(IDEX Online) - De Beers say it's confident it can avert strike action by 1,500 workers at its Venetia mine, in South Africa.The National Union of Mineworkers (NUM) is threatening an indefinite walkout to support its demand for a nine per cent wage increase. De Beers has offered six per cent.Four months of wage talks have broken down, but De Beers is now offering a five-year salary deal. It has not disclosed details, but says it will provide "a measure of certainty".Venetia resumed production in June after a $2.2bn switch from open-pit to underground mining, which is expected to extend its life until at least 2045. The mine accounts for 40 per cent of De Beers' production in South Africa. The NUM, representing around a third of the mine's workforce, has accused De Beers of arrogance."We are very much convinced that De Beers is not a poor company and that it could afford workers' demands," it said.De Beers said: "We are confident that, through continued engagement with the union and our employees, we will reach a sustainable settlement with the NUM."Pic of Venetia, courtesy De Beers.