An undetermined Native Title area joint venture proponents believe is home to one of the world's best underdeveloped iron ore sites has been removed from a $400 million exploration proposal.

The Rhodes Ridge JV between Rio Tinto and Wright Prospecting lodged an amendment to its proposal with the federal government to remove the proposed Giles Mini deposit in Western Australia's East Pilbara region due to environmental concerns and cultural impacts on Traditional Owners.

Removing Giles Mini from the exploration equation means the development no longer intersects with an undetermined Native Title area of the Ngarlawangga People.

"Removal of the Giles Mini deposit and associated infrastructure reduces resource demands on Traditional Owners," Rio Tinto said in the application.

"As a result of the amendment, reference to the Ngarlawangga Traditional Owner Group will be removed, as the proposed variation will result in a revised development envelope, which no longer intersects with the Native Title determination area."

Rio Tinto has earmarked $400 million over five years for exploration at the Rhodes Ridge site until 2028. The operation now comprised only the main Rhodes Ridge deposit, and the Arrowhead deposit, a 22 per cent reduction to 47,923ha, from 61,301 hectares.

The proposed open pit deposit at Giles Mini lays across the southern-most boundaries of the Rhodes Ridge expansion, approximately 40km north-west of Newman. It not only intersects the undetermined Native Title area, but is also home to a roosting habitat of ghost bats.

The vulnerable species relies on specific habitats – usually deep natural caves or disused mines that sustain a stable temperature between 23-28 degrees Celsius and humidity between 50 and 100 per cent – to raise their young and protect them from the arid environment.

These 'maternity caves' are often in the banded ironstone formations that coincide with mining activity in the Pilbara and their retentions is vital to the survival of ghost bats, as not all roost caves function as such.

A map provided as part of environmental documents suggested other ghost bat populations in the main Rhodes Ridge deposit, which the JV still intended to develop, with 51 roost caves recorded across the greater survey area.

"The area of the Giles Mini deposit contains one of two ghost bat sub-populations, referred to as the 'southern sub-population', with the 'northern sub-population' located at Rhodes Ridge main," the JV partners said in its amendment from August.

"In the first instance, removal of Giles Mini from the proposed action avoids all direct impacts to the southern sub-population, through retaining two adits and 10 caves, which provide roosting habitat, and retains surrounding foraging habitat."

A map provided as part of environmental documents suggested other ghost bat populations in the main Rhodes Ridge deposit, which the JV still intended to develop.

The ghost bat is a vulnerable species and globally unique, being the only one in its genus, Macroderma, and the only extant representative of the Megadermatidae family in Australasia.

The estimated global population of ghost bats is less than 10,000, with almost 2000 persisting in the ancient Pilbara bioregion, whose isolation is crucial to the species' distribution.

Pre-feasibility studies for Rhodes Ridge are expected by 2025, while environmental applications were made to the WA Government in February.

The mine could be producing iron ore by 2030 and is critical to Rio Tinto's operations in the Pilbara.

In December, Rio Tinto Iron Ore chief executive Simon Trott said the size and quality of the resource base at Rhodes Ridge could underpin its flagship Pilbara iron ore business for decades.

"Longer term, the resource could support a world-class mining hub with a potential capacity of more than 100 million tonnes of high-quality iron ore a year," he said.

"We are committed to working closely with the Traditional Owners, the Nyiyaparli and Ngarlawangga People, as we progress this project."

The joint venture utilises Rio's existing rail, port and power infrastructure, including planned renewable power assets in the vast north-west region.