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Cold climate mining and the dangers of permafrost at tailings facilities

Permafrost has a huge impact in the prospecting of mines in the arctic north — it affects the entire mining lifecycle from planning and operation to eventual abandonment. Mining operators with tailings facilities in cold climates need to ascertain the durability of the active layer of permafrost as there may be implications on the feasibility of mining operations.

Soil or rock that remains at or below the freezing temperature of water (0ºC) for at least two years is considered permafrost, or perennially frozen ground. It comprises a perennially frozen layer, as well as an active layer that freezes and thaws every year. But given huge variations in ground and surface air temperature that may occur at some mining regions, the thickness of this active permafrost layer may vary.

Disturbance from climate change and miners’ activities may alter or even eliminate this active layer permafrost. When that happens, there is no longer a guarantee that the “permafrost” in cold climate mining operations is a permanently frozen layer of soil or rock. The effects of permafrost erosion may halt operations, lead to the abandonment of the mining or tailings site, and incur additional financial costs for mining operators.

There may be significant environmental damage if inadequate actions are taken to mitigate permafrost degradation on tailings dam structures. As dams are constructed for long-term tailings containment, liquids or slurries of contaminated earth dumped into tailings reservoirs during warm summers may have moisture content that heats the cold soil. With natural freezing and thawing cycles, liquids expand and contract. In the presence of unfrozen “wet” tailings, embankments can be deformed and have their structural integrity compromised. This may result in an overflow of wet tailings or the complete destruction of the dam, and that would pollute a huge area of land downstream from the tailings reservoir. 

Nine of the top ten coldest mines are found in Russia’s Sakha Republic, where vast diamond, coal, and gold resources can be found. Mining operators have to take precaution of the temperature fluctuations, as the air temperature changes more than 100ºC over the course of the year. While winter temperatures may dip below -50ºC, summer temperatures may hit 50ºC, and the effects of climate change are exacerbating the extremes in temperature difference. 1 Warmer summers thaw and cause greater degradation to permafrost. To reduce the possibility of structural failure in tailings dams under cold climate conditions, mining operators may need to consider stripping out the permafrost layer of the tailings facility in its entirety, or preserving permafrost with heat exchangers and refrigeration systems that remove the heat. However, these solutions require additional equipment to be brought to the remote mining locations in the arctic north, and come at huge labour and financial cost.

In recent years, stricter environmental standards have required remediation work to be made on tailings dams, and this translates into higher costs for mining operators. Clean Mining’s non-toxic gold recovery agent and de-watering process remove the necessity of creating tailings dams and dumping toxic, wet effluent into containment ponds. This removes the risk of tailings-related mining disasters and also reduces the creation of stranded assets in the far north, allowing mining operators to reap the benefits of cost savings by extending the economic lifespan of a mine.

 

Clean Mining is part of the Clean Earth Technologies group.

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[1]  Frik Els, “The World’s 10 Coldest Mines,” MINING.COM, November 9, 2016, https://www.mining.com/the-worlds-10-coldest-mines/.

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