April 12 (Reuters) - Antipa Minerals Ltd AZY.AX
* Rio Tinto (LON:RIO) elects to proceed to stage 2 of Citadel farm-in
* Rio Tinto Exploration Pty Limited has confirmed that it will continue to stage 2 of the $60 million citadel project farm-in
* Rio Tinto to become operator of the Citadel project joint venture Source text for Eikon: ID:nASX9M4phX Further company coverage: AZY.AX