REFLECTANCE SPECTROSCOPY OF BIOGENICALLY PRECIPITATED OPAL-A FROM OHAAKI HOT SPRINGS, NEW ZEALAND; SPECTRAL SIGNATURES THAT MAY IDENTIFY HYDROTHERMAL SYSTEMS ON MARS

Reflectance and absorption values between 6-13 µm were collected from a suite of amorphous silicates (opal-A) from the Ohaaki Hot Springs located in the Taupo Volcanic Zone, New Zealand. At this site, the precipitation of opal-A (SiO₂·H₂O) was controlled by filamentous and coccoid microbes, which produced a broad array of fabrics. Using twenty hand samples and core, and examining cut and natural surfaces, the research focused on three goals (1) to collect and document the major thermal-infrared reflectance features of opal-A in conjunction with work being completed by the Thermal Emission Imaging System (THEMIS), a spectrometer on 2001 Mars Odyssey, (2) to categorize results and attempt to identify endmember spectra for distinct classes, and (3) to attempt to explain the cause of these different spectral signatures for materials of seemingly identical compositions while bearing in mind that these rocks were formed at different temperature and flow regimes, and by different bacterial processes. Two major classes of spectral signatures have been identified, as well as additional subclasses, none of which are currently available in current spectral libraries. Further research will highlight any correlation between spectral signature and grain thickness, bound water concentration, and/or bacterial processes.