Characterization of Precamrian Basement Formations using Geophysical Methods in Ago-Iwoye Southwestern Nigeria

Abstract

The characterization of basement rock is essential for obtaining the detailed information for the geological and mineral potential exploration resolves. The study presents the integrated use of electrical resistivity and magnetic methods for characterizing basement rock within Ago Iwoye, Southwestern Nigeria. The study aimed to determine the subsurface geology and alteration of the basement rocks in the area of study and to understand its mineralogical and engineering purposes. The Electrical Resistivity survey was conducted using the integrated of Dipole - Dipole and Vertical Electrical Sounding techniques in order to obtain 1 and 2 Dimensional results. The Magnetic survey used a proton precession magnetometer with a sensitivity of 0.1nT to measure the Magnetic Field Intensity. The acquired data were modeled using inversion techniques to obtain 1-D and 2-DElectrical Resistivity Tomography (ERT) that is capable of unraveling the subsurface information. The results of the electrical resistivity survey revealed a subsurface layer with resistivity values ranging from 600 to 1500 Ohm-m, which correlates with the weathered and fractured layer of the basement rocks. Below this layer, the resistivity increased to a range of 2000 to 8000 Ohm-m, indicating the presence of fresh basement rock. The magnetic survey results showed that the basement rocks have weak and variable magnetic susceptibility values, which suggest weak to moderate magnetite content. The Total Magnetic Intensity (TMI) map revealed that the underlying basement within the study area ranges from 32576-  33404.9nT. The integration of both electrical resistivity and magnetic methods provided a comprehensive understanding of the subsurface geology, structure, and alteration of the basement rocks within the study area. The results revealed that the basement rocks consist of highly resistive fresh rock overlain by a weathered/faulted layer that shows moderate conductivity. The weak magnetic susceptibility values suggest a low magnetic mineral content in the basement rocks.