Overview

Mine Type	Open Pit
Status	Active
Commodities	Copper Molybdenum
Mining Method	Truck & Shovel / Loader
Production Start	...
Mine Life	...
Snapshot	Los Bronces is one of the world’s largest copper mines. Los Bronces remains a world-class copper deposit, accounting for more than 2% of the world’s known copper resources. The environmental permit for the Los Bronces open pit expansion and underground development was issued by the authorities in November 2023. Development work for the next higher grade, softer ore phase of the mine, Donoso 2, is now under way and is expected to benefit production and unit costs from early 2027. Pre-feasibility studies for the Los Bronces underground expansion are ongoing and are expected to be finalised in mid-2025. While the operation works through the challenges in the mine, and until the economics improve, the older, smaller and more costly Los Bronces processing plant will be placed on care and maintenance from mid-2024.

Deposit type

• Porphyry
• Breccia pipe / Stockwork

Summary:

The Los Bronces deposit is part of the Miocene Pliocene Río Blanco – Los Bronces porphyry copper system with mineralisation extends 9km from North to South and 3km from East to West. The deposit is open at depth and laterally.

The orebodies are located in a mineralised corridor of 1 km wide by 8 km long, which is part of the late Miocene to early Pliocene Río Blanco-Los Bronces porphyry copper system. The host rocks are the volcanic sequence of the Farellones Formation and the plutonic rocks of the San Francisco Batholith, which intrude the Farellones Formation.

Copper mineralisation is associated with the emplacement of a breccia complex (hydrothermal and magmatic breccias) related to a system of porphyry intrusions. The breccia complex comprises at least seven hydrothermal breccia pipes forming a large elliptic body of 4 km in length, 0.7 km in width and 2 km in depth. The shape of the breccia system is ‘funnel-like’, with sharp contacts with the host rocks in the upper part of the column and transitional contacts at depth. The main phase of copper and molybdenum mineralisation is hosted in the high grade breccia bodies and is disseminated throughout the host volcanic and igneous rocks. This is overprinted by later structurally controlled veins that contain erratic copper-arsenic mineralisation confined locally to parts of the deposit. Late porphyries and a diatreme complex post-date the mineralisation event.

The main ore body is a complex assemblage of hypogene copper-molybdenum sulphide breccia hosted mineralisation that was subsequently overprinted by surface-related supergene processes. The hypogene sulphide mineralisation shows a close relationship with the intrusion of porphyry dykes and sills, development of large-scale alteration zones, vein development, and breccia emplacement. The ore body is related to at least seven hydrothermal breccia pipes forming a large elliptic body of 2km in length, 0.7km wide and 1.0km in depth. The shape of the breccia system is ‘funnel-like’, characterised by sharp contacts with the host rocks in the upper part of the column and transitional at depths.

The host rocks are the volcanic sequence of the Farellones Formation and the plutonic rocks of the San Francisco Batholith which intrude the Farellones Formation. Copper mineralisation is associated with the emplacement of a complex system of porphyry intrusions (quartz monzonites and quartz monzodiorites) and hydrothermal breccias. Early copper and molybdenum mineralisation is hosted in the porphyry stock, in high-grade breccia bodies and is disseminated throughout the bordering country rocks.

Breccia-hosted mineralisation is typically a blend of mineralisation inherited from the source rock and hosted in the breccia clasts and sulphides disseminated in the breccia matrix, or in the case of the matrix-poor Donoso breccia, rimming the clasts. Breccia mineralisation is dominated by pyrite- chalcopyrite.

The early copper and molybdenum mineralisation is overprinted by later structurally controlled and erratic Copper-Arsenic (enargite) mineralisation confined locally to parts of the deposit. On a regional scale the main breccia complex is oriented 10°N to 15°W, with a distance of 9km between the two largest known breccias bodies. Late porphyries and a diatreme complex postdate the mineralisation event.

Uplift and erosion of the Andean cordillera eventually exposed the deposit to surface, where meteoric waters played an important role in remobilising and enriching copper in the higher parts of the deposit. Supergene surface waters penetrated and opened the rock fractures and breccia matrix chemically altering and leaching minerals. Leached copper was redeposited as secondary copper sulphides, mainly chalcocite (Cu2S) with minor covellite (CuS) in the chemically reducing environment below the water table. This is the supergene (secondary) material that is extracted via leaching and SX/EW processes. This copper enrichment process was favoured by the porous nature of the breccia bodies, particularly that of Infiernillo to the south, where secondary sulphides are found at depths of 600m. However, the degree of enrichment decreases gradually giving way in depth to hypogene (primary) copper minerals (chalcopyrite – CuFeS2) which is recovered via flotation at Las Tórtolas.

Mining Methods

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Comminution

Crushers and Mills

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Processing

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Production

Commodity	Product	Units	2023	2022	2021	2020	2019	2018	2017	2016	2015
Copper	Cathode	t	....	....	....	....	39,000	39,000	38,300	36,000	35,000
Copper	Metal in concentrate	t	....	....	....	....	296,000	330,500	270,000	271,200	366,700

Operational metrics

Metrics	2023	2022	2021	2020	2019	2018	2017	2016	2015
Ore tonnes mined	....	....	....	....	65,915,300 t	59,207,400 t	49,339,600 t	51,109,700 t	50,258,500 t
Tonnes processed	....	....	....	....	42,008,400 t	50,583,000 t	46,040,000 t	47,697,000 t	45,396,900 t

Personnel

Job Title	Name	Profile	Ref. Date
.......................	.......................		Mar 19, 2024
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Employees	Contractors	Total Workforce	Year
......	......	......	2021
......	......	......	2019
......	......	......	2018