n Journal of Emerging Trends in Engineering and Applied Sciences - Geoelectric reserve estimation of laterite deposits along a basement complex underlain Osogbo-Iwo Highway, Southwest Nigeria

Volume 3, Issue 3
  • ISSN : 2141-7016
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Geoelectrical investigation, involving the Vertical Electrical Sounding (VES), was carried out at eight borrow pit sites within the corridor of the Osogbo - Iwo Highway with a view to estimating the reserve of laterite for the highway rehabilitation works. The area is underlain by a suite of basement rocks which vary from gneiss/migmatite to schist pegmatised, charnockite, meta-intrusives and fine-medium grained granite. The VES involved the Schlumberger array with half current-current electrode spacing varying from 1 to 65 m. The subsurface sequence beneath the proposed borrow pits is generally made up of four geologic layers comprising the topsoil (which is lateritic in places), laterite, weathered layer and the basement bedrock. The 1st and or the 2nd layer constitute(s) the lateritic layer with resistivity values generally greater than 300Ω-m and average thickness varying from 0.8 m to 13.3 m. The areal extent of the investigated sites ranges from 2,368 to 6,056 m2. The estimated volume of laterite deposit at the sites ranges from 3,816 m3 to 59,731m3. Out of the eight borrow pits investigated, only three (Pits 1, 2 and 6) are considered as viable for mining, from the point of view of the reserve while Pit 3 is considered marginally viable. The remaining four sites (Pits 4, 5, 7 and 8) have low reserve of laterite. The overburden thickness within the proposed borrow pits are generally thin, making open cast mining attractive. This study shows that lateritic soils required for road construction are more developed on schist and charnockitic rocks than on quartzites and granitic rocks.

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