Fortescue has proposed an extension to its current open pit mine about 120 kilometres north of Newman by 8,133 hectares.

The expansion would allow an ore production increase to about 50 million tonnes per annum and increase the life of the mine by more than 10 years, according to Fortescue's propossal.

New pits and waste dumps would be developed, along with new infrastructure and dewatering and water disposal activities and an upgrade of the ore processing facility, under the plan.

But Environmental Protection Authority chairman Paul Vogel has only granted conditional approval for the Cloudbreak expansion, citing potential impact to several ecologically important vegetation in the area.

"While the percentage impacts to the Mulga and Samphire vegetation are relatively small, these areas are important due to their good condition, for the habitat they provide for fauna and because part of the proposal falls within a proposed conservation reserve," Dr Vogel said.

The EPA recommended Fortescue offset the predicted impacts by contributing to a Pilbara conservation initiative to protect the Night Parrot and Greater Bilby.

Restrictions have also been placed on groundwater mounding and drawdown at the fringe and within the marsh.

The EPA recommended that progressive rehabilitation and successful surface water management practices are also implemented to ensure that the predicted impacts to surface water are not exceeded and the environmentally significant Fortescue Marsh remains protected.

Public appeals to the EPA's recommendations close February 22.