MINNEAPOLIS — PolyMet Mining Corp. is offering the state a $544 million package of financial assurances to serve as an insurance policy to protect taxpayers from potentially having to cover the costs of closing and cleaning up a controversial copper-nickel mine it wants to build in northeastern Minnesota.

The company said the package of surety bonds, irrevocable letters of credit and a trust fund would be sufficient to cover all costs, including treating the mine’s wastewater “as long as necessary,” if the mine were to close and the company couldn’t cover the costs.

PolyMet used an estimate of 100 years in its financial modeling, spokesman Bruce Richardson said. But the company isn’t saying that’s how long the water would need treatment. He said new purification technologies, as they’re developed, may shorten the required time.

The financial assurances package has been one of the most contentious issues in the fight over the proposed mine near Babbitt and processing plant near Hoyt Lakes, which would be Minnesota’s first copper-nickel mining operation. PolyMet’s critics say copper-nickel mines elsewhere have a long track record of environmental damage from acid mine drainage — and of going bankrupt — and leaving taxpayers stuck with the cleanup costs.

The package is a key component of PolyMet’s updated application for a permit to mine, which was released Wednesday by the state and runs about 22,000 pages, including appendices.

The revisions reflect feedback from technical experts with the Department of Natural Resources and its outside consulting company.

Minnesota law requires PolyMet to submit bankruptcy-proof assurances before the department can approve the permit to mine. The plan is meant to ensure that the state has enough money to close the mine and reclaim the site if PolyMet can’t, and it must cover costs for long-term monitoring and water treatment.

“We’re pretty excited about this,” PolyMet President and CEO Jon Cherry told The Associated Press.