The mining giant controlled by the Luksic family, Antofagasta, took full control of the project in 2015, and its executives have called it the company’s “most advanced international opportunity.” Antofagasta, which is publicly traded in London, is poised to benefit from the growing use of copper in renewable-energy technologies like wind and solar. It lists Mr. Luksic as a board member, and his younger brother, Jean-Paul Luksic, as chairman.

The company has spent more than $450 million so far on the project, run by the subsidiary, Twin Metals Minnesota. It says the project will generate hundreds of mining jobs.

The promise of employment resonates in Minnesota’s Iron Range, which has lost a quarter of its mining jobs since 2000. “The mining industry brings a tsunami effect for the community with regard to jobs, schools, everything,” said Andrea Zupancich, the mayor of Babbitt, a town of 1,500 near the proposed mine.

Antofagasta’s environmental record, however, has raised concerns. In Chile, the company’s Los Pelambres copper mine has suffered toxic spills, according to environmental groups. The company said the mine had experienced only “minor incidents involving limited spills” which were not toxic, and said it was proud of its environmental record.

In a 2016 analysis, Thomas Tidwell, who was then chief of the United States Forest Service, warned of risks to the Boundary Waters from the proposed Twin Metals mine, including the leaching of harmful metals. Mining, he concluded, risked “serious and irreplaceable harm to this unique, iconic, and irreplaceable wilderness.”

Twin Metals called the analysis “riddled with errors” and said “environmental risks will be properly managed.”

Still, the fears have divided nearby residents. “In the summer, we drink out of this water,” said Susan Schurke, who runs Wintergreen Northern Wear, an outdoor clothing company. “Once that’s tainted, it’s over. How can we risk that?”