The company has been developing an environmental impact statement that it plans to lodge with the NSW Department of Planning, Industry and Environment in the second half of 2020.
"The Narrabri Underground Mine Stage 3 Extension Project is a proposal to convert the existing Narrabri South Exploration Licence into a Mining lease and extract coal," it said.
"This extension accesses 80-100 million tonnes of coal using the established infrastructure, including the existing coal handling preparation plant, rail loop, portals and offices."
Under the proposal, Whitehaven will continue using the longwall mining method and hopes to create employment of the existing workforce at Narrabri by extending its life from 2031 to 2045.
The project has received its Secretary's Environmental Assessment Requirements from the NSW government as well as its Environmental Protection and Biodiversity Conservation Act referral from the federal government.