Hydrothermal sulfate surges promote rare earth element transport and mineralization

• Published in: Geology (Boulder) 2023-05, Vol.51 (5), p.449-453
• Main Authors: Wan Ye, Wan Ye, Chou I-Ming, Chou I-Ming, Wang Xiaolin, Wang Xiaolin, Wang Ruoheng, Wang Ruoheng, Li Xiaochun, Li Xiaochun
• Format: Article
• Language: English
• Subjects: alkaline earth metals; dense nonaqueous phase liquids; EDS spectra; electron microscopy data; Fluids; Geochemistry; Geology; hydrothermal alteration; metals; metamorphism; metasomatism; Mineral deposits; Mineralization; nonaqueous phase liquids; P-T conditions; Pressure reduction; Raman spectra; Rare earth elements; rare earths; retrograde metamorphism; rock, sediment, soil; SEM data; Solubility; spectra; Sulfates; Thermodynamic models; Trace elements; Transport; X-ray spectra
• ISSN: 0091-7613; 1943-2682
• DOI: 10.1130/G50848.1

The generation of sulfate-rich hydrothermal fluids is of great significance to investigate because it is closely associated with the formation of many important ore deposits, such as hydrothermal rare earth element (REE) deposits. However, the transport of REEs in sulfate-rich hydrothermal fluids is complicated by the retrograde solubility of common sulfate minerals depicted in current thermodynamic models. We present in situ and ex situ hydrothermal experimental evidence suggesting that the solubility of alkali sulfate changes from retrograde at low pressures to prograde at elevated pressures. Accordingly, we propose a sulfate surge temperature and pressure (T-P) window (250°C, 90 MPa), above which the solubility of alkali sulfate increases significantly with increasing P and T. Although REE sulfates are weakly soluble in water, sulfate-rich hydrothermal fluids can transport high contents of REEs under the T-P conditions above the sulfate-surge window. Our results indicate that depressurization, cooling, and alkali loss are key factors controlling REE mineralization, which agrees well with geological observations.