# Lithium Concentrations in Saline Brines of the Shu-Sarysu Depression
## 2 Geological Characteristics of the Study Area
The overall thickness, mainly composed of sands and sandy loans, amounts to 15.0 m. (5) Aeolian formations are found on Middle to Upper Quaternary and contemporary sediments, creating accumulations of small ridges and fine hillocks comprised of aeolian sands that exhibit hues of yellowish-gray and grayish-yellow. (6) Lake sediments consist of clays, sands, and salts of complex mineral composition, with depths varying between 1.5 m and 14.0 m.  
In terms of tectonics, the Shu-Sarysu depression is characterized as an intermountain hollow that emerged during the Carboniferous and Permian periods. The geological makeup of its pre-Hercynian base remains inadequately understood. The lower segment of the epi-Caledonian cover predominantly consists of Carboniferous deposits, comprising both terrigenous and carbonate formations, which are subsequently overlain by Permian formations characterized by a mix of carbonate, terrigenous, and saline materials. The Hercynian shifting in this region was notably feeble, with the overall tectonic activity resembling that of a platform. The geological structure of the area involves formations from the pre-Paleozoic and Paleozoic eras, capped by a Mesozoic-Cenozoic platform layer [10]. Within the Middle-Upper Paleozoic deposits, we observe Devonian volcanic-sedimentary rocks and their associated tuffs, which have undergone low- to very-low-grade metamorphism. As we move up the section, these materials transition into reddish conglomerates and sandstones, eventually giving way to domitized limestones, aleurolites, and argillites of the Lower Carboniferous. These formations commonly feature layers of rock salt, gypsum, and anhydrite. The Upper Paleozoic rocks of the Shu-Sarysu depression comprise red and gray sandstones alongside fine-grained conglomerates. Additionally, we find terrigenous red marls, argillites, and sandstones, with occasional occurrences of Permian limestones. Salt deposits are noticeable in the middle part of the section. The rock layers show minor displacement, with numerous disruptions recorded across all surveyed local structures, affecting both dome-shaped and sloped formations. The zone containing subterranean brine, as observed in vertical cross-sections, is associated with Paleozoic sedimentary and sedimentary-volcanic complexes. The water in this zone is artesian and rich in sodium chloride, exhibiting mineralization levels ranging from 60.6 to 253.8 g/kg at sampling depths reaching up to 2236 m [10]. The selection of the Shu-Sarysu depression as a promising area for exogenous lithium mineralization is primarily due to the fact that the rivers Shu and Sarysu are quite extensive and flow through large of volcanic-plutonic belts leaching easily soluble alkali metals such as Li, K, Na, and Ca. The Sarysu River is about 800 km long and is formed by the confluence of the small rivers Jaman Sarysu, Jaksy Sarysu, Atasu, Taldisai, Kurmanak, Taldymanak, Kumdyespe, and Karakengir. The Sarysu River passes through volcano-plutonic formations of intermediate to felsic composition, sometimes with increased alkalinity, of the continental-margin Devonian volcanic-plutonic belt. The Shu River originates in the Tian Shan mountain range and flows along the western edge of the Shu-Ile Mountains. The products of mechanical erosion, particularly chemical weathering, accumulate in the path of the river's flow, forming large alluvial deposits in the Shu-Sarysu Depression (Figure 2). During the Upper Cretaceous period within the Shu-Sarysu Depression, the climate exhibited variations ranging from tropical to savannah-like conditions, which supported the presence of river systems [10]. The spatial distribution of these rivers was largely influenced by active tectonic sutures. The accumulation of Cretaceous and Paleogene sediments is closely associated with the activity of ancient rivers and aligns territorially with their valleys. Underground saline waters in the Neogene deposits primarily flow toward areas where a lowering of groundwater is anticipated.