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Sulfide Mining

What is sulfide mining?

Acid mine drainage at 40-year-old mineral exploration site near the BWCAW
Acid mine drainage at 40-year-old mineral exploration site near the BWCAW

Toxic pollution from new sulfide mine proposals near the Boundary Waters Canoe Area Wilderness (BWCAW) threaten our lakes, rivers, streams, wetlands and groundwater. The most toxic polluting industry in the U.S. can’t be allowed to pollute the BWCAW, and that’s why we are leading efforts to protect the Boundary Waters from this industry.

Sulfide mining extracts copper, nickel, and other metals from sulfide ores. The environmental risks are different from and greater than Minnesota’s traditional iron ore mining. When rain falls on the waste from iron mining, it makes rust; when rain falls on sulfide ore waste, sulfuric acid is produced.

Sulfuric acid leaches out metals and chemicals from the waste and creates acid mine drainage which:

  • Contaminates lakes, rivers, and groundwater
  • Harms human health, fish, wildlife, and damages entire ecosystems

Sulfide mining has caused environmental problems all over the world like:

  • Contaminated drinking water
  • Destruction of fish and wildlife habitat from polluted lakes and rivers
  • Pollution that continues decades, even millenia after a mine’s closure
  • Mining companies often go bankrupt or refuse to pay for clean-up when problems occur, leaving taxpayers with millions of dollars in costs

In some tragic cases, dams holding back billions of gallons of mine waste have failed and devastated communities and downstream waters. In August 2014, the dam holding back toxic mine waste at the Mount Polley copper-gold mine burst, flooding a pristine lake at the headwaters of the Fraser River. In 2015, the Samarco iron ore mine in Brazil burst its dam, and the resulting flood killed 17 people. In the aftermath of the Mount Polley disaster, an expert panel hired by British Columbia’s government declared that there was no tolerable failure rate for mine waste dams, because the cost was so high.

The pond which stores toxic waste from the Mount Polley Mine had its dam break, spilling its contents into the Hazeltine Creek causing a wide water-use ban in the area. THE CANADIAN PRESS/Jonathan Hayward


Despite decades of exploration, there has never been a sulfide mine in Minnesota. But spikes in copper and other metal prices have revived interest in the low-grade sulfide ore of the “Duluth Complex,” a geological formation that runs in an arc from north of the city of Duluth into the BWCA. While federal and state laws prohibit mining in the BWCAW, several companies are currently exploring mineral deposits and developing mine proposals near the Boundary Waters where polluted water would flow into the wilderness.


PolyMet’s open pit sulfide mine proposal has proceeded the furthest toward reality, and now stands on the precipice of being the first sulfide mine in Minnesota. PolyMet’s mine would be located on land that is currently part of the Superior National Forest using private mineral rights that PolyMet leases. PolyMet’s mine proposal is in the St. Louis River watershed, the largest U.S. tributary of Lake Superior. It’s also just one mile from the BWCAW watershed, and could pollute the BWCAW through contaminated groundwater flowing into an adjacent mine pit.

How the State of Minnesota and federal agencies respond to PolyMet’s proposal will set precedents that will affect what happens with other sulfide mine proposals that might follow. One mining company CEO said that PolyMet is ‘plowing the way’ for projects that follow in its wake, which shows the intense interest the sulfide mining industry has in this proposal. Also, if PolyMet receives a permit to mine, their processing plant has three times the capacity they need, and PolyMet could become the processing facility for other proposed mines. That’s why Friends of the Boundary Waters Wilderness has been leading efforts to ensure that the PolyMet proposal isn’t allowed to pollute our precious water resources.

PolyMet’s proposal has had a rocky road. After receiving thousands of public comments opposing PolyMet’s mine plan, in February 2010, the U.S. Environmental Protection Agency (EPA) stated that PolyMet’s draft Environmental Impact Statement (EIS) described “unacceptable environmental impacts” — particularly in regard to water quality. PolyMet went back to the drawing board and issued a supplement draft EIS in December 2013. Friends led turnout efforts and over 4,000 people attended three public hearings on PolyMet’s proposal. Over 58,000 written comments were filed, smashing the previous record and over 95% of these comments opposed the mine proposal. Despite this, the Minnesota Department of Natural Resources declared that the EIS was “adequate” in March 2016, and PolyMet has now filed for state and federal permits. The first draft permits for water appropriations o dewater the mine pits and to use in processing the ore were put on public notice in August 2017 and the public comment period has closed. We expect draft permits and public comment periods for the permit to mine, wastewater discharge, wetlands destruction, tailings dam safety and others during the fall and winter of 2017-2018.

PolyMet is also seeking a land exchange with the U.S. Forest Service to acquire the surface land they want for the mine site. The Campaign to Defend Lake Superior is fighting this exchange in federal courts, arguing that the land exchange illegally undervalues public land and understates the number of acres of land that should be received by U.S. taxpayers in exchange.


Twin Metals is proposing a mine operation with miles of pipelines and tunnels.
Twin Metals is proposing a mine operation with miles of pipelines and tunnels.

Twin Metals is proposing a sulfide mine operation with miles of pipelines and tunnels.

In 2010, a Chilean mining company Antofagasta bought a share of a mine proposal at the edge of the BWCAW, forming a joint venture named Twin Metals Minnesota. In 2014, Antofagasta bought out the other partner in the joint venture and now owns 100% of the proposed project.

While Antofagasta and their proponents insist that “no mine has been proposed,” in March 2014, Twin Metals published a “pre-feasibility study” laying out a detailed mine proposal for Canadian securities regulators. It included a map showing the possible scope of their proposal with miles of pipelines moving water, ore, and waste across an area stretching from the Ely Airport to the city of Babbitt. The proposed mine would be about twice as big as the PolyMet project in daily ore mining and processing.

In 2016, the U.S. Forest Service announced that it was “deeply concerned” about the impact that the Twin Metals proposal would have on the BWCAW and announced that it would hold a public comment period on whether to veto two federal mineral leases held by Antofagasta. After holding two hearings and receiving tens of thousands of comments opposing the project, the Forest Service vetoed Antofagasta’s request to extend these leases and the U.S. Department of Interior revoked them. Antofagasta has filed suit in an attempt to overturn the federal government decision, and that lawsuit is now pending in federal court. 

The company leases thousands of additional acres of state and private mineral rights in the area and has proposed a number of actions that the Friends are responding to. One is for permission to drill hundreds of wells to gather information about the groundwater movement in the area near Birch Lake.


Thousands of acres of mineral leases have been granted near the BWCA
Thousands of acres of mineral leases have been granted near the BWCA

Thousands of acres of mineral leases have been granted near the BWCAW.

Besides the two more advanced proposals, several other mining companies continue to explore the Superior National Forest and surrounding areas for sulfide minerals. Much of the mineral exploration is focused on an area on the southern edge of the Boundary Waters Canoe Area Wilderness (BWCAW), in the area around the South Kawishiwi River and Birch Lake. This exploration is occurring on mineral rights leased from the federal and state government, and also on land with private mineral rights.

Currently, the U.S. Forest Service is preparing an Environmental Impact Statement on a proposal to stop leasing federal mineral rights to mining companies for twenty years. Friends of the Boundary Waters Wilderness strongly supports this action.

If exploration results in actual mines, they would be adjacent to and under lakes and rivers that flow into the BWCAW. The Spruce Road deposit, which is part of the Twin Metals project, is located approximately three miles from the BWCAW, near the Little Gabbro Lake and South Kawishiwi River entry points. In 2010, the Friends of the Boundary Waters Wilderness documented sulfide ore test mining sites on Spruce Road that hadn’t been cleaned up since the 1970′s and were discharging polluted water. 


“Other states have suffered because their leaders saw dollar signs when they should have seen question marks. Leaders believed promises that the mines wouldn’t pollute, but ignored all the times those promises had been broken.”

– Friends Executive Director Paul Danicic, Minneapolis Star Tribune editorial, March 10, 2009

In states like Montana, New Mexico, and Nevada, sulfide mining has contaminated thousands of streams and devastated entire ecosystems. The problem is extensive: 500,000 abandoned mines pollute 40% of the river systems in the western U.S., according to federal authorities. And these abandoned mines can create pollution crises decades after closure. The Gold King mine in Colorado closed in 1925, still unleashed millions of gallons of orange colored polluted water in 2015.

Faced with millions of dollars of clean-up costs, companies frequently file for bankruptcy, leaving taxpayers to pick up the tab. For example, at the Gilt Edge Mine Superfund Site in South Dakota, which operated from 1988 to 1998, mining unexpectedly produced acid mine drainage. Ultimately, the company that owned the mine went bankrupt. Because the financial assurance the state required only covered a fraction of the clean-up costs, the site was declared a federal Superfund site. The cleanup cost to taxpayers reached $105 million in 2015, and continues to mount. Minnesota Governor Mark Dayton visited the Gilt Edge Superfund site in October 2015 to see an example of a mine with inadequate pollution controls and that set aside insufficient clean up funds.


Chino copper mine, New Mexico
Chino copper mine, New Mexico

Sulfide mining companies are full of rosy projections and responsible-sounding rhetoric, but are often terribly wrong about the actual impacts on water quality of mine proposals. One peer-reviewed study found that, while all projects that were reviewed predicted they would not pollute, at least 76 percent of the time they did. The same study found that 89 percent of mines that have polluted said they would not. This history of reassuring predictions that don’t match the reality of pollution left behind is one of the biggest reasons for worry about proposals to mine sulfide ores near the Boundary Waters Wilderness. The Gilt Edge Mine, mentioned above, is also an example of the mismatch between predictions and reality. There, the mining company assured South Dakota that the mine would not produce acid mine drainage because the ore was low in sulfides. The mine still created acid pollution, killing all the fish in streams nearby. The mining industry in Minnesota frequently states that because the ore here is low sulfide, it won’t cause acid mine drainage. Sound familiar?


Most states, including Minnesota, require mining companies to provide “financial assurance,” a damage deposit to fund clean up if the company goes bankrupt. Despite this, there are two common problems that result in taxpayers still bearing the brunt of clean up costs:

  • Difficulty predicting the extent of pollution and clean-up costs. Because it has proven so difficult to predict when, where and to what extent acid mine drainage will occur, it is hard to determine how much it will cost to clean up a mine. For this reason, when mining companies go bankrupt, states frequently discover that the financial assurance the company provided is insufficient for the clean up job.
  • Assets of bankrupt mining companies are awarded to other creditors. When a mining company goes bankrupt, there is usually a long line of creditors – banks, investors, vendors – that attempt to get paid. If financial assurance isn’t provided in a bankruptcy-safe method, the state is just another creditor clamoring for reimbursement. Even financial instruments like insurance or surety bonds can fail to pay out when needed, money held in a trust fund by the government is the safest approach.

PolyMet’s own application to the State of Minnesota for a permit to mine shows that the cost of closing the mine and paying for long-term treatment of polluted water if the mine closed unexpectedly would exceed $900 million. Unless iron-clad financial assurance is required in advance, this cost could fall to taxpayers. Unfortunately, the industry’s track record of not paying to clean up its messes is long and shameful. A few examples include:

  • Gilt Edge Mine, South Dakota – nearly $200 million
  • Summitville Mine, Colorado – $235 million and counting
  • Grouse Creek Mine, Idaho – $53 million


The perils of sulfide mining have prompted a variety of responses from other states.

In Wisconsin, the legislature passed a “Prove It First” law in 1997. This law says that, before opening a mine, a company must be able to point to a similar mine to what it is proposing that a) has operated for 10 years without polluting and b) has been closed for 10 years without polluting. Unable to point to such an example, no new copper-nickel sulfide mines have been proposed in Wisconsin since the law passed.

In New Mexico, in response to catastrophic pollution and abandoned mines, the state raised the amount of financial assurance on two dangerous mines to about $400 million each.

In Michigan, the law says mines may not be operated in such a way that they will require “perpetual care.”

Friends is also closely analyzing specific mining proposals and advocating for the public interest and our legacy of clean water in working with federal and state government agencies. Sulfide mining’s potential for pollution is directly tied to the presence of water, and it has usually been done in more arid climates than Minnesota’s. Even dry areas, sulfide mining has still created enormous toxic messes. The chance that it can be done in northeastern Minnesota’s watery ecosystem without polluting our cherished lakes, rivers, and streams is slim. And the price we could all pay is very high.