Hydrothermal transport of Sn and W: in-situ constraints on fluid composition and metal complexes at the magmatic-hydrothermal transition

Magmatic-hydrothermal processes involving high-temperature fluids of magmatic origin (T > 400 °C) are associated with the development of metal enrichment in the Earth’s crust, including the formation of Cu-Au-Mo-Ag porphyry and epithermal, Sn-W-Mo greisen or rare earth elements (REE) deposits. Modeling of magmatic-hydrothermal processes and their role in the concentration of Cu, Au, Sn, W or the REE requires us to understand how metals are extracted from crystallizing magma bodies and later transported to their deposition horizons. Especially, it is critical to quantify how the source composition and changes in pressure, temperature, pH or redox conditions may affect the composition and properties of the fluid phase (e.g., amounts of F and B; speciation of C and S, etc…) and in turn control the fluid/melt partitioning and hydrothermal transport of ore metals. While significant efforts have been dedicated to describe fluid/melt partitioning, aqueous solubility and speciation of certain metals (Cu, Au, REE), experiments describing the volatile composition and the stability of metal complexes in (F, B, P)-rich fluids involved in the hydrothermal concentration of Sn, W and Mo are extremely scarce. This lack of experimental constraints hinders the development of thermodynamic models for vein and greisen (Sn, W, Mo) ore genesis.This proposal aims at developing a better understanding of Sn and W transport in magmatic-hydrothermal systems through novel experimental in-situ approach. Especially, I propose to install a new Raman set-up for the characterization of volatiles speciation in H2O-CO2-NaCl (+F, B, P, S) fluids up to 700 °C and 150 MPa at the WWU Muenster. Additional in-situ X-ray absorption spectroscopy (XAS) measurements at the DESY and ESRF synchrotrons will be used to identify the effect of fluid composition, pressure and temperature on Sn and W hydrothermal complexes.