Berlo, K.

Crossey, L.

Das, D.

Gasda, P.J.

Leveille, R.J.

Schwenzer, S,

Turner, S,

Wiens, R.C.

Open Research Online (The Open University)

Open Research OnlineThe Open University’s repository of research publicationsand other research outputsModeling the Behavior of Selected Water-SolubleElements in Calcium Sulfate Veins of Gale CraterConference or Workshop ItemHow to cite:Das, D.; Gasda, P.J.; Schwenzer, S,; Crossey, L.; Turner, S,; Leveille, R.J.; Berlo, K. and Wiens, R.C. (2020).Modeling the Behavior of Selected Water-Soluble Elements in Calcium Sulfate Veins of Gale Crater. In: 52nd Lunarand Planetary Science Conference, 15-19 Mar 2020 (Virtual), Houston, USA.For guidance on citations see FAQs.c© [not recorded]https://creativecommons.org/licenses/by-nc-nd/4.0/Version: Version of RecordLink(s) to article on publisher’s website:https://www.hou.usra.edu/meetings/lpsc2021/pdf/2155.pdfCopyright and Moral Rights for the articles on this site are retained by the individual authors and/or other copyrightowners. For more information on Open Research Online’s data policy on reuse of materials please consult the policiespage.oro.open.ac.ukMODELING THE BEHAVIOR OF SELECTED WATER-SOLUBLE ELEMENTS IN CALCIUM SULFATE VEINS OF GALE CRATER. D. Das1, P. J. Gasda2, S. P. Schwenzer3, L. Crossey4, S. M. R. Turner3, R. J. Leveille1, K. Berlo1, R. C. Wiens2 1Department of Earth and Planetary Sciences, McGill University, Quebec, Canada (debarati.das@mail.mcgill.ca), 2Los Alamos National Laboratory, New Mexico, USA, 3AstrobiologyOU, The Open University, Milton Keynes, United Kingdom, 4University of New Mexico, New Mexico, USA.  Introduction: From late 2017 to early 2019, the NASA Curiosity rover crossed a morphologically re-sistant feature in Gale crater named Vera Rubin ridge (VRR). VRR is a ~200 m wide and ~6.5 km long ridge that is inferred to have formed due to preferential hard-ening caused by late-stage diagenetic processes such as enhanced crystallization and/or cementation [1]. The rover’s ChemCam instrument suite detected water-sol-uble elements B and Li in Ca-sulfate veins throughout VRR [2]. ChemCam has made similar detections in Gale crater prior to arriving at VRR [3]. Due to the over-all high solubilities of B and Li relative to Ca-sulfate and the difference in relative solubilities between the two elements, their abundances can be a marker of pro-gressing evaporation of Gale crater fluids and improve the understanding of the crater’s late-stage diagenetic events [2].  Ca-sulfates of Gale crater contain relatively high amounts of B and Li (highest concentration of B and Li respectively observed in Gale crater: ~300 and 65 ppm [2, 3]) compared to Ca-sulfates or basalts on Earth (Ca-sulfates: <20 ppm B [4], < 7 ppm Li [5]; basalts: <20 ppm B [6], <30 ppm Li [6]). The B and Li abundances in Ca-sulfate veins of Gale crater also show a broad in-verse correlation between them (especially in VRR) [2].  We hypothesized that the enrichment of B and Li was caused by progressive dehydration of late-stage di-agenetic fluids and the relationship between B and Li is a result of a combination of processes such as sequential evaporation (B precipitating as salts faster than Li due to B’s solubility which is about ten times lower than Li in water at 1atm and 20°C [7]), adsorption to clays, and/or remobilization of B and Li after clay dissolution in an acidic fluid environment [2]. The hypothesis is based on the presence of crystalline akaganeite and jar-osite indicating acidic and warm fluids [1, 8] and lower Li abundance in VRR [9], in addition to the observed B and Li concentrations. Elevated Li and clay content be-low VRR is also inferred to indicate an impermeable layer [9] which could mean that B and Li in VRR may have been sourced locally or upslope (i.e., due to disso-lution of clays). To summarize, we hypothesized that adsorption, dissolution, sequential evaporation, and possibly multiple generations of dissolution and re-pre-cipitation caused the enrichment and the broad inverse correlation of B and Li in Ca-sulfates of VRR and that the B and Li were locally sourced [2]. However, the re-lationship between B and Li abundances in Gale Ca-sul-fates is not an exact correlation and not all targets show this trend [2]. Hence, we surmised that geochemical modeling would be required to confirm our hypothesis and to what additional processes may have occurred to produce the observed data. We aim to understand the processes and the se-quence of events using a combination of analog sample investigations and reaction-pathway modeling of the terrestrial situation, followed by extrapolation to Mars. We focus on analog samples from Death Valley, USA [10], published results of evaporites and groundwater around dry lakes of Death Valley [11] and Valles Cal-dera [12] in USA, ground and spring water from Iceland [6], and evaporites and ground water from dry lakes of Bolivia [13]. In this abstract we will focus on the meth-odology developed for geochemical modeling of low-temperature (<100°C) fluids in an evaporative setting to understand the reasons behind enrichment of B and Li after adding the relevant B and Li phase thermochemi-cal data to the existing model databases.  Methodology: As Li and B phases observed in our analogs and their thermochemical constants are not cur-rently included in geochemical models, we start by ex-panding the thermochemical database from the litera-ture [14, 15]. Thermochemical modeling is performed using Gibbs free energy calculations between chosen starting materials using CHIM-XPT. CHIM-XPT [16] is a program for computing equilibria between multiple components in aqueous-mineral-gas systems and will be used for the initial thermochemical modeling. Geo-chemist’s Workbench [17] will be used to further refine the model and include processes such as adsorption of B and Li to clays. The modeling process is divided into three stages which iteratively increase in complexity with respect to geological processes as shown in Fig 1a. Stage 1 in Fig 1a shows that the model will start by com-posing a fluid that has reached equilibration with Gale crater rocks (e.g. in 1 liter of water with ions: Ca2+, SO42-, Na+, Cl-, B(OH)4- and Li+). Evaporation and dissolution for this fluid will then be modeled using CHIM-XPT. The resultant phases (both fluid and precipitates) will be used as starting materials for a second stage of the mod-eling process. The final stage will take into 2155.pdf52nd Lunar and Planetary Science Conference 2021 (LPI Contrib. No. 2548) Figure 1. a) Three stages of thermochemical modeling. Pro-cess block indicates possible sets of geological events such as precipitation, dissolution and adsorption. b) Task sets in each thermochemical modeling stage shown in a). consideration multiple events such as precipitation, dis-solution, adsorption and intergenerational interaction of fluids and precipitates. Each stage will consist of three sets of tasks as shown in Fig 1 b. The first task will con-sist of setting up the starting materials for the model, the second task will consist of simulating evaporation and dissolution using CHIM-XPT, and the third task will consist of comparing the resultant phases to Mars obser-vations and terrestrial analogs. With each stage we will iteratively increase the complexity of the model by sim-ulating evaporation, dilution, and by adjusting the ionic composition of the starting fluid based on the compari-sons with Mars observations and terrestrial analogs. The first stage of the modeling process will focus on the broad understanding of the composition, temperature, pH, and water-rock ratio of fluids that formed primary (or first generation) evaporites in Gale crater. The sec-ond stage will focus on determining the parameters of fluids that formed Ca-sulfates in Gale crater [18] and the final stage will refine the model to understand what flu-ids formed the veins in VRR [2]. At each stage we will test the model using a terrestrial analog (for which we have published mineral, brine, and groundwater compo-sitional data) using the model to establish a ground truthing. The terrestrial analogs are chosen based on similarity to conditions in Gale crater and the availabil-ity of relevant data (trace and major element concentra-tions of varying lithologies, stream and ground water data, etc.). For example, Iceland is a promising candi-date due to the extensive availability of rock [6], stream [19, 20] and ground-water [21] data.  Preliminary Results: CHIM-XPT was used to evaporate 1 L of fluid containing Ca2+ (200 ppm), SO42- (200 ppm), Cl- (200 ppm), Na+ (100 ppm), and Li+ (100 ppm) over 1-60°C. The resultant phase abundances with varying H2O content is shown in Fig 2. With decreasing water content phases NaCl, LiCl, CaCl2 form more readily than CaSO4, gypsum and anhydrite (Fig 2 inset). Figure 2. Resultant aqueous and precipitated phases (y-axis) plotted v/s total H2O in the solution (x-axis shown in log scale). Inset shows CaSO4, gypsum, and anhydrite on a linear scale for x-axis. Future Work: Common B phase thermochemical data are yet to be added to the CHIM-XPT database. On addition of the thermochemical data, refining the start-ing fluid composition and temperature range the result-ant mineral species are expected to include borate salts (such as: inyoite, ulexite, kernite and borax for neutral to high pH, low-temperature environments; colemanite for neutral to high pH, high-temperature environments, and sassolite for low pH, low-temperature environments [3, 22, 23]), providing an insight about the initial B con-tent of Gale diagenetic fluids. With increasing number of iterative steps of the model, the resultant phases and reaction pathways are expected evolve to a closer ap-proximation of the late-stage diagenetic events of Gale crater. Acknowledgement: NSERC Discovery prog., CSA support for NASA MSL Participating Scientists, LANL, UKSA Aurora. References: [1] Fraeman et al., (2020) JGR:P; [2] Das et al., (2020) JGR:P; [3] Gasda et al., (2017) GRL; [4] Ma et al., (2017) Tlnta. 175, 250-255; [5] Dutrizac et al., (2017) Hydromet. 174, 38-46; [6] Lacasse et al., BOV 64.4, 373; [7] Dalton et al., (2016) NIST Sol. DB; [8] Rampe et al., (2020) JGR:P; [9] Frydenvang et al., (2020) JGR:P; [10] Das et al., (2020) LPI 2326, 1080; [11] Janick et al., (2019), JOP, 62.1, 105-120; [12] Goff et al., (2002) JVGR 116, 299-323; [13] Haferburg et al., (2017) Microb. Res. 199, 19-28; [14] Anovitz et al., (1996) RIM 33,181-222; [15] Monnin et al., (2002) JCED 47.6, 1331-1336; [16] Reed et al., (2010) U.Oregon; [17] Bethke et al., (2007) U. Illinois; [18] Na-chon et al., (2017) Icarus 281, 121-136; [19] Ólafsson et al., (1978) Chem. Geo 21.3, 4; [20] Arnórsson et al., (1995) GCA 59.20, 4125-4146; [21] Giroud et al., (2008) U. Iceland; [22] Christ et al., (1967) GCA, 31.3, 313-337; [23] Birsoy et al., (2012) CAE, 27.1, 71-85. 2155.pdf52nd Lunar and Planetary Science Conference 2021 (LPI Contrib. No. 2548)

Modeling the Behavior of Selected Water-Soluble Elements in Calcium Sulfate Veins of Gale Crater

Modeling the Behavior of Selected Water-Soluble Elements in Calcium Sulfate Veins of Gale Crater

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