"Willow Lake has had issues performing at an acceptable standard for safety, compliance and productivity despite aggressive programs targeting improvement," company spokeswoman Beth Sutton said of the mine near Harrisburg, Ill.
The St. Louis Post-Dispatch reported Wednesday that 400 jobs will be lost as the mine closes.
The mine produced 2.2 million tons of coal in 2011, but production at the mine has been waning.
Safety issues did play a part in the decision to close, with the company citing the death of a worker less than two weeks ago as a contributing factor.
The worker was pinned by a piece of equipment.
The company and a spokesman for United Mine Workers of America both said the closure was not related to ongoing contract talks. "We were very surprised. We felt like [talks] were on the right path," said union spokesman Phil Smith.
The company also said negotiations were not over, as it would still operate a coal preparation plant that processes coal from two other nearby mines.
Notable deaths of 2014 [PHOTOS]