Mining of metallic ores exposes metal-bearing minerals in wall rock, tailings, and waste rock to accelerated rates of weathering; this can lead to increased metal loading to the environment. Waters draining natural exposures of metalliferous rocks and rocks exposed through mining or mineral exploration commonly contain high concentrations of metals.
For natural attenuation processes to mitigate the effects of increased rates of metallic mineral weathering on the environment, it is necessary that metals removed from metalliferous waters be stored in a form that is stable over the range of conditions which exist at the attenuating site. Long term storage of metals is essential for natural attenuation processes to be of any practical value. Short term storage (e.g., seasonal retention) may result in periods of metal accumulation followed by large metal fluxes to the receiving environment over a short time period resulting from changes in site conditions (e.g., seasonal changes such as high spring flows). Understanding the temporal stability of different forms of metal storage and the processes by which natural attenuation in soils occurs will allow more accurate estimates of metal fluxes to the receiving environment. This knowledge may also prove beneficial in the design of passive water treatment systems for northern mines and exploration sites.
