On Tuesday we drove to the Steelpoort River Valley, about a hundred kilometers away. Work on a new dam and road has begun since we were here last, in 2006 and 2007. Once it’s finished, the dam will flood much of our field area, submerging some of the rocks we are studying. It’s a good thing we collected some when we did. The project will bring running water to the Sekhukhune villages, where most people still rely on outhouses and water delivered in drums.
To build the dam, the department of water affairs is buying up the surrounding farms but ownership is not always clear. Electric fences and locked gates line much of this land and on our first day of sampling, we had to contact both the farmers and the department of water affairs to ask for access. We also notified the district magistrate and local police to be safe.
In this region, we’re studying how Bushveld Complex rocks were intruded, or thrust, into “country rock,” a mix of granite, granite-lavas called granophyres, and other lavas we were sampling earlier in the week. My research suggests that the lavas and possibly the granophyre originated in the Bushveld Complex. In that case, the Bushveld would not have been intruded into these rocks. The contact among these layers is particularly important for us in testing this hypothesis while we are here.
Today we slogged up a valley of thorny trees where the Bushveld, granophyre, granite and lavas have all been mapped. At one point, while stopping for water, we heard loud barking – almost like a dog. I worried it might be an angry animal. We never caught a glimpse but figured out later it was probably a bushbuck, similar to a deer.
On our hike we found a black rock with pink cross-sections of feldspar, probably lamprophyre, the rock that cross-cuts the rocks we are studying and that may be related to a younger magmatic event in this area. Eventually, we locate a place where Bushveld rocks are touching leptite, a rock formation that has been heated, melted and recrystallized. The leptite in this area has pink veins of granophyre surrounding what may be sedimentary rocks. If you squint, you can almost imagine the granophyre melting into the grey blobs of sedimentary rock.
In the coming days, we hope to visit more areas with this type of contact to collect samples that will tell us how the chemistry is changing from one place to another.
