Title: Utilization of airborne magnetic and ground geophysical models in regional exploration of mineral deposits in inland basins in southeastern Nigeria

Abstract

In this study, airborne and ground-based geophysical data are analysed to identify areas that are favourable for mineral ore occurrence as well as image sub-surface geological structures of mining interest. To achieve these objectives, four basins (Abakaliki, Ikom-Mamfe, Bamenda, and Oban Massif), occupied by several mining districts in south-eastern Nigeria are selected due to the presence of mineralized veins, primarily consisting of galena (PbS), sphalerite (ZnS), and barite (BaSO4) in their order of relative abundance. Of these basins, the Abakaliki and Ikom-Mamfe Embayment (IME) is studied in relation to unraveling mineral-bearing geological structures with mining implications. The study’s main purpose is to improve the process of ‘ground selection’ for mining operations and thus, halt the cancellation and abandonment of exploration and mining contracts within the areas. The total magnetic intensity data (TMI) was reduced to the equator to prepare the magnetic data for further enhancements. The first vertical derivative (FVD) was applied to enhance the residual features while the tilt derivative were computed to delineate edges of sub-surface source bodies. Thereafter, lineaments were identified as a reliable indicator of mineral bearing geological structures. Results show the presence of aeromagnetic anomalies, which reflect the existence of sub-surface mineral bearing structures and/or near-surface or exposed crystalline basement complex rocks that have been intruded by igneous bodies, in the basins. It is observed that major lineament orientations in the Abakaliki Basin and Bamenda Massif are NE-SW and NW-SE, and in the IME and Oban Massif NE-SW and NNE-SSW, while the dominant lineament trend for the entire study area is in NE-SW direction. The models of ground geophysical traces obtained from the IME and Abakaliki Basin show outstanding anomalies characterized mainly by low resistivity and moderate to high chargeability values at shallow depths (2.50 - ~40 m), with the results indicating good correlation. On the other hand, the host rock is clearly mapped, showing substantial chargeability and resistivity contrast. Analysis of the integrated results suggests that the location of the delineated ore bodies corresponds to zones of moderate to high magnetic intensity, zero tilt angle contour, high analytical amplitudes and dense lineament occurrence, which shows reasonable agreement between both primary research data. These geophysical anomalous sites require test drilling to confirm their certainty and ascertain their depth persistence. This work, therefore, demonstrates the efficiency of airborne magnetic data as a suitable first pass ground selection tool for mineral ore exploration in inland basins.