AfricaArray Field School – Day 3

Today started with a short lecture about the petrology and geochemistry of the Bushveld Complex. I was a bit out of my depth, since the last time I used a petrographic microscope in anger was in about 2010. Luckily the bit of prac tutoring that I did last year helped me at least remember what plagioclase and pyroxenite looked like. There are some seriously cool rocks in the BC, and it is absolutely massive.

One million cubic kilometres of mafic magma, between seven and nine kilometres thick. And the age dates suggest that it emplaced and cooled within a million years or so. I mean, that is a lot of magma, in a very short space of time. This made me wonder why it never made to surface, like other large igneous provinces, such as the Deccan and Siberian Traps. Answers on a postcard (or a journal article cover), please.

As a side-note, the Wits Petrology Lab is seriously cool. I think it only opened last year, and it looks like a great place to teach and learn petrology: great microscopes, an easy way for the lecturer to show specific examples of thin sections. I was slightly jealous, I will admit.

The Wits Petrology Lab

We also had some hand specimens to have a look at, including a seriously magnetised piece of magnetite.

Some of the magnetitie is seriously magnetised.

A former Wits geophysics student, Dylan Morgan came in and gave us a talk about what he has been doing for the last 15 years, especially during the hard times. This was really interesting, and I certainly took away some good insights, especially in terms of general approaches to keeping sane and doing interesting things in difficult times in the mining industry.

Sue Webb gave a very interesting talk about the geophysics of the Bushveld Complex and how geophysics can inform new discoveries; this included presenting some strong evidence for the eastern and western limbs being connected at depth, including Bushveld xenoliths recovered from a kimberlite pipe in the centre of the complex.

In order to collect reliable data, it needs to be located accurately. As such, a basic introduction to the GPS systems we will be using was in order. There are two major systems we will use: handheld Garmin eTrex 10s, and a differential GPS. The former are accurate to about five metres, while the latter is accurate to within a few centimetres. It is also a much more serious piece of equipment, which takes some time to set up.

Explaining how to set up the dGPS.

The handheld ones are much simpler to use and explain.

Practice with handheld GPS units.

After that, we continued with the bid creation until supper. I am writing this earlier than usual, because there is a Dutch jazz saxophonist playing nearby, and some of us are probably going to wander over and check out.