ST. PAUL (AP) — Minnesota Gov. Mark Dayton has planned trips to mines in South Dakota and Michigan as his administration prepares for a major decision on whether to advance copper and nickel mining on the Iron Range.

Dayton spokesman Matt Swenson said the governor will tour the Gilt Edge mine in western South Dakota on Oct. 27 and Eagle Mine in northern Michigan on Oct. 30. Dayton’s administration is evaluating environmental issues surrounding the proposed PolyMet mine.

The PolyMet project has already caused divisions in Dayton’s Democratic Party between those who see its job potential and those who worry about environmental damage.

Swenson said Dayton wants to assess the community impact of the mines. The tours will be private.

“Both visits are part of the Governor’s due diligence to see first-hand the operations and impacts of mine sites similar to the PolyMet project proposal,” Swenson said.

The Minnesota Department of Natural Resources plans to issue the final environmental impact statement on PolyMet next month.  The DNR plans to rule on the adequacy of the massive document in February. If it gets the green light, PolyMet could then start applying for the necessary permits.

Mineral mining is ingrained in Minnesota’s history, but the extraction proposed by PolyMet would be unique. Dayton has called the permitting decision the “most difficult and consequential decision I’ll make as governor.”

The Eagle Mine is about 40 miles west of Marquette on Michigan’s Upper Peninsula. It went into production in September 2014 after a 12-year legal and political battle with parallels to the struggle over PolyMet.

Environmental groups and the Keweenaw Bay Indian Community fought to prevent the underground mine from being built, saying it poses a serious risk to groundwater and a nearby river.

Similar to PolyMet’s ore deposit, the Eagle Mine’s nickel and copper are bound up in sulfide minerals that can leach sulfuric acid when exposed to air and water.