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.

The main mineralized body at the Candelaria mine is hosted in rocks of the Punta del Cobre Formation. Specifically, the host rocks are massive andesite and breccias of the lower andesite, and volcanic tuffs and volcaniclastic rocks at the base of the upper andesite. In the metasedimentary rock, the mineralization is confined to a few isolated layers (mantos).

The mineralized body is up to 400 metres thick in its central part and thins towards the edges. In east-west sections, the mineralization has a lenticular, downward concave shape with a steep eastern limb and a shallowly dipping western limb. The shape of the mineralized body in north-south section is irregular. In plan view, the extent of the mineralization is approximately 1,400 metres by 2,400 metres. The mineralized body was folded after its formation. The north-northeast-trending fold axis corresponds to the Tierra Amarilla anticline.

The mineralization assemblage in the Candelaria mine consists of chalcopyrite, magnetite, pyrite, pyrrhotite, and sphalerite. Biotite, calc-silicate minerals, and potassium feldspar constitute the gangue minerals. Pervasive potassic alteration is associated with the mineralization.

Dominant copper mineralization styles are mantos, veins, breccia filling, and veinlets along foliation planes. Gold occurs within chalcopyrite and in fractures in pyrite. Chalcopyrite and pyrite also occur in secondary northwest and north-northwest-striking faults.

Minera Candelaria consists of the Candelaria Open Pit and the Candelaria Underground mines.

The Candelaria Open Pit operates with an overall mining rate of approximately 270,000 tonnes per day including 64,800 tonnes per day of ore sent to the Candelaria concentrator. The average grade of the ore mined from the open pit over the remaining life of mine is estimated at 0.53 percent copper while stockpiled work-in-progress material at an average of 0.34 percent copper. The mine operates seven electric shovels, 43 haulage trucks, eight production drills, and a fleet of support equipment.

The open pit was designed to be mined in several phases of development. As of June 2017, five phases of development remain in the LOM plan (Phases 9 to 13). The overall strip ratio is expected to be 2.7:1 including ore that is initially delivered to stockpiles. The total in-pit waste is 871.6 million tonnes and the overall life of the open pit mine is 18 years. The new phase designs will reduce phase operations interaction, recover waste stripping and provide and should improve copper production profile from 2021. These new phase designs will require an increase in waste stripping in 2018 and 2019. Candelaria is planning a substantial mine equipment recapitalization program to replace the aged mining equipment fleet and a change in the loading methodology to increase capacity and efficiency while improving equipment availability and reliability. The forecast total cost over the next four years of this mine equipment recapitalisation programme is US$218.8 million.

The Candelaria Underground mine is forecast to produce 7,000 tonnes per day of ore in 2017, ramping up to a steady state of 14,000 tonnes per day by 2021 as per the life of mine plan. The average life of mine grade is 0.89 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.