EE was assisting miners in making belt splice at 3-head.EE was pounding nails into splice w/ hammer,hammer struck his left thumb.EE sustained dislocated thumb and needed 2 sutures.EE was released to RTW on 1/16/08.EE worked part of his shift on 1/16/08.EE went back to doctor and is not scheduled to RTW until 1/22/08.Miner proficency and awareness were factors in incident.