The Witwatersrand goldfield forms
Rivers concentrate gold into gravel beds that will eventually yield nearly half the gold ever mined.
- When
- —
- Duration
- 60 million years
- Known to
- ± 40 million years
- Era
- Mesoarchean, Archean
Between about 2.90 and 2.84 billion years ago, braided rivers deposit conglomerates on the Kaapvaal Craton, concentrating gold with pyrite and uraninite. That uraninite survived at all is itself evidence the atmosphere held no oxygen — it would have dissolved otherwise. The basin has produced roughly 40% of all gold ever recovered on Earth, and the city of Johannesburg exists because of it.