Voicing grave concerns about threats to Minnesota's cherished northern wilderness, Gov. Mark Dayton said Monday that he will not grant access to state land for the development of a controversial copper-nickel mine next to the Boundary Waters Canoe Area (BWCA).

In a letter to a top executive of Twin Metals Minnesota, one of two firms exploring copper deposits in the region, Dayton said he has an obligation to protect an extraordinary natural legacy.

Monday's letter was the first time Dayton definitively and publicly stated that he opposes mining in the pristine watershed that holds the Boundary Waters wilderness. It followed last week's state approval of a 10-year environmental review for another mining project, proposed by PolyMet Mining Corp.

PolyMet's project lies in a watershed that drains southeast into Lake Superior, while the Twin Metals watershed drains north toward the BWCA.

Dayton's blunt statement surprised and delighted environmental groups, but outraged Iron Range legislators who have been pushing him to allow copper-nickel mining projects to move forward.

"As you know, the BWCAW is a crown jewel in Minnesota and a national treasure," Dayton wrote in a letter to Twin Metals, a subsidiary of the giant Chilean mining conglomerate Antofagasta. "I am unwilling to take risks with that Minnesota environmental icon."

The governor's office released the letter late Monday, detailing Dayton's reasons for denying the company access to state land.

Company officials could not be reached for comment.

Dayton also said he had made his views clear to the director of U.S. Bureau of Land Management, which oversees federal land nearby and is close to a pivotal decision in its own review of the Twin Metals project.

Aiming for 2018

Twin Metals is in the preliminary stages of a proposed underground mine near Birch Lake and the Kawishiwi River, which flows into the BWCA. It said in a recent report that it plans to start seeking regulatory approval in 2018 for a mine that would take about three years to build at a cost of $2.8 billion. It would be a massive construction project and the mine would eventually employ 850 people, a far larger operation than the proposed PolyMet open pit mine.

Twin Metals asked for access to state land for development work, which the Minnesota Department of Natural Resources had approved. But Dayton blocked it, saying he would not advance any copper-nickel mining projects until PolyMet has completed the regulatory process.

PolyMet is expected to apply for formal mining permits this year. Dayton has said he has not made up his mind on whether to move forward with that mine either.

His firm and public stance on the subject is likely to roil the politics of the upcoming legislative session, which will debate more jobless benefits to laid-off taconite mine workers.

The response from pro-mining legislators was swift.

"The governor is once again putting the interests of extreme environmentalists ahead of job creation in northern Minnesota," said Tom Hackbarth, R-Cedar, who chairs the House Mining and Outdoor Recreation Policy Committee. "Today's letter from Governor Dayton begs the question: Does he believe mining is a part of Minnesota's future?"

But environmental groups said they agreed with Dayton's concerns over the risks from a type of mining that has the potential to cause pollution more severe than taconite operations. The ore can create an acid that leaches heavy metals and other pollutants from rock, a major risk in an area known for its many lakes, rivers and wetlands.

"It's gratifying that he's committed to stewardship of that area," said Aaron Klemz, communications director for Friends of the Boundary Waters Canoe Area.

It's not clear at this point how or whether the project will move forward. The Bureau of Land Management (BLM) is expected to soon announce its decision on whether to require an environmental review of some kind on the federal mineral leases Twin Metals owns. Those leases have been in place since the mid-1960s, long before federal laws took effect requiring environmental review of mining. The leases are critical to the project as they would provide the company access to the copper ore.

"I believe that the BLM decision will offer further guidance on the future of mining in the area," Dayton said.