Geochemistry of discharge at Waiotapu geothermal area, New Zealand – Trace elements and temporal changes

• Review of published analyses at Waiotapu.
• An extensive suite of trace elements analyses for all springs at Waiotapu.
• Relationships between aqueous components and geothermal processes.
• Relationships between aqueous trace elements and other components.
• Temporal changes in chemistry at a selection of springs for several decades.

The Waiotapu Geothermal system in the Taupo Volcanic Zone in New Zealand contains springs with diverse chemistry. The major cation and anion concentrations can be interpreted to reflect alteration minerals present in the geothermal system and the processes that operate in the geothermal system. Analysis of the concentrations of major components at several springs over 2–7 decades indicates that the conservative components such as Cl and Na have relatively stable concentrations over this time period. Other components for which analytical data are available have much more variable concentrations throughout this period. This indicates that analysis of many chemical components within springs provides a snapshot of chemistry and that the processes that control their concentrations are unstable over the span of several decades.Analysis of trace element concentrations indicates that diverse geochemical processes control the concentration of trace elements in the Waiotapu Geothermal system. Some trace elements are relatively conservative, Ge and V. Other trace element concentrations such as Sb and As are influenced by several processes. And other trace elements have strong relationships with pH (Fe and Al), other major components (Sr and Mn) or other trace elements (Ti and Sc). A strong relationship between Mn and Mg concentrations in Waiotapu springs indicates that similar minerals and geothermal processes control concentrations of both elements.