We examine crystallization conditions for saturated brines of calcium, potassium, and magnesium chlorides from the Angara‑Lena artesian basin, Siberian Platform. The study focuses on temperatures matching actual thermal conditions in wells of the “Lithium” site at the Kovykta gas‑condensate field. This critical type of lithium‑bearing raw material is classified as hard-to-recover reserves. In most wells (depths to 2.2 km), rock temperatures in the upper geological section remain below 20 °C. During well operation, various salts precipitate from saturated magnesium-calcium chloride brines within the production line. This leads to rapid wellbore clogging and eventual production shutdown. Thermodynamic analysis of phase diagrams reveals that crystallization yields antarcticite CaCl₂·6H₂O, tachhydrite Mg₂CaCl₆·12H₂O, minor amounts of carnallite KMgCl₃·6H₂O, bischofite MgCl₂·6H₂O, and several other chlorides, depending on temperature. At temperatures above 55 °C, salt precipitation becomes negligible. Thermohydrodynamic simulations of a single flowing well under hydrogeological conditions similar to those at the Kovykta area (southern Siberian Platform) demonstrate the feasibility of long-term (1 month to 1 year) exploitation of saturated sodium-chloride and calcium-chloride lithium-bearing brines. Such operations can yield lithium production rates of 31.2 to 4.2 t per well.

The temperature in the Valley of Geysers (Kamchatka) geothermal reservoir calculated using the feldspar Na-K-geothermometer has been steadily increasing over the past 10 years on average from 165 to 235 °C, which is close to the temperature values of a hydrothermal explosion of the steam and water mixture. For the analysis of chemical geothermometers, TOUGHREACT-simulation was used, with the help of which the previously known Na-K feldspar geothermometer was reproduced on a single-element model and new formulas were obtained for three Na-K geothermometers: zeolite, smectite, and based on volcanic glass. Data of chemical analysis for the period 1968-2018, in which the chloride ion is considered as an inert tracer of geofiltration processes, indicates that after 2007 a significant inflow of infiltration water (its mass fraction is estimated from 5 to 15 %) into the Geyser reservoir. It is assumed that the Na-K increased values of the feldspar geothermometer are not the result of the temperature increase in the Geyser reservoir, but the effect of smectite water dilution.