Acid rock drainage
One of the most serious environmental risks for the mining industry is 'acid rock drainage' (ARD) from mineral waste.
ARD can be created when rocks that contain naturally occurring sulphide minerals - such as pyrite - are disturbed and exposed to air and water. This accelerates the natural weathering process and may lead to the release of low pH contact water with elevated salinity and metals concentrations. If improperly managed, ARD can prevent revegetation of mining wastes, and degrade surface and groundwater quality.
How we deal with ARD
To prevent or minimise these potential environmental impacts, we have adopted leading practice in mine planning, operation and waste management, while new projects are designed to ensure that the risk is minimised and that any generated ARD will be captured and treated. Our strategies are also being refined to better characterise acid-generating materials, improve mineral waste handling procedures, develop effective closure strategies and improve collection and treatment of ARD.
We use a number of techniques to prevent or control ARD. These include selective handling and encapsulation, disposal under water, blending waste materials and using either synthetic or engineered earth covers.
All operations where ARD could occur are required to maintain a management plan which must be reviewed every four years by an external expert. Our internal risk reviews are now regarded as the industry benchmark in this key risk area, and we continue to play a leading role in the International Network for Acid Prevention (INAP).
In addition, our Acid Rock Drainage Prediction and Control Standard continues to be periodically updated in response to technological advances and new issues identified at the operations. The Environment Due Diligence Guidance and Checklist has also been strengthened with regard to ARD issues.
Our results
Since 2004, 22 operations have been visited by the ARD risk review programme which assesses each operation's ARD hazards and management strategies. All existing mines and advanced projects where ARD could pose a significant risk have been visited by the programme.
This year we rolled out a new diagnostic tool to improve the management of all types of chemically reactive mineral waste. In addition to ARD, this programme also focuses on wastes that pose salinity, radioactivity, metals soluble or bioavailable at neutral pH and naturally occurring asbestos risks. Four mines and advanced projects have now completed this diagnostic program.
All managed operations visited by the ARD risk review and mineral waste optimization programmes since 2004 were in compliance with the relevant government regulations and permit conditions.
Six monthly reporting by these operations indicates that significant progress is being made to address the issues raised by the site visits. Given the long-term strategic nature of many of the ARD issues identified, and the long lead times to design and implement some of the studies and corrective actions, it is anticipated that this work will continue for many years.