GIS-based geospatial tools for estimating the magnetic anomaly depth of hydrothermal mineral deposits using inverse distance weights method
The data used in this study consist of high-resolution airborne magnetic datasets for solid mineral exploration acquired across the Nigerian nationwide Terrains by the two Canadian firms awarded the contracts (a.g., Fugro Airborne Survey Services, and Patterson Grant and Watson), by the Nigerian Geological Survey Agency (NGSA). The Canadian firms had obtained the airborne magnetic data between 2003 and 2009, approximately along the NW–SE flight lines that were positioned at 90 degrees to the most significant narrow geological strike in the areas covered. Aircraft was flown at typical spaced of about half kilometers intervals to acquire the data, with a 2 km tie-line spacing along the northeast-southwest (NE-SW) directions at 80 m nominal flight elevation. The magnetometer settings were set at 0.1 s intervals to record the data. The combination of the nominal flight height—that was set exceptionally close to the ground surface using narrow line spacing—and the extremely small recording time gaps, helped to achieved a higher resolution of the magnetic anomalies than the general high-altitude airborne magnetic surveys. Prior to the data distribution by the Nigerian Geological Survey Agency, (NGSA) to the interested users, Fugro Airborne Surveys Company preprocessed the essential magnetic data corrections: the geomagnetic gradient was removed from the data using the existing model with the International Geomagnetic Reference Field (IGRF), January 2005 version, as specified in the World Geodetic System 1984 ellipsoid. The Universal Transverse Mercator (UTM) coordinate system was used to project the airborne magnetic data. The airborne magnetic survey data presented in this study covered the Omu-Aran Schist belt zone in parts of the Nigerian South-western Precambrian basement complex (NSPBC), with moderately shallow overburden lithologies.