Rare Earth Elements in Mineral Deposits: Speciation in Hydrothermal Fluids and Partitioning in Calcite

Table 4

Fluid characteristics of selected natural alkaline and carbonatite systems based on available fluid inclusion data.

Location; deposit type; references	(°C)	(kbar)	Salinity (wt.%  )	X	Fluid Composition
Gallinas Mountains, New Mexico; syenite; Williams-Jones et al. (2000) [69]	416	≤1	12–18	CO2 present but not quantified	(i) Sulfate-rich NaCl-KCl-brines; (ii) Later CO2-NaCl-bearing, sulfate-poor brine; (iii) daughter minerals: gypsum, celestite, and barite
Okorusu, Namibia; carbonatite; Bühn et al. (2002) [25]	250–420	0.8 to 1	<3	0.171	Orthomagmatic in origin; high in alkali + F, low in Ca; (i) daughter minerals: halite, sylvite, nahcolite, K-feldspar, Ba/Ca hydroxides, galena, cerussite, fluorapatite, cryolite, burbankite, pyrite, fluorite, barite
Kalkfield Complex, Namibia; carbonatite; Bühn and Rankin (1999) [23]	180–250	Not reported	Saline	0.340–0.520	Volatile rich (~40 wt% H2O + CO2) with Na-Ca-REE-Sr components
Fen, Norway; carbonatite; Andersen (1986) [10]	221–374	≥4	8–24	(A) 0.05–0.07; (B) Not reported	Fluids all magmatic in origin. Type A fluids are most primitive with phases H2O + CO2 + CO2(v) + solid carbonates; Type B are more evolved but derived from A, with phases H2O + vapor + solid (carbonates or halite)
Bayan Obo, China; carbonatite; Smith et al. (2000) [70]	~221–>480	>0.7 to 2	0.1–20.2	0.10–0.45	(i) Early monazite stage: 280–360°C and >0.7 kbar and 1–5 wt.% NaCl, XCO2 from 0.28–0.45; (ii) Main stage bastnäsite-(Ce): ~300 to >400°C, 0.9–1.4 kbar, 6–10 wt.% NaCl, XCO2 of 0.10–0.30

eported homogenization temperatures of fluid inclusions. ole fraction calculated based on all components present in the fluid chemistry data, that is, not necessarily CO₂/(CO₂ + H₂O).