Lithological characterization of Ijebu-Ife, Southwest, Nigeria using aero-radioactivity data

Abstract

In this work, aeroradioactivity (airborne radiometric) data was used to characterize the lithology of Ijebu Ife, Southwest Nigeria. Measurements were made using Sodium Iodide [NaI (Tl)] detector mounted on a fixed-wing aircraft by Nigerian Geological Survey. Geochemical information on potassium (40K), thorium (232Th) and uranium (238U) concentrations were extracted from the raw data after correction and normalization due to contributions from soil, atmosphere, aircraft and cosmic radiation. The data was further subjected to photogeological analysis and image-enhancing techniques using minimum curvature gridding with cell size of 25 m after which single band, ratio and ternary images were generated and used to characterize the lithology of the area. Six lithologies including granite lithology, shale lithology, sandstone lithology, Lekki lagoon lithology, schist and clay lithologies were characterized after combining the single band, ratio and ternary maps. Results of radiometric analysis showed the relative abundances of each radioelement concentration within each lithologic unit. 232Th had 16.33 ± 0.62 ppm as the highest mean value of radioelement abundance within the granite lithology with the range of 2.93–62.42 ppm. 40K had the lowest mean concentration of 0.04 ± 0.00% within the Lekki lagoon lithology. These values reflected the overall average concentration and the nature of bedrock lithologies within their respective location of occurrence. This work showed the usefulness of aeroradioactivity data in the characterization of lithologies, environmental monitoring and assessment in terms of radiological distributions and radionuclide concentrations.