AN UNPLANNED DETONATION OF A BLASTING CAP &/OR PRIMER OCCURRED AS A BE 2507W DRAGLINE WAS DIGGING OVERBURDEN FROM A PREVIOUSLY DETONATED CAST SHOT. THE UNPLANNED DETONATION OCCURRED APPROX. 5'ABOVE THE SURFACE OF COAL & APPROX. 65'BELOW DRAGLINE BENCH. THE BLAST SEPARATED A TOOTH FROM THE BUCKET. THE LAMINATED SAFETY GLASS OF THE UNOCCUPIED LEFT OPERATOR CAB WAS ALSO DAMAGED.