Gold transport in hydrothermal fluids: Competition among the Cl-, Br-, HS- and NH3(aq) ligands
MetadataShow full item record
Since the Au(I) and Au(III) ions are not stable in water, gold transport and deposition in hydrothermal ore fluids are dependent on the identity and stability of the predominant aqueous gold complexes. Gold(I) bisulfide (e.g., Au(HS)2 -) and in some instances Au(I) chloride complexes are widely acknowledged to account for gold transport in hydrothermal ore fluids. This study investigates the potential of the unconventional ligands Br- and NH3(aq) to increase gold mobility. This was achieved by determining the predominant gold species in hydrothermal fluids with binary mixed ligands (Br-–Cl-, Br-–HS-, HS-–NH3), and measuring their structural properties using in situ synchrotron X-ray absorption spectroscopy (XAS). The capacity of XAS to follow the progress of ligand exchange reactions was demonstrated using Au(III) at room temperature: the Au(III)Br4 - complex was found to predominate in mixed Br-–Cl- solutions (Br-/Cl- = 0.2–1), with average ligand numbers derived from XAS data in good agreement with the UV–vis study of Usher et al. (Geochim. Cosmochim. Acta 73, 3359–3380, 2009). At elevated temperatures up to 400 °C at 600 bar, the XA measurements show that Au(I)–HS- complexes are the only stable gold species in mixed HS-–Br- and HS-–NH3 fluids (HS-/Br-=0.1;HS-/NH3 = 0.2), suggesting that hydrosulfide is the most important ligand for gold transport in the hydrothermalfluid under our experimental conditions, i.e., hydrosulfide complexes outcompete bromide, chloride and ammine complexes in S-bearing fluids.
Showing items related by title, author, creator and subject.
Properties of lithium under hydrothermal conditions revealed by in situ Raman spectroscopic characterization of Li2O-SO3-H2O (D2O) systems at temperatures up to 420 °CWang, X.; Wang, X.; Chou, I.; Hu, W.; Wan, Y.; Li, Zhen (2017)© 2017 Elsevier B.V.Lithium (Li) is an important component of hydrothermal fluids, especially submarine hydrothermal fluids. Investigation of the species and ion complexation of Li+ at elevated temperature and pressure ...
An atmospheric source of S in Mesoarchaean structurally-controlled gold mineralisation of the Barberton Greenstone BeltAgangi, Andrea; Hofmann, A.; Eickmann, B.; Marin-Carbonne, J.; Reddy, Steven (2016)The Barberton Greenstone Belt of southern Africa hosts several Mesoarchaean gold deposits. The ores were mostly formed in greenschist facies conditions, and occur as hydrothermal alteration zones around extensional faults ...
Phillips, G.; Evans, Katy (2004)Much of global gold production has come from deposits with uneconomic concentrations of base metals, such as copper, lead and zinc. These 'gold-only' deposits are thought to have formed from hot, aqueous fluids rich in ...