Bolt crew had set ATRS preparing to bolt the face of #4 entry. Operator was starting to swing drill boom out to install 1st Roof bolt. A piece of slate 0-8"" thick x 30"" x 60"" fell between T-bar and last permanent support. Rock hit operator on head & shoulders & hit bolter canopy. Canopy had not yet been raised. Neck was jammed up & shoulders bruised.