Imaging lateritic bauxite bearing zones in Ekiti, Southwestern Nigeria, using magnetic and electrical resistivity tomography techniques

Abstract

This research uses geophysical techniques such as magnetic and electrical resistivity tomography to image the lateritic bauxite bearing zones in Orin Ekiti, Southwestern Nigeria. The high-resolution aeromagnetic data were utilized for generating the total magnetic intensity (TMI) map. Different filtering techniques such as Euler deconvolution and total horizontal derivative were also carried out to enhance better understanding of bauxite deposit, with the generation of different maps therein. Low magnetic intensities were observed over charnockitic rock which is a host material for bauxite occurrence. Magnetic low trending NE–SW was observed in the study area. The (EUD and THDR) maps were then superimposed on the geologic map to geo-reference areas that have dominant charnockite. The depth extent and structural signature interpreted from magnetic interpretations show that significant deposit in the study area is at shallow depth which tallies with the geology of bauxite as being a supergene enrichment (surficial deposit). 2D ERT results obtained from five traverses with inter-traverse separation of 45 m and traverse length of 100 m each, established in the NW–SE direction to image the lateritic bauxite deposit based on the prospect shown from the aeromagnetic analysis. The images display the constant resistivity regimes beneath the traverses with different colour bands. The 2D ERT profiles and 3D inversion results show bauxitic zones to be of high resistivity which ranges from 154 to 3814 Ω m, the migmatite gneiss and granitic rocks (unaltered parent rocks) are of considerably lower resistivity than the weathered charnockitic rock and by extension bauxitic zones. These different techniques used in this study have however shown that the area of interest for bauxitic deposit in Orin Ekiti trends in the NE–SW direction with a dominant concentration in the north-eastern (NE) part. By the same token, this research has been able to substantiate the fact that bauxite deposits occur as supergene enrichment.