The Murchison-Thabazimbi-Lineament in northern South Africa is up to 20 km wide, with polyphase deformation traced for more than 500 km, in a punctuated history of more than 2 500 Ma. The east-northeast-trending lineament is one of the world’s most important structures for its Archaean structure, control on Proterozoic sedimentary basins, igneous intrusions and world-class mineral deposits. The lineament penetrates the Archaean granitoid-greenstone terrain where it is the 2980 to 2960 Ma Murchison Belt, an exhumed Archaean island arc sequence with a basal layered meta-igneous complex with Ti-V-bearing magnetites, overlying calc-alkaline volcanic rocks with volcanic massive sulphides, and a mafic-ultramafic volcanic sequence and clastic sediments with orogenic gold-antimony. It lies along a cratonic sub-terrain boundary but is not a suture with ophiolites. Formation, deformation, granitoid intrusion and mineralisation all occurred prior to Limpopo Orogeny to the north at 2672 to 2620 Ma. Murchison Sb-Au mineralisation formed at ~2832 Ma. This makes the Murchison Belt rare as one of the world’s few goldfields with gold known to be introduced prior to the global event at ~2 650 Ma. Murchison antimony-gold mineralisation is hydrothermal, structurally controlled and post-dates belt formation by >100 Ma.

Reference(s)

Vearncombe, J.R., McNaughton, N.J., Porter, J., Zi, J-W. and Talavera, C. 2021. Age of the Archaean Murchison belt and mineralisation, South Africa. (Special memorial volume for Maarten de Wit.) South African Journal of Geology. 124: 315-342. https://doi.org/10.25131/sajg.124.0001