Thermodynamics of selected hydrothermal minerals of As and Sb

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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.