Endogenous, yet Exotic, Sulfur in the Lunar Mantle

In situ sulfur isotope analyses of sulfides found in regolith particles from the recently opened Apollo 17 drive tube 73001/2 reveal variable ³⁴S/³²S and ³³S/³²S that range from that of typical lunar basalts to strongly ³⁴S- and ³³S-depleted values (δ³⁴S = −4.1 ± 0.35 to +1.5 ± 0.029; Δ³³S = −2.8 ± 0.48 to −0.1 ± 0.27 (2σ)). All Δ³³S and δ³⁴S data are positively correlated. The correlation indicates mixing between at least two distinct sources of sulfur in the lunar mantle, one of which is associated with photochemically processed sulfur from a gaseous environment (strongly negative Δ³³S). The gaseous precursor and its preservation in endogenous sulfides require that either the sulfur was delivered to the lunar mantle early in its history through unknown processes or it is a remnant of the giant Moon-forming impactor.