The fate of seafloor massive sulphide deposits, insights from natural and accelerated oxidation and implications for future mining activity

摘要

As mining of seafloor massive sulphide (SMS) deposits edges closer to reality, with Nautilus Minerals Inc. poised to commence production offshore of Papua New Guinea by 2019, it is imperative that we have a full understanding of the deposit characteristics, the natural processes affecting their economic worth and the environmental impact associated with the mining process. Acid rock drainage is a natural oxidation process that is often exacerbated by mining activities, and this type of pollution is common in terrestrial sulphide mines. A related weathering process also occurs on SMS deposits, and the prospect of seafloor mining in the future raises similar environmental concerns. Unlike terrestrial deposits, it is assumed the seafloor sulphides are converted to oxides with negligible metal release and minimal net acid generation due to the buffering capacity of seawater and low solubility of iron at near neutral pH. Whilst a few dissolution studies of specific sulphide minerals in seawater exist, the majority are within the context of acid mine drainage related to terrestrial mines.