Li and REE Geochemical Behaviour During Mineral Precipitation in Hyperalkaline Soda Brines: Insights from the Rincón De Parangueo Maar (Mexico)

This study focuses on the geochemistry of Rare Earth Elements (REE) and Li in the hyperalkaline soda brine of the remnant Rincón de Parangueo (RDP) maar lake, Mexico, a system characterized by the ongoing precipitation of trona, thermonatrite, halite and sylvite. Total REE concentrations in water range between 13.5 and 26.9 μg kg-1, while higher concentrations (688-1,302 μg kg-1) were found in the associated bulk mineral precipitates (trona, thermonatrite, halite and sylvite). Lithium concentrations are higher than REE concentrations, in both RDP waters and bulk minerals. Lithium concentrations in RDP waters and bulk minerals precipitated are quite similar, ranging from 53.8 to 126.5 mg kg-1 and from 51.3 to 149.1 mg kg-1, respectively. Post Archean Australian shale (PAAS) normalized REE patterns in the waters increase from La to Lu. In contrast, PAAS normalized REE patterns of the bulk minerals are different from those of waters, also increasing from La to Lu but with a less pronounced trend. The distribution coefficient (KD) of REE and Li were calculated between the bulk precipitated minerals and the coexisting lake water. KD values of REE decrease from La to Lu and are significantly higher (6-1154), compared to KD values of Li (0.5-0.8). The REE patterns in waters, which increase from La to Lu, can be explained by the KD values, indicating preferential removal of LREE relative to HREE during mineral precipitation. Similar lithium concentration ranges in waters and bulk minerals are consistent with the low KD of Li, indicating a limited removal of Li from the solution during mineral precipitation.