Abstract

Nine Regional Aeromagnetic data sheets from the Lower Benue Trough, Nigeria have been interpreted using the centroid and forward modelling technique of spectral analysis with the aim of delineating structures that can possibly control mineralization within the trough. The residual magnetic map was analyzed using the geological cross-section to determine the number of anomalies and the Fourier transform method was used to estimate the depth to the top and bottom of the anomaly, the analytical signal amplitude, the first vertical derivative, Rose diagram and power spectrum. From the spectral analysis results, the estimated depth value to the top of the anomalous body ranges from 0.5 km to about 12 km, with the highest depth to the top of the anomaly located within the south-western and north-western axis of the study area. The estimated depth to the bottom of the anomalous body ranges from about 20 to 50 km with the highest depth located within the north eastern axis of the study area. The analytical signal amplitude map highlights the discontinuities or boundaries of the anomalous (granitic) body. It also enhances variations in the magnetic properties of the magnetic sources within the study area. The analytical signal amplitude map gave figures that range from 0.001 to about 0.047 nT/m. The map of the first vertical derivative depicts the near surface geological features such as fold, faults and geological structures within the trough. It is observed from the map of the first vertical derivative that most of the structures are trending in NE-SW (northeast to southwest), while some trends in NW-SE (northwest to southeast) directions. The major fault in the study area trends E-W (east to west) direction and these trends also conform to the trends indicated by the Rose diagram. The study also identified areas of high sedimentary thickness which could favour accumulation of hydrocarbon within the trough.

Key words: Analytical signal amplitude, first vertical derivative, Rose diagram, power spectrum.