“Against the backdrop of a record performance in our iron ore business and our focus on decarbonisation and green energy, Fortescue is well-placed to finish the financial year strongly,” Ms Gaines said.

Average revenue for the quarter was $US100/dry metric tonne, realising 70 per cent of the benchmark Platts price for ore containing 62 per cent iron.

RBC Capital Markets analyst Kaan Peker said production and costs were in line with expectations but the 30 per cent discount to the market price was more than expected.

Fortescue’s ore attracts a higher discount than production from its bigger Pilbara rivals BHP and Rio Tinto as on average it is a lower grade, or percentage of iron ore.

Higher grade iron ore requires less energy to be turned into steel and is expected to have strong demand in coming years as China battles to reduce air pollution and greenhouse gas emissions.

Fortescue plans to boost its average grade with the Ironbridge project that will mine low-grade magnetite and with an energy-intensive process produce a high-grade concentrate for export.

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However, the complex project that cost three senior executives their jobs will now cost an additional $US300 million ($421 million) and the first production could be as late as March 2023.

Well-regarded chief operating officer Greg Lilleyman and two project executives left Fortescue in February 2021 as part of a review of Ironbridge that resulted in the cost estimate rising from $US2.6 to $US3 billion in February 2021 and then to $US3.3 to $US3.5 billion three months later. The new estimate is $US3.6 to $US3.8 billion.

Guidance for the first production from Ironbridge slipped from December 2022 to the March quarter of 2023 and full production is expected to be achieved 12 to 18 months afterwards.

Fortescue is liable for 69 per cent of the cost with its joint venture partner Formosa Steel picking up the rest.

Ms Gaines said a shortlist of her potential replacements was before the board, but a decision would “take as long as it needs to take to find the right person.”

The first concrete progress in Dr Forrest’s much-publicised push for Fortescue to produce the clean fuel green hydrogen is expected to be an investment decision for a plant at Incitec Pivot’s Gibson Island plant in Queensland that Ms Gaines expected in the first half of 2023.

Ms Gaines said another emissions reduction initiative - a train to carry Fortescue’s iron ore downhill to port using the power of gravity - could have a prototype operating within two years.

Fortescue shares were up 8.1 per cent on Thursday to close at $21.73 a share.