Investigators blame methane gas for the explosion that killed two workers who were helping dig a diamond mine in Siberia last week. The Sakha republic\'s investigative committee issued a written statement Sunday saying a \"methane-air mixture\" led to the blast about a quarter-mile below the surface at the Yakutia mine operated by the Russian mining company Alrosa. Two men were killed and four others were injured in the explosion, which remains under investigation by the Sakha committee, Russia\'s ITAR-Tass news agency said.