Estimation of Depth and Locations of Mineral Rocks using Magnetic Survey Method: Case of Sajiyan-Ero town, Ondo State, Southwest Nigeria

Abstract

A ground magnetic survey was carried out to determine the locations and approximate depth of suspecting mineral rocks at the surroundings of a site in Sajiyan-Ero town off Ogbese-Owo highway, Ondo State, Nigeria. This research was conceived as a result of suspicious presence of mineral rocks in the area and also to add to magnetic field database of southwestern Nigeria as no magnetic data have been acquired in the area. A total of 190 magnetic data points were acquired from twenty (20) profiles using a G-816 proton precession magnetometer with 10 m spacing intervals between each profiles and points. The magnetic data obtained were processed and analyzed after some corrections and presented into magnetic plots, contour, base and 3D maps. The slope method of depth interpretation was used to estimate the depth to the magnetic sources. The magnetic signature acquired show significant irregular amplitude from a positive peak with minimum value of 0.6 nT at an average depth to top of 5.5 m and center 17.6 m to a maximum value of 17.1 nT at an average depth of 7.92 m and 25.3 m to top and center of magnetic anomaly respectively. This corresponds to profiles 1 and 5. The negative peak values vary from -8.9 nT to -1.0 nT with an average depth to top of magnetic anomaly of 10.0 m and 4.58 m respectively. The average estimated depth to top of anomaly for the study area was 22.0 m with profile 2 having the maximum. The variations in depth determination from anomaly behavior have considerable environmental and geological significance. This depth at various points on the subsurface allows for mapping to infer thickness of mineral rocks deposits.