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

Abstract

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.