EE WAS ATTEMPTING TO ADJUST FEED GATE OPENING BY SHORTENING THE 3/8 INCH CHAIN THAT HOLDS THE GATE OPEN ON THE FEED CONVEYOR UNIT 2200 THAT FEEDS THE CRUSHER. HE OPENED THE GATE & SECURED IT W ITH A BLOCK. THE BLOCK SLIPPED WHILE HE WAS ADJUSTING THE GATE & PULLED HIS RIGHT INDEX FINGER & THUMB THROUGH THE CHAIN OPENING CAUSING LACERATIONS.