It is widely accepted that most Archaean granite–greenstones are dominated by TTG, although Late Archaean terranes, such as in the Yilgarn Craton, are dominated by potassium-rich granitoid rocks that are derived through remelting of older felsic TTG-dominated crust.
Archaean |
Nevertheless, ancient Archaean lead ores of galena have been used to date the formation of Earth as these represent the earliest formed lead-only minerals on the planet and record the earliest homogeneous lead-lead isotope systems on the planet.
350 km to the west of Johannesburg and the Witwatersrand reef (the ridge that contains the gold), the mines around Barberton contain visible nugget gold in quartz veins, in addition to fine particles, that are embedded in metamorphosed late Archaean age rocks dating to 3.2-3.4 billion years ago.
The Acasta Gneiss in the Canadian Shield in the Northwest Territories, Canada is composed of the Archaean igneous and gneissic cores of ancient mountain chains that have been exposed in a glacial peneplain.