Detection of Copper by the ChemCam Instrument Along Curiosity's Traverse in Gale Crater, Mars: Elevated Abundances in Glen Torridon

Abstract

Laser‐induced breakdown spectroscopy, as utilized by the ChemCam instrument onboard the Curiosity rover, detected enhanced abundances of the element copper. Since landing in Gale crater (6 August 2012), 10 enhancements in copper abundance were observed during 3007 Martian days (sols) of rover operations and 24 km of driving (as of 20 January 2021). The most prominent ones were found in the Kimberley area on the crater floor (Aeolis Palus) and in Glen Torridon (GT) on the lower flanks of Aeolis Mons (Mt. Sharp). Enhancements in copper record the former existence of modestly acidic and oxidizing fluids, which were more oxidizing in Kimberley than in GT. Of the two main types of bedrock in the lowest part of GT, Mg‐rich “coherent” and K‐rich “rubbly” (named based on their outcrop expression), copper was detected only in coherent, not in rubbly bedrock. The difference between these two types of bedrock may be due to difference in provenance. Alternatively, based on a recently developed lacustrine‐groundwater mixing model, we suggest that rubbly bedrock was altered by modestly acidic, shallow‐subsurface lake water that leached out both copper and manganese, while coherent bedrock was affected by dominantly alkaline fluids which would be consistent with its mineralogical composition (including siderite) as returned by the CheMin instrument onboard the rover. Higher up in GT, ChemCam data indicated significant gradients in the copper concentration in coherent bedrock on a local scale of only a few meters, which suggests a different alteration style and possibly different types of diagenetic fluids.

Overview of the Morphology and Chemistry of Diagenetic Features in the Clay‐Rich Glen Torridon Unit of Gale Crater, Mars

“…We observed FeO T ‐rich dark‐toned strata to one side of the MA/GR drill sample locations. The FeO T ‐rich dark‐toned strata are enriched in Cu compared to the surrounding area (Goetz et al., 2022). We also observed a spatial separation of Mn and Fe in the PFU nodular bedrock, where FeO T ‐rich nodules only occur on the western side of the approach to the PFU, and MnO‐rich nodules only occur on the PFU and the drive away from it.…”

“…Mn oxides could have adsorbed some phosphate from solution (e.g., Yao & Millero, 1996). The presence of Cu can further constrain the formation conditions to near neutral (Goetz et al., 2022) because adsorption of Cu to sediments occurs most efficiently at pH 6–7 (Bradl, 2004). In summary, we suggest that at least two separate fluids interacted with bedrock at MA/GR to form the Mn‐ and P‐rich nodules in the Ayton targets, and the Fe‐ and Cu‐rich dark strata.…”

“…The few nodules in the rubbly bedrock are enriched in MnO compared to the surrounding bedrock (Figure S37 in Supporting Information ). Given that the rubbly bedrock is quite extensive in lower Glen Torridon (Dehouck et al., 2022; Goetz et al., 2022), it may be the source of Mn and Cu rich fluids if slightly acidic (pH ∼5) or reducing alteration occurred, suggested by Goetz et al. (2022).…”

“…It is suggested by Dehouck et al (2022) that the rubbly bedrock is more altered than the coherent bedrock. Moreover, the rubbly bedrock is depleted in Mn and Cu compared to the coherent bedrock (Goetz et al, 2022) (Table S1 and Figure S37 in Supporting Information S1). The few nodules in the rubbly bedrock are enriched in MnO compared to the surrounding bedrock (Figure S37 in Supporting Information S1).…”

“…For these elements, the relative amount of an element can be determined by comparing relative peak heights or areas in the spectra obtained in Gale crater to each other or laboratory spectra. This method has been used for the elements B (Gasda et al, 2017), S (Clegg et al, 2020;Rapin et al, 2019), Zn (Lasue et al, 2016), Cu (Goetz et al, 2022;Payré et al, 2019), Ni (Meslin et al, 2017(Meslin et al, , 2019, Cr (Ollila et al, 2017), P (Meslin et al, 2018), and Cl (Thomas et al, 2019). In particular, Li has a calibration range up to 72 ppm (Payré et al, 2017), but we observe targets in Glen Torridon that have predicted compositions outside of this range.…”