Fluid Evolution and Scheelite Precipitation Mechanism of the Large-Scale Shangfang Quartz-Vein-Type Tungsten Deposit, South China: Constraints from Rare Earth Element (REE) Behaviour during Fluid/Rock Interaction
Fluid Evolution and Scheelite Precipitation Mechanism of the Large-Scale Shangfang Quartz-Vein-Type Tungsten Deposit, South China: Constraints from Rare Earth Element (REE) Behaviour during Fluid/Rock Interaction
复制标题
华南上方大型石英脉型钨矿床流体演化与白钨矿沉淀机制：流体/岩石相互作用过程中稀土元素行为的制约
DOI：
10.1007/s12583-020-1283-0
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发表时间：
2020-06-04
影响因子：
3.3
通讯作者：
Hu, Qinghai
中科院分区：
文献类型：
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作者：
Chen, Runsheng;Zhu, Luyun;Hu, Qinghai
与典型的矽卡岩型白钨矿床直接从周围灰岩中获取充足的Ca 2+不同，上方钨（W）存款的白钨矿体均以角闪岩为主，这为钨矿床的成矿机理提供了新的视角。热液白钨矿（CaWO 4）在其Ca 2+晶格中结合RE 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。本文采用激光烧蚀电感耦合等离子体质谱（LA-ICP-MS）原位测定了上坊钨矿床中白钨矿和部分硅酸盐矿物的稀土元素组成，以评价上坊钨矿床中流体-岩石相互作用的程度。根据白钨矿和硅酸盐矿物中CaO和REE的变化，角闪岩中的角闪石和阳起石在蚀变过程中可能向成矿流体中释放大量的Ca 2+和RE 3+，这是白钨矿沉淀的关键。采用改进的间歇结晶模型模拟了白钨矿的析出和流体演化过程。原位测量和模型计算结果均表明，中稀土富集、[Eu/Eu*]N<1. 0的早期白钨矿的沉淀作用主要发生在中稀土富集阶段。早期白钨矿对MREE的消耗大于对流体的轻、重REE消耗，逐渐形成MREE亏损强烈、[Eu/Eu*]N>1的残余流体。即使稀土元素的分配系数保持不变，后期白钨矿也会从残余流体中继承一定程度的MREE亏损和[Eu/Eu*] N未来。作为一种常见的矿物，白钨矿形成于各种类型的热液矿床中（例如，钨和金矿床）。因此，改进的分批结晶模型也可以用于获得其他类型热液矿床流体演化的详细信息。模型计算结果还表明，白钨矿Eu异常不是与流体氧逸度相关的有效指标，而是受白钨矿连续沉淀的控制。
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 systematicallyin-situby 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 thein-situmeasurements 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*]Nfuture 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.