Mining and ore processing waste

Our mining operations produce significant volumes of waste rock and tailings. Of particular importance is waste that is chemically reactive and that poses risks due to acid rock drainage and other geochemical hazards. In addition, associated activities give rise to large volumes of waste, some of which is hazardous. Consequently, appropriate waste management is required to minimise environmental impacts and risks associated with waste disposal infrastructure.

Over the reporting period the operations produced 169 million tonnes of waste rock and 12.7 million tonnes of tailings. Most (97 per cent) of the waste rock generated was placed in rock dumps within the mining areas, with the remainder placed in pit or as underground backfill, or used for the construction of mine infrastructure (Figure 1). Similarly, nearly all (96 per cent) of tailings waste was placed in engineered surface tailings storage facilities. The remainder of the tailings was disposed as underground backfill.

Ninety five per cent of total waste rock generation for the group occurred at Century and Prominent Hill. At Century mine, 95 million tonnes of waste rock generation included the removal of overburden at the western cutback to expose additional ore at depth. At Prominent Hill, 65 million tonnes of overburden material was removed as part of the development of the new open-cut mine. Of that amount, 2.9 million tonnes was used for the construction of new mine infrastructure including the embankment of the tailings storage facility.

To prevent or minimise the potential environmental impacts associated with waste rock and tailings disposal, we implement a range of strategies during project development and operations. They include the geochemical characterisation of acid-generating materials, resource modelling, selective handling and encapsulation of waste rock, disposal of tailings into specially designed and engineered facilities, linking operational planning to long-term closure management and the containment and treatment of mine waters to meet regulatory discharge criteria. In addition, the group standards for Waste Rock Management and Tailings Management define the requirements for the management of waste rock to prevent environmental impacts, promote beneficial post-mining land uses and reduce post mining rehabilitation and closure liability.

Of the total tonnage of waste rock produced in 2008, 97 million tonnes (57 per cent) is considered to be potentially acid forming, 59 million tonnes (35 per cent) is non-acid forming, and the remaining 13 million tonnes (8 per cent) has not been characterised for its acid generating potential (Figure 2). Virtually all waste rock (97 per cent) with acid generating potential is disposed in waste rock dumps. At Century and Sepon, emphasis during operations in placed on selective placement of the waste rock, the installation of drainage to capture and contain contaminated seepage for treatment, and monitoring of the local environment. Once construction of the waste rock dump has been completed, dump top surfaces may be compacted and covered to reduce the ingress of water. At the Avebury, Golden Grove and Rosebery operations, a majority (66 percent) of the acid generating waste rock is placed in the underground mine workings.