Unions say there was a real belief a deal could be agreed
Workers at Anglesey Aluminium have voiced shock and disappointment after the company announced it will cease its smelting work at the plant next month.
They say they had been hopeful that high-level talks on the government's £48m rescue-package would bear fruit.
Careers and redundancy advice is being made available to the 390 people who will lose their jobs.
Anglesey council leader Clive McGregor described the announcement as "desperately bad news" for the economy.
Workers, speaking at the plant on Friday morning, said the area was already a jobs black-spot.
"There's a sad feeling here, the morale has gone," said Peter Owen, who has been working at the plant for five years.
"We were quite positive up to yesterday, thinking a deal would be possible, so it came as a big shock (when the closure announcement came) as a lot of the lads depend on here for their livelihoods, to keep their families.
There will be some already thinking of moving away, applying for jobs elsewhere because there's nothing on the island
Richard Williams, employee and union rep
Mr Owen, who grew up on the island, said he wanted the same thing for his own children, and so he was reluctant to think about moving away to find other work.
He said many of the workers saw fault in the way the company had dealt with the situation.
There had been no explanation of why the £48m rescue package had been turned down.
"I can't understand what happened," he added.
Anglesey Aluminium opened in 1970.
The history of the plant, which is a major electricity user, has been closely tied in to an energy deal with the nuclear power station at Wylfa, 14 miles away.
But the station is due to be decommissioned and there have been ongoing efforts to secure the aluminium plant's future.
Unite, the union, is also bitterly disappointed by the closure news.
Gwilym Owen said he felt "disappointment, coupled with disgust, at the failure to secure the long term future".
He said there had been huge efforts made by the workforce and everybody involved to get the deal through.
"It is totally disappointing," he said.
Many of the staff have been with the company for many years and union representative Richard Williams has 24 years under his belt.
"I'm a bit disappointed as I believe we could have secured something here if we'd have all got together and tried for something different," he said.
"To be told at the 11th and a half hour that no, there is no deal, that is the disappointing part of it."
The effect of the closure of the smelting work - around 80 jobs will remain on site to carry out re-smelting - will affect much more than the Holyhead area, he added.
"There will be some already thinking of moving away, applying for jobs elsewhere because there's nothing on the island that's going to compare to Anglesey Aluminium.
"Myself, I have to think what I'll do...I don't know to be honest."
Anglesey Council leader Clive McGregor said the he had hoped that the fact talks to save the plant had gone on for a few weeks had meant a "glimmer of light at the end of the tunnel".
"It is devastating news for Holyhead and it's environs because we are losing good quality jobs, jobs that are going to be pretty difficult to replace with the economic climate as it is," he said.
He added that it was currently difficult to find any job.
Current claimant count unemployment on the island is 4.2%.
"Finding jobs for 500 people is going to be well nigh impossible," he said.
Mr McGregor said he hoped there would be better news in three to four years time with "potentially" a new power station being built (to replace the Wylfa nuclear power station which is due to close next year).
In the short-term however he acknowledged there was a risk that young people in particular would leave the island in search of work.
"Anglesey needs its young people, who don't want to be a retirement island," he added.
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