Antimony isotope fractionation in stibnite – constraints from δ123Sb values and infrared microthermometric data of stibnite-hosted fluid inclusions“Antifrac”

锑（Sb）是一种“关键”元素。作为辉锑矿（Sb 2S 3），Sb在不同类型的矿床中高度富集：- 低硫化浅成热液脉型-温泉矿床、某些斑岩和钼-部分造山金或沉积物容矿卡林型金-沉积物容矿热液石英-辉锑矿脉-某些SEDEX型-或块状交代碳酸盐交代在某些矿床中，辉锑矿化还与相当高浓度的金、汞、银、锡、钨或贱金属（例如，Gumiel and Arribas 1987; Dill 1998; Peng et al. 2002;瓦格纳and博伊斯2003; Hagemann and Lüders 2003; Yang et al. 2006;布赫霍尔茨et al. 2007; Bortnikov et al. 2010; Eudouris et al. 2019; Pohl，2020）。热液矿床中锑的来源往往没有得到很好的限制，仍然是一个有争议的问题。锑在地壳中的平均丰度为0.2 ppm（Taylor和McLennan 1995）。据报告，黑色页岩中的锑平均浓度较高，约为5 ppm（Ketris和Yudovich，2009年），因此，黑色页岩的蚀变可能构成热液石英辉锑矿矿床中锑的潜在来源（例如，瓦格纳和Boyes，2003年; Sojnicka等人，2021年）。辉锑矿矿床也与长英质岩浆岩有关。在这种情况下，锑富集是否与岩浆流体或热液蚀变过程直接相关并不总是清楚的（Krolop等人，2018）。先前对辉锑矿同位素组成的研究表明，不同产状辉锑矿中的123 Sb/121 Sb比值可提供一种解读辉锑矿矿床来源的方法（Zhai等人，2021年及其中的参考文献）。然而，到目前为止，关于Sb同位素分馏的大多数结论都是基于观察到的存款或矿石类型中某些δ 123 Sb值的变化，以及Sb（III）Sb（V）氧化还原反应的实验数据（例如，Lobo等人，2012年; Dillis等人，2019年）。 高温下热液流体中Sb（III）的迁移取决于流体中的pH值和硫化物浓度，并以HS-或OH-络合物的形式发生（例如Krupp 1988; Olsen等人，2019），而Sb氯化物络合物仅在强盐酸性流体中稳定（例如Obolensky等人，2007）。然而，Sb同位素分馏的辉锑矿沉淀，无论是从盐水或低盐度流体在不同温度下的依赖性还没有研究到目前为止。由于辉锑矿在近红外光下显示出极好的透明度（Lüders 2017），因此当使用红外显微测温法时，可以对辉锑矿中的流体包裹体进行常规研究，并可以获得辉锑矿形成流体的T-x信息。结合辉锑矿流体包裹体显微测温资料，对辉锑矿Sb同位素体系进行详细研究，将为Sb同位素体系在存款研究中的应用提供新的思路。

Antimony (Sb) is a “critical” element. As Stibnite (Sb2S3), Sb is highly concentrated in different types of deposits: - Low-sulfidation epithermal vein-type - hot spring deposits, some porphyry and molybdenum - parts of orogenic gold or sediment-hosted Carlin-type gold - sediment-hosted hydrothermal quartz-stibnite veins - some SEDEX-type - or massive metasomatic carbonate replacement In some deposits, stibnite mineralization is also associated with considerable concentrations of gold, mercury, silver, tin, tungsten, or base metals (e.g., Gumiel and Arribas 1987; Dill 1998; Peng et al. 2002; Wagner and Boyce 2003; Hagemann and Lüders 2003; Yang et al. 2006; Buchholz et al. 2007; Bortnikov et al. 2010; Voudouris et al. 2019; Pohl, 2020). The source(s) of Sb in hydrothermal ore deposits are often not well constrained and still a matter of debate. The average abundance of Sb in the Earth´s crust is 0.2 ppm (Taylor and McLennan 1995). Higher average Sb concentrations of about 5 ppm are reported from black shales (Ketris and Yudovich 2009) and thus, alteration of black shales may constitute a potential source for Sb in hydrothermal quartz-stibnite deposits (e.g. Wagner and Boyes 2003, Sośnicka et al. 2021). Stibnite deposits are also associated with felsic magmatic rocks. In this case is not always clear whether Sb enrichment is directly related to magmatic fluids or hydrothermal alteration processes (Krolop et al. 2018). Previous studies of isotope compositions of stibnite have shown that the 123Sb/121Sb ratios in stibnite from various occurrences may provide a means to decipher the source(s) of stibnite deposits (Zhai et al. 2021 and references therein). However, most of the conclusions about Sb isotope fractionation that are drawn so far are based on observed shifts of some δ123Sb values within a deposit or ore types, and experimentally data on Sb(III) Sb(V) redox reactions (e.g. Lobo et al. 2012; Dillis et al. 2019). The transport of Sb (III) in hydrothermal fluids at high temperatures is dependent on ph and the sulfide concentration in the fluid and occurs in from of HS- or OH- complexes (e.g. Krupp 1988; Olsen et al. 2019) whilst Sb chloride complexes are only stable in strong saline acidic fluids (e.g. Obolensky et al. 2007). However, the dependence of Sb isotope fractionation in stibnites that precipitated from either brines or low-salinity fluids at different temperatures has not been studied so far. Since stibnite shows extremely good transparency in near IR light (Lüders 2017) fluid inclusions hosted in stibnite can be studied routinely when using IR microthermometry and information about T-x of the stibnite-forming fluids can be obtained. Studying Sb isotopic systematics in stibnite in detail in selected ore deposits in combination with microthermometric data of stibnite-hosted fluid inclusions will provide new insights for the applicability of the Sb isotope system for questions related to ore deposit research.