Submitted by Andrew du Toit on Tue, 24/11/2015 - 10:34 | Last updated: Tue, 24/11/2015 - 10:34
The Kariba porphyritic biotite granitoid gneiss is coarse-grained, with a weak gneissic fabric, and contains large K-feldspar phenocrysts, and numerous decimetric slab-like mafic xenoliths. It contains small garnets rimmed and replaced by biotite. The zircons dated have oscillatory zoning in the centre (of igneous origin), but the margins have been affected by metasomatic alteration zones, and in some cases have discrete overgrowth rims. The zircons have yielded ages of 1962.9 ± 8.5 Ma and 2.1-2.17 Ga.