Hebei Messi Biology Co., Ltd. stated that as a common hydrous magnesium-rich carbonate mineral, hydromagnesite [Mg5(CO3)4(OH)2•4H2O] can be used as a high-quality mineral flame retardant filler in the field of polymer flame retardancy. Studies have shown that hydromagnesite is mainly found in carbonate salt lakes and Quaternary lacustrine strata, and has also been found in lacustrine deposits in Jezero Crater on Mars, and the Mg/Ca value of lake water is considered to be the key condition for the mineralization of hydromagnesite. The traditional view is that the formation of lacustrine hydromagnesite is mainly related to the weathering of ultrabasic rocks to provide magnesium-rich source replenishment, but the Mg/Ca values of surface river water and groundwater related to the weathering of ultrabasic rocks rarely reach the threshold sufficient for the direct precipitation of hydromagnesite in salt lakes. Therefore, identifying the geochemical cycle of Mg in salt lake systems is a key link in cracking the mineralization process of hydromagnesite.
In response to the above key scientific issues, relying on the Qinghai-Tibet Plateau Salt Lake Field Scientific Observation and Research Station of the Ministry of Natural Resources, the Institute of Mineral Resources of the China Geological Survey (hereinafter referred to as “Resources Institute”) and its collaborators took the Dujiali Salt Lake in Tibet as an example to systematically carry out Mg isotope research on salt lake water, river water, groundwater and hydromagnesite. This work used Mg isotope analysis and combined with the hydrochemical simulation software Phreeqc to first establish a semi-quantitative hydrochemical evolution model of the Mg/Ca value and δ26Mg changes of the Dujiali Salt Lake under evaporation conditions, and explored the geochemical cycle process of Mg in the salt lake system. The results show that under strong evaporation conditions, aragonite first reaches saturation and precipitates during the evolution of Dujiali Lake, resulting in an increase in the Mg/Ca value and alkalinity of the lake water, thereby driving hydromagnesite to saturation and precipitation, and Mg isotopes provide a good parameter limit for the model. In the vast majority of lacustrine hydromagnesite deposits in the world, hydromagnesite is usually coexisting or alternately deposited with aragonite, which further confirms the model results. In summary, this work suggests that although surface river water or groundwater associated with the weathering of Mg-rich rocks provides an important Mg source for salt lakes, aragonite precipitation under evaporative conditions may be an important mineralization process driving the deposition of magnesite in salt lake water.