The EE was bolting on 9 North Mains Section, in crosscut 2-4. EE removed the steel from the rib to install a rib bolt. The rib broke loose at the same time, and the EE hit the rotation on the rib drill. EE's right hand got caught by the rib steel causing abrasions/lacerations to EE's right pinky finger. Received 9 stitches.