Downer has been the contractor at Boggabri since the mine started production in 2006. The original contract ended in November 2011 and then Downer was awarded a five-year contract, extending its involvement until December 2016.
The new extension means the contract now runs until November 30, 2017.
Downer also announced that it has sold some of its mining equipment to Idemitsu for approximately $100 million.
Downer CEO Grant Fenn said Downer and Idemitsu had been working closely together to reduce the overall costs at Boggabri coal mine.
“We are very pleased to have been granted a one year extension at Boggabri and to have achieved a mutually beneficial outcome for the project,” Fenn said.
“We look forward to continuing to deliver high-quality and efficient solutions for Idemitsu at the Boggabri coal mine.”