The world's fourth-largest iron ore miner, overseen by founder Andrew Forrest as executive chairman, has been beset by senior management turnover over the past two years while its key Iron Bridge project has seen multiple delays and cost overruns.

Fortescue has been expanding into green energy and has reorganised into two divisions under energy and metals, with the CEOs of each unit reporting to Forrest and the board.

"This organisation does not rely on just one or two people to drive direction," said incoming Fortescue Metals CEO Dino Otranto, who took the helm of the company's iron ore division two years ago and will replace Hick.

"I am left with no doubt whatsoever that we have the most amazing team behind this crazy vision that we have got, and we are going to nail it," Otranto said.

The decision by Fortescue's board and Hick, who took on the co-CEO role in February, to part ways was made on Sunday. Hick was at a party hosted by Forrest in Western Australia over the weekend to celebrate 20 years in operation, CEO Mark Hutchinson of the firm's energy division confirmed.

Hick said in a statement on Monday she valued her experience at Fortescue and would take time to consider her next move.

When pressed for more information on Hick's departure on an earnings call, Hutchinson declined to provide further details on the reasons for her exit or around the decision that elevated Otranto to the co-CEO spot.

"I do think shareholders deserve a better explanation given that she departed only after five months in the role and also considering the C-Suite changes over the past two to three years," said Goldman Sachs analyst Paul Young on the call.

Ian Wells, Fortescue's former chief financial officer, stepped down at the end of January, meaning almost all of the senior executives from a year previous had changed.

Executive chairman Andrew Forrest, who has been taking a greater role speaking to stakeholders on results, was absent from the earnings call.

"He was not available today," Hutchinson said.