In situ determination of sulfur speciation in fluids at high temperature and pressure at controlled redox conditions: implications for magma degassing and formation of magmatic ore deposits

含硫气体或流体在自然界中的岩浆脱气过程中大量产生，但在工业玻璃生产中的熔体澄清过程中也会释放。由于高温流体通常是不可淬灭的，因此本项目的中心问题是使用拉曼光谱作为分析工具在高温高压下原位研究此类流体。为此，我们开发了一种新的基于锂离子电池的电池，该电池允许在恒定温度下突然或连续改变压力，在高达200 MPa的压力和高达800°C的温度下工作。氧逸度（fO 2）是决定流体中硫物种稳定性的关键参数。在实验中，氧化还原条件将通过加载的流体组分预调节或通过添加填充有Fe/FeO、Co/CoO、Ni/NiO或其它氧化还原对的特别设计的缓冲胶囊来控制。为了进行比较，将使用热液金刚石对顶砧技术来研究在较高压力和密度的等容条件下的流体。在溶液中的形态是已知的条件下，这些实验的目的也是为了确定与本研究相关的相对拉曼散射截面，并测试文献数据的适用性。为了便于解释拉曼光谱，我们希望从仅含有一种硫组分的相对简单的含水体系开始（例如，H2SO4、H2S、MgSO4、Na2SO4、Na2S）。计划通过使用不同硫源或中间氧化态源（Sx、Na 2S 2 O3、Na 2SO 3）的组合以及通过向电池中添加作为固体的硅酸盐材料（例如石英、流纹岩）来接近更复杂的岩浆流体。研究结果对岩浆脱气和岩浆矿床形成的模拟具有重要意义。

Sulfur-bearing gases or fluids are produced in tremendous amounts during degassing of magmas in nature, but are also released during fining of melts in industrial glass production. Since high temperature fluids are often not quenchable, central issue of the proposed project is to study such fluids in situ at high temperature and pressure using Raman spectroscopy as analytical tool. For doing so, we develop a new sapphire-based cell which allows abrupt or continuous changes of pressure at constant temperature, operating at pressures up to 200 MPa and temperatures up to 800°C. Oxygen fugacity (fO2) is a key parameter determining the stability of sulfur species in the fluid. In the experiments the redox conditions will be either pre-adjusted by the loaded fluid components or controlled by adding a specially designed buffer capsule filled with Fe/FeO, Co/CoO, Ni/NiO or other redox pairs. For comparison, the hydrothermal diamond anvil cell technique will be used to study fluids under isochoric conditions at higher pressures and densities. At conditions at which the speciation in the solution is known, these experiments are also aimed at determination of relative Raman scattering cross-sections relevant to this study, and to test the applicability of literature data. In order to facilitate interpretation of the Raman spectra, we want to start with relative simple hydrous systems containing only one sulfur component (e.g., H2SO4, H2S, MgSO4, Na2SO4, Na2S). It is planned to approach more complex magmatic fluids by using combinations of different sulfur sources or source of intermediate oxidation state (Sx, Na2S2O3, Na2SO3) and by adding silicate materials (e.g. quartz, rhyolite) as solids to the cell. The results of our studies will be useful for modeling of magma degassing and formation of magmatic ore deposits.