Investigating Mineral Weathering and Metal Transport through Century-Old Ore Chimney Waste Rock

This thesis investigates the long-term weathering of a 100-year-old waste-rock pile at the Ore Chimney mine. Three vertical trenches were excavated, and waste-rock material was sampled at 0.5 m depth intervals. Waste-rock material was sieved into fine (< 0.5 mm) and coarse (0.5 to 2.0 mm) grain size fractions and used to investigate solid-phase geochemical signatures and porewater geochemistry. Solid-phase geochemical investigations revealed a sulfide mineral assemblage composed of highly weathered sphalerite and galena, with frequent occurrence of relatively un-weathered pyrite and chalcopyrite. Porewater pH was near-neutral suggesting ongoing acid neutralization. Porewater Zn concentrations as high as 87.5 ppm are attributed to the prolonged weathering of sphalerite. High alkalinity levels (μ = 60.2 mg/L CaCO3) suggests that carbonate phases are potentially controlling Pb, Zn, Cd, and Cu in the porewaters. Results from this study suggest that weathering processes may continue for some time, but abundant carbonates will provide long-term buffering.