Great pic that brings back memories of my years working on the...

Great pic that brings back memories of my years working on the Wits (the real one). One thing that you will notice is the presence of what we used to term bedding parallel fractures. These are those lineations that pass through the clasts (typically pebbles or cobbles) and hosts the gold and carbon. Many reefs do not contain much carbon but many do. These fractures are mostly simple dilation (with pressure fringes) but can be shears (rotated pressure fringes) or splays where the brittle deformation bifurcates (third pebble from LHS) and later dies out in more plastic deformation in more arenaceous material. Another thing that is evident is the cataclasis that is ubiquitous in the Wits reefs where clasts are literally ground up in situ in places of movement. Look below the market py-c and how that quartz clast above it has been terminated on one site in the zone of cataclasis. Also the rounded clast above py-p. All this is damning evidence for some shock / dynamic metamorphic event. Alan Spry wrote a book called "Metamorphic Textures" and the chapter on Dynamic/Shck Metamorphism describes exactly what we see in the Wits in the reefs.

The paragenisis is very clear. Uranium first, then carbon then gold. Uranium start off as a rounded clasts, then gets fractured and infiltrated and even assimilated by carbon (radiogenic polymerisation). Gold precipitates on the outside of the carbon and away from carbon but in the presence of carbon.

Uranium also alters to brannerite and uraniferous leucoxene (very fine, cannot be resolved). Gold also precipitates on the leucoxene.

Note the gold is very fine grained, typically <50µm.

The question is do we see these features in the Pilbara?