Mining for copper and zinc could return to Anglesey's Parys Mountain mine after an absence of almost 100 years.
Millions of gallons of polluted water were drained from the mine in 2003
As a result of recent increases in world metal prices, owners Anglesey Mining plc are starting exploratory drilling work.
Finance director Ian Cuthbertson said they were confident of "significant reserves" at the site, which has been mined since the Bronze Age.
It could lead to more than 100 jobs at the site, near Amlwch.
"There have been quite a number of attempts to revive [mining at the site], but the world situation now is different and we are upbeat about the prospects," said Mr Cuthbertson.
He said that demand for metals from China was pushing up prices across the world.
"At present metal prices, Parys mountain will certainly be viable, the question is whether current metal prices will continue," he said
"We are confident there are significant reserves of zinc and copper. Our initial estimates of six million tonnes at 10% metal could easily be on the low side.
"More than 100 people would be required as a minimum to operate the mine plus ancillary jobs off site."
He said that, although the metal was expensive to retrieve, he was confident of securing finances "providing the numbers stack up".
"This initial phase of drilling has been funded by funds from the stock exchange and a good proportion of any further monies is likely to come from the same source," he said.
"We will do our drilling and rework our calculations for the viability of the project, and we hope then to be in a position to go to the exchange and to banks and to finance the project and put it into operation."
He said the future depended not necessarily on the drilling results, but the results of the feasibility studies and on the outlook for metal prices.
Two years ago, millions of gallons of polluted water were drained from mine workings at the site.
Copper mining had taken place at Parys Mountain for centuries, until it was brought to a halt in 1915.
It has since been used as a location for TV programmes and science fiction films, and also featured on BBC's Restoration programme but lost out to Llanelly House in Llanelli in a viewer's vote.