Speaker
Description
Martian concretions, the hematite-rich spherules discovered at Meridiani Planum by the Opportunity rover, provide important clues to the aqueous and geochemical evolution of ancient Mars. To investigate their potential as indicators of metal-enrichment processes, we studied three terrestrial concretion analogues: spherules from the Cretaceous Dakota Formation and Jurassic Navajo Sandstone in Utah, and large Miocene “Trovants” from Romania. Their mineralogical and chemical composition was investigated using optical microscopy, energy-dispersive X-ray spectroscopy (EDS), and electron microprobe analyses.
The terrestrial concretions contain iron oxides and sulfides as well as Cu- and Sn-rich mineral phases, indicating significant mineralization. In Navajo Sandstone concretions, EDS measurements yielded 44.78–53.15 wt.% Cu and 8.49–11.13 wt.% Sn, while electron microprobe analyses of selected phases in crystal inclusions revealed 78–85 wt.% Cu and 13–16 wt.% Sn. These results demonstrate that concretion-forming environments can locally concentrate metals within relatively small mineral structures.
Mini-TES observations from Meridiani Planum are consistent with ore-associated minerals including pyrite, ilmenite, hematite, and jarosite, while APXS data indicate iron sulfates and oxides, magnesium sulfates, and chlorides. The closest terrestrial analogue identified in this study is the Navajo Formation, where iron oxides occur within a siliceous-clay matrix and concretion formation is associated with diagenetic, cementation and recrystallization processes.
Our results suggest that some Martian concretions may record localized low-temperature ore-forming processes associated with groundwater circulation or hydrothermal activity. If metal-enriched concretions occur in the Martian subsurface, they could serve as mineralogical pathfinders for broader zones of metal enrichment, including potentially economically significant elements.