The Meandu thermal coal mine has operated since 1978 and has five working pits that produce up to 7 million tonnes of coal annually.
Stanwell's expansion project will focus on the King 2 East pit about 14km southwest of Nanango.
The pit size will increase 7% as part of the brownfield development.
Stanwell noted that while the pit would get bigger, the production rate from the mine would not increase.
"Mining in the proposed K2E additional surface area will be conducted using the same mining equipment types as currently used for existing mining operations," Stanwell said.
An extension of the existing mine haul road network will need to be developed to accommodate the expansion of the pit.
"The resource to be extracted … will be transported to the neighbouring Tarong power stations to be used as a fuel for power generation," Stanwell said.
Because the pit expansion is large Stanwell requires both Queensland government and federal government approval.
The federal Department of Agriculture, Water and the Environment has launched a public consultation for the project.
Meandu is operated by Downer EDI, which was awarded a five-year mining contract last year.
Stanwell recently invested in the mine by upgrading the mine fleet and adding another excavator,
It announced in April it would look to phase out its coal consumption in the future.