T. Nelson | Geology Reports

USGS2026

Corundum discovered by SuperCam and the Perseverance rover at Jezero crater, Mars

Mars is primarily composed of mafic mineral assemblages and their alteration products, but small, scattered rocks strewn across the landscape offer clues to greater petrological diversity. While traversing the Jezero crater rim, the Perseverance rover encountered several plagioclase-rich light-toned float rocks. SuperCam identified the distinctive signature of corundum (α-Al 2 O 3 ) in these rocks using time-resolved luminescence spectroscopy. Two strong peaks (692.7 and 694.1 nm) with millisecond lifetimes, and additional supporting lines, are consistent with Cr 3+ substitution for Al 3+ in corundum. Corundum forms in Al-rich, Si-depleted environments through magmatic or metamorphic processes. Given the rocks' small size, association with plagioclase, and location on the crater rim, we interpret the most plausible formation scenario to be impact induced metamorphism at the interface of a felsic and a mafic/ultramafic member with the likely action of fluids at some stage, although other possibilities are not excluded.

Geophysical Research Letters↗

USGS1964

Paleo-channels at the Guayacan copper mine, Cabildo District, Aconcagua Province, Chile

An uneven erosion surface separates calcareous sedimentary rocks above and vesicular andesite porphyry below at the Guayacan mine of central Chile . Channel -like depressions filled with sedimentary rock flank elongate, stratiform bodies of disseminated copper ore which impregnate the vesicular crests of andesite lava flows. The " channels " lie parallel to and mark the margins of tongues of lava. Erosional features such as scour surfaces, conglomerate and crossbedding mark some of the channels . Other channels show no evidence of erosion, suggesting that some, at least, represent depressions or spaces that were not filled during extrusion of the lava. The flows strike east. Their crests are vesicular and impregnated with copper sulfide minerals, mainly bornite, to depths as much as 3 m below the contact. Bornite fills vesicles and fractures, impregnates the andesite ground mass, and replaces andesine phenocrysts, mainly along cleavage planes. Chalcopyrite is mixed with bornite in the upper, more vesicular part of the flows and occurs with fine-grained pyrite as disseminations and replacing fossils in the base of the overlying sedimentary rock. The channel axes also strike roughly east and, in most places, are underlain by barren ground. These mappable features, when recognized, are valuable in determining the size, shape, and orientation of adjacent ore bodies and, thereby, assist in the evaluation, exploration and mining of these stratiform copper deposits.

Economic Geology↗