REE Distribution During Sedimentation in Soda Lake Doroninskoye (Eastern Transbaikalia)

Abstract

Data are presented on detailed sampling of the surface and pore waters of soda Lake Doroninskoye (Eastern Transbaikalia, Russia). Particular attention has been paid to the possible REE precipitation species from both water types. Thermodynamic modeling at 25°C and 1 bar total pressure was performed with the “HCh” code using a free-energy minimization algorithm. We modeled the heterophase 43-component system; both individual minerals and ideal solid solutions of the REE and numerous dissolved species were incorporated into the model. According to the calculations, redox conditions in the lake waters are established by the sulfur species. The main result is that the surface water is slightly supersaturated with respect to CaCO3-REE (65%) and F-apatite-REE (35%) solid solutions, as well as bastnäsite Ce0,5La0,25Nd0,2Pr0,05CO3F. A trend of the HREE predominance in the solution during the process of early diagenesis has been confirmed. Nevertheless, the thermodynamic model does not entirely explain the REE fractionation in pore waters (pore solutions are enriched in the LREEs in situ but are drastically depleted according to the thermodynamic model). The results of this study suggest that further considerations about solid solutions should be taken into account to model and understand exact REE fractionation during water-rock interaction in salt lakes.