BHP Billiton has finally exited the diamonds industry, after concluding a marathon sale negotiation for its EKATI diamond mine in Canada. Almost a year after starting a sale process for the asset, BHP sold its 80 per cent stake to specialist diamond company Harry Winston for $US500 million ($A479 million): a sum that appears to be a bargain basement price. BHP said divestment of EKATI would result in a $US200 million impairment to the carrying value of the asset, which will be reflected as an exceptional item in the company's financial results. Minority partners in EKATI - the geologists who found the deposit - have 60 days to match the offer under their joint venture agreement, but the sale to Harry Winston is expected to be completed before March 2013, subject to approval from Canadian regulators. Harry Winston had long been suspected as a likely buyer, and gave regular indications throughout 2012 that it was interested in striking a deal.