An assessment of the environmental impact of the weathering of sulphide-rich rocks at Citronen Fjord, North Greenland, provided information on sulphide oxidation rates and metal release from outcrops of sediment-hosted, stratiform ore that may be mined for its zinc content. In situ oxygen uptake rates were measured at the surface of partly weathered sulphide-rich outcrops and compared with metal contents in streams and soil water. The oxygen uptake rates measured during August 1996 were of the same order of magnitude as those reported from mine tailings at lower latitudes. The variation in metal concentrations and pH of the drainage waters reflects the spatial variation in sulphide oxidation and carbonate buffering. High weathering rates of sulphide minerals occur in the High Arctic during the summer, and release of heavy metals must be considered a potential environmental issue if mining is initiated.