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Gold mineralization at the Hunt mine, Kambalda, is situated in a 20-m-thick, steeply dipping shear zone within a sequence of rather uniform metabasalts. Zonal alteration of the host rocks occurred around fractures which acted as conduits during gold mineralization. Limited major element mobility ensured assemblages of low variance over most of the alteration zone, providing a suitable environment for the application of thermodynamics in conjunction with detailed petrographic, geochemical (electron microprobe analysis of mineral compositions), and fluid inclusion studies (microthermometry).Equilibrium equations involving fluid components and alteration minerals are used to determine conditions during the alteration event, and in particular, activity gradients of components. Profiles across the schist zone show increasing fHas around auriferous quartz veins (1ogfH•s = < -0.75 to > -0.6) but constant fo• (1ogfo• = -29.7). These results are near the magnetite-pyrrhotite-pyrite triple point for the inferred temperature of 350øC and explain the pyrite-pyrrhotite-magnetite zonation sequence outward from veins. The profile of X•coay is very close to the value of 0.25 determined independently from fluid inclusions.The K+/H + profile shows increases adjacent to auriferous veins corresponding to the zone of biotite stability. Using a value for fluid salinity of 2 equiv wt percent NaCI, pH was calculated to be around 6.9.The solubility of gold in solution was estimated for the calculated conditions: for the complex Au(HS)• the maximum solubility is around 0.5 mg kg -1 (i.e., 0.5 ppm), for Au(C1)• it is close to 10 -6 mg kg -1, indicating the efficacy of sulfide transport of gold, compared to chloride transport, under these conditions. The calculated decrease in f, as away from the auriferous quartz veins results in an 80 percent (or greater) decrease in gold solubility, suggesting hat the sulfidation of Fe-rich wall rocks is a geologically reasonable and very efficient mechanism for precipitating gold from solution at elevated temperatures.

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The perovskite CaTiO3 is one of the major phases of the Synroc titanate mineral assemblage. Its chemical durability in an aqueous environment, which is relevant to the Synroc concept, has been investigated by solution analysis, surface analysis and electron microscopy. In general it has been found that dissolution due to base catalyzed hydrolysis is the most significant mechanism of attack; the results suggest that an ion exchange mechanism is confined to the first monolayer. Below 90°C the extent of attack, and release of Ca into solution, is limited by the formation of a titanaceous amorphous layer (” 100A thickness) which imposes a reaction constraint at the film-solid interface. Dissolution may also be constrained by the pH and Ca2+concentration in the bulk liquid. Above 90°C dissolution is relatively less constrained due to instability of the amorphous layer which is replaced by nucleation and epitaxial growth of TiO2 on the dissolving substrate. Thermodynamic stability of CaTiO3 for T< 90°C can easily be engineered into the waste repository, while hydrothermal stability (T > 90°C) is more difficult to achieve.