Rio Tinto has approved a $1.2bn investment in Western Australia’s Pilbara region to increase the state’s annual iron ore production capacity to 283 million tons per annum (Mt/a).

The capital will be used for significant expansions at the Brockman 4 and Western Turner Syncline mines of the region.

The investment is part of Rio Tinto’s broader plan to expand capacity by more than 50% over the next five years to 333Mt/a, which, according to the company, makes it the largest mining project in Australian history.

Rio Tinto chief executive, iron ore and Australia, Sam Walsh said the expanded mines would provide the bulk of the additional throughput for the recently announced $3.1bn rail and port works around Cape Lambert.

The Brockman 4 mine is set to be expanded from an annual capacity of 22Mt/a to 40Mt/a, while the Western Turner Syncline mine will be expanded from its current 6Mt/a capacity to 15Mt/a.

The mines are wholly owned by Rio Tinto, and the ore from each deposit will contribute to its Pilbara Blend lump and fines products.