Antamina Mine

An expansion of the Antamina project was completed in 2012 boosting operating capacity production of copper and zinc by approximately 30%. The mine is expected to produce until 2028.

In April 2022, Antamina announced a $1.6bn expansion project to extend the mine's useful life from 2028 to 2036 by modifying the property’s Environmental Impact Study. The company expects to receive approval from Peru’s environmental authority for the modification in 2023.

Location and site details

Antamina mine is located in northern Peru, around 270km north of Lima and 103km east of the Pacific Ocean.

The property includes mining concessions and claims across an area of approximately 92,300ha. All of the mining concessions are situated in San Marcos District, Province of Huari, Ancash Department.

The mine can be accessed via an access road maintained by CMA.

History

Initial exploration at Antamina site was conducted by the Cerro de Pasco Corporation between 1952 and 1970. In October 1970, the mining assets were transferred to the Government of Peru.

Subsequently, around 2,200ha of mining rights were transferred to the mining administration agency Minero Perú, which formed the Empresa Minera Especial (EME) in partnership with the Government of Romania mining agency Geomin in 1974.

EME completed a series of full feasibility studies of Antamina. However, EME was disbanded in 1981-82 after it failed to finance the project.

In 1995 and 1996, Canadian entities Rio Algom and Inmet Mining Corporation conducted extensive reviews and secured the project through auction. Thereafter, they formed Compañía Minera Antamina (CMA) as a 50:50 owned company.

Inmet sold its 50% stake in CMA and the ownership was restructured among Rio Algom (37.5%), Noranda (37.5%) and Teck (25%). Mitsubishi Corporation joined by purchasing a 10% share in March 1999 from the other partners.

The current shareholders of CMA are BHP Billiton (33.75%), Glencore (33.75%), Teck Resources (22.5%) and Mitsubishi Corporation (10%).

Geology, Mineralisation and Reserves

Antamina is situated on the eastern side of the Western Cordillera in the upper part of the Rio Marañon basin. The deposit lies at an average elevation of 4,200m.

The polymetallic deposit is skarn-hosted and unusual in its persistent mineralisation and predictable zonation. The deposit has a southwest-northeast strike length of more than 2,500m with a width of up to 1,000m.

The well-zoned skarn has four major subdivisions, while other skarn types are randomly distributed throughout the deposit.

Mineralisation in the polymetallics belt exhibits a Zn-Pb-Ag-Cu-Au association, primarily in hydrothermal deposits related to Middle to Upper Miocene calc-alkaline subvolcanic and high level intrusions.

Copper is present mainly as chalcopyrite, while Zinc generally occurs as sphalerite. Other significant sulphides found are molybdenite and pyrite.

Molybdenite is usually located within the intrusive core and the surrounding endoskarn with silver is found in any of the skarn lithologies. Lead occurs in green garnet exoskarn, diopside exoskarn and hornfels.

As of 31 December 2016, Antamina mine’s Proven reserves stand at 174Mt graded at 1.01% copper, 0.82% zinc, 11g/t silver and 0.028% molybdenum.

Measured and Indicated Reserves and Resources total 1,085Mt graded at 0.89% copper, 0.78% zinc, 11g/t silver and 0.021% molybdenum.

In 2021, Antamina produced 445,300 tonnes of copper, 462,200 tonnes of zinc and 4.9 million pounds of molybdenum.

Mining and processing

Antamina employs an open pit, truck-and-shovel operation for mining.

The ore is crushed within the pit and transported via a 2.7km tunnel to a coarse ore stockpile at the mill. Two SAG mills then process the crushed ore, followed by ball mill grinding and flotation procedures to produce separate copper, zinc, molybdenum and lead/bismuth concentrates.

The mill’s current operating capacity has been increased to 145,000 tonnes per day after throughput expansion was completed in 2012.

A 302km long slurry concentrate pipeline transports copper and zinc concentrate to the Punta Lobitos Port in Huarmey where it is dewatered and stored before loading the mineral onto vessels for shipment.

The molybdenum and lead/bismuth concentrates are transported by truck.

Electricity for the mine is provided by the Peru national energy grid through an electrical substation located at Huallanca.

The project sources freshwater from a dam-created reservoir from the tailings impoundment facility, which is located next to the mill. The water reclaimed from the tailings impoundment is used as process water in the mill operation.

Key Contractors

At Antamina, Stantec was responsible for overall project implementation for design coordination, mine operations coordination, bidding construction packages, procurement, and overall project controls.

Metso Process Technology & Innovation (PTI) was contracted to assist in increasing the throughput of the difficult ores by implementing a Process Integration and Optimization (PIO) project.

SRK Consulting has been involved in producing and updating a 3D model of the major structures in the vicinity of the Antamina open pit since 2004.

The mine also used MineSense Technologies’ ShovelSense technology to identify ore and waste, classify ore at the earliest stage possible in the mining process and increase ore loading accuracy.

WSP Golder performed the role of an Engineer of Record for the design and construction of the tailings dam.