Adsorption Behaviour of Gold(I)-Thiosulfate Complex Anions on the Surface of Alumina and Silica Gels: Approach to the Formation Mechanism of Low Sulfidation Epithermal Gold Deposits

Abstract

In order to elucidate the chemical relationship between gold and aluminum in quartz veins of low-sulfidation epithermal gold deposits, it is important to investigate the role of aluminum for the enrichment of Au(I) ions. Adsorption behavior of [Au(S2O3)2]3- complex anions (Au(I)-S) on the surface alumina and silica gels was examined in this study. In the pH range of 4 to 9, the amount of Au(I)-S adsorbed on alumina gel decreased with increasing pH and the amount abruptly decreased between 6 and 7. The amount became almost zero at pH 8 and 9 under 30 °C. Based on the zeta potential of the alumina gel, its isoelectric point was around pH 7, indicating that its surface charge was positive below pH 7. The results suggest that the adsorption of Au(I)-S on the alumina gel was mainly controlled by electrostatic interaction. While, Au(I)-S were significantly adsorbed under 60 °C even at pH 8 and 9. This fact suggests that they were adsorbed due to formation of Al-O-Au bonds (chemical adsorption) at 60 °C. On the other hand, only a little adsorption of Au(I)-S occurred on the surface of silica gel at 30 °C and 60 °C. We deduce us that aluminum may play a more important role for enrichment of gold than silica (quartz) during the formation of low-sulfidation epithermal gold deposits.