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When we extract minerals from rock we create waste. This includes mined rock, tailings & slag, which have only limited value but can pose environmental hazards if poorly managed. Much of our mineral waste therefore goes back into mined areas or is stored.

One of the most serious environmental risks for the mining industry is "acid rock drainage" (ARD) from mineral waste. When rocks containing sulphides are disturbed and exposed to air and water, they can generate acid which, over time, may leach contaminants out of the rocks. Left unchecked, this can reduce water quality in the long term. We minimise the potential for ARD generation by adopting leading practice in mine planning, operation and waste management.

Our ARD reviews are regarded as the industry benchmark

At Rio Tinto Iron Ore's Tom Price operation in the Hamersley province of Western Australia, mineral waste management and mitigation strategies are integrated into all stages of mine planning.

Acidic rock drainage and spontaneous combustion issues, are associated with the iron ore deposits in the Hamersley province - specifically with the waste shale that is removed to get to the ore. This shale is generally safe when oxidised but when unoxidised it poses risks of both ARD and spontaneous combustion.

Successfully preventing spontaneous combustion

Our black shale management plan has successfully prevented spontaneous combustion. However, because much of the sulfidic material in waste rocks can still come into contact with oxygen, oxidation can occur throughout the dumps, generating contaminants that can lead to ARD. As part of our ongoing work to protect regional water resources, we are developing an integrated approach involving placement of store and release cover systems on waste rock dumps containing pyritic black shale or the backfilling of final pit voids with pyritic black shale exposures, and backfilling of the voids with black shale placed below the water table.

The integrated approach will be used to minimise the potential to influence water receptors (permanent surface water bodies, water extraction bores used for livestock etc.) in the region.

What is our black shale management plan?

1. Identifying the distribution of black shale and its character.
2. Minimising the exposure and mining of the shale to the greatest extent possible.
3. Identifying and using special handling of the shale that must be mined.
4. Encapsulating the shale inside inert waste rock dumps to limit water contact and allow the dumps to be revegetated.
5. Placing the shale below the water table in backfilled open pits, and flooding the pit, to limit oxygen contact.

We also monitor ground and surface water quality, and the potential release of contaminants from the waste shale.