Investigation of Magnetic Anomalies of Ubiaja and Illushi Areas in Northern Anambra Basin Using Aeromagnetic Data

ABSTRACT The aeromagnetic data of Ubiaja and illushi area that fall within latitude to and longitude to were interpreted qualitatively and quantitatively. The qualitative interpretation revealed that the area is intensely faulted with major anomalies (faults) trending in the northeast and southwest directions. Standard Euler deconvolution, source parameter imaging (SPI), spectral analysis and modelling (forward and inverse) methods were employed in the quantitative interpretation aimed at determining the depth or thickness of the sedimentary basin, magnetic susceptibilities and type of mineralization prevalent in the area. The results obtained by employing SPI have shown the minimum to maximum depths of 258.2 m to 3497.7 m of anomalous source bodies. Applying standard Euler deconvolution method for the structural index (SI), the depth obtained for SI = 0.5 ranges from 1377.3 m (outcropping and shallow magnetic bodies) to 2510.9 m (deep lying magnetic bodies); for SI = 1, the depth to magnetic source ranges from 1482.0 (outcropping and shallow magnetic bodies) to 3003.3 m (deep lying magnetic bodies); for SI = 2, the depth to magnetic source ranges from 1627.8 m (outcropping and shallow magnetic bodies) to 2984. 3 m (deep lying magnetic bodies); and for SI = 3, the depth ranges from 1853.9 m (outcropping and shallow magnetic bodies) to 3089.9 m (for deep lying magnetic bodies). The spectral depth obtained revealed two source depths, shallow and deeper. The deeper depth ranges from 1114.085 m to 3978.874 m with an average value of 2105.014 m, while the shallow depth ranges from 163.836 m to 460.057 m with an average value of 295.708 m. The results from forward and inverse modelling for profiles 1, 2, 3 and 4 showed depths of 4118 m, 3611 m, 2964 m and 5489 m respectively. From the results of susceptibility values obtained, profiles 1 and 2 with susceptibility value of 0.0100 is underlain by a body associated with group of minerals like hematite, gneiss, granite or gabbro. Profile 3 with susceptibility value of 0.0613 is typical of igneous rock porphyry. Profile 4 with susceptibility value of 0.0288 is typical with minerals like slate and hematite. The depth obtained from the four methods show thick sediment but on an average, the sedimentary thickness of the area is fairly sufficient for hydrocarbon accumulation.