Material source and genesis analysis of lithium-rich claystone in Balun Mahai Salt Lake, Qaidam Basin

Abstract

The potential resources of the clay-type lithium ore in the Balun Mahai Salt Lake of the Qaidam Basin are considerable. However, systematic theoretical research on the metallogenic enrichment regularity of the clay-type lithium ore is still lacking. In this paper, the Quaternary clay layer in the Balun Mahai Basin is taken as the research object. By adopting the methods of rock geochemistry and isotope geochemistry, the sedimentary environment, material source, evolution process and lithium source of the lithium-rich clay layer are explored. The distribution pattern diagrams of rare earth elements indicate that the lithium - rich clay rocks in the Mahai Basin are enriched in light rare earth elements and depleted in heavy rare earth elements, presenting distinct fractionation within the rare earth element assemblage, and the materials of the source rock and the weathering conditions remain stable. The elemental indicators of the sedimentary environment and the isotope indicators of B, C, and O suggest that the sedimentary water body was in a non - marine brackish water environment with weak oxidation - weak reduction conditions, which was affected by a climate characterized by aridity and scarce precipitation. The sediment provenance discrimination diagrams and rare earth element distribution pattern diagrams suggest that the clay source rocks are primarily derived from the biotite adamellite, quartz diorite, gneissic granite of Little Seshten Mountain, adamellite of Qaidam Mountain in the South Qilian Mountains and the granitic gneisses in the Yuqia River region. Weathering indices such as Chemical Index of Alteration (CIA) and Index of Compositional Variability (ICV) indicate that the source rocks generated detrital materials under the influence of weak weathering processes. These detrital materials were then transported to the basin via rivers and, through sedimentation and diagenesis, gave rise to clay minerals. Subsequently, in an alkaline fluid environment, the potassium feldspar was transformed into illite. The isotopic characteristics of Li and B suggest that the lithium in the clay has two sources: lithium in the enriched brine and lithium in the detrital materials of the retained source rocks. Moreover, the amount of lithium adsorbed from the brine is higher than that of the structural lithium in the source rock detritus. Through a comprehensive analysis of the sedimentary environment, material sources, evolution process, and lithium sources of the lithium - rich clay, its genesis can be divided into multiple stages, including the weathering of parent rocks, material transportation, sedimentation, and diagenesis.