Manganese Mobility in Gale Crater, Mars: Leached Bedrock and Localized
In Gale crater on Mars, the rover Curiosity has discovered
evidence of fluid mobilization of the redox-sensitive element manganese.
We present results for Mn from Curiosity’s Alpha Particle X-ray
Spectrometer (APXS), which show that the average MnO concentration in
mudstone-dominated sedimentary units (0.22 wt%) is about one-half of
the concentration in the average Mars crust (0.44 wt%). Geochemical
trends indicate that Mn in the sedimentary bedrock, most of which has a
basaltic provenance, was leached by chemical alteration and dissolution.
In >350 vertical meters of mudstone-dominated strata, the
apparent leaching of Mn and retention of Fe in Fe-O-H phase(s) resulted
in the fractionation of Fe and Mn, indicating relatively moderate Eh-pH
fluid conditions that were not highly alkaline, reducing, or oxidizing.
Exceptions are fracture-associated, silica-rich haloes where both Mn and
Fe were leached by low pH fluids. The rover also discovered Mn-rich
veins, nodules, and patchy, dark coatings on rock surfaces, which are
variably associated with enrichments in Fe, P, Cl, and/or Zn. These
Mn-rich features represent ~1% of the 1,029 APXS
measurements acquired over ~25 km of rover traverse. A
thermochemical model shows that dissolved Mn2+ could
have been concentrated via evaporation, sublimation, and/or freezing.
Manganese was then likely precipitated in localized features when
> 99.99% of the Mn2+-bearing water was
removed from the system. These findings indicate that Mn was mobile in
Gale crater and therefore bioavailable as a potential energy source for