Gallium
occurs at above background levels in most samples collected from 11 of the major
geothermal areas in the Taupo Volcanic Zone. Concentrations of Ga in the 48
samples ranged from 8 to 144 mg kg-1 and varies widely from place to
place within each geothermal area. Gallium is contained within the
alumino-silicate structure of clay in the mud, having substituted mainly for
Al. Suggested deposition
mechanisms for Ga also involve co-precipitation with Sb, As, and SiO2
colloids. Digestion trials, carried out to determine extraction conditions for
possible commercial exploitation, showed that heating the mud to 500 - 600C for
1 hour followed by acid/alkali treatment gave complete
recoveries.