THE MECHANIC WAS REMOVING A COLLET FROM THE BUCKET ON 510904 LHD. AS THE MECHANIC WAS TIGHTENING THE JACK BOLTS TO REMOVE THE COLLET, IT BROKE LOOSE AND SPUN IN THE BORE. ONE OF THE JACK BOLTS SWUNG AROUND AND STRUCK THE MECHANIC ON HIS RIGHT INDEX FINGE.R HIS SUPERVIOSR AND THE MAINTENANCE COORDINATOR WERE CONTACTED AND RESPONDED TO THE MINE SITE AT 0300,TRANSPORTED TO HOSPITAL, 4