Multi-Spectral Field Study of Planetary Analog Material in Extreme Environments—Alteration Products of Volcanic Deposits of Vulcano/Italy

The potential of multi-spectral investigations for planetary exploration strongly depends on the specific geologic environment and related science questions. In this work, we used a visible-near infrared spectrometer, a laser-induced breakdown spectroscopy (LIBS) instrument, and a Raman spectrometer for studying acid alteration of volcanic deposits in the field as an analog for what can be potentially observed on Mars. These deposits were studied on Vulcano, one of the Aeolian Islands/Italy, where volcanic deposits are affected by active hydrothermal alteration processes and fumarolic activity. The results show that VIS-NIR spectroscopy is sufficient to identify the major minerals formed through the alteration process. This is the only technique that can identify and characterize hydrated silica, the major alteration residue, whose spectral properties vary depending on environmental conditions and the formation process. However, only LIBS spectra allow a detailed insight into the geochemistry of the pristine volcanic deposits, which is needed to define the starting point of the alteration process. LIBS also indicated the existence of chemical elements for which no corresponding mineral could be identified in the VIS-NIR data, presumably since their spectral signature is masked by strongly absorbing species. These minerals, however, could be confirmed in the Raman spectra—nicely completing the achieved results and highlighting the high potential of the sensor suite for our study.