Toward quantitative experiment using hydrothermal diamond anvil cell: Solubility of sylvite up to 1.6 GPa

Abstract

Potassium chloride is a common component in geofluids and sylvite is a broadly observed daughter mineral in fluid inclusions along with halite, especially in skarn- and porphyry-type deposits. Interpretation of fluid inclusion microthermometric results requires knowledge of high pressure and temperature (P-T) solubility of salts, which is, however, incomprehensive for sylvite in the KCl-H2O system. In this study, the high P-T solubility of sylvite is determined within the compositional (salinity) range of 38–62 wt% KCl, using a new method that applies the three-dimensional reconstruction function of confocal laser fluorescence microscopy (CLFM) to hydrothermal diamond anvil cell (HDAC) experiments. This method is used to retrieve the volumes of phases (i.e., sylvite, aqueous solution and bubble) in the sample chamber of HDAC and thus to achieve quantitative analysis of sylvite solubility at elevated P-T. Combining experimental results in this study with those published in previous literature, the P-T dependence of the solubility of sylvite is retrieved and applied to data interpretation of microthermometric results. For inclusions containing both halite and sylvite daughter minerals, the commonly used approach for evaluating fluid salinity and P is to simplify the inclusions as the binary NaCl-H2O system. This simplification would lead to underestimation of fluid salinities by up to ~34% and homogenization P by up to 0.25 GPa, for fluid inclusions having relatively high T of daughter mineral dissolution, which are typical of magmatic-hydrothermal ore deposits.