GRAIN SIZE AND HEAVY MINERAL ANALYSES OF TWO BOREHOLES IN RECENT TO MIOCENE AQUIFER IN BENIN FORMATION

Abstract

Recent studies have revealed that groundwater contamination is dependent on the porosity and permeability of the overlying and underlying bed rocks and the mineral composition of the aquifer geometry with respect to depth. This study became important due to several reports on groundwater contamination and in order to understand the mineral composition and the grain sizes of the aquifer in the study areas. Two boreholes were drilled 4.2km apart; one at Okabere and the other at Evbuabogun community both in Ikpoba-Okha Local Government Area of Edo State. The communities have been merged with the capital city as a result of urbanization and population growth. Grain size and heavy mineral analyses were carried out on the soil samples collected from the boreholes at an interval of 15ft. The results obtained indicate that the heavy minerals in Okabere borehole is dominated by Zircon, Tourmaline, Rutile, Biotite and Garnet while Evbuababegun borehole is mainly of Zircon, Kyanite, Rutile, Staurolite, Garnet and Tourmaline which indicate that the sediments were of igneous and metamorphic origin. Grain size analysis of both wells show that mean, inclusive standard deviation, skewness and kurtosis generally indicates very coarse sand to medium sand; very well sorted to moderately sorted and very platykurtic in nature. The foregoing revealed that the aquifer geometry of the study areas is unconfined and vulnerable to contamination. It is recommended that groundwater quality assessment study should be carried out in order to determine the potability of the groundwater bodies.