Manganese Phase and Oxidation State for Martian Analog Samples from Evolved Gas Analysis

Session: Advancing Mineral Science and Exploring Planetary Surfaces: In Honor of MSA Dana Medalist, Elizabeth B. Rampe (Posters)

Presenting Author:

Patrick Casbeer

Authors:

Casbeer, Patrick¹, Clark, Joanna Victoria², Morris, Richard³, Lanza, Nina⁴, Mitra, Kaushik⁵, Sutter, Brad⁶, Rampe, Elizabeth⁷

(1) Amentum JETSII, NASA Johnson Space Center, Houston, TX, USA, (2) Texas State University – Amentum JETSII Contract at NASA Johnson Space Center, Houston, TX, USA, (3) XI3, NASA Johnson Space Center, Houston, TX, USA, (4) Los Alamos National Laboratory, Los Alamos, NM, USA, (5) Department of Earth & Planetary Sciences, The University of Texas at San Antonio, San Antonio, TX, USA, (6) Amentum JETSII, NASA Johnson Space Center, Houston, TX, USA, (7) XI1, NASA Johnson Space Center, Houston, TX, USA,

Abstract:

Manganese (Mn) enrichments have been identified by the APXS and ChemCam instruments onboard the Curiosity rover in fracture fills, coatings, and nodules at Gale crater, Mars. The enrichments can provide information about past geochemical conditions (e.g., oxidizing vs. reducing fluids) provided that the precise oxidation state and associated mineral phases of Mn are known or estimated. The goal of this study was to explore if analysis of martian samples by the Sample Analysis at Mars-Evolved Gas Analyzer (SAM-EGA) can constrain the Mn-bearing phase and oxidation state.

Sixty-eight Mn-bearing samples (synthetic and natural) were analyzed using a thermal gravimetry (TG)/differential scanning calorimetry (DSC) instrument connected to a quadrupole mass spectrometer, configured to operate similarly to SAM (e.g., heating rate, furnace pressure, carrier gas). Results for evolved O₂ Mn(II) oxides did not produce significant O₂ peaks below 1000°C and therefore would not be detectable with SAM-EGA. Evolved O₂ for higher valence Mn oxides (e.g., Mn₂O₃ and MnO₂) took place between 460-1000°C and therefore would be detectable with SAM-EGA if present above SAM’s O₂ detection limit of 0.01 wt. %. Laboratory EGA results for amorphous MnO and MnO₂ were consistent with crystalline MnO and MnO₂, respectively. This indicates that higher valence Mn oxides that are potentially in the X-ray amorphous component of drill samples could also be detectable by SAM-EGA.

Mn(II) carbonate, Mn(II) sulfate/sulfide, Mn(II) perchlorate, and Mn(II) oxalate are detectable by SAM-EGA as pure phases, showing characteristic CO₂, SO₂, HCl, and H₂O, CO, and CO₂ evolutions, respectively. In contrast, hydrated Mn phosphates would be difficult to discern with SAM-EGA because their water releases overlap with more abundant water-evolving phases such as hydrated salts or clays.

SAM-EGA could detect most but not all Mn-bearing phases if present above instrument detection limits. SAM-EGA is effective for detecting higher valence Mn oxides. Therefore, drill samples containing Mn oxides (detected by other rover instruments) that did not evolve O₂ must be Mn(II) oxides or below detection. In oxidizing conditions Mn could precipitate into multiple phases detectible by SAM, and if detected would constrain Eh-pH to a greater degree than Fe alone.