Assessment of Electrical Resistivity Tomography for Mapping Laterite Profiles in Ogun State

This study assesses the accuracy and resolution of electrical resistivity tomography for mapping laterite profile variability relevant to road construction and mineral extraction applications in Ogun State, South West Nigeria. Laterite is a critical construction material in Southwest Nigeria and is also the primary ore-forming horizon for iron and aluminium in the weathering profile. Conventional characterisation by trial pitting is expensive and provides only point data, while ERT offers two-dimensional profiling with depth sensitivity extending through the laterite profile. This study designs and executes an evaluation programme comparing ERT results with extensive trial pit data across three laterite profiles in Ijebu North, Sagamu, and Remo North local government areas. ERT data are acquired using Wenner, dipole-dipole, and Schlumberger arrays at 2-metre electrode spacing for direct comparison of array sensitivity and resolution. RES2DINV inversion produces resistivity sections that are independently validated against trial pit descriptions and penetrometer test profiles. Findings reveal that the combined Wenner-dipole-dipole protocol produces the most accurate laterite-overburden boundary delineation, with boundary depth errors averaging 0.32 metres compared to 0.61 metres for single-array surveys. Laterite quality zones, distinguishing ferricrete (above 800 ohm-metres), mottled zone (150 to 500 ohm-metres), and pallid zone (20 to 80 ohm-metres), are correctly mapped in 81 percent of comparison points. High-quality construction-grade laterite (above 800 ohm-metres) shows thickness variability of 0.5 to 4.2 metres across the sites, confirming that ERT mapping improves volume estimation accuracy significantly over pit-based methods. The study recommends ERT as a standard tool for laterite resource assessment in Ogun State.

Keywords: electrical resistivity tomography, laterite profiles, Ogun State, road construction materials, mineral characterisation.