The approval extends the company's existing development consent by 13 months, meaning operations at the site will now likely cease in December 2030.

The Department of Planning, Industry and Environment finalised its whole-of-government assessment of the Mangoola Coal Continued Operations project in January this year. It concluded the project was "approvable, subject to comprehensive conditions".

However, the IPC is the consent authority for the state significant development application because the DPIE received more than 50 "unique" public objections to the project.

Supporters of the proposed mine extension cited the projected social and economic benefits to the local area, Upper Hunter region and to NSW, including job creation and retention. Those opposed to the project raised concerns about air quality, biodiversity, greenhouse gas emissions and climate change, impacts on water resources, noise impacts, traffic and transport impacts, socio-economics, Aboriginal cultural heritage, and rehabilitation.

As a result of concerns raised about air quality, the IPC met with the Environment Protection Authority, NSW Health and the Department to discuss air quality trends and impacts in the Upper Hunter.

In its Statement of Reasons for Decision, the IPC noted the project "represents a reasonable ‘brownfield' extension of the existing Mangoola coal mine that would enable the economic and beneficial reuse of existing infrastructure and an orderly and economic use of land.

"Notwithstanding the concerns raised … the commission finds that on balance and when weighed against the impacts under the current policy and regulatory framework, the project would generate net positive social and economic benefits for the local area, Hunter region and to NSW," it said.

The project - anticipated to create 145 construction and 80 operational jobs, and provide ongoing employment for 400 workers - will use existing infrastructure including the Mangoola mine coal handling and processing plant, rail loop and mining fleet and involve the development of a haul road overpass that would also traverse Wybong Road and Big Flat Creek, to connect the northern extension area with the Mangoola mine.

A Glencore spokesman said the project has successfully met every step of the NSW environmental assessment requirements and would enable mining to continue for a further five years to 2030.

"This will provide ongoing employment for our workforce of around 400 people, the majority of them from local communities; support for more than 60 local companies with whom Mangoola spent around $100 million in 2020, and continue to provide royalties that help the NSW government continue to pay the wages of nurses, teachers and Police and to build much-needed infrastructure.

"We look forward to a timely execution of federal government and Muswellbrook Shire Council approvals."