Paper No. 36-3
Presentation Time: 2:15 PM
CO2 FLUX INVESTIGATION AT WAIRAKEI, A LOW-CO2 GEOTHERMAL SYSTEM IN THE TAUPO VOLCANIC ZONE, NEW ZEALAND
A CO2 flux survey was undertaken at Te Mihi, Wairakei, a well described geothermal area in New Zealand. The objective was to determine if a wide-spacing (~100m) survey approach could resolve previously mapped faults and the geothermal system boundary defined by geophysical surveying. In addition, previously mapped faults were examined in detail using reduced measurement spacing, both for transects (perpendicular to strike), and along strike. 13CO2 isotope samples were collected from the accumulation chamber for a subset of total measurements. This allowed both the magnitude of CO2 flux, and the relative proportions of biological and geothermal CO2 present to be determined. Results from surveying that utilised reduced spacing located anomalies associated with a previously mapped fault, a deep geothermal well, and thermal ground. The wide spacing survey was unable to resolve the system boundary or confirm geothermal CO2 degassing associated with previously mapped faults. It is likely that the well-developed hydrothermal capping formation at Wairakei (Huka Falls mudstone) prevents widespread diffuse degassing, directing it to areas where the Huka Falls formation is absent (i.e. Karapiti). The lack of a clear surficial, geothermally-sourced CO2 flux signal at Te Mihi may also be explained by the relatively low CO2 content of the reservoir. Our results show the combination of CO2 flux and 13C isotope measurements provides a powerful approach to distinguish geothermal from biological CO2 flux where the magnitude of CO2flux alone is ambiguous.