Preliminary Geophysical Investigation of Orin Clay Deposit, Southwestern Nigeria: Deductions, Implications and Possible Applications

Abstract

Clay resources exploration and exploitation has been on a steady increase in a bid to satisfy a growing mineral resource utilization industry. This necessitated a preliminary geophysical investigation of Orin - Ekiti clay deposit aimed at investigating the subsurface lithology, make deductions on the depth and thickness of any clay deposit encountered in the region as well as implications on possible industrial and engineering uses respectively and finally suggest possible areas for groundwater prospecting as a solution to the prevailing need for water in the area. Prospecting for clay deposits in the study area employed the vertical electrical sounding (VES) technique of the electrical resistivity geophysical survey method utilizing Schlumberger array. Six (6) VES at six (6) stations in the study area were carried out with maximum electrode spacing of 55.0m. Preliminary VES results revealed three main sounding curves namely HK (VES 1), KH (VES 2, VES 3 and VES 4) and K (VES 5 and VES 6). Indication of three to four geoelectric layers representing subsurface lithological formations was observed namely the top soil (0.5 – 1.9m), sandy clay (2.2m), compacted lateritic clay/hardpan (2.2 - 10.8m), weathered basement {clayey – 7.1 m and above, clayey sand (4.2 – 7.4m)}, fractured basement (9.2 m and above)  and fresh basement (9.9m and above). Preliminary assessment from 2D maps and 3D models indicates layer 2 of the geoelectric sections corresponding to the lateritic hardpan formation have moderate to high potential while the weathered clayey zone (layer 3) have low to moderate potential for future mining purposes. Groundwater potential in the area is rated low to medium based on overburden thickness {VES 5 (>12.4m) and VES 6 (>8.4m)} and clayey sand formation composition {VES 3   (>9.2m) and VES 4(>11.4m)} although the presence of fractured basement of undetermined thickness in VES 3 and VES 4 could significantly increase the odds. Any engineering construction project in the area would have to take into consideration the considerable thickness of the clay layers (≥ 10.8m) during planning and execution.

Keywords: Clay, vertical electrical sounding, Geo-electric section, lateritic hardpan, overburden.