More than 170 businesses and outdoor groups signed letters opposing the U.S. Department of the Interior's decision to reinstate Twin Metals' expired mineral leases in May and the mining company's new plans released last week.

The three separate letters were each signed by a coalition of conservation, businesses and outdoor sporting groups and sent to Agriculture Secretary Sonny Perdue and Interior Secretary Ryan Zinke.

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"These are three very separate coalitions, and that's on purpose. We have a lot of different audiences that love the Boundary Waters for very different reasons," said Lauren Eggert, communications director for Save the Boundary Waters, the environmental group distributing the letters.

Critics say that the company's proposed copper-nickel mine could send tainted runoff into the pristine Boundary Waters Canoe Area Wilderness watershed, no matter how many precautions are taken.

Bob McFarlin, Twin Metals spokesman, responded to the letters in an emailed statement Thursday.

"Twin Metals Minnesota recognizes environmental stewardship as a core value and strives to be a leader in protecting Minnesota's wilderness, natural environment, and recreational and cultural resources," McFarlin said. "Unfortunately, opponents of mining and mining jobs in Northeast Minnesota are fighting facts with fear."

In a telephone interview with the News Tribune, Frank Ongaro, executive director of MiningMinnesota, a copper-nickel mining advocacy group, agreed that copper-nickel mining opponents employed fear to push their agenda. He added that many of the groups signing the letters weren't local.

"A lot of outside groups from outside of Northeastern Minnesota trying to tell us how to live our lives," Ongaro said.

One company, Patagonia, an outdoors clothing and gear company, has been a "supportive partner" in signing the letters and distributing news releases, Eggert said.

In early May, Twin Metals won back critical federal mineral leases that had been withheld by the Obama administration. The leases cover areas at and around the proposed mine site along the Kawishiwi River and Birch Lake just outside the Boundary Waters Canoe Area Wilderness.

In its updated plans released last week, the company explained that the concentrator and processing plant - the major above-ground feature of the operation - would be located just south of the mine site, just east of Birch Lake on land that Twin Metals already owns. Earlier plans had considered a site south of the Ely airport, west of Birch Lake.