The copper-gold sulphide mineralization found at the Candelaria Copper Mining Complex is generally referred to as iron oxide copper gold (IOCG) mineralization. The sulphide mineralization occurs in breccias, stockwork veinlets, disseminations in andesite, and as an internal tuff unit. There are also some localized controls to mineralization in the form of faults, breccias, veins, and foliation. Candelaria has become an exploration model for Andean-type IOCG deposits that display close relationships to the plutonic complexes and broadly coeval fault systems. Depending on lithology and the structural setting, the polymetallic sulphide mineralization can occur as veins, hydrothermal breccias, replacement mantos, and calcic skarns. The Candelaria IOCG system lies within the thermal aureole of the Lower Cretaceous magmatic arc plutonic suite in the Candelaria-Punta del Cobre district.

Chalcopyrite is the only primary copper sulphide present in the Santos mine. Additionally to copper mineralization, there are economic values of gold. Most frequent gangue minerals are pyrite, magnetite, actinolite, k-feldspar, chlorite, biotite and hematite.

In the Santos mine, three types of mineralized bodies are observed: veins, mantos, and breccia bodies. An important vein in the Santos mine is the Isabel, which is oriented northwest-striking, and extends over 1 kilometre in length and between 4 and 30 metres in width. Manto-type mineralization occurs as tabular bodies hosted in two sedimentary horizons located in the floor and roof of the albitophyre. The manto mineralization is characterized by variable iron contents with magnetite common in the north and deeper areas, and specular hematite in the south. Mineralization occurs within breccia bodies is typically contained with the albitoforo and lower andesite and is formed by steeply west-dipping and north-northwest- to northwest-striking bodies.

Mineralized bodies at the Alcaparrosa mine have a manto-type geometry that trend to the northeast and dip to the west. Ore and gangue mineralogy consists of chalcopyrite, pyrite, and magnetite, with trace pyrrhotite, molybdenite, and arsenopyrite.

Mineralization styles at the Alcaparrosa mine also occurs as veinlets defining dense stockwork, breccias (hydrothermal potassium feldspar and magnetite), as well as fine dissemination in biotite meta-andesites. High grade bodies are also found in massive veins striking north-northwest, north, and east.

Minera Ojos del Salado consists of the Santos and Alcaparrosa underground mines.

The Alcaparrosa mine currently produces 4,300 tonnes per day of ore and is expected to keep it as a steady state production rate. The life of mine average grade is 0.77 percent copper. The Santos mine will continue to produce at its current rate of production of 5,100 tonnes per day of ore with an average life of mine grade of 0.94 percent copper.

The three underground mines (Candelaria Underground, Santos, and Alcaparrosa) utilize a sublevel stoping mining method for ore extraction. This method is ideal for relatively large, vertical, as well as thick deposits with favourable and stable host rock. Stopes can typically be up to 100 metres high with sublevels at 20 to 60 metre intervals. The length of the stopes is generally 20 to 80 metres with widths varying between 20 to 30 metres. Stopes are drilled down from the sublevel drilling drifts as benches using 4.5 inch diameter downthe-hole holes. The holes are loaded and blasted in vertical slices towards an open face. The blasted ore gravitates to the bottom of the stope and is collected through drawpoints at the production level below. Ore is mucked from the drawpoints using surface type front-end loaders and load haul dumps. The mucked ore is dumped into 30-tonne highway type trucks and hauled up the ramp to a surface stockpile for subsequent rehandling and processing.

The Candelaria processing plant receives ore from the Candelaria Open Pit and the Candelaria Underground (North Sector) and Alcaparrosa underground mines. It has a nameplate capacity of 75,000 tonnes per day. The Pedro Aguirre Cerda (PAC) processing plant receives ore from the Santos underground mine and has a design capacity of 3,800 tonnes per day.

The historical processing performance of Minera Candelaria from 2000 to mid-2017 averaged 25.6 million tonnes per year, equivalent to approximately 70,000 tonnes per day with a utilization of 93 percent. During this period, metallurgical recovery averaged 94 percent for copper, 75 percent for gold, and 83 percent for silver.

The Candelaria processing plant flowsheet is conventional, comprising two parallel process lines for grinding and flotation, reclaimed process water from a conventional tailings dam, final concentrate filtration, and shipping of bulk copper concentrates. Run of mine ore is trucked to a primary gyratory crusher. Grinding takes place in a multi-stage closed circuit using semi-autogenous grinding (SAG) mills, ball mills, and pebble crushing. A multi-stage flotation circuit using an arrangement of mechanical cells, regrind mills and column cells produces copper concentrate. Final flotation copper concentrate with gold and silver by-product metals is thickened, filtered, and stored on site. Final flotation tails are conventionally thickened and disposed of in a rockfill embankment tailings storage facility. Process water is reclaimed from the tailings dam for reuse in the processing plant.

The PAC processing plant has been in operation since 1929. The plant processes 3,800 tonnes per day of fresh feed from the Santos underground mine with an average historical head grade of 0.85 percent copper and a copper recovery of 94 percent. The historical gold and silver recoveries are 72 percent.

The PAC processing plant flowsheet comprises a closed-circuit crushing plant including a primary jaw crusher, a secondary cone crusher, and two tertiary cone crushers. The grinding circuit has three ball mills operating in parallel and in direct closed circuit with hydro-cyclone classification. The flotation plant uses conventional multi-stage, mechanical, self-aspired and forced-air flotation cells, regrind milling, and column cells for the final concentrate cleaning stage. The final concentrate is thickened and filtered using a ceramic disc filter. Final flotation tailings from the PAC plant are pumped to the main Candelaria tailings storage facility.

Copper concentrates containing precious metals are trucked to the Punta Padrones port, near Caldera. In 2017, the typical Candelaria copper concentrate is forecast to average 29.5 percent copper, 5.3 g/t gold, and 97 g/t silver with a moisture content of 8.0 percent after filtration. The copper concentrate of the PAC plant is forecast to average 29.7 percent copper, 4.9 g/t gold, and 50 g/t silver.

Minera Candelaria has an agreement with a third-party company to process Candelaria’s flotation tailings to produce a magnetite concentrate and this produces an additional source of by-product revenue.

The current Candelaria tailings storage facility receives the flotation tails from the Candelaria and PAC processing plants. The Candelaria flotation tails are thickened and then pumped to the tailings storage facility at an average solids concentration of 50 percent. The PAC flotation tails are pumped unthickened at an average concentration of 35 percent. The forecast tailings storage capacity at the end of 2017 is estimated at 7.1 million cubic metres, sufficient to receive tailings until the June 2018. At the end of October 2017, the construction of the new Los Diques tailings storage facility is 84 percent complete. It is expected to receive its first tailings during the first quarter of 2018. The Los Diques tailings storage facility is located to the southwest of the open pit and plant sites and will have an approximate designed capacity of 600 million tonnes, more than what is required by the current projected mine life.