Apatite and fluorite control the transport of tungsten in calcium-bearing hydrothermal fluids
Apatite and fluorite control the transport of tungsten in calcium-bearing hydrothermal fluids
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DOI：
10.1016/j.gca.2023.02.001
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发表时间：
2023-04
影响因子：
5
通讯作者：
Xin-Song Wang;A. Williams-Jones;R. Hu;Zi-qi Jiang;L. Shang;X. Bi
中科院分区：
文献类型：
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作者：
Xin-Song Wang;A. Williams-Jones;R. Hu;Zi-qi Jiang;L. Shang;X. Bi
与矿石共生的矿物（脉石矿物）记录了成矿流体的物理化学条件。然而，它们是否和/或如何影响矿石矿物的溶解度，很少被评估。在这里，我们提出了白钨矿（占全球钨供应量的70%以上）溶解度的实验研究结果。他们表明，磷酸盐和氟化物从白钨矿中螯合钙，形成磷灰石和/或萤石。这些脉石矿物在钨矿床中很常见，其丰度取决于流体的pH值和磷/氟含量。由于白钨矿的沉淀，白钨矿溶解释放数百ppm的钨到流体中，特别是在接近中性的pH值。这表明含钨热液流体中磷/氟的存在可能会阻止白钨矿的沉积，由于磷灰石/萤石的形成，或导致白钨矿的溶解，从而使流体中的钨富集。根据我们的数据模型表明，岩浆热液中富含磷和氟的流体在高温蚀变过程中富含钨，最高可达220倍，并在冷却时形成高品位的ferberite矿床，或白钨矿，因为它们与富钙岩石相互作用。因此，氟、磷浓度和pH值是影响钨在含钙热液体系中迁移和沉积的关键因素，如果它们协同作用，可以有效地活化早期低品位钨矿化，富集成矿流体中的钨，从而形成超大型矿床。矿石和脉石矿物对成矿流体成分的竞争也可能是涉及其他金属的热液系统的一个特点，在今后研究相应矿石的成因时应加以考虑。
Minerals associated with ores (gangue minerals) record the physicochemical conditions of ore-forming fluids. Whether and/or how they affect the solubility of ore minerals, however, is rarely evaluated. Here, we present results of an experimental study of the solubility of scheelite (responsible for >70% of the global supply of tungsten). They show that phosphate and fluoride sequester calcium from scheelite to form apatite and/or fluorite. These gangue minerals, which are common in tungsten deposits, vary in abundance depending on pH and the phosphorus/fluorine content of the fluid. Because of their precipitation, scheelite dissolution releases hundreds of ppm of tungsten to the fluid, especially at near neutral pH. This suggests that the presence of phosphorus/fluorine in a tungsten-bearing hydrothermal fluid may prevent the deposition of scheelite due to the formation of apatite/fluorite, or lead to the dissolution of scheelite and, in turn, enrich the fluid in tungsten. Models based on our data show that magmatic-hydrothermal phosphorus- and fluorine-rich fluids are enriched in tungsten by a factor of up to 220 during high-temperature alteration, and form high-grade deposits of ferberite on cooling, or of scheelite because of their interaction with calcium-enriched rocks. Thus, the concentration of fluorine and phosphorus, as well as pH, are key factors affecting the transport and deposition of tungsten in calcium-bearing hydrothermal systems that, if they act synergistically, can efficiently remobilize early low-grade tungsten mineralization and enrich the ore-forming fluids in tungsten, leading to the formation of giant deposits. Such competition between ore and gangue minerals for components of the mineralizing fluid is also probably a feature of hydrothermal systems involving other metals and should be considered in future studies of the genesis of the corresponding ores.