Precious Metals in Deep Geothermal Waters of the Taupo Volcanic Zone

Abstract

Sampling and analyses of deep waters from Wairakei and Rotokawa geothermal systems indicate a wide range of precious metal concentrations ( less than 0.1 to 23 ppb Au; 6 to 2400 ppb Ag), suggesting that eastern ìandesiticî TVZ geothermal systems (e.g. Rotokawa) have higher aqueous gold and silver compared to western ìbasalticî geothermal systems (e.g. Wairakei); this interpretation is consistent with known occurrences of high grade precipitates in wells from eastern systems. The fact that the deep waters are undersaturated in gold further suggests that the aqueous gold concentrations of deep waters are limited by metal availability. Wairakei has a gold flux of 100 kg/yr and a silver flux of 5200 to 11,140 kg/y. More study is required to assess the financial feasibility of precious metal extraction.