Geophysica Vol. 55, No. 1, 2020
Abstract
This study entails the detailed analyses of high-resolution gravimetry dataset using enhancement techniques for characterising and delineating the locations, edges/boundaries, trends, and depths of lithostructural features around Precambrian basement complex of Igabi region, Northwestern Nigeria with a view of evaluating the structural architectures that harbor mineralization in the study area. The analyzed results of the bouguer anomaly and residual maps of study area showed the distribution of the gravity anomalies and magnitudes of the concealed structures based on the observed low to very high gravity anomalies. Bouguer anomalies around Igabi area ranged between -67.77 to -53.34 mGal reflecting the density variations within bedrock. The upward continued bouguer anomaly maps at distance 500 m, 1 km, 2 km, 3 km, and 4 km revealed the variations of the deep-seated basement rocks, the structures and the concealed anomalous bodies with general regional trends in NW-SE, E-W, and NE-SW directions. The bouguer analytic signal and its superimposed maps further revealed that areas with low amplitude signals may be associated with migmatites, schists, less dense felsic rocks (porphyritic granites) and fractures, and areas of high amplitude signals may be associated with denser biotite granitic and gneissic rocks. In addition, the second vertical derivative and tilt derivative maps clearly revealed the density of shallow basement rocks and near circular closures anomalies associated with fractures within the granitic rocks. Spectral analysis suggests depth to gravity sources range between 0.3 km and 0.67 km for shallow, 0.90 km to 0.97 km for intermediate and 1.5 km to 1.86 km for deep sources while Euler sources depths ranged from <1392.3 m to >2059 m. Based on the calculated bouguer anomalies such as variation in rocks densities, different structures and varying trends of litho-structures in with subsurface depth may have suggested intense deformation of the Basement rocks with varying tectonic framework in the study area over time.