Application of induced polarization method to delineate sulphide ore deposit in Osina area of Benue state, Nigeria

Abstract

The occurrence of sulphide ore bodies in Osina area of Benue state has been reported earlier in the geology of Nigeria map, but the extent and abundance of the mineral was not known. In this work, we investigated the
thickness and depth of the mineral deposit. Ground Induced Polarization (GIP) survey employing the dipole-dipole array was conducted. The survey consisted of three lines, each of length 600 m with a dipole separation of 30 m in the E-W direction covering an area of approximately 1 km². A total of 150 data points were taken in the survey area. Measurements were taken for chargeability in the time domain and Percentage Frequency Effect (PFE) in the frequency domain. Using an iterative process, an inversion scheme was carried out on the measured data to find a model M that minimizes the objective function ö_m subject to fitting the data to a specified degree. This model was formed and used to solve the optimization problem defining a global objective function Ö. Measured data obtained from the field work and theoretical data derived from the model recovered by inverting the data set were also plotted as pseudo-sections to get the estimated depth of the ore deposit from the surface. The results showed eight anomalous zones revealing certain mineralization having attributes of galena, sphalerite and pyrite with a resistivity ranging from 100-300 ohm-m at an estimated depth of 50 m. The plots of chargeability along the three traverse lines also showed a consistent range of values between 20-90 m V/V over the distance of 90-100 m along the lines. Different regions of high anomaly are evident in the inverse model resistivity section for the first two lines but due to bulk resistivity of the disseminated body investigated, no distinct zone could be localized. The quantitative interpretation showed that the range of overburden thickness to the top of base-metal sulphide is about 30m. Based on the result of this investigation, it was concluded that the sulphide ore in this area is not economically viable and can be best mined through shafts or tunnels due to the depth and dipping shape of the deposit

Keywords: Sulphide ore bodies, Osina area, induced polarization, chargeability,