FLUORITE SOLUBILITY IN H2O UP TO 873 K AND 1 GPa

Fluorite is often found in fissure veins and is considered a replacement deposits in many hydrothermal systems, often closely associated with igneous activity. This study sought to estimate the solubility of fluorite (CaF₂) in aqueous solutions by using a hydrothermal diamond anvil cell (HDAC) and an in situ weight loss technique. Our method allowed direct observation of the sample though the diamonds, eliminating any experimental errors associated with quench. A single optically clear and unaltered fluorite chip was placed into the sample chamber with an aqueous solution. The sample was heated until the fluid homogenized to either a vapor, liquid or supercritical fluid. The volume of the sample chamber and the fluorite chip were estimated through visual measurements and by using Visual Inspector image capture and annotation software. The calculated mass of the chip during the experiment was compared to measurements of the chip taken prior to heating to determine the mass of fluorite lost into the solution. The experiments conducted thus far in a pure water are in good agreement with the lowest temperature and pressure data of Tropper and Manning (2007) which determined the solubility of fluorite in the range of 873-1273 K and 0.5-2.0 GPa. Maximum observed solubilities of fluorite in this study in pure water along the 0.60 g/cm³ isochore up to 648 K and 0.35 GPa is 260 ppm, and along the 0.97 g/cm³ isochore up to 873 K and 1 GPa is 530 ppm. Thus, the solubility of fluorite in H₂O is dependent on temperature, pressure, and the density of the aqueous fluid.