AT ABOUT 8:45 AM A LHD OPERATOR NOTICED THE RIB WORKING IN 925 RAMP. HE RETREATED & GUARDED THE AREA & CALLED THE SHIFT FOREMAN. AT ABOUT 9:30AM A SECTION OF THE RIB 40'LONG X 15'HIGH X 8'WIDE CAVED BEYOND BOLT ANCHORAGE INTO THE DRIFT. THERE WAS A SLIP (FAULT CONTACT) RUNNING AT 45DEG. AWAY FROM THE SILL THAT HAD BEEN PENETRATED BY A DIAMOND DRILL STRING & SUBJECTED TO WATER.