HELENA, Mont. (AP) — A Canadian company studying the feasibility of building a copper mine in central Montana has preliminary approval to increase its ore testing.The Department of Environmental Quality on Monday released a draft environmental assessment that found Tintina Alaska Corp. Inc. will be able to mitigate any possible impacts from its ongoing exploration at the Black Butte Mine at the headwaters of the Smith River. The DEQ is taking public comment on the draft through Aug. 26.

The company has been drilling core samples in the field northwest of White Sulphur Springs for the past three years. Earlier this year, Tintina sought a permit to dig a nearly mile-long tunnel and extract up to 10,000 tons of ore to further gauge the mine's viability.