Geothermal potential of the Amagmatic Aswa Shear Zone in Uganda: An assessment using geochemical signatures

Abstract

Okidi and Elegu, located in the Aswa Shear Zone of Northern Uganda are few of the amagmatic geothermal prospects situated outside the western arm of the East African Rift System. The two areas were first documented in 1935 and 2014 respectively. According to a reconnaissance survey done in 2023, Okidi thermal area is marked by hot springs issuing at a maximum temperature of 80? from a riverbed covered with alluvial sediments. Conversely, Elegu is a blind system proven by shallow boreholes discharging mineralized anomalously warm fluids (44.7?) and H2S gas. Geological and geochemical data showed an extensional-type system controlled by tectonism and slightly alkaline (pH 7.5-8.3) thermal fluids with relatively low TDS compared to other areas of similar surface temperatures. Detailed geochemical and hydrogeological surveys conducted in 2024 show Na-Cl or Na-SO4-Cl or Na-SO4-HCO3 type thermal fluids of meteoric origin and equilibrium reservoir temperatures of 150-170? for Okidi and 90-120? for Elegu.