An Experimental Investigation of Germanium-Bearing Phases Deposited from Magmatic Gases: Implications for Germanium Enrichment in Gale Crater, Mars

Sedimentary rocks in Gale Crater, Mars have been found to be enriched in Ge; similar enrichments have been observed in Gusev Crater and Meridiani Planum, on both local and broad scales. Past studies have attributed this germanium enrichment to hydrothermal alteration, while few have considered the possibility of magmatic vapor deposition relating to these enrichments, and fewer still have attempted to constrain the Ge-bearing phases that could be deposited through this process. Although previous work has shown that germanium is lost from magma during degassing, no experiments have indicated which phases may be deposited. We have conducted experiments exploring which germanium-bearing phases are produced and could be contributed to Martian fines through degassing of Martian magmas. Glasses of Wishstone composition doped with Cl, S, and trace elements (including Ge) were synthesized at 1300 °C and 1 GPa; this glass was then degassed in an evacuated silica glass tube at 1200 °C under a strong thermal gradient. Mineral deposits coating the inside of these tubes were analyzed via SEM, TES, XANES, EPMA, and ICP-OES. Preliminary results suggest that germanium can be deposited as GeO2 hexagonal crystals (similar to tridymite; fig. a), pyroxenes (possibly an FeGeO3 clinopyroxene; fig. b), nearly pure germanium-oxide cubes (possibly with the formula Ge2O3; fig. c), and incorporated into iron oxides (notably maghemite octahedra; fig. c). These phases were deposited over the temperature range 300-750 °C; SEM images are included below. These phases would likely be modified as they react with water on the Martian surface.