A Brief Science Diversion
Hands up if you’ve heard of pseudotachylite? No? Neither had I until 1984 when – as a fresh faced geology graduate- I landed my first job underground in the South African gold mines. To be honest, I’d never heard of tachylite let alone pseudotachylite. One’s real and the other a poor copy? I didn’t have a clue. Then at 21 I started a 3-year contract working down a deep hole in the Witwatersrand Basin where pseudotachylite – which I’ll call PT because I can’t be arsed to write it out every time- became part of my every day geological life.
The Wits mines exploit ancient gold-bearing gravelly rocks accumulated in a huge sedimentary basin; a 2.7 billion-year-old accumulation of what were once sandstones and conglomerates but are now metamorphic quartzites. The basin was big, possibly 300km or more along its long axis and the experts tell us it looked a little bit like the photo below. Huge fan deltas formed where 5 or 6 rivers flowed into a large depression or basin.
