At issue was a 2017 challenge by the Menominee Indian Tribe of Wisconsin and an individual owing property near the project site, who questioned the validity of the final mining permit.

Following hearings and testimony, a judge on May 3 ruled the proposed mining operation would operate in compliance with the state's non-ferrous metallic mining statute.

"Aquila will continue its efforts with the state of Michigan and local communities to demonstrate our commitment to environmental responsibility and sustainable resource development that benefits all stakeholders," said CEO Barry Hildred. "The Back Forty mine will be a safe, disciplined operation that promotes and supports local community socioeconomic development and is protective of the environment."

He said in an interview with Mining Journal last week the project would have renewed momentum once the legal challenge had been dealt with.

"We continue with environmental monitoring and are conducting baseline studies in support of our planned development phase. We are shovel ready and following the outcome of the permitting challenge, things will move fast once we get going," Hildred said.

He added work was underway on an 'enterprise PEA', that would evaluate the economic case for a combined openpit-underground operation, with more on that plan to come mid-year.

Back Forty is a volcanogenic massive sulphide deposit with underground potential along the mineral‐rich Penokean Volcanic Belt in Michigan's Upper Peninsula. The project hosts about 1.1 billion pounds of zinc and one million ounces of gold.

A 2018 feasibility study outlined a seven-year mine plan with total payable gold output of 468,000oz at an average 67,000oz/y and zinc production of about 512Mlb at an average 73Mlb/y.

"It's important to consider the fact metal prices have materially increased since we published our August feasibility study. We don't need a price turnaround to be successful at Back Forty," Hildred said.

Initial project capex has been pegged at about US$294 million with a 24-month construction period, and sustaining capital costs are expected to total about $110.6-million.

Aquila (TSX:AQA) C1c or 5.41% Monday to close at 19.5c, capitalising it at $66 million.