The Great Dyke is a layered complex similar to that of the Bushveld Complex. It extends for 550 kilometres and has a maximum width of 11 kilometres. Within the Great Dyke four geological complexes are known to contain PGM and base metal deposits. These are the Wedza Complex (Mimosa – Aquarius and Implats), the Selukwe Complex (Unki – Anglo Platinum), the Hartley Geological Complex (Hartley and Ngezi Platinum Mines – Zimplats) and the Musengezi Complex. The Hartley Geological complex is the largest of the PGM bearing complex’s containing 80% of the known PGM resources in Zimbabwe.
The stratigraphy is broadly divided between a lower ultramafic and an overlying mafic sequence. The ultramafic sequence hosts the P1 pyroxenite, which in turn hosts the economic PGM-bearing Main Sulphide Zone (MSZ). The MSZ is a continuous layer generally between 2 to 3 metres thick. Optimal mineralisation varies.
Mimosa has a well-defined grade profile where peak base metal and PGM values are offset vertically, with palladium dominant at the base, platinum in the centre, and nickel towards the top. Visual identification of the MSZ is difficult.