ST. PAUL — PolyMet has formally applied for a permit with the Department of Natural Resources to build a copper-nickel mine in northeastern Minnesota.

The application is a key step in the process to build the proposed mine near Babbitt, and now triggers an extended review of the company’s finances and the project’s potential environmental impact.

In March, the DNR approved the project’s final environmental review, which paved the way for this permit application. The DNR said it’s the first copper mining permit application in Minnesota’s history, and the review will take months.

While supporters say the mine would bring new jobs to northeastern Minnesota, environmental groups and local Indian tribes have worried that approving it could lead to other mines in the area. The groups also have been critical of the DNR’s environmental review, saying it relied on flawed data provided by PolyMet contractors and underestimates the potential for water pollution.

PolyMet said Thursday that the permit is the last of the major permit applications it had to submit, after filing its water-related and air quality permit applications to the DNR and Minnesota Pollution Control Agency earlier this year.