– Democrats averted a nasty public fight Sunday over a controversial Iron Range copper-nickel mining proposal that has vividly split powerful party factions.

Activists at the state DFL convention decided against debating a proposal to make support of mining part of the state party platform. The move took on enormous implications as environmentalists and labor supporters are bitterly divided over PolyMet Mining Corp.’s proposal to extract copper and nickel from the long-closed LTV mine in Hoyt Lakes.

“The mining issue has the potential to rip up the last remaining hard-core Democrats,” said Joel Holstad, a DFL activist from Forest Lake. “I have no idea which way this is going to go, but I think this issue has the potential to be incredibly impactful on the future of the party.”

Some elected Democrats, who control the governor’s office and the House and Senate, were dreading a bruising public fight that would have overshadowed DFLers’ overwhelming endorsements of Gov. Mark Dayton and U.S. Sen. Al Franken, who are heading into tough re-election fights.

Convention activists had seemed primed for an explosive battle over the mining issue just the day before. Dayton and Franken were even asked about their positions on PolyMet during cele­bratory news conferences after their endorsements.

“There are some who are willing to die on their sword over this, regardless of what happens politically to people,” said Nancy Larson, a longtime DFL activist who grew up on the Iron Range and supports copper-nickel mining.

In the end, activists on both sides came to the microphones to urge hundreds of feisty dele­gates to delay the vote indefinitely, a remarkable showing for a party that has seen conventions erupt into damaging fights with political scars that can last decades.

“I think people on both sides understand that we can have respectful differences, but we need to make sure we don’t do anything that is going to take away from our candidates’ ability to win this fall,” said Ken Martin, DFL Party chairman. “So there was a lot of discipline here. People understand the ramifications of the issue.”

PolyMet has pledged to invest $650 million initially and create up to 360 jobs if it gets approval. The firm expects to infuse another $500 million a year over the two-decade life of the mine.

Other companies already are lining up to tap what they have found to be one of the world’s largest untouched deposits of copper, nickel and other precious metals used for everything from smartphones to hybrid cars. Local officials are hoping the area is on the leading edge of a mining resurgence on the scale of the oil boom in North Dakota.

The Dayton administration may face a make-or-break decision on the PolyMet project this year, creating a sense of urgency for activists on both sides.

The fight pits a strong and influential conservation-minded wing of the party against Iron Range DFLers, who strongly support the mining expansion.

Environmentalists warn that similar mines have a disastrous history of pollution in other states and countries, and that a mine expected to last two decades could result in centuries of water cleanup in a fragile watershed that feeds Lake Superior.

“Issues about water and water quality have not been brought to light like they should be,” said Mary T’Kach, a first-time DFL delegate from Inver Grove Heights. “This is some of the most pristine land in the country, and this mining will destroy this water that we need and rely on.”

Republicans are using PolyMet to stoke the divide among groups whose support Dayton and Franken will need.

GOP gubernatorial candidate Scott Honour drove to Duluth to criticize Dayton for not demonstrating more full-throated support for the PolyMet project.

“That’s harming lives in Minnesota,” Honour said.

Martin said the DFL has a deep connection to mining and the labor faction of the party largely sprouted from the unions in the mining industry. He called the GOP’s interest in the issue “completely disingenuous.”

“If you look at the Republicans in the state Legislature over the last 10 or 15 years, they have done nothing to support the Iron Range,” Martin said. “This is political opportunism at its best. When you strip this away, it’s about trying to gain an advantage for the election coming up.”

Elected Democrats must navigate tricky political terrain on the issue.

Dayton gently addressed the simmering furor in his convention speech, talking at length about the need for jobs. But he added, “We’re going to make Minnesota the best place to breathe the air, to drink the water, and to catch fish in it.”

Freshman state Rep. Jason Metsa, DFL-Virginia, said both sides had “heartburn” about the platform measure as they girded for a fight.

“Why come here and talk about the things that divide us when we should be here talking about the things that we have accomplished,” said Metsa, a strong supporter of the PolyMet project.

State Rep. Rick Hansen remains deeply skeptical that copper-nickel mining can be done safely. He is trying to find ways in the Legislature to better ensure that mining companies provide the state with adequate financial resources to deal with water cleanup in the future.

“You saw both sides, pro-mining and pro-environment, come together today and say, ‘We don’t want to have this battle,’ ” said Hansen, DFL-South St. Paul. “People know there are deep feelings, but people wanted to come out of here united.”