WHILE DRILLING #1 PARTING WITH DM50 DRILL, THE MAST PULLDOWN CHAIN BROKE AND EE, DRILL SUPERVISOR, WAS CALLED TO THE DRILL. EE WAS LOCATED T THE FRONT OF THE DRILL, LOOKING UDNER THE DECK AT T HE DRILL STEEL, WHEN A SINGLE ROCK (APPROX 34""X18"") FELL FROM THE HIGHWALL APPROX. 35' HITTING THE DRILL DECK AND BOUNCING INTO EE LEFT ARM AND SIDE. HIS LEFT ARM WAS FRACTURED AND HE HAD CON