PolyMet Mining has secured a favourable ruling on air permit issued for its NorthMet Project from the Minnesota Supreme Court.

The $945m NorthMet copper-nickel-platinum mine, which is located within the Duluth Complex in northeastern Minnesota, is planned to be developed in two phases.

The latest court ruling overturned the Minnesota Court of Appeals’ order which remanded the Clean Air Act permit back to the issuer, the Minnesota Pollution Control Agency (MPCA).

PolyMet said that the central legal argument rejected by Minnesota Supreme Court relied on by the project opponents and the decision to remand the air permit was based on ‘erroneous interpretation’ of federal law.

PolyMet chairman, president and CEO Jon Cherry said: “This decision is another big win and a major step forward in the defense of our air permit.

“We believe strongly that the facts and the law are on our side, and we are pleased that the court agreed with us on the law. This is a victory for the company, our many stakeholders and for everyone that supports responsible mining in Minnesota.”

PolyMet said that the case against the proposed mine will now return to the appeals court relating to few remaining issues that were not addressed specifically in its original decision.

Last week, the US District Court in Minneapolis ruled in favour of PolyMet in a case filed by the US Environmental Protection Agency against the mine’s water quality permit.

Last year, Polymetal announced its decision to go ahead with its $80m Kutyn gold project located in the Tugur-Chumikan District of the Khabarovsk Territory in Far East Russia.