Evaluation of Thermal Spring Geothermal Potential Using Gravity and Magnetic Surveys at Afor Oba, Nsukka

Thermal spring occurrences at Afor Oba near Nsukka, Enugu State, suggest the presence of elevated subsurface heat flow that may be exploitable as a low-enthalpy geothermal resource. This study evaluates geothermal potential at Afor Oba using gravity and aeromagnetic surveys complemented by spring temperature profiling and hydrochemical analysis. Ground gravity measurements were acquired at 100 m intervals along eight profiles using a Scintrex CG-5 gravimeter. Aeromagnetic data for the area were extracted from the national survey archive and processed to derive the first vertical derivative, total horizontal gradient, and Curie point depth estimates. Spring water temperatures ranging from 38 to 57 degrees Celsius were measured at five active spring vents, and water samples were analyzed for major ion chemistry. Gravity anomaly patterns reveal a northwest-trending negative Bouguer anomaly associated with a granitic intrusion that likely provides the heat source for the thermal springs. Curie point depths estimated from aeromagnetic spectral analysis range from 18 km to 28 km, implying a geothermal gradient of approximately 45 to 60 mK/m, elevated above the regional average. Hydrochemical data indicate sodium-chloride water type with elevated silica and fluoride concentrations, consistent with high-temperature water-rock interaction at depth. Preliminary resource assessment suggests low-to-medium enthalpy geothermal potential suitable for direct use applications. This study represents a first systematic geophysical assessment of geothermal potential in the Nsukka area.

Keywords: geothermal, Curie point depth, gravity, aeromagnetics, thermal spring