BHP Billiton said on Wednesday that a third of its customers had signed contracts to buy iron ore on the basis of contracts linked in part to the nascent spot market, breaking with more than 40 years of tradition of annually negotiated prices.

The move by the Anglo-Australian miner, the world’s third largest iron ore producer, is the clearest signal yet of the collapse of the so-called benchmark system, in which the first annual price mutually agreed between a big miner and a steelmaker is followed by the rest of the industry.