Mine Tailings and the Environment

Dust blowing off the top of copper mine tailing piles. Witold Skrypczak/Lonely Planet Images/Getty

Tailings are a type of rock waste from the mining industry. When a mineral product is mined, the valuable portion is usually embedded in a rock matrix called ore. Once the ore has been stripped of its valuable minerals, sometimes through the addition of chemicals, it is piled up into tailings. Tailings can reach immense proportions, appearing in the form of large hills (or sometimes ponds) on the landscape.

Tailings deposited as large piles can cause a variety of environmental problems:

  • Slumps, landslides. Tailing piles can be unstable, and experience landslides. In 1966 in Aberfan, Wales, a hill of mining debris famously collapsed onto buildings, resulting in 144 deaths. There are also cases where wintertime avalanches occurred on tailings, with loss of life for residents below.
  • Dust. Dry tailing deposits contain small particles that are picked up by the wind, transported, and deposited on communities nearby. In the tailings of some silver mines, arsenic and lead is present in the dust in high enough concentrations to cause serious health problems.
  • Leaching. When rain falls on tailings, it leaches away materials that can create water pollution, for example lead, arsenic, and mercury. Sulfuric acid is sometimes produced when water interacts with tailings, or it can be a by-product of ore processing. As a result, highly acidic water leaks from the tailings and disrupts aquatic life downstream. Tailings from copper and uranium mining often produce measurable levels of radioactivity.

    Tailing Ponds

    Some mining wastes become very fine after they have been ground up during processing. The fine particles are then generally mixed with water and piped into impoundments as a slurry or sludge. This method cuts down on dust problems, and at least in theory, the impoundments are engineered to let excess water flow out without leaking tailings. Coal ash, while not a type of tailing, is a coal burning by-product stored the same way, and carrying similar environmental risks.

    In reality, tailing ponds also carry several environmental risks:

    • Dam failure. There have been numerous instances where the dam holding back the impoundment collapsed. The consequences to the aquatic communities below can be serious, for example in the case of the Mount Polly Mine Disaster.  
    • Leaks. Tailing ponds can be hundreds of acres in size, and in those cases leaks into surface and ground waters are probably inevitable. The heavy metals, acids, and other contaminants end up polluting groundwater, lakes, streams, and rivers. Some very large ponds in Canada’s tar sands operations leak large amounts of tailings in the underlying soil, in the aquifer, and ultimately into the nearby Athabasca River.
    • Wildlife exposure. Migrating waterfowl has been known to land on tailing ponds, and in some cases with dramatic consequences. In 2008, about 1,600 ducks died after landing on a tar sands tailing pond in Alberta, contaminated by floating bitumen, a tar-like substance. However, simple deterrent measures can reduce that risk significantly.