Escondida open-pit mine in Chile is one of the largest copper mines in the world. The mine has been operating continuously since commencing production in late 1990.
As of June 2022, the property mines from two copper deposits of very similar characteristics- Escondida and Escondida Norte.
Escondida mine is owned by BHP (57.5%), Rio Tinto (30%), JECO Corporation (10%), and JECO 2 (2.5%). It is operated by Minera Escondida Limitada (MEL), a joint venture between BHP, Rio Tinto and JECO.
The mine produces copper concentrates and cathodes. The copper concentrates also contain gold and silver, which are recovered as by-products.
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The capacity of the mine has been increased through multiple phased expansions. In FY2022, Escondida produced around 1 million tonnes (Mt) of copper.
In the medium term, MEL aims to achieve an annual average production of 1.2Mt.
Escondida operations are expected to be powered by 100% renewable energy sources by the mid-2020s. It has also stopped using groundwater for operational purposes.
Location details
The Escondida mine site is located in the Atacama Desert, approximately 170km south-east of Antofagasta in Chile.
The average elevation at the site is 3,100m above mean sea level.
Overall, MEL holds approximately 178km2 area with mineral rights under a mining lease. Active mining areas are located on various parcels of land.
Ownership history of Escondida mine
In 1978, Utah International and Getty Oil entered into a temporary partnership, called the Atacama Project, to explore porphyry deposits beneath the sedimentary and volcanic cover between Calama and Copiapó in northern Chile.
Both companies were jointly acquired by BHP and Texaco in 1984. In the same year, Texaco sold its shares to BHP.
In 1985, MEL owners included BHP (57.7%), Rio Tinto Zinc (30%), JECO (10%), and World Bank (2.5%).
BHP, in 2001, merged with Billiton and formed BHP Billiton. JECO acquired World Bank’s share which belonged to BHP Billiton in 2010. In 2017, BHP Billiton was renamed BHP.
Geology and Mineralisation
The mineral deposits in the property are related to multiphase biotite Granodiorite Porphyry stocks. The early porphyry phases host the highest-grade copper (Cu) mineralisation consistently.
The two active Escondida and Escondida Norte are porphyry copper deposits, similar to majority of Chilean/Andean copper deposits.
The deposits exhibit supergene-enriched copper porphyries with primary mineralisation associated with several phase intrusions of monzonite to granodiorite composition into host volcanics.
Before mining, copper mineralisation used to start at approximately 150m to 200m depth below surface.
Copper oxide minerals are primarily brochantite, antlerite, and chrysocolla along with iron oxides. Supergene zone minerals include copper mineral chalcocite with lesser covellite and chalcopyrite occurring with iron sulphide mineral pyrite.
Mineral Resource Estimate
A technical report, effective June 2022, reported Escondida mine’s Measured and Indicated Mineral Resources of 1,640Mt at 0.49% Cu. Inferred Resources of the property stand at 5,380Mt at 0.53% Cu
The property’s combined proven and probable ore reserves were 3,560Mt at 0.59% Cu.
The mineral resources and mineral reserves were reported for the first time under the new S-K 1300 Regulation for the fiscal year ending 30 June 2022.
Expansion of the Escondida mine
In mid-1993, the first phase of expansion was started by MEL, increasing the ore processing capacity of the first concentrator plant (Los Colorados) from 35,000 tonnes per day (tpd) to 37,500tpd.
The Phase II expansion began in August 1994 and increased the ore processing capacity to 55,000tpd. The third phase began in August 1995 and took processing capacity of ore to 105,000tpd.
The phase 3.5 expansion in 1997 added leaching of oxides at mine and increased ore processing capacity to 127,000tpd.
Following the phase IV expansion, Los Colorados plant and Laguna Seca increased production to 236,000 kilo tonnes per day (ktpd).
In 2011, BHP approved the $554m Escondida Ore Access Project (EOA) that involved relocating the crushing and conveying facilities inside Escondida’s main pit to improve access to high grade ore and increase production.
BHP Billiton invested a total of $2.6bn in Organic Growth Project 1 (OGP1) and Oxide Leach Area Project (OLAP) in 2012.
The OGP1 involved replacing Los Colorados concentrator with a new 152,000tpd plant to access higher grade ore located underneath the existing facilities. It commenced operations in 2015.
The OLAP created a new dynamic leaching pad and mineral handling system.
In 2013, MEL announced the start of construction for second desalination plant and awarded the construction contract for the Kelar power plant, which will supply power to Minera Escondida and other BHP mines.
The second desalination plant started operations with a capacity 2,500l/s in 2017.
The Escondida Water Supply (EWS) Expansion Project, that aimed to provide the mine with 100% desalinated water and eliminate use of groundwater, was completed in 2020.
In 2019, BHP announced four renewable power agreements as part of its plan to meet Escondida’s energy requirements from 100% renewable energy sources. From FY23, MEL’s energy demand is expected to be met through Kayros renewable Power Purchase Agreements (PPAs).
Mining and Ore Processing
At Escondida, conventional open pit mining methods are used to extract mineral reserves, which contain economic quantities of copper to produce cathodes and copper concentrates.
It involved the use of trucks and shovels/excavators since the start of mining operations.
Mining begins with drilling and the samples are sent to an assay laboratory for analysis. The results help in identifying ore, leach, and waste rock zones.
After blasting, ore and waste are mined by excavators and loaded on trucks for transfer. For processing, the ore has three destinations; mills, sulphide bio leach, and acid leaching.
Ore for mills, is sent to one of two locations- the Los Colorados Plant beside the Escondida pit or Laguna Seca Line 1/ Line 2 plants located approximately 6km south of the pit.
Ore for Los Colorados is sent to Crusher 1 (4,500 tonnes per hour (tph) capacity) and then transported to Los Colorados by conveyor.
For the other location, the ore is sent to Crusher 2 (7,420tph capacity) or Crusher 3 (9,330tph capacity) and then transported to Laguna Seca Line 1/ Line 2 via one of two conveyors.
The ore from Nortje pit is sent to either to Los Colorados or Laguna Seca Line 1 from Crusher 5 (9,330tph capacity).
The ore is sent via trucks to the ROM pad located 8 km east of the Escondida pit for sulphide bio leaching and to Crusher 4 (5,000tph capacity) for acid leaching.
The Cu concentrate is transported as a pulp with 65% solids via pipelines to the Coloso Port, where it is filtered and placed in stockpiles for shipment on bulk carriers.
The oxidised ores are processed by a sequence of leaching, SX and EW processes, while the low-grade sulphide ores are processed by a sequence of bioleaching, SX, and EW processes.
The recovery of Cu from the solutions arising from oxides and sulphides leaching heaps is done by selective extraction using specific organic compounds (SX) to deliver a Cu enriched solution after a re-extraction process.
The dissolved Cu is deposited on stainless steel plates by EW to constitute copper cathodes. These 99.999% pure cathodes are transported by rail to the Antofagasta or Mejillones port for export.
Power infrastructure
The power infrastructure at the site includes electricity supply systems comprising substations; transmission lines; electrical rooms; and service roads.
A 220kv high voltage power supply infrastructure connects with the generating sources directly, an important part of the National Electricity System (SEN) and South-Cordillera System.
The infrastructure has more than 1,000km of high voltage electrical lines at 220kv, 215km of electrical lines to transmit electrical energy at voltage levels of 69kV, and more than 600km of lines (less than 34.5kV) for electricity distribution.
Key Contractors involved
Bechtel Corporation won the Engineering, Procurement, and Construction (EPC) contract for phase IV expansion of Escondida mine. The scope included building a new concentrator, upgradation of crushing and material-handling systems, and constructing a 10km long conveyor system.
Ausenco has been providing heap leach engineering services since 2005.
In September 2021, a consortium of Macquerie Group, Besalco Group, and Arrigoni Group-Sociedad Concesionaria del Norte was commissioned to renovate an access road between the mine and the city of Antofagasta.
FLSmidth and local Chilean supplier MIRS developed Trommel Maintenance Robot, a robotic arm to sort minerals in different sizes. The robotic arm was used at Escondida mine to perform the task.
The expansion of the mine included the construction of a corrugated steel structural plate arch tunnel, which will be used to carry a haul road over the mine’s conveyor system. Simpson Gumpertz & Heger (SGH) assessed distress in the tunnel structure and its reinforced concrete footings, and designed repairs.
Sigdo Koppers (SK) and Bechtel conducted construction of buildings and structures, mechanical equipment, civil works, piping, electrical equipment, metal fabrication, instrumentation, and pre-commissioning of phase OGP1 copper concentrator.
The engineering design, procurement, field inspection, and pre-commissioning for the marine works and desalination components of the Escondida Water Supply (EWS) project was completed by Black & Veatch Holding Company.
Enpure was associated with the EWS Expansion project.