The Norilsk 1 intrusion (Russia), renowned for its abundance of sulfide ores, contains an upper contact zone, which hosts sulfide-poor and Cr spinel and platinum group element (PGE)-rich discontinuous reefs with significant economic potential. Located within strongly inhomogeneous contact rocks of various compositions, the origin of these reefs is complex and debated. Enrichment in PGEs in these rocks is distributed heterogeneously, occasionally occurring in extremely dense disseminations of Cr spinel, which are unusual for other rocks of the Norilsk 1 intrusion. The compositions of Cr spinel vary significantly between individual samples, even within the same samples across clusters of several Cr spinel grains and single grains. Chromium spinel grains are broadly characterized by low Mg# (3–50 mol %), moderate to extremely high TiO₂ content (1–18 wt %), diverse Fe²⁺/Fe³⁺ ratios, and elevated V and Zn. Multiphase silicate inclusions hosted by Cr spinel are dominated by orthopyroxene, alkali-feldspar, clinopyroxene, Na phlogopite, high-Al amphibole, chlorite, and albite, along with minor felsic glass, sulfide, apatite, baddeleyite, titanite, calcite, halite, and cordierite. Heating experiments (1,250°C) on the silicate inclusions failed to produce homogeneous glasses but showed evidence of partial melting and reactions with precursor minerals that crystallized new phases. The experimentally obtained glasses are characterized by compositions that strongly differ from any known igneous rock in the Norilsk region, and the assemblage of phases in these inclusions is not supportive of the entrapment of a homogeneous silicate melt. Trace element patterns of the glasses of the experimentally heated inclusions are compositionally distinct from the Norilsk trap basalts, and instead are closer to the sedimentary rocks of the Norilsk region. We suggest that an in situ interaction between the mafic melt and the sedimentary rocks was responsible for Cr spinel mineralization and the formation of the host rocks. The subsequent subsolidus modification of the initial rocks expanded the Cr spinel compositional range and formed muscovite-albite-chlorite assemblages, which replaced the original silicate minerals.

中文翻译：

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Norilsk 1侵入的含铂族元素富铬铁矿岩石的混合性质：Cr尖晶石和尖晶石主持的多相包裹体的遗传约束

以丰富的硫化矿石而闻名的Norilsk 1侵入岩（俄罗斯）包含一个上部接触区，该区域拥有富含硫化物和Cr尖晶石以及富含铂族元素（PGE）的不连续珊瑚礁，具有显着的经济潜力。这些礁石位于各种组成的强烈非均质的接触岩中，其起源是复杂的，并且存在争议。这些岩石中PGE的富集分布不均，偶尔会在极尖的Cr尖晶石扩散中发生，这对于Norilsk 1侵入岩的其他岩石而言是罕见的。Cr尖晶石的成分在各个样品之间变化很大，甚至在多个Cr尖晶石晶粒和单个晶粒簇的相同样品中也是如此。铬尖晶石晶粒的普遍特征是低Mg＃（3–50 mol％），中等至极高的TiO₂含量（1-18 wt％），不同的Fe ²⁺ / Fe ³⁺比率和升高的V和Zn。Cr尖晶石所含的多相硅酸盐夹杂物主要由邻苯二茂铁，碱长石，斜辉石，钠金云母，高铝角闪石，绿泥石和钠长石，以及次要长英质玻璃，硫化物，磷灰石，磷灰石，钛铁矿，钛铁矿，方解石、,石和堇青石。对硅酸盐夹杂物的加热实验（1,250°C）未能产生均匀的玻璃，但显示出部分熔化的证据以及与使新相结晶的前体矿物发生反应的证据。实验获得的玻璃的特征是其组成与Norilsk地区的任何已知火成岩都存在很大差异，并且这些包裹体中的相组合不支持均质硅酸盐熔体的截留。经过实验加热的夹杂物的玻璃中的痕量元素形态在成分上与Norilsk捕集玄武岩截然不同，而是更接近Norilsk地区的沉积岩。我们认为，镁铁质熔体与沉积岩之间的原位相互作用是造成Cr尖晶石矿化和基质岩形成的原因。随后对原始岩石进行的亚固相改性扩大了Cr尖晶石的成分范围，并形成了白云母-亚氯酸盐-绿泥石组合，从而替代了原始的硅酸盐矿物。我们认为，镁铁质熔体与沉积岩之间的原位相互作用是造成Cr尖晶石矿化和基质岩形成的原因。随后对原始岩石进行的亚固相改性扩大了Cr尖晶石的成分范围，并形成了白云母-亚氯酸盐-绿泥石组合，从而替代了原始的硅酸盐矿物。我们认为，镁铁质熔体与沉积岩之间的原位相互作用是造成Cr尖晶石矿化和基质岩形成的原因。随后对原始岩石进行的亚固相改性扩大了Cr尖晶石的成分范围，并形成了白云母-亚氯酸盐-绿泥石组合，从而替代了原始的硅酸盐矿物。