LIMA, Dec 29 - Antamina, a leading copper-zinc mine in Peru, said on Tuesday its $1.2 billion expansion plan should be formally approved by shareholders in the coming days.

Antamina -- a joint venture between BHP Billiton Ltd (BHP.AX) (BLT.L), Xstrata (XTA.L), Teck Cominco Ltd (TCKb.TO) and Mitsubishi Corp (8058.T) -- has said the expansion would lift the volume of ore moving through its mills by 38 percent.

It produced 358,179 tonnes of copper and 382,842 tonnes of zinc last year, according to the mining ministry of Peru, the world's second-largest producer of zinc and third-largest producer of copper.

The project should be approved before the end of the year, an Antamina official said. Up to $1.2 billion will be invested.

Construction is expected to start in the first half of 2010 and be operational in the second part of 2011. It is expected to extend the life of the mine to at least 2029.

Miners in Peru delayed investments in late 2008 during the depths of the global economic crisis, but lately have decided to move ahead with expansion efforts.

In September, Antamina's president, Ian Kilgour, said the mine had already ordered new mills for the project. (Reporting by Patricia Velez; editing by Jim Marshall)