The recently discovered Xiaobeigou fluorite deposit is situated in the southern part of the Southern Great Xing'an Range metallogenic belt. Fluorite‐bearing veins are rather common over the whole area. So far, 11 mineralized veins have been delineated at the Xiaobeigou deposit. Orebodies of the deposit are mainly hosted in Permian and Jurassic volcano‐sedimentary rocks. The orebodies in this mining district exhibit a well‐developed vertical zonation: from top to bottom, the orebodies can be divided into upper, central, and lower zones. The central zone is the most important part for mining operations, and it shows lateral zonation of fluorite mineralization. Rare earth element (REE) contents of the investigated samples are relatively low (less than 30.2 ppm). Furthermore, the REE contents of the fluorite grains from early to late ore stages exhibit a decreasing trend. All the fluorite samples show no or slightly positive Eu anomalies. Three types of fluid inclusions (FIs) are distinguished in the quartz and fluorite samples, including pure‐liquid single‐phase (PL‐type), liquid‐rich two‐phase (L‐Type), and vapor‐rich two‐phase (V‐type) FIs. The FIs hosted in early‐stage quartz were homogenized at 159.5–260.7°C (mainly 160–240°C); their salinities range from 0.18 to 1.22 wt.% NaCl eqv. The FIs hosted in early‐stage fluorite yield slightly lower homogenization temperatures of 144.4–266.8°C (peaking at 140–220°C), which correspond to salinities of 0.18–0.88 wt.% NaCl eqv. Homogenization temperatures and salinities for the late stage are 132.5–245.8°C (mainly 160–180°C) and 0.18–1.40 wt.% NaCl eqv., respectively. Laser Raman spectroscopy of FIs shows that both the vapor and liquid compositions of the inclusions are dominated by H₂O. The H–O isotopic compositions at Xiaobeigou suggest that the ore‐forming fluids are predominantly of meteoric water origin. The Xiaobeigou deposit can be classified as a typical low‐temperature hydrothermal vein‐type fluorite deposit. Combined with regional data, we infer that the fluorite mineralization occurred during the Late Mesozoic in an extensional setting.

中文翻译：

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内蒙古小北沟萤石矿床的性质和成因：来自流体包裹体和稳定同位素的证据

最近发现的小北沟萤石矿床位于大兴安岭南部成矿带的南部。含萤石的脉在整个地区相当普遍。到目前为止，在小北沟矿床已经划定了11条矿脉。该矿床的矿体主要集中在二叠纪和侏罗纪火山沉积岩中。该矿区的矿体表现出良好的垂直地带：从上到下，矿体可分为上部，中央和下部区域。中心区域是采矿作业中最重要的部分，它显示了萤石矿化的横向区域。所研究样品中的稀土元素（REE）含量相对较低（小于30.2 ppm）。此外，从早期到晚期，萤石颗粒的稀土元素含量呈下降趋势。所有萤石样品均未显示Eu异常或略有正异常。石英和萤石样品中区分出三种类型的流体包裹体（FIs），包括纯液体单相（PL型），富液两相（L型）和富蒸气两相（ V型）FI。早期石英中的FIs在159.5–260.7°C（主要是160–240°C）下均质；其盐度范围为0.18至1.22 wt。％NaCl当量。早期萤石中的FI产生的均质温度稍低，为144.4–266.8°C（峰值为140–220°C），对应于盐度为0.18–0.88 wt。％NaCl当量。后期的均质温度和盐度分别为132.5-245.8°C（主要为160-180°C）和0.18-1.40 wt。％NaCl当量。₂ O.小贝沟的H–O同位素组成表明，成矿流体主要来自陨石水。小贝沟矿床可以归为典型的低温热液脉状萤石矿床。结合区域数据，我们推断萤石矿化发生在中生代晚期的伸展环境中。