The behaviour of Sn and W at the magmatic-hydrothermal transition: Insights from natural and synthetic fluid inclusions

Tin (Sn) and tungsten (W) have been established as strategic metals, whose resources are mainly related to highly evolved, volatile-rich granitic systems and related hydrothermal fluids. Their transport and enrichment results from a combination of melt- and fluid-driven processes. To evaluate the relative importance of these processes, we propose to combine the study of natural and synthetic fluid inclusions (FIs). Natural FIs occurring in early (associated with cassiterite) to late hydrothermal (associated with wolframite) quartz of the Argemela magmatic-hydrothermal system (Central Portugal) are mainly of aqueous (average XH2O = 0.94±0.04) L+V±S type. Raman spectrometry revealed an evolution from V-rich CO2-CH4-N2 to L-rich CO2±N2-CH4 inclusions through the transition and graphite is present in several early inclusions, suggesting relatively reduced conditions and a potential inheritance from the source. In addition, and because further work is needed to understand the fluid/melt partitioning of Sn and W, several experiments were conducted at 700 and 800°C, 200MPa and variable fO2 and salinities to synthetize FIs. A synthetic glass was produced to mimic the major element composition of the Argemela highly peraluminous intrusion and concentrations of W, Sn, P and Li were varied. Inclusion-free quartz were used to trap the fluids. First results prove the feasibility of the study. Microthermometry and LA-ICP-MS analyses are in progress for both natural and synthetic FIs.