Institute of Applied Geoscience (IAG)

Trace element mobility and concentration in Cu-Au magmatic hydrothermal systems

NERC CASE PhD project (Mr Hugh Graham)

Critical metals are those which are key to our modern way of life - used in technological devices, batteries and solar cells.  Often found as minor components in ore deposits, their enrichment and transport processes are often relatively poorly-understood, meaning that it is difficult to predict their occurrence in economically viable quantities.  In contrast,  there is a significant amount of effort associated with understanding the mineralisation of gold, due to its commercial and industrial value. Consequently, the mineralogy of gold deposits is frequently well characterized, and several critical elements (for example Palladium (Pd), Selenium, (Se)  or Tellurium (Te)) may show a strong association.   There has been far less work undertaken on  the trace element chemistry associated with gold, and its relation to the tectonic and geochemical environment.

This project focuses on three questions:

1.  What are the trace elemental signatures associated with magmatic hydrothermal gold mineralisation?

2.  What can they tell us about the evolving chemical environment during ore genesis?

3.  Which other critical metals can be co-genetic with gold, and what are the controlling factors?

This study will investigate a suite of samples of  in-situ gold mineralisation across the porphyry-epithermal transition. By examining an intial suite representing a global sampling of different deposits, an initial overview framework can be developed. This will be contrasted against much more detailed studies of specific mineralisation, that will be sampled through field work and analysed in the lab. Specific case studies of Canadian alkalic and calc-alkalic porphy-epithermal systems, will characterise fluid evolution and associated mineralization using a raft of techniques including petrography, electron microscopy, electron beam microanalysis, fluid inclusion analysis and trace elemental analysis. In addition, the project will apply laser ablation ICP-MS to Au grains to inform trace element partitioning in the first systematic study of its kind. Questions of elemental mobility, speciation, partitioning and the sequence of enrichment, mobilisation and deposition events within the porphyry systems will be addressed, to establish the physio-chemical controls of both ore and trace element distribution.

Regarding our three key elements - gold (Au), palladium (Pd), and tellurium (Te), this project considers how these elements interact during the precipitation of gold particles from hydrothermal fluids.  In common Au-precipitating systems, the gold and palladium can be co-variant where Pd is present, with Pd incorporated into the Au alloy phase. However, in the presence of appreciable Te causes a quantitative shift in behaviour and the formation of separate Pd-Te phases. In examining such changes from field and fluid perspectives, a P-T-X view of the mineralising system will be attained. The study of trace element behaviour provides opportunity to develop new insights into the fluid evolution and associated mineralization of complex but economically important hydrothermal systems.

 

 

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