Preliminary Results of Precious Metal Analyses of Downhole Samples from Kawerau and Ngawha Geothermal Systems

Abstract

We report analyses for precious and related metals on deep waters obtained from Kawerau and Ngawha geothermal systems with a purpose-built titanium sampler. Solutions were analysed by ICPMS. Lab testing using blank solutions shows minimal sources of contamination from materials used in the construction and sampling procedure (Le. titanium, MilliQ water and aqua regia). At Kawerau, samples were obtained from deep wells at 21000 m depth at temperatures of 260 to 295" C, while at Ngawha samples were taken from > 800 m depth at temperatures of 225" to >235" C. Gold, silver and thallium are at ppb levels, while arsenic, antimony and copper range from hundreds to thousands ppb. Comparing these results with calculated solubilities of gold, silver and acanthite, suggests deep waters are undersaturated in gold but close to saturation in silver, These results are preliminary in the absence of, blank samples subject to downhole conditions and sampling procedures.