Mining giant Rio Tinto has announced $US200 million ($A226.4 million) in funding to begin expanding its Cape Lambert port facilities as part of a wider expansion of its Pilbara iron ore operations.

The funds will allow the company to issue dredging contracts as part of early works on the Cape Lambert expansion to boost export capacity.

The port expansion will support increasing the export capacity of Rio's Pilbara operations to 330 million tonnes a year, the company said in a statement.

Rio also proposes an additional 1.8km, four-berth jetty and wharf at Cape Lambert to increase its current annual capacity of 80 million tonnes by a further 100 million tonnes.

Rio plans to expand its Pilbara iron ore operations to produce 330 million tonnes a year by 2016.

The expansion will be staged, rising to 225 million tonnes a year by the first quarter of 2011, 230 million tonnes by the second quarter of 2012, and 280 million tonnes by 2014.

Rio Tinto iron ore chief executive Sam Walsh said the dredging works would help ensure subsequent decisions on the expansion of operations could be implemented as quickly and efficiently as possible.

"While the Australian Government's decision to abandon its Resource Super Profits Tax in favour of the proposed Minerals Resource Rent Tax was a major step forward, we remain cautious over what legislation will finally be in place," he said.

The dredging works require a number of government and other approvals, including those of Robe River's joint venture partners in the Cape Lambert port.