Fortescue Metals Group is considering major design changes to limit the cost blow outs on its troubled Iron Bridge magnetite project, which now appears set to cost up to $US400 million ($515 million) more than originally thought.

Confirmation that Fortescue will investigate abandoning one of the most expensive aspects of the project came as the cashed up miner confirmed the exit of senior executive Greg Lilleyman was driven by the fact he oversaw a team that was not escalating bad news to him.