The new chairman of Rio Tinto has quit following a boardroom row over a multibillion-dollar fundraising likely to involve one of its main customers, Chinese firm Chinalco. The plan, to raise about $5bn (£3.4bn), could be announced this week. Jim Leng, who took up the post four weeks ago, said he had resigned because of a "difference of opinion" over how to reduce the mining group's $39bn debt. Rio Tinto is in talks with aluminium firm Chinalco, which owns a 9% stake in the miner, about buying some of its assets and increasing its stake in the business. Most analysts expect Rio, which is desperate to raise cash to pay its debt, to announce its plan when it reports annual results on Thursday. Rio has also been considering a rights issue. But analysts said Leng's sudden departure meant it was more likely Rio would tap Chinalco for cash instead. Charles Kernot, analyst at Evolution Securities, said: "It sounds like Jim Leng was against doing the deal with Chinalco.