Fig. 4: A model showing PGE scavenging on the lunar surface, resulting from the terrestrial like PGE enrichment process, can explain the observed fractionation of PGE/Ir ratios in impact breccias.

a Schematic showing a possible scenario in order where basin-forming impact on the lunar crust taps into shallow S-rich layers providing enough volume of melt and sulfur needed for sulfide saturation which further leads to scavenging of PGE by metal + sulfides. Then, later impacts on the already PGE-enriched lunar surface, and subsequent minor (<1%) metal segregation gives rise to the observed fractionation in impact breccias. The schematic also show that fractionated PGE signatures are possibly recorded in PGE-enriched sulfide phases which are likely incorporated within some lunar impact breccia rocks. b Modeling results showing that the terrestrial-style PGE-enriched lunar crust and its subsequent fractionation in an impact melt pool can produce the observed PGE/Ir ratio in Y981031. The model assumes fractionation in the Fe-Ni-S system, and <1% fractionation matches the observed composition (Methods; Supplementary Text S8 and Supplementary Table S7). PGE platinum group elements, IC impactor composition, CMB crystalline matrix breccias, FB feldspathic breccias, IM impact melt rocks, PB polymict breccias .