The sudden departure of Rio Tinto’s chairman designate Jim Leng has fuelled talk of a boardroom split at the heavily indebted mining group and raised questions over its strategic direction.

Mr Leng, currently chairman of Corus, the UK steelmaker, dramatically quit the board of the Anglo-American mining group over the weekend less than a month after he was named a director and the chosen successor to chairman Paul Skinner, who was due to retire in April.

Rio is struggling with a net debt burden of $39bn, the result of its expensive acquisition of Canadian aluminium producer Alcan in 2007. The group has pledged to cut its debt by $10bn by the end of this year, and is looking at raising cash either through a rights issue or a two-part deal with Chinalco, the Chinese state-owned metals group, that could be valued at up to $20bn.