Leighton subsidiary Thiess has won a $135 million contract from Western Desert Resources to lead the mining operations at the Roper Bar iron ore mine in the Northern Territory.

The contract starts on Monday, with iron ore to be exported from the Bing Bong loading facility.

The Roper Bar iron ore project is about 600 kilometres southeast of Darwin.

Thiess on Monday said it had been working with Western Desert Resources for some time, providing on-the-ground mobilisation and project support since November 2013.