A Multi-Instrument Investigation of a Low-Temperature, CO2-Rich Geyser: Crystal Geyser, Utah, USA: Implications for Mars Geobiology

We investigated Crystal Geyser (Utah, USA), a unique low-temperature, CO2-rich geyser relevant to Mars that is actively precipitating carbonate-silica. This site was investigated largely in the context of how a Mars rover would characterize such a site. Samples from the site had a range of textural and color differences; however, they contained similar mineral assemblages dominated by carbonates (calcite and aragonite). The identification of calcite and aragonite is important as they can indicate unique formation conditions and possess the ability to preserve biogenic fingerprints and entomb microbial fossils., This analysis confirmed that the most effective method for identifying and distinguishing calcite and aragonite is through a combination of several techniques. Specifically, reflectance spectroscopy was able to determine the presence of different iron oxyhydroxides, and calcite-aragonite mixtures across a wide range of end member abundances. Raman spectroscopy was able to identify and distinguish calcite and aragonite through diagnostic peaks in the low Raman-shift region. Scanning electron microscopy imaging provided sub-micrometer images of textures and sedimentary fabric, such as laminations, crystal structures, and entombed microbial fossils. X-ray diffractometry and X-ray fluorescence were used to determine and verify the mineralogy of the samples., The low-temperature origin of these carbonates and the relative youth of the deposits (ranging from thousands of years to actively depositing) are likely the factors responsible for the lack of homogeneity within the samples. Carbon dioxide degassing is likely the primary factor supporting the active precipitation of aragonite, despite the low temperature. The results have implications for carbonate detection and characterization and the recognition of low-temperature carbonate precipitates on a number of planetary bodies, including Mars.