Glencore subsidiary Mt Owen sought approval to extend the Barrett Pit at Glendell, 20km northwest of Singleton, to recover an additional 1.97 million tonnes of run-of-mine coal.
The Department of Planning, Industry and Environment's whole-of-government assessment report found the proposed modification would result in a net increase in disturbance area of 4.3 hectares but no additional noise and dust impacts.
The modification application came to the IPC for determination in December because the department received more than 25 public objections during exhibition.
The panel met with the applicant, department, Singleton Council and inspected the site and surrounding areas.
It also held a public meeting in Singleton In February to listen to the community's concerns, which centred around air quality; greenhouse gas emissions; Aboriginal heritage; rehabilitation; mine closure; and water impacts.
"After careful consideration of all the evidence, the commission has determined to approve the modification application," the IPC said.
In its statement of reasons, the commission concluded the application was "in the public interest" and "on balance the benefits outweigh the costs of the application".
"The commission acknowledged the concerns raised by the community in relation to potential air quality impacts but ultimately found the application would result in a reduction in terms of air quality impacts at nearby receivers compared to the currently approved operation," it said.
Originally Glencore proposed to recover an extra 2.5Mt but revised this to 1.97Mt as a result of further mine design and scheduling information.
This modification will allow the company to continue mining until the first quarter of 2023 by extending the existing approved pit shell 130m north and 60m west.
This will also allow progression of mining operations into the Glendell open cut area, provide for continued employment of the Glendell mine workforce, and allow for efficient resources recovery.