Interpretation of Airborne Gravity Data over Kushaka Schist Belt, Northwestern Nigeria

Abstract

The Kushaka Schist Belt has a peculiar importance due to its minerological potential. The area is located on the Latitudes 10°30’-110 and Longitude 6°30’-7° in the northwestern part of Nigeria. Kushaka airborne dataset (Sheet 222) obtained from Nigerian Geological Survey Aagency was interpreted to delineate litho- structural architectures that could favour the exploitation of potential economic minerals over the area. The analyzed results of the bouguer map of Kushaka show the distribution of the gravity anomalies and magnitudes of the concealed shear and weak zones being characterized by low to very high gravity anomalies. The upward continued bouger anomaly map at distance of 3000m reveal the regional trends so as to generate a subsequent residual field where several filtering operations were carried out. Several enhancement techniques were carried out on the airborne gravity data to reveal the locations, edges/boundaries, trends, and depths of gravity anomalies. The analytic signal gravity and its superimposed maps reveal areas with low to high amplitude signals. Low amplitude regions are suggested to be dominated by highly fractured schistose, quartzitic rocks and fractures. On the other hand, high amplitude regions are likely occupied by denser biotite granitic and gneissic rocks. Also, the First Vertical Derivative gravity anomaly map shows low gravity region which indicate the presence of fracture. The horizontal gravity gradient map shows high, positive gravity regions which may be attributed to the presence of a regional structure trend in the area. Low gradient anomalies can also denote presence of graben-like structures or other geological depressions. The depth analysis over Kushaka schist Belt suggests depth to top for shallow bodies ranging from 385m to 560 m with an average depth of 440.55 m while the deep sources have depths ranging from 1910m to 2480m with an average depth of 2111.1m. The obtained Euler anomalies depths ranged from <2607m to >5858m suggesting that mineralization around the study area is structurally controlled, an evidence of hydrothermal alteration zones. The structural solution (S.I=0) result displays two NW-SE trending short linear features, an indication of tectonic metamorphic phases of Pan-African orogeny that harbor mineralization. The results therefore, suggested intensed deformation of the basement rocks with tectonic framework suitable for mineralization.