¡¡Field Trip!!

Last Tuesday, the 25th of November, we had a field trip for my mineralogy class and we went to a pegmatite mine and a greisen. It was amazing, mostly because it was a field trip, but we did get to see some fun rocks.

The first mine that we went to was nearly in Portugal. We could see Portugal from the mine, and I could have jumped over the river that separates Spain and Portugal. I had brought my passport because the field guide said in bold letters that the mine was not in Salamanca (meaning the province), and since I'm not an EU citizen, I could have problems getting into different countries. As it turned out the mine was not officially in Salamanca because it was in an international park on the boarder, but I guess it's better safe than sorry. Also, the mine was not really a pegmatite mine, because they hadn't actually gotten to the pegmatite yet, and they were just mining the aplite in veins above the pegmatite. The mine was started as a cassiterite mine, since the cassiterite formed at the margins of the intrusion, but now they also mine REE's and uranium. According to my professor, this area of Spain has some of the richest uranium deposits in Europe.


A typical zoning pattern in this mine. The top of the rock is slate, followed by an area that contains cassiterite and muscovite, which is followed by a quartz and spodumene zone, and then there's the aplite, which is rich in quartz, lepidolite, and alkali-feldspars.


Andalucite and cordierite porphyroblasts

The mine wall with lots of interesting veins.

Portugal!!!

The second mine that we went to had some historical significance. It was a scheelite, arsenic, and kaolinite mine, and during WWII, the Spanish (who were officially neutral) mined scheelite and sold it to the Germans. However, since Portugal was an ally-leaning neutral country and this mine is visible from Portugal, the Spanish mined the scheelite by night and carried it across the country by donkey. Luckily for the Spanish, scheelite has interesting fluorescent properties, which made it easier to mine by night. Right now, there's also a British company looking into re-openning the mine, but they have to figure out what to do with all of the arsenic-rich water that's in it right now.

Slickenfibers! on faults associated with the formation of the greisen. I think that they were indicating movement of the footwall in the direction of the pencil.

Arsenic-rich pond and more Portugal, although Portugal is a little further away in this picture. It's just visible as hills in the distance.