Investigating the Formation Conditions of Evaporitic Chloride, Carbonate, and Sulfate Paragenetic Assemblages on Early Mars

Eashan Das , Kaushik Mitra, Joel A Hurowitz, Timothy Glotch, Yatharth Bahl

Aqueous alteration minerals, such as chlorides, carbonates, and sulfates, have been discovered on the surface of Mars by both orbital and in situ rover observations. Alteration minerals require liquid water for their formation and can place critical constraints on the geochemistry of the aqueous systems in which they are formed. Primary mineralization facilitated by evaporation of weathering fluids is an important mineral formation pathway that can produce alteration minerals, such as chlorides, carbonates, and sulfates on Mars. Here, we simulate basalt weathering under diverse Mars-relevant conditions and study the chemical composition of the resultant fluid ‘leachates.’ We categorize and group ~60 different leachates on the basis of relative concentrations of major cations (Na⁺, Mg²⁺, Ca²⁺, Fe²⁺) and anions (Cl-, SO42-, HCO3-) and predict 8 major leachate types possible on early Mars. We simulated the evaporation of all leachates and studied the consequent precipitation of evaporite minerals. Our results indicate that sulfate-rich leachates were the most prevalent, which upon evaporation generated a variety of Mg/Ca/Fe sulfates. Siderite (FeCO3) precipitated during closed system weathering of basalt under relatively low volcanic activity on Mars. The results of our study can explain the widespread presence of sulfate salts and the recent detection of siderite in the sulfate-rich Mirador formation at Gale crater. Halite (NaCl) was the major chloride mineral that precipitated in our models and was exclusively produced in closed system, water-limited, and high initial acidity conditions.