Rio Tinto has approved a further $1.2bn investment to lift annual iron ore production capacity in Western Australia's Pilbara region to 283m tonnes per annum.The capital will be used for significant expansions at the Brockman 4 and Western Turner Syncline mines and is part of Rio Tinto's broader plan to expand capacity by more than 50% over the next five years to 333 Mt/a, which is the largest mining project in Australian history. Rio Tinto has announced new investment of $7.2bn in Pilbara since July this year and has upped its spending after the planned merger of the operation with BHP Billiton's similar business collapsed in October.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. "These decisions highlight our strategy of bringing on new capacity in line with infrastructure developments, using 100% Rio Tinto-owned brownfield developments to dovetail with existing infrastructure where possible," he said.