Geophysical Investigations Inferred from Airborne Potential Field Data of Parts of the Lower Benue Trough in Nigeria

Abstract

The aeromagnetic data of Nkalagu and Abakaliki areas were interpreted using spectral analysis and modeling to estimate depth to the sedimentary thickness, nature of intrusive, susceptibility values and types of minerals associated with them. The total magnetic intensity was processed to produce the residual magnetic map which was divided into 21 overlapping blocks. Each block was subjected to a spectral program plot (SPP) developed with MATLAB to obtain depths to the top boundary Zt and depth to the centroid Z0. The spectral analysis revealed depths to the top boundary Zt, which is the depth to magnetic basement ranging from 0.77 to 2.34 km with an average value of 1.72 km and the centroid depth ranging between 2.22 and 5.93 km, with an average depth of 3.55 km. The modeling estimated depths of profile 1, 2, 3, and 4 at 5 km, 1 km, 1.68 km and 1.32 km respectively with an average depth of 2.3 km and respective susceptibility values of 0.002, 0.003, 0.003 and 0.003 respectively, indicating the presence of igneous intrusions of gabbro, diabase and metamorphosed sedimentary rocks of quartzite and schist, with iron rich minerals like pyrite, limonite, cassiterite and arsenopyrite. The maximum depth values of 2.34 km and 5 km obtained from the two depth estimation methods confirm feasibility depths for hydrocarbon accumulations. In view of the above results, it is evident that the presence of intrusions delineated from the modeling results accounts for the mineralization in the area and can also destroy any hydrocarbon present since the presence of numerous intrusions are an indication of exceedingly high temperature history.