Both Escondida and Escondida Norte are porphyry copper deposits, being the deposit type typical of the majority of Chilean/Andean copper deposits. The deposits lie in the Escondida-Sierra de Varas shear lens of the Domeyko Fault System. The deposits are supergene-enriched copper porphyries with primary mineralisation associated with multiple phase intrusions of monzonite to granodiorite composition into host volcanics. The deposits are related geographically and geologically to porphyry bodies intruded along a regional lineament which exerts strong control over the regional distribution of deposits of this age and type. The Escondida cluster is formed by the Escondida (including Escondida Este) and Escondida Norte - Zaldívar porphyry copper deposits. The latter corresponds to the same ore body mined by two different companies and operations. Additionally, the porphyry copper deposits of Chimborazo and Pampa Escondida, as well as Pinta Verde, have been recognised. Escondida Deposit Alteration and Hypogene Mineralisation Much of the feldspathic porphyry shows sericitic alteration in shallow levels already exploited an advanced argillic zone and at deeper only along fault zones. Quartz, pyrophyllite and subordinate alunite, diaspore, and svanbergite are reported (Brimhall et al., 1985; Alpers and Brimhall, 1988). At depth and as remnants in the sericitic zone, patches of chlorite-sericite alteration exist, which give way downward to biotite in andesitic volcanic rocks and k-feldspar > biotite in the porphyries (Padilla-Garza et al., 2001). The superimposed potassic and sericitic alteration contains abundant A and B type quartz veinlets. The Granodiorita Verde unit shows a weak potassic alteration in veinlets with a generalised chlorotic overprint within which the remaining hydrothermal k-feldspar stands out. The Intermineral Porphyry unit presents diverse alteration associations with variable intensities and showing as a characteristic element, the truncation of veinlets. In some sectors of the pit, there is a marked superimposition of hydrothermal events that originate an intense obliteration on the primary texture, leaving only some quartz relics, which evidence the presence of the intermineral unit (Technical Note, SI Geology, 2021). This unit can be presented primarily with a Chlorite - Sericite - Illite association (Event 1) or affected by superimposition of hydrothermal events such as Sericite - Quartz (Event 2), Sericite (Event 3) and Pyrophyllite - Alunite or Pyrophyllite (Event 4). The hypogene sulphide mineralisation at Escondida is obliterated by the effects of the supergene enrichment. However, chalcopyrite and bornite are identified in relict potassic zones along with chalcopyrite and pyrite from the overprinted chlorite-sericite and sericite zones. The high sulphidationmineralisation occur in the advanced argillic zone. In the underlying Green Granodiorite intrusion, pyrite dominates over chalcopyrite and copper grades are 0.05 to 0.25%, decreasing at depth. Supergene Mineralisation Escondida is characterised by a mature supergene profile with high kaolinite contents, which include a hematitic leaching layer, with an average thickness of ~ 200 m, but locally, can reach 400 m. This leaching zone is supported by a NW-trending enrichment zone that covers an area of 4.5 × 1.8 km with a maximum thickness of ~ 400 m. NW-trending faults, fractures, and veins intersecting the NW trend combined with higher hypogene copper contents appear to have been the main controls on both the shape and depth of the enrichment zone (Ojeda, 1986, 1990; Padilla-Garza et al., 2001). The zone is dominated by chalcocite-group minerals in its higher grade upper part with lower-grade covellite and hypogene sulphides remaining that become dominant at depth. The supergene event is dated between ~ 18 to 14 Ma (Alpers and Brimhall, 1988) in supergene alunite at the limit of the leaching and enrichment zone. Copper oxide mineralisation at Escondida is mainly found in andesitic volcanic rocks altered with biotite and chlorite-sericite in which brochantite and antlerite are the main minerals along with minor chrysocolla, atacamite, various copper phosphate minerals, cuprite, and native copper with the last two being concentrated in the upper part of the enrichment zone. Escondida Norte Deposit Alteration and Hypogene Mineralisation Potassic alteration is present at depth throughout the deposit, with biotite-feldspar-K association in the felsic rocks and biotite and minor magnetite predominate in the andesitic volcanic rocks and diorites. The potassic alteration have biotite and magnetite veinlets and abundant feld-K and quartz-feldspar-K veinlets,the latter of A-type. Grey sericite veinlets overlie the potassic zone. At shallower levels, the generalised alteration is chlorite-sericite, which is characterised by the occurrence of chlorite-sulphide veinlets overlaying and destroying the potassic association. This is covered by a sericitic zone, which is locally overlain by quartz-pyrophyllite ± alunite alteration, closely associated with the NW-directed high sulphidation vein zones. Most of the hypogene sulphide mineralisation at Escondida Norte consists of chalcopyrite and pyrite with the development of only localised centres of chalcopyrite - bornite ± chalcocite mineralisation in the potassic zone. Supergene Mineralisation A well-developed supergene profile is present at Escondida Norte, which include a leached hematitic surface, averaging 100 to 200 m (up to 350 m) thick, and a 20 to 250 m thick enrichment zone. The enrichment zone has a surface of 2 × 1.5 km, trending NE; it is divided into a high-grade, chalcocite-dominated upper zone (High Enriched), and a lower-grade basal part with covellite and lower chalcocite (Low Enriched). Supergene kaolinite is present throughout the zone and supergene alunite is dated to be ~ 17 to 14 Ma (Morales, 2009). Copper oxide mineralisation is irregularly developed above the enrichment zone, mainly with antlerite and brochantite in the higher-grade central parts (Maturana and Saric, 1991; Monroy, 2000; Williams, 2003), and chrysocolla and atacamite peripherally.

Minera Escondida Limitada(MEL) is a mining operation that uses conventional open pit methods to extract mineral reserves containing economic quantities of copper to produce both cathodes and copper concentrates. The mineral reserves are based on the LOM plan which only considers open pit mining. Since the start of operations at MEL, the mine has operated using an open pit mining method, utilising trucks, and shovels/excavators. This method is suited to the large copper porphyry deposits mined by MEL as the deposits are low grade, high tonnage and located relatively close to the surface. Drill and Blast The mining operation begins with the drilling process; drill samples are sent to an assay laboratory for analysis. The assay results are used to mark out zones of ore, leach, and waste rock, which are mined separately. Waste Removal and Storage After the blasting is completed, ore and waste are mined by excavators loading onto trucks. Overburden and waste loads can be used for fixing roads, building ramps, or simply placed on the Overburden Storage Facility. The mine design criteria are listed below: • Surface mining approach • Minimum operating width of 80 m • Haul road design width of 40 m • Bench height of 15 m • Maximum road grade of 10% • Bench face angle and catch berms vary based on geotechnical sector • Typical blasting grid ranging from 7x7 until 11x14m • Final wall Control Drill Pattern 2.0, 2.5 and 3.0 m depending on sector • Blasthole diameter of 6.1/2, 9, 10 5/8 and 12 inches • Rock density average of 2.5

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The infrastructure comprises two open-pit mines, three concentrator plants (comprising milling, grinding, flotation and thickening), an acid heap leach pad facility (on/off heap leach - oxides), a ROM bioleach pad facility (permeant dump leach - sulphides) and a solvent-extraction and electro-winning plant producing copper cathodes from both leach facilities.

Copper concentrate is transported through two pipelines to the filtration plant, located at the coast in Coloso port, where it is loaded for shipping to end customers. The copper cathodes are transported to the Antofagasta port of Mejillones from where they are shipped to customers.

Ore Removal and Transport
There are three destinations for ore based on the processing method to include mill, sulphide bio leach, and acid leaching.

Ore being sent to the Mills is sent to one of two locations, the Los Colorados plant which is adjacent to the Escondida pit, or Laguna Seca Line 1 / Line 2 plants located approximately 6km south of the Escondida pit. Ore coming from the Escondida pit being sent to Los Colorados is sent to Crusher 1 (with a capacity of 4,500 tonnes per hour [tph]) and then transported by conveyor to Los Colorados. Ore coming from Escondida pit being sent to Laguna Seca Line 1 or Line 2 is sent to Crusher 2 (capacity of 7,420tph) or Crusher 3 (capacity of 9,330 tph) and then via one of two conveyors to Laguna Seca Line 1 or Line 2. Ore from Norte pit is sent from Crusher 5 (capacity of 9,330 tph) and transported to either Los Colorados or Laguna Seca Line 1.

Ore being sent to Sulphide Bioleaching is sent via trucks to the ROM pad located 8 km east of the Escondida pit / 6 km southeast of the Escondida Norte pit. This pad has a design capacity of ~1,600 Mt.

Acid Leaching Ore is taken via trucks to Crusher 4 (capacity of 5,000tph), it then undergoes secondary and tertiary crushing and finally agglomeration before being sent via conveyor to be placed on the dynamic pad approximately 7km to the Northwest of the Escondida pit.

Concentration Process Description
The main product of Minera Escondida Ltd. consists of copper contained in a concentrate of copper and iron sulphides. This is currently produced by three plants located at the mine site to include; 1), Los Colorados; 2), Laguna Seca Line 1; and 3), Laguna Seca Line 2, which collectively have a total nominal capacity of 413,700 tpd of ore.

A general scheme for the concentration process was designed to process only sulphide ores and consists of the following stages:
• Coarse ore Stockpile receiving crushed ore from primary crushers;
• Primary grinding is undertaken in SAG mills, operating in closed circuit with pebble crushing systems;
• Secondary grinding is undertaken in ball mills, operating in closed circuit with hydrocyclones;
• Rougher flotation cells;
• Cleaner flotation cells, operating in closed circuit with a regrind circuit;
• Concentrate dewatering in conventional thickeners;
• Tailings dewatering in thickeners.

In the flotation stage, the different physicochemical properties between the valuable copper minerals and the gangue are used to produce the separation, incorporating a series of chemical reagents. When air is injected into the system, the copper sulphide particles adhere to the bubbles, producing a froth in the flotation separation process. The froth is copper concentrate. The particles that do not float are eliminated as tailings. These are silicates and other gangue minerals, which includes some iron sulphides.

Primary, or rougher flotation, aims to maximize the recovery of valuable mineral species. Cleaning flotation stages have the purpose of eliminating impurities and improving the copper grade in the concentrate to achieve the final product grade. The scavenger cells reduce the losses in cleaner tailings. There are minor differences in the configuration of the flotation circuits at the three plants.

Oxide Leach Process Description
The oxide leach process has been designed to treat ore containing oxide minerals following the traditional flowsheet for heap leaching of copper ores. The battery limits of the process are the coarse ore stockpile and electro-winning with the metal production. The stages of the process are the following:
• Coarse ore reclaiming from stockpile receiving crushed ore from the mine.
• Secondary and tertiary crushing operating in closed circuit with screens.
• Agglomeration with sulphuric acid and water in tumbling drums.
• Stacking of the agglomerated ore in a dynamic heap.
• Irrigation using an acid solution operating in closed circuit with a solution treatment plant denominated solvent extraction (SX).
• Transferring of the dissolved copper contained in the output solution to a cleaned solution using selective solvents.
• Transformation of the dissolved copper in metal using electric energy through an electrolytic process called electrowinning (EW).
• Spent ore disposal in waste dump called a ripios dump.

The process starts with the coarse ore reclamation from the stockpile. The ore is then transported to the crushing plant where secondary crushers reduce the size of the ore from an average size of 100 mm to about 19 mm in diameter. The ore is transported to the tertiary crushing stage operating in closed circuit with screens. The final product from crushing must comply with the 80 % of the mass passing 19 mm.

Next the crushed ore is agglomerated using concentrated sulphuric acid and water to increase dissolution kinetics of the copper species and to generate stability before irrigation.

The ore is stacked in the area in the form of a 6-metre-high heap and then a solution of sulphuric acid is used to irrigate the ore and dissolve the copper. The irrigation cycle is 150 days. The drainage solution containing the dissolved copper is treated in a solvent extraction plant (SX), where the objective is to remove impurities and produce a cleaned solution without other elements that can affect the following stages. Finally, the clean copper solution is pumped to a tank house where electrolyses is applied to transfer copper in solution to stainless steel plates, where the copper deposits in the form of metal. This is called electrowinning and the final product is copper cathodes.

The leached ore (ripios) are reclaimed using a bucket wheel excavator that uses an overland and series of mobile conveyors to transport the ripios out of the leach pad. Subsequently, a shiftable conveyor with tripper discharges the ripios on the spreader, which will finally deposit the waste material onto the ripios dump.

Bioleaching Process Description
The bioleaching process started operations in 2006. It was designed as a low-cost method to process low grade sulphides. Since this material is mined to access ore for the sulphide concentrators this material would be sent to marginal stocks or to waste dump. The bioleaching process realizes value from this this material. In general, the stages at the process can be described as:
• Transport of the run of mine (ROM) ore from the existing pits or stockpiles to the leach pads
• Stacking of the ore in a permanent heap.
• Irrigation using an acid solution operating in closed circuit with a solution treatment plant denominated SX.
• Transferring of the dissolved copper contained in the output solution to a cleaned solution using selective solvents.
• Transformation of the dissolved copper in metal using electric energy through an electrolytic process, EW.

The process involves the extraction of copper from ROM material with copper content above 0.25%, through bioleaching of the sulphide ore. The ore is placed in a permanent (static) leach pad with seven lifts of 18 m each one and irrigated with acid solution for more than 350 days. Copper is then recovered from pregnant leach solutions via dedicated facilities for SX and EW. The sulphide leach maximum irrigation capacity is 16,500 m³/h.