Rio Tinto's $US1.9 billion ($2.4 billion) Amrun bauxite project is being built with foundations to support a much bigger expansion in the future, with the project now more than 75 per cent complete.

Approved by the Rio board in November 2015, the Amrun team will soon award some of the major contracts associated with the project, including for shiploaders, reclaimers and stackers.