This paper presents the geophysical investigation for groundwater at Gbongudu area, Akobo Ojurin, Ibadan, Southwestern Nigeria. The area is underlain by the crystalline basement complex rocks and accessibility to potable water especially in the dry period of the year has been a major challenge. The Vertical Electrical Sounding using the Schlumberger configuration was employed. Twelve (12) vertical electrical sounding points were established in order to delineate the geo-electric layers in the area as well as evaluate the groundwater potential. The results are presented as profiles, geologic sections, curves, and maps. The VES results revealed a maximum of five geo-electric layers, viz: topsoil/lateritic sand, shale/clay, weathered layer, fractured basement and fresh basement respectively. Geo-electric sounding results were critically analyzed and interpreted. The yields of wells dug in most of these locations may be insufficient, even for domestic use because of its relatively small thicknesses. However, at a depth of 9.1 m a fracture zone occurs in VES 6 with resistivity value of 17.8 Ωm suggesting the presence of groundwater. Groundwater potential in this area is low on the average with VES 6 and VES 7 considered to be the main aquifer units suitable for groundwater exploration. © JASEM https://dx.doi.org/10.4314/jasem.v21i3.14

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AbstractThe article presents the grain size distribution of soil samples from the Precambrian basement within the purview of the textural properties, deduced transportation history and the numerical assessments using statistical parameters. The fourteen soil samples collected from the study area were subjected to sieve analysis in the laboratory for the determination of their grain size distribution. The statistical parameters’ study includes the graphic mean, skewness, sorting and kurtosis. The result of the analysis of the soil samples ranged from coarse to fine-grained samples, moderately and poorly sorted, positively and negatively skewed and the kurtosis also shows leptokurtic as the most dominant which suggests the samples poorly distributed and moderately sorted at the centre of the grain size distribution. These results also suggest the geological environment of the soil samples could be responsible for the poorly and moderately sorted exhibited by the samples deposited in the location.

The slope method is one of the earliest magnetic depth estimate techniques which can determine the depth to the top of magnetic basement. Reduction-to-pole was applied to the aeromagnetic data of Ilesha southwest, Nigeria with sheet number 243. The data which was originally partitioned into different profiles was later processed to generate reduction-to-pole graph. The contour map of the study area was partitioned into four quadrants, with the highest magnetic anomaly occurring at the third quadrant (southwest region), while the northwest region has the lowest magnetic anomaly. The depth to top for very thin body, intermediate body and very thick body was determined using the Peter's half slope method. These values range between 2.40 km and 10.60 km for the very thin body, 1.8 km to 7.93 km for the intermediate body and 1.41 km to 6.35 km for the very thick body. These results revealed the extent of the depth of the source of the magnetic anomaly that was produced by the aeromagnetic data of the study area.

Ground magnetic survey is an essential geophysical method employed in locating subsurface magnetic materials for possible exploration. In geophysics, the anomalous magnetization might be associated with local mineralization that is potentially of commercial interest. Hence a ground magnetic survey was carried out at a site in Tajimi area of Lokoja, Kogi State, Nigeria. The study is aimed at locating the position of iron deposited minerals within the study area. The study area lies within Latitude 8 0 0292ˈN to 8 0 0625ˈN and Longitude 6 0 5833ˈE to 6 0 6167ˈE in the basement complex of Southern Nigeria. A total of fifteen magnetic transverse lines were established in an E-W direction in the study area covering 140m by 75m. Data were taken and recorded using Proton Precession magnetometer; the data were presented in magnetic profiles, 2D contour map and 3D surface map which aided the qualitatively interpretation. The study area was characterized by completely varying magnetic anomaly amplitudes across the field. The field data were quantitatively interpreted and the results gave values for the total component measurements of the ground magnetic anomaly that varied between a minimum negative peak value of about -23428.7nT and a maximum positive peak value of about 5840.9nT. The residual anomalies obtained were plotted against distance using Microsoft Excel and Analytic signal method was used to estimates the depth to the magnetic source body. The estimated depths of the magnetic source body/rocks from the Earth surface fall in the interval of 1.28m to 13.57m, which indicates the magnetic source body suspected to be magnetic mineral, are near surface features. Hence a careful analysis of the magnetic anomaly maps can give vital information about the magnetic distribution and mineral potential of the study area at Tajimi.