Sulfide Mining

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the risks of sulfide mining in northeastern Minnesota.

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Acid mine drainage at 30-year-old mineral exploration site near the BWCAW

Toxic pollution from new mine proposals threaten our lakes, rivers, streams, wetlands and groundwater.


What is sulfide mining?

Sulfide mining extracts copper, nickel, and other metals from sulfide ores. The environmental risks are much different from Minnesota’s traditional iron ore mining. Here’s just one reason why: 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
Some of the reasons for concern:

  • Long-term acid and toxic metal water pollution — for instance, PolyMet’s draft Environmental Impact Statement predicts 2,000 years of contaminated
  • water leaching
  • Mercury contamination in fish and wildlife
  • Expensive clean-up operations often fall to taxpayers
  • Mining and associated pollution, noise, and other serious impacts in areas near the Boundary Waters Canoe Area Wilderness that are important tourism and recreation areas

Despite mining companies’ claims about the minimal environmental impacts, sulfide mining has caused environmental and financial problems all over the world:

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

What is being proposed in Minnesota?

There has never been a sulfide mine in Minnesota, but recent advances in ore processing technology means that, for the first time ever, our state’s low-grade sulfide ore could be mined profitably.

Several companies are currently exploring mineral deposits, developing mine proposals, and working through the environmental review process in northeastern Minnesota. Since 2008, mining companies have applied for over 100 permits to conduct exploratory drilling on federal public lands. In November 2009, PolyMet Mining Corp. became the first company to release a draft Environmental Impact Statement (EIS). This draft EIS was deemed environmentally unacceptable and inadequate by the U.S. Environmental Protection Agency in 2010, forcing PolyMet to return to the drawing board. Their next attempt at a draft EIS is expected to be released in summer 2013.

At the edges of the Boundary Waters

Sulfide Mining Activity in Northeastern Minnesota map

Map of sulfide mining activity in northeastern Minnesota (PDF)

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. Around-the-clock drilling is already causing noise pollution problems in the area. If the mines are approved, they would be near lakes and rivers that flow into the BWCAW. Thousands of acres in the Boundary Waters watershed have been leased to mining companies for mineral exploration.

The Twin Metals project is located approximately three miles from the BWCAW, near the Little Gabbro Lake and South Kawishiwi River entry points.

PolyMet: The ‘snowplow’ leading the way

PolyMet Mining Corp., a Canadian company, has never actually operated a mine. They propose to use unproven techniques to mine a site in a sensitive wetland environment near Hoyt Lakes, in the Lake Superior watershed.

PolyMet’s mine proposal is the furthest along in the development process of the proposed sulfide mines in Minnesota. In addition to the mine’s serious and unacceptable pollution potential, officials from other sulfide mining companies have repeatedly stated that PolyMet is ‘plowing the way’ for their projects. How the State of Minnesota and federal agencies respond to PolyMet’s proposal will influence what happens with other proposals that follow.

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. According to the EPA, the EIS was also inadequate to fully assess the proposal. The Minnesota DNR and the U.S. Army Corps of Engineers produced the DEIS and approved its release. 

Twin Metals: Three miles from the BWCAW

In 2010, Duluth Metals signed a $227 million deal with a Chilean firm to advance its mine proposal — three miles from the BWCAW. The combined project, dubbed “Twin Metals,” would be twice as big as the PolyMet project. It would extract about 40,000 tons of ore each day. The company is actively drilling in the area and plans to enter the environmental review phase within three years.

A history of problems

“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. Faced with clean-up costs in the tens of millions of dollars, companies have frequently filed for bankruptcy, leaving taxpayers to pick up the tab.

For example, at the Brohm Mine in South Dakota, which operated from 1988 to 1998, mining unexpectedly produced acid mine drainage (including turning the waters of a nearby stream more acidic than lemon juice). Ultimately, the company went bankrupt and, because the financial assurance the state had received was only sufficient to cover about 1/8 of the clean-up costs, the site was declared a Superfund site, meaning that American taxpayers are now paying to clean up the pollution.

Failed predictions

Chino copper mine, New Mexico

Chino copper mine, New Mexico

One of the biggest factors in the dark history of sulfide mining is how frequently mining companies are wrong about what their impacts on water quality will be. 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 still did.  The same study found that 89 percent of mines that have polluted said they would not.

It is this history that is one of the biggest reasons for worry about proposals to bring the mining to Minnesota. The industry says they won’t pollute our prized waters, but they’ve said that before, and they’ve been wrong more often than not.

The Brohm Mine, mentioned above, is also a useful illustration of this problem. There, the mining company assured the state that the mine would not produce acid mine drainage because the ore was low in sulfides, around one percent average. The mine still created terrible pollution, killing all the fish in that stream turned acidic.

This is an important point, because the mining industry in Minnesota frequently states that because the ore here is low sulfide,  it won’t cause acid mine drainage. The companies claim that the ore averages about one percent sulfide. Sound familiar?

Taxpayers left holding the bag

Confronted with astronomical clean-up costs and battered by a volatile metals market with frequent boom-and-bust cycles, mining companies often abandon their polluted mines, walking away and leaving taxpayers holding the bag.

Most states, including Minnesota, require mining companies to provide financial assurances to fund clean up if the company goes bankrupt or is otherwise unable to perform the work itself. But, there are two common problems that contribute to taxpayers still bearing the brunt of clean up costs:

  1. 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.
  2. 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.

The industry’s track record of not paying to clean up its messes is long and shameful. A few examples include:

  • Zortman-Landusky Mine, Montana – $33 million and counting
  • Summitville Mine, Colorado – $185 million and $1.5 million/year
  • Grouse Creek Mine, Idaho – $53 million


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

  • In Wisconsin, the legislature in 1997 passed a “Prove It First” law. 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 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.”

In the 2009 Minnesota legislature, the Friends supported legislation introduced by Rep. Alice Hausman and Sen. Jim Carlson meant to achieve those protections. The bill would have done three things:

  • Prohibit mines that would require water treatment after closure
  • Ensure mining companies put up enough money to pay for clean-up in case they go bankrupt or otherwise abandon the mine
  • Increased government transparency so citizens are informed of how mines are regulated

Unfortunately, the legislation was blocked from passing by intense opposition from mining companies and pro-mining legislators.

In addition to improving Minnesota’s laws, the Friends is also closely analyzing specific mining proposals and advocating for the public interest and our legacy of clean water in working with 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 in those dry areas, the 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.

What is sulfide mining?
Sulfide mining extracts copper, nickel, and other metals from sulfide ores,
which is very different from Minnesota’s traditional iron mining.
➔ When rain falls on the waste from iron mining,
it makes rust; when rain falls on sulfide waste,
sulfuric acid is produced.
Sulfuric acid leaches out metals and chemicals from the waste and
creates acid mine drainage:
 Contaminates lakes, rivers, and groundwater
 Harms human health, fish and wildlife, and damages entire
Sulfide mining has caused environmental destruction all over the world:
 Drinking water supplies contaminated
 Destruction of fish and wildlife habitat from polluted lakes and rivers
 Predictions about environmental impacts are often wrong
 Pollution often occurs years or even decades after mine closure
➔ Mining companies are often bankrupt or refuse to pay
for clean-up when problems occur, leaving taxpayers
with bills of tens of millions of dollars