AT START OF SHIFT- SHIFTER AND MINE CREW INSPECTED THE 1715 3550 TEST STOPE. THERE WAS A MUCK PILE AND THE HEADING SEEMED TO BE IN GOOD SHAPE,MUCKED HEADING OUT AND CREW WAS TAKING A BOLTER INTO HEADING WHEN OPERATOR NOTED 12'SPILLING WASTAKING WEIGHT HE PULLED BACK & NOTIFIED SUPERVISOR, APPROX. 50' OF BACK CAME PULLING PAST ANCHORPR.