Tailings storage facilities store-and-release cover design for the Cobar region

Abstract

The Cobar region (the region) is located approximately 700 km west of Sydney in central western New South Wales (NSW). The region has a semi-arid climate with low humidity, low rainfall and high evaporation. Annual rainfall is approximately 400 mm while evaporation averages 2,000 mm annually. The Cobar basin is one of the most significant metalliferous regions in Australia, containing extensive base and precious metal deposits. The typical large, high-grade deposits of the region are hosted by marine sediments and consist of multiple lenses in steeply plunging, pipe-like clusters. There are currently five operational mines in the region that mine a range of metals including copper, lead, zinc, silver and gold. During ore processing, potentially acid forming (PAF) tailings are generated and discharged underground or to tailings storage facilities (TSF). PAF tailings require careful rehabilitation to minimise the risk of harm to the receiving environment. Typically, the rehabilitation of a TSF involves two controls. First, controlling the potential for PAF tailings to form acid mine drainage (AMD) by limiting interaction with oxygen that promotes oxidation of sulphides to form AMD. Second, once the tailings are unsaturated, limiting interaction with water to reduce the potential for AMD to be transported to the receiving environment. These two forms of control are often employed in the form of a cover. In semi-arid environments, there are many Australian examples of covers that have been built to limit interactions of tailings with oxygen and water. Typically, the covers contain two or more layers and are built from soil and rock that may include run-of-mine waste rock. The purpose of this paper is three-fold and describes the cover design process employed by two mines (Mine A and Mine B) in the region (the mines). That is, the paper describes the desktop cover design process that the mines used to develop cover options for the TSFs. Secondly, the paper describes the method and results of large column trials that were used as a cost-effective way to trial multiple cover options for the TSFs. Finally, the paper describes the cover design models that were built from the column trial results and how the models were used to scale up and assess the potential future performance of the covers if they were built on the TSFs. From this data, suitable cover designs for TSFs in the region will be identified.