Mt Pleasant coal mine near Muswellbrook has applied to extend its life by 22 years and double the amount of coal it extracts annually.
Plans for the project, a joint venture between MACH Energy and JCD Australia, are on exhibition with the NSW Department of Planning Industry and Environment.
The proposal would increase the extraction, handling and processing of run-of-mine (ROM) coal to 21 million tonnes per annum from its current 10.5-million-tonne rate.
The company expects its workforce would reach 600 with a peak of 830 full-time equivalent personnel with the proposed upgrades.
"The proposed staging of the ROM coal production rate would result in a gradual build-up in operational employment at the Project, with the peak projected in 2041," the environment impact statement says.
"This would allow sufficient time for service providers to plan for any associated minor changes in regional population, and may also offset other coal mine closures and ramp-downs that are expected to occur over the life of the project."
Upgrades to coal handling preparation plant and coal handling infrastructure will also be required for the output increase.
Mount Pleasant's additional coal reserves, including lower coal seams in the north pit will be mined to increase extraction.
The current 10.5-million-tonne rate has been approved until December 22 2026.
Mach hopes to boost the time limit of mining operations at Mount Pleasant until December 22 2048.
The company is aiming to transport up to 17 million tonnes per annum of its coal via rail for domestic and international customers.
It has also proposed to construct and operate water management an water storage infrastructure and reject dewatering facilities.
Mach said its rehabilitation and closure plans had been designed to ensure revegetation and post-mining land use was compatible with the surrounding environment.
"The originally approved Mount Pleasant Operation final landform includes two final voids in the north pit and south pit open cuts, and a smaller third final void located in a low-lying area between the two larger final voids," the environmental impact statement says.
"However, for the project, a single final void would remain in the western portion of the site at the cessation of mining .
"MACH has designed the final project final landform to be safe, geotechnically stable and minimise the catchment reporting to the void, whilst still maintaining geomorphological design concepts."
The final void has been designed to avoid water spillage.