Evaluating links between microscale mineralogy and neutral rock drainage chemistry in mine waste materials

Quantitative automated mineralogical analysis is commonly used in mineral exploration, processing and increasingly in mine waste management. Yet, full integration between the microscale mineralogical dynamics of mine waste materials and the evolution of (bulk) wastewater quality remains challenging, especially for complex, heterogeneous materials. We experimented with syenite and skarn waste rock in 32-week leaching experiments under oxic versus sub-oxic conditions and examined the potential controls of (modal) mineralogical composition and mineral textures on select hydrochemical features of the resulting leachate. Circumneutral leachate pH was maintained throughout all experiments, and Ca, Sr, and Mn, and bicarbonate and sulfate were the most abundant solutes mobilized through mineral dissolution. Mineralogical analyses reveal carbonates and sulfates as the most reactive phases with generally higher exposures (liberation) and significant alteration to their textural properties, particularly in experiments under oxic conditions. Descriptive statistical analyses (time series, partial correlations and principal component analyses) helped identify plausible mechanistic controls on leachate trends, e.g., elevated Ca and Mg leachate concentrations attributed to carbonate dissolution and a mobilization of Sr from celestine dissolution. This study demonstrates that automated mineralogical analyses can provide valuable mechanistic insight into selected drainage features, while highlighting the challenges of establishing robust quantitative relationships between microscale mineralogical properties and bulk wastewater quality in heterogeneous mine waste materials.