Massey said in a regulatory filing Monday that the box was found July 30 and removed from the Raleigh County mine the same day. A citation issued by the federal Mine Safety and Health Administration says the small locked box was found deep inside the mine, between two areas involved in the explosion.
Virginia-based Massey says the explosives are not related to the fatal blast.
MSHA is still investigating the explosion, considered the nation's worst coal mining disaster in 40 years. It's also the subject of a federal criminal investigation.