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Kotaro Yonezu, Kyushu University (Japan)
Takushi Yokoyama, Kyushu University (Japan)
Akira Imai, Kyushu University (Japan)
Koichiro Watanabe, Kyushu University (Japan)
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In order to elucidate the formation mechanism of epithermal Au-Ag deposits, synthetic experiment of aluminosilicate containing Au and Ag at high temperature (<250°C) is conducted. As preliminary experiments, coprecipitation behaviors of Au(I) and Ag(I) complexes by aluminosilicate with various Si/Al ratios (end members: aluminum hydroxide and silica) are investigated at 30°C. The Au(I) and Ag(I) complexes selected in this study are [Au(S2O3)2]3- and [Ag(S2O3)2]3- for convenience. The results show that the amount of both Au(I) and Ag(I) coprecipitated by aluminum hydroxide decreased with increasing pH and increasing Al/Si ratio. Coprecipitation of Au(I) and Ag(I) by aluminum hydroxide effectively occurred at near neutral pH, while almost no coprecipitation by silica. These results indicate that the Au(I) and Ag(I) complexes are coprecipitated mainly due to electrostatic force. In addition, it also suggests that aluminum plays an important role for the concentration of Au(I) and Ag(I) complexes. The characterization of Au or Ag coprecipitated by aluminosilicate is done by XPS, XRD, NMR and SEM/EDX. The Au coprecipitated by aluminum hydroxide is determined as metallic gold by XPS however, the any gold particles are not observed by SEM, suggesting that Au is present as fine particles (less than 1m). The more detailed investigation is still going on and included in the presentation.
The model experiment at high temperature is aimed to make the solution boiled. A boiling of ore-forming fluid introduces the decrease of temperature and pressure, and increase in pH due to degas of acid gasses, and subsequent precipitation of gold associated with aluminosilicate. Therefore, this process is one of the most important for the concentration of gold from the ore-forming fluid. The sample solution containing Au(I), Ag(I), aluminum and silicon as well as redox sensor with a given concentration is prepared in a reactor. With agitation, the reactor is heated to designed temperature and maintained for desired period. After adequate time, a valve is opened and the makes the sample solution boiled. In order to discuss the distribution of gold, silver and other metals between solid and aqueous solution, the obtained product of solid material and rest solution are characterized by XPS, XRD, NMR and SEM/EDX, and AAS or ICP-MS, respectively. The formation mechanism of epithermal gold deposit will be proposed in the presentation.
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