Groundwater chemistry in the Schefferville, Quebec iron deposits

Summary

Input precipitation quality, soil clay mineral reactions and aquifer mineral dissolution control the quality of groundwater in an area of discontinuous permafrost in the Laborador Trough iron deposits near Schefferville, Quebec. Na and Cl are derived from precipitation and K from clay minerals. Ca, Mg and HCO₃ concentrations and pH are governed by the extent of mixing of saturated water from a dolomite unit with water from other, non-carbonate units. Local conditions govern the equilibrium concentrations in the dolomite-saturated water. On ridge tops carbonate materials are absent and the closed-system evolution path is followed but in one lower area, where a carbonate-containing till is present, evolution is open-system. Iron species concentrations and pE values suggest that groundwater in equilibrium with the iron oxyhydroxide minerals is anoxic. Groundwater temperatures are similar to the annual recharge temperature (4.7°C) and pumping associated with mining may cause an alteration in the permafrost distribution by inducing groundwater flow.