Newcrest Mining has started construction of Australia's largest underground mine near Orange, New South Wales.
The $2bn Cadia East gold project will extend the lifespan of Cadia Valley operations and become one of the biggest underground mines in the world.
Operations at Cadia East are expected to last for 21 years and other potential ventures could extend that for another 30 to 50 years.
Newcrest's Cadia Hill open-cut mine has just 18 months left of its lifespan.
The company approved the Cadia East gold project in April.