(IDEX Online) - Petra Diamonds is seeking a buyer for its loss-making Koffiefontein mine, in South Africa.The UK-based miner says otherwise it will close the underground deposit, in Free State province, when it reaches the end of its life in 2025."The focus of this disposal process will be to identify a technically and financially suitable buyer that could potentially unlock further value from Koffiefontein," it said in a statement."Given the gross resource base of c. 5.25 million carats as at 30 June 2021, including c. 1.11 million carats in the indicated resource category associated with underground resources, it may be feasible for another owner to extend the mine's life."Petra has already informed the National Union of Mineworkers (NUM) of "restructuring/ retrenchments" plans which could impact 150 jobs.Last year Petra failed to attract a buyer for its three mines in South Africa as revenues plunged and it struggled to repay $650m of debts. It struck a deal that reduced shareholders' stake in the company to just nine per cent.The company, founded by Adonis Pouroulis in 1997, also owns the Finsch and Cullinan mines in South Africa, and the Williamson deposit in Tanzania, which is currently mothballed.Questco Corporate Advisory is handling the proposed sale. Closing date for registering an interest is 9 May.Pic shows Koffiefontein