Thermodynamics of selected hydrothermal minerals of As and Sb

在这里，我们提出了在温度高达400℃、硫化物含量低的流体中参与热液过程的选定As和Sb矿物的合成或获取、表征和热力学性质的测量。所选As矿物包括Co-Ni-Fe三砷化物，与世界各地许多矿床中Ni-Co-Fe- bi矿的形成有关的滑石群[(Co,Ni,Fe)As3-x]。选定的锑矿物包括沙石（FeSb2O4）和chapmanite (Sb3+Fe3+2(SiO4)2(OH))，这两种锑矿物可能来自缺硫流体。感兴趣的相将在真空硅胶管中合成或从天然样品中获得。所有样品将用各种矿物学技术进行表征。本方案的主要方法是高温氧化物熔体量热法。将进行一些检查，以确保所收集的数据对热力学建模具有足够的准确性和精度。熵和高温热容将分别由松弛和差示扫描量热法测量。这些数据将与现有的水离子状态方程（在热力学软件包中实现，例如SUPCRT）结合起来，并计算相图。计算出的溶解度及其随温度的变化将极大地有助于理解热液成矿，特别是在硫化物含量较低的流体中。

Here, we propose synthesis or acquisition, characterization, and measurement of thermodynamic properties of selected As and Sb minerals which participate in hydrothermal processes, under temperatures up to 400 ºC, in fluids poor in sulfide. The selected As minerals include the Co-Ni-Fe triarsenides, the skutterudite group [(Co,Ni,Fe)As3-x], relevant to the formation of the Ni-Co-Fe-Bi ores at many occurrences around the world. The selected Sb minerals include schafarzikite (FeSb2O4) and chapmanite (Sb3+Fe3+2(SiO4)2(OH)), two minerals of antimony that may form from sulfur-deficient fluids. The phases of interest will be synthesized in evacuated silica tubes or acquired from natural samples. All samples will characterized by a variety of mineralogical techniques. The principal method in this proposal will be high-temperature oxide-melt calorimetry. A number of checks will be performed to ensure that the collected data are of sufficient accuracy and precision for thermodynamic modeling. Entropies and high-temperature heat capacities will be measured by relaxation and differential scanning calorimetry, respectively. The data will be combined with the existing equations of state for aqueous ions (implemented in thermodynamic software packages, e.g., SUPCRT) and phase diagrams will be calculated. Calculated solubilities and their changes with temperatures will significantly aid in the understanding of hydrothermal ore formation, especially in sulfide-poor fluids.