The Cerro Casale gold–copper deposit is located in the Aldebarán sub-district of the Maricunga Volcanic Belt in northern Chile. The Maricunga belt is made up of a series of coalescing composite, Miocene andesitic to rhyolitic volcanic centres that extend for 200 km along the western crest of the Andes. Reverse faults parallel to the axis of the Andes have uplifted hypabyssal intrusive rocks beneath the extrusive volcanics, exposing porphyry-hosted gold-copper deposits in the Aldebarán area. In addition to Cerro Casale, the Aldebarán property is host to several, less-explored, satellite deposits including Zona de Vetas, Eva, Cerro Roman, Estrella, Anfiteatro, Jotabeche, and Romancito Sur.

At Cerro Casale, gold–copper mineralization occurs in quartz–sulphide and quartz–magnetite–specularite veinlet stockworks developed in the dioritic to granodioritic intrusives and in adjacent volcanic wall rocks. Stockworks are most common in two dioritic intrusive phases, particularly where intrusive and hydrothermal breccias are developed. Mineralization has been encountered to at least 1,450 m vertically and 850 m along strike. The strike of mineralization follows west–northwest fault and fracture zones, and is open at depth along this strike. The main zone of mineralization pinches and swells from 250 m to 700 m along strike, and down dip steeply to the southwest. The highest grade mineralization is coincident with well-developed quartzsulphide stockworks in strongly potassic-altered intrusive rocks.

Oxidation resulting from weathering and/or high oxygen activity in the last phase of hydrothermal alteration overprints sulphide mineralization in the upper portion of the Cerro Casale deposit. Copper oxides are not common. Oxidation locally extends deeply along fault zones or within steeply-dipping breccia bodies.

Cerro Casale is considered to be an example of a gold–copper porphyry system based on the following:

- Hosted in a Mesozoic orogenic belt;

- Gold–copper mineralization at Cerro Casale formed during emplacement of multiple phases of diorite and granodiorite intrusions into a coeval sequence of intermediate to felsic volcanic rocks;

- Mineralization appears to be most closely related to strong potassic to phyllic alteration of the latest phases of intermediate to felsic intrusives and associated intrusive and hydrothermal breccias;

- Mineralization is focused in well-developed quartz–sulphide stockworks; veins, crackle and breccia zones are also present;

- Large tonnage but low grade.

Open pit mining will be carried out with haul trucks and a combination of electric shovels, hydraulic excavators, and large front-end loaders. All rock will require drilling for sampling and blasting purposes.

Mine design and production schedules were developed for a nominal mining rate of 225 Mt/a, smoothed for truck requirements. Mine production and processing facilities will operate 24 h/d, 7 d/wk, 365 d/a.

The optimized Cerro Casale final pit limit was divided into a sequence of nine pit phases of decreasing profitability in order to facilitate an efficient mining schedule and realize the highest project NPV. The last two of these phases were split into east and west sub-phases in order to defer waste mining and keep the peak mining rate as low as possible.

Considerable pre-stripping will be required to access the deeper, more profitable sulphide ore in the early stages of production. The primary crusher is located 500 m south of the ultimate pit limit, although a 2 km haul road is required out of the Stage 1 pit around the east side of Cerro Casale. Waste dumps and low-grade stockpiles are located within 500 m of the pit entrance.

All mining will be carried out on 16 m benches, with final pit wall berms at 32 m intervals. The overall wall slope angles vary from 34° to 47°. Haulage ramps are designed to a maximum grade of 10% and to a width of 40 m.

Approximately 2,231 Mt of waste will be mined over the 20 year life of the proposed mining operation. Of this total, approximately 170 Mt of waste rock were scheduled for tailings dam construction over the mine life. It is proposed to mine waste rock by a conventional truck and shovel operation using 360 t end-dump trucks. The average peak waste dump production rate is about 475,000 t/d.

The initial production fleet will consist of:
- Fifty-five 360 t trucks (increasing to 57 between 2022 and 2023);
- Five 1,200 t class electric shovels;
- Two 700 t class hydraulic shovels;
- Two 40 m3 rubber-tired loaders.

All rock will require drilling for sampling and blasting purposes. A fleet of seventeen 200 mm diesel-powered blasthole drills will perform this function for ore. Three 311 mm electric-drive blasthole drills (increasing to nine between 2016 and 2021) will be required for waste.

The proposed Project consists of a large open pit with a strip ratio of 2:1, a process plant of 160,000 t/d, and an heap leach operation of 100,000 t/d production throughput. The Project is planned to generate 16.8 Moz of payable gold, 4,832 Mlb of payable copper and 36.5 Moz of payable silver in three saleable products: copper concentrate, gold doré, and SART copper concentrate.

Sulphide ore will be processed in a 160,000 t/d flotation plant facility designed to recover a copper/gold flotation concentrate, followed by dewatering and then dispatch via pipeline to a filtration plant adjacent to a port facility. Filtered concentrate will be loaded into sea-going vessels and shipped to smelters overseas. Additional gold metal will be recovered by submitting the flotation cleaner tailings to a cyanide leaching stage.

Oxide ore will be processed through a run-of-mine (ROM) heap leach facility. The leach solution is treated in a carbon-in-column (CIC) circuit for recovery of the gold content. A nominal tonnage of 100,000 t/d of fresh ore will be placed under leach (the actual deposition rate onto the heap from the mine may exceed this figure).

Flotation Plant.
Two parallel gyratory crushers will reduce the ROM material to a product with 80% of the ore passing (P80) 180 mm. The crushed product will be deposited onto a covered stockpile with a live capacity of 75,000 t.

The primary crushing circuit equipment will be designed for a circuit utilization of 75%, accounting for maintenance requirements as well as truck waiting time. The rest of the flotation plant circuits located at the mine site will be designed with a utilization rate of 92%.

The comminution circuit is completed by two additional stages of crushing, with the secondary stage including eight cone crushers operated in closed circuit with four dry screens featuring a cut-size of 45 mm. This is followed by the tertiary crushing stage, featuring six HPGR units operated in closed-circuit with 12 wet vibrating screens with a cut-size of 10 mm. A 30,000 t live capacity fine ore stockpile is used to increase the grinding circuit utilization despite HPGR maintenance.

The grinding circuit comprises six parallel ball mills to handle the oversize from each pair of wet screens and the cyclone underflow.

The comminution circuit is designed to process 160,000 t/d of the design ore, corresponding to the Year 1–5 composite crushing and grinding characteristics, delivering material to the flotation circuit at a P80 of 120 µm.

The cleaning circuit comprises three stages of flotation to upgrade the concentrate to a minimum grade of 25% Cu and one cleaner scavenger stage to increase the cleaning circuit recovery.

The cleaner scavenger stage tailings are brought to a cyanide leaching circuit for recovery of gold values. The tailings are first thickened before being diluted with cyanide solution recovered from the SART circuit and then introduced into a CIL circuit featuring two parallel trains of five tanks each, providing a 20-hour retention time.

The rougher tailings are thickened prior to flowing by gravity to the TSF (first 10 years).

The CIL tailings are diluted with reclaimed water from the cleaner tailings facility and then thickened to recover a higher solution volume to the thickener overflow, for diversion as feed to the SART circuit, where it is combined with flow inputs from the heap leaching and gold recovery circuits.

Heap Leaching and Gold Recovery Circuits.
The oxide ROM ore will be deposited by mine trucks on top of the heap in 15 m lifts. The material will be bulldozed and once a cell is complete, the irrigation distribution system will be laid out. The emitters, delivering 5,250 m3/h of leach solution (at a unit rate of 12 L/h/m2) are buried to prevent freezing under winter conditions. New ore irrigation is set at 100,000 t/d, although ore placement rate from the mine will periodically reach 150,000 t/d.

The PLS passes through four parallel trains of six activated carbon-loaded contacting columns each. The exiting barren solution will be returned to a pair of barren solution tanks where reagent make-up, as cyanide and milk-of-lime, is added before the solution is pumped back as irrigation solution for leaching. The retained moisture in the heap on fresh ore and evaporative losses are made-up in the barren leach solution system by bringing cyanide-laced water returning from the SART circuit.

The carbon handling area for the loaded carbon will consist of an acid wash circuit and a modified pressure Zadra circuit for stripping carbon. There is one acid wash column followed by two parallel elution columns. Carbon will be reactivated in an electric kiln. These facilities are used both for stripping the CIC and CIL circuits carbon loads.

The gold is recovered as a sludge in two parallel banks of two EW cells each. The sludge from EW is dried and processed in a mercury retort, before being melted in an induction furnace to produce gold doré bars for shipment and final treatment off site.

Cerro Casale will produce and sell copper/gold concentrate, gold dore and SART copper sulphide concentrate to generate revenue for the project. Over the life of the mine the flotation plant will produce 8.2 million tonnes of concentrate containing 13.44 M oz payable gold and 4,832 Mlbs payable copper. The CIL and heap leach plants will produce dore containing 3.35 Moz gold and the SART copper sulphide concentrate will contain 73Mlbs payable copper.