Modern mining generates large volumes of tailings (finely ground rock remaining after extracting ore) and waste rock (non-mineralized rock; low-grade ore), often containing iron sulphide minerals (e.g. pyrite). Exposed to the surface environment, these can react with water and oxygen to form sulphuric acid, producing acid metalliferous drainage (AMD). AMD can degrade water quality and impact aquatic biodiversity. Recent tailings dam failures (e.g. Mount Polley, Canada; Samarco, Brazil) demonstrate that mine wastes escaping into the environment can also significantly impact aquatic ecosystems and biodiversity, with tailings particles smothering riverbeds, reducing light penetration and oxygen levels, and affecting river geomorphology (Mudd et al. 2013).
Figure 9.6: Examples of surface streams affected by acid and metalliferous drainage (AMD) and/or tailings discharges: (left) Urban stream severely affected by AMD in western Witwatersrand Basin, Johannesburg, South Africa; (right) Tailings sediment from Samarco Dam
Figure 9.7: Rivers originating in the Hindu-Kush Himalayas are among the most meltwater-dependent systems
Sources: UNEP and Global Environment Facility [GEF] 2018; Global Land Ice Measurements from Space [GLIMS] 2018. Freshwater 243