Rio Tinto said it will invest a further $790m in its drive to expand the annual capacity of iron ore operations in the Pilbara to 330 million tonnes.This brings total investment funds approved in recent weeks to $1bn. Rio Tinto chief executive Iron Ore and Australia Sam Walsh said the new investment highlighted the miner's intention to forge ahead with the expansion."Rio Tinto has a proven track record of managing large-scale iron ore development projects, and has successfully implemented three significant increases in port capacity in the past seven years - Dampier to 140 million tonnes [in two stages] and Cape Lambert to 80 million tonnes," he said. "As with previous expansions, a key factor in this project will be minimising any disruption to existing operations and production schedules. We are confident this will be achieved."