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

Figure 3

Model Ic (CO₂-NaCl-rich) showing the speciation of REE in a deeper carbonatite system. Results show the speciation of Ce, Nd, and Er as function of pH at 150 to 350°C and 1 kbar. The starting fluid had a composition of 100 ppm REE, CO₂ of 0.1, and 20 wt.% NaCl. The blue field represents the field of REE(OH)₃(s) stability, while the yellow field corresponds to the stability field of calcite.

(a) 100 ppm Ce, 150°C

(b) 100 ppm Ce, 350°C

(c) 100 ppm Nd, 150°C

(d) 100 ppm Nd, 350°C

(e) 100 ppm Er, 150°C

(f) 100 ppm Er, 350°C