EE AND COWORKER WERE WORKING TOGETHER AT THE TRACKS OF THE MINING UNIT. WHILE USING PROPANE TORCHES TO THAW FROZEN TRACKS OF MINING UNIT, A LARGE PIECE OF CLAY MATERIAL (~500-700#) FELL FROM A BOVE (~12') SCREEN AND HIT EE ON THE BACK. EE WAS KNOCKED TO THE GROUND. THIS INJURY REQUIRED XRAYS, PRESCRIPTION MEDICINE, AND MISSED DAYS.