Stability of gold nanoparticles in sulfur-bearing hydrothermal fluids: an experimental study

Liu, Weihua1, Chen, Miao1, Yang, Yi1, Mei, Yuan1, Etschmann, Barbara1, Brugger Joël1, Johannessen, Bernt 1

1CSIRO Mineral Resources, Clayton,, Australia, 2Monash University, Clayton,, Australia, 3Australian Synchrotron, Clayton,, Australia

Current theories of the gold deposit formation from hydrothermal fluids have been challenged by recent field and laboratory observations, suggesting that gold nanoparticles/colloids could be important in gold transport/deposition in ore fluids. In this study, the stability of gold nanoparticles (colloidal gold) in sulfur-bearing and citrate-bearing solutions was investigated at temperatures up to 225˚C using Synchrotron X-ray Near-edge Spectroscopy (XANES), and up to 350˚C with a visual check of colour change. The citrate-based colloidal gold solutions, with or without colloidal silica in the solution, are only stable up to 225˚C. In contrast, the gold colloids in Na2S solutions are not stable upon heating to 150˚C, but stable up to 300˚C when 0.5-1.5 wt% of colloidal silica is present in the solution. The colloidal gold particles started to aggregate and deposit from the solution with the aggregation and growth of silica particles at 350 ˚C. The concentrations of gold as colloids in the solutions are up to 0.5 mmol (~95 ppm), more than three orders of magnitude higher than gold solubility as aqueous complexes under the same condition calculated based on available thermodynamic data. These results provide the first evidence that high concentrations of gold nanoparticles are stable in sulfur-bearing fluids at elevated temperatures (~300˚C). This implies that the formation of gold nanoparticles is an effective way to concentrate gold in hydrothermal sulfur-bearing fluids to form high-grade gold ores.


Dr. Weihua Liu is a senior research scientist at the Commonwealth Scientific and Industrial Research Organisation (CSIRO) and was an Australian Research Council Future Fellow

Weihua’s research has been focused on the investigation of metal mobility and mineral/fluid reactions in hydrothermal systems, combining both experimental and theoretical techniques.

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