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, and some of these plutonic rocks are evident in the Cordillera Blanca (one of many large granitic mountain ranges). 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 Peru, 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.
Final thoughts
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!
-Stephanie
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Hi Stephanie
Thanks for the Central Andes notes and photos. Certainly a remarkable place to do geology.
I’m a retired geo, living in Lima. I just read your two Lihir papers in Econ Geol 113,
congratulations on a great job. I was there as site manager in 1983-84, when we found Lienetz on the basis of the vegetation anomaly, mostly. Minifie was discovered a couple of year later by Rod Davies. Our exploration manager, Gavin Thomas, gave the name Lienetz to that deposit, although the real name of the hill is something like Linataenetz as far as I remember.
I wonder if anyone remembers where the name Minifie comes from. It is named after a Lihir Geo, Graham Minifie. Graham was killed on October 9, 1986, in a helicopter accident in the PNG highlands, which also took the lives of Greg Drake (another geo) and the pilot Mike Massey, and severely injured Bill Somboba. The accident happened when the helicopter was on the way back late in the afternoon to pick me up from my sample site. We found the wreckage and the one survivor the next day. Your Econ. Geol. papers papers got me thinking about those PNG days, not all of them good, but the early days on Lihir were an exciting time.
Hi Dave,
Thanks for the compliments, glad you enjoyed the two Lihir papers. My work is obviously built upon the years and years of previous work at the Lihir deposit from maybe other people 🙂
I remember seeing photos from back in the days when Lihir was initially found, looks very exciting indeed. I didn’t know where the name Minifie came from, but I’m glad you wrote about it, even though it is quite sad to hear. It is very dangerous in the highlands with helicopters, even nowadays…
Thank you again for the feedback and sharing your story, it is nice to hear from someone who used to work there. If you have any photos from then it would be neat to see them, my email is sykorastephanie@gmail.com if you do and want to send them. All the best!
-Stephanie
Wow! Must be more than twice as many alpacas as we’ve ever seen in an antelope herd (about 50).
And that’s high! we live just under 3 km (just over 6000 feet, about 20 air miles west of the Rocky Mtn Continental Divide).
We do enjoy getting out and “rockhounding” (not geologists, but we like it, and I grew up near an iron mining town.) 2 weekends ago my daughter and I were out some 60 miles from the nearest gas station, and found a tiny vivid green something in one of our samples. Might be either copper or turquoise; don’t know. (A few years ago our daughter and son were out there again, that time 80 or 90 miles from that gas station, and found a group of anthills just filled with grains of hematite. Only, according to the geologic maps we’ve seen, there should be no hematite within more than 100 miles of there – just sedimentary rock. But looks like the ants haven’t seen those maps!)
Very interesting; very good pics. Keep it up. I’ve gotten more & more impressed with the University of Tasmania.
Hi Peter,
Wow, so living at 3 km is pretty high too, I guess you get used to it after a while? Interesting story about the anthills and hematite. Sometimes hematite can form as a secondary “weathering” process and is often not on geological maps as it is too small and not a main rock unit. Not sure what the vivid green thing is in your samples, but feel free to send me a photo and I can try and identify it for you.
Thanks again for the comments and following along with my blog, cheers 🙂
-Stephanie
Beautiful photos once again. Thanks for sharing!
You’re welcome! Thanks Marina 🙂
Love your blog and photos. I’ve always been interested in geology and plate tectonics and you make it all look so awesome!
Thank you very much Sandy, glad I can make it look awesome for you 😉
I can’t wait for watching a video about this trip! Always a pleasure to read more about geology!
Thanks Billy! 🙂