44-4 Comparisons Between Fe-Sulfate Detections in Gale Crater, Mars and the ~433 nm Feature in ChemCam Passive Spectra

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

Presenting Author:

Alivia Eng

Authors:

Eng, Alivia Michelle¹, Rivera-Hernández, Frances², Johnson, Jeffrey Roy³, Sutter, Brad⁴, Clark, Joanna Victoria⁵, Wray, James J.⁶

(1) Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, Georgia, USA, (2) Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, Georgia, USA, (3) Johns Hopkins University, Applied Physics Laboratory, Laurel, MD, USA, (4) NASA Johnson Space Center, Houston, TX, USA, (5) NASA Johnson Space Center, League City, TX, USA, (6) Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, Georgia, USA,

Abstract:

Fe-sulfates have been detected in Gale crater, Mars by the Curiosity rover payload, providing important constraints on past environmental conditions (e.g. pH, temperature, pressure). Evolved Gas Analyses from the Sample Analysis at Mars (SAM) instrument have shown the presence of Fe-sulfate in almost every drill target analyzed. However, CheMin detected jarosite (0.4-4.6 wt%) in only 9 of the drill targets, implying that Fe-sulfate is amorphous in the remainder. Fe-sulfate abundances are challenging to derive with SAM, although Smith et al. (2022) estimated that 0.1 to 3.8 of the SO₃ wt% in select targets is associated with Fe-S phases. There are discrepancies between SO₃ abundances derived from SAM and the Alpha Particle X-ray Spectrometer, in part because Ca-sulfates decompose above SAM’s temperature range. Here, we utilize ChemCam passive spectroscopy to further characterize these Fe-sulfate detections and other candidates. Reflectance spectra of certain Fe-sulfates have a diagnostic absorption near 433 nm that is shown by McCollom et al. (2014) to be strongest in synthetic natroalunite-natrojarosite solid solutions with Fe/(Al+Fe) ratios 0.10 to 0.49. Building off Johnson et al. (2015), we find that 12 drill targets, confined to the lower Murray and Stimson formations, show this feature in ChemCam passive spectra.  

We explore the controls on the presence of the 433 nm feature in the ChemCam passive data and assess potential relationships with other datasets (e.g. CheMin, SAM). First, we observe this feature only in spectra of drill tailings and rock crushed by rover wheels, which suggests that exposure and/or surface texture play a role. Second, we hypothesize that phyllosilicates may mask this feature and that a more transparent/amorphous matrix could enhance it (Johnson et al., 2015). Interestingly, targets with the largest 415 nm/435 nm ratio show significant amounts of magnetite and/or hematite in CheMin results, which typically dominate ChemCam passive spectra. Third, we acknowledge that amorphous Fe-sulfates do not typically show this feature (Sklute et al., 2015) and thus we propose that these materials are quasi-amorphous (Wang et al., 2011). The mineralogic assemblages that include magnetite and a quasi-amorphous ferric-sulfate may be explained by a partial Fe(II)-driven transformation of jarosite to magnetite under alkaline conditions, which was observed to result in amorphous and weakly crystalline phases (Liu et al., in review).

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

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