In a major victory for environmentalists, the federal government said it will not renew two mineral leases held by Twin Metals Minnesota, saying its proposed copper mine near Ely poses too great a risk of contaminating the Boundary Waters Canoe Area Wilderness.

“The Boundary Waters is a national treasure, special to the 150,000 who canoe, fish and recreate there each year, and is the economic life blood to local businesses that depend on a pristine natural resource,” U.S. Agriculture Secretary Tom Vilsack said in announcing the decision Thursday.

The ruling slams the brakes on one of two copper-nickel mines proposed for northern Minnesota, and is likely to intensify an emotional debate that pits the region’s storied mining industry against a rare and much-loved forest wilderness.

An agency spokeswoman said the decision is not unprecedented, but added: “It is uncommon for the Forest Service to withhold consent for hard-rock mining lease renewals, except in situations like this, where there are unique and irreplaceable environmental values at risk.”

Twin Metals called the decision inconsistent with federal law and government precedent — arguments it has pressed in a federal lawsuit — and said it would continue pursuing legal remedies.

“If allowed to stand, the [decision] will have a devastating impact on the future economy of the Iron Range … eliminating the promise of thousands of good-paying jobs and billions of dollars of investment in the region,” company spokesman Bob McFarlin said.

MINNESOTA’S COPPER • Twin Metals Minnesota has proposed a $2.8 billion copper-nickel mine near Ely, in the Boundary Waters watershed. Regulators denied a renewal of the company’s mineral leases. • PolyMet Mining has proposed an open-pit mine near Hoyt Lakes, in a watershed that drains toward Lake Superior. PolyMet is applying for state mining permits.

In a related and emphatic step, the Forest Service said it also wants to protect 234,000 acres outside the Boundary Waters from mining and geothermal activity — an expanse considerably larger than the area covered by Twin Metals’ mineral leases.

The Forest Service said it has applied to the Secretary of the Interior to withdraw the affected acres, all of which lie inside Minnesota’s Superior National Forest, from mining activity for the next 20 years. A final decision on that request could take up to two years.

Federal officials said the Forest Service made its decision after hearing from about 30,000 people, including former Vice President Walter Mondale and residents who attended listening sessions in Ely and Duluth in July. Gov. Mark Dayton has also weighed in against mining near the Boundary Waters.

‘Beyond unhappy’

The much-anticipated ruling instantly sent ripples across Minnesota’s political and environmental communities.

“I’m beyond unhappy,” said Ely Mayor Chuck Novak. “Where are you going to get the copper you’re going to put in your cellphones and computers?” Novak called the decision a “circumvention of law,” referring to the 1978 Boundary Waters Canoe Area Wilderness Act.

Rebecca Rom, an Ely native and retired attorney who spearheaded the national Campaign to Save the Boundary Waters, said she was “tremendously excited.”

“It’s very reassuring and rewarding to hear that the voice of the people and good science prevailed,” Rom said. “Protecting the Boundary Waters has been a Democratic and Republican priority for the past 100 years.”

Dayton said the announcement was “tremendous news for the protection of the BWCA, a crown jewel in Minnesota and a national treasure,” adding that it is not a blanket indictment of mining in northern Minnesota. Democratic U.S. Rep. Betty McCollum of St. Paul called it “a major victory for Minnesota and the environment.”

But Minnesota House Speaker Kurt Daudt, R-Crown, blasted the decision as a misguided step by the “lame-duck” Obama administration.

“It is astounding that Democrats are blocking what would be one of the largest private construction projects in state history, while also depriving Iron Range workers of hundreds of good-paying jobs that would follow,” Daudt said.

The Twin Metals project, a $2.8 billion underground mine, has been a painful flash point on Minnesota’s Iron Range, where mining jobs have been on the decline for years. The proposal, and one by PolyMet Mining, have kicked off a struggle between those who foresee a revival of the region’s mining industry and those who say it’s more important to protect wilderness and the recreation industry that has sprung up around it.

At issue in copper-nickel mining is the risk from acidic mine drainage and toxic metals that can be produced when the copper-bearing rock is exposed to air and water.

The risk from such drainage is acute because water from the area of the proposed Twin Metals mine flows north into the Boundary Waters and Voyageurs National Park. The result could be “catastrophic” for fish and other wildlife, an Agriculture Department official said in an interview.

Specifically, the Agriculture Department’s U.S. Forest Service said it has decided to deny the renewal of Twin Metals’ two hard-rock mineral leases near the Boundary Waters, which were first granted decades ago and expired in 2013. The Bureau of Land Management (BLM), which oversees mineral deposits, said it is rejecting Twin Metals’ application for renewal.

Whether the decision could be reversed by the incoming Trump administration is unclear. A BLM official said the decision is final and not subject to any appeal. The mining company’s only option now is to sue, the official said, which Twin Metals has already done.

In September, Twin Metals sued the federal government in U.S. District Court over lack of action on the leases. It accused the government of suddenly changing its position regarding automatic renewal of the long-held mineral leases it has used to drill and prospect for the proposed mine. The leases were first issued in 1966, the company argued, “with a right of unlimited, successive 10-year renewals.”

Twin Metals is owned by Chilean mining giant Antofagasta PLC. In the complaint the company said it has spent more than $400 million developing the project, which would lie between Ely and Babbitt. It says Minnesota has the largest untapped copper-nickel deposit in the world, worth more than $40 billion.

The federal government has asked a judge to dismiss the Twin Metals suit.

To officially withdraw the 234,000 acres of land in Superior National Forest from mining would involve extensive public input and scientific work that must be completed within two years. During that two-year period there can be no mining activity.

That move affects about 46 other applications for various types of exploration. The Twin Metals mineral leases were the only active leases on that land, officials said.

In the announcement, U.S. Interior Secretary Sally Jewell called the twin decisions “the right action to take.”

“There’s a reason that the Boundary Waters is one of the most visited wilderness areas in America: It’s an incredible place.”