Unlike classic skarn-type scheelite deposits directly acquiring sufficient Ca²⁺ from surrounding limestones, all of the scheelite orebodies of the Shangfang tungsten (W) deposit occur mainly in amphibolite, and this provides a new perspective on the mineralization mechanism of W deposits. The ability of hydrothermal scheelite (CaWO₄) to bind REE³⁺ in their Ca²⁺ crystal lattices makes it a useful mineral for tracing fluid-rock interactions in hydrothermal mineralization systems. In this study, the REE compositions of scheelite and some silicate minerals were measured systematically in-situ by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) to assess the extent of fluid-rock interactions for the Late Mesozoic quartz-vein-type Shangfang W deposits. According to the variations in CaO and REE among scheelite and silicate minerals, the amphibole and actinolite in amphibolite may be able to release large amounts of Ca²⁺ and REE³⁺ into the ore-forming fluids during chlorite alteration, which is critical for scheelite precipitation. Furthermore, an improved batch crystallization model was adopted for simulating the process of scheelite precipitation and fluid evolution. The results of both the in-situ measurements and model calculations demonstrate that the precipitation of early-stage scheelite with medium rare-earth elements (MREE)-rich and [Eu/Eu*]_N<1. The early-stage scheelite would consume more MREE than LREE and HREE of fluid, which will gradually produce residual fluids with strong MREE-depletion and [Eu/Eu*]_N>1. Even though the partition coefficient of REE is constant, the later-stage scheelite will also inherit a certain degree of MREE-depletion and [Eu/Eu*]_N future from the residual fluids. As a common mineral, sheelite forms in various types of hydrothermal ore deposits (e.g., tungsten and gold deposits). Hence, the improved batch crystallization model is also possible for obtaining detailed information regarding fluid evolution for other types of hydrothermal deposits. The results from model calculations also illustrate that the Eu anomalies of scheelite are not an effective index correlated to oxygen fugacity of fluids but rather are dominantly controlled by the continuous precipitation of scheelite.

中文翻译：

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华南大型上房石英脉状钨矿床的流体演化和白钨矿沉淀机理：流体/岩石相互作用过程中稀土元素（REE）行为的约束

不同于典型的矽卡岩型白钨矿床直接从周围的石灰岩中获取足够的Ca ²⁺，上方钨（W）矿床的所有白钨矿矿床主要存在于角闪岩中，这为W矿床的成矿机制提供了新的视角。热液白钨矿（CaWO ₄）结合其Ca ²⁺晶格中的REE ³⁺的能力使其成为追踪热液成矿系统中流体-岩石相互作用的有用矿物。在这项研究中，对白钨矿和某些硅酸盐矿物的稀土元素进行了系统的原位测量。通过激光烧蚀电感耦合等离子体质谱法（LA-ICP-MS）评估晚中生代石英脉型上房W矿床的流体-岩石相互作用程度。根据白钨矿和硅酸盐矿物中CaO和REE的变化，闪石中的闪石和阳起石可能能够在绿泥石蚀变过程中将大量的Ca ²⁺和REE ³⁺释放到成矿流体中，这对白钨矿至关重要沉淀。此外，采用改进的分批结晶模型来模拟白钨矿的沉淀和流体演化过程。既有原位结果测量和模型计算表明，具有中等稀土元素（MREE）丰富且[Eu / Eu *] _N <1的早期白钨矿的沉淀。早期白钨矿消耗的MREE比LREE和HREE的流体多，这将逐渐产生残留的流体，其中的MREE消耗很强，[Eu / Eu *] _N > 1。即使REE的分配系数恒定，后期白钨矿也将继承一定程度的MREE损耗和[Eu / Eu *] _N剩余流体的未来。作为常见的矿物，钙铁矿形成于各种类型的热液矿床中（例如钨和金矿床）。因此，改进的批量结晶模型对于获得有关其他类型水热矿床流体演化的详细信息也是可能的。模型计算的结果还表明，白钨矿的Eu异常不是与流体的氧气逸度相关的有效指标，而是主要由白钨矿的连续沉淀控制。