RELATION BETWEEN THE MOLOPO FARMS AND BUSHVELD COMPLEXES: AN ANALYSIS OF PYROXENE EXSOLUTION LAMELLAE

The Molopo Farms Complex (MFC) is a ~2.05 Ga layered igneous intrusion in Botswana, about 200 km west of the Far Western Limb of the Bushveld Igneous Complex (BIC). The BIC is the world’s largest layered mafic intrusion, and hosts ~85% of the world’s exploitable platinum group elements (PGEs), while the similarly aged MFC has no accessible PGEs and has therefore received less attention. Improved understanding of the conditions of formation of the MFC vs. the BIC may shed light on why and how such large quantities of PGEs came to be concentrated in the latter. The Main Zone of the Rustenburg Layered Suite of the BIC is characterized by complex exsolution textures in pyroxenes. Using optical microscopy and scanning electron microscopy (SEM) paired with an energy-dispersive spectrometer (EDS), pyroxenes with exsolution lamellae from both complexes were compared. Clinopyroxenes from both complexes show two sets of exsolution lamellae along different crystallographic axes, suggesting that the MFC and the BIC experienced similar cooling histories. This finding is consistent with contemporaneous emplacement of similar magma bodies into two different sedimentary basins to form the MFC and the BIC intrusive complexes.