Minnesotans have debated for years now whether to open the state to copper-nickel mining. But even those who follow the news closely might have a difficult time keeping the details straight on the two proposed copper-nickel mine projects — Twin Metals and PolyMet — for Minnesota's Iron Range. Here are answers to commonly asked questions about the two mines.

What are the Twin Metals and PolyMet Mining's NorthMet mines?

They are a pair of proposed copper-nickel mine projects in northern Minnesota being pursued by separate international mining companies. This is hardrock mining, which is new in Minnesota. While the state has a long history of iron ore and taconite mining, non-ferrous mining — mining for things other than iron ore — carries greater environmental risks because of the type of ore, how it's extracted and the large volume of waste produced. A key concern in hardrock mining is the creation of toxic sulfuric acid runoff, sometimes called acid mine drainage, when the metal sulfide minerals in the crushed rock are exposed to air and water. Both Twin Metals and PolyMet have said this will not be a problem at their sites because of how they handle the waste rock and the fact that the rock being mined has a lower sulfur content.

Where are they located?

Both mines would be on the Iron Range in northeast Minnesota. The Twin Metals mine would be underground at Birch Lake, just outside the Boundary Waters Canoe Area Wilderness near Ely.

PolyMet's mine would have two parts: an open-pit mine in wetlands south of Babbitt and a processing site at the former LTV taconite mining operation near Hoyt Lakes. This is in the headwaters of the St. Louis River, the largest tributary to Lake Superior, and upstream from Duluth and the Fond du Lac Band of Lake Superior Chippewa reservation.

How soon will the mines be operational?

Short answer: not soon.

The Twin Metals project has no obvious path forward after the Biden Administration cancelled two federal minerals leases the company held that were crucial for the mine. The Department of the Interior concluded in January 2022 that the two leases "were improperly renewed in violation of applicable statutes and regulations." The leases had been renewed by the Trump Administration after the Obama Administration declined to do so.

Twin Metals said it "intends to take formal legal action to defend its valid mineral rights" and that it has six years to make a claim.

The Biden Administration is also seeking a 20-year moratorium on mining on more than 220,000 acres in Superior National Forest near the Boundary Waters, which it called a "unique natural wonder." The action involves restarting a previously cancelled study on the mining impacts that could take two years. Depending on the results, Twin Metals said it may appeal.

As for PolyMet, it's also stalled. The mine was fully permitted at the start of 2019 but those permits are caught up in legal challenges by environmental groups and the Fond du Lac Band of Lake Superior Chippewa.

One of them, a wetland permit issued by the U.S. Army Corps of Engineers, was suspended following a legal challenge by the Fond du Lac Band. That permit allows the company to fill or dredge more than 900 acres of wetlands that were once part of Superior National Forest, where PolyMet plans to dig the mine pit and stockpile waste rock. The Corps held a hearing May 5-7 on whether the Band will be affected by downstream pollution from the mine. The Corps must decide whether to reinstate, revoke or modify the permit. There is no deadline for that decision.

In a separate action, the state Supreme Court in 2021 paused PolyMet's permit to mine, ruling that the state Department of Natural Resources (DNR) must hold a hearing on the company's plan to line the tailings dam with a bentonite clay mixture, which they said would prevent leakage of contaminated mine waste. That hearing has not been scheduled, but is expected to happen this year.

Who owns the mines?

The projects are operated by publicly traded companies. PolyMet is owned by Switzerland-based mining giant Glencore via its 72% stake in Toronto-based PolyMet Mining Corp.

Twin Metals is owned by Antofagasta, a major mining company in Chile controlled by the Luksic family, one of Chile's wealthiest.

What are the controversies surrounding the projects?

The mines have plenty of supporters because of the higher-wage jobs and spinoff benefits they provide in an economically challenged area with a deeply-rooted mining history, and the general need for copper and nickel. The U.S. needs to be less dependent on foreign sources for these crucial minerals, they say.

Environmentalists argue the short-term economic gains are not worth destroying pristine habitat and potentially polluting northern Minnesota's clean waters with contaminants like sulfide and heavy metals. The Fond du Lac Band has specifically opposed the PolyMet mine, and says its concerns were not addressed in the permitting process.

Opponents have also raised concerns with the safety of the huge PolyMet tailings dam the company plans to use to store contaminated mine processing waste in perpetuity.

There have also been questions about how state environmental regulators managed the issuance of some PolyMet permits. A leaked e-mail in 2019 revealed that a Minnesota regulator asked EPA staff not to file their written criticisms of the draft water pollution permit during the public comment period, which had the effect of keeping the EPA's serious concerns out of the public record. EPA staff read their comments to Minnesota staff over the telephone. A leaked EPA memo showed how a career EPA staffer documented the agency's many concerns about PolyMet's water permit, and showed that many concerns were not resolved before the state approved the permit.

Accusations of "procedural irregularities" with the water permit led to an unusual evidentiary hearing into the matter in district court. The court largely cleared the Minnesota Pollution Control Agency, saying the regulator did not deviate from most of its standard practices when it issued the water permit.

Are there similar mines in other places?

Yes, all over the world. Chile is the world's largest copper producer. In the U.S., most copper mining is done in dry regions in Arizona, Utah, New Mexico, Nevada and Montana.

How many jobs are they promising?

PolyMet estimates 360 full-time jobs; Twin Metals estimates 700 full-time jobs.

How long would the mines be in operation?

PolyMet says it intends to mine for 20 years, though its permit to mine does not specify that time limit. Twin Metals planned to apply for a permit to mine for 25 years. The number of years the mine actually operates could be less. The jobs last as long as the mine operates.

How will the mines impact the surrounding environment?

The mining companies say they can mine safely. Research and the industry track record show that hard-rock mining is highly polluting because of the large amounts of waste rock generated; the sulfuric acid, cyanide and other hazardous chemicals used in the mining process; and the risk of leaks and spills of contaminated wastewater. Metals mining is a leading source of toxic waste, according to the U.S. EPA, and the cleanup costs can fall to taxpayers. There are more than 100 abandoned hardrock mine and mineral processing sites on the U.S. EPA's Superfund National Priorities List.

I hear people saying that these mines are in the Lake Superior or Boundary Waters watersheds. What does that mean?

A watershed is a land area where all the water flows into the same outlet. The PolyMet mine would be in the St. Louis River watershed, which drains into Lake Superior.

The Twin Metals mine would be in the Rainy River watershed, which includes the Boundary Waters Canoe Area Wilderness, and drains into Canada's Hudson Bay.

Why do these companies want to mine here?

Northeast Minnesota is home to the Duluth Complex, ancient rocks holding large, undeveloped reserves of copper, nickel, cobalt and platinum group metals.

Why are the minerals needed?

The metals are used in a wide array of industrial processes and consumer goods. Copper is used in pipes and wiring, electronics and electric vehicles, among other products, and nickel is used in making steel and stainless steel and rechargeable batteries. Platinum group metals are used in such products as jewelry, spark plugs and medical implants. Cobalt is used in lithium-ion batteries to power electronics such as laptops and electric vehicles.