EE STATED HE WAS OPERATING RIGHT SIDE OF DRILL. AFTER MAKING VISUAL AND SOUND TEST, OPERATOR MOVED DRILL HEAD OUT TO INSTALL RIB BOLT, WHEN AN UNDETECTED ROCK STRUCK EE ON HEAD AND SHOULDER. A FTER ER VISIT, HE RETURNED TO WORK WITH NO RESTRICTIONS. WORKED UNTIL 4/12/01, WHEN THE MEDICAL SPECIALIST PLACED HIM ON RESTRICTED DUTY.