By Reuters Staff (Adds details on Congo Iron, and extension of negotiation process with Cameroon) JOHANNESBURG, Feb 18 (Reuters) - Australia’s Sundance Resources Ltd said on Thursday it was advancing its plans to start international arbitration proceedings against Congo Republic after the African country cancelled its Nabeba iron ore project in December. Sundance, which delisted from the Australian Stock Exchange on Dec. 21, said arbitration proceedings would be conducted under International Chamber of Commerce rules, before a tribunal of three arbitrators in London. A presidential decree i...