USC Dana and David Dornsife College of Letters, Arts & Sciences > Blog

June 24, 2013

Deep in a mine, deep back in time

Filed under: Andean Fossil Hunt — admin @ 7:55 pm

Monday June 24
9:30 pm
Another wild day of adventure in the jungle.

 

Sampling rocks from the walls of the mine

Sampling rocks from the walls of the mine

 

I spent the morning deep underground, and deep back in time. I’ve got a schematic of the mine that shows how deep down we were, and how far from an exit, but I haven’t read the specifics yet. In particular, I avoided reading this while actually in the mine.

 

These dark mudstones record the slow accumulation of marine sediments

These dark mudstones record the slow accumulation of marine sediments

 

At the moment I’m interested in a series of black shales between fifty and two hundred meters thick, laid down some time in the Early Jurassic sea. Shales weather into mud, so in the jungle, farm, high plains, or mountains, they’re not well enough exposed to examine the conditions of the sedimentary environment. But underground, in a freshly cut tunnel through the mines, the rocks are as fresh, complete, and well exposed as one could dream about. We got a quick look yesterday, and made arrangements to spend the this morning taking samples.

The idea was that I would measure the section and mark the sampling sites with red paint, then the team would follow behind and make the samples. Taking samples requires time and caution. The rock needs to be selected from the correct level, with a piece likely to show sedimentary or fossil features. The piece needs to be labeled with a number, a location, a date, etc.

It was dark, and LOUD. We sloshed through water up to our boots, and searched for signs both geological and man-made on the walls of the tunnel. We could have been in the middle of the world. It was actually a huge relief that every 20 minutes or so a truck or huge earthmover would drive through. We’d stand along the walls or in an alcove to let it pass. Very strange to me was when individual miners would pass by on foot. A point of light in the distance would materialize into a person who, after brief greetings, would continue down the impossibly dark long tunnel in the other direction.

Every time miners came by they approached us, shook hands, exchanged greetings and questions. In general people here are very big on introductions. People will stop what their doing in an office, walk across the room, shake my hand, exchange greetings, then go back to work. Its awkward for me that the standard greeting with women is a little cheek touch, without actually kissing, but making kind of a kissing sound. I’m just too uptight and American to do this with total strangers. Guys seem to recognize this, but they don’t want to be rude either. Ever experience that encounter where one person moves in for a hug and the other for a handshake? Same thing, only more awkward. Anyway, in the mine there’s no kissing, haha, but certainly lots of handshaking. I think maybe spending one’s day in the dark and noisey and challenging depths makes human contact all the more vital and welcome.

It was an adventurous experience and a scientifically challenging one. We used all of our heads to compare the schematics with what we saw in the rocks and with our expectations. In the abstract we conceive of sediments deposited over time slowly in a marine environment. This turns into rock and we can, 200 million years later, sample those same sediments for chemical signs of life and environmental conditions. But a lot went on in those two hundred million years. Building the Andes, for example. And these rocks are smack in the middle of it. This introduces breaks and faults in the rocks, fluids that burn through and bring new minerals, ore deposits, and destructive forces that change the chemistry completely.

 

Those aren't fossils! Carbonate sediments in this rock core are scrambled with minerals added by hydrothermal fluids. Sometimes this adds ore, which is why there's a mine here.

Those aren’t fossils! Carbonate sediments (dark grey) in this rock core are scrambled with minerals added by hydrothermal fluids. Sometimes this adds ore, which is why there’s a mine here.

 

The sampling was altogether a success, followed by a lunch on patio overhanging the jungle. Pear juice, empenadas, and as always soup, rice, potatoes, and meat.

The warehouse for cores of rock sampled from the mountains and mines.

The warehouse for cores of rock sampled from the mountains and mines.

 

After lunch I got another treat: the core warehouse. This is where they store all the cylindrical tubes of rock taken with a large drill. From the surface down, or from the mine up, a huge machine can drill out a tube of rock tens of meters long. This can expose the transitions between bodies of rock. The miners keep a huge stock of these to look for valuable ore. For me, they laid out several meters of core that form an example of the contact between two important units. One is terrifically altered, making it promising for mining. The other, my black shale, is fairly intact. An afternoon of photographing and observing, followed by the bouncy ride back to the housing units.

 

 

Home sweet home in the jungle mining enclave

Home sweet home in the jungle mining enclave

They’re putting us up in this lovely house on a property like an old resort. I went for a walk around sunset to look at the jungle. Along the drive from the mine there’s a rope and wood plank swinging bridge high across a rushing river. More than anything I want to walk across it, and indulge my millionth Indiana Jones experience. But, like examining bats caught in my corridor or identifying the butterflies, crossing rope bridges is not what I came here to do. All in due time.

At dinner we sat with some miners and talked about sports and politics. It was good practice for my Spanish which is still very inadequate to hold a conversation. There are just too many holes in my vocabulary. But already I’m doing better than last year, and I’ve only been in the mountains two days. Let’s see how I’m doing in two more weeks.

Thanks all for following! Tomorrow night we move to a different mine, and I may or may not have internet. Hasta luego!

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