Making wealth: precipitating synthetic gold from hydrothermal solutions to understand gold deposition processes

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Highlights: -Design and undertake new experimental procedures to generate synthetic gold veins in the first systematic study of its kind-Produce some seminal work on understanding the process of gold precipitation and its relationship to gold compositional variations-Produce the first crystallographic-compositional characterization of gold from different deposit styles and use experimentation and modelling to investigate post- depositional changes -Synthesize new data from all experimental avenues to develop a novel and holistic approach to gold particle characterization -Apply new understanding to refine methodologies for exploration geology leading to close contact with industry Natural gold, precipitated from hydrothermal systems exhibits a wide range of mineralogical features. The degree of heterogeneity within gold particles has only recently been recognised and comprises zones or tracks of alloy exhibiting elevated concentrations of other metals such as Ag, Cu, Hg or Pd. New analyses of polished gold sections by ToF-LA-ICP-MS show that trace element distribution is highly heterogeneous because of inclusions of other minerals (typically 1-20um) and as a consequence of localised micron scale concentrations ('clusters') of elements in the Au-Ag alloy. The initial compositional features may be modified by grain boundary migration, either in late stages of mineralization or subsequent residence in the hypogene setting. At present we have little understanding of the controls of initial compositional heterogeneity or subsequent modification. You will address these questions through compositional and crystallographic characterization of gold precipitated in a synthetic hydrothermal system, and the relation of outcomes to observations of natural gold from different ore deposit styles. Project elements i. Gold synthesis will focus on simulating hydrothermal systems typical of orogenic and porphyry- epithermal systems. The high temperature (>200C) fluids contain low Cl and low CO2 and transport gold as a bisulphide complex, and silver as a chloride complex. Gold precipitation results from changes in P and T associated with fracturing or through change in chemical parameters such as pH or fS2 associated with fluid-rock interaction. Synthetic gold will be characterized according to composition, microtextures and crystallography. ii. Generation of the first data base to characterize gold from different deposit styles according to trace element chemistry (ToF-LA-ICP-MS and atom probe tomography) and crystallography (EBSD). iii. Definition of parameters which control crystallographic modification of pre - existing gold through design of experiments to observe changes in real time using optical and SEM techniques. Correlation of experimental data with Elle simulation models to generate a predictive tool.iv. Synthesis of all project results to interpret characteristics of natural gold in terms of processes of formation. v. Application of project outcomes to refine existing approaches to the use of detrital gold as an indicator mineral during exploration.Expertise gained and opportunities flowing from the projectYou will gain experience of laboratory based research through design of new experimental approaches, and application of various high- end analytical tools. Geological expertise in ore deposits will be greatly enhanced through study of gold from a range of deposit styles. Depending on project direction a field component could be included involving learning traditional prospecting techniques to collect further gold samples. Finally the research has a practical application in mineral exploration facilitating dialogue with industry professional. The project provides an excellent foundation for further academic or applied ore deposit studies.