Campbell had been with the company since 2004 and yesterday's resignation was effective immediately.

It leaves Mark Thomas to continue as company secretary.

Meanwhile, The West Australian reported that long-serving head of external affairs Julian Tapp had also gone in the cuts.

It comes as Macquarie Private Wealth praised the miner for moving so quickly to battle funding pressures after the iron ore price fell more than 25% over the past month.

"One must respect FMG's prudence in moving swiftly to combat building funding pressures in the current spot iron ore price environment," Macquarie said.

"In saying that, we believe market fundamentals dictate iron ore prices with a normalised plus $US120 per tonne floor over at least the next few years.

"As such, we are attracted to the margin and balance sheet leverage that FMG's rapid growth profile - even under its now more staged format - provides to this dynamic.

"However, this combined leverage clearly also amplifies the downside investment risks should we see a sustained environment of sub-$110/t iron ore prices."

Macquarie said the deferral effectively plugged the $1.5-$2 billion funding gap it had forecast for the miner.

The analysts added that the move was more of a re-sequencing than an outright deferral.

Macquarie dropped its price target for FMG to $A6.70 from $7.

It comes as FMG shares shed more than 12% on Tuesday and Wednesday.

Shares fell a further 2.4%, or 7.5c, to $3.045 this morning.