Mechanistic Investigation of Acid Mine Drainage Generation and Geochemical Attenuation in Artisanal Mining Terrains of Zamfara State: Implications for Remediation Design

Acid mine drainage from sulphide mineral oxidation in artisanal gold mining areas represents one of the most chemically complex and ecologically damaging pollution phenomena in northern Nigeria, yet mechanistic understanding of its generation and natural attenuation remains uncharacterised. This dissertation presents an original mechanistic investigation of acid mine drainage generation chemistry, metal mobilisation pathways, and geochemical attenuation processes in artisanal mining terrains across Anka, Maru, and Gummi Local Government Areas of Zamfara State. Field campaigns encompassing solid waste characterisation, surface water and pore water chemistry, mineralogical mapping, and in-situ electrochemical measurements were conducted over two seasonal cycles. Acid-base accounting, static tests, and kinetic humidity cell experiments on mine waste samples provided mechanistic drainage generation data. Geochemical modelling using MINTEQ and PHREEQC was applied to evaluate mineral saturation states, speciation of dissolved metals, and predicted downstream metal attenuation via precipitation and co-precipitation reactions. Stable isotope ratios of sulphur-34 and oxygen-18 in sulphate were used to trace sulphide oxidation mechanisms and distinguish bacterial from abiotic reaction pathways. Results identify pyrite and arsenopyrite as primary acid-generating minerals, with bacterial oxidation accounting for 65 to 80 percent of sulphide oxidation kinetics at active sites. Ferrihydrite and jarosite precipitation are identified as dominant natural attenuation mechanisms. Lead mobility is primarily controlled by pyromorphite and plumbojarosite stability fields. The dissertation contributes an original geochemical framework directly applicable to passive treatment system design and integrated remediation planning in the Zamfara context. Keywords: acid mine drainage, Zamfara, geochemical attenuation, sulphide oxidation, remediation