EMPLOYEE WAS REPAIRING A DAMAGED CORNER OF AN OVERCAST MADE FROM CEMENT BLOCKS. EMPLOYEE WAS LAYING BLOCKS AT BOTTOM OF OVERCAST WHEN A CEMENT BLOCK BROKE OFF THE OVERCAST ABOVE THE AREA HE WA WORKING. THE PIECE OF BLOCK STRUCK HIS LEFT HAND. THERE WAS NO DAMAGE OR IMPAIRMENT TO THE MINING OPERATION.