Soil Gas Flux Geothermometer for Geothermal Exploration

Abstract

A new geothermometer (TCO2 Flux) is described based on soil diffuse CO2 flux and shallow temperature measurements made on areas of steam heated, thermally altered ground above active geothermal systems. TCO2 Flux provides a valuable exploration tool for estimating subsurface temperatures in high-temperature geothermal systems. The geothermometer was developed from a previous gas (CO2) geothermometer. Surveys using TCO2 Flux reveal the location of major upflow zones previously reported at the Rotokawa (New Zealand) and Wairakei (New Zealand) geothermal systems. Geothermometry estimates agree with the range of deep drill hole temperatures at Wairakei, Rotokawa, Tauhara (New Zealand), Ohaaki (New Zealand), Reykjanes (Iceland) and Copahue (Argentina). TCO2 Flux at the White Island active volcano is the highest of the systems considered in this study (320 °C). The geothermometer gives a high temperature at Reporoa (310 °C). This indicates Reporoa has a separate upflow from the nearby Waiotapu geothermal system.