Quantification of MnO using the ChemCam LIBS Instrument and Comparison with the Alpha-Particle X-ray Spectrometer
Manganese oxide (MnO) values exceeding 50 wt% have been reported by the ChemCam (CCAM) laser-induced breakdown spectroscopy (LIBS) instrument onboard the Mars rover: Curiosity. These observations have raised speculation on the habitability of the early Mars environment. This work recreates the univariate calibration used for the quantification of MnO using CCAM spectra, and provides a novel comparison to the Alpha-Particle X-ray Spectrometer (APXS) also on-board Curiosity. Between instruments, systematic deviations of MnO values are found for groups of targets with a characteristic chemical and physical matrix. A multivariate calibration is introduced, which accounts for the relative abundance of SiO2, TiO2, Al2O3, FeO, MgO, CaO, Na2O, and K2O in the sample. The multivariate method corrects for impacts of the normalization to the manganese signal as well as chemical matrix effects, which reduces the MnO prediction error by a factor of >3.5 and agrees more favourably with the APXS in general.