Most of the global indium resources are from deposits associated with felsic rocks. Considering that the indium concentration in the average upper crust is extremely low, magmatic-hydrothermal processes play a critical role in the enrichment and mineralization of indium. However, the extraction efficiency of indium by magmatic fluids remains unclear. We performed experiments at 800 °C, 150 MPa and oxygen fugacity of Ni-NiO buffer to determine the partition coefficient of indium between aqueous fluids and granitic melts (). To counteract the rapid loss of indium into the noble metal container wall, the were obtained by the method of local equilibrium between microscopic-sized fluid bubbles and surrounding silicate melt. The results show that indium has the highest fluid-melt partition coefficients of all metals investigated so far. At a constant aluminum saturation index (ASI = 1.07–1.12), correlates linearly with the total Cl concentration in the coexisting fluid (), increasing from 61 ± 11 (1σ) at = 1.0 mol/kg HO to 895 ± 105 (1σ) at = 16 mol/kg HO. When the HCl concentration in the solution increases from 0.13 to 0.49 mol/kg HO at a fixed = 2 mol/kg HO, increases parabolically from 129 ± 21 to 320 ± 24. The observed partitioning data suggest that indium was dominantly present as In(OH)Cl in the low-HCl and In(OH)Cl in high-HCl aqueous fluid at the experimental conditions. Numerical modeling indicates that the extraction efficiency of indium from S-type felsic magmas is very high (>85 %) and magmatic fluids may be the major source of indium for most indium deposits. Due to the high values, fluid saturation and exsolution result in a sharp drop of indium concentration in both the residual melt and crystallized minerals, which makes the indium concentration in whole rock and minerals an indicator of fluid exsolution.

中文翻译：

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硅酸盐熔体和岩浆流体之间的铟分配：对铟矿成因和岩浆脱气追​​踪的影响

全球大部分铟资源来自与长英质岩相关的矿床。考虑到上地壳中的平均铟浓度极低，岩浆热液过程对铟的富集和成矿起着至关重要的作用。然而，岩浆液提取铟的效率仍不清楚。我们在 800 °C、150 MPa 和 Ni-NiO 缓冲液的氧逸度下进行了实验，以确定含水流体和花岗岩熔体之间的铟分配系数 ()。为了抵消铟快速损失到贵金属容器壁中，通过微观尺寸流体气泡与周围硅酸盐熔体之间的局部平衡方法获得。结果表明，迄今为止研究的所有金属中，铟具有最高的流体-熔体分配系数。在恒定的铝饱和指数 (ASI = 1.07–1.12) 下，与共存流体中的总 Cl 浓度线性相关 ()，从 1.0 mol/kg H2O 时的 61 ± 11 (1σ) 增加到 895 ± 105 (1σ) at = 16 mol/kg H2O。当溶液中的 HCl 浓度从 0.13 mol/kg H2O 增加到固定 = 2 mol/kg H2O 时，从 129 ± 21 抛物线增加到 320 ± 24。观察到的分配数据表明，铟主要以 In(在实验条件下，低 HCl 中的 OH)Cl 和高 HCl 水溶液中的 In(OH)Cl。数值模拟表明，从S型长英质岩浆中提取铟的效率非常高（>85%），岩浆液可能是大多数铟矿床的主要铟来源。由于数值较高，流体饱和和溶出导致残余熔体和结晶矿物中的铟浓度急剧下降，这使得整个岩石和矿物中的铟浓度成为流体溶出的指标。