The REE s in Hydrothermal Systems

Abstract

Extensive use of the rare earth elements (REEs, mostly represented by the lanthanide group from La to Lu) in renewable energy applications and defense‐related technologies triggered high and growing interest to the processes responsible for migration, separation, and concentration of these elements in natural processes. Understanding these processes and the behavior of REEs in them is essential for exploration of new resources of these elements and efficient use of REEs in industrial applications. There is now an almost universal agreement that hot aqueous fluids play a significant and, in some cases, a dominant role in concentration and separation of REEs in nature. This article reviews high‐temperature experimental data collected over the past 15 years on the stability of the REE aqueous species and minerals and discusses the mechanisms responsible for hydrothermal transport and deposition of the REEs.

Chemical changes during endoskarn and porphyry‐style alteration and Cu—Fe exoskarn mineralization in the Tonglushan system, eastern China

“…The most likely explanation for the relatively high REE in the endoskarn is their introduction via F‐bearing fluids (Gieré, 1986; Smith et al, 2002). REE can be mobile in solutions rich in F − , Cl − , HCO 3 − , $$$ {\mathrm{CO}}_3^{2-} $$$, $$$ {\mathrm{HPO}}_4^{2-} $$$, $$$ {\mathrm{PO}}_4^{3-} $$$, or with a combination of such ligands (Cui et al, 2020; Lottermoser, 1992; Migdisov et al, 2019; Wan et al, 2021; Williams‐Jones & Migdisov, 2014). Skarn‐forming fluids typically contain chloride‐complexes (e.g., Meinert et al, 2005) but fluoride ligands (also enhancing Zr, Hf and U solubility as mentioned above) are considered to be the main control on hydrothermal mobilization of REE (Gieré, 1986, 1990; Pan & Fleet, 1990; Smith et al, 2002).…”

Burbankite and pseudomorphs from the Main Intrusion calcite carbonatite, Lofdal, Namibia: association, mineral composition, Raman spectroscopy

“…The appearance of abundant fluorite in association with pseudomorphs after burbankite is indicative that F probably played an important role in the breakdown of REE minerals. The role of fluorine has been demonstrated in many carbonatite complexes (Simonneti and Bell, 1995;Bühn et al, 2003;Xu et al, 2011) but recent experimental studies in hydrothermal systems (Williams-Jones et al, 2012;Migdisov et al, 2016) have suggested that, although fluorine is the strongest REE-binding ligand, the presence of fluorine in hydrothermal solutions, rather than facilitating REE transport it causes precipitation of F-bearing REE carbonate or phosphate minerals (Migdisov and Williams-Jones, 2008;Migdisov et al, 2009;Williams-Jones et al, 2012). If the REE are transported as sulphate complexes, precipitation of sulphates, e.g.…”