Overview

Deposit type

• Porphyry
• Breccia pipe / Stockwork
• Vein / narrow vein

Summary:

Cerro Corona is a copper-gold porphyry type deposit, with some epithermal facies at the top of its volcanic column, hosted by a sub-vertical, cylindrical-shape diorite porphyry (600-700 m in diameter). The intrusion has undergone significant meteoric processes at the top of the column, generating an upper level known as the leached cap, underlain by mixed and copper enriched zones which overlie the main hypogene portion of the deposit. The gold-only leached cap is free of copper, which is concentrated in the supergene enriched horizons.

Around 80 % of the orebody is hypogene and the remaining 20 % is oxide or supergene, notwithstanding that most of the supergene and oxide ore has already been mined and the remnant ore is primary sulphide in nature.

The Cerro Corona porphyry system is strongly altered, ranging from propylitic in the distal zones to predominantly argillic in the central zone. Varying proportions of clay-sericite are encountered and potassic alteration intensity increases with depth.

The entire system contains a strongly developed stockwork system. The stockwork has an annular disposition within the porphyry, with a low-grade or barren zone in the central part.

The upper oxidised zone of the porphyry system is up to 40 m thick and is characterised by the presence of iron oxides (goethite > jarosite > hematite + tenorite). The supergene zone contains chalcocite-covellite occurring as disseminated nodes and infill within fractures and quartz veins. Bornite occurs less frequently and on a local scale, copper sulphate is impregnated into the host rock.

At depth, the hypogene zone is characterised by sulphide mineralisation as disseminated nodes, small patches, infill in fractures, and within stockwork quartz veins. The mineralisation within the stockwork is mainly pyrite-marcasitechalcopyrite + bornite + covellite + hematite + magnetite. The veins and veinlets have been classified into the following types:
• Type A: Early veinlets, millimetre to centimetre-wide, containing magnetite-specular hematite-chalcopyritebornite-pyrite.
• Type B: Intermediate-age, millimetre to centimetre wide, containing quartz-magnetite-specular hematitechalcopyrite.
• Type D: Late veinlets, centimetre to tens of centimetre-wide, containing quartz-pyrite-chalcopyrite.
• Type M: Late magnetite-rich veins and veinlets clearly identified by their cross-cutting relationships with younger veining.

Two low-grade or barren zones are present within the deposit. The “NE Barren Core” is located in the northeastern quarter of the deposit and is irregular in shape, encompassing approximately 50,000 m² at the surface. The NE Barren Core is characterised by plagioclase-biotite ± quartz porphyry with large euhedral biotite and plagioclase phenocrysts in an aphanitic matrix. The porphyry has been subjected to argillic alteration of the plagioclase phenocrysts. Rare quartz veinlets contain minor pyrite and traces of chalcopyrite.

Deeper drillhole intercepts around the NE Barren Core show weak secondary biotite alteration and incipient to moderate potassium-feldspar flooding, and discontinuous quartz veinlets containing weak pyrite-chalcopyrite ± specularite mineralisation. The contact relationship with the surrounding stockwork-veined and mineralised porphyry has not been demonstrated.

The “SW Barren Core” is in the southwestern portion of the deposit. It is entirely enclosed by the mineralised annulus and encompasses an area approximately 200 m long in a north–south direction and 50-100 m wide in an east-west direction. The SW Barren Core is characterised in part by strongly altered intrusive diorite with strong quartz-pyrite veining and in part by the presence of plagioclase-biotite ± quartz porphyry similar in appearance to the weakly altered porphyry present in the NE Barren Core. No copper or gold mineralisation is present within the SW Barren Core except for a small high-grade zone at approximately 225 m depth in the central part of the barren zone. Hydrothermal breccias with quartz-pyrite dominant matrices have been identified in drill core near the inferred limits of the SW Barren Core but the precise contact relationship has not been established.

The interpreted sequence of intrusions based on field mapping and extensive blast hole logging. The Cerro Corona intrusive complex is defined by at least four mineralised intrusive pulses preceded by a former dry intrusion. The first (barren) intrusion acted as a sealing layer for the surrounding sedimentary rocks, yielding only marbelisation and at the same time preventing later mineralising fluids to penetrate the limestones to generate skarn. The pulses have very diffuse contacts between them with subsequent alteration making it difficult to differentiate boundaries in the mapping process. Nevertheless, a previously executed a petrographic study on 30 samples well distributed in the mine did not find significant differences between them. This supports the hypothesis that all intrusions came from a single magma chamber with slight differences due to magmatic differentiation.

The footprint of metal distribution is in the outer portion of each intrusion and the most recent and best preserved is the assigned pulse 5 in the southwest of the deposit. Pulse 5 crosscuts all the former ones. All pulses are intensively mineralised on their external crust preserving a barren or lower grade core in the central portion. The annular shape of the mineralisation distributed in the outer part of the intrusive bodies results from violent quenching of the external halo during rapid magma ascent to the surface. This causes intense fracturing and dilational intrusions at the contact zone, creating permeability and then allowing the flow of hydrothermal fluids responsible for the alteration and hypogene mineralisation throughout the shattered portion of the rock (outer halos). Cores remained barren or at most poorly mineralised except for rare structures which allowed the flow of alteration and mineralising fluids to the inner part of the pulses without significant extension and economic potential.

Although structural activity has played a key role by preparing the geological setting prior to ore emplacement allowing porphyritic intrusions and subsequent hydrothermal flow, surface mapping shows that there is no significant movement or disruption of the orebodies caused by fault displacement.

Mining Methods

• Truck & Shovel / Loader

Summary:

The Cerro Corona open pit is mined by conventional drill and blast methods with truck and excavator fleets. Mining benches are generally 10 m high in limestone, silica and potassic units. Haul roads have 10 % of maximum gradient configuration. All material requires drill and blast with varying powder factors according to rock hardness using 200 mm diameter production BHs.

The operations quarry is being mined to provide limestone for the TSF construction. A proportion of the clay waste removed from the pit is also used for this purpose.

All operation and maintenance of mining equipment is completed by the mining contractor.

The new mining contractor has flexibility relating to its mining fleet and is committed to mobilising a fleet of 45 t trucks as the material movement rate increases.

Mining fleet and machinery requirements
Load and haul activities are carried out by 11 x 40 t trucks, 13 x 45 t trucks, 23 x 55 t trucks and 5 excavators with a bucket capacity varying between 4.8 and 6 m³.

Comminution

Crushers and Mills

Summary:

The crushing circuit includes two independent lines (one on duty and one spare) to supply an overland conveyor feeding the SAG mill. Each line has a Lokotrack LT-140E as a primary crusher and MMD Sizer as a primary/secondary crusher that receives coarse material with a top size of 1 m. Fine ore from the mine (-0.23 m) is fed to the hoppers through a belt conveyor (each line includes a 300 t hopper). From the hopper, a 1.07 m apron feeder sends the ore to a MMD Sizer crusher that reduces the ore size from 0.15 m to 0.10 m. The crushed ore is then conveyed by a 1.4m belt feeder to the 1.07 m overland conveyor.

The grinding area includes a 24’ x 14.5’ SAG mill that reduces the ore size to 1” particle and 20’ x 34’ ball mill working in a closed circuit with a 26” hydro cyclone nest that reduces the ore particle size to 80 % passing the 140-160 um mesh range. The pulp is discharged into a conditioning tank which is fed to the flotation plant. A cone crusher was implemented in this area to process pebbles from the SAG mill with the product fed back to the ball mill.

Plant upgrades and development
Replacement of Abon Sizers with MMD Sizers
Replacement of both Abon Sizers with upgraded MMD Sizers with higher hardness rock crushing capacity was completed during 2021 and 2022.

SAG mill grates configuration change
During 2019 and 2020, Cerro Corona engaged Fluor to review the set-up and performance of the comminution circuit. One of the recommendations made to increase capacity of the circuit was to increase the aperture and open area of the SAG mill discharge grates. Following trials undertaken in 2020 and 2021, all the discharge grates were replaced with larger apertures of 45-50 x 34 mm, targeting a throughput increase of approximately 4 t/hr.

Processing

• Gravity separation
• Centrifugal concentrator
• Crush & Screen plant
• Flotation
• Dewatering
• Filter press

Summary:

The Cerro Corona process plant is a conventional crush-grind-float circuit producing a copper-gold concentrate. The life of mine plan is built on a throughput assumption of 800 t/hr or 6.7 Mt/a with an availability of 91.32 %.

The flotation plant includes a rougher stage of seven 160 m³ Outokumpu flotation cells to produce a concentrate recovering 85 %-90 % of the copper and 65 %-70 % of the gold. The rougher flotation tails are thickened in a 36.6 m diameter thickener to a density of 45-52 % solids and then piped to the TSF.

The concentrate is processed through two stages of cleaning cells of different size to deliver a concentrate of 20 % copper and 30 g/t gold. The cleaning circuit also includes four regrind mills and five 50 m³ Outokumpu cleanerscavenger flotation cells. The cleaner tails from this circuit are piped to the TSF.

A Falcon gravity concentrator is included in the circuit for the recovery gold in iron from the rougher concentrate, which is then sent to the final concentrate thickener. The tailings from the gravimetric process continues the normal process to the cleaning flotation circuit.

The final concentrate is thickened in a 16 m diameter thickener to 63 % solids and then pumped to a fully automatic Metso filter. Concentrate with 7-9 % moisture is stored in a dome with a 5,000 t capacity before loading into 30 t trucks that transport the concentrate in seven vehicle convoys over 380 km to Salaverry port. The concentrate is loaded in ships for export to copper smelters in Japan and Germany.

Several plant improvement or optimisation projects were recently completed or remain in progress.

Gravity circuit reconfiguration
The existing Falcon gravity concentrator was recently reconfigured for incorporation into the concentrate regrind circuit, recirculating load instead of being fed rougher concentrate. This provides an opportunity for multiple passes of coarse gold to be presented to the concentrator due to recirculation of gold through the regrind circuit hydrocyclones, with the aim to increase gravity recovery.

Replacement of Abon Sizers with MMD Sizers
Replacement of both Abon Sizers with upgraded MMD Sizers with higher hardness rock crushing capacity was completed during 2021 and 2022.

SAG mill grates configuration change During 2019 and 2020, Cerro Corona engaged Fluor to review the set-up and performance of the comminution circuit. One of the recommendations made to increase capacity of the circuit was to increase the aperture and open area of the SAG mill discharge grates.

Following trials undertaken in 2020 and 2021, all the discharge grates were replaced with larger apertures of 45-50 x 34 mm, targeting a throughput increase of approximately 4 t/hr.

Water Supply

Summary:

The operational requirement for water is approximately 200,000 m³ per month. Volumes of water stored in the TSF per month are defined according to the season to control risk, thus oscillating the volume of clear water in the TSF between 1.5 and 2.4 Mm³ to cover the demand of the operation and ensure the operation of the installed pumping systems.

Rainwater from the mine and other flows are the main sources of water supply for Cerro Corona which is stored in the TSF. Water required for the process plant is sourced from the TSF and returned to the TSF together with the tailings.

Ground and runoff water from the Cerro Corona open pit is pumped to the TSF and is included in the global water balance. When required, a portion of the water stored in the TSF is pumped to a water treatment plant and discharged to the Tingo River in accordance with national discharge regulations and the Water Discharge Licence.

Water supply for the Cerro Corona camp comes from pit dewatering and the UCB drainage system as well as from PPC-1 pumping. A portion of the water pumped from the pit is treated on-site and sent to the camp. Some of this water is also sent to the Hualgayoc basin.

Production

Operational metrics

Personnel

Job Title	Name	Profile	Ref. Date
Engineering Manager	Ricardo Caycho		Aug 7, 2024
Exploration Manager	Juan Carlos Sarmiento Arias		Aug 7, 2024
Mine Superintendent	Rafael Guerrero Valqui		Aug 7, 2024
Technical Services Manager	Julio Torres		Aug 7, 2024
VP Operations	Ronald Diaz Vásquez		Aug 7, 2024