REMOTE SENSING AND GEOPHYSICAL BASED ASSESSMENT OF GOLD MINERALISATION POTENTIAL OF ALAGBEDE GOLDFIELD, ILORIN, SOUTHWESTERN NIGERIA

Abstract

Gold occurrence has been reported in Alagbede goldfield southwestern Nigeria but there is yet no mineralisation potential map to guide both the academia and investors in the area. Consequently, remote sensing (Landsat 8 Imagery) and geophysical (aeromagnetics and aeroradiometrics) methods were deployed to assess gold mineralisation potential of the Alagbede goldfield, southwestern Nigeria. Image enhancement technique was applied on the Landsat imagery for lineament extraction. Several magnetic enhancement filters were also applied to the aeromagnetic data for better understanding of the subsurface geology. The enhancement filtering applied to the airborne radiometric data are ratio map (K/Th), ternary, F-parameters and deviation from the ideal K values (Kd) in the study area. The lineaments extracted from the Landsat imagery were used to constrain structural architectural map from the aeromagnetic and aeroradiometric datasets. The results from the aeromagnetic and aeroradiometric data analyses were used for geology reconstruction while aeroradimetric data was mainly used for hydrothermal alteration mapping. It was observed from the geophysical methods that the migmatite gneiss rock unit present in the study area are of two varieties (migmatite gneiss and undifferentiated migmatite gniess). The major trend observed from the composite structural framework map from the remote sensing and aeromagnetic data was NE-SW while few ones are in the NW-SE and E-W directions. These observed trends show that, the study area has suffered at least three deformational episodes. The geological evidences of gold mineralisation such as favourable lithology, geologic structures (lineaments) and hydrothermal alteration were used to produce a Mineralisation Potential Map (MPM) of the study area. The location of active and abandoned mining sites in the investigated area was used to validate the developed mineralisation potential map. Plots of the mining sites were spatially located and found to be close or lie directly on geologic structures (lineaments). This further confirm that gold mineralisation in the investigated area was structurally controlled. It can be concluded that, the remote sensing, aeromagnetic and aeroradiometric data sets have been effectively used to develop a mineralisation potential map (MPM) of the study area.