(IDEX Online) - Petra has reclassified the mothballed Williamson mine, in Tanzania, as an "asset held for sale", prompting speculation that it could sell the deposit in Tanzania.The London-based miner says Williamson has been "classified as an asset held for sale for financial reporting purposes" in its preliminary annual results published last week.It says that as a discontinued mine it represents an accounting loss of $52.1m for the company. In March Petra Diamonds concluded a debt-for-equity restructuring to secure its future, after failing to attract a buyer for its three mines in South Africa.Revenues had plunged and it was struggling to repay $650m of debts. The deal reduced shareholders' stake in the company to just nine per cent.Wiliamson (pictured) was put on care and maintenance in April 2020 as the global pandemic hit, resulting in an "unprecedented depressed market environment".Last month Petra's chief executive Richard Duffy said the company aimed to restart operations to in the first quarter of 2022, forecasting an output for the year of 220,000 to 270,000 carats.Petra owns 75 per cent of Williamson, which was was among the oldest continuously operating diamond mines in the world. The remainder is owned by the government of Tanzania.