A COAL HAULER WAS TRANSPORTING COAL FROM THE COAL PIT TO THE CRUSHING FACILITY WHEN THE OPERATOR NOTICED THE ENGINE COMPARTMENT AREA WAS ON FIRE. THE FIRE SUPRRESSION SYSTEM AND EMERGENCY RESP ONSE TEAMS EXTINGUISHED THE FIRE IN 45 MINUTES. INITIAL INVESTIGATION POINTS TOWARD A MAJOR ENGINE FAILURE AS THE CAUSE OF THE FIRE.