Intro: The high Andes in central Peru is home to unbelievably high hills, ridiculous roads, remarkable little communities and funny furry animals. It is also home to beautiful geology and prospective ground for mineral exploration. I recently traversed the roads and hills in this energetic country, and learnt that things are a lot harder to do when you have to do it up high (e.g., > 4 km)! In this post I’ll share a bit of the landscapes and geology of central Peru, and what it is like working at altitude!
The Peruvian Andes mountains
South America is pretty special in that it is one of the only places in the world that has had consistent subduction along the same coastline for hundreds of millions of years! The eastward subduction of the Nazca Plate (i.e., the Pacific Ocean) under South America is what created the Andes mountain chain (i.e., the longest mountain chain in the world) starting ~ 570 million years ago (e.g., Jordan et al., 1983; Stern, 2004). In areas along the coast of South America the angle of this subducting plate is shallow, known as “flat-slab” subduction. Here there is a compression in the crust, which is related to a lack of active volcanoes and a “surplus” of copper ± gold ± molybdenum ore deposits (e.g., Benavides-Cáceres,1999; Noble and McKee, 1999). For more information on this check out my posts on “The Andes, copper mines and volcanoes of Chile!” and “Hidden gold mines and stone forests of Northern Peru“.
One of the most prominent and dominant rock groups of the high Andes mountains are Cretaceous sedimentary rocks of the Marañón fold-and-thrust belt. These were deposited in a basinal environment, which was later folded and contorted (sometimes referred to as thin-skinned deformation), possibly due to the flattening of the subducting plate (Mégard, 1987; Ramos and Aleman, 2000; Scherrenberg et al., 2014).
The Marañón fold-thrust belt was intruded in the Miocene by volcanic and plutonic rocks. The plutonic rocks are evident in the Cordillera Blanca and consist of large granitic mountain range. The volcanics are less visually striking, but still compose lots of the very high mountains, and are typically the host rock unit to more epithermal-type gold deposits in the region (e.g., as in the north near Cajamarca). Towards the coast of Peru the geology is dominated by another large batholith, but this one is much older (Cretaceous, ~ 150 to 65 million years) and is known as the Coastal Batholith.
Working in the Andes
Areas we like to explore in, alas, happen to be very very high up. Some of the places I was in are close to 5,000 metres above sea level! Things work a bit differently when you are so high up… Simply walking up several metres on a steep hill suddenly becomes a struggle for breath! The lack of oxygen and lower pressure can (and typically does for foreigners) induce altitude sickness, resulting in headaches, nausea and other symptoms. It can be more severe and life-threatening though, so it is important to take it seriously! I was lucky and only got a mild-case of it with a headache, but apparently it affects you differently each time you go up, so figures crossed for the next time!
Another thing unique to the Andes, and spotted quite often working at high altitude, are funny furry creatures. These are llamas, alpaca and vicuñas, which are all members of the camelid family and usually live at over 4,000 m! They are all famous for their soft wool which typically composes Peruvian garments. Vicuña wool is the softest and rarest as they are only wild and can be shorn every 3 years.
There are many unique things about Peru, and the central highlands offers exposure to lots of them. Driving through the little towns and communities, and the crazy pencil-thin roads on the steep mountain sides, make you really appreciate how what would be a very challenging thing (i.e., living up here) comes natural to the locals Peruvian of the central highlands. The landscapes in the central highlands of Peru can be both ominous and alluring, making it a challenging but rewarding place to explore… with heights that can literally take your breath away!
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