An Airborne Radiometric Survey for Lithological Identification of Part of South-Western Nigeria

A gamma ray spectroscopy of an airborne radiometric survey was employed to measure the surface distribution of Potassium (%K), equivalent Uranium (eU) and equivalent Thorium (eTh)) in rocks underlying part of South-western Nigeria. The study aims at employing the alpha-α, beta-β and gamma-γ radiations that emanated from the decay of radioactive elements in the rock units beneath the area to achieve greater accuracy in facies delineation in order to unravel the possible variations in the concentration of naturally occurring radioelements, which is a function of primary geologic processes of mineralizing solution and metamorphic gradient. The data for the study area which lies within latitudes 7°00’N to 7°30’N and longitudes 3°00’E to 3°30’E of Abeokuta sheet 260 SE was obtained from Nigerian Geological Survey Agency (NGSA). The acquired datasets were processed by digitizing maps in numeric fonts which enabled the use of gridding technique by applying color images obtained from Minimum Curvature Grids (MCG). Enhanced composite images, ratio maps, %K, eTh and eU maps were consequently generated. The gridded maps were used to interpret the different rock types as inferred from high and low radiation anomalies with respect to the variation in geology at different locations within the study area. The results of this study defined concentration ranges of %K (-0.2 - 5.0 ppm), eU (0-12 ppm) and eTh (0-115 ppm). Based on the observed variation in the concentration of the three identified radioelements; the radiometric data revealed that the study area is underlain by six (6) major rock types namely, Felsic Volcanics, Gneissic rock, Ultramafic Volcanics, Intermediate Volcanics, Aplites and Pegmatites. The ternary map showed a high intensity of the three radioelements at the Northern part of the study area while the K/eTh ratio maps identified a high hydrothermal activity at the Southwestern part indicating a high potential of rock...