Reading Gold: Investigating the link between chemical composition, microstructure and geological history of gold

Unlike gold fabricated from smelting operations, natural gold formed in hydrothermal systems may be highly compositionally heterogeneous. Tracks or enriched zones of Ag, Cu, Hg or Pd may be revealed in polished sections of both gold extracted directly from ores and detrital gold grains collected by panning. Some features are replicated in gold from different areas and suggest that generic processes are at work. Recent detailed analysis of the distribution of other elements at a trace level revealed highly heterogeneous textures which appear to comprise localised concentrations (‘clusters’ ) of various elements within the gold. These clusters may be related to larger inclusions of stoichiometrically definable mineral inclusions, but the origins of all these features are currently unclear.
Separate studies have focussed on the crystallography of gold as revealed in electron back scattered diffraction (EBSD). Initial attempts at correlation of crystallographic and compositional data at the same scale strongly suggests interplay between changes in crystal boundaries and local alloy composition. This study aims to be the first to systematically explore features within natural gold in terms of the crystallographic environment. Leeds is uniquely positioned to undertake this research because of its unique collection of natural gold samples and the range of expertise of the supervisors (with experts in Gold mineralisation, mineral microstructure, experimental geochemistry, elemental microanalysis and elemental diffusion).

The classification of gold particles underpins other studies which seek to exploit the diverse mineralogy of gold to develop an indicator mineral methodology. Compositional and textural characteristics of gold formed in different geological settings are inherited by detrital grains which may be collected during exploration. Characterisation of these gold particles according to the same criteria can provide vectors to undiscovered mineralisation, or reveal the geological setting of the source, where this remains undiscovered. It seems likely that some compositional characteristics of natural gold are a consequence of the environment of precipitation, whereas others are generated in post-depositional processes. It is clearly of paramount importance to know which features are related to the genesis of the mineralisation and which are a consequence of subsequent modification.

The dual approach to gold characterisation which forms the basis of the present project will illuminate the processes responsible for these heterogeneous features. You will benefit from the range of expertise of the supervisors and the specialist gold-specific field and laboratory skills developed at Leeds over the last 25 years: ranging from field skills of the traditional prospector to the cutting edge instrumental analysis which will reveal the true nature of this surprisingly complex material. The choice of area for gold collection will depend on the detailed direction of the project but could include localities in the British Isles, Europe, Australia or North America. Instrumental analysis will be carried out at Leeds with the potential to use cutting edge equipment at world leading facilities elsewhere (e.g atom probe, Sydney, SIMS, Edinburgh).

You will join a vibrant community of researchers active in a wide range of geoscience disciplines. In particular you will benefit from membership of the Ores and Minerals Group, (OMG) which currently supports seven post graduate students. Leeds OMG works closely with both the Institute of Geophysics and Tectonics and the Institute of Applied Geosciences within the School and organisers regular internal seminars (with an emphasis on contributions form postgraduate students) together an external speaker program. We have strong links with the Leeds Chapter of the Society for Economic Geology and postgraduate students benefit from the networking opportunities provided by SEG activities, including attendance at the Vancouver Exploration Roundup held each January. The proposed project provides a platform for post-doctoral employment either in industry or in an academic arena.