An experimental and thermodynamic study of sphalerite solubility in chloride-bearing fluids at 300–450 °C, 500 bar: implications for zinc transport in seafloor hydrothermal systems
An experimental and thermodynamic study of sphalerite solubility in chloride-bearing fluids at 300–450 °C, 500 bar: implications for zinc transport in seafloor hydrothermal systems
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300-450°C、500 bar 下闪锌矿在含氯流体中溶解度的实验和热力学研究：对海底热液系统中锌传输的影响
DOI：
10.1016/j.gca.2022.03.026
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发表时间：
2022
影响因子：
5
通讯作者：
Seyfried, William E.
中科院分区：
文献类型：
--
作者：
Xing, Yanlu;Brugger, Joël;Scheuermann, Peter;Tan, Chunyang;Ji, Shichao;Seyfried, William E.
高温高压条件下锌在含氯水溶液中的溶解度和形态对于理解锌在天然热液系统中的迁移和相关成矿过程具有重要意义。在这里，我们测量了闪锌矿在NaCl-HCl-H2O流体中的溶解度，使用固定体积的钛合金水热反应器，配备了新设计的气密钛活塞采样器。这种新型的反应器取样系统能够在高温高压下采集内部过滤的流体。实验在300-450 °C、500巴下分别在具有0.5m和lm NaCl的流体中进行。在300-400 °C下，测量的闪锌矿溶解度与使用先前的热力学数据预测的值一致，但在400 °C以上显著偏离。为了解决这一矛盾，我们调整了锌矿物的溶解度积，通过修改热容量和玻恩系数，描述的吉布斯自由能的基础上新的溶解度数据的Zn 2+水离子的元素的形成。改进后的Helgeson-Kirkham-Flowers（HKF）状态方程（EoS）根据经验再现了以前实验研究中Zn矿物在温压范围（25-600 °C，Psatto 2 kbar）内的溶解度数据，但将准确预测扩展到深海热液系统的典型条件，低至0.35 g/cm 3的流体密度。热力学建模使用修订的EoS的Zn 2+表明，较高的温度，氯度和较低的pH值增加锌的溶解度，和锌的氯化物络合物是主要的物种。盐度对锌溶解度的影响是不太显着的低pH值的流体。应用于海底热液系统，我们的研究结果表明，除了温度，pH值和总溶解氯化物，流体/岩石比可能是一个重要的因素，有助于在大洋中脊喷口流体中的锌浓度。
The solubility and speciation of zinc (Zn) in chloride-bearing aqueous fluids at high temperature and pressure are important for understanding Zn transport in natural hydrothermal systems and associated mineralizing processes. Here, we measured sphalerite solubility in NaCl-HCl-H2O fluids using a fixed-volume titanium alloy hydrothermal reactor equipped with a newly designed gas-tight titanium piston sampler. This novel reactor-sampling system is capable of acquiring internally filtered fluids at high temperature and pressure. The experiments were conducted at 300–450 °C, 500 bar, in fluid with 0.5 m and 1 m NaCl, respectively. The measured sphalerite solubilities are consistent with predicted values using previous thermodynamic data at 300–400 °C, but diverge significantly above 400 °C. To resolve this discrepancy, we adjusted the solubility product of Zn minerals by modifying the heat capacity and Born coefficients that describe the Gibbs Free Energy of formation from the elements of the Zn2+aqua ion based on the new solubility data. The refined Helgeson-Kirkham-Flowers (HKF) equation of state (EoS) of Zn2+empirically reproduces the solubility data of Zn minerals from previous experimental studies well over the covered T-P range (25–600 °C, Psatto 2 kbar), but extends accurate predictions to conditions typical of deep sea hydrothermal systems, down to fluid densities of 0.35 g/cm3. Thermodynamic modelling using the revised EoS of Zn2+shows that higher temperatures, chlorinity and lower pH increase Zn solubility, and that Zn chloride complexes are the predominant species. The influence from salinity on Zn solubility is less significant in fluids with low pH. Applied to seafloor hydrothermal systems, our results suggest that in addition to temperature, pH and total dissolved chloride, fluid/rock ratio may be an important factor contributing to Zn concentrations in vent fluids at Mid Ocean Ridges.