El Teniente ("The Lieutenant") is an underground

copper Copper is a chemical element with the symbol Cu (from la, cuprum) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pink ...

mine located in the

Chile Chile, officially the Republic of Chile, is a country in the western part of South America. It is the southernmost country in the world, and the closest to Antarctica, occupying a long and narrow strip of land between the Andes to the eas ...

Andes The Andes, Andes Mountains or Andean Mountains (; ) are the longest continental mountain range in the world, forming a continuous highland along the western edge of South America. The range is long, wide (widest between 18°S – 20°S ...

above mean sea level Height above mean sea level is a measure of the vertical distance ( height, elevation or altitude) of a location in reference to a historic mean sea level taken as a vertical datum. In geodesy, it is formalized as '' orthometric heights''. Th ...

. It is in the commune of

Machalí Machalí is a Chilean commune and city in Cachapoal Province, O'Higgins Region. Demographics According to the 2002 census of the National Statistics Institute, Machalí spans an area of and has 28,628 inhabitants (14,297 men and 14,331 wome ...

Cachapoal Province Cachapoal Province ( es, Provincia de Cachapoal) is one of three provinces of the central Chilean region of O'Higgins (VI). Its capital is the city of Rancagua (pop. 214,344). Geography and demography According to the 2002 census by the Nation ...

, Libertador General Bernardo O'Higgins Region, near the

company town A company town is a place where practically all stores and housing are owned by the one company that is also the main employer. Company towns are often planned with a suite of amenities such as stores, houses of worship, schools, markets and re ...

of Sewell. This was established for the workers and their families. Mining at El Teniente is reported to have started as early as 1819. In the early 20th century, two men from New York, United States set up a mining operation there, starting operations in 1906. Kennecott Copper Corporation, based in

Utah Utah ( , ) is a state in the Mountain West subregion of the Western United States. Utah is a landlocked U.S. state bordered to its east by Colorado, to its northeast by Wyoming, to its north by Idaho, to its south by Arizona, and to its ...

, United States, later operated the mine through their subsidiary company. The Chilean government bought a 51% interest in the mine in 1967. Some 15,000 people lived in Sewell at its height as a company town. In 1971 Chile nationalized copper production under President Salvador Allende and formed the

state-owned State ownership, also called government ownership and public ownership, is the ownership of an industry, asset, or enterprise by the state or a public body representing a community, as opposed to an individual or private party. Public owne ...

copper mining company

Codelco Codelco (''Corporación Nacional'' ''del'' ''Cobre de Chile'' or, in English, the National Copper Corporation of Chile) is a Chilean state-owned copper mining company. It was formed in 1976 from foreign-owned copper companies that were nationalise ...

. This company still operates the mine. Workers began to live in other areas. With over of underground drifts, El Teniente is reportedly "the world's biggest underground copper mine", and is the largest of Codelco's operations. Typically more than 5,000 workers were involved in production.''Emol,'' June 20, 2005
''"La Tragedia del Humo":'' A 60 años del peor accidente minero en Chile
(in Spanish) Since 2011, a structural project called New Mine Level (NML) has been underway at El Teniente. It consists of expanding the mine deeper into the hill at 1,880 meters above sea level. The project is being carried out without interrupting the operation of El Teniente Division.

History

According to legend, the El Teniente mine was discovered in the 1800s by a fugitive Spanish official. Exploitation of the resource began in 1819. The best ore was mined manually in what would be called the Fortuna sector, and transported out of the mine by animal, such as ponies and mules. It was worked until 1897, when the high-grade ore was exhausted. In 1904 William Braden (an

engineer Engineers, as practitioners of engineering, are professionals who Invention, invent, design, analyze, build and test machines, complex systems, structures, gadgets and materials to fulfill functional objectives and requirements while considerin ...

from

New York City New York, often called New York City or NYC, is the List of United States cities by population, most populous city in the United States. With a 2020 population of 8,804,190 distributed over , New York City is also the L ...

, United States) and E.W. Nash formed the

Braden Copper Company Braden Copper Company was an American company that controlled the El Teniente copper mine in Chile until 1967 when its copper holdings were nationalized. History Braden Copper Company was founded on 18 June 1904 by E.W. Nash, Barton Sewell, Willi ...

. They built a road for carts and a concentrating plant, which was in operation by 1906. In June 1910, Guggenheim Exploration took control of the mine and provided financing. In 1916 Braden became a subsidiary company of Kennecott Copper Corporation, which was based in

. Chileans have referred to such large-scale copper mining operations as ''La Gran Minería del Cobre'' (a major copper mine). Before nationalization, these operations generated a large proportion of the foreign currency which the country received. In 1945 there was a disaster at El Teniente mine, resulting in the deaths of 355 men and injury to 747 more. It was the largest mining accident in Chilean and has the highest death toll in world history associated with metal extraction. Some 1,000 miners were down in the pits when the fire started in a nearby warehouse. Dense smoke spread in the underground tunnels. Most of the dead and injured suffered

carbon monoxide poisoning Carbon monoxide poisoning typically occurs from breathing in carbon monoxide (CO) at excessive levels. Symptoms are often described as " flu-like" and commonly include headache, dizziness, weakness, vomiting, chest pain, and confusion. Large ...

. Emergency exits were not well marked. In Chile, this incident is known locally as the Smoke Tragedy ( es, La tragedía del humo). In 1967 the Chilean government bought a 51% stake in the mine and founded Sociedad Minería El Teniente. Under this agreement Kennecott built a new concentrator, and the mine expanded production to per day. On July 11, 1971,

President President most commonly refers to: *President (corporate title) * President (education), a leader of a college or university * President (government title) President may also refer to: Automobiles * Nissan President, a 1966–2010 Japanese ...

Salvador Allende ordered the Chilean nationalization of copper, in an effort for the country to gain more benefit from the mines. Corporación Nacional del Cobre de Chile (known as

) was formed, and El Teniente became a state-owned operation. The Chilean government paid Kennecott $92.9-million for the property. The mine increased production to of ore per day, and in 2006 the mine produced over of copper. The

Vancouver, British Columbia Vancouver ( ) is a major city in western Canada, located in the Lower Mainland region of British Columbia. As the most populous city in the province, the 2021 Canadian census recorded 662,248 people in the city, up from 631,486 in 2016. The ...

-based,

Canadian Canadians (french: Canadiens) are people identified with the country of Canada. This connection may be residential, legal, historical or cultural. For most Canadians, many (or all) of these connections exist and are collectively the source of ...

company Amerigo produces both a copper and

molybdenum Molybdenum is a chemical element with the symbol Mo and atomic number 42 which is located in period 5 and group 6. The name is from Neo-Latin ''molybdaenum'', which is based on Ancient Greek ', meaning lead, since its ores were confused with lead ...

concentrate from El Teniente's

tailings In mining, tailings are the materials left over after the process of separating the valuable fraction from the uneconomic fraction ( gangue) of an ore. Tailings are different to overburden, which is the waste rock or other material that ove ...

. It has been granted the right also to treat higher grade tailings from a large, abandoned tailings impoundment near the El Teniente property.

Geology

The copper ore deposits are those of a typical copper porphyry and associated alteration-mineralization. These altered zones include chalcopyrite,

pyrite The mineral pyrite (), or iron pyrite, also known as fool's gold, is an iron sulfide with the chemical formula Iron, FeSulfur, S2 (iron (II) disulfide). Pyrite is the most abundant sulfide mineral. Pyrite's metallic Luster (mineralogy), lust ...

bornite Bornite, also known as peacock ore, is a sulfide mineral with chemical composition Cu5 Fe S4 that crystallizes in the orthorhombic system (pseudo-cubic). Appearance Bornite has a brown to copper-red color on fresh surfaces that tarnishes to v ...

and

molybdenite Molybdenite is a mineral of molybdenum disulfide, Mo S2. Similar in appearance and feel to graphite, molybdenite has a lubricating effect that is a consequence of its layered structure. The atomic structure consists of a sheet of molybdenum ato ...

as hypogene minerals and

chalcocite Chalcocite (), copper(I) sulfide (Cu2S), is an important copper ore mineral. It is opaque and dark gray to black, with a metallic luster. It has a hardness of 2.5–3 on the Mohs scale. It is a sulfide with a monoclinic crystal system. ...

as a

supergene A supergene is a chromosomal region encompassing multiple neighboring genes that are inherited together because of close genetic linkage, i.e. much less recombination than would normally be expected. This mode of inheritance can be due to genom ...

mineral. The ore body surrounds the Braden

Pipe Pipe(s), PIPE(S) or piping may refer to: Objects * Pipe (fluid conveyance), a hollow cylinder following certain dimension rules ** Piping, the use of pipes in industry * Smoking pipe ** Tobacco pipe * Half-pipe and quarter pipe, semi-circular ...

in a continuous ring with a width of 2000 feet. The pipe is a geologic structure in the shape of an inverted cone, having a surface diameter of 4000 feet, and consisting of post-pipe

breccia Breccia () is a rock composed of large angular broken fragments of minerals or rocks cemented together by a fine-grained matrix. The word has its origins in the Italian language, in which it means "rubble". A breccia may have a variety of ...

called the Braden

Formation Formation may refer to: Linguistics * Back-formation, the process of creating a new lexeme by removing or affixes * Word formation, the creation of a new word by adding affixes Mathematics and science * Cave formation or speleothem, a secondar ...

. The boundary of the pipe is marked by this post-pipe breccia and a pre-pipe breccia forming a belt up to 200 feet wide. "The Braden Pipe was a center of strong mineralization and structural weakness before the pipe was formed." Copper mineralization and pipe formation occurred in the

Pliocene The Pliocene ( ; also Pleiocene) is the epoch in the geologic time scale that extends from 5.333 million to 2.58andesite Andesite () is a volcanic rock of intermediate composition. In a general sense, it is the intermediate type between silica-poor basalt and silica-rich rhyolite. It is fine-grained (aphanitic) to porphyritic in texture, and is composed predo ...

or in andesitic flow breccia adjacent to the pre-pipe breccia." Mineralization at El Teniente is thought to be indebted to its position at the intersection of two large fault systems. This favoured the rise of magma and the subsequent circulation of mineral-rich fluids.

Labour disruptions

As of 2007 Codelco employed 17,000 direct-hire company employees and 28,000 contract employees across all their operations. There have been multiple labour disruptions at the El Teniente mine, where about 5,000 workers produce the ore.

1983

In 1983 El Teniente and two other Codelco mines closed when approximately 13,000 workers voted to strike "indefinitely" in protest of a union leader's arrest for calling for an end to military rule in Chile. In total among the three mines, at least 3,300 workers and 37 labour leaders were fired for participating in the strike.

2008

Contract workers went on strike at Codelco mines in 2008. El Teniente and two other Codelco mines were closed, El Teniente for the shortest length. Company employees continued to work; however, striking workers closed access to the mines and threw stones at buses transporting employees from the mine to the town of Rancagua. At least one employee was injured; he was hit by a metal object thrown by a protester on the highway leading to the mine.

References