Boron and Lithium in Calcium Sulfate Veins: Tracking Precipitation of Diagenetic Materials in Vera Rubin Ridge, Gale Crater.

The NASA Curiosity rover's ChemCam instrument suite has detected boron in calcium‐sulfate‐filled fractures throughout the sedimentary strata of Gale crater including Vera Rubin ridge. The presence of elevated B concentration provides insights into Martian subsurface aqueous processes. In this study we extend the data set of B in Ca‐sulfate veins across Gale crater, comparing the detection frequency and relative abundances with Li. We report 33 new detections of B within veins analyzed between Sols 1548 and 2311 where detections increase in Pettegrove Point and Jura members, which form Vera Rubin ridge. The presence of B and Li in the Ca‐sulfate veins is possibly due to dissolution of preexisting B in clays of the bedrock by acids or neutral water and redistribution of the elements into the veins. Elevated frequency of B detection in veins of Gale crater correlates with presence of dehydration features such as desiccation cracks, altered clay minerals and detections of evaporites such as Mg‐sulfates and chloride salts in the host rocks. The increased observations of B also coincide with decreased Li concentration in the veins (average Li concentration of veins drops by ~15 ppm). Boron and Li have varying solubilities, and Li does not form salts as readily upon dehydration as B, causing it to remain in the solution. So the weak negative correlation between B and Li may reflect the crystallization sequence during dehydration on Vera Rubin ridge. Plain Language Summary: Boron and lithium were measured in cracks in the rocks that were filled with whitish, calcium sulfate. These were found in Gale crater using the ChemCam instrument on the Mars Science Laboratory Curiosity rover. Both elements are highly water soluble and may indicate late‐stage ground water activity. Boron's lower solubility compared to that of lithium means it forms salts relatively easily, while Li remains dissolved in the brine with progressive evaporation. In our study we find that on Vera Rubin ridge, boron detection frequency is inversely proportional to the concentration of lithium. This finding suggests that, based on their different solubilities, boron may have precipitated in the fractures before lithium. Lithium possibly moved away with the remaining brine, leaving boron behind as precipitates. Key Points: ChemCam analyses of calcium sulfate veins in Vera Rubin ridge (VRR) show the presence of boron and lithiumBoron detection frequency in the Ca‐sulfate veins increases in the Jura member of VRR and is inversely correlated with lithiumThe relationship between B and Li suggests an evaporative sequence formed during dehydration on higher elevations of VRR [ABSTRACT FROM AUTHOR]