(IDEX Online)- Troubled Petra Diamonds has blamed the coronavirus pandemic for a 36 per cent drop in sales.The UK-listed miner is currently seeking a buyer as it faces mounting debts and says it's been dealt a significant extra blow by the combination of COVD-19, an already weak market and a series of power cuts affecting its mines in South Africa."The unprecedented impact of COVID-19 has significantly reduced activity throughout the diamond market pipeline from production, rough sales, trading, cutting and polishing, right through to consumer sales," it said.Petra bought up some of De Beers' less profitable mines in the late 1990s, including Cullinan, source of the largest rough gem-quality diamond ever - the 3,106.75-carat Cullinan Diamond that became part of the British Crown Jewels. It also operates the Finsch and Koffiefontein mines, also in South Africa, and the Williamson deposit in Tanzania, currently on care and maintenance. It has a limited exploration program in Botswana and South Africa.Revenue for the fiscal year ending June 30 was down 36 per cent to $295.8m (from $463.6m) and sales volume declined 23 per cent to 2.9m carats, according to its latest trading statement.Petra's tenders were canceled in May and June because of travel restrictions and significantly reduced demand from the midstream. It realized $10.5m from inventory in Q4, including unsold goods from the March tender, mainly to the domestic cutting and polishing market.As for the future, Petra said it was "continuing to explore strategic options to evaluate the optimal capital structure for the long-term success of the business, which includes running a formal sale process to invite suitable and deliverable offers for either the group or one or more of its assets.It said an employee at Cullinan employees had died of COVID-19 and 39 more across its South Africa operations had tested positive for the virus.Pic shows a 424.89 carat D-Color Type II diamond recovered at Cullinan on 29 March 2019