Under the terms of the deal, Downer will be responsible for work to provide power to a new mine at the operation.
Work would include the supply and installation of electrical power and control components for two new substations.
It will also undertake modifications to existing substations and transmission lines and install a new power line between the town of Newman and the Jimblebar mine.
In 2011, BHP approved $3.4bn for the development of the Jimblebar mine and rail links as part of a wider expansion of its mining capacity in the Pilbara.
The infrastructure improvement program is expected to deliver initial capacity of 35 million metric tons a year.
