A FALL OF ROOF OCCURED IN THE 1ST SOUTHWEST SUBMAINS IN THE #3 ENTRY AT X-CUT #10 APPROX 3400 FT FROM #1 UNIT. THE FALL WAS APPROX 25'X20'X6 1/2"". THE AREA WAS SUPPORTED WITH 6' FULLY GROUTE D ROOF BOLTS. IT APPEARED TO BE CAUSED BY AN UNDETECTED BREAK IN ROOF STRATA.