(IDEX Online) - Petra Diamonds is seeking a buyer as debts mounts and revenue slumps.The UK-listed company operates the world-famous Cullinan mine in South Africa, source of the largest rough gem-quality diamond ever - the 3,106.75-carat Cullinan Diamond that became part of the British Crown Jewels. In addition, it operates the Finsch and Koffiefontein mines, also in South Africa, and the Williamson deposit in Tanzania, currently on care and maintenance, and has a limited exploration program in Botswana and South Africa.Petra was founded by Adonis Pouroulis in 1997, bought up mines that were deemed unprofitable by De Beers and operated then with a focus on value over volume.But it is now struggling with the impact of COVID-19, together with plunging revenues - down 32 per cent year to $91.3m in the quarter ending March 31- and $650m debts in senior secured bonds, due for payment in May 2022. The company is for sale either whole or in parts. "The company is not in receipt of any offer for the company or any parts of the group's business or assets at the time of this announcement," it says in a strategic review of its formal sale process.Pic shows a 424.89 carat D-Color Type II diamond recovered at Cullinan on 29 March 2019