SYDNEY (AFP) - Anglo-Australian mining giant Rio Tinto announced a US$14 billion (S$17 billion) writedown related to its Mozambique coal assets and ailing aluminium business on Thursday, prompting its chief executive to resign.

"The Rio Tinto board fully recognises that a write-down of this scale in relation to the relatively recent Mozambique acquisition is unacceptable. We are also deeply disappointed to have to take a further substantial writedown in our aluminium businesses," said chairman Jan du Plessis.