Making Wealth: Precipitation of Gold from synthetic hydrothermal solutions

Natural gold, precipitated from hydrothermal systems exhibits a wide range of mineralogical features which sets it apart from metallic gold fabricated through smelting. These features are revealed in polished sections of gold particles and include local concentrations of metals such as Ag, Cu, Hg or Pd as zones or tracks. The boundaries of such features may be diffuse, or sharp which has been interpreted as variation in the conditions of mineralization, or possible thermal history post deposition. However the interpretation remains speculative in the absence of experimental data in which the characteristics are replicated under controlled conditions.

Gold alloy composition is a function of pressure- temperature and chemical environment at the point of deposition (P-T-X) and the alloy heterogeneity may be further modified by time dependent processes. In this project you will grow gold in a variety of synthetic environments designed to replicate different hydrothermal systems. The characteristic of the gold so produced will then be examined using the same methodologies routinely employed to characterise natural gold. In this way we aim to generate a compositional template defined by P-T-X-t conditions against which natural gold may be correlated. The extensive library of natural gold at Leeds included samples of detrital gold from many areas where the signature of the source mineralization remains undiscovered. The outcomes of this research seeks to illuminate the conditions under which the gold particles formed to aid targeting the geological context of the source.
Natural gold occurs in a wide range of particle sizes, ranging from the extremes of large (multi kg) nuggets to ‘invisible’ gold within quartz. It is possible to get a large particle size of gold in economically unattractive mineralization, but elsewhere important deposits ay comprise very finely divided gold particles. The controls on gold particle size are not understood. The range of experiments undertaken during the project will investigate the relationship between depositional conditions, and mineral substrates. This element of the project will also generate new understanding which is generically applicable.

The study will focus on two synthetic hydrothermal systems which correspond to those found in different styles of mineralization. Hydrosulphide complexing of gold (in tandem with chloride complexing of silver) is dominant in the majority of gold forming systems such as orogenic gold, intrusion related gold and many environments in porphyry- epithermal systems. These are in general high temperature (>200ºC) systems buffered by rock interactions in contact with a low Cl, low CO2 fluid. Gold may precipitate in response to changes in P, T or through change in pH or fS2. In contrast, low temperature (<200ºC) highly oxidizing systems transport gold as a chloride complex often in conjunction with palladium. The metal chloride complexes are instantaneously destabilized by catastrophic lowering of Eh, associated with contact with reducing lithologies or associated fluids.

You will be supported by a team of academics whose range of expertise underpins the project. There is an opportunity to gain the specialist field skills of the traditional gold prospector during sample collection. Field locations will be decided according to the direction of the project but could include sites in the British Isles and Ireland, Europe and North America. In particular you will be involved in the design of the first experiments to systematically synthesise hydrothermal gold according to a range of P-T-X-t regimes. The possibilities to contribute to our basic understanding of the characteristics of natural gold and the implications for interpretation of gold from different geological systems is both wide ranging and of great general value to both academic and industrial communities.
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 with 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.