For more than 40 years, iron ore prices have been settled in secretive – and often acrimonious – negotiations between global steelmakers and miners. The tradition fell apart on Wednesday as BHP Billiton said the iron ore price for a third of its customers would be determined by prices on the spot market.

The move – a victory for BHP’s chief executive Marius Kloppers – has an unexpected winner: Wall Street’s banks. Analysts and bankers say it will be a critical boost to the nascent derivatives swap market, where investors can bet on the direction of iron ore prices.