干旱区生态环境知识资源中心

The importance of biogeochemical and hydrogeological data to understand the formation of acid mine drainage and to select the most appropriate strategy for remediation of mine waste is highlighted by using three examples of mine tailings deposits. The first case of the Piuquenes tailings impoundment at the La Andina mine in Chile shows the biogeochemical interactions in the formation of a ferrous iron-rich plume, the first step in acid mine drainage formation. In the two other cases at Cha (n) over tilde aral, Chile and at Bahia de Ite, Peru (both marine shore tailings deposits), very similar settings could lead, on a fist glance, to the selection of similar remediation strategies for the mine wastes. Both tailings deposits formed after decades of deposition of flotation tailings through a riverbed from porphyry copper deposits in bays in the Pacific Ocean, and were exposed to oxidation in the hyper-arid climate of the Atacama desert. However, the data reveals that the hydrological situation of the two mine waste sites is completely different and is therefore crucial for the selection of the remediation strategy. In the case of Cha (n) over tilde aral, water supply is scarce and the water infiltrates into the tailings deposit as highly saline Submarine Groundwater Discharge (SGD), containing high copper concentrations (up to 19 mg/L at neutral pH). This setting might lead to a potential enrichment and makes therefore the site economically interesting for exploration. In case of Bahia de Ite the supply of high quantities of alkaline freshwater infiltrating the tailings deposit made the implementation of a wetland on the oxidized tailings deposit possible, resulting in a very effective bioremediation, limiting the oxidation and release of elements to the environment from the tailings. The studies show that a combination of mineralogical, geochemical, hydrological and microbiological studies is needed in order to understand the biogeochemical element cycling in these systems and to ensure a sustainable management of the mine waste.