| Summary: | The behaviour of platinum-group elements (PGE: Ir, Os, Rh, Ru, Pd and Pt) on a nano level may be the key to the enrichment of PGE in mafic ore bodies, like the Bushveld complex. Temperature controlled sulphide melts were used to investigate possible PGE-rich nano phases or clusters, in a magmatic environment, and the influence these structures may have on PGE enrichment.
The sulphide portion of a natural Cu-Ni-S ± PGE system was mimicked experimentally. Sulphides are of the first minerals to form in a magmatic system and more likely to carry PGE-clusters. Samples were prepared using the dry powder silica tube technique. The starting powders consisted of a base mixture of an S, Cu and Fe. These were doped with variable concentration of PGE (either Pt or Pd or Ru) and chalcogene ligand (As). The samples were cooled at different rates to monitor the influence of environmental changes (time, chemistry, kinematic- and thermodynamic) on possible cluster formation.
A variety of primary and secondary nano structures (<100nm) were measured in the synthetic samples, using semi-quantitative scanning Auger microscopy (SAM). The size, morphology and composition of the nano entities were a function of the PGE-system (chemistry) and allowed cooling time. The structures formed irrelevant of the PGE concentration. Several of the identified nano structures were re-classified as potential PGE-clusters. These structures fall within the size range of clusters (10-100nm) and were a good indication whether clusters could form.
Although no conclusive clusters were measured evidence from time of flight secondary ion mass spectrometry (TOF-SIMS) analysis supported the notion that the PGE can form PGE-ligand agglomerations of 10-100nm. Scans showed irregular distribution of PGE-ligand ion bundles in compatible and incompatible phases. The PGE-ligand bundles were conclusive evidence that potential clusters can stay preserved in a system with changes in environment.
If this interpretation is correct, it might indicate that a physical enrichment process is at work during the early stages of crystallization in a magmatic environment. However clustering is only one of several mechanisms that may contribute to PGE enrichment of Bushveld-type deposits
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