Waste rock

Waste rock is composed of unconsolidated overburden and bedrock that must be removed to uncover or access ore during mining. 

The volume of waste rock generated at most mines is much larger than the volume of tailings and the management of it can be challenging for several reasons. A large footprint must be devoted to waste rock disposal and unless the facilities are properly designed, they can be prone to erosion and failure. In addition, some waste rock may be geochemically reactive and can pose environmental risks because of acid rock drainage, salinity or other contaminants.

How we deal with waste rock

Whenever possible, we try to use waste rock to backfill open pits or underground workings.  This minimises the footprint of land that must be disturbed by mining and often allows the open pit footprint to be returned to a productive post-mining use.

When backfilling is not possible, the waste rock is usually placed in engineered waste rock dumps.  To minimise haulage distances, waste rock is usually placed as close to the point of mining as possible.  This not only reduces the handling costs, but also reduces fuel consumption and air emissions per tonne of waste rock moved. 

At older mines, waste rock is usually placed on surfaces and in drainages that have already been disturbed by historic waste rock disposal.  New waste rock dumps are also sited and designed to minimise environmental impacts and to allow the waste rock surface to ultimately be reclaimed and revegetated.

Waste rock that poses geochemical hazards because of acid rock drainage, salinity or other contaminants requires additional management. Contaminated contact water is collected and recycled or treated for release from permitted discharge points. Chemically reactive waste rock is also encapsulated or capped at many operations so that the mineral waste can be revegetated, the runoff water quality can be protected and direct exposure risks are lessened.

All operations that generate mineral waste are required to maintain a mineral waste management plan.  The scope and level of detail of the plan must be commensurate with the hazards posed by the mineral waste that is generated on site.            

Our results

• In 2007, we produced 1,754 million tonnes of mining mineral waste (predominantly waste rock), 1.7 per cent more than 1,725 million tonnes generated in 2006. 
• The increase in 2007 was the result of increased overburden stripping at Hail Creek and Jacobs Ranch, and commissioning of new areas at Yandicoogina. 
• Much of the material generated in 2007 was moved within mined areas and placed as in-pit backfill (66 per cent) or rock dumps (25 per cent) close to where it was generated, six per cent in tailings dams, and the remainder was either recycled/reused, stored or disposed of at other locations.
• In 2006, 68 per cent of mineral waste was placed back into the mine, 23 per cent in rock dumps, six per cent in tailings dams, and the remainder was either recycled/reused, stored or disposed of at other locations.  More than 400 hectares devoted to mining mineral waste disposal was reclaimed in each of 2006 and 2007. 
• Only 8 per cent of the mining mineral waste produced in 2007 is considered to have acid generating potential or to be pose other geochemically hazards and six per cent of the mining mineral waste produced in 2006 (see Acid Rock Drainage).  Almost all of this reactive mining waste is stored in engineered waste rock dumps.

• The acquisition of Alcan is expected to have marginal impact on our mineral waste profile. Alcan operations generated 3.2 million tonnes of fairly inert Bauxite waste in 2007.