(IDEX Online) - Troubled Petra Diamonds has yet to receive any offers from potential buyers as its debts mounts and revenue slumps.The UK-listed miner launched a formal sales process in June to sell the company either as a whole or in parts.Petra, founded by Adonis Pouroulis in 1997, bought the famous Cullinan mine, in South Africa, and other deposits deemed unprofitable by De Beers, including the Finsch and Koffiefontein mines, also in South Africa, and the Williamson deposit in Tanzania.So far it has received no offers for the mines, according to Tanzania's The Citizen news website, which also reports that the country's government, a 25-per cent shareholder, has opposed plans to sell Williamson.Petra has seen Q1 revenues plunge 32 per cent to $91.3m and faces $650m of debts in senior secured bonds, due for payment in May 2022. Its famous Cullinan mine was the source of the largest rough gem-quality diamond ever - the 3,106.75-carat Cullinan Diamond that became part of the British Crown Jewels.