Jarosite dissolution rates and maximum lifetimes in high salinity brines: Implications for Earth and Mars

Earth and Planetary Science Letters 357–358 (2012) 327–336

Contents lists available at SciVerse ScienceDirect

Earth and Planetary Science Letters journal homepage: www.elsevier.com/locate/epsl

Jarosite dissolution rates and maximum lifetimes in high salinity brines: Implications for Earth and Mars B.N. Pritchett, M.E. Elwood Madden n, A.S. Madden School of Geology and Geophysics, University of Oklahoma, 100 E Boyd, Suite 710, Norman, OK 73019, USA

a r t i c l e i n f o

abstract

Article history: Received 13 July 2012 Received in revised form 11 September 2012 Accepted 12 September 2012 Editor: T. Spohn Available online 25 October 2012

Jarosite is a ferric sulfate salt ((K, H, Na)Fe3(SO4)2(OH)6) that forms in acidic, oxidizing environments on Earth and has also been observed in outcrops on Mars. High chloride concentrations within the outcrops at Meridiani Planum suggest that jarosite likely interacted with high salinity brines. This study examines jarosite dissolution in H2O–CaCl2, and H2O–NaCl brines (activity of water, aH2O¼ 0.35 and 0.75 respectively) to determine the effects of high salinity brines and aH2O on jarosite dissolution rates. Within brines with aH2O¼ 0.75 and 0.35, initial K-jarosite dissolution rates at 298 K decrease from log r ¼  9.9 to  11.6 mol m  2 s  1, and Na-jarosite rates decrease from log r ¼  10.6 to  11.2 mol m  2 s  1, respectively. In addition, K-jarosite dissolution in NaCl brine at 263 K yielded an average dissolution rate of log r ¼  11.6 mol m  2 s  1. Applying a shrinking sphere model to determine 1 mm jarosite particle lifetimes extends the maximum duration of fluid alteration from lifetimes of o 500 years calculated for dilute solutions up to 30,000 þ years in cold, high salinity conditions. While reduced activity of water in high salinity systems decreases the initial rate of jarosite dissolution, increased activity of chloride ions and water in solution due to sulfate precipitation effectively increased the jarosite dissolution rate over days to weeks. This suggests that jarosite dissolution rates increase with time within eutectic brines, perhaps due to Cl  attack on residual Fe3 þ left on the surface of jarosite grains. If brines on Mars became highly concentrated in chlorine ions through sulfate precipitation, the dissolution rate of jarosite, and perhaps other minerals as well, could accelerate with time, shortening particle lifetimes and the inferred duration of aqueous diagenesis significantly. & 2012 Elsevier B.V. All rights reserved.

Keywords: Meridiani Planum chemical weathering diagenesis sulfate chloride

1. Introduction The presence of jarosite, an ephemeral salt, provides evidence of liquid water and can supply valuable information on the geochemistry of formation fluids and diagenetic environments (McLennan et al., 2005; Elwood Madden et al., 2009). Since the discovery of jarosite by the Mars Exploration Rover (MER) Opportunity at Meridiani Planum (Klingelhofer et al., 2004; Squyres et al., 2004; Grotzinger et al., 2005; McLennan et al., 2005; Morris et al., 2007), it has also been identified at other locations on the Martian surface based on spectra obtained by orbiting spacecraft (e.g., Glotch and Bandfield, 2006; Farrand et al., 2009; Roach et al., 2010). Jarosite on the surface of Mars has been interpreted as evidence of ephemeral, acidic fluids that were once active across Mars (Elwood Madden et al., 2004; Benison, 2006; King and McSween, 2005; McLennan et al., 2005; Bibring et al., 2006; Bibring et al., 2007; Hurowitz and McLennan, 2007).

n

Corresponding author. E-mail addresses: [email protected] (B.N. Pritchett), [email protected] (M.E. Elwood Madden), [email protected] (A.S. Madden). 0012-821X/$ - see front matter & 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.epsl.2012.09.011

A wide range of terrestrial jarosite formation mechanisms including precipitation from acid-saline lakes or acid-mine drainage, and alteration of rocks in volcanic systems by fumaroles have been proposed as potential analogs for jarosite-forming environments on Mars (McLennan et al., 2005; Acero et al., 2006; Barron et al., 2006; Benison, 2006; Bowen et al., 2008; Golden et al., 2008). Terrestrial jarosite has been observed to precipitate directly out of low pH, high salinity brines found in acid saline lakes in Western Australia (Alpers et al., 1992; Benison et al., 2007; Bowen and Benison, 2009). Jarosite can also form via several volcanic mechanisms: through volcanic ‘acid-fog’ alteration (Banin et al., 1997), interaction of acidic hydrothermal water with basalt (Golden et al., 2008), or reaction of volcanic ash with condensed SO2 and water-bearing vapors from fumaroles (McCollom and Hynek, 2005). Perhaps the most common jarosite formation mechanism on Earth is through aqueous oxidation of iron-sulfide minerals in acid mine drainage or acid rock drainage (Burns, 1987; Zolotov and Shock, 2005; West et al., 2009; Lacelle and Leveille, 2010). Impact processes have also led to jarosite formation through oxidative weathering of sulfides due to stimulation of geothermal and perhaps microbial activity (Parnell et al., 2010). In addition,

328

B.N. Pritchett et al. / Earth and Planetary Science Letters 357–358 (2012) 327–336

jarosite may form as a product of acid weathering of silicates within thin films of water formed through radiant heating and sulfate aerosols trapped in ice deposits (Niles and Michalski, 2009). Salts and aerosols in ice films would be dissolved during incipient melting, creating highly concentrated eutectic brines that would then continue to interact with other minerals such as jarosite. At Meridiani Planum, jarosite is observed within sandstones composed of altered mafic sediments. These sandstones have been interpreted by the MER team as eolian/playa deposits (Squyres et al., 2004; Grotzinger et al., 2005). Hematite/ferric iron spherules are also found in jarosite-bearing outcrops at Meridiani Planum and may have formed as reaction products of jarosite dissolution (McLennan et al., 2005; Madden et al., 2010). In most terrestrial aqueous systems, jarosite is metastable above pH 2.5 and begins to break down to form either goethite or hematite – both more thermodynamically stable phases – in the presence of dilute near-neutral solutions (Elwood Madden et al., 2004). The transformation of jarosite to hematite has been observed under acidic, low temperature conditions similar to proposed Martian conditions during the period of geologic history associated with formation and weathering of sulfate-rich deposits (Barron et al., 2006; Elwood Madden et al., 2012). Therefore, observations of jarosite spatially co-located with deposits concentrated in iron oxides suggest that rocks at Meridiani Planum likely underwent a period of aqueous diagenesis after jarosite formation (Barron et al., 2006; King and McSween, 2005; Tosca et al., 2008; Elwood Madden et al., 2009; Niles and Michalski, 2009; Rao et al., 2009; Elwood Madden et al., 2012). In fact, jarosite dissolution rates can be used to constrain the duration of aqueous diagenesis, providing a maximum estimate for aqueous alteration events (Elwood Madden et al., 2009; Elwood Madden et al., 2012). In addition to jarosite and hematite, chloride salts have also been observed at Meridiani Planum as well as numerous other locations on Mars (e.g., Rieder et al., 2004; Clark et al., 2005; McLennan et al., 2005; Keller et al., 2006; Osterloo et al., 2008). Widespread Cl, along with SO4 and Br, on Mars may have been sourced from volcanic aerosols and mineral leaching by aqueous solutions (Brass, 1980; Burns, 1993; Rao et al., 2009). Aqueous transport and deposition of Cl through evaporation and/or freezing of ground and surface water likely contributed to Cl enrichment at Meridiani Planum (McLennan et al., 2005; Rao et al., 2009). The sulfates found within the sediments at Meridiani Planum could have also precipitated directly from brines similar to those proposed by Brass (1980). As long as the brines contained

an excess of sulfate over chloride, sulfates, such as jarosite, could precipitate (King and McSween, 2005; Tosca and McLennan, 2009). Vugs in the sediment at Meridiani Planum record the former presence of unknown soluble minerals (McLennan et al., 2005); epsomite (MgSO4  7H2O) and/or melanterite (FeSO4  7H2O) are possible candidates for the former vugfilling phases (Tosca et al., 2008). Thermodynamic calculations of these phases in equilibrium with aqueous solution suggest a maximum projected activity of water (aH2O) of 0.78 for Meridiani brine (Tosca et al., 2008). Once sulfates precipitated, the residual brine would have been dominated by chloride. The presence of chloride salts and other solutes lowers the activity of water in brines, and may have significantly affected jarosite dissolution rates and processes at Meridiani Planum (Barron et al., 2006; Tosca et al., 2008; Elwood Madden et al., 2009). Previous studies have examined jarosite dissolution rates in a range of pH conditions and at various temperatures, but in dilute solutions with relatively high activities of water (Baron and Palmer, 1996; Gasharova et al., 2005; Smith et al., 2006; Welch et al., 2008; Elwood Madden et al., 2009; Elwood Madden et al., 2012). This study examines jarosite dissolution rates in brines under a range of ionic strength and temperature conditions (Table 1). Three different brines (eutectic H2O–CaCl2, and H2O– NaCl, as well as less concentrated H2O–CaCl2 brine) were used to determine the effect of aH2O on jarosite dissolution rates at 295 K and compared to previous measurements of jarosite dissolution in pure water at aH2O¼1 for reference. Experiments were also conducted at 265 K in NaCl eutectic brine to determine the effect of temperature on jarosite dissolution rates in high salinity solutions.

2. Methods 2.1. Jarosite synthesis K-jarosite was synthesized by heating 200 mL of ultrapure (18 MO) H2O and adding 34.4 g of ferric sulfate hydrate and 11.2 g of potassium hydroxide in a glass beaker and mixing for 4 h at 371 K, following the method of Driscoll et al. (2005). Sodium hydroxide was used in lieu of KOH to synthesize Na-jarosite. After 4 h the slurry was centrifuged and the excess liquid was decanted three times. Residual jarosite was placed in the oven at 383 K for 24 h.

Table 1 Experimental conditions. Jarosite A site cation

T (K)

Salt

Wt%

aH2O

Duration (days)

Rate trenda

Source

K K K K Na Na Na Na Na K K K K K

265 295 295 295 295 295 277 295 323 280 296 313 323 295

NaCl CaCl2 CaCl2 NaCl CaCl2 CaCl2 None None None None None none None None

23 50 50 23 50 33 – – – – – – – –

0.75 0.35 0.35 0.75 0.35 0.75 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0

12 14 29 1 16 12 2 1 1 2 1 1 1 14

Increase Increase Increase Decrease Increase Decrease Decrease Decrease Decrease Decrease Decrease Decrease Decrease Decrease

This study This study This study This study This study This study Zahrai et al. (2012) Zahrai et al. (2012) Zahrai et al. (2012) Elwood Madden et al. Elwood Madden et al. Elwood Madden et al. Elwood Madden et al. Kendall et al. (2012)

(2012) (2012) (2012) (2012)

a Increase indicates that dissolution rate increased as the experiment progressed. Decrease indicates that jarosite dissolution slowed with time.

B.N. Pritchett et al. / Earth and Planetary Science Letters 357–358 (2012) 327–336

2.2. Powder X-Ray Diffraction (XRD) Powder XRD was used to identify phases present in the synthesized starting material and reaction products (Supplementary material, Fig. S1 and S2). The starting materials were centrifuged and then the dense slurries were placed into sample holders. To mount reaction products remaining in the experimental slurries at the end of experiments, materials were filtered using a Millipores vacuum filtration system with 0.2 mm filters. After collecting sample materials, filters were cut and secured to sample holders using a thin film of petroleum jelly. XRD analysis was performed using a Rigaku Ultima IV X-Ray diffractometer with a Cu tube operated at 40 kV and 44 mA and a curved graphite monochromator that passes predominantly Cu Ka radiation. The data were collected over 2–651 2y at 0.021 step size. Data analysis and processing was done in MDI Jade 9 software. 2.3. BET surface area analysis BET surface area analysis was conducted on the synthetic jarosite samples using a Beckman Coulter SA 3100. A mass of 1–2 g of each sample was outgassed for 24 h at 303 K to avoid any phase changes that may occur with temperature. The samples were then analyzed with a six-point BET N2 isotherm. The resulting surface area of the jarosite was used to normalize the reaction rates. 2.4. Brines Eutectic salt solutions (NaCl and CaCl2) and less concentrated CaCl2 brine were chosen to cover a range of water activities but also allow for accurate solution-phase K- and Na-analysis. These salts were also selected so that the brine would not contain any of the chemical constituents of jarosite. Sulfate salts in particular were avoided as the high concentrations of SO24  in solution could affect the saturation state of jarosite and therefore impede dissolution. NaCl was used only in the 0.75 aH2O K-jarosite experiments. For the 0.75 aH2O Na-jarosite experiment an unsaturated 33 wt% CaCl2 brine was used. KCl and CuCl2 were also tested. Unfortunately, dissolution rates could not be calculated in these brines due to interferences with aqueous potassium or sodium measurement. Eutectic CaCl2 brine was made by mixing 250 g of CaCl2 salt with 250 g of ultrapure water. The solution was then allowed to cool and stirred for 24 h. The NaCl brine was made by mixing 150 g of NaCl with 368 g of ultrapure water. See Table 1 for properties of the brines and full experimental conditions. 2.5. Batch reactor experiments Either K-jarosite or Na-jarosite (0.1 g) was mixed with 100 ml of brine for each experiment. Each set of conditions was replicated in duplicate or triplicate. For aqueous analysis, 10 ml samples of the jarosite–brine slurry were removed and passed through a 0.2 mm filter. The room temperature experiments (295 K) were sampled over several hours to days, while the 263 K experiments were conducted in a freezer and samples were taken over the course of 9 days. Longer term experiments were conducted to test the reproducibility and collect solid phases from certain experiments where unexpected results were observed. 2.6. Atomic Absorption Spectrophotometry (AAS) A PerkinElmer AAnalyst 800 flame atomic absorption spectrophotometer was used to determine K and Na concentrations in

329

the filtered samples from dissolution experiments. Samples were diluted 1:8 to reduce the salinity prior to analysis. Standard solutions were prepared in matrix-matched brines. The AAS was first calibrated using brine-free standards (1 ppm, 2.5 ppm, 5 ppm, 7.5 ppm, and 10 ppm Na or K) to reduce the amount of salt introduced to the AA and to confirm that the instrument was working properly. A second set of matrixmatched standards, prepared in brines identical to those used in the dissolution experiments, was then tested. These standards were diluted 1:8 to match the samples. The 1:8 dilutions of the matrix-matched standards and samples were completed by mixing 0.375 ml of sample/brine, 1.125 ml of water, and 1.5 ml of 0.1 N nitric acid solution with 0.1 wt% NaCl or KCl. NaCl was added to the 0.1 N nitric acid solution to be used with K-jarosite experiments, and in turn the KCl was added to the solution to be used with Na-jarosite experiments to prevent ionization in the flame. In one case, a Na-jarosite experiment (aH2O¼0.75) was diluted 1:32 to further reduce the salinity; standards for this experiment were also diluted 1:32. Due to the high salinities, the spectrophotometer drain tube was rinsed with ultrapure water before starting measurements. The burner head was inspected for salt deposition and cleaned if necessary. Between each sample analysis, an ultrapure water blank was re-analyzed to check the calibration of the instrument. If the blank signal adsorption rose above 0.009, then the AA was shut down, the burner head and drain tube were rinsed with ultrapure water, and the set of samples was re-analyzed in whole. The burner head was also removed and soaked overnight to remove any salt accumulations following each set of analyses. 2.7. Data analysis To determine the initial jarosite dissolution rate, the concentration of Na or K in solution over time was fit to a polynomial. The derivative of the concentration versus time curve produced the initial dissolution rate at t ¼0 (Rimstidt and Newcomb, 1993). These rates were then normalized using measured BET surface areas to yield surface area normalized dissolution rates (mol m  2 s  1). Estimates of jarosite lifetimes for 1 mm particles in aqueous solutions and brines were determined using a shrinking sphere model (Lasaga, 1998):

Dt ¼

d 2vm r

where Dt is the lifetime of the particle (sec), d is the diameter of the particle (cm), Vm is the molar volume of the mineral (cm3 mol  1), and r is the rate of dissolution (mol cm  2 s  1). The shrinking sphere model assumes that the surface of the particle is in continuous communication with the surrounding fluids, allowing uninterrupted dissolution to occur (Lasaga, 1998). The largest particle size found within the matrix of the outcrops at Meridiani Planum is 1 mm, however most terrestrial jarosites are o20 mm in size. Therefore, the lifetime of 1 mm particles provides a conservative estimate of jarosite lifetimes at Meridiani Planum.

3. Results 3.1. Dissolution rate Initial jarosite dissolution rates in NaCl and CaCl2 brines determined in this study were significantly slower than initial dissolution rates measured in dilute aqueous solutions by Baron and Palmer (1996), Gasharova et al. (2005), Smith et al. (2006),

330

B.N. Pritchett et al. / Earth and Planetary Science Letters 357–358 (2012) 327–336

Table 2 Initial jarosite dissolution rates. aH2O

0.75 0.75 0.75 0.35 0.35 0.35 0.75 0.75 0.75 0.75 0.75 0.35 0.35 0.35 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1

pH

5.0 4.4 4.3 4.0 0.9 2.0 3.0 4.0 4.5 4.7 5.0 6.7 10.9 6.2 7.5

2 8 3.7 4 3 4 3 5.5 2

T (K)

Solution

Log r (mol m  2 s  1)

Jarosite A-site

Source

273 273 273 273 273 273 263 263 273 273 273 273 273 273 280 296 313 323 296 296 296 296 296 296 296 296 296 296 296 296 296 298 298 298 298 298 298 298 298 298

NaCl NaCl NaCl CaCl2 CaCl2 CaCl2 NaCl NaCl CaCl2 CaCl2 CaCl2 CaCl2 CaCl2 CaCl2 Water Water Water Water H2SO4 H2SO4 H2SO4 H2SO4 NaOH NaOH NaOH NaOH NaOH MES MES Water Water HCl CaOH Water HCL HCL H2SO4 H2SO4 Water HCl

 10.0  9.98  9.83  11.52  11.46  11.68  11.55  11.55  10.31  11.01  10.41  11.00  11.33  11.25  9.71 (0.16)  9.2 (0.05)  8.59(0.03)  8.24(0.10)  7.15(0.08)  8.54(0.06)  9.09(0.05)  9.28(0.02)  9.24(0.23)  9.20(0.10)  8.93(0.05)  8.71(0.09)  6.59(0.07)  8.49(0.07)  7.95(0.13)  9.1 (0.4)  8.2 (0.5)  8.8  9.1  11.2 (0.1)  11.3 (0.9)  11.4 (0.4)  11.3 (0.5)  11.8 (0.3)  6.8 (0.4)  8.5 (0.03)

K K K K K K K K Na Na Na Na Na Na K K K K K K K K K K K K K K K Na K K K K K K K K K K

This study This study This study This study This study This study This study This study This study This study This study This study This study This study Elwood Madden et al. (2012) Elwood Madden et al. (2012) Elwood Madden et al. (2012) Elwood Madden et al. (2012) Elwood Madden et al. (2012) Elwood Madden et al. (2012) Elwood Madden et al. (2012) Elwood Madden et al. (2012) Elwood Madden et al. (2012) Elwood Madden et al. (2012) Elwood Madden et al. (2012) Elwood Madden et al. (2012) Elwood Madden et al. (2012) Elwood Madden et al. (2012) Elwood Madden et al. (2012) Elwood Madden et al. (2009) Elwood Madden et al. (2009) Smith et al. (2006) (first 85 days) Smith et al. (2006) (first 85 days) Welch et al. (2008) Welch et al. (2008) Welch et al. (2008) Welch et al. (2008) Welch et al. (2008) Gasharova et al. (2005) Baron and Palmer (1996)

-8.5 K-Jar 263 K K-Jar Na-Jar

-9.0

log r (mol/m2s)

-9.5 -10.0 -10.5 -11.0 -11.5 -12.0 0.0

0.2

0.4

0.6

0.8

1.0

Activity of Water

Fig. 1. Relationship between activity of water and the log initial dissolution rate of K- and Na-jarosite. As the activity of water decreased, so did the initial dissolution rate. The dissolution rate also decreased at lower temperatures. Error bars represent one standard deviation.

and Elwood Madden et al. (2012) (Table 2). In addition, initial jarosite dissolution rates measured in this study decrease significantly with decreasing activity of water (Fig. 1). Within brines with aH2O¼0.75 and 0.35, initial K-jarosite dissolution rates decrease from log r¼ 9.9 (mol m  2 s  1) to  11.6 (Fig. 2a and b), and the

Na-jarosite rates decrease from log r¼  10.6 (mol m  2 s  1) to  11.2 (Supplementary materials, Fig. S3), respectively. In addition, K-jarosite dissolution in NaCl brine at 263 K yielded an average dissolution rate of log r¼  11.6 mol m  2 s  1 (Fig. 2b). However, within both the room temperature CaCl2(0.35 aH2O) K- and Na-jarosite experiments and the 263 K NaCl brine K-jarosite experiment, a significant increase in K þ /Na þ concentration was noted around the fifth to seventh day of the experiments (Fig. 3 and Supplementary materials, Fig. S3). In these experiments, apparent K þ /Na þ release accelerated over days to weeks, resulting in increased dissolution rates with time. However, this increase in concentration was neither seen in room temperature 0.75 aH2O (unsaturated CaCl2 brine) Na-jarosite experiments, nor in room temperature 0.75 aH2O (eutectic NaCl brine) K-jarosite experiments or similar long term K-jarosite dissolution experiments in ultrapure water (Kendall et al., 2012) (Table 1).

3.2. Particle lifetimes Jarosite particle lifetime estimates based on the observed initial dissolution rates are illustrated in Fig. 4. Since increasing ionic strength had a significant effect on initial dissolution rates, estimated particle lifetimes are considerably affected by aH2O. Decreasing aH2O from 1.0 to 0.75 (NaCl eutectic brine), increased

B.N. Pritchett et al. / Earth and Planetary Science Letters 357–358 (2012) 327–336

Fig. 2. Aqueous K-jarosite dissolution measurements from experiments. (a) Short term (  6 h) experiments comparing K-jarosite dissolution in ultrapure water (aH2O¼ 1), eutectic NaCl (aH2O¼ 0.75) and eutectic CaCl2 (aH2O¼ 0.35) at 295 K. (b) Longer experiments ( 2 weeks) comparing dissolution rates in eutectic NaCl (aH2O¼ 0.75) and eutectic CaCl2 (aH2O ¼0.35) at 295 K with eutectic NaCl brine at 265 K. Note that the y axis in graph A has a logarithmic scale and the legend in A applies to both graphs.

331

Fig. 3. K-jarosite dissolution experiments in dilute solution (A), and eutectic CaCl2 brine (B and C). Initial rates of jarosite dissolution are slow by 2 orders of magnitude in CaCl2 brine (A and B) compared to dilute solutions, likely due to reduced water activity (0.35 compared to 1.0 in the dilute fluid). However, after a period of several days, jarosite dissolution accelerates (C) likely due to enhanced Cl  surface complexation. See Fig. 6 for further description of the chloride attack mechanism.

particle lifetimes from 100 to 1100 years for K-jarosite, and 70 to 2300 years for Na-jarosite. When water activity was decreased from 1.0 to 0.35 (CaCl2 eutectic brine), particle lifetimes increased to 36,000 and 10,300 years for K- and Na-jarosite, respectively. At low temperatures (263 K), the lifetime of a 1 mm K-jarosite particle in NaCl brine increased to 36,500 years (Fig. 4).

4. Discussion 4.1. Initial dissolution rates Initial jarosite dissolution rates determined in this study represent the slowest initial synthetic jarosite dissolution rates reported in the literature, compared with Baron and Palmer (1996), Gasharova et al. (2005), Smith et al. (2006), and Elwood Madden et al. (2012) (Table 2). This demonstrates that initial jarosite dissolution is slowed significantly in high salinity brines, likely due to the reduced activity of water in solution. In fact, decreasing the activity of water 25–65% decreases initial jarosite dissolution rates by 1–2 orders of magnitude. However, pH, temperature, grain size, field versus laboratory measurements, saturation state and hydrodynamics also affect mineral dissolution rates (Olsen and Rimstidt, 2007). Elwood Madden et al. (2012) found that pH and temperature significantly affect K-jarosite dissolution rates, with minimum dissolution rates observed at pH 3.5 and low temperatures. Room temperature

Fig. 4. Jarosite lifetimes. Using a shrinking sphere model, the effects of pH, temperature, activity of water, thermodynamics, field versus lab observations, grain size, and hydrodynamics on jarosite lifetimes vary from o1 to 44 orders of magnitude. The solid line including the pH-dependent rate of K-jarosite dissolution in dilute solutions was calculated from Elwood Madden et al. (2012). Figure design after Olsen and Rimstidt (2007).

dissolution rates at pH 1 and 10 were 2 orders of magnitude faster than rates observed at pH 3–4. Natural jarosite samples also dissolved slower than synthetic laboratory samples (Welch et al., 2008). Discrepancies between field observations and rates determined via laboratory mineral

332

B.N. Pritchett et al. / Earth and Planetary Science Letters 357–358 (2012) 327–336

dissolution experiments are not well understood (Velbel, 1986). The ratio of effective surface area to total surface area in natural systems versus the laboratory, unreliability in the estimates of total surface area in natural systems, and hydrologic factors could all in part lead to slower observed rates in the field (Velbel, 1986; White and Brantley, 2003). Indeed, mass transport significantly affected dissolution rates in olivine experiments, where unstirred experiments dissolved 2.5 times slower than stirred experiments (Rosso and Rimstidt, 2000). This slower rate is thought to be caused by a decrease in the transport rate of H þ to the olivine surface (Rosso and Rimstidt, 2000); in the case of jarosite, H þ or OH  mass transport could also limit the field dissolution rate. Transport control of mineral dissolution is increasingly important closer to equilibrium, such that the relative importance of transport versus surface reaction control in some cases relates to mineral solubility (Berner, 1978). For example, carbonates can exhibit either transport, surface reaction, or mixed reaction control depending on conditions (Morse et al., 2007). The solubility of jarosite (Baron and Palmer, 1996) places it in the range where surface-controlled dissolution should be significant (Berner, 1978) far-from equilibrium. 4.2. Increased dissolution rates with time The saturation state of the dissolving phase in solution also affects the dissolution rate. As the system approaches equilibrium, jarosite dissolution rates are expected to decrease, as observed in previous dilute batch reactor experiments (Baron and Palmer, 1996; Gasharova et al., 2005; Smith et al., 2006; Elwood Madden et al., 2012). However, in a subset of the brine experiments reported here, K þ /Na þ concentrations increase more rapidly around day 6 of the low temperature (263 K) K-jarosite in NaCl brine experiment and in both of the 295 K K- and Na-jarosite experiments in eutectic CaCl2 brine, producing a significantly different trend in dissolution rate vs. time as has been previously observed in dilute solutions. We conducted a series of replicate experiments to better understand this unexpected and intriguing result. Visual inspection of some liquid filtrates separated for aqueous analysis indicated precipitation was occurring during storage. XRD analysis of these precipitates showed that antarcticite

4.280 Α

8 day sample pattern 5 day sample pattern 2 day sample pattern 8 hour sample pattern

1000 7.610 Α

Intensity (Counts)

1500

(CaCl2  6H2O) had formed within some of the samples which were kept in a refrigerator at 278 K post sampling (Supplementary materials, Fig. S4). Therefore, we initially hypothesized that as antarcticite precipitated in the refrigerator prior to AA analysis, it removed water from the system, forcing the same number of moles of K þ /Na þ into a smaller amount of solution and increasing the apparent concentration of K þ /Na þ in the samples. We tested this hypothesis by replicating a previous eutectic CaCl2 brine experiment, but took two subsamples at each sampling interval and placed one sample in the refrigerator, while the replicate sample was stored at room temperature. The samples kept at 278 K in the refrigerator developed the same antarcticite crystals seen in the refrigerated samples from the previous experiments, while antarcticite was not observed in the samples kept at 295 K. However, both experiments had nearly identical K þ concentrations over time (Supplementary material, Fig. S5). Therefore, the two subsample sets produced the same apparent dissolution rate, negating our original hypothesis that antarcticite precipitation after sampling affected K and Na concentrations in solution. However, XRD analysis of the jarosite and reaction products filtered from the slurry at the end of the experiments and maintained at 295 K showed that the final slurry contained gypsum (CaSO4  2H2O) and K-jarosite, along with small amounts of Teflon from the stir bars (Fig. 5). We subsequently modified our original hypothesis to suggest that SO4 2 released during dissolution of K and Na-jarosite reacts with Ca2 þ cations in the saturated CaCl2 brine to form gypsum. The removal of water, Ca, and SO4 from solution appears to significantly affect jarosite dissolution rates over periods of days to weeks. This increased dissolution rate with time may be due to (1) removal of water from the system as gypsum precipitates, yielding higher measured concentrations and thus, faster apparent dissolution rates as the same number of moles of K þ /Na þ remain in a smaller amount of solution, (2) Cl  ions form surface complexes with Fe3 þ which remains on the surface of jarosite grains due to incongruent dissolution, breaking Fe–O bonds in the jarosite and thus increasing the dissolution rate, or (3) removal of Ca2 þ and SO24  due to gypsum precipitation increases the activity of water in the brine, therefore generating a faster dissolution rate. Similar results are also observed in NaCl eutectic brines at 265 K

3.8000 Α

500

0 10

11

12

13

14

15

16

17

18

19

20

21

22

23

Two-Theta (deg)

Fig. 5. XRD patterns of the filtered material from K-jarosite dissolution in 0.35 aH2O CaCl2 experiments. Gypsum peaks were noted at 2y 11.6, 20.8, and 23.45. All the other peaks are attributed to K-jarosite, with the exception of the 181 peak where a peak due to Teflon from the stir bar is observed.

B.N. Pritchett et al. / Earth and Planetary Science Letters 357–358 (2012) 327–336

(Supplementary materials, Fig. S3), likely due to thenerdite (Na2SO4) precipitation. To test the first of these three proposed mechanisms, we determined the quantity of water removed from the system due to gypsum precipitation, assuming all of the sulfate released by jarosite dissolution was precipitated as gypsum (2 mol SO24  for every 1 mol K þ released from jarosite; 2 mol SO24  released produces 2 mol CaSO4  2H2O, consuming 4 mol H2O), and corrected the concentration of K þ /Na þ by replacing the water removed by gypsum formation in the system. Taking into account the diminishing liquid from sampling and the removal of water by gypsum, a corrected concentration of K þ was calculated. However the observed and calculated K þ concentrations were nearly identical, demonstrating that the effect of water removal due to gypsum precipitation was negligible. Instead, precipitation of gypsum likely changes Cl  activity in the brine significantly, affecting jarosite surface complexation (Fig. 6). Incongruent jarosite dissolution results in greater than stoichiometric concentrations of Fe remaining at the surface of the residual mineral (Smith et al., 2006; Elwood Madden et al., 2012; Kendall et al., 2012). As Ca2 þ is removed from solution due to gypsum precipitation, Cl  remaining in solution likely complexes with Fe3 þ that remains at the surface of jarosite particles due to incongruent dissolution. Since Fe3 þ has the highest ionic potential of the cations found in the jarosite–Ca–Cl–water slurry, the Cl  anions are more likely to complex with Fe3 þ rather than K þ or Na þ to balance charge in the solution. Cl  surface complexation has been shown to accelerate dissolution rates in iron oxides, relevant to the iron-rich residual framework in the near-surface environment of dissolving jarosite. Increased Cl  concentrations in HCl solutions correlated with increasing iron oxide dissolution rates because Fe–Cl surface complexes weaken Fe–O bonds (Sidhu et al., 1981). Similarly, Cl  surface complexation with Fe3 þ in jarosite may break Fe-O bonds, accelerating the rate limiting dissolution mechanism and producing a total rate increase. All the CaCl2 experiment solutions also showed a distinct yellow coloring that increased in intensity

333

with reaction time, indicating aqueous Fe3 þ –Cl complexes are present in solution (Supplementary materials, Fig. S6). Precipitation of gypsum and subsequent formation of Fe–Cl complexes may also increase the activity of water remaining in solution. This increase in activity of water could potentially cause an increase in jarosite dissolution rates up to an order in magnitude, also contributing to the rapid increase in measured K þ /Na þ concentrations. However, quantitative activity calculations in brines are extremely difficult due to complex interactions that occur within saturated solutions.

4.3. Implications for Mars Our study shows that high salinity brines decrease initial jarosite dissolution rates by approximately 1–2 orders of magnitude compared to dilute water systems. The results from this study show that K- and Na-jarosite initial dissolution rates are significantly affected by changes in activity of water, extending Na and K-jarosite lifetimes up to 30,000þ years in high salinity and cold environments and allowing for prolonged periods of aqueous alteration at Meridiani Planum (Fig. 4). While jarosite dissolution rates are initially slowed in all high salinity brines examined here, the accelerated dissolution rates observed over days to weeks in the eutectic room temperature CaCl2 and low temperature eutectic NaCl experiments suggest that mineral dissolution mechanisms and rates in high salinity systems depend on secondary mineral precipitation. These results also suggest that jarosite dissolution, and perhaps other mineral alteration as well, proceed differently in eutectic or near-eutectic fluids than in dilute solutions which are far from mineral saturation. Since eutectic or near-eutectic brines are the fluids most likely to be stable under near-surface conditions on Mars today (Brass, 1980; Haberle et al., 2001; King and McSween, 2005; Altheide et al., 2009; Fairen et al., 2009; Moehlmann and Thomsen, 2011; Tosca et al., 2011), mineral dissolution and alteration on Mars may be significantly different from dominant chemical weathering and alteration processes observed in terrestrial systems.

Fig. 6. Cartoon of Cl  complexation model of accelerated jarosite (Jar) dissolution in eutectic CaCl2 brine. When jarosite is added to saturated CaCl2 brine, Fe3 þ , SO24  , and K þ are released. The Ca2 þ in solution then bonds with the SO24  to form gypsum (CaSO4  2H2O). As more and more gypsum forms, the Cl  in solution becomes increasingly charge imbalanced. The Cl  then complexes with Fe3 þ remaining on the jarosite surface due to incongruent dissolution, promoting further jarosite dissolution. Similar results are also observed in NaCl eutectic brines at 265 K, likely due to thenerdite (Na2SO4) precipitation.

334

B.N. Pritchett et al. / Earth and Planetary Science Letters 357–358 (2012) 327–336

Under open-system conditions, where brines flow through sediments and precipitation of secondary phases does not control the distribution of anionic species, the presence of high salinity fluids would likely retard jarosite dissolution, preserving it within the rock record. However, if the high salinity fluids were part of a closed system, such as a playa environment as suggested by the MER team (Grotzinger et al., 2005) or ice-hosted sediments and initial meltwater as proposed by Niles and Michalski, 2009; Michalski and Niles, 2012 jarosite dissolution may have accelerated due to precipitation of less soluble sulfate phases and subsequent Cl  attack and/or increasing activity of water. Ionic strength, temperature, and seasonal variability would greatly affect the continuity of liquid water Mars, which could potentially increase the lifetimes of jarosite further. Temperatures at Meridiani Planum and other jarosite-bearing localities at the time of jarosite formation/diagenesis are unknown. However, high salinity brines may remain liquid at temperatures below 225 K (Brass, 1980; Haberle et al., 2001; Marion et al., 2008; Chevrier and Altheide, 2008; Fairen et al., 2009; Tosca et al., 2011; Moehlmann and Thomsen, 2011) and jarosite dissolution may continue below the freezing point of pure liquid water (Niles and Michalski, 2009), as demonstrated by our 263 K NaCl brine experiments. Since secondary mineral solubility is often suppressed at lower temperatures, precipitation of secondary minerals in closed systems, including gypsum, may lead to accelerated jarosite dissolution due to increased water and Cl  activity in solution. Several experimental and thermodynamic modeling studies of fluids at Meridiani Planum suggest that brines acted in a closed system, with limited water:rock ratios which likely formed sulfates, including Mg–SO4 phases (Marion et al., 2009; McLennan et al., 2005; Hurowitz and McLennan, 2007; Treguier et al., 2008; Berger et al., 2009; Dickson and Giblin, 2009; Rao et al., 2009; Tosca and McLennan, 2009; Moore et al., 2010). Sulfate and chloride minerals have also been observed in rocks and soils at Gusev crater (Haskin et al., 2005; Cabrol et al., 2006; Hurowitz et al., 2006; Wang et al., 2006; Schmidt et al., 2008; Yen et al., 2008; Amundson et al., 2008; Wang and Ling, 2011) indicating that this region was also exposed to high salinity fluids for one or more periods. Numerous CRISM and OMEGA observations of sulfate and polyhydrated salt deposits suggest that sulfate-rich fluids were widely distributed over the surface of Mars during the late Noachian–early Hesperian (e.g. Bibring et al., 2006; Hurowitz and McLennan, 2007; Murchie et al., 2009a, 2009b). Large sulfate-bearing dune fields formed from material released from the northern polar cap suggest that sulfate-rich aqueous alteration may have continued through the Amazonian (Horgan et al., 2009). These widespread Cl and S-rich deposits on Mars were likely sourced from volcanic aerosols and/or mineral leaching by aqueous solutions (e.g. Settle, 1979; Brass, 1980; Burns, 1987; Banin et al., 1997; Tosca et al., 2004; Treguier et al., 2008; Rao et al., 2009; Michalski and Niles, 2012). Hydrothermal fluids and fumaroles (e.g. Newsom et al., 1999; Yen et al., 2008), as well as fluid circulation associated with impact processes (e.g. Osinski et al., 2001; Knauth and Burt, 2002; Parnell et al., 2010) may have also contributed salts to near-surface materials. Evaporation and/ or freezing of surface water or near-surface groundwater concentrates salts in the liquid phase, eventually leading to high salinity eutectic brines (Brass, 1980; Clark and Van Hart, 1981; King and McSween, 2005; Marion et al., 2008; Fairen et al., 2009; Tosca et al., 2011) As near-surface water reservoirs evaporated and/or froze in the early-mid Hesperian, the last remaining aqueous liquids were likely high salinity eutectic brines. These eutectic solutions may have been stable over geologically relevant time periods, even at

low temperatures and pressures similar to those observed today (Zent and Fanale, 1986; Haberle et al., 2001; Knauth and Burt, 2002; Richardson and Mischna, 2005; Hurowitz and McLennan, 2007; Chevrier and Altheide, 2008; Altheide et al., 2009; Fairen et al., 2009; Gallagher et al., 2011; Moehlmann and Thomsen, 2011). An alternative model suggests that widespread sulfate-rich deposits formed from eutectic melting of ice mixed with volcanic aerosols (Niles and Michalski, 2009; Michalski and Niles, 2012). Recent observations of gypsum-bearing sediments released from the northern polar cap via sublimation (Langevin et al., 2005; Horgan et al., 2009; Masse et al., 2012) support the hypothesis that significant aqueous alteration may occur through partial melting of ice deposits. Therefore, eutectic brine–mineral reactions may be an important geochemical process over much of Mars’ history. Gypsum has also been observed in evaporite assemblages associated with gossan-hosted jarosite deposits in the terrestrial Arctic (West et al., 2009), indicating that similar processes may occur as jarosite-alteration fluids freeze/evaporate within polar systems. Gypsum, jarosite, and iron oxides observed in acid saline lakes in western Australia (Beninson et al. 2007; Story et al., 2010) suggest that sulfate precipitation during brine evaporation may significantly affect terrestrial jarosite diagenesis as well, perhaps leading to abundant gypsum, chloride, and iron oxides observed in terrestrial and martian red-bed deposits (Beninson and Goldstein, 2002; Benison, 2006).

Acknowledgments The authors thank D. Ambuehl, V. Priegnitz, M. Miller, M. Kendall, and S. Zahrai for laboratory assistance and M. Soreghan for reviewing an earlier draft of this manuscript. Funding was provided by NASA MFRP Grant NNX09AL18G.

Appendix A. Supporting information Supplementary data associated with this article can be found in the online version at http://dx.doi.org/10.1016/j.epsl.2012.09.011.

References Acero, P., Ayora, C., Torrento, C., Nieto, J., 2006. The behavior of trace elements during schwertmannite precipitation and subsequent transformation into goethite and jarosite. Geochim. Cosmochim. Acta. 70, 4130–4139. Alpers, C.N., Rye, R.O., Nordstrom, D.K., White, L.D., King, B.S., 1992. Chemical, crystallographic and stable isotopic properties of alunite and jarosite from acid hypersaline Australian lakes. Chem. Geol. 96, 203–226. Altheide, T., Chevrier, V., Nicholson, C., Denson, J., 2009. Experimental investigation of the stability and evaporation of sulfate and chloride brines on Mars. Earth Planet. Sci. Lett. 282, 69–78. Amundson, R., Ewing, S., Dietrich, W., Sutter, B., Owen, J., Chadwick, O., Nishiizumi, K., Walvoord, M., McKay, C., 2008. On the in situ aqueous alteration of soils on Mars. Geochim. Cosmochim. Acta 72, 3845–3864. Banin, A., Han, F.X., Kan, I., Cicelsky, A., 1997. Acidic volatiles and the Mars soil. Geophys. Res. Lett. 102 (E6), 13341–13356. Baron, D., Palmer, C.D., 1996. Solubility of jarosite at 4–35 degrees C. Geochim. Cosmochim. Acta 60, 185–195. Barron, V., Torrent, J., Greenwood, J.P., 2006. Transformation of jarosite to hematite in simulated Martian brines. Earth Planet. Sci. Lett. 25, 380–385. Benison, K.C., 2006. A Martian analog in Kansas: comparing Martian strata with Permian acid saline lake deposits. Geology 34, 385–388. Benison, K.C., Bowen, B.B., Oboh-Ikuenobe, F.E., Jagniecki, E.A., LaClair, D.A., Story, S.L., Mormile, M.R., Hong, B.Y., 2007. Sedimentology of acid saline lakes in southern Western Australia: newly described processes and products of an extreme environment. J. Sediment. Res. 77, 366–388. Benison, K.C., Goldstein, R.H., 2002. Recognizing acid lakes and groundwaters in the rock record. Sediment. Geol. 151, 177–185. Berger, G., Toplis, M.J., Treguier, E., d’Uston, C., Pinet, P., 2009. Evidence in favor of small amounts of ephemeral and transient water during alteration at Meridiani Planum, Mars. Am. Mineral. 94, 1279–1282.

B.N. Pritchett et al. / Earth and Planetary Science Letters 357–358 (2012) 327–336

Berner, R.A., 1978. Rate control of mineral dissolution under Earth surface conditions. Am. J. Sci. 278, 1235–1252. Bibring, J.P., Langevin, Y., Mustard, J.F., Poulet, F., Arvidson, R., Gendrin, A., Gondet, B., Mangold, N., Pinet, P., Forget, F., 2006. Omega Team, 2006. Global mineralogical and aqueous mars history derived from OMEGA/Mars express data. Science 312, 400–404. Bibring, J.-P., Arvidson, R.E., Gendrin, A., Gondet, B., Langevin, Y., Mouelic, S.L., Mangold, N., Morris, R.V., Mustard, J.F., Poulet, F., Quantin, C., Sotin, C., 2007. Coupled Ferric Oxides and Sulfates on the Martian Surface. Science 317, 1206–1210. Bowen, B.B., Benison, K.C., 2009. Geochemical characteristics of naturally acid and alkaline saline lakes in southern Western Australia. Appl. Geochem. 24, 268–284. Bowen, B.B., Benison, K.C., Oboh-Ikuenobe, F.E., Story, S., Mormile, M.R., 2008. Active hematite concretion formation in modem acid saline lake sediments, Lake Brown, Western Australia. Earth Planet. Sci. Lett. 268, 52–63. Brass, G.W., 1980. Stability of brines on Mars. Icarus 42, 20–28. Burns, R.G., 1987. Ferric Sulfates on Mars. Geophys. Res. Lett. 92, E570–E574. Burns, R.G., 1987. Ferric sulfates on Mars. J. Geophys. Res.—Solid Earth Planets 92, E570–E574. Burns, R.G., 1993. Rates and mechanisms of chemical weathering of ferromagnesian silicate minerals on Mars. Geochim. Cosmochim. Acta 57, 4555–4574. Cabrol, N.A., Farmer, J.D., Grin, E.A., Richter, L., Soderblom, L., Li, R., Herkenhoff, K., Landis, G.A., Arvidson, R.E., 2006. Aqueous processes at Gusev crater inferred from physical properties of rocks and soils along the Spirit traverse. J. Geophys. Res. 111, E02S20. Chevrier, V.F., Altheide, T.S., 2008. Low temperature aqueous ferric sulfate solutions on the surface of Mars. Geophys. Res. Lett. L22101, http://dx.doi.org/10.1029/2008GL035489. Clark, B.C., Morris, R.V., McLennan, S.M., Gellert, R., Jolliff, B., Knoll, A.H., Squyres, S.W., Lowenstein, T.K., Ming, D.W., Tosca, N.J., Yen, A., Christensen, P.R., Gorevan, S., Bruckner, J., Calvin, W., Dreibus, G., Farrand, W., Klingelhoefer, G., Waenke, H., Zipfel, J., Bell, J.F., Grotzinger, J., McSween, H.Y., Rieder, R., 2005. Chemistry and mineralogy of outcrops at Meridiani Planum. Earth Planet. Sci. Lett. 240, 73–94. Clark, B.C., Van Hart, D.C., 1981. The salts of Mars. Icarus 45, 370–378. Dickson, B.L., Giblin, A.M., 2009. Features of acid–saline systems of Southern Australia. Appl. Geochem. 24, 297–302. Driscoll, R.L., Leinz, R.W., 2005. Methods for Synthesis of Some Jarosites. U.S. Geological Survey Techniques and Methods 5-D1, p.5. Elwood Madden, M.E.E., Bodnar, R.J., Rimstidt, J.D., 2004. Jarosite as an indicator of water-limited chemical weathering on Mars. Nature 431, 821–823. Elwood Madden, M.E.E., Madden, A.S., Rimstidt, J.D., 2009. How long was Meridiani Planum wet? Applying a jarosite stopwatch to determine the duration of aqueous diagenesis. Geology 37, 635–638. Elwood Madden, M.E., Madden, A.S., Rimstidt, J.D., Zahrai, S., Kendall, M.R., Miller, M.A., 2012. Jarosite dissolution rates and nanoscale mineralogy. Geochim. Cosmochim. Acta 91, 206–321. Fairen, A.G., Davila, A.F., Gago-Duport, L., Amils, R., McKay, C.P., 2009. Stability against freezing of aqueous solutions on early Mars. Nature 459, 401–404. Farrand, W.H., Glotch, T.D., Rice, J.W., Hurowitz, J.A., Swayze, G.A., 2009. Discovery of jarosite within the Mawrth Vallis region of Mars: implications for the geologic history of the region. Icarus 204, 478–488. Gallagher, C., Balme, M.R., Conway, S.J., Grindrod, P.M., 2011. Sorted clastic stripes, lobes and associated gullies in high-latitude craters on Mars: landforms indicative of very recent, polycyclic ground-ice thaw and liquid flows. Icarus 211, 458–471. Gasharova, B., Gottlicher, J., Becker, U., 2005. Dissolution at the surface of jarosite: an in situ AFM study. Chem. Geol. 215, 499–516. Glotch, T.D., Bandfield, J.L., 2006. Determination and interpretation of surface and atmospheric miniature thermal emission spectrometer spectral end-members at the Meridiani Planum landing site. J. Geophys. Res. 111, E12S06. Golden, D.C., Ming, D.W., Morris, R.V., Graff, T.G., 2008. Hydrothermal synthesis of hematite spherules and jarosite: implications for diagenesis and hematite spherule formation in sulfate outcrops at Meridiani Planum, Mars. Am. Mineral. 93, 1201–1214. Grotzinger, J.P., Arvidson, R.E., Bell, J.F., Calvin, W., Clark, B.C., Fike, D.A., Golombek, M., Greeley, R., Haldemann, A., Herkenhoff, K.E., Jolliff, B.L., Knoll, A.H., Malin, M., McLennan, S.M., Parker, T., Soderblom, L., Sohl-Dickstein, J.N., Squyres, S.W., Tosca, N.J., Watters, W.A., 2005. Stratigraphy and sedimentology of a dry to wet eolian depositional system, Burns formation, Meridiani Planum, Mars. Earth Planet. Sci. Lett. 240, 11–72. Haberle, R.M., McKay, C.P., Schaeffer, J., Cabrol, N.A., Grin, E.A., Zent, A.P., Quinn, R., 2001. On the possibility of liquid water on present-day Mars. J. Geophys. Res.—Planets 106, 23317–23326. Haskin, L.A., Wang, A., Jolliff, B.L., McSween, H.Y., Clark, B.C., Des Marais, D.J., McLennan, S.M., Tosca, N.J., Hurowitz, J.A., Farmer, J.D., Yen, A., Squyres, S.W., Arvidson, R.E., Klingelhofer, G., Schroder, C., de Souza, P.A., Ming, D.W., Gellert, R., Zipfel, J., Bruckner, J., Bell, J.F., Herkenhoff, K., Christensen, P.R., Ruff, S., Blaney, D., Gorevan, S., Cabrol, N.A., Crumpler, L., Grant, J., Soderblom, L., 2005. Water alteration of rocks and soils on Mars at the Spirit rover site in Gusev crater. Nature 436, 66–69. Horgan, B.H., Bell III, J.F., Dobrea, E.Z.N., Cloutis, E.A., Bailey, D.T., Craig, M.A., Roach, L.H., Mustard, J.F., 2009. Distribution of hydrated minerals in the north polar region of Mars. J. Geophys. Res.—Planets, E01005, http://dx.doi.org/10.1029/ 2008JE003187.

335

Hurowitz, J.A., McLennan, S.M., 2007. A similar to 3.5 Ga record of water-limited, acidic weathering conditions on Mars. Earth Planet. Sci. Lett. 260, 432–443. Hurowitz, J.A., McLennan, S.M., Tosca, N.J., Arvidson, R.E., Michalski, J.R., Ming, D.W., Schroder, C., Squyres, S.W., 2006. In situ and experimental evidence for acidic weathering of rocks and soils on Mars. J. Geophys. Res.—Planets, E02S19, http://dx.doi.org/10.1029/2005JE002515. Keller, J.M., Boynton, W.V., Karunatillake, S., Baker, V.R., Dohm, J.M., Evans, L.G., Finch, M.J., Hahn, B.C., Hamara, D.K., Janes, D.M., Kerry, K.E., Newsom, H.E., Reedy, R.C., Sprague, A.L., Squyres, S.W., Starr, R.D., Taylor, G.J., Williams, R.M.S., 2006. Equatorial and midlatitude distribution of chlorine measured by Mars Odyssey GRS. Geophys. Res. Lett. 111, 18. Kendall, M.R., Madden, A.S., Elwood Madden, M.E., Hu, Q., 2012. Influence of Arsenic Incorporation on Jarosite Dissolution Rates and Reaction Products. Goldschmidt 2012, Montreal, Abstract, 1354. King, P.L., McSween, H.Y., 2005. Effects of H2O, pH, and oxidation state on the stability of Fe minerals on Mars. J. Geophys. Res.—Planets, E12S10, http://dx.doi.org/10.1029/2005JE002482. Klingelhofer, G., Morris, R.V., Bernhardt, B., Schroder, C., Rodionov, D.S., de Souza, P.A., Yen, A., Gellert, R., Evlanov, E.N., Zubkov, B., Foh, J., Bonnes, U., Kankeleit, E., Gutlich, P., Ming, D.W., Renz, F., Wdowiak, T., Squyres, S.W., Arvidson, R.E., 2004. Jarosite and hematite at Meridiani Planum from Opportunity’s Mossbauer spectrometer. Science 306, 1740–1745. Knauth, L.P., Burt, D.M., 2002. Eutectic brines on Mars: origin and possible relation to young seepage features. Icarus 158, 267–271. Lacelle, D., Leveille, R., 2010. Acid drainage generation and associated Ca–Fe–SO4 minerals in a periglacial environment, Eagle Plains, Northern Yukon, Canada: a potential analogue for low-temperature sulfate formation on Mars. Planet. Space Sci. 58, 509–521. Langevin, Y., Poulet, F., Bibring, J.P., Gondet, B., 2005. Sulfates in the north polar region of Mars detected by OMEGA/Mars express. Science 307, 1584–1586. Lasaga, A.C., 1998. Kinetic Theory in the Earth Sciences. Princeton University Press, Princeton, New Jersey (pp. 728). Madden, A.S., Hamilton, V.E., Madden, M.E.E., Larson, P.R., Miller, M.A., 2010. Lowtemperature mechanism for formation of coarse crystalline hematite through nanoparticle aggregation. Earth Planet. Sci. Lett. 298, 377–384. Marion, G.M., Catling, D.C., Kargel, J.S., 2009. Br/Cl partitioning in chloride minerals in the Burns formation on Mars. Icarus 200, 436–445. Marion, G.M., Kargel, J.S., Catling, D.C., 2008. Modeling ferrous–ferric iron chemistry with application to Martian surface geochemistry. Geochim. Cosmochim. Acta 72, 242–266. Masse, M., Bourgeois, O., Le Mouelic, S., Verpoorter, C., Spiga, A., Le Deit, L., 2012. Wide distribution and glacial origin of polar gypsum on Mars. Earth Planet. Sci. Lett. 317, 44–55. McCollom, T.M., Hynek, B.M., 2005. A volcanic environment for bedrock diagenesis at Meridiani Planum on Mars. Nature 438, 1129–1131. McLennan, S.M., Bell, J.F., Calvin, W.M., Christensen, P.R., Clark, B.C., de Souza, P.A., Farmer, J., Farrand, W.H., Fike, D.A., Gellert, R., Ghosh, A., Glotch, T.D., Grotzinger, J.P., Hahn, B., Herkenhoff, K.E., Hurowitz, J.A., Johnson, J.R., Johnson, S.S., Jolliff, B., Klingelhofer, G., Knoll, A.H., Learner, Z., Malin, M.C., McSween, H.Y., Pocock, J., Ruff, S.W., Soderblom, L.A., Squyres, S.W., Tosca, N.J., Watters, W.A., Wyatt, M.B., Yen, A., 2005a. Provenance and diagenesis of the evaporitebearing Burns formation, Meridiani Planum, Mars. Earth Planet. Sci. Lett. 240, 95–121. Michalski, J., Niles, P.B., 2012. Atmospheric origin of Martian interior layered deposits: links to climate change and the global sulfur cycle. Geology 40, 419–422. Moehlmann, D., Thomsen, K., 2011. Properties of cryobrines on Mars. Icarus 212, 123–130. Moore, J.M., Bullock, M.A., Newsom, H., Nelson, M., 2010. Laboratory simulations of Mars evaporite geochemistry. J. Geophys. Res.–Planets, E06009, http://dx.doi.org/10.1029/2008JE003208. Morse, J.W., Arvidson, R.S., Luttge, A., 2007. Calcium carbonate formation and dissolution. Chem. Rev. 107, 342–381. Morris, R.V., et al., 2007. Iron mineralogy and aqueous alteration on Mars from the ¨ MER Mossbauer spectrometers. In: Bell, J.F., III (Ed.), The Martian Surface: Composition, Mineralogy, and Physical Properties (Chapter 15). Murchie, S.L., Roach, L., Seelos, F., Milliken, R., Mustard, J., Arvidson, R., Wiseman, S., Lichtenberg, K., Andrews-Hanna, J., Bishop, J., Bibring, J.-P., Parente, M., Morris, R., 2009a. Evidence for the origin of layered deposits in Candor Chasma, Mars, from mineral composition and hydrologic modeling. J. Geophys. Res.—Planets, E00D05, http://dx.doi.org/10.1029/2009JE003343. Murchie, S.L., Mustard, J.F., Ehlmann, B.L., Milliken, R.E., Bishop, J.L., McKeown, N.K., Dobrea, E.Z.N., Seelos, F.P., Buczkowski, D.L., Wiseman, S.M., Arvidson, R.E., Wray, J.J., Swayze, G., Clark, R.N., Marais, D.J.D., McEwen, A.S., Bibring, J.P., 2009b. A synthesis of Martian aqueous mineralogy after 1 Mars year of observations from the Mars Reconnaissance Orbiter. J. Geophys. Res.—Planets, E00D06, http://dx.doi.org/10.1029/2009JE003342. Newsom, H.E., Hagerty, J.J., Goff, F., 1999. Mixed hydrothermal fluids and the origin of the Martian soil. J. Geophys. Res.—Planets 104, 8717–8728. Niles, P.B., Michalski, J., 2009. Meridiani Planum sediments on Mars formed from weathering in massive ice deposits. Nat. Geosci. 2, 215–220. Olsen, A.A., Rimstidt, J.D., 2007. Using a mineral lifetime diagram to evaluate the persistence of olivine on Mars. Am. Mineral. 92, 598–602. Osinski, G.R., Spray, J.G., Lee, P., 2001. Impact-induced hydrothermal activity within the Haughton impact structure, arctic Canada: generation of a transient, warm, wet oasis. Meteorit. Planet. Sci. 36, 731–745.

336

B.N. Pritchett et al. / Earth and Planetary Science Letters 357–358 (2012) 327–336

Osterloo, M.M., Hamilton, V.E., Bandfield, J.L., Glotch, T.D., Baldridge, A.M., Christensen, P.R., Tornabene, L.L., Anderson, F.S., 2008. Chloride-bearing materials in the southern highlands of Mars. Science 319, 1651–1654. Parnell, J., Boyce, A., Thackrey, S., Muirhead, D., Lindgren, P., Mason, C., Taylor, C., Still, J., Bowden, S., Osinski, G.R., Lee, P., 2010. Sulfur isotope signatures for rapid colonization of an impact crater by thermophilic microbes. Geology 38, 271–274. Rao, M.N., Nyquist, L.E., Sutton, S.R., Dreibus, G., Garrison, D.H., Herrin, J., 2009. Fluid-evaporation records preserved in salt assemblages in Meridiani rocks. Earth Planet. Sci. Lett. 286, 396–403. Richardson, M.I., Mischna, M.A., 2005. Long-term evolution of transient liquid water on Mars. J. Geophys. Res.—Planets, E03003, http://dx.doi.org/10.1029/ 2004JE002367. Rieder, R., Gellert, R., Anderson, R.C., Bruckner, J., Clark, B.C., Dreibus, G., Economou, T., Klingelhoffer, G., Lugmair, G.W., Ming, D.W., Squyres, S.W., d’Uston, C., Wanke, H., Yen, A., Zipfel, J., 2004. Chemistry of rocks and soils at Meridiani Planum from the alpha particle X-ray spectrometer. Science 306, 1746–1749. Rimstidt, J.D., Newcomb, W.D., 1993. Measurement and analysis of rate data—the rate of reaction of ferric iron with pyrite. Geochim. Cosmochim. Acta 57, 1919–1934. Roach, L.H., Mustard, J.F., Swayze, G., Milliken, R.E., Bishop, J.L., Murchie, S.L., Lichtenberg, K., 2010. Hydrated mineral stratigraphy of Ius Chasma, Valles Marineris. Icarus 206, 253–268. Rosso, J.J., Rimstidt, J.D., 2000. A high resolution study of forsterite dissolution rates. Geochim. Cosmochim. Acta 64, 797–811. Schmidt, M.E., Ruff, S.W., McCoy, T.J., Farrand, W.H., Johnson, J.R., Gellert, R., Ming, D.W., Morris, R.V., Cabrol, N., Lewis, K.W., Schroeder, C., 2008. Hydrothermal origin of halogens at Home Plate, Gusev Crater. J. Geophys. Res.—Planets, E06S12, http://dx.doi.org/10.1029/2007JE003027. Settle, M., 1979. Formation and deposition of volcanic sulfate aerosols on Mars. J. Geophys. Res. 84, 8343–8354. Sidhu, P.S., Gilkes, R.J., Cornell, R.M., Posner, A.M., Quirk, J.P., 1981. Dissolution of iron-oxides and oxyhydroxides in hydrochloric and perchloric acids. Clays Clay Miner. 29, 269–276. Smith, A.M.L., Hudson-Edwards, K.A., Dubbin, W.E., Wright, K., 2006. Dissolution of jarosite [KFe3(SO4)(2)(OH)(6)] at pH 2 and 8: insights from batch experiments and computational modelling. Geochim. Cosmochim. Acta 70, 608–621. Squyres, S.W., Grotzinger, J.P., Arvidson, R.E., Bell, J.F., Calvin, W., Christensen, P.R., Clark, B.C., Crisp, J.A., Farrand, W.H., Herkenhoff, K.E., Johnson, J.R., Klingelhofer, G., Knoll, A.H., McLennan, S.M., McSween, H.Y., Morris, R.V., Rice, J.W., Rieder, R., Soderblom, L.A., 2004. In situ evidence for an ancient aqueous environment at Meridiani Planum, Mars. Science 306, 1709–1714. Story, S., Bowen, B.B., Benison, K.C., Schulze, D.G., 2010. Authigenic phyllosilicates in modern acid saline lake sediments and implications for Mars. J. Geophys. Res.—Planets, E12012, http://dx.doi.org/10.1029/2010JE003687. Tosca, N.J., Knoll, A.H., McLennan, S.M., 2008. Water activity and the challenge for life on early Mars. Science 320, 1204–1207.

Tosca, N.J., McLennan, S.M., 2009. Experimental constraints on the evaporation of partially oxidized acid-sulfate waters at the martian surface. Geochim. Cosmochim. Acta 73, 1205–1222. Tosca, N.J., McLennan, S.M., Lamb, M.P., Grotzinger, J.P., 2011. Physicochemical properties of concentrated Martian surface waters. J. Geophys. Res.—Planets, E05004, http://dx.doi.org/10.1029/2010JE003700. Tosca, N.J., McLennan, S.M., Lindsley, D.H., Schoonen, M.A.A., 2004. Acid-sulfate weathering of synthetic Martian basalt: the acid fog model revisited. J. Geophys. Res.—Planets, E05003, http://dx.doi.org/10.1029/2003JE002218. Treguier, E., d’Uston, C., Pinet, P.C., Berger, G., Toplis, M.J., McCoy, T.J., Gellert, R., Bruecker, J., 2008. Overview of Mars surface geochemical diversity through Alpha Particle X-Ray Spectrometer data multidimensional analysis: first attempt at modeling rock alteration. J. Geophys. Res.—Planets, E12S34, http://dx.doi.org/10.1029/2007JE003010. Velbel, M.A., 1986. Influence of surface-area, surface characteristics, and solution composition on feldspar weathering rates. ACS Symp. Ser. 323, 615–634. Wang, A., Haskin, L.A., Squyres, S.W., Jolliff, B.L., Crumpler, L., Gellert, R., Schroder, C., Herkenhoff, K., Hurowitz, J., Tosca, N.J., Farrand, W.H., Anderson, R., Knudson, A.T., 2006. Sulfate deposition in subsurface regolith in Gusev crater, Mars. J. Geophys. Res.—Planets, E02S17, http://dx.doi.org/10.1029/ 2005JE002513. Wang, A., Ling, Z.C., 2011. Ferric sulfates on Mars: a combined mission data analysis of salty soils at Gusev crater and laboratory experimental investigations. J. Geophys. Res.—Planets, E00F17, http://dx.doi.org/10.1029/ 2010JE003665. Welch, S.A., Kirste, D., Christy, A.G., Beavis, F.R., Beavis, S.G., 2008. Jarosite dissolution II—reaction kinetics, stoichiometry and acid flux. Chem. Geol. 254, 73–86. West, L., McGown, D.J., Onstott, T.C., Morris, R.V., Suchecki, P., Pratt, L.M., 2009. High lake gossan deposit: an Arctic analogue for ancient Martian surficial processes? Planet. Space Sci. 57, 1302–1311. White, A.F., Brantley, S.L., 2003. The effect of time on the weathering of silicate minerals: why do weathering rates differ in the laboratory and field? Chem. Geol. 202, 479–506. Yen, A.S., Morris, R.V., Clark, B.C., Gellert, R., Knudson, A.T., Squyres, S., Mittlefehldt, D.W., Ming, D.W., Arvidson, R., McCoy, T., Schmidt, M., Hurowitz, J., Li, R., Johnson, J.R., 2008. Hydrothermal processes at Gusev Crater: an evaluation of Paso Robles class soils. J. Geophys. Res.—Planets, E06S10, http://dx.doi.org/10. 1029/2007JE002978. Zahrai, S.K., Elwood Madden, M.E., Madden, A.S., Rimstidt, J.D., 2012. Comparing Na–jarosite and K–jarosite dissolution rates to determine the effects of crystal chemistry on jarosite lifetimes. In: Abstract #1658 Presented at the 43rd Lunar and Planetary Science Conference, The Woodlands, TX, Abstract 1658. Zent, A.P., Fanale, F.P., 1986. Possible Mars brines—equilibrium and kinetic considerations. J. Geophys. Res.—Solid Earth Planets 91, D439–D445. Zolotov, M.Y., Shock, E.L., 2005. Formation of jarosite-bearing deposits through aqueous oxidation of pyrite at Meridiani Planum, Mars. Geophys. Res. Lett. L21203, http://dx.doi.org/10.1029/2005GL024253.