Ground Magnetic Survey in Otukpo Area Benue State Nigeria

Abstract

Ground Magnetic data was obtained along four profiles during a field work lasting three weeks where a G-816 model portable proton magnetometer was used for the survey. The survey was accomplished along a 30km Utoton – Oturkpo road at a sampling frequency of 1km., a 50m sampling frequency was used for Oturkpo –Okpamaja, 15 km traverse, while 1km frequency was used for both Oturkpo –Adoka, a 32 km traverse and Oturkpo –Aliade, a 51.5 Km traverse.  High and low frequency components of the profiles were isolated by moving average filters. Depths to magnetic sources were calculated for the resulting high and low frequency anomalies on the profiles. High frequency anomalies were interpreted to arise from narrow steeply dipping dykes or fractures which in some cases are mineralized at shallow depths of about 20m-1.66km while low frequency anomalies were the result of low dipping sills or basement surfaces with a depth range of 1.66-5.006 km. The profile intersecting a broad aeromagnetic east-west anomaly south of Oturkpo is known to be mineralized in veins within sills of dolerite with magnetic susceptibility in the range of 0.299 - 0.34 electromagnetic units.  Model direction of magnetization is 10^0. Sills and dykes dipping southward or northwards within the Asu River Group Formation and Ezeaku formations/ Markudi sandstone underlying the study area are responsible for folding and faulting with associated magnetic anomalies.

Keywords: Magnetic profiles data, modelling, interpretation