Montana environmental regulators gave only partial approval on Friday to a long-stalled  silver and copper mine proposed beneath a federal wilderness area, casting uncertainty over the $500 million project that would bring hundreds of jobs to the Libby area.

Department of Environmental Quality Director Tom Livers approved an air quality permit and transmission line that would connect to the mine.

But Livers said in Friday’s decision that he would not issue a water pollution permit sought for the Montanore mine until hearing more public comment. Livers gave conditional approval to an operating permit for the evaluation phase of the mine, making it contingent on the outcome of the water pollution permit.

Sponsor Mines Management Inc. of Spokane previously said that anything less than full approval could make it difficult to attract investors.

Opponents of the project that would tunnel beneath the Cabinet Mountains Wilderness have raised concerns about its effects on waterways including Rock Creek and the Bull River. The mine would cause permanent changes in groundwater flows, according to federal wildlife officials.

Just last month, the mine appeared to have cleared one of its most significant hurdles when the DEQ and U.S. Forest Service finalized a long-awaited environmental review of the project.

U.S. Sen. Steve Daines and Rep. Ryan Zinke, both Republicans, last month urged Gov. Steve Bullock to grant full approval. They warned that a “staged” approval would delay much-needed job creation and tax revenue for Lincoln County, which has the highest unemployment rate in the state.

The mine would employ about 500 people during construction and about 350 people during mining.  It would disturb more than 1,500 acres and remove up to 120 million tons of ore.

Its entrance would be just outside the wilderness area — a rugged, remote landscape that is one of a handful of areas in the United States where the government is seeking to restore grizzly bear populations.