Aeroradio-spectrometric geothermal analysis of Abeokuta, southwestern Nigeria

Abstract

Weathered basement terrains of Precambrian origin are increasingly recognized as important targets for geothermal assessment and renewable energy exploration; yet systematic assessments integrating airborne radiometric data remain limited in south-western Nigeria. This study applies an aeroradio-spectrometric approach to evaluate and quantify the radiogenic heat production, geothermal gradient, and lithospheric heat flow associated with the diverse lithological assemblages of the Abeokuta area, southwestern Nigeria. The study area comprises of six lithological units, namely; biotite–garnet gneiss and schist, porphyroblastic gneiss, migmatite, pegmatite intrusions, and sedimentary successions of sand-clay-shale and sandstone–limestone. The concentrations of uranium (238U), thorium (232Th), and potassium (40K) were extracted from airborne gamma-ray spectrometric data and converted into radiogenic heat production (HP, µWm⁻³) and heat generation units (HGU). Surface heat flow, thermal conductivity, and radiogenic heat produced in each lithological unit are integrated into a 1-D steady-state conductive heat-flow model. The descriptive results obtained show uranium concentrations ranging from 1.16 to 11.94 ppm, thorium from 0.07 to 101.85 ppm, and potassium from 0.01 to 1.90%. Total heat production varies between 0.52 and 9.82 µWm⁻³ (mean = 5.04 µWm⁻³), while total heat generation spans 1.25 to 23.38 HGU (mean = 12.00 HGU). Both exceed the commonly adopted geothermal favourability thresholds of 4.20 µWm⁻³ and 10.00 HGU, emphasizing the presence of potentially exploitable radiogenic heat sources. Computed geothermal gradients range from 19.6 °C km−1 (sandstone–limestone) to 29.4 °C km−1 (sand–clay–shale), consistent with average heat-flow ranged between 36.9 and 44.9 mWm−2. The hot zone (≥ 120 0C) was experienced between 4 and 7 km depth, suitable for medium enthalpy geothermal systems. Statistical analyses reveal that thorium dominates radiogenic contributions, with uranium providing secondary support and potassium remaining negligible. Spatial anomaly maps and box plots confirm localized enrichment zones, while multivariate analyses highlight strong clustering of Th and U-driven parameters. These findings demonstrate that the Abeokuta weathered basement complex possesses economically relevant geothermal potential, particularly within thorium-rich lithologies. The study establishes a landmark by coupling airborne radiometric data with lithospheric thermal modeling to identify geothermal anomalies that cannot be recognized from radioelement concentrations alone. Aeroradio-spetrometric method has therefore found to be versatile, efficient and robust framework for preliminary geothermal resource assessment in weathered Precambrian terrains, with implications for sustainable energy development in south-western Nigeria.