The country’s only fully operational lithium mine had an air pollution problem, Nevada regulators found.

An Australian mining company’s lithium-boron mine in Nevada passed all environmental hurdles on Thursday, and an environmental group immediately notified the federal government that it plans to sue.

It also holds a portfolio of exploration properties in Nevada, Canada, Mexico, and Argentina. The company was formerly known as US Gold Corporation and changed its name to McEwen Mining Inc. in ...