The Minnesota Department of Natural Resources has rejected a request by environmental groups to reconsider the mine and dam safety permits for the NorthMet copper/nickel project.

Commenting on the department’s decision, developer PolyMet Mining president and CEO Jon Cherry said in a statement that the permits were issued after a comprehensive and lengthy environmental review and permitting process that involved “considerable” public involvement and, in the case of the dam safety permit, independent review by outside experts.

“The tailings dam design is configured to achieve and exceed the project-specific factors of safety and stability required by the state. Our proposed tailings basin has undergone more scrutiny and independent expert review than any tailings basin in the state, and arguably, any tailings basin in the country,” he said.

The company will reuse an existing tailings basin formerly used in taconite mining, with some enhancement, which was found to be environmentally preferable over a greenfield site.

Separately, the Minnesota Court of Appeals on Tuesday placed a temporary stay on the company’s water quality permit, pending a lower court’s resolution of a procedural matter between the Minnesota Pollution Control Agency and the US Environmental Protection Agency related to the permit.

A scheduling hearing was held on Wednesday in Ramsey County District Court to begin the process for that court proceeding.

“We remain confident that the water quality permit will ultimately be upheld in the Court of Appeals, and we look forward to the District Court’s contribution to that process,” said Cherry.

Located within Minnesota’s Mesabi Iron Range, the NorthMet project has a measured and indicated resource of 649-million tonnes. PolyMet plans to develop the mining operation in two phases, the first of which involves development of 225-million tons – nearly one-third of NorthMet’s known resource – into an operating mine processing 32 000 t/d over a 20-year mine life. It also includes rehabilitating the former LTV Steel Mining Company processing plant.

Capital costs for Phase 1 are estimated at $945-million and include refurbishment of the existing primary crushing circuit and replacing the existing rod and ball mill circuits with a new, modern semi-autogenous grinding mill, ball mill and flotation circuit. It also includes rail upgrades, mining equipment and a state-of-the-art wastewater treatment plant.

Phase 2 involves construction and operation of a hydrometallurgical plant to treat nickel sulphide concentrates into upgraded nickel/cobalt hydroxide and recover additional copper and platinum-group metals. Phase 2 would increase the project’s capital costs by about $259-million.

The NorthMet deposit will be mined by openpit methods to a depth of about 210 m below the surface.

PolyMet is a US-based company with corporate headquarters in Toronto. Swiss-headquartered global miner Glencore has a 28.8% shareholding in PolyMet and recently appointed senior executive Peter Freyberg to the developer’s board.