Magnetic Susceptibility Mapping of Rocks and Depth Estimation of Anomalies: A Case Study of Igarra and Its Environs

Abstract

Magnetic Susceptibility Mapping and Depth Estimation of Anomalies were carried out on Igarra and its environs, Southwest Nigeria. This was to assist in mineral exploration in the area. The study area is located within the Igarra schist belt which is underlain by rocks of Precambrian basement complex. The Total Magnetic Field over the study area was obtained by digitizing the aeromagnetic map of Auchi (Sheet 226) acquired from the Nigerian Geologic Survey Agency (NGSA). A total of 19 (nineteen) magnetic anomalies were identified on the map; 5 magnetic highs and 14 lows. 8 anomalies have a NW-SE strike direction, 4 in the NE-SW and 7 in the E-W direction. The amplitude of the anomalies and strength of the total field were used to determine the susceptibility values for each of the anomalies. The Susceptibility values were used to generate a Magnetic Susceptibility map of the study area on SURFER 13 software. TMI plots on the anomalies were carried out on MICROSOFT EXCEL 2010. Depth estimates of the anomalies were got using three methods: The Half Width rule, Hannel rule and Tirburg rule. The Susceptibility map shows a noticeable pattern of increase in magnetic minerals from the Southwestern to the Northeastern part of the map. The Depth of the basement anomalies were relatively shallow ranging from 0.8 km to 2.6 km. The results of this work provide a preliminary guide to those that engage in mineral exploration / exploitation in the area.