Tara Mines in Co Meath has been sold to a Swedish metals firm Boliden as part of an asset sale by Tara's Finnish owners, Outokumpu.
Outokumpu is to take a 49 per cent stake in Boliden in return for a €736 million asset sale.
The assets that Boliden will acquire include the Tara Mines and copper smelters in Finland and Norway plus a unit in The Netherlands. Boliden will also take a 2.8 per cent stake in Outokumpu.
As a result of the transaction, Boliden will become one of the world's leading smelting companies and the fourth-largest zinc mining company in the world.
Boliden has recently been involved in a compensation row resulting from a toxic spill in 1998 at the Aznalcóllar mine, near Seville, which led to Spain's worst ever ecological disaster.
The mine was closed in April 1998 when a dam containing toxic mining effluents burst, releasing five million cubic metres of contaminated sludge and water over a 45 square kilometre area. The mine has since been reopened.
A final agreement is expected next month with the deal going to competition authorities soon after. The deal is expected to be completed this year.