Distribution and origin of brine-type Li-Rb mineralization in the Qaidam Basin, NW China

The Qaidam Basin on the Qinghai-Tibet Plateau is well endowed with a variety of critical metals, such as Li and Rb. However, little is known about the distribution, source, and enrichment mechanisms of these elements. In this paper, we present results of systematic geochemical and H-O-B isotopic analyses of brines in the Tertiary and Quaternary sediments of the Qaidam basin. The results reveal that the paleobrines from oil-bearing anticlines at Dafengshan, Nanyishan, Youquanzi, Jiandingshan, and Jianshishan are significantly enriched in Li and Rb, whose contents are 81.1-128.9 mg L-1 and 4.5-29.2 mg L-1, respectively, reaching levels of economic significance. High Rb contents (up to 12.5 mg L-1) and well-endowment of Li also characterize the Dongtai, Xitai, Yiliping, and Senie salt lakes in the Qaidam Basin. The Tertiary paleobrine average in delta D and delta O-18 at -40.7 parts per thousand and 2.84 parts per thousand, respectively. The paleobrine with the highest Li and Rb has delta D and delta O-18 values close to magmatic water. The delta B-11 values are lower than those of river water but close to those of geothermal fluids, suggesting that replenishment by deep magmatic hydrothermal fluid is most likely the key mechanism for the anomalous enrichment of these elements in the paleobrines, though evaporation and water-rock reactions have contributed to the critical metal mineralization. The anomalous enrichment of Li and Rb in modern salt lake brines is closely related to the input of volcanic geothermal water. The relatively high Li and Rb contents of intercrystalline brines in salt lakes of the western Qaidam Basin and the increase of Li and Rb contents with increasing depth were caused by upwelling of local paleobrines along the fault zones.

Automated summary

This paper presents the results of systematic geochemical and isotopic analyses of brines in the Tertiary and Quaternary sediments of the Qaidam Basin on the Qinghai-Tibet Plateau. The study reveals the enrichment of lithium (Li) and rubidium (Rb) in paleobrines, with the input of volcanic geothermal water being a key mechanism. The research also highlights the influence of river water replenishment and water-rock reactions on critical metal mineralization.