Convincing watchdogs that mingling $116bn of assets was in no way anti-competitive was never going to be easy. After announcing plans to form an iron ore joint venture in June, Rio Tinto and BHP Billiton stressed that what they had in mind was a simple, no-frills production JV, wrapping contractual obligations around pooled assets without changing any underlying ownership. They'd dig it up together, they'd sell it individually. But clause 4.8, under which up to 15 per cent of output was to be sold by the joint venture itself, separately from both partners, muddied that picture.

Neither side would have relished yesterday's announcement that that clause is no more. By setting aside a portion of ore to sell into spot markets or into shorter-term contracts, BHP and Rio had given themselves a basic hedge against spot prices running way ahead of the benchmark. But expunging the clause is the sensible thing to do. Mofcom, the competition authority in China, where about two-thirds of the world's seaborne iron ore will be headed this year, made its displeasure obvious. The agreement may well have fallen foul of Article 20 of the nation's new anti-monopoly law, under which business operators jointly establishing a new independent entity constitute a “concentration” – and thus fair game for Mofcom's ex ante review.

However, now that BHP and Rio have removed an incentive not to gouge each other on price, the pretence they are anything other than sworn enemies in the ore-rich Australian outback may be dropped, opening up rifts elsewhere. Clause 6.6 of the term sheet, which outlines procedures for handling conflicting capital spending plans, could be a flashpoint. There is nothing to stop BHP, for example, expanding Rio's prized Hamersley facility, even if Rio – suitably compensated – chooses not to. Removing the “joint” from joint venture may have some nasty consequences.