Galmoy Mines in north Co Kilkenny is to close down on a phased basis from December with the loss of 221 jobs.
Talks between SIPTU and management went on through the night after which it emerged that the company will go out of operation within two years.
Dennis Hynes, SIPTU branch organiser in Kilkenny, said the decision to close the mine was based on fuel and shipping costs.
However, the Chief Executive of Galmoy, Stefan Masson, has told RTÉ News that the closure is largely due to the fact that the mine will be exhausted by 2011.
He said the news would not come as a shock to staff as redundancies were part of an expected wind-down process.
Mr Hynes said the main concern now was that if zinc dropped in price and oil prices went up, Galmoy Mines might even close sooner than 2011.
Mr Hynes also said the impact of the closure would extend beyond the 221 workers losing their jobs.
'There are also a lot of businesses, small businesses, people that have contracts in and out of Galmoy who are going to be affected by this as well,' he said.
'It's going to have a huge impact on the area and it's a big, big loss.'
Company's withdrawal puts 100 jobs at risk
A company that has been carrying out maintenance on the Bord Gáis network has decided to leave the Irish market putting more than 100 jobs at risk.
Enterprise Managed Services employs 200 people in Ireland. Negotiations are continuing in an attempt to ensure some of the jobs are retained by a new contractor.
In a statement Bord Gais said: 'Enterprise Managed Services Ltd, the company contracted to carry out maintenance and development work on the Bord Gáis network in the eastern region, has confirmed that it has made a strategic decision to exit the Irish market.'
'Consultation between Enterprise and trade union groups has commenced with respect to Enterprise employees. The Bord Gáis maintenance contract will transfer to a new contractor on 24 October 2008.
'In the transition period, Bord Gáis and Enterprise will work closely together to ensure a smooth and effective transfer of operation and the continuous and safe supply of natural gas to customers.
'Bord Gáis will continue to ensure that the natural gas network is operated and maintained to the highest international safety standards at all times and that customer service expectations will continue to be met.'