Many Canadian mine tailings contain iron sulphides, which are oxidized by microorganisms. This causes extensive acid leaching ‘and consequently contamination of the environment. It is known that, if the tailings are flooded, there is insufficient oxygen dissolved in the water for this oxidation to take place. This method is currently being considered for the prevention of oxidation in certain sites. However it is impractical to flood -many old tailings, so we suggest that a self-sustaining anaerobic cover of peat bog will both prevent acid leaching and reclaim old tailings dumps with a natural environment. Part of the methane produced by degradation of biomass is trapped in the peat and prevents both the penetration of oxygen and the movement of water in the tailings.