The proposed Twin Metals mining site was an ambitious project that planned to use state-of-the-art strategies to target specific minerals in the Duluth Complex while building jobs in the industry for northern Minnesota. So, what happened to it and why haven’t the next steps towards operation seen the light of day?
Twin Metals is a subsidiary of Chilean mining giant Antofagasta PLC that formed in 2010. The company spent nearly a decade forming the proposal necessary to begin production of a mine targeting copper, nickel, cobalt and platinum group metals in the Maturi mineral deposit of the Duluth Complex about 14 km southeast of Ely, Minn.
This proposal included environmental research and feasibility, geological and hydrogeological studies that would give an in-depth look at how the company would go about its operation in a manner that produces zero acid runoff all the while mining in a notoriously acidic rock formation.
However, despite studies and plans to minimize risk of acid exposure to the watershed, Twin Metals faced criticism from environmental advocacy groups and the Democrat-led state government of Minnesota, as well as legal interruptions in the approval of mining leases due to concerns of long-term impacts on Canada-U.S. boundary waters.
This resulted in Minnesota Governor Tim Walz signing an executive order last August that halted state leases on nonferrous mining within the Rainy River Headwaters Watershed (RRHW) and Boundary Waters Canoe Area Wilderness (BWCAW) that will remain in place until the end of his term in January 2027.
“The long-term health of the lakes and rivers in the Rainy River Headwaters Watershed that flow into the BWCAW is critical to the viability of the BWCAW itself and the resources and lifeways integral to the Tribal Nations and Ojibwe communities who share geography with Minnesota,” Walz’s order read.
“The RRHW is teeming with biodiversity, boasting some of the lowest levels of pollutants and highest quality fisheries in the state. Its unique biological, chemical, and physical features are worthy of additional protection. The RRHW is home to nonferrous mineral deposits owned by a mix of private entities, the State, and the federal government. Corporations continue to pursue the mining and development of these minerals, including a proposal by Twin Metals in December 2019. If one or more proposals within the RRHW proceeds to development and operation, the long-term health of the BWCAW could be threatened.”
To this, Twin Metals immediately responded, stating that Minnesota environmental regulations are being adhered to by the mining company and that the decision unnecessarily hindered the operation.
“As an April 2026 legal decision by the Minnesota Department of Natural Resources makes clear, our state’s existing environmental laws are strong enough to protect the waters of the BWCAW and the RRHW from pollution, impairment or destruction,” Twin Metals’ director of public affairs and communications, Kathy Graul, said in a press release.
“This decision was reached through a process that included expert testimony, opportunities for public comments, and review by an administrative judge. This morning’s executive order by the Walz administration directly contradicts these independent findings and unnecessarily hinders the responsible development of Minnesota’s natural resources. Minnesota’s regulatory framework already requires proposed mining projects to prove they can meet some of the world’s most rigorous environmental and labour standards before they are allowed to proceed.”
The company said the order undermines the established environmental review and permitting process by preventing the project from being assessed through what it described as a neutral, science-based framework. It argued the decision delays development of critical mineral resources and said it remains committed to advancing the Twin Metals project through the required review process and regulatory approvals.
So, if environmental studies were completed and Twin Metals was confident in the proof that there was no risk of the mine forming acid runoff, why all the concern?
The answer is that acid runoff is not the only risk identified by the project’s opponents. The nonprofit organization Save the Boundary Waters claims that heavy metal pollutants, unrecovered processing chemicals and elevated sulphate levels that won’t be noticed for years to come are the real long-term environmental threats.
Save the Boundary Waters
U.S.-based Save the Boundary Waters was formed in 2013 with the goal of maintaining protection of shared Canada-U.S. bodies of water from copper mining in sulphide ores.
Save the Boundary Waters is led and funded by Northeastern Minnesotans for Wilderness (NMW), another leader among environmental advocacy organizations that was formed in 1996 and works to protect wilderness areas from potential harm that could be caused by negligent commercial and industrial development.
Since the conceptualization of the Twin Metals project first came to light, a major concern for Save the Boundary Waters has been the alleged potential for pollutants to cause long-term spikes in sulphate levels that would create a chain of effects on the ecosystem and eventually result in heightened mercury levels in the Rainy Lake-Lake of the Woods Watershed.
“Sulphate is a fairly conservative pollutant,” said Matt Norton, policy and science director at Save the Boundary Waters. “It does not interact a huge amount, but it does interact some. And compared to most other pollutants, it stays in the water a very long time, and you can trace it downstream a long way.”
Although it reacts slowly compared to most other pollutants, that’s not to say sulphate’s overall impacts after years of constantly heightened levels would be negligible. An example of this, Norton said, is Birch Lake, which receives output from the now closed Dunka Mine and currently active Peter Mitchell Mine in Minnesota.
The now-abandoned Dunka Mine is an open-pit mine located in the Duluth Complex and operated by LTV Steel Mining Co., which ran the site from 1964 to 1994.
In order to reach the taconite (an iron-bearing rock) in the mine, the stone was drilled and blasted; however, portions of the stone being dug into contained the highly acidic mineralized copper-nickel sulphide that the complex is now well known for.
To neutralize the acid, passive systems were built for the wastewater to run through; however, this didn’t filter out the sulphate entering Birch Lake, which naturally sits around one mg of sulphate per litre of water.
The Peter Mitchell Mine is another taconite project operated by Northshore Mining in Babbitt. To keep its pit dry, large volumes of water containing mining discharge are pumped out to the Dunka River. Although acid in the water is neutralized, it still contains sulphate.
“Dunka River starts out just as clean as these other tributaries, but after receiving pit water discharge, sulphate concentrations go up drastically,” Norton said. “With all the copper-nickel sulphide mineralized waste rock, sulphate concentrations where it seeps out might be between 1,000-1,800 mg per litre. By the time it gets to a little unnamed creek, it’s more like 300 mg per litre, about 300 times what these other portions of the watershed are.”
These areas have flow in and dilution from other natural bodies of water; however, even three decades after the closure of the Dunka Mine, sulphate has not returned to its normal levels. According to Norton, this creates a chain of bioaccumulation (a gradual buildup of a substance in an organism’s tissue after exposure) that eventually leads to higher mercury in fish humans eat.
“The water still shows this right here at the wilderness boundary; we still have about 90 per cent excess sulphate compared to what it should be,” he said. “What that means is more nitrogen, more phosphorus, more mercury in the water column, more methylmercury in the system and more mercury in fish.
Although the effects are not immediately noticeable from simply looking at the water, sulphate fuels the metabolism of bacteria in the sediments at the bottom of the lake, and amplifying the amounts causes their metabolism to increase. Increasing their metabolism means increasing what these bacteria eat: organic matter containing mercury.
“If it’s locked away in the sediment, then it’s generally not bioavailable, but as soon as it’s released from the organic matter that’s digested by the bacteria, then it’s in the water column, and it can be methylated,” Norton said. “It usually doesn’t bioaccumulate, but if it’s methylated, it has a methyl group attached to it, and it does.
“The photosynthesizing organisms in the water might have a tiny little bit of mercury in them, then the zooplankton that eat the phytoplankton would have maybe 10 times as much. Then you have the macroinvertebrates that eat them; maybe they eat 100,000 zooplankton, so they’re getting a bit more in them. Little fish eat the macroinvertebrates, and so on. By the time you get to the sport fish, like walleye, there’s a lot of mercury compared to what’s in the water column. Maybe a million times more concentrated in the fish tissue than in the water column, and once it gets into the fish tissue—or our tissue—it really doesn’t leave.”
Though it is an intimidating prospect for anyone in the boundary watershed, Twin Metals stands firm that their site poses no environmental risk because it will be a “non-discharge facility.”
Non-discharge facility
Twin Metals’ non-discharge facility, often referred to in similar projects as zero-liquid discharge or non-point source/no-discharge water management, uses a process that aims to constantly treat and reuse any water that comes into contact with the mining operation.
“Any water that comes into contact with our processing system will not be discharged off-site,” Graul told The Times. “We have a system where we’re able to reuse the water that we need for the processing part of the operation over and over again to recycle it essentially, so we won’t be discharging any water that comes into contact with the process.”
Graul said there has been extensive testing by both Twin Metals and the Minnesota Department of Natural Resources (DNR) on the leftover mine waste stone, called tailings, that would come from the proposed site.
“The tailings storage method that we’re proposing is called dry stack tailings,” she said. “Essentially what we’d do is build what will ultimately look like a hill with the tailings. Half of our tailings will go as a cemented backfill back into the underground mine, and about half will go on the dry stack facility. The great thing about the dry stack facility is we can reclaim it with native vegetation throughout our operational period. Essentially, it will look like a hill when we’re done and close the mine.”
Despite testing from Twin Metals and the DNR, Save the Boundary Waters fears failure of the non-discharge facility.
“Your coffee cup in the morning is supposed to be non-discharge, and yet people walk around and spill their coffee all the time,” Norton said.
“The idea that an industrial site that would be stretched across miles in a very wet landscape where wetlands are everywhere with lakes and rivers; and where precipitation, rainfall and snowmelt exceeds evaporation by eight or nine inches every year is not believable.”
Aside from accidents, Norton said unexpected weather events also pose significant risk. Runoff collection ponds, which he explains are designed to prevent precipitation events from sending tailings into local water bodies, are typically “once in 100-year, 48-hour rain event.”
Although dry stack tailings do not rely on traditional large ponds with retaining dams, they do require smaller collection systems.
With increasing numbers of long and unpredictable rain events as a result of climate change, this is a difficult system to rely on.
“Even if they designed it for a once-in-500-year event, we’re still seeing major rain events happening at an accelerating pace,” he said.
“As soon as there’s a rain event like a big warm rain on top of late season snowpack, and you get tonnes of water to deal with, it could overwhelm whatever water handling capacity that they’ve got. Once these mines are apologizing for a spill, it’s already too late.”
Regarding evaporation rate, Graul said a good example of dry stack tailings succeeding is the Greens Creek Mine of Juneau, Alaska, a location operated by the Hecla Mining Company that has utilized a dry stack facility for over 20 years.
“They receive two to three times as much precipitation as we do in Minnesota,” she said. “Operating a dry stack facility is actually quite a bit more costly than the more traditional tailings ponds. We made the switch to that because of the evidence that it’s been done well at places like Greens Creek, and because it’s considered the gold standard for modern tailings management.”
Lease cancellation
Environmental concerns weren’t the only halting factor in the Twin Metals project.
On Sept. 11, the Minnesota DNR informed Twin Metals that one of its state mineral leases would be cancelled.
The cancellation of MM-9455-N, the lease that covers an area near Birch Lake, will take effect Nov. 10 due to Twin Metals allegedly failing to meet the mandatory performance and production terms.
This decision, though a slight hindrance, will not impede Twin Metals from seeing its goal, as the company still holds 26 other leases. This particular lease covers a small deposit that the company is not currently seeking to mine. The main target of the mining group remains the Maturi Deposit, about 6.5km away.
For now, the main force stopping the Twin Metals project is Walz’ executive order, which will remain in place as long as he is in office. However, given that Walz announced last January that he will not be seeking a third term, whether the next Minnesota governor chooses to uphold, alter or let this order expire remains to be seen.
