THE USE OF INTEGRATED GEOPHYSICAL METHODS TO EVALUATE CLAY DEPOSIT IN IRE - EKITI, SOUTHWESTERN NIGERIA

Abstract

Clay has found its use in every century and at this period in Nigeria a lot of demand for cement and cement products warrants a search for alternatives of which clay fits in perfectly. Thus, there is need to explore and evaluate clay deposits in order to establish the nation’s clay reserves with the purpose of setting up and expanding clay products industries. Hence, a clay deposit in Ire-Ekiti was chosen for geophysical investigation with the aim of characterizing and quantifying its reserve. The survey covered a total area of 55,322m2 along five traverses while the target area of 25,224.78m2 was divided into six blocks. Magnetic, VLF-EM and combined Vertical Electrical Sounding (VES) and Horizontal Profiling (HP) technique of electrical resistivity methods were used for the preliminary study. The magnetic method gave depth estimates to structures and the bedrock. While VLF-EM method is rarely used on clay deposits, it was employed in this work to delineate enhanced conductive structures, if any, that may cause geotechnical problem at the period of mining. The dipole-dipole survey was used to determine the areal distribution of clay and its electrical properties. The study also involved VES technique using the Schlumberger electrode configuration to delineate the geoelectric layers and determine their thicknesses. A maximum of three to five layers were delineated, namely; top soil, sand, lateritic clay, clay, and partly weathered/fractured/fresh bedrock. The resistivity and thickness values ranges of the clay layer are 54 - 99 Ωm and 5.3 - 67m respectively. Two methods were used to estimate the clay reserve and the excavable volume. Method 1 involved the generation of thickness contour lines by krigging method across the study area while the Method 2 utilized the thickness of clay as obtained at VES data points. The results were 858.78 tonnes and 482,461.24m3; and 896.41 tonnes and 137,086.03m3 respectively. And statistically, Method 2 proved more representable.