Reactive gossans in permafrost as indicators of ancient hydrothermal activity on Mars

Abstract:

Over the past decade, spaceborne and in situ remote sensing instruments have identified a wide variety of alteration minerals on the surface of Mars. These studies have also highlighted the potential occurrence of oxidized iron and sulfur species resulting from the alteration of basaltic material under acid sulfate and oxidizing conditions. The detection of these minerals, such as the potassium and iron hydrous sulfate jarosite, implies rock-water interactions that could have taken place in ancient hydrothermal systems. Jarosite has been identified at several locations on Mars in CRISM images (e.g., Melas Chasma, Aureum Chaos, Eridania basin), HiRISE images (e.g., Noctis Labyrinthus, Mawrth Vallis, Nilli Fossae) and rover-based investigation (e.g., Meridiani Planum, Gale crater). It is particularly interesting as it can potentially retain textural, chemical, and isotopic evidence of past history, including possible biological activity, on Mars.

On Earth, jarosite can form in ore deposits or from alteration near volcanic vents, but only persists in arid environments such as reactive gossans. Reactive gossans in permafrost were mapped at several locations in the Canadian Arctic. These surficial deposits are particularly abundant in the High Arctic Large Igneous Province exposed on Axel Heiberg Island, in Nunavut. Geomorphic studies of gossans and their host rocks suggest that some deposits are linked to paleo-hydrothermal systems. Thus, we hypothesize that fluids derived from ancient hydrothermal systems on Mars could have melted the thick permafrost and led to the formation of gossanous soils, explaining some of the jarosite occurrences reported.

Consequently, we studied the mineralogical composition and spectral signature of reactive gossans in the field and in the laboratory with the objective of building a spectral database of minerals that could be detected on the surface of Mars. Additionally, comparative studies of genetic links between gossans and buried hydrothermal systems on Earth will be carried out to advance our current knowledge of similar geological deposits on Mars and test their potential to preserve biogenic signatures.