Evaluation of the geothermal potential of Okigwe and environs using aeromagnetic method

Abstract

Investigation of geothermal potential in Okigwe embraced the use of aeromagnetic methods. Okigwe is found between the latitudes of 5 ̊ 56̍ 24̎ N and 5 ̊ 42̍ 19̎ N and the longitudes of 7 ̊ 12̍ 58̎ E and 7 ̊ 24̍ 02̎ E. The LGA is bordered to the North by Orumba South LGA in Anambra and Umunneochi LGA in Abia, to the East by Isikwuato LGA in Abia, to the South by Umuahia North LGA also in Abia and to the West by Onuimo and Ideato North LGA̕s in Imo State. The aeromagnetic data sheet 312 which covers Okigwe and its environs was used in the study and it reveals the presence of both magnetic sources and non-magnetic sources as inferred from the total magnetic intensity values ranging from -61.3 nT – 182.9 nT. The magnetic analyses done include regional anomaly, residual anomaly, reduction to equator, analytical signal, vertical derivatives, source parameter imaging and tilt derivative which show a result range of -198.4 nT to – 161.4 nT, -19.4 nT to 16.6 nT, -49 nT – 167.8 nT, 0.003 nT to 0.04 nT, -3.4 x 10^-5 nTm^-1 to 1.5 x 10^-5 nTm^-1, 0.0947 km to 2.27 km and -1.4⁰ to 1.1⁰ respectively indicating the presence of magnetic bodies in the study area. Spectral analyses were also done with the study area being divided into 25 spectral blocks to obtain deep depth and shallow depth of the magnetic sources, Curie depth, geothermal gradient and heat flow for each of the spectral blocks and an average was thereafter obtained. It was observed that the study area has geothermal potential with a geothermal gradient range of 80 ⁰Ckm^-1 to 170 ⁰Ckm^-1 and an average value of 125.67 ⁰Ckm^-1. From the study it was inferred that Okigwe has magnetic sources with a Curie depth of about 4.7 km and has geothermal heat potential and it is most likely to be a zone for mineral exploration as well as geothermal sources.