Mineralogy and Geochemistry of Xenoliths and Phreatomagmatic Deposits in Potrillo Volcanic Field, New Mexico, Determined from Portable Instruments: Applications to Surface Exploration of the Moon and Mars

Abstract

Instruments that yield information about the mineralogy and chemistry of surface materials will be part of future robotic and human exploration of the Moon and Mars. Accurate interpretation of such data can be informed by coordinated analyses of relevant materials in terrestrial analog terrains. We used a suite of portable instrumentation—visible-to-shortwave infrared (VSWIR) spectroscopy, thermal infrared (TIR) spectroscopy, and X-ray fluorescence—to conduct coordinated mineralogical, geochemical, and visual characterization of a suite of outcrops and loose rocks in Kilbourne Hole and Hunts Hole, New Mexico. A variety of textures, particle sizes, and petrogenetic origins were examined. Data were interpreted using spectral models, spectral library comparisons, and chemical calibration curves and compared to mineralogical information derived from X-ray diffraction. Insights and limitations for each technique are presented in terms of surface type; for example, both the VSWIR and TIR instruments exhibited limitations in discerning the full mineralogy of the fine-grained tuff beds. The diverse suite of xenoliths was apparent in TIR spectral images, and the dominant mineral component was identifiable through linear unmixing of TIR spectra. However, inaccuracies in mineral abundance were also observed, highlighting the need for use of more advanced analysis methods. Known lithological diversity was less apparent in VSWIR spectra, which were dominated by minor amounts of phyllosilicates within or coating the rocks. Finally, based on the dearth of mafic minerals and the abundance of quartz, we infer that the Kilbourne/Hunts tuff beds are dominated by fragments of country rock (“accidentals”) rather than juvenile magmatic materials.