ELY, Minn. (FOX 9) - Twin Metals has revealed a strategy for handling mine tailings from its proposed underground copper-nickel mine in the Superior National Forest, just five miles from the edge of the Boundary Waters.
Mine tailings are what is left over after the 4% of the ore that contains copper, nickel, platinum, palladium, gold and silver are extracted. Mine tailings generally contain sulfur, which, when exposed to air and water, produce acid runoff.
Half of the mine tailings will be mixed with cement and go back underground to support the mine structure.
The company revealed Thursday the other half will remain above ground using a process called "dry stacking." The tailings will be the consistency of “sandcastle sand” in a lined basin that will be topped with native soil and vegetation, said Julie Padilla, Chief Regulatory Officer for Twin Metals.
The so-called dry stack will be a 120-foot tall hill near the processing facility that is “consistent with the topography of the area,” Padilla said.
The company said the dry stacking method will have a gravity drainage system to collect moisture into holding ponds that will then be recycled back into the processing plant in what they called a “closed-loop” system.
But, Twin Metals claims its mine tailings will be “non-acid producing” and contain between .12 and .15 percent sulfur, which the company said is below a .2 percent threshold that is consistent with the local geology.
The fear of environmentalists is that acid run off from the mine will get into the Rainy River watershed and eventually make its way to the nearby Boundary Waters. Scientists say the Boundary Waters is particularly vulnerable to acid run off because the geology doesn’t contain limestone and calcium to absorb the acid.
In a statement, Becky Rom, Chair of Save the Boundary Waters said, “…the project never should have gotten this far.”
"That unacceptable risk is in no way reduced by today’s announcement, and is actually made worse by the fact they are putting the tailings basin right next to the Wilderness,” Rom said in a statement.
Twin Metals' plan is focusing on an area known as the Maturi Deposit, which is believed to be one of the largest undeveloped deposits of copper and nickel ore in the world. The area is about 15 minutes from the town of Ely.
The company has already spent $450 million in exploration, mostly on extensive core samples that reveal a narrow band of mineral deposits about 200 to 400 feet wide and between 400 and 5,000 feet deep.
In a recent interview the company said on-going hydrology tests have revealed there is no ground water below 400 feet and they expect it will be a “dry mine.”
The company plans to dig the underground mine at a 30 degree angle. Rock will be crushed underground before conveyed up to a processing facility where the sulfide minerals will be separated from the rock.
In May, the Trump Administration renewed Twin Metals leases for mining that the Obama Administration failed to renew. Various incarnations of the company had held those leases for 50 years.
Twin Metals is a wholly owned subsidiary of Antofagasta, a Chilean mining conglomerate.
Rom of Save The Boundary Waters said in a statement, “Minnesotans can't rely on hollow promises from an international mining company with a history of environmental degradation and political corruption to protect the Boundary Waters."
Twin Metals is expected to submit a formal plan of operation in the coming months. That plan with then go through a year-long environmental review process, followed by a permitting process with the Minnesota Pollution Control Agency (MPCA) and the Minnesota Department of Natural Resources (DNR).