Mythrium mining is a perilous business. Not only do the creatures found underground not like to be disturbed, but inhaling Mythrium particles causes tumors. These tumors are not fatal in most cases, but the body swells in various places, as if it wanted to keep growing but in a disordered way, while the victim's consciousness gradually fades.
Ogres are particularly popular for mining, thanks to their resistance to both tumors and underground dwellers.