Although the man’s death on Wednesday had originally been reported as a mining accident, union district president Peter Jordan said inspectors had confirmed the man had suffered a heart attack while behind the wheel of an articulated truck known as a “wobbly”.

Mr Jordan said the man worked for a Singleton contractor, MJR Excavations, which had been hired to move topsoil as part of the mine’s rehabilitation processes.

He said the man was discovered at about 1.15pm on Wednesday.

A union check inspector and the police were called to the mine, along with a “CPR medical team” from Singleton.

Despite the team’s best efforts, they were unable to revive the contractor.

The mine is located near Ravensworth, halfway between Singleton and Muswellbrook.

- Ian Kirkman

The NSW government is investigating a death at an open cut coal mine in the Hunter Valley.

Details remain scarce, however the Department of Planning and Environment’s Resources Regulator has confirmed it is responding to a report of a fatality on Wednesday.

Mine safety inspectors and investigators from the Resources Regulator were on their way to the scene yesterday, the state government said in a statement.

The Resources Regulator will publish an investigation information release within the next 14 days to provide information on the potential cause and circumstances of the incident, and to assist the mining industry to reduce the likelihood of a similar event occurring.

The government says as the investigation is underway, no further information is available at this time.

In December 2016, a 53-year-old man died at the Rix’s Creek Coal Mine near Singleton, from severe head injuries he suffered in an accident involving a truck, when its tailgate swung down and struck him in the head.