The Cerro Lindo polymetallic underground mine, located in the Chincha province of Peru, is one of the biggest zinc producing mines in the world.
Nexa Resources Peru (Nexa Peru), a subsidiary of Luxembourg-based Nexa Resources, owns and operates the mine, which has been producing zinc, copper, lead and silver since 2007.
Discovered in 1967, the Cerro Lindo property was acquired by Peruvian mining company Minera Milpo in 1984, which constructed and commissioned the mine after completing feasibility studies in 2002.
Brazilian zinc producer Votorantim Metais (VM) Holdings (now Nexa Resources) gained control of the Cerro Lindo mine by increasing its stake in Milpo to 50% in 2010 and further increasing it to 80.2% in 2016, before renaming Milpo as Nexa Resources Peru in December 2017. Floating shares constitute the remaining 19.76% stake in Nexa Peru.
Cerro Lindo had an ore processing capacity of 5,000 tonnes a day (tpd) at the time of commissioning in 2007, which was increased in four phases to 21,000tpd by 2018. The current estimated reserves at Cerro Lindo support a productive mine life at least until 2029.
Zinc, copper, lead and silver production at Cerro Lindo
The Cerro Lindo mine produced 102 thousand tonnes (kt) of zinc, 29kt of copper, 13kt of lead, and 3.8 million ounces (Moz) of silver in 2021.
Location, geology and mineralisation
The Cerro Lindo mine is located in the Chavín district, Chincha province, Department of Ica, Peru, 268km south-east of Lima.
Situated in the middle of the Andes Mountains, the project comprises 68 mineral concessions covering a total area of 43,750ha and one beneficiation concession of 518ha.
Cerro Lindo is a Kuroko-style volcanogenic massive sulphide (VMS) deposit hosted within a 30km-long and 10km-wide north-west trending belt of marine volcano-sedimentary rocks of the Huaranguillo Formation that belongs to the Casma stratigraphic group in central Peru.
The polymetallic deposit consists of lens-shaped sulphide ore bodies containing pyrite, sphalerite, galena, chalcopyrite, and barite. A total of 19 mineralised zones have been identified at Cerro Lindo, each measuring up to 300m thick and 100m wide.
Reserves at Cerro Lindo
Cerro Lindo was estimated to hold 52.1 million tonnes (Mt) of proven and probable mineral reserves grading 1.44% zinc, 0.20% lead, 0.61% copper and 21.2g/t silver, as of 31 December 2020.
In addition, the measured and indicated resources stood at 7.86Mt grading 1.72% zinc, 0.22% lead, 0.57% copper and 22.0g/t silver.
Mining and ore processing
Cerro Lindo is a mechanised underground operation with mining carried out in ten separate orebodies using bulk sublevel longhole stoping methods. The stopes are up to 30m high and 25m long, which are backfilled with a low cement content paste fill produced from flotation tailings.
Access to the underground mine is facilitated by fifteen portals servicing adits, drifts, and declines. The mining fleet at Cerro Lindo includes 11 jumbos, eight production drills, 10 bolters, 10 excavators, and 68 haul trucks.
The ore extracted from underground stopes is moved by a fleet of 35t and 52t haul trucks to the grizzly feeders for crushing in the jaw crusher installed underground on a 1,830m level. The crushed ore is brought up to the surface stockpile areas via an inclined conveyor.
Ore from the stockpile areas is conveyed to the 21,100tpd process plant where it undergoes two more stages of crushing and grinding in two parallel ball mill circuits, prior to bulk rougher and scavenger flotation to produce copper, lead, and zinc concentrates.
The concentrates produced at Cerro Lindo are transported via the Panamericana Sur road to the Port of Callao located 255km away from the mine site, or to Nexa’s Cajamarquilla smelter near Lima. The tailings from the plant are thickened and sent to the paste backfill plants or the dry stack tailings filtration plant located onsite.
Silver streaming agreement
Triple Flag Mining Finance Bermuda signed a $250m silver streaming agreement for the Cerro Lindo mine in December 2016.
Under the agreement, Triple Flag is entitled to buy up to 19.5Moz of silver from the mine at one tenth of the of the spot silver price.
The Cerro Lindo mine site is accessible from the capital city Lima via the Pan American Sur Highway to Chincha and then via an unpaved road from Huamanpuquio.
Other infrastructure facilities for the project include a desalination plant located at the coast 60km away from the mine, three pump stations along the water pipeline route, and two paste backfill plants, one tailings filtration plant and two dry-stack tailings storage facilities (TSFs) at the mine site.
A new freshwater pipeline was completed to connect the desalination plant with the mine in February 2020. The desalination plant supplies approximately 60% of the industrial fresh water required by the Cerro Lindo operation, while the remaining 40% is sourced from five local boreholes.
The total electricity requirement of the mine complex is estimated to be 36.5MW, which is supplied through the National Grid by state-owned power utility Electroperú. The mine also uses a backup generator to support the main ventilation system.
The local mine contractors engaged at Cerro Lindo include Administracion De Empresas, American Renta Car, Dinet, Exsa, Inciment, Tumi Contratistas Mineros and Union De Concreteras, whereas Explomin serves as the drilling contractor.
Nexa has trucking contracts with Transaltisa and Servicios Generales Saturno for the transportation of concentrates.
Caterpillar and Atlas Copco operate two equipment maintenance shops underground. Metso (now Metso Outotec) supplied the ball mills and crushers for the mine.
Veolia, a transnational water, waste and energy management company based in France, was contracted by Milpo to operate and maintain the desalinated water plant for the mine in December 2015.
Canada-based Roscoe Postle Associates (RPA) and SLR Consulting prepared the two latest technical reports on the Cerro Lindo mine in 2019 and 2021, respectively.
SRK Consulting provided geotechnical engineering and geomechanical 3D modelling services for the mine in 2016 and 2017. SRK also prepared an environmental impact assessment report for the expansion of the Cerro Lindo processing plant in 2018.
AMEC (now Wood Group) performed independent geotechnical assessment for the project in 2013 and prepared a technical report on Cerro Lindo operations in 2017.
AMEC, together with GRD Minproc, had also prepared a definitive feasibility study report for the mine in 2002, which was revised by Peruvian consulting company GEMIN in 2005.