At this point in my column you may be thinking, “So you crash around in the forest and carry around a lot of rocks, but what do you actually do? Why are you being paid to do this? Are you making this job up and just running around Northern Ontario for four months?” To that I say I promise it’s a real job… I am “mapping geologic bedrock”. What does that mean? Put simply it means identifying the rocks that I see. Yes, someone is paying me to identify rocks.
But there’s more to it than that. When I go out for a day, be it on a foot traverse through the forest or an ATV drive down a path or just along the highway in the truck, I have a number of things I have to do. The first is stop when you see rock. Sounds simple enough, right? Wrong. You can’t just stop for any pebble you see, people! Have standards! Everyone knows boulders are useless for bedrock mapping because they were just deposited there from some clumsy glacier rolling through! Wait, not everyone knows that? Ok, so we don’t focus on rocks that aren’t clearly part of the underlying bedrock of the area. The purpose of a geologic map is to show people where they can find certain rock types and thus maybe expect so see certain (gold) mineral deposits. So, if you see a giant granite boulder in an area, you ignore it until you see a large outcrop of granite. And then you continue to ignore it because it’s a boulder and we ignore those.
Once you’ve found your outcrop, you usually have to peel a lot of moss off it. Don’t feel bad about this because the rock was there first. That way you can get a better picture of what you’re looking at: are there pillows? Is there breccia? Could that be a fold? Is that patch there lichen or some kind of xenolith? Then let your supervisor take a look at the rock and do the hard work of asking questions while you take out the tools of your trade.
First, you’ve got to mark the spot in your GPS, then use your bright orange flagging tape that’s going to get ripped off or blown away and never seen again to mark your spot visually on a nearby tree or bush – in case people have a hard time distinguishing rock from tree (this can be surprisingly difficult sometimes). The next thing you do is use your magnetic susceptibility meter. This thing measures, you guessed it, the magnetic susceptibility of the rock. This has some ulterior geophysics application that I will never profess to understand… until the end of next term when I should have understood enough of the course I’m supposed to take on it to pass.
Finally comes my favourite tool: the rock hammer. If you’ve done therapeutic boxing or just like to hit things to get your stress out, you might understand why I enjoy this part of the job. Some call this “sample collection”, I call it smashing rocks. We’re supposed to get a big hunk of rock so that a “thin section” can be made of it later for a study of the rock’s textures under microscope. We also need to collect chips of fresh unweathered rock for chemical analysis. This means I have to smash at the rock until there is only fresh surfaces on it. Sometimes this can take up to 20 minutes if the rock is really hard to break. Yes, my hammer weighs 4 lbs but I don’t have a blacksmith arm… yet. Sometimes I stand there wailing at the rock again and again to no avail. And then finally something in you or the rock breaks and it shatters under your hammer. Thor, I feel a new connection to you, man. I used to think hammers were dumb, but I really get it.
There are also a bunch of measurements and information that need to be recorded. These include the direction and orientation of veins in rock and the way a rock may have been sheared. Days are long stretches of looking for outcrops and taking down the measurements from about 8 AM to as long as we can hack it, or until we can get out of the forest, which sometimes takes longer than expected.
When we get back with all our samples at the end of the day we sort them into buckets for later lab analysis. After that, we input the data from our magsus meters into the mysterious spreadsheet. It’s extremely interesting but tiring as well and unfortunately there’s no engineering involved. I have no idea what I can possibly write my work term report on and the internet here isn’t really conducive to a literature review. I guess time can only tell what I’m going to do; in the meantime I’m waiting for a director to get here and interview us for a movie he wants to make about geologists in the field! I’m starting to fit in.
Pillows: Small lava flows that form in rounded “pillow-shaped” blobs. They’re interesting to see in the field and can sometimes have very distinctive “rinds”, the material between pillows, due to sulfides which cause a rusty look or hyaloclastites which are caused by very rapidly cooled volcanic material which is brecciated.
Breccia: Broken up rock chunks held together by a matrix of different rock material.
Xenolith: A foreign piece of rock embedded in a different rock type.
Geophysics: I haven’t taken that course yet, stop asking me about it!