Abstract
Oxidation of pyrrhotite and related sulfide minerals in the vadose zone of the Ore Knob Mine tailings pile generates dissolved Fe+2, SO 4 −2 , and acidity, which are rapidly transported through the pile by infiltrating surface water. Significant spatial variations in the physical and hydraulic characteristics of the tailings cause large variations in air-filled porosity and effective oxygen diffusion into the pile. Tailings in the upstream areas are more fine-grained, with less air-filled porosity and oxygen diffusivity. The original tailings in the downstream areas are more coarse-grained, with less water retention and greater oxygen diffusivity. However, weathering processes have increased the fine-grained fraction in the oxidized zone and hardpan layer, increasing water retention and lowering oxygen diffusivity. The thickness of the downstream oxidized zone combined with increased water retention due to weathering may have significantly reduced acid generation in these areas.
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