The $15m contract extends the existing contract at West Cliff colliery for two years. Work under the latest contract would deliver similar revenue to the prior contract.
Mastermyne CEO Tony Caruso said: "we are very pleased to have rolled over the scope of the existing contract for a further two years.
"We are looking forward to building on this success in the coming months with further contract renewals and new contract wins."
Illawarra Coal operates three underground coal mines in the southern coalfields of New South Wales, including Appin, West Cliff and Dendrobium.
It also runs two coal preparation plants – West Cliff Coal and Dendrobium Coal as well as the Port Kembla Coal Terminal that was leased from the New South Wales Government.
