No abstract

The Greens Creek Mine's 3.5M tonne dry-stack tailings pile receives about 800 tonnes of filter-pressed tailings daily. The silt-sized tailings are placed in thin, compacted lifts using a bulldozer and vibratory roller. Carbonate minerals produce a long lag time to acid generation despite a net-neutralization potential of-210 tonnes CaCO3/ktonne. Key influences on pore water compositions include near-surface pyrite and thiosulfate oxidation, vadose zone iron and manganese reduction and saturated zone sulfate reduction. Annual precipitation in excess of 1450 mm poses the largest challenge to achieving design placement densities in this seismically active region. Despite higher operational costs relative to slurry-tailings disposal, the decision to produce dewatered tailings provided economic and environmental advantages. It reduced the ultimate footprint of the facility, lowered closure and water treatment costs, improved pile stability and reduced environmental liability by allowing half of the tailings to be returned underground for use as structural backfill.