Precious metal enrichment during impacts on the Moon

Any sustained space exploration is likely to depend on the Moon and its resources. Understanding lunar mineral deposit potential, particularly for precious metals including Os, Ir, Ru, Rh, Pt, Pd, and Au (the platinum group elements, or PGE) and their distribution, however, is limited. Pristine endogenous basalts and crustal rocks, including mare basalt meteorite A-881757, indicate a well-mixed lunar mantle with PGE abundances too low to ever be exploitable. Here we show that the most likely location for PGE enrichment is in lunar impact melt sheets. Platinum group element abundances and Re-Os isotopes in samples from lunar impact melt sheets have fractionated PGE enrichments inconsistent with any known impactor compositions and consistent with sulfide-silicate segregation. Models show that basin-forming impacts with large melt volumes (≥106 km3) and 0.1–1% impactor contribution provided potential conditions for significant PGE-enrichment, akin to economic levels (~1–5 g/t) in the largest layered intrusions on Earth today.