Deep hydrothermal and shallow groundwater borne lithium and boron loadings to a mega brine lake in Qinghai Tibet Plateau based on multi-tracer models

Brine lakes are good natural laboratories to investigate groundwater influences on the hydrologic and chemical evolutions in arid environments, and the mineralization processes under intensive evaporation. Lacustrine groundwater discharge (LGD) is the vital conveyor for the loadings of resource elements in the brine lakes. Da Qaidam Lake, located in the Qaidam basin of the Qinghai-Tibet Plateau (QTP), is one of the largest brine lakes for boron and lithium resources in China. Lithium and boron in the lake are considered to be dominantly sourced from deep hydrothermal groundwater and shallow groundwater, but the partitioning of deep and shallow components to the lake and the derived lithium and boron loadings remain unknown, LGD derived boron and lithium provide the primary source of the salt lake. vitally regulates the formation, evolution and mineralization of Li and B resources in the brine lake. This study performs systematical investigations of radium isotopes (Ra-226, Ra-228, Ra-224 and Ra-223), lithium, boron, and other hydrogeochemical parameters in different water endmembers around the brine lake. The results indicate that radium isotopes are significantly enriched in the hydrothermal groundwater and will be removed by co-precipitation with barite precipitates in the lake water. The multi-tracer models coupled radium bass balance, conservative tracer buildup and water budget were deployed to precisely constrain radium co-precipitation rates, and to quantify the deep and shallow LGD (total LGD = LGD(D) + LGD(S)) and the derived lithium and boron loadings. Radium co-precipitation coefficient is obtained to be 4.7-6.1 y(-1). LGD(D) and total LGD are estimated to be 8.8 x 10(6) and 3.3 x 10(7) m(3) y(-1), respectively, which account for 11.9% and 57.2% of the total water input. LGD(D) and total LGD derived lithium/boron loadings constitute up to 70.2/60.1%, and 79.0/77.7% of the total loadings, respectively, indicating the significance of disproportionate LGD(D) in delivering resource elements into the brine lake. This study presents the first attempt to partition the deep hydrothermal and shallow LGD to a mega the QTP brine lake by multi-tracer models and the findings contribute to the understanding of lithium and boron budgets in the brine lakes of the QTP and worldwide.