(IDEX Online) - The newest diamond mine in Sierra Leone is to hold its maiden sale of rough production later this month.The Tongo Diamond Mine, operated by Australia-based Newfield Resources, has signed an exclusive sales and marketing agreement with Bonas, in Antwerp.Newfield describes the mine as "an 8.3m carat JORC compliant indicated and inferred diamond resource, primarily based on five kimberlites".It said in a quarterly activities report: "The current mine plan is focussed on developing and mining the Kundu and Lando kimberlites, for which a JORC compliant probable reserve of 1.1 million carats has been declared for the upper 110m of these kimberlites."Work on the mine has been taking place over the last decade and so far there are 1,229 metres of of underground development.The mine previously belonged to London-based Stellar Diamonds.Tender viewings will take place in Antwerp from 16 May 16 until the online sale, on 20 May.Pic courtesy Newfield Resources.