WHILE LEAVING PIT AREA LOADED ROCK TRUCK STOPPED NEAR TOP OF RAMP. EMP REFUSED ASSISTANCE OF 994 LOADER AND DECIDED TO BACK DOWN RAMP ON HIS OWN. AFTER TRUCK WAS PUT INTO REVERSE AND RETARDER APPLIED THE TRUCK FREE-WHEELED DOWN RAMP. WHEN BRAKES WERE APPLIED THE FRONT END OF THE TRUCK RAISED UP AND BACK DOWN TO GROUND.