Using Geophysical Methods for Environmental Compliance Monitoring at a Solid Mineral Mining Site in Zamfara State, North West Nigeria

Artisanal and small-scale gold mining in Zamfara State has expanded rapidly in recent years, raising serious environmental compliance concerns related to heavy metal contamination of soils and shallow groundwater that regulatory authorities lack the geophysical monitoring infrastructure to address effectively. This professional study applies electrical resistivity monitoring and soil radiometry to support environmental compliance assessment at a licensed artisanal mining site in Anka Local Government Area. Time-lapse two-dimensional electrical resistivity tomography was conducted along four permanent profile lines established at baseline and repeated at six-month intervals over an 18-month monitoring period. Changes in subsurface resistivity distribution between monitoring epochs were attributed to the migration of metal-contaminated leachate from tailings storage areas. Soil sampling for heavy metal analysis (lead, mercury, arsenic, cadmium) was conducted at 50 geophysically guided locations at each monitoring round. The time-lapse ERT difference sections reveal progressive low-resistivity anomaly expansion from tailings areas toward nearby community water sources, with a migration rate of approximately 15 metres per month in the dominant hydrological flow direction. Lead concentrations in soil samples at 15 downslope locations exceed Nigerian FEPA soil quality thresholds. The study develops a geophysically informed compliance monitoring framework that meets the requirements of the Nigerian Mining Environmental Guidelines and can be operationalised by state environmental protection agencies with limited geophysical expertise. Keywords: environmental monitoring, artisanal mining, Zamfara, resistivity, heavy metals