Tourmaline stability in hydrothermal systems: estimation and testing of thermodynamic data

摘要

Tourmaline is a common mineral in a variety of mineral deposits. It occurs either in association with ore elements or within wallrock alteration haloes. In order to study the stability olf tourmaline at hydrothermal conditions, we estimated the thermodynamic properties of five tourmaline end members (dravite, schorl, alkali-free dravite, Al-foitite and Fe-foitite) using established estimation methods. The results were tested by predicting the solubility of boron in a natural hydrothermal assemblage of Fe-rich tourmaline, musco-vite, adularia and albite. The boron concentration in the fluid in equilibrium with this assemblage was independently known from Laser Ablation-ICP-MS analysis of coexisting fluid inclusions. Agreement well within the uncertainty of experimental and thermodynamic data supports the validity of the estimation methods. This study indicates more generally that the devleopment of new microanalytical techniques for measuring the composition of natural fluid inclusions in well-constrained mineral assemblages represents a promising tool for estimating or testing thermodynamic data for complex silicates.