Origin of lithium-rich deep formation waters in Upper Devonian – Lower Carboniferous sediments of Shu-Sarysu gas fields, Kazakhstan, studied by hydro-chemical modeling

This study analyses the origin of the deep, highly mineralized artesian groundwater of the Shu-Sarysu gas fields based on hydro-chemical modeling. Owing to the local geology these Na-Ca-Cl and Ca-Na-Cl brines contain lithium and other rare metals in concentrations suitable for industrial extraction. Once brine compositions were chemically characterized and their origin studied, three brine formation scenarios were considered: evaporation of the ancient seawater, dissolution of evaporates by ancient seawater, and dissolution of evaporates by fresh water. Following the inverse PHREEQC modeling, the main processes forming calcium-chloride and sodium-calcium-chloride composition of the brines are the dissolution of evaporites by ancient seawater or by freshwater, dolomitization, gypsum and halite dissolution, sulfate reduction and cation exchange with clayey material. Water-rock interaction is suggested to be the main lithium enrichment process.