The Moon accreted meteoritic material towards the end of Solar System formation. Quantification of this late accretion requires an estimation of the abundance of highly siderophile, or iron-loving, elements in the lunar mantle. As lunar mantle samples are not available, estimates are derived from lunar basalt compositions, but the melting phase relations needed to derive the mantle composition are poorly constrained. Here we present sulfur solubility measurements from laboratory experiments, combined with thermodynamic calculations, which show that the lunar basalt source is likely to be saturated in a sulfur-poor, iron-rich sulfide melt that concentrates some highly siderophile elements more than others. We found that the observed range in the ratios of highly siderophile elements in primitive lunar basalts is much smaller than expected from residual sulfide control alone. Instead, the elemental ratios are consistent with mixing between primary sulfide-saturated melts and minute (<1%) amounts of lunar regolith that contain impact debris. Although the composition of some samples suggests a highly depleted lunar mantle, the exact level of depletion is unclear, because mixing trajectories overlap at the inferred level of regolith contamination. We conclude that the composition of the lunar mantle is veiled by regolith contamination of the lunar basalts. If so, highly siderophile element abundances in lunar mantle-derived materials cannot be used to determine the mass of material accreted late onto the Moon.

月亮在太阳系形成结束时吸收了气象物质。要量化这种后期积聚，就需要估算月幔中高度嗜铁或嗜铁元素的含量。由于没有月球地幔样品，因此估计是从月球玄武岩成分推导出来的，但是很难推导得出地幔成分所需的融相关系。在这里，我们提供了来自实验室实验的硫溶解度测量结果，并结合了热力学计算，结果表明，玄武岩源可能在贫硫，富铁的硫化物熔体中饱和，该熔体比其他元素更富集一些高铁亲元素。我们发现，原始月球玄武岩中高度嗜铁亲和元素比例的观测范围远小于仅由残留硫化物控制所预期的范围。相反，元素比与一次硫化物饱和熔体与包含撞击碎屑的微量（<1％）月牙重石之间的混合相一致。尽管某些样品的成分表明月幔高度耗竭，但确切的耗竭水平尚不清楚，因为混合轨迹在推断的硬质硅酸盐污染水平上重叠。我们得出的结论是，月球玄武岩的重新碎屑污染掩盖了月幔的组成。如果这样，月球幔源物质中的高度嗜铁亲和元素丰度就不能用来确定月球后期积聚的物质的质量。元素比与一次硫化物饱和熔体和微量（<1％）的月球重石的混合相一致，月球重石含有冲击碎屑。尽管某些样品的成分表明月幔高度耗竭，但确切的耗竭水平尚不清楚，因为混合轨迹在推断的硬质硅酸盐污染水平上重叠。我们得出的结论是，月球玄武岩的重新碎屑污染掩盖了月幔的组成。如果这样，月球幔源物质中的高度嗜铁亲和元素丰度就不能用来确定月球后期积聚的物质的质量。元素比与一次硫化物饱和熔体和微量（<1％）的月球重石块中含有冲击碎屑的混合相一致。尽管某些样品的成分表明月幔高度耗竭，但确切的耗竭水平尚不清楚，因为混合轨迹在推断的硬质硅酸盐污染水平上重叠。我们得出的结论是，月球玄武岩的重新碎屑污染掩盖了月幔的组成。如果这样，月球幔源物质中的高度嗜铁亲和元素丰度就不能用来确定月球后期积聚的物质的质量。尽管某些样品的成分表明月幔高度耗竭，但确切的耗竭水平尚不清楚，因为混合轨迹在推断的硬质硅酸盐污染水平上重叠。我们得出的结论是，月球玄武岩的重新碎屑污染掩盖了月幔的组成。如果这样，月球幔源物质中的高度嗜铁亲和元素丰度就不能用来确定月球后期积聚的物质的质量。尽管某些样品的成分表明月幔高度耗竭，但确切的耗竭水平尚不清楚，因为混合轨迹在推断的硬质硅酸盐污染水平上重叠。我们得出的结论是，月球玄武岩的重新碎屑污染掩盖了月幔的组成。如果这样，月球幔源物质中的高度嗜铁亲和元素丰度就不能用来确定月球后期积聚的物质的质量。