Gravity Method for Delineation of Iron Ore Deposit Geometry in Oko, Southwestern Nigeria

Abstract

Solid mineral deposits possess significant economic advantage to a nation if they are properly mapped and exploited. Several researches have shown that there are myriads of solid mineral resource deposits in Nigeria with significant portions in the southern part of the nation, but there is a knowledge gap in the quantity and quality of geophysical and geological information available about them. This study is therefore aimed at providing more information by estimating the thickness and depth to iron ore formations in Oko, South-Western Nigeria using gravity method of geophysical survey due to its efficiency in mapping the density contrast between the iron deposit and the host rocks. Ground gravity survey was carried out at 220 gravity stations and 11 traverses using a Scintrex CG-5 gravimeter to cover a 25000m2 area. Coordinates, time and elevation were also taken at each gravity station, gravity reductions and removal of regional trend were also carried out. Qualitative analysis using first vertical and horizontal derivatives was used to identify positive bouguer anomalies in the map while quantitative analysis using Half width, Peter’s half slope and Gradient Amplitude methods with Euler de-convolution and source parameter imaging methods were applied to image the sub-surface and to determine the depths to top and centre of the anomalous bodies. The qualitative analysis revealed E-W trending geological structures which Euler solution confirmed to be a fault. Depth estimation revealed that average depth to the centre of the deposit ranged from 5.61±2.48m to 14.57±6.45m and the depth to top estimates ranged from 6.77±3.14m to 11.28±5.24m while the thickness of the ore body was also estimated to range between 3m to about 20m. The study revealed that the Oko banded iron formation (BIF) is occurring in lineaments trending majorly in the E-W direction with a depositional thickness of about 20m.