Fifteen (15) Vertical Electrical Sounding (VES) and three (3) Constant Separation Traversing (CST) data were acquired within the study area using Pasi Terrameter (model 16GL). The Schlumberger electrode array was deployed for the VES while Wenner array was used for the 2-D CST. Both qualitative and quantitative approach were used for the VES measurements. The raw data were Curve-matched and inversion of the data using WinResist (1.0) to create a model of perfect fit indicating layer thickness and resistivity values for individual layers while the 2D resistivity data were processed using Res2Dinv software. The 2D resistivity structures revealed the lateral and the vertical variations of the subsurface information having resistivity values ranging from 81.8 to 5250 Ωm. The geoelectric sections revealed five to six geoelectric layers, which correspond to the topsoil, clayey sand, lateritic clayey sand and sand. The topsoil is characterized by resistivity values ranging from 29.8 to 358.5 Ωm and layer thickness of 0.6 to 0.8 m. The clayey sand had resistivity and layer thickness values ranging from 81.4 to 278.0 Ωm and 2.4 to 7.1 m respectively. The lateritic clayey sand had resistivity values ranging from 782.0 to 2414.1 Ωm. and layer thickness of 5.4 to 61.2 m. The sand in the third layer in VES 1 to 7, 9 and 10 has resistivity values ranging from 398.6 to 600.7 Ωm and layer thickness of 2.3 to 25 3 m is characterized as seasonal aquifer. The result of this study has further highlighted the capabilities of the electrical resistivity techniques in groundwater investigation
The Wenner – Schlumberger array was used for Constant Separation Traversing (CST) to investigate subsurface lithology in Auchi Polytechnic, Auchi. All the traverses were carried out with electrode spacing of 5 m with a spread of 200 m. The data was obtained using Pasi terrameter (16-GL) and processed with the Dipro software. The subsurface resistivity values ranged from 207 Ωm – 8357 Ωm. The results obtained from this survey classified the subsurface lithology into topsoil, clayey sand, sandy clay and sand. The maximum depth penetrated was 50 m. Keywords: Lithology, resistivity, subsurface, Wenner-Schlumberger, 2-Dimensional.
The Schlumberger array method was used to carry out a total of eight (8) Vertical Electrical Sounding (VES) with a spread of 350 m in the study area. The Pasi 16-GL Terrameter was used to acquire the data. The data obtained were analyzed with the Winresist 1.0 software to obtain the curves of best fit to the theoretical models. The modeling program converted the apparent resistivity into true resistivity values in 1-D model curves. Five (5) to seven (7) layers were delineated which correspond to the topsoil, sandy clay, clayey sand, sand, dry sandstone and saturated sandstone. The depth to aquifer ranges from 95.0 to 169.6 m with resistivity values ranging from 324.3 to 1524.7 Ωm. Keywords: Apparent resistivity, Aquifer, lithology and vertical electrical sounding.
A total of three electrical imaging lines were measured using the Wenner configuration. And a total of fifteen VES was carried out within the area of investigation and six water samples was collected. The results were presented as profiles, model sections, inverted sections and tables. Interpretations of these results involve both qualitative and quantitative deductions from 1D and 2D geoelectric models and laboratory analysis for the water analysis. The VES data were processed by partial curve matching to generate the 1st order geoelectric parameters and inverted in 1D using the WinResist. The 2D resistivity data were processed by inversion using the DIPROFWIN to generate the 2D resistivity section across each traverse while the water samples were taken to the laboratory for comprehensive analysis. The 2D resistivity structures reveal the lateral and the vertical subsurface information with resistivity values ranging from 0.130 to 4741 Ωm. The resistivity values are representative of the clay, clay (saline), clayey sand (saline), clayey sand and sand. From the quantitative interpretation five to six distinct layers were identified. The layers are: topsoil, clayey sand, clay, saline clayey sand, saline clay and sand. The resistivity of the topsoil varies from 38.2 Ωm to 155.3 Ohm-m. The resistivity of the sand varies from 100.8 Ωm to 115.8 Ωm. The resistivity of clayey sand varies from 56.6 Ωm to 90.1 Ωm. The resistivity of clay varies from 12.7 Ωm to 41.2 Ωm. The resistivity of the saline layer (saline clayey sand/clay) varies from 2.1 Ωm to 51.2 Ωm. The depth of saline clay interface varies from 25.7 m to 72.6 m. The depth to the saline clayey sand interface varies from 25.7 - 72.6 m. The chemical analysis of water samples showed that the pH varies from 7.05 to 8.42, total dissolved solids vary from 1786 to 2116 mg/L and electrical conductivity varies from 2106 to 2656 µS/cm. The anions and cation concentrations such as Ca2+, Mg2+, Na+, K+, Cl- and HCO3- ranges from 158 to 185 mg/L, 36 to 48 mg/L, 222 to 287 mg/L, 3.2 to 3.8 mg/L, 10.86 to 20.87 mg/L and 2.33 to 3.88 mg/L respectively. The ratio of Cl/HCO3- ion ranges from 4.05 to 7.67. The interpreted results show saline water intrusion where they occur in different part of the area investigated. The results showed the effectiveness and usefulness of electrical resistivity method in mapping saline water intrusion problem in coastal areas. However, it is necessary to carry out integrated geophysical surveys involving electrical resistivity and induced polarization methods prior to drilling in the study area.
2D Electrical Resistivity (ER) and Instantaneous Potential (IP) geophysical techniques were used at Eziama village in Abia state of Nigeria to investigate possible Pb-Zn mineralization. The dipole-dipole electrode configuration was employed for data acquisition and Earth Imager software was used for inversion of the acquired data. The analysis of the result of the study showed the presence of the Pb-Zn ore along traverses 1, 2 and 3 while traverses 4 and 5 appear barren. Along traverse 1, the mineralized zone falls within the fractured basement and is characterized by low resistivity (about 316 – 5623 ohm-m) and high chargeability (33.2 – 128 ns) at lateral distance of 73 – 103 m. On traverse two, the ore body was identified at lateral distance of about -18 to 53 m as delineated on the IP structure with resistivity and chargeability of the anomalous zone ranging from 4.6 – 677 ohm-m and 41.8 – 142 ns respectively at depth of about 21.4 m while on traverse three, two ore bodies labeled a, a’ and b, b’ on the ER and IP cross-sections were delineated at lateral distance of about -130 to -93 m and 78 to 98 m respectively with depth to the top of the suspected ore bodies ranging from about 7.1 m for body ‘a’ and about 14.3 m for ‘a’. Traverses four and five however showed no prospect for Pb-Zn mineralization. The result of this investigation has once again demonstrated the usefulness of combined electrical resistivity and induced polarization techniques in solid mineral exploration.
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