Abstract
Snowmelt and rainfall infiltrate into the Bunker Hill Mine of northern Idaho, USA, oxidatively dissolve pyrite, and produce acid rock drainage that discharges from the mine portal. The complex geology of the Mesoproterozoic Revett Formation of the Belt Supergroup and alteration from past mining produced a highly heterogeneous environment for mine drainage. A university-industry partnership was developed to trace the origin, flowpaths, and traveltime of the mine drainage to provide the new mine owners with the necessary information to reduce infiltration and acid rock drainage. Snowpack, creek, and mine water samples were collected twice a month over a 1-year period for analysis of δ2H, δ18O, and 3H, along with the in-situ measurement of temperature, specific conductance, pH, discharge dissolved oxygen, and discharge. The δ2H and δ18O values were used to unmix mine water from perceived source waters upgradient of each sample location. Results indicate lower elevation snowmelt and overland flow infiltrating relatively quickly through anthropogenic conduits and causing the largest generation of acidic drainage. Slower, natural conduits associated with faults, fractures, and bedding planes produce mostly neutral waters with source waters typically originating at higher elevations. Unmixing of mine drainage sources and analysis of 3H indicate traveltimes ranging from < 1 to 23 years and greater dampening of seasonal source waters signals with increased depth in the mine. Correlation of 3H and δ18O with field parameters indicates the mixing of short and long pathways occurs throughout the mine.