The aqueous speciation of gold plays an important role in our ability to understand

and predict gold mobility and geochemistry in many environments and systems. The

stability of Au(III)-halide complexes has been investigated using spectrophotometric

studies and a technique for the ultra-trace analysis of dissolved gold in chloridedominated

solutions has been developed.

The UV absorption spectra of solutions of Au(III)-Cl-Br, Au(III)-Cl-OH and Au(III)-

Br-OH were measured with varying concentrations of the ligands present. The

Au(III)-Cl-Br system was investigated at 25, 50 and 80 ºC and the hydroxidecontaining

systems were investigated 25 ºC. Quantitative interpretation of the

experimental spectra was used to determine the nature of Au(III)-containing

complexes present in solution together with their molar absorptivities and formation

constants. A number of mixed-ligand species were identified which play a role in

gold speciation and mobility in oxidised, saline to hypersaline environments or

lixiviant solutions for cyanide-free gold extraction.

An analytical method for the ultra-trace analysis of dissolved gold in saline to

hypersaline solution has been developed. Nearly quantitative and highly reproducible

pre-concentration of dissolved gold by sorption to granular activated carbon may be

achieved in chloride-dominated solutions, followed by analysis of the carbon with

epithermal neutron activation analysis. 0.1 – 1 g of carbon per kg of solution allows

the accurate measurement of dissolved gold to 3 – 4 ppt. The effect of other variables,

such as sorption of gold to the sample bottles, pH and the presence of selected other

ligands, has also been investigated.

Applications of the carbon sachet based analytical technique have been demonstrated.

The technique is directly applicable to natural groundwater matrices by the method of

standard addition. A pilot study of the solubility of elemental gold in saline to hypersaline

solution was also achieved using the technique.