Sulfide mineralogy and redox conditions in some shergottites

Magmatic sulfide mineralogy has been studied in 2 olivine-phyric shergottites (DaG 476 and SaU 005) and 4 basaltic shergottites (Zagami, Shergotty, Los Angeles, and NWA 480). Modal abundances of magmatic sulfides, as estimated by image analysis on thin section, are high (0.16 to 0.53 area percent) and correlate positively with abundances of Fe-Ti oxides. Sulfides are mesostasis minerals, being mostly interstitial grains or locally enclosed in post-cumulus melt inclusions (e.g., SaU 005) in olivine. Sulfides in shergottites are composed of major pyrrhotite containing pentlandite exsolutions associated with minor amounts of Cu sulfides (chalcopyrite and/or cubanite). Hot desert finds (e.g., DaG 476) show abundant fracture-filling iron (oxy)hydroxides of probable terrestrial origin. Unaltered sulfides show metal-rich hexagonal pyrrhotite compositions with metal/sulfur (M/ S) ratio ranging between 0.936 ± 0.005 and 0.962 ± 0.01. This compositional range corresponds to the two-phase structural domain 2C + nC of the Fe-S system; however, the high-temperature disordered hexagonal 1C pyrrhotite structure would be in better agreement with magnetic properties of shergottites. Ni contents in pyrrhotite increase from Los Angeles (