Original Contribution to Mine Tailings Geochemistry and Long-Term Environmental Fate Modelling in the Nigerian Basement Complex

Mine tailings deposited in the Nigerian Basement Complex release trace metals through weathering, dissolution, and erosion processes over timescales that greatly exceed typical post-closure monitoring periods, yet predictive models of long-term environmental fate have not been developed for this geological and climatic context. This dissertation makes an original contribution to tailings geochemistry and long-term environmental fate modelling in the Nigerian Basement Complex, synthesising data from six active and legacy mine sites across Plateau, Nassarawa, Kogi, and Zamfara states. A multi-disciplinary methodology integrates sequential extraction geochemistry, mineralogical analysis by automated scanning electron microscopy, column leaching experiments under simulated Nigerian rainfall chemistry, and reactive transport modelling using PHREEQC and TOUGHREACT codes. The research constructs the first geochemically parameterised long-term leachate transport models validated against field monitoring data for Nigerian mine tailings. Original findings include the identification of secondary jarosite and scorodite phases as critical long-term arsenic and lead release controls unique to lateritised tailings profiles in the humid tropical basement complex environment. A 100-year fate trajectory model predicts persistent groundwater quality exceedances at 40 percent of modelled scenarios under current management practices. The dissertation proposes an original tailings geochemical risk classification system for Nigerian conditions and recommends design standards for passive containment engineered on the basis of geochemical reactivity class. Keywords: mine tailings, geochemistry, environmental fate modelling, Nigerian Basement Complex, reactive transport.