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Alteration of gold nuggets enriched with Platinum Group Elements (PGEs)

Sperring, Sophie (2017) Alteration of gold nuggets enriched with Platinum Group Elements (PGEs). Honours thesis, Murdoch University.

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Understanding the mechanisms of incorporation, the form, and the solid-state solubility of Platinum Group Elements (PGEs) in gold nuggets at the nanoscale is critical to future works in gold (Au) nanoscale crystallography. Current works looking at similar samples include Mineral company research into extraction methods of similar samples and research in progress at the University of Western Austral using the alloy of the Au samples for medical purposes.

The work completed by this this used Au nugget samples that were taken from Ruby Creek, British Columbia, Canada. The geology specific to the Au samples used is a sub type of the placer alluvial is: Atlin gold placers, which are known for hosting a variety of metals, specific to the Atlin region.

Traditional thought for Au nuggets for monocrystalline structures. This steams from research completed by the minerals industry to extract the gold that lent into mineralogical studies. The gold rich rim consists of spherical particles that do not display the silver rich core parallel lamellae texture. The core structure is truncated where it meets the rim of the particle. No PGE particles within the sample area observed.

As seen with previous studies the Au samples display a rim that is silver (Ag) enriched. The rim could be a leaching mechanism experience by the gold in the presence of aqueous material. The relationship between the Au and the Ag was established as inversely proportional. The PGEs accumulated in the rounded, poly crystalline nanoparticulate Au-rich rim. The rim exhibited greater porosity within this rim area.

Majority of gain boundaries in the silver rich core of gold particles show a pile up of dislocations which result in multiplication of the diffraction maxima. The rim observed on the Au nugget samples were shown to have a PGE accumulation of between 10 to 20 μm.

The presence of the PGEs in solid solution is likely due to their relatively low concentrations and/or association with other trace elements such as Arsenic (As), Selenium (Se) and Sulphur (S), which may help to dissolve PGEs in the gold structure. The distribution seen of the PGEs suggests that during alteration of gold particles under supergene conditions, PGEs are subjected to the enrichment process due to a selective dissolution of Ag. Homogeneous distribution of Ru, Rh and Pd in the gold matrix and lack of PGEs nanoparticles in the pores support this postulation.

The irrefutable evidence obtained from this study is that the PGEs are in solid solution in crystal structure in this sample. Exsolution does not occur at the nanoscale. It can also be said that during the process of alteration, the PGE accumulate in the Ag removed area.

The interest in this project will extend into Nano-SIMS academic activity to have a closer look at the isotopic complexity and to look at the distribution of isotopes of PGEs in gold sample. Looking for exsolution at absolute nanoscales and to see if the isotopes of the PGEs fractionate in the gold formation are also main features of the future work in this area of mineralogy.

Publication Type: Thesis (Honours)
Murdoch Affiliation: School of Engineering and Information Technology
Supervisor: Deditius, Artur
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