Overview

Deposit type

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

Summary:

The BVC deposit in the Cananea mining district is divided into two target zones, namely BVC and BVZ. The BVZ deposit conformably underlies the BVC deposit and is located to the northwest of the BVC deposit.

The BVC mine, formerly the Cananea Mine, is a porphyry Cu deposit, considered to be the largest in Mexico. Primary Cu mineralization in the Cananea mining district is centered around porphyry intrusions of quartz monzonite and some breccia chimneys. The main production centers at the district level are concentrated in brecciated bodies with high Cu grades. La Colorada Breccia hosts significant Cu, Au, and Ag mineralization.

Northwest of the BVC deposit is the BVZ deposit, a poly-metallic deposit containing mainly Zn, Cu, and Ag. Carbonate rocks of the Capote Basin and Puertecitos area show alteration and mineralization effects associated with multiple events of granitic intrusive rocks and quartz monzonitic porphyry. The skarn deposits at Puertecitos and the Elisa mine are related to favorable replacements in mantles.

Several types and styles of mineralization are present in the BVC deposit, including magmatic hydrothermal breccias (Cu-molybdenum [Mo]), skarn (Cu-zinc [Zn]), and sulfides (Cu-Mo).

The BVC deposit is underlain by the volcanic units of the Henrietta and Mesa Formations. The Henrietta Formation is widely distributed towards the western portion of the operational areas, while the volcanic sequences of the Mesa Formation extend to the east of the mining operation. These volcanic units are intruded by a series of porphyritic dykes that are located in the central and deep portion of the mining phases.

The predominant alteration in the main lithologies is phyllic alteration, characterized by the development of sericite, quartz, and pyrite. The Capote Quartzite only exhibits sericite between the quartz grains that constitute the rock. The alteration in the rocks of the Henrietta Formation is characterized by the presence of silica, sericite, pyrite, and chlorite as an alteration product of the ferromagnesian minerals. The volcanic rocks of the Mesa Formation have a higher proportion of sericite. The coarse-grained quartz-feldspar porphyry in the west slope expansion shows strong silicification. Volcanic rocks in the southeastern portion of the operation show moderate concentrations of sericite.

Diabase dykes with strikes N60°W to 80°W and N40°E, cut the volcanic and porphyry units in the area of the mine workings. Mineralized breccias in the BVC pit (Breccia 301), on the east slope of the Phase 8 development are the remnants of the La Colorada Breccia. All these breccia structures occur near the porphyry intrusion. Contact zones between porphyry and volcanic rocks throughout the district contain economic supergene and hypogene mineralization.

The BVZ deposit, is found within the Paleozoic sequence, comprising skarn-type mineralization hosted mainly in the Horquilla and Escabrosa formations. The skarn zone is delimited to the north by the Elisa Fault, with a west-northwest (WNW) orientation, and to the south by the Capote Pass Fault (Meinert, 1982), forming a monocline with a NW-SE direction and a dip of 40 to 60 to the NE. The skarn zone is also present in the Esperanza Formation.

Much of the Cu mineralization in the Cananea mining district is found in disseminated form and in veinlets in stockwork zones in the volcanic and intrusive rocks. Higher Cu grades are hosted in breccia structures, contact zones and some replacement bodies. Supergene enrichment constitutes important zones of Cu mineralization in the Cananea mining district, formed by chalcocite - covellite - digenite, generally replacing pre-existing primary minerals (pyrite - chalcopyrite). The distribution of mineralization in this zone is in disseminated form associated with volcanic rocks and porphyries of quartz-monzonite composition; in the replacement zone the occurrence of mineralization is in disseminated, nodular (patchy) form by cavity filling and replacement along the bedding planes. Below the supergene enrichment is primary mineralization consisting mainly of chalcopyrite with a small amount of bornite. The distribution of mineralization is predominantly in veinlets, in disseminated form occurring in very fine grains with abundant occurrence of chalcopyrite-based copper minerals. Above the supergene enrichment is a coating of goethite - hematite - jarosite.

A layer of hematite - goethite - jarosite oxides rests above the supergene enrichment between elevations 2,200 m to 1,800 m. The presence of native limonite in this layer suggests early enrichment cycles. The chalcocite-based supergene enrichment zone lies between elevations 1,800 m to 1,650 m amsl. The zone of supergene chalcocite and hypogene chalcopyrite mixed sulfides is between elevations 1,650 m to 1,400 m amsl. The occurrence of mineralization in the mixed zone is in two forms: disseminated and veinlets. As one goes deeper, disseminated mineralization decreases and veinlet mineralization increases. In this zone calcocite – chalcopyrite coexists.

Hypogenic primary chalcopyrite mineralization occurs below elevation 1,400 m and is known up to an elevation of 400 m amsl. In some unique geological structures (fault 8-125), it is common to observe the presence of iron oxides and supergene minerals at depths of more than 300 m from the current surface.

Mining Methods

• Truck & Shovel / Loader

Summary:

The Buenavista del Cobre (“BVC”) deposit is divided into two pit areas, namely BVC and Buenavista Zinc. The BVZ pit area lies within the largest BVC pit.

Buenavista is currently applying conventional open-pit mining methods to extract copper ore for further processing in the concentrator.

A life-of-mine (LOM) plan and pit design were developed for 2023 through 2050. LOM plan pit design is based on current geotechnical and hydrology designs, and extraction limits, which are dictated by mining recovery and dilution factors, cut-off grade (COG) estimation, and economic pit optimization analysis. Pit design includes detailed design factors for wall slopes, berm widths, pit bottom, and access ramp grades and widths.

The LOM plan includes annual forecasts of waste removal and transportation and ore extraction and beneficiation. Waste is hauled to one of the 2 ex-pit waste dumps, or overburden storage facilities (OSFs).

Overburden material is loaded by 15 electric rope shovels loading 360-t haul trucks. Dozers assist the loading fleet with general clean-up and material removal, as necessary. Dozers are used to push overburden down the sides of the OSFs on an as-needed basis.

The following recommendations were made for the Buenavista mine: inter-ramp slope design angles for the 15-year pit plan for all of the 21 design sectors defined on a rock-fabric-based catch bench analysis, using double bench, can range from 48° and 55°, and the inter-ramp slope angles are based on geometries obtained from the back-break analysis using 80% reliability of achieving the required 7.6 meter catch bench width for a single bench configuration and 10.6 meter catch bench width for a double bench configuration. Preliminary observations suggest the 15-year pit walls may be relatively free-draining; the back-break analysis assumed depressurized conditions of mine benches, and the inter-ramp stability analysis were performed for both saturated and depressurized conditions.

Comminution

Crushers and Mills

Summary:

- Size reduction of the ore by a primary gyratory crusher to reduce the ore size from ROM to minus 200 mm;
- Stockpiling primary crushed ore and then reclaiming by feeders and conveyor belts;
- Size reduction of the ore by secondary and tertiary crushing to reduce the ore size from 200 millimeters to 80 percent minus 8-9 mm;
- Crushed ore conveyed to the fine ore stockpile building;
- Fine crushed ore reclaimed and conveyed to the grinding circuit;
- Grinding ore in a conventional ball mill circuit prior to processing in a flotation circuit. The ball mills will operate in closed circuit with hydro-cyclones to deliver an ore size of 80 percent passing 105 microns to the flotation circuit.

Processing

• Sulfuric acid (reagent)
• Crush & Screen plant
• Flotation
• ROM/dump leach
• Dewatering
• Solvent Extraction & Electrowinning

Summary:

Ore is mined, transported, and crushed for processing to recover copper concentrate, molybdenum concentrate, and zinc concentrate. Two copper beneficiation plants, Concentrator 1 and Concentrator 2, are in operation at BVC.

Concentrator
Concentrator 1 has been in operation since 1988 and Concentrator 2 since 2016. The two concentrators follow a conventional process of crushing, screening, ball milling and sequential flotation to separate copper and molybdenum concentrates. The differences between the two plants are size of the equipment and the number of machines dedicated to each unit operation, because Concentrator 2 was designed and built with modern equipment 30 years after Concentrator 1.

Buenavista uses state-of-the-art computer monitoring systems at the concentrators, the crushing plant and the flotation circuit in order to coordinate inflows and optimize operations. In the original concentrator, material with a copper grade above a cut-off grade of approximately 0.30% is currently loaded onto trucks and sent to the milling circuit, where giant rotating crushers reduce the size of the ore to approximately one-half of an inch. The ore is then sent to the ball mills, which grind it to the consistency of fine powder. The finely ground powder is agitated in a water and reagents solution and is then transported to flotation cells. Air is pumped into the cells producing a froth, which carries the copper mineral to the surface but not the waste rock, or tailings. Recovered copper, with the consistency of froth, is filtered and dried to produce copper concentrates with an average copper content of approximately 24%. Concentrates are then shipped by rail to the smelter at La Caridad.

In the second concentrator, material with a copper grade above a cut-off grade of approximately 0.30% is sent to a three-phase milling circuit, where the ore size is reduced to approximately one-half inch. The ore is then sent to a circuit of six ball mills, which grind it to the consistency of fine powder. The finely ground powder is agitated in a water and reagents solution and is then transported to flotation cells. Air is pumped into the cells producing a froth, which carries the copper mineral to the surface but not the waste rock, or tailings. Recovered copper, with the consistency of froth, is filtered and dried to produce copper concentrates with an average copper content of approximately 24%. Concentrates are then sent by trucks or by railroad to the LaCaridad smelter or to the Guaymas port, at Sonora, for export.

SX-EW Plant
The Buenavista unit operates a leaching facility and three SX-EW plants. All copper ore with a grade lower than the mill cut-off grade of 0.30%, but higher than 0.15%, is delivered to the leach dumps. A cycle of leaching and resting occurs for approximately five years in the run-of-mine dumps and three years for the crushed leach material. A review of the cut-off grades based on economics is recommended to be reassessed as described above.

The L-SX-EW process encompasses leaching, solvent extraction, and electrowinning for the production of pure copper cathode. Copper is recovered as a solution of copper sulfate from low-grade ore by irrigating the ore with acidic leach solutions returning from the SX plants.

The leach solutions are loaded with copper as they percolate through the ore heaps and become pregnant leach solutions (PLS) that are fed to the SX-EW plants. The PLS from all the areas is pumped to two central PLS surge ponds, from where the PLS is fed to the solvent extraction (SX) plants.

In the SX plants the PLS is mixed with an organic solution, a mixture of a reagent diluted with kerosene, that extracts the copper from the PLS and releases acid. The organic solution loaded with copper (LO) then passes to the stripping section where it is mixed with a highly acidic solution, called spent or lean electrolyte (SE). The high acid content of the SE causes the LO to release copper to the SE and pick-up acid, regenerating the reagent molecules and the SE becomes Rich Electrolyte (RE) to feed the Electrowinning plant (EW).

In EW, the RE from SX is recirculated through electrowinning cells with multiple stainless-steel cathodes and lead anodes. A direct electrical current is applied to the cells that causes the copper in the RE to be deposited in the cathodes and the RE becomes SE that returns to SX to strip more copper from the LO.

As part of the expansion program for this unit, in 2013 the Company completed the construction of the first molybdenum plant with an annual production capacity of 2,000 tonnes of molybdenum contained in concentrate. The plant was designed to process 1,500 tonnes of copper-molybdenum concentrates per day with a content recovery of approximately 80% copper and 50%molybdenum. The molybdenum plant consists of thickeners, homogenizer tanks, flotation cells, column cells and a holo-flite dryer. The second molybdenum plant was designed to process 3,040 tonnes of copper-molybdenum concentrates per day for a content recovery between 80% and 87% for copper and 60% for molybdenum. The plant generated its first production lot in July 2016 and fully initiated operations in November 2016.

Buenavista Zinc - Sonora: This project is located within the Buenavista deposit, where the Company has built a new concentrator plant. This facility has a production capacity of 100,000 tonnes of zinc and 20,000 tonnes of copper per year. When operating, the concentrator will double the Company’s zinc production capacity and will provide more than 2,000 jobs on the operating front.

Project update: the capital budget for the project is $439 million, most of which has already been invested. Progress is 99%; the Company has initiated the commissioning process. The ramping up of the plant began in the first quarter of 2024 after technical adjustments to the concentrator. The company expects to produce 54,500 tonnes of zinc and 11,900 tonnes of copper in 2024 and an average of 90,200 tonnes of zinc and 20,700 of copper per year in the next five years.

Water Supply

Summary:

In Mexico, water is deemed public property and industries that are not connected to a public service water supply must obtain a water concession from Comision Nacional del Agua (the National Water Commission or the “CNA”). At Buenavista facility, Southern Copper maintains own wells and pay the CNA for water usage.

The wells pump approximately 35 million cubic meters (Mm3) annually and are connected to a distribution piping network that feeds water to different consumers. The site has plans in place for freshwater conservation by reducing the consumption and recycling for reuse, when possible.

Production

Operational metrics

Personnel

Job Title	Name	Profile	Ref. Date
Chief Engineer	Jorge Vazquez		Aug 7, 2024
Consultant - Mining & Costs	Danny Tolmer		Feb 24, 2022
Maintenance Superintendent	David García		Aug 7, 2024
Maintenance Superintendent	Alejandro Marquez		Aug 7, 2024
Mine Manager	Christian Torrecillas		Aug 7, 2024