Komatiites require external sulfur from country rocks to generate immiscible sulfide liquid, which concentrates metals to form economic nickel sulfide deposits. Although signatures related to mass-independent fractionation of S isotopes (MIF-S, denoted as Δ³³S) may identify external S sources, their values may not be directly indicative of the S reservoirs that were tapped during the ore-forming process, because of dilution by S exchange between assimilated sulfide xenomelt and komatiite silicate melt. To quantify this process and be confident that MIF-S can be effectively used to track S sources in magmatic systems, we investigated the effect of silicate melt-sulfide liquid batch equilibration, using the proxy of silicate/sulfide mass ratio, or R factor, on the resulting MIF-S signatures of pentlandite-rich ore from the Mount Keith MKD5 nickel sulfide deposit, Agnew-Wiluna greenstone belt, Western Australia. We carried out in situ multiple S isotope and platinum group element (PGE) analyses on pentlandite from a well-characterized drill core through the deposit. The variability in Pd tenor and MIF-S signature suggests that these are decoupled during batch equilibration and that the latter is not controlled by metal-derived R factor. Rather, the observed spread of MIF-S signatures implies that the sulfide xenomelt was initially heterogeneous and that chemical equilibration of S isotopes is incomplete as opposed to that of PGEs in a komatiite melt. Consequently, magmatic sulfides, which formed in the hottest, most dynamic, and likely fastest equilibrating magmatic systems on Earth, may still preserve their initial MIF-S isotope compositions, reflecting the range of crustal S reservoirs that were available upon komatiite emplacement.

中文翻译：

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科马提矿矿石系统中铂族元素的硫同位素特征解耦：来自西澳大利亚基思山 MKD5 镍（钴）矿床的证据

科马提岩需要来自围岩的外部硫来生成不混溶的硫化物液体，该液体浓缩金属以形成经济的硫化镍矿床。尽管与质量无关的硫同位素分馏（MIF-S，表示为 Δ ³³ S）相关的特征可以识别外部硫源，但它们的值可能不能直接指示在成矿过程中开采的硫储层，因为通过同化硫化物异熔体和科马提石硅酸盐熔体之间的 S 交换进行稀释。为了量化这一过程并确信 MIF-S 可以有效地用于追踪岩浆系统中的硫源，我们使用硅酸盐/硫化物质量比或 R 因子作为代表，研究了硅酸盐熔体-硫化物液体批次平衡的影响，西澳大利亚阿格纽-威卢纳绿岩带基思山 MKD5 硫化镍矿床富含镍铁矿的矿石的 MIF-S 特征。我们对矿床中特征良好的钻芯中的镍黄铁矿进行了原位多硫同位素和铂族元素 (PGE) 分析。Pd 基期和 MIF-S 特征的可变性表明它们在批量平衡过程中是解耦的，并且后者不受金属衍生的 R 因子控制。相反，观察到的 MIF-S 特征的扩散意味着硫化物异熔体最初是异质的，并且与科马提石熔体中的 PGE 相比，S 同位素的化学平衡是不完全的。因此，在地球上最热、最具活力、可能也是最快平衡的岩浆系统中形成的岩浆硫化物可能仍保留其最初的 MIF-S 同位素组成，反映了科马提岩就位时可用的地壳硫储层的范围。