The seal was placed over the last of the tunnels miners used to get underground, The Register-Herald of Beckley, W.Va., reported Thursday.
On April 5, 2010, the mine was the site of a fatal explosion, the worst U.S. coal mining disaster in 40 years, the newspaper said.
At the time of the explosion, Upper Big Branch mine was owned by Massey Energy. Last summer, the company was bought out by Virginia-based Alpha Natural Resources, which decided to seal the mine portals in what Ted Pile, vice president of corporate communications, called a "clearly consensus decision."
"We expect to be finished with all activities at Upper Big Branch within the next few weeks," he said.