Sulfide-rich scale occurs in steam
and water lines at the Ohaaki geothennal field,Taupo Volcanic
Zone, New
Zealand. Precious metals show very high
concentrations around areas ofpressure reduction (Au 15500 ppm, Ag 68800 ppm).
Pyrrhotite dominates at the orifice plate due to low
PH2s1PH2 conditions. Sulfide mineralogy in the scales is
consistent with alteration mineralogy of the reservoir rocks. Separated steam
then produces a mainly pyrite/magnetite mineralogy, with lesser chalcopyrite,
where textures reflect high flow rates and high levels of supersaturation. This
study outlines the effect that pressure and subsequent temperature decreases
have on the mineralogy, chemistry and textures of sulfide
scales.