Aeromagnetic mapping of basement structures and mineralisation characterisation of Ilesa Schist Belt, Southwestern Nigeria

Abstract

This paper analysed aeromagnetic data over the southern Ilesa schist belt of Nigeria with a view to assessing the sub surface structural settings that might favour mineralisation in the study area. Enhancement of the total magnetic intensity map was carried out to improve the anomaly characteristic of source bodies through upward continuation and reduction to the equator (RTE) of the magnetic field intensity. Estimation of depth to the deep, intermediate and near surface structures was based on the Spectral analysis and Euler deconvolution of the aeromagnetic data. Extracted magnetic anomalies from the RTE map range in amplitude from −115 to 134 nT, with the high magnetic intensities occurring over amphibolite, schist, porphyritic granite, gneiss and undifferentiated Migmatite, while low magnetic intensities were observed over quartzite and the undifferentiated schist. The Euler deconvolution solutions revealed that the area is mainly affected by sill/dyke and horizontal cylinder/pipe geologic model with estimated depth to the magnetic source ranging from 73 m–345 m. The depth estimated from the spectral analysis was in the range of 100 m–300 m for the intermediate and shallow sources; this compares reasonably well with the results from the Euler deconvolution. The orientations of lineaments extracted from the total horizontal derivative, source edge detection and Euler deconvolution suggest predominantly NE-SW trending structures, characteristic of primary geologic events in the area, while few E-W trending lineaments are imprints of secondary structural alteration in magnetic fabrics in this direction. Thus, the delineated structures are believed to be the hosts to the mineralised targets as observed from small scale mining activities in the area.