The Qaidam Basin, located in northwestern China, is characterized by extensive aeolian landforms, gravel deposits, and playas. This region, a prime example of a typical evaporite deposit, closely mirrors early Mars, having experienced millions of years of aridification following the end of a wetter climate. This study seeks to explore the hydrochemical and mineralogical properties of an evaporite-dominated environment and assess the potential for habitability under conditions akin to early Mars. Hydrological samples were gathered along a central axis across a longitudinal aridity gradient in the Qaidam Basin. The samples included various types of water such as meteoric, freshwater, standing water from precipitation, salty lacustrine water, and hypersaline brines. As evaporation increased, the salt composition shifted from HCO₃-Ca·Na to Cl·SO₄-Na or Cl-Mg. Over time, carbonate salts were progressively replaced by sulfates and chlorides, resulting in a more dilute and less detectable mineral content. Additionally, trace amounts of oxyhalides were found in some of the water samples, suggesting the preservation of these compounds in arid environments and potentially indicating the presence of microbial enzymes. The isotopic signatures of water, carbon, and nitrogen compounds provide important clues for distinguishing between abiotic and biotic processes. Furthermore, the Qaidam Basin exhibits diverse geomorphological and mineralogical features that resemble those of Mars. This study focuses on geomorphological types such as alluvial fans, dunes, debris flows, gullies, yardangs, salt flats, and polygonal formations. We utilized a range of techniques, including short-wave infrared spectroscopy, laser-induced breakdown spectroscopy, X-ray diffraction, X-ray fluorescence, elemental analysis-isotope ratio mass spectrometry, and acid-based decarbonation to analyze the surface soil samples. The results revealed that the surface samples from Mars-like landforms in the Qaidam Basin are primarily composed of quartz, albite, gypsum, and smaller quantities of calcite, illite, chlorite, microcline, and halite. Different landforms exhibited varying stages of geological evolution, showcasing evaporite deposits or clastic sediment compositions. Notably, samples from yardangs and alluvial fans demonstrated enhanced preservation of carbonates, clay minerals, and organic matter.
Building on our findings, we propose that water-rock interactions offer a comprehensive framework for assessing habitable conditions, as these interactions indicate the presence of key elements for life, such as water, organic molecules, bioavailable nutrients, energy sources, and greenhouse gases, along with environments capable of preserving these compounds. Therefore, the products of water-rock interactions could offer valuable insights into potential life-supporting niches on celestial bodies like Mars.

Hydrogeochemistry,Halophiles,Evaporite,Qaidam Basin,Water-rock interaction