Monday, May 14, 2012

Exploration Geochemistry, Part 1

Exploration Geochemistry.

Sounds vaguely like an oxymoron, right? Or, perhaps more like apples and oranges?

Bear with me, because this is an important one. The wonders of modern chemistry reach far wider in your life than that extra-body shampoo you used this morning. I referred earlier to a bumper sticker seen in Tucson, Arizona, during a huge environmentalist vs. mining company political fight years ago. The bumper sticker said in large, 5-cm (2") letters: "BAN MINING."  In smaller letters beneath this were these words: "Let the Bastards Freeze in the Dark."

Yes, a bit extreme (on both sides) but it points out something. If you banned mining, then you WOULD freeze in the dark. No matter how much you may dislike mining corporations (or oil corporations) on principle - and there are people who don't and people who do - then you should at least think of the consequences:
  • ALL your electricity (and maybe your heat, too) gets to you via copper wires.
  • MOST of the car you drive is made of iron.
  • ALMOST ALL of your heat comes from coal, oil, or hydroelectric dams.
  • THAT computer you are typing on is full of Rare Earth Elements. And copper and aluminum.
  • ANY light you see by, if it doesn't come from the Sun, required mining.
In other words, any comfort you have in your life - even if you were a Clatsop tribal member who met Lewis and Clark on their 1805 visit - came from natural resources around you that had to be harvested. That includes any shelter you live under.

So mining is an unavoidable consequence to living a comfortable life. And geochemistry is as essential to mining as breathing is to you and me.

Years ago I led a US Geological Survey mission to Venezuela. I started the mission and ran it for three years. Our task? to map the southern half of Venezuela - the jungle-covered half. At the time, Venezuela was just completing the first road down the east side of the country to connect with Brazil. The only way into the interior was by dugout canoe or helicopter. From personal experience I can tell you that you don't just "walk" through the jungle. You have to cut your way through it... and for this reason it was almost totally undeveloped when we first arrived. The northern half of Venezuela held all the oil and farm lands - so who needed the dark green southern half, anyway? It was full of snakes! Actually, so was the rest of Venezuela...

We went, paid for by the Venezuelan government, to affect a technology transfer: teach the Venezuelans all that the USGS had figured out in economic geology, exploration geochemistry, and geophysics. Again, from personal experience, I will tell you that we learned at least as much from the Venezuelans as they learned from us. 

Case in point. We arrived in a mining district named Piston de Uroy late one Fall. That was in the days before we figured out how dangerous helicopters really were, and we arrived via helicopter... 

We were directed up a path to a clearing, where a "casita" had been set up. This is, literally, a little house. Actually a frame of a house, with plastic sheeting tied across the top, and hammocks hanging from the frame. This was to be "home" for the next several weeks. I set up my hamaca (Hammock) and the Venezuelan geologist offered to take us to what may have been the biggest gold-bearing quartz vein on the planet Earth: 11 meters thick, and hundreds of meters long. If you recall the last chapter, that had to be a very wide crack that hot fluids passed through until precipitating minerals clogged it off and it became a mineralized "vein" in mining parlance.

"How did you find this thing?" asked the economic geologist among us.

The Venezuelan party chief smiled patiently and noted that we were uphill from a huge gold mining operation centered on where these creeks we were standing on emptied into the Chicanan River. The gold had to come from somewhere... how about uphill from there? Duh.

Then he offered to show us how they had found the Piston vein. We walked down to the mining district, and an obrero (worker bee) threw a batea (a conical-shaped wooden gold pan about 75 cm or a bit over two feet across) into the creek at our feet. With a small shovel he dug into the creek and loaded the result into the batea - which stopped floating in the water. With some practiced rocking of the batea, he threw out the big rocks on the top and let the water lift the lighter material and float it away. After only about a minute, the bottom of the batea had only black sand in it... and some "sparklies." The party chief asked the obrero how many "puntos" (points of "flash" - gold flakes) he counted.

9 puntos...

We then machete-chopped our way up the stream to just above a tributary and repeated this exercise. 

16 puntos.  We hiked farther uphill to just beyond another tributary coming in. 

0 (zero) puntos

We then backed down and went UP that tributary we had just passed. 

26 puntos. With only about an hour's effort, we were standing at the base of the Piston Vein this way.

I would call this a primitive - but stunningly effective - example of exploration geochemistry. It works!

Next chapter: Exploration Geochemistry, Part 2 - How to use halos to home in on the bacon.


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