Hot and Cold Spring Deposits as a Source of Palaeo-fluid Samples on Mars

Introduction: Fluid inclusions are micron-scale volumes of fluid entrapped during the precipitation of minerals. Fluids are entrapped during primary mineral growth, and during healing of later fractures. The water in fluid inclusions in minerals precipitated in the upper crust of Mars contains a record of the ambient environment during precipitation. This includes data on fluid temperature and ion chemistry, which can constrain the likelihood of life in that environment. More significantly, the fluid chemistry could include a biomolecular signature of life. Mineral precipitation in the upper crust on earth (down to depths of a few km) occurs at the surface and in pore spaces and fracture systems. Precipitation in the subsurface is enhanced by the circulation of fluids carrying dissolved ions, which also function as nutrients for life. Surface precipitation may also be biologically mediated. As precipitation occurs, micron-scale volumes of fluid are trapped as inclusions in the minerals. Thus mineral precipitates are both associated with life and contain entrapped water, and we can use the water as a source of information about the life. If life existed in the environment of mineral precipitation , all the requirements for detecting it can be met [1]. A number of environments have been suggested as possible places for life on Mars, including evaporitic, lacustrine, chemosynthetic, speleothem and hy-drothermal deposits. This is a terrestrial analogue study investigating the preservation of surface fluids from modern day hot and cold spring deposits, which could have preserved molecular biomarkers. Spring deposits have been suggested as particularly valuable targets for astrobiological exploration, based on their association with flourishing biotas on earth [2, 3, 4] Samples of study and results: Travertines, which are composed of carbonate and sometimes silica minerals , are developed in hot springs, rivers, waterfalls coastal marshes and lakes. They develop is response to degassing of calcium carbonate-bearing waters and are frequently associated with a rich bacterial flora. The bacteria can directly precipitate calcium carbonate by removal of dissolved carbon dioxide during photo-synthesis. They also can provide a framework for the nucleation of calcium carbonate crystals. Travertines were sampled from active hot springs at Bagno Vignone in Italy and Tehuacan in Mexico that occur in associated with recent volcanic centres. These travertines, which are composed of fine-grained,