The decision by a three-person panel was the final word in the contested case challenge to the mining permit that started in April 2018.
The Menominee Indian Tribe of Wisconsin appealed the court's initial decision, but the EGLE panel voted unanimously in support of the prior ruling, determining that "the proposed mining operation will not pollute, impair, or destroy the air, water, and other natural resources, or the public trust in those resources".
"Michigan's environmental standards for mining are among the strictest in the world, and we look forward to continuing to demonstrate our commitment to environmental responsibility and sustainable resource development that benefits all stakeholders," said Aquila 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."
The Menominee previously filed a federal lawsuit against a wetlands permit issued to Aquila for the project in 2018, but the US District Court for the Eastern District of Wisconsin dismissed the lawsuit in December 2018.
The US$294 million project is now shovel ready and contains proven and probable openpittable reserves of 11.65 million tonnes. The mine plan calls for producing 512Mlb zinc and 468,000oz gold at average reserve grades of 6.7% and 4.3g/t, respectively, over a seven-year mine life.
An August 2018 feasibility study also outlines copper production of 51.1Mlb over the project's life.
Aquila shares (TSX:AQA) remained unaffected by the news on Wednesday, closing flat at C17.5c, having traded between 14c-25c over the past 12 months. The company has a market capitalisation of $59 million (US$44.4 million).