Program > Browse abstracts by speaker > Louvel Marion

An accurate knowledge of metal aqueous speciation and the stability of different complexes with OH-, Cl- or HS- to pressure-temperature (P-T) conditions relevant to ore formation is critical to understand and model the solubility of ore-forming minerals and the capacity of hydrothermal fluids to transport metals from their source to their deposition environment.

In the last 20 years, in-situ X-ray Absorption Spectroscopy (XAS) has become the preferred method to describe the nature and structural geometry (number of neighbouring atoms, interatomic bond distances) of aqua ions, hydroxide, chloride, or more exotic sulfate and carbonate complexes to (magmatic-)hydrothermal conditions [1,2]. Yet, this method comes with different limitations, the main one being the scarce access to synchrotron sources.

Here, we present an in-situ Raman set-up installed at ISTO that allows for the study of volatiles and metals speciation to 800 °C and 1500bars. Aqueous and solid samples are loaded in transparent sapphire cells and placed in an He-pressurized Internally-Heated-Pressure Vessel (IHPV) equipped with 3 sapphire windows. Raman data are obtained with a 355nm UV-laser and collected by an Andor Shamrock 500i spectrometer. The set-up also includes a high-resolution camera that enables direct monitoring of phase transformation upon increasing P-T conditions (e.g., mineral dissolution or phase separation in salt-rich fluids).

Our first experiments have been conducted on Zn, W, and Te in Cl and S-bearing fluids of varying pH. Raman spectra collected from room conditions to high P-T either validate pre-existing XAS results and ab initio MD simulations or indicate the formation of previously unsuspected species. Examples of each new species will be presented and their relevance in term of ore-forming processes discussed.

References: [1] Brugger et al., 2016. Chem. Geol. 447, 219-253. [2] Louvel et al., 2022. Nat. Comm. 13, 1456.