subsurface water containing dissolved mineral substances in high concentrations. According to V. I. Vernadskii (1931-36; All-Union State Standard [GOST] 17403–72), underground brines include waters with a mineralization in excess of 50 g/l. Other classification systems are based on the salinity of the world ocean and define underground brines as waters with a mineralization in excess of 36 g/l. Underground brines are often found in sedimentation basins, where they usually lie below the fresh and saline waters and are confined to the thickest part of the sedimentary mantle. In the basins of the Eastern European Platform, for example, the zone of fresh subsurface waters is 25 to 350 m thick, that of saline water is 50 to 600 m thick, and that of the brines is 400 to 3,000 m thick. Underground brines have also been found in sedimentary series lying under the bottom of the Red and Caspian seas, the Gulf of Mexico, and other bodies of water; they have also been found within the limits of shelfs (for example, close to the Florida peninsula) and in the zone of supergene jointing of crystalline shields, including the Baltic, Ukrainian, and Canadian shields. In arid regions, underground brines saturate the bottomset beds of bodies of water with subsurface drainage, such as Inder Lake in the USSR and Searles Lake in California, both of which are halogenic lakes; the same holds true for salt bottoms, salinas, chotts, and halogenic marine bays and lagoons, such as Kara-Bogaz-Gol in the USSR, Bocana de Virrila in Peru, and the sebkhas of the Mediterranean coast of Africa and Arabia.
Depending on the predominant anion, underground brines are classified as chloride, sulfate, or hydrocarbonate. Of these three, only chloride brines—sodium, calcium, and magnesium brines—are widely found. Within salt-bearing sedimentation basins, the varying stratification conditions cause a distinction to be made between hypersaline, intersaline, and hyposaline brines. Hyper-saline brines are predominantly sodium brines, and their salinity does not exceed 300-320 g/l. Intersaline and hyposaline brines are predominantly multicomponent, with salinity to 600 g/l.
Underground brines are used to obtain common salt, iodine, bromine, and lithium. They are a potential source of rubidium, cesium, boron, and strontium. Certain underground brines are used for therapeutic brine baths.
REFERENCESmirnov, S. I. Proiskhozhdenie solenosti podzemnykh vod sedimentatsionnykh basseinov. Moscow, 1971.
S. I. SMIRNOV