South Dakota officials say a drilling substance that leaked into a creek isn't likely to cause environmental damage.
A gold exploration company says the leak allowed bentonite to seep into Battle Creek near Keystone, about 20 miles southwest of Rapid City.
Bentonite is a clay-like material that is used as a drilling lubricant. Mineral Mountain Resources Ltd. Of Vancouver, British Columbia, has been exploring for gold in the area. A company spokesman declined comment.
South Dakota environmental engineering manager Mike Cepak says the leak lasted about two hours. He says the drilling substance is "basically benign" and shouldn't cause any serious environmental problem.
Battle Creek is a cold-water fishery and has some trout. The leak happened Thursday.