Sulfide Mineralization and Associated Platinum Group Elements in Mafic-Ultramafic Units of the Tantalite Valley Complex, Southern Namibia

Abstract

Abstract The formation of an immiscible sulfide melt, with associated base, semiprecious, and precious metals, is an important ore-forming process in mafic-ultramafic systems. These magmatic deposits are of great economic importance because they are our primary source of global platinum group element (PGE) reserves—metals that will play a crucial role in facilitating the green energy transition. This study focuses on the Tantalite Valley Complex in southern Namibia and the formation of sulfides within mafic-ultramafic layers, as well as their potential to host valuable metals (PGEs + Ni-Cu-Co). The study investigates the source of sulfur, the fractionation of precious metals between sulfide phases including subsequent alteration assemblages, and the textures and distribution of these minerals, as well as approximating the R factor of the system to assess the mineralization potential of the complex. In situ sulfur isotope and S/Se studies suggest that the origin of the sulfur in the system was derived from the mantle. Sulfide saturation likely occurred because of high degrees of crystal fractionation, and the resultant immiscible sulfide melt percolated into the ultramafic layers (notably an orthopyroxenite layer), accumulating in the basal parts of the magma chamber. Noble metals exist in both solid solution and discrete precious metal-bearing minerals found closely associated with sulfide phases. The R factor for the complex stands at approximately 3,000, which suggests that a small fraction of sulfide melt formed and mixed at moderate to high degrees with the silicate magma. This study provides the first indication of PGE occurrence, and thus further prospectivity, in a poorly explored mafic magmatic suite located in the underexplored geologic terrane (i.e., the Gordonia subprovince of the Namaqua Natal metamorphic province).