State regulators say a proposed underground copper mine in central Montana would emit up to 340 tons a year of dust and other small particles.
The Montana Department of Environmental Quality detailed the emissions in a draft air quality permit issued for the Black Butte copper mine near White Sulphur.
The Great Falls Tribune reports that the public has until July 5 to comment on the document.
Black Butte is sponsored by a subsidiary of Sandfire Resources, based in Australia. The company says the mine would employ about 240 people and remove 1.3 million tons of rock annually.
Conservation groups are concerned about potential pollution into a tributary of the Smith River, which is so popular among boaters that the state conducts an annual lottery to regulate access.