Characterising The Hydrothermal Alteration Of The Broadlands-Ohaaki Geothermal System, New Zealand, Using Short-Wave Infrared Spectroscopy
Journal Article: Characterising The Hydrothermal Alteration Of The Broadlands-Ohaaki Geothermal System, New Zealand, Using Short-Wave Infrared Spectroscopy
AbstractHydrothermal clay minerals present in the Broadlands-Ohaaki geothermal field were characterised by field portable short-wave infrared spectroscopy. Three major alteration zones, an upper smectite, a middle illite and a lower illite-chlorite, are spectrally separable. The zoning pattern is generally consistent with the thermal structure of the geothermal field, although occasionally zone boundaries cut present-day isotherms. The data indicate that temperature is the major control on clay zoning and permeability plays a subordinate role. Both beidellite and montmorillonite are common in the upper, low-temperature smectite zone. Kaolinite, mainly of low crystallinity, marks the margin of the field where cool acidic ground waters inflow. In the middle alteration zone, illite, dominantly K-rich, shows a narrow compositional variability. Some highly permeable zones are characterised by illite with low octahedral Al contents. Ammonium-bearing illite and buddingtonite are present locally in permeable horizons within the illite zone, where temperatures are above 200°C. Chlorite is most abundant in the lower alteration zone (temperature >250°C), although it also occurs unevenly in the upper and middle alteration zones. Chlorite varies from Mg- to Fe-rich varieties (but mostly with Mg# values <0.5), but no compositional trends with respect to depth are spectrally detectable.
- K. Yang, P. R. L. Browne, J. F. Huntington and J. L. Walshe
- Published Journal
- Journal of Volcanology and Geothermal Research, 2001
- Not Provided
Check for DOI availability: http://crossref.org
K. Yang,P. R. L. Browne,J. F. Huntington,J. L. Walshe. 2001. Characterising The Hydrothermal Alteration Of The Broadlands-Ohaaki Geothermal System, New Zealand, Using Short-Wave Infrared Spectroscopy. Journal of Volcanology and Geothermal Research. (!) .