London mining group Billiton has expanded its interests in Canada by buying local mining and metal distribution firm Rio Algom for £800 million.

The agreed offer for the Toronto-based firm will give Billiton a valuable route into the global copper business and opportunities to expand into other base metals.

Rio Algom has extensive copper interests in Chile, Argentina and Canada and copper and zinc assets in South Africa.

Its development projects are expected to treble the firm's copper production by 2005 and this is one of the most appealing aspects of the firm for Billiton.

Billiton chief executive Brian Gilbertson said: "We look forward to realising the potential of the Rio Algom assets by growing our new copper and base metals business into an important source of earnings and value for shareholders."

Billiton has operations in Australia, Brazil, Canada, Columbia, Mozambique, South Africa and Surinam.

In June the company made a £183 million bid for a share in a bauxite-alumina mining project in Australia and agreed a joint venture with China's LanPing Non-Ferrous Metals Company.

In July it claimed an indirect stake in Companhia Vale do Rios Doce last month to gain a foothold in the lucrative Brazilian iron ore industry.

Billiton's offer beat a previous bid for Rio Algom from Moranda, one of Canada's largest metals firms. If that offer had been successful Codelco, a Chilean operation, would have bought half of Rio Algom's assets.

Billiton is among the world's top producers of aluminium, alumina and nickel. It also produces chrome and maganese ores.

It also has a metals distribution business which processes aluminium.