(IDEX Online) - Petra Diamonds suffered a sharp fall in its quarterly sales to 31 March, down almost 52 per cent to 67.8 per cent on Q3 2022.It also sold almost 37 per cent fewer diamonds - 465,138 carats - than during the same period last year.The miner's Williamson deposit, in Tanzania, remains closed after the breach of a tailings dam, which released a five-mile river of gray sludge, damaging homes, farmland and infrastructure.It is also planning the closure of its loss-making Koffiefontein mine, in South Africa, where it has so far laid off 382 workers, incurring costs of almost $5.5m.Despite having two of its four mines out of action, the company reported a three per cent increase in overall diamond production to 653,700 carats (up 14 per cent at Finsch and seven per cent at Cullinan).Richard Duffy, Petra's CEO, said: "We expect to deliver on our revised guidance of 2.75-2.85 Mcts for FY 2023. With Williamson targeted to resume production in Q1 FY 2024, we are well positioned to increase production by c.1Mct to 3.6-3.9 Mcts in FY 2025."He said prices had picked up recently, largely as a result of China's post-Covid re-opening."We continue to expect a supportive diamond market in the medium to longer-term as a result of the structural supply deficit, while noting potential volatility in the near-term owing to recent geopolitical and macroeconomic uncertainty," he said.Pic shows Koffiefontein mine