The Andes, copper mines and volcanoes of Chile!
Intro: Chile is one of the best countries in the world for geology and metal deposits. It’s elongated western margin is bounded by an earthquake-inducing, mountain-building and ore deposit-forming subduction zone! I recently took part in a field course run by our university that explored the northern-region of the country where the Atacama desert and some of the largest copper deposits in the world are located. In this post I will highlight some of the places I went and talk about the general geology of Chile, it’s ancient and active volcanic arc, and some of it’s largest copper deposits.
Science Spiel: Mountains, volcanoes and copper (Geology, Volcanology, Ore Deposit Geology)
Chile is home to the Andes. The Andes are the longest mountain chain in the world, and the run parallel to the western coastline of South America. The mountain chain formed < 570 Ma when the Pacific oceanic crust began subducting eastward, underneath South America (Jordan et al., 1983; Stern, 2004). The Andes are the most ideal example of an orogenic system, where the compressive forces of the subducting oceanic plate created large fold-and-thrust belts and elevated the Andes mountains to the high elevation they currently reside at. We could see the expression of this beautifully at the Valley of the Moon and Salar de Atacama, which are folded evaporate beds and a salt lake, currently at > 2500 m above sea level (asl). The Salar de Atacama is also one of the largest modern halite systems on earth!
An active volcanic arc in Chile is resultant from the subducting Pacific oceanic plate, and has this arc has migrated from west to east since its initiation ~ 570 Ma. Plutonism and volcanism has migrated with time and the current active volcanoes are therefore at the far east margin of Chile, near the border of Argentina.
We drove near some of these volcanoes, such as Volcan San Pedro (6145 m asl) Volcan San Pablo (6092 m asl) and Cerro Palomna (6023 m asl) in northeast Chile, and Volcan San Jose (5865 m asl) in east-central Chile. However, the story isn’t as simple pure subduction and volcanoes. The ~570 Ma history the subduction zone has experience transient periods of accelerated convergence rates of subduction, different angles of convergence, and areas of flat-slab subduction (i.e. where the subduction of off-shore sea mounts and other buoyant features had created a shallow-angle of subduction along the margin; Isacks, 1988). The areas of flat-slab subduction and absence of volcanism are where the majority of the copper and gold deposits in Chile are located…
Northern Chile has some of the largest copper (± gold ± iron) deposits in the world. These copper deposits formed from a combination of factors, but are generally associated with intrusive-extrusive magmatism and tectonic activity on the western boundary of the South American plate (Davidson, 1987; Camus, 1990; Sillitoe and Perelló, 2005). The eastward migration of the volcanic arc (i.e. tectonic activity) has resulted in an east-west zonation of several metallogentic belts that developed on the margin (Sillitoe and Perelló, 2005). Belts are interpreted as reflection of changes in the tectonic setting and igneous activity during the evolution of the Andean oreogen (Skewes and Stern, 1994; Mpodozis and Perelló, 2003).
These copper deposits are known as “porphyry copper” deposits (due to their association with a porphyritic-intrusion), and most of these formed during the Eocene to Oligocene in Chile (~ 43 – 32 Ma; Mpodozis and Cornejo, 2012). Examples of some of the giant porphyry copper deposits that are Chuquicamata and Rio Blanco-Los Bronces. I got to visit some of these copper deposits, which are now active mines… and the sizes of these operations are absolutely incredible! We also went to a massive magnetite (i.e. iron) mine called Los Colorados. The magnetic content of the rocks is so large that the dust is magentic enough to build up on a pen-magnet and show the polarity of the earth’s magnetic fields!
Final Thoughts: I was extremely fortunate to be able to participate in a course that took me into the heart of an ancient copper-rich and modern volcano-rich region of earth. The scope of the volcanoes and the amount of copper, gold and other precious metals contained within this narrow north-trending country of Chile is awe-inspiring. I briefly touched on the metal-endowment in this blog post, insteading giving a more broad overview of what makes Chile so spectacular geologically. As a researcher in copper and gold porphyry deposits I could think of no other place that exemplifies the ideal end-members of our understanding of what these large copper (and sulfur) anomalies are.
In conclusion, not only is Chile a beautiful and exhilarating country to travel and explore, but it has a thriving economy fueled by the spectacular endowment of copper and other metals embedded within it’s land. What a fantastic way it is to explore a country by learning the earth science of it all! Well, that’s my opinion… but maybe I’m a bit biased!
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