BHP chief Andrew Mackenzie says Olympic Dam is the only part of his portfolio that is not generating acceptable returns, as the miner deals with yet another breakdown at the South Australian copper, gold and uranium mine.

Olympic Dam is one of Australia's highest-profile mines and its expansion has been keenly anticipated in political circles for decades, but accounts filed by BHP on Tuesday contained some harsh realities, including the fact the mine made less money in fiscal 2018 than the Nickel West operation that BHP has been trying to discard for the best part of six years.