The mine was already enduring bad recent publicity due to reports and images of the environmental damage caused by unplanned subsidence and an earlier grout spill mid-year in the SSCA.

In regard to the recently discovered second incident, a Glencore Xstrata spokesman told the Newcastle Herald it was unaware of this 120m by 1m spill for more than seven months.

The newspaper, which first broke the SSCA damage news last month, reported that this spill flowed down a hill and occurred in February.

West Wallsend staff reportedly made the discovery on Friday afternoon and immediately informed the New South Wales government.

‘‘We are requesting a full report on this incident and Office of Environment and Heritage staff will be undertaking an inspection of this latest incident as soon as possible,” the office chief Sally Barnes reportedly said.

The Department of Planning and Infrastructure is heading investigations at this stage.

This latest incident will further fuel green groups with the Total Environment Centre campaigning for the state government to launch an inquiry into environmental impacts from longwall mining.

“Sugarloaf is just the tip of the iceberg,” TEC director Jeff Angel said a week before news of the second spill emerged.

“There are equally disturbing instances of cliff collapses, drained rivers, failing swamps and methane leeks across Sydney's drinking water catchment.

“Massive cliff falls and destruction of endangered swamps is taking place in the Blue Mountains as well. Whole water catchments are being totally compromised and the common theme is longwall mining.”

In relation to the subsidence in the SSCA, Glencore Xstrata has previously blamed abnormal geological conditions” for damage that was tracked over more than 2km within the conservation area adjacent to the mine's Longwall 41.