Waste rock definition

What is Waste Rock?

Waste rock is barren or marginal ore that has been mined, but which has so little value that it is not worthwhile to engage in additional treatment, so it is discarded. Waste rock is usually removed in order to gain access to a commercially-producible mineral deposit.

Accounting for Waste Rock

If waste rock is being removed to gain access to a mineral deposit, then the cost should be capitalized along with other development costs and amortized over the life of the mine. If the removed waste rock does not provide access to a commercially-producible mineral deposit, then the related cost should be charged to expense as incurred.

What are the Characteristics of Waste Rock?

Here are some of the key characteristics of waste rock:

  • Composition. Waste rock may contain low-grade ores or other minerals that were not worth processing, as well as minor amounts of valuable metals.

  • Particle size. Waste rock is generally coarser than tailings (the fine-grained waste produced after ore processing). It ranges from small rocks to large boulders.

  • Environmental concerns. Due to the potential for acid generation and heavy metal leaching, waste rock piles need to be carefully managed to mitigate their impact on local ecosystems and communities.

  • Volume. Waste rock often comprises a significant volume in mining operations and requires substantial space for storage.

  • Reusability. Some waste rock can be repurposed for construction materials (e.g., road base or fill) if it is chemically and physically stable and does not pose environmental risks.

Related AccountingTools Course

Accounting for Mining