrence of the ores is fracture controlled. However, they usually overflow into the unfractured sedimentary zones and become interstratified with the sediments. The ores maintain NW-SE trend even within structures of different orientations. The earlier view that structures with NE-SW trend are barren in the study area is not supported by the result of the present work. Shallow ore bodies occur before 30-m depth, while deep-seated ones are as far as 50 m below the surface.