Los Bronces project in Chile is one of the largest copper mines in the world. Besides copper, the open-cut mine also produces molybdenum and copper cathodes.
The project is part of Anglo American Sur, which is majority owned by Anglo American (50.1%). The Codelco-Mitsui consortium (29.5%) and Mitsubishi (20.4%) are the other stakeholders.
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Compañía Minera Disputada de Las Condes Limitada (CMD), a subsidiary of Exxon Mobil, was the previous owner of the project.
Anglo American acquired CMD in 2002 for $1.3bn. Subsequently, the name of the company was changed to Anglo American Sur.
An expansion of the Los Bronces project was completed in 2011 increasing the mine’s production capacity to around 400,000tpa.
In April 2022, the Environmental Assessment Service of Chile (SEA), an environment regulator, recommended rejecting the permitting application for the Los Bronces Integrated Project (LBIP).
The mine life extension project planned to expand the current open pit within the operating site to access higher grade ore from a new underground section of the mine.
Location and Geology
Los Bronces mine is located around 65km northeast of Santiago at an altitude of around 4,000m above sea level.
It features porphyry cluster adjacent to Codelco’s Andina operations. The ore body includes chalcopyrite-bornite primary sulphides with a thick overlaying blanket of chalcocite.
Reserves and Production
In 2011, the ore reserve at Los Bronces was estimated to be 2.17 billion tonnes (bt) at grading 0.62% Cu.
Proved ore reserve estimates were 1.11bt grading 0.53%TCu, as at 31 December 2017.
In 2001, the project produced 171,000 tonnes of copper in concentrate. The figure expanded to 221,800tonnes of copper in 2011 and to 365 kilo tonnes (kt) in 2018.
As of 2017, the mine has a reserve life of 23 years. The project has environmental approval until 2036.
Mining
The Los Bronces open pit mining involves drilling and blasting techniques to extract ore. The ore is extracted, crushed and transported through a 56km slurry pipeline to the Las Tórtolas flotation plant.
The plant produces copper and molybdenum concentrates.
The expansion of the Los Bronces, which was completed in 2011, involved multiple sub-projects across different geographical areas.
This included the installation of a primary crusher near the Los Bronces open pit. The extracted ore is crushed and transported to a grinding plant at Confluencia through a conveyor belt.
At Confluencia, a new stockpile, one SAG mill and two ball mills, thickeners and other associated equipment were installed to produce the slurry, which is then transported to a new copper and molybdenum concentrator plant (flotation) adjacent to a concentrator at the Las Tórtolas complex.
The copper and molybdenum concentrates are separated from the slurry through a froth flotation process.
The ore slurry transport system included five choke stations due to more than 3,000m difference in elevation between Confluencia and Las Tortolas. Four pumping stations are used to return water from Las Tortolas to Confluencia.
Anglo American has also built a pilot photovoltaic plant (PV) comprising 256 photovoltaic panels of 330 watts capacity each on a floating island to reduce carbon dioxide emissions at Los Bronces copper mine.
The panels, installed on Las Tórtolas pond, will generate 86kW of energy.
The company also plans to stop using fresh water at the copper mine by 2030 and switch to using desalinated and recycled water for its operations.
Contractors Involved
In December 2007, Bechtel secured a $1.7bn engineering, procurement and construction (EPC) contract from Anglo American for the development of the Los Bronces project. Bechtel was responsible for project management, engineering and procurement for 70% of the project.
Direct hire construction was provided through a joint venture of Bechtel and Sigdo Koppers (BSK).
Ausenco was engaged to perform a full range of services throughout the pipeline system of the Los Bronces mine. The pipeline system includes a 52km long, 28-inch diameter, 37.5 million tonnes per year (mt/y) ore pipeline and a 52km, 24-inch diameter water pipeline.
SRK Consulting offered conceptual and basic engineering design services for the Los Bronces Exploration Tunnel.
Techint E&C was associated with the delivery of the ore slurry transportation system featuring five new energy dissipating choke stations and four pumping stations with centrifugal pumps.
Techint E&C also signed a contract in November 2020 to replace a section of the Tailings Transportation System of the Los Bronces mining complex. The company signed another contract in January 2021 regarding replacement of pipelines.
GeoSIG, along with GeoMediciones, were responsible for installing a seismic network for tailings dam.
In June 2022, Komatsu announced plans for deploying the Komatsu FrontRunner Autonomous Haulage System (AHS) on a total of 62 930E ultra-class haul trucks by 2024 at Los Bronces mine.
