The Tia Maria copper mine is a greenfield project located in the Islay Province of Peru. Southern Peru Copper Corporation, a unit of Grupo Mexicano, owns the project.

The mining activity is expected to be carried out through two open pits Tapada and Tia Maria. The operational output of the mine is expected to be 120,000 tonnes per annum over a mine life of 20 years.

Southern Copper has put forward a capital expenditure of £1.08bn ($1.4bn) for the development of the copper mine. The project is expected to generate 3,500 jobs during the construction phase and 600 direct and 2,000 indirect jobs during its operational phase.

Tia Maria Copper mine controversy and development history

The Tia Maria copper mine has faced local opposition since 2009. The main opposition came predominantly from the regional farming population. Their concern apart from mine discharge contaminating their water supply was that the project would affect water availability from the nearby Tambo River.

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Southern Copper held a public presentation of the Environmental Impact Assessment (EIA) in September 2009 for the six districts of the Islay Province including Cocachacra, Islay-Matarani, Mollendo, Punta de Bombón, Dean Valdivia and Mejía to decide on the project’s execution. The residents of Cocachacra rejected the mining project by 93.4% votes.

The Ministry of Energy and Mines in support of the local opinion rejected the EIA in April 2011 and ordered machinery from the mine area to be removed.

A revised EIA with changes to the water supply where sea water would be pumped through a pipeline was approved by the Ministry of Energy and Mines in August 2014. This was again met with violent protests causing the project to be put on hold in March 2015.

The project was granted construction approval in June 2019 although Southern Copper announced that it would not start works until it received full local support. The government, however, cancelled the permit later in August owing to public unrest.

As of October 2019, Southern Copper announced that the Peruvian Mining Council had ratified the construction permit for the project.

Tia Maria copper mine location and geology

The Tia Maria copper project is located in the Islay Province of the Arequipa region in southern Peru. The project area lies in the Cachuyo Ravine, 90km from the capital city of Arequipa and 9km north of Cocachacra.

The project concessions cover an area of 32,989.64ha.  The mine is located in the Cordillera de la Costa of southern Peru, which comprises  a wide range of undivided metamorphic rocks and undifferentiated Jurassic plutons. The rocks vary in age from the Precambrian to recent quaternary.

The Tia Maria deposit is contained within granulite to amphibolite facies gneisses of the Proterozoic Complejo Basal de la Costa, which is part of the Arequipa Massif.

Mineralisation and reserves

Mineralisation at Tia Maria occurs in the form of quartz-chalcopyrite-pyrite stockwork veins, which mainly comprise of anhedral quartz crystals up to 0.5mm in size. The copper oxide mineralisation at the mine occurs at depths of more than 300m and is mainly made of chrysocolla and lesser malachite.

As of December 2017, Tia Maria is estimated to have proven and probable reserves of 2.6Mt of copper.

Mining at Tia Maria

Mining operations at the Tia Maria will be carried out in two major stages. The first stage of the operations is expected to start between the third and fifth year, post construction works. The second stage of mining activities will be executed between the 15th and 21st year.

The first stage will involve exploitation of the mineralised deposits at the Tapada and Tia Maria blocks through conventional open pit mining methods. The project will extract mineral oxidised sulphur and conglomerate material including low grade oxides.

Ore processing

The crushed ore from the primary crusher located near the pit will be transported via a conveyor to the coarse ore storage with a capacity of 60,000t. The ore  will be then fed into three lines of secondary crushers followed by six tertiary crushers. Girdles will collect the final product for acid curing and agglomeration, which will be done in agglomerating drums by adding water to a refining solution along with concentrated sulphuric acid.

The agglomerated ore is then transported via a set of belts to the dynamic leaching stack. Dynamic piles with a base layer of low permeable compacted clay will be used to leach the mineral.

A drainage system will collect the leached solution in a sedimentation pool from where the overflow will be transferred to two leaching pools to produce pregnant leach solution (PLS). The PLS will be processed at the electrolytic solution circuit, which will transfer copper to an electrolytic solution using an organic solution.

Copper will be extracted from the electrolytic solution with the help of a diluent.

Infrastructure facilities

The project can be accessed from the Pan American Highway in the Cachendo sector through a 5km paved road, which will be modified to an all-weather access road. A new 32km railway line from Guerrero to the mining facilities will also be constructed.

Power supply required during construction will be met with portable electric generators. Once mining operations start, power will be received from the Montalvo substation owned by the National Interconnected Electric Service (SEIN).

A permanent resident camp will be constructed with a maximum accommodation capacity for 650 employees.

Desalinated seawater will be used for mining operations, which will be transported through a series of pipelines.