RIO TINTO ACID-SULFATE MIXTURES: SPECTRAL MASKING RELATIONSHIPS AND IMPLICATIONS FOR MARS

In the past decade, visible- to near-infrared (VNIR) spectroscopy has revealed an array of hydrated minerals on the surface of Mars. The hydrated sulfate and iron phases have been particularly interesting, as most only form under specific pH conditions, making them useful markers of past environmental conditions. However, when mixed together, some sulfate and iron phases are able to mask the spectral signatures of others in the VNIR. Identifying all major phases is critical to interpreting past environmental conditions. Here, we report VNIR spectra of two-phase mineral combinations obtained from the Río Tinto acid mine drainage system of southern Spain. Our results show that in VNIR reflectance spectroscopy, many masking relationships exist between major sulfate and iron phases. We compare mixtures of natural samples from Rio Tinto to VNIR spectra from Mawrth Vallis and Noctis Labyrinthus on Mars.