My interests are focused upon enabling materials research at the nanoscale via the microscopy techniques of atom probe tomography (APT) and field ion microscopy (FIM). APT is a technique capable of material characterisations at the atomic-scale, in which each atom is identified chemically and located in three-dimensions with very high accuracy. Hence, it is a technique rapidly rising in prominence. The Atom Probe Group in the Department of Materials at the University of Oxford is interested and active in all areas of this research across a broad range of material systems.
In particular, I am developing a variety of new analytical techniques to improve the three dimensional reconstructions generated by APT and the subsequent atom-by-atom analysis of the resulting data. I am interested in applying these techniques to the characterisation of a wide variety of systems to inform materials research projects.
A Nanoscale Investigation of Carlin-Type Gold Deposits: An Atom-Scale Elemental and Isotopic Perspective
Carlin-type gold deposits are one of the most important gold mineralization styles in the world. Despite their economic importance and the large volume of work that has been published, there remain crucial questions regarding their metallogenesis. Much of this uncertainty is due to the cryptic nature of the gold occurrence, with gold occurring as dispersed nanoscale inclusions within host pyrite rims that formed on earlier formed barren pyrite cores. The small size of the gold inclusions has made determining their nature within the host sulfides and the mechanisms by which they precipitated from the ore fluids particularly problematic.
This study combines high-resolution electron probe microanalysis (EPMA) with atom probe tomography (APT) to constrain whether the gold occurs as nanospheres or is dispersed within the Carlin pyrites. APT offers the unique capability of obtaining major, minor, trace, and isotopic chemical information at near-atomic spatial resolution. We use this capability to investigate the atomic-scale distribution of trace elements within Carlin type pyrite rims, as well as the relative differences of sulfur isotopes within the rim and core of gold-hosting pyrite.
We show that gold within a sample from the Turquoise Ridge deposit (Nevada) occurs within arsenian pyrite overgrowth (rims) that formed on a pyrite core. Furthermore, this As-rich rim does not contain nanonuggets of gold and instead contains dispersed lattice-bound Au within the pyrite crystal structure. The spatial correlation of gold and arsenic within our samples is consistent with increased local arsenic concentrations that enhanced the ability of arsenian pyrite to host dispersed gold (Kusebauch et al., 2019). We hypothesize that point defects in the lattice induced by the addition of arsenic to the pyrite structure facilitate the dissemination of gold. The lack of gold nanospheres in our study is consistent with previous work showing that dispersed gold in arsenian pyrite can occur in concentrations up to ~1:200 (gold/arsenic). We also report a method for determining the sulfur isotope ratios from atom probe data sets of pyrite (±As) that illustrates a relative change between the pyrite core and its Au and arsenian pyrite rim. This spatial variation confirms that the observed pyrite core-rim structure is due to two-stage growth involving a sedimentary core and hydrothermal rim, as opposed to precipitation from an evolving hydrothermal fluid.