Integrated Geological and Geoelectrical Investigation of Groundwater Potential in Part of Sheet 54 SE (Gusau SW), Zamfara State, Nigeria

Abstract

This study presents the results of detailed geological mapping and geoelectrical investigation 
carried out in Sheet 54SE (Gusau SW), Zamfara State, northwestern Nigeria, with the 
objective of characterizing lithological units, structural features, and evaluating groundwater 
potential within the crystalline basement terrain. Geological field mapping involved systematic 
in-situ examination of rock outcrops, structural measurements, and lithological identification. 
The area is characterized by low-lying ridges and whaleback exposures dominated by coarse
grained granitic rocks. Structural features mapped include joints, faults, quartz vein 
intrusions, and zones of differential weathering, all of which play a significant role in 
controlling secondary porosity and permeability within the basement rocks. Petrographic 
analysis of representative rock samples under plane-polarized light (PPL) and cross-polarized 
light (XPL) reveals that the granites are predominantly composed of quartz, orthoclase, 
biotite, and hornblende, confirming their affinity with the Pan-African granites widely 
distributed across northwestern Nigeria. Groundwater potential was further evaluated using 
the Vertical Electrical Sounding (VES) technique with the Schlumberger electrode 
configuration and a maximum current electrode spacing (AB/2) of 100 m. A total of fifteen 
VES stations were occupied along five traverses across the study area. Interpretation of the 
geoelectrical data delineated three to four subsurface geoelectric layers comprising topsoil, 
weathered basement, fractured basement, and locally fresh basement. The topsoil layer 
exhibits thicknesses ranging from 0.545 to 20 m with resistivity values of 15.6–39 Ωm, while 
the weathered basement layer varies between 0.758 and 60 m with resistivity values of 34.4
146.6 Ωm. The fractured basement layer occurs at depths of 23–93 m and displays resistivity 
values of 161.2–408.9 Ωm. The weathered and fractured basement horizons constitute the 
principal aquifer units in the area. Among the sounding locations, VES 4, VES 5, and VES 6 
exhibit the most promising groundwater potential due to their relatively thick conductive 
weathered zones and well-developed fractured basement. The results demonstrate that 
integrated geological and geoelectrical investigations provide a reliable approach for 
groundwater exploration and aquifer delineation in crystalline basement terrains.