Mineralogy of saline perennial cold springs on Axel Heiberg Island, Nunavut, Canada and implications for spring deposits on Mars

Abstract

In recent years evidence for spring deposits on Mars has been mounting. It seems increasingly likely that groundwater upwelling and surfacing as springs may be responsible for some mineral deposits on Mars’ surface. In order to more easily detect and better understand potential spring deposits on Mars, it is pertinent that we gain a better understanding of the distribution of minerals at cold spring systems on Earth. Here, we report on the detailed mineralogy and distribution of precipitates in crusts and sediments of three non-volcanic perennial saline cold spring systems associated with gypsum/anhydrite diapirs on Axel Heiberg Island, Canada: Wolf spring (WS; also known as Lost Hammer), Colour Peak springs (CP), and Gypsum Hill springs (GH). At these sites permafrost, frigid winter temperatures, and arid atmospheric conditions approximate conditions of present-day, as well as past, Mars. Mineralogy of the three springs is dominated by halite (NaCl), calcite (CaCO3), gypsum (CaSO4·2H2O), thenardite (Na2SO4), mirabilite (Na2SO4·10H2O), and elemental sulfur (S°). Minerals at WS are more sodium-rich than at the other two sites, and water salinity is much higher, suggesting water flows through halite in the subsurface. Mirabilite is likely deposit at WS during winter months and dehydrates to thenardite during summer months. Elemental sulfur is typically associated with gypsum, and may be related to microbial metabolism. Spring sediments are home to thriving microbial communities in winter and summer months, and presumably year round. If spring systems did exist on the surface of Mars, they may represent environments capable of supporting microbial life. It is not known to what extent mineral crusts in cold saline spring systems on Earth preserve evidence of microbial life, or if they ever did on Mars. Therefore, studying terrestrial saline spring mineral deposits such as those on Axel Heiberg Island may help us to better understand cold spring precipitation on Mars and guide us in the search for minerals that may have been precipitated in spring systems and that may contain evidence of life. Additionally, spectral data from Europa indicates the presence of mirabilite. While the depositional environment on Europa differs from Axel Heiberg Island, the springs may still be a good mineralogical analogue, given the precipitation of mirabilite by the upwelling of cold, salty subsurface water, in a cold, semi-arid desert environment.