Integrated geophysical methods for subsurface characterisation and health hazard assessment in parts of southwestern basement Nigeria

Aeromagnetic and radiometric data of Ikole Sheet 245 were interpreted for structural mapping, rock characterization and radionuclides hazard indices assessment. The data acquired were processed, filtered and enhanced to improve signal to noise ratio of rocks magnetisation. The Total Magnetic Intensity (TMI) map revealed high and low intensity values between 65 and 180 nT and -150 to -65 nT respectively. The residual map revealed clearer the undistorted signatures of the area geology and the interpretive boundaries of the underlying geology. Reduction to Magnetic Equator (RTE) map showed NE-SW regional lineament (R-R') that diagonally divides the study area into approximately two equal halves; a central ridge between two depressions trending in NW-SE direction within Akoko complex and N–S faults of F1-F'1, F2-F'2 and F3-F'3 within Ikole axis. The upward continued maps (1 km, 2 km and 4 km) revealed the attitude of the basement rocks and structures with depth, some of the identified structures are deep-seated beyond 1.6 km downward, and as well revealed a general trend of NW-SE for the basement rocks. The radioelement maps revealed varying radioelement concentrations. Areas with high concentrations implied that the rocks are crystalline, undeformed and rich in feldspar with U-Th bearing minerals majorly within Ikole complex. Other regions with low concentrations on the other hand depicted varying geologic framework compositions. The maps also revealed uranium deposit in Ikole and mineralized structures such as veins, joints, fractures and dykes. The Ternary map showed that the two depressions (A) and deep-seated faults (F-F') contain low and high radioactive rich bearing-minerals respectively. The spectral depth analysis result showed that the shallow and deeper magnetic sources have an average depth estimate of 20 m and 3.60 km respectively. The Absorbed dose and Annual effective dose equivalent (AEDE) of the study area are below the world standard limit for radiological hazard. Hence, the study areas are mineralized and have several structures that retain important radioactive minerals with no hazardous risk.