Gov. Mark Dayton plans to visit two mines in other states — examples of good and bad environmental outcomes — as he prepares to decide whether Minnesota should move forward with a controversial project proposed by PolyMet Mining Corp. on the Iron Range.

The $650 million open-pit operation would be Minnesota’s first copper-nickel mine. It promises to bring some 300 to 350 jobs to northeastern Minnesota, but it also would bring unprecedented environmental risks to a region known for beautiful lakes and forests.

A 10-year environmental review of the project is due for completion in November, and shortly after that PolyMet is expected to apply for a permit to start construction. Dayton has called it “the most momentous, difficult and controversial decision I will make as governor.”

That’s why he is taking the unusual step of examining mines in other states on Oct. 27 and Oct. 30.

Environmental groups suggested his first stop, the Gilt Edge Mine in the Black Hills of South Dakota, as an example of the worst that can happen. Opened in the late 1800s, it produced gold and silver until 1999, when the owner declared bankruptcy and abandoned it. It is now a highly contaminated Superfund site.

Like PolyMet’s project, Gilt Edge involves mining for metals in sulfide-bearing rock, which can cause highly acidic water pollution when exposed to air and water.

The U.S. Environmental Protection Agency and South Dakota have spent more than $105 million to clean up the site, but the mine continues to pollute surrounding creeks.

At the suggestion of mining supporters, Dayton will head to the Upper Peninsula of Michigan on Oct. 30 to see modern mining at its best — a copper-nickel mine about 40 miles west of Marquette.

The Eagle Mine went into production in September 2014 after a 12-year legal and political battle, and it remains controversial among local environmental groups and Indian tribes.

The Eagle Mine is an underground mine that produces ore transported by trucks to a nearby mill for processing. It is smaller than the mine proposed for Minnesota, but it will use a similar treatment process to cleanse contaminated water and was once overseen by an executive who now works for PolyMet.