Nickel and cobalt are potentially critical metals in many countries because of their great significance for national security and economic development, and they are mainly derived from magmatic Ni-Cu‑platinum-group element (PGE) sulfide ore deposits hosted in mafic-ultramafic intrusions. Although Cu isotopes have been used to trace the metallogenic processes in Ni-Cu-(PGE) sulfide deposits, the Cu isotopic fractionation mechanism during magma generation and evolution in convergent tectonic settings is still debated. The Xiarihamu magmatic NiCu sulfide deposit, located in the East Kunlun orogenic belt, northern Tibetan Plateau, is the world's largest known magmatic NiCu sulfide deposit in an orogenic setting. Here we report the whole-rock element and sulfide CuS isotope compositions of samples from the Xiarihamu deposit. The δCu and δS values of the sulfide grains from the massive, heavily disseminated, and disseminated sulfide ores range from 0.19 ‰ to 0.79 ‰, and from 4.2 ‰ to 9.4 ‰, respectively. Most of the samples have δCu values higher than normal mantle values, except for two samples with δCu values within the mantle composition range. The whole rock S/Se ratios range from 3200 to 22,500, and the Cu/Pd ratios range from 330 to 820,000, which are also mainly higher than the corresponding mantle values. Modeling calculations of the δCu, S/Se, and Cu/Pd values reveal that the sulfide liquid to silicate melt mass ratio (R factor) is not the main reason for the observed δCu variations in the Xiarihamu deposit. The variations in the Cu/Pd ratios of the whole-rock samples, and the sulfide δCu and δS values with depth indicate that sulfide segregation and crustal contamination can reasonably jointly produce the Cu isotope variations in the Xiarihamu deposit, and the variations of samples from different parts of the deposit are caused by variations in these controlling factors. Therefore, Cu isotope fractionation in convergent tectonic settings is mainly caused by magma evolution. The complicated controlling factors of the Cu and S isotopes indicate that the correlation between δCu and δS values may not be helpful in evaluating the metallogenic potential of Ni-Cu-(PGE) sulfide deposits. Cu isotopes can be used to ascertain the migration path of magmas.

中文翻译：

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汇聚构造背景下岩浆演化过程中的铜同位素分馏：夏日哈木镍铜硫化物矿床硫化物Cu-S同位素和全岩PGE的制约


镍和钴对国家安全和经济发展具有重要意义，是许多国家潜在的关键金属，它们主要来源于镁铁质-超镁铁质侵入体中的岩浆镍铜铂族元素（PGE）硫化物矿床。尽管铜同位素已被用来追踪镍铜（铂族元素）硫化物矿床的成矿过程，但聚合构造环境中岩浆生成和演化过程中的铜同位素分馏机制仍然存在争议。夏日哈木岩浆镍铜硫化物矿床位于青藏高原北部东昆仑造山带，是世界上已知最大的造山环境岩浆镍铜硫化物矿床。在这里，我们报告了夏日哈木矿床样品的全岩元素和硫化物 CuS 同位素组成。块状、重浸染状和浸染状硫化矿的硫化物颗粒的δCu和δS值分别为0.19%～0.79%和4.2%～9.4%。除两个样品的 δCu 值在地幔成分范围内外，大多数样品的 δCu 值均高于正常地幔值。整个岩石S/Se比值范围为3200~22,500，Cu/Pd比值范围为330~820,000，也主要高于相应的地幔值。 δCu、S/Se 和 Cu/Pd 值的模型计算表明，硫化物液体与硅酸盐熔体质量比（R 因子）并不是夏日哈木矿床中观察到的 δCu 变化的主要原因。 全岩样品的 Cu/Pd 比值以及硫化物 δCu 和 δS 值随深度的变化表明，硫化物偏析和地壳污染可以合理地共同产生夏日哈木矿床中 Cu 同位素的变化，并且矿床的不同部分是由这些控制因素的变化造成的。因此，汇聚构造环境中的Cu同位素分馏主要是由岩浆演化引起的。 Cu、S同位素控制因素复杂，表明δCu与δS值的相关性可能无助于评价Ni-Cu-(PGE)硫化物矿床的成矿潜力。铜同位素可用于确定岩浆的运移路径。