Walter spokesman Paul Blalock told ILN that it was in the consultation phase of the proposal, during which time the mine’s workers would be off but receiving full pay.

“However, up to 100 employees may be required to continue working at the mine during this consultation period to continue development works within the upper drift,” he said.

“If Walter Energy proceeds with the proposals outlined, early indications are that only a small number of employees would be retained to keep the mine in a safe condition until operations resume.”

The producer cited the declining demand “that continues to heavily impact the global coal industry” for the closure decision.

Blalock said it would soon start formal consultations with employee and trade union representatives, but declined further comment.

Union representatives told the BBC that the news was a “bitter blow”, but noted that the mine’s workers were already in a redundancy process that was projected to impact about a third of its payroll.

Additionally, a representative said, production had been cut by roughly half to 200,000 tonnes per annum over a couple of years due to resources needed for ne seam drilling.

Aberpergwm, near Glynneath, is believed to have a 6.8 million tonne reserve base.

Its main customer, according to Walter’s web site, is the Aberthaw power generation plant.

The mine, according to the BBC report, first opened in the late 1800s and employed its peak payroll of 1500 workers in the 1930s. It was closed for one year in 1985, then re-opened with a private owner.

Aberpergwm is not far from Walter’s other colliery, Tower. Its other holdings in the region include the Forest quarry opencast and the Dulais Valley Restoration.