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High-temperature SiO2-rich springs are one of the most indicative manifestations of deep geothermal activities. Although they often represent the valuable geothermal potentials and significances of the areas, their high SiO2 contents usually bring some non-negligible problems when we exploit the geothermal resources, especially the silica scales. To understand the sedimentation sequences of SiO2-rich hot springs and to expose its potential relationships with natural sinter deposits and silica scales in geothermal plants, this study make a couple of analyses of the water and solid samples collected from a natural SiO2-rich hot spring in Tengchong (i.e. Dagunguo spring) and isothermal evaporation experiments, including water chemistry analyses, X-ray diffraction, thin-section observation, and electron microscopy analyses. The modern sinters in Dagunguo spring are amorphous SiO2 which is largely formed of tight siliceous layers and some amorphous SiO2 spheres. Some silicified microorganisms, elemental sulfur, and clay are also found. The Dagunguo spring water is Na–Cl–HCO3-type SiO2-rich water, with a pH of about 8 and low dissolved concentrations of Al3+, Fe3+ and Mg2+. Isothermal evaporation (T = 84 °C) resulted in a sequence of precipitated minerals: amorphous SiO2 → halite → sodium sesquicarbonate dihydrate (trona) → potassium chloride (sylvine), accompanied by calcite, hydrous sodium sulfate (mirabilite) and sodium bicarbonate (baking soda). The amorphous SiO2 produced in the evaporation experiments exhibited different shapes and structures than the spherical opal-A formed by hot spring water precipitation under natural conditions. The study of precipitation sequence and minerals of hot spring water provides insight into the scaling mechanism of silica-rich geothermal water and anti-scaling measures that can be applied in the process of exploitation and utilization of geothermal resources.

The El Ghine-Oum El Khialate sebkha extends in southeast Tunisia on over than 75 km2. This depression is filled by recent Quaternary deposits containing a brines aquifer situated at a depth varying from 1 to 10 m. This aquifer is highly rich in sodium sulphate. At the surface, noticeable is the deposition of mirabilite and thenardite encrusting. To quantify the salt reserves for a rational exploitation, thirty dry cores (approximately 160 m of core) were carried out in the sebkha. They underwent integrated geological, geochemical and hydrogeological studies. The estimated reserves are in the range of 8.106 t: Na2SO4, 2.106 t NaCl and 1.106 t MgCl2. The extraction of these salts is restricted by the relatively poor hydrodynamic characteristics of the reservoir evaluated during pumping tests.

A rare lacustrine rhythmite from the Qiulinanmu Playa Lake in Tibet is presented, which was composed of distinct layers of mirabilite, borax, and clay with thickness measuring 1.5–75 cm, 0.5–20 mm, and 0.5–30 mm, respectively. The thickness of each layer was measured in the field and dating was performed using 14C and U data. The lake was previously supplied by river water, groundwater, and hot springs enriched in sodium, sulfur, and boron. Control factors on the rhythmite were climate oscillations and compositional differences of water. The adsorption of boron by clay minerals could be attributed to the alternation between clay and borax layers. Low temperature, high pH, and high evaporation exerted significant influences on the precipitation of original borax and mirabilite. In the evaporative lake, the precipitation of mirabilite (a mineral indicative of a cold-dry environment) was dominant and produced the asymmetric couplets. The lake water was poor in chloride and rich in sodium sulfate, and an abrupt change was observed at 11.4 cal. kyr bp. According to the laminated sediment and the thickness of the minerals, the climate was dry-cold with four sub-warm phases before 11.4 kyr bp (after 20.6–11.4 kyr bp), and wet-warm with four sub-cold pulses after 11.4 kyr bp (11.4–5.2 kyr bp). The two thickest mirabilite layers suggested extremely hard conditions after 20.6 kyr bp, and before 11.4 kyr bp, respectively.

Large amounts of halophilic organisms and their fossils that are found in the Barkol mirabilite deposit are identical to those of its modern biological community residing in its surface brines.