As significant as what BHP Billiton announced yesterday was what it didn't. Half-year results for the world's largest miner were better than expectations on almost every line: net income up 134 per cent, abundant free cash flow, net gearing less than half of the group's 10-year average. But there was no news of a widely anticipated share buy-back.

The big question now is what Jacques Nasser, succeeding Don Argus as chairman early this year, does with the sector's best-looking balance sheet. Investment in the business, rather than outside it, looks the smartest option.

Mr Nasser will be keen not to do anything rash. He inherited a $24bn cash pile when he took over as chief executive of Ford in 1999, but subsequent deals – including buying BMW's Land Rover unit and Volvo cars for a combined $9.2bn – were considerably less successful than