Platinum-group element mineralisation in the Great Dyke, Zimbabwe, and its Relationship to Magma Evolution and Magma Chamber Structure

The platinum-group element (PGE) resources of the Great Dyke are second only to those of the Bushveld Complex and principally comprise the potentially economic Main Sulphide Zone (MSZ) and the thicker, but lower grade, Lower Sulphide Zone (LSZ). Located a few tens of metres stratigraphically apart within the uppermost P1 Pyroxenite of the Ultramafic Sequence, both mineralised zones are present in all remnants of the PI Pyroxenite along the entire length of the Great Dyke. Other less significant PGE mineralised zones include chromitite C1d, in dunites and harzburgites a few tens of metres beneath the PI Pyroxenite, the Middle Mafic Unit of the Mafic Sequence and the Mineralised Marginal Zone of the extreme marginal facies and Border Group. This paper describes the general geology of the Great Dyke, and the stratigraphic and structural setting and internal characteristics and lateral variations of the main PGE mineralised zones. The stratigraphic location, complex internal layering and systematic transverse variations of the MSZ, LSZ and chromitite C1d are here related to the emplacement and the chemical and physical evolution of the magma body and to the structure of the magma chamber.