Multi-scale characterization of preferential contaminant transport pathways in the Igbeti marble mining environment in southwestern Nigeria: Integrating VES, XRD, and SEM-EDS analyses

Abstract Mining activities in fractured basement terrains pose severe groundwater contamination risks, yet the precise micro-hydrogeological mechanisms governing contaminant migration remain poorly understood due to the inherent non-uniqueness of standalone geophysical interpretations. This study develops a multi-scale conceptual model of groundwater vulnerability in the Igbeti marble mining district, Nigeria, by integrating macro-scale Vertical Electrical Sounding (VES), meso-scale X-ray Diffraction (XRD), and micro-scale Scanning Electron Microscopy with Energy Dispersive X-ray Spectroscopy (SEM-EDS). The geophysical vulnerability assessment revealed uniformly extremely high aquifer vulnerability and poor protective capacity across the study area, driven by thin overburden (0.3–3.6 m) and highly fractured media, yielding exceptionally low longitudinal conductance values (S = 0.004–0.427 mhos). Ground-truthing these anomalies with XRD and SEM-EDS demonstrated that this vulnerability is fundamentally rooted in the intrinsic lithological and mineralogical properties of the basement complex. The aquifer matrix is predominantly composed of highly resistive, unweathered quartz (e.g., 62.63 wt% in TSRK1) and feldspars, exhibiting advanced chemical leaching and a distinct lack of protective, high-cation-exchange-capacity clay layers. Furthermore, while localized carbonate-rich zones (70.74 wt% dolomite in ARK1) provide some geochemical buffering, the dominant quartz-rich zones lack neutralizing capacity, facilitating the rapid mobilization of acidic leachates and heavy metals. These findings confirm that the fractured silicate and carbonate aquifers offer negligible natural attenuation to mining leachates. Consequently, mitigating groundwater contamination in this and similar mining environments requires moving beyond passive reliance on natural attenuation to implementing strict, science-based buffer zones, engineered impermeable tailings dams, and continuous hydrogeochemical monitoring to safeguard regional water resources.