El Teniente: A Deep Dive into the World's Largest Underground Copper Mine
El Teniente, high in the Chilean Andes south of Santiago, is the largest underground copper mine in the world — and the longest continuously operated copper mine anywhere. Sewell, its abandoned company town, is a UNESCO World Heritage Site.
Geology
El Teniente is a vast porphyry copper deposit centred on the Braden pipe, a 1.3 km-diameter breccia funnel rich in chalcopyrite. Total contained copper exceeds 100 million tonnes — more than any other single deposit.
History
Copper extraction at El Teniente began in 1905 under American ownership (Braden Copper Company, later Kennecott). Production was initially shipped via the Andean railway to Rancagua. The mine was nationalised by Chile in 1971 under the Allende government.
Sewell — the city of stairs
Built on a 35 % gradient on the slopes above the mine, Sewell housed up to 16 000 workers from the 1910s to the 1970s. Connected only by stairs — no streets — it was inscribed by UNESCO in 2006.
Codelco era
Since 1971 the mine has been operated by Codelco, the Chilean state copper corporation, now the largest copper producer in the world. El Teniente accounts for around a third of Codelco output.
The mine today
El Teniente extends over 3000 km of underground galleries and is currently being deepened by the New Mine Level Project, intended to extend operating life to 2068.
Visitor access
Sewell is open to tours operated by VTS Chile from Rancagua — a full-day excursion including the railway, the city itself and several active mine viewpoints. Underground tours are not generally available.
Mining methods
El Teniente pioneered block caving on a vast scale — large blocks of ore allowed to collapse under gravity and drawn out through draw points. The technology was developed here and exported worldwide.
Cultural legacy
Chilean labour culture, from the 1907 Santa María de Iquique massacre onwards, owes much to the copper miners' unions. El Teniente and Chuquicamata were the laboratories.
Practical advice
Tours run year-round but weather above 2000 m can close the road. Bring warm clothes, water and altitude tolerance — Sewell sits at 2200 m above sea level.
Explore on the map
Find El Teniente and related mining heritage sites on the interactive map, with opening hours and accessibility notes.