A Review of Mineralization in the Bushveld Complex and some other Layered Intrusions

Abstract

Layered mafic intrusions are significant sources of the platinum-group elements, base metal sulphides, chromite, magnetite, and ilmenite. The distribution of these ores is reviewed, with special attention to the economic deposits and subeconomic occurrences. The geological setting, composition, mineralogy, and textures of the ores are described for the Bushveld and Stillwater Complexes, the Great Dyke, the Munni Munni Intrusion, complexes in Finland, and some smaller intrusions. Both the platinum-group element (PGE) mineralization and the often associated base metal sulphides have characteristic geochemical and mineralogical styles; these are variable in even a single layered intrusion, and are even more so when different intrusions are compared. The distinction between constant and variable metal contents in relation to thickness variations of the PGE sequences is emphasized. Oxide ore deposits are less variable but the compositions, especially for chromite, are specific to the layered intrusion in question. Subsolidus re-equilibration and ore-mineral alteration are usually present as variable processes in all the mineralized sequences. Mineralization models are briefly addressed in the light of these variations. The primary geochemical character of PGE ores, and the occurrence and character of the oxide ores, probably reflect the influence of the magma source region at depth rather than processes in the magma chamber at the site of emplacement. © 1996 Elsevier B.V. All rights reserved.