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

• Published in: Earth and planetary science letters 2012-12, Vol.357-358, p.327-336
• Main Authors: Pritchett, B.N., Elwood Madden, M.E., Madden, A.S.
• Format: Article
• Language: English
• Subjects: chemical weathering; chloride; diagenesis; Meridiani Planum; sulfate
• ISSN: 0012-821X; 1385-013X
• DOI: 10.1016/j.epsl.2012.09.011

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, aH2O=0.35 and 0.75 respectively) to determine the effects of high salinity brines and aH2O on jarosite dissolution rates. Within brines with aH2O=0.75 and 0.35, initial K-jarosite dissolution rates at 298K decrease from logr=−9.9 to −11.6molm−2s−1, and Na-jarosite rates decrease from logr=−10.6 to −11.2molm−2s−1, respectively. In addition, K-jarosite dissolution in NaCl brine at 263K yielded an average dissolution rate of logr=−11.6molm−2s−1. Applying a shrinking sphere model to determine 1mm jarosite particle lifetimes extends the maximum duration of fluid alteration from lifetimes of