I’ve had interesting work to do in collaboration with Dr. Glen Nwaila and Prof. Hartwig Frimmel. The result of which is below posted illustrations of Mesoarchaean-Neoarchaean environments within which the Witwatersrand-type gold deposits formed.
Fig. 1
Fig. 2
Fig. 3
The genesis of conglomerate-hosted (Witwatersrand-type) gold deposits have been debated for over a century. Recent work by Nwaila and Frimmel (2019), Nwaila et al. (2019), Nwaila et al. (2017), and Frimmel (2014) has provided important details on how these deposits were formed. In South Africa, the formation of these deposits involves two-time slices (i.e. the Mesoarchaean and Neoarchaen). During the Mesoarchaean, in the midst of CO2 degassing atmosphere and acidic rains, finely dispersed gold was leached from granite-greenstone rocks (Fig. 3), transported as dissolved Au via palaeoriver systems and precipitated in shallow sea systems where early life forms resided. Preservation of these deposits was brought by continental flood basalts (Fig. 2), an analogy of modern-day Hawaii or Iceland. In their new research (Fig. 1), they have used palinspastic restoration combined with U-Pb dating to demonstrate how younger Witwatersrand-type deposits such as the Black Reef in South Africa was formed through a mechanical recycling of older reefs. Upgrading of the ore grade was facilitated by intense hydrothermal activity. In the next coming months, research papers and presentation by Dr Glen Nwaila and Prof Hartwig Frimmel will be showcasing this latest work.
I’ve done the little illustration part but if you are interested in Witwatersrand geology here are some links to Dr. Glen Nwaila, Prof. Hartwig Frimmel and their colleagues work:
http://www.minsocam.org/msa/RIM/rim81.html
https://link.springer.com/article/10.1007%2Fs00710-018-0650-3
https://www.journals.uchicago.edu/doi/abs/10.1086/701678?mobileUi=0
https://www.journals.uchicago.edu/doi/full/10.1086/692329
https://link.springer.com/chapter/10.1007%2F978-3-319-78652-0_10
P.S. 3D models of the environments: