The new reserve estimate was developed using a new resource model based on data from more than 105,000 m of core drilling carried out from late 2006 through September 2007. The new resource model, along with revised metal prices, was used to design a new open pit. The resulting design generated the significant reserve increase.

Antamina is now engaged in studies evaluating expansion alternatives based on its increased ore reserves base, with expanded production capacity of around 30% already indicated from a pre-feasibility study. Antamina has retained Aker as engineering contractor for the expansion and has placed letters of intent for a SAG mill, a ball mill and key mining equipment.

Cía Minera Antamina is a joint venture company held 33.75% by BHP Billiton, 33.75% by Xstrata, 22.5% by Teck Cominco, and 10% by Mitsubishi Corp. The mine is located in the Andes mountains in northern Peru, approximately 270 km northeast of Lima, at an elevation of 4,300 m. The mine currently produces about 275,000 mt/y of copper and 165,000 mt/y of zinc in concentrates. Reserves are extracted by open-pit mining, followed by conventional grinding and flotation to produce concentrates. The concentrates are slurried and transported by a 300-km pipeline to the Pacific coast, where they are filtered for shipment.