Rio Tinto is exploring ways to alter its $19.5bn fundraising move with Chinalco to ensure that the deal's basic structure wins approval from regulators and shareholders when they review it in June.

Since the deal was proposed in mid-February, shareholders in the Anglo-Australian mining group have strongly opposed one component of the deal: a $7.2bn convertible bond offered to Chinalco that would raise the state-owned Chinese miner's stake in Rio to 18 per cent, but dilute other Rio shareholders.

Approval of the deal package in outline – part bond issue, part asset sale, for a transaction value of about $20bn – is so important to both sides that they are considering all answers the question: “What will make this an acceptable transaction?” according to a source close to the deal.