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Pyrite Weathering by Chlorate and Bromate between 273 and 277 K: Implications for Elemental Sulfur and Iron Oxyhydroxide Formation on Mars

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

Presenting Author:

Amber Miller

Authors:

Miller, Amber¹, Pamula, Krishnakumari², Mitra, Kaushik³

(1) Department of Earth and Planetary Sciences, The University of Texas at San Antonio, San Antonio, Texas, USA, (2) Department of Earth and Planetary Sciences, The University of Texas at San Antonio, San Antonio, Texas, USA, (3) Department of Earth and Planetary Sciences, The University of Texas at San Antonio, San Antonio, Texas, USA,

Abstract:

Bulk Mars is enriched in sulfur. The larger size of the less dense core of Mars may also result from sulfur enrichment in the metallic core. The surface of Mars is also replete with sulfate deposits, which are globally distributed and ubiquitous. While sulfur in its most oxidized form, sulfate, is one of the most common secondary minerals on the Martian surface, the recent discovery of elemental sulfur at Gale crater, Mars was perplexing and interesting at the same time. Currently, the exact formation process is unknown. Multiple plausible processes have been discussed and debated.

One of the possible geochemical pathways that could produce elemental sulfur on the Martian surface is through the oxidative weathering of sulfide minerals. Iron sulfide minerals, such as pyrite (FeS₂) and pyrrhotite (FeS), are expected to be present on early Mars. The oxidative weathering of iron sulfide minerals under Martian-relevant conditions by oxyhalogen brines has demonstrated the production of elemental sulfur, along with other common iron oxyhydroxide and sulfate minerals. At ~25℃, sulfide ions underwent oxidation to first form elemental sulfur and then to an even higher oxidation state in sulfate (SO₄^-2). At lower temperatures, sulfide alteration by oxyhalogen brines would likely facilitate a greater production of elemental sulfur as a stable end product. Although oxidizing potential of oxyhalogen species of chlorate (ClO₃^-) and bromate (BrO₃^-) has been studied at room temperature in Mars relevant fluids, the oxidizing potential under cryogenic conditions remains poorly understood.

Here, we explore the oxidative weathering of iron sulfide minerals in the presence of NaClO₃ and NaBrO₃ at 4℃ and 0℃. Batch experiments were conducted inside an anaerobic chamber (O₂ < 1 ppm) in 50 mL glass serum bottles to investigate the oxidative weathering of sulfide minerals (pyrite and pyrrhotite) by chemical oxidants (chlorate and bromate) in different Mars-relevant fluids (MgCl₂ and MgSO₄) at acidic to alkaline fluids. All experiments were initiated at 0℃ inside the anaerobic chamber, sealed, and then moved to a cold-room maintained at 4℃. A set of experiments were kept in ice-bath for the entire duration of the experiment (~100 days). At the end of the experiment, the alteration mixture will be filtered and characterized to test if lower temperature alteration of sulfide can yield greater proportions of elemental sulfur.