Lithium sources in oilfield waters from the Qaidam Basin, Tibetan Plateau: Geochemical and Li isotopic evidence.

The widely distributed δ7Li values indicate different sources of Li in the oilfield waters. Even in the same oil-bearing tectonic belt (e.g., Shizigou), there is a high degree of heterogeneity of δ7Li values. The origin of oilfield waters in the Qaidam Basin is restricted by the various genetic types of water, including residual water from ancient lakes, alpine snow water infiltrating along deep and large faults, springs and deep hydrothermal fluid. [Display omitted] • New hydrochemical data covered all the oil-bearing anticlines in the Qaidam Basin were reported. • The δ7Li data of oilfield waters in the Qaidam Basin were reported for the first time. • There are significant differences in Li and δ7Li for oilfield waters. • Significant Li-enrichment are associated with hydrothermal activity. Oilfield waters represent an important source of lithium resources to meet increasing global demand. However, the distribution of Li resources in the western Qaidam Basin is still unclear, and the enrichment mechanism of Li remains to be explained. In this study, we present new hydrochemical data for all the oil-bearing anticlines in the Qaidam Basin. Oilfield waters in the Nanyishan and Dafengshan oilfields are characterized by Li concentrations ranging from 110.1 to 237.5 mg/L, and Mg concentrations ranging from 0.70 to 1.52 g/L. These concentrations are readily recovered and represent a key target for oilfield water exploitation in the future. In oilfield water samples from the Qaidam Basin, δ7Li values show large variation, possibly implying multiple sources of Li, including residual water from ancient lakes, alpine snow water infiltrating along deep faults, springs, and deep hydrothermal fluids. δ7Li values of the oilfield waters from Nanyishan and Dafengshan are lower than those of the river and spring water samples, but close to those of volcanic rocks around the world. These results indicate that the oilfield waters with significant Li-enrichment are associated with local hydrothermal activity. This is the first time that the δ7Li data of oilfield waters in the Qaidam Basin have been reported. It appears that δ7Li is a good tracer for determining the origin and the key controlling factors of Li accumulation processes in oilfield waters. [ABSTRACT FROM AUTHOR]